In a message dated 08/21/2000 1:41:53 PM US Eastern Standard Time,
[log in to unmask] writes:

> Any manufacturers in here have experience with peelable mask?

Sure.  Both good and bad............

>  Only the good points are ever discussed in the sales brochures.

I'm shocked.

>  I'm looking for the evil
>  side. It seems to go against everything I've ever tried to accomplish with
a
>  solder mask and it makes me a little nuts to think a customer wants to undo
>  what we try so hard to do! I'm afraid next they'll want removable
>  traces.....Any thoughts or comments appreciated.

We have done a number of failure analysis in which the latex peelable mask
was the source of detrimental halide residues.  A couple have been published
in Circuits Assembly and one upcoming one in PC Fab.  I think they are on our
web site (Library section of www.residues.com).

We found that the latex masks leave high levels of chloride and sulfate on
the surface of the boards.  The organic residues can inhibit soldering and
the halide residues cause leakage and corrosion.  Not a good idea to use
these in a no-clean application.  The mask itself can (depending on the mask)
absorb the flux it comes into contact with.  The vendors say this is not a
problem because you throw away the mask later.  Unfortunately, the residues
remain on the board surface.  In other cases, we have found that the reaction
mechanism leaves by-products on surrounding surfaces.  As one other
contributor pointed out, the masks may be ammonia based.  If you can smell
the reaction byproducts, then it is depositing on other surfaces as well.

I have played around with SIR testing on the latex masks and don't get very
good response from either the material or the residues left by the material.

Doug Pauls
CSL

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