Whoa Chuck!
Have you looked at the edge of your reflowed solder product
lately? There is plenty of exposed copper along the edges
of those traces. Nickel/Gold is a viable etch resist though
it is prone to slivering and undercut becomes an issue.
Usually Ni/Au is chosen as the final finish and is used as
an etch resist only as an afterthought, but it works in
alkaline etchant.
I've found that, in order to avoid excessive slivers, the
nickel thickness has to be 0.0002" thick so it won't break
when undercut in etching.
Do we want to open the Pandora's Box of "exposed copper on
trace edges" discussion? How about exposed copper on trace
surfaces? I know our customers are dead set against exposed
copper when soldermask chips off the PWB during assembly,
yet these boards have exposed copper on trace edges all the
time and in greater area.
Regards,
Dave Sullivan
Rockwell Collins, Inc.
[log in to unmask]
______________________________ Reply Separator _________________________________
Subject: Re: Gold as Etch Resist
Author: [log in to unmask] at ccmgw1
Date: 1/29/97 9:50 PM
So, if you use the Ni/Au as an etch resist, what protects the trace edges
corrosion? Do you plan to plate it twice or strip the gold? I think
the photo resist is cheaper.
Chuck Brummer, Acuson.
______________________________ Reply Separator _________________________________
Subject: Gold as Etch Resist
Author: [log in to unmask] at ccUnix
Date: 1/29/97 3:35 PM
Hello,
Please post information, experiences, and anecdotes, on using
electroplated gold as an etch resist. In particular how is the etch
rate controlled. How can the undercut be reduced to eliminate the
chance of slivers.
(Gold/Nickel/Copper/FR4 :The copper gets etched)
Thanks
Rich
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