George et al,
I believe that Au is worse than Ag because AuSn4 forms at a much higher
volume percent in the SnPb microstructure than Ag3Sn for a fixed ratio
of Ag & Au. I.E. Gold has a much higher embrittlement potential.
Regards,
Ed Hare
SEM Lab, Inc.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bev Christian
Sent: Friday, February 21, 2003 5:25 AM
To: [log in to unmask]
Subject: Re: [TN] Question For Werner (Ag More Detrimental than Au?)
George,
Good question! I have asked this question several times on Technet, but
have not got much in the way of a response. All I know, and I am sure
Werner will elaborate if he has more to say on the matter, is that in
the 80's there was a really bad "incident" with silver, but the research
data was figuratively speaking poured down a mine shaft and the
participants were told not to say anything under threat of legal action.
This is NOT saying that the new silver based board coatings are a
problem. We are now talking about very thin layers of silver here and
you and I both know from our former employment as rival companies that
these new coatings are not a problem.
regards,
Bev
-----Original Message-----
From: Wenger, George M. [mailto:[log in to unmask]]
Sent: February 21, 2003 8:15 AM
To: [log in to unmask]
Subject: [TN] Question For Werner (Ag More Detrimental than Au?)
Werner,
Bev indicated in his response to Jeff that you've "said more than once
that he (i.e., Werner) believes that silver is more detrimental to
solder joint reliability than gold." Is this a "belief"? or can you
point me to reference material
Regards,
George
George M. Wenger (908)-546-4531
Reliability Engineer
RF Power Amplifier Group
Andrew Corporation, 40 Technology Drive, Warren, NJ 07059
[log in to unmask]
-----Original Message-----
From: Bev Christian [mailto:[log in to unmask]]
Sent: Friday, February 21, 2003 7:32 AM
To: [log in to unmask]
Subject: Re: [TN] Gold thickness
Jeff,
It is more complicated than that. First, you talk about contacts and
then you talk about solder joints, so I am a little confused. I presume
you will have lots of pads and some will be the basis for solder joints
and some will be physical contact points, but will not be soldered. Is
that a correct interpretation? If that is so, then you have to worry
about not only the gold limit for your solder joints, but the effect of
the silver! Werner has said more than once that he believes that silver
is more detrimental to solder joint reliability than gold. Now if you
overplate a silver pad with gold and then cover with eutectic tin/lead
solder paste and reflow the gold will surely dissolve and I would expect
a significant amount of the silver as well. This will mean that your
"noble metal" content could be quite high.
In addition, we need to know how high a temperature your system will
see, because I would expect the metal boys may have something to say
about silver/gold diffusion if you get high enough in temp.
Have fun!
regards,
Bev Christian
Research in Motion
-----Original Message-----
From: Jeff Brown [mailto:[log in to unmask]]
Sent: February 20, 2003 7:05 PM
To: [log in to unmask]
Subject: [TN] Gold thickness
Dear Technetters,
We want to protect silver plated contacts on solar cells from tarnishing
by overplating with a thin layer of gold.
I believe that the gold content of the final solder joint shouldn't
exceed 3% (by volume of metal) to avoid embrittlement, but that means
our gold thickness will be 4 microns or less.
Is 4 microns thick enough to provide a non-porous gold layer and prevent
the silver from tarnishing?
Thanks in advance.
Jeff Brown
Research Engineer
Centre for Sustainable Energy Systems
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