Lead-free Solder Quality Investigation

New Pb-free solders ask thorough verification because their properties as wetting, solderability and mechanical characteristics are different from these SnPb. In this paper are presented some characteristic changes coming with lead-free soldering including their impact on solder joint quality. The basic sample for mechanical properties of solder 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 (ETMS). This equipment enables to measure displacement as a function of shear stress applied on sample that is fixed in jaws. ETMS can also control the temperature on the sample by changing current through the tested device. Temperature is sensed from thermocouple attached to the solder joint and fed to the controller which uses feed back loop to adjust current through the sample.