Earl,

The immersion silver process I was referring to is not an electroless, or
-- to be more precise -- not an autocatalytic process. Electroless
nickel-phosphorous and the problems associated with it do not come into
play here as well, since it is not used as an intermediate layer for
immersion silver.

The coating should not tarnish on standing at ambient conditions, provided
it is not subjected to aggressive chloride or sulfide containing
environment.  It is not unusual, however, to observe a slight yellow tint
with multiple reflows, which does not present a solderability problem.

Again, if you are interested in actual solderability measurements after
steam/temperature ageing/cycling, please contact me off line.

Best regards.

Eric Yakobson








[log in to unmask] on 11/23/98 10:58:53 PM

To:   [log in to unmask]
cc:    (bcc: Eric Yakobson/AlphaPCFabUS/Cookson)
Subject:  Silver Migration




Eric,

Thanks for responding to what I hope was not taken as a negative comment
concerning silver
migration. I tout your electroless process, but keep facing reactions
concerning the issue. I base
my positive interest purely on solderability effects determined during
assembly operations.

All that withstanding, I would appreciate any information you might lend to
reinforce the facts as
you objectively view them. Also, I have been monitoring several samples
your people provided. I can
say I see no problems except shelf life after extended periods as silver
"tarnishing" or oxidation.
Any information about this also would be appreciated.

The biggest concern I have now is directed toward the nickel barrier and
the phosphorous issue
seeming to condem both gold and silver to an early demise. I, as do we all,
really want an
alternative to HASL and OSP. I really believe gold and silver to be those
alternatives, but
phosphorous intermetallics seem to be what everyone is talking about (Dr.
Mei et al). Do you have
any solutions (not a pun) concerning phosphorous content in plating
composition (the 7% solution?)?

Enjoy,

Earl Moon

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