February 25, 2005

MIL-PRF-38535 microcircuit specification is confusing since in one section it identifies that to select a lead finish, include a suffix letter as part of the part number.  The available suffix letters are Finish "A", "B", "C":, "D" and "X".  "D" is for Palladium.  "X" means either "A", "B", or "C" Finish  

However, Appendix A of the specification indicates that only lead Finishes "A" through "C" (or "X") are allowed. 

It appears that Finish "D", Palladium finished microcircuit leads are not allowed.  Is this true?  If so, why the apparent prohibition on Palladium lead finish?

The question relates to selecting the lead finish for a microcircuit that is mounted in a socket having Gold-plated socket contacts.  Normally, one should specify a Gold-plated microcircuit lead (Finish "C") to mate with the Gold-plated socket contact.  However, from a galvanic corrosion standpoint, either Gold or Palladium should be ok.


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