Improvement of elasticity of drawn gold bonding wire by texture control

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Gold wires with fine diameter of 〜20μm are widely used for bonding semiconductor devices. Due to the decrease of IC chip size, the development of gold wires with increased mechanical properties such as tensile strength and elasticity is required. For gold single crystal, it is known that Young's modulus of a crystallographic <111> direction is almost three times as much as that of a crystallographic <100> direction. It is therefore expected that ~ polycrystalline gold wires with high elasticity are available by texture control (i.e., fabrication of <111> orientated wires). In the present study, texture evolution during wire drawing and annealing of fine gold bonding wire was investigated by means of the orientation distribution function (ODF). Cold drawing texture of high-purity gold (99.999 wt.%) consisted of strong <111> and weak <100> fiber components below 99% reduction in area. Above 99% reduction in area, recrystallization occurred during wire-drawing process, resulting in increased <100> component. Cold drawing texture of gold wires with trace alloying elements (99.95 wt.% purity) also consisted of strong <111> and weak <100> fiber components similar to high-purity (99.999 wt.%) gold wires. However, for gold wires added trace alloying elements, recrystallization did not occur above 99% reduction in area, and thereby the <111> textural component retained beyond 99% reduction in area. Consequently, it is found that trace alloying addition to high-purity gold wire is useful for suppression of recrystallization during wire-drawing process and results in highly <111> orientated gold wires.