Investigating current density in the lead free solder joints of surface mounted resistors with experimental approach

The paper presents a research, where modeling and experimental investigation of current density was performed in the lead-free solder joints of different surface mounted chip-size resistors. The currently presented work is based on previous research in the field, where the footprints, the interconnecting copper track on the printed circuit board and the three dimensional joint structure defined the local current routes in the solder meniscus. Investigated corner effects at selected track-to-pad joining angles result in higher local current densities at given points of the solder volume, increasing the possibility of electro-migration. For the experiments 0402 and 0603 zero ohm jumper resistors were used. Soldering was performed with conventional SAC305 lead-free solder alloy, on 1.5 mm thick FR4 boards. The paper presents the results of modelling, and the respective physical experiments to validate the results obtained with the simulation. The test board, and the measurement setup is optimized to help the validation procedure. Failure analysis methods (X-ray, cross-section analysis with optical and scanning electron microscopy) are used to reveal any possible alterations due to the increased current density. The results present the critical configuration of the interconnecting tracks and findings of the failure analysis.