Fine Pitch Solder Paste (T7) for System in Package (SiP) Applications

System in Package (SIP) is a high level integration of different components, dies and chips in one package to achieve multiple function in one system. Solder paste, as a common assembly material, plays the role to connect the components, dies and chips to the substrate to form one package. The dimension of components, die and chip have a big variation in one package, it needs a few different application process to complete the entire package assembly. A new water soluble solder paste (T7 powder) with good printing performance was developed, it can be applied in SiP through printing process to achieve the passive component attach, die attach and flip chip all in one process. The printing performance of a solder paste is critical to improve the production yield in System in Package (SiP). This research work studied the impact of powder type -Type 5, Type 6, Type 7 on the paste printing performance in fine pitch application, mainly on the paste volume deposition and consistency with small opening. The highlight of this paper is to present the excellent printing performance of the newly developed water soluble paste (T7 powder), which can print down to 50um stencil opening with consistent volume deposition and no bridging with line space down to 40um. The void, tombstone and solder bead performance were also tested with 01005 components under actual component attach simulation. The existence of void in solder joint would affect the thermal conductivity and electrical conductivity of the device and hence, minimizing the void in solder joint is critical to improve the reliability of the whole package. This research work also studied on how to reduce void by adjusting reflow profile and applying vacuum during reflow, especially with flip chip and bigger die sizes.