March 2, 2008

Folks, we have an OEM that purchased axial leaded diodes from On 
Semiconductor.  Since the diodes were not mil-spec parts, the OEM sent them 
to a test house for qualification and electrical screening testing.  The 
screening is performed at 175C which I believe is the max storage temp of 
the part.  They also performed solderability testing which failed (<90% 
wetting).

The OEM subsequently solder dipped the parts in Sn63 solder and was able to 
solder them OK.

The part manufacturer indicated the solderability problem was most likely 
caused by tin migration due to the testing at 175C.

Seems to me that since MIL-PRF-19500 includes electrical screening testing, 
the parts should have been able to withstand the full screening testing with 
no solderability failures since the parts most likely were made on the same 
line and samp processing as mil spec parts.

Any info you can provide on tin migration or on the manuf position that the 
solderability failure was the result of the testing at 175C would be 
appreciated.  Have other folks experienced solderability issues for matte 
tin plated parts?

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