JPH0445209Y2 - - Google Patents

Description

[Detailed description of the invention] [Field of industrial application] The present invention relates to a semi-fixed variable resistor that allows fine adjustment of the resistance value during or after assembly of an electric circuit, and is particularly applicable to reflow soldering. This invention relates to a semi-fixed variable resistor suitable for soldering.

[Conventional technology]

Recently, a mounting structure in which semi-fixed variable resistors are soldered using dip soldering has become widely adopted, and along with this, an airtight cover has been installed to prevent solder and flux from entering during dip soldering. Semi-fixed variable resistors are becoming popular.

FIG. 3 is a side sectional view showing a conventional example of this type of semi-fixed variable resistor. In the figure, 1 is a molded case, and the molded case 1 consists of a square base 2 and a cylindrical part 3, and has an opening 3a on the upper side of the cylindrical part 3. 4 is the mold case 1
a resistance board housed in the cylindrical part 3 on the base 2 of the
5 is a slider rotatable on the resistance board 4;
The slider 5 is provided with a groove-shaped engagement portion 5a. Reference numeral 6 denotes an eyelet member that is loosely fitted into the insertion hole 4a of the resistance board 4, and the upper end of the eyelet member 6 is caulked to the inner circumference of the slider 5 so as to be in sliding contact with the slider 5. , one end of the eyelet member 6 forms an intermediate terminal 6a and penetrates the molded case 1;
It holds the base 2 and is led out to the lower surface of the base 2. Terminals 7 (not shown) are connected to both ends of the resistor, and similarly to the intermediate terminal 6a, they hold the base 2 of the molded case 1 and are led out to the lower surface of the base 2. 8 is a heat-resistant airtight cover made of polyimide or the like, which is attached to the mold case 1.
The opening 3a is fixed to the upper end surface of the peripheral edge of the opening 3a by adhesive, welding, or the like, thereby closing the opening 3a.

When attaching such a semi-fixed variable resistor to a circuit board (not shown), after temporarily fixing the terminals 6a and 7 of the semi-fixed variable resistor to the pattern of the circuit board together with other electronic components, The surface is immersed in a solder bath to perform dip soldering, and each terminal 6a, 7 is soldered to the pattern. During this dip soldering, if solder or flux intrudes into the inside of the mold case 1, there is a risk that the function of the semi-fixed variable resistor will be inhibited. There is no need to worry about this, and since the sealing cover 8 is heat resistant and can withstand the temperature of molten solder (approximately 260°C), the sealing cover 8 itself will not melt.

After the semi-fixed variable resistor is attached to the circuit board in this way, an adjustment jig such as a screwdriver is engaged with the engaging portion 5a of the slider 5 to rotate the slider 5. This allows a desired resistance value to be set.

[Problem that the invention attempts to solve]

By the way, in the dip soldering method in which electronic components are immersed in a solder bath, the heat of the molten solder acts directly on the electronic components. The dip soldering method is not suitable for soldering on the same surface. Therefore, in such a case, after temporarily fixing the terminals 6a and 7 of the semi-fixed variable resistor to the cream solder applied to the pattern of the circuit board, the cream solder is removed by radiant heat from a heat source such as an infrared lamp. However, in such reflow soldering, the radiant heat from the heater acts on the resistor board 4 through the transparent or translucent sealing cover 8, so the resistance characteristics deteriorate at high temperatures. It was not possible to use carbon resistors, and expensive metal-grace resistors had to be used.

Therefore, the purpose of the present invention is to solve the above-mentioned problems of the prior art, and even if an inexpensive carbon resistor is used,
To provide a semi-fixed variable resistor that does not cause characteristic deterioration of resistance value during reflow soldering.

[Means to solve the problem]

The object of the present invention described above is to rotatably provide a slider having an engaging part for engaging an adjustment jig on a resistor board, and to install the slider in a molded case having an opening at the top. In a semi-fixed variable resistor equipped with a resistor substrate, this is generally achieved by attaching a cover made of a synthetic resin film and a heat reflective layer provided on the upper surface of the synthetic resin film to the opening of the molded case. be done.

[Effect]

That is, with the above configuration, the heat radiated from the heat source during reflow soldering is reflected by the heat reflective layer of the cover attached to the opening of the mold case, so that the resistor disposed inside the opening A carbon resistor that is sensitive to heat but inexpensive can be formed on the substrate.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a side sectional view showing an embodiment of a semi-fixed variable resistor according to the present invention, in which reference numeral 9 denotes a cover;
9a is a base film, 9b is a heat reflective layer,
Parts corresponding to those in FIG. 3 are given the same reference numerals.

In the figure, a molded case 1 includes a rectangular base 2 and a cylindrical portion 3 having a rectangular outer shape, and has a circular opening 3a on the upper side of the cylindrical portion 3. A resistance board 4 installed on the base 2 and a slider 5 rotatable on the resistance board 4 are housed in the cylindrical part 3 of the molded case 1. A groove-shaped engaging portion 5a is provided in the groove-shaped engaging portion 5a. An eyelet member 6 is loosely fitted into the insertion hole 4a of the resistance board 4, and the upper end of the eyelet member 6 is caulked to the inner circumferential surface of the slider 5 and comes into sliding contact with the slider 5. ing. Further, one end of this eyelet member 6 forms an intermediate terminal 6a, passes through the molded case 1, embraces the base 2, and is led out to the lower surface of the base 2. Further, although not shown, a resistor made of carbon ink is printed on the resistor substrate 4, and the terminals 7 connected to both ends of the resistor are molded into the mold case 1 as well as the intermediate terminals 6a. It embraces the base 2 and is led out to the lower surface of the base 2.

On the other hand, a cover 9 is fixed to the upper end of the periphery of the opening 3a of the molded case 1 by adhesive, fusion, or the like. This cover 9 has a two-layer structure including a lower base film 9a made of polyimide or the like, and a heat reflective layer 9b formed by vapor depositing or sputtering aluminum or the like on the base film 9a.

In the semi-fixed variable resistor having the above configuration, each terminal 6a, 7 is soldered to a pattern on a circuit board (not shown) by performing reflow soldering. That is, after temporarily fixing the terminals 6a and 7 of the semi-fixed variable resistor to the cream solder applied to the pattern of the circuit board, if this semi-fixed variable resistor is sent below a heat source such as an infrared lamp, the heat source will be removed. The cream solder is melted by radiant heat and reflow soldering is performed. At this time, most of the radiant heat to the upper surface of the molded case 1 is reflected by the heat reflective layer 9b of the cover 9, so the temperature rise of the carbon resistor located inside the opening 3a is suppressed, and the resistance characteristics are improved. It will not deteriorate.

FIG. 2 is a side sectional view of a semi-fixed variable resistor according to another embodiment of the present invention, in which reference numeral 10 indicates a positioning mark and 11 an adjustment jig, parts corresponding to those in FIG. Detailed explanation will be omitted by assigning the same reference numerals to .

In the case of this embodiment, a positioning mark 10 is displayed on the upper surface of the cover 9 in advance by printing or other means, and the display position of the positioning mark 10 corresponds to the engaging portion 5a of the slider 5 during assembly. The cover 9 is fixed to the molded case 1 in this state, that is, with the positioning mark 10 positioned above the engaging portion 5a. Therefore, the cover 9 has become opaque due to the presence of the heat reflective layer 9b.
The position of the engaging portion 5a of the slider 5 housed below can be visually recognized indirectly from the outside by the positioning mark 10.

In the semi-fixed variable resistor having the above configuration, each terminal 6a, 7 is soldered to a pattern on a circuit board (not shown) by performing reflow soldering as in the first embodiment. Then, when adjusting the resistance value after installing the semi-fixed variable resistor on the circuit board,
As shown in FIG. 2, an adjustment jig 11 such as a driver
As long as the tip of the holder is brought into contact with the positioning mark 10 and the cover 9 is broken through, the engaging portion 5a will automatically close.
This eliminates the need for complicated operations such as peeling off the cover 9 and finding the engaging portion 5a by trial and error. The resistance value can be set.

[Effect of idea]

As explained above, according to the present invention, the heat reflective layer of the cover can suppress the radiant heat from the heat source for melting the solder from reaching the inside of the mold case. It is now possible to use carbon resistors, which are considered to be weak against heat, and since the cover has a two-layer structure of a synthetic resin film and a heat reflective layer, it has high breakage strength against impact, but cannot be broken by jigs such as screwdrivers. It is possible to provide a semi-fixed variable resistor that has a simple cover, is inexpensive, and does not deteriorate its resistance characteristics.

[Brief explanation of the drawing]

FIG. 1 is a side sectional view of a semi-fixed variable resistor according to an embodiment of the present invention, FIG. 2 is a side sectional view of a semi-fixed variable resistor according to another embodiment of the present invention, and FIG. 3 is a conventional FIG. 2 is a side cross-sectional view of an example semi-fixed variable resistor. 1...Mold case, 3a...Opening, 4...
Resistance board, 5...Slider, 5a...Engaging portion, 9...
... Cover, 9a ... Base film, 9b ... Heat reflective layer, 10 ... Positioning mark, 11 ... Adjustment jig.

Claims (1)

[Scope of utility model registration request] A slider having an engaging part for engaging an adjustment jig is rotatably provided on a resistor board, and the slider and the resistor board are arranged in a molded case having an opening at the top. 1. A semi-fixed variable resistor, characterized in that a cover made of a synthetic resin film and a heat reflective layer provided on the upper surface of the synthetic resin film is attached to the opening of the mold case.