A new coating technology on solder powders to improve solderability

Solder paste is widely used to connect surface mount devices to printed circuit boards [1]. As the components become smaller and thinner, solderability and voiding are more challenging [2]. It has been reported that a majority of assembly defects occur in the reason of quality decay of solder paste, resulting in solder paste dried-out and short shelf life. The chemical reactions between flux and solder powders, which are believed in detecting metal ions concentration in flux by inductively coupled plasma-mass spectrometer (ICP), are very critical and relevant to the quality of solder paste. Hence, a new coating technology on solder powders is introduced to eliminate this issue. In the first part of this research, a new coating solution with polymer compositions inside is developed [3]. Thermal characteristics were analyzed by thermogravimetric analyzer (TGA) to find out the optima temperature for solution activating, forming a coating layer on solder powders. The coating efficiency was found related to the ratio of coating solution and solder powders, and carried out to observe the powders surface by Focused Ion Beam (FIB). The study on effects of coating technology on solderability was performed in the second part of the research. It is realized that viscosity and rheological properties of solder paste in the condition of long-time storage are more stable for the solder paste with coating technology. On the other hand, dried-out issue was observed in the case of normal solder paste without coating. Besides, solderability and voiding were also improved by coating technology. Therefore, based on the innovation of this study, coating technology can be applied in a variety of metal surface to offer a layer to prevent from interference.