JP4569399B2 - 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 A conductor layer provided on the one surface side and covering the conductor circuit while leaving a part of the conductor circuit; and a conductor plate provided on the coating layer on the one surface side of the flexible substrate , the conductor The plate has a protruding portion that protrudes toward the conductor circuit, located at a portion facing the part of the conductor circuit, and the conductor plate is electrically connected to the conductor circuit at the protruding portion. It is connected.

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 for reinforcing the mechanical strength of the flexible substrate but also a function as a shield layer for shielding electromagnetic waves that cause noise. For this reason, a circuit board having a sufficient shielding effect is realized.

  Furthermore, the conductor plate is provided with a protrusion, and the conductor plate and the conductor circuit are electrically connected to each other at the protrusion. With this configuration, the electrical connection between the conductor plate and the conductor circuit can be more reliably obtained as compared with the case where the connection portion of the conductor plate with respect to the conductor circuit is flat.

  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 has a protruding portion 42 that protrudes toward the conductor circuit 20. The protruding portion 42 is provided at a position facing the part of the conductor circuit 20, that is, the portion of the conductor circuit 20 that is not covered by the coating layer 30. The conductor plate 40 is electrically connected to the ground circuit of the conductor circuit 20 at the protruding portion 42. In the present embodiment, the protruding portion 42 and the conductor circuit 20 are not directly connected but are connected via the solder 54.

  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.

  On the surface S3 of the conductor plate 40 opposite to the conductor circuit 20, a portion corresponding to the back side of the protruding portion 42 is recessed. In other words, the recess 44 is provided in the surface S3 of the conductor plate 40. In the present embodiment, the conductor plate 40 is partially curved, and the curved portion constitutes the above-described protruding portion 42 and the recessed portion 44. Further, the thickness d1 (see FIG. 2) of the protruding portion 42 of the conductor plate 40 and the thickness d2 of the portion of the conductor plate 40 located on the coating layer 30 are substantially equal to each other.

  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, prior to adhering the conductor plate 40 to the covering layer 30, an adhesive 52 is applied on the covering layer 30, and solder 54 is provided in the opening 30a (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. At this time, the protruding portion 42 of the conductor plate 40 is connected to the conductor circuit 20 via the solder 54 (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.

  Furthermore, the conductor plate 40 is provided with a protrusion 42, and the conductor plate 40 and the conductor circuit 20 are electrically connected to each other at the protrusion 42. With this configuration, the electrical connection between the conductor plate 40 and the conductor circuit 20 can be more reliably obtained as compared with the case where the connection portion of the conductor plate 40 to the conductor circuit 20 is flat.

  This point will be described in more detail with reference to FIGS. 5 (a) and 5 (b). In FIG. 5A, the conductor plate 90 does not have a protruding portion, and the connecting portion to the conductor circuit 20 is flat. In this case, in order to obtain an electrical connection between the conductor plate 90 and the conductor circuit 20, it is necessary to deposit the solder 54 so that the liquid level of the solder 54 is higher than the opening surface of the opening 30a. is there. On the other hand, if the amount of the solder 54 is too large, the solder flows out onto the coating layer 30. Therefore, the tolerance is relatively narrow with respect to the amount of solder required to obtain an electrical connection between the conductor plate 90 and the conductor circuit 20.

  On the other hand, FIG. 5B shows the case of the circuit board 1. In this case, since the conductor plate 40 has the protruding portion 42, the electrical connection between the conductor plate 40 and the conductor circuit 20 can be achieved even if the liquid level of the solder 54 is lower than the opening surface of the opening 30a. Obtainable. In addition, even after the conductor plate 40 is connected to the conductor circuit 20, there is a large space for the solder 54 to escape, so that an allowance regarding the amount of solder necessary to obtain an electrical connection between the conductor plate 40 and the conductor circuit 20. The range is relatively wide. For this reason, in the circuit board 1, the electrical connection between the conductor plate 40 and the conductor circuit 20 can be obtained more reliably. Therefore, the circuit board 1 having a structure suitable for improving production stability and manufacturing yield is realized.

  Further, since the allowable range for the amount of solder 54 is wide, the amount of solder 54 can be easily managed in the manufacturing process of the circuit board 1. Therefore, the circuit board 1 that is easy to manufacture is realized.

  Further, since the protrusion 42 is provided, even if a crack occurs in a part of the contact surface between the conductor plate 40 and the solder 54, the conductor plate 40 is flat (that is, the contact surface is also flat). The cracks are less likely to propagate to the rest of the contact surface. That is, if the contact surface is flat, the crack can propagate with a constant velocity vector, so that the fracture energy required for propagation is small. On the other hand, if the contact surface is not flat, cracks cannot propagate with a constant velocity vector, so that a large fracture energy is required for propagation. Therefore, the circuit board 1 is also excellent in reliability.

  On the surface S3 of the conductor plate 40 opposite to the conductor circuit 20, a portion corresponding to the back side of the protruding portion 42 is recessed. For this reason, the stress due to the thermal expansion of the conductor plate 40 can be relieved by the recess 44. Moreover, if it is this structure, the protrusion part 42 can be easily formed by curving a part of flat conductor plate, for example. Actually, in the circuit board 1, as described above, a part of the conductor plate 40 is curved, and the curved part constitutes the protruding portion 42.

  Further, the thickness of the protruding portion 42 of the conductor plate 40 and the thickness of the portion of the conductor plate 40 located on the coating layer 30 are substantially equal to each other. With such a structure, the protruding portion 42 can be formed by curving a part of a flat conductor plate having a uniform thickness.

  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, as shown in FIG. 6, the conductor plate 40 and the conductor circuit 20 may be connected via an anisotropic conductive paste (ACP) 55.

  As shown in FIG. 7, the conductor plate 40 and the conductor circuit 20 may be directly connected. That is, in the figure, the conductor plate 40 is in contact with the conductor circuit 20, thereby achieving electrical connection between them. At this time, the conductor plate 40 and the conductor circuit 20 may or may not be bonded using an adhesive such as solder or ACP. When bonded, the electrical connection between the two can be further ensured. On the other hand, when not adhered, the conductor plate 40 is easily peeled off intentionally, so that a circuit board excellent in repairability can be obtained.

  It is not essential that the conductor plate 40 has the recess 44. Therefore, as shown in FIG. 8, the conductor plate 40 may be configured to have only the protruding portion 42 among the protruding portion 42 and the recessed portion 44.

  As shown in FIG. 9, a hole 43 that penetrates the conductor plate 40 may be formed in the protruding portion 42. In the figure, solder 54 is also provided in the hole 43. Since the hole 43 is provided in this manner, the solder 54 can be supplied between the conductor circuit 20 and the protruding portion 42 through the hole 43 even after the conductor plate 40 is stuck on the coating layer 30. It becomes possible. As a result, the amount of solder 54 can be easily adjusted, so that an electrical connection between the conductor plate 40 and the conductor circuit 20 can be obtained more reliably. Further, as shown in FIG. 9, since the solder 54 can be filled into the hole 43, a stronger connection can be obtained between the conductor plate 40 and 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 sectional drawing for demonstrating the structure of a conductor board. (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. (A) And (b) is sectional drawing for demonstrating the effect 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 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.

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 Protrusion part 44 Depression part 52 Adhesive 54 Solder 60 Electronic component 70 Electromagnetic wave shield layer 72 Adhesion layer 74 Conductive thin film 76 Insulation layer

Claims (7)

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,
A coating layer which is provided on the one surface side of the flexible substrate and covers the conductor circuit leaving a part of the conductor circuit;
A conductor plate provided on the coating layer on the one surface side of the flexible substrate ,
The conductor plate has a protruding portion that is located at a portion facing the part of the conductor circuit and protrudes toward the conductor circuit;
The circuit board, wherein the conductor plate is electrically connected to the conductor circuit at the protruding portion. The circuit board according to claim 1,
A circuit board in which a surface of the conductor plate opposite to the conductor circuit is recessed in a portion corresponding to the back side of the protruding portion. The circuit board according to claim 1 or 2,
A circuit board in which the protruding portion of the conductor plate is provided with a hole penetrating the conductor plate. The circuit board according to any one of claims 1 to 3,
The thickness of the protruding portion of the conductor plate and the thickness of the portion of the conductor plate located on the covering layer are substantially equal to each other. The circuit board according to claim 1,
A portion of the conductor plate is curved,
A circuit board in which the curved portion constitutes the protrusion. The circuit board according to any one of claims 1 to 5 ,
The circuit board is a reinforcing board that reinforces the mechanical strength of the board. In the circuit board according to any one of claims 1 to 6,
The circuit board is a stainless steel plate, an iron plate, a copper plate, or an aluminum plate.

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