Allen:  Regarding the question you asked about the 0.2 mm solder thickness
(Dimension "G") of IPC-A-610B.  First, understand that the minimum thickness
of the  solder connection is intended to apply to leadless surface mount
components and is required so that the (presumably leadless) surface mount
component is far enough above the pwa surface to assure that a cleaning
system can extract process residuals, thereby yielding a clean assembly. When
CFC's were banned, tests were conducted to identify alternative cleaning
solvents and systems.  During the tests it was found that the alternative
solvents were capable of extracting process residuals only if certain SMT
components were elevated above the pwa surface a minimum of 0.008 inch (now
known as 0.2 mm).   The 0.2 mm is not such a problem with leaded components
because most of them have that much clearance anyway.  In attaching leadless
SMTcomponents, the thicker the solder (Dimension G), the better.  Werner E.
has long (and correctly) advocated that a tall solder connection adds greatly
to the reliability of the connection.  So much for history, now to your
question.
- From your question, I must presume that you are attaching a radial or axial
lead component with round leads to the surface of the pwa by planar soldering
the leads to terminations on the surface of the pwb.  The thickness of the
solder connection (Dimension G) should not be a concern as long as it is
within reason.  I would suggest that as an absolute maximum, Dimension G
should not be greater than twice the lead diameter.  What I would worry about
are the relationship of the component body to the pwb surface and the height
and length of the side joint fillet.  Surface mounting radial and axial lead
components frequently results in the center of gravity of the component body
being excessively high, reducing reliability in a vibration or shock
environment.  If the component body is not against the pwb surface (and
perhaps even if it is) I would recommend that if at all possible you
stabilize the component with a mounting clip or adhesive to provide
mechanical reinforcement.  I also recommend that the height of the solder
fillets along the length of the "foot" of the component leads be a minimum of
2/3 (66%) of the diameter of the component lead and that the length of the
solder fillet (side joint length) be as long as possible (a side joint length
that is 1.5 times the lead diameter - as required by A-610 and J-STD-001 - is
pretty minimal in this application).
- Hope the above helps.  Regards, Jim Moffitt, Electronics Training Advantage

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