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Date: | Sat, 22 Feb 1997 06:33:41 -0600 |
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I have found all the factors listed in Mr. Grosso's message to be a
cause of uneven plating in our electroless nickel/immersion gold
plating line as well. I'd like to add a couple more:
-- incomplete removal of microetch residues before the activate step
-- activate bath that is near or past the suppliers recommended metal
turnovers or is that is significantly under operating temperature
Michael Holan
Radian International L.L.C.
Electronics Division
michael_holan @radian.com
______________________________ Reply Separator _________________________________
Subject: Re: electroless nickel finish
Author: John Grosso <[log in to unmask]> at Internet
Date: 2/20/97 12:53 PM
Uneven electroless nickel plating has been traced in the past to following
factors
1) Residual tin lead
2) Overstable electroless bath (normally caused by over adds of replenishments)
3) Excessive agitation level in the electroless bath
4) Too low a loading factor in the electroless bath
5) Poor solder mask development (in processes where Ni/Au is applied after
mask)
In the Technet message, tin is described as the etch resist. We have actually
used immersion tin as a pretreatment for electroless nickel in the past. It is
not clear whether incompletely stripped electrolytic tin might lead to
initiation problems. However, the fact that the uneveness was visible at the
tin strip stage suggests that the stripping or the tin deposit might be the
problem.
The effects of traces attached to pads are usually caused by larger areas of
copper helping to overcome the reluctance of a particular pad to initiate.
Gold thickness is normal on the dull pads, since the immersion gold bath will
also deposit a similar thickness on bare copper.
Hope this is of some help.
The Shipley Company
John S. Grosso
Director
PWB R&D
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