Mike I doubt it's that simple ;
while you have a relatively good feel one way (more dispersed negative
effect) ;
it's the Ag factor which is very similar in it's embritteling effect to Au
(being less known due to less usage on bare cards and metalisation).
Apart from plasticity modulus being shifted with absence of Pb (having a
play in the recommendation) ;
if you'd take Wassink's recommendation of no more than 4% Au in a joint you
have :
3.5%Ag + X%Au bare card + X%Au component metalisation (bad stories on LED's
overplate) which gives you a snowflake in hell chance of staying under 4% on
bottom line .

The recommendation is correct Steve ; look for silver embritteling
documentation ; more of tin dispersing effect is minimal compare to massive
set back on the silver character ;
unless you have less than 0.3um (metric) of gold on the nickel and NO gold
parts ; you have a slim chance of living more than say 1-3 years (pending
geometries) with that particular card .
A probability to high not to be conveyed to your customer in my humble
opinion .

Let's see what Werner says ; this is as far as I know .
Won't bother you with my piles of files .

You've been testing us Mike didn't you ? ; can't believe Bob's trainee would
miss silver in line ?
Sorry to differ ; don't want to see buddy in a ditch .

See you

Paul Klasek
http://www.resmed.com

-----Original Message-----
From: Michael Fenner [mailto:[log in to unmask]]
Sent: Wednesday, 25 August 1999 5:21
To: [log in to unmask]
Subject: Re: [TN] SN96 solder...


Standby for a welter of responses!
Here is a simple answer.
The Au issue for Sn96 is the same for Sn63. Except that as there is about
50% more
tin present per joint the amount of gold per unit of tin is less, so Au
embrittlement
is less likely. So basically if you reckno you could do it in Sn63 you will
be OK in
Sn96. For further details refer to almost anything written on lead free I
guess.

Mike Fenner
BSP, OX15 4JQ, England
T: +44 1295 722 992
M: +44 789 999 7715
F: +44 1295 720 937

For product information visit www.belzona.com
-----Original Message-----
From: Stephen R. Gregory <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: 24 August 1999 17:52
Subject: [TN] SN96 solder...


>Hi ya'll!
>
>I've got a project coming where it's called out to use a SN96 solder. Not
>having the characteristics on the top of my head, I went to a web page to
>refresh my memory. A SN 96 alloy is 96.5% Tin, and 3.5% Silver. It's a
>eutectic alloy with the liquidous and solidus temperature at 221-degrees C.
>
>The page stated the typical use was in applications where standard lead
based
>solders did not meet the safety or strength requirements. It also went on
to
>say that a SN96 was not recommended against gold plated surfaces. Guess
what?
>I was told the PCB is gold plated!
>
>So what is the issue, gold embrittlement? Undesirable intermetallics? Would
>sure like to know something about this...
>
>Appreciate any info!
>
>-Steve Gregory-
>
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