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An Introduction to MEMs Engineering - Nadim Maluf and Kirt Williams Part 13

Tham khảo tài liệu 'an introduction to mems engineering - nadim maluf and kirt williams part 13', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 220 Packaging and Reliability Considerations for MEMS provided the vibrations are not sufficiently large to cause damage. In addition to mechanical protection an electrically grounded cover also shields against electromagnetic interference EMI . Naturally the cap approach is not suitable for sensors such as pressure or flow sensors or actuators that require direct and immediate contact with their surrounding environments. Thermal Management The demands on thermal management can be very diverse and occasionally conflicting depending on the nature of the application. The main role of thermal management for electronic packaging is to cool the integrated circuit during operation 1 . A modern microprocessor containing millions of transistors and operating at a few gigahertz can consume tens of watts. By contrast the role of thermal management in MEMS includes the cooling of heat-dissipating devices and especially thermal actuators but it also involves understanding and accounting for the sources of temperature fluctuations that may adversely affect the performance of a sensor or actuator. As such thermal management is performed at two levels the die level and the package level. Thermal analysis is analogous to understanding electrical networks. This is not surprising because of the dual nature of heat and electricity voltage current and electrical resistance are dual to temperature heat flux and thermal resistance respectively. A network of resistors is an adequate first-order model to understand heat flow and nodal temperatures. The thermal resistance 0 of an element is equal to the ratio of the temperature difference across the element to the heat flux this is equivalent to Ohm s law for heat flow. For a simple slab of area A and length l 0 equals 1 kA where K is the thermal conductivity of the material see Figure 8.2 . The nature of the application severely influences the thermal management at the die level. For example in typical pressure sensors that dissipate a .