Dougal,

Very good point.  We have done no experiments to determine if the matte
finish is inferior to the glossy finish with regard to contamination.  This
was strictly conjecture on our part.  Are you able to share the mask
material that you have found particularly compatible with immersion white
tin, if not to the whole forum at least off-line?

Regards,

Seth Goodman
Goodman Associates, LLC
[log in to unmask]

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Stewart, Dougal
Sent: Thursday, August 23, 2001 3:52 AM
To: [log in to unmask]
Subject: Re: [TN] White Tin


Immersion tin (white tin) is a particularly aggressive process for bare
board fab - it is operated at high temperature, long immersion times and
uses two chemistries that find it easy to work their way through the
soldermask resin structure, namely MSA and Thiourea. There are lower MSA
versions available which reduce the attack, but we now use immersion tin as
the metal finish to benchmark soldermask performance. We have identified a
soldermask that stands up well to the immersion tin process and meets all
the requirements on SIR and e-corrosion, but surface preparation before
coating, and screening technique do have an influence on the ability of the
mask to perform.
With reference to your comment on the mattness of the ink, their seems to be
a big rift in the understanding of the effect of mattness on contamination,
and too many generalisations made. The way that the matte is achieved is
different with different masks, even by the same manufacturer, so I would
rely on data, not theory, when you want to know if it has an effect. You
can't beat real undisputable facts !

Dougal Stewart
Director of Technology Development,
Viasystems Europe
tel:   +44 191 206 2081
mob:+44 780 221 1958
 The information supplied here is a personal view, and may, or may not
reflect the view of my employer.

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