Electrical resistors – Mechanically variable – Resistance value varied by removing or adding material
Reexamination Certificate
2000-07-21
2001-09-18
Easthom, Karl D. (Department: 2832)
Electrical resistors
Mechanically variable
Resistance value varied by removing or adding material
C338S287000, C338S307000, C029S620000
Reexamination Certificate
active
06292091
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a resistor of the type which includes an insulating substrate and a resistor layer formed on the substrate. The present invention also relates to a method of adjusting the resistance of such a resistor.
2. Description of the Related Art
Conventionally, resistors of the above type have been widely used e.g. for manufacturing various kinds of electric appliances. An example of such resistors is shown in
FIG. 13
of the accompanying drawings. The conventional device includes a rectangular substrate
20
made of e.g. a ceramic material, an elongated resistor layer
21
formed on the substrate, a pair of terminal electrodes
22
, and a protection cover (not shown) for protecting the resistor layer
21
and the terminal electrodes
22
. In the resistor layer
21
, a trimming groove
23
is formed for adjusting the resistance of the device. The conventional device is mounted on a printed circuit board (not shown) with the terminal electrodes
22
soldered to the wiring pattern of the circuit board.
The trimming groove
23
of the conventional device is provided at a longitudinally central portion of the resistor layer
21
. Due to this arrangement, the conventional device has the following disadvantage.
Specifically, the trimming groove
23
causes the central portion of the resistor layer
21
to have a higher resistance than the remaining portions of the resistor layer. Thus, in use, much heat (Joule heat) will be generated at the central portion of the resistor layer
21
other than the remaining portions of the layer. In an extreme case, most of the heat may be generated only at the central portion of the layer
21
(“localization of heat generation”). According to the conventional arrangement, however, the heat at the central portion of the layer
21
cannot be effectively conducted to the wiring pattern of the circuit board via the terminal electrodes
22
, since the central portion of the layer
21
is located apart from these terminal electrodes. As a result, Joule heat may build up at the central portion of the resistor layer
21
, which is disadvantageous for maintaining the proper function as a resistor.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a resistor by which the above-described problem of localization of heat generation is overcome.
Another object of the present invention is to provide a resistor in which adjustment of resistance by laser trimming is accurately performed.
Still another object of the present invention is to provide a method of adjusting the resistance of a resistor.
According to a first aspect of the present invention, there is provided a resistor which includes: an insulating substrate; a resistive layer formed on the substrate and divided into at least a first portion of greater resistance and a second portion of smaller resistance; and first and second terminal electrodes connected to the resistive layer. The first portion is closer to the first terminal electrode than the second portion is.
With such an arrangement, the localization of heat generation is advantageously overcome since the first portion of greater resistance is arranged closer to the first terminal electrode than the second portion is.
Preferably, the second portion of smaller resistance is formed with a trimming groove for resistance adjustment. In this manner, the resistance adjustment is performed more finely than when the trimming groove is formed in the first portion of greater resistance.
According to a preferred embodiment, the first portion may have a wavy configuration. In this manner, the effective length (i.e., the length measured along the wavy path) of the first portion can be rendered sufficiently long even in a rather small area.
Preferably, the resistive layer may be provided with a bypass element connected to the first portion of the resistive layer for enabling optional adjustment of the resistance of the resistor.
In a preferred embodiment, the first portion is provided with a plurality of turns at which the bypass element is connected to the first portion.
Preferably, the resistive layer may include a third portion whose resistance is greater than the resistance of the second portion. The third portion may be arranged adjacent to the second terminal electrode for facilitating heat conduction from the third portion to the second terminal electrode.
Preferably, each of the first and the third portions may have a wavy configuration.
In a preferred embodiment, the resistor of the present invention may further comprise first and second sets of connection bumps, wherein the first set of connection bumps are connected to the first terminal electrode, while the second set of connection bumps are connected to the second terminal electrode.
Preferably, the resistor of the present invention may further comprise a protection cover formed on the substrate to cover the resistive layer and the terminal electrodes. In this case, the connection bumps are arranged to protrude from the protection cover for establishing connection to an external component.
In a preferred embodiment, the second portion of the resistive layer may have a strip-like configuration.
In another preferred embodiment, the second portion of the resistive layer may have a lattice-like configuration.
The second portion may be trimmed in an L-shaped manner, a crank-shaped manner, a spiral manner, etc.
According to a second aspect of the present invention, there is provided a resistor comprising: an insulating substrate; a resistive layer formed on the substrate; first and second terminal electrodes formed on the substrate; and first and second connectors to connect the resistive layer to the first and the second terminal electrodes, respectively. The resistive layer has a lattice-like configuration for enabling the user to perform accurate adjustment of the resistance of the resistor.
Preferably, the resistive layer may include a plurality of first segments extending in one direction and a plurality of second segments extending in another direction perpendicular to said one direction.
According to a third aspect of the present invention, there is provided a method of adjusting resistance of a resistor. The method may comprise the steps of: forming a resistive layer provided with a lattice-like portion which includes a plurality of first segments extending in one direction and a plurality of second segments extending in another direction perpendicular to said one direction; and trimming at least one of the first and the second segments.
Preferably, the trimming may be performed first for rough adjustment of resistance and then for finer adjustment of resistance. For achieving this, the lattice-like portion may be trimmed in an L-shaped manner. Further, the resistive layer may include a wavy portion provided with a bypass element, and this bypass element is to be selectively trimmed for resistance adjustment.
Other features and advantages of the present invention will become apparent from the detailed description given below with reference to the accompanying drawings.
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Kiang et al. “Fold. Patt. Filim Resist. w. Trimm. Elem. in
Kambara Shigeru
Teramae Toshihiro
Bednarek Michael D.
Easthom Karl D.
Rohm & Co., Ltd.
Shaw Pittman LLP
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