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Selective Underfilling of Regions in a Flip-Chip Assembly Enabling Continued Functionality of Micro Electrical Mechanical Systems (MEMS) on Die and/or Substrates

IP.com Disclosure Number: IPCOM000009589D
Original Publication Date: 2002-Sep-04
Included in the Prior Art Database: 2002-Sep-04
Document File: 5 page(s) / 27K

Publishing Venue

Motorola

Related People

Thomas Koschmieder: AUTHOR [+2]

Abstract

Micro Electrical Mechanical Systems (MEMS) are becoming more commonplace as sensors. MEMS, for example, are used as accelerometers which are used in air bag safety systems in automobiles to sense an extremely rapid deceleration (i.e. an automobile accident). Packaging the MEMS devices into electronic packages is an evolving art in itself while it uses some of the technology coming from existing packaging technology used for microprocessors and similar electronic devices.

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Selective Underfilling of Regions in a Flip-Chip Assembly Enabling Continued Functionality of Micro Electrical Mechanical Systems (MEMS) on Die and/or Substrates

Thomas Koschmieder and Dave Mahadevan

Abstract: Micro Electrical Mechanical Systems (MEMS) are becoming more commonplace as sensors. MEMS, for example, are used as accelerometers which are used in air bag safety systems in automobiles to sense an extremely rapid deceleration (i.e. an automobile accident). Packaging the MEMS devices into electronic packages is an evolving art in itself while it uses some of the technology coming from existing packaging technology used for microprocessors and similar electronic devices. One important difference between a MEMS device and a microprocessor is that the MEMS structure frequently needs a free surface to function correctly. This is due to the MEMS having mechanical features that need to move freely. Microprocessors as the state of the art today do not have mechanical features that move. Due to this reason MEMS are usually protected by a cap, which could either be another silicon wafer bonded to the MEMS wafer using substances like glass frit (for hermetical sealing) with an opening wherever required. Another method (patent pending) is to provide a micron thick cap made of some polymeric material that serves the purpose of the cap and thus protects the MEMS. When using the microprocessor packaging technology of flip-chip assembly, one basic enabling technology is the epoxy underfill of the volume between the die and the substrate. Capillary action pulls the liquid epoxy between the surfaces of the die and substrate causing the entire volume between the two to be filled with epoxy. For a MEMS device the above mentioned epoxy underfill may cause the breakage of the micron thick cap resulting in catastrophic failure of the MEMS or flex it to the point of affecting the mechanical performance. Flip-chip assembles also make use of technology called “bumps” that make the electrical and mechanical interconnect between the die and substrate. These bumps come in a wide variety of metal alloys, shapes, sizes, etc. They serve two purposes as mentioned. First, the power source to cause a microprocessor to function and to allow the microprocessor to send signals between itself and the rest of the world are through the bumps. Secondly, the bumps provide a method for attaching the die to the substrate. MEMS devices can use this technology directly. Given the problem of needing not to underfill portions of the MEMS surface and the need for some version of bumps for a flip-chip assembly for a MEMS device alternatives are needed to classic flip-chip construction of bumped die with complete epoxy underfill. One group of solutions comes from replacing the bumps and underfill with anisotropically conductive films (ACF). These films have the electrical property of conducting power, current, signals, etc., along one axis but not in the other two axial directions....