Virtually all lead-free bare PCB finishes are intended as interim, pre-
assembly finishes. Yet I also see a growing occurence of circuit features
that are sent into the post-assembly world without protection of assembly
solder, solder mask or conformal coating. Which begs the question:

Are the lead-free PCB surface finishes safe in the field as final finishes?

There's a design before me at this writing: It has nearly 100 test points.
All immersion silver. They'll go through assembly as immersion silver, then
they'll go out into the field as immersion silver. The assembler is very
interested in knowing how long the silver can sit on his shelf and still
promote soldering, but hasn't any interest in how long immersion silver
will sit in the field and still protect copper.

Immersion silver isn't being singled-out: Trade it with OSP or imersion
tin, and I don't feel any better or worse.

In-fact I have yet to find any producer of immersion silver, immersion tin
or OSP that rates their products as final, in-service finishes.

But it's happening...

I'm not too concerned about lead-free HASL or even ENIG, but the immersion
and OSP coatings seem like long term risks in circuit reliability.

Anybody else thought about this?

Is there a paper that can be recommended?

Bob Lazzara

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