Kinuko Mishiro

Effect of the drop impact on BGA/CSP package reliability

Abstract In this study, ball grid arrays (BGAs) and chip size packages (CSPs) were evaluated with respect to their solder joint reliabilities under drop impacts. The correlation between solder joint stresses and motherboard strains was confirmed by numerical analysis, and the motherboard strains caused by the drop impacts were measured to evaluate the BGA/CSP reliability. The authors found that the stress at a solder joint differs depending on the package structure, even if the motherboard strain is the same, and that underfilling eases the motherboard strain and disperses the stress concentrated on a solder joint.

Method of Shock Analysis for PCB subjected to Ball Impact

The LSI packages of mobile devices are mainly BGA (Ball Grid Array) packages, which are soldered onto PCBs using minute solder balls. Obviously, the solder joints of these packages must be strong so the device can withstand being dropped, and this is usually checked by conducting drop tests. However, because it is difficult to reproduce the same device orientation and kinetics at the time of impact in each test, the results are not very consistent. To improve the results, we examined a testing method in which the device under test is subjected to the same forces as in a free fall by striking it with a falling steel ball. Then, we developed a device that tests resistance to repeated impacts by a falling steel ball and evaluated its performance. Also, we analyzed the strains and distortions that occur on PCB surfaces during free-fall impacts and impacts by falling steel ball and then compared the analysis results with measurements made in experiments with actual devices. This paper describes the method of shock analysis we used in this investigation.