Effective Conformal EMI Shielding Coating for SiP modules with Multi-shaped Nano-Ag Fillers

With the increasing demands for thinner, lighter and portable electronic devices, advanced electronic packaging technologies, such as SiP (System-in-Package), are becoming the most important approaches. However, the high-integrated components are more sensitive to the electromagnetic interference (EMI). Conformal EMI shielding is a critical supporting technology for SiP modules. So far, the conformal shielding technology by sputtering is not satisfactory for its high costs, low UPH and weak adhesion. Preparing conformal EMI shielding coating by spraying process is a desirable alternative to overcome these drawbacks.The spraying materials for EMI shielding are usually pastes consisting of conductive fillers and resin binders or conductive inks without resins. In the current solutions, conductive fillers, such as Ag nanoparticles, are of low stacking density because of the single shape and severe shrinkage. Although some compositional formulations of fillers with different shape and size are raised, the EMI shielding efficiency has been raised by a very small range due to the poor contact of the fillers. On the other hand, the conductive fillers in the composite are simple physical contact, which decrease the EMI efficiency compared to sintered metal coatings.To address these challenges, a unique multi-shaped nano-Ag fillers synthesized by chemical reduction method are employed as the fillers for EMI shielding coating. The nano-Ag consist of nanoparticles (NPs) with the diameter of 50-150 nm and nanoflakes (NFs) with the diameter about 200-800 nm and thickness about 50 nm. The multi-shaped nano-Ag shows high stacking density and excellent sintering performance at the temperature about 175 °C for 30 min. Further, a conductive paste containing the as-synthesized multi-shaped nano-Ag and epoxy resin has been prepared. The EMI shielding coating though spraying and heat curing process shows EMI shielding efficiency about 90dB at 30 MHz-3000 MHz with the thickness of 8-20 μm. In addition, the adhesion, reliability and the top to sidewall thickness ratio are better than those from PVD methods.