Research Of Mechanical Behavior Of Crack Initiation In Micro-electronic Package EMC-Cu Interface

The microelectronic packaging devices are composited by a variety of materials.During production,testing and service process,interface delamination failure will occur within packaging due to mechanical and thermal properties mismatch between different materials.The thesis focuses on interface delamination failure within microelectronics packaging devices.The main research was concentrated on interface between Epoxy Molding Compound(EMC)and Copper substrate.In the thesis simulation and experiment method were combined to study mechanical behavior of interface delamination initiation base on Cohesive Method.The main purpose of the thesis is to find out a testing method to get the ultimate tensile strength of the interface initiation,so that to establish a set of cohesive zone model parameters which can characterize the initiation and propagation of EMC-Cu interface.The following researches were launched:(1)A dual-cantilever test structure without pre-crack and a method for testing the ultimate tensile strength of the interface delamination initiation were proposed.The method of establish interface delamination initiation and propagation simulation analysis model was discussed according to the test structure.According to cohesive zone model theory,the relationship between the stress change in delamination initiation point and the experimentally measurable force-displacement curve was analyzed crack during initiation process.Simulation results showed that tensile stress will dominates the delamination initiation process during testing.The maximum tensile force which will lead to delamination initiation was only related to the ultimate tensile strength,but not affected by the ultimate shear strength.This demonstrate that it is possible to obtain the ultimate tensile stress values of EMC-Cu interface by combination of experimental and simulation methods.(2)Test samples without pre-crack were manufactured and the EMC-Cu interface delamination initiation mechanical test was carried out.Firstly,based on lever principle a lever tensile test device was designed which can be used in DMA Q800 equipment.Then the detailed of sample molding,separation and loading brock bonding process were introduced.Finally,the maximum tensile force which will lead to the cracking initiation of the EMC-Cu interface was obtained through a tensile test.(3)Cohesive zone model parameters which can characterize the interface delamination initiation and propagation were determined by a combination of experiments and simulations.Firstly,the elastic modulus of EMC and Cu substrates were obtained through experimental testing,which provided material parameters for the later finite element simulation molding.Secondly,the test samples with pre-crack was prepared and the EMC-Cu interface delamination propagation test was conducted to obtain the interfacial delamination propagation curve.Then,combined with the interface delamination propagation test curve,the critical energy release rate(Gc)under pure tensile mode was calculated through simulation based on the virtual crack closure method.Subsequently,according to the Gc,the interfacial delamination propagation test was predicted by cohesive zone method.The simulation result was consistent with experiment result.On the one hand,it shows the accuracy of the calculation results of the critical energy release rate.On the other hand,it also shows that the cohesive force model used in the simulation can characterize the EMC-Cu interfacial delamination propagation.At the end,some values of the ultimate tensile strength were tried to simulate interface delamination initiation mechanical test base on a set of cohesive model parameters which can characterize interface delamination propagation.The real ultimate tensile strength was determined when the maximum tensile force of simulation was the same as test results.