Thermal and Mechanical Reliability Tests of Lead - free soldered SMT Joints

Abstract

One of the main goals in development of electronics manufacturing technology, after implementation of EU Directive RoHS, is the reliability improvement of electronic interconnection systems. Investigations of lead -free technologyfor small producers of electronic equipment (SME s) were made in Warsaw University of Technology (WUT) in frame of GreenRoSE Project financed by EC. Achieved results of accelerated thermal and mechanical cycling fatigue tests of SnPb3 7 and lead-free SMT solder joints are presented. Two PC test boards finishes. immersion tin and leadfree HASL were applied. The samples were assembled and soldered on GreenRoSE pilot line. Thermal cycling( air to air) tests were performed in two zone thermal shock chamber For mechanical tests was used new laboratory stand designed by WUT [1]. The failures occurred during the tests were detected by four point resistance measurements and visual inspection. The results showed that achieved reliability data of lead -free soldered joints are satisfactory, however, for high reliability applications, further investigations are necessary.

Life-time of lead-free soldered SMT joints

“…In described investigations as failure criteria were selected the measured variations of electrical resistance [2] and extent of the cracks formation. The test results are presented on Weibull plots.…”

“…The difference in failure rate characteristics between SnPb and SAC solders are particularly visible by thermal cyclic testing of 1206 resistors, because the creep rate of SAC solders is smaller and the shear forces by thermal cycling are larger [3]. …”

“…The test samples are assembled and soldered on the pilot line installed in industry. The test methods and parameters were published in [3]. New results and observations achieved after industrial implementation of new manufacturing technology of test samples with lead -free HAL surfaces, realized in industrial conditions, range of test performed and achieved more satisfying results are presented.…”

“…Present results of reliability investigations discussed in [1] and [2] showed that the estimation of field life from accelerated test data is not yet possible with sufficient certainty for the most safety critical applications. For this reason in Warsaw University of Technology (WUT) are continously performed comparative reliability tests of lead -free and SnPb soldered joints.…”