tailieunhanh - MEMS and Microstructures in Aerospace Applications - Robert Osiander et al (Eds) Part 12

Tham khảo tài liệu 'mems and microstructures in aerospace applications - robert osiander et al (eds) part 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 272 MEMS and Microstructures in Aerospace Applications When designs also require high-frequency RF signals the signals can be introduced into the package along metal lines passing through the package walls or they may be electromagnetically coupled into the package through apertures in the package walls. Ideally RF energy is coupled between the system and the MEMS without any loss in power but in practice this is not possible since perfect conductors and insulators are not available. In addition power may be lost to radiation by reflection from components that are not impedance matched or from discontinuities in the transmission lines. The final connection between the MEMS and the DC and RF lines is usually made with wire bonds although flipchip die attachment and multilayer interconnects using thin dielectric may also be possible. TYPES OF MEMS PACKAGES Each MEMS application usually requires a new package design to optimize its performance or to meet the needs of the system. It is possible to loosely group packages into several categories. Four of these categories are 1 metal packages 2 ceramic packages 3 thin-film multilayer packages and 4 plastic packages are presented below. Metal Packages Metal packages are often used for microwave multichip modules and hybrid circuits because they provide excellent thermal dissipation and excellent electromagnetic shielding. They can have a large internal volume while still maintaining mechanical reliability. The package can either use an integrated base and sidewalls with a lid or it can have a separate base sidewalls and lid. Inside the package ceramic substrates or chip carriers are required for use with the feedthroughs. The selection of the proper metal can be critical. CuW 10 90 Silvar a Ni-Fe alloy Semiconductor Packaging Materials Armonk NY CuMo 15 85 and CuW 15 85 all have good thermal conductivity and a higher CTE than silicon which makes them good choices. Kovar ESPI Ashland OR a Fe-Ni-Co alloy is also