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| Reply To: | (Leadfree Electronics Assembly Forum) |
| Date: | Thu, 23 Nov 2006 15:49:24 -0500 |
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Guenter,
why did you use Sn36Pb2Ag paste for the experiments? Will the findings stand for Sn37Pb?
Thanks,
Ioan
-----Original Message-----
From: Leadfree [mailto:[log in to unmask]]On Behalf Of Guenter Grossmann
Sent: Thursday, November 23, 2006 5:30 AM
To: [log in to unmask]
Subject: [LF] Antw: [LF] SnPb attachment of SAC BGAs
Gordon
We looked at the alloying of SnCuAg balls with SnPb:
Soldering & Surface mount Technology
Volume 17, Number 2, 2005
Right now we are microsectionning the specimen from thermal cycling.
Best regards
Guenter
EMPA
Swiss Federal Laboratories for Materials Testing and Research
Centre for Reliability
Guenter Grossmann, Senior Engineer
8600 Duebendorf
Switzerland
Phone: xx41 44 823 4279
Fax : xx41 1 823 4054
mail: [log in to unmask]
>>> "Davy, Gordon" <[log in to unmask]> 22.11.2006 17:03 >>>
This is a request for info. It has been shown that soldering a SAC BGA using SnPb solder results in a connection that does not hold up well to thermal cycling. The cause of the problem has been attributed to non-uniform distribution of Pb in the solder ball after soldering. That nonuniformity is the result of too little time for the Pb to reach equilibrium concentration in the ball before it freezes.
I am pretty sure that I have heard of some contract manufacturers using this process and making it work (i.e., obtaining a uniform Pb distribution) by increasing the reflow solder profile so that the peak temperature is not less than 225°C. This can be done provided that the moisture content of all the plastic-encapsulated microcircuits on the assembly is low enough (so that there is no popcorning).
Who can comment on this? Is there any publicly available documentation to confirm?
Gordon Davy
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