Chi-Min Cheng, Hsi-Wei Chao, Chu-Chiao Yen, Kun-Ting Chiang, Wei-Yao Chang, Chia-Wen Chang, Ya-Ping Chen, Hsien-Wei Ho, Chun-Yu Ko, Chun-Liang Kuo
With the rapid development of technology, the number and demand for handheld devices are increasing, and the new technology product development and launch are getting faster and faster. Also, handheld devices need to withstand various movements, fall-down situations, and even normal use in different temperature environments. Therefore, solder joint reliability is really crucial for handheld devices. Moreover, how to seize the key factors during the design development phase and fulfill market demands are also significant.
According to the definition of JESD22-B111, the drop test requires that the board should be horizontal with the package facing in the downward direction (-Z) during the experiment. Therefore, under the influence of the acceleration of gravity, the weight of the BGA (ball grid array) package, the number of balls, solder ball material, and the solder ball pad size in the drop test are recognized as important factors affecting the board-level reliability of the drop test. This paper will explore these key factors, and how they affect board-level reliability of the drop test.
Two of the key factors, solder ball pad size, and solder ball number would both affect and determine the total contact area of the ball. Then, the interaction of the key factors, there was a conclusion through experiments and calculations: when the package weight was divided by the contact area of the solder ball, the weight per unit area could be obtained. The greater the load-bearing capacity per unit area, the greater the risk of failure for the samples. Conversely, reducing the package weight or increasing the solder ball contact area can substantially reduce the risk of failure.
In this study, samples with different ball contact unit areas and different package weights were collected for testing, and the solder balls were fixed using SAC1205. The characteristic life (63.2%) data was obtained by Weibull analysis, and the load-bearing capacity per unit area of the ball contact was analyzed and compared with the characteristic life (63.2%). Finally, we could get the trend curve to predict the performance trend by the risk level and the characteristic life (63.2%). Furthermore, it could even predict the board-level drop test ability of the load-bearing capacity under different unit areas.
This prediction trend can provide designers with a design reference. In the product development stage, the prediction model can improve design capabilities and accelerate the product development schedule. Additionally, using this analysis method could meet market demands, avoid the waste of experiment costs, and finally, improve industrial competitiveness.