Tim:

This issue of solder spikes protruding from via usually occurs when the via is
not cleared of solder (remains plugged) during HASL and then the via is capped
or plugged with solder mask.  If the solder mask plug is on the secondary side
and that side is assembled first, then the solder will protrude from the
primary side.  The theory is that during the via solder mask cap process, air
is entrapped between the mask plug and the solder.  During reflow the air
expands and the solder plug takes the path of least resistance and moves out
the uncapped end of the via.  The obvious fix is to change to OSP, or no via
plugging, or the least desirable, have the fabricator increase the air
pressure to assure that vias are not completely closed down with solder.

Ryan

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