Scott

I cannot answer your question about the Enteck and the tarnishing, but I am 
wondering why you have selective gold plating and the Enteck process.  

The electroless gold plating can be used to ensure solderability of SMT 
pads.  We presently populate and reflow a PCB that is electroless gold over 
electroless nickle.  The gold plate ensures the solderability of the nickle 
and the thickness of the gold plate is such that you do not have a gold 
embrittled joint..  We have been running this in production for well over a 
year with no solderability problems.

This process was chosen because we needed a nickle pad on the PCB that 
contacted a nickle terminal within the housing(like metals) for wear 
purposes.  Originally the PCB was going to be the nickle plate with HASL 
and the one pad would be masked off so it would stay nickle.  The bare 
board fabrication cost was less by using the nickle plate and then the gold 
plate.  The other process was lengthier and required masking of the one pad 
during the HASL step and then removal of the mask.  Since gold is a noble 
metal, we can leave it on the contact pad with no problems and the gold 
ensures the solderability of the nickle.

To re-ask my question--Why have a PCB with some pads gold plated and the 
other Enteck, thus requiring more steps in the PCB fabrication when you 
could have the entire PCB electroless gold plated and still have proper 
solderability.
-------------
Original Text
From: C=US/A=INTERNET/DDA=ID/TechNet-request(a)ipc.ipc.org, on 9/18/96 7:30 
AM:
From: Scott Westheimer
Date: 9/17/96

Sorry if my message of last night was not very clear, but what can you
expect at 2:30 am. 

The issue is with entek coating not the gold plating. The panels have
selective gold plating on some pads and the others have entek. The problem
is that when the panels are first gold plated( electrolydicly ), then S/M 
the entek pads are fine. However, when the panels are first S/M and then
gold plated the entek pads are tarnished around the edges. Does anyone have
experience with this problem.

Thanks,

PS Before anyone makes the comment, the boards are enticed after all the
processes have been completed.

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