Aluminum metallization and wire bonding aging in power MOSFET modules

Abstract

A limiting factor for the long-term reliability of power MOSFET-based devices is the electro-thermal and/or thermo-mechanical aging of the metallic parts. In this paper we assess the bonding wire and source metallization degradation of power devices, designed for applications in the automotive industry. Our approach consists in characterizing the metal microstructure before and after accelerated aging tests, by scanning electron microscopy, ion milling and microscopy, focused ion beam tomography, transmission electron microscopy and grain structure mapping. To focus on the wire-metallization bonding interface, we have set up a dedicated sample preparation that allows us to disclose the metallization under the bonding wires. This critical location is significantly different from the naked metallization, as the bonding process induces plastic deformation prior to aging. The main mechanism behind the device failure is the generation and propagation of fatigue cracks in the aluminum metallization. Away and under the wire bonds, they run perpendicularly from the surface down to the silicon substrate following the grain boundaries, due to an enhanced self-diffusion of aluminum atoms. Moreover, initial imperfections in the wire-metallization bonding (small cavities and aluminum oxide residues) are the starting point for harmful cracks that propagate along the wire-metallization interface and can eventually cause the wire lift-off. These phenomena can explain the local increase in the device resistance occurring at failure.

The Sensitivity of an Electro-Thermal Photovoltaic DC–DC Converter Model to the Temperature Dependence of the Electrical Variables for Reliability Analyses

“…X-ray imaging has been performed in order to determine the dimensions of the various material layers. The materials used in this MOSFET are a copper Cu baseplate/heatsink, a solder Sn3Ag0.5Cu die-attach, a silicon Si die, aluminum Al bond wires/leads and an epoxy resin with SiO 2 filler encapsulant soldered onto an FR − 4 PCB [37,38]. The constructed 2-D FEM model together with the X-ray images and a photograph of the used MOSFET are illustrated in Figure 11.…”

Reliability Comparison of a DC-DC Converter Placed in Building-Integrated Photovoltaic Module Frames

“…However, this type of capacitor can nowadays be replaced by several active or passive decoupling film capacitors [6] at the cost of a small increase in ripple current and voltage. The reliability focus has therefore shifted towards semiconductor switching devices such as the power MOSFET whose main failure mechanism is known to be bond wire lift-off and solder degradation [7]. This effect is caused by the mismatch in thermal expansion coefficients of aluminum (wires) or metal alloys (solders) and silicon (chips) [8].…”

Microstructural evolution during the crack propagation at the bond-wire contact area of IGBT power modules upon power cycling

“…The crack propagation is responsible for the failure of top metallic parts in power modules. This may signify a relationship between both crack propagation and reconstruction processes [1][2][3][4]. Thus, several microstructural features were analyzed in this paper and then related to the cracking manner.…”