Molded resin casing of electronic part incorporating flexible board

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, and the flexible board is inserted inside the synthetic resin casing in such as manner that the electric conductor patterns are exposed to the interior of the casing.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
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. 
2. Description of the Related Art 
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 film and connected to 
the terminals of the various patterns. 
SUMMARY OF THE INVENTION 
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.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
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 metallic 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 Al formed in its central 
portion, an annular groove A2 formed about the periphery of the flat 
surface Al, and a columnar hole A3 formed in the central portion of the 
flat surface Al. 
The flat surface Al 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 Bl in a portion to which the 
flat surface Al 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 Bl. 
The recess Bl 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 Dl. Owing to this injection of the molten resin, the molten resin 
fills the recess Bl 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. 
lf, 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 
flexible 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 Bl 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 Bl 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 Bl 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 d.sub.2 of the hole 3a is made 
less than one-half the diameter d.sub.1 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. 
lf 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 I 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 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 8-4 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 heatresistant 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 metallic 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 Al 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 Bl for forming the bottom portion of the 
molded casing 54 formed at a portion thereof which corresponds to the flat 
portion Al 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 Bl 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 Bl 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 Bl 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 Dl 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 Al of the 
first die A. 
If the elongated channel B2 extending longitudinally along the center of 
the recess Bl 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 Bl 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 Bl 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 Bl 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 Bl 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 
Al of the first die A. In other words, the molten resin material will not 
flow into the area between the flat surface Al 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 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 film 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 slidingtype 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 view 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 extension 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 metallic 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 Al 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 Al, A3 for forming the side 
portions 74-1 of the molded casing 74. 
The second die B has a recess Bl for forming the bottom portion of the 
molded casing 74 formed at a portion thereof which corresponds to the flat 
surface Al, flat surface A3 and groove A2 of the first die A. In addition, 
projections B2, B2 are provided in the recess Bl 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 Bl. 
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 Dl. Owing to the injection of the molten resin, the 
resin material flows into the recess Bl 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 Bl, 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 Bl 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 Bl 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 Bl, the flow of the molten resin 
material in the longitudinal direction of the recess Bl 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 Al 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 slider 80. Further, a pair of engagement members 82, 82 that 
are engaged with two edge portions of the outer surface of the bottom of 
molded casing 74 are formed on both sides of the slider 80. 
With the upper part of the molded casing 74 abutting against the engagement 
members 82, 82 of the slider 80 having the above-described structure, the 
slider 80 is pressed. As a result, the engagement members 82 are spread 
apart, in which state they descend along the outer side surfaces of the 
slider 80 and, eventually, the respective projections of the engagement 
members 82, 82 engage with the outer peripheral bottom surface of the 
casing 74. Thus, a variable resistor prepared using the molded resin 
casing 74 is completed. 
When the operating knob 81 of the variable resistor having the 
above-described construction is operated to move the slider 80 
longitudinally of the molded resin casing 74, the contacts 83, 84 are 
caused to slide on the respective upper surface of the resistor patterns 
73-1 and collector patterns 73-2, thus causing a change in the resistance 
between the metallic terminal pieces 75, 75. 
In the foregoing embodiment, an arrangement has been described in which the 
collector patterns 73-2 on the flexible board 73 are exposed at the two 
opposing inner side wall surfaces of the molded causing 74. However, the 
collector patterns 73-2 may be exposed at one inner side surface of the 
casing 74. Further, it is of course possible to vary the number of 
resistor patterns 73-1 and collector patterns 73-2 according to need. In 
addition, it is obvious that an arrangement can be adopted in which the 
resistor patterns 73-1, 73-1 are exposed at the inner side wall surfaces 
and the collector patterns 73-2, 73-2 are exposed at the bottom surface. 
As has been described above, the flexible board 73 formed with the resistor 
patterns 73-1, 73-1 and collector patterns 73-2, 73-2 and the board 
extension portions 73-3 formed with the lead patterns 72-1, 72-1 are 
formed using a heat-resistant film 71 of a thermoplastic resin, and 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.