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January 1999

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Tue, 12 Jan 1999 12:02:03 EST
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In response to Jim Trainors comment on solderability of OMIKRON White Tin
after ageing,

1.  In a test performed by Trace labs comparing solder paste wettability among
three surface finishes:  HAL, OMIKRON and Alpha Level, it looked at the
surface area as measured by a planimeter and OMIKRON wet the no clean solder
paste the best!  Sure--the wettability is less after aging--whether dry or
steam, but the degree to which it falls is less than HAL or Silver!

2.  Wetting balance tests (reference to the meniscus) is just one way of
measuring wettability.  I think this test does not very accurately depict real
conditions.  When one reflows solder paste, you are looking not at the
instantaneous force, but a reflow time of 30 seconds or so (the time the
reflow temperature is above the liquidus)--take a look at your typical solder
paste reflow profile.  This is why we typically look at how well the solder
paste spreads over the surface and this is the type of test Lucent Technology
does as well.

3.  Sure--the reason for the degradation in wettability is due to growth of
intermetallics--however the key is surface tin.  As long as there is surface
tin, the surface will wet.  Our test results show that surface tin remains
after aging combined with multiple reflow cycles.

4.  Finally, I would be more than happy to supply you with all of our test
data, in house as well as Trace Labs (an independent lab).  It will address
this issue and others that may interest you.
  There are more than 30 shops throughout the U.S. currently running Omikron
as an alternative to HAL, all their boards are not being assembled inside of
one week.  The shelf life is safely rated at one year min with the correct
deposit.

Kind Regards,

Stephen M. Wentz
Florida CirTech
VM#(408)233-0443

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