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Date: | Thu, 25 Apr 96 07:32:13 EST |
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I'm in the same boat! Identical process. Tried everything under the
Sun. No go - No way. <For me> The gold lands must be completely
isolated with no outerlayer traces. (Solder to gold demarcation line)
The gold plating basically poisons the solder which disappears in
the etcher (or is it itcher?) and wul-ah, an open.
Groovy
BTW-Isn't the itcher located next to the board stretcher?
Or was it the on the shelf by the box of tooling holes?
<Poor guy. I guess everybody gets initiated into the buis
one way or another.>
______________________________ Reply Separator _________________________________
Subject: gold plating problem
Author: [log in to unmask] at SMTPLINK-HADCO
Date: 4/24/96 8:18 PM
Our Process
Isolated tabs in the center of the board to be gold plated are defined
by a primary layer of resist. After copper and tin-lead plating them,
we vacuum laminate 3 mil dry film resist.(over the plated tin-lead and
over the primary layer or resist) This top layer of resist is
selectively imaged to produce an opening exposing the area to be gold
plated (which now has tin-lead on it). Then the tin-lead is stripped,
and the nickel and gold are plated using our usual sulfamate
nickel/soft gold process.
The Problem
The plated nickel peels from the copper surface. The peeling is
always near traces connecting to the tabs.
Therefore I suspect that tin-lead stripper is being trapped under the
top layer of resist and coming out during plating.
Solutions?
I don't suspect the nickel/gold process is the problem, as the usual
yield on products without this tin-lead stripping step is nearly 100%.
We have no option to change the design of the board to facilitate
manufacturing. ie: No bussing of the tabs is possible therefore base
copper must be used as a conductive path prior to etching.
We've tried: 140 degree F water rinse after stripping, conveyorized
nitric tin-lead stripper, immersion and conveyorized peroxide tin-lead
strip, a second strip cycle, UV bump (160mJ), among other things.
Any help would be appreciated.
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