Proposal of Evaluation Method for Wire-Liftoff Lifetime of Power Modules Using Cyclic 4-Point-Bending Fatigue Test

Abstract

This paper presents a novel method for estimating the wire-liftoff lifetime of wire bonds used in power modules; a mechanical fatigue test using 4-point bending is proposed. The paper describes the system and method of the cyclic 4-point-bending fatigue test. After reviewing the formulae for wire-liftoff lifetime and the methodology for estimating wire-liftoff lifetime in the design phase, we propose a methodology for acquiring a design diagram from the experimental data of the 4-point bending fatigue test. The fatigue lifetime (N_f) can be determined from the 4-point-bending fatigue test, and the inelastic strain range (Δε_in) can be calculated from an inelastic finite element analysis. This design diagram, N_f –Δε_in curve, can then be used to estimate the wire-liftoff lifetime in the design phase. It is also shown that the proposed scheme can be certified using thermal cyclic tests.