Development of Miniature Quad SAW filter bank based on PCB substrate

A miniaturization and integration are most important design factor in design of mobile handheld phone to enhance multi-function such as Bluetooth, camera and music so on. Especially in RF stage of multi-band GSM mobile phone, dozens of matching L, C passive components and several SAW filters occupy quite a little space, so phone makers partially use 7.0 times 3.5mm SAW filter bank instead of separate components. Current commercial filter bank is fabricated on PCB or LTCC base with 1.4 times 1.1 or 2.0 times 1.4(1.6)mm RF SAW end products, so the cost of this component is still similar to original one. This paper describes the development of a new 5.0 times 3.2 mm SAW filter bank which is consist of 12 L, C matching components and 4 SAW bare chips on PCB substrate with CSP technology. This technology can reduce the cost of materials down to 50% due to the elimination of 4 HTCC ceramic packages. We have investigated the multi-layered PCB substrate structures and raw materials to find out the optimal flip-bonding condition between the LiTaO₃ wafer and PCB substrates. Also the optimal materials and processing conditions of epoxy laminating film were found out through the experiments which can reduce the bending moment caused by the difference of the thermal expansion between the PCB substrate and laminating film. The new PCB SAW filter bank shows good electrical and reliability performances with respect to the present one.