Surface-mount attachment reliability of clip-leaded ceramic chip carriers on FR-4 circuit boards

The reliability of the attachment of 100 I/O ceramic chip carriers (CCs) surface mounted to FR-4 epoxy/glass circuit boards using clip-leads has been investigated. Clip-leads, commercially available from two vendors, of significantly different designs were utilized. The accelerated tests involved the accurate reproduction of the thermal and physical conditions-internal cyclic power dissipation, external thermal cycling of forced air stream, thermal gradients, mounting hardware, etc.-encountered by the product in use. The test acceleration (by acceleration factors between 12 and 20 for mean time to failure) was accomplished with shorter dwell times at the temperature extremes, resulting in 96 accelerated fatigue cycles per day. The distinct difference in lead compliancy between the two clip-lead designs is clearly reflected in the results of the accelerated reliability tests. The Type-A 'J-lead design' clip-lead (K=58 lb/in) CCs showed a median life to failure of 12000 cycles, while the Type-B 'hinged S-bend design' clip-lead (K=7.5 lb/in) CCs exhibited no failures when the test was terminated at 100000 cycles. Failure mode analysis shows that all Type-A clip-lead solder joints have failed after 48000 accelerated cycles due to the CC/substrate expansion mismatch: at 100000 accelerated cycles a significant number of clip joints showed cracks due to the solder/ceramic CC material expansion differential.<
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