Microelectronics Packaging:Packaging in Wireless Applications

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Packaging in Wireless Applications

Wireless applications typically involve RF, high-frequency digital, and mixed-mode circuits. In these cases, circuit performance could be altered by the undesired coupling of a signal from one part of the circuit to another. Hence, wireless packaging requires minimal electrical parasitic effects that need to be well characterized.

Wireless circuitry differs from DC and low-frequency circuits in that the signals carried in both the conductors and the dielectric surrounding the conductors are influenced strongly by the high-frequency electrical properties of the dielectric. Hence the dielectric properties of packages which contain wireless circuits are quite important. Ceramic materials are applied, both as parts of the package as well as for subsystem carrying RF transmission lines. To this end, and to provide electromagnetic shielding, these materials have to be metallized partly. Aluminum nitride, beryllium, aluminum silicon carbide, and CVD diamond show the best thermal conductivity and are therefore applied in high-power applications, while alumina is well known for standard microwave applications (see Table 8.6D).

The trend in wireless applications is to integrate multiple modules on a single chip. So, the thermal management of the whole chip becomes crucial. The IC package must have good thermal properties. Metal as a material shows optimal properties concerning electrical conductivity, thermal conductivity,

electromagnetic shielding, mechanical and thermal stability. For thermal expansion, the best match to semiconductor and ceramic material can be achieved with molybdenum, tungsten, or special composites like kovar. At high frequencies, interconnections need to be carefully designed. Microstrip interconnects, coplanar waveguide are mostly used for microwave packaging. Flip-chip packaging has tremendous potential for future RF packaging [55–60]. To improve the performance of the wireless system, it is crucial to reduce the extrinsic parasitics. System integration is key to reduce the parasitics, the size, and cost of a wireless system. Integration of passive components is a major challenge in wireless packages. More and more efforts are being made to integrate passive components and power devices on a chip with the other mixed-signal circuits. The size of the package becomes an issue. Micromachining technology provides a way to make miniature packages that conform to RF circuits, while providing physical and electrical shielding. Conformal packages made by applying micromachining technology provide the capability to isolate individual components between the adjacent circuits.

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