Hong Yuen Electronics Ltd. wrote:
>
> At 10:23 PM 1997/12/7 EST, you wrote:
> >Assuming your developing process is in spec, soldermask residue is indicative
> >of too high a temperature at tack cure; overexposure could also cause the
> >problem.
> >
> >Where is the residue?  Is it on the fiberglass or the copper or both?
> >Give me your process parameters and I'll try to help.
> >
> >Mark Dowding
> >Regional Technical Service Manager
> >INSULECTRO
> >
> Our Process Parameters as follow : -
> Pre Heat 15min for first side, 30min for second side, temp. 72 +/- 3degreeC
> the residue was occured on the surface of the gold, especially on the edge
> of the hole,
> also, the Stuffer Step is 10 - 12.
> By the way, all the parameters we have used for more than one year.
> Please advise

Let me offer something different, but its a very long shot!  It there
any change you are using non-UV block laminate?  We have been using
Dynachem Epic since it was first introdued (Epic 100 then).  We
frequently had soldermask residue when using non-UV block laminate.
Normally, the redidue would be on the glass, not on the copper.
However, on a few designs, we actually had solder mask on annular rings
and on the very edges of finger that were to be gold plated.  When the
light from the exposure unit starts bouncing around inside the laminate
it does crazy things.  This is especially true when using a diffused
lighting source in your exposure unit and 5KW or larger lamps.  You can
test this by blocking the opposite side of the panel.  If the residue
goes away, then thats your problem.

P.S. When I was in the assembly end of the business we purchased boards
from you.  Glad to see that you are still around.

Hans Rohr

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