JPH0744324B2 - Flexible and rigid printed wiring board - Google Patents

Description

[Detailed Description of the Invention] [Table of Contents] -Outline-Industrial application field-Conventional technology (Fig. 4) -Problems to be solved by the invention-Means for solving problems-Actions-Examples (Figs. 1, 2, 3) -Effect of the invention [Outline] A flexible and rigid printed wiring composite substrate,
A flexible substrate and a rigid substrate are joined together via an insulating adhesive layer, and the through holes of the both boards are connected to each other, or the through hole and the connection pattern are connected to each other. By providing a slit groove through which molten solder can enter due to its surface tension, the two substrates can be reliably connected to each other, and the inner diameters of the through holes of the two substrates can be formed to be the same.
It is possible to remove the solder bumps on the through-hole lands exposed to the outside of the both boards and to make the insides of the through-holes of both boards hollow, and particularly to improve the reliability of the connection portion. It was done.

[Industrial application field]

The present invention relates to a flexible and rigid printed wiring composite board formed by joining a flexible printed wiring board (flexible substrate) and a rigid printed wiring board (rigid substrate) via an insulating adhesive layer, and particularly to a through hole of the flexible printed wiring board. And a through hole of the rigid printed wiring board or a connection pattern. Here, the flexible printed wiring board means a flexible printed wiring board, and the rigid printed wiring board means a rigid printed wiring board.

In recent years, there has been an increasing demand for miniaturization and improvement of productivity of electronic devices, and in response to this demand, a rigid substrate excellent in component mounting, planar wiring and planar circuit configuration, and flexible three-dimensional wiring configuration A composite board has been developed which has a function of a multilayer wiring board and a connection function of a flexible board by combining and forming an excellent flexible board.

In this type of composite substrate, one of the important points in the construction is the quality of electrical connection between the flexible substrate and the rigid substrate by soldering.

[Conventional technology]

FIG. 4 is a side sectional view showing an essential part of a conventional flexible and rigid printed wiring composite board. In the figure, reference numeral 1 is a flexible printed wiring board (hereinafter referred to as FPC board), 2 is a rigid printed wiring board (hereinafter referred to as RPC board), 3 is an adhesive layer made of an insulating adhesive, and 4 is solder. Shown in each. In this conventional example, the through holes 1-1 and 1-2 formed at predetermined positions of the FPC board 1 are aligned with the through holes 2-1 and the connection pattern 2-2 formed on the RPC board 2, respectively. , FPC board 1 through the adhesive layer 3
And the RPC board 2 are joined, and the through holes 1-1 and 1-2 of the FPC board 1 are connected to the through hole 2-1 of the RPC board 2 and the connection pattern 2-2 by the solder 4, respectively, so that the connection portion P is formed. Is formed. In this case, the inner end surface 3a of the adhesive layer 3 in the connection portion P is formed to have substantially the same inner diameter as the inner peripheral surfaces of the through holes 1-1 and 1-2 of the FPC board 1. Reference numeral 1a is a through hole 1-of the FPC board 1.
An inner plating layer applied to the inner surfaces of 1, 1-2, 1b is a through hole land formed on the upper and lower surfaces of the substrate 1 by a plating layer continuous with the inner plating layer 1a, and 2a is a through hole of the RPC substrate 2. Reference numeral 2b denotes an inner plating layer applied to the inner surface of 2-1 and reference numeral 2b denotes through hole lands formed on the upper and lower surfaces of the substrate 2 by a plating layer continuous with the inner plating layer 2a. Further, in this conventional example, the through hole 1 of the FPC board 1 connected to the through hole 2-1 of the RPC board 2 is used.
-1 is formed such that its inner diameter is larger than the inner diameter of the through hole 2-1 of the RPC board 2, and a step is provided between the two. That is, since the adhesive layer 3 does not get wet with solder (does not adhere), the through hole 1-1 of the FPC board 1
Since the solder is connected to the through hole 2-1 of the RPC board 2 in a bridge shape as shown in the figure, the above step is required.

[Problems to be solved by the invention]

 The above conventional example has the following problems.

The inner end surface 3a of the adhesive layer 3 at the connection portion P is the FPC board 1
Since the through holes 1-1 and 1-2 are formed to have substantially the same inner diameter as the inner peripheral surfaces of the through holes 1-1, the solder 4 does not get wet to the inner end surface 3a of the adhesive layer 3 at the time of soldering and is repelled in the opposite direction. Therefore, as described above, it becomes a bridge shape and the through hole 1
-1, 1-2 is connected to the through hole 2-1 of the RPC board 2 and the connection pattern 2-2, and the adhesion area of the RPC board 2 to the through hole land 2b or the connection pattern 2-2 becomes small, There is a problem that the connection state becomes unstable and the connection reliability is low. In particular, when the through hole 1-2 of the FPC board 1 and the connection pattern 2-2 of the RPC board 2 are connected, the solder 4 is repelled by the adhesive layer 3 and a connection failure easily occurs.

When connecting the through hole 1-1 of the FPC board 1 and the through hole 2-1 of the RPC board 2, the through hole 1-
Since it is necessary to make the inner diameter of 1 larger than the inner diameter of the through hole 2-1, the connection portion P becomes large and the wiring efficiency of the FPC board 1 is reduced. Further, because of the reason described in the above section, it is necessary to sufficiently fill both the through holes 1-1 and 2-1 with the solder 4 and to perform the soldering in such a manner that the solder 4 is raised on the through hole lands 1b and 2b. Is increased, and the solder 4 is raised, which makes it more difficult to form a multilayer board.

As described above, since the through holes 1-1 and 2-1 are filled with the solder 4, there is an inconvenience that the component lead (not shown) cannot be inserted here to mount the component.

The present invention was created in view of the above problems, and enables reliable connection between the FPC board and the RPC board to improve reliability, prevent the connection part from becoming large, and prevent the wiring efficiency from decreasing. However, it is an object of the present invention to provide a flexible and rigid printed wiring composite board which can reduce the amount of solder used and further make the board multi-layered and can eliminate the inconvenience of component mounting.

[Means for Solving the Problems] According to the present invention, the flexible printed wiring board and the rigid printed wiring board are joined via a connecting layer made of an insulating adhesive, and the through holes of the both boards are joined together, or In a flexible and rigid printed wiring composite board formed by connecting a through hole of the flexible printed wiring board and a connection pattern of the rigid printed wiring board, a through hole of the flexible printed wiring board and a through hole of the rigid printed wiring board. Alternatively, the inner end surface of the adhesive layer in the connection portion for connecting with the connection pattern is recessed outward in the radial direction from the inner surface of the through hole to form a slit groove having a concave cross section, and the upper and lower surfaces of the slit groove are formed. It is defined by the land of the through hole or the connection pattern and is adapted to the molten solder on the upper and lower surfaces. It is characterized by improving wettability.

[Action]

According to the present invention, the inner end surface of the adhesive layer at the connecting portion between the flexible substrate and the rigid substrate is receded radially outward from the inner surface of the through hole to form a slit groove having a concave cross section, and the upper and lower surfaces of the slit groove are formed. Since the wettability of the upper and lower surfaces with respect to the molten solder is improved by defining the through holes by the land or the connection pattern, the molten solder has a surface tension that causes the slits when the soldering is performed by a method such as solder dipping. Even if excess solder is removed by a solder leveler etc. after entering the groove and after solder dipping, the solder remains in the slit groove, and this solder can securely connect the through hole lands of both boards. it can. Further, according to the present invention, by providing the slit groove as described above, the inner diameter of the through hole of the flexible substrate can be formed to be the same as the inner diameter of the through hole of the rigid substrate, and the outside of both substrates can be formed. Since the swell of the solder on the through hole land exposed to the inside can be removed, it is possible to make the inside of the through hole hollow.

〔Example〕

FIG. 1 is a side sectional view showing an essential part of an embodiment of the present invention, FIG. 2 is an external perspective view of the embodiment of the present invention, and FIG. 3 is a view showing an embodiment of the present invention. In addition, in these drawings,
The same or corresponding parts as those in the figure (conventional example) are designated by the same reference numerals.

In FIGS. 1 and 2, reference numeral 1 is a flexible printed wiring board (hereinafter referred to as FPC board), 1-1 is a through hole provided in the board 1, and 1a and 1b are inner surface plating of the through hole (1-1). Layers and through hole lands, 2 is a rigid printed wiring board (hereinafter referred to as RPC board), 2-1 is a through hole provided in the board 2, 2a and 2b are through holes (2-
1) Inner plating layer and through hole land, 3 is substrate 1
And 2 and an adhesive layer made of an insulative adhesive that bonds the two (1, 2) to each other, 3a is an inner end surface of the adhesive layer (3), 4 is solder, and Q is the present invention. The reference numeral 5 designates a connecting portion formed by the above, and 5 indicates a slit groove formed in the connecting portion Q and having a concave cross section.

As shown in FIG. 2, the appearance of this example is such that the FPC board 1 is bonded on the entire surface of the RPC board 2 via the adhesive layer 3, the connection portion Q is provided at a predetermined position, and the edge of the FPC board 1 is provided. Is partially extended and bent so that it can be three-dimensionally wired, thereby forming a composite board having the function of a multilayer wiring board and the function of connecting to another FPC board.

The main feature of this example is as shown in FIG.
The inner diameter of the through hole 1-1 is formed to be the same as the inner diameter of the through hole 2-1 of the RPC board 2, and the inner end surface 3a of the adhesive layer 3 at the connection portion (solder connection portion) Q is formed through the through hole 1-.
1 (2-1) Recessed from the inner peripheral surface to the outside in the radial direction of the through hole 1-1, and formed between the FPC board 1 and the RPC board 2 at the connection portion Q (usually the through hole land 1b).
2b) and the solder 4 melted into the through hole 1 is provided with a slit groove 5 having a concave cross section through which the solder 4 can enter due to its surface tension.
-1 (2-1) is provided along the circumferential direction.
The width of the slit groove 5 (strictly speaking, the through hole land 1b
And 2b mutual interval) ts, the depth Ds is set sufficiently large, and the molten solder 4 is formed so as to be able to enter by the action of the surface tension. FIG. 3 shows the width ts of the slit groove 5
6 is a diagram in which the setting range of the depth Ds and the depth Ds is obtained by an experiment. As shown in FIG. 3, the connection failure occurrence limit line is used as a boundary to divide into a good connection area (area in which molten solder can enter the slit groove) and a poor connection occurrence area. Therefore, for example, when the width ts of the slit groove 5 is 40 μm, the depth Ds is about 0.35.
Good connection Q if set larger than mm (350 μm)
(FIG. 1) is obtained. When connecting the through hole 1-1 of the FPC board 1 and the connection pattern (not shown, corresponding to 2-2 in FIG. 4) of the RPC board 2 by providing the slit groove 5 in the same manner as above. , A good connection is obtained.

In this example, by providing the slit groove 5 as described above, when the soldering is performed by a method such as solder dipping, the molten solder enters the slit groove 5 due to its surface tension. Even if hot air is blown to the connecting portion Q by a method such as a solder leveler to remove excess solder, as shown in FIG.
Those that remain as a thin solder layer on the through hole lands 1b and 2b exposed on the inner surface of 2-1 and the upper surface of the FPC board 1 and the lower surface of the RPC board 2 and that have entered the slit groove 5 are not removed. The through hole lands 1b and 2b can be reliably connected to each other.

Therefore, according to this example, the FPC board 1 and the RPC board 2 can be reliably connected to each other, and the inner diameter of the through hole 1-1 of the FPC board 1 can be made equal to the inner diameter of the through hole 2-1 of the RPC board 2. It is possible to remove the swelling of the solder 4 on the vertically exposed through hole lands 1b and 2b and to make the insides of the through holes 1-1 and 2-1 hollow.

The present invention is of course applicable to the case where the through holes 1-1 and 2-1 do not have the same inner diameter (different diameters) as in the above embodiment. However, in this case, the wiring efficiency is slightly reduced.

〔The invention's effect〕

As is clear from the above description, according to the present invention, the slit groove (5) is formed in the connecting portion (Q) between the flexible printed wiring board (FPC board) (1) and the rigid printed wiring board (RPC board) (2). The FPC board (1)
It is possible to reliably prevent the occurrence of a connection failure between the RPC board (2) and the RPC board (2) and significantly improve the connection reliability. Also, FP
Since the inner diameter of the through hole (1-1) of the C board (1) can be formed to be the same as the inner diameter of the through hole (2-1) of the RPC board (2), the wiring efficiency of the FPC board 1 can be improved. it can. Further, since the swell of the solder (4) on the through hole land (1b, 2b) exposed to the outside can be removed and the inside of the through hole (1-1, 2-1) can be made hollow, It is possible to increase the number of substrates and reduce the amount of solder (4) used, and it is possible to eliminate the inconvenience of component mounting.

[Brief description of drawings]

FIG. 1 is a side sectional view showing an essential part of an embodiment of the present invention, FIG. 2 is an external perspective view of an embodiment of the present invention, FIG. 3 is a view showing an embodiment of the present invention, and FIG. It is a side surface sectional view showing an important section. In FIGS. 1, 2, and 3, 1 is a flexible printed wiring board (flexible printed wiring board: F
PC board), 2 is rigid printed wiring board (rigid printed wiring board: RPC board), 1-1 and 2-1 are through holes, 1a and 2a are inner plating layers, 1b and 2b are through hole lands, and 3 is insulation. 3a is an inner end surface, 4 is a solder, 5 is a slit groove, Q is a connecting portion (solder connecting portion), ts is a slit groove width, and Ds is a slit groove depth.

Claims (1)

[Claims] 1. A flexible printed wiring board (1) and a rigid printed wiring board (2) are joined together through a connecting layer (3) made of an insulating adhesive, and the through holes of the both boards (1, 2) are joined. In the flexible and rigid printed wiring composite board, which is formed by connecting each other or through holes of the flexible printed wiring board (1) and the connection pattern of the rigid printed wiring board (2), the flexible printed wiring board (1) The inner end surface () of the adhesive layer (3) at the connection portion (Q) for connecting the through hole (1-1) with the through hole (2-1) of the rigid printed wiring board (2) or the connection pattern. 3
a) is recessed outward in the radial direction from the inner surface of the through hole (1-1 or 2-1) to form a slit groove (5) having a concave cross section, and the upper and lower surfaces of the slit groove are connected to the through hole (5). A flexible and rigid printed wiring composite board, characterized in that the wettability of the upper and lower surfaces with respect to the molten solder is improved by defining the land (1a, 2b) 1-1, 2-1) or the connection pattern.