Investigation On Sintering Process Optimization Of Nano-Copper Die Attach Composite

With the development of semiconductor devices to smaller configuration,high density and high power,especially the application of wide band gap semiconductor materials in power electronic devices,it is crucial to develop high thermal conductivity die attach materials.In addition,low packaging temperature and high operation temperature are expected.Low cost high thermal conductivity copper is promising for all-copper packaging to attach a chip on direct-bonding-copper substrate(DBC)with a simple process and high reliability.Therefore,sintering nano-copper attracted more attention.However,copper nanoparticles tend to be oxidized,resulting lower thermal conductivity than expected with low density and much porous in sintered nano-copper.The sintering process was optimized to achieve low-temperature and low-pressure packaing with ascorbic acid treatment to remove copper oxide.It is found that thermal conductivity of 109.9 W/m·K and shear force of 17.23MPa can be achieved with sintering at 255?and 5MPa for 30 minutes with(300?and 5MPa for 30min),higher performance can be zchieved,such as shear force of 38.49MPa,thermal conductivity of 123.6W/m·K,electric resistivity of 0.22u?·m,and thermal expansion coefficient of 13.5×10^-6/?.Graphene oxide(GO)was used to enhance performance of sintered nano-copper with optimized sintering process.With 0.1wt%GO,the thermal conductivity of sintered composite is increased by 32.6%to 163.9 W/m·K,the electric resistance is reduced by55%to 0.10u?·m,the thermal expansion coefficient is reduced by 17%to 11.2×10^-6/?.However,with 0.1wt%pristine graphene,the thermal conductivity of sintered composite is only to 66.6W/m·K,the resistivity is 0.14 u?·m.The functional groups on GO play a critical role to enhance the graphene-copper interfacial interaction and reduce the interfacial thermal resistance.It is proved that significant improvement of the thermal,electrical,and mechanical properties achieved with GO in sintered die attach materials.It is promising to break through the bottleneck of thermal management in high-temperature,high-power wide band gap semiconductor power electronic packaging and other high-power packaging.