Alcon: To expand on what Doug Pauls and Jon Roberts said, and throw in some
additional information.  The fracture of a connection, as depicted in A-610,
is considered a serious defect because the fracture will normally propagate
around the circumference of the lead and then along the length of the lead
until an intermittent open circuit exists.  Propagation of the fracture is
usually through the IMC at the lead surface.  For that reason a reflow of the
effected connection is preferred.
- Re covering the lead ends with solder.  That is an old military requirement
(Mil-S-45743, Mil-Std-2000, etc.) and was meant to inhibit the condition that
Doug described.  The Navy had observed random cases of equipment failure
throughout the years where the failure was attributable to an iron based lead
(Kovar, Alloy 42) not having the lead end capped by solder, thus allowing the
exposed material to be attacked by the salt fog environment in which Navy
systems operate.  An inspector using a good light source (having a 3000K
color temp.) could differentiate between exposed copper and exposed
Kovar/Alloy 42.  Industry representatives ultimately convinced DOD officials
that using expensive light sources (quartz halogen) was a  cost driver in the
production of DOD equipment and the requirement for such illumination source
was deleted from Mil-Specs.  Absent the ability to differentiate between
exposed copper and exposed Kovar/Alloy 42, DOD advocated (for a short time)
that no basis metal should be exposed (DOD never really cared about exposed
copper because exposed copper has minimal, or no, reliability impact).  The
words "solder cap" apply to covering lead ends because in normal assembly
environments the exposed Kovar/Alloy 42 oxidizes so rapidly that achieving a
solder bond is impossible (not to mention the need for a really gee-whiz flux
to wet the surface of the material).
- Hope the above helps demystify some of the earlier requirements.
Regards, Jim Moffitt, Technical Director, Electronics Training Advantage,
Indianapolis IN