Form-in-place EMI gaskets

Details Form-in-place EMI gaskets Form-in-place EMI gaskets

2000-01-05

2001-12-18

Nakarani, D. S. (Department: 1773)

Stock material or miscellaneous articles

Structurally defined web or sheet

Physical dimension specified

C174S034000, C174S034000, C174S034000, C252S510000, C252S511000, C252S514000, C252S521300, C428S328000, C428S425800, C428S425900, C428S450000, C428S458000, C428S480000

Reexamination Certificate

active

06331349

ABSTRACT:

The present invention relates to conductive form-in-place gaskets. More particularly, it relates to conductive form-in-place gaskets having two, three or more axes of direction (e.g. X, Y and/or Z) and a process and system for making them.
BACKGROUND OF THE INVENTION
EMI shielding gaskets are used on electronic equipment to provide protection against interference from electromagnetic energy, including radio frequency interference (RFI) and more broadly all bands of interference commonly called electromagnetic interference (EMI). The shielding has an electrically conductive element, be it a wire mesh, conductive filler or conductive plating, coating or fabric which prevents external EMI from interfering with an electronic device and/or protects other adjacent electronic devices from EMI emitted by an electronic device.
Typically, EMI gaskets are prepared in one of three configurations: linear, die cut or compression molded. By linear, it is meant as an extrusion, molding, etc. of a defined, straight length. By die cut, it is meant that a gasket configuration is formed from a conductive sheet material which is cut by a die to the desired shape, such as round, square, etc. By compression molded, it is meant that the gasket configuration is formed by placing uncured elastomer which may contain conductive filler or a conductive mesh, into a specifically designed mold which is then subjected to compression (pressure) and then cured to cause the elastomer to assume the desired gasket configuration.
All three methods have disadvantages especially when used to form complex multidirectional or multiaxial gaskets, such as may occur in devices with a number of compartments that each need to be shielded, from each other as well as the external environment. Moreover, the problems are even more critical on smaller devices, such as cellular phones, notebook computers and other hand held devices, where the diameter of the gasket becomes very small and the ability to manufacture and attach such gaskets securely becomes very difficult and labor intensive.
Using linear gasketing material to form complex multiaxis/multidirectional gaskets (e.g. either x and y or in the x, y and z planes), is difficult, time consuming and costly. Each gasket portion must be hand cut and bonded to the adjacent portions of other linear gaskets and then bonded or secured in position upon the substrate.
Die cutting of conductive sheet stock will work in many instances especially in two plane (e.g. flat; x,y) applications, provided that each portion of the gasket is wide enough and/or thick enough to be self supportive. Die cutting parts however results in significant waste of the sheet stock because the material is typically a crosslinked resin such as silicone or polyurethane. This is not acceptable as it drives up the cost of such parts unacceptably. Further as diecutting is a rough process, the sheet stock needs to be fairly stiff and self supportive which is opposite that desired by the gasket user (i.e. soft and flexible).
Compression molding is slow and again generates scrap in the form of flash which must be removed. Further, each gasket design must use a specifically designed mold, making the process expensive for all but large volume stock items.
A form in place EMI gasket and system for forming complex multiaxis/multidirectional EMI gaskets which generates a minimum of scrap, which forms the gasket in place and requires no special tooling is desired. The present invention provides such a system.
OBJECTS AND SUMMARY OF THE INVENTION
The present invention relates to a form-in-place EMI gasket and a system for forming such a gasket using a table and/or dispenser that are capable of moving in multiaxial directions relative to each other and the substrate to be gasketed. The invention also relates to a process of providing a conductive elastomer, forming it in place along a desired gasket configuration so as to create form-in-place EMI gasket.
An object of the present invention is an EMI shielded substrate comprising:
a.) a first electrically conductive substrate;
b.) a second electrically conductive substrate adjacent to the first substrate;
c.) a formed in place electrically conductive gasket formed on and bonded to a predetermined portion of the first substrate so as to provide an electrical connection and EMI shielding between the first and second substrates.
A further object of the present invention is an EMI shielded substrate comprising:
a.) a substrate having an electrically conductive surface;
b.) a cover for the substrate, the cover having an electrically conductive surface which corresponds to and is in register with the conductive surface of the substrate; and
c.) a formed in place electrically conductive gasket formed on and bonded to a predetermined portion of the conductive surface of the substrate or cover so as to provide an electrical connection and EMI shielding between the substrate and cover upon the mating of the cover to the substrate.
Another object of the present invention is an EMI gasket comprising a composition formed of:
a.) a first component which is a primary polymer having end groups that are capable of chemically reacting with each other in the presence of moisture to form a derivative polymer having a longer average chain length than said primary polymer;
b.) a second component which is a noncross-linked elastomer that is not substantially chemically reactive with itself or with said first component; and
c.) a third component which is one or more electrically conductive fillers, wherein when said first, said second, said third components are intimately mixed, said composition, when maintained in the absence of moisture and other active hydrogen donor materials, are readily extrudable and otherwise conventionally moldable thermoplastic composition but, upon exposure to moisture, become essentially thermoset.
These and other objects of the invention will become clear from the following description and claims.


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