Hi TechNet!
     
     Shaun - there are people in the electronics industry that do use Sn/Pb 
     plated parts in gold sockets so don't think that it is never done. But 
     those folks have taken into consideration the issues that Dr. Lei 
     brought up - e.g. they seal the PWA so that water can't get to the 
     connection or they use very high insertion forces plus make design 
     considerations such that the micro-motions that occur don't impact the 
     electrical functionality. Most people follow Dr. Lei's suggestion and 
     avoid the gold-Sn/Pb issue altogether. IPC-GH-850 "Handbook of 
     Interconnect Contact Finishes" has some good general info on 
     gold-Sn/Pb that may be helpful.
     
     Hey IPC - What happened to IPC-GH-850? I do not see it listed in the 
     IPC catalog! Is it still procurable?
     
     
     Dave Hillman
     Rockwell Collins
     [log in to unmask]


______________________________ Reply Separator _________________________________
Subject: Re: Gold Migration into Tin/Lead
Author:  [log in to unmask] at ccmgw1
Date:    12/2/96 4:26 PM


Shaun
     
I suggest that you do not use tin/lead plated part with gold socket.  The 
contact interface will become unstable and contact integrity will be 
compromised.  The circuit will experience intermittent and/or open after a 
while, depending on the operating condition.  Tin/lead WILL form oxide and 
cause contact resistance to increase to the undesirable level.  This effect 
will be greatly accelerated by contacting gold due to the galvanic effect.  
In fact, any dissimilar metal contact is not recommended.  Furthermore, 
micro-motions between the contact interface will probably move (smear) gold 
and tin/lead around, which does not help in this situation.     
     
Kuan-Shaur Lei, Ph.D.
Senior Member of Technical Staff
Advanced Technology Department
Compaq Computer Corporation
(281) 518-8099 (phone)
e-mail: [log in to unmask]
     
     
     
Date: Mon, 2 Dec 1996 08:29:54 -0600
From: [log in to unmask] (SDalton) 
To: [log in to unmask]
Subject: Gold migration into tin/lead
Message-ID: <[log in to unmask]> 
Content-Type: text/plain; charset=US-ASCII 
Content-Transfer-Encoding: 7bit
Content-Description: cc:Mail note part
     
     Has anyone heard of problems with seating a tin/lead leaded part into 
     a gold socket?  I have heard concerns that the gold will migrate into 
     the tin/lead even though it is only a mechanical connection.  I would 
     appreciate any input you can give me on this issue.  
     
     Thanks,
     
     Shaun Dalton
     [log in to unmask]
     
     
     
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