Circuit board

A circuit board for use in a keyboard has a lower insulating sheet, an insulating sheet, and an upper insulating sheet stacked on top of each other. Switch circuit patterns are formed on the upper and lower insulating sheets so as to be opposed to each other. Circuit patterns acting as electrical parts such as rheostats are formed on the insulating spacer.

FIELD OF THE INVENTION 
The present invention relates to a circuit board and, more particularly, to 
a circuit board for use in a keyboard. 
BACKGROUND OF THE INVENTION 
A conventional circuit board for use in a keyboard is shown in FIGS. 6 and 
7, where the board is indicated by reference numeral 28. This board 28 
consists of a first pattern sheet 25, a second pattern sheet 26, and an 
insulating sheet 27 sandwiched between the pattern sheets 25 and 26. Each 
of the pattern sheets is made from a flexible insulating material and has 
a circuit pattern arranged thereon such that the circuit patterns on the 
two sheets 25 and 26 are opposed to each other. The insulating sheet 27 is 
provided with a hole. When the circuit board 28 and electrical parts 30 
such as rheostats are mounted, the board 28 is joined to a support base 
29, while the terminals 33 of the electrical parts 30 are inserted into 
holes 32 formed in a printed circuit board 31 that is provided independent 
of the circuit board 28. The terminals 33 of the parts 30 are connected 
with the circuits of the printed circuit board 31 as by soldering. The 
circuit board 28 has edge connectors 22c and 22d for making connections to 
other circuits. Also, the printed circuit board 31 on which the electrical 
parts 30 are mounted has an edge connector 34 for making connections with 
other circuits. 
However, the edge connectors for making connections to an external circuit 
and an insulating circuit board having resistors, for example, thereon are 
indispensable to the electrical parts such as rheostats. Further, the 
electrical parts are required to be mounted above the surface of the 
printed circuit board in a spaced relation from the surface to prevent 
flux from flowing into the electrical parts when the parts are soldered to 
the printed circuit board. For these reasons, such a problem arises that 
the assembly of the printed circuit board and the electrical parts has a 
large height. Therefore, in spite of the fact that the circuit board 
forming a portion of a control panel is thin, the whole control panel 
occupies a considerable portion of the volume of the electrical product. 
This makes it difficult to manufacture the product in small size and small 
thickness. Another problem with the prior art structure is that the 
printed circuit board on which electrical parts are mounted and the edge 
connectors formed on the printed circuit board are necessary. Further, 
soldering operations are needed to make connections with these portions. 
Hence, the product is expensive to fabricate 
SUMMARY OF THE INVENTION 
Accordingly, it is the object of the present invention to provide a circuit 
board which allows an electrical product to be manufactured in small size 
and small thickness, is made up of a less number of components than 
conventional, can be fabricated with a less number of manufacturing steps 
than conventional, and is inexpensive to manufacture. 
The above object is achieved by a circuit board having a lower insulating 
sheet, an insulating spacer, and an upper insulating sheet which are 
stacked on top of each other in this order, the upper and lower insulating 
sheets having their respective switch circuit patterns opposed to each 
other, the insulating spacer having circuit patterns which act as 
electrical parts such as rheostats. At least one of the two insulating 
sheets is flexible film. The insulating spacer can be a filmy body printed 
on the film forming the insulating sheet. In this case, subsequent to the 
printing of the insulating spacer, said circuit patterns acting as the 
electrical parts such as rheostats can be easily formed by printing 
process. Further, it is not necessary that the film constituting the 
insulating spacer is bonded to the insulating sheets with bonding members. 
Preferably, the terminals of the circuit patterns formed on the insulating 
spacer are connected with the leads in the switch patterns formed on the 
insulating sheet. This allows the terminals of the circuit board on the 
insulating spacer to be introduced in a set of terminals formed around one 
end of the insulating sheet via leads on the insulating sheet, the first 
mentioned terminals of the circuit board being adapted to be connected to 
a circuit outside the circuit board rather than directly connected with 
the switch circuit patterns on the insulating sheet. Where the connection 
with the external circuit is made by printing using conductive ink, the 
circuit board can be manufactured by a continuous printing operation 
including the formation of the insulating spacer and the formation of the 
circuit patterns on the insulating spacer. Thus, the circuit board can be 
manufactured in a sufficiently controlled manner and inexpensively.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIGS. 1 and 2, there is shown a circuit board according to the 
present invention. This board has upper and lower insulating sheets which 
are formed by first and second pattern sheets 1 and 2, respectively. These 
insulating sheets are made from polyethylene terephthalate, polyimide, or 
other resin. A contact pattern 3a and a circuit pattern 4a are printed 
with conductive ink on the first sheet 1. Similarly, a contact pattern 3b 
and a circuit pattern 4b are printed with conductive ink on the second 
sheet 2. These patterns 3a, 4a and 3b, 4b are formed so as to be opposed 
to each other, for making a switch that is closed when depressed. An 
insulating spacer 5 in the form of a sheet is made from polyethylene 
terephthalate, polyimide, or other resin exhibiting flexibility, or it is 
made of a laminate consisting of phenolic resin or epoxy resin. The spacer 
5 is provided with holes 6 for allowing the switch to be closed. Also, the 
spacer 5 has circuit patterns 8 formed by printing at other locations, the 
patterns 8 acting as electrical parts such as rheostats. Print patterns 7 
form portions of the circuit patterns 8, which are formed with holes 9 for 
connection with the circuit patterns on the second pattern sheet 2. The 
first pattern sheet 1 has an opening 10 so that the circuit patterns 8 on 
the insulating spacer 5 are partially exposed. 
A support plate 11 is a hard plate such as a laminated plate or iron plate. 
The second pattern sheet 2, the insulating spacer 5, and the first pattern 
sheet 1 are stacked on the support plate 11 in this order and bonded to 
the plate 11 with bonding member such as adhesive or double-sided adhesive 
tape. 
Referring next to FIG. 3, each first connector pattern 12 extends from the 
circuit pattern 8 of the electrical part on the insulating spacer 5 to the 
fringe of each hole 9. Each second connector pattern 13 extends to a 
position at which it is exposed through each opening 9 in the insulating 
spacer 5, under the condition that the insulating spacer 5 is stacked on 
the second pattern sheet 2. The first connector patterns 12 are 
electrically connected with their respective second connector patterns 13 
by electrically conductive connector member 14 which fills the holes 9 and 
is an electrically conductive adhesive or the like. Thus, a circuit board 
is formed. 
Referring back to FIGS. 1 and 2, round holes 19 extend through the second 
pattern sheet 2, the insulating spacer 5, and the support plate 11 of the 
circuit board constructed as described above. The casings 16 of the 
mechanisms 15 of the electrical parts are mounted to rectangular shafts 18 
which are rotatably held by the holes 19. The mechanism 15 of each 
electrical part is composed of the casing 16 that is open on its lower 
side, a slider support (not shown) on which a slider (not shown) sliding 
on the circuit surface on the insulating spacer 5, and the rotatable shaft 
18 fixed in coaxial relation to the the slider support. Retaining portions 
20 extend downward from the ends of the opening of the casing 16, and are 
inserted in rectangular holes 17 formed in the circuit board. The end of 
the shaft 18 is inserted in the round hole 19. The lower ends of the 
retaining portions 20 are bent so that the mechanisms 15 of the electrical 
parts are anchored to the circuit board. The first pattern sheet 1 has an 
edge connector 21a which extends outwardly from one side of the sheet. 
Similarly, the second insulating sheet 2 has an edge connector 21b 
extending outwardly from its one side. These edge connectors have 
terminals 22a and 22b which form the ends of the circuit patterns on the 
pattern sheets. The terminals 22b on the second pattern sheet 2 include 
the output terminals of the circuit patterns of the electrical parts on 
the insulating spacer 5. 
Referring next to FIGS. 4 and 5, there is shown another circuit board 
according to the invention. It is to be noted that like components are 
denoted by like reference numerals throughout FIGS. 1-5, and they will not 
be described hereinafter for simplicity. Switch circuit patterns (not 
shown) including the contact patterns 3b are printed with conductive ink 
on the second pattern sheet 2. Insulating ink is applied to the second 
pattern sheet 2, except for the contact patterns 3b the edge connector 
22b, and the holes 24 for making connections of the circuit patterns 8 of 
the electrical parts with the circuit patterns on the sheet 2, to form an 
insulating spacer 23. The circuit patterns 8 of the electrical parts such 
as rheostats are formed on the spacer 23 by printing. The circuit patterns 
8 include first connecting patterns 12' overlying the surface of second 
connecting patterns 13 which extend from circuit patterns 4b on the second 
pattern sheet 2, the second patterns 13 being partially exposed at holes 
24. Thus, the circuit patterns 8 of the electrical parts on the insulating 
spacer 23 are electrically connected with the circuit patterns 4b on the 
second pattern sheet 2 to thereby form a circuit board. 
A first pattern sheet 1 is placed on and bonded to the laminate formed as 
described above. A support plate 11 is bonded to the underside of the 
laminate. For these bonding operations, bonding member such as adhesive or 
double-sided tape is inserted between neighboring layers. Then, the 
mechanisms 15 of the electrical parts are mounted in the same manner as in 
the circuit board already described in connection with FIGS. 1-3. 
In the above examples, the electrical parts include rotary type rheostats, 
rectilinearly sliding type rheostats, rotary type switches, rectilinearly 
sliding rheostats, and fixed resistors. 
As described thus far, the novel circuit board according to the invention 
has a lower insulating sheet, an insulating spacer, and an upper 
insulating sheet which are stacked on top of each other in this order, the 
upper and lower insulating sheets having their respective switch circuit 
patterns opposed to each other. The insulating spacer has circuit patterns 
acting as electrical parts such as rheostats. Therefore, the laminate 
consisting of the insulating spacer in the form of a sheet, pattern 
sheets, and a support plate can be used as an insulating plate on which 
circuit patterns of electrical parts such as rheostats are formed, the 
laminate essentially forming a key unit. Terminals for making connections 
to an external circuit is made unnecessary. Further, a printed circuit 
board on which electrical parts are mounted is dispensed with. In 
addition, it is not necessary that electrical parts are mounted above said 
printed circuit board in a spaced relation from the board to prevent flux 
from flowing into the electrical parts. Hence, the height of the structure 
on which the mechanisms of the electrical parts is made low. Consequently, 
the product can be manufactured in small size and small thickness. 
Furthermore, the novel circuit board can be made up of a less number of 
components than conventional. Additionally, soldering operation can be 
omitted. These contribute to a reduction in the manufacturing cost.