| With the advent of the 5G era,electronic products are developing rapidly towards miniaturization,function diversification and high power,which puts forward higher requirements for the packaging process of electronic devices and the reliability of interconnection solder joints.Sn-Ag-Cu lead-free solder alloys have been widely used in the field of microelectronic packaging because of their good comprehensive properties.However,the melting point of Sn-Ag-Cu series solder alloy is only 220 ℃,which is not suitable for higher temperature working environment,due to the high melting point and high strength of Sn-Cu intermetallic compounds,the development of Sn-Cu all-intermetallic solder joints is of great significance for high temperature environment service.In this project,a carbonaceous material prepared by low-cost biomass residue and a simple ball mill homogenization/calcination step was added as a reinforcing phase to lowsilver tin-based solder paste.The reinforced solder paste is filled with copper foam with a large specific surface area to increase the effective reaction area of Cu and Sn.Narrowpitch metal foil sheet made of physical rolling of copper foam filled with solder paste shortens welding time.Finally,the traditional transient liquid phase connection method is used to use the metal foil as the intermediate layer during welding to obtain a high melting point weld to achieve the purpose of "low temperature reflux and high temperature service".The influence of different C-SCG contents on the wetting performance of Sn-Ag-Cu solder was studied by spreading area method.The results showed that the addition of an appropriate amount of C-SCG could help to improve the wettability of Sn-Ag-Cu filler,and the spreading area was the largest and the wetting performance was the best when the C-SCG content was 0.005%,and the wettability of the filler was reduced due to the aggregation phenomenon of C-SCG.Scanning electron microscopy and energy spectroscopy were used to analyze the microstructure of Cu/Sn-0.3Ag-0.7Cu-x(SCG)/Cu solder joint matrix and the growth of intermetallic compound,and the influence of C-SCG content on the mechanical properties of solder joints was tested.The addition of C-SCG can inhibit the growth of scallop-like IMC layer in the solder joint,the scallop-like bulge is more obvious,the IMC thickness is the lowest when the C-SCG content is 0.01%,which is reduced by 35.71% co MPared with no addition,and the shear strength is the highest when the C-SCG content is 0.02%,which is increased by 28.4% co MPared with no addition.The influence of welding time on the microstructure and shear strength of the welding joint was studied,the Sn atom in the weld fully participated in the reaction when the welding time was 20 min,the weld was composed of Cu6Sn5,Cu3 Sn and Cu skeleton,forming a full IMC solder joint can withstand a higher temperature working environment,because the IMC fracture mechanism is brittle fracture,the shear strength of the solder joint at this time is 26.96 MPa,which is 27.05% lower than the 36.96 MPa when the shear strength is the highest in 5min welding time.In summary,this paper successfully prepared a high-temperature interconnect material that can be used in third-generation power semiconductors,which can bond and merge Ni/Solder/Cu solder joints that can maintain a stable structure in service at high temperatures at low temperatures. |
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