Eddie - when we wrote 4553, Alpha Metals was providing a thin I Ag deposit,
typically of the 2 to 4 microinch range, everyone else was in the 8-12 range
for a similar pad size. Because of the large discrepancy in deposit
thickness, there was no way to spec a single value, hence both specs. Since
it was released, alpha has introduced thick silver similar to the rest of
world. I believe they are still supporting the old Alpha Level, but are
definitely marketing the new Alpha Star.
To answer your questions, if you apply a thinner deposit of a silver that
should be applied at 12 micro inches you will see compromised shelf life.
I have answered # 2. For #3 given the relative light deposit for both
deposits there is no perceived performance difference for press fit
applications, 2 vs. 10 micro inches -


Regards


Gerard O'Brien
Photocircuits Corporation
Co-chair 4-41 plating committee.

-----Original Message-----
From: Eddie Rocha [mailto:[log in to unmask]]
Sent: Wednesday, March 01, 2006 10:33 AM
To: [log in to unmask]
Subject: [TN] Thin vs thick silver

I have some questions regarding immersion silver. IPC-4553
standard refers to a thin and thick deposit silver as if
there are two different type of silver formulations. I've
spoken to multiple domestic chemical suppliers of the
silver process and they all offer the thick deposit
version. One supplier stated that they can provide a thin
deposit with their thick deposit version with no
solderability issues. The IPC standard states not to do
this.

Question 1: Why can't a thick deposit silver version be
used to deposit a thin deposit (3-5 uin)?

Question 2: Who supplies a thin deposit silver?

Question 3: Would the thin silver deposit perform better
than a thick deposit silver when press fitting pins?

Thank you,
Eddie Rocha

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