Hi 'afng',
Where have you been all these years tghe industry has been struggling with
fatigue failures of solder joints. Creep certainly plays a role, but what you
are experiencing is thermal expansion induced creep-fatigue of the solder
joints.
Get yourself a copy of IPC-D-279 "Design Guidelines for Reliable Surface Mount
Technology Printed Board Assemblies" and read Appendix A to give you some
background.
What you have is a design inappropriate for the severity and number of thermal
cycles experienced by your product. The primary problem is a bad combination
of materials with large CTE (coefficient of thermal expansion)-mismatches.
Depending on your application, your FR-1 laminate may also swell due to
moisture absorption. Also, very likely your design did not provide for any
standoff of your DIPs from the PCB.
All of these things put cyclic loads on your solder joints which causes
fatigue damage which leads to failure.
The solution(s) will depend on your application and design details.

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]

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