U.S. patent number 3,573,703 [Application Number 04/823,350] was granted by the patent office on 1971-04-06 for resistor and method of adjusting resistance.
Invention is credited to Darnall P. Burks, John P. Maher.
United States Patent |
3,573,703 |
Burks , et al. |
April 6, 1971 |
RESISTOR AND METHOD OF ADJUSTING RESISTANCE
Abstract
A resistor is formed on an insulating support between a pair of
electrode terminals, a portion of the resistor extending out of the
direct field established between the electrodes. The resistance
value is precisely adjusted by removing resistor material in the
fringing field.
Inventors: |
Burks; Darnall P.
(Williamstown, MA), Maher; John P. (North Adams, MA) |
Family
ID: |
25238509 |
Appl.
No.: |
04/823,350 |
Filed: |
May 9, 1969 |
Current U.S.
Class: |
338/309; 338/195;
29/620 |
Current CPC
Class: |
H01C
17/245 (20130101); Y10T 29/49099 (20150115) |
Current International
Class: |
H01C
17/22 (20060101); H01C 17/245 (20060101); H01c
007/00 () |
Field of
Search: |
;338/195,309,308
;29/620 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Goldberg; E. A.
Claims
We claim:
1. A method of precisely adjusting a thick film resistor which
comprises the steps of:
positioning a pair of electrode terminal on an insulating
substrate;
depositing a resistor film on the substrate overlying the area
between said electrode terminals and an additional area extending
beyond said area between said terminals, whereby a direct field is
established across the film between the electrodes while a fringing
field is established across the resistor film lying outside the
electrode encompassing area;
first removing a portion of the resistance film lying in said
direct field to cause a rough adjustment in the resistance value;
and
second removing a portion of the resistance film lying in said
fringing field so as to adjust to the final desired resistance
value.
2. A resistor comprising an insulating support; a pair of electrode
terminals carried by said support; a resistance film on the support
having a first portion of nonuniform width extending between and in
contact with both of said terminals and across which a direct field
will be established, a second portion of said resistance film
extending beyond the area confined between the two electrodes and
across which a fringing field will be established, the extending
portion also being of a nonuniform width, the nonuniform width of
the two portion resistance film having been made by removing parts
of the film for adjusting resistance value.
Description
BACKGROUND OF THE INVENTION
This invention relates to thick film resistors, and more
particularly to adjusting deposited thick film resistors to their
final value.
Present techniques call for trimming the required resistor material
from an area lying in the direct field of the electrodes. Trimming
critically affects the resistance value and requires extremely fine
trimming techniques. Present trimming techniques either result in
unacceptable tolerance levels or have percentage of adjustment
limitations imposed by the amount of area available for
trimming.
It is therefore an object of the present invention to provide a
thick film resistor trimmed to a very precise value.
It is a further object to provide a method for accurately adjusting
such a resistor.
It is a still further object to provide such a resistor adjustable
to up to 30 percent.
SUMMARY OF THE INVENTION
Broadly, this invention provides accurate adjustment of a thick
film resistor deposited on a substrate between two electrodes. A
sufficient amount of the resistor lying outside of the direct area
between the electrodes is provided to permit the establishment of a
fringing field above the direct field established between the two
electrodes.
In one embodiment, the resistor is precisely adjusted by trimming
away resistor material wholly contained within the established
fringing field. In another embodiment, resistor material in both
fields is trimmed.
It has been found that removal of resistor material located in the
fringing field has less of an effect than removal of the same
amount of material in the direct field i.e., more resistor material
must be removed from the fringing field than in the direct field to
effect the same unit change in resistance. This discovery permits
extremely fine adjustments not possible by conventional methods,
and also permits larger percentage adjustments depending on the
amount of the available resistor material in the fringing
field.
DETAILED DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a top view of a resistor formed according to this
invention; and
FIG. 2 illustrates a top view of an alternate embodiment of the
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1, the component 10 comprises an insulating
substrate 11 upon which is positioned a pair of spaced electrodes
12 and 13. Resistor material 14 is deposited between the
electrodes. A portion 15 of the material 14 lies in the direct
field established between the two electrodes 12, 13 while the
remaining portion 16 of the resistor material 14 lies in the
fringing field of the electrodes. The resistor 10 has been adjusted
to a desired value by removing a selected area 17 from resistor
material portion 16. Since resistor material 16 lies within the
fringing field, more resistor material can be removed per unit
change in resistance than if the material to be trimmed lay in the
direct field. This characteristic permits an extremely precise
resistance adjustment to be made. Actual trimming may be performed
by any desired abrasive technique.
The above adjustment technique may be used to provide the complete
adjustment required or it may be used in conjunction with the
method of trimming shown in FIG. 2. There, an initial rough
adjustment is made by cutting away area 20 from resistor material
24 in the direct field between electrodes 22 and 23. The fine
adjustment is made by trimming away the required amount of material
27 from area 26 in the fringing field resistor material.
An example of the invention is as follows. A pair of spaced silver
electrodes is deposited on a substrate of A1.sub.2O.sub. 3.
Deposited over and between the electrodes as shown in FIG. 1 is a
resistance film having a resistivity of 1.1 Kilohms per square. The
film has approximately 50 percent of its area in the direct
electrode field with the remaining area in the gradually weakening
electrode fringing field.
The overall resistance of the unit was originally 820 ohms and it
was desired to trim the value to 1 Kilohms with an adjustment
tolerance of 0.03 percent. Twenty percent of the film lying in the
direct field was removed by sand abrasion, bringing the resistance
to 960 ohms. Then 60 percent of the area of the fringing field was
removed to bring the resistance to the final value of 1,000
ohms.
* * * * *