Study On Silicon Nitride Whisker Modified Epoxy Resin Packaging Materials

With the rapid development of high-tech industries such as high-speed rails,electric vehicles and charging piles,power transmission,5G communication and etc.,the electronics packaging of devices and their systems are facing severe challenges.The mechanical and thermal properties of epoxy resin packaging materials that are widely used at present are difficult to meet the requirements of packaging for vibration and impact loads,high power,high frequency and high voltage.Therefore,the modification of epoxy resin becomes more and more important issue.Silicon nitride whisker(Si₃N_4w)has not only excellent mechanical,thermal and electrical properties,but particular one-dimensional morphology and nano-scale.The Si₃N_4wmodified epoxy resin(Si₃N_4w/EP)can possess excellent strength,toughness,thermal properties and dielectric properties simultaneously,addressing the current packaging issue.In this study,one-dimensional Si₃N_4w is chosen as filler of epoxy,Using XRD,SEM,universal testing machine,thermal conductivity meter and thermal expansion instrument characterized Si₃N_4w/EP.The effects of interface bonding state and filler content on the mechanical properties,fracture surface morphologies and thermal properties of Si₃N_4w/EP are investigated.The major experimental results are shown as follows:(1)When the epoxy resin is modified with an anionic dispersant APMAA coated Si₃N_4w,the interfaces between filler and matrix create weak interface bond by van der Waals force.When the epoxy resin is modified with the silane coupling agent KH-560,the interfaces between filler and matrix generate strong interface bond of a large number of C-N covalent bonds;Compared with pure epoxy resin,Si₃N_4w/EP has excellent mechanical properties.In the case of the weak interface,the bending strength,K_IC and work of fracture of Si₃N_4w/EP with filler content of 3.0 vol%increases by 34.05%,57.53%and 513.50%,respectively.In the case of strong interface,the bending strength with the filler content of 5.0 vol%increases by 25.29%,and the work of failure with the filler content of 7.0 vol%increases by 454.80%.(2)The reinforcing effect of Si₃N_4w on epoxy resin is mainly due to its excellent mechanical properties,mechanicaly restrict effect and interfacial properties.The excellent toughening effect of Si₃N_4w is manifested by a large number of coexisting energy dissipation mechanisms in Si₃N_4w/EP,including the shear band,step and gapped layer,stress whitening,plastic flow,interface debonding,secondary crack,crack shielding,pinning and deflection,Si₃N_4w bridging and pulling out,crater or depression,furrow and ridge.(3)The fracture process of Si₃N_4w/EP is divided into four stages.Stage I stress distributing:the local yielding and plastic flow in Si₃N_4w/EP cause stress redistribution;Stage II crack forming:microcracks,main cracks and secondary cracks are formed,debonding and brittle fracture are occured in local areas;Stage III stable expansion of main crack stage:stress concentration leads to the expansion of the main cracks,and the secondary cracks near crack propagation path merges into the main crack;Stage IV rapid expansion of main crack stage:the main cracks expand rapidly,there is no time and capacity for the stress relaxation and energy dissipation,massive torn-like structures are produced,resulting in the very rough fracture surface.(4)In the case of strong interface,the thermal conductivity of Si₃N_4w/EP increased by 34.78%in comparison with that of neat epoxy at 7.0 vol%filler content,indicating that Si₃N_4w has significant thermal conductivity modification advantages;On the other hand,the extreme specific surface area of Si₃N_4w causes a large interfacial thermal resistance in Si₃N_4w/EP,which is a key reason for hindering the great potential of Si₃N_4w exerts its thermal conductivity.