Modeling of impression testing to obtain mechanical properties of lead-free solders microelectronic interconnects

Abstract

The increasing structural functionalities of materials in microelectronics and MEMs packages has led to an explosion of interest in characterizing the mechanical properties of small volumes of materials in the micrometer to nanometer regime. In microelectronics packages, one of the main challenges in reliability assessment is the prediction of solder joint failure during service applications. To a large extent, this is hindered by the difficulty in measuring the properties of micro-scale solder balls, which can be quite different from those of bulk solders. Recently, there has been substantial interest in miniaturized impression testing for measuring creep and other mechanical properties of microelectronic solder joints. Since impression testing produces punch stress versus impression strain data, it is necessary to find the appropriate correlations to convert the properties obtained by impression stress-strain testing to equivalent uniaxial properties. Therefore, in this work, finite element modeling using ANSYSTM is employed to obtain the elastic, plastic and creep properties of these Sn-Ag solder joints from impression testing, which uses a flat-tip cylindrical indenter, so that correlations may be drawn with corresponding properties from uniaxial testing.