Semiconductor device manufacturing: process – Making device or circuit responsive to nonelectrical signal – Thermally responsive
Reexamination Certificate
1999-09-03
2001-05-01
Tsai, Jey (Department: 2812)
Semiconductor device manufacturing: process
Making device or circuit responsive to nonelectrical signal
Thermally responsive
C438S066000, C438S014000, C361S748000
Reexamination Certificate
active
06225141
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to methods for manufacturing electrical temperature sensors, and more particularly to techniques for calibrating such sensors.
Electrical sensors are used to measure temperature in circuits which control a wide variety of equipment, such as building heating, ventilation and air conditioning (HVAC) systems and refrigeration cases. A common type of sensor utilizes a positive temperature coefficient (PTC) silicon detector which has a resistance that varies in relation to the ambient temperature. Thus, the sensors can be connected to a control circuit to provide an input signal which indicates ambient temperature.
Each type of detector has an ideal temperature to resistance response characteristic. However, a particular detector of that type has an actual response characteristic that typically differs from the ideal response. Thus, detectors of the same type will produce slightly different electrical signals when exposed to the same temperature. Furthermore, it often is desirable to optimize the response characteristic for a range of temperatures, for example a range which enables the device to be used in either a refrigeration case or a building room. The detector response characteristics also may have to be adjusted to be compatible with the control circuits.
As a consequence, in order to accurately measure temperature, it is necessary to calibrate the detector, that is change the actual response of the detector to match the ideal desired response as closely a practical. Calibration typically is accomplished by connecting trimmer resistors to the detector to form the complete temperature sensor. Specifically, one trimmer resistor is placed in series with the detector to offset the actual temperature response to the level of the ideal desired response. Another trimmer resistor is placed in parallel with the temperature detector to change the gain of the sensor (i.e. adjust the slope of the temperature response characteristic) to match the ideal desired response.
Previous calibration techniques required a significant amount of manual labor. Specifically, individual detectors were placed into a precision oven and heated to two different temperatures near the extremes of the desired temperature range for the completed sensor. The electrical signal produced by the sensor at each temperature was measured. These measurements then were fed into a computer which calculated values for the two trimmer resistors. Assembly workers then selected the appropriate valued resistors which were hand soldered to the detector in order to produce a finished calibrated temperature sensor. This process not only was labor intensive, but time consuming.
SUMMARY OF THE INVENTION
The present invention is directed to a process for mass producing calibrated temperature sensors which lends itself to the utilization of automated production equipment. The method involves defining a plurality of cells on a printed circuit board. Each cell contains electrically conductive first and second contact pads and first and second detector pads, with the first detector pad electrically connected to the first contact pad. A separate temperature detector is attached to the first and second detector pads in each cell.
Then a temperature response characteristic of the separate temperature detector in each cell is measured, thereby producing a measured temperature response characteristic associated with each cell. In the preferred embodiment the temperature response characteristic measurement includes exposing the printed circuit board to a first predefined temperature and then reading a first electrical signal from the temperature detector in each cell. Next, the printed circuit board is exposed to a second predefined temperature, and a second electrical signal is read from the temperature detector in each cell.
The measured temperature response characteristic associated with the given cell then is employed to derive a series resistance and a parallel resistance for the given cell, where the series resistance and the parallel resistance compensate for a difference between the measured temperature response characteristic and a desired response characteristic. First and second resistors having values corresponding to the series and parallel resistances are electrically connected to the temperature detector in the given cell. The derivation of the resistances and connection of resistor is performed for each cell of the printed circuit board.
Finally the printed circuit board is severed into the individual cells thereby producing a plurality of calibrated temperature sensors.
REFERENCES:
patent: 5844238 (1998-12-01), Sauer et al.
patent: 6118426 (2000-09-01), Albert et al.
Garcia Fernando F
Rudich George
Schultz Bruce R
Stier Frank J
Van Eldick Henkerikus C
Haas George E.
Johnson Controls Technology Co.
Quarles & Brady
Tsai Jey
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