Finite Element Simulation Study Of Interface Delamination And Thermal Fatigue Behavior Of C4 Solder Joints In Heterogeneous Integration 2.5D Package

With the development of integrated circuit(IC) technology,it is extremely difficult to improve the performance of electronics and reduce power dissipation by means of continued scaling technology of integrated circuits.In the“More than Moore”era,heterogeneous integration has been developed as a key technology to realize higher-density integrated circuit,higher-performance and more-function IC and electronic products,which has been increasingly applied in many new areas,such as 5G,big data and artificial intelligence.Through heterogeneous integration,dies/chips with different manufacturing processes,different functions and different sizes are included in one package based on advanced substrate and wiring layer,thereby forming a complex system with the feature of multi-material,multi-interface and cross-scale.However,due to mismatch of coefficient of thermal extensions among the materials in the heterogeneous integration package,high thermal stress would appear at different bimaterial interfaces during packaging manufacturing,testing and service of IC products,which may lead to interface cracking even delamination and thus has posed a serious challenge to reliability of dies and solder joints in packages.In this thesis study,based on finite element(FE) analysis theory,FE models of a single through-silicon-via(TSV)structure and 2.5D heterogeneous integration package structure were constructed by means of finite element analysis software ANSYS.TSV interface delamination behavior was investigated at elevated temperature,and fatigue life of critical controlled collapsed chip connection(C4)joints in the 2.5D heterogeneous integration package structure during temperature cycling was predicted.Further,the distribution of energy release rate and fracture mode ratio for the annular crack at the underfill/passivation interface and the underfill/solder mask interface around the critical C4 joint in the underfilled package structure were characterized systematically.The simulation results by using incorporated cohesive zone model(CZM)with the finite element(FE)model show that the presence of Si O₂ insulation layer in TSV structure leads to a significant reduction of stress concentration at the Cu/Si O₂ interface and thereby a lower fracture risk.However,variation of Si O₂ insulation layer thickness has a minor influence on the mechanical performance and cracking behavior at the Cu/Si O₂ interface.The use of an overlaying Cu pad in TSV structure is beneficial to decreasing damage and reducing risk of cracking at the Cu/Si O₂ interface.The crack initiated at the opening of TSV prefers to propagate vertically,and a thicker Cu pad may result in retardation of crack delamination propagation along the Cu/Si O₂ interface.Underfill with high modulus and low coefficient of thermal expansion(CTE)could provide effective protection for solder joints and enhance the fatigue life.Underfill with higher glass transition temperature yet unchanged modulus and CTE leads to higher fatigue life.Small scale delamination at the interface(such as underfill/passivation,underfill/solder mask,and underfill/solder interfaces)around the critical C4 joint would reduce the fatigue life to 67%of the reference value,while large scale delamination of interface(such as underfill/passivation and underfill/solder mask interfaces)leads to decrease in fatigue life being less than 50%of the reference value.Energy release rate of annular crack around C4 joints reaches the maximum value during low temperature dwelling.Redistribution of energy release rate along the annular crack occurs with increasing temperature cycle number.Underfill/passivation interface crack in the scope of?=0°?256°(?is the crack tip position angle)is dominated by shear fracture mode(i.e.,mode II fracture),which means higher critical fracture energy;while crack within?=256°?360°is controlled by opening fracture mode(i.e.,mode I fracture)with lower critical fracture energy.For the crack at the underfill/solder mask interface,opening fracture mode is dominant in?=65°?195°,where the critical facture energy is lower,while shear fracture mode dominates in other sites with higher critical fracture energy.