As perhaps the only person still around that attended the meetings resulting
in the equivalence factors and IPC Cleaning & Contamination Chair at that
time, perhaps a few points would facilitate the discussion:
1. The Navy set up the ionic testing development program to solve a serious
failure problem in S.E. Asia.
It worked.
2. In the timeframe when the test was developed and put in place by the
military, most of the rest of the electronics industry in the US used the mil
specs since they were free.
3. As the IPC set up and adopted Classes 1-3 (basically toys up to
military/high rel), I asked the committee if we used the mil test result for Class 3,
could we use 1.5x that limit for Class 2 and 2-3x for Class 1?
The response was that with proper cleaning, the mil limit could readily be
achieved while serving to monitor daily production. So the industry continued
to use the (free) mil spec test standard.
4. The ionic contamination test was a valuable monitoring tool, since the
SIR tests were done on coupons, not on actual assemblies, and took 1-2 weeks to
complete. Needless to say, a high volume electronics producer could turn out
a significant volume of PWAs during that time, often shipping them into the
field as soon as assembly was completed.
5. As noted in my SMT column (offered yesterday) T. O. Duyck of Northern
Telecom was charged with implementing water soluble flux for NT electronics
production. During that time he observed and reported the differences in flux
residue release rates, pointing out that rosin ca 90% of rosin flux residues
release from the PWA surface during the 10-15 test time for ionic test
equipment, while water soluble flux residues may take up to 2 hrs. to achieve the same
level of release. Thus the release rate should be checked to ensure the flux
used, time test time and the instrument employed provide reliable results
and guidance to the production engineer.
6. In the late 1980's, the materials and acceptance of the no clean or low
residue or acceptable dirt concept became widely accepted and implemented on
the designs of the time. Outsourcing to contract assemblers (both in the US and
overseas) became widely practiced, so much of the former 'in-house' cleaning
expertise disappeared.
7. This was seen at IPC as the number of company sponsored volunteers
dwindled. Could we take on projects today to develop an updated ionic test for pr
ocess monitoring? Find enough participants to conduct statistically sound round
robin testing?
Bill Kenyon
Global Centre Consulting
3336 Birmingham Drive
Fort Collins, CO 80526
Tel: 970.207.9586 Cell: 970.980.6373
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