Mike,
     
     Although I have no experience with X-ray techniques for excessive 
     Sn/Pn migration on what sounds like a populated board, I would have to 
     be absolutely convinced that x-raying is allowed from an independent 
     source - publication, standard, etc.  
     
     Depending upon the field intensity, flooding semiconductor material 
     with x-rays can:
     
     1. Knock electrons loose starting current flow and voltage potentials.
     
     2. Introduce interstitial defects into semiconductor material.
     
     If you are working with an unpopulated board, please ignore.
     
     Doug


______________________________ Reply Separator _________________________________
Subject: Re: Intermetalic
Author:  [log in to unmask] at internet-mail
Date:    3/28/96 8:15 PM


Hello !!
     
Q: Is there any standards for maximum acceptable intermetalic thickness for 
63Sn/37 Pb solder? How much is too much?
A: ???
     
Q: Wihout performing any destructive test, is there any way  to detect 
excessive Sn/Pn migration? ( X-Ray dispresion????? )
     
A:  I have used SEM/EDS (Line Profiling) successfully to perform reliability 
studies on intermetallic formation and growth on flip chip 10/90 solder.  
     
I have also used SEM/EDS (X-Ray Mapping) to study tin phase growth and migration
for this flip chip system.
     
You will have to perform accelerated heat treatments on different samples for 
different times then you can determine the intermetallic growth rate and the 
rate of migration. You will also need high quality cross-sections of these 
samples.
     
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Nick Biunno
Zycon Corporation
[log in to unmask]
     
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Thanksfor you response.
     
Mike Yuen