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Date: | Thu, 18 Sep 1997 11:27:12 -0500 |
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Hi Yuan -
One possible source for the bromide could be the component body material.
It has been well documented in several residue studies that when printed
wiring board materials that undergo thermal excursions that some compounds
(like bromine, etc.) can become extractable in the next process step. Good
Luck.
Dave Hillman
Rockwell Collins
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[log in to unmask] on 09/17/97 12:14:55 PM
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Subject: [TECHNET] causes of electromigration in SOIC16 resistor net
Hello,
Currently we are finding electromigration problem on SOIC16 resistor
networks of a particular datecode (9551, pretty old) assembled on a
particular card early July. We found from the component supplier that
this lot (9551) was produced in a site in China (closed now due to
business reasons as claimed by the supplier). Mystically this lot
(produced on 9551) ended up in our assembly contractor several months
ago.
The analysis found Bromide inside the components. The component
supplier claimed that there was no way that Bromide could be generated
by their process and the problem was caused by the PCB assembly
process. However, they were not aware of moisture sensitivity levels
when asked (which is surprising I think). Checked with the assembly
and found all processes, i.e. reflow, wave and clean, were not
abnormal. The assembly uses water soluble paste. The resistor networks
in question experiences 4 thermal excursions (top and bottom reflow,
selective wave and fountain wave). These components are near a TH
connector which is fountain soldered using mini-wave.
From the above history, could anyone tell what might be the possible
causes? The analyses we are doing are C-SAM looking for cracks and
delaminations and moisture content.
Appreciate any comments.
Thanks,
Yuan
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