Fatigue life time modelling of Cu and Au fine wires

Golta Khatibi,Bernhard Czerny,Martin Lederer,Mitra Delshadmanesh,Ali Mazloum-Nejadari,G. Hénaff

doi:10.1051/matecconf/201816506002

Golta Khatibi, Bernhard Czerny + Show 4 more

Open Access

https://doi.org/10.1051/matecconf/201816506002

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Abstract

In this study, the influence of microstructure on the cyclic behaviour and lifetime of Cu and Au wires with diameters of 25μm in the low and high cycle fatigue regimes was investigated. Low cycle fatigue (LCF) tests were conducted with a load ratio of 0.1 and a strain rate of ~2e-4. An ultrasonic resonance fatigue testing system working at 20 kHz was used to obtain lifetime curves under symmetrical loading conditions up to very high cycle regime (VHCF). In order to obtain a total fatigue life model covering the low to high cycle regime of the thin wires by considering the effects of mean stress, a four parameter lifetime model is proposed. The effect of testing frequency on high cycle fatigue data of Cu is discussed based on analysis of strain rate dependency of the tensile properties with the help of the material model proposed by Johnson and Cook.

Highlights

Fine metallic Cu and Au wires with diameters in the range of 15 μm to 75 are used for electrical connection between the semiconductor chip and the package in microelectronic devices
Electronic flame-off process is applied to melt the tip of the wire by an electrical discharge and to form a free air ball (FAB) which is ultrasonically bonded to the substrate
Based on the experimental stress-strain curves and using the Johnson and Cook model, the strain rate dependency of material properties of Cu wires were assessed at strain rates of 1e-4 s-1 and 32 s-1

Summary

Introduction

Fine metallic Cu and Au wires with diameters in the range of 15 μm to 75 are used for electrical connection between the semiconductor chip and the package in microelectronic devices. The influence of sample size and microstructure on the static mechanical properties of miniaturized materials has been extensively studied by using micro tensile-, compression tests or nano- indentation techniques. It was found that the number of grains in the sample volume or the ratio of thickness to grain size plays a major role on the mechanical response of small scaled materials [3] Due to their high aspect ratio, investigation of the fatigue properties of thin wires requires especial experimental set-ups. The influence of strain rate and testing frequency on the tensile and fatigue properties of copper as a reference material has been studied more extensively with the results being partly controversial [10,11,12,13,14,15]. A lifetime model for Au and Cu fine wires covering the low to high cycle regime is suggested

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