Morning All -

Why not stay with HASL or OSP?  The assemblers dealing with smaller and
smaller packages, particularly BGA and micro-BGA are in need of both flatter
surfaces and more finite control of the solder volumes at the individual
solder joints.  They are also faced with multiple solder cycles, in many
cases.

The white tins yield a very flat surface, which retains its solderability
(much like HASL) during both storage and processing.  The white tins also
eliminate one or more high heat cycles during board fab, which helps
minimize early intermetallic formation.

Most of us have had a number of situations where the crowning of HASL really
complicated life for both placement and soldering.  We've also encountered
any number of situations where, even the best of the OSP's (can't mention
the name) fizzled and we encountered marginally solderable pads during the
second or third solder cycle.

Don't get me wrong, HASL and OSP are great on the more conventional boards,
and I like 'em both, but they do have their limitations on the denser
designs.

Regards - Kelly

-----Original Message-----
From: Franklin D Asbell <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: Tuesday, November 07, 2000 6:29 AM
Subject: Re: [TN] Board Whit Tin finish


>Interesting comments...taking it a bit further, why not stick with
>HASL...it is by far the less expensive of the more prominent finishes.
>
>Yes, the OSP process is the easiest to maintain for the fabricator;
>however, this finish does not provide for much flexibility to the
>assembler, i.e. thermal cycles, risk of contamination, etc. The
>immersion tin solves a few of these by increased thermal cycles in
>comparison to OSP as well as providing a surface prior to wave/uv solder
>that is more forgiving of contaminates found in even the most spot-free
>assembly shop. Just those two conditions alone make the immersion tin a
>more attractive finish over OSP.
>
>Actually, when the process is well maintained, immersion tin is not much
>more costly to the fabricator or the assembler...again, when it is well
>maintained and in control.
>
>Franklin
>
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