Journal of SMT Article


Author: V.Srirama Sastry
Company: Lucent Technologies
Date Published: 1/1/2001   Volume: 14-1

Abstract: Solder joint fatigue life is commonly determined through accelerated tests by subjecting electronic assemblies to temperature cycling. These tests are time consuming and expensive, but essential in evaluating attachment reliability of packages to printed wiring boards. Faster thermal cycles can reduce the test times and lower the test cost, provided that the failure mechanism remains unaffected. The thermal cycle time is composed of dwell times at the high temperature (Tmax) and low temperature (Tmin) and the time taken to ramp between the temperature extremes. The dwell time allows for creep and stress relaxation of the solder joint. Therefore, cycle time can be reduced by decreasing ramp times which result in higher ramp rates.

The objective of this work is to determine the effect of ramp rate on the failure mechanism and the fatigue life of solder joints. Thermal cycling tests were conducted with chip scale packages (CSPs) using varying ramp rates and dwell times.

For the ramp rate range of 10 degrees C/min to 20 degrees C/min, there was no difference in either the failure location or the failure mode. It can be concluded that, for the BGA/CSP family of packages, all three thermal cycles can be used without impacting the nature of the results. Also, the 20 minute 0 degrees C to 100 degrees C thermal cycles produced essentially identical results to the 30 minute 0 degrees C to 100 degrees C thermal cycles, with a 30% savings in test duration.

Key words: Attachment reliability testing.

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