JP2002109997A - Connector part structure of membrane circuit and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a connector part structure of a membrane circuit which can prevent migration of a conductive material generated at the connector insertion-coupling part. SOLUTION: Wirings 3a to 3c formed at a tail part 1 of a membrane switch are each formed of Ag paste in width 35 μm and at 0.5 mm pitch on an insulation film by a screen printing method or the like, on which an insulation 2b is laminated. The insulation film 2b is not laminated at a tip side of the tail part 1 forming a connector part of the wirings 3a to 3c. Since the wirings 3a to 3c of this part are normally exposed, they are to be protected by forming a protective film 6 of resin in stead, which is made in such a material and a film thickness that it is easily burst through by the terminal of a mating connector at time of insertion-coupling to realize an electric conduction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a membrane circuit such as a membrane switch incorporated in a keyboard or the like of a personal computer, and more particularly, to a circuit in a connector fitting portion which is an electrical connection between a membrane circuit and other components. The present invention relates to a connector structure of a membrane circuit capable of suppressing migration of a conductive member of a wiring and a method of manufacturing the same.

[0002]

2. Description of the Related Art A flexible printed circuit board (FPC) is used as an electrode sheet, and wirings (electrodes) formed of conductive members formed on the electrode sheet are arranged so as to face each other, and an insulating film is interposed between the electrode sheets. Membrane switches can secure high electrical reliability while realizing space saving and cost reduction.
For example, it has been widely used for electronic devices equipped with a thin electronic circuit board such as a keyboard of a personal computer and a button of a mobile phone.

FIG. 9 is a schematic view showing a conventional membrane switch. The conventional membrane switch 100 has an F
A first insulating film 101 made of, for example, polyethylene terephthalate (PET) or polyethylene naphthalate (PEN) is disposed on a support plate (not shown) made of a metal plate such as e (iron) or Al (aluminum). The second insulating film 102 and the second insulating film 102 are superposed via an insulating spacer 103. The opposing surfaces of the first and second insulating films 101 and 102 are, for example, Ag
A plurality of first and second electrodes 104 and 10 made of (silver)
5 and first and second wirings 1 connecting these electrodes.
06 and 107 and a connection wiring 108 connected to the first wiring 106 are formed by a printing method such as screen printing, for example, to form a first electrode sheet 109 and a second electrode sheet 110. . An opening 111 is formed in the insulating spacer 103 at a position where the first and second electrodes 104 and 105 face each other, and the first and second electrodes 104 and 105 come into contact with each other through the opening 111. A switch operation is performed. The first and second electrode sheets 109 and 110 and the insulating spacer 103 are strictly aligned by using an assembling jig or the like, and then formed by a plurality of ultrasonic waves oscillated from a fusion horn. Fusion part 1
12 are joined. Also, the second wiring 107
And the connection wiring 108 are integrated in the tail portion 113 of the membrane switch 100. The tip of the tail portion 113 forms a connector portion for electrically connecting to other circuits, for example, FPC, FFC (flexible flat cable), and PCB (printed circuit board).

FIG. 10 shows a conventional membrane switch 10.
FIG. 11 is a schematic top view showing the tip of the tail portion 113 of FIG.
FIG. 11 is a sectional view taken along line DD ′ of FIG. 10. Tail part 113
Comprises the second insulating film 102 as a base material,
On the surface of the insulating film 102, a plurality of second wirings 107 and connection wirings 108 made of Ag paste or the like, which is a conductive member electrically connected to wirings to be connected, are alternately arranged at predetermined intervals. Are installed side by side. An insulating protective film 114 made of PET or PEN is formed on portions of the insulating film 102 and the wirings 107 and 108 other than a portion except a predetermined range from the tip side of the tail portion 113 to protect them. I have. Further, the tail portion 113
A reinforcing plate 1 made of PET or PEN is provided on the lower surface of the insulating film 102 at the tip of
15 is joined via a thermosetting adhesive 116 made of, for example, an epoxy resin to reinforce the tail portion 113.

[0005]

The wiring 10 of the tail portion 113 of the membrane switch 100 configured as described above.
When a DC voltage is applied to 7, 108, for example, in a humid environment (in water or in a state where dew condensation occurs),
The so-called migration (Ag ion migration) in which the component ions in the Ag of the wirings 107 and 108 move to the outside of the conductive material and electrically connect the wirings 107 and 108 to each other occurs. In particular, membrane switches and membrane circuits used in home electric appliances and the like can be used in an environment that is easily exposed to water and moisture. In comparison, such migration is more likely to occur.

That is, when the Ag paste is used as the conductive material for the wirings 107 and 108 as described above, a chemical reaction expressed by the following formula occurs in the conductive material on the anode (Anode: + pole) side.

[0007]

Embedded image Ag + OH ⁻ → AgOH + e ⁻

The product at this time, AgOH (silver hydroxide), is a very unstable compound. For this reason, the silver hydroxide produced here dissolves by a chemical reaction (decomposition reaction) according to the following formula in the same high humidity environment.

[0009]

Embedded image 2AgOH → Ag ₂ O + H ₂ O

The product at this time, Ag ₂ O (silver oxide), is colloidal and undergoes a chemical reaction represented by the following formula to generate Ag ⁺ ions. At this time, the conductive material on the anode side is in an equilibrium state.

[0011]

Embedded image

On the other hand, the Ag ⁺ ions generated at this time gradually move to the cathode (Cathode: − pole) side with the passage of time, and finally reach the cathode side, and on the surface of the conductive material on the cathode side, This Ag ⁺ ion is reduced, and white reduced silver precipitates as represented by the following formula.

[0013]

Embedded image Ag ⁺ + e ⁻ → Ag

Thus, Ag reduced on the cathode side
Gradually expands toward the anode side, and a so-called Ag metal tree made of the generated compound (reduced silver) is formed. When the above-described chemical reaction occurs in the conductive material of the wirings 107 and 108, the Ag metal tree 117 finally bridges between the wirings 107 and 108, as shown in FIG. Connection, the membrane circuit may be short-circuited, and the membrane switch may not function. It should be noted that such migration is mainly performed by A
The conductive material made of g is generated in a terminal portion such as the tail portion 113 where the conductive material is exposed.

On the other hand, in order to improve the slidability of the connector portion, C (carbon) or a mixture of C and Ag is sometimes printed on Ag in a superimposed manner. In this case, the occurrence of migration is suppressed to some extent. Can be.

However, this method is not perfect,
Further, as the interval (pitch) between the wirings 107 and 108 of the tail portion 113 becomes narrower, it becomes technically more difficult to print carbon on the surface thereof.

The present invention has been made in view of such a problem, and provides a connector portion structure of a membrane circuit capable of preventing migration of a conductive member generated at a connector fitting portion, and a method of manufacturing the same. The purpose is to:

[0018]

The connector structure of the membrane circuit according to the present invention is characterized in that the tail portion of the membrane circuit is formed by forming a conductive pattern made of Ag on an insulating film having a tail portion formed at an end. In a connector portion structure formed by concentrating at least a part of the conductive pattern and mating with the mating connector, the entire portion of the tail portion where the conductive pattern is concentrated, when mating with the mating connector A resin protective film is formed to cover the conductive pattern with a thickness that can be broken through by a terminal of a mating connector.

The protective film is preferably made of a copolymer mainly composed of C ₂ H ₂ Cl ₂ .

The thickness of the protective film is preferably 2-3 μm.

In the method of manufacturing a connector structure of a membrane circuit according to the present invention, Ag is formed on an insulating film having a tail portion formed at an end so that a part of the conductive pattern is concentrated on the tail portion. A step of forming a conductive pattern, and a resin covering the conductive pattern with a film thickness capable of being pierced by the terminal of the mating connector at the time of fitting with the mating connector over the entire portion of the tail portion where the conductive pattern is concentrated. Forming a protective film.

In the step of forming the protective film, the conductive pattern in the tail portion is preferably formed by screen printing or spraying a solution comprising a copolymer mainly composed of C ₂ H ₂ Cl ₂ and water. The method includes a step of applying the solution to the concentrated portion, and a step of drying the solution applied in this step with hot air.

Preferably, the step of forming the protective film is a step of forming the protective film to a thickness of 2 to 3 μm.

According to the present invention, since the protective film is formed on the insulating film and the conductive pattern in the portion where the conductive pattern in the tail portion of the membrane circuit is exposed,
Even if the tail portion is exposed to moisture, the occurrence of migration of the conductive material forming the conductive pattern can be suppressed. Thereby, it is possible to prevent a short circuit between the conductive patterns in the tail portion. In addition, when the protective film is fitted to the mating connector, the protective film is broken through by the electrode of the mating connector, and electrical conduction is achieved.

[0025]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an upper perspective view showing a tail portion of a membrane circuit according to one embodiment of the present invention.
Is a sectional view taken along the line AA 'in FIG. 1, and FIG. 3 is a sectional view taken along the line BB' in FIG. The tail part 1 of the membrane switch forms a connector part to be fitted with a mating connector.
Insulating film 2 made of synthetic resin such as PET or PEN
a, 2b, a plurality of wirings 3a to 3c patterned on the surfaces of the insulating films 2a, 2b, a reinforcing plate 5 made of a synthetic resin such as PET or PEN for reinforcing the insulating films 2a, 2b from the back surface, It comprises a thermosetting adhesive 4 made of an epoxy resin or the like for connecting the insulating films 2a and 2b and the reinforcing plate 5, and a protective film 6 covering the whole of the plurality of wirings 3a to 3c.

The wirings 3a to 3c are formed on the insulating film 2a by, for example, an Ag paste at a thickness of 35 μm and an interval (pitch) of 0.5 mm on the insulating film 2a by a screen printing method or the like.
Are laminated. This insulating film 2b is not laminated on the tip side of the tail part 1 forming the connector part of these wirings 3a to 3c. Wirings 3a to 3c of this part
Is usually in an exposed state, so that the wiring 3a to 3c is conventionally devised so as to protect the wirings 3a to 3c from corrosion or the like by applying an Au (gold) plating process, or to print C to prevent migration. In this embodiment, the wirings 3a to 3c are protected by forming a protective film 6 made of resin instead of these. The protective film 6 is set to a material and a film thickness such that the protective film 6 can be easily pierced by a terminal of the mating connector when the mating with the mating connector is performed, so that electrical conduction is achieved. As a material of the protective film 6, for example, vinyldene chloride copolymer latex (a copolymer mainly composed of C ₂ H ₂ Cl ₂ ) or the like is preferable, and a film thickness of 2 to 3 μm is preferable.

FIG. 4 is a flow chart showing a process of forming a membrane circuit having the above-described tail portion 1. First, a circuit substrate such as a sheet constituting an insulating film or the like serving as a base of a membrane circuit made of PET or PEN is processed into a desired shape (including a tail portion) (S1). Next, a conductive pattern such as an electrode or a wiring made of Ag or the like forming a membrane circuit is printed on a predetermined surface of the insulating film by, for example, a screen printing method to form each electrode sheet (S2). Thereafter, in order to form a protective film on the exposed portion of the wiring of the tail portion of each formed electrode sheet, a mixed solution obtained by mixing about 49% of vinyldene chloride copolymer latex and about 51% of water in a printing method is used. Or by spraying by a spray method (S3), and then 80 to 12
Perform hot air drying at 0 ° C. for 10 to 20 minutes to form a film having a thickness of 2 to 3 μm.
A degree of protection film is formed (S4). It should be noted that, when manufacturing a membrane switch, it is necessary to go through some further steps using a membrane circuit formed by such a process, but it is the same as the conventional manufacturing process, and the gist of the present invention Since it is not directly related, the description is omitted in this embodiment.

Next, the performance of the thus formed membrane circuit will be described. FIG. 5 is a diagram showing a table of a change with time of an insulation resistance value between wires in a moist heat environment of a membrane circuit. When measuring the insulation resistance between wires in a humid environment, the PCB (Printed
Circuit Board) (not shown) with 0.5mm pitch F
A connector for PC or FFC (not shown) is mounted, and the respective wirings of the anode and the cathode in the tail part of the formed membrane circuit are connected to the respective positive and negative lead wires and connectors formed on the PCB. It was set to be connected via. Then, a DC voltage (DC) of 5 volts (5 V) is applied between the lead wires to expose the circuit to a high humidity (95% RH) and high heat (70 ° C.) environment, and an insulation resistance measuring device connected to the circuit The change of the insulation resistance value indicated by was measured. In addition, the graph of FIG. 5 shows the case where the wiring of the membrane circuit is made only of Ag,
The graph shows the case of g + C, and the graph shows the case of Ag + protective film.

As shown in the figure, the wiring using the Ag + C conductive material in the graph has the highest electrical insulation performance at the initial value, but after 250 hours and 500 wirings.
When the time passes, it can be seen that the wiring using the Ag + protective film conductive material in the graph has the highest electrical insulation performance. The reason why the wiring shown in the graph at the initial value has slightly better electrical insulation performance is that in the wiring shown in the graph, the connection terminal of the connector must break through the protective film of the wiring shown in the graph And the contact area between the terminals is small. However, it can be seen that the wiring made of the conductive material of the Ag + protective film is stable with almost no change in the electrical insulation performance until 500 hours elapse from the initial value.
From this, it can be said that by forming the protective film on the exposed portion of the wiring of the membrane circuit, excellent electrical insulation performance can be exhibited even in a high-humidity and high-temperature environment, and a short circuit can be prevented.

FIG. 6 is a table showing a change with time of the inter-wiring voltage value after the pure water is dropped on the connector portion of the tail portion 1. In measuring the voltage between wirings after dropping pure water, for example, a chart recorder (not shown) that records changes in wiring and voltage of each of an anode and a cathode in a tail portion of a membrane circuit formed at a pitch of 0.5 mm. And a DC voltage of 5 V is applied between the positive electrode and the negative electrode, and pure water (deionized water) is dropped by 0.02 to 0.03 ° so as to connect at least predetermined wirings. The change was recorded. The graph showing the measurement results shown in FIG. 6 shows the case where the wiring of the membrane circuit is made of only Ag, the graph shows the case of being made of Ag + C, and the graph shows the case of being made of the Ag + protective film. Also,
Environment at the time of measurement is room temperature 21-24 ° C and humidity 38-59%
Met.

As shown in the figure, the wiring using Ag or Ag + C as the conductive material in the graph causes electrical continuity immediately after the pure water is dropped, causing a short circuit, and the applied voltage of 5 V No change was shown until the end of the measurement while displaying. On the other hand, the wiring using the Ag + protective film in the graph shows no change even when pure water is dropped, and the voltage between the wirings is 0.
It was still. From this, it can be said that by forming the protective film, it is possible to prevent the occurrence of migration due to moisture, and to reduce the possibility of short circuit.

When the tail portion 1 of the membrane circuit having such characteristics is inserted into a connector (a whole image is not shown) having connection terminals, as shown in FIG. 7 and FIG. Each connection terminal of the connector is connected. That is, FIG. 7 is a sectional view taken along the line AA ′ showing a case where the tail portion 1 of the membrane circuit shown in FIG. 1 is inserted into the connector, and FIG. 8 is a sectional view taken along the line BB ′. Connector 10
Has connector housings 8a and 8b made of a synthetic resin such as epoxy resin, for example. The upper connector housing 8a is provided with connection terminals 9a to 9c at positions opposed to predetermined positions of the wirings 3a to 3c. The connection terminals 9a to 9c have projections 11a to 11c on the connection surface side, and these projections 11a to 11c break through the protective film 6 formed on the tail portion 1 and pierce the wirings 3a to 3c. Electrical conduction between the terminals 9a to 9c and the wirings 3a to 3c is obtained. Since these protrusions 11a to 11c are formed to be extremely small (though the protrusion height required to break through the protective film and pierce the wiring is necessary), the protrusions 11a to 11c are formed.
The hole formed in the protective film 6 due to the penetration of the hole 11c becomes a very small pinhole. For example, even if moisture is applied to the tail 1 after the tail 1 is pulled out from the connector 10, migration hardly occurs. Become.
By forming the protective film 6 in this manner, a short circuit of the membrane circuit can be prevented.

[0033]

As described above, according to the present invention,
Since the protective film is formed on the insulating film and the conductive pattern in the portion where the conductive pattern of the tail portion of the membrane circuit is exposed, the conductive material that forms the conductive pattern even when the tail portion is exposed to moisture. There is an effect that generation of migration can be suppressed. Thereby, it is possible to prevent a short circuit between the conductive patterns in the tail portion. In addition, when the protective film is fitted to the mating connector, the protective film is broken through by the electrode of the mating connector, and electrical conduction is achieved.

[Brief description of the drawings]

FIG. 1 is an upper perspective view showing a tail portion of a membrane circuit according to one embodiment of the present invention.

FIG. 2 is a sectional view taken along line AA ′ of FIG.

FIG. 3 is a sectional view taken along the line BB ′ of FIG. 1;

FIG. 4 is a flowchart showing a process of forming a membrane circuit having the tail portion 1;

FIG. 5 is a table showing a change with time of an insulation resistance between wirings in a humid environment of a membrane circuit formed in the same step.

FIG. 6 is a diagram showing a table of ぅ change over time of a voltage value between wires after the pure water is dropped in the membrane circuit.

FIG. 7 is a sectional view taken along the line AA ′ showing a case where a tail portion of the membrane circuit shown in FIG. 1 is inserted into a connector.

FIG. 8 is a sectional view taken along the line BB 'in FIG.

FIG. 9 is a schematic view showing a conventional membrane switch.

FIG. 10 is a schematic top view showing a tip portion of a tail portion of a conventional membrane switch.

FIG. 11 is a sectional view taken along the line DD ′ of FIG. 10;

FIG. 12 is an enlarged schematic top view showing an Ag metal tree generated between wirings at tail portions of a conventional membrane switch.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Tail part, 2 ... Insulating film, 3 ... Wiring, 4 ... Thermosetting adhesive, 5 ... Reinforcement plate, 6 ... Protective film, 8 ... Connector housing, 9 ... Connection terminal, 10 ... Connector, 11 ... Projection .

Claims (6)

[Claims] A conductive pattern made of Ag is formed on an insulating film having a tail formed at an end thereof. At least a part of the conductive pattern is formed on the tail of the membrane circuit. In the connector structure to be fitted with the mating connector, the conductive pattern has a film thickness that can be pierced by the terminal of the mating connector when the mating with the mating connector is performed on the entire portion of the tail portion where the conductive pattern is concentrated. A connector structure for a membrane circuit, wherein a protective film made of resin is formed to cover the connector. 2. The connector structure for a membrane circuit according to claim 1, wherein said protective film is made of a copolymer mainly composed of C ₂ H ₂ Cl ₂ . 3. The connector structure for a membrane circuit according to claim 1, wherein said protective film has a thickness of 2 to 3 μm. 4. A step of forming a conductive pattern made of Ag on an insulating film having a tail portion formed at an end so that a part of the conductive pattern is concentrated on the tail portion; Forming a protective film of a resin covering the conductive pattern with a film thickness capable of being pierced by the terminal of the mating connector at the time of fitting with the mating connector, over the entire portion where the conductive pattern is concentrated. A method of manufacturing a connector structure of a membrane circuit. 5. The step of forming the protective film, wherein the conductive pattern of the tail portion is formed by screen printing or spraying a solution comprising a copolymer containing C ₂ H ₂ Cl ₂ as a main raw material and water. 5. The method for manufacturing a connector structure of a membrane circuit according to claim 4, comprising a step of applying the solution applied to the concentrated portion and a step of drying the solution applied in this step with hot air. 6. The method according to claim 4, wherein the step of forming the protective film is a step of forming the protective film to have a thickness of 2 to 3 μm. .