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| From [log in to unmask] Fri Apr 26 13: |
49:37 1996 |
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The pure Difunctional has basically been replaced with a
tetrafunctional additive. The reasoning for this is to
provide a UV blocker for the LPISM (liquid photoimable
solder mask) process. Without the UV blocker, the potential
of ghosting, or image transfer thru the laminate from one
side to the other is highly possible and highly detrimental
to the soldermask image integrity. Especially since SMT is
hear amongst us! It sounds like difunctional by choice would
be past experience or strictly a cosmetic issue. The Thermal
properties of the tetra or multi functional are somewhat
superior to the difunctional. There still are a few
suppliers building straight difunctional, but from a
fabrication stand point, most select the the raw stock with
the tetra or pigment additive.
Dave Hoover
Senior Process Engineer/Hadco Corp. Tech Center Two
Watsonville, CA
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