A study of Wafer Level Packaging of SAW filter for module solution

In the cellular market, the demand for miniaturization becomes more severe year by year. The introduction of multiband and multimode systems has accelerated the need for further miniaturization of RF components. For SAW devices in the RF module function, low insertion loss and high attenuation performance are needed. Moreover, in the structural point, miniaturization and resistance to high molding pressure are demanded. Ceramic packaging with hermetic-sealing has efficient reliability from the structural point of view against molding pressure used in the module fabrication process. However, with the current ceramic packaging method it is difficult to miniaturize the device size. A packaging method using resist with air-gap over the IDT is introduced for further miniaturization. The problem of the resist structure with air-gap is the reliability against humidity and it´s strength against deformation. In this paper, we propose an improved method of reliability and strength. The WLP-SAW device for module applications is realized by improving the reliability of IDT and improving the molding resisting pressure of the resist with air-gap. The device size is 0.93×0.92 mm, and the height is 0.4 mm typ.. Moreover, the electrical performance is much improved compared to the current ceramic packaged devices due to the decreased parasitic impedance from the package. In this paper, we would like to discuss the possibility of a SAW device with the resist structure with air-gap. Moreover, we would like to discuss a method to improve the characteristics and molding pressure resistance in WLP.