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September 2003

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Subject:
From:
Dave Chapman <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Fri, 26 Sep 2003 06:52:12 -0500
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We have been using I.S. for two years, follow manufacturers recommendations
for storage and handling and you will be fine. Require your board supplier
to vacuum seal the packages and make sure they have a slip sheet (non sulfur
bearing paper) on top and bottom of the stack. Since the finish is actually
below the surface of the board you don't have to worry about every board
getting scratches. Aperture selection of stencils is important. Since there
is no HASL to add solder volume you have effectively changed your product to
Lead-Lite, some apertures may need to be 1:1 but we have had good results
with fine pitch reductions by using a round rectangle.

If assembly is double sided you should process the second side as soon as
practicle to minimize tarnish which may statistically decrease your
solderability. But tarnish does not always mean it won't solder.
Replating Immersion silver is very easy. Check out the Alpha Level and Mac
Dermid websites for some good papers on Immersion silver finish.
Shelf life? 12 months. We don't wear gloves, we started that way but
realized NO board should have peoples fingers on them so we follow good
handling and you should be fine.
Cost should be less than HASL.
At the ATE show yesterday I heard many references to Immersion Gold and
Black Pad. Most of the Lead Free studies are recommending Immersion Silver
for the transition.

Dave Chapman
Manufacturing Engineer
Circuit Service Inc.

-----Original Message-----
From: Brooks,Bill [mailto:[log in to unmask]]
Sent: Thursday, September 25, 2003 3:08 PM
To: [log in to unmask]
Subject: [TN] Silver Immersion right for fine pitch?


Hi Technetters,

I have just attended a meeting of the IPC Designers Council where the
subject of finishes for PCB's came up and it was revealed that Silver
Immersion seems to have great benefits for assembly, shelf life,
solderability, rework, etc...

Can anyone give me their experiences with the process and its benefits and
down sides?  Have you personally used it, how long, what sort of problems
have you seen, what are the cost issues?

Best Regards,

Bill Brooks
"Politics is more difficult than Physics" - Albert Einstein

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