Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package – Outside periphery of package having specified shape or...
Reexamination Certificate
1998-11-18
2001-05-22
Chaudhuri, Olik (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
Outside periphery of package having specified shape or...
C257S528000, C257S623000, C257S777000, C257S786000, C257S787000
Reexamination Certificate
active
06236111
ABSTRACT:
FIELD OF THE INVENTION
The present invention is related to micro-electromechanical components, and more particularly to a chip integrating a micro-system formed by means used in integrated circuit technology, namely deposit, photolithography and micro-manufacturing of successive layers on a substrate, generally of silicon (sometimes of another material, such as glass or quartz).
BACKGROUND OF THE INVENTION
The term “micro-system” refers to a component which transforms a physical magnitude into an electrical signal (i.e., a micro-sensor, for example, a micro-accelerometer or, on the other hand, which varies a physical magnitude, generally in the form of a displacement of a movable part, by application of an electrical signal (i.e., a micro-actuator, for example, a micro-pump, typically for a micro-syringe, or a micro-motor).
These components often comprise movable parts which move on the order of a micrometer (“micro-moving”), and are therefore, by their very nature, very sensitive to mechanical constraints imposed by their environment.
Thus, in the typical case of a micro-accelerometer, if the component is glued directly onto the substrate with a rigid glue of the epoxy resin type, for example, the simple mechanical constraints generated by this gluing could alter the sensitivity of the micro-sensor, reduce its capability to support overloads, or perhaps block its functionality completely.
For this reason, in the current state of the art, the direct transfer of such components onto a hybrid circuit substrate is a delicate task necessitating the utilization of flexible glue and of a silicon substance to protect the electrical connections.
A known direct transfer technique calls for first mounting the device on a chip-carrier which in turn is then mounted on the substrate, but then economy of space becomes a concern.
Even with advances in known techniques, to absorb any differences in dilation (i.e., expansion) coefficients between the material of the substrate (ceramics, glass epoxy, etc.) and that of the component (silicon, quartz, etc.), the presence of an intermediate resin is nevertheless indispensable. Typically, a first transfer of the component onto an intermediary silicon substrate (the silicon/silicon interface not presenting any such dilation coefficient related difficulty), is followed by a transfer from the intermediary substrate to the hybrid circuit substrate, which, for example, is ceramic, with interpositionning of the resin between these two substrates.
OBJECTS AND SUMMARY OF THE INVENTION
One of the goals of the present invention is to provide a particular component structure that overcomes the foregoing difficulties and permits the direct transfer of the component onto a hybrid circuit substrate while protecting the micro-system from any mechanical constraints which may be caused due to the application and hardening of an intermediate resin.
Another goal of the invention is to provide a component which, after transfer onto the substrate, will occupy on the substrate a surface area identical to that of one chip alone. In other words, the addition of resin to the chip for coating the component will not increase the surface area occupied by the component on the substrate.
This technology, known as “CSP” (Chip Scale Packaging), is particularly advantageous in areas where the miniaturization of circuits is an essential parameter, as, for example, in circuits of a cardiac stimulator.
To this end, the present invention provides a micro-electromechanical component with a chip comprising a micro-system formed particularly by deposit, photolithography and micromanufacturing of successive layers, in which the micro-system comprises a plurality of contact pads for electrical connection.
According to one embodiment of the present invention, the chip is provided with an external coating to allow its transfer onto a substrate. This coating has a plurality of external metallizations on its surface which are electrically connected, through the coating material, to the opposing contact pads of the chip and embedded in the thickness of the material of coating.
The coated component has roughly the same dimensions (length and width) as those of the chip before coating. The coating is formed only on a reduced portion of the chip, essentially in the region of the contact pads and the metallizations, the non-coated part being the sensitive (i.e., sensing) part of the micro-system, protected from mechanical constraints which may arise due to the application and the hardening of the coating material.
In other words, the coating covers only the electrical connections of the micro-system that are electrically and mechanically linked to the substrate. The rest of the sensor, typically made of silicon, does not necessitate coating and will be able to rest freely on the substrate without rigid connection to the substrate.
Thus, only a small portion of the component (that supporting electrical connections), which is preferably a mechanically inactive portion, will be coated with resin so as to minimize mechanical constraints which may be caused due to the hardening of this resin.
Incidentally, it should be noted that the term “coating” should not be interpreted in a restrictive sense suggesting a complete encapsulation of the chip of the component. This term as used herein refers only to the particular technology employed (i.e., “coating”), where the resin can be applied, as will be explained, only on a face of the component (that is, a layer of material deposited on the surface), and more particularly, on a localized region thereof.
In alternative embodiments, various advantageous subsidiary characteristics and features of the present invention will be appreciated.
In one embodiment, the component comprises a groove in the direction of the width of the chip, notably a lateral groove formed on an edge of the chip, which is filled by the coating material, and very advantageously the coating material levels the surface of the non-coated part to achieve a uniform surface, preferably, substantially flat and smooth.
In an alternative embodiment, the contact pads and the metallizations are situated on the same side, preferably the side of smaller dimension, of the chip. The metallizations are distributed preferably on an inclined face of a beveled chamfer of the component in a manner that the aforementioned inclined face always makes an angle with the substrate regardless of the configuration of the transfer of the component on this substrate, i.e., whether flat or on its side.
In another embodiment, the chip is formed from a plurality of superposed tablets, with an active tablet supporting the micro-system and at least one passive protection tablet sealed onto the active tablet, the length of the passive part is less than that of the active one such as to form a region where the contact pads are not covered by the passive tablet and to define in this region a lateral groove filled by the coating material.
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Patent Abstracts of Japan, vol. 14, No. 316, Jul. 6, 1990, Japan publication No. 02103967, dated Apr. 17, 1990.
Campenhout Yves
Gilet Dominique
Legay Thierry
Chambliss Alonzo
Chaudhuri Olik
ELA Medical S.A.
Orrick Herrington & Sutcliffe LLP
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