Reliable and repeatable bonding technology for high temperature automotive power modules for electrified vehicles

Abstract

This paper presents the feasibility of highly reliable and repeatable copper–tin transient liquid phase (Cu–Sn TLP) bonding as applied to die attachment in high temperature operational power modules. Electrified vehicles are attracting particular interest as eco-friendly vehicles, but their power modules are challenged because of increasing power densities which lead to high temperatures. Such high temperature operation addresses the importance of advanced bonding technology that is highly reliable (for high temperature operation) and repeatable (for fabrication of advanced structures). Cu–Sn TLP bonding is employed herein because of its high remelting temperature and desirable thermal and electrical conductivities. The bonding starts with a stack of Cu–Sn–Cu metal layers that eventually transforms to Cu–Sn alloys. As the alloys have melting temperatures (Cu3Sn: > 600 °C, Cu6Sn5: > 400 °C) significantly higher than the process temperature, the process can be repeated without damaging previously bonded layers. A Cu–Sn TLP bonding process was developed using thin Sn metal sheets inserted between copper layers on silicon die and direct bonded copper substrates, emulating the process used to construct automotive power modules. Bond quality is characterized using (1) proof-of-concept fabrication, (2) material identification using scanning electron microscopy and energy-dispersive x-ray spectroscopy analysis, and (3) optical analysis using optical microscopy and scanning acoustic microscope. The feasibility of multiple-sided Cu–Sn TLP bonding is demonstrated by the absence of bondline damage in multiple test samples fabricated with double- or four-sided bonding using the TLP bonding process.

Wide Bandgap Technologies and Their Implications on Miniaturizing Power Electronic Systems

“…Au-Sn SLID has been shown to yield stable bonds at temperatures above 350°C [64]. A number of researchers have recently demonstrated TLP bonding as a die attach method using Au-InSn, Ni-Sn, and Cu-Sn [65]- [67]. Besides being Pb-free, the TLP processes have the advantage that processing is performed at a lower temperature (usually at or below 300°C), while the resulting bond reflows at a much higher temperature.…”

Au–Sn bonding material for the assembly of power integrated circuit module

“…Power electronics is one of the key components of power control units of electrical vehicles [1,2]. A power electronics module typically consists of an IGBT chip and a diodes.…”

Reliable low-temperature die attach process using Ag/Sn/Ag sandwich structure for high-temperature semiconductor devices

“…This die attach process using the ASA sandwich structure is highly similar to the solid–liquid interdiffusion (SLID) bonding, which is also called transient liquid-phase bonding. SLID bonding has been typically studied for the joining of high-temperature semiconductor devices 27–29 . The benefits of SLID bonding are the low bonding temperature near the melting point of the low-melting point bonding metal and high-temperature stability after the bonding process.…”