Hello Victor,

I hope you do not mind me responding to this message sent to Steve.  Steve
I also hope that you do not mind as well.  However, we have just completed
a study for a company that was using immersion silver (IAg) surface finish
along with lead-free pastes. As part of our study we did some heavy
research into the IAg process and its benefits and pitfalls, as it were.
Here is what we found as a result of our research:

Advantages of IAg:

* Cost, the cost is comaparble to HASL.
* The surface after application is flat, unlike that of HASL.
* IAg produces better signal integrity, especially in higher frequency
applications.
* Applied silver by electroless application doesn't require high
temperature excursions or exposure to unpleasant chemistries.  It is a
very simple process.
* Shelf life of IAg boards is approxiamately one year, this is comparable
to HASL.
* Lastly, the IAg surface finish has 100% wettability and is not prone to
discoloration.

Disadvantage:
* Silver nitrate used in the application process is very light sensitive,
thus the immersion bath should be enclosed.

In the past IAg surface finish had issues with electromigration
(dendrites), this is now an urban myth.  IAg has progressed to the point
that it is no longer at any more of a risk than any other surface finish
for electromigration.

We were able to derive alot of information about IAg from Don Cullen of
MacDermid and our research fell in line with what he told us. He was
gracious enough to talk at length with us about this particular finish.  I
would imagine he would also speak with you or whoever.  Should you desire
to speak with him, his phone number is (203) 575-5658.

As far as what we have seen with LF pastes at this point, it appears to
work well, at least for the pastes that we have tested.

I hope this helps!

Best Regards

Joe Russeau
Process Analyst

Precision Analytical Laboratory



Steve,
>
>    Can you share your experience with PWB Immersion Silver Finish?
> ie.   shelf life, usage after package is opened, storage of non process
> PWB, surface oxidation, compatibility with LF solder.
>
> Victor,
>
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