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Acid copper is treeing

 

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


 

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

 

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
- Australia


 

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
- Charlotte


 

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
- Melbourne, Australia


August 14, 2009

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

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