Hi Werner,
Here we go again :-). I wish I had at least one sample of that PLCC.
I'm completely with you on the "Red Herring" issue, though :-)
There is one more interesting thing, though, with a thick layer of Ag finish on a component.
A few years back I had to deal with a Panasonic part with 2-3 microns (or even thicker) layer of Ag. The layer had never completely dissolved in the solder. As a result, I could see any Sn/lead metal intermetallic in X-section.
Regards,
Vladimir
SENTEC
11 Canadian Road, Unit 7.
Scarborough, ON M1R 5G1
Tel: (416) 899-1882
Fax: (905) 882-8812
www.sentec.ca
-----Original Message-----
From: Werner engelmaier <[log in to unmask]>
Date: Tue, 27 Jan 2009 11:30:27
To: <[log in to unmask]>
Subject: Re: [TN] SnPbAg solder and Immersion Silver PCBs
Hi Kevin,
That "thin (?) silver finishes...prevent the dissolution of the component lead into the solder joint" is a Red Herring.
All you may be getting is AG-embrittlement which is just as bad as Au-embrittlement. It was just such 'silver finishes' on TI PLCCs that caused those PLCCs to fall off PCBs during bed-of-nail testing in 1982 at IBM-Austin and resulted in the formationof the IEEE Compliant Lead Task Force.
Also, how would an Ag-finish prevent the formation of IMCs with the lead metal?
Werner
-----Original Message-----
From: Kevin Glidden <[log in to unmask]>
To: [log in to unmask]
Sent: Tue, 27 Jan 2009 8:35 am
Subject: [TN] SnPbAg solder and Immersion Silver PCBs
Morning all,
Question today about SnPbAg solder. We have always used Sn63Pb37 solder
alloy for all products, with exception of some high temp solders for special
cases. The lion's share of our PCBs are ImAg finish, 5 to 12 micro-inches,
per IPC-4553. In reading about SnPbAg solder, it appears to be recommended
for use on SMT components with thin (?) silver finishes. This is to prevent
the dissolution of the component lead into the solder joint. Drawbacks
appear to be only that the joint is not as shiny and reduced mobility of the
solder. Is it also considered good practive to use an SnPbAg alloy for
immersion silver PCBs for the same reasons? Any tech articles available on
this?
Thanks (again!)
Kevin Glidden
Manufacturing Engineer
Luminescent Systems Inc.
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