To add to the considerations on wetting balance and solder spread:
True, the wetting balance test is simulating wave soldering somewhat closer
than reflow, but in any case it is the test of the eagerness of the
component or the pad surface to participate in the solder process (which is
needed on both sides of the joint formation). And we test for wetting after
various pretreatments, where we for instance simulate the sequence "(double
side) reflow - wave/selective soldering". The wetting balance is seen as a
"worst case condition" test, with test temperature below solder wave
temperature, no or little flux on the pin resp. pad surface, and start with
room temperature on the surface to be joined.
Schön' Gruß
Thomas Ahrens, Boostedt
e-mail [log in to unmask]
----- Original Message -----
From: "Werner Engelmaier" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, February 17, 2005 3:16 AM
Subject: Re: [LF] PCB Solderability tests
Hi Jovan,
Be careful about the conclusions drawn from 'spreading tests'—spreading is
NOT the same as wetting. Paticularly with ENIG, the spreading is facilitated
by
the rapid dissolution of the Au into the Sn, but the wetting has to take
place
to the Ni, which requires significantly more thermal energy than wetting to
Cu.
Regards,
Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL 32174 USA
Phone: 386-437-8747, Fax: 386-437-8737, Cell: 386-316-5904
E-mail: [log in to unmask], Website: www.engelmaier.com
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