Development of the RF SAW filters based on PCB substrate

Recently produced RF SAW (surface acoustic wave) filters are made using HTCC (high temperature cofired ceramic) with CSP (chip scale package) technology. This paper describes the development of a new 1.4 times 1.1 and 2.0 times 1.4 mm RF SAW filter based on PCB (printed circuit board) substrate instead of HTCC package, which reduces the cost of materials by 40%. We have investigated the multilayered PCB substrate structure and raw materials to determine the optimal flip-bonding condition between the LiTaO₃ wafer and PCB substrates. Also, optimal materials and processing conditions for the epoxy laminating film were experimentally determined that can reduce the bending moment caused by thermal expansion differences between the PCB substrate and laminating film. The new PCB SAW filter shows better electrical and reliability performances than those observed with present SAW filters