JP2003258401A - Multilayer wiring board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multilayer wiring board where a flexible wiring board can be connected to its surface center and which contributes to the reduction of an electronic product in size without spoiling the merit of a wiring board having a multilayer structure. <P>SOLUTION: A plurality of surface lands 21 of the same shapes for an external circuit are arranged in an array on the surface of the multilayer wiring board; wiring 15 and inner lands 61, 62, and 63 are equally arranged through inner layers under the surface lands 21, corresponding to the surface lands 21; and the surface lands 21 provided on the multilayer wiring board and surface lands 23 provided on the flexible wiring board are soldered and connected to each other by heating. By this setup, heat diffused into the surface lands 21 and 23 can be set equal to each other in amount, so that the surface lands 21 and 23 can be uniformly soldered to each other. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer wiring board, and more particularly to a multilayer wiring board suitable for connecting a flexible wiring board to its surface.

[0002]

2. Description of the Related Art A printed circuit board (P)
CB) has been widely and generally used as a wiring board for mounting electronic components and connecting the mounted electronic components to each other. The PCB is not flexible due to mounting electronic components. The PCB also has a single-layer structure in which a wiring pattern is arranged on the surface of an insulator, but when there are many electronic components to be mounted and miniaturization is required, a multilayer structure in which the wiring pattern is arranged inside the insulator is also used. A PCB with is used. The PCB having such a multilayer structure is formed by printing a metal paste on the insulating ceramics before firing to form a multilayer and then firing integrally, or by forming a thermoplastic resin having a conductor pattern into a multilayer and then integrally bonding by heating. To form.

On the other hand, a flexible wiring board (Flexible P
The rinted circuit (FPC) is formed, for example, by sandwiching a patterned copper foil with a polyimide film and has flexibility as its name implies. FPC
Is characterized by the fact that it can be used with bending and twisting, and is often used as a connecting wire.

In the electronic product using a large number of electronic parts by utilizing the characteristics of the PCB and the FPC as described above, the PCB divided into blocks according to the circuit function is the basis of the circuit configuration, and the PCBs divided into the respective blocks are adjacent to each other. Are connected by FPC.

A typical example of such a PCB-FPC connection configuration is shown in FIG. Figure 5 shows PCB1 and PCB2 as F
It is the one schematically showing the state of being connected by the PC 3. FIG. 5A is a top view and FIG. 5B is a side view. Further, FIG. 5C is an enlarged perspective view showing a connecting portion between the PCB 1 and the FPC 3, and the PCB 1 having a multi-layer structure is shown exploded for each layer.

As shown in FIG. 5A, in PCBs 1 and 2, a large number of electronic components 41 and 42, a connector 50, etc. are mounted on the surface of each substrate, and wirings 11 and 12 for connecting the respective electronic components are provided. Are formed. On the other hand, the wiring 13 is formed in the FPC 3 used as the connecting wire.

When connecting a PCB to an external circuit, connection has been made so far using the end portion (broken line 6 in the figure) of the PCB, as shown in FIG. Surface lands 21 and 22 formed by making a part of the wirings 11 and 12 wider than the wiring width are provided at the surface end portions of the PCBs 1 and 2 having a multi-layer structure in order to connect to an external circuit. Similarly, the front surface land 23 of the FPC 3 is formed by making a part of the wiring 13 wider than the wiring width in order to connect to the external circuit.
24 are provided. In the PCBs 1, 2 and FPC 3, the wirings 11, 12, 13 are covered with resin for circuit protection, but the surface lands 21, 22, 2 are not covered.
3, 24 are exposed and arranged without a resin cover for connection. In this way, PCB1,2
The surface lands 21 and 22 provided at the ends of the FPC 3 and the surface lands 23 and 24 provided at the ends of the FPC 3 are electrically connected to each other by applying heat to the FPC 3 to connect the circuits of the PCBs 1 and 2. Connect to.

A general connection method of PCB and FPC is schematically shown in FIG. In FIG. 6, the same parts as those in FIG. 5 are designated by the same reference numerals, and the description thereof will be omitted. PCB
A solder layer is formed on at least one of the surface lands of the FPC 1 and the surface lands of the FPC 3 so that the surface lands to be connected to each other overlap each other.
1 and FPC3 are piled up. Next, the PCB 1 and the FPC 3 which are superposed as shown in the drawing are sandwiched by the heater 4 and the heater cradle 5, and the solder layer is melted by applying heat to the connection portion while applying pressure, and the both are adhered.

[0009]

In the method of connecting the PCB1 and the FPC3 by pressurization / heating shown in FIG. 6, when a PCB having a general multilayer structure in which a wiring pattern is arbitrarily formed is used, the surface land The soldering state is likely to vary from time to time. For this reason, the adhesive strength and electrical characteristics differ between individual surface lands, and connection reliability cannot be obtained so much. It is considered that this variation in the soldering state is caused by the fact that the heat applied to the surface lands does not diffuse uniformly over all the surface lands.

As a solution for reducing such variations in soldering state, P having a conventional multilayer structure is used.
In the CB, as shown in FIG. 5C, in the broken line 7 immediately below the front surface land, 2 other than the connection layer (first layer) is formed.
The wiring patterns 14, 15 and 16 are not formed in the layer and thereafter. As a result, it is possible to reduce the variation in the soldering state for each surface land. On the other hand, the portion 7 shown by the broken line in FIG. 5C becomes a dead space with no wiring pattern accordingly, which is an obstacle to downsizing the PCB.

FIG. 5 shows the ends of PCB1 and PCB2 as F
Although the PC3 is used for connection, it may be desirable to shorten the FPC3 as a connecting wire and connect the PCB2 to the center of the PCB1 depending on the circuit configuration divided into blocks. However, if it is attempted to connect the FPC 3 to the center of the PBC 1 in order to realize such an arrangement, the dead space 7 shown by the broken line in FIG. The subsequent wiring patterns 14, 15 and 16 all need to be arranged bypassing the dead space 7 arranged in the central portion. Such a design is not practically applicable because it significantly deteriorates the mounting efficiency of electronic components.

Therefore, an object of the present invention is to connect a flexible wiring board to the central portion of the board surface without impairing the advantages of a wiring board having a multilayer structure, and to contribute to miniaturization of electronic products. To provide a wiring board.

[0013]

According to a first aspect of the present invention, there is provided a multi-layered wiring board having wiring in an inner layer on a surface thereof.
A plurality of surface lands, each of which has a part of the wiring having a width equal to or wider than the wiring width for connecting to an external circuit, are arranged in an array with the same shape. For each inner layer, the wiring pattern is evenly arranged over the inner layer corresponding to each surface land, and a part of the wiring for connecting to an external circuit is formed on the surface of the flexible wiring board having flexibility. A plurality of surface lands that are the same as or wider than the wiring width are arranged in line with the same shape, and the surface lands provided on the wiring board of the multilayer structure and the surface lands provided on the flexible wiring board are It is characterized by being connected by applying heat.

According to this, immediately below the surface lands that are arranged in the same shape and aligned, for each inner layer,
Since the wirings are evenly arranged in the inner layer corresponding to the individual surface lands, the structure over all the inner layers immediately below the plurality of surface lands is the same for each surface land. Therefore, when connecting the flexible wiring board, the heat applied to melt the solder is
Diffuses directly downward from each surface land. Therefore, it is possible to reduce the variation in the molten state of the solder for each surface land, and it is possible to improve the reliability of the connection of the flexible wiring board.

According to a second aspect of the present invention, in the wiring pattern arranged immediately below the plurality of front surface lands and corresponding to each front surface land in each inner layer, the wiring pattern includes the wiring and the wiring. An inner layer land having a width equal to or wider than the wiring width of the wiring, and in at least one inner layer, the inner layer lands are equal over the inner layer corresponding to each surface land. It is characterized by having been placed.

According to this, by arranging the inner layer lands having a part of the wiring equal to or wider than the wiring width corresponding to the individual surface lands, the inner layer in the inner layer immediately below the surface lands is arranged. The heat capacity and the thermal conductivity of the part where the land is arranged are made larger than those of the wiring part around the part. As a result, when the heat applied when connecting the flexible wiring board diffuses in the direction directly below the surface land, the influence of the surroundings on the heat diffusion becomes relatively small in the portion where the inner layer land is arranged, and the stability is more stable. The heat can be diffused directly downward. Therefore, it is possible to further reduce the variation in the molten state of the solder for each surface land, and it is possible to further improve the reliability of the connection of the flexible wiring board.

The invention according to claim 3 is characterized in that the inner layer lands are arranged in all the inner layers. As a result, the heat capacity and heat conductivity of the portion directly below the surface land are made larger than that of the surrounding portion. Therefore, when heat is diffused in the direction directly below the surface land,
In the portion directly below the surface land, the influence of the surroundings is further reduced, and the heat can be more stably diffused in the direction directly below the surface land. Therefore, it is possible to further reduce the variation in the molten state of the solder for each surface land, and it is possible to further improve the reliability of the connection of the flexible wiring board.

The invention according to claim 4 is characterized in that the inner layer lands have the same shape over all the inner layers. According to this, the heat capacity and the thermal conductivity of the portion where the inner layer land is arranged are the same in each inner layer, and the heat applied to the surface land is more uniform than when the shape of the inner layer land is different for each inner layer. It spreads in the direction directly below. Therefore, the flexible wiring board can be more stably connected to the front surface land, and the reliability of the connection of the flexible wiring board can be further increased.

According to a fifth aspect of the present invention, the plurality of surface lands are arranged in the central portion of the substrate surface. In the multilayer wiring board, the structure immediately below each surface land is the same for all the surface lands, so there is no limitation on the arrangement position of the plurality of surface lands with respect to the board. On the other hand, by arranging the plurality of surface lands at the center of the multilayer wiring board and connecting the wiring board of the connection partner with the flexible wiring board as short as possible, the overall occupied area is reduced and the signal delay due to the wiring is delayed. Can be reduced, which can contribute to miniaturization and higher performance of electronic products.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic perspective view of the connection portion between a PCB and an FPC having a multi-layer structure according to the present invention, in which the PCB is exploded for each layer. In FIG. 1, the same parts as those in FIG. 5 are designated by the same reference numerals, and the description thereof will be omitted.

In the example of FIG. 1 according to the present invention, four surface lands 21 for connecting the FPC 3 are arranged in the same shape in the central portion (broken line 8 in the figure) of the first layer of the PCB 1 in the same shape. The wiring 11 for electrically connecting the external circuit and the circuit in the PCB 1 is integrally formed on the surface land 21. The surface lands 21 are arranged at equal intervals in order to improve the formation density while making the heat capacities equal.

In the second and subsequent layers of the PCB 1, the wirings 14, 15, 16 and 17 of each inner layer are connected to the individual surface lands 2 in the broken line 9 in the drawing, which is immediately below the surface lands 21.
Corresponding to No. 1, they are equally arranged in the inner layer.
Further, in the second layer, the fourth layer, and the n-th layer, an inner layer land in which a part of the wiring is made wider than the wiring width in order to increase the heat capacity in a broken line 9 in the drawing immediately below the front surface land 21. 61, 62, 63 are individual surface lands 21
Corresponding to the above, they are equally arranged in the inner layer. That is, the inner layer lands 61, 62, 63 are respectively
It has the same shape and is arranged at the same position with respect to the surface land 21.

The wirings 14, 16 and 17 and the inner layer land 61,
As a typical size of 62 and 63, an inner layer land having a width of 0.5 mm and a length of 10 to 20 mm is arranged with respect to a wiring having a wiring width of 0.1 mm. Among the wirings, there are wirings 18 connected to other electronic components or circuits, and dummy wirings 19 separated from the other electronic components or circuits. The surface lands 21 and the broken lines 8 and 9 in the figure immediately below the land 21.
In the portion indicated by, the wirings 14, 15, 1 are provided for each layer.
6, 17 or inner layer lands 61, 62, 63 are arranged equally.

For the surface land 21 of the PCB 1 of FIG.
The surface land 23 of the FPC 3 is connected using the same connection method as shown in FIG. In the PCB1 and the FPC3, the wirings 11 and 13 are covered with resin for circuit protection, but the surface lands 21 and 23 are exposed and arranged without a resin cover for connection. A solder layer is formed on at least one surface of the surface land 21 of the PCB1 and the surface land 23 of the FPC3, and the PCB1 and the FPC3 are superposed so that the surface lands to be connected to each other overlap each other. Next, the superposed PCB1 and FPC3 are sandwiched between the heater 4 and the heater pedestal 5 shown in FIG.
The solder layer is melted at 0 ° C., and the two are bonded while applying pressure.

At the time of this soldering, the wiring 14, 15, 16, 17 or the inner layer lands 61, 62, 63 are equally arranged for each layer in the surface land and the portions immediately below the land shown by broken lines 8 and 9 in the figure. Therefore, the heat applied for melting the solder is applied to the individual surface land 21.
Spread evenly in the direct downward direction. Therefore, it is possible to reduce the variation in the molten state of the solder for each surface land 21, and it is possible to improve the reliability of the connection of the FPC 3.

Further, in FIG. 1, although the surface land 21 for connection is arranged in the central portion of the PCB 1, the wiring exists in the portion 9 shown by the broken line in FIG. Therefore, the portion 7 directly below the front surface land 21 does not become a dead space, the substrate area can be effectively utilized, and the PCB 1 can be downsized.

FIG. 2 and FIG. 3 are modified examples relating to the relationship between the surface lands 21 arranged in the first layer of the PCB and the inner layer lands 61, 62, 63 arranged in the inner layers of the second and subsequent layers of the PCB. It is shown. In a PCB having a multi-layered structure in FIG.
2 (a) for each layer only for
2D are arranged side by side in the order of FIG. Further, wirings connected to the surface land 21 and the inner layer lands 61, 62, 63 are all omitted in the drawing for simplification.

In FIG. 2, the surface land 2 is provided on each layer of the PCB.
The example in which the inner-layer lands 61, 62, 63 are provided corresponding to No. 1 is shown. In the example shown in FIG. 2, the inner layer land 6 is provided for each layer.
Although the shapes of 1, 62 and 63 are different, the shape is the same in any one inner layer. Also, FIG.
As can be seen by penetrating through any p-th surface land laterally, the p-th surface land and the p-th inner layer land of each layer corresponding thereto are arranged at the same position. By adopting such a configuration, the structure immediately below each surface land 21 becomes the same over all the surface lands 21.

On the other hand, the heat applied to the surface land 21 for melting the solder when connecting the FPC 3 to the surface land 21 diffuses from left to right in FIG. Therefore, the structure immediately below the front surface land 21 is replaced by the entire surface land 2.
By making the temperature the same over 1, the heat applied for melting the solder diffuses evenly and directly downward over all the surface lands 21. As a result, it is possible to reduce variations in the solder melting state of the individual surface lands 21 and improve the reliability of FPC connection.

In order to make the heat diffusion in the direction directly below the surface land 21 more uniform, a PCB having a multi-layer structure like the third layer in FIG. 1 includes a layer in which inner layer lands are not arranged. , It is advantageous to arrange the inner layer lands in all the inner layers of the PCB. That is, as shown in FIG. 2, in all the inner layers, the inner layer lands 61, 62,
By disposing 63, the heat capacity and the thermal conductivity in the broken line 9 immediately below the front surface land 21 can be made larger than that in the surrounding portion (outside the broken line 9 in the figure). As a result, heat is applied to the surface land 21.
The influence of the surroundings can be reduced in the portion immediately below the surface land 21 when the light is diffused in the direction immediately below. Therefore, the heat can be more stably diffused in the direction directly below the surface land 21, which is preferable for ensuring the stability and reliability of the connection.

In FIG. 2, the surface land 21 and the inner layer land 6 are shown.
Although the wirings connected to the wirings 1, 62, 63 are not shown, in the sense that the heats are prevented from escaping by the wirings and the heats are uniformly diffused, the surface land 21 and the inner layer lands 61, 6
It goes without saying that it is preferable that the line width of the wirings connected to 2, 63 be as thin as possible.

FIG. 3 shows an example in which the inner layer lands 61 having the same shape are arranged over all the inner layers of the PCB having a multilayer structure. In FIG. 3, the thermal diffusion in the direction directly below the surface land 21 is constant over each layer, which is more preferable for ensuring the stability and reliability of the connection.

FIG. 4 is a PC having the multilayer structure shown in FIG.
FIG. 4A shows an example in which B1 and another PCB2 are connected via an FPC3, and FIG.
(B) is a side view. In this way, flexible FP
By using C1 and PCB1 with improved connection reliability,
PCB2 is placed vertically at the center of PCB1 and connected with FPC3, which has the shortest possible cable length.
The occupying area of the entire CB2 is reduced.

As described above, in the embodiment of the present invention, FIG.
4 shows an example in which the front surface land 21 is arranged in the central portion of the PCB, it goes without saying that the same effect can be obtained even if the front surface land 21 is arranged in the end portion of the PCB.

As described above, according to the present invention, it is possible to connect the FPC to the central portion of the PCB without impairing the advantages of the PCB having the multilayer structure, and the wiring board having the multilayer structure is used. It greatly contributes to miniaturization of electronic products.

[Brief description of drawings]

FIG. 1 is a schematic perspective view of a connection portion between a multilayer wiring board and a flexible wiring board according to the present invention, in which the multilayer wiring board is exploded for each layer.

2A to 2D are views showing a surface land of a multilayer wiring board according to the present invention and a structure immediately below the surface land, arranged side by side for each layer.

3 (a) to 3 (d) are views showing a structure in which each inner layer land of the multilayer wiring board according to the present invention has the same shape, arranged side by side for each layer.

FIG. 4 is a diagram in which another wiring board is connected to the multilayer wiring board according to the present invention through a flexible wiring board, FIG. 4 (a) is a plan view, and FIG. 4 (b) is a side view. is there.

5A is a plan view in which another wiring board is connected to a conventional multilayer wiring board via a flexible wiring board, FIG. 5B is a side view thereof, and FIG. 5C is a conventional view. FIG. 3 is a schematic perspective view showing the structure of the multilayer wiring board disassembled layer by layer in the connection portion between the multilayer wiring board and the flexible wiring board.

FIG. 6 is a schematic diagram showing a method of connecting a wiring board and a flexible wiring board.

[Explanation of symbols]

1, 2 PCB (wiring board) 3 FPC (flexible wiring board) 11, 12, 13, 14, 15, 16, 17, 18, 1
9 wiring 21, 22, 23, 24 surface land 40 electronic component 50 connector 61, 62, 63 inner layer land

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 5E317 AA07 BB01 BB11 CC15 GG07                 5E344 AA02 AA12 AA22 AA23 BB02                       BB04 CC03 CC07 DD04 DD16                       EE17 EE26                 5E346 AA29 BB11 BB16 EE44 FF19                       HH07 HH17 HH22 HH31

Claims (5)

[Claims] 1. A surface land, in which a part of the wiring is made to be the same as or wider than the wiring width in order to connect to an external circuit, on the surface of a wiring substrate having a multilayer structure having wiring in an inner layer, in the same shape. A plurality of them are arranged side by side, immediately below the plurality of surface lands, for each inner layer,
The wiring patterns are arranged equally in the inner layer corresponding to each surface land, and a part of the wiring is the same as the wiring width or connected to the external circuit on the surface of the flexible wiring board having flexibility. A plurality of surface lands that are wider than the width are arranged in the same shape, and the surface lands provided on the multilayer wiring board and the surface lands provided on the flexible wiring board are heated together. A multilayer wiring board characterized by being connected. 2. In a wiring pattern, which is arranged just below the plurality of surface lands, corresponding to each surface land in each inner layer, the wiring pattern is the same as the wiring and the wiring width of the wiring. The inner layer land has a width wider than the wiring width of the wiring, and in at least one inner layer, the inner layer land is arranged equally over the inner layer corresponding to each surface land. The multilayer wiring board according to claim 1. 3. The multilayer wiring board according to claim 2, wherein the inner layer lands are arranged in all the inner layers. 4. The multilayer wiring board according to claim 3, wherein the inner layer lands have the same shape over all the inner layers. 5. The multilayer wiring board according to claim 1, wherein the plurality of surface lands are arranged in a central portion of the surface of the board.