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topic 29673

Problem for the REAL Experts


We would like to electroless plate (simultaneously) to a variety of materials --- Alloy 42, Copper and plastic (specifically the body of a TSOP). Plating needs to be a good electrical contact/conductor. We are having limited success using Copper/Nickel/Gold. Problem is we can't pass the tape test for adhesion. Different surface preps yield good adhesion to the mold compound -- but not the copper or Alloy 42. Or - good to the copper but not to the mold compound or Alloy 42. Or good to the Copper and mold compound but bad to the Alloy 42. NEVER all three! Any suggestions on surface prep - metal system to use to get the desired results?

Dan Michaels
Electronics Mfg. - Costa Mesa, California, USA



I do not know the configuration of your parts, but if it is possible, I would use an electrolytic Woods nickel strike to give the same surface to the A42 and the copper and then use the preplate process that gives adhesion to A42 and epoxy. If the copper and A42 can be bussed together this approach should work. if they can not be bussed together then perhaps they can both be given a nickel strike before assembly.

Pat Mentone
Pat Mentone
St Paul, Minnesota


Whilst I am no expert on IC technologies, I can see some problems in what you are trying to do. Alloy 42, as I understand it, is a mixture of 42% nickel, balance Fe. This will need careful activation to obtain adequate adhesion, possibly using a Woods nickel strike. Plating onto plastics is a technology within itself and although you do not specify the type of plastic, it will almost certainly need etching. This is conventionally done with chromic acid, but I wonder if your circuit components will be safe under the etching conditions. Plating onto copper shouldn't be a problem, especially if it is dull copper and doesn't have any nasty organic additives in the bath. Whatever the system, the different components will require different pre-plating processing. I would therefore recommend you think about either plating the individual components (Alloy 42, Cu and plastic) separately before final assembly and then use the common metal conductivity to overplate the final product, or you think about vacuum coating. Vacuum coating can be done by PVD, CVD or even sputtering. The surfaces can be prepared and activated by plasma discharge and/or ion bombardment and since the whole operation will be under vacuum, you will maintain a very active surface that will be responsive to good adhesion.

trevor crichton
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK

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