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September 1999

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From:
"Ingemar Hernefjord (EMW)" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 9 Sep 1999 09:22:33 +0200
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We had a crazy application some years back, with the absolute requirement to mount an Al2O3 substrate on an 6061Al part, mounted by means of Sn63/Pb37 or better. Would never work I thought, but the designer said the equipment is already sold, so I sighed and went to ask my brain for  help. With brain I mean Manko and Wassink, indispensible references. As I suspected, solder's nature is so complicated and non-linear that I felt I had better tell the designer about the whole bad idea. But...the bumble-bee can't fly, math's say, but does still, so I ordered an FE and NASTRAN-simulation of solder joint behavior over the temp range. We couldn't get safe E-and S-modulus info from the solder source, at least not covering -55/+125C, so we put estimations into the model. The CAD simulation showed local and global tensions in such places we hadn't expected, and we got inspiration to go on. Following the simulator results, we designed the solder joint geometry in a new way, and alas, instead of getting microcracks in 
Good Luck
Ingemar Hernefjord
Ericsson Microwave Systems


-----Original Message-----
From: Werner Engelmaier [mailto:[log in to unmask]]
Sent: den 9 september 1999 04:52
To: [log in to unmask]
Subject: Re: [TN] acceptable solder joint shear strength?


In a message dated 09/08/99 9:51:32, [log in to unmask] writes:
>Does anyone know what the minimum acceptable solder joint shear strengths
>are for Sn63/Pb37 and In50/Pb50 ?
>We are trying to optimize our soldering to gold interconnect process and
>need some baseline/ industry standard numbers.
Hi Ron,
There is no shear strength standard for solder joints, nor can there be.
If solder joints are properly wetted, they have more than ample strength for
normal, even severe,  handling and operating conditions. If they are not
properly wetted, the strength will be inadequate; because you really do not
have a solder joint. Solder joint reliability for properly wetted SJs is not
a function of SJ strength.
The solder joint strength in pull/shear will vary with lead geometry, solder
volume, lead metal/metallization, the way the test is done. For 50-mil-pitch
gullwings pull strength between 2000 and 5000g are typically measured.
What do you mean by "gold interconnect process"?

Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL  32174  USA
Phone: 904-437-8747, Fax: 904-437-8737
E-mail: [log in to unmask], Website: www.engelmaier.com

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