Vibration test as a new method for studying the mechanical reliability of solder interconnections under shock loading conditions

摘要

This thesis presents a new large-amplitude vibration test method for studying the reliability of electronic assemblies under mechanical shock loadings. The vibration test has two important advantages as compared to the widely employed JESD22-B111 drop test: firstly, the vibration test is a more versatile method and, secondly, the testing can be carried out very rapidly, in the matter of seconds. The impact forces caused by dropping of portable devices make their component boards to vibrate excessively, which causes failures in solder interconnections between component bodies and the bending circuit boards. The component boards can be drop tested according to the JEDEC standard or vibration tested with the method developed in this work. The loading conditions and the failure modes during the tests are compared by making use of the finite element method, experimental measurements, and the standard methods of failure analysis. The finite element method is used to analyse the vibration of the component boards during the tests and the stresses produced in the interconnections. The plastic properties needed for the analyses are measured for the three solders (Sn2Ag0.5Cu, Sn3.4Ag0.8Cu, and Sn4Ag0.5Cu) as a function of strain rate and temperature. Due to the high strain rates during the rapid bending in the tests, the magnitudes of stresses increase significantly as compared to those during thermal cycling. According to the analyses, the vibration system generates equivalent stresses as the drop test, if the bending frequency and amplitude are properly adjusted. Strain gauges are used to determine the bending of the component boards during the drop tests, and similar vibratory bending is reproduced with the help of the vibration system. When the bending frequencies and amplitudes of the component boards in the vibration test are similar to those in the drop test, the same failure modes are observed. Because of the similar strain rates, maximum strains, calculated stresses, and the same observed failure modes, it is concluded that the vibration test can be used for studying the reliability of solder interconnections under shock loading conditions.