JP2007250815A - Flexible printed board and electronic component mounting circuit using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flexible printed board capable of preventing an increase of contact resistance and a connection failure caused by a difference between thermal expansion coefficients of an electronic component and a flexible printed board, while maintaining the mounting density of the electronic component. <P>SOLUTION: The flexible printed board 10 includes a base film 1; and a connection electrode 2 composed of copper foil, and formed on the surface of the electrode. The connection electrode 2 is connected with a terminal electrode 4 of an electronic component 3 via a solder. Around the connection electrode 2, a slit 6 is formed for thermal stress relaxation with a predetermined interval so as to sandwich the connection electrode 2. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a flexible printed circuit board on which various electronic components are mounted and an electronic component mounting circuit using the same.

  Generally, when an electronic component is mounted on a flexible printed circuit board, the terminal electrode on the component side and the connection electrode formed on the substrate side are connected by solder. Here, the mounted electronic component is made of a material such as LCP (Thermotropic Liquid Crystal Polyester), PPS (Polyphenylene Sulfide), 6T, 9T nylon, etc., while the flexible printed circuit board is made of a material such as PI (polyimide), LCP, or the like. Therefore, when electronic components are mounted, a difference in the thermal expansion coefficient between the two members occurs due to a temperature change in the operating environment, and a thermal stress is generated in the solder portion which is a connection location.

  In recent years, flexible printed circuit boards on which electronic components are mounted are used in various products such as digital cameras, mobile phones, and automobiles. When such products are used in an environment where temperature changes are severe, electronic components and flexible printed circuit boards are used. Cracks occur in the solder, which is the connecting part, and a malfunction or connection failure occurs due to an increase in contact resistance.

In order to solve such a problem, an electronic component mounting circuit is known in which the connection strength between the wiring substrate and the electronic component is increased by increasing the electrode area of the electronic component and the wiring substrate (Patent Document 1).
Japanese Patent Laid-Open No. 2001-210749

  However, such a circuit has a problem in that the mounting area of the substrate is inevitably lowered and the size of the substrate is increased because the electrode area of the electronic component and the wiring substrate is increased.

  The present invention has been made in view of these points, and prevents an increase in contact resistance and a connection failure due to a difference in thermal expansion coefficient between the electronic component and the flexible printed circuit board while maintaining the mounting density of the electronic component. An object of the present invention is to provide a flexible printed circuit board and an electronic component mounting circuit using the same.

  A flexible printed circuit board according to the present invention includes a flexible base film made of an insulator, a plurality of connection electrodes formed on the base film and connected to a plurality of terminal electrodes of an electronic component to be mounted. The base film is characterized in that a slit or a hole is formed so as to cross a line connecting the plurality of connection electrodes.

  The electronic component mounting circuit according to the present invention includes the above-described flexible printed circuit board and a plurality of terminal electrodes, and these terminal electrodes are mounted on the flexible printed circuit board by being soldered to the plurality of connection terminals, respectively. And an electronic component.

  According to the present invention, by providing a slit or a hole so as to cross a line connecting a plurality of connection electrodes of the flexible printed circuit board, a connection portion between both members due to a difference in thermal expansion coefficient between the flexible printed circuit board and the electrical component is provided. Such stress can be absorbed by deformation of the slit or hole. As a result, it is possible to prevent an increase in contact resistance and a connection failure due to a difference in thermal expansion coefficient between the electronic component and the flexible printed board while maintaining the mounting density of the electronic component.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a plan view of a flexible printed circuit board according to the first embodiment of the present invention. 2 is a plan view of an electronic component mounting circuit in which electronic components are mounted on the flexible printed circuit board, and FIG. 3 is a cross-sectional view taken along line A-A ′ of FIG. 2.

  The flexible printed circuit board 10 has flexibility like PI, and has a base film 1 made of an insulator and a plurality of connection electrodes 2 made of copper foil patterned on the surface thereof. The connection electrode 2 is connected to the terminal electrode 4 of the electronic component 3 mounted on the flexible printed board 10 via the solder 5. Further, a slit 6 is provided around one connection electrode 2 at a predetermined interval so as to cross the line connecting the two connection electrodes 2 and sandwich the one connection electrode 2. The slit 6 can be formed at the same time as the flexible printed circuit board 10 is punched. The electronic component 3 is made of a material such as LCP, PPS, 6T, or 9T nylon, and the flexible printed circuit board 1 is made of a material such as PI or LCP.

  Next, the operation of the flexible printed circuit board 10 configured as described above will be described.

  Here, a slit located on the right side of the connection electrode 2 provided on the flexible printed board 10 is referred to as a slit 6R, and a slit located on the left side is referred to as a slit 6L. As shown in FIG. 4A, when stress in the X direction is applied to the flexible printed circuit board 10 due to the difference in thermal expansion coefficient between the flexible printed circuit board 10 and the electronic component 3, the slit 6L is deformed to open, The slit 6R is deformed so as to be closed. Further, as shown in FIG. 4B, when stress in the Y direction is applied to the flexible substrate 1 due to the difference in thermal expansion coefficient between the flexible printed circuit board 10 and the electronic component 3, the slit 6L is deformed so as to close. The slit 6R is deformed so as to open.

  In this way, the slits at both ends of the connection electrode 2 provided on the flexible printed circuit board 1 are deformed, so that the stress applied to the connection part of both members due to the difference in thermal expansion coefficient between the flexible printed circuit board 1 and the electrical component 3 is absorbed. be able to. As a result, it is possible to prevent an increase in contact resistance and a connection failure due to a difference in thermal expansion coefficient between the electronic component and the flexible printed board while maintaining the mounting density of the electronic component.

  FIG. 5 is a plan view of a flexible printed circuit board according to the second embodiment of the present invention.

  In the second embodiment, slits 6A and 6B common to the two connection electrodes 2 are provided, and a slit 6C cut into a cross is provided at the center of the four connection electrodes 2 arranged in four directions. Yes. Thus, by sharing the slit with a plurality of connection electrodes, the present invention can be implemented even when the mounting density of electronic components is high.

  FIG. 6 is a plan view of a flexible printed circuit board according to the third embodiment of the present invention.

  In the third embodiment, holes 7 are provided at both ends of the connection electrode 2 instead of the slits of the first embodiment. As described above, by disposing the hole having a larger deformation amount than the slit around the connection electrode, it is possible to absorb the stress applied to the flexible printed circuit board and the solder of the connection portion even in an environment where the temperature changes drastically.

It is a top view of the flexible printed circuit board concerning a 1st embodiment of the present invention. It is a top view at the time of mounting of the flexible printed circuit board. FIG. 3 is a cross-sectional view taken along line A-A ′ of FIG. 2. It is a top view of the flexible printed circuit board. It is a top view of the flexible printed circuit board concerning a 2nd embodiment of the present invention. It is a top view of the flexible printed circuit board concerning a 3rd embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Base film, 2 ... Connection electrode, 3 ... Electronic component, 4 ... Terminal electrode, 5 ... Solder, 6 ... Slit, 7 ... Hole, 10 ... Flexible printed circuit board.

Claims (3)

A flexible base film made of an insulator;
In a flexible printed circuit board comprising a plurality of terminal electrodes formed on the base film and connected to a plurality of terminal electrodes of an electronic component to be mounted,
The flexible printed circuit board, wherein the base film has slits or holes formed so as to cross a line connecting the plurality of connection electrodes.   The flexible printed circuit board according to claim 1, wherein the slit or the hole is formed during punching of the flexible printed circuit board. The flexible printed circuit board according to claim 1 or 2,
An electronic component mounting circuit comprising: a plurality of terminal electrodes; and the electronic components mounted on the flexible printed circuit board by soldering these terminal electrodes to the plurality of connection terminals, respectively.

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