JPH1056242A - Flexible printed circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow electric resistance values of respective conductive routes between the right and left terminals to be the same substantially. SOLUTION: This flexible printed circuit board is provided with a plurality of conductive routes extending from one end side to the other end side. The conductive routes are formed of rolled copper foil, and in the respective conductive routes, a-side part of respective route is made larger in width and b-side part thereof is made smaller in width, so that electric resistance values of the respective routes are set at the same value substantially.

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 in which a plurality of conductive paths have substantially the same electric resistance.

[0002]

2. Description of the Related Art In general, a flexible printed circuit board is used mainly for the purpose of simply connecting a certain functional part of a device or the like to another functional part except in a high frequency region where its characteristic impedance affects. Have been. Therefore, almost no consideration was given to the electric resistance value of the conductive path (wiring pattern) of the flexible printed circuit board. In this type of flexible printed circuit board, each conductive path is formed by arranging a plurality of wiring patterns having the same width in parallel at a predetermined interval. Therefore, in the case of a flexible printed circuit board having a complicated shape, for example, when the conductive paths are juxtaposed so as to have a U-shape, the electric resistance value of each conductive path necessarily has a different value. . For example, if each conductive path is lined up and has a U-shape as a whole,
The length of the conductive path inside the U-shape and the length of the conductive path outside the U-shape are different (the outside is longer), and the electrical resistance value of each conductive path is different. That is,
The conductive path in the outer portion of the U-shape is longer than the inner portion and has a higher resistance value.

[0003]

However, with the expanded use of flexible printed circuit boards, there has been a demand for making the electrical resistance of each conductive path formed on the flexible printed circuit board the same. Of the printed circuit boards, in particular, the flexible printed circuit board has a significantly more complicated shape than a general printed circuit board or a thermal head, so that the width of each conductive path greatly changes, and the resistance value of the electric resistance. Is extremely difficult to control.

On the other hand, instead of such a flexible printed circuit board, as a printed circuit board used for a thermal head or the like, the width of each conductive path is set over the entire length of the conductive path.
A technique has been developed in which the electric resistance of each conductive path is kept within a relatively approximate range by making them different from each other (JP-A-60-194593). By doing so, the electrical resistance value of each conductive path can be kept within a relatively small range, but changing the width of the entire conductive path as described above requires extremely high precision of the width of the conductive path. Due to high demands, it is not easy in actual operation. In particular, the application of such a rigid type printed circuit board technology to a flexible printed circuit board having a significantly complicated shape and a drastic change in the width of the conductor path is in relation to the precision of the control of the conductor path width described above. It's not easy.

[0005]

In order to achieve the above object, a flexible printed circuit board according to the present invention is a flexible printed circuit board having a plurality of conductive paths extending from one end to the other end. Each of the conductive paths is made of rolled copper foil, and the electric resistance of each conductive path is set to be substantially the same by changing the width of a part of each conductive path.

[0006]

In other words, the present inventors have described a specific method for making the electric resistance values of the respective conductive paths of a flexible printed circuit board whose shape is extremely complicated and in which the widths of the conductive paths change drastically substantially substantially the same. Repeated research. As a result, the width of each conductive path is not partially changed, but is partially changed, for example, when a plurality of conductive paths are arranged side by side and the whole is in a U-shape, the length of the conductive path is changed. The length of the conductive path on the outer side of the U-shape where the length of the conductive path becomes longer is increased, and the width of the conductive path corresponding to that part is reduced toward the inner side of the U-shape, so that each conductive path is reduced. It has been found that the electric resistance value of each conductive path can be made substantially the same without changing the overall shape of the conductive path, for example, a U-shape, and arrived at the present invention.

Next, the present invention will be described in detail.

[0008] The electric resistance of the conductive path is represented by the following equation.

[0009]

(Equation 1)

R: electric resistance value p: electric conductor resistivity
l: circuit wiring length a: conductor width t: conductor thickness c: factor due to processing

As is apparent from the above equation (1), except for the factor c caused by processing, the electric resistance value R of the conductive path becomes
When the resistivity p of the conductive path, the length l of the conductive path, and the thickness t of the conductive path are set to design values, the values become smaller as the width a of the conductive path becomes wider. Therefore, by controlling the width a of each conductive path partially in proportion to the length of each conductive path, the electric resistance R of each conductive path can be set to be substantially the same. Mainly controlling the width a has an advantage over the control of the length l and the thickness t in that the applicable range is wider and a resistance value which is generally lower than that of the latter can be obtained. . Processing was performed in this manner, and a plurality of conductive paths were formed on the flexible printed circuit board from one end to the other end. In some cases, the thickness t of the conductive path may be changed by removing the surface portion of the conductive path in order to adjust the electric resistance value during processing.

The conductive paths formed on the flexible printed circuit board according to the present invention are not limited to the above-described U-shaped conductive paths, but may correspond to conductive paths of various shapes. Further, it is possible to cope with a case where the electric resistance value of only a part of the many conductive paths is set to be substantially the same.

When two or more types of flexible printed circuit boards are used in combination,
It is possible to cope with the case where the electric resistance value of the conductive path of a certain circuit board and the electric resistance value of the conductive path of another circuit board are set to be substantially the same. In addition, by partially changing the width of the conductive path in the middle part of the conductive path excluding the terminal portion, it is possible to cope with the case where the electrical resistance of each conductive path is made substantially the same. . Then, it is desirable to use a rolled copper foil for forming the conductive path.
More preferably, the rolled copper foil is an annealed rolled copper foil or a low-temperature annealed rolled copper foil from the viewpoint of the effect.

As described above, the flexible printed circuit according to the present invention uses the rolled copper foil to form the conductive path. Here, the conductive path is formed from the rolled copper foil when the terminal portion or the like is used. In some cases, the rolled copper foil is formed of another metal material instead of the rolled copper foil.

Next, examples will be described together with comparative examples.

[0016]

1 and 2 show an embodiment of the present invention. In the printed circuit board (flexible printed circuit board) of this embodiment, 50 conductive paths are formed in a U-shape from annealed rolled copper foil between a and b in FIG. Therefore, the number is seven). As is clear from FIGS. 1 and 2, in the flexible printed circuit board, the conductive path (circuit) in the U-shaped upper portion (a-side portion) is longer, and the lower portion (b-side portion) is longer. The conductive paths are shorter. Therefore, the width of the conductive path on the a-side part is large, and the width of the conductive path on the b-side part is small.
As a result, the electrical resistance of each conductive path is substantially the same over the entire conductive path (part A, part A, part C) of the flexible printed circuit board. Here, “substantially the same” means that each conductive path is vertically included in a range of 10 to 20% based on a middle point between the maximum value and the minimum value. .

In particular, in this flexible printed circuit board, changing the width of the conductive path involves changing only the width of the conductive path portion of portion a of the flexible printed circuit board, and changing the width of the portions a and c. The width of the conductive path is not changed. That is, the part A is a connector insertion part, which cannot be changed because there is a definition of the width and thickness of the conductive path required for the connector insertion part. The c portion is also a contact portion of a contact type having a small wiring area, and it is difficult to control the width of the conductive path and the like. Therefore, the control of the width of the conductive path in this portion is avoided. The portion A connecting the portion A and the portion C has a relatively long conductive path, and the width of the conductive path is easily controlled. Therefore, the width of the conductive path in this portion is controlled.

As described above, the portion A has a length that is 80% of the total length of the portion A and the portion A. Therefore, in the present invention, "changing the width of a part of the conductive path" means within 80% of the length of the conductive path.

Such a control of the width of the conductive path is performed by using a raster scan method, drawing a mask pattern of a photomask on a mask film, and manufacturing a photomask. Can be performed with higher accuracy by drawing the portion corresponding to the portion A in FIG. 1 at an angle with respect to the scanning direction (lateral direction). That is,
Rendering the linear pattern at an angle with respect to the scanning direction can be performed by devising input to a minicomputer provided in the raster scanning system. The angle in the case where an angle is provided with respect to the scanning direction is
Even small angles are fully effective. That is,
Since the pixel size in the raster scan method is small, even at a small angle, the effect is sufficient even though it depends on the line length of the linear pattern. In this way, when the pattern is drawn based on the design values (the width A of the conductive path and 3.2 pixels) shown in FIG. 3, a mask pattern (a mixed pattern of 3 pixels and 4 pixels) as shown in FIG. Can be obtained. As can be seen from the comparison between FIG. 3 and FIG. 4, in the drawn pattern (FIG. 4), small steps (jaggies) occur at the upper and lower portions of the linear portion. However, the width A 'of the pattern as a whole is the width A of the design value.
Is almost the same as In this way, the width of each conductive path can be controlled to an arbitrary width. In this manner, the width of each conductive path is changed to make the electric resistance substantially constant.
Among the conductive paths (wiring patterns) of the books, the conductive path on the longest a-side and the conductive path on the shortest b-side had a difference in the length of the conductive path by a factor of 1.7. Thus, when the width of the conductive path on the a-side was set to 0.52 mm and the width of the conductive path on the b-side was set to 0.23 mm, the electric resistance could be controlled to be substantially the same. That is, when the target set value was 0.80 Ω, the electric resistance of the entire conductive path was controlled to be within 0.841 ± 0.010 Ω (mean ± standard deviation). That is, in the flexible printed circuit board of FIG. 1, the fluctuation of the electric resistance value of each conductive path could be kept within about 1.2% (standard deviation).

FIGS. 5 and 6 show another embodiment. This embodiment is substantially the same as that of FIG. 1 except that the length of the flexible printed circuit board is shortened, so that the description will not be repeated. In this embodiment, when the target set value of each conductive path is 0.80Ω, the electric resistance value of each conductive path is 0.810 ± 0.010Ω (mean ± standard deviation). Almost the same result as the conductive path of the circuit board was obtained. In actual use, the flexible printed circuit board shown in FIG. 1 and the flexible printed circuit board shown in FIG. 5 are used in combination vertically, and even in this case, the flexible printed circuit board shown in FIG. The difference between the electrical resistance value of the conductive path on the a-side portion of the flexible printed circuit board and the electrical resistance value of the conductive path on the d-side portion of the flexible printed circuit board in FIG. It was within 5%.

In the above embodiment, the widths of the conductive paths are different from each other.
Set the width of the conductive path constant by setting a set of two to several pieces from the longest conductive path, and then set the width of the conductive path by setting a set of two or several conductive paths below it. Set,
Further, the width of the conductive path is set in groups of two or several for the lower conductive path, and by changing the width of each conductive path in units of a plurality, the overall electric resistance value is substantially reduced. The same control may be performed. That is, when there are as many as 50 conductive paths as described above,
Even if the width of each conductive path is changed little by little, it may not appear as desired due to variations in the manufacturing process. Therefore, it is rational to control the electric resistance value by making two or several pieces into one set and changing the width of the conductive path for each set. Further, in the above embodiment, the width of the conductive path only in the straight portion is changed, but the resistance value may be made substantially the same by changing the width of the entire conductive path.

The flexible printed circuit board in which the electric resistance value of each conductive path is controlled to be substantially the same can be used, for example, for a cable for transmitting an electric signal. That is, when an electric signal of the same strength is given to one terminal of each of the plurality of conductive paths, a signal transmitted to the opposite terminal is equivalent to the given electric signal, and the transmission signal of each conductive path is Variations in strength are reduced.

Another application of the flexible printed circuit board according to the present invention is to control the value of a current flowing through a conductive path when a constant voltage is applied between the left and right terminals. Power consumption can be controlled by controlling the current value. Depending on the circuit shape, it can be used for controlling the heat generation temperature, electromagnetic induction, and the like.

[0024]

As described above, the flexible printed circuit board of the present invention is a flexible printed circuit board having a plurality of conductive paths extending from one end to the other end, and a part of each conductive path. , The electric resistance value of each conductive path is set to be substantially the same. Therefore, the present invention can be applied to a new use that requires that the electric resistance value of each conductive path between the left and right terminals be substantially the same. That is,
In the present invention, since the width of the conductive path is changed, it is possible to easily adapt to the shape of the substrate. Due to the limited space on the board, it has the advantage that the width can be changed avoiding places where it cannot be changed functionally. It is simpler and more accurate to make the resistance values the same by changing the widths. Further, since each of the conductive paths is made of a rolled copper foil, the resistance value can be easily controlled by changing the width of the conductive path as compared with an electrolytic copper foil or the like, and the effect is large.

In the present invention, when the rolled copper foil is an annealed rolled copper foil or a low-temperature annealed rolled copper foil, the resistance value can be easily controlled by changing the width of the conductive path, which is extremely effective.

[Brief description of the drawings]

FIG. 1 is a plan view of an embodiment of the present invention.

FIG. 2 is a partially enlarged plan view of a portion A surrounded by a circle in FIG.

FIG. 3 is an explanatory view of forming a conductive path in FIG. 1;

FIG. 4 is an explanatory view of forming a conductive path in FIG. 1;

FIG. 5 is a plan view of another embodiment of the present invention.

FIG. 6 is a partially enlarged plan view of a portion B surrounded by a circle in FIG. 5;

Claims (2)

[Claims] 1. A flexible printed circuit board having a plurality of conductive paths extending from one end to the other end, wherein each of the conductive paths is made of rolled copper foil, and one of the conductive paths is A flexible printed circuit board wherein the electrical resistance of each conductive path is set to be substantially the same by changing the width of the portion. 2. The flexible printed circuit board according to claim 1, wherein the rolled copper foil is an annealed rolled copper foil or a low-temperature annealed rolled copper foil.