Lead-free Solder Joint Quality Investigation

New Pb-free materials ask thorough verification because their properties as wetting, solderability and mechanical properties are different from these SnPb. In this paper are presented some new facts from creep and stress relaxation investigation including new arrangement for measurement. Results from creep, stress, shear and bend testing are presented for three types of solder (Sn/3.5Ag, Sn/3.8Ag/0.7Cu and Sn/37Pb). The basic sample was made from copper plate with thickness of 2 mm. An aperture was created through the middle of sample with the length of approximately 2/3 of its length to be filled with solder paste. Since solder paste changes its volume after soldering is applied, the samples were polished to provide flat surface. For creep and stress relaxation testing was used Electro-thermal Mechanical system. This enables to measure displacement as a function of shear stress. Most failures of solder joints, which occur in electronic systems, are troubles caused by the thermal mismatch among different materials involved in electronic system construction. One of main reasons is different coefficient of thermal expansion (CTE) of materials that are assembled together. During the manufacturing and operation time, the structure goes through various temperature cycles, which cause thermal expansion. Materials cannot expand freely, because they are constrained by the packaged assembly. Therefore, significant stresses are induced in solder joints. These stresses creating destruction of solder joints can be mathematically modeled using ANSYS software and compared with experimental results.