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Bare spots on electroless gold parts

(-----) January 7, 2008

We run a electroless barrel plating process. We are having trouble running more than 1200 pieces at one time..We have tried a 1600 piece lot and 2000 both have failed. We use a 6x6 barrel for the procedure and the parts have DP Ni on them prior to the gold plating... The spots look as if tho they have no gold on them at all, in spots... Could this have something to do with our Dp Nickel or Electroless Au or could it just simply be the parts sticking together... thanks...

Jason Combs
Plating - Chattanooga, Tennessee, USA

January 10, 2008

Sounds like the barrel is too full and you are not getting solution flow to the inner parts or the solution is depleted by the time it gets to the center parts. Also, tank overloading prevents proper part movement.
Greed is probably the biggest problem in barrel plating.

James Watts
- Navarre, Florida

January 16, 2008

I'm assuming you are talking about a direct displacement immersion plating bath, ~2-5 microinches of Au. It sounds to me like you are either not getting enough agitation of the parts for the initiation of the plating reaction. The parts must be agitated well when first placed in the bath. Another common problem with plating Au over Ni is oxidation of the nickel deposit. One solution we found to this problem is prewetting the parts in the dragout for the gold bath for 2 minutes. Another issue with overloading the Au bath can be the temperature drop when the parts are placed in the bath. This can be addressed by increasing the heating capacity and/or the circulation of the bath or by increasing the bath volume. As previously mentioned the you may also be depleting the Au content or raising the Ni content of the bath beyond the effective limits too quickly. I hope this helps. Good luck.

Brian DeBadts
- Rochester, New York

January 17, 2008

The barrel is probably about 1/2 shot and 1/8 parts or so... Does anyone think that this is too much shot?

Jason Combs
- Chattanooga, Tennessee, USA

January 17, 2008

I have limited barrel experience, but thought that you never loaded the barrel more than half full, total load to get proper mixing.

James Watts
- Navarre, Florida

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