Hiroaki Hokazono

Effect of additive elements on tensile, creep and low cycle fatigue strength for SnBi solders

This paper presents tensile, creep and low cycle fatigue properties of three kinds of SnBi lead-free solders. Tensile, creep and low cycle fatigue tests were performed using miniature specimens of the three solders. The effects of additive elements on tensile, creep and fatigue properties were discussed. Three kinds of solders showed almost the same tensile strength of around 55MPa and the same tensile ductility of about 70%. The creep rupture lifetimes of Sn57.5Bi0.5AgCuNiGe were about 1.5 – 2 times longer than those of Sn58Bi and Sn57.5Bi0.5Ag solders at 313K, 353K and 373K. The three kinds of solders showed almost the same low cycle fatigue strength at 313K. These mechanical properties were discussed in relation with the microstructure.

Creep Characteristic of Sn1.0Ag0.7Cu Lead-Free Solders with Element Addition

In this study, creep properties of lead-free solders based on Sn1.0Ag0.7Cu were investigated. In the solders, germanium, nickel and bismuth were added to improve their mechanical properties. The effect of element addition on their microstructure and creep properties were studied. Creep properties were improved with the element addition. Creep rupture lifetime was the longest for SnAgCuBiNiGe, and that of SnAgCuBi was the second longest. It was made clear that a minimum creep strain rate is useful for lifetime prediction of the solders. An observation of microstructure was performed and coarsening of intermetallics after creep test was identified, resulting in creep rupture. It was found that the addition of bismuth hinders the coarsening of intermetallics and is effective to improve the creep properties of the solders.

Aging effect on creep properties of SnBi solders

This paper discusses the effects of additive elements and aging on creep properties of SnBi solder system. Creep tests were performed on unaged and aged SnBi, SnBiAg and SnBiAgCuNiGe solders at three temperatures and the effects of them on creep rupture lifetimes and creep strain rates were discussed. The additive elements decreased creep strain rates and elongated creep rupture lifetimes. Causes of the effects were discussed from EBSD observations. The additive elements reduced the grain size and the aging coarsened grain size. The grain size had a pronounced effect on the creep strain rates and rupture lifetimes.

Effect of additive elements on crack propagation behavior for Sn-Bi solders at high temperatures

This paper discusses the effect of additive elements on crack propagation behavior for Sn-Bi solders at high temperatures. Sn-Bi solders are lower melting point materials, so that it is useful for low temperature soldering. Crack initiation and propagation behavior of three kinds of Sn-Bi solders were observed in this study. There were effects of additive elements Ag, Cu, Ni and Ge on crack propagation rate although there was no effect on crack initiation. The crack propagation of Sn57.5Bi0.5AgCuNiGe solder seems to have a slower rate than Sn58Bi and Sn57.5Bi0.5Ag solders. The J-integral range parameter evaluates the crack propagation rate independent of the additive elements at high temperatures.