Ed
The problem is allway the same:
Cracks occur if too much strain in induced too fast into a solder joint.
- Leaded components do, because of the low assembly stiffnes, relive the
stress in the solder joint an hence slow down the deformation process in
thermal cycling.
- Alloy 42 is a material with a pretty high youngs modulus. Therefore leads
will be stiff.( Stiffer as copper leads )
- Short leads are stiffer than long leads
- If you have too much solder it will cover the leads and stiffen them.
- Every soldering process is a theraml cycle

However, to me cracks after soldering seem to be a extreme cause of crack
growth. But to say something definitive you need a analysis of the solder
joints with microsections. ( Excessive solder at the legs, point of the
occurrence of the cracks in the solder process ).

Copper leads will ease the problem

Use of components with high standoff is positive ( Longer leads ).

Reducing the solderjoint by means of reduced stencil-openings or reduced
padsize until a sufficient solderjoint without solder along the vertical
part of the leads or solder in the bends will help ( Optimization neeeds
analysis of the joints )

A reduced ramp during preheating and cooling down will also contribute to
reduced growth of cracks. ( I know here comes the problem of the growth of
intermetallic compounds. It's a compromise )

I think thats all I can tell you right now. We have to wait, until we can
send pictures by E- Mail until a more profound  discussion is possible.

Best regards

Guenter Grossmann

P.s.: You are not by chance at SEMI 96 in Austin? We could meet there. I am
at the IEMT Simposium.


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