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Date: | Thu, 05 Sep 96 06:26:23 CST |
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We are looking for an explanation as to the cause of defects found in
some areas of a PWB laminate. The affected areas were observed in
microsections of an assembly to have the following characteristics.
1. A dramatic difference in the color and pattern compared to the rest
of the innerlayer material. Defective sections are of a very light
color, and are almost completely translucent. Only small traces of
the usual weave pattern are seen there.
2. The affected areas usually surround barrels or vias, and at times
span several innerlayers between barrels and/or vias.
3. Although the sides of the barrels are somewhat distorted, no cracks
have been seen in the plating.
4. Distortions in the geometry of innerlayer traces are seen around
the affected areas.
5. After one of the microsections was prepared, a probe was touched to
one of these areas, and the laminate felt soft. In time it became
hardened.
The assembly was microsectioned because of intermittent resistive
paths between certain nodes and either ground or Vcc. At times,
following chamber testing, the paths had alternated between the nodes
and ground or Vcc!
Thank you for any suggestions.
Myron Papiz
MSL
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