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Solder causing adhesion problems





2000

Hi All:

We have a company that is plating electroless nickel onto a heat sink that has had copper fins soldered to the main body (also copper). The solder turns black when process through the cleaning operations: alkaline soak, alkaline electroclean, HCl pickle. This has caused adhesion problems , so the platers give the parts a quick copper strike prior to e/n.

I would like to avoid the copper strike for several reasons, including process efficiency: The parts are processed on a hoist up until the copper strike, when they need to be manually handled.

Is the strike acting more as a cleaner than a strike? Note that there are times that the solder is not entirely covered.

So, are there any methods to clean the parts that don't involve current, such as a cyanide based cleaner, microetch, etc.?

Thanks in advance for any help/guidance you can give.

Chris Ford
MA Toxics Use Reduction Inst. - Lowell, Massachusetts



2000

Any major supplier of cleaning chemicals can help with the selection of a proper clean and etch cycle.

If this is tin -lead solder, the lead is the problem and you will probably have to go to a fluoboric acid etch. If I remember right, lead does not like high alkalinity and long soaks.

If the solder is not tin-lead, that needs to be known.

You also need to look and see if it the flux causing the problem.

You do not mention the size of the part.

You may have to find another plater if your current one can not adapt his line.

James Watts
- Navarre, Florida



2000

Chris:

I suspect the cause of your problem is the HCl pickle. It can normally be counted on to turn solder or tin lead plate quite black. The copper strike is probably a sulfate bath and the sulfuric acid can remove some of the black oxide from the pickle, but obviously not all. I would suggest using a different acid as a final pickle. You would not want to use a microetch with solder and Cu together. Try an acid cleaner designed to be a pre-plate cleaner and use 10% sulfuric as the final pickle. I don't know what to expect of electroless nickel over solder, but you must de-oxidize both surfaces to have good results. If you continue to have trouble, give me a call. We specialize in surface treatments and pre-plate cleaners in circuit manufacture and can probably brain-storm a solution together.

Good luck,

Jim Taylor

James M. Taylor
DURATECH INDUSTRIES, INC. - Orange, CA 92865


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