JP2000036644A - Double-sided flexible printed circuit board - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To realize a through hole in a land, which leads to downsizing of a double-sided FPC and downsizing of a device, without causing mounting defects. SOLUTION: A double-sided flexible printed board 6 on which at least one of the electrical components 7 to be mounted is soldered and mounted by reflow, and a flexible printed board with a non-through through hole 3a formed by a non-through hole by laser processing. 6, electrically connecting the front and back conductive patterns, at least one of the non-through through holes 3a is installed so as to be connected to a mounting land of the electric component, and the mounting land is connected to the non through through hole 3a. A double-sided flexible printed circuit board (6), which is provided on a surface on the back side of the provided surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flexible printed circuit board, and more particularly, to a double-sided flexible printed circuit board on which electric components are soldered and mounted by so-called reflow.

[0002]

2. Description of the Related Art Flexible printed circuit boards (hereinafter referred to as FPCs)
Is abbreviated as) and is used in various devices, including cameras, due to its thinness and good flexibility. Above all, when a relatively large-scale circuit is formed by mounting electric components, a double-sided FPC is often used. This double-sided FP
In C, through holes (hereinafter abbreviated as T / H) are used to electrically connect the front and back conductive patterns. Conventional T / Hs are configured such that a through hole is formed by drilling in a base of an FPC to which a conductor is attached, and the through hole is plated to connect conductive patterns on the front and back.

FIG. 4 is a cross-sectional view showing a manufacturing process of a general double-sided FPC as a first conventional example. Reference numeral 31 denotes a base on which conductors 32a and 32b are attached on both front and back surfaces (FIG. 4A). Generally, polyimide is used for the base and copper foil is used for the conductor. A through hole 33 is drilled at a location where the T / H is to be set (FIG. 4B). T / H
By applying the plating 34, the conductors 32a and 32
b to form a through T / H 33a.
(C)). The conductors 32a and 32b on the front and back are etched to obtain a desired conductive pattern (FIG. 4D). Opening 3
5a is laminated with a coverlay 35 provided as needed (FIG. 4E). Thereafter, the conductors 32a and 32b exposed at the opening 35a are subjected to a desired surface treatment and then the outer shape is punched to complete the double-sided FPC 36. FIG. 3 shows a cross section of an electric component 37 mounted on the double-sided FPC 36 by reflow. 38 is a solder.

On the other hand, in recent years, many non-penetrating T / H technologies for a multilayer substrate have been proposed as disclosed in Japanese Patent Application Laid-Open No. 6-77662. This electrically connects the outermost layer of the multilayer substrate and the layer immediately below the outermost layer. FIG. 6 is a cross-sectional view showing a manufacturing process of such a non-penetrating T / H as a second conventional example. The base 51 to which the conductor 52a is attached is laminated as the outermost layer of the substrate (FIG. 6A). The T / H setting portion of the conductor 52a is removed by etching (FIG. 6B). When laser irradiation is performed on the T / H setting location, the base 51 exposed by etching is removed,
The conductive pattern 52c immediately below is exposed (FIG. 6C).
At this point, a hole is formed in the outermost layer conductor 52a and the base 51, but no hole is formed in the conductive pattern 52c immediately below, so that the non-through hole 53 is formed. By applying the T / H plating 54 in this state, the non-penetrating T / H 53a is formed by connecting the outermost layer conductor 52a and the conductive pattern 52c immediately below the outermost conductor 52a (FIG. 6D). The outermost conductor 52a is etched to obtain a desired conductive pattern (FIG. 6E). After applying the resist 55, an opening 55a is formed as needed (FIG. 6F). Since the non-through holes 53 are formed by etching and laser irradiation, the diameter can be made smaller than that of the through holes 33 formed by the drill in the first conventional example. FIG. 5 shows a cross section of an electric component 57 mounted on the multilayer substrate 56 by reflow. 58 is a solder.

[0005]

However, the above-mentioned prior art has the following drawbacks.

In the first conventional example, a penetration hole having a relatively large diameter remains in the penetration T / H 33a formed by drilling. Therefore, when this is installed in the mounting land of the electric component, FIG.
As shown in the figure, the solder melted during reflow has penetrated T / H3
Inevitably flows into the through-hole 33 formed by 3a, which causes mounting defects due to insufficient solder, swelling of the coverlay on the back surface, and cracks due to the difference in the thermal expansion coefficient between the solder and the conductive pattern. Would. If the mounting land and the penetrating T / H 33a are independently installed to prevent this, the cost of the double-sided FPC is increased and the size of the device itself is increased.

In the second conventional example, the non-penetrating T / H 53a formed by etching and laser irradiation has a relatively small diameter but the non-penetrating hole 53 remains. When the mounting land is installed, it is inevitable that the solder melted during the reflow flows into the non-penetrating T / H 53a, and there is a concern that mounting failure due to insufficient solder may occur. In view of the above-described drawbacks of the prior art, the problem to be solved by the present invention is to realize a T / H in a land that leads to downsizing of a double-sided FPC and downsizing of a device without generating mounting defects. is there.

[0008]

In order to achieve the above object, the invention according to claim 1 of the present application is directed to a double-sided flexible print in which at least one of the mounted electrical components is mounted by reflow soldering. A substrate, electrically connecting the conductive patterns on the front and back of the flexible printed circuit board with non-through through holes formed by non-through holes by laser processing, at least one of the non-through through holes is a mounting of the electric component; The mounting lands are provided so as to be connected to the lands, and the mounting lands are provided on a surface on the back side of the surface provided with the non-through through holes.

According to the above configuration, the object of the present invention is to provide:
T in land that leads to miniaturization of double-sided FPC and miniaturization of equipment
/ H can be realized without causing a mounting defect.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) First, an embodiment of a manufacturing process of a double-sided FPC to which the present invention is applied will be described with reference to FIG. Reference numeral 1 denotes a base on which conductors 2a and 2b are attached on both front and back surfaces (FIG. 2A). Generally, polyimide is used for the base and copper foil is used for the conductor. T / H of conductor 2b
The installation location is removed by etching (FIG. 2B). When laser irradiation is performed from the conductor 2b side to the T / H installation location, the base 1 exposed by etching is removed, and the conductive pattern 2a on the opposite side is exposed (FIG. 2C). At this point, a hole is formed in the base 1 and the conductor 2b on one surface, but no hole is formed in the conductive pattern 2a on the opposite side, so that the non-through hole 3 is formed. By applying T / H plating 4 in this state, the conductors 2a, 2b
To form a non-penetrating T / H3a.
(D)). Since the non-through hole 3 is formed by etching and laser irradiation, it is possible to make the diameter smaller than the through hole 33 formed by the drill in the first conventional example. The conductors 2a and 2b on the front and back are etched to obtain a desired conductive pattern (FIG. 2E). The coverlay 5 provided with openings 5a as needed is laminated (FIG. 2F).
At this time, the connection land 5b is provided on a surface where no non-penetrating T / H is formed. Generally, polyimide is also used for the coverlay. Thereafter, the conductor 2 exposed at the opening 5a
After a desired surface treatment is applied to a and 2b, the outer shape is punched to complete the double-sided FPC 6.

FIG. 1 is a cross-sectional view of an electric component 7 mounted on the double-sided FPC 6 by reflow soldering, and is a view best representing the features of the present invention. 8 is solder. As is clear from this drawing, in the double-sided FPC 6 to which the present invention is applied, since the mounting land 5b is provided on the back side of the surface on which the non-penetrating T / H 3a is formed by the laser processing, the T / H is electrically controlled. Even if the component 7 is installed so as to be connected to the mounting land 5b, the mounting land 5b does not have any holes or dents into which the solder 8 flows. Therefore, mounting defects due to insufficient solder, swelling of the coverlay on the back surface, and cracks due to the difference in thermal expansion coefficient between the solder and the conductive pattern do not occur. The T / H in the connected land can be realized without causing a mounting defect.

[0012]

As described above, according to the present invention, at least one of the electric components to be mounted is a double-sided flexible printed circuit board to be mounted by reflow soldering, and is formed by a non-through hole by laser processing. Electrically connecting the conductive pattern on the front and back of the flexible printed circuit board with the non-through through hole, at least one of the non-through through holes is installed so as to be connected to the mounting land of the electric component, and the mounting land is Since it was configured on the back side of the surface provided with the non-through through hole,
Even when electrical components are soldered and mounted by reflow, there are no holes or dents in the connection lands that allow molten solder to flow in.Therefore, mounting defects due to insufficient soldering, swelling of the coverlay on the back surface, and solder and conductive patterns Cracks and the like due to the difference in thermal expansion coefficient between the two FPCs can be prevented, and the T / H in the land, which leads to downsizing of the double-sided FPC and downsizing of the device, can be realized without generating mounting defects. effective.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a double-sided FPC on which an electric component according to an embodiment of the present invention is mounted.

FIG. 2 (A), (B), (C), (D), (E),
(F) is sectional drawing which shows one Embodiment of the manufacturing process of the double-sided FPC of this invention.

FIG. 3 (A), (B), (C), (D), (E)
Sectional drawing which shows the manufacturing process of the double-sided FPC as a 1st conventional example.

FIG. 4 is a first conventional double-sided FPC on which electric components are mounted.
FIG.

FIG. 5 (A), (B), (C), (D), (E),
(F) is a sectional view showing a manufacturing process of a multilayer substrate provided with a non-penetrating T / H as a second conventional example.

FIG. 6 is a sectional view of a second conventional multilayer board on which electric components are mounted.

[Explanation of symbols]

 1: Base 2a, 2b: Conductor 3: Non-through hole 3a: Non-through T / H 4: T / H plating 5: Cover lay 6: Double-sided FPC 7: Electric component 8: Solder

Claims (1)

[Claims] 1. A double-sided flexible printed board on which at least one of the electrical components to be mounted is soldered and mounted by reflow, and a non-through through hole formed by a non-through hole formed by laser processing. The conductive pattern is electrically connected, at least one of the non-penetrating through holes is installed so as to be connected to a mounting land of the electric component, and the mounting land is on the back side of the surface provided with the non-penetrating through hole. Double-sided flexible printed circuit board characterized by being installed on the surface of