Research on a novel and ultra-thin SMT gasket of compressible conductive silicone/tinned copper foil composites for PCBA

In this study, we present an ultra-thin silicone-based gasket for miniaturized PCBA, which is much thinner than the traditional foam-type SMT gasket. The tinned copper (Sn-Cu) foil was used as the conductive solder layer and the conductive silicone composed of silicone matrix and hybrid conductive fillers was used as the low compression stress layer. The two layers were laminated into sheets through interface treatment technology followed by heat curing to fabricate a novel SMT gasket of conductive silicone/tinned copper foil (CS/Sn-Cu). The fabricated gasket was characterized by SEM, adhesion strength test and EMC grounding applications, etc. When the CS/Sn-Cu gasket was compressed by 25% in the vertical thickness direction, the resistance of the gasket is as low as 0.05 Ω and the corresponding compressive pressure is about 150 psi. The electromagnetic interference (EMI) shielding effectiveness (SE) of the CS/Sn-Cu gasket is higher than 90 dB in a wide wave range of 10 MHz to 3 GHz. After SMT reflow process, the welding strength between the gasket and the PCB reaches higher than 20 N/cm ² . It is worth to note that, the CS/Sn-Cu gasket can be cut into small pieces and packaged into roll material tape for automatic SMT assembly process and the minimum thickness of 0.5 mm can be achieved.