Dear David

I still believe this is a reliability issue.
We produce plasma etched microvia boards for many years and have a
couple of applications running with microvias in BGA pads. Our blind
vias are tea cup shaped to provide easy plating. In addition, the
craters itself are easy to clean in final processing. But I saw a lot of
strange plated laser vias while expecting some boards of our
competitors. They also showed some debris inside as a result of very
steep or overhanging via walls. To avoid trouble try to get boards with
vias having no smaller aspect ratio than 1:1 or 2:1...
Some of our customers also made the experience that steep wall shaped
laser blind vias are causing trouble with entrapped air bubbles after
BGA soldering... In addition, copper plating becomes critical in too
small vias.

In general, we handle our plasma etched microvia boards as we do with
common PWB, there is no special treatment or packaging to avoid
mechanical debris in the tiny features. (Perhaps we should also look at
this?)

Kind regards
Thomas Jacob
DYCONEX LTD Switzerland
http://www.dyconex.com/html/whats_new/whats_new.htm
http://www.dyconex.com/html/whats_new.htm#laser

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