Measuring and testing – Instrument proving or calibrating – Fluid pressure
Reexamination Certificate
2001-01-04
2004-02-10
Oen, William (Department: 2855)
Measuring and testing
Instrument proving or calibrating
Fluid pressure
Reexamination Certificate
active
06688156
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a tester for pressure sensors in a wafer structure or for isolated pressure sensors as well as for isolated open pressure sensors having a recess for the pressure sensors as well as means for electrical contacting of the electrical connections of at least one of the pressure sensors.
BACKGROUND OF THE INVENTION
Pressure sensors on a micromechanical basis contain a pressure-sensitive element that upon the application of pressure are at least partially deflected from a resting position. As a result of this deflection/bending, a change in electrical voltage similar to a piezoelectric structural element is indicated. This change in electrical voltage is generally amplified by a corresponding evaluation circuit and is largely proportional to the compressive load. Such pressure sensors are commonly produced by semiconductor technology in a wafer compound and have, for example, a sensor chamber etched into the silicon substrate, one side of which is designed as a diaphragm or sensor element, and which are provided with an aperture or a sensor intake facing this sensor element. In addition, electrical connections for the power supply for the reading the measured values are found on one side of the pressure sensor, while logic circuits and/or amplifying circuits may also be incorporated.
After completion of the pressure sensors in a wafer structure, the sensors are separated by abrasive cutting into individual pressure sensors/chips, which are then assembled in housings. This final assembly is then followed by functional testing and, if necessary, calibration of the amplifier circuit to the pressure sensor, while any defective pressure sensors are removed.
It is apparent that the fabrication of pressure sensors requires a considerable expenditure of resources and that it is especially disadvantageous that functional testing of pressure sensors is only performed in the completed state.
OBJECTS AND SUMMARY OF THE INVENTION
An object of the invention therefore is to provide a tester for pressure sensors which can test pressure sensors which are partially assembled, pressure sensors that are still in the wafer structure, as well as isolated open pressure sensors for their proper function and with which it is possible to accommodate the functional characteristics of the pressure sensors.
The object on which the invention is based is accomplished in a tester by which a static or dynamic pressure of a specified amount and duration is capable of being exerted on the sensor element of at least one selected pressure sensor so that its sensor element is moved out of its resting position while the electrical connections of the selected pressure sensor are connected with an electrical evaluation unit.
A first embodiment of the invention includes an assembly that is designed as a pressure chamber for the production of a static pressure, in which the tester is wholly or partially arranged with the pressure sensors located in a recess.
In a second embodiment of the invention, a pressure head is provided which has an interior space open on one side, the open face of which is capable of being mounted on the selected pressure sensor in such a way that the interior space is tightly sealed by the latter. When the tight seal has been obtained, the desired internal pressure can then be built up, including for example stepwise, and the varying electrical parameters on the electric contacts measured.
This makes it possible to select each of the pressure sensors in the wafer structure successively and to mount it on the pressure head accordingly. In addition, this design also makes it possible to test the operation of individual pressure sensors removed from the wafer structure or even partially assembled pressure sensors.
In addition, the pressure head can be connected with a device for the production of a specified pressure in the interior space of the same.
For the control of internal pressure, a pressure-measuring probe is preferably located in the interior space of the pressure head.
In an additional embodiment of the invention, an arrangement of electrical connections of the pressure sensor is assigned to the pressure head. This electrical contacting may be effected by needle probes provided in the interior space of the pressure head. This is advantageous when the electrical connections are arranged on the upper surface of the pressure sensor.
Since the electrical connections may alternatively be provided at a different location on the pressure sensor, another embodiment of the invention is characterized in that the arrangement of the electrical connections of the pressure sensor and the pressure head are positionable independently of one another on or under the selected pressure sensor.
In order to obtain a sufficient seal between the pressure head and the pressure sensor, in another embodiment of the invention the pressure head is capable of being mounted on the pressure sensor with a specified compressive force, where the compressive force is produced by a weight or elastic force. There the face of the pressure head may be designed as a sealing surface, or a sealing element can be inserted in the face. The compressive force required for a sufficient seal may alternatively be produced by suction with vacuum. To this end, a vacuum groove that is connected with a vacuum-producing device, is incorporated in the face of the pressure head.
A third embodiment of the invention includes a thermochuck for the accommodation of pressure sensors located in the wafer structure. In this case, the wafer is arranged face down on the thermochuck in such a way that the sensor intakes of the pressure sensors, arranged in a grid, rest directly on the thermochuck. The thermochuck is provided with a grid of holes, and the grid of the sensor intakes matches the grid of the holes of the thermochuck. This embodiment of the invention is generally provided for pressure sensors in which the electrical connections lie on the back, i.e., are arranged on the side that faces the sensor element.
In order to ensure sufficient adhesive force on the thermochuck during the application of pressure to individual pressure sensors, the holes in the thermochuck are selectively individually connectable with a means for production of a positive pressure or with a means for production of a negative pressure such that if a positive pressure is produced in a hole, then adjacent holes must simultaneously be impacted by a negative pressure.
In order to reduce the expenditure for control of the pressure applied to the holes, a preferred refinement of the invention that the holes are capable of being acted on by pressure in a groupwise or alternatively linewise manner, and the holes adjacent to the selected group or line are capable of being acted on by negative pressure, also in a groupwise or linewise manner. For establishing electrical contact, the pressure sensors of a selected line can be electrically contacted simultaneously, so that simultaneous evaluation of the test results is possible.
A fourth embodiment of the invention is characterized in that a pressure head for production of a flow in the direction of a sensor intake or a sensor element of a selected pressure sensor for production of a dynamic stagnation pressure is provided. This embodiment of the invention, universally applicable per se, is especially suitable for pressure sensors that have a particularly sensitive or uneven surface structure since, in contrast to the other embodiments of the invention, it is not necessary here for the pressure head to be mounted on the pressure sensor. Hence, the risk of any mechanical damage is avoided.
The pressure head is preferably equipped with a vertically aligned tubule whose lower opening in working position ends at a specified distance above the pressure sensor and whose other end is connected with a pressure-measuring chamber and a test pressure supply line.
Since the pressure head is positioned over each selected sensor element, a further development of the invention is characterized in that,
Dietrich Claus
Hirschfeld Botho
Runge Dietmar
Schneidewind Stefan
Teich Michael
Baker & Botts LLP
Karl Suss Dresden GmbH
Oen William
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