JP2002050844A - Flexible printed board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid bad influence to electronic parts, which is mounted to the opposite surface of a rigid board, by the heating temperature of a head by maintaining prescribed strength when connecting a flexible printed board to the rigid board by thermocompression bonding of a head. SOLUTION: In the flexible printed board constituted by connecting a copper foil to the land of the rigid board, the second hole 14 is bored at a place facing with a land 5 of the copper foil 12 mounted to the lower surface of a cover film 11, and the first hole 13 is bored at the film 11 to be coaxially with the hole 14 and to expose a part of the foil 12 at the outer site of the second hole 14. Furthermore, on the rear surfaces of the first and second holes and the foil 13, solder plating 15 is given and the heat of the head part 6 pressurizing from the front surface side of the film 11 is transmitted to the land 5 through the plating 15 to connect the foil 12 to the land 5.

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 flexible printed circuit board having a head attached to the upper surface of a cover film so that a copper foil mounted on the lower surface of the cover film can be mounted on a rigid board. The present invention relates to a flexible printed board for thermocompression bonding to a land.

[0002]

2. Description of the Related Art A conventional flexible printed circuit board of this type, in which the flexible printed circuit board is thermocompression-bonded to a rigid board, will be described with reference to FIG.

In FIG. 1, reference numeral 1 denotes a flexible printed circuit board. A copper foil 3 is mounted on the lower surface of the cover film 2 of the flexible printed board 1. The copper foil 3
Is in contact with a land 5 made of copper foil disposed on a rigid substrate 4 via a cream solder 7 applied on the land 5, and a head 6 is applied from the upper surface of the cover film 2. The flexible printed board 1 is connected to the rigid board 4 by heating to melt the cream solder 7.

In the conventional example, the head 6
Is in contact with the upper surface of the cover film 2, and the heat of the head 6 is transferred to the copper foil 3, the cream solder 7, and the land 5 via the cover film 2. In order to perform thermocompression bonding, the heating temperature of the head 6 must be sufficiently increased, and the heating time must be set long. In such a case, not only heat stress is applied to the electronic components mounted on the opposite surface of the rigid board 4 but also
Solder is displaced, and there is a problem in connection strength.

Therefore, when a flexible printed board is connected to a rigid board, it is necessary to maintain a predetermined connection strength and to perform soldering without adversely affecting electronic components mounted on the opposite surface of the rigid board. A technical problem to be solved arises, and an object of the present invention is to solve the problem.

[0006]

Means for Solving the Problems The present invention has been proposed to achieve the above object, and is a flexible printed board, wherein the flexible printed board is provided by a head pressed from the front side of a cover film. In a flexible printed circuit board configured such that a copper foil disposed on the back side of the cover film is bonded to a land of the rigid board, the copper foil mounted on the lower surface of the cover film has the land The second place where confronts
A hole is provided, and a first hole is provided so that a part of the copper foil outside of the second hole is exposed. Further, the first hole exposed portion, the second hole, and the back surface of the copper foil are provided. Is configured so that the copper foil can be joined to the land by applying solder plating and transferring the heat of the head pressed from the surface side of the cover film to the land via the solder plating. A flexible printed circuit board is provided.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below in detail with reference to FIGS. For convenience of explanation, the conventional example and the target part will be described using the same reference numerals.
In the figure, reference numeral 10 denotes a flexible printed circuit board of the present invention. The flexible printed circuit board 10 has a copper foil 12 mounted on the lower surface of a cover film 11 as in the conventional example. Then, the copper foil 1 is placed on the land 5 on the rigid substrate 4.
2 is configured to be thermocompression-bonded by a head 6.

The cover film 11 of the flexible printed circuit board 10 according to the present invention is provided with a first hole 13 which is formed to have a diameter smaller than the width of the copper foil 12 and which is open up and down. Therefore, the rigid substrate 4 is provided on the lower surface of the first hole 13.
A part of the copper foil 12 to be thermocompression-bonded to the land 5 is exposed. Further, a second hole 1 having a diameter smaller than that of the first hole 13 and being open up and down substantially in a central portion of the exposed portion 12a of the copper foil 12.
4 is opened. The exposed portion 12a and the second hole 14 of the first hole 13 and the lower surface of the copper foil 12 are previously plated with solder 15.

In the flexible printed circuit board 10 of the present invention thus configured, the copper foil 12 mounted on the lower surface of the cover film 11 is brought into contact with the land 5 of the rigid board 4 via the cream solder 7, A head 6 is provided on the upper surface of the first hole 13 formed in the cover film 11.
Is applied, the cream solder 7 and the solder plating 15 are melted, and the copper foil 12 is thermocompression-bonded to the land 5. At this time, the heat of the head 6 does not pass through the cover film 11 and the exposed portion 12a of the first hole 13 and the second hole 14
And solder plating 15 attached to the lower surface of copper foil 12
Is transmitted directly to the land 5 via the copper foil 12 and the cream solder 7. Therefore, since the heating temperature during the thermocompression bonding by the head 6 can be reduced as much as possible, the heating temperature of the head 6 in the thermocompression bonding process by the head 6 can reduce the rigidity as in the conventional example. Substrate 4
There is no adverse effect on the electronic components mounted on the other side. Furthermore, the heating time by the head 6 can be reduced as much as possible.

Further, since the first holes 13 are formed to be smaller than the width of the copper foil 12, most of the cover film 11 except for the first holes 13 has the copper foil 12 to be thermocompression-bonded to the lands 5. Since the copper foil 12 is protected by covering the portion, a reduction in the strength of the flexible printed circuit board 10 itself is prevented.

Further, since a fillet is formed by soldering in the second hole 14 provided in the copper foil 12, the bonding strength between the copper foil 12 and the land 5 is improved. Also, during the thermocompression bonding step, since the first hole 13 is closed by the head 6, the solder plating and the cream solder 7 that melts do not rise above the first hole 13 and harden. The finished height of the crimping portion can be reduced. Further, the heating time by the head 6 is reduced as much as possible, so that the soldering operation is performed very efficiently.

The present invention can be variously modified without departing from the spirit of the present invention, and the present invention naturally extends to the modified ones.

[0013]

According to the present invention, there is provided a cover film for a flexible printed circuit board, in which a first hole having a diameter smaller than the width of the copper foil mounted on the lower surface of the cover film is formed at a position facing the land of the rigid board. Since it is perforated, the copper foil mounted on the lower surface of the cover film is exposed by the first hole. Further, a second hole having a smaller diameter than the first hole is formed in the copper foil of the exposed portion, and the copper foil exposed portion and the second hole of the first hole and the lower surface of the copper foil are previously soldered. Plating is applied.

Therefore, the copper foil is brought into contact with the land,
Then, it is natural that the operation of applying a head to the upper surface of the first hole provided in the cover film and connecting the copper foil to the land by thermocompression bonding of the head is performed extremely efficiently. Since most of the cover film except one hole covers the copper foil to protect the copper foil, the strength of the flexible printed board itself is prevented from being reduced. or,
As described above, a part of the copper foil is exposed by perforating the first hole of the cover film, and a second hole having a smaller diameter than the first hole is also perforated in the copper foil at the exposed portion, and No. 1
Since the copper foil exposed portion of the hole, the second hole and the lower surface of the copper foil are preliminarily solder-plated, the copper foil is brought into contact with the land of the rigid board via the cream solder 7, and
When a head is applied to the upper surface of the first hole and the copper foil is thermocompression-bonded to the land, the heating temperature of the head is directly transmitted to the lower land via the solder plating without passing through the cover film. Therefore, since the heating temperature during the thermocompression bonding by the head can be reduced as much as possible, the heating temperature of the head adversely affects the electronic components mounted on the opposite side of the rigid board as in the related art. And the working time can be greatly reduced.

Further, since fillets are formed by soldering in the second holes provided in the copper foil, various types of extremely large sizes such as an improvement in bonding strength between the copper foil and the land can be obtained. It is an invention that has an advantageous effect.

[Brief description of the drawings]

FIG. 1 is a partially cutaway plan view of a flexible printed board according to the present invention.

FIG. 2 is a longitudinal sectional view showing a state where the flexible printed circuit board of FIG. 1 is connected to a rigid board.

FIG. 3 is a longitudinal sectional view showing a state in which a conventional flexible printed board is joined to a rigid board.

[Explanation of symbols]

 Reference Signs List 4 rigid board 5 land 6 head 7 cream solder 10 flexible printed board 11 cover film 12 copper foil 12a exposed portion 13 first hole 14 second hole 15 solder plating

Claims (1)

[Claims] 1. A flexible printed circuit board, wherein a copper foil disposed on a back surface side of the cover film is joined to a land of a rigid board by a head pressed from a front surface side of the cover film. In the flexible printed circuit board configured as described above, the copper foil mounted on the lower surface of the cover film is provided with a second hole at a position facing the land, and a portion outside the second hole is provided. A first hole is provided so that a part of the copper foil is exposed, and further, the first hole exposed portion, the second hole, and the back surface of the copper foil are plated with solder, and the front side of the cover film is provided. Flexible heat is transferred to the land via the solder plating, so that the copper foil can be joined to the land. Printed circuit board.