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Several of our PWB suppliers have used a via hole plugging process with the
following sequence: LPI, HASL, partially plug via hole (component side).
With mixed technology boards, our assemblers (in house, contracted etc.)
all experience a phenomenon where the solder erupts from the top of the via
during the wave process. The eruption looks like a volcano and varies in
severity. This eruption results in several problems including solderballs.
Most of the plugged vias lie under components and the spacing between vias
can be equal to or <8mils. Many components sit very close to the board's
surface.
This seems the PWB industry preferred method to plug holes when LPI is
used. How do assemblers prevent the eruption of the solder through the
top of the plugged via during wave? Is this a common problem in assembly
or rare?
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