JP4569400B2 - Circuit board - Google Patents

Description

  The present invention relates to a circuit board.

  Conventionally, a flexible circuit board has mainly played a role of electric wires for electrically connecting rigid circuit boards. However, in recent years, flexible circuit boards have been used instead of rigid circuit boards mainly in mobile devices such as mobile phones, PDAs, and liquid crystal display devices because they are thin, light, and excellent in flexibility. For this reason, mounting electronic components on a flexible circuit board has been increasing rapidly in recent years. In recent devices, the problem of noise due to electromagnetic waves has surfaced with the progress of digitalization and higher frequency, and some countermeasure is required for the problem.

  One possible countermeasure is to provide a shield layer on the flexible circuit board (for example, Patent Documents 1 and 2). The flexible circuit board described in these documents includes a base material (flexible board), a conductor circuit formed on one surface of the base material, and an insulating layer covering the conductor circuit. An opening is provided in a portion of the insulating layer provided on the ground circuit of the conductor circuit. The shield layer formed of a conductive printed circuit and the ground circuit are connected through the opening, and an insulating layer is provided on the shield layer.

The shield referred to here is a so-called electromagnetic wave shield. When the electric field in the electromagnetic wave is E, the magnetic field is H, and the wave impedance is Zs, these relationships are generally expressed by the following equations.
E = Zs · H

The greater the difference in wave impedance Zs between the shield layer and another layer (for example, the air layer) adjacent thereto, the greater the reflectivity of the shield layer with respect to electromagnetic waves. For example, the wave impedance Zs in the air is 377Ω as in the vacuum, whereas the wave impedance Zs in the metal is as small as Zs << 1. Therefore, when the material of the shield layer is a metal, the ratio of the electromagnetic waves incident on the shield layer to reflect there is very high. It has been.
Japanese Utility Model Sho 62-124896 Japanese Utility Model Sho 62-145399

  By the way, as described above, the flexible circuit board may be provided with electronic components such as connectors, ICs or chip components. The chip component is, for example, a resistor or a capacitor. In such a case, a reinforcing plate may be attached to the flexible substrate in order to ensure sufficient mechanical strength to hold the electronic component.

  At this time, if a reinforcing plate is stuck on the shield layer, the reinforcing plate may be easily peeled off. Therefore, from the viewpoint of the reliability of the circuit board, it is preferable not to provide a shield layer in the portion where the reinforcing plate is attached. However, in that case, there is a problem that a sufficient shielding effect cannot be obtained as compared with the case where the shield layer is provided on the entire surface of the substrate.

Circuit board according to the present invention is a circuit board on which electronic components are mounted on the conductor circuit of the flexible substrate, and the flexible substrate, and the conductor circuit provided on one surface of the flexible substrate, the flexible substrate An insulating coating layer that is provided on the one surface side and covers the conductor circuit while leaving a part of the conductor circuit; and a conductive conductor plate provided on the coating layer. The portion of the conductor circuit facing the part has a leaf spring structure, and the conductor circuit is biased at the connecting portion, and the part of the conductor circuit facing the part is the conductor. It is electrically connected to a circuit .

  In this circuit board, the conductor plate is electrically connected to the conductor circuit. Thereby, the conductor plate can have not only a function as a reinforcing plate that reinforces the mechanical strength of the substrate but also a function as a shield layer that shields electromagnetic waves that cause noise. For this reason, a circuit board having a sufficient shielding effect is realized.

  Further, the conductor plate urges the conductor circuit at the connection portion with the conductor circuit. Thereby, even if it does not adhere | attach a conductor board and a conductor circuit, the electrical connection between both can be obtained reliably.

  According to the present invention, a circuit board having a sufficient shielding effect is realized.

  Hereinafter, preferred embodiments of a circuit board according to the present invention will be described in detail with reference to the drawings. In the description of the drawings, the same reference numerals are assigned to the same elements, and duplicate descriptions are omitted.

  FIG. 1 is a cross-sectional view showing an embodiment of a circuit board according to the present invention. The circuit board 1 includes a substrate 10, a conductor circuit 20, a covering layer 30, and a conductor plate 40.

  The substrate 10 is a flexible substrate. The substrate 10 is, for example, a resin film base material. Examples of the resin film substrate include polyimide resin films such as polyimide resin films, polyetherimide resin films, polyamideimide resin films, polyamide resin films such as polyamide resin films, and polyester resins such as polyester resin films. System film. Among these, a polyimide resin film is particularly preferable from the viewpoint of improving flexibility, elastic modulus, and heat resistance.

  Although the thickness of the board | substrate 10 is not specifically limited, Preferably it is 5-50 micrometers, More preferably, it is 12.5-25 micrometers. When the thickness is within this range, the flexibility is particularly excellent, while sufficient hardness is obtained to ensure good workability.

  On one surface (surface S1) of the substrate 10, a conductor circuit 20 is provided. In the present embodiment, the conductor circuit 20 is also provided on the surface S <b> 2 of the substrate 10. That is, the conductor circuit 20 is provided on both surfaces of the substrate 10. The substrate 10 is provided with a through hole 12. Through this through hole 12, the conductor circuit 20 on the surface S1 and the conductor circuit 20 on the surface S2 are electrically connected to each other.

  A coating layer 30 is provided on the surface S1 side of the substrate 10 to cover the conductor circuit 20 while leaving a part of the conductor circuit 20. In the present embodiment, the coating layer 30 is also provided on the surface S2 side of the substrate 10. The covering layer 30 is a cover lay film that includes an adhesive 32 and an insulating resin film 34. However, it is not essential to use a coverlay film as the covering layer 30. For example, as the coating layer 30, a liquid resin composition containing a thermosetting resin may be formed by screen printing or the like and then heat cured. From the viewpoint of bending properties, it is preferable to use a coverlay film.

  The adhesive 32 is preferably composed of a resin composition containing a thermosetting resin such as an epoxy resin, a polyester resin, a polyimide resin, a polyamide resin, a polyamideimide resin, or a polyurethane resin. . Among these, epoxy resins are particularly preferable from the viewpoint of improving adhesion and heat resistance.

  As the material of the insulating resin film 34, the same material as the substrate 10 can be used. As for the insulating resin film 34, a film containing a polyimide resin is particularly preferable from the viewpoint of improving the elastic modulus and heat resistance.

  A conductor plate 40 is provided on the coating layer 30 provided on the surface S1 side. Specifically, the conductor plate 40 is fixed to the insulating resin film 34 of the coating layer 30 with an adhesive 52. The conductor plate 40 is a reinforcing plate that reinforces the mechanical strength of the substrate 10. The conductor plate 40 is electrically connected to the ground circuit of the conductor circuit 20 at a portion facing the part of the conductor circuit 20 (that is, a portion of the conductor circuit 20 that is not covered by the coating layer 30). In particular, in the present embodiment, the conductor plate 40 is in contact with the conductor circuit 20 and thereby directly connected to the conductor circuit 20. Further, the conductor plate 40 and the conductor circuit 20 are not bonded to each other by the adhesive and are in a non-bonded state.

  The conductor plate 40 biases the conductor circuit 20 at the connecting portion. Specifically, the conductor plate 40 has a leaf spring structure at a portion facing the part of the conductor circuit 20, thereby storing a restoring force. The conductor plate 40 biases the conductor circuit 20 by this restoring force. In other words, the conductor plate 40 exerts pressure on the conductor circuit 20 due to its restoring force.

  The conductor plate 40 has an opening 42 and a protruding piece 44. The opening 42 is provided in a portion facing the part of the conductor circuit 20. Further, the projecting piece 44 extends to the top of the opening 42 and extends to the conductor circuit 20. The projecting piece 44 forms a leaf spring structure. Here, FIG. 2 is a plan view of the conductor plate 40. In the figure, a dotted line indicates a connection portion with the conductor circuit 20. Further, as can be seen from FIG. 1, a part of the protruding piece 44 is bent, and the bent surface is in contact with the conductor circuit 20.

  As the conductor plate 40, a metal plate is preferably used. Examples of the metal plate include a stainless steel plate, an iron plate, a copper plate, and an aluminum plate. Among these, it is particularly preferable to use a stainless steel plate. By using a stainless steel plate, it is possible to achieve sufficient strength to support electronic components even if the plate thickness is reduced. Although the thickness of the conductor board 40 is not specifically limited, Preferably it is 0.025-2 mm, More preferably, it is 0.1-0.5 mm. If the thickness of the conductor plate 40 is within this range, it can be easily incorporated into a small device, and sufficient strength can be obtained to support the electronic component.

  An electronic component 60 is provided on the surface S2 side of the substrate 10. The electronic component 60 is electrically connected to the conductor circuit 20. The electronic component 60 is, for example, a connector, an IC, a chip component, or the like. The chip component is, for example, a resistor or a capacitor. The conductor plate 40 described above is provided on the opposite side of the electronic component 60 with the substrate 10 interposed therebetween.

  An electromagnetic wave shielding layer 70 is also provided on the surface S1 side of the substrate 10. The electromagnetic wave shielding layer 70 is provided in a region other than the region where the conductor plate 40 is provided on the surface S1 side of the substrate 10. That is, in the circuit board 1, the conductor plate 40 and the electromagnetic wave shielding layer 70 are provided in different regions without overlapping each other. In the present embodiment, the electromagnetic wave shielding layer 70 includes a conductive adhesive layer 72, a conductive thin film 74, and an insulating layer 76, and has a multilayer film shape. That is, in the electromagnetic wave shielding layer 70, a conductive thin film 74 is formed on the insulating layer 76, and a conductive adhesive layer 72 containing conductive particles and an adhesive is further formed thereon.

  Examples of the metal constituting the conductive thin film 74 include gold, silver, copper, titanium, aluminum, and other alloys. Among these, silver is particularly preferable from the viewpoint of improving electromagnetic wave shielding properties. Moreover, as said electroconductive particle, what has electroconductive materials, such as silver or copper, for example is preferable. The thickness of the conductive thin film 74 is preferably 0.01 to 50 μm, more preferably 0.2 to 10 μm.

  Examples of the insulating layer 76 include polyimide resin films such as polyimide resin films, polyetherimide resin films, polyamideimide resin films, polyamide resin films such as polyamide resin films, and polyester resin films such as polyester resin films. It is done. Among these, from the viewpoint of improving the elastic modulus and heat resistance, it is particularly preferable to use a film made of a polyimide resin.

  The thickness of the insulating layer 76 is preferably 5 to 50 μm, more preferably 12.5 to 25 μm. When the thickness is equal to or greater than the lower limit, sufficient insulation can be obtained. Moreover, sufficient flexibility is acquired because thickness is below the said upper limit.

  However, as the electromagnetic wave shielding layer 70, a conductive resin paste is formed by screen printing or the like and then heat-cured, and further, an insulating resin ink or the like is formed on the surface by the screen printing method or the like and then heat-cured It may be used. In addition, the above-mentioned film-like electromagnetic wave shielding layer is more preferable as a shielding means in that the process can be simplified.

  An example of a method for manufacturing the circuit board 1 will be described with reference to FIGS. First, a double-sided copper-clad laminate in which copper foils 20a are formed on both sides of the substrate 10 is prepared (FIG. 3 (a)). Next, the copper foils 20a on both surfaces of the substrate 10 are patterned into a desired shape by etching or the like. As a result, the conductor circuit 20 is formed (FIG. 3B).

  Subsequently, the coating layer 30 is formed on the conductor circuit 20 (FIG. 3C). The coating layer 30 can be formed by attaching a cover lay film in which an adhesive 32 is applied to the insulating resin film 34. Examples of the method for forming the coverlay film include a method of pressure bonding with a hot-pressure forming apparatus. In this case, the pressure bonding conditions are, for example, a pressure bonding temperature of 80 to 220 ° C. and a pressure bonding pressure of 0.2 to 10 MPa.

  The covering layer 30 is formed leaving a part on the conductor circuit 20. That is, in the covering layer 30, an opening 30 a for electrically connecting the conductor plate 40 to the conductor circuit 20, an opening 30 b for mounting the electronic component 60, and the electromagnetic wave shielding layer 70 are electrically connected to the conductor circuit 20. An opening 30c is provided for connection. These openings 30a, 30b, and 30c may be formed in advance by punching or the like, or may be formed after the coating layer 30 is formed.

  Next, before adhering the conductor plate 40 to the coating layer 30, an adhesive 52 is applied on the coating layer 30 (FIG. 4A). In this state, the conductor plate 40 is stuck on the coating layer 30 via the adhesive 52 so as to cover the opening 30a (FIG. 4B). Further, the electromagnetic wave shielding layer 70 is formed so as to cover the opening 30c (FIG. 4C). Further, by providing the electronic component 60 in the opening 30b, the circuit board 1 shown in FIG. 1 is obtained.

  The effect of the circuit board 1 will be described. In the circuit board 1, the conductor plate 40 is electrically connected to the conductor circuit 20. Thereby, the conductor plate 40 can have not only a function as a reinforcing plate that reinforces the mechanical strength of the substrate 10 but also a function as a shield layer that shields electromagnetic waves that cause noise. For this reason, the circuit board 1 having a sufficient shielding effect is realized.

  Further, the conductor plate 40 urges the conductor circuit 20 at a connection portion with the conductor circuit 20. Thereby, even if it does not adhere | attach the conductor board 40 and the conductor circuit 20, the electrical connection between both can be obtained reliably. Actually, in the circuit board 1, the conductor plate 40 and the conductor circuit 20 are not bonded to each other. Therefore, since the conductor plate 40 can be easily peeled intentionally, the circuit board 1 excellent in repairability is realized.

  Further, since there is no need to bond the conductor plate 40 and the conductor circuit 20, the manufacturing process of the circuit board 1 can be simplified accordingly. Therefore, the circuit board 1 that is easy to manufacture is realized.

  The conductor plate 40 has a restoring force, and the conductor circuit 20 is urged by the restoring force. Thereby, the structure which the conductor board 40 urges | biases the conductor circuit 20 is easily realizable. The conductor plate 40 has a leaf spring structure. Thereby, a restoring force can be applied to the conductor plate 40 while utilizing the shape of the plate-like conductor plate 40.

  The conductor plate 40 has an opening 42 and a projecting piece 44, and the projecting piece 44 forms a leaf spring structure. Thereby, a leaf spring structure can be obtained with a simple configuration.

  A part of the projecting piece 44 is bent, and the bent surface is in contact with the conductor circuit 20. As a result, the strength of the conductor plate 40, particularly the strength of the connecting portion with the conductor circuit 20, is increased, and the reliability of the circuit board 1 is further improved. Further, the conductor plate 40 and the conductor circuit 20 can be brought into line contact. In the case of line contact, the pressure exerted by the conductor plate 40 on the conductor circuit 20 is greater than in the case of surface contact, so that the electrical connection between the two becomes more reliable.

  The substrate 10 is a flexible substrate. For this reason, it is particularly useful to provide a conductor plate 40 that functions as a reinforcing plate that reinforces the mechanical strength of the substrate 10. Further, the portion of the substrate 10 where the electronic component 60 is mounted is a portion that receives a particularly large load. In the circuit board 1, since the conductor plate 40 is provided so as to cover this portion, it effectively functions as a reinforcing plate of the conductor plate 40.

  The circuit board according to the present invention is not limited to the above embodiment, and various modifications are possible. For example, in the above-described embodiment, the example in which the conductor plate 40 and the conductor circuit 20 are directly connected is shown, but these may be connected via a conductive member 82 as shown in FIG. . Also in this case, the conductor plate 40 biases the conductor circuit 20 via the conductive member 82.

  As shown in FIGS. 6 and 7, a protrusion 46 may be provided at a connection portion between the conductor plate 40 and the conductor circuit 20. FIG. 7 shows a plan view of the conductor plate 40 in FIG. In the present example, a plurality of protrusions 46 are provided along the connection portion (dotted line in FIG. 7) between the conductor plate 40 and the conductor circuit 20. However, only one protrusion 46 may be provided. By providing the protrusions 46 in this way, the conductor plate 40 and the conductor circuit 20 can be brought into point contact. Thereby, the pressure which the conductor board 40 exerts on the conductor circuit 20 can be made larger than the case of a line contact.

  In the above-described embodiment, a configuration in which a part of the projecting piece 44 is bent and the bent surface is connected to the conductor circuit 20 is shown, but such a configuration is not essential. For example, as shown in FIG. 8, the tip of the projecting piece 44 may be connected to the conductor circuit 20.

  The circuit board according to the present invention can be suitably used in electric devices such as mobile phones and personal computers.

It is sectional drawing which shows one Embodiment of the circuit board by this invention. It is a top view which shows the conductor board of FIG. (A)-(c) is process drawing which shows an example of the manufacturing method of the circuit board of FIG. (A)-(c) is process drawing which shows an example of the manufacturing method of the circuit board of FIG. It is sectional drawing which shows the modification of the circuit board of FIG. It is sectional drawing which shows the modification of the circuit board of FIG. It is a top view which shows the modification of the circuit board of FIG. It is sectional drawing which shows the modification of the circuit board of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Circuit board 10 Board | substrate 12 Through-hole 20 Conductor circuit 30 Covering layer 32 Adhesive material 34 Insulating resin film 40 Conductor board 42 Opening part 44 Projection part 46 Protrusion 52 Adhesive 60 Electronic component 70 Electromagnetic wave shield layer 72 Adhesion layer 74 Conductivity Thin film 76 insulating layer

Claims (6)

A circuit board in which an electronic component is mounted on a conductor circuit of a flexible board,
The flexible substrate ;
And the conductor circuit provided on one surface of the flexible substrate,
An insulating covering layer that is provided on the one surface side of the flexible substrate and covers the conductor circuit leaving a part of the conductor circuit;
A conductive conductor plate provided on the coating layer,
The conductor plate has a leaf spring structure at a portion facing the part of the conductor circuit, biases the conductor circuit at the connection portion, and faces the part of the conductor circuit. A circuit board, wherein the portion is electrically connected to the conductor circuit . The circuit board according to claim 1 ,
The conductor plate is
An opening provided in a portion facing the part of the conductor circuit;
And a projecting piece that extends to the opening and extends to the conductor circuit,
A circuit board in which the protruding piece portion forms the leaf spring structure. The circuit board according to claim 2 ,
A part of the protruding piece is bent, and the bent surface is in contact with the conductor circuit. The circuit board according to any one of claims 1 to 3 ,
The circuit board and the conductor circuit are in a non-bonded state with each other. In the circuit board according to any one of claims 1 to 4,
The circuit board is a reinforcing board that reinforces the mechanical strength of the flexible board. The circuit board according to any one of claims 1 to 5 ,
The circuit board is a stainless steel plate, an iron plate, a copper plate, or an aluminum plate.

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