Hi Poh,
Solder joint quality (that is good wetting, not geometry other than height)
is necessary, but not sufficient to assure solder joint reliability. Solder
joint reliability can ONLY be assured by a 'Design for Reliability' where
assembly geometry, materials properties, use (or test) conditions, design
life, and acceptable failure probability are considered. TSOPs with Alloy 42
lead frames are very bad as far as reliability is concerned, and I am not at
all surprised that you get solder joint failures on thermal cycling no matter
how good the solder joint quality is. The notion, that solder joint
reliability can be 'inspected into' a product, is a hang-over from the old
military visual inspection criteria.
At the very least, get yourself a copy of IPC-D-279, 'Design Guidelines for
Reliable Surface Mount Technology Printed Board Assemblies' and read Appendix
A. I give a workshop for clients (and at some conferences) entitled
"Practical Design and Prediction Methods for Surface Mount Solder Joint
Reliability" that deals with the underlying issues in great detail.



Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
23 Gunther Street                                In December:                                            Jasmine Run
Mendham, NJ  07945                                                                  Ormond Beach, FL  32174  USA
Phone & Fax: 973-543-2747                         Phone: 904-437-8747, Fax: 904-437-8737
E-mail: [log in to unmask]

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