CATEGORIES:
BiologyChemistryConstructionCultureEcologyEconomyElectronicsFinanceGeographyHistoryInformaticsLawMathematicsMechanicsMedicineOtherPedagogyPhilosophyPhysicsPolicyPsychologySociologySportTourism
Application Drivers and Interfaces
The process of selecting materials, packages, processes and techniques for MEMS is driven by the end item application. For example, in an RF end item application, a major design problem is to have controlled impedance of the input and output signals. Therefore, the package should not limit the electrical performance of the MEMS components.
Another application driven requirement is the need for hermeticity. Designers must decide if their components need to be isolated from oxygen, nitrogen, ambient
| Microcircuit | Microcircuit packaging solutions | MEMS | MEMS packaging solution |
| Structures with no moving parts and may be stacked | Easy to assemble and mass produce | 3-D structures which may involve delicate components and precision movements | Require application specific packaging often with cavities or vacuum spaces |
| Packaging styles are often generic or independent of application | Industrial and military standards exist | Applications are a variety of specific functions such as biological, chemical, electromechanical and optical | Packaging styles are application driven and custom to unique functions |
| Packaging techniques are mature | Paths to follow for design, material selections, fabrication processes and reliability and assurance testing | Mature packaging techniques may not work for most applications | New packaging schemes must be developed at the design concept phase |
| IC are protected from the environment | Environmental protection is straightforward and provided by sealed encapsulation | In many applications sensitive moving or stationary components are interfaced with with the environment | Complex balance of protection from and access to the environment is required |
| IC transmits power for specific electrical operations | Only external ties are through inductive or conduction coupling | Many components and functions are required within the package | Increased complexity and interfaces provide new failure mechanisms |
moisture, etc. before making a decision on what level of hermetic packaging is necessary. For example, ambient moisture often deteriorates MEMS devices, however, in the instance the package needs only to be a dry package and not fully hermetic. Then, the use of appropriate getters will suffice; but if long-term reliability is a requirement, the packages still need to be near hermetic since the getters have a limited capacity [1]. Figure 12.1 shows a variety of ceramic package structures for sensor applications.
12.1.4 Interfaces to Other System Components
As the package is the primary interface between the MEMS and the system, it must be capable of transferring operating power and a multitude of signals. In addition, the package may be required to distribute both operating power and other signals to other components inside the package. The integration of more MEMS devices and 
other components into a single package increases the packaging complexity as the number of interconnects within the package increases.
12.1.4.1 Power and Signals Interface
When designs require high frequency RF signals, they can be introduced into the package along metal lines passing through the package walls, or they may be elec-tromagnetically coupled into the package through apertures in the package walls. RF energy losses between the MEMS device and the system can be due 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 or ribbon bonds; although flip-chip die attachment and multi-layer interconnects, using thin dielectrics have also been used.
Date: 2015-02-28; view: 1288
| <== previous page | | | next page ==> |
| Packaging Classes | | | Optical Interface |