Study on Impact Strength Evaluation of Micro-Solder Joints in Mobile Electronic Units

点击翻译按钮获取中文摘要

Recently, the speed-up of the information processing and operation treatment speed due to multimedia needs of the electronic machine, and mobile trend of information technology units are proceeding rapidly. The miniaturization and lightening technologies are the keywords for mobile units electronic units. Furthermore the probability increase of mobile units dropping causes that the impact strength dominates its reliability. The purposes of this study are to develop a effective stress evaltuation method for the dropping behavior by using static finite element analytical system, and make clear dynamic failure mechanics of solder joints in mobile electronic units.The conclusions of this study were given as followings ;1) An impact testing equipment was developed to investigate the dynamic behavior of micro solder joints. Based upon the experimental results of dynamic tests of solder material properties, it was found that the dynamic yield stress is much higher than its static yield stress … More . This restults suggest that solder material can be treated elasticly, when dynamic behavior of solder joints is investigated.2) Cyclic dropping tests of PCB (printed circle board) mounted with a BGA (ball grid array) package were carried out. It was found that the interface fatigue crack is the main failure mode of BGA solder joints, and the interface crack concentrating in the intermeterics layer between the solder and Cu pad. Furthermore it was found that this interface crack mode is caused by the increase of solder yield stress due to dynamic deformation.3) Instead of dynamic finite element analysis, a static analytical method and a mode analytical method have been developed to simulate the dynamic behavior of PCB and solder joints. The proposed methods cant shorten the simulation time to 1/10 and can be used to study the effect of PCB vibration modes beside its first mode on the dynamic stress behavior in solder joints.Based upon the analytical results, it was found that the dynamic stress behavior in solder joints is affected greatly by the vibration modes of PCB and the location of the package. As a conclusion the impact reliability design of BGA package can be dealt by controlling the position of package corresponding to the vibration modes of PCB. Less