JP2000077812A - Board connection method - Google Patents

Abstract

(57) Abstract: To improve the bonding strength of solder by increasing the bonding area on the side surface of a connection terminal of an FPC. SOLUTION: A connection terminal 13 of an FPC 10 is plated with solder. Further, cream solder is printed on the surface of the wiring electrode 16 of the wiring board 15 and solder plating is performed by reflow melting. Next, the plurality of connection terminals 13 are simultaneously bent, and the copper foil in this portion is doubled. Then, pressure is applied so that the connection terminal 13 contacts the wiring electrode 16. Next, the terminal portion 10a is heated using a heating tool of a thermocompression bonding method, and the solder formed on the connection terminals 13 and the wiring electrodes 16 is melted. The melted solder moves to the bent portion 18 and the terminal portion 19 of the connection terminal 13 and is hardened. In this state, in the cross section along the longitudinal direction of the connection terminal 13, the effective cross-sectional area of the solder increases, and the connection strength increases.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for connecting a flexible printed board to a board on which electronic circuits or display elements are formed.

[0002]

2. Description of the Related Art Film-shaped wiring components (referred to as flexible printed circuit boards or FPCs) are widely used to electrically connect wiring boards of electronic equipment. F
PC is a flexible film that is made by laminating a conductor such as copper foil on both sides or one side of a base film, forming a wiring pattern by a method such as etching, and forming an insulating film or a resist film on the surface except for connection terminal parts. There is a certain substrate. FPC
The connection terminal portion is subjected to plating for the purpose of improving the solderability, and the insulating film is cut and removed except for the connection terminal portion to form a connection terminal.

[0003] Such an FPC is easy to increase the density of a wiring pattern and has mechanical flexibility and flexibility. For example, wiring inside a video camera, a printer head and a drive circuit board are used. And the connection between a liquid crystal panel and a drive circuit board. In particular, the pitch of the wiring in the liquid crystal panel and the wiring in the thermal head is narrow, and the number of wirings is very large. Such FP
In order to electrically connect the connection terminal of C and the wiring electrode of another substrate having no flexibility, soldering is performed in a press-contact state, but since there is no plating on the cut surface of the connection terminal of the FPC, Many of the terminals have poor solderability. Therefore, there may be a case where a side surface plating such as a through hole is performed on the tip of the connection terminal.

[0004] Such a conventional FPC connection method will be described with reference to FIG. FIG. 2 is a partial view of a connection terminal portion of an FPC used for conventional board connection.
(A) is a top view, and (b) is a cross-sectional view. This FPC 20 laminates a conductor such as copper foil on a base film 22 such as polyimide or polyester,
The conductor is formed into a predetermined wiring pattern by photoetching, and is covered with an insulating film 21 as necessary. In the terminal portion 20a of the FPC 20, the insulating film 21
Are removed, and a plurality of connection terminals 23a,
23b are exposed. Each connection terminal 23a, 23b
Have through holes 24a, 24b,... Formed in advance, and are cut so as to cut through each through hole when punching the terminal portion 20a. Also, the lower surfaces of the connection terminals 23a, 23b.
are subjected to solder plating.

In order to connect the FPC 20 to the wiring board 25, the wiring electrodes 26 formed on the wiring board 25 are connected.
are connected to the connection terminals 23a, 23a of the FPC 20.
3b are pressed so as to be in contact with each other, and the terminal portion 20a is heated using a heating tool of a thermocompression bonding method to melt the solder formed on each connection terminal. Then, as shown in FIG. 2B, a part of the melted solder is removed from through holes 24a and 24a.
5b ... move to the wall. After the solder is cooled, the wiring electrodes 26a, 26b,...
23b are fixed.

[0006]

In such a connection method, the bonding strength of the solder is determined by the connection terminals 23a, 23b.
Only the tip of The bonding strength of the solder depends more on the cross-sectional area of the solder as viewed from the side of the bonding surface than on the bonding area as viewed from the bonding surface. The cross section this time is through holes 24a, 24b
.. Alone, and considering that the through-hole diameter is smaller than the line width of the connection terminal, it cannot be said that the junction cross-sectional area is sufficiently ensured.

SUMMARY OF THE INVENTION The present invention has been made in view of such a conventional problem, and by increasing the bonding cross-sectional area on the side surface of the connection terminal of the FPC, the bonding strength of the solder is improved to improve the productivity. -It is an object of the present invention to realize a method of connecting substrates that can improve reliability.

[0008]

In order to solve such a problem, a connection method for connecting a first substrate having flexibility and a second substrate having no flexibility is provided. Conductive foil of a predetermined pattern is adhered to a base film having properties,
Further, the first conductive foil has a surface coated with an insulating film.
For the substrate, a part of the insulating film is removed so as to leave the connection terminal of the conductive foil at the end, and solder plating is performed on at least one surface of the connection terminal, and the solder plating surface is on the outside. The connection terminal is bent to form a two-layer state, and the wiring electrode and the bent layer of the connection terminal are applied to the second substrate on which the wiring electrodes having the same arrangement pitch as the connection terminal are sandwiched by the solder plating surface. The connection terminal portion of the first substrate and the wiring electrode portion of the second substrate are pressed against each other so as to be in contact with each other, and the connection terminal portion of the first substrate in the pressed state is heated, thereby plating the connection terminal portion. Connecting the first substrate and the second substrate by melting the solder and curing the solder in a state where the molten solder has moved to the bent portion and the terminal portion of the connection terminal; Is also characterized by It is.

According to such a connection method, the solder cross-sectional area on the side surface can be enlarged by bending the connection terminal.
The connection strength per connection terminal can be increased.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for connecting substrates according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 shows a connection state between a flexible printed circuit board (FPC) 10 as a first substrate used in the present embodiment and a wiring substrate 15 on which an electronic circuit or a liquid crystal active element or the like is mounted as a second substrate. FIG. The FPC 10 has a base film 12 such as polyimide or polyester.
Then, a conductor such as a copper foil is laminated thereon, the conductor is formed into a predetermined wiring pattern by photoetching, and the insulating film 11 is further covered. Terminal part 10 of FPC 10
In a, the insulating film 11 is removed, and the plurality of connection terminals 13 which are conductor patterns are exposed by a mechanical method or a chemical method. Each connection terminal 13 is made of a copper foil patterned in a line shape, and has a line width of, for example, 0.3 mm.
And the arrangement pitch is 0.65 mm. The length of the connection terminal 13 is the same as that of the wiring electrode 16 formed on the wiring board 15.
About twice as long as the connection length.

[0011] At least one surface of the copper foil of the connection terminal 13 is subjected to solder plating using, for example, a solder dip.
Also on the wiring board 15, a solder resist 14 is printed on a predetermined portion, and cream solder is printed on the surface of the wiring electrode 16 without the resist 14 and solder plating is performed by reflow melting. Next, the plurality of connection terminals 13 are simultaneously bent together with the base film 12, and the copper foil in this portion is doubled. Copper foil is excellent in malleability and plastic deformation,
Such a bending process can be easily performed without breaking the conductor.

Next, in order to connect the FPC 10 to the wiring board 15, a plurality of wiring electrodes 16 formed on the wiring board 15 are formed.
Then, the terminal portion 10a is pressed so that the connection terminals 13 of the FPC 10 come into contact with each other. Then, the terminal portion 10a is heated using a heating tool of a thermocompression bonding method, and the solder formed on the connection terminals 13 and the wiring electrodes 16 is melted. Then, as shown in FIG. 1, most of the molten solder moves to the bent portion 18 and the terminal end portion 19 of the connection terminal 13 due to the action of surface tension, and the solder connection portion 17 as shown is formed. You. After cooling the solder, the wiring electrode 16 and the connection terminal 13 are fixed at this portion. In this state, the effective cross-sectional area of the solder in the cross section along the longitudinal direction of the connection terminal 13 is much larger than that of the conventional example, and the solder has a full line width even when viewed from the cross section along the width direction of the connection terminal 13. Because of the adhesion, the effective area of the solder is larger.

In addition to the thermocompression bonding method, a manual work using a soldering iron, a local automatic heating device using a laser, an infrared heating device, an entire heating device using hot air, and the like can be used as the heating and melting source for the solder.

According to such a connection method, assuming that the effective cross-sectional area of the through-hole in the conventional example is half of the cutting area of the connection terminal, a solder cross-sectional area four times as large as in the conventional example can be secured. Can be. The connection terminal 13 and the wiring electrode 1
The solder adheres also to the contact surface with the solder 6, but since the effective sectional area of the solder at this portion is small, it does not contribute to an increase in connection strength. Further, since the connection portion of the connection terminal can be reduced in the longitudinal direction, the mounting density of the circuit components on the second substrate is further increased.

[0015]

According to the present invention, in the connection portion between the first substrate and the second substrate, the soldering area (hulet) on the connection side surface is formed by both the bent portion and the terminal portion of the connection terminal. Therefore, the adhesive strength can be improved. Further, since the connection portion of the connection terminal can be shortened, the mounting density of the second substrate is further increased.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a method for connecting an FPC and a wiring board according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a connection method between an FPC and a wiring board in a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Flexible printed circuit board (FPC) 10a Terminal part 11 Insulating film 12 Base film 13 Connection terminal 14 Resist 15 Wiring board 16 Wiring electrode 17 Solder connection part 18 Bend part 19 Termination part

Claims (1)

[Claims] 1. A connection method for connecting a flexible first substrate and a non-flexible second substrate, wherein a conductive foil of a predetermined pattern is bonded to a flexible base film. Further, a part of the insulating film is removed from the first substrate having the surface of the conductive foil coated with an insulating film so as to leave a connection terminal of the conductive foil at an end thereof, and at least one surface of the connection terminal And the connection terminals are bent into two layers so that the solder plating surface is on the outside, and the wiring is formed on the second substrate on which the wiring electrodes having the same arrangement pitch as the connection terminals are formed. The first electrode is so arranged that the electrode and the bent layer of the connection terminal abut on each other with the solder plating surface interposed therebetween.
By pressing the connection terminal portion of the substrate and the wiring electrode portion of the second substrate, and heating the connection terminal portion of the first substrate in the pressed state, the plated solder is melted, A substrate connecting the first substrate and the second substrate by curing the solder in a state where the molten solder has moved to the bent portion and the terminal portion of the connection terminal. Connection method.