Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
1999-06-23
2001-02-27
Gandhi, Jayprakash N. (Department: 2841)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C361S704000, C361S752000, C361S816000, C174S034000
Reexamination Certificate
active
06195267
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention is directed toward electronic devices, and more particularly toward mounting and protecting microelectronic assemblies.
2. Background Art
Electronic devices, particularly portable microelectronic devices such as cellular phones, are subject to a wide variety of conditions which can interfere with proper operation of the device. For example, vibrations can cause wear at contact interfaces internal to the microelectronic device. This wear may generate contaminants, such as metal particles, that can migrate through the microelectronic device and degrade the performance of the microelectronic device. Additionally, such wear can increase the resistance of the contact interface, which also inhibits the performance of the microelectronic device. Still further, shock loads (e.g., from dropping the device) which may not be sufficient to visibly break the device can nevertheless cause the microelectronic circuitry to lose contact interfaces so as to prevent proper operation of the circuitry.
Such devices are also subjected to environmental contaminants, including moisture and dust which, if allowed to reach to the circuitry, can also interfere with its proper operation.
Thermal loads resulting from the operation of the circuitry can also cause the device and/or the microcircuitry to degrade over time. Still further, electro-magnetic impulses (EMI) or other radio frequencies (RF) in the environment can interfere with the proper operation of the microcircuitry, including particularly wireless communication devices such as cellular telephones. Such problems are common to all microelectronic assemblies using chip scale packages (CSP's) and Flip Chip packages.
Electronic circuit components have been mounted within their devices in a wide variety of manners. For example, thermally conductive gels have been used to dissipate heat from the microcircuitry of such devices.
Further, shield structures such as cans, lids, and metalized frames having electrical connection through an ohmic connection along the periphery of the shielding member have been used to provide EMI shielding and thermal control and CSP's and Flip Chip architectures. The ohmic connection is usually made with solder, conductive elastomers or compression contacts using precious metals. Thermal control has commonly been provided by conductive materials in intimate contact with the power dissipating packages which provide a low resistance path to the body of the device.
However, mounting devices such as metal cans with solder sealing for ohmic contact are difficult to assemble automatically and therefore are subject to high assembly costs and further are subject to possible uneven assembly among multiple devices. Further, if pressure contacts are used for ohmic contact for EMI shielding, high force levels are required for each contact point which can also cause problems in assembly. For example, the force required is usually greater than that which can be provided by a plastic housing without yielding the plastic, and therefore secondary fasteners or clips can be required, further increasing not only assembly costs but also costs of materials. Use of conductive elastomers require even greater force levels to maintain ohmic contact. Still further, none of these structures are entirely satisfactory for excluding moisture and dust, nor do they provide the full combination of protection of the microcircuitry from contaminants and from vibrations and shocks while also providing EMI shielding and thermal dissipation.
The present invention is directed toward overcoming one or more of the problems set forth above.
SUMMARY OF THE INVENTION
In one aspect of the present invention, a shielding and thermal dissipation structure is provided for an electronic assembly including a distribution circuit and at least one electronic component mounted on a surface of the distribution circuit. The structure includes a plastic housing overlaying the at least one electronic component. The housing includes an outer periphery defining a housing interior and substantially surrounding the outer periphery of the at least one electronic component, and a closed end on one side of the housing outer periphery, the closed end having an interior surface facing the at least one electronic component. A metal coating is provided on the closed end interior surface. An electrically conductive gel is in the housing interior about the plastic housing outer periphery and a thermally conductive gel is disposed between the at least one electronic component and the housing closed end interior surface.
In one preferred form, the electrically conductive gel is in intimate contact with the distribution circuit. In another preferred form, the electrically conductive gel is in intimate contact with the distribution circuit and the metal coating.
In still another preferred form, the electronic assembly includes an exterior housing, and a second thermally conductive gel is provided between the exterior housing and an exterior surface of the plastic housing closed end.
In yet another preferred form, the metal coating is about 5 microns thick, if deposited as a pure metal. Metal coatings composed of silver particles in a polymer matrix are useful at 10-20 microns thick.
Another preferred form of this aspect of the invention has the metal coating chosen from the group of nickel and gold and the electrically conductive gel includes carbon. In still further preferred forms, the carbon comprises carbon particles or carbon fibers, and/or the thermally conductive gel includes particles of at least one of the group of aluminum oxide, aluminum nitride, and boron nitride.
In another aspect of the present invention, a shield and thermal dissipater is provided for an electronic assembly including an electronic chip on a printed circuit board. A plastic housing is open on one side and defines a central interior region and a peripheral interior region around the central interior region, with an interior surface facing the interior regions. A metalized plating is provided on the plastic housing interior surface, and an electrically conductive gel is provided in the housing peripheral interior region on the metalized plating. A thermally conductive gel is provided in the housing central region on the metalized plating, and includes a cavity facing the housing open side for receiving the electronic chip on the printed circuit board.
Preferred forms of the invention such as described with the first aspect of the present invention may also be used with this aspect of the invention.
It is an object of the invention to provide an inexpensive and reliable structure for protecting electronic components against vibrations and shock, and against the performance degrading effects of heat and electro-magnetic fields.
REFERENCES:
patent: 4008300 (1977-02-01), Ponn
patent: 4770641 (1988-09-01), Rowlette
patent: 4855868 (1989-08-01), Harding
patent: 5074799 (1991-12-01), Rowlette, Sr.
patent: 5294826 (1994-03-01), Marcantonio et al.
patent: 5424652 (1995-06-01), Hembree et al.
patent: 5561265 (1996-10-01), Livshits et al.
patent: 6090728 (2000-07-01), Yenni, Jr. et al.
MacDonald, Jr. James D.
Marcinkiewicz Walter M.
Ericsson Inc.
Gandhi Jayprakash N.
Wood Phillips VanSanten Clark & Mortimer
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