Investigating the self-alignment of chip components during reflow soldering

Abstract

Since the application of lead-free soldering has become obligatory in the electronic industry by the 1^st of July 2006, the in-depth analysis of the soldering process is more important than ever. The small chip components of the present days demand very accurate component placement machines to prevent common reflow failures such as skewing or tombstoning. The ability of components to be self-aligned during soldering works against these failures, therefore it matters to what extent the solder promotes this effect. Dynamic behaviour of SMT (Surface Mount Technology) chip components during lead-free reflow soldering will be demonstrated in the paper. A force model has been introduced with the five main forces which determine the movement of the chip component during reflow soldering, namely: the force originating from the surface tension, the forces originating from hydrostatic and capillary pressure, the force of gravity, and the force of dynamic friction. The self-alignment of 0603 size chip components has been investigated by real experiments. SM chip components are misplaced intentionally by semi-automatic pick & place machine, and before and after reflow soldering the exact location of components was measured. The results have shown that the self-alignment of components does occur even in the case of 400-500 \mu m lateral misplacements. The explanation of the equations of the applied theory and the results of the experiments are presented in the paper in details.