The Study Of The Chip Reliabilty About The Failure Of Packaging Epoxy Molding Compound

As the outer packaging of chips, Epoxy Molding Compound (EMC) is used to avoid the interference of external factors, such as dust, moisture, impact, vibration and chemical materials, etc. It is a kind of new-style composite material. So, electrical components would work normally with it. Combining experimental studies and FEM analysis, the micro-mechanical properties and dynamic properties under high strain rates of EMC were studied. The main procedures and conclusions are as following.1. The KL-4500-1S EMC was tested by using Hysitron's nanomechanical testing instrument. The load-displacement curve, elastic module and hardness of EMC were obtained. Using reverse analysis method and numerical simulation, the relationship of load-displacement and elasto-plastic parameters of EMC were ascertained and the representative stress and representative strain of EMC were gained. Then the elastic-plastic constitutive equation for EMC was achieved.2. Using a micro Hopkinson pressure bar which includes temperature controlling system,a series of dynamic compressive experiments of EMC with diameter of 6mm and height of 3mm were conduct. Compared with quasistatic tests, the results indicate that EMC has fragility in quasistatic experiments, while in dynamic experiments, the yield strength and flow stress increase remarkably with the increase of strain rate. Therefore, EMC has effects of strain rate. Between the temperature of 20℃and 160℃, EMC is slightly softened and its strength decreases along the increase of temperature, on the contrary, if it becomes harder, its intensity will increase. Further more, EMC has properties of strain hardening, i.e. the flow stress increases with the increase of strain. When the adjacent temperature is 60℃, Cowper-Symonds elasto-plastic constitutive model and Zhu-Wang-Tang constitutive model were adopted. Using experimental results, the constants of above constitutive relationships were obtained, so, the constitutive equation of EMC was determined.3. Adopting Input-G method, limited in the B condition of JEDEC standards, the reliabilities of EMC loaded with Half-Sine Accelerate wave on which the action time was 0.5ms were analysed by using software ANSYS/LSDYNA, when VFBGA packaging was in the drop impact conditions. The results indicate that the bending and vibration of PCB caused by mechanical impact are the basic reason for EMC's failure. The damage of packaging layer is aroused by vertical stress of EMC. Failure stress in the center of EMC is higher than that in the periphery and corresponding circuit board has higher stress in the long edge than in the short edge.