Measurement of Nonlinearity as a Diagnostic Tool for Quality Determination of Lead-free Solder Joints

At present there are directions RoHS-WEEE in European Union which restrict the use of certain hazardous substances in new electric and electronic products. Therefore mass usage of lead-free soldering in electronic production started. A typical alloy for lead-free soldering is based on Sn, Ag and Cu (SAC). For the most of types of lead-free solders is necessary to use technological process of soldering in reduced oxygen concentration atmosphere for improvement of wettability of soldered surfaces. Quality of these soldered joints is evaluated according of their electrical and mechanical properties. This paper is focused on measurement of nonlinearity, electrical resistance and mechanical strength. Especially evaluation of nonlinearity as a diagnostic tool for the prediction of solder joints reliability has been tested. Also effect of different surface finish of PCBs and influence of reduced oxygen concentration on quality of joints has been examined.