Hi Peter

We had several cases to analyse in our lab with the same problem. In one
case  a whole machine started to burn because of dendritic growth between
the ground layer and a via. All of the cases where caused by delamination
of the glas-fibres with the epoxy. This may happen by:

- Voids forming in the delamination process.
- High forces in the drilling process of the vias.
- Using the drills too long so that they are not well cutting ( don't know
the appropriate english expression for that. Numb? ) anymore.

In the plating process, galvanic fluids are entering the delaminations
leaving electrolytic residues when they dry. Since dendritic growth is a
thermally activated process enhanced temperature will speed up the growth
of cracks.
I recommend to check the quality of the vias with microsections.

Best regards
Guenter Grossmann


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