DON: I suggest that you speak to your chemistry supplier about this.
Immersion silver
finishes contain an organic additive to preserve solderability.  I don't know
enough about the tin finishes to be certain, but I believe that they use
similar organics.
BOB: They do; e.g., Omikron's current offering uses the organic Ormecron.

DON: Elevated temperatures (used to cure mask and nomenclature) degrade the
final finish resulting in diminished shelf life and possibly reduced
solderability.
BOB: Agreed. With only 1 - 1.4 microns average immersion tin thickness it
doesn't take much intermetalic growth to impact solderability. Most companies
today apply immersion tin after the final thermal cycle for optimum material
condition upon delivery.

Bob Lazzara
Circuit Connect, Inc.

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