Fine feature solder paste printing for SiP applications

Abstract

Due to the rapid development of IoT “smart” devices, the industry has seen a surge in demand for system-in-package (SiP) devices, which are capable of increased functionality in a smaller package design. This continues to push miniaturization to an even greater level, therefore creating assemblies with smaller components and greater density. Fine feature solder paste printing for passive component sizes, from 01005 (0.4 × 0.2mm) and now down to 008004 (0.25 × 0.125mm), has become more challenging in SiP assembly. Due to small stencil aperture designs, finer powder size solder pastes, typically type 5 (15– 25µm), type 6 (5–15µm), and type 7 (2–11µm), are used for these applications. Since more components are being packed into a SiP, the rheology of the solder paste is an important attribute, as the gap between neighboring pads can be as close as 50µm. Solder paste with minimal slump behavior will be required to minimize bridging in such designs. Consistency in solder paste printing transfer efficiency, stencil life, good wetting, graping resistance, and minimal voiding are other key attributes of solder paste for SiP assembly as well. This paper will focus on the attributes of these finer powder size solder pastes, review the tests conducted for critical-to-function characteristics, and discuss the results.