Molded resin casing of electronic part incorporating flexible board.

An electronic part such as a rotary- or sliding-type variable resistor, a rotary- or sliding-type code switch or the like which finds use in electronic apparatus includes a board on which various patterns are formed, a casing, and a slider having contacts brought into sliding contact with the patterns formed on the board. The board is fixed to the bottom of the casing and the slider is supported on the board so as to rotate or slide freely. The components such as the board, the casing and the slider are manufactured as separate elements and are subsequently assembled into a finished electronic part by an assembly process.

As the result of success in achieving a reduction in the size and thickness of electronic parts, it has also been attempted to reduce the size and thickness of the casings for rotary- or sliding-type variable resistors and rotary- or sliding-type switches in recent years. However, since the rotary- and sliding-type electronic parts of the conven­tional construction are composed of elements that are manu­factured separately and then assembled into a whole, there is a limitation upon the size and thickness reduction that can be achieved. The more progress that is made in reducing size and thickness, the more difficult it is to assemble the individual elements into the finished product.

An electronic part that has recently been developed is disclosed in the specification of Japanese Patent Public Disclosure (KOKAI) No. 62-49601, by way of example. In this electronic part, electric conductor patterns for electrodes and resistor patterns are formed on a synthetic resin film in such a manner that the resistor patterns are connected to the electric conductor patterns, metallic terminals are fixedly secured to the film to form a terminal portion, and both the terminal portion and the reverse side of the synthetic resin film are molded in a synthetic resin.

Though a reduction in the size and thickness of an electronic part can be obtained by fabricating the casing of a rotary- or sliding-type electronic part through use of the aforementioned technique in which a synthetic resin film is molded of a synthetic resin, various problems need to be solved to achieve this. For example, one problem is how to design the terminal structure formed on the top surface of the fllm and connected to the terminals of the various patterns.

Accordingly, an object of the present invention is to solve the aforementioned problems and provide a molded resin casing of an electronic part in which a flexible board com­prising a thermoplastic synthetic resin film is used as the aforementioned board and is inserted in the casing, thereby integrating the board and the casing to dispense with the need to assemble the board and the casing, thus making possible a great reduction in size and thickness required for modern electronic parts.

According to the present invention, the foregoing object is attained by providing a molded resin casing of a rotary- or sliding-type electronic part internally accom­modating a board on which are formed electric conductor patterns slidingly contacted by contacts of a slider of the electronic part, wherein a flexible board having the elec­tric conductor patterns formed on a film comprising a synthetic resin material is used as the board, a terminal portion having metallic terminal pieces electrically con­nected to ends of the patterns is formed, and the flexible board is inserted in the synthetic resin casing in such a manner that the electric conductor patterns are exposed to the inner walls of the casing and distal ends of the metallic terminal pieces of the terminal portion project to the outside of the casing.

Other features and advantages of the present inven­tion will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof. <ul id="ul0001" list-style="none"><li>Fig.1 illustrates the structure of a molded resin casing of an electronic part in which the casing has an internal flexible board in accordance with the present invention, in which Fig. 1(A) is a back view of the casing, Fig.1(B) a side view of the casing and Fig.1(C) a plan view of the casing;</li><li>Figs. 2 and 3(A), (B) are views useful in describing the structure of the flexible board and a method of manufac­turing the same;</li><li>Figs. 4(A), (B) and (C) are views useful in describ­ing a method of inserting the flexible board in the molded resin casing;</li><li>Fig. 5 is a sectional side view illustrating a rotary-type variable resistor fabricated using a molded resin casing having an internal flexible board;</li><li>Fig. 6 illustrates the structure of a molded resin casing of an electronic part in which the casing has an internal flexible board in accordance with another embodi­ment of the present invention, in which Fig. 6(A) is a back view of the casing, Fig. 6(B) a side view of the casing and Fig. 6(C) a plan view of the casing;</li><li>Fig. 7 is an exploded, perspective view illustrating a rotary-type variable resistor using the molded resin casing shown in Fig. 6;</li><li>Fig. 8 is a sectional view showing the rotary-type variable resistor in the assembled state;</li><li>Fig. 9 illustrates the structure of a molded resin casing of an electronic part in which the casing has an internal flexible board in accordance with a third embodi­ment of the present invention, in which Fig. 9(A) is a plan view of the casing, Fig. 9(B) a partial side section of the same, Fig. 9(C) a back view, and Fig. 9(D) a sectional view taken along line A-A of Fig. 9(A);</li><li>Figs. 10 and 11(A), (B) are views useful in describ­ing the manufacturing process of a flexible board portion and terminal portion;</li><li>Figs.12(A) and (B) are views useful in describing a method of inserting the flexible board in the molded resin casing;</li><li>Fig.13 is a sectional side view illustrating the structure of a sliding-type variable resistor fabricated using the casing of the rotary-type variable resistor;</li><li>Figs. 14 and 15 are views illustrating the structure of a molded resin casing of an electronic part in which the casing has an internal flexible board in accordance with a fourth embodiment of the present invention, in which Fig.14 is a perspective view, Fig.15(A) a plan view of the casing,</li><li>Fig. 15(B) a partial side section thereof, Fig.15(C) a back view thereof, Fig.15(D) a sectional view taken along line A-A of Fig. 15(A), and Fig.15(E) a sectional view taken along line B-B of Fig.15(B);</li><li>Fig.16 is a vlew for describing a process for manufacturing the flexible board and a terminal portion;</li><li>Figs.17(A), (B) and (C) are views useful in describ­ing a method of inserting the flexible board in the molded resin casing;</li><li>Fig.18 illustrates the structure of a variable resistor using the molded resin casing of Fig. 14, in which Fig. 18(A) is a partial side section [a sectional view taken along line E-E of Fig.18(B)] and Fig. 18(B) is a sectional view taken along line F-F of Fig.18(A);</li><li>Fig.19 is a perspective view illustrating the struc­ture of a molded resin casing of an electronic part in which the casing has an internal flexible board in accordance with a fifth embodiment of the present invention; and</li><li>Fig. 20 is a sectional view illustrating a rotary-­type variable resistor using the molded resin casing of Fig. 19.</li></ul>

Preferred embodiments of the invention will now be described with reference to the drawings.

Fig. 1 illustrates the structure of a molded resin casing of an electronic part in which the casing has an internal flexible board in accordance with the present invention, in which (A) is a back view of the casing, (B) a side view of the casing and (C) a plan view of the casing. In this embodiment, the description will relate to a rotary-­type variable resistor as an example of the electronic part.

As illustrated in the figures, a casing 1 of a rotary-­type variable resistor consists of molded synthetic resin from one side of which metallic terminal pieces 2-1 through 2-5 constituting a terminal portion 2 project. A flexible board 3 is inserted within the molded casing 1.

The interior of the molded casing 1 is generally circular in shape and is provided with a side wall 1-2 along its periphery. The bottom of the casing 1 is provided at its central portion with a support 1-1 on which a rotary slider, described below, is supported for free rotation. The back side of the molded casing 1 is formed to have protrusions 1-3, 1-4.

The flexible board 3 includes collector patterns 3-1, 3-2 and resistor patterns 3-3, 3-4 formed on a resin film by printing. These collector patterns 3-1, 3-2 and resistor patterns 3-3, 3-4 on flexible board 3 are exposed at the bottom of the casing 1.

The structure, shape and method of manufacture of the components making up the foregoing rotary-type variable resistor casing will now be described.

Figs. 2 and 3 are views useful in describing the structure and method of manufacturing the flexible board 3 inserted in the molded resin casing of the rotary-type variable resistor set forth above.

To manufacture the flexible board 3, first a strip of thermoplastic, heat-resistant synthetic resin film is prepared. The collector patterns 3-1, 3-2 and the resistor patterns 3-3, 3-4 are formed on predetermined portions of the synthetic resin film by printing, thereby defining a portion corresponding to the flexible board 3, and electric conductor patterns 3-5 through 3-9 are formed on the board portion so as to be continuous with the collector patterns 3-1, 3-2 and resistor patterns 3-3, 3-4. After these patterns are formed, the synthetic resin film is cut, leaving the portion corresponding to the flexible board 3 and support strips 10, 11 at the upper and lower ends of the flexible board. In this way a number of flexible boards 3 connected by the support strips 10, 11 can be made. In this case, it is obvious that the formation of the collector patterns 3-1, 3-2 and resistor patterns 3-3, 3-4 by printing can be carried out after the synthetic resin film is cut leaving the portion corresponding to the flexible board 3 and support strips 10, 11. Examples of the synthetic resin film are films made of polyparabanic acid, polyether imide and polyethylene terephthalate.

Next, metallic terminal pieces 2-1 through 2-5 formed integral with a support strip 20 are prepared. A hot-melt electrically conductive adhesive layer is formed on the electric conductor patterns 3-5 through 3-9 of the flexible board 3, and the tips of the metallic electrode pieces 2-1 through 2-5 are placed on respective ones of these electric conductor patterns 3-5 through 3-9 to be affixed thereto by the adhesive.

Next, a reinforcing sheet 2-6 made of a synthetic resin film of a substance the same as that of the flexible board 3 is placed on the metallic terminal pieces 2-1 through 2-5 that have been affixed to the electric conductor patterns 3-5 through 3-9 of the flexible board 3, a horn (not shown) for emitting ultrasonic waves is placed upon portions [indicated at 2-7 in (A) of Fig. 3] of the rein­forcing sheet 2-6 at which the metallic terminal pieces 2-1 through 2-5 are not present, and these portions are irradi­ated with ultrasonic waves from the horn. As a result, the synthetic resin film forming the reinforcing sheet 2-6 and the synthetic resin film forming the flexible board 3 are fused locally by ultrasonic heating, so that the metallic terminal pieces 2-1 through 2-5 are rigidly secured onto the respective electric conductor patterns 3-5 through 3-9 by the contractile force of the synthetic resin films.

The metallic terminal pieces 2-1 through 2-5 are then heated by a heating iron from above the reinforcing sheet 2-6 or flexible board 3 to melt the aforementioned electri­cally conductive adhesive layer, thereby reliably bonding the metalllc terminal pieces 2-1 through 2-5 onto the electric conductor patterns 3-5 through 3-9.

It should be noted that since the synthetic resin films are strongly fused together by the ultrasonic heating process, it may be permissible in certain cases to omit the step in which the electric conductor patterns 3-5 through 3-9 and the metallic terminal pieces 2-1 through 2-5 are bonded together by the electrically conductive adhesive.

Fig. 3(A) is a plan view showing the metallic terminal pieces 2-1 through 2-5 secured onto the electric conductor patterns 3-5 through 3-9 along the edge of the flexible board, as set forth above, and Fig. 3(B) is a sectional view taken along line D-D of Fig. 3(A). By cutting the flexible board 3 thus manufactured along lines A-A, B-B and C-C in Fig. 3(A), a flexible board 3 having the terminal portion 2 is completed.

The terminal portion 2 of flexible board 3 construct­ed as described above not only exhibits a strong connection between the flexible board 3 and the metallic terminal pieces 2-1 through 2-5 but is also of a very thin structure whose thickness is the sum solely of the thicknesses of the synthetic resin film forming the flexible board 3, the metallic terminal pieces 2-1 through 2-5, the reinforcing sheet 2-6 and the electrically conductive adhesive layer.

A method of inserting the flexible board 3 having the foregoing construction into the resin molded casing 1 will now be described.

As shown in (A) of Fig. 4, the flexible board 3 is clamped between a first die A and a second die B.

The first die A has a planar, flat surface A1 formed in its central portion, an annular groove S2 formed about the periphery of the flat surface A1, and a columnar hole A3 formed in the central portion of the flat surface A1.

The flat surface A1 is closely contacted by the collector patterns 3-1, 3-2 and resistor patterns 3-3, 3-4 of the flexible board 3, the annular groove A2 forms the side wall 1-2 of the molded casing 1, and the hole A3 forms the support 1-1 of the molded casing 1.

The second die B is formed to have a recess B1 in a portion to which the flat surface A1 and annular groove A2 of the first die A correspond, a channel B2 of a prescribed width for promoting the inflow of molten resin toward the terminal portion 2 formed at the edge of the flexible board 3, and a filling bore B3 formed substantially at the central portion of the channel B1.

The recess B1 is for forming the bottom portion of the resin molded casing 1, and the channel B2 is for facili­tating the inflow of molten resin to the terminal portion 2, which is formed at the edge of the flexible board 3, when the molten resin is introduced under pressure from the filling bore B3.

As shown in (B) of Fig. 4, a molten resin material (e.g., polyphenylene sulfide, polyethylene terephthalate or the like) is injected under pressure from the filling bore B3 of the second die B, as indicated by the arrow D1. Owing to this injection of the molten resin, the molten resin fills the recess B1 and channel B2 of the second die B as well as the annular groove A2 of the first die A, and the synthetic resin film forming the flexible board 3 is punctured by the synthetic resin material, which therefore is allowed to fill the hole A3 that forms the support 1-1 of the molded casing 1, as indicated by arrow D2. As a result of the filling of the hole A3 by the molten synthetic resin material allowed by puncturing of the flexible board 3, the synthetic resin film is brought into close contact with the inner surface of the hole A3 and will not peel away from this inner surface.

If, instead of adopting the foregoing method, an inflow hole for allowing inflow of the molten resin material were to be provided beforehand in a portion of the flexible board 3 corresponding to the position of the hole A3, the molten resin material which has flowed into the hole A3 through the inflow hole would impact against the inner surface of the hole A3 and reverse in direction. Conse­quently, this portion of the synthetic resin material would make its way between the flexible board 3 and the wall surface of the first die A, thereby causing the flexible board 3 to separate from the wall surface of the first die A so that the surfaces of the collector patterns 3-1, 3-2 and resistor patterns 3-3, 3-4 of the flexible board 3 would become covered with the resin material. The result would be a defective product. This problem is solved by allowing the flexlble board 3 to be punctured by the injection of the molten resin material, as described above, instead of adopt­ing the arrangement in which the flexible board 3 is provided with the inflow hole in advance.

If the second die B were not formed to have the channel B2, the molten resin material at the time of fill­ing operation would flow around the die from the recess B1 through the surrounding annular groove A2 and would fill the die from the upper surface of the terminal portion first, as a result of which the terminal portion 2 would be urged downwardly toward the recess B1 of the second cavity B. In extreme cases, there is the danger that this might cause the terminal portion 2 to become exposed at the back surface of the casing.

In this embodiment, the foregoing problem is avoided by forming the channel B2 in the second die B so that the flow of the molten resin material from the central portion of the recess B1 to the terminal portion 2 will be fastest at the portion (the direction indicated by arrow D3) where it flows in through the channel B2. By virtue of this expedient, the periphery of the terminal portion 2 is filled with the molten resin material while the terminal portion 2 is urged against the wall of the first die A. In other words, since a force indicated by arrow D3 acts before a force produced by the inflow of the molten resin material in the direction of arrow D4 in Fig. 4(B), the terminal portion 2 will not be peeled off the first die A.

After the clearance between the first die A and the second die B is thus filled with the molten resin material and the latter is allowed to solidify, the first and second dies A, B are parted. The result is the molded resin casing 1 incorporating the flexible board 3 inserted therein. It should be noted that the raised surface 1-5 on the back side of the molded casing 1 shown in (A) and (B) of Fig.1 is formed by the channel B2 of second die B.

In the embodiment described above, the flexible board 3 is not formed to have a molten resin inflow hole at the portion corresponding to the position of the hole A in the first die A. However, if the flexible board 3 is formed beforehand to have a molten resin inflow hole 3a, as shown in (C) of Fig. 4 the molten resin material which has flowed into the hole 3a can be prevented from seeping between the flexible board 3 and the wall surface of the first die A if the diameter d₂ of the hole 3a is made less than one-half the diameter d₁ of the hole A3 for forming the support 1-1. It has been confirmed that the flexible board 3 will not separate from the wall surface of the first die A if such an arrangement is adopted.

Fig. 5 is a side sectional view illustrating a rotary-type variable resistor in which use is made of the above-described molded resin casing having the internal flexible board.

As shown in Fig. 5, a rotor 5 has a structure com­prising a disk-shaped rotor main body 5-1 consisting of a synthetic resin, and a slider 5-2 furnished on the bottom surface of the rotor main body 5-1. The support 1-1 of the molded casing 1 is inserted into a hole formed in the central portion of the rotor main body 5-1, and the rotor 5 is freely rotatably supported within the molded casing 1 by thermally caulking the distal end of the support 1-1. Rotating the rotor 5 causes contacts on the slider 5-2 to slide on the collector patterns 3-1, 3-2 and resistor pat­terns 3-3, 3-4 formed on the flexible board 3, thereby changing the resistance values between the metallic terminal pieces 2-1 through 2-5.

If the rotary-type variable resistor having the above-described construction is mounted on a printed circuit board 100, the variable resistor is positioned and attached using the protrusions 1-3, 1-4 formed on the back surface of the molded casing 1 near the opposing edges thereof. At such time the metallic terminal pieces 2-1 through 2-5 are positioned on the wiring patterns formed on the printed circuit board 100. Various other electronic parts are placed on the printed circuit board 100 and the parts are mounted in place on the printed circuit board 100 by solder­ing.

By forming the flexible board 3 of the rotary-type variable resistor of a synthetic resin film and integrating the flexible board 3 with the molded resin casing 1 in the form of an insert within the casing, not only is it no longer necessary to assemble the molded casing 1 and the flexible board 3, but it is also possible to achieve a reduction in size and thickness.

Further, as shown in Fig. 5, the rotary-type variable resistor constructed as described above can be directly mounted on the printed circuit board 100 in the same manner as other parts such as capacitors, resistors and IC chips. This facilitates the automation of the mounting operation.

With the rotary-type variable resistor having the foregoing construction, the terminal portion 2 to which the metallic terminal pieces 2-1 through 2-5 are attached is also inserted inside the molded resin casing 1, as shown in Fig. 5. Therefore, when the rotary-type variable resistor is placed on the printed circuit board 100 and soldered into position via the use of a flux, there is no danger of the flux penetrating the interior of the molded casing 1 through the terminal portion 2.

Further, it has been described in the foregoing em­bodiment that the patterns are formed on the flexible board 3 by the printing application of an electrically conductive paste. However, the invention is not limited to this embodiment. By way of example, it is possible to form the patterns by forming an electrically conductive foil such as of aluminum or copper on the synthetic resin film by adhe­sion using an adhesive or by vacuum deposition, followed by forming the foil into predetermined pattern shapes by an etching treatment.

Fig. 6 illustrates the structure of a molded resin casing of an electronic part having an internal flexible board in accordance with a second embodiment of the present invention, in which (A) is a back view of the casing, (B) a side view of the casing and (C) a plan view of the casing. The casing of this embodiment differs from that shown in Fig. 1 in that the four corners at the periphery of the molded casing 1 are each formed to have a plate-shaped edge portion 1-6 integral with the casing, and each edge portion 1-6 is formed to have an upstanding protrusion 1-7.

Fig. 7 is an exploded, perspective view illustrating a rotary-type variable resistor using the molded resin casing shown in Fig. 6. The rotary-type variable resistor includes the molded resin casing 1, a rotor 6, a cover plate 7 and a rotating knob 8.

The rotor 6 has the shape of a disk and consists of a resin material. The central portion thereof is formed to have a columnar projection 6-4, and the back side is provided with a hole 6-5 coaxial with the projection 6-4. The rotor 6 is also formed to include a pair of locking fingers 6-1, 6-2 on either side of the projection 6-4 for the purpose of attaching the rotating knob 8, and a projection 6-3 for limiting the rotation of the rotor 6 to a predetermined range. Though not shown, a slider 6-6 for coming into sliding contact with the collector patterns 3-1, 3-2 and resistor patterns 3-3, 3-4 of the flexible board 3 is attached to the lower portion of the rotor 6 (see Fig. 8).

The cover plate 7 comprises a metal plate having a central portion formed to include a through-hole 7-2 through which the locking fingers 6-1, 6-2 of the rotor 6 are passed, and four corner portions each formed to include a hole 7-1 through which a corresponding one of the projec­tions 1-7 of molded casing 1 is passed. The central portion of the front edge of the cover plate 7 is provided with a downwardly projecting leg 7-3.

The rotating knob 8 is a disk-shaped member the periphery of which is roughened. As will be described below, a projection 8-4 (see Fig. 8) the central portion whereof is formed to have a hole 8-3 (Fig. 8) into which the projection 6-4 of rotor 6 is inserted is provided on the lower central portion of the rotating knob 8, and holes 8-2, 8-2 into which the locking fingers 6-1, 6-2 of rotor 6 are inserted are formed in the knob 8 on either side of the projection 8-4. The holes 8-2, 8-2 each have a wall face provided with a step portion engaged by the corresponding locking finger. Fig. 8 is a sectional view showing the rotary-type variable resistor comprising the foregoing components in the assembled state mounted on the printed circuit board 100.

To assemble the rotary-type variable resistor, the rotor 6 is placed on the molded resin casing 1 with the support 1-1 formed on the central portion of the molded resin casing 1 being inserted into the hole 6-5 formed in the lower central portion of the rotor 6. Next, the projec­tions 1-7 at the four corners of the molded resin casing 1 are inserted into the holes 7-1 at the four corners of the cover plate 7 and the tips of the projections 1-1 are thermally caulked, thereby attaching the casing 1 to the cover plate 7. Thus, the projection 6-4 and the pair of locking fingers 6-1, 6-2 of the rotor 6 are passed through the through-hole 7-2 of the cover plate 7.

Next, the projection 6-4 of rotor 6 is inserted into the hole 8-3 formed in the projection 8-d on the bottom of rotating knob 8, and the locking fingers 6-1, 6-2 are inserted into the holes 8-2, 8-2 and made to engage the step portions formed on the wall faces of the holes 8-2, 8-2, thereby attaching the rotating knob 8 to the rotor 6.

When the rotating knob 8 in the rotary-type variable resistor having the foregoing construction is turned, the rotor 6 rotates so that the slider 6-6 attached to the lower portion thereof is brought into sliding contact with the collector patterns 3-1, 3-2 and resistor patterns 3-3, 3-4 on the flexible board 3. When the rotor 6 rotates a pre­determined amount, the projection 6-3 formed on the circumferential portion thereof abuts against a projection 1-8 formed on the inner peripheral surface of the side wall 1-2. As a result, the rotation of rotor 6 is limited to a predetermined range.

In the foregoing embodiment, an example has been described in which the molded casing is that of a rotary-­type variable resistor. However, the molded casing can also be used as the molded casing of rotary-type electronic parts such as rotary-type code switches. In such case, most of the component parts of the above-described embodiment can be utilized, and only the shapes of the electric conductor patterns formed on the flexible board 3 need be changed.

Fig. 9 illustrates the structure of a molded resin casing of an electronic part having an internal flexible board in accordance with a third embodiment of the present invention, in which (A) is a plan view of the casing, (B) a partial side section of the same, (C) a back view, and (D) a sectional view taken along line A-A of Fig. 9(A).

In this embodiment, the casing is that of a sliding-­type electronic part and includes a flexible board portion 53 and terminal portions 52 integrally formed of a thermo­plastic, heat-resistant film 51, with the flexible board portion 53 and the terminal portions 52 being inserted into a molded resin casing 54.

Resistor patterns 53-1 and collector patterns 53-2 are formed on the flexible board portion 53 by printing, and electric conductor patterns 52-1 continuous with the end portions of the collector patterns 53-2 and resistor pat­terns 53-1 are formed on the terminal portions 52 by print­ing. The electric conductor patterns 52-1 of the terminal portions 52 are provided with metallic terminal pieces 55. The surface of the flexible board portion 53 on which the resistor patterns 53-1 and the collector patterns 53-2 are formed is exposed at the bottom portion of the molded resin casing 54 in the interior thereof.

The structure, shape and method of manufacture of the components making up the foregoing sliding-type variable resistor casing will now be described.

Fig. 10 is useful in describing a process for manu­facturing the flexible board portion 53 and the terminal portions 52. A thermoplastic, heat-resistant film 51 which is rectangular in shape is connected to support strips 51-1, 51-1 at both ends. The two resistor patterns 53-1, 53-1 and the two collector patterns 53-2, 53-2 are formed by printing on the surface of the heat-resistant film 51 at predeter­mined positions, and the conductor patterns 52-1 are printed on the heat-resistant film so as to be continuous with both ends of the resistor patterns 53-1, 53-1. Conductor patterns 52-1, 52-1 are printed on one end of each of the collector patterns 53-2, 53-2. The portions of the heat-­resistant film 51 on which the resistor patterns 53-1 and collector patterns 53-2 are formed by printing define the flexible board portion 53 which serves as the board of the sliding-type resistor, and the portions of the heat-­resistant film 51 on which the conductor patterns 52-1 are formed define the terminal portions 52.

As shown in Fig. 10, a plurality (three in the illustration) of the metallic terminal pieces 55 are formed by pressing so as to be integrated with a support strip 58 at a spacing corresponding to that of the electric conductor patterns 52-1. A hot-melt electrically conductive adhesive layer is formed on the electric conductor patterns 52-1 of the terminal portions 52, the metallic electrode pieces 55 are placed on respective ones of these electric conductor patterns 52-1, a terminal securing film 57 of a substance the same as that of the heat-resistant film 51 is placed on the metallic terminal pieces 55 from above, and portions of the terminal securing film 57 at which the metallic terminal pieces 55 are not present are irradiated with ultrasonic waves from a horn (not shown) which emits ultrasonic waves. As a result, the terminal securing film 57 and the heat-­resistant film 51 of the terminal portions 52 are fused by ultrasonic heating, so that the metallic terminal pieces 55 are rigidly bonded to the respective electric conductor patterns 52-1. The metallic terminal pieces 55 are then contacted and heated by a heating iron from above the terminal securing film 57 or the heat-resistant film 51 of the terminal portion 52 to melt the aforementioned electri­cally conductive adhesive layer, thereby reliably bonding the metallic terminal pieces 55 onto the electric conductor patterns 52-1.

Fig. 11 illustrates the state in which the metalllc terminal pieces 55 have been attached to the electric conductor patterns 52-1 of the terminal portion 52 by the above-described process, in which (A) is a plan view and (B) a sectional view taken along line B-B of Fig. 11(A). It should be noted that since the terminal securing film 57 and heat-resistant film 51 are strongly fused together by the ultrasonic heating process so that the metallic terminal pieces 55 and the electric conductor patterns 52-1 are brought into highly reliable surface-to-surface pressured contact, it may be permissible in certain cases to omit the step in which the electrically conductive adhesive layer is formed on the electric conductor patterns 52-1.

The board with the metallic terminals of the sliding-­type variable resistor formed as described above is very thin since the thickness thereof, even at the terminal portion where the thickness is greatest, is the sum solely of the thicknesses of the heat-resistant film 51, the metallic terminal pieces 55 and the terminal securing film 57.

The flexible board portion 53 of the heat-resistant film having the metallic terminal pieces 55 attached thereto as described above is inserted into the molded synthetic resin casing 54 in such a manner that the metallic terminal pieces 55 project to the outside. Thereafter, the molded product is cut along the lines C-C and D-D in Fig. 11(A) to thereby remove the support strips 58. The product is then cut along lines E-E and F-F in Fig. 11(A) to thereby remove the overlapped portions of the support strips 51-1 and terminal securing films 57, thus completing the molding casing 54 of the sliding-type variable resistor.

The side portions of the casing 54 are formed so as to cover the outer peripheries of the flexible board portion 53 and the terminal portions 52, and four securing projec­tions 54-2 for securing a cover plate, described below, and four guide projections 54-3 for guiding the cover plate are formed at both ends on one side portion 54-1. The rear side of the casing is integrally formed to include two fixing projections 54-4, 54-4 for fixing the molded resin casing 54 to a printed circuit board, described below.

Next, a method of inserting the heat-resistant film 51 having the metallic terminal pieces 55 attached to the terminal portions 52 into the molded resin casing 54 will be described with reference to Fig. 12.

As shown in (A) of Fig. 12, the flexible board por­tion 53 and the terminal portions are formed integral with each other and the heat-resistant film 51 having the metal­lic terminal pieces 55 attached to the terminal portions 52 is clamped between a first die A and a second die B.

The first die A is formed to have a flat surface A1 which is brought into close contact with the surface of the flexible board portion 53 of the heat-resistant film 51 having the resistor patterns 53-1 and collector patterns 53-2 formed thereon, and a groove A2 for forming the side portions 54-1 of the molded casing 54. Though not shown, the bottom portion of the groove A2 is formed to have recesses for forming the securing projections 54-2 and the guide projections 54-3 of the molded resin casing 54.

The second die B has a recess B1 for forming the bottom portion of the molded casing 54 formed at a portion thereof which corresponds to the flat portion A1 and groove A2 of the first die A, and a channel B2 of a predetermined width for promoting the inflow of a molten resin material toward the terminal portions 52 of the heat-resistant film 51 and the parts of the side portions 54-1 penetrated by the metallic terminal pieces 54-1. The channel B2 is formed longitudinally of the recess B1 at the approximate center thereof. (An elongated projection on the rear side of the molding casing 54 is formed by this channel B2.) The second die B also has columnar recesses B3 formed at the center of the recess B1 at predetermined positions longitudinally thereof for forming the fixing projections 54-4, 54-4 on the rear side of the molded casing 54. Though not shown, the peripheral portion of the bottom of recess B1 is formed to have recesses for forming projections 54-6 on the molded casing 54.

Next, as shown in (B) of Fig. 12, a molten resin material (e.g., polyphenylene sulfide, polyethylene tereph­thalate or the like) is injected under pressure in the direction of the arrows D1 from filling bores B4 formed at the base ends of the recesses B3 of the second die B. Owing to this injection of the molten resin, the heat-resistant film 51 of the flexible board portion 53 is urged against the flat surface A1 of the first die A.

If the elongated channel B2 extending longitudinally along the center of the recess B1 of the second die B were not provided, the molten resin material at the time of the charging operation would flow around the die from the recess B1 through the surrounding groove A2 and would fill the die from the upper surface of the flexible board portion 53 and terminal portions 52 at the periphery thereof, as indicated by arrow D2. As a result, the peripheral portions of the flexible board portion 53 and terminal portions 52 would be urged downwardly toward the recess B1 of the second cavity B. In extreme cases, there is the danger that this might cause the peripheral portions to become exposed at the back surface of the molded casing 54.

In this embodiment, the foregoing problem is avoided by forming the channel B2 longitudinally of the recess B1 along the center thereof in the second die B so that the flow of the molten resin material is promoted by the channel B2. The injection of the molten resin material is such that first the recess B1 is filled from the longitudinal direc­tion thereof along its center (the direction indicated by arrow D3), then the periphery of the cavity is gradually filled, and finally the groove A2 at which the peripheral portions of the flexible board 53 and terminal portions 52 are located is filled. During this filling process, therefore, the flexible board portion 53 and the terminal portions 52 are urged against the side of the first die A, so that they will not separate from the flat surface A1 of the first die A. In other words, the molten resin material will not flow into the area between the flat surface A1 of the first die A and the flexible board portion 53. Conse­quently, when the first and second dies A, B are parted after the molten resin material solidifies, as will be described below, the surface of the flexible board portion 53 will be completely exposed at the bottom of the molded resin casing 54.

After the molten resin material thus charged into the area between the first and second dies A, B has solidified, the first and second dies A, B are parted. As a result, a casing of a sliding-type variable resistor such as that shown in Fig. 9 is completed.

Fig. 13 is a side sectional view illustrating the structure of a sliding-type variable resistor in which use is made of the above-described sliding-type variable resistor casing.

As illustrated, a sliding body 59 is placed upon the flexible board portion 53 of the heat-resistant film 51 inserted into the molded resin casing 54. Provided on the bottom portion of the sliding body 59 is a slider 60 brought into sliding contact with the resistor patterns 53-1 and collector patterns 53-2 formed on the flexible board 53. The upper portion of the sliding body 59 is formed integral with an operating lever 59a. A cover plate 61 is placed upon the upper part of the side portions 54-1 of molded casing 54 and the distal ends of the securing projections 54-2 are thermally caulked, whereby the sliding body 59 is retained between cover plate 61 and the flexible board portion 53. This completes the sliding-type variable resistor.

When the operating lever 59a in the sliding-type variable resistor having the above-described structure is operated to move the sliding body 59, the slider 60 slides on the resistor patterns 53-1 and collector patterns 53-2 to change the positions at which the contacts of the slider 60 contact the resistor patterns 53-1, thereby changing the resistance between the metallic terminal pieces 55 connected to respective ones of the collector patterns 53-2 and resis­tor patterns 53-1.

As described hereinabove, the flexible board portion 53 on which the resistor patterns 53-1 and collector patterns 53-2 are formed and the terminal portions 52 on which the electric conductor patterns 52-1 are formed are made of the thermoplastic, heat-resistant film 51 consisting of synthetic resin, and the heat-resistant fllm 51 is insertion-molded in the molded casing 54 consisting of synthetic resin. As a result, not only is it no longer necessary to assemble the molded casing 54 and the flexible board portion 53, but it is also possible to reduce the size and thickness of the sliding-type variable resistor.

In the foregoing embodiment, the invention is described in connection with a sliding-type variable resis­tor. However, the invention can be applied to a sliding-­type code switch by changing the patterns formed on the flexible board portion 53.

Furthermore, though the structure adopted in the foregoing embodiment is one in which the metallic terminal pieces 55 project from both ends of the molded casing 54, it is possible to adopt a structure in which the metallic terminal pieces are provided on only one end of the casing.

Further, it has been described in the foregoing embodiment that the patterns are formed on the flexible board 53 by the printing application of an electrically con­ductive paste. However, the invention is not limited to this embodiment. By way of example, it is possible to form the patterns by forming an electrically conductive foil such as of aluminum or copper on the synthetic resin film by adhesion using an adhesive or by vacuum deposition, followed by forming the foil into predetermined pattern shapes by an etching treatment.

Figs. 14 and 15 are views illustrating the structure of a molded resin casing of an electronic part in which the casing has an internal flexible board in accordance with a fourth embodiment of the present invention, in which Fig. 14 is a perspective view, Fig. 15(A) a plan view of the casing, (B) a partial side section thereof, (c) a back view thereof, (D) a sectional vlew taken along line A-A of Fig. 15(A), and (E) a sectional view taken along line B-B of Fig. 15(B). In this embodiment, a variable resistor will be described as the electronic part.

As illustrated, the casing of the electronic part has a structure in which a flexible board 73 (described below) printed with resistor patterns 73-1, 73-1 and collector patterns 73-2, 73-2 and board extension portions 73-3 printed with lead patterns 72-1, 72-1 continuous with the respective end portions of the resistor patterns 73-1, 73-1 are integrally formed of a heat-resistant film 71. Metallic terminal pieces 75 are brought into contact with and rigidly secured to the upper surfaces of the lead patterns 72-1, 72-­1 on the board extension portions 73-3 to define terminal portions 72, and the flexible board 73 and terminal portions 72 of the heat-resistant film 71 are inserted into a molded resin casing 74. The resistor patterns 73-1, 73-1 on the heat-resistant film 71 are exposed at the bottom surface of the casing, and the collector patterns 73-2, 73-2 are exposed at the two opposing inner side wall surfaces of the casing.

The arrangement and method of manufacture of the components making up the foregoing electronic part casing will now be described.

Fig. 16 is a view useful in describing a process for manufacturing the flexible board 73 and the terminal por­tions 72. A thermoplastic, heat-resistant film 71 which is rectangular in shape is connected to support strips 71-1, 71-1 at both ends. Examples of the material usable to form the heat-resistant film 71 are polyparabanic acid, polyether imide and polyethylene. Two resistor patterns 73-1, 73-1 and two collector patterns 73-2, 73-2 are printed on the surface of the heat-resistant film 71 at predetermined posi­tions to define a flexible board 73, and lead patterns 72-1, 72-1 are printed on the board extensionn portions 73-3 that are continuous with the flexible board 73. The resistor patterns 73-1, collector patterns 73-2 and lead patterns 72-1 are connected in such a manner that one end of each resistor pattern 73-1 is connected to one end of the corresponding collector pattern 73-2 and one end of a lead pattern 72-1 is connected to the junction of the resistor and collector patterns 73-1, 73-2. The width of the flexible board 73 of the heat-resistant film 71 is a predetermined dimension larger than the width of the board extension portion 73-3.

As illustrated, a plurality (two in the illustration) of metallic terminal pieces 75 are formed integral with a support strip 78.

A hot-melt electrically conductive adhesive layer is formed on the lead patterns 72-1 on each of the board extension portions 73-3 of heat-resistant film 71, and the respective end portions of the metallic electrode pieces 75 are placed thereon. Next, a terminal securing film 77 of a substance the same as that of the heat-resistant film 71 is placed on the metallic terminal pieces 75 from above, and portions of the terminal securing film 77 at which the metallic terminal pieces 75 are not present, namely portions between the metallic terminal pieces 75, 75, and both end portions are irradiated with ultrasonic waves from a horn (not shown) which emits ultrasonic waves. As a result, the terminal securing film 77 and the board extension portions 73-3 of the heat-resistant film 71 are fused by ultrasonic heating, so that the metallic terminal pieces 75 are rigidly bonded to the respective lead patterns 72-1, 72-1 [see (E) of Fig. 15].

The metallic terminal pieces 75 are then contacted and heated by a heating iron from above the terminal secur­ing film 77 or the board extension portion 73-3 to melt the aforementioned hot melt-type electrically conductive adhe­sive layer, thereby reliably bonding the metallic terminal pieces 75 onto the lead patterns 72-1. A terminal portion 72 is thus formed on the board extension portion 73-3 of the heat-resistant film 71.

The board with the metallic terminals of the variable resistor formed as described above is very thin since the thickness thereof, even at the terminal portion where the thickness is greatest, is the sum solely of the thicknesses of the heat-resistant film 71, the metalllc terminal pieces 75 and the terminal securing film 77.

The flexible board portion 73 of the heat-resistant film 71 having the metallic terminal pieces 75 attached thereto as described above is inserted into a molded syn­thetic resin casing 74 in such a manner that the metallic terminal pieces 75 project to the outside. Thereafter, the molded product is cut along the lines C-C and D-D in Fig. 16 to thereby remove the support strips 78 and 71-1, 71-1, thereby completing the molded casing of the variable resistor.

The side portions 74-1 of the molded resin casing 74 are formed so as to cover the outer peripheries of the flexible board portion 73 and the terminal portions 72, and projections 74-3 serving as stoppers are formed at both ends on one side of the casing 74. In addition, sloping surfaces 74-2 which slope inwardly of the casing 74 are formed at predetermined positions on the tops of the side portions 74-1.

Next, a method of inserting the flexible board 73 having the terminal portions 72 into the molded resin casing 74 will be described with reference to Fig. 17.

First, as shown in Fig. 17(A), the flexible board 73 and the terminal portions 72 are clamped between a first die A and second die B.

The first die A is formed to have a flat surface A1 which is brought into close contact with the surface of the flexible board portion 73 having the resistor patterns 73-1, 73-1 formed thereon, flat surfaces A3 brought into intimate contact with the surfaces of the terminal portions 72, and a groove A2 provided around the flat surfaces A1, A3 for form­ing the side portions 74-1 of the molded casing 74.

The second die B has a recess B1 for forming the bottom portion of the molded casing 74 formed at a portion thereof which corresponds to the flat surface A1, flat surface A3 and groove A2 of the first die A. In addition, projections B2, B2 are provided in the recess B1 at a predetermined spacing for the purpose of impeding the flow of a molten resin material in the longitudinal direction of the heat-resistant film 71 and promoting the flow of the molten resin material in the lateral direction of the film 71. Further, a filling bore B3 for charging a molten resin material is formed in the center of the recess B1.

A molten resin, such as polyphenylene sulfide, polyethylene terephthalate or the like, is introduced from the filling bore B3 under pressure as indicated by the arrow D1. Owing to the injection of the molten resin, the resin material flows into the recess B1 of the second die B. The flow of the resin material in the lateral direction (at right angles to the plane of the drawing) of the heat- resistant film 71 is promoted by the projections B2 formed in the recess B1, as shown in (C) of Fig. 17. As a result, the collector patterns 73-2 on the flexible board 73 of the heat-resistant film 71 are urged by the molten resin material, as shown in (B) of Fig. 17, so that the collector patterns 73-2 are bent along one side surface of the groove A2 and are thus brought into close contact with the side surface.

If the recess B1 of the second die B were not provided with the projections B2, B2, the molten resin would flow radially from the filling bore B3 when introduced from the bore. In such case, the molten resin material which flows longitudinally of the recess B1 would flow into the groove A2 from the side portions of the terminal portions 2 and part of this resin would enter the area between the side surface of the groove A2 and the parts of the flexible board 73 on which the collector patterns 73-2 are formed, result­ing in the surfaces of the collector patterns 73-2 being covered with the resin material. However, since in this embodiment the projections B2 are formed on the bottom of the recess B1, the flow of the molten resin material in the longitudinal direction of the recess B1 is impeded, while the flow of the molten resin in the lateral direction of the heat-resistant film 71 is promoted. Accordingly, the molten resin material which thus flows into the groove A2 causes the surface of the flexible board 73 to be bent along the slide surface of the groove A2, thus bringing the surface of the flexible board into close contact with the side surface of the groove. Thus, the front surfaces of the collector patterns 73-2 of flexible board 73 will not be covered with the resin material.

More specifically, since the molten resin material will not flow into the area between the side surfaces of the flat surface A1 of the first die A and the flexible board 73, when the first die A and second die B are parted after the resin material has solidified, as described below, the resistor patterns 73-1, 73-1 on the flexible board 73 are exposed at the bottom of the molded casing 74, and the collector patterns 73-2, 73-2 are exposed at the two oppos­ing inner side walls.

After the molten resin material thus charged in the cavity between the first and second dies A, B has solidi­fied, the first and second dies are parted. As a result, a variable resistor casing such as that shown in Fig. 14 is completed.

Fig. 18 shows the structure of a variable resistor fabricated using the above-described molded resin casing 74, in which (A) is a partial side section [a sectional view taken along line E-E of Fig. 18(B)] and (B) is a transverse sectional view [a sectional view taken along line F-F of Fig. 18(A)]. As illustrated, a slider 80 is provided on the outer periphery of the variable resistor casing having the above-described structure. The slider 80 is molded of a resin material and has an operating knob 81 integral with one side portion thereof. Numeral 83 denotes contacts in sliding contact with the resistor patterns 73-1, 73-1 on the flexible board 73. Numeral 84 denotes contacts in sliding contact with the collector patterns 73-2. The contacts 83 and 84 are formed integral with each other in the form of a contact member 85, which is inserted in the body of the the flexible board 93 is inserted into a molded resin casing 91 so as to be exposed at the inner surface of a side wall 91-2 and the outer peripheral surface of a support 91-1 of the casing 91. Here a flat cable 92 formed integral with the flexible board 93 extends outwardly from the side por­tion of the molded resin casing 91. The method of inserting the flexible board 93 into the molded casing 91 is substan­tially the same as the method indicated in Fig. 4 and need not be described again.

By adopting this arrangement, a resistor pattern 93-4 is exposed at the inner surface of the side wall 91-2 of the molded resin casing 91, a resistor pattern 93-3 and a collector pattern 93-2 are exposed at the inner bottom surface, and a collector pattern 93-1 is exposed at the outer peripheral surface of the support 91-1. Further, the flat cable 92 extends from the side portion of the molded resin casing 91. With the exception of a terminal portion 92-2, the flat cable 92 has its upper surface coated with a resin material that forms an insulative film.

Fig. 20 is a sectional view showing the rotary-type variable resistor, which is fabricated using the molded resin casing 91 having the above-described construction, mounted on the printed circuit board 100. The structure of this arrangement is substantially the same as that of the rotary-type variable resistor of Figs. 7 and 8.

To assemble this rotary-type variable resistor, a rotor 96 is placed on the molded resin casing 91 with the support 91-1 formed on the central portion of the molded resin casing 91 being inserted into a hole 96-5 formed in the lower central portion of the rotor 96. Locking fingers 96-1, 96-2 are inserted into holes 98-2, 98-2 and made to engage step portions formed on the wall surfaces of the holes 98-2, 98-2, thereby attaching the rotating knob 98 to the rotor 96.

When the rotating knob 98 in the rotary-type variable resistor having the foregoing construction is turned, the rotor 96 rotates so that a slider 96-6 attached to the lower surface thereof is brought into sliding contact with the heat-resistant film 71 is arranged in such a manner that the resistor patterns 73-1, 73-1 are exposed at the bottom surface of the casing 74, while the collector patterns 73-2, 73-2 are exposed at the two opposing inner side wall sur­faces. Therefore, it is possible to effectively utilize the inner surfaces of the molded casing 74 and, hence, reduce the size and thickness of the variable resistor, and it is no longer necessary to assemble the flexible board 73 and the molded casing 74 together.

Although in the above-described embodiments the present invention has been described by way of example in which the invention is applied to a sliding-type variable resistor, it should be noted that the molded casing of the invention is not limited thereto but can be utilized as the molded casing of a sliding-type switch as well. For example, it is possible to fabricate a miniature code switch by forming fixed contact patterns of a code switch on the inner bottom surface and both inner side surfaces of the above-­described molded resin casing 74.

Further, it has been described in the foregoing embodiment that the patterns are formed on the flexible board 73 by the printing application of an electrically conductive paste. However, the invention is not limited to this embodiment. By way of example, it is possible to form the patterns by forming an electrically conductive foil such as of aluminum or copper on the synthetic resin film by adhesion using an adhesive or by vacuum deposition, followed by forming the foil into predetermined pattern shapes by an etching treatment.

Fig. 19 is a perspective view illustrating the struc­ture of a molded resin casing of an electronic part having an internal flexible board in accordance with a fifth em­bodiment of the present invention. In this embodiment, the flexible board 73 is inserted into a molded resin casing 91 so as to be exposed at the inner surface of a side wall 91-2 and the outer peripheral surface of a support 91-1 of the casing 91. The method of inserting the flexible board 93 into the molded casing 91 is substantially the same as the methods indicated in Figs. 4 and 17 and need not be described again.

By adopting this arrangement, a resistor pattern 93-4 is exposed at the inner surface of the side wall 91-2 of the molded resin casing 91, a resistor pattern 93-3 and a collector pattern 93-2 are exposed at the inner bottom surface, and a collector pattern 93-1 is exposed at the outer peripheral surface of the support 91-1. Further, a terminal portion 92 has a structure substantially the same as that of the terminal portion 2 of the molded resin casing illustrated in Fig. 1 and is provided with metallic terminal pieces 92-1 through 92-5.

Fig. 20 is a sectional view showing the rotary-type variable resistor, which is fabricated using the molded resin casing 91 having the above-described construction, mounted on the printed circuit board 100. The structure of this arrangement is substantially the same as that of the rotary-type variable resistor of Figs. 7 and 8.

To assemble this rotary-type variable resistor, a rotor 96 is placed on the molded resin casing 91 with the support 91-1 formed on the central portion of the molded resin casing 91 being inserted into a hole 96-5 formed in the lower central portion of the rotor 96. Locking fingers 96-1, 96-2 are inserted into holes 98-2, 98-2 and made to engage step portions formed on the wall surfaces of the holes 98-2, 98-2, thereby attaching the rotating knob 98 to the rotor 96.

When the rotating knob 98 in the rotary-type variable resistor having the foregoing construction is turned, the rotor 96 rotates so that a slider 96-6 attached to the lower surface thereof is brought into sliding contact with the resistor pattern 93-2 and collector pattern 93-2 exposed at the inner bottom surface of the casing 91, a slider 96-7 attached to the inner peripheral surface of the rotor 96 is brought into sliding contact with the collector pattern 93-1 exposed at the outer peripheral surface of the support 91-1, and a slider 96-8 attached to the outer peripheral surface of the rotor 96 is brought into sliding contact with the resistor pattern 93-3 exposed at the inner surface of the side wall 91-2. This causes the resistance between the metallic terminal pieces 92-1 through 92-5 to change.

By constructing the molded resin casing in the manner described above, the inner surface of the molding casing 91 can be utilized effectively to make it possible to greatly reduce the size of the rotary-type variable resistor.

Although in the above-described embodiments the present invention has been described by way of example in which the invention is applied to a variable resistor, it should be noted that the molded casing of the invention can be utilized as the molded casing of a rotary-type code switch or the like by changing the various patterns formed on the flexible board.

Further, in the foregoing embodiment, the patterns can be formed on the flexible board 93 by the printing application of an electrically conductive paste, and it is possible to form the patterns by forming an electrically conductive foil such as of aluminum or copper on the syn­thetic resin film by adhesion using an adhesive or by vacuum deposition, followed by forming the foil into predetermined pattern shapes by an etching treatment.

As many apparently widely different embodiments of the present invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims.