Investigation On Thermal Performance Of Graphene Reinforced Die Attach Materials For Power Electronic Packaging

As the application of wide bandgap semiconductors becomes more and more widespread,the development of high-performance die attach materials is critical to meet the requirments of low-temperature packaging and high-temperature operation for wide bandgap semiconductor packaging.Sintered nanocopper is promising to be used as die attach material and meet the requirments at low cost.However,copper nanoparticals tend to be oxidized,resulting in lower perfomance than expected especially at low sintering temperature and pressure.Graphene,with advantages of high thermal conductivity,is commonly used reinforcement to improve metal matrix composites performance.The lattice structure quality of graphene and the bonding force with copper are the critical factors to improve the thermal conductivity of nanocopper die attach materials.Therfore,this thesis focuses on investigation of improving interfacial interaction between graphene and copper without seriously damaging the crystalline structure and degrading the thermal conductivity of the graphene.（1）The preparation and sintering process optimization of nanocopper die attach materials were investigated.Anti-oxidation treatment of nanocopper was carried out before sintering.The results show that thermal conductivity of 97.5 W/（m·K）was achieved at optimized sintering conditions（300℃and 5 MPa）.（2）The effects of properties of graphene and its derivatives on the thermal conductivity of nanocopper die attach materials were investigated.The pristine graphene（Gr）,oxygen plasma treated graphene（PTG）,graphene oxide（GO）and reduced graphene oxide（r GO）were selected as the reinforcements of nanocopper die attach materials.The results show that Gr has high quality lattice structure but poor wettability;PTG has better wettability without seriously damaging the crystalline structure;the quality of r GO lattice structure is poor;GO has low lattice structure quality but excellent wettability.At the same sintering process,the thermal conductivity test results show that the thermal conductivities of the composite die attach materials with 0.1wt%r GO,Gr,GO and PTG are 75.6,80.6,125.4 and 143.4W/（m·K）,respectively.The thermal conductivity of the composite die attach materials with0.1 wt%PTG is increased by 49.5%compared with that of sintered pure nanocopper die attach materials.（3）The thermal conductivity of nanocopper die attach materials was further enhanced by garphene decorated with copper nanoparticles.C-O-Cu bond was proved to be formed at PTG-copper and GO-copper interfaces,significantly improve the interface interaction and as a result,thermal conductivity of composite die attach materials.At the same sintering process,the thermal conductivity test results show that the thermal conductivities of the composite die attach materials with 0.1 wt%GO/Cu and PTG/Cu-Cu₂O are 156.2 and 177.7W/（m·K）,respectively.The thermal conductivity of the composite W/（m·K）with GO/Cu and PTG/Cu-Cu₂O are 60.2%and 85.3%higher than that of the sintered pure nanocopper die attach materials.The properties of developed graphene reinforced copper matrix composites meet the requirements of die attach materials for wide bandgap power electronic packaging.