Tony and Lisa:
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. Elevated temperatures (used to cure mask and nomenclature) degrade
the final finish resulting in diminished shelf life and possibly reduced solderability.
IMO the best practice is to apply mask and nomenclature before the final finish.
The fewer thermal excursions that the finish is exposed to, the longer the
shelf life of the board.
Don Vischulis
>Lisa,
>Being in the pcb manufacturing, we have installed immersion tin as a final
>finish surface.
>As I suspect, with any immersion process such as tin, silver, gold,
>soldermask and nomenclature
>adhesion sometimes become bigger problems than the actual process itself. We
>experienced
>the same problems. Through many agonizing weeks of evaluation we have come
>up with using
>a predip prior to the application of LPI or legend, which consists of a
>diluted version of
>an oxide replacement bath. This chemistry contains adhesion promoters for
>which gave us the
>the ability to withstand IPC tape test.
>
>
>Tony Steinke
>Circuit Technologies Inc.
>----- Original Message -----
>From: Lisa Angle <[log in to unmask]>
>To: <[log in to unmask]>
>Sent: Thursday, December 21, 2000 3:45 PM
>Subject: [TN] Nomenclature with Immersion Tin/Silver
>
>
>> All,
>> I was wondering how you go about putting nomenclature on copper surfaces
>> and subsequently processing thru immersion tin or immersion silver without
>> experiencing nomenclature peel? I have of course thought of the
>> alternative which is to process the boards thru immersion processes and
>> subsequently nomenclature them, however, our current inks require a long
>> cure time and very high temperature which artificially ages the finishes.
>> Thanks.
>> Lisa Angle
>> Alternative Surface Finish Engineer
>> Teradyne
>>
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