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Bad solderability after immersion gold plating

December 14, 2009

Hi,

I am an electroplating engineer in a Chinese company. Now I am facing a problem of bad solderability after thinner gold plating by immersion plating. I checked all process parameters and no abnormality found, such as nickel pollution of gold solution, or bad hot water cleaning process after gold plating.

I need your experience and help.

thank you.

Philco Wang
plating shop employee - DongGuan, Guangdong, China

I would start with asking the gold vendor, the solder vendor and possibly even equipment vendors if it is possible to solder on fresh and/or old gold plate. You may not be using an adequate resin or other flux to properly work. Solder temperatures can be critical also.

James Watts
- Navarre, Florida
December 16, 2009

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December 21, 2009

Immersion gold is both thin and porous.

It dissolves immediately in molten solder.

The process is now soldering to the underlying nickel which may be passive due to the porosity of the immersion gold depending on the storage conditions.

It is necessary to choose a type of flux suitable for this operation. Simple rosin fluxes will not be sufficiently aggressive. You should speak to your solder supplier.

You cannot cure the problem by applying thicker (electroplated) gold. Since this dissolves in the solder and can produce brittle intermetallic compounds there is a possibility of "good" solderability but a weak solder joint. The small amount of gold in an immersion deposit is insufficient to cause this problem.

Geoff Smith
Hampshire, England