Enhanced solder fatigue life of chip resistor by optimizing solder shape

As surface-mounted components get smaller, especially passive components such as chip resistor or chip capacitor, small apertures on a stencil are required, which generates higher variations in the printed solder paste volume and solder joint shape. In this study, the board-level fatigue life of chip resistor assemblies with SAC305 was investigated. Different volumes of solder paste are printed, which varies the shape of solder joints. Four solder joint shapes are compared: concave, straight, tiny convex, and convex, which are achieved using a stencil with differently sized openings. Thermal shock cycling shows that the convex shape exhibits the best thermal shock reliability while the concave shape has the shortest fatigue life. Additionally, different sizes of chip resistor package are compared. A comparison of the size of components concludes that the R0402 chip resistor has relatively better thermal shock resistance than the larger chip resistor, R1005 due to larger change in length of R1005 during thermal cycling. Based on the experimental results of fatigue life, the parameters of a constitutive equation are calculated to evaluate the fatigue life of the solder joint. This study provides criteria manufacturers can use to improve the reliability of chip assemblies though inspecting solder paste volumes and shapes.