Electrical resistors – Mechanically variable – Movable contact electrically adjustable over length of...
Reexamination Certificate
2000-11-30
2001-11-13
Easthom, Karl D. (Department: 2832)
Electrical resistors
Mechanically variable
Movable contact electrically adjustable over length of...
C338S163000, C338S166000, C338S174000
Reexamination Certificate
active
06317022
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a low-profile and small-sized variable resistor, and more particularly, to the structure of the external connection portion of a metallic terminal that is insert-molded in a board.
2. Description of the Related Art
As a known example of a variable resistor, Japanese Unexamined Patent Application Publication No. 9-223608 discloses a variable resistor wherein a first metallic terminal having a grommet is insert-molded in a board, second metallic terminals are also insert-molded in the board. A substantially arcuate resistor conductive to the second metallic terminal is provided on the top surface of the board. A slider having a drawn portion with a hole provided at the center thereof is fitted to the grommet of the first metallic terminal. The grommet is caulked in a outwardly opened state, and thereby the slider is rotatably installed on the board to be being electrically connected with the first metallic terminal. A contact arm portion sliding on the resistor, and an adjusting portion rotationally operated with a tool such as a driver, are integrally provided with the slider.
In the above-described variable resistor, since the external connection portions of the first and second metallic terminals are constructed to be led out of the bottom of the board, and folded upwardly toward the top surface side, the product can be made low-profile, and soldering of the external connection portions to the board is facilitated.
When bending is performed with respect to the external connection portions of the metallic terminals, bending stresses are concentrated on the board portions holding the external connection portions. However, once the external connection portions of the metallic terminals are led out along the bottom of the board as described above, the terminal holding power of the board is reduced, such that the metallic terminals generate looseness. In particular, since one end portion of each of the second metallic terminals is exposed on the top surface of the board, and this exposed portion is electrically connected with the resistor provided on the top surface of the board, the occurrence of the loose metallic terminals causes an unstable electrical connection between the metallic terminals and the resistor, and deteriorates the characteristics of this variable resistor.
SUMMARY OF THE INVENTION
To overcome the above described problems, preferred embodiments of the present invention prevent bending strain from spreading from the conductive portions to a resistor when bending is executed with respect to the external connection portions of the metallic terminals, and provide a low-profile variable resistor capable of stabilizing the electrical connections between the metallic terminals and the resistor.
A first preferred embodiment of the present invention provides a variable resistor including a board in which a first metallic terminal is insert-molded, on the top surface of which a substantially arcuate resistor is provided, and in which second metallic terminals having conductive portions conductive to the resistor are insert-molded, and a slider having a contact arm portion sliding on the resistor and having an adjustable portion rotationally operated with a tool, the slider being rotatably attached on the board in a state of being electrically connected with the first metallic terminal. In this variable resistor, external connection portions led out of the bottom of the board are integrally provided with the first and second metallic terminals and a notch is provided at a portion of each of the external connection portions, the portion being adjacent to the board, and the external connection portions are each folded upwardly at the positions of the notches, along the corresponding sides of the board.
When folding the external connection portions of the metallic terminals upwardly, bending stresses act on the metallic terminals, and the board is subjected to a load caused by the stress. However, since the external connection portions each have notches previously provided therein, they can be folded without imposing a substantial load on the board. This prevents the loosening of the metallic terminals from occurring, and allows the electrical connection between the metallic terminals and the resistor to be stabilized. At the same time, the electric connection between the first metallic terminal and the slider is also stabilized.
Since the external connection portions of the first and second metallic terminals are led out of the bottom of the board, the product is low-profile. Also, since the external connection portions of the metallic terminals are each folded upwardly along the corresponding sides of the board, fillets are each provided between the external connection portions and the printed circuit board when the variable resistor is soldered to the printed circuit board, and thereby an outstanding solder connection is easily achieved.
As in the above-described conventional example, when folding external connection portions of the metallic terminals each having no notches at right angles, the outer peripheral surfaces thereof is expanded, such that cracks occur on the plated surfaces of the terminals, and the wettability of solder is susceptible to deterioration. On the other hand, as in various preferred embodiments of the present invention, when folding each of the external connection portions of the metallic terminals at the position of a notch provided therein, the expansion amount of the outer peripheral surface of each of the external connection portions is greatly reduced, and the occurrence of cracks on the plated surface thereof is prevented.
Preferably, a gap having a space is provided in which no capillary effect of the soldering flux occurs between each of the folded portions of the first and second metallic terminals and the corresponding side of the board. In general, when decreasing the height of the variable resistor, there is the possibility that soldering flux intrudes into each of the gaps between the metallic terminals and the printed circuit board during the soldering of the variable resistor to the board, and that the flux is sucked up by the capillarity with the result that the flux adheres to the printed surface of the resistor. As a consequence, the electrical connection between the resistor and the slider is unstable, and the characteristics of the variable resistor are prone to deteriorate.
In contrast to this, in accordance with a second preferred embodiment of the present invention, the possibility of flux adhering to the printed surface of the resistor is eliminated, by setting the above-described gap to a dimension such that no capillary effect of soldering flux occurs. Meanwhile, in various preferred embodiments of the present invention, since each of the bending positions of the external connection portions is defined by a notch, the distance between each of the folded portions and the corresponding side of the board is set to a constant value.
Other features, characteristics, elements and advantages of the present invention will become apparent from the following description of preferred embodiments thereof with reference to the attached drawings.
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patent: 09/223608 (1997-08-01), None
Easthom Karl D.
Keating & Bennett LLP
Murata Manufacturing Co, Ltd.
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