There has been significant work in both the US and the UK on the
ultrasonic (u/s) issue.
The Navy undertook a comprehensive program to assess the impact
of modern u/s on modern packages. At about the same time, GEC in
the UK was also running a program along similar lines. The
results of both studies were presented at the China Lake
Soldering Symposium and Nepcon West. [The GEC work was published
in a series of reports by component type, it is unclassified
work.) The rule of thumb used was that if no damage was seen
after 10x normal cleaning time, there wasn't going to be a
problem. B. Richards was the team leader for this work, he is now
at the National Physical Laboratory in UK.
Out of this came the effort within IPC to make u/s socially
acceptable as a cleaning option. The U/S Task Group generated two
test methods; both in the IPC TM-650 Test Methods Manual:
2.6.9.1  "Test to Determine Sensitivity of Electronic Assemblies
to Ultrasonic Energy"
2.6.9.2  "Test to Determine Sensitivity of Electronic Components
to Ultrasonic Energy"
[The first test is to test components in the constrained
(soldered state), while the second would simulate component
cleaning when the components were loose in a basket. Both these
test methods are called out in the revision of IPC-SC-60A:
Solvent Cleaning Handbook, that is being circulated as a Proposal
this month.]
Also, the IEC version of J-STD-001 had wording in it that u/s was
an acceptable cleaning option. I have not seen a recent copy of
the document after it was split into four sections, so don't know
if it was retained.
Bottom Line- there are good data available and new developments
in u/s technology that make it an excellent cleaning option to
help cleaning agents clean blind holes and under tightly spaced
parts.
-Bill Kenyon
Global Centre for Process Change, Inc.
Tel. 302-652-4272

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