Acid Copper Plating issues and problems, Q&A
Acid copper is treeing
Q. Recently we have increased the acid content from 80g/l to 200g/l in our acid copper plating tank. This was done to improve throwing power (plating of printed circuit holes). The deposits we desire are non bright and smooth up to about 100 um. However, since the addition of acid the deposits became very rough and treeing is visible. Copper content is 20g/l. No additives or chloride have been added because originally when acid was low, we found the deposits to be relatively smooth. Cathode CD ranging from 1 to 2 A/dm^2 has little effect. Could the absence of chloride ion be responsible for tree growth ? Are additives essential for smooth (non bright) deposits in high acid baths ? Would anyone recommend reverse pulse plating as a solution ?Adam Seychell
- Melbourne, Australia
A. I have never seen circuit boards plated in an acid copper bath that did not have additives. Does not mean it cannot be done. Temperature should be 70-90 degrees F. You should have phos-copper anodes, not pure copper anodes.
An additive promotes smooth copper deposits, assists plating in thru holes, assists in trying to obtain 1:1 thickness in the hole to the surface of the board. If you use an additive, the chloride must be present at 70-90 ppm. Don't know if no chlorides in your bath is the problem.
Should be using oil free air agitation. Side to side movement of the plating rack helps. Pulse plating may help, more expensive than standard rectifier.Bill Hemp
tech svc. w/ chemical supplier - Grand Rapids, Michigan
A. You did not need to add so much sulfuric. You can turn the current down some. Adjust a little at a time. Move your anode around some, away from trees to low spots. If you will calculate the total sulfuric and in proportion add copper sulfate and distilled water, you should come out with approx. 240 g/l copper sulfate and 60 g/l sulfuric. If you do want to try chloride then separate a liter from your revised bath and try 0.08 g/l chloride. Try this first before you add to entire bath. Make sure you have air beneath the object in large bubbles. Use a very small amount of a mild liquid soap. Very small at a time. Try in the 1 liter bath first till you get the results you need. Mainly reduce the current density. Approx. 1/10th amp per S.I..Clinton Driggars
- CELINA, Texas
Thanks Clinton & Bill for replying to my post. All the recipes I've seen for printing of circuit boards plating recommend a high acid and low copper bath. Something on the order of 200 g/l H2SO4 and 60 g/l CuSO4.5H2O. Going by my experience it may be such baths require additives for smooth deposits. I have now contacted a local supplier for additives.
One interesting outcome with the change to high acid low copper bath was a significant improvement in hole wall plating. We are currently experimenting with our own carbon black method for preparing the holes for plating, and found the plate-ability over the carbon surface depends greatly on the bath throwing power.Adam Seychell [returning]
A. Both previous answers are correct. Lack of Cl will cause treeing in high c.d. area. Keep CuSO4 180- 220 g/l and H2SO4 60- 75 g/l. Some call it maintaing a ratio of three. Avoid any contamination of Fe, Cr.Payal Mag
Q. Sorry, I'm getting slightly confused. Are we mixing up the numbers ? My local plating supplier recommend 180-220g/l of H2SO4 and around 60-80g/l of copper sulfate. An online article on copper plating also shows similar ranges.
Is it sulfuric acid or copper sulfate that should be 180-220 g/l ?Adam Seychell [returning]
- Melbourne, Australia
August 14, 2009
A. There is obviously some confusion here and it is likely that decorative acid copper formulations are being mistaken for printed circuit ones. The high metal/low acid variety would generally be used for decorative baths and the low metal/high acid type are used for printed circuit boards. The low metal concentration limits the current density that can be applied to the boards but the high sulfuric acid content certainly makes this blend effective for building a thickness of copper in the holes about equal to that which is plated onto the face of the boards. And, the additives become very critical in the production of fine grained and ductile, low stress deposits.Larry Abbott
- New Berlin, Wisconsin
Removing excess chloride from bright acid copper plating solutionJune 12, 2014
Q. I have trouble in my bright copper acid solution: an excess of chloride ion (124 ppm), how to lose the chloride ion to stabilize the solution?
- siantar, north sumatera, Indonesia
A. Hi Mirzal. Chloride ions are in general among the most soluble of all ions. To my knowledge there is no practical way (except dilution) to remove them from an acid copper plating solution. Although there are some insoluble metal chloride salts, I know of no feasible way to employ those reactions.
As a matter of curiosity though, I see that CuCl is insoluble, and that there is a laboratory method to precipitate it from the soluble CuCl2 by adding copper powder and steam, while excluding air, then filtering it out. See, for example, www.inc.bme.hu/en/subjects/genchem/chlorides.pdf
If I am wrong and there is a practical way to remove chlorides, or if anyone has attempted this "CuCl2 + Cu -> 2CuCl" method, please advise.
Ted Mooney, P.E. RET
Pine Beach, New Jersey
June 16, 2014
1) BRIGHT ACID COPPER PLATING
SULPHURIC ACID = 45 TO 65 G/LR
CHLORIDE = 40 TO 80 PPM
ADDITIVES FOR LEVELING & BRIGHTENING.
2) HIGH THROW ACID COPPER PLATING (MOSTLY USED FOR PCB FOR 1:1 RATIO)
SULPHURIC ACID = 90 TO 110 G/LR
CHLORIDE = 30 TO 70 PPM.
ADDITIVES FOR SMOOTH LEVELING.
Ludhiana, Punjab, India
June 20, 2014
A. There is quite a lot of information on the internet concerning the removal of chloride from acid copper baths.
Although I have never done this, the most common method seems to be the addition of a silver compound, usually silver nitrate, silver sulfate, or silver carbonate. A silver nitrate solution would be the most convenient but the nitrate ion would remain in the bath and I don't know how this would effect the plating. In any case, 3.04 grams of silver would precipitate 1 gram of chloride, in the form of silver chloride, AgCl.
Another method that was mentioned in two references was the use of zinc dust in exact amounts. This would reduce some of the copper(II) to copper(I), which would then precipitate some of chloride as cuprous chloride, CuCl.
In any case, the precipitate formed would have to be completely removed by filtration before using the bath. Otherwise, any remaining in the bath would most surely produce roughness on the plated parts. It would be best to treat the solution in a separate treatment tank. In one reference, a 5 micron filter is suggested for the removal of the precipitate.
If it were me, I would first try one or more of these methods on a small portion of the bath, say a liter or so.
- Nevada, Missouri, USA
June 23, 2014
Silver sulfate works. Other than the expense, this is a reliable method to remove excess chlorides. High chlorides increase stress in the copper deposit.Lyle Kirman
water treatment systems - Cleveland, Ohio