Source Reduction Technologies in Printed Circuit Board Manufacture

Doc. No. 539

SOURCE REDUCTION TECHNOLOGIESIN CALIFORNIA PRINTED CIRCUITBOARD MANUFACTURE

Gray Davis, GovernorState of California

Peter M. Rooney, SecretaryCalifornia Environmental Protection Agency

Jesse R. Huff, DirectorDepartment of Toxic Substances Control

California Environmental Protection Agency

Department of Toxic Substances Control

Office of Pollution Preventionand Technology Development

January 1999

DTSC

State of California Department of Toxic Substances Control Office of Pollution Prevention and Technology Development Contact: Ben Fries Phone: (916) 322-8701

SOURCE REDUCTION TECHNOLOGIESIN

CALIFORNIA PRINTED CIRCUIT BOARD MANUFACTURE

Prepared by Benjamin Fries

State of California Department of Toxic Substances ControlOffice of Pollution Prevention and Technology Development

January 1999

This report was prepared by Benjamin Fries under the direction of Alan Ingham and KimWilhelm, Source Reduction Unit, Office of Pollution Prevention and Technology Development

DISCLAIMER

The mention of any products, companies or source reduction technologies, their source or theiruse in connection with materials reported herein is not to be construed as either an actual orimplied endorsement of such products, companies or technologies.

Cover image courtesy of Environmental Protection, August 1997

SOURCE REDUCTION TECHNOLOGIESin California

Printed Circuit Board Manufacture

1. SUMMARY . ............................................................................................................................ 1

2. INTRODUCTION .................................................................................................................... 2 2.1 Information Limitations..................................................................................................... 2 2.2 Proprietary Information. .................................................................................................... 2

3. PRINTED CIRCUIT BOARD MANUFACTURE .................................................................. 3 3.1 Wastestreams ..................................................................................................................... 3 3.2 Source Reduction............................................................................................................... 3 3.3 Recycling ........................................................................................................................... 3

4. SOURCE REDUCTION OF PROCESS CHEMICALS .......................................................... 4

5. SOURCE REDUCTION OF DRY FILM PHOTORESIST DEVELOPER............................. 4 5.1 Aqueous Dry Film Developer ............................................................................................ 4

6. SOURCE REDUCTION OF DRY FILM PHOTORESIST STRIPPER .................................. 56.1 Source Reduction by Bath Operation and Maintenance ................................................... 56.2 Source Reduction by Chemical Substitution. .................................................................... 56.3 Source Reduction by Process Substitution ........................................................................ 56.4 Onsite Recovery ................................................................................................................ 5

7. COPPER ETCHANTS ............................................................................................................. 67.1 Ammoniacal Etchant ......................................................................................................... 67.2 Cupric Chloride Etchant. ................................................................................................... 6

8. RECOVERY OF AMMONIACAL COPPER ETCHANT....................................................... 88.1 Ion Exchange Recovery.....................................................................................................88.2 Electrolytic Recovery. ....................................................................................................... 88.3 Electrolytic Recovery Bleedstream ................................................................................... 88.4 MECER Onsite Regeneration System............................................................................... 9

9. SOURCE REDUCTION AND RECOVERY OF CUPRIC CHLORIDE ETCHANT .......... 109.1 Source Reduction of Hydrochloric Acid - Sodium Chlorate Etchant ............................. 109.2 Onsite Recovery .............................................................................................................. 109.3 Onsite Recovery Limitations ........................................................................................... 10

10. OFFSITE ETCHANT RECOVERY .....................................................................................11

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11. MICROETCHANTS AND MICROETCHANT RECOVERY ............................................ 1211.1 Hydrogen Peroxide CobraEtch. ..................................................................................... 1211.2 Microetch “D” ................................................................................................................ 12

12. ONSITE TREATMENT WITH COPPER RECOVERY ...................................................... 1312.1 Carbamate Precipitation of Copper. .............................................................................. 1312.2 Onsite Recovery of Etchant Rinse ................................................................................ 13

13. TIN OR TIN/LEAD SOLDER PLATE ................................................................................ 1413.1 Fluoroboric Acid Anti-Oxidant. .................................................................................... 1413.2 Material Substitution using Methanesulfonic Acid Anti-Oxidant ................................ 1413.3 Product Modification using Tin Plate .......................................................................... 14

14. SOURCE REDUCTION OF SOLDER OR TIN STRIPPER .............................................. 1514.1 Chemical Substitution of Fluoride Formulations .......................................................... 1514.2 Chemical Substitution using Nitric Acid. ..................................................................... 1514.3 Chemical Substitution using Ferric Nitrate .................................................................. 1614.4 Process Modification with Material Substitution ......................................................... 16

15. ONSITE RECYCLING OF SOLDER STRIPPER .............................................................. 1715.1 Electrodialysis ............................................................................................................... 17

16. OXIDE PROCESS................................................................................................................ 1716.1 Material Substitution using a Textured Copper Surface ............................................... 1716.2 Product Modification using a Waterblasted Surface ..................................................... 17

17. SOURCE REDUCTION OF PERMANGANATE BATH ................................................... 18

18. SPENT SULFURIC ACID REUSE...................................................................................... 18

19. SHADOW PROCESS........................................................................................................... 1919.1 Innovative Shadow Process ........................................................................................... 1919.2 Shadow Process Applications ....................................................................................... 1919.3 Shadow Process Limitations ......................................................................................... 19

20. ELECTROLESS RINSEWATER RECOVERY ................................................................... 20

21. CONTINUOUS FEED AND BLEED .................................................................................. 2121.1 Feed and Bleed Operation............................................................................................. 2121.2 Feed and Bleed Advantages .......................................................................................... 2121.3 Quality Control and Source Reduction ......................................................................... 2121.4 Copper Etchant ............................................................................................................. 2121.5 Photoresist Stripper Bath .............................................................................................. 2221.6 Electroless Copper and Sodium Borohydrate ............................................................... 2221.7 Rinsewater Tank ............................................................................................................ 2221.8 Feed and Bleed Recirculation and Recovery ................................................................ 2221.9 Spray Stream Recirculation with Feed And Bleed ....................................................... 2321.10 Rinsewater Spray Stream ........................................................................................... 23

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22. MATERIAL SUBSTITUTION ............................................................................................ 2422.1 Finishing Solution for Etchant Residues ...................................................................... 2422.2 Plating Tape Residue Cleaning ..................................................................................... 24

23. PROCESS MODIFICATION ............................................................................................... 2423.1 Plastic Plating Racks.....................................................................................................2423.2 Baking Procedure..........................................................................................................24

24. PROCESS SUBSTITUTION ............................................................................................... 2524.1 Additive Process for Printed Circuit Board Manufacture ............................................. 2524.2 Aluminum Oxide Abrasive Cleaning ............................................................................ 25

25. PRODUCT SUBSTITUTION .............................................................................................. 25

26. HEAVY METALS WASTE TREATMENT ......................................................................... 2626.1 Electroplating Wastewater ............................................................................................ 2626.2 Process Substitution and Waste Treatment .................................................................. 2626.3 Heavy Metals Precipitation by Ferrous Sulfate ............................................................ 2626.4 Heavy Metals Precipitation with Dithiocarbamate Acid ............................................. 2626.5 Heavy Metals Precipitation with Calcium Polysulfide ................................................. 2726.6 Heavy Metals Precipitation with Sodium Hydroxide ................................................... 2726.7 Copper Precipitation with Sodium Borohydrate........................................................... 2726.8 ElectroStrip Recovery Systems..................................................................................... 27

27. WATER CONSERVATION ................................................................................................. 28

28. ADMINISTRATIVE IMPROVEMENTS ............................................................................ 2828.1 Cost Control .................................................................................................................. 2828.2 Inventory Control .......................................................................................................... 28

29. CLOSING COMMENTS ..................................................................................................... 2929.1 Information Sources...................................................................................................... 2929.2 Shared Information ....................................................................................................... 29

PUBLICATIONS ......................................................................................................................... 30

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A detailed technical review was made ofhazardous waste source reduction technologyused by California printed circuit boardmanufacturers. The purpose of the review wasto assess the implementation of hazardouswaste source reduction technology availablefor the printed circuit board manufacturingindustry.

At the request of the Department of ToxicSubstances Control (DTSC), 33 printed circuitboard manufacturers submitted SB 14 Hazard-ous Waste Source Reduction EvaluationReview and Plan (Plan) documents for reviewby DTSC. The documents were prepared bySeptember 1, 1991, by each of the firms, asrequired under the Hazardous Waste SourceReduction And Management Review Act of1989 (SB 14). SB 14 requires DTSC reviewthe documents of at least two industries everytwo years.

Technical review was conducted of the 19submitted plans that had evaluated or imple-mented source reduction technologies for usein their operations. The process engineer orscientist of each of the manufacturers wascontacted by DTSC, to discuss detailed techni-cal information not included in their docu-ments. The information indicated that innova-tive source reduction technologies were beingused at 13 of the manufacturers. Dependingupon the process, many of the innovativetechnologies reviewed have general applica-tions throughout the printed circuit boardmanufacturing industry.

The innovative technologies found in thereview are discussed in this report. Most arecommercially available, yet innovative in thatthey are new or improved technologies thatoffer economic and/or environmental advan-tages over conventional technologies.

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SOURCE REDUCTIONTECHNOLOGIES

IN CALIFORNIA PRINTED CIRCUITBOARD MANUFACTURE

1. SUMMARY

2.2 Proprietary Information

This report does provide many examples ofsource reduction measures pursued by circuitboard manufacturers, some are notably inno-vative. However much of the information islimited as proprietary or confidential. Oftenonly the proprietary name is provided, and thedetailed chemical formulation is not available.Also, the technology is often unique to a givenoperation, process, or product. For thesereasons. this document does not providedetailed information about the technologydiscussed nor about its source. Rather, thisreport provides examples of innovative sourcereduction technologies that have been imple-mented or investigated. The printed circuitboard manufacturer can use the examplesprovided in this document as a source of ideasto investigate and develop specific sourcereduction technology to fit higher specificneeds and limitations.

The manufacturing process for a printedcircuit board varies according to the processand product. The following process is used atmany circuit board manufacturing operations.

This document is intended to stimulate theimplementation of source reduction measuresacross California’s printed circuit boardindustry. Advancing technology can bringbenefits including improved products, im-proved process operations, reduced environ-mental impact, and better economics. Thiscorresponds favorably to the rapidly changingtechnology in the printed circuit board indus-try. For that reason printed circuit boardmanufacturers should include source reductionin their ongoing investigation to improve theirproducts and processes. This report describessome product and process changes that areunderway, or currently under investigation bycircuit board makers.

2.1 Information Limitations

While this document is intended to providesufficient detail to encourage further investiga-tion, it is not meant to answer questions thatarise when investigating source reductionapplications. Nor is this document intended asa technical information source or bibliographyfor manufacturing technology. Due to rapidlychanging technology in the electronics indus-try, such comprehensive information wouldrapidly become outdated. To pursue furtherinformation, the reader is encouraged topursue common information sources sug-gested herein.

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2. INTRODUCTION

The manufacture of a multi-layer circuitboard typically starts with preparing theboard laminates. Each laminate has a core offiberglass-reinforced polymer resin, withboth sides of the core laminated over withcopper foil surfaces. The resulting laminateis then baked, to cure and stabilize the poly-mer core. Subsequent processing etches thecopper surfaces, so that the copper circuitpatterns are formed on each surface. Afteradditional processing, the laminates arelayered onto each other using isolationsheets, and fabricated into the multi-layerprinted circuit board. Holes are then drilledthrough the board, according to the intendedcircuit design. After etching and deburringthe drillholes, the board is electroless-platedwith copper to deposit a conductive coppercoating onto the wall of each drillhole. Thisconductive surface is then electroplated withcopper, to strengthen and build up the coppersurfaces on the drillhole walls. The purposeof the copper-coated drillhole walls is toconnect the circuit pattern on each boardlaminate into a continuous circuit designamong the laminated layers of the completedprinted circuit board.

The copper-coated, multi-layered board thenundergoes additional processing to completethe circuitry. Initially in this process, a dryfilm mask is applied onto the exposed coppersurfaces on both sides of the board. Themask is applied as a pattern so that a circuitdesign is traced onto the copper surface.Subsequent processing exposes the coppertracings by removing the dry film maskaccording to the circuit design. The exposedcopper tracings are plated with solder toprotect the copper circuit. The mask is thenstripped from the unplatted copper areas,which are then etched to remove anyunsoldered copper strips. The ammoniacaletchant removes the unmasked copper, butdoes not remove the tin/lead solder plating

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that protects the copper circuit tracings.Then the panel is rinsed, and processed in10% sulfuric acid as an oxidation inhibitor.

3.1 Wastestreams

For circuit board manufacture, the mostprevalent hazardous wastestreams are spentaqueous process solutions, spent rinsewater,other metal-laden wastewaters, and the metal-laden sludge that is precipitated by the treat-ment of the spent solutions, rinsewater, andother wastewaters. Many of the innovativesource reduction measures listed here wouldreduce or eliminate sludge generation. Someof the measures would reduce the volume ofaqueous wastestreams.

3.2 Source Reduction

Hazardous waste source reduction reduces oreliminates the quantity of hazardous wastegenerated at the source generating the waste.Source reduction can simplify and economizehazardous waste management.

Source reduction of process solutions includesseveral process substitution measures thatreduce or eliminate the use of some processbaths that generate hazardous waste. Some ofthe substitutions still do generate spent pro-cess solutions, but often at reduced volume, oras spent solutions that can be easily regener-ated for reuse.

3.3 Recycling

Onsite and offsite recycling are a complementto source reduction. While source reductionavoids generation of waste at the source,recycling manages the waste to derive furtherbenefit. Like source reduction, recycling is apreferable alternative to treatment or disposalof the waste. Recycling can recover spent

3. PRINTED CIRCUIT BOARD MANUFACTURE

Spent process chemicals often become hazard-ous waste due to their original chemicalproperties. Chemical substitution is a com-monly used source reduction method, wherebya hazardous process chemical is replaced by aless-hazardous or nonhazardous chemical.

Various alternative process solutions are oftenavailable from chemical suppliers. Some may

process chemicals or rinsewaters. Recyclingcan also recover contaminants like copper andother etched metals. Like source reduction,recycling can reduce the risk and impact to

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5.1 Aqueous DryFilm Developer

The chemical bath used as the dry film devel-oper often uses an alkaline solution to developthe photoimage on the dry film surface of eachlaminate. One circuit board company recentlychanged its operation to fully aqueous dry filmdeveloper, precluding need for the ethyleneglycol monobutyl ether component of dry filmdeveloper. The bath is now 99% water and 1-2% potassium carbonate. The spent bath is nolonger a hazardous waste, because it does notcontain hazardous chemical components.

human health and the environment. Recyclingcan reduce or delay the need for storage,handling, transport, and disposal of spentprocess chemicals.

4. SOURCE REDUCTION OF PROCESS CHEMICALS

provide source reduction opportunities thateliminate the use of hazardous chemicals.Successful waste reduction improvements alsoreduce waste management costs. Specificexamples are discussed below. Detailedtechnical information on substitute chemicalsand their application can be obtained fromvendors, trade journals, and industry exposi-tions.

5. SOURCE REDUCTION OF DRY FILM PHOTORESIST DEVELOPER

To establish the copper-coated laminate circuitdesign, a dry film mask is applied to theexposed copper surface. The dry film isexposed to an image according to the desiredcircuitry. The dry film is then developed andprocessed into the image pattern. The imageguides the plating, etching, and other opera-tions to produce the final circuitry. The dryfilm is subsequently removed from the coppersurface as part of the process. Technicaldetails of this process and its operationalsequence vary according to the process andproduct.

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Processes that use a photoresist procedure,produce the circuitry from a photo image onthe circuit board surfaces. The photoresistcontrols the formation of circuitry on thecopper surface of the laminate.

As part of the processing, unexposed photore-sist is stripped from the board surface. Strip-per solutions are used to selectively removedry film mask and copper laminate during theprocessing that forms the copper circuitpatterns on the laminate surfaces.

Dry film stripper is usually an alkaline solu-tion that removes dry film from copper lami-nate surfaces, as part of the processing. Astripper solution in common use is 80-95%water, containing potassium hydroxide,monoethanolamine, ethylene glycolmonobutyl ether, and other ingredients.

Once spent, the solution is typically shippedoffsite to a solvent treatment/recycle/disposalfacility, or treated onsite.

6.1 Source Reduction byBath Operationand Maintenance

One operation changed the criteria for addingreplenishment chemicals to the dry film stripperbath. Formerly, chemicals were routinelyadded based on the passage of time alone.Now, bath parameters are continuously moni-tored, with replenishment chemicals added asnecessary to maintain bath performance.

6.2 Source Reduction byChemical Substitution

To supplement vendor information, onemanufacturer’s approach did its own source

reduction research on process chemical alter-natives. The firm has tested 4 alternative dryfilm stripper solutions over a six-monthperiod, to replace a stripper solution havinghazardous components. While the tests pro-vided no immediate benefits to apply opera-tionally, the firm is hopeful that continuedtesting of alternative chemistries will result inan acceptable alternative.

6.3 Source Reduction byProcess Substitution

One operation has implemented a fully aqueouschemistry for photoresist stripper that does notremove as much copper as it removes the photo-resist. One source reduction benefit of this newstripper is that less copper removal results in lesstoxicity in the spent stripper solution.

6.4 Onsite Recovery

Other considerations that affect source reductiondecisions include reliability and economics. Asalternatives to offsite management of spentstripper, some firms routinely treat the solutionfor discharge to the publicly owned treatmentworks (POTW).

One firm investigated onsite management ofspent dry film stripper solution. Availabletechnology could recycle the solution to theprocess. However the alternative technologiesthat were found to be available, are not proven.Also, considering the modest amount of strippersolution recycled, the equipment cost recoveryfor onsite treatment was found to be prohibi-tively expensive.

6. SOURCE REDUCTION OF DRY FILM PHOTORESIST STRIPPER

In the process that produces the circuit on thecircuit board, copper etchant is used to removecopper from the copper foil surfaces of thecircuit board. The copper that is removed, isetched away according to the circuit pattern onthe film mask. The copper that is removedwith etchant, is that which is not to be part ofthe circuitry. The copper which is not re-moved, is the copper that forms the circuitryof the circuit board. Details of the etchingprocess vary according to the process technol-ogy and product. A number of copper etchantprocesses are discussed below, along withsource reduction highlights and waste man-agement practices.

7.1 Ammoniacal Etchant

Alkaline (ammoniacal etch) ammonia-basedetchant and cupric chloride (CuCl

2 etch) acid-

based etchant are both well established copperetch process technologies. The ammoniacaletchants, either ammonium chloride or ammo-nium sulfate, are most commonly used.

The ammoniacal etch and the CuCl2 etch

function differently, each having uniqueadvantages and limitations. The choicebetween the two processes is also affected bypersonal preference, according to the familiar-ity of the operating personnel with eachtechnology. Due to the unique advantages ofeach process, some operations use both am-moniacal etch and CuCl

2 etch.

The ammoniacal etch has been in common usefor 20 to 30 years. It has the advantage ofbeing able to etch exposed copper from thesurface of the circuit board, while not remov-ing the tin/lead solder plating that covers theprotected portions of the copper circuit.

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However ammoniacal etch cannot achieve thefine-line etching that CuCl

2 etch can provide.

Regarding hazardous waste generation, anadvantage of ammoniacal etch is that CuCl

2 etch

onsite recovery often involves use of chlorinegas, a significant health and environmentalconcern. However CuCl

2 etch has a longer

solution service life than ammoniacal etch.

7.2 Cupric Chloride Etchant

The formulations for CuCl2 etch vary, accord-

ing to the needs of the operation. CuCl2 etch

is basically a solution of hydrochloric acid andCuCl

2. The hydrochloric acid etches the

copper from the laminate, producing CuCl2 as

a reaction product. However CuCl2 is also an

active ingredient in the solution. It is neededin the solution to have a proper etch reaction,because the CuCl

2 controls the rate and quality

of etching. Some CuCl2 etch solutions consist

of hydrochloric acid and sodium chlorate. Thesodium chlorate is an oxidizing agent.

For etching, the CuCl2 etch solution is sprayed

onto the PC board, where the etchant removescopper. The CuCl

2 accumulates in the etch

solution as a reaction product, as a result ofetching the copper from the copper laminate.For that reason the etch solution eventuallybecomes spent by becoming laden with cupricion, and must be replaced with fresh CuCl

2

etch.

CuCl2 etch solution is better than ammoniacal

etch, for some product types. For a boardhaving close traces, CuCl

2 etch is better by not

over-etching or undercutting the traces. CuCl2

etch achieves the fine-line etching that someproducts require.

7. COPPER ETCHANTS

CuCl2 etch also has some process advantages.

CuCl2 etch is not a chelator1, while ammonia-

cal etch is. Chelation can be a useful propertyfor controlling metal ions in solution. How-ever a chelator has the disadvantage of inhibit-ing sodium hydroxide precipitation of metalsduring waste treatment.

CuCl2 etch has a longer solution service life

than does ammoniacal etch, since CuCl2 etch

can retain much more copper in solution beforeit becomes spent. CuCl

2 etch will hold up to 26

ounces copper per gallon, compared to 18 to22 ounces/gallon for the ammoniacal etch.Also, when the CuCl

2 etch solution becomes

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1A chelator (kee-lay-tor) keeps metals in solution. A chelator is also used when manufacturing with the electrolesscopper process. Because a chelator will hold metals in the wastestream, a spent ammoniacal etchant wastestreamwill inhibit sodium hydroxide precipitation of metals during waste treatment.

spent, the higher copper content is of benefitto the offsite metal recovery vendor. For acompany that generates large volumes of spentCuCl

2 that can be sold to a recovery vendor,

some vendors will pay a higher price for thehigher copper content.

One disadvantage is that CuCl2 etch cannot be

used to etch copper in the outer layer process-ing. This is because it will strip from the outerlayer surface, the tin/lead solder plating thatprotects the copper circuit. For this reasonammoniacal etchant is used for the outercircuit layer.

Some spent etchants can be recovered onsiteusing electrowinning, ion exchange, or pre-cipitation, to remove copper from spentetchant solution. Spent ammoniacal etch canalso use solvent extraction to remove copperand recycle the etch solution. The recoveredetchant can be recycled to the process. Oftenthe copper-laden recovery residue can be soldto an offsite metal reclaimer.

Regeneration of spent ammoniacal etch ismuch less hazardous than CuCl

2 etch regenera-

tion. Spent ammoniacal etch can be regener-ated onsite as a closed loop with minimalpersonnel exposure, making it safer to handle.Alternatively, spent ammoniacal etch, likeCuCl

2 etch, is often sent to an offsite waste

management service, for copper recovery andetchant regeneration.

8.1 Ion Exchange Recovery

Onsite ion exchange recovery of spent ammo-niacal etch often uses a liquid-liquid ionexchange system employing kerosene or otherimmiscible organic solvent. The extractionsystem sprays the solvent upward into thespent etchant as fine droplets in liquid-liquidextraction. The solvent holds an ionic charge,and works like resin beads to draw the coppercations from the spent ammoniacal etch. Thecopper-laden solvent rises to the surface, thenis processed with dilute sulfuric acid in acone-shaped process vessel. The sulfuric acidreacts with the copper to precipitate coppersulfate. The copper sulfate precipitate can besold to an offsite metals reclaimer for itscopper content. The recovery system returnsthe ion exchange effluent back to the etchprocess as recovered ammoniacal etchant.

8.2 Electrolytic Recovery

Electrolytic recovery uses an electrolytic cellto remove the copper from the spent ammo-niacal etch. The recovered etch is recycleddirectly back to the process. The copperdeposits at the cathode as metallic sludge,metallic flakes, or solid copper, and can besold to an offsite metals reclaimer. Thisprocess, also called “electrowinning,” canreadily be operated onsite.

Often, the best economic and operationalapproach to onsite electrolytic recovery doesnot attempt to remove all the copper. It re-moves enough copper to reactivate the etchantfor recirculation back to the process. Anelectrowinning unit might remove only aportion of the ionic copper, by loweringcopper content of the etchant solution from1500 parts per million to 1000 ppm. Theprocess parameters are determined by consul-tation between the equipment vendor and theplant technical personnel.

8.3 Electrolytic RecoveryBleedstream

For electrolytic recovery, some of the spentetchant must be periodically, or continually,bled off from the recycle loop and dischargedfrom the process as wastewater. The bleed-offprevents excessive impurity accumulation inthe etchant solution recycle loop. This bleed-off is necessary for an electrolytic recoveryunit, because the unit selectively removes onlycopper or other metal. The unit does notremove contaminants such as the trace impuri-ties that enter the process with the freshetchant replenishment chemicals and makeupwater. The bleed-off waste can be treated anddischarged to the sewer, or managed offsite torecover the copper.

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8. RECOVERY OF AMMONIACAL COPPER ETCHANT

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8.4 MECER OnsiteRegeneration System

Offsite recovery of spent ammoniacal etch canbe replaced by the MECERTM onsite recoverysystem. The MECER system uses solventextraction and electrowinning to recoveretchant, recover rinsewater, and reclaim highpurity copper.

Several operations in this review have evalu-ated onsite ammoniacal etch regeneration,including the MECER. The MECER is oftennot cost effective, because the maintenanceand installation costs are high. Some opera-tions find better economics with offsiteetchant recovery services that return theregenerated ammoniacal etch.

The MECER process is from Sweden. Re-portedly, one operation has the MECERsystem in California. Another companylocated in southern California, is interested ininstalling the MECER system. It has beeninstalled in two other US locations; in Oregon,and in Nashua, NH. The MECER system hasalso been installed outside the continental US.In Puerto Rico, it was installed to overcomethe difficulty of obtaining the fresh processsolution.

The MECER system is not a proprietaryprocess:

• The MECER system has three stages. Anextraction stage extracts copper from theetchant; another extraction stage extractscopper from rinsewater; and an electrolyticstage removes copper from the extractant.

• The MECER system removes copper fromspent etchant and spent rinsewater bysolvent extraction. After copper removal,the etchant is regenerated by adding makeupsolvent and ammonia. Makeup ammonia isadded automatically during processing.Ammonia content is monitored by pHmeasurement.

• The MECER system can recover 95% of theammoniacal etch. The regenerated ammo-niacal etch is usually recirculated directlyback to the process.

• The MECER system can also be used toremove copper from spent rinsewater inelectrolytic recovery units. The recoveredrinsewater is likewise recirculated to theprocess.

• The MECER system reclaims copper fromthe solvent in electrolytic cells. The copperis peeled off the cell electrode as copperfoil. The copper foil has a 99% purity. Thereleased copper foil can be sold to an offsitecopper reclaimer.

• The MECER system has its greatest costadvantage in its elimination of the need totransport spent etchant for offsite recovery.

9. SOURCE REDUCTION AND RECOVERY OF CUPRIC CHLORIDEETCHANT

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9.1 Source Reductionof Hydrochloric Acid -Sodium Chlorate Etchant

One operation that uses an etchant of hydro-chloric acid with sodium chlorate, has im-proved its blending of the acid and sodiumchlorate. The blending proportions are nowmonitored by a Reduction-Oxidation Potential(ROP) instrument. The ROP monitor is amuch more accurate control of the correctproportions than the former colorimetricVisuetch instrument.

9.2 Onsite Recovery

Some operations replenish the spent CuCl2

etchant onsite with hydrochloric acid. Someoperations replenish the spent CuCl

2with Cl

2

gas. Spent etchant that is not replenished

onsite, can be manifested for offsite manage-ment, where the copper can be recovered.

9.3 Onsite RecoveryLimitations

Chemical replenishment is difficult for CuCl2

etch recovered onsite. One onsite replenish-ment method uses chlorine. This entailsonsite hazardous materials storage and han-dling of chlorine, either in Cl

2 gas cylinders or

as HOCl crystals. The risks related to onsitechlorine storage and handling is one reasonwhy some operations do not use CuCl

2 etch.

Hydrogen peroxide can also replenish spentCuCl

2 etch. This can provide onsite recovery

of CuCl2 etch. However, concentrated hydro-

gen peroxide is a strong oxidizer, whichrequires special onsite hazardous materialstorage and handling procedures.

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10. OFFSITE ETCHANT RECOVERY

Offsite waste management services for spentetchant are commonly used by circuit boardmanufacturers. The offsite services are avail-able for spent etchant pickup and recycling,with copper recovery.

For spent ammoniacal etch, one offsite servicecan process the spent etchant as well as thecopper-laden sludge generated from onsitetreatment of spent etchant. The vendor alsoprocesses other copper wastes.

The vendor can recover the etchant as well asthe copper when treating ammoniacal etch.Thus, the offsite recovery of spent etchant canbe contracted to the vendor as a completelyclosed-loop service. The vendor servicebrings fresh etchant to the circuit board manu-facturing site, and takes the spent etchant to itsoffsite facility for recovery of both the etchantand copper. The vendor is paid a packageprice per gallon, which includes vendor pick

up of the spent etchant, return of freshetchant, transportation, and processing costs.

The offsite recovery process distills off theammonia as vapor, and then condenses theammonia vapor to make fresh etchant. Thestill bottoms are processed to remove copper,as either copper oxide or copper sulfate. Thecopper compound is often sold to pesticideformulators, as an ingredient in agriculturalfungicides and wood preservatives. Theresidual water is also recovered and used tomake fresh etchant.

Spent CuCl2 etch is processed using electro-

lytic recovery of copper. Often, the residualsolution can be neutralized and discharged tothe POTW under a permit. For some wastes,the copper is precipitated from the spentsolution. The sludge is sent to a vendor wherethe copper is recovered. There are severalvendors available to receive the sludge andrecover the copper.

Microetchants are used where precision etch-ing is needed. Like CuCl

2, microetchants are

acid-based to achieve fine-line etching. Somesource reduction approaches for proprietarymicroetchant processes are discussed below.

11.1 Hydrogen PeroxideCobraEtch

CobraEtchTM has been installed at one opera-tion, to replace Microetch “D.” The activeingredient in CobraEtch is hydrogen peroxide.Spent CobraEtch can be recycled onsite byadding H

2SO

4 to precipitate copper sulfate

crystals. The precipitated copper sulfateresidue is recyclable offsite. The supernate isdecanted off and recycled back to the process,after replenishing the hydrogen peroxideconcentration.

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11. MICROETCHANTS AND MICROETCHANT RECOVERY

11.2 Microetch “D”

Microetch “D” is still used in some processes.Microetch “D” is an acidic etch solution,using potassium persulfate or sodiumpersulfate as the active etchant. Microetch “D”becomes spent at a copper content of3 ounces/gallon. Unlike peroxide sulfuricetchant, Spent Microetch “D” doesn’t crystal-lize its excess copper.

Spent Microetch “D” is usually retained in anonsite waste treatment tank. In the tank, anelectrolytic recovery process plates the copper out of solution and onto the cathodes.The recovered copper can be peeled from theelectrode as a foil, and sold as high puritycopper scrap. The electrolytic recoveryeffluent solution then goes to an ion exchangeprocess, so that it can then be discharged tothe sewer according to permit conditions.

Onsite treatment of aqueous wastestreams isoften needed to meet regulatory requirements.This can occur if the copper content exceedspermit limits for discharge to the municipalsewer. Wastewater needing onsite treatmentcan include spent etchant, as well as spentrinsewater. Onsite treatment can includecopper recovery.

Water conservation often results in the coppercontent of spent rinsewater exceeding thepermit limits for discharge to the municipalsewer. The spent rinsewater can be treatedonsite so that the treatment effluent meets thedischarge limits.

12.1 Carbamate Precipitationof Copper

One operation uses carbamate to precipitatecopper from spent etchant. Following treat-ment, the wastewater is discharged to thepublicly owned treatment works (POTW). Therecovered sludge is sent offsite for copperrecovery, which is easier on sludge precipi-tated from carbamate.

12.2 Onsite Recoveryof Etchant Rinse

The etch process is followed by a rinse step.Electrolytic recovery of spent rinsewater canrecover the copper. One operation reportedthat fifty percent of their spent rinsewater canbe recycled using electrolytic recovery toremove the metal content.

For efficient electrolytic recovery, rinsewaterusage must be minimized to keep the copperconcentration as high as possible. Waterconservation can help minimize the dilution ofspent rinsewater. Rinsewaters that are toodilute for electrolytic recovery, might berecoverable with a fixed bed ion exchangeunit. Alternatively, reverse osmosis or dialysiscould be used to concentrate the copper andrecycle the rinsewater. The copper in theconcentrate could then be recovered usingelectrolytic recovery.

In some manufacturing operations, an electro-plate of solder or tin is applied to the coppersurfaces, to protect the copper surface andfacilitate the fabrication of the circuit board.

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12. ONSITE TREATMENT WITH COPPER RECOVERY

13. TIN OR TIN/LEAD SOLDER PLATE

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13.1 Fluoroboric AcidAnti-Oxidant

Fluoroboric acid is commonly used as apreparation to prevent electroplated copperfrom oxidizing or tarnishing before the solderplate is applied.

13.2 Material Substitutionusing MethanesulfonicAcid Anti-Oxidant

One operation changed its tin/lead anti-oxidanttreatment from the electrolytic fluoroboricacid dip, to a methanesulfonic acid dip. Thepurpose of the change is to reduce toxicity, andto reduce the number of process steps. Otheradvantages of using methanesulfonic acidinstead of fluoroboric acid, is thatmethanesulfonic acid is less corrosive topumps and motors, it won’t etch the concretefloor if it spills from the process, and it is lesstoxic to human health.

13.3 Product Modificationusing Tin Plate

Due to the hazards associated with metalliclead, most operations are phasing out the tin/

lead solder plating process, in favor of a tinplating process. The modification involvesinstalling a bright tin acid bath to plate solder-mask-over-bare-copper (SMOBC) boards.The plate contains tin, and no lead. By elimi-nating lead from the solder, the modificationwould eliminate lead from spent solder strip-per. The result is that solder related wasteswill be lead-free and therefore of less toxicity.

However, the tin/lead plate provides a surfacethat is more resistant to oxidation, comparedto tin plate. The tin/lead plate has betterstorage properties for work-in-process inven-tory, because its surface does not oxidize asreadily as that of tin. The tin/lead plate doesnot need a protective coating to preventoxidation of its exposed surfaces. The tinplate would need a protective surface coatingfor oxide prevention.

Some customers are slow to accept the tinplate as a substitute for tin/lead plate. This ispartly due to reluctance to change from anestablished process, when that change mightaffect the product that presently works wellfor the customer. The circuit board manufac-turer must work with its assembly plantcustomers to implement product modificationsof this kind, because the circuit board assem-bly plants must meet the end customer expec-tations.

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14. SOURCE REDUCTION OF SOLDER OR TIN STRIPPER

Solder stripper is not to be confused withetchant. Etchant removes copper from thecircuit board laminate for the purpose ofdefining the circuit traces. Solder stripperremoves the solder that was applied to thecircuit board to protect the circuit traces frombeing etched during processing.

Solder stripper is also used to remove thesolder from inside the plated-throughdrillholes. The result is a laminate with circuittraces and plated-through drillholes of onlycopper, so that the final circuitry is free of theetch resist solder that was used to protect thecircuitry during processing. Nitric and sulfu-ric acid formulations are used to strip off etchresist solder, tin or tin/lead. Some formula-tions include a fluoride base. The solderstripper attacks only the tin/lead solder, andnot the copper. There are three establishedsolder stripper technologies.

14.1 Chemical Substitution ofFluoride Formulations

By changing to a more efficient solder stripperwith a higher loading capacity, less volume ofspent solder stripper is generated and thestripper is more economically treated formetal recovery.

One operation formerly used C-Strip. Now ituses RSS-1 by Cherokee Chemical. RSS-1can hold more dissolved solder per gallon,resulting in longer bath life and a more con-centrated waste. The solder loading contentincreases from 12 to 14 ounces solder pergallon of spent stripper.

Both C-Strip and RSS-1 are fluoride-basedformulations. Fluoride based strippers areextremely hazardous. The fluoride-basedspent stripper cannot be treated onsite under aPermit By Rule.

14.2 Chemical Substitutionusing Nitric Acid

One operation explored the use of a non-fluoride, nitric acid based solder stripper, toeliminate the classification of the spent strip-per as an extremely hazardous waste. Thisnitric acid based material can strip solder morerapidly, and hold more stripped solder insolution. However, early efforts with the non-fluoride stripper did not work well, withresulting product quality problems. As aresult, the operation continued its use of afluoride-based solder stripper.

The previous decision to continue using afluoride based solder stripper was based on aninability to find a nitric acid based stripper thatwould meet quality control needs. As a resultof additional research since that time, such astripper was found, and the operation hasthereby switched from the fluoride basedCherokee Chemical RSS-1 to the nitric acidbased Florida Cirtech EZ-5001.

The operation also upgraded the solder strip-ping line from a manual dip tank to a convey-orized spray unit. Their main purpose was toimprove quality, but source reduction benefitshave resulted as well. The nitric acid basedsolder stripper in conjunction with the convey-orized line now removes 18-20 ounces solderper gallon of stripper. This is a significantimprovement over the earlier fluoride-basedchemistry, thus reducing raw material con-sumption as well as waste generation.

Another improvement was to convert one tin-lead plating bath to a tin plating bath. Withthis elimination of lead usage, the spent solderstripper loses its D008 (lead-bearing) hazard-ous waste characteristic, although it doesretain a D002 (corrosive) hazardous waste

classification. Furthermore, the operation hasreduced the thickness of the plated tin depositthat will be stripped off from 0.3 mils to 0.2mils. In so doing, the number of panelsprocessed per gallon of solder stripper hasincreased by about 50%.

14.3 Chemical Substitutionusing Ferric Nitrate

One operation now uses Ardrox PC 1115 inlieu of nitric/fluoroboric solder stripper,Tinstrip TLS-120, by Duratech. ArdroxPC1115 contains no fluoroboric acid. Itcontains nitric acid plus ferric nitrate as keyingredients. The new chemistry was found tobe more efficient, and it works more com-pletely than the nitric/fluoroboric stripper.The substitution reduces spent acid from 55gallons/day to 55 gallons/week. Savings areestimated at $35,000/year.

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14.4 Process Modification withMaterial Substitution

At one operation, a two-step solder stripperwas replaced with a vendor-supplied one-stepstripper. The two-step dip tank was replacedby a one-step conveyorized process. As theboard passes through the process on theconveyor, the stripper is sprayed onto bothsides of the board. Then the work passesthrough a spray rinse. The machinery isenclosed, with a recirculating pump.

The conveyorized system improved strippingquality. The former system generated 100gallons of spent solution per week that neededwaste treatment. This was reduced to 100gallons in six weeks.

The one-step process uses a chemistry similarto the two-step process, with the exceptionthat the one-step stripper uses a nitric acid base.

15. ONSITE RECYCLING OF SOLDER STRIPPER

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16.1 Material Substitution usinga Textured Copper Surface

The brown oxide process line can be elimi-nated by material substitution. This optionrequires the purchase of copper-clad blanklaminates that have a textured surface pre-rolled into the copper foil surfaces. After thedesired circuitry has been etched into thecopper surfaces, the epoxy adhesive can bedirectly applied to the textured copper surfacefor bonding the laminates without use of thebrown oxide process.

The raw material cost is somewhat higher forthe copper-clad blank laminate having thetextured copper surface, when compared tocopper-clad blank laminates that have a slick

Onsite recycling of spent solder stripper couldcomplement source reduction and benefit acompany’s waste management program. Onsiterecycling could replace either onsite treatment oroffsite management of spent stripper.

Onsite recycling can save money by reducingthe cost of purchased chemicals. Additionally,it can also reduce the cost of fees and servicesfor waste management, by reducing the needfor offsite waste management. However onsiterecycling may require a hazardous wastefacilities permit, depending on the technology.

15.1 Electrodialysis

One operation proposes to recycle nitric acidonsite using a membrane electrodialysis systemto remove metals from the spent solder stripper.The electrodialysis purifies the nitric acid.Other stripper chemicals are replenished asneeded, and the reconstituted nitric acid stripperis returned to the process bath. This system

removes the copper, the tin/lead solder metals,and other contaminants as filter sludge. Thefilter sludge can be sold to an offsite metalsreclaimer. The installed cost is $30,000. Onebarrier to onsite electrodialysis is the classifica-tion of the spent stripper or filter sludge residueas a toxic substance, which may require apermit for onsite treatment or storage. Anotherbarrier is the 50 to 60% water content in thesludge. Metal recovery smelters need thesludge to be below 10 to 15% water content.Filter presses are available, that can achievelower water content by circulating hot waterthrough the filter unit to evaporate water fromthe filtercake.

After the mask, etch, plate, and strip processingcompleted, a brown oxide layer is formed onthe laminate copper surfaces. This provides aroughened surface so that the laminates can bebonded together with epoxy, when fabricating amulti-layer circuit board. Without the roughoxide layer, the copper surface is normally tooslick to properly adhere to the epoxy bond.

16. OXIDE PROCESS

surface. However, the textured-surface optioneliminates the entire oxide process line. That,in turn, eliminates hazardous waste generationfrom the oxide line, as well as the associatedequipment and operating costs for the line.

16.2 Product Modification usinga Waterblasted Surface

The brown oxide process can also be elimi-nated by using aluminum oxide particlesapplied as a waterblast slurry. The waterblastslurry impacts upon the copper surface,causing a textured surface of micro-indenta-tions. The aluminum oxide does not impact asan abrasive, so that no copper is removed fromthe copper surface when making the indenta-tions with the waterblast slurry.

17. SOURCE REDUCTION OF PERMANGANATE BATH

Spent sulfuric acid is sometimes reused onsitefor fume scrubbing. The reuse occurs in theammonia fume scrubber. When used asscrubbing solution, the spent acid pH of 1rises to about 4 or 5 pH. Using the spent acidto scrub ammonia fumes results in less quan-tity of sodium hydroxide needed to neutralize

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During the fabrication process, holes aredrilled through the laminates to provideinterconnecting circuitry between the cir-cuitry that is in each of the laminates. Be-cause the laminate core is fiberglass-rein-forced polymer resin, the drillhole wall mustbe copper plated to make it electrically con-ductive. Prior to copper plating, the drillholewall must first be resin-etched, to clean andprepare it copper plating.

Preceding the resin-etch, the process typicallyuses a MLB-496 bath. MLB-496 is a strongalkaline solution which swells and exposes theloose fibers left in the hole after drilling,making them more prominent and removable.

Then the drillhole walls that were sensitizedusing MLB-496 are cleaned with MLB-497solution. The MLB-497 bath is a very strongoxidizing alkaline solution containing potas-sium permanganate and sodium hypochlorite.The potassium permanganate and sodiumhypochlorite etches the drillhole wall bydissolving the fiberglass resin. Following theMLB-497 operation, the board is cleaned andneutralized. The board is now ready to enterthe electroless copper plating line.

A chemical replenisher is available, MLB-497C, containing the sodium hypochloritecomponent of the bath. Using the replenisherextends the bath service life to six months.

18. SPENT SULFURIC ACID REUSE

the spent acid to pH of 7, prior to dischargingthe spent acid to the municipal sewer.

The arrangement works well. The spentsulfuric acid reuse also conserves the use ofvirgin sulfuric acid, so that virgin sulfuric acidis not needed in the ammonia fume scrubber.

19. SHADOW PROCESS

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problems that included sporadic voids in holecoverage. This occurred primarily on thickboards in the 0.093" to 0.125" panels. Thinnerlaminates were successfully processed. Thefirm expects that the quality problems could beovercome with operational adjustments. As ofDecember 1995, the firm felt that the overallperformance of the Shadow process wassatisfactory. The increased throughput andlower waste generation justifies the conver-sion.

Another board maker that was contacted,reports having considered the Shadow systemover electroless copper plating, along withseveral other source reduction technologies.The firm has postponed their installation of theShadow system. It is too costly for now,requiring a $140,000 investment with a pay-back of eight years. Another board makerexpressed lack of confidence in the Shadowprocess.

19.3 Shadow ProcessLimitations

The Shadow process is innovative and not widely proven in application. Some applica-tions have had problems with its reliability.For that reason no recommendation should bemade for installing this process. Yet theShadow process is successful in some opera-tions. The process offers hope for dramaticcost reduction and waste reduction in themanufacture of printed circuit boards. Tech-nologically aggressive companies could findthe Shadow process worthwhile to investigateas a source reduction opportunity.

The “Shadow” brand process is an innovationthat can replace the electroless process that isused to deposit copper onto the drillhole walls.The Shadow process reduces the number ofprocess steps and replaces the hazardouschemicals commonly used in the electrolessprocess with nonhazardous chemicals.

19.1 InnovativeShadow Process

The Shadow process is a direct metallizationsystem. The process uses carbon-graphite tobond the copper electroplate onto the polymersurface of the drillhole walls. This processhas 4 chemical formulations, with 10 processsteps. By comparison, conventional electro-less plating uses 9 chemical formulations and20 steps.

Hazardous waste constituents in the electro-less process include chelated copper, formal-dehyde, and trace cyanide. Additionally, theelectroless line consumes large amounts ofwater for processing and rinsing. Hazardouswaste management is costly and difficult withthe electroless process. The Shadow processuses no toxic chemicals.

19.2 Shadow ProcessApplications

One circuit board manufacturer that wascontacted, had successfully converted fromtheir electroless copper process to the Shadowprocess in 1995. They reported quality

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20. ELECTROLESS RINSEWATER RECOVERY

One circuit board manufacturer achieveswastewater source reduction with the Kineticowater system. The system uses ion exchangeand carbon filters to purify spent rinsewaterfrom the electroless plating line. The systemrecycles purified water back to the process in aclosed loop. The system had recycled over250,000 gallons of water during the first sixweeks of operation.

The ion exchange process uses a solid phaseresin, with beads that ionically pull copperfrom solution and onto the beads. The carbonfilters remove organic impurities and turbidity.

The recycled water can be used forrinsewaters, and also for makeup water forbath preparation. The system is not used forrecycling a spent process bath, because themetal concentrations in the bath would over-load the ion exchange units.

Many process baths are used in printed circuitboard manufacture. Uses include plating,etching, stripping, and rinsing. During itsoperation, a process bath solution graduallybecomes spent and must be replaced or replen-ished. The solution becomes spent because itaccumulates unwanted materials such ascopper ions etched from the copper-cladlaminate, film or solder mask stripped fromthe laminate surface, or other impurities.Another cause is the depletion of the activechemical ingredients in the bath solution.Another cause is rinsewater carryover into thebath that dilutes the bath solution, whichdilutes the effectiveness of the bath chemicals.The accumulation, depletion, and dilution inthe bath compels periodic replacement of thebath solution to maintain process perfor-mance.

A source reduction alternative to periodic,batchwise replacement of the bath solution isthe continuous feed and bleed replacement.Like batchwise replacement, feed and bleedremoves accumulated materials and maintainschemical ingredients of the bath solutionwithin process parameters.

21.1 Feed and Bleed Operation

The feed and bleed system continuously feedsfresh makeup solution to the bath, whilecontinuously bleeding an equal flow of solu-tion from the bath as spent solution. The flowrate of feed and bleed is controlled by moni-toring the quality of the bath contents, and sothat fresh solution is added to keep the bathcontents within specified process parameterlimits. The system operates at steady state, sothat the feed adds ingredients at the rate whichthey are being depleted by the bath process,while the bleed depletes the unwanted materi-als at the rate they accumulate.

21. CONTINUOUS FEED AND BLEED

21.2 Feed and BleedAdvantages

The feed and bleed bath has advantages overthe batch bath. Instead of changing the bathnightly in a batchwise replacement with freshsolution, feed and bleed allows the bath to bechanged bi-weekly or beyond. In that way, thebath is changed only when a system purge isneeded to clean out the tank surfaces, the tankbottom sludges, and other contamination. Thelonger bath life minimizes process downtimeand saves money. A bath change is costlybecause it means process downtime to cleanout the system, prepare the new bath solution,and heat up the bath, with all this occurringwhile the operating crew stands by idle.

21.3 Quality Control andSource Reduction

Another advantage of a continuous feed andbleed bath is that it maintains steady stateprocess operating conditions; instead of theswings in concentrations, impurities, anddilution that occur in a batch bath operation.The steady state operation provides consistentconditions for product quality control.

Steady state operation also allows optimumprocess operation. Optimum operation oftenminimizes the feed and bleed flow rate. Theminimum flow rate is that which maintains thebath at or near the highest impurity concentra-tion at which the bath can properly operate,while still maintaining effectiveness and prod-uct quality.

21.4 Copper Etchant

One operation minimizes the feed and bleedflow rate for copper etchant solution. Mini-mized flow rate means savings in operating

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costs, as well as source reduction from mini-mized waste generation.

Flow rate is minimized by maintaining copperloading for the solution, as close as possible tothe upper load capacity of the solution, withoutcausing operating problems and product qualityimpairment. The copper content of the solutionis maintained at 90% of the copper load capac-ity of the solution. This leaves a residual 10%copper loading capacity to maintain solutioneffectiveness. Another benefit of maintainingthe copper loading near the upper limit for thesolution, is improved recovery of copper fromthe spent solution when the bath is changed out.

21.5 Photoresist Stripper Bath

One operation uses feed and bleed to maintainthe photoresist stripper bath. The bath is usedto remove the polymer photoresist film fromthe surface of the circuit board. The photoresistfilm is removed as polymer particles, whichbecome suspended in the bath solution. Toremove the polymer particles from the bath, thebath solution is continually withdrawn, circu-lated through a filter, and returned to the bath.

The fine particles and other impurities thatpass through the filter, can be removed to anacceptably low level. The bleed is dischargedfrom the process as spent stripper solution.The filter extends the bath life by removingparticles from the bath solution. Fresh make-up solution is added as feed, to replace thespent solution discharge.

The filter, along with the feed and bleed,improves the process operation and providessource reduction. The continuous feed andbleed keeps a consistent bath quality, so theprocess operating parameters can be moreclosely adjusted to optimum conditions. Thecontinuous spent solution discharge allows thebath to operate on a longer, more consistenttime period. All shifts can operate with thesame bath composition, instead of the first

shift with fresh bath having rapid stripping,and the late shift with the near-spent bathbeing very slow to strip. The extended bathlife saves chemical costs, reduces processdowntime, and reduces waste generation.

21.6 Electroless Copper andSodium Borohydrate

Feed and bleed can be used to maintain theelectroless copper bath. Raw materials arepumped into the bath to maintain bath param-eters. The displaced solution flows out asspent solution. At one operation, the bath isnever changed, except for unusual conditions.

At another installation, the spent electrolessbath solution goes into a drum. The copper ischemically precipitated as metallic copper,using sodium borohydrate (Section 26.7).

Alternatively, onsite treatment can use anelectrowinning system to recover copper fromthe spent solutions.

21.7 Rinsewater Tank

Rinsewater becomes spent due to carryover ofa chemical bath solution into the rinsewatertank, similar to a chemical bath solutionbecoming spent due to carryover of rinsewaterinto the chemical bath. Similarly, continuousfeed and bleed can be applied to the rinsewatertank, to remove spent rinsewater. Feed andbleed can minimize chemical accumulation inthe rinsewater.

21.8 Feed and BleedRecirculation andRecovery

Some feed and bleed systems recover thebleedstream, and recirculate it back into thebath, as part of the feed. Rinsewater recircula-tion and recovery is a common example.

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laminate, instead of immersing the laminateinto an etchant bath or rinse tank. The spraystream can include a recirculation loop with arecovery unit, so that the spray stream isreused. The loop can include a feed and bleedto help maintain the spray stream at suitableconcentrations. The recovery unit wouldremove etched copper or other unwantedmaterials. A continuous feed stream enablesthe addition of fresh chemicals into the recov-ered etchant, as needed to maintain batheffectiveness. A bleed stream would removean equal volume from the loop, to removeaccumulated trace impurities.

21.10 Rinsewater Spray Stream

Often the rinse step is a spray system. Therinsewater spray is often applied countercur-rently to the movement of the laminate beingprocessed through the operation, often as avertical cascade rinse. In such applications, thespent rinsewater at the bottom of the cascadehas a high contaminant level, and the spentrinsewater is continually discharged from theprocess as wastewater. Often a spray rinse cansave water compared to a rinse tank.

Instead of discharging the spent rinse aswastewater, the spent rinsewater can be treatedin an ion exchange unit to remove metals,filtered to remove other contaminants, andrecycled to the process as part of the freshwater supply.

More water savings and reduction of wastegeneration can be provided by including afeed and bleed in the spray rinsewater system.Similar to spent etchant, the feed and bleedcan minimize spent rinse waste generation.

Recirculation can also be used for chemicalbaths including etchant, stripper, or plating.

In the recirculation loop, unwanted materialsin the bleed, like plastic particles, copper, orcarryover, are removed by the recovery unit.If needed, fresh chemical ingredients areadded to maintain specifications.

The recirculation loop often needs a secondarybleed stream. The secondary bleed stream isneeded to bleed off impurities which are notremoved by the recovery unit, like traceimpurities that enter with the fresh makeupchemicals. Without the secondary bleed, thetrace impurities would gradually accumulatein the recirculation loop to a level that couldimpair bath performance. Usually such asecondary bleed undergoes treatment as ahazardous waste, and is then discharged to aPOTW. The water leaving with the secondarybleed is replaced by adding fresh water withthe makeup chemicals, as needed.

An alternative to the secondary bleed isperiodic changing of the bath or rinse tank aswastewater, to purge out the accumulated traceimpurities. However, periodic changingusually means non-steady, cycling operatingparameters; process downtime; and wastegeneration; all of which often increase operat-ing costs as discussed above.

21.9 Spray StreamRecirculation withFeed And Bleed

Some operations have process steps that use aspray to apply an etchant or rinse to the

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Several material substitution chemicals arediscussed below. Some show promise forsource reduction in circuit board manufacture,yet have not been fully investigated. Somesubstitution chemicals were found unsuitablefor operations involved.

22.1 Finishing Solutionfor Etchant Residues

High speed finishing solution is used toneutralize etchant residues and remove stannictin residues. The process leaves a clean soldersurface. Finishing solutions free of thioureahave not been found satisfactory to date. Thesolution still contains hydrochloric acid.When the hydrochloric acid becomes spent, itis hazardous waste due to corrosivity.

22.2 Plating TapeResidue Cleaning

Plating tape is used to mask areas prior to goldplating, to avoid plating gold onto surfaceswhere it is not wanted. A substitute cleaner,EC-1, can be used to replace 1,1,1trichloroethane to remove tape residues fol-lowing the nickel-gold plating steps. EC-1 isnon-toxic, biodegradable, and can be dis-charged to the POTW.

Alternatively, the tape can be replaced by anon-residue tape. This eliminates the need touse either of the cleaners, 1,1,1 trichloroethaneor EC-1. The product name of the non-residuetape is 9190, and is made by Ideal.

22. MATERIAL SUBSTITUTION

23. PROCESS MODIFICATION

Process modification involves productionprocess changes. These can include equipmentmodifications, changes in production methodsor techniques, changes in process operatingconditions, process automation; or recycling,if hard-plumbed within the process.

23.1 Plastic Plating Racks

A nitric acid stripping bath is sometimes usedto remove copper deposits from electroplatingracks and tanks. The copper deposits accumu-late on stainless steel racks and tanks duringplating service.

One operation installed plastic plating racks toreplace its stainless steel racks. Because copperwill not readily plate onto the plastic, thesubstitution eliminates the need for the nitricacid stripping bath. By eliminating the strip-ping bath, the substitution also reduces the need

to manifest the spent stripping solution ashazardous waste for offsite management.

The operation had invested $8748 into thesubstitution, including laboratory tests, equip-ment purchase and installation, and operatortraining. The installation resulted in a savingsof $31,000/year, mostly from reduced wastemanagement costs. The investment provided athree month payback.

23.2 Baking Procedure

One operation uses a lubricant release agent(Sprayway) on the baking plates used to formthermoset plastic laminated boards. TheSprayway precludes the use of chlorofluoro-carbon (CFC) solvents to clean residualthermoset plastic (prepreg contact residue)from the sheet-forming baking plates. Therelease agent contains non-toxic, organic-based, biodegradable ingredients.

25. PRODUCT SUBSTITUTION

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Process substitution includes replacing anexisting process with a different process toproduce the same product, but generating lesswaste toxicity or quantity. Process substitutionmight include input changes in raw material orfeedstock.

24.1 Additive Process forPrinted Circuit BoardManufacture

Some operations are conducting research tochange from the current subtractive process toan additive process, to form the conductiveprinted circuits. An image of the desiredcircuit pattern is printed onto the etch resistfilm in the subtractive process. The etch resistfilm covers the entire copper-clad surface ofthe laminate. The film is then developed,followed by the non-image areas of etch resistfilm being stripped off. This exposes thecopper surface areas that are not to be part ofthe circuit. The exposed copper is then etchedaway, leaving the desired copper circuit on thelaminate surface. Therefore with the subtrac-tive process, most of the copper surface thatwas originally on the laminate is etched off.

Conversely, an additive process would print orscreen the circuitry image directly onto the

polymer laminate base. The copper wouldthen be deposited onto the printed image usinga process similar to an electroless deposit.Copper electroplating would follow. Theadditive process negates the need for extensiveetching of copper with its attendant costs andwaste generation.

A couple of additive processes are in operation,and continuing research is underway at otheroperations. However the additive processtechnology has not yet been proven for exten-sive use in all applications. Technical tradejournals and conferences are possible sourcesfor obtaining the most recent informationregarding this process.

24.2 Aluminum OxideAbrasive Cleaning

Aluminum oxide abrasive cleaning can elimi-nate the chemical cleaning process and itsgenerated waste. The abrasive cleaner elimi-nates six chemical process steps, includingalkaline cleaning, hydrochloric acid cleaning,microetching, and the final rinse step. Underroutine service, the abrasive material lasts fourmonths, at which time it is changed. Onecompany made a capital investment of$120,000 with only a 2 year payback.

24. PROCESS SUBSTITUTION

Product substitution involves producing adifferent product that meets the same purposeas the product that was replaced, but thereplacement would not posess the same levelof environmental risks during production, use,

or disposal as the previous product. Thisreport did not include a review of productsubsitution measures as alternatives to printedcircuit boards.

26. HEAVY METALS WASTE TREATMENT

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Several vendor-supplied waste treatmentsystems can reduce the generation of hazard-ous waste sludge in the precipitation of metalsfrom wastewater. Trade journals and exposi-tions are sources of vendors who can provideperformance information on treatment chemi-cals and equipment. Often the chemicalformulations are proprietary, and are identifiedby their trade names.

26.1 Electroplating Wastewater

Title 40, Code of Federal Regulations, listswastewater treatment sludges from electroplat-ing operations as F006 hazardous waste.Proper selection of precipitation chemicals fortreating electroplating wastewaters, canprovide source reduction opportunities.

Several operations have improved the precipi-tation and flocculation of metals from electro-plating wastewaters. Results include reducedvolume and improved recyclability of thetreatment residue sludge.

26.2 Process Substitutionand Waste Treatment

One operation had very good results by usingprocess substitution. Like the former chemis-try, the new process chemistry includedremoval of the heavy metals. The new chem-istry, however, greatly reduced the use ofsulfuric acid and bleach. Formerly, the waste-water treatment system generated muchsludge. It had to be cleaned weekly, includingthe waste treatment system and the membranefiltration system. Now, the treatment systemuses new process chemistry which extendedthe time between weekly cleanings to 6 to 8weeks. The change to the new chemistry hashad little impact on amount of sludge gener-ated; the sludge generation remained the same.

26.3 Heavy MetalsPrecipitation byFerrous Sulfate

Heavy metals precipitation using ferroussulfate is a long-standing process. Thisprocess required a large proportion of ferroussulfate to be added for adequate metals pre-cipitation, resulting in a large volume ofgenerated sludge.

Less sludge is generated by using other chemi-cals instead of ferrous sulfate. Successfulexamples are discussed below. It is importantto perform a cost/benefit analysis to determinethe possible savings from this substitution.

26.4 Heavy MetalsPrecipitation withDithiocarbamate Acid

Replacing ferrous sulfate with precipitationusing dithiocarbamate acid (DTC) has reducedsludge volume and increased the coppersludge concentration. DTC breaks the chela-tor effect, resulting in less sludge generation.The higher cost of DTC can be offset by thesavings in the sludge transportation and wastemanagement costs.

At one operation, the reduced sludge volumeprovided by DTC precipitation was an essen-tial part of operational changes. This isbecause increased heavy metals precipitationwas needed to meet more stringent POTWdischarge limits, while also accommodating a50% increase in production.

The sludge precipitated by DTC is managed asa hazardous waste. However the effect ofdithiocarbamate on mobility of the toxicsludge components would need evaluation, ifthe sludge were sent to land disposal.

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26.5 Heavy MetalsPrecipitation withCalcium Polysulfide

Following two years of operating with a DTCbased precipitation system, one operationswitched to a calcium polysulfide (CaPS)precipitation system. This generates even lesssludge than the DTC system, as well as con-suming a lower volume of chemicals overall.After about fifteen months on the CaPS system,the weight of sludge generated is 40% less thanthat generated by the DTC system. This sourcereduction occurred despite a slight increase insquare footage of circuit boards manufactured.

The sludges generated by CaPS and DTC arehazardous waste, characterized as F006 underthe federal guidelines. As such, they aresubject to the Land Disposal Restrictions(LDR) for hazardous wastes, and are notsuitable for land disposal. However, theInstitute for Interconnecting and PackagingElectronic Circuits (IPC), a circuit boardindustry trade association, is working with theUSEPA Project XL to exempt this sludge fromclassification as hazardous waste. It wouldthen be classified as hazardous solely on itsability to meet the Extraction Procedure (EP)toxicity test. This is significant because CaPSchemically bonds to heavy metals more tightlythan does DTC; thus CaPS sludge will have ahigher likelihood of meeting the EP toxicitytest for the purposes of LDR classification.

There are some reasons why this exemptionmay not translate into immediate benefits forthe printed circuit board manufacturing inCalifornia. First, California’s waste extractiontest (WET) is used in place of the USEPA EPtoxicity test, and is similar but not identical tothe EP toxicity test. Therefore meeting the EPtoxicity test does not guarantee meeting theWET. Secondly, California regulates copper,while the USEPA normally does not. The gen-erator intends to closely monitor this proposedexemption in pursuing source reduction efforts.

26.6 Heavy MetalsPrecipitation withSodium Hydroxide

One operation used sodium hydroxide(NaOH) to precipitate metals from spentrinsewater and spent process baths. Howeverfor wastewater containing chelator, NaOH willnot pull metals from the chelator. The result isthat the metals would pass through the NaOHprecipitation step with the chelator. Thisproblem can be solved by the use of DTC toprecipitate the heavy metals, mostly copperand some lead and nickel, from the chelator.

26.7 Copper Precipitation withSodium Borohydrate

At one system, a feed and bleed system dis-charges spent electroless plating solution fromthe electroless copper bath (Section 21.6). Thespent bath solution goes into a drum. Thecopper is chemically precipitated as metalliccopper, using sodium borohydrate. Theborohydrate also consumes accumulated formal-dehyde. Following precipitation of the copperfrom solution, there is no detectable copper andno formaldehyde remaining in the solution. Thetreated effluent solution contains sodium saltsand some sodium hydroxide, and is managed astreatment residue which can be discharged to thePOTW. The precipitated copper is shipped to anoffsite recycling facility, with other metal-ladenwastes. If this precipitation is done onsite, itmight require an onsite treatment permit.

26.8 EectroStripRecovery Systems

RC Chemical Ultima ElectroStrip is a possiblesubstitution for onsite waste management ofspent process solutions containing copper.This process deposits the etched copper onto acathode, for recovery as nonhazardous metal-lic copper tank bottoms sludge.

27. WATER CONSERVATION

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Water conservation is becoming increas-ingly important as water and energy re-sources become more limited and costly.The cost of water and sewer services, andthe treatment cost of spent rinsewater, aremajor cost impacts.

New equipment often includes cascade rinses,counterflow rinsing, and other water savingtechnology. In one operation, new systemswhich use about 6 gallons/minute replaced 6year old systems which used much more waterat about 18 gallons/minute. This is a majorsavings over an 18 hour daily operation.Savings are $35,000 year.

28. ADMINISTRATIVE IMPROVEMENTS

Publications available from regulatory agen-cies and environmental outreach programs canprovide source reduction ideas for administra-tive procedures. Industry newsletters areanother source of ideas and information.Vendor literature and equipment bid proposalsoften include operating cost information thatcan be a source of information for administra-tive costs, for process equipment procuredfrom the vendor or being considered forprocurement.

28.1 Cost Control

Improved cost accounting can be highlyeffective for reducing waste generation andimproving process economics. The processengineer or staff scientist should work withthe accounting department to identify andaccount for all of the costs and benefits ofsource reduction. The company should estab-lish a cost center for the company’s wastemanagement and source reduction program, asseparate from its other environmental andindustrial health and safety programs.

Manufacturing costs should include watersupply costs and waste management costs.

Costs and waste generation quantities shouldbe unitized according to the number of panelsproduced or other units of production. Costand waste generation then should be assignedto the specific processes producing those unitcosts. This information will enable specificsource reduction activities to be compared onthe actual cost savings provided. This wouldnormalize cost information based on produc-tion. The cost information can be comparedfrom budget year to year. Through careful costaccounting, one operation found that wastemanagement costs were among its top fiveoperating expenses.

28.2 Inventory Control

Inventory control can be a simple and valuablesource reduction opportunity. Chemicalsupplies can be purchased on a “just-in-time”basis. This can minimize the inventory ofsupplies kept onsite. The result is savings ininventory overhead; and less waste generationfrom obsolete, outdated, and surplus chemicalsupplies. Vendor recommendations can helpestablish the timing of delivery. The generatorcan choose from available vendors to getimproved service and reduced costs.

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29. CLOSING COMMENTS

substitute chemicals and process systems thatare compatible with its processes, products,and customer needs.

29.2 Shared Information

Professional acquaintances in the industry areoften willing to share their environmentaltechnology with plant visits and other infor-mation. Such information sharing helps theindustry to minimize its overall environmentalimpact. Shared knowledge of advancingtechnology can provide the generator and theindustry with cost-effective source reductionalternatives that can lead to improved opera-tions, less waste generation, and more cost-efficient operations.

Information provided in this document islimited to that which the source chose torelease. The reader is encouraged to pursuereadily available information sources forinvestigating source reduction opportunities.Good sources are available for comprehensive,state-of-the-art technical knowledge in sourcereduction and recycling for printed circuitboard manufacture.

29.1 Information Sources

Detailed technical information can be ob-tained from vendors, process chemicals andequipment suppliers, equipment expositions,conferences, industry association newsletters,and trade journals. Such professional informa-tion sources can help the circuit board manu-facturer select economical and effective

PUBLICATIONS

The following publications are available from the Department of Toxic Substances Control. Thepublications can assist the printed circuit board manufacturer in organizing an active sourcereduction and pollution prevention program. To obtain pollution prevention publications fromthe Department of Toxic Substances Control, please call (916) 322-3670.

Hazardous Waste Minimization Checklist and Assessment Manual for the Electronics Industry(1996, 76 pp.), Document #405

Assessment of the Semiconductor Industry Source Reduction Planning Efforts (1994, 85pp.),Document #530

Waste Minimization Fact Sheet on Printed Circuit Board Manufacturers (1992, 4 pp.), Document#209

Publications are also available from the U. S. Environmental Protection Agency, regional andlocal governmental authorities, and industry organizations. New publications are continuallybeing released by these and other sources, which can be a valuable source of technical andregulatory information.

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