JPH0535589B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to an electrical connection structure of a flexible printed circuit board, and in particular, to solder connection with the interconnection portion of a flexible printed circuit board facing each other. The present invention relates to an improvement in a connection structure for a flexible printed circuit board that can suitably achieve automatic soldering and the like by adopting such a connection mode.

"Prior art" As a method for electrically connecting a flexible printed circuit board and another circuit board by soldering, the fifth
As conceptually shown in the figure, a flexible base member 2A made of a suitable resin insulating film is generally covered with a required circuit wiring pattern 3 made of a conductive foil such as copper foil via an adhesive 6. The adhesive 5 is applied to other areas of the circuit wiring pattern 3 except for the connecting portion 3D.
A flexible printed circuit board 1A is provided with a thin surface protection member 4 such as a cover film material, an insulating coat, or other resist material, with or without the use of Both boards 1A and 8 are engaged with adhesive 12 so that 3D faces the corresponding connection part 10A in the circuit wiring pattern 10 of the other circuit board 8,
Both circuit wiring patterns 3 and 10 are melted by melting the preliminary solder provided in advance on both or at least one of the connection portions 3D and 10A using an appropriate heat source placed on the flexible printed circuit board 1A side, for example. In some cases, the connection may be made using solder 14. In the figure, reference numeral 9 indicates a base member of the circuit board 8, and reference numeral 11 indicates an adhesive to which the base member 9 and the circuit wiring pattern 10 are attached.

"Problems to be Solved by the Invention" In the above connection structure using solder connection, the facing connection parts 3D and 10A of both circuit boards 1A and 8 are as follows:
It is connected with solder 14, but one connection part 10A
Connecting portion 3D of flexible printed circuit board 1A to
are arranged at positions separated by a distance corresponding to the thickness of the surface protection member 4 and adhesives 5 and 12, and both connection parts 3D and 10A are in a substantially sealed state to prevent occurrences due to solder connections. Since there is no place for the gas to escape, there is a high rate of failure in the connection of the solder 14 due to melting of the preliminary solder.Furthermore, it is extremely difficult to determine whether the connection is good or bad and to correct the failure of the connection, which reduces the reliability of the solder connection structure. There was a risk that it would be lacking. In addition, in such a face-to-face connection structure using solder, if the two lands to be connected are separated by 50 μm or more, it becomes difficult to form a solder fillet, so it is desirable to use a simple automatic soldering process such as reflow, dip solder, or flow solder. However, it is structurally impossible and it is difficult to reduce the connection cost.

"Means for Solving the Problems" In view of the above, the present invention provides a flexible base member in which a required circuit wiring pattern made of conductive foil is interposed between a flexible base member and a surface protection member while being insulated. In the case of a connection structure in which both the connection parts of the flexible printed board and another circuit board are placed facing each other and are connected by solder, the above-mentioned circuit wiring to be connected by solder to the circuit wiring pattern part formed on the above-mentioned other circuit board. An access hole for solder connection is formed in which a required portion of the pattern is exposed through the opening in the flexible base member and the surface protection member, and the exposed portion of the access hole is adjacent to the circuit wiring pattern portion of the other circuit board. The present invention provides a connection structure for flexible printed circuit boards that suitably solves the above-mentioned problems by forming a bent portion in the direction of contact. According to a flexible printed circuit board equipped with such an access structure for solder connection, it is possible to arrange the connecting parts of both circuit boards in a substantially contacting state, and electrical connection can be made through a simple and highly efficient automatic soldering process means. A mechanically strong, stable and highly reliable solder connection structure can be realized at low cost.

"Embodiment" In FIGS. 1 and 2, 1 is a flexible printed circuit board constructed according to an embodiment of the present invention, and 2
3 is the same base member as described above, and 3 is the base member 2.
A required circuit wiring pattern made of conductive foil such as copper foil is deposited thereon, 4 also represents the equivalent surface protection member, and 5 and 6 are adhesives between these constituent members. The circuit wiring pattern 3 is interposed between the flexible base member 2 and the surface protection member 4. In the case of this embodiment, the connection portion of the circuit wiring pattern 3 is exposed across the access hole 7 for solder connection, which is formed by opening the corresponding portions of both the base member 2 and the surface protection member 4. As shown in FIG. 2, it is configured to include a bent portion 3A that bulges downward. Such a bent part can be formed in a straight line as shown in Fig. 1, or, for example, as shown in Fig. 3, the connecting part can be formed into a land shape as before, and a pair of long groove-shaped through holes 3C are provided. It is also possible to perform a bending process on the portion 3B during or after processing it into a flange shape.

FIG. 4 shows a state in which the flexible printed circuit board 1 having the above structure and another flexible or rigid circuit board 8 are connected by soldering, and the same reference numerals as in FIG. 5 represent the same components, as shown in the figure. When the connecting portions of both circuit boards 1 and 8 are aligned and bonded with adhesive 12, the connecting bent portion 3A or 3B on the flexible printed circuit board 1 side is bent as much as possible with respect to the connecting portion 10A of the circuit board 8. Since they are arranged close to each other or in a state where they are in face-to-face contact as shown in the figure, the generated gas is applied in such a manner that a sufficient amount of solder 13 is properly attached to both the connecting parts exposed in the open access hole 7. A mechanically and electrically strong and stable solder connection structure can be quickly achieved by an automatic soldering process such as reflow, dip means, or flow solder while dissipating the solder in a suitable manner.

"Effects of the Invention" Since the flexible printed circuit board connection structure according to the present invention has the above-described configuration, at least the following effects can be achieved.

(1) Since the solder access hole has an open structure, it allows the generated gas to be appropriately released during solder connection, while creating a mechanically and electrically strong and stable solder connection structure using automatic reflow, dip means, or flow solder. This can be quickly achieved using the soldering method.

(2) Therefore, it is possible to construct a highly reliable solder connection structure that is electrically and mechanically strong and stable with the mating circuit board.

(3) Since it is equipped with an open access hole that allows cross-exposure of the connection part, highly efficient solder connections can be made by adopting the optimal automatic soldering process.

(4) It is possible to easily determine the quality of solder connections by visual inspection, etc.

(5) Correcting and repairing solder connections is easy, and a substantial improvement in the rate of good connections can be expected.

(6) Since the connecting portions of both circuit boards can be placed as close as possible or in contact with each other, it is possible to reduce or omit connection resistance reduction treatments such as solder wetting or plating for these connecting portions.

(7) Contributes to cost reduction of solder connection structure.

[Brief explanation of drawings]

FIG. 1 is a conceptual enlarged plan view of the main parts of a flexible printed circuit board equipped with a connection structure according to an embodiment of the present invention, and FIG. 2 is a conceptual enlarged cross-sectional view of the main parts thereof. FIG. 3 is a conceptual planar configuration diagram according to another example of the connection part, and FIG. 4 is a conceptual cross-sectional view showing a solder connection structure between the flexible printed circuit board of FIG. 1 and another circuit board. FIG. 5 is a similar cross-sectional configuration diagram of a conventional opposing solder connection structure. 1...Flexible printed circuit board, 2...Flexible base member, 3...Circuit wiring pattern, 3A, 3B...
...Bending portion, 4...Surface protection member, 5, 6...Adhesive, 7...Access hole, 8...Other circuit board, 9...Base member, 10...Circuit wiring pattern, 10A...Connection Parts 11, 12...Adhesive, 13, 14...Solder for connection.

Claims (1)

[Claims] 1. In a flexible printed circuit board configured such that a required circuit wiring pattern made of conductive foil is interposed between a flexible base member and a surface protection member under insulation, a circuit formed on another circuit board A solder connection access hole is provided that exposes the entire surface of a required portion of the circuit wiring pattern to be soldered connected to the wiring pattern portion, and the circuit wiring pattern of the other circuit board is provided in the exposed portion of the circuit wiring pattern that crosses the access hole. 1. A connection structure for a flexible printed circuit board, characterized in that it is configured to include a bent portion in a direction that is close to or in contact with the other portion.