Research on Vacuum Soldering Technology of Military IGBT Module

Abstract

Insulated Gate Bipolar Transistor (IGBT)module is the core device of power electronics which integrates Metal Oxide Semiconductor Field Effect Transistor (MOSFET) and Giant Transistor(GTR)together. It has fast switching speed, reduced saturation voltage, soft-off characteristics and short-circuit resistance. IGBT has been widely used in industrial, aerospace, defense and military industries and rail transit, smart grid and new energy vehicles. As the power density of IGBTs continues to increase, the reliability requirements for IGBT packages are becoming higher and higher, and any failure may cause paralysis of the entire system. The soldering process of the MOSFET and GTR and the substrate is important to the IGBT module packaging. A high quality soldering process can reduce the interface thermal resistance and increase the welding strength and the long-term reliablility. The defects of the solder layer may lead to the increasing of the interface thermal resistance and reducing the product life. At the same time, the defective solder layer will easily cause fatigue failure such as solder layer peeling, chip and substrate crack under the action of ambient temperature cycle and power cycle.This paper is mainly studying the vacuumsoldering process of IGBT module .Using the vacuum soldering process with solder pre-form and formic acid, the low-cavity soldering layer can be achieved. Through material pretreatment, tooling fixture and solder selection, the precise positioning of two sintering and chip, DBC (Direct Bonding Copper) substrate and copper substrate is solved. The control of temperature curve in different temperature zones is optimized, and the vacuum in the soldering process is ensured. Temperature, vacuum rate, vacuum holding time control accuracy, while systematic research on formic acid concentration, activation time, activation temperature control, etc., and non-wetting, soldering, solder overflow, chip substrate Evasion methods such as offset and hole exceeding the standard are proposed. Finally, the high strength, low void rate and position consistency of the soldering interface are realized through the visual inspection, X-ray photography and shear force test to which are shown that the IGBT soldering process has high reliability. (Abstract)