Measuring and testing – Speed – velocity – or acceleration – Acceleration determination utilizing inertial element
Patent
1996-03-01
1998-03-31
Williams, Hezron E.
Measuring and testing
Speed, velocity, or acceleration
Acceleration determination utilizing inertial element
7351432, 73754, 361280, G01P 1500, G01L 900, H01G 700
Patent
active
057341060
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
The present invention relates to an integrated electronic sensor for characterizing a physical quantity incorporating a characterizing member, whereof one part is mobile.
The invention more particularly applies to the field of microelectronics, where the development of micromachining methods permits the production of characterizing members able to transform quantities such as acceleration, pressure or flow into characterizable electrical effects by the measurement or acquisition of signals on a hit and miss basis.
Sensors of this type have a characterizing member mobile relative to a substrate which, on deforming or moving, creates either an electrical potential, or gives rise to the modification of the value of a capacitor, inductance or resistor. The modification of these characteristics is exploited by an electronic reading circuit associated with the component. An illustration of the technologies involved in sensors is given by the article "Low-cost integrated silicon sensor" by Fouad Rahali et al., 9th European Hybrid Microelectronics Conference, pp 243 to 249.
These sensors also have a cover, which has a number of functions. It must protect the characterizing member against environmental stresses and must permit its maintenance, particularly in the case of physical stresses exceeding the mechanical limits of the member.
In an accelerometer incorporating a seismic mass able to move under the effect of an acceleration, the cover serves as an abutment for preventing an exaggerated displacement of the mass, which may give rise to the deterioration thereof.
Generally, a spacing is provided between the cover and the sensitive characterizing member so as to prevent, in normal operation, contact between said two parts. Thus, the cover does not impede the movement of the characterizing member and leads to no deterioration of the result of the measurements. Such an arrangement is described in U.S. Pat. No. 5,164,328, where the cover is also formed by an integrated circuit substrate. It is known from the latter document to assemble the cover and the substrate having the characterizing member by means of an interconnection procedure using meltable material balls and generally known as flip chip.
This procedure consists of depositing on one of the parts to be assembled, meltable material assembly rolls or balls and to raise the two parts to be assembled, which face one another, to a temperature slightly above the melting point of the material of the balls, so as to bring about a type of brazing.
Preferably, on the parts to be assembled are previously formed interconnection elements constituting a wetting surface with respect to the balls or rolls. The elements respectively of each part to be assembled are positioned facing one another and the balls are only deposited on the elements of one of the parts.
The assembly of the cover and the substrate incorporating the characterizing member by the flip chip procedure is very interesting, because the interconnection balls ensuring the cohesion of the structure also permit an electric contact when they are conductive. Another essential function of the balls is to maintain and define the spacing between the cover and the characterizing member.
Unfortunately, this solution is difficult to apply in numerous sensors.
Thus, due to a miniaturization of the sensors linked with the emergence of new machining technologies on the surface (such as etching), the spacing between the cover and the sensitive characterizing member must be very small and in particular obtained with very high precision. For example, in the case of an accelerometer, there is a spacing of 2 to 5 .mu.m between the cover and the seismic mass.
However, with existing flip chip interconnection procedures, it is very difficult to attain spacings below 15 .mu.m with a sufficient accuracy.
Moreover, when the interconnection balls are of small size for reducing the spacing between the cover and the characterizing member, thermomechanical behavioural problems occur.
As the expansion coefficients of the
REFERENCES:
patent: 4930043 (1990-05-01), Wiegand
patent: 5164328 (1992-11-01), Dunn et al.
patent: 5355283 (1994-10-01), Marrs et al.
Quinnell, "Silicon Accelerometers Tackle Cost-Sensitive Applications," End-Technology Update (EDN Electrical Design News)--vol. 37(18), pp. 69-76 (1992).
Rahali, et al., "Low-Cost Integrated Silicon Sensors for Industrial Applications," 9th European Hybrid Microelectronics Conference (Session 2B)--pp. 242-249.
Commissariat a l 'Energie Atomique
Moller Richard A.
Williams Hezron E.
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