Study On Low Temperature Transient Liquid Phase Bonding Technology And Mechanism Of Cu/In System

With the rapid development and application of the third generation wide band gap semiconductor materials like SiC and GaN,the power devices electronic devices based on SiC and GaN can be applied more than 300 C.As a result,the power electronic devices in high temperature applications require more advaned pachaging technology and materials.Low Temperature Transient Liquid Phase(TLP)bonding technology,as a low temperature welding technology with simple process and low cost,can be applied to the interconnection of high-temperature power devices.Cu used as an interconnection material of power devices can achieve good performance.In has good conductivity and thermal conductivity and low melting temperature(156 C)can react with Cu to form high melting temperature intermetallic compounds(IMCs).Therefore,the TLP bonding process using In as the connecting material to connect the Cu substrate has a very broad application prospects in the formation of heat-resistant solder joints applied in high temperature environment.In this paper,TLP bonding process was used to connect the joints of Cu/In/Cu,Cu/In-xCu/Cu and Cu/In-45Cu/Cu with different size of Cu particles.In this process,the technological parameters of TLP bonding were optimized,and the microstructure evolution of IMCs interlayer and shear properties of solder joints were studied.The joining of Cu/In/Cu solder joints was connected by TLP bonding process,and the effects of bonding process parameters on the structure of Cu/In/Cu solder joints were studied.The results show that the optimum bonding parameters for preparing Cu/In/Cu solder joints are 0.10 MPa of bonding pressure,260 C of bonding temperature and 120 min of bonding time.With the increase of bonding temperature,Cu11In9 in TLP bonded Cu/In/Cu solder joints increases gradually.When the bonding temperature is 260 C,In is basically depleted,and the Cu/In/Cu solder joints form full IMC solder joints.The shear strength of solder joints increases with the increase of bonding time.When bonding time is 30 min,the shear strength of solder joints is 4.8 MPa,and then increases to 11.1 MPa at the bonding time of 720 min.With the increase of bonding time,the precipitation of Cu11In9 phase increases gradually,and the fracture mechanism of solder joints changes from the mixed mode of plastic fracture and brittle fracture to brittle fracture,respectively.The process parameters were optimized by In-25 wt.%Cu solder paste used as the bonding material and the effect of the content of Cu particles on the microstructure and mechanical properties of Cu/In-xCu/Cu solder joints was studied.The results show the optimum bonding parameters for preparing Cu/In-25Cu/Cu solder joints are are 0.10 MPa of bonding pressure,260 C of bonding temperature and 60 min of bonding time.With the increase of the content of Cu particles,the residual In in the solder joints decreases,Cu11In9 and Cu2In increase,and the thickness of the interface reaction zone becomes thinner.The volume shrinkage caused by formation of Cu11In9 results in the formation of voids.When the content of Cu is 45 wt.%,a new phase Cu2In is formed and a denser solder joint structure is obtained.When the content of Cu is 55 wt.%,the structure of diffusion reaction zone becomes discontinuous,the structure of in situ reaction zone presents a large number of voids and unreacted Cu.The shear strength of solder joints increases first and then decreases and the fracture mode gradually changes from the mixed mode of plastic fracture and brittle fracture to brittle fracture mode with increasing the Cu contentThe effects of Cu particle size on the microstructure and mechanical properties of solder joints were investigated,and the growth of IMCs on the surface of Cu particles was studied.The results show that there are larger voids and residual In and Cu in solder joints containing large size Cu particles,while Cu and In in solder joints containing small size Cu particles react adequately.There are a small amount of residual Cu particles in the mixed particle solder joints.However,the number and size of solder joints with the large Cu particle are smaller than that of solder joints with the large Cu particle.With the deerease of the size of Cu particles,the shear strength of the solder joints first increases and then decreases.With the increase of bonding time,the thickness of Cu11In9 and Cu2In around Cu11In9 particles increases gradually,and Cu11In9 drops off on the surface of Cu11In9 particles.The main reasons for Cu11In9 dropping are mutual extrusion during the growth of Cu11In9 and compression of liquid In on Cu11In9.