Metal finishing Q&As since 1989
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Gold Plating of Copper Plating
Q. Hello Users,
I am a process engineer working on MEMS based structures and have a lot of plating involved in my process. I am interested in knowing about plating Au on Cu. After plating Cu ~150 µm (in a typical H2SO4 bath with no additives) I plate Au ~2-3 µm from a sulfite bath and notice that my Au is a light brownish color (I notice this same type of color when doing hull cell test on a brass panel). This is not the color I get when I introduce Ni between Cu and Au or when I plate Au on a Au seed layer of about 1000A. Any Comments? Is this just visual and has no effect on performance, like adhesion to Cu or adhesion to lets say Au wire bonding?. Any insight or direction to published information would be appreciated.
- San Jose, California
2003
A. I do not know much about plating but I do know that Cu alloys readily with Au and therefore you need a barrier layer (Ni) between the two metals.
Scott Campbell- Tempe, Arizona, USA
2003
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A. I cannot say to the situation at hand, except to have your gold checked for copper content, but in the long haul the gold will diffuse into the copper or the other way around, I forget, Long term the parts are junk.
One more thought the "seed layer" giving better result is most likely a short term result. When you break contact the grain of the deposit is disturbed and when you add more gold it is most likely giving a short term barrier effect. I do use this method on some parts for better test results, but not over copper.
- Minneapolis, Minnesota
2003
A. Definitely there will be a problem when gold is plated directly on copper. The copper will get diffused into the gold layer and this is more predominant at elevated temperatures, More than 120 °C. Nickel as 'barrier layer' of thickness 5 microns will prevent the diffusion of copper ion into the gold layer. One more point is instead of going directly to copper in H2SO4 (acid copper bath) it is better to give a flash of copper in cyanide copper bath,then in acid copper bath followed by nickel plating-cyanide activation-acid dip-gold flash (gold concentration 2-3 gms/ltr) followed by gold plating
STG.S.Ramanujam- HYDERABAD, A.P, INDIA
2003
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