PRINTED CIRCUIT BOARD

Abstract: A printed circuit board (1) comprising a dielectric film substrate (2) and a plurality of circuit patterns for a capacitor switch formed on said dielectric film substrate at a certain space from each other. Each of the circuit patterns comprisies a switch electrode pair (5A, 5B) formed on one surface of the dielectric film substrate, a first fixed electrode connected to one of the switch electrode pair, a first lead pattern connected to the other of the switch electrode pair, a second fixed electrode formed on the other surface of the dielectric film substrate in such a manner as to be opposed to the first fixed electrode through the dielectric film substrate, said first and second fixed electrodes forming a fixed electrode pair, and a second lead pattern connected to the second fixed electrode. A plurality of the fixed electrode pairs are arranged at an enlarged space larger than the certain space defined between the circuit patterns, and the density of the first and second lead patterns disposed in the enlarged space is reduced.

Description: The present invention relates to an improved printed circuit board, and more particularly to a printed circuit board for a capacitor keyboard. Fig. 11 shows a sectional view of the structure of a known printed circuit board for a capacitor keyboard. A dielectric film substrate 31 is located on a base board 37, and lower and upper capacitor electrodes 32 and 33 are disposed on opposite surfaces of the dielectric film substrate 31 at a desired position. Thus, the lower and upper capacitor electrodes 32 and 33 and the dielectric film substrate 31 form a capacitor CA having a desired capacitance. A spacer 34 having an aperture 34A is located on the dielectric film substrate 31 in such a manner that the aperture 34A is opposed to the upper capacitor electrode 33. A movable film 35 having a contact 36 is located on the spacer 34 in such a manner that the contact 36 is opposed in spaced relationship to the upper capacitor electrode 33 through the aperture 34A of the spacer 34. When the movable film 35 at the position of the contact 36 is depressed, the contact 36 is brought into contact with the upper electrode 33 to allow a charge in the capacitor CA to be discharged. Such a capacitor keyboard switch having a dielectric film substrate, fixed electrodes formed on both surfaces of the dielectric film substrate, and a switching movable electrode arranged in opposed relationship to the fixed electrodes is disclosed in Japanese Patent Laid-Open Publication No. 60-117512, and U.S. Patent Nos. 4,659,879 and 3,951,250, for example. As described above, the conventional capacitor keyboard has a structure such that the lower electrode 32 and the upper electrode 33 are formed on opposite surfaces of the dielectric film substrate 31, and the contact 36 of the movable film 35 is opposed in spaced relationship to the upper electrode 33 through the aperture 34A of the spacer 34, so as to be made contactable with the upper electrode 33. However, it is necessary to make the pitch between adjacent switches coincident with a dimension defined by an International Standard on keyboards (ISO Standard). Accordingly, the possible mounting positions of the capacitor electrode pairs is restricted, and the distance therebetween is resultantly fixed. As a result, lead patterns formed to pass between the adjacent capacitor electrode pairs are arranged close together, and the lead patterns formed on both surfaces of the dielectric film substrate tend to be superimposed, causing the generation of cross talk or noise trouble. It is an object of the present invention to provide a printed circuit board which can reduce the cross talk and the noise trouble due to the high-density arrangement of the lead pattern. According to the present invention, there is provided a printed circuit board comprising a dielectric substrate and a plurality of circuit patterns for capacitor switches formed on said dielectric substrate, each of said circuit patterns comprising a switch electrode pair formed on one surface of said dielectric substrate, said switch electrode pairs being at a particular spacing from each other, a first capacitor electrode connected to one electrode of said switch electrode pair, a first lead pattern connected to the other electrode of said switch electrode pair, a second capacitor electrode opposed to said first capacitor electrode, said first and second capacitor electrodes forming capacitor electrode pairs, and a second lead pattern connected to each second capacitor electrode, wherein the spacing between the edges of at least some adjacent capacitor electrode pairs is greater than it is between other adjacent pairs, so that the density of said first and second lead patterns disposed in said greater spaces between adjacent capacitor electrode pairs can be reduced. In some embodiments of the present invention, the increased spacing between capacitor electrode pairs is provided by the shapes of the capacitors being different from each other, with the areas of the capacitors remaining equal. Alternatively, the increased spacing can be achieved by adjusting the positions of the capacitor electrode pairs with respect to each other. In the present invention, each switch electrode pair is arranged separately from the corresponding capacitor electrode pair to which it is connected. That is, the capacitor electrode pair comprising the first and second capacitor electrodes formed on both surfaces of the dielectric substrate, and the switch electrode pair connected to the capacitor electrode pair is formed spaced from the capacitor electrode pair. The second capacitor electrodes may be on the opposite side of the dielectric substrate which is usually a film, from the first capacitor electrodes. Alternatively, each second capacitor electrode may be formed on an insulating layer covering the corresponding first capacitor electrode. With the invention, the first and second capacitor electrodes may be arranged without the positional limitations which govern the switch electrode pairs. Further, as the shape of the first and second capacitor electrodes is changeable, with the areas and capacitance thereof remaining equal to each other, it is possible to adjust the space for passing the lead. The invention will be more fully understood from the following description given by way of example with reference to the drawings in which: Fig. 1 is a top plan view of a printed circuit board as partially shown in a first embodiment of the present invention; Fig. 2 is an enlarged view of Fig. 1; Fig. 3 is a bottom plan view of Fig. 2; Fig. 4 is an enlarged view similar to Fig. 2, of a second embodiment; Fig. 5 is a top plan view similar to Fig. 2, of a third embodiment; Fig. 6 is a bottom plan view of Fig. 5; Fig. 7A is a top plan view similar to Fig. 2, of a fourth embodiment; Fig. 7B is an enlarged view of the encircled part P shown in Fig. 7A; Fig. 8 is a vertical sectional view of a part of the keyboard, of a fifth embodiment; Fig. 9 is a perspective view of Fig. 8; Fig. 10A is a vertical sectional view of the printed circuit board in the prior art, mounting LED; Fig. 10B is a vertical sectional view of a sixth embodiment, similar to Fig. 10A; Fig. 11 is a vertical sectional view of the printed circuit board in the prior art; Fig. 12 is a vertical sectional view of a seventh embodiment of the present invention; and Fig. 13 is a vertical sectional view of an eighth embodiment similar to Fig. 12. Referring to Figs. 1 to 10 which show some embodiments of the present invention, reference numeral 1 designates a printed circuit board for a keyboard of a typewriter or a wordprocessor, for example. The printed circuit board 1 is formed by a dielectric film substrate 2 having a desired shape and formed of polyethylene terephthalate, for example. There are formed on the dielectric film substrate 2 a plurality of capacitors C1 to C3, contact patterns 5A and 5B for switches and wirings 6 having a desired shape. Although a part of the printed circuit board 1 is shown for the simplicity of explanation, the other parts are formed similarly. Referring to Fig. 2 which shows an enlarged view of Fig. 1, there are formed on the upper surface of the dielectric film substrate 2 first capacitor electrodes 4A, 4B and 4C forming the capacitors C1, C2 and C3, respectively, and first led patterns 7. The various first lead patterns 7 are electrically connected to various contact patterns 5A at respective one ends which form the switches. The first capacitor electrodes 4A, 4B and 4C are adapted to be electrically connected to the contact patterns 5B of the switches. The first capacitor electrodes 4A, 4B and 4C are formed to have a dimension or area providing a desired capacitance. In this embodiment, the capacitor electrode 4A has a circular shape having a desired diameter, and the first capacitor electrodes 4B and 4C are of an elongated circle having the same area as the first capacitor electrode 4A. Instead of such a circular or part circular configuration, the present invention may employ any other configurations such as a rectangular shape. The wiring patterns 6 include the first lead pattern 7 and a shield pattern 8. The first lead pattern 7 is located in a space between adjacent pattern elements comprising the contact pattern pairs 5A and 5B and the first capacitor electrodes 4A, 4B and 4C. The first lead patterns 7 come together at a connection portion 3. The first lead patterns 7 are singly or multiply arranged in the space as mentioned above. Each of the first capacitor electrodes 4A, 4B and 4C is surrounded by a linear shield pattern 8, and the first lead patterns 7 are interposed between the shield patterns 8 or additional linear shield patterns 9. In the case that a plurality of lead patterns 7 are provided, they are separated by the shield patterns 9, thereby preventing cross talk between the lead patterns 7 or noise trouble. As shown in Fig. 2 the left first capacitor electrode 4A has a fundamental configuration, that is, a circular shape in this embodiment, and the central and right first capacitor electrodes 4B and 4C have an elongated circular shape of the same area as the first capacitor electrode 4A. The space between the elongated capacitor electrodes 4B and 4C is larger than that defined between the circular capacitor electrode 4A and the elongated electrode 4B. The first lead patterns 7 are disposed so as mainly to pass in the larger space. With this arrangement, the density of lead patterns 7 can be reduced as compared with the prior art. In this embodiment, a single lead pattern 7 is arranged in the smaller space defined between the capacitor electrodes 4A and 4B, and a plurality of lead patterns 7 are arranged in the larger space defined between the capacitor electrodes 4B and 4C. Referring to Fig. 3 which partially shows a bottom plan view of the printed circuit board, second capacitor electrodes 14A, 14B and 14C are arranged on the lower surface of the dielectric film substrate 2 in such a manner as to be opposed to the first capacitor electrodes 4A, 4B and 4C formed on the upper surface of the dielectric film substrate 2, respectively. The second capacitor electrode 14A has the same shape as the first opposed capacitor electrode 4A. Similarly, the second capacitor electrodes 14B and 14C have the same shape as the opposed first capacitor electrodes 4B and 4C. In other words, the right second capacitor electrode 14A as seen in Fig. 3 has a circular shape, and the central and left second capacitor electrodes 14B and 14C have an elongated shape. The second capacitor electrodes 14A, 14B and 14C are connected to each other by second lead patterns 17, which come together at a connecting portion 3. The second capacitor electrodes 14A, 14B and 14C and the second lead patterns 17 are surrounded to be protected by shield pattern 18. The contact patterns 5A and 5B, the first lead patterns 7, the first capacitor electrodes 4A to 4C and the shield pattern 8 are formed on the upper surface of the dielectric film substrate 2 by etching a conductive metal foil or printing a conductive coating material. Similarly, the second lead patterns 17, the second capacitor electrodes 14A to 14C and the shield pattern 18 are formed on the lower surface of the dielectric film substrate 2 by etching a conductive metal foil or printing a conductive material. In the printed circuit board 1 according to the present invention, the capacitor switches C1 to C3 are constructed by the first and second capacitor electrodes 4A to 4C and 14A to 14C and the dielectric film substrate 2 disposed between the first and second capacitor electrodes. Then, the printed circuit board 1 is used in the same manner as in the prior art. Referring to Fig. 4 which shows another embodiment of the present invention, a first capacitor electrode 24A having a square shape as a basic structure and the other first capacitor electrodes 24B and 24C having a rectangular shape are formed on the dielectric film substrate 2. The square of the capacitor electrode 24A has the same area as of the rectangle of the capacitor electrodes 24B and 24C, and the space defined between the capacitor electrodes 24A and 24B is larger than that defined between the capacitor electrodes 24B and 24C, so that the number of wirings 29 including first lead patterns 26 and shield patterns 28 arranged between the capacitor electrodes 24A and 24B is higher than that between the capacitor electrodes 24B and 24C. The first lead patterns 26 and the shield patterns 28 are arranged in the same manner as in the first embodiment. Figs. 5 and 6 show a third embodiment of the present invention, and correspond to Figs. 2 and 3 showing the first embodiment. In this third embodiment, the corresponding elements are designated by the same or similar reference numerals as in the first embodiment. According to the third embodiment, circular first capacitor electrodes 4A₁, 4A₂ and 4A₃ have the same shape, and the first capacitor electrode 4A₃ is further removed from the adjacent first capacitor electrode 4A₂ to define an enlarged space therebetween. Similarly, a rectangular capacitor electrode 4C is moved from an elongated circular capacitor electrode 4B to define an enlarged space therebetween. Figs. 7A and 7B show a modification in which the same reference numerals designate the same elements as before. The first lead pattern 7 and the second lead pattern (not shown, but provided on the back surface of the substrate 2) are so arranged as to form a matrix. As shown in Figs. 7A and 7B, there is provided in the vicinity of one end of the lead pattern 7 a check terminal X for checking for a defect such as break in the lead pattern 7. In this embodiment, the check terminal X is so formed as to outwardly project from the lead pattern 7 as specifically shown in Fig. 7B. That is, prior to installation of the printed circuit board into the keyboard, a check signal is inputted to a terminal X′, for example, and it is detected whether or not a predetermined detection signal is outputted from the check terminal X connected to the terminal X′. If the predetermined detection signal is not outputted, it is determined that the line of the circuit pattern is broken. Similar operation is conducted between the other terminals and the other check terminals, so as to check a defect such as break of the circuit pattern. Figs. 8 and 9 show a modification in which the same reference numerals designate the same elements as before. In this modification, a chattering prevention pattern 41 is interposed between the dielectric film substrate 2 and a substrate mounting board 40 located under the substrate 2. The chattering prevention pattern 41 is preferably formed in a circular shape such that it surrounds switch electrode pair 5A and 5B, and has a thickness equal to that of the second capacitor electrode 14A. The chattering prevention pattern 41 is electrically connected to a shield pattern 18A surrounding the second capacitor electrode 14A. In a switching operation where a key top 42 is manually depressed to bring a movable electrode 43 to electrically contact with the switch electrode pair 5A and 5B and thereby effect an on-state, when a depression force applied to the key top 42 is released to cause the movable electrode 43 to be moved away from the switch electrode pair 5A and 5B by an elastic force of a rubber spring 44, thereby effecting an off-state, the switch electrode pair 5A and 5B are prevented from unstably moving vertically. That is, the upper surface of the switch electrode pair 5A and 5B is always kept at the same level as of the first capacitor electrode 4A due to the chattering prevention pattern 41. Accordingly, chattering in the switching operation may be prevented. Although the shape of the chattering prevention pattern 41 is circular in this preferred embodiment, any other appropriate shapes such as rectangular shape may be employed. Reference numeral 45 designates a guide member for guiding a stem portion of the key top 42. Fig. 10B shows a further preferred feature of the present invention, and Fig. 10A shows a prior art construction corresponding to Fig. 10B. Fig. 10A shows a mounted condition where an element such as LED 50 is mounted to a pattern terminal, legs 50A of the LED 50 are inserted through insertion holes 2A of a substrate 2, and they are then fixed to the substrate 2 by soldering 51. In the case that the substrate 2 is a film substrate, the legs 50A of the LED 50 are inserted through the insertion holes 2A, so as to be firmly fixed to the substrate 2. In this case, the substrate 2 is raised by the legs 50A to disadvantageously form a waving portion 2B. The preferred embodiment shown in Fig. 10B solves the above problem by forming a recess 60 in the substrate mounting board 40 for receiving the legs 50A of the LED 50. With this construction, even when the legs 50A are inserted through the film substrate 2, and are fixed thereto, the above-mentioned waving portion 2B of the substrate 2 is prevented from being generated. Referring to Fig. 12 which shows a further embodiment of the present invention, the circuit patterns are formed on only one surface of a substrate 2 rather than on both surfaces thereof as in the previous embodiments. The substrate 2 may be a rigid substrate or a film substrate. A first capacitor electrode 4A is formed on the substrate 2 by etching a copper foil or the like or printing a conductive coating such as carbon, copper and silver paste thereon. A shield pattern 8 is formed on the substrate 2 in such a manner as to surround the first capacitor electrode 4A. An insulator layer 60 is formed so as to cover the first capacitor electrode 4A and the shield pattern 8. The insulator layer 60 is formed of a usually available insulating coating material such as an epoxy resin coating material. A second capacitor electrode 14A is formed on the insulator layer 60 in opposed relationship to the first capacitor electrode 4A. A switch electrode pair has a first electrode 5A connected to the second capacitor electrode 14A and a second electrode 5B connected to a lead pattern 7 formed on the substrate 2. As shown, the switch electrode pair 5A and 5B is formed on the substrate 2. The second capacitor electrode 14A and the switch electrode pair 5A and 5B are formed by printing the afore-mentioned conductive coating material. This embodiment can have a distinction of the switch electrodes and capacitor electrodes as in previously discussed embodiments. Fig. 13 shows another embodiment. In this embodiment, the insulator layer 60 extends to the switch electrode pair 5A and 5B in such a manner that the switch electrode pair 5A and 5B are formed on the insulator layer 60. With this arrangement of this embodiment, the switch electrode pair 5A and 5B is less formed with stepped edges 61 as compared with the embodiment shown in Fig. 12 since the insulator layer 60 is interposed between the switch electrode pair 5A and 5B and the substrate 2. Accordingly, the thickness of the switch electrode pair 5A and 5B may be made uniform. Having thus described the preferred embodiments of the invention, it should be understood that numerous structural modifications and adaptations may be made without departing from the scope of the claims.

Claims: A printed circuit board comprising a dielectric substrate (2) and a plurality of circuit patterns for capacitor switches formed on said dielectric substrate (2), each of said circuit patterns comprising a switch electrode pair (5A, 5B) formed on one surface of said dielectric substrate (2), said switch electrode pairs (5A, 5B) being at a particular spacing from each other, a first capacitor electrode (4A, 4B, 4C) connected to one electrode (5B) of said switch electrode pair, a first lead pattern (7) connected to the other electrode (5A) of said switch electrode pair, a second capacitor electrode (14A, 14B, 14C) opposed to said first capacitor electrode (4A, 4B, 4C), said first and second capacitor electrodes forming capacitor electrode pairs, and a second lead pattern (17) connected to each second capacitor electrode (14A, 14B, 14C), wherein the spacing between the edges of at least some adjacent capacitor electrode pairs is greater than it is between other adjacent pairs, so that the density of said first and second lead patterns (7, 17) disposed in said greater spaces between adjacent capacitor electrode pairs can be reduced. A printed circuit board as defined in claim 1, wherein non-uniform spacing between capacitor electrode pairs is provided by the shapes of at least some of said capacitor electrode pairs being different from each other, with the areas of said capacitor electrode pairs remaining equal. A printed circuit board as defined in claim 1 or 2, wherein non-uniform spacing between capacitor electrode pairs is provided by the centres of at least some of the capacitor electrode pairs being at distances from each other different from the distances between the switch electrode pairs. A printed circuit board according to any preceding claim wherein the second capacitor electrodes (14A, 14B, 14C) are on the opposite side of the dielectric substrate from the first capacitor electrodes (4A, 4B, 4C). A printed circuit board according to claim 1, 2 or 3 wherein each second capacitor electrode (14A, 14B, 14C) is formed on an insulating layer covering the corresponding first capacitor electrode (4A, 4B, 4C). A printed circuit board as defined in any preceding claim wherein said first lead pattern (7) and said second lead pattern (17) are so arranged as to form a matrix, and said printed circuit board further comprises a check terminal formed in the vicinity of one end of each of said first and second lead patterns (7, 17) for checking for a break in said circuit patterns. A printed circuit board as defined in claim 6, wherein said check terminal outwardly projects from said first lead pattern (7). A printed circuit board as defined in any preceding claim further comprising a chattering prevention pattern provided on the lower surface of said dielectric substrate for preventing chattering of said switch electrode pair (5A, 5B) upon switching operations, said chattering prevention pattern having a thickness equal to that of said second capacitor electrode (14A, 14B, 14C). A printed circuit board as defined in claim 8, wherein said chattering prevention pattern is of circular shape and surrounds said switch electrode pair (5A, 5B). A printed circuit board as defined in claim 8 wherein said chattering prevention pattern comprises a shield pattern. A printed circuit board as defined in any preceding claim further comprising a substrate mounting board having a recess for receiving a leg portion of an electronic element, so as to prevent waving of said dielectric film substrate. A printed circuit board comprising a substrate (2) and a plurality of circuit patterns for capacitor switches formed on one surface of said substrate (2), each of said circuit patterns comprising a switch electrode pair (5A, 5B) formed on said one surface of said substrate, said switch electrode pairs (5A, 5B) being at a particular spacing from each other, a first capacitor electrode (4A) formed on said one surface of said substrate (2), a first lead pattern (7) connected to one electrode (5B) of said switch electrode pair, an insulator layer (60) covering at least said first capacitor electrode (4A), and a second capacitor electrode (14A) formed on said insulator layer (60) in opposed relationship with said first capacitor electrode (4A) and connected to the other electrode (5A) of said switch electrode pair, said first and second capacitor electrodes (4A, 14A) forming capacitor electrode pairs, wherein the spacing between the edges of at least some adjacent capacitor electrode pairs is greater than it is between other adjacent pairs so that the density of said first lead pattern disposed in said greater spaces between adjacent capacitor pairs can be reduced. A printed circuit board as defined in claim 12, wherein said switch electrode pair is formed on said substrate. A printed circuit board as defined in claim 14, wherein said switch electrode pair is formed on said insulator layer.

Inventors: HIRANO, SADASHI, KAKO, MITSUMASA
Applicants: BROTHER KOGYO KABUSHIKI KAISHA
Application year: 1987
Main classification: H01H13
IPC codes: H03K17, H05K1, H01H1, H01H13