HASL'd boards can vary from day to day, lot to lot, and vendor to vendor. This is one of the
reasons many want a new surface coating. I wrote an article, some years ago, describing the
uncontrollable solder leveling process - or at least why it is so difficult to control. The
issue and article still prevail.

Re-coating may work temporarily to "fix" the problem. However, solderability problem
recurrence is likely as copper oxidation and excessive intermetallic formations may already
have rendered the boards defective and no amount of re-coating will bring them back from the
dead.

X-sectioning may reveal defects as excessive intermetallic formation. Further, scanning
electron microscopy (SEM) used with energy dispersive x-ray (EDX) may provide better
indications of the defect causing mechanism as the oxidation medium.

Earl Moon

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