JP2006261466A - Connecting structure of circuit board and its connecting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the connecting structure of a circuit board having an excellent productivity and superior electrical characteristics. <P>SOLUTION: The connecting structure of the circuit board 1 is used for electrically connecting a flexible wiring 4 and a circuit wiring 3. A top-face electrode 6 and an underside electrode 7 connected to the circuit wiring 3 at the same ends 1c of a top face 1a and an underside 1b are formed to the circuit board 1. A flexible board 5 has a first surface 5a holding the end 1c of the circuit board 1 and being opposed to the top-face electrode 6 at the end 1c of the top face 1a of the circuit board 1, a second surface 5b opposed to the lower electrode 7 at the end 1c of the underside 1b of the circuit board 1, and a third surface 5c held by the first surface 5a and the second surface 5b and opposed to the side face 1d of the end 1c of the circuit board 1. The first surface 5a has a first electrode 8 connected to the flexible wiring 4 and connected to the top-face electrode 6, and the second surface 5b has a second electrode 9 connected to the flexible wiring 4 and connected to the underside electrode 7. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a connection structure for connecting a flexible board to a circuit board made of a printed circuit board or a ceramic board on which an electronic component is mounted, and a method for connecting the same, and is particularly excellent in productivity, low cost, and excellent electrical characteristics. is there.

  Conventionally, in order to reduce the size of a portable electronic device, first, an electronic device that is a functional component is disposed at a desired position, and secondly, a plurality of circuit boards on which the electronic device is mounted are three-dimensionally disposed. This is very important. Specifically, it is necessary to connect the circuit board of the electronic device and the mother board with a flexible board, and it is also necessary to connect the circuit boards with the flexible board. When connecting with a flexible substrate, how to reduce the area required for connection is a major issue in miniaturization. As a conventional technique, a method for connecting an end face of a circuit board and an electrode of a flexible board will be described below.

  For example, in order to reduce the size of the display cell of the “display device”, lead electrodes are formed on the side surfaces of the upper and lower glass substrates using vapor deposition, and are formed with a structure in which the copper foil portion of the flexible circuit board is soldered. (For example, refer to Patent Document 1). As another method, since the device of the “printed circuit board connection terminal structure” has been miniaturized and the printed circuit board needs to be made smaller, a printed circuit board (hereinafter abbreviated as PWB) is used to narrow the connection terminal pattern. These are formed with a structure in which a flexible printed circuit board (hereinafter abbreviated as FPC) is connected to the side recesses of. As for the connection method, the FPC is brought into contact with the side surface of the PWB, the FPC terminal pattern and the end surface recess of the PWB are aligned, solder is poured into the end surface recess, and the FPC terminal pattern and the PWB terminal pattern are connected. It fixes (for example, refer patent document 2).

Japanese Patent Laid-Open No. 57-14872 JP-A-1-289190

  The following problems occur in the conventional technology. First, since the flexible substrate is bonded only on the side surface of the circuit board, the bonding area is reduced and the bonding strength is insufficient when the circuit board is thinned. Second, since the electrodes are formed on the side surfaces of the circuit board, the cost is high for this formation. Specifically, in the former prior art, a mask is placed on the side surface of the circuit board and the lead electrode is formed by vapor deposition, so that a large number of devices are required and productivity is poor. In the latter method of providing the end surface recesses on the side surface of the circuit board of the prior art, new steps of forming the end recesses and forming the metallization of the end surfaces are required. Third, since the connection portion between the electrode on the side surface of the circuit board and the electrode on the surface becomes a corner portion of the substrate, stress concentration is likely to occur, and the risk of disconnection is increased.

  The present invention has been made in order to solve the above-described problems, and an object of the present invention is to provide a circuit board connection structure and a connection method thereof that are excellent in productivity, low in cost, and excellent in electrical characteristics.

  The present invention relates to a circuit board connection structure for electrically connecting a flexible wiring formed on a flexible board and circuit wirings formed on an upper surface and a lower surface of the circuit board, respectively. The first surface portion opposite to the upper surface electrode at the upper end of the circuit board sandwiches the end portion of the circuit board between the upper surface electrode and the lower surface electrode connected to the circuit wiring at the same end of the circuit board. And a second surface portion facing the lower electrode at the end portion of the lower surface of the circuit board, and a third surface portion sandwiched between the first surface portion and the second surface portion and facing the end side surface of the circuit board. A first electrode connected to the flexible wiring and connected to the upper surface electrode on the first surface portion, and a second electrode connected to the lower surface electrode connected to the flexible wiring on the second surface portion. Those with is.

  The circuit board connection structure of the present invention is a circuit board connection structure for electrically connecting a flexible wiring formed on a flexible board and circuit wirings formed on the upper surface and the lower surface of the circuit board, respectively. The upper surface electrode and the lower surface electrode connected to the circuit wiring are respectively formed at the same end portion of the upper surface and the lower surface, and the flexible substrate sandwiches the end portion of the circuit board. A first surface portion facing the second surface portion, a second surface portion facing the lower electrode at the end of the lower surface of the circuit board, and a third surface sandwiched between the first surface portion and the second surface portion and facing the end side surface of the circuit board. The first surface portion is connected to the flexible wiring and connected to the upper surface electrode, and the second surface portion is connected to the flexible wiring and connected to the lower surface electrode. Since that with the second electrode, respectively, it is possible to take the connection between the flexible substrate and the circuit board at upper and lower surfaces of the circuit board, it is a low cost high productivity and has excellent electrical characteristics.

Embodiment 1 FIG.
Embodiments of the present invention will be described below. 1 is a perspective view showing a circuit board connection structure according to Embodiment 1 of the present invention, FIG. 2 is a cross-sectional view showing a cross section of the circuit board connection structure shown in FIG. 1, and FIG. 3 is a circuit shown in FIG. FIG. 4 is a cross-sectional view showing a connection method of the circuit board connection structure shown in FIG. 1. In the figure, each circuit wiring 3 and flexible wiring of the circuit board 1 having the circuit wiring 3 formed on the upper surface 1a and the lower surface 1b and the flexible substrate 5 having the flexible wiring 4 formed of a base material 50 such as a polyimide film. 4 is a connection structure of a circuit board 1 for electrically connecting the circuit board 1, the electronic component 2 electrically connected to the circuit wiring 3, and the same end 1 c of the upper surface 1 a and the lower surface 1 b. The upper electrode 6 and the lower electrode 7 connected to the circuit wiring 3 are respectively formed.

  The flexible substrate 5 sandwiches the end 1 c of the circuit board 1, the first surface 5 a facing the upper surface electrode 6 of the end 1 c of the upper surface 1 a of the circuit board 1, and the end of the lower surface 1 b of the circuit board 1. A second surface portion 5b facing the lower electrode 7 of 1c, and a third surface portion 5c sandwiched between the first surface portion 5a and the second surface portion 5b and facing the side surface 1d of the end portion 1c of the circuit board 1. The first electrode 8 is connected to the flexible wiring 4 and connected to the upper surface electrode 6 on the first surface portion 5a, and is connected to the lower surface electrode 7 and connected to the flexible wiring 4 on the second surface portion 5b. Second electrodes 9 are respectively formed.

  The flexible wiring 4 is covered with an insulating film 10 made of, for example, a solder resist or a polyimide film. Further, a first bonding material 80 is provided between the upper electrode 6 and the first electrode 8, and a second bonding material 90 is provided between the lower electrode 7 and the second electrode 9. 8 and the electrodes 7 and 9 are formed to be electrically joined. These first and second bonding materials 80 and 90 are made of, for example, solder bumps or a conductive adhesive. The conductive adhesive is made of an adhesive made of, for example, an epoxy resin mixed with a conductive filler. The first and second bonding materials 80 and 90 are shown separately from the electrodes 6 and 8 and the electrodes 7 and 9 for convenience, but constitute a part of one of the electrodes. And

  Next, a connection method of the circuit board according to the first embodiment configured as described above will be described. First, the flexible substrate 5 will be described. On the base material 50, a first electrode 8 is formed on a first surface portion 5 a connected to the flexible wiring 4, and a second electrode 9 is formed on a second surface portion 5 b connected to the flexible wiring 4. (FIG. 3A). The flexible wiring 4 is covered with an insulating film 10 (FIG. 3B). Then, a first bonding material 80 and a second bonding material 90 are formed on the first electrode 8 and the second electrode 9, respectively. When each bonding material 80, 90 is formed by solder, the solder paste is applied to each electrode 8, 9 by printing and heated, and the solder paste is applied by a dispenser and then heated. There is a way to make a bump. In the case of a conductive adhesive, there is a method in which bumps are formed by applying by printing or dispenser (FIGS. 3C and 4A).

  Then, the side surface 1d of the end portion 1c of the circuit board 1 is placed on the third surface portion 5c of the flexible substrate 5 so as to face each other (FIG. 4B). And the heating tool 11 which provided the groove | channel in the center is made into the state pressed from the back surface of the flexible substrate 5, and the heating tool 11 is heated. Thus, the end portion 1c of the circuit board 1 is sandwiched between the first surface portion 5a and the second surface portion 5b of the flexible substrate 5, and the first surface portion 5a and the second surface portion 5b of the flexible substrate 5 are connected to the circuit substrate 1. The upper surface 1a and the lower surface 1b are disposed so as to face each other. Then, the first electrode 8 and the second electrode 9, the upper surface electrode 6 and the lower surface electrode 7 are brought into contact with each other via the first bonding material 80 and the second bonding material 90, and are heated. And the 2nd electrode 9, the upper surface electrode 6, and the lower surface electrode 7 are joined, respectively. The heating temperature is 290 ° C. in the case of Sn-based solder, and 200 ° C. in the case of a conductive adhesive. The heating temperature is appropriately changed depending on the melting point of the solder used or the curing temperature of the conductive adhesive (FIG. 4C). Then, the heating tool 11 is removed, and a circuit board connection structure can be formed as shown in FIGS.

  Since the connection structure of the circuit board according to the first embodiment configured as described above is bonded to the flexible board and the upper and lower surfaces of the circuit board, it is bonded as compared with the case of bonding only on one side of the circuit board. Since the area can be reduced to about half, the component mounting area can be increased. In addition, since the upper surface electrode and the lower surface electrode of the circuit board can be formed on the surfaces of the upper surface and the lower surface, they can be easily formed, a fine electrode can be formed, and a fine electrode connection can be realized at low cost. .

Furthermore, as shown in FIG. 5, if the first electrode and the second electrode are formed so as not to be connected, the number of connection pins to the circuit board can be approximately double that of the upper surface and the lower surface. A density connection can be realized.
Note that FIG. 5 shows an example in which the first electrode and the second electrode are alternately formed at every other place, but the present invention is not limited to this, and the first electrode and the second electrode such as every two places are formed. Durability can be ensured if the electrodes are formed in an alternate planar positional relationship with no bias.
Further, since the first surface portion and the second surface portion are sandwiched between the upper surface and the lower surface, the connection between the upper surface electrode and the first electrode and the connection between the lower surface electrode and the second electrode are formed simultaneously. Therefore, it is excellent in productivity.

  In the first embodiment, the thickness, the number of layers, and the material of the circuit board are not particularly limited. For example, a ceramic substrate may be used. Moreover, as a flexible substrate, you may use what formed the conductor of thickness 25 micrometers on the polyimide film of thickness 25 micrometers, for example. Further, the thickness of 12.5 μm may be used because it is easy to bend. Further, the flexible substrate may use a liquid crystal polymer instead of a polyimide film. However, any material can be appropriately selected as long as it is easily bent and can withstand the soldering temperature.

In the first embodiment, an example is shown in which one circuit board is connected to one end of the flexible board. However, as shown in FIG. 6, another circuit board 100 is connected to the other end of the flexible board separately from the circuit board 1. In the case of connection, as shown in FIG. 7, it is possible to connect three circuit boards 1, 100, 101 to a flexible board, and it goes without saying that a plurality of circuit boards can be connected. However, since the relationship between the circuit boards 100 and 101 and the flexible substrate 5 is the same as the relationship between the circuit substrate 1 and the flexible substrate 5, the description and illustration thereof will be omitted as appropriate.
Further, in the present embodiment, the first bonding material and the second bonding material are formed on each electrode of the flexible substrate, but may be formed on each electrode on the circuit board. In the case where solder is used as the first bonding material and the second bonding material, the solder for surface mounting the electronic component may be formed on each electrode of the circuit board.

Further, although an example in which the first electrode and the second electrode of the flexible substrate are connected to each other is not shown, the present invention is not limited to this, and it is needless to say that a connecting portion may be appropriately provided.
Further, a resin may be filled between the joints between the upper electrode of the circuit board 1 and the first electrode of the flexible substrate and between the joints between the lower electrode and the second electrode to increase the mechanical strength.
As the resin, an epoxy resin, a urethane resin, a silicone resin, or the like is used.

Embodiment 2. FIG.
8 is a cross-sectional view showing a circuit board connection structure according to Embodiment 2 of the present invention, and FIG. 9 is a plan view showing a configuration of a flexible board in the circuit board connection structure shown in FIG. This will be described with reference to the drawings. The same parts as those in the first embodiment are denoted by the same reference numerals and the description thereof is omitted. An insulating layer 12 is formed between the third surface portion 5 c of the flexible substrate 5 and the side surface 1 d of the end portion 1 c of the circuit substrate 1. That is, as shown in FIG. 9, the insulating layer 12 on the third surface portion 5 c that is a region between the first electrode 8 and the second electrode 9 of the flexible substrate 5 is formed. As the insulating layer 12, a cover lay such as a solder resist or a polyimide film can be used.

  According to the circuit board connection structure of the second embodiment configured as described above, an insulating layer is provided between the third surface portion of the flexible substrate and the side surface of the end portion of the circuit substrate. At the time of joining, the first and second joining materials flow out and collect on the end face of the circuit board, and an unexpected short circuit between adjacent electrodes can be prevented. It goes without saying that this insulating layer can be formed in the same process as the insulating film covering the flexible wiring of the flexible substrate, and can also be formed in another process.

Embodiment 3 FIG.
10 is a diagram showing a configuration of a flexible substrate in a circuit board connection structure according to Embodiment 3 of the present invention. Parts similar to those in the first embodiment described above will be given the same reference numerals and will not be described. As in the above embodiments, the first electrode 8 is formed on the first surface portion 5a on the flexible substrate 51, and the second electrode 9 is formed on the second surface portion 5b. When there are a plurality of first electrodes 8, the size of any one of the electrodes is different from the size of the other electrodes and is formed as the first electrode 81. Then, similarly to the first bonding material 80 formed on the first electrode 8, the first bonding material 82 is formed on the large first electrode 81.

  In the circuit board connection structure according to the third embodiment configured as described above, a part of the electrodes of the flexible board is formed larger, so that the joining area is increased and the joining force with the circuit board is improved. It is possible to improve the reliability and durability of bonding. In Embodiment 3, the electrode to be enlarged is a part of the first electrode, but it goes without saying that the same effect can be obtained even if a part of the second electrode is formed to be large.

It is a perspective view which shows the connection structure of the circuit board in Embodiment 1 of this invention. It is sectional drawing which shows the cross section of the connection structure of the circuit board shown in FIG. It is a figure which shows the structure of the flexible substrate of the connection structure of the circuit board shown in FIG. It is sectional drawing for demonstrating the connection method of the connection structure of the circuit board shown in FIG. It is a figure which shows the structure of the flexible substrate of the connection structure of the circuit board shown in FIG. It is sectional drawing which shows the other structure of the circuit board connection structure in Embodiment 1 of this invention. It is sectional drawing which shows the other structure of the circuit board connection structure in Embodiment 1 of this invention. It is sectional drawing which shows the connection structure of the circuit board in Embodiment 2 of this invention. It is a figure which shows the structure of the flexible substrate in the connection structure of the circuit board shown in FIG. It is a figure which shows the structure of the flexible substrate of the connection structure of the circuit board in Embodiment 3 of this invention.

Explanation of symbols

1 circuit board, 1a upper surface, 1b lower surface, 1c end, 1d side surface, 2 electronic component,
3 circuit wiring, 4 flexible wiring, 5,51 flexible substrate,
5a 1st surface part, 5b 2nd surface part, 5c 3rd surface part, 6 upper surface electrode,
7 bottom electrode, 8, 81 first electrode, 9 second electrode, 10 insulating film,
11 Heating tool, 12 Insulating layer, 50 Base material, 80, 82 First bonding material,
90 Second bonding material.

Claims (6)

In the circuit board connection structure for electrically connecting the flexible wiring formed on the flexible board and the circuit wiring formed respectively on the upper and lower surfaces of the circuit board, the circuit board has the same end on the upper and lower surfaces. The upper electrode and the lower electrode connected to the circuit wiring are respectively formed in the portion, and the flexible substrate sandwiches the end portion of the circuit substrate, and the first electrode is opposed to the upper surface electrode at the end portion of the upper surface of the circuit substrate. A surface portion, a second surface portion facing the lower electrode at the end of the lower surface of the circuit board, and a third surface sandwiched between the first surface portion and the second surface portion and facing the end side surface of the circuit board. A first electrode connected to the flexible wiring on the first surface and connected to the upper surface electrode, and connected to the flexible wiring on the second surface. Re and connection structure of a circuit board, characterized in that it comprises respectively a second electrode connected to the lower electrode. The circuit board connection structure according to claim 1, wherein an insulating layer is formed between the third surface portion of the flexible substrate and an end side wall of the circuit substrate. 3. The circuit board connection structure according to claim 1, wherein the flexible substrate has a portion where the first electrode and the second electrode are not connected. 4. The first electrode or the second electrode on the flexible substrate is formed such that the formation positional relationship thereof is alternated in a planar manner in any one of claims 1 to 3. The circuit board connection structure described. 2. A plurality of electrodes having at least one of a first electrode and a second electrode on the flexible substrate, wherein the plurality of electrodes have different sizes. 4. The circuit board connection structure according to any one of 3 above. 6. The connection method for a circuit board connection structure according to claim 1, wherein the first electrode and the second electrode of the circuit board or the first electrode and the second electrode of the flexible board are provided. Forming a solder bump or a conductive adhesive layer on any of the above, and deforming the flexible substrate so that the first surface portion and the second surface portion are placed on the upper surface and the lower surface of the circuit board, Are arranged so as to face the side walls of the end of the circuit board, sandwich the end of the circuit board, and connect the first electrode, the second electrode, the upper surface electrode, and the lower surface electrode to the solder. And a step of bringing the first electrode and the second electrode into contact with the upper surface electrode and the lower surface electrode by heating through contact with a bump or a conductive adhesive layer. Connection method of the circuit board that.

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