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Detection of Banned and Restricted Ozone-DepletingChemicals in Printed Circuit BoardsRichard N. Lee a & Bob W. Wright aa Chemical and Biological Sciences, National Security Directorate, Pacific Northwest NationalLaboratory , Richland, WA, USAPublished online: 11 Dec 2008.
To cite this article: Richard N. Lee & Bob W. Wright (2008) Detection of Banned and Restricted Ozone-Depleting Chemicals inPrinted Circuit Boards, Environmental Forensics, 9:4, 320-339
To link to this article: http://dx.doi.org/10.1080/15275920802502083
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Environmental Forensics, 9:320339, 2008Copyright C Taylor & Francis Group, LLCISSN: 15275922 print / 15275930 onlineDOI: 10.1080/15275920802502083
Detection of Banned and Restricted Ozone-Depleting Chemicalsin Printed Circuit Boards
Richard N. Lee and Bob W. Wright
Chemical and Biological Sciences, National Security Directorate, Pacific Northwest National Laboratory, Richland, WA, USA
A more-than-5-year study directed toward the detection of trace residual halogenated solvents in circuit boards was recently completed.This work was undertaken to demonstrate the potential for reliable detection of solvents used during the fabrication of printed circuitboards found in a wide variety of electronic products. Residual solvent detection was demonstrated for spiked boards after an agingperiod of 5 months and for printed circuit boards removed from a variety of used (at least 5 years old) and new electronic products.The analytical system and standard operating procedure developed during this study provide the tools required to assess and confirmcompliance with regulations associated with the use of ozone depleting chemicals.
Keywords: ozone-depleting chemicals, Montreal Protocol, residual solvents, purge and trap, precision cleaning, thermal desorptionanalysis
The objective of this work was to develop and validate a purgeand trap (P&T) technique to detect residual solvents used in thefabrication of printed circuit boards (PCBs), or their compo-nents, and to provide a tool for measuring regulated and bannedindustrial chemicals related to stratospheric ozone depletion andglobal warming. P&T is a widely applied technique (Bianchiet al., 1991) for the concentration of volatile and semi-volatileanalytes in environmental samples before separation and analy-sis by gas chromatography (GC). Highly sensitive analyte detec-tion (Simmonds et al., 1974, Shapiro et al., 2004) was achievedfor the halogenated solvents of interest by employing an electroncapture detector (ECD).
Previous studies directed at the detection of residual sol-vents are dominated by work focusing on environmental ma-trices, primarily soils, sediments and solid wastes. Where in-terest has extended to commercial products, it was initiated inresponse to concerns related to surface ozone concentrationsand the inhalation or ingestion of solvents, and the consequentimpact on human health. Sampling methods applied to the de-tection of emissions from commercial products have benefitedfrom the wealth of information developed for characterizationof ambient and workplace atmospheres. This information isdocumented in methods developed under United States Envi-ronmental Protection Agency (USEPA) direction in responseto its mandate to understand, characterize and provide guid-ance for responding to environmental issues (USEPA, 2002 and
Received 11 July 2007; accepted 6 March 2008.Address correspondence to Bob W. Wright, Chemical and Biolog-
ical Sciences, National Security Directorate, Pacific Northwest Na-tional Laboratory, P. O. Box 999, Richland, WA 99352, USA. E-mail:email@example.com
USEPA, 1999a, 1999b). Products examined for residual sol-vents include building materials (American Society for Test-ing and Materials [ASTM], 2005, 2006; California Departmentof Health Services [DHS], 2004), pharmaceuticals (Schuberth,1996; Wittrig et al., 2004; International Conference on Harmo-nization [ICH], 1996, 1997), foods (Fleming-Jones et al., 2003;Heikes et al., 1995), as well as personal care products (CaliforniaEPA, 2003, 2005a, 2005b; Rickman et al., 1997a, 1997b) andelectronic products (Bjorn-Hansen, 2003; European ComputerManufacturers Association [ECMA], 2001). Analytical meth-ods utilized during these studies employed several different va-por concentration techniques, including P&T (Schumacher andWard, 1997), headspace (George et al., 1997) and solid phasemicroextraction (Urakami et al., 2004) followed by GC anal-ysis. While many of the volatile organic compounds (VOCs)associated with these investigations are also ozone-depletingcompounds (ODCs), the study reported here represents a sig-nificant departure from a focus on local, health-related impactsto addressing the ultra-sensitive detection of restricted chem-icals in industrial parts manufacturing. Studies that have fo-cused on electronic products were generally not restricted tosingle components, such as PCBs, and were concerned withhealth related impacts from inhalation. Only widely used indus-trial solvents were reported (chloroform, trichloroethene [TCE]and tetrachloroethene [PCE]) and a single reference to PCBsreports the detection of only aldehydes and ketones associatedwith phenol/paper-based and glass/epoxy-based PCBs (USEPA,1998).
Rigid substrates employed for the production of PCBs usedin many consumer products are resin-impregnated paper (FR-2)or glass fiber (FR-4). These matrices are sufficiently porous andadsorptive to trap cleaning solvents used during PCB fabrica-tion. Since a circuit board and its components may be exposed
Ozone-Depleting Chemicals 321
to a variety of solvents during assembly and associated oper-ations, these solvents could be retained by the circuit boardsfiber reinforced polymer matrix and released over time (Manko,1995). The detection of these residual solvents is dependenton the rate of their release and the sensitivity of the detectionmethod. Given the detection sensitivity of the ECD to halo-genated compounds, the question was reduced to whether thesesolvents were retained within the circuit board matrix for suf-ficient time and released at a rate that permitted unequivocalidentification over an aging period spanning months to years.Such residues should be released, concentrated and detected byapplication of a P&T sample collection procedure preceding GCanalysis. This technique can be used to ensure compliance withrelevant laws and regulations restricting use of industrial sol-vents associated with adverse environmental impact. Althoughthis study focused on small PCBs (up to approximately 6 10 inches), the technique described could be applied to largerboards.
A discussion of solvents identified as ODCs is presented inthe Appendix. Precision cleaning operations represent a sig-nificant application area for these chemicals. Of particular in-terest were 1,1,2-trifluoro-1,2,2-trichloroethane (CFC-113) andmethyl chloroform (TCA) (solvents historically linked to cir-cuit board production), and common industrial halocarbons thatmight be available as substitutes for these solvents. In the mod-ified P&T procedure reported here, a circuit board sample isenclosed in a container and purged with high-purity helium toremove ambient air. Subsequent purge of the container with highpurity helium was accompanied by cryogenic collection of aconcentrated purge gas sample for GC/ECD analysis. A bread-board system was used to investigate analyte detection usingsolvent spiked circuit boards and aged boards removed from re-tired laboratory and office equipment. This system also providedoperational experience essential to the design of a dedicated GCsystem specifically devoted to residual solvent detection thatwas developed during this study for use in assessing compliancewith restrictions placed on ODC solvents. Both analytical sys-tems are described in the following sections along with variousstudies used to assess system performance and data interpre-tation. Finally, the results of these studies led to developmentof a dedicated P&T system and a standard operating proce-dure (SOP) (Pacific Northwest National Laboratory [PNNL],2007) for trace detection of residual solvents associated withPCBs.
Method development work emphasized halocarbons that havebeen or could be used in the electronics industry for PCBproduction. The chromatographic retention properties of thesechemicals were characterized as a prerequisite to their iden-tification during the examination of PCBs taken from com-mercial products or purchased off the shelf. Prominent halo-
carbon solvents, freon replacements, and the ODC chemicalscarbon tetrachloride, 1,1,1-trichloroethane (TCA), and CFC-113 for chromatographic standard preparation were purchasedfrom Sigma-Aldrich Chemical (St. Louis, MO) or Chem Service(West Chester, PA). Other ODCs, not available in the US, werepurchased from ABCR Specialty Chemicals (Karlsruhe, Ger-many). In addition to their use in standards, some halocarbonswere used to prepare spiked PCBs for investigating solvent re-tention by circuit board matrices. This required preliminary anal-ysis of a PCB blank, exposure to one or more known solventsand a sufficiently long pre-analysis aging time to demonstratethat solvent loss rates were low enough to provide evidence thatresidual solvent detection in products received at retail outletswas a practical objective. Test boards, previously examined forresidual solvents, were placed on a flat surface and treated witha measured volume of one or more solvents. After all tracesof the solvent(s) had disappeared, by evaporation or migrationinto the PCB matrix, spiked boards were stored open to ambientair in a laboratory or office isolated from chemical storage anddispensing operations. These boards were then examined over aperiod of several months to determine the potential for residualsolvent retention and detection over an extended time period.
Breadboard Gas Chromatography System
Analysis was based on the cryogenic collection of volatiles inthe purge gas stream followed by chromatographic separationusing a Hewlett-Packard (HP [Little Falls, New Jersey]) 5890Series II GC fitted with an HP 63Ni or Valco 140BN ECD([Houston, Texas]). Chromatograms were recorded using a HP3396B recording integrator. Selected circuit board samples werereexamined to confirm residual solvent identity employing aVarian Instruments Saturn 4D ion trap mass spectrometer (MS)(Walnut Creek, California). Data from these confirmatory exper-iments were recorded and processed using Saturn GC/MS workstation software (Version 5.41) and a Dell Optiplex GX1 (RoundRock, Texas) computer. As illustrated in Figure 1, the basic an-alytical system consisted of a sample container (new, uncoated,1-gallon metal paint can fitted with a Swagelok [Solon, Ohio]bulkhead union), associated purge gas flow system, cryotrap, andGC. Ultrahigh-purity helium was passed through a purificationsystem (high capacity gas purifier, Supelco 23800-U [St. Louis,Missouri], with purifier tube, 22396) before entering a Swageloktee to feed both the purge and carrier gas streams. Purge gas(20 mL/min) from the sample container was passed through aU-tube trap (nickel, 1/16 inch outer diameter, 0.040-inch in-ner diameter, 50-cm length) immersed in a liquid nitrogen-filledDewar to trap and concentrate volatiles released from circuitboard samples. Purge gas flow was measured with a mass flowmeter and periodically confirmed using a bubble flow meterwhile a helium leak detector was used to confirm the absenceof leaks. At the end of the collection period (20 to 100 minutesduring the method development phase of this work), the in-line6-port valve (Valco Instruments, D6UWE) was rotated to theinject position to divert carrier gas flow through the trap, which
322 R. N. Lee and B. W. Wright
Figure 1. Schematic illustration of the breadboard residual solvent analysis system.
was removed from the liquid nitrogen bath, and allowed to warmto room temperature to permit transport of the collected ana-lytes to the GC. The capillary GC column (Supelco SPB-624column, 30 m 0.25 mm, df = 1.4 m, Cat. No. 24255) washeld at 20C during the 3-minute transfer period before initiat-ing the temperature program, 20C (0.0-min hold) followed by10C/min to 80C (0.0-min hold) and then 20C/min to 205C(4.0-min hold), for separation and detection of collected sol-vents. Sample components were identified by their retentiontimes determined from the analysis of external standards andfrom internal standards (chloroform, TCE and PCE) consistentlyobserved at measurable levels as a consequence of ambient aircontamination. Use of an ECD permitted selective and highlysensitive detection (10100 femtogram range) (Agilent Tech-nologies, 2001) of halocarbon solvents free of interference fromother organics present in the circuit board matrix.
Dedicated Ozone-Depleting Compound Gas Chromatograph
Initial experimental work with the breadboard system demon-strated the feasibility of the...