Simulation And Experimental Verification On The Reliability Of BGA Packaging

With the development trend of the electronic products being light, thin, small andfunctional diversification, BGA （Ball Grid Array） packaging has become one of the mostadvanced technologies in IC （integrated circuit） packaging. The major obstacle for the newgeneration of BGA packaging technology is that when the electronic products were used, thechip will generate a lot of heat to make the temperature of components of packaging rise;furthermore the packaging system is made of different materials and the difference of theirthermal expansion coefficients is so large that the changes of temperature will producethermal stress in packaging to make the weak material strength of solder ball appear cracksand failure, and then the whole electronic products fail at last. Moreover, with the growingpopularity of portable electronic products, the solder joints of BGA packaging will alsoendure high strain rate damage （such as dropping bruising） resulting in a new failure mode forsolder joint.In this paper, the finite element method is used to simulate a series of temperature field,thermal stress﹠strain and the shear behavior under different strain rate for simplified BGApackaging（mainly including Si chip, Sn-3.0Ag-0.5Cu lead-free solder ball and substrate）, andthe relevant experiments were carried out to verify the simulation results. All these canprovide some theoretical basis and experimental data for the reliability of electronic productsdue to many problems lead by temprtature, thermal stress, fatigue and impack vibration.On the reseach of temperature field, when adding the current （I₁=0.5A、I₂=1.5A、I₃=2.5A）to the solder joint, both the experimental and simulation results indicate that the temperatureon the both sides （namely chip side and substrate side） of BGA packaging solder jointincreases with the increasing of current and obey the parabolic law; when assuming the chipas the sole heat resource（power is0.1W） and considering heat conduction and naturalconvection, the temperature simulation results of3-D and2-D BGA packaging show that thetemperature of solder ball is higher and close to the temperature of the chip, and the substrateis lower, this may be due to the thermal conductivity difference among the substrate, the chipand the solder ball.On the thermal stress analysis, BGA packaging components （especially is solder ball） are suffering displacements and stress＆strain response for either in steady-state temperature fieldor under thermal cycling （-40～125℃） conditions. The radical reason lies in the mismatch ofthe thermal expansion coefficient for materials in the BGA packaging. Furthermore, theshortest thermal fatigue life of Sn-3.0Ag-0.5Cu solder ball is704cycles based onCoffin-Manson equation under thermal cycling.The thickness and morphology of IMC after the processes of different aging time wereobserved by SEM, and BGA ball was carried out the shear strength test and simulation underthe different shear rates（≤10mm/s）. The results indicate that the thickness ofSn-3.0Ag-0.5Cu/Cu interfacial IMC increases, the morphology of interfacial IMC changesfrom dendritic to continuous even lamellar and the solder ball shear strength decreasesgradually with the increasing time. It is also confirmed that the solder shear strength increaseswith the increasing of the shear rate and its shear strength decreases with the increasing of theshear height.