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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