Temperature of acid copper solution
Q. Can anyone give me information as to why bright acid copper plating takes longer during the hot summer months we are plating small (40mm)diameter lead medals .
- I think that when tanks are at 20 °C they plate perfect.
- At 25 °C they plate slow
- At 30 °C and over, impossible !
Does anyone have the same problem if so what suggestions can you give me.?Mick Long
MEDALS - Australia
It is the nature of the beast. You will have to add cooling coils to keep up quality and production when the air gets warm, or the tank heats up from the pasage of current. This information should be available in the Technical Bulletin for the acid copper additives. The higher temperature also chews up brightener, and this creates organic impurities, and the need to carbon treat more often. It would be worthwhile to run the bath at the correct temperature. Please see the finishing.com directory for suppliers.
Falls Township, Pennsylvania
"The Nature of the Beast" referred to above is well known and can be used to your advantage if you so desire. It is as follows:
Electroplating solutions are actually chemical etching solutions that you force to run in reverse with your rectifyer. Especially Acid copper which is heavily laden with 10%v/v of Sulfuric Acid or more. As you have no doubt observed in other systems, as temperature of an etch bath rises, etch rates increase. This is the phenomena you are fighting in the summer months. Acid Zinc baths are even worse than your copper. So on your workpiece, you are trying to plate at say, for example, 20 ASF with temperature cold at 20'C, and it works fine. You get 20 ASF worth of Copper at the cathode. At 25'C, the etching of copper off your part is no longer negligible, and probably has a rate equivalent to 10 ASF but in the reverse direction. So of your 20 ASF supplied by your rectifyer, 10 ASF's worth of the copper is being etched away by your bath, so you only net out a slow 10 ASF at your cathode. At 30'C, the etch rate is so high that it may account for greater than 20 ASF, so you net out with nothing at your cathode. Now just imagine what is happening at your anode! It is dumping copper into your bath! Also the organic brighteners may lose their activity or become sparingly insoluble at these temperatures.
How to use this to your advantage? Higher temperatures can support higher rates of plating if you engineer for them. 100's of ASF. Your throughput can increase 100's of %. But it requires a bit more than just turning up the current.
WOW Dave !
Your information has really got me thinking, back to the books for me I guess.
As I am new to this type of work I have discovered that previous platers have had great difficulty because current consultants informed them that they could plate at temperatures up to 32C.
It's winter now but summer's coming.Mick Long [returning]
MEDALS - Australia
I agree with Tom. The low efficiency in acid copper plating at high temperature is mainly caused by failure in additive functions. With adequate additives, copper deposition can be performed at around 30 °C.
The chemical dissolution of plated coatings can be ignored in the majority cases of plating. In the case of copper deposition, the acid with complexing agents dose not considerably attack copper because the equilibrium potential of copper is more noble than that of hydrogen. Only possible etching results from the disproportional reaction of Cu(++) and Cu to 2Cu(+) at the condition of off-power. This reaction can not take place under plating. Even for zinc plating, the chemical attack almost does not exist during plating. At the off-power, zinc dissolution can not reach the rate as high as 20 ASF at 30C because the overpotential of hydrogen evolution on pure zinc is very high.Ling Hao
- Grand Rapids, Michigan
To prove your assumption that the acid copper bath starts etching the deposit at higher temperatures, try to run this test:
1. weigh 2 pieces of copper
2. suspend them in copper bath samples (in beakers) maintained at 20 and 40 deg. C for as long as you think it will take to etch the copper (1-2 hours?)
3. re-weigh your samples
4. let us know if you detect any weight loss of copper
Did anyone hear of copper anodes dissolving in the sulfuric bath without current? - I have not!
Regards from PlaterB
"PlaterB" Berl Stein
Rochester, New York
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