Effects of Reflow Profile and Miniaturisation on the Integrity of Solder Joints in Surface Mount Chip Resistors

The integrity of solder joints of components in an electronic device is critical to the device reliability. The miniaturisation trend in the development of electronic products has continued to challenge the shear strength of the solder joints in these devices and necessitates implementation of optimal reflow profiles to achieve maximum joint strength. This study proposes an optimal parameter combination of reflow profile factors which demonstrate potential for delivering maximum shear strength of solder joints. The Taguchi design of experiment (DoE) is employed to generate eight orthogonal array designs of L24 reflow profiles. The factors/parameters investigated are preheat gradient, time above liquidus (TAL), peak temperature and cooling rate. Three test vehicles of varying solder joint sizes are made from R1206, R0805 and R0603 resistors. Reflow profile number 3 constituting 1.2°C/s preheat, 45 s TAL, 245°C peak temperature and 60% cooling rate is optimal because it yielded joints with the highest strength and ca. 4 µm intermetallic compound thickness. The solder joint shear strength decreased with a decrease in the size of the lead-free joint irrespective of the reflow profile implemented. These results will be useful for electronic packaging and reliability engineers faced with challenges of improving device operational mechanical performance in the continuing trend of product miniaturisation.