Microstructure of Ag-Sn Bonding for MEMS Packaging
ABSTRACT Different metallization systems and bonding designs of Ag-Sn bonding were investigated to achieve good bonding. The bonding strength was evaluated by shear force. The microstructure of bonding interface was inspected by scanning electronic microscopy and ED AX. Shear force test was performed for as-bonded dice. The test results indicate differences among different metallization systems. The bonding pair with Ti/Au as the UBM has a quite low shear strength because of the bad adhesion on the silicon substrate. The bonding pair of Ti/Ni/Sn/Au and Ti/Ni/Au/Ag obviously has higher shear strength than that of Ti/Ni/Sn/Au and Ti/Ni/Au/Ag/Au. The former is 55.17 MPa on average while the later is 36.05 MPa. The shear strength of the pair of Ti/Ni/Sn/Au and Ti/Ni/Au/Ag is similar to that of Ti/Ni/Sn/Au and Ti/Ag which has the shear strength of 55.32 MPa on average. The Ni and Au in the Ag-Sn bonding system have significant effect on the microstructure of the bonding interface. The diffusion of Au into Sn is quicker than both Ag and Ni. The diffusion between Au and Sn would induce the obstacle of the inter-diffusion between Sn and Ag. Ni will also diffuse quickly into Sn and form Ni3Sn4. The existence of Ni in Sn will also influence the diffusion of Ag into Sn and make the bad wettability during bonding. After several metallization systems have been investigated, finally a uniform bonding layer has been achieved by excluding Ni and Au in the bonding system. The bonding interface is Ag3Sn layer dispersed with some pure Ag.
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ABSTRACT: With RF MEMS technology rapid development, the distributed RF MEMS phase shifters have exhibited excellent RF performance, such as high isolation, high phase shifts, low insertion loss and wide bandwidth operation features at high frequency. However, the applications of RF MEMS phase shifter are hampered by the lack of production-worthy wafer level packaging. Therefore, the problems on packaging solved are very stringent. This paper mainly investigates on the influence of wafer level packaging modes on the RF performance of distributed RF MEMS phase shifters. The insertion loss S<sub>21</sub>, return loss S<sub>11</sub> and phase shifts parameters are analyzed using 3D electromagnetic simulation tool - microwave studio (CST). Simulation results show that the insertion loss of the distributed RF MEMS phase shifters for bonding wafer packaging and wafer level micropackaging is -0.59dB and -0.061dB at l0GHz, -0.79dB and -0.25dB at 50 GHz, respectively. The return loss -11.8366dB and -26.66906dB at l0GHz, -14.50227dB and -32.30596dB at 50GHz, and the phase shift is 170.78deg and 161.82deg at 50GHz, respectively. Therefore, we concluded that different wafer level packaging modes distinctly affect the microwave performance of the distributed RF MEMS phase shifters. Comparing the RF performance parameters of two modes, the wafer level micropackaging mode shows excellent RF performance (the average insertion loss of -0.ldB and the average return loss of deg22 dB) and no resonances at 1-60 GHz, and adapted to the packaging of distributed RF MEMS phase shiftersElectronic Packaging Technology, 2006. ICEPT '06. 7th International Conference on; 09/2006
Conference Paper: Wafer Level Micropackaging for Distributed MEMS Phase Shifters[Show abstract] [Hide abstract]
ABSTRACT: A novel packaging structure which is performed using wafer level micropackaging on the thin silicon substrate as the distributed MEMS phase shifters wafer with vertical feedthrough is presented. The RF performances of proposed structure are investigated using Microwave Studio (CST). The results show that the insertion loss (S<sub>21</sub>) and return loss (S<sub>11</sub>) was -0.4-1.84 dB and under -10 dB at 1-50 GHz. respectively. And especially, the phase shifts of 360deg are obtained at 48 GHz. Tins indicate that the proposed packaging structure for the distributed MEMS phase shifters can provide the maximum amount of phase shift with the minimum amount of insertion loss and with return loss of less than -10 dB.Electronic Packaging Technology, 2007. ICEPT 2007. 8th International Conference on; 09/2007
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ABSTRACT: This paper reports on the methods, feedthrough modes and RF performance of wafer level packaging for RF MEMS switches. By analyzing the effects of packaging methods and feedthrough modes on the cost, weight, size, loss, RF performance and function of switches, a novel wafer level packaging structure which is performed using the wafer-level microencapsulation on the thin silicon substrate as the RF MEMS switches wafer with the vertical feedthroughs is presented. This structure has some advantages, such as low thickness, low parasitic capacity, short electric path, lightweight, no real ring and compatibility with the devices fabrication processes. Therefore, for RF applications, the packaging structure obviously reduces electric path loss and fabrication cost, and provides better RF performance of RF MEMS switches