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

近年来，由于电子机器的多媒体需求，信息处理和运算处理速度的加快，以及信息技术单位的移动化趋势正在迅速推进。小型化和轻量化技术是移动单元、电子单元的关键技术。此外，移动单元掉落概率的增加导致冲击强度主导其可靠性。本研究的目的是利用静态有限元分析系统，建立一种有效的跌落行为应力评估方法，明确移动电子元器件焊点的动态失效机理。本研究的主要结论如下：1)研制了微焊点动态行为冲击试验装置。根据焊料性能动态测试的实验结果，发现动态屈服应力远高于静态屈服应力…更多。结果表明，在研究焊点的动态行为时，可以弹性地处理焊料材料。2)对安装在BGA(球栅阵列)封装上的印刷圆板进行了循环跌落试验。结果表明，界面疲劳裂纹是BGA焊点的主要失效形式，界面裂纹主要集中在焊料与铜焊盘之间的中间层。3)代替动态有限元分析，提出了模拟印制板和焊点动态行为的静态分析方法和模式分析方法。该方法不能将仿真时间缩短到1/10，可以用来研究印制电路板一阶振动模式对焊点动态应力行为的影响，分析结果表明，焊点动态应力行为受印制电路板振动模式和封装位置的影响很大。因此，BGA封装的冲击可靠性设计可以通过控制封装位置与印刷电路板的振动模式相对应来进行。较少

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