Mechanical Properties And The Interface Failure Mechanism Of Epoxy Resin Under Hygrothermal Condition

Cross-linked epoxy resin is widely used as coatings, adhesives, composites, and so on inelectronics and aerospace industries because of the excellent thermal and mechanicalproperties. However, the weaker mechanical properties and interfacial delamination caused byexpansion and aging under hygrothermal conditions are also increasingly prominent. In thispaper, the molecular dynamics simulation was performed to study the mechanical propertiesof epoxy resin and the interface failure mechanism of epoxy-SAM-Cu considering the effectsof temperature, moisture content, cross-link conversion, strain rate and SAMs.Cross-linked epoxy resins exhibit much more complexity in molecular structure than thelinear homopolymers and copolymers，which poses significant difficulty to the experimentalcharacterization. In this regard, a new algorithm was thus developed for constructing themolecular model of polymeric network. Then the model was used to predict the thermal andmechanical properties. It was seen that glass transition temperatures, coefficients of thermaland moisture expansion, Young’s modulus, bulk modulus, shear modulus and Poisson’s ratioof the systems are in good agreement with experimental data. In addition, the simulationresults showed that the cross-link conversion, temperature and moisture content affect thethermal mechanical properties of epoxy resin significantly. So the effects of these factors areimportant to improve properties of epoxy resin.Molecular dynamics simulation was performed to study the moisture diffusion incross-linked epoxy resin, with the influence of temperature, water concentration and polymerconversion taken into account. The simulation results showed that the moisture diffusioncoefficients increase with the increase in the temperature. And generally, with the increasedmoisture concentration or decreased polymer conversion, the moisture diffusion coefficientsreduce. However, the moisture diffusion is strongly inhibited when the number of epoxygroups in completely reacted epoxy resins is equal to the number of water molecules.Molecular dynamics method was employed to investigate effects of moisture content,cross-link conversion, strain rate and temperature on the tensile and compressive deformationof epoxy resin. Simulation results showed that the compression performance of cross-linkedepoxy resin is better than its tensile performance. The mechanical properties of epoxy resindecrease obviously with increasing moisture content and temperature. However the highcross-link conversion and strain rate enhance the mechanical properties of resin. At roomtemperature, the Young’s modulus of89%cross-linked epoxy resin is higher than that of non cross-linked resin about2-3GPa. This study obtained the mechanical properties at hightemperature and high strain rate and explained the deformation with the microscopicmolecular energy, providing a guide to the modification of epoxy resin.Due to poor adhesion, the Cu-epoxy interface under hot and humid conditions is a weakpart in electronics and aerospace industries. Molecular dynamics simulation was conducted toinvestigate the interfacial interaction energy of Cu-SAM-epoxy resin, which is widely used inelectronic packages, and the effects of temperature, moisture, crosslink conversion andoxidation degree. The results showed that interaction energy of Cu-SAM-epoxy resin isalmost independent of crosslink conversion of epoxy resin, while is weakened by increasingtemperature, moisture and oxidation. In addition, the simulation revealed that the covalentbonds between SAMA and epoxy enhance the interfacial adhesion of Cu-epoxy. However, thenon-bond interactions of SAME and epoxy resin weaken the interfacial adhesion. This paperprovided a new method for research and valuation the effects of SAM or other adhesive oninterfacial adhesion.Interfacial delamination is one of the typical failure modes in electronic packages. Toobtain good reliability of electronic packages, it is important to study the interface properties.Molecular dynamics simulations of opening mode loading of interfaces are proposed to studysuch interfaces resulting in traction-separation relations that have been used to characterizethe failure process of the interfaces. The results showed that the cross-link conversion,temperature and tensile rate have less effect on the strength of epoxy-Cu interface. But themoisture reduces the interface tensile strength. For the epoxy-SAM-Cu interface, both thehigh temperature and high moisture content reduce the tensile strength, while the highcross-link conversion increases interface reliability. In addition, the interaction force versusdisplacement curve and the interfacial failure mode for epoxy-SAM-Cu system showed thatthe covalent bonds are the main interaction force between cross-linked epoxy and SAMA,while the non-bond interaction is mainly for the interface of epoxy-SAME.