Research On Cu-Cu Sinter Bonding For The Third Generation Semiconductor Power Device

As the operating temperature of power devices such as power electronics,microwave radio frequency,etc.becomes higher and higher,it brings great challenges to the working stability of its packaging interconnect materials.At present,the main high temperature packaging interconnect materials are Zn-based solder and Au-based solder.The disadvantages of Zn-based solder are high hardness and poor stress relaxation ability.The alloy formed by Au-based solder is relatively hard,so that the thermal stress generated by the joint is directly transferred to the semiconductor device,resulting in the failure of the entire packaged device.In addition,the cost of Au-based solder is too high to be popularized.The key to solving these problems lies in finding the packaging interconnect materials suitable for high temperature operation and the corresponding packaging interconnect technology.Nano copper material can be sintered at low temperature because of its small size effect and surface effect.The melting point of the sample after the diameter sintering is comparable to that of the copper block,and the same material as the copper substrate,with good shear,electrical conductivity and other properties.It has gradually become a research hotspot for power device packaging materials.However,due to the different particle size and morphology of the nano-copper particles(Cu NPs),resulting in different affinity for different sintering processes,a suitable sintering process is needed to match the Cu NPs in different states.At the same time,because the surface of the Cu NPs is prone to oxidation,the existence of the surface oxide layer hinders the exchange of substances,and also increases the difficulty of application in low-temperature packaging interconnects.In this paper,through the research of sintering process such as holding time,heating rate and sintering pressure,It was found that during pressureless sintering,the effect of holding time on the shear strength of Cu-Cu joints increased first and then decreased.The shear strength reaches the maximum at the holding time of 30 minutes(30 min),the maximum is 5.0MPa;At a slow heating rate of 0.1 °C/s,the joint pores are small and the shear force is relatively large;The application of sintering pressure greatly enhances the shear strength.The shear strength increases with the increase of sintering pressure.This is because under the conditions of holding time of 30 min,slow heating rate of 0.1 °C/s and application of sintering pressure,the porosity of the Cu-Cu joint is reduced,and the shear performance is improved.Based on the research of the sintering process,the sintering accelerator is mixed into the nano-copper paste(Cu NP paste)to prepare the sintering accelerator to treat the Cu NP paste.The effect of sintering accelerator on the shear properties of Cu-Cu joints and sintering structure morphology was explored,and the mechanism of sintering accelerator removing oxides on the copper surface is revealed.The experimental results show that the sintering accelerator composed of rosin and cetyltrimethylammonium bromide uniformly mixed together has the most significant improvement in the shear properties of the joint.Incubate at260 °C for 30 min,the shear strength of the Cu-Cu joint reaches 33.0 MPa.In the lowtemperature sintering process,the sintering accelerator removes the oxides on the copper surface,so that the material exchange between them can be fully carried out,forming a good metallurgical bond.A Cu-Cu interconnection joint with good shear performance is obtained,which basically meets the application requirements of semiconductor packaging devices.