The Investigation On The Shear Reliability Of BGA Package Under Board-level With Cycling Shear Loading

The reliability on BGA(Ball-Grid-Array) board-level is so important to the lifetime of electronic products. The BGA joints in board always undertake the dual roles that the mechanical connection and electric connection. Being the important part in whole structure of electronic products, the BGA joints under board-level is the key to the reliability to the package.This paper use the finite element software to do the simulation of cycling shear loading of Sn-3.0Ag-0.5Cu( SAC305) BGA under board-level. The paper is aim at figure out the impact mechanism and impact regulation of some impact factor of solder joints such as the number of joints, the diameter of joints, the distance between joints and the size of pad to the shear resistance ability.The study shows that, Firstly, the largest equivalent stress and strain joint in package is located in the first joint under cycling shear loading. And the phenomenon will stay stable with the increase of the number of solder joint. The largest stress and strain point where is not the crack appears is taken under the compressive stress and strain. The buckling deformation will continue caused by the cycling increase of the compressive stress and strain. And it will also lead to the increase of the tensile stress and strain value of the point where the crack occurs. The interconnection and interactionwill become stronger and stronger with the increase of the number of joints. The residual equivalent stress will stay at a stable area and or decrease slightly with the increase of the number of joints. But the equivalent strain will decrease largely with the increase of the number of the joints. The regulation reflects that the shear reliability of BGA package under board-level will grow exponentially with the increase of the number of the joints.Secondly, under cyclic loading conditions, the increase of the spot pitch weaken the interactions between joints in board-level, stress is mainly borne by each individual solder joints. Therefore, the solder joint's stress-strain values increase and the cyclic shear reliability decrease accordingly; When the pad size expand continuously, the interaction between pad and solder get enhance at inception phase thus the solder joint' cyclic shear reliability get increased. When the pad size keeps expanding, the relative volume of IMC layer increase, so the difference of linear expansion coefficient cause the stress strain generating at the interface increases rapidly, thereby the stress concentration and equivalents plastic strain at the interface are enlarged.Thirdly,wth the increase of peak load, the stress and strain of BGA board structure will also increase, the corresponding area of the hysteresis loop increases too, so the accumulation of plastic deformation increases. With the increase of holding time, while equivalent plastic strain will increase year-onyear, the board structure equivalent stress won't have significant change. Increase range of equivalent plastic strain show a growth trend first and then gradually flatten out and eventually equivalent variable approaches to a fixed value. With the increase of the cycling times, the equivalent variable of the maximum stress points shows a small increase, but the equivalent plastic strain values of the maximum stress increases sharply first and then increases slightly and finally tends to be stable.