We have had similar problems with the White Tin process.  There appears to
be an oxide or contaminate that occurs after more than one reflow operation.
This inhibits the solder wetting.  We are trying to get to the root cause.
Our CM also recommended HASL for the same reasons.  However, we don't feel
that this will yield a planar surface.  We are also looking at Immersion
Silver or Nickel/Gold as alternatives.  But they may have similar or
different process issues.

Regards,
Spencer

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