Bga Packaged Devices Ball Shear Test And Simulation Studies

BGA (Ball Grid Array) is an important packaging form featured by high density, small volumes, good reliability and slight signal delay. The devices are connected to PCB (Printed Circuit Board) through solder balls to form functional modules in BGA packaging, so failures occur frequently in solder balls. Recently, traditional Pb-Sn solders are gradually being substituted by lead-free solders because of environmental concerns. External forces and vibrations during assembly and in use, existence of intermetallic compounds (IMC) and BGA voids induced during soldering lead to solder ball destructions which result in BGA packaging failures. While the researches on the failures in BGA solder balls are insufficient since the new lead-free technologies are used, so it is very important to study the performance of the lead-free BGA packaging to guide the application of lead-free BGA packaging devices.In this paper, shear tests on BGA packaging with different materials, including Pb-Sn, Sn-Ag3.0-Cu0.5, Sn-Ag3.0-Bi3.0-Ni0.5, and assembled in different reflow conditions are carried out in different shear speeds. Researches are conducted on the influence of reflow times, reflow peak temperature and shear speed on the shear strength of solder balls and the microstructure of the fracture interface and fracture mode of the solder balls.In addition, IMC growth during reflow is studied to find out the influence of IMC on soldering strength of the solder balls. The IMC thickness, morphology and composition under different reflow temperature and after different reflow times are investigated with SEM (Scanning Electron Microscope) and EDX (Energy Dispersive X-ray Detector). And these results are compared with the shear test results to qualitatively analyze the influence of IMC layer on the soldering strength of solder balls. The influence of IMC growth during long-time temperature cycling on solder ball fatigue lifetime is studied using FEA (Finite Element Analysis) tools. Adaptive algorithm is used to realize IMC growth during simulation, and energy fatigue model is used to predict solder ball lifetime. The influences of BGA voids on temperature and thermal stress distribution are also studied.The results showed that the shear strength increases with the increase of shear speed and then decreases with the increase of shear speed, which can be explained by different fracture sites and modes: in relatively high speed, the brittle fracture mode prevails. The shear strength of Sn-Ag3.0-Bi3.0-Ni0.5 solder balls is higher than that of Sn-Ag3.0-Cu0.5 solder balls. The reflow temperature and reflow times influence shear strength through the changes of IMC layer, and thick IMC layer leads to the decrease of shear strength. The simulation shows that the predicted lifetime with IMC growth is shorter as much as 30% than that without IMC growth, indicating that IMC growth affects solder ball lifetime. The simulation of BGA voids shows that temperature and thermal stress distribution in solder balls are affected by the size of the BGA voids, which raise the probability of failure in solder balls.