Abstract
White light-emitting diodes (LED) are widely applied in many fields for its special advantages compared with other light sources. Chip-scale-package (CSP) is one of the hotspots in the research of microelectronics, and also the main stream and development direction to the future package technology. Within a CSP, the solder layer between LED chip and substrate is usually achieved via reflow processes. The weldability of solder layer with substrate directly determines CSP's reliability and service life. Therefore, optimizing reflow soldering process can improve the performance of solder layer, and improve the reliability of CSPs. The Sn-3.0Ag-0.5Cu (SAC305) has been widely used in high power LED CSPs for its good solderability and favorable shear strength. In this paper, the reflow soldering process for SAC305 is optimized, by considering the reflow profile, the volume of solder paste and the substrate materials, to improve the bonding strength between solder layer and substrate. Then the shear tests and simulation results are used to verify the mechanical performance of CSP solder layer. Finally, an optimized reflow process is proposed for white LED CSP packaging. The results show that the reflow temperature curve should be in an appropriate level, and the performance of the ceramic substrate is more suitable for the SAC305 solder paste than the aluminum substrate.
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