JP2868475B2 - Printed board - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed circuit board having a conductive pattern for wiring made of carbon paint and a copper foil circuit on an insulating substrate. 2. Description of the Related Art In a conventional printed circuit board of this type, a fixed contact pattern for a key switch, a conductive pattern, and a copper foil circuit are provided on the same surface of the board. When soldering each electronic component to a copper foil circuit by flow soldering, it is necessary to take measures to prevent the solder from adhering to the fixed contact pattern provided in an exposed state. Therefore, conventionally, a step of exposing the fixed contact pattern by masking the fixed contact pattern with a solder resist film and removing the resist film after the soldering step of the electronic component is completed has been performed. Recently, fixed contact patterns have been formed using carbon paint.However, since conductive patterns for wiring the fixed contact patterns to predetermined portions of the circuit were formed using silver paint, printing of these patterns has been performed. Each had to be performed in separate steps. As described above, this type of conventional printed circuit board requires an extra step of masking the fixed contact pattern and also requires a step of removing the masking after mounting the electronic component. Since the conductive pattern had to be formed in different steps, there was a disadvantage that the number of steps was increased and the cost was increased. The inventor of the present application formed a fixed contact pattern for a key switch and a conductive pattern for wiring on one surface of an insulating substrate, and formed a copper foil circuit on the insulating substrate. It was considered that the pattern and the conductive pattern of the fixed contact for the key switch were formed only on the other surface, and the conductive pattern was formed with carbon paint. In the case of forming a fixed contact pattern for a key switch and a conductive pattern using a carbon paint, if a through-hole conductor is formed after forming a circuit pattern on both surfaces of a substrate, there arises a problem that a sufficient through-hole conductor cannot be formed. For example, if the circuit pattern is formed so that the end of the pattern extends to a position just near the opening end of the through hole, the carbon paint will partially flow into the opening end of the through hole when forming the circuit pattern. . However, the surface of the inflow part formed by curing the carbon paint is
Relatively poor compatibility with conductive paint for forming through-hole conductors such as silver paint. Therefore, when forming a through-hole conductor later using a conductive paint such as a silver paint, the conductive paint for forming the through-hole conductor flows down from an inflow portion formed by the carbon paint formed in the through-hole. The possibility is high, and connection failure between the circuit pattern and the through-hole conductor is likely to occur. It is also conceivable to form a circuit pattern using carbon paint so as to leave the opening end of the through hole, but in this case, the conductive paint for forming the through hole conductor is formed by the corner of the opening end of the through hole. In some cases, the connection may be broken, and in this case, a connection failure may easily occur between the circuit pattern and the through-hole conductor. Therefore, the inventor considered forming the fixed contact pattern and the conductive pattern with a carbon paint after forming the through-hole conductor first. [0005] However, since sharp edges are formed at the corners of the pattern of the copper foil circuit formed by etching, when a large number of printed circuit boards are transported in a stacked state, the upper printed circuit board is printed. There has been a problem in that the conductive pattern and the fixed contact pattern formed by the carbon paint of another printed circuit board disposed below are cut by the sharp edge of the copper foil circuit of the board. In particular, since the surface of the end of the through-hole conductor has large irregularities, when a conductive pattern is formed with a carbon paint to cover the surface of the end, the carbon paint on the end is rubbed. It will be easier. When the carbon paint is rubbed and scattered, there is a problem that the insulating property between the fixed contact patterns is adversely affected. Further, even if the ends of a pair of through-hole conductors connected to a pair of conductive patterns connected to a pair of fixed contact patterns for a key switch forming one fixed contact are covered with a carbon paint, a pair of the through-hole conductors may be formed. Migration may occur between the ends of the through-hole conductor. An object of the present invention is to prevent the carbon paint on the end of the through-hole conductor from being rubbed and scattered even when transported in an overlapping manner, and to prevent the conductive pattern from being easily broken and to prevent migration. An object of the present invention is to provide a printed circuit board which is less likely to occur. According to the present invention, in order to achieve the above object, a conductive pattern for power distribution and a fixed contact pattern for a key switch are formed on one surface of an insulating substrate by a carbon paint. A printed circuit board in which a copper foil circuit is formed on the other surface of the insulating substrate, and a predetermined portion of the copper foil circuit and a predetermined portion of the conductive pattern are connected by a through-hole conductor penetrating the insulating substrate. And In the present invention, the terminal portions (4a, 4'a ) are formed by covering the ends of the through-hole conductors with the conductive pattern. Then, the conductive pattern is covered with an insulating protective layer.
As a result, a polymerized layer is formed on the end of the through-hole conductor. Also, a pair of through-hole conductors connected to a pair of conductive patterns connected to a pair of key switch fixed contact patterns constituting one fixed contact are formed outside the region where the pair of key switch fixed contact patterns are formed. To place. Then, one of the pair of conductive patterns is connected to a pair of terminal portions (4
a, 4'a ). If the conductive pattern is formed so as to cover the end of the through-hole conductor, the contact area between the through-hole conductor and the conductive pattern is increased, and the disconnection becomes difficult. If a conductive layer and an insulating protection layer are formed on the protruding end of the through-hole conductor to form a superposed layer, a protruding portion that is considerably protruded from the surface of the substrate can be formed. The edge of the copper circuit formed on the other surface of the other substrate acts as a spacer between the other substrate and the possibility that the contact pattern not covered with the insulating protective layer will be cut. Can be reduced to Further, one of the pair of conductive patterns (4 ')
Is formed so as to cross between a pair of terminal portions (4a, 4'a ) formed on the pair of through-hole conductors, one of the through-hole conductors is located between the ends of the pair of through-hole conductors having different potentials. A part of the conductive pattern (4 ') made of the carbon paint having the potential substantially equal to the potential of the carbon paint exists. When a part of such a conductive pattern is located between the pair of terminal portions (4a, 4'a ), the potential gradient between the terminal portions of the pair of through-hole conductors becomes small, so that the end portions of the pair of through-hole conductors are formed. It is possible to suppress the occurrence of migration occurring therebetween. An embodiment of the present invention will be described below with reference to the drawings. FIGS. 1 and 2 show an embodiment of the present invention. In these figures, reference numeral 1 denotes an insulating substrate made of a paper phenol laminate, a paper epoxy laminate, a glass epoxy laminate, or the like. On one surface of the insulating substrate 1, a copper foil circuit 2 having a predetermined pattern is formed by etching.
On the other surface of the substrate 1, fixed contact patterns 3 and 3 'for key switches and conductive patterns 4 and 4' for wiring for connecting these patterns to predetermined positions on the substrate are both made of carbon paint (carbon powder). Is added to a resin binder). Thus, the fixed contact patterns 3, 3
If both 'and the conductive patterns 4 and 4' are formed of carbon paint, both patterns can be formed by one printing, so that the number of steps can be reduced. Conductive pattern 4,
The terminal portions 4a and 4'a which can be connected to the copper foil circuit 4 'are connected to predetermined portions of the copper foil circuit 2 by through-hole conductors 5 provided through holes 1a penetrating the substrate 1. In the illustrated example, the through-hole conductor 5 is provided before the conductive patterns 4, 4 'are formed, and the conductive patterns 4, 4' are arranged such that the terminals 4a, 4'a overlap the ends of the through-hole conductor 5. Is printed. A portion of the copper foil circuit 2 where solder is to be prevented from being adhered is covered with a solder resist 6. As shown in FIG. 1, a pair of through-hole conductors connected to a pair of conductive patterns 4, 4 'connected to a pair of key switch fixed contact patterns 3, 3' forming one fixed contact. The (through-hole conductors formed below the terminal portions 4a, 4'a ) are arranged outside the region where the pair of key switch fixed contact patterns 3, 3 'is formed. One conductive pattern 4 'of the pair of conductive patterns 4 and 4' is formed to be curved so as to cross between the pair of terminal portions 4a and 4'a. The conductive patterns 4, 4 'are covered with an insulating protective layer 7 formed by printing. At the corners of the pattern of the copper foil circuit 2 formed by etching,
Sharp edges are formed. However, if the insulating protective layer 7 is formed on the conductive patterns 4, 4 ', the conductive patterns 4, 4 formed from a mechanically weak carbon paint are used.
′ Can be protected, so that the conductive pattern is not cut by the sharp edge of the copper foil circuit 2 of another printed circuit board even when the printed circuit boards are transported in a stacked state. In particular, since the conductive patterns 4 and 4 'are formed so as to cover the ends of the through-hole conductors 5, there is little possibility that the conductive patterns are cut off. In this embodiment, all of the through-hole conductors 5 are insulated and protected. Since it is covered with the layer 7, the conductive patterns 4, 4 'hardly break. Also, the conductive pattern 4 is formed so as to cover the end of the through-hole conductor 5.
′, So that it protrudes considerably above the end of the through-hole conductor 5 beyond the fixed contact patterns 3, 3 ′, so that when this protruding portion is overlapped with another printed circuit board, the spacer means Function as Therefore, cutting of the fixed contact pattern can be reliably prevented. According to this embodiment, the conductive pattern and the fixed contact pattern for the key switch are formed by the carbon paint, but the carbon paint on the through-hole is rubbed, and the carbon paint on the contact is rubbed and scattered. Can be prevented. Further, even if the carbon paint of the contacts is scattered, the insulating properties between the fixed contact patterns are not adversely affected. Although not shown, on the surface of the substrate 1 on which the fixed contact patterns 3, 3 'and the conductive patterns 4, 4' are provided, another required number of other fixed contact patterns and conductive patterns are provided. Have been. A hole (not shown) for mounting an electronic component was provided through a predetermined portion of the substrate 1 and the copper foil circuit 2, and a copper foil circuit was provided in a state where an electronic component lead wire was inserted into this hole. By applying flow soldering to the surface, soldering of the electronic component to the copper foil circuit is performed. In this case, the fixed contact patterns 3, 3
′ And the conductive patterns 4 and 4 ′ are on the surface opposite to the copper foil circuit 2, so that solder does not adhere to these patterns. Therefore, it is not necessary to mask the fixed contact pattern and the wiring conductive pattern. As described above, when both the fixed contact pattern and the conductive pattern are formed of carbon paint, the operating resistance of the key switch cannot be prevented from becoming 500Ω or more, but the key switch is almost always “1”. And the state of "0" can be selectively obtained, so that almost no problem is caused in most cases even with such an operating resistance. In the above embodiment, the fixed contact patterns 3, 3 '
Are formed in a U-shape, but the shape of the fixed contact pattern is arbitrary, and it can be formed in an appropriate shape such as a comb-like shape or a T-shape so as to easily contact the movable contact of the key switch. In the above embodiment, other patterns such as a printed resistor and a resistor for a variable resistor can be further provided on the surface of the substrate 1 on which the fixed contact pattern is provided, if necessary. As described above, according to the present invention, since the conductive pattern is formed so as to cover the end of the through-hole conductor, the contact area between the through-hole conductor and the conductive pattern is increased. , It is difficult to disconnect. If a conductive layer and an insulating protection layer are formed on the protruding end of the through-hole conductor to form a superposed layer, a protruding portion that is considerably protruded from the surface of the substrate can be formed. The edge of the copper circuit formed on the other surface of the other substrate acts as a spacer between the other substrate and the possibility that the contact pattern not covered with the insulating protective layer will be cut. There is an advantage that can be reduced. In particular, since the surface of the end of the through-hole conductor has large irregularities, if a conductive pattern is formed with a carbon paint to cover the surface of the end, the carbon on the end of the through-hole conductor The paint is easily rubbed, but if the conductive pattern covering the surface of the end of the through-hole conductor is also covered with an insulating protective layer as in the present invention, the end of the through-hole conductor can be covered even when another substrate is overlaid. There is an advantage that the above carbon paint is not rubbed and scattered. In particular , when one of the pair of conductive patterns is formed so as to cross between a pair of terminal portions formed on the pair of through-hole conductors as in the present invention, a pair of the through-hole conductors having different potentials are formed. Since there is a portion of the conductive pattern made of carbon paint that has substantially the same potential as the potential of one through-hole conductor between the terminal portions, the potential gradient between the ends of the pair of through-hole conductors is small. As a result, it is possible to suppress the occurrence of migration occurring between the ends of the pair of through-hole conductors.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view showing a main part of an embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view showing a cross-section taken along a line II-II of FIG. [Description of Signs] 1 Insulating substrate 2 Copper foil circuit 3, 3 'Fixed contact pattern for key switch 4, 4' Conductive pattern 5 Through-hole conductor

Claims (1)

(57) [Claims] A conductive pattern for power distribution and a fixed contact pattern for a key switch are formed on one surface of an insulating substrate by a carbon paint, a copper foil circuit is formed on the other surface of the insulating substrate, and a predetermined portion of the copper foil circuit is formed. An end of the through-hole conductor (5) is covered with the conductive pattern (4, 4 ') on a printed circuit board in which a predetermined portion of the conductive pattern is connected by a through-hole conductor penetrating the insulating substrate. terminal portions (4a, 4'a) is formed Te
Is, the conductive pattern is covered with an insulating protective layer, the solid for a pair of the key switches constituting one fixed contact
A pair of conductors connected to a constant contact pattern (3, 3 ')
A pair of said throughs connected to the electric pattern (4, 4 ')
The hole conductor (5) is connected to the fixed connection for the pair of key switches.
Arranged outside the area where the point pattern (3, 3 ') is formed
And one (4 ′) of the pair of conductive patterns (4, 4 ′)
The one formed on the pair of through-hole conductors (5)
It is formed so as to cross between the pair of terminal portions (4a, 4'a).
A printed circuit board characterized by being formed .