Electrolytic Copper Plating Additives and Contaminants

Electrolytic Copper Plating Additives and Contaminants

Wayne JonesWayne Jones

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Electrolytic Copper Plating Chemistry

Typical DC Acid Copper Electroplating Solution contains:

> Inorganic Sulfuric Acid (180 - 250 g/l) Copper Sulfate (40 - 100 g/l) Hydrochloric Acid (25 - 100 mg/l)

> Organic Brightener (2 - 10 mls/l) Leveler (5 - 15 mls/l) Carrier (25 - 100 mls/l)

> Water (Balance)

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Electrolyte Control

Sulfuric Acid Virtually unconsumedDragoutTitration or Specific Gravity

Copper Sulfate Maintained by Anode ErosionTitration, UV/Vis

Chloride Maintained by chemical analysisTitration, Ion Specific Electrode, UV/Vis

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Additives Mostly Proprietary

Brighteners are plating accelerators, which act as a micro-leveler and impact grain refinement. They tend to be attracted to cathode induction zone points of higher electro-potential, temporarily packing the area and forcing copper to deposit elsewhere. As the copper deposit levels, the local point of high potential disappears and the brightener drifts away, as well as depleting (hydrolysis) to a higher level of activity. Chemical Family - Organic Sulfides, Disulfides, Thioethers, Thiocarbamates.

Levelers are strong secondary plating inhibitors, which typically co-function with Brighteners to reduce copper growth at protrusions and edges. They improve mass transfer to localized sites of lesser electro-potential or feature height. Chemical Family Quaternary Nitrogen Cmpd.

Carriers are plating inhibitors or suppressors, they create and maintain a defined diffusion layer at the Anode (which regulate the flow of Cu+2 ions into the electrolyte and ultimately to the cathode (board surface). Carrier depletion occurs as the PEG cleaves. Chemical Family Polyethylene Glycol (PEG), Polyalkylene Glycol (PAG)

Chlorides mild plating inhibitors, which stabilizes the Cu+1 ion that serves as an intermediate in the electro-deposition process during reduction to Cu +2. Additionally they modify adsorption properties of carrier to influence thickness distribution. Chemical Family Hydrochloric Acid

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Hull Cell Additive Control

Carbon Treated Copper Bath

ASF 75, Needs Brightener

ASF 90, Proper Operating Range

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CVS/CPVS Cyclic (Pulse) Voltammetery Stripping

CVS/CPVS is an indirect bath measurement which measures the combined effect of the

additives and by-products on the plating quality

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CVS and CPVS Instrumentation

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Copper Anodes

Phosphorized: 150 650 ppm POxygen Free Casting

Grain structure grows from surfaceto the center, resulting in uniformcorrosion of the anode.

Anodes are conditioned when new by developing a necessary black CuO film Dummying.

Balls, Nuggets, Bars.

Anode surface area and continuous bath agitation is critical.

Contaminant Concentration, Wt %Lead 0.0002Zinc 0.0001Nickel 0.0002Iron 0.0004

Sulfur

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Pattern Plating

1) Full panel Electroless Copper deposition.2) Photoresist apply, expose with positive image artwork -

majority of copper surface shielded, develop.a) Reduced electroplated surface. b) Lower current capacity required. c) Less copper anode bank consumption.d) Less copper in etchant.

3) Plate Copper, Plate Tin (Etch Resist)a) Adds several additional wet process baths.

4) Strip Photoresist Potassium Carbonate5) Etch Copper Ammoniacal 6) Strip Tin Resist Nitric Acid7) Antioxidant - BTA

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Panel Plating

1) Full panel Electroless Copper deposition.2) Full panel Electrolytic Copper plated.

a) Higher current capacity required.b) Significant copper anode bank erosion. c) Smooth, even, bright finish on panel and hole walls. d) Easily cleaned/prepd for downstream processing.

3) Photoresist apply Negative Image4) Develop - Carbonate5) Etch Ammoniacal or Cupric Chloride

a) Significant copper buildup in etch, more maintenance.

6) Strip Potassium Hydroxide7) Antioxidant - BTA

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Contaminants Drag in / Leach Out

Inorganics ICP / GFAA analysis Trace MetalsIron (Fe)Calcium (Ca)Tin (Sn)Lead (Pb)Nickel (Ni)Antimony (Sb)

Organics Hull Cell / CVS / TOCCleaner/Predip surfactants (inactive)Resist Photo-initiators (inactive)Anode Bag Sizing (inactive)Additive breakdown products / fragmentation (active)

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Chemistry Impact / FMEA

CuS04 H2SO4 Cl- Brightener Leveler Carrier

Burned Copper Deposit Low Low / High Low Low

Poor Throwing Power High LowPoor Leveling Low Low / HighRoughness LowPitting

Streaking HighPoor response to additives High HighStep Plating LowGrain Structure Poor High Low Low LowAnode Color Green HighAnode Color Dark LowAnode Color Bright HighSoft Copper Deposit LowBrittle Copper Deposit HighLow Tensile Strength

Dull/Matte finish

Copper Nodules HighSpiked Copper Deposit Low / High

Defect / Failure ModeInorganic Organic

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Contaminant & Process Impact / FMEA

TOC Particulates Trace ASF Anodes Circulation Agitation Temp

Burned Copper Deposit High High High Low Low

Poor Throwing Power High HighPoor Leveling High LowRoughness High High High / Low FiltrationPitting High High LowStreaking High HighPoor response to additives High High High / Low HighStep Plating

Grain Structure Poor

Anode Color Green

Anode Color Dark

Anode Color Bright

Soft Copper Deposit HighBrittle Copper Deposit High HighLow Tensile Strength High HighDull/Matte finish

Copper Nodules High Low / HighSpiked Copper Deposit Low / High

Contaminant / Impurities Mechanical / ElectricalDefect / Failure Mode

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Burnt Plating Unbalanced CD / ASF

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Even After Microetch

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Plating Characteristics Impact Etch Differential

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Topography Differential SEM/BSE

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Copper Topography Variations (80x)

Burnt Copper Plating Transitional

Detectable Bright / Leveled

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Spiked Copper Surface / Knee

Courtesy Sanmina-SCI, Owego

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Spiked Copper Hole Wall

Courtesy Sanmina-SCI, Owego

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Grain Structure Failure Blind Via

Courtesy Sanmina-SCI, Owego

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Courtesy Sanmina-SCI, Owego

Copper Chicklets Grain Structure

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Cobblestones Hole Wall

Courtesy Sanmina-SCI, Owego

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Cobblestones Hole Wall

Courtesy Sanmina-SCI, Owego

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Surface Nodule Process Debris

Courtesy Sanmina-SCI, Owego

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Surface Nodule - Debris

Courtesy Sanmina-SCI, Owego

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Barrel Crack / Lam Voids 6x TS

Courtesy Sanmina-SCI, Owego

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Summary: Surface Contaminant Evaluation

Macro Level: PCB fabricator - SPC, IPC TMs and specs, customer requirements, cleanliness, water quality, post process residues,solderability, visual inspection.

Micro Level: Post fab evaluations employing FTIR, Raman Spectroscopy, HPLC, SEM - EDS/Auger, IC, ICP/GFAA.

What to look for:Process residues (MOP, Resist Remnants, HW Salts, OSP)? Co-plated contaminants (inorganic / organic)?Hydrides, Oxides, Sulfides, Carbides, Halides?Gas entrapment?

Whats changed the most:Etch Resists (Sn vs Sn/Pb) and strip chemistry?High Temp OSPs?DC or Pulse (Reverse and Duplex) Plating and chemistry High aspect ratio?