Metal fusion bonding – Process – Metal to nonmetal with separate metallic filler
Patent
1992-08-17
1994-03-29
Heinrich, Samuel M.
Metal fusion bonding
Process
Metal to nonmetal with separate metallic filler
228254, 228 62, 228 447, 361283, 361326, G01D 524, H01G 516, B23K 3102, B23K10136
Patent
active
052977200
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to the technical field of methods or processes for assembling a mechanical part on a support, which part includes a flexible element that co-operates with the support to define a variable capacitor. Such parts are intended preferably, but not exclusively, to constitute a capacitive type membrane or sensor of mechanical magnitudes.
In specific fields of application, it appears necessary to use a capacitive sensor of mechanical magnitudes such as force, pressure, or acceleration, for the purpose of delivering electrical signals representative of the measured magnitudes and suitable for application to electronic processing systems to enable automatic measurements, monitoring, regulation, or control to be performed.
In a preferred application, such a capacitive sensor is in the form of a cantilevered beam, made from a monolithic semiconductor substrate, and it includes at least one flexible element of determined thickness attached to an anchor block on the substrate. The flexible element constitutes a moving plate of a variable capacitor whose stationary plate is constituted by a conductive zone formed in the substrate. The space between the plates is constituted by the empty gap between the flexible element and the substrate.
PRIOR ART
The technique of manufacturing such sensors suffers from a first special difficulty which is that of accurately determining the thickness of the flexible element. This dimensional feature must be determined accurately so as to make it possible to obtain a sensor of given sensitivity. A second manufacturing difficulty lies in obtaining the proper difference in level between the substrate and the flexible element, where this difference constitutes the distance between the plates which determines the initial capacitance of the variable capacitor formed in this way.
A first method of manufacturing such sensors, as described in U.S. Pat. No. 4,670,092, consists in etching a base substrate over a given depth having a relationship with the initial thickness of the substrate, thereby allowing a flexible element of corresponding thickness to remain. A drawback of that technique lies in the fact that the flexible element cannot be of small thickness since the substrate must be of relatively great thickness in order to have sufficient mechanical strength. In addition, that technique turns out to be incapable of providing a flexible element of specified thickness since base substrates have different initial thickness due to manufacturing tolerances.
To remedy that drawback, in part, it might be imagined that such sensors could be manufactured from base substrates made to tighter manufacturing tolerances. However such a solution has the consequence of increasing the manufacturing costs of such substrates prohibitively.
A second manufacturing method disclosed in the document "Extended abstracts of the Electrochemical Society", Vol. 82-1, May 1982, abstract No. 120, pp. 188-189, Pennington, N.J. USA, consists in forming an epitaxial layer serving as a stop layer for chemical etching and enabling the thickness of the flexible element to be delimited. That technique suffers from the drawback that the outline of the flexible element is poorly determined because of the anisotropic nature of chemical etching. In addition, such a method requires an epitaxial layer to be made accurately to a given thickness, thereby increasing the cost of manufacturing such sensors in a manner that is not negligible.
As disclosed in EP 89 420-370.2, a third manufacturing method has been developed for avoiding the above-specified drawbacks and enabling a sensor to be made in which the sensitive element has a thickness that can be determined at will and accurately regardless of the initial thickness of the base substrate.
That manufacturing method consists in performing operations of photoetching sensitive layers deposited on opposite faces of the substrate so as firstly to form a peripheral zone delimiting the outline of the sensor, and secondly to delimit the
REFERENCES:
patent: 4670092 (1987-06-01), Motamedi
patent: 4998179 (1991-03-01), Grantham et al.
patent: 5067647 (1991-11-01), Schwarzbauer
IBM Technical Disclosure Bulletin, vol. 30, No. 1, Jun. 1987, pp. 114-116, rmonk, N.Y., "Robotic Hot Air Solder/Desolder Placement Device".
Heinrich Samuel M.
Societe Anonyme: Vectavib
Societe d'Applications Generales d'Electricite et de Mecanique S
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