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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