Just a little clarification on the term "peelable" soldermask.
The peelables are not just latex based. They also include vinyl, silicone
and urethane based chemistries.
Although I personally am not a big fan of peelable masks they are not all
the same in their ionic properties and flux absorption characteristics. So
we need to be careful in not painting them all with the same broad brush.
The Lackwerke Peters SD 2954 that Mickey Weiner spoke of is a vinyl based
compound and behaves differently than the latex masks.
If it was me I would choose an unfilled water soluble mask if a high
dissolution rate coupled with a decent inline aqueous cleaner that had a
prewash to drain.
Just my 2 cents.
regards
Michael Barmuta
Staff Engineer
Fluke Corp.
Everett WA
425-356-6076
-----Original Message-----
From: Douglas Pauls [mailto:[log in to unmask]]
Sent: Wednesday, August 23, 2000 6:06 AM
To: [log in to unmask]
Subject: Re: [TN] Peelable SolderMask
In a message dated 08/23/2000 12:47:47 AM US Eastern Standard Time,
[log in to unmask] writes:
> I am not aware of any contamination issues- Always glad to learn
Yes, but I hope you don't have to learn the *hard* way!
My colleague, Dave Morrow, will be publishing an article in PC Fab on a case
study we did involving peelable latex mask. Or at least he will once I stop
redlining his drafts...............
The one in the study, while not named, is a very popular one. The
fabricator
would put it on the panels at the request of the assembler. In the state it
was delivered to the assembler, the mask material itself had roughly 2
micrograms per square inch of chloride and about 3 micrograms/in2 of
sulfate,
when measured by ion chromatography. As soon as it had been exposed to the
assemblers process, a no-clean RMA, it had chloride levels in the 185-200
microgram/in2 range. The mask either chemically broke down after thermal
exposure or it absorbed flux, or both. The surface of the assembly UNDER
the
mask went from about 1-2 micrograms per square inch to about 35 micrograms
per square inch. We recommend a maximum of 4.5. The result was corrosion
found during temperature cycling.
A point I would like to make is that people don't pay much attention to
materials that are not part of the final assembly. Why worry about the
latex
mask? I'm just going to throw it away anyway. Well, they can have
detrimental effects. The same thing applies to other "temporary" materials
like water soluble solder mask, water soluble temporary spacers, water
soluble tapes, etc. Just keep in mind that every material has an effect,
and
every material has to go somewhere.
Doug Pauls
Contamination Studies Labs
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