Size-on-demand preparation of SAC305 solder balls based on pulsated orifice ejection method

Abstract

Drop-on-demand ejection of solder droplets has significant potential applications in field such as ball grid array packaging and microcircuit printing. To apply this technique successfully, it is important to ensure stability during the ejection of droplets and control the size of the droplets accurately as required. In this study, the pulsated orifice ejection method (POEM) is used to investigate the relationship between key parameters and the stability and size of SAC305 droplet ejection. Additionally, the microstructural morphology changes in solder balls with different sizes are investigated. Reducing the duration of the tup, increasing of voltage, and decreasing rod distance all lead to bigger solder balls. To achieve stable and size-on-demand droplet ejection, key parameters should be coordinated to ensure the deviation between the actual solder ball size and the target solder ball size remains within a range of ±10 μm. Observation and analysis of the microstructure reveal that as the size of solder ball increase, the cooling rate decreases rapidly, resulting in significant differences in the dendritic growth within the solder balls. This study presents an effective method and parameter selection for the drop-on-demand droplet ejection process, providing a solid foundation for direct solder bump deposition and microcircuit printing.