Study On High Temperature Solder Used In Power Devices DIE Attachment With Ag@In Core-Shell Structure

Power devices are widely used in almost all the electronics manufacturing industry,covering the traditional 4C industry and the recent smart grid,new energy and many other fie lds.Power devices need to handle high current,high voltage,which causes thermal problems of chips.The miniaturization,high integration and high power density have been the focus of electronic devices all the time.Higher performance,smaller size and higher power density make thermal problems in power devices even worse.The traditional Si-based chips can not satisfy the requirement.At present,the third-generation semiconductors such as SiC,which have better high-temperature performance,have practical application capabilities but lack corresponding die attachment materials with high temperature resistance.In order to solve this problem and avoid damaging the device due to high connection temperature,the subject aims to develop a new type of power device die attachment material with "connecting at low temperature and servering at high temperature" performance.Indium melts at 156.6?,and silver melts at 961.8?.The two metals can react to produce a variety of phase s with high melting points.This project proposed the preparation of powder with Ag@In core-shell structure.When reflowing at the low temperature,Indium is melted and reacted with the inner Ag core through solid-liquid interdiffusion and generates connection of intermetallic compound?IMC?.The melting point of the Ag-In intermetallic compound can be higher than 660?.Thus this method can achieve the purpose of high temperature service.This study prepared the Ag@In core-shell structure metal powder by electroless plating method.EDTA-2Na and TEA as complex complexing agent react with In³⁺to form complex In³⁺in alkaline bath to prevent the direct precipitation of In³⁺.This complex In³⁺is reduced to metal In by Sodium borohydride as a reducing agent,and deposited on the Ag powder,forming the final Ag@In core-shell structure powder.In this paper,the optimal particle size of Ag powder was determined to be 38?m-48?m.Plating effect on the amount of indium is good,when the amount of EDTA-2Na and TEA was 2 times and 4times of that of In,respectively.Considering the amount of In plating and agglomeration,the optimal bath pH value should be between 9.0 and 9.5,then the corresponding bath temperature is between 30?and 35?.When plating is completed,the actual powder has a structure of Ag@AgIn₂@In due to the rapid reaction between Ag and In.The thickness of the outer In layer is less than 1?m.The powder is pressed into a preform and then interconnect with two silver-plated copper substrates.A bondline with melting point of 300?can be formed at the temperature of 175?for 5 min.The subsequent aging of the bondline can further increase the melting point to 660?.Increasing the reflow temperature to 200?,a bondline with melting point higher than 660?can be acheived and the main composition of this bondline is Ag₃In.The bondline has excellent thermal and electrical properties.Its electrical resistivity is 9.1??·cm,and thermal conductivities are 226.7 W·m^-1·K^-1,135.7 W·m^-1·K^-1,125.3W·m^-1·K^-1,at 30?,150?and 250?,respectively.The average shear strength of the bondline is 15.2 MPa.After aging at 250?for 14 days,the shear strength did not decrease obviously.All the properties meet the requirements.The Ag@In core-shell structured powder prepared in this project possesses the potential for die attachment in power devices.