Fatigue Properties Of COG Assembly Under Thermal-electric-mechanical Loading

With the development of high density packaging technology, the electronicproducts are developing towards further miniaturization and green. The chip-on-glasspackaging technology, depending on the various advantages, is widely used inelectronics module. In this paper, the uniaxial ratcheting behavior of ACF afterthermal cycling was investigated, the fatigue and property of COG module usingthermo-electro-mechanical coupling method was also studied, providing guidance fordesigning more electronic products with lower dissipation rate, higher efficiency,better working voltage and temperature.After the experiments of uniaxial ratcheting of aged ACF, it is found that theratcheting strain of unaged ACF is obviously higher than that of aged ACF, and thestrain is smaller and smaller with the increase of thermal cycles. Moreover, during theinitial stage of temperature circulating, the ACF was second cured and the resistdeformation ability was enhanced leading to the highest ratcheting strain at thermalcycles of50. However, the mechanical properties were further destroyed due to thedehydration reaction and thermal oxidation with increasing thermal cycles.Meanwhile, the higher mean stress (stress amplitude) or the lower stress rate, thehigher ratcheting strain. Finally, the loading history on the effects of uniaxialratcheting behavior of aged ACF is significant.The fatigue behavior of COG modules with the help of fatigue machine andprogrammable DC current under different working environment was also conducted.The results show that, after omitting the mechanical displacement, the load is almostlinearly increased with the increase of displacement. When the chip failed from theglass substrate, the resistance was viewed as infinite and the module was destroyedand at this time the shear strength was61.09N. Moreover, during the fatigue process,the fatigue life-time decreased with increasing loading amplitude. When consideringthe module subjected to singly cyclic load, the absolute resistance changedinstantaneously and periodically with the periodic load, but the changing trend ofresistance was not completely uniform with the loading change. The relativeresistance of COG module increases with increasing loading amplitude, but theresistance before failure increases firstly and then decreases. What’s more, theelectronic failure is earlier than the mechanical failure when the module is subjectedto lower stress level. High temperature and humidity, temperature cycling exert critical influence on the fatigue behavior and working resistance of COG module, andthe effects of hygrothermal environment on the module is more obvious than that ofthermal cycling.The Basquin model, Smith model, SWT model and Gerber model can predict thefatigue lives of COG modules well. Simultaneously, the fatigue life of COG modulesunder hygrothermal aging and thermal cycling were predicted well by using thedamaged factor model, and the relationship between the damaged factor and relativeresistance occured.