Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package
Reexamination Certificate
2002-07-03
2004-10-26
Nhu, David (Department: 2818)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
C257S777000
Reexamination Certificate
active
06809412
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention pertains to microelectromechanical devices and circuits, and more particularly, to formation of such devices within and upon an integrated package. The invention also pertains to packaging of microelectromechanical devices and circuits using a thermoplastic.
2. Description of the Related Art
The following descriptions and examples are not admitted to be prior art by virtue of their inclusion within this section.
Microelectromechanical devices, or devices made using microelectromechanical systems (MEMS) technology, are of interest in part because of their potential for providing miniaturized sensors and actuators and performing functions not done or poorly done by semiconductor integrated circuit (IC) technology. As compared to transistor switches formed with conventional IC technology, for example, MEMS switches may exhibit lower losses and a higher ratio of off-impedance to on-impedance. Although the fabrication steps used to form MEMS devices are similar to those for forming integrated circuits, packaging of MEMS devices presents some additional complexity. Because MEMS devices tend to have moving parts, they cannot be encapsulated in the manner used for protection of purely electronic circuits. Instead, a hermetically sealed enclosure, or “cavity”, around the MEMS device typically needs to be formed. The final step in fabrication of the MEMS device itself is typically a “release” of the device, in which a sacrificial layer is removed so that the device may move freely. The release process may be quite critical, involving, for example, careful anneals, etching and drying processes. After release of the MEMS device, any processing steps which may contaminate the device must be avoided until the protective enclosure around the device is formed.
As is done in IC manufacturing, many MEMS devices (or circuits) are typically formed on a single substrate, which is subsequently diced, or singulated, to separate the individual devices. The dicing is typically done using a saw, and is a particularly “dirty” and mechanically stressful process. Therefore it is preferable that MEMS have enclosures formed over them if they are released before dicing (also referred to as being released at “wafer level”). Alternatively, the devices may be singulated first and then released before additional packaging is done. In either case, the individual MEMS die are typically put into packages fairly similar to IC packages. The packaging could involve, for example, attaching the back side of the MEMS device substrate to the top side of a packaging substrate, then wire-bonding contact pads on the top side of the MEMS device substrate to contact pads on the packaging substrate, and affixing a cap to form the sealed cavity over the MEMS device (unless the device was already covered prior to singulation). This type of packaging scheme has disadvantages, however. For example, the individual handling of each die needed to place it into a package is expensive and potentially unreliable. The package size also has to be relatively large in order to accommodate the MEMS chip substrate and the wire bonds. Furthermore, the use of wire bonding can limit the performance of high-frequency devices by introducing parasitic impedances.
One alternative approach, also used in IC packaging, is to eliminate wire bonds through flip-chip bonding with solder bumps or balls. If the solder bumps are large enough, a MEMS chip can be flip-chip bonded to a packaging substrate with enough clearance for the (now upside-down) MEMS device to operate. An enclosure can be formed around the MEMS device using the packaging substrate, MEMS substrate, and an additional underfill material applied laterally around the device, as described in U.S. Pat. No. 6,214,644. Although this flip-chip approach may improve the reliability and performance of the package connections by removing the wire bonds, it is still necessary to handle individual MEMS die one at a time during packaging, and to perform multiple packaging steps (e.g. forming solder bumps, flip-chip bonding, underfill application and cure).
It would therefore be desirable to develop a MEMS packaging method and structure which reduces the need for individual device handling, improves package size and cost, and improves high-frequency performance.
SUMMARY OF THE INVENTION
The problems outlined above may be in large part addressed by formation of a is MEMS device upon a packaging substrate, rather than upon a separate device substrate.
A packaging substrate as used herein is a substrate similar to those used in packaging of integrated circuits. A packaging substrate is formed from an insulating material and includes conductive features on its lower surface. The conductive features, which may include conductive pads, pins, bumps or balls, are adapted for use in electrical coupling of the substrate to a circuit board or other circuit carrier. “Circuit board” as used herein may refer to a circuit board, carrier, or other surface to which a miniature circuit may be mounted. The packaging substrate may also include conductive interconnects extending within and through the substrate, where the interconnects are adapted to connect the conductive features to the upper surface of the substrate. The “upper surface” of the substrate as used herein is the surface upon which an IC would be mounted if the substrate were used in an IC-mounting context, while the “lower surface” is the surface that would face the circuit board in such a context. When a MEMS device is formed upon a packaging substrate, the underside of at least one element of the device is in contact with the upper surface of the substrate. This is in contrast to formation of the MEMS device upon a separate MEMS substrate, which might then be mounted upon the packaging substrate (either die-up mounting which would typically include wire bonds, or flip-chip, die-down mounting). In an embodiment, the underside of the MEMS device element may be formed upon an exposed end of a conductive interconnect within the substrate, allowing electrical coupling of the device element to the lower surface of the substrate or to another device or circuit formed on the substrate. Alternatively, the device element may be connected to an interconnect within the substrate through an interconnect formed on the surface of the substrate.
An embodiment of a microelectromechanical circuit as contemplated herein may further include a cover spaced above the device and the substrate. The cover may be spaced sufficiently above the device to permit proper electromechanical operation of the device. The circuit may further include a sealing structure interposed between the substrate and cover, where the sealing structure laterally surrounds the device. The sealing structure may include, for example, an adhesive or a metal layer. In an embodiment, the substrate, cover and sealing structure combine to form a protective enclosure around the device. In an additional embodiment of the microelectronic circuit, an IC may be mounted on the packaging substrate in a position laterally spaced from that of the MEMS device. The IC may be electrically coupled to the MEMS device by wire bonds or through interconnects within the substrate, and may be included within a protective enclosure formed around the device. In some embodiments, the IC may alternatively be external to the protective enclosure.
Some embodiments of the circuit described herein are believed to provide cost, manufacturability, and/or performance advantages. For example, multiple MEMS devices may be formed simultaneously upon a packaging substrate. In a preferred embodiment, the devices may be released and then covered before dicing. At the time of dicing, the MEMS devices are already packaged and protected. The devices may therefore be ready for assembly to a circuit board or carrier, with no further packaging required. Costly and unreliable handling of individual devices during packaging may therefore be avoided. Fabrication of the packaged MEMS device i
Flynn Gregory
Rice Janet L.
Tourino Cory G.
Conley & Rose, P.C.
Daffer Kevin L.
Nhu David
Teravictu Technologies
LandOfFree
Packaging of MEMS devices using a thermoplastic does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Packaging of MEMS devices using a thermoplastic, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Packaging of MEMS devices using a thermoplastic will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3303468