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 via clip-leads has been investigated. Clip-leads from two vendors, Berg and NAS, were utilized in this study. 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 factors between 12 and 20) was accomplished with shorter dwell times at the temperature extremes, resulting in 96 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 Berg clip-lead CCs showed a median life to failure of 12,000 cycles, while the NAS "hinged S-bend design" clip-lead CCs exhibited no failures when the test was terminated at 100,000 cycles. An acceleration transform is used to extrapolate the accelerated test results to obtain functional use condition (1 cycle per day) reliability estimates. The estimated mean cyclic lives are 2500 and 304,000 cycles for the Berg and NAS leaded CCs, respectively. The respective 1% failure hazards are projected to be at 310 and 37,000 cycles.