Guest Editorial -For Plateworld.com                                                 

 Don Baudrand, Don Baudrand Consulting,   e-mail:donwb@tscnet.com

COPPER PLATING II

Acid copper plating

  1. Sulfuric acid copper plating solutions formulations: for the conventional plating solution, copper sulfate 5 waters of crystallization 200-250 gm/L and 45 to 90 g/L sulfuric acid.
  2. The high throw copper uses 60-100 g/L copper sulfate. 5H20, 180-270 gm/L sulfuric acid and 50-100 ppm chloride.

Comments: from experience, I found that adding 50 to 60 ppm chloride is beneficial for conventional acid copper solutions. Chloride reduces anode polarization, aids brightness with or without addition agents. Below 30 ppm chloride the deposit is large grained and dull. Above 120 ppm chloride the deposit is grainy and dull.

Anodes

Electrolytic copper sheets have been used for many years for both cyanide and acid copper plating solutions. Cast bars, and rolled copper are also used. High purity-oxygen-free anodes are used because there is less anode sludge to clog the anode bags. However, the very best anodes for acid copper are phosphorized copper anodes that contain from 0.004% to 0.006% phosphorus. Less sludge and particles result. These anodes come in various forms. Common is bagged titanium baskets with copper balls or chunks of copper

Anode current density should be less than 5 amps/sq decimeter. Using vigorous agitation the anode current density can be higher. Anode area should be about 2 times the cathode area. Less anode area can result in polarized anodes, generating more particles and reducing the current available for plating.

Impurities

Iron, Nickel and Zinc do not co-deposit at copper plating current densities. Nickel and iron reduce the conductivity. Higher copper concentration can overcome this temporarily. Nickel and iron cannot be removed from the solution. Arsenic and antimony embrittle the deposit, but will plate out at about the same current density as for copper and thus the solution will deplete these impurities as plating continues as long as no new source of these impurities is introduced. Lead is insoluble in acid copper solutions forming a lead sulfate precipitate. Organic impurities can be removed by carbon treatment. Impurities can come form anodes. It is important to use high purity anodes and appropriate anode bags, I like polypropylene felt or a combination of polypropylene inner bag and the felt outer bag. It is important to keep the bags clean to prevent clogging that leads to anode polarization. Periodic cleaning of the bags is recommended.

TROUBLE SHOOTING ACID COPPER PLATING SOLUTIONS

Rough deposits -Cause

Remedy

Particles, grease, buffing compound, Dust and dirt Filter the solution
Anode to cathode ration wrong Adjust to 2:1 ratio
Wrong anodes Use Phosphorized copper anodes , Phosphorus too low
Current density too high Lower CD
Low sulfuric acid Add sulfuric acid
Rectifier ripple Add filter to rectifier, equalize tap switches
Step Plating or large grain size Chloride too low, adjust to about 50 ppm
Pitting

Remedy

Substrate has pits, grease or oil Filter or carbon treat
Excessive or non-uniform agitation Check spargers and correct
Inadequate cleaning Improve cleaning
Burning

Remedy

Low copper content Add copper
Chloride is out or range Adjust Cl to 40-60 ppm
Low temperature Adjust to 70 degrees F or higher
Poor agitation Increase agitation
Brightener low Add brightener
Anodes too long Work should be lower than anodes.
Poor throwing power

Remedy

Copper content too low Raise copper content
Sulfuric acid too low Add sulfuric acid
Temperature too high 70-78F
Metallic contamination Analyze and purify if possible, Low CD electrolyze (Dummy plate)
Large grain size

Remedy

Chloride too low Adjust to 40-50 ppm
Brightener too low Add brightener
Treeing and nodulation

Remedy

Chloride too low Add chloride to 50 ppm
Poor response to brighteners

Remedy

High brightener content, Organic contamination Carbon treat
High chloride Reduce
Anode polarization Add anodes
Metallic contamination Dummy plate at low CD
Temperature too high Lower temperature to about 70F
Poor leveling

Remedy

Low brightener or excessive brightener Adjust brightener
Low Current Density Raise
Organic contamination Carbon treat
Streaking

Remedy

High brightener or organic contaminations Carbon treat
Poor cleaning or poor rinsing Adjust cycle
Deposit too hard

Remedy

Metallic contamination especially High iron Dummy plate (Iron is not removed by dummying at low CD)
Organic contamination Carbon treat
High sulfuric content Decant
Low temperature Raise to 70F

ACID COPPER FOR PRINTED CIRCUITS

Dishing or poor deposit around the holes-Cause

Remedy

Leaching organics from resist, High brightener and/or other organic contamination Carbon treat
Cleaner drag in Improve rinsing
Incorrect agitation Analyze and adjust
Nodules in the holes

Remedy

Poor drilling Use sharp drills
Temperature out of range Adjust to suppliers recommendations
Particulate matter in solution Filter
High brightener Carbon treat and adjust


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