Failure Modes of Solder Interconnections under Mechanical Shock Loading at Elevated Temperatures

Abstract

Portable electronic products meet varying environments in ordinary daily use and therefore their reliability should be studied with tests that simulate the components' strains and stresses as realistically as possible. Portable equipment are primarily exposed to local temperature fluctuations by internally generated heat dissipation as well as to mechanical shock loadings due to accidental droppings. The reliability of test boards was studied under mechanical shock loadings at elevated temperatures. Component boards were loaded by using a high amplitude (high-frequency) vibration tester because very similar loading conditions can be produced with the vibration tester as compared to the JESD22-B111 type drop tester with much less time and effort. The same experimental design was repeated with the JESD22-B111 drop tested to conform that the failure modes and mechanism are equal. The lead-free materials used in the reliability tests were chosen to represent those typically used in portable electronic products. The reliability tests were carried our in three different temperatures (room temperature, 70 degC and 110 degC), and the heating of the component was carried out with integrated heater elements inside the component as well as in the printed wiring boards. Reliability under the tests decreased as the test temperature was increased. The differences in the mean load-cycles-to-failure were statistically significant. Increased bending of the printed wiring board at elevated temperatures and the subsequent increase in the stresses experienced by the solder interconnections is the most likely reason for the observed behavior. The failure analyses revealed that cracks in the component side interfacial region of the solder interconnections was the primary failure mode leading to electrical failure of the component boards. The failure modes were the same in both the tests