Printed Circuit Board

Abstract

To provide a printed board having a structure in which a fuse portion dissipates heat well while a current within a rated current is flowing, and a fuse portion is more reliably blown within a fusing time when a current higher than a fusing current flows.SOLUTION: A printed board 100 includes a flexible film-like base material 10, and a conductor pattern 20 formed on one main surface 10a of the base material 10. A portion of the conductive pattern 20 in the extending direction is a fuse portion 31, and the film thickness of the fuse portion 31 is thinner than the film thickness of the non-fuse portion 36, which is the portion of the conductive pattern 20 other than the fuse portion 31.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a printed circuit board. [Background technology]

[0002] The printed circuit board described in Patent Document 1 has a conductor pattern (referred to as a wiring pattern in the document), and a portion of the conductor pattern in the extension direction is a fuse portion (referred to as a pattern fuse in the document), and is configured so that when a current equal to or greater than the fusing current flows through the printed circuit board, the fuse portion melts within the fusing time. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2007-311467 A Summary of the Invention [Problem to be solved by the invention]

[0004] It is desirable for the fuse portion to be structured so that it dissipates heat well while a current within the rated current flows, and reliably melts within the melting time when a current equal to or greater than the melting current flows; however, the technology of Patent Document 1 leaves room for improvement in this regard.

[0005] The present invention has been made in consideration of the above-mentioned problems, and relates to a printed circuit board having a structure in which the fuse portion dissipates heat well while a current within the rated current flows, and the fuse portion melts more reliably within the melting time when a current equal to or greater than the melting current flows. [Means for solving the problem]

[0006] According to the present invention, a flexible film-like base material and A conductor pattern formed on one main surface of the base material; Equipped with a portion of the conductor pattern in an extending direction thereof is a fuse portion, The thickness of the fuse portion is thinner than the thickness of a non-fuse portion, which is a portion of the conductor pattern other than the fuse portion. Ku, A plating layer is selectively formed on the non-fuse portion out of the fuse portion and the non-fuse portion, so that the film thickness of the non-fuse portion is thicker than the film thickness of the fuse portion. A printed substrate is provided. Effect of the Invention

[0007] According to the present invention, it is possible to provide a printed circuit board having a structure in which the fuse portion dissipates heat well while a current within the rated current flows, and the fuse portion melts more reliably within the melting time when a current equal to or greater than the melting current flows. [Brief description of the drawings]

[0008] [Figure 1] 1(a) and 1(b) are diagrams showing a fuse portion of a conductor pattern and its surrounding structure in the first embodiment, with FIG. 1(a) being a plan view and FIG. 1(b) being a perspective view. [Diagram 2] 2(a) is a cross-sectional view taken along the line AA shown in FIG. 1(a), and FIG. 2(b) is a partially enlarged cross-sectional view of part A shown in FIG. 2(a). [Diagram 3] 3(a) to 3(e) are a series of process diagrams illustrating an example of a method for forming the conductor pattern in the first embodiment. [Figure 4] 4(a) and 4(b) are a series of process diagrams illustrating an example of a method for forming a conductor pattern in the first embodiment, in which FIG. 4(a) is a plan view of the state shown in FIG. 3(a) and FIG. 4(b) is a plan view of the state shown in FIG. 3(b). [Diagram 5] 5(a) and 5(b) are diagrams showing a fuse portion of a conductor pattern and its surrounding structure in the second embodiment, with FIG. 5(a) being a plan view and FIG. 5(b) being a perspective view. [Figure 6]6(a) is a cross-sectional view taken along the line AA shown in FIG. 5(a), and FIG. 6(b) is a partially enlarged cross-sectional view of part A shown in FIG. 6(a). [Figure 7] 7(a) to 7(e) are a series of process diagrams illustrating an example of a method for forming a conductor pattern in the second embodiment. [Figure 8] 8(a) and 8(b) are diagrams showing a fuse portion of a conductor pattern and its surrounding structure in the third embodiment, with FIG. 8(a) being a plan view and FIG. 8(b) being a perspective view. [Figure 9] FIG. 9 is a cross-sectional view taken along the line AA shown in FIG. [Figure 10] 10(a) to 10(e) are a series of process diagrams illustrating an example of a method for forming a conductor pattern in the third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In all the drawings, the same components are denoted by the same reference numerals, and the description thereof will be omitted as appropriate.

[0010] [First embodiment] First, the first embodiment will be described with reference to FIG. 1(a) to FIG. 3(e).

[0011] The printed circuit board 100 of this embodiment comprises a flexible film-like base substrate 10 (FIG. 2(a)) and a conductor pattern 20 formed on one main surface 10a (FIG. 2(a)) of the base substrate 10. A portion of conductor pattern 20 in the extending direction is fuse portion 31, and the film thickness of fuse portion 31 is thinner than the film thickness of non-fuse portion 36 which is the portion of conductor pattern 20 other than fuse portion 31.

[0012] The width and thickness of the fuse portion 31 are set so that when a current equal to or greater than a preset fusing current flows, the fuse portion 31 will melt before the non-fuse portion 36 in the conductor pattern 20 within the melting time. On the other hand, while a current equal to or less than the rated current flows, the heat dissipation properties of the fuse portion 31 are ensured in order to prevent fire or short circuit due to heat generation in the fuse portion 31 and melting of the fuse portion 31 at an unintended timing.

[0013] According to the present embodiment, the film thickness of the fuse portion 31 is thinner than the film thickness of the non-fuse portion 36 in the conductor pattern 20. This makes it possible to ensure a larger surface area of ​​the fuse portion 31 while maintaining a desired cross-sectional area of ​​the fuse portion 31, compared to a case in which the film thickness of the fuse portion 31 is equal to the film thickness of the non-fuse portion 36. This makes it possible to improve the heat dissipation property of the fuse portion 31 while maintaining a structure that allows the fuse portion 31 to generate heat well. Furthermore, since the film thickness of the conductor pattern 20 can be configured to be locally thin in the fuse portion 31, when a current equal to or greater than the fusing current flows, the fuse portion 31 can be made to melt before the non-fuse portion 36 in the conductor pattern 20 within the fusing time. Thus, according to this embodiment, it is possible to realize a printed circuit board 100 having a structure in which the fuse portion 31 dissipates heat well while a current within the rated current flows, and the fuse portion 31 melts more reliably within the melting time when a current equal to or greater than the melting current flows. The cross-sectional area of ​​fuse portion 31 herein means the area of ​​a cross section along a direction perpendicular to the extension direction of fuse portion 31. Furthermore, since the heat dissipation properties of the fuse portion 31 are improved, fires and short circuits caused by heat generation in the fuse portion 31 can be more reliably prevented.

[0014] As an example, the printed circuit board 100 is incorporated into a voltage monitoring module (not shown) and is used to monitor voltage by connecting the conductor pattern 20 to a bus bar (not shown) that connects multiple battery cells (not shown). More specifically, the printed circuit board 100 is provided with, for example, a connector (not shown) and is connected to a measuring device that performs various controls via the connector, enabling voltage monitoring. Furthermore, each conductor pattern 20 connected to the bus bar is provided with a fuse portion 31. Typically, the fuse portion 31 is disposed near the corresponding bus bar, but the location of the fuse portion 31 is not limited to this example. Note that the printed circuit board 100 may include, for example, a conductor pattern 20 that is connected to a thermistor (not shown) that senses temperature, in which case the conductor pattern 20 does not have a fuse portion 31.

[0015] In the following, when describing the positional relationship between the components of the printed circuit board 100, the upper side in Fig. 2(a) will be referred to as the upper side or upper side, etc., and the opposite side will be referred to as the lower side or lower side, etc. However, these directional definitions are for convenience only, and do not limit the directions during manufacture or use of the printed circuit board 100.

[0016] 2(a) and 2(b), the printed circuit board 100 is a laminate formed in a plate or sheet shape. More specifically, the printed circuit board 100 further includes, in addition to the base substrate 10 and the conductive pattern 20, a protective film 71 covering at least a portion of the conductive pattern 20 from above, a reinforcing film 61 covering the protective film 71 from above, a first adhesive layer 66 bonding the reinforcing film 61 and the protective film 71 to each other, and a second adhesive layer 76 bonding the protective film 71 and the base substrate 10 to each other. In the present embodiment, the second adhesive layer 76 is laminated on the base substrate 10 via the conductive pattern 20, and the protective film 71 is laminated directly on the second adhesive layer 76. In addition, the first adhesive layer 66 is laminated directly on the protective film 71, and the reinforcing film 61 is laminated directly on the first adhesive layer 66.

[0017] The base substrate 10 is a relatively thin film-like substrate having two main surfaces, namely, front and back surfaces. The base substrate 10 may be any substrate that contains a thermoplastic resin layer and exhibits thermoplasticity as a whole. Here, thermoplasticity refers to the property of softening when heated and hardening again when cooled. The base substrate 10 is made of a thermoplastic resin, and in this embodiment, the material is polyimide. However, the material of the base substrate 10 is not limited to this example, and it is possible to use, for example, polyethylene naphthalate (PolyEthylene Naphthalate: PEN), polyethylene terephthalate (PolyEthylene Terephthalate: PET), liquid crystal polymer (Liquid Crystal Polymer: LCP), fluorine-based resin (PolyTetra FluoroEthylene: PTFE), or resin containing these.

[0018] The printed circuit board 100 has, for example, a plurality of conductor patterns 20. Each conductor pattern 20 is formed, for example, by processing copper foil. As shown in Figs. 1(a) and 1(b), each conductor pattern 20 includes straight line portions 21 extending linearly along a first direction (the left-right direction in Figs. 1(a) to 2(b)) among directions along one main surface 10a of the base substrate 10. The straight line portions 21 are arranged spaced apart from each other (e.g., at equal intervals) in a second direction (the up-down direction in Figs. 1(a) and 1(b)) perpendicular to the first direction. A second adhesive layer 76 fills at least a portion of the gap between each of the straight line portions 21. The distance of the fuse portion 31 from the other conductor patterns 20 is determined so that the fuse portion 31 is reliably melted under a predetermined condition. The width dimension of the straight line portion 21 of each conductor pattern 20 is substantially constant regardless of the position in the extension direction of the conductor pattern 20, except for a tapered portion 33 which will be described later. In the following, when describing the positional relationship between the components of the printed circuit board 100, the left side in FIG. 1(a) may be referred to as the left side, and the opposite side may be referred to as the right side.

[0019] In this embodiment, as shown in Figures 1(b) and 2(b), as an example, at the boundary portion 32 between the non-fuse portion 36 and the fuse portion 31, the film thickness of the conductor pattern 20 can be gradually thinner from the non-fuse portion 36 toward the fuse portion 31. This allows conductor pattern 20 to be configured to smoothly switch from non-fuse portion 36 to fuse portion 31. Therefore, for example, when printed circuit board 100 is bent, it is possible to prevent stress from concentrating on boundary portion 32 between non-fuse portion 36 and fuse portion 31, and therefore it is possible to sufficiently ensure the structural strength of printed circuit board 100. In the following description, the portion of boundary portion 32 where the film thickness of conductive pattern 20 gradually decreases from non-fuse portion 36 toward fuse portion 31 is referred to as slope portion 34. It should be noted that the present invention is not limited to this example. For example, in boundary portion 32, the film thickness of conductive pattern 20 may be gradually reduced from non-fuse portion 36 toward fuse portion 31.

[0020] Furthermore, in the case of this embodiment, as an example, at the boundary portion 32 between the non-fuse portion 36 and the fuse portion 31, the width dimension of the conductor pattern 20 can be configured to gradually narrow from the non-fuse portion 36 toward the fuse portion 31. This allows conductor pattern 20 to be configured to more smoothly switch from non-fuse portion 36 to fuse portion 31. Therefore, for example, when printed circuit board 100 is bent, it is possible to more reliably prevent stress from concentrating on boundary portion 32 between non-fuse portion 36 and fuse portion 31, thereby further improving the structural strength of printed circuit board 100. However, the present invention is not limited to this example. For example, the width dimension of the conductor pattern 20 in the boundary portion 32 does not necessarily have to gradually narrow from the non-fuse portion 36 toward the fuse portion 31.

[0021] In the present embodiment, as one example, the width dimension of fuse portion 31 can be narrower than the width dimension of non-fuse portion . This makes it easier for heat to be generated locally in the fuse portion 31 when a current greater than or equal to a preset value flows through the conductor pattern 20, thereby ensuring that the fuse portion 31 melts within a preset time period. However, the present invention is not limited to this example, and as will be described later, for example, the dimension may be equal to or larger than the width dimension of non-fuse portion 36.

[0022] In the example shown in Fig. 1(a) and Fig. 1(b), the fuse portion 31 is located at the center in the extension direction of the straight portion 21, and both ends of the fuse portion 31 are non-fuse portions 36. Therefore, in the extension direction of the straight portion 21, the fuse portion 31 is formed linearly from the non-fuse portion 36 at one end to the non-fuse portion 36 at the other end. However, the non-fuse portion 36 does not have to be linear. Note that Figs. 1(a) to 2(b) show, as an example, the fuse portion 31 of the middle conductor pattern 20 of three conductor patterns 20 arranged side by side in the second direction, and the fuse portions 31 of the remaining two conductor patterns 20 are arranged outside the illustrated range. The width dimension (W2 shown in FIG. 1(a)) of fuse portion 31 is constant regardless of the position in the extension direction of fuse portion 31. On the other hand, the width dimension (W1 shown in FIG. 1(a)) of non-fuse portion 36 includes, for example, a relatively wide portion and a relatively narrow portion. The fuse portion 31 may be formed in a meandering shape in plan view, for example, as in a second embodiment described later. This ensures a sufficient length of the fuse portion 31, increases the electrical resistance of the fuse portion 31, and allows heat to accumulate in the conductor pattern 20, centered around the fuse portion 31.

[0023] Each boundary portion 32 includes a tapered portion 33 in which the width dimension of the conductor pattern 20 gradually narrows from the non-fuse portion 36 toward the fuse portion 31 . In a tapered portion 33 of a boundary portion 32 at one end (hereinafter, the left side) in the extension direction of the fuse portion 31 (left-right direction in FIGS. 1(a) and 1(b)), the width dimension of the conductor pattern 20 gradually narrows toward the other end (hereinafter, the right side) in the extension direction of the fuse portion 31, for example, in a plan view. The right end of the tapered portion 33 of the left boundary portion 32 is connected to the left end of the fuse portion 31. Similarly, in tapered portion 33 of boundary portion 32 at the other end (right end) in the extension direction of fuse portion 31 (left-right direction in FIGS. 1(a) and 1(b)), the width dimension of conductor pattern 20 gradually narrows toward one end (left side) in the extension direction of fuse portion 31, for example, in a plan view. The left end of tapered portion 33 of right-side boundary portion 32 is connected to the right end of fuse portion 31. The minimum width dimension (W1 shown in FIG. 1(a)) of the non-fuse portion 36 is set to be larger than the maximum width dimension W2 of the fuse portion 31.

[0024] As described above, at each boundary portion 32, a slope portion 34 (see FIG. 2(b)) is formed in which the film thickness of the conductor pattern 20 gradually becomes thinner from the non-fuse portion 36 toward the fuse portion 31. Note that while FIG. 2(b) illustrates an example in which the film thickness of the conductor pattern 20 becomes thinner at a constant rate at each slope portion 34, at each slope portion 34, for example, the film thickness of the conductor pattern 20 may change in a curved manner. In a slope portion 34 of the boundary portion 32 on the left side of the fuse portion 31, the film thickness of the conductive pattern 20 gradually decreases from the left side toward the fuse portion 31 side (right side). Similarly, in a slope portion 34 of the boundary portion 32 on the right side of the fuse portion 31, the film thickness of the conductive pattern 20 gradually decreases from the right side toward the fuse portion 31 side (left side). Here, in the example shown in Figures 1(a) and 1(b) as a first arrangement, in the extension direction (left-right direction) of the straight portion 21, position P1 where the slope portion 34 of the left-side boundary portion 32 terminates on the fuse portion 31 side coincides with the position of the left end of the left-side tapered portion 33. However, in the present invention, as a second arrangement, position P1 where slope portion 34 of left boundary portion 32 terminates on the fuse portion 31 side may be located, for example, to the left (non-fuse portion 36 side) of the left end of left tapered portion 33. In this way, slope portion 34 and tapered portion 33 are configured to be spaced apart from each other in the extension direction of straight portion 21, so that when the plate surface of printed circuit board 100 is bent, the stress concentration point is more reliably located in non-fuse portion 36 which is wide and has a constant width, rather than in tapered portion 33 which gradually narrows, and the structural strength of printed circuit board 100 can be improved. In addition, in the present invention, as a third arrangement, position P1 where slope portion 34 of left-side boundary portion 32 terminates on the fuse portion 31 side may be located, for example, to the right (fuse portion 31 side) of the left end of left-side tapered portion 33. By doing so, a sufficient film thickness of conductor pattern 20 in tapered portion 33 can be ensured, thereby improving the structural strength of tapered portion 33 and its vicinity. According to the first arrangement (position P1 coincides with the position of the left end of the left taper portion 33), the respective advantages of the second and third arrangements can be realized in a well-balanced manner. In the third arrangement, in the extension direction (left-right direction) of straight portion 21, start position P2 of slope portion 34 of left-side boundary portion 32 may be closer to the non-fuse portion 36 (to the left) than left-side tapered portion 33, or may be located in tapered portion 33. That is, in the third arrangement, left-side tapered portion 33 may include the entirety or a part of slope portion 34. Similarly, in the example shown in Figures 1(a) and 1(b), as a first arrangement, in the extension direction of the straight portion 21 (the left-right direction in Figures 1(a) and 1(b)), position P3 where the slope portion 34 of the right-side boundary portion 32 terminates on the fuse portion 31 side coincides with the position of the right end of the right-side tapered portion 33. However, in the present invention, the position P3 where the slope portion 34 of the right-side boundary portion 32 terminates on the fuse portion 31 side may be, for example, located to the right of the right end of the right-side taper portion 33 as a second arrangement, or may be located to the left of the right end as a third arrangement. In the third arrangement, in the extension direction (left-right direction) of the straight portion 21, the start position P4 of the slope portion 34 of the right-side boundary portion 32 may be closer to the non-fuse portion 36 (to the right) than the right-side tapered portion 33, or may be located in the tapered portion 33. That is, in the third arrangement, the right-side tapered portion 33 may include the entirety or a part of the slope portion 34. Furthermore, as shown in FIG. 2( b ), the minimum thickness T1 of the non-fuse portion 36 is set to a dimension larger than the maximum thickness T2 of the fuse portion 31 .

[0025] In the present invention, the width of fuse portion 31 does not have to be narrower than the width of non-fuse portion 36, for example. That is, the width of fuse portion 31 and the width of non-fuse portion 36 may be equal to each other. In this case, only slope portion 34 constitutes boundary portion 32. In slope portion 34, a step may be formed by abruptly changing the film thickness of conductor pattern 20.

[0026] The maximum width dimension W2 of the fuse portion 31 is not particularly limited, but is preferably, for example, not less than 0.05 mm and not more than 0.9 mm. The minimum thickness T1 of the non-fuse portion 36 is not particularly limited, but is preferably 1.5 to 6 times the maximum thickness T2 of the fuse portion 31, for example.

[0027] The protective film 71 covers the conductive pattern 20 from the side opposite to the base substrate 10. In this embodiment, the protective film 71 contains a thermoplastic resin like the base substrate 10, and may be a layer formed only of a thermoplastic resin, or may be a layer containing a resin other than a thermoplastic resin. In this embodiment, as an example, the protective film 71 is made of polyimide, which is the same type of material as the base substrate 10.

[0028] The reinforcing film 61 is disposed in a region overlapping at least a portion of the fuse portion 31 in a plan view. The reinforcing film 61 is made of, for example, polyimide, which is the same material as the base substrate 10 and the protective film 71 .

[0029] The first adhesive layer 66 is provided, for example, over substantially the entire upper surface of the protective film 71 . The second adhesive layer 76 is provided on the upper surface of the conductive pattern 20 and on an area of ​​one main surface 10a of the base substrate 10 where the conductive pattern 20 is not formed. Each of the first adhesive layer 66 and the second adhesive layer 76 is made of, for example, an adhesive or prepreg made of an epoxy resin, an acrylic resin, or a PI resin.

[0030] An example of a method for forming the conductive pattern 20 will be described below with reference to Figures 3(a) to 4(b). Figures 3(a) to 3(e) are cross-sectional views taken along line AA in Figure 1(a). First, as shown in FIG. 3(a) and FIG. 4(a), a copper-clad substrate is prepared by laminating copper foil 110 over the entire surface of one main surface 10a of a base material 10. 3(b) and 4(b), a resist material is applied onto the copper foil 110 and exposed to light to create a resist pattern 120 having a planar shape and planar arrangement corresponding to the conductor pattern 20. The copper-clad substrate is then immersed in an etching solution to form the conductor pattern 20. Next, as shown in Fig. 3(c), the resist pattern 120 is removed from the conductive pattern 20, and then, as shown in Fig. 3(d), the portions of the conductive pattern 20 that will become the non-fuse portions 36 are covered with a masking 130, and the copper-clad substrate is again immersed in the etching solution to perform half-etching. However, the portions of each boundary portion 32 that will become the slope portions 34 are exposed from the masking 130, for example. By doing so, the film thickness of the fuse portion 31 can be made thinner than the film thickness of the non-fuse portion 36, as shown in FIG. 3(e). Furthermore, by forming the fuse portion 31 in this manner, the manufacturing variation in the film thickness of the fuse portion 31 can be more easily suppressed compared to the case where the manufacturing variation in the width dimension of the fuse portion 31 is suppressed, thereby improving the productivity of the printed circuit board 100. However, in the present invention, for example, the film thickness of fuse portion 31 may be made thinner than the film thickness of non-fuse portion 36 by locally polishing (buffing) the portion of formed conductor pattern 20 that will become fuse portion 31. Also, in the present invention, the conductor pattern 20 may be formed, for example, by printing a conductive paste as ink on the base substrate 10. In this case, the amount of conductive paste applied to the portion that will become the fuse portion 31 can be made smaller than the amount of conductive paste applied to the portion that will become the non-fuse portion 36, thereby making the film thickness of the fuse portion 31 thinner than the non-fuse portion 36. Alternatively, the portion of the printed conductor pattern 20 that corresponds to the fuse portion 31 can be polished (buffed) to make the film thickness of the fuse portion 31 thinner than the non-fuse portion 36.

[0031] Second Embodiment Next, a second embodiment will be described with reference to FIG. 5(a) to FIG. 7(e). The printed circuit board 100 of this embodiment differs from the printed circuit board 100 of the first embodiment described above in the points described below, but in other points is configured in the same way as the printed circuit board 100 of the first embodiment described above.

[0032] In this embodiment, a plating layer 50 is selectively formed on the non-fuse portion 36 out of the fuse portion 31 and the non-fuse portion 36, so that the film thickness of the non-fuse portion 36 is thicker than the film thickness of the fuse portion 31. Even with this configuration, the film thickness of the fuse portion 31 can be made thinner than the film thickness of the non-fuse portion 36 in the conductor pattern 20, so that a larger surface area of ​​the fuse portion 31 can be secured while maintaining a desired cross-sectional area of ​​the fuse portion 31, and the film thickness of the conductor pattern 20 can be locally made thinner in the non-fuse portion 36. Thus, the heat dissipation properties of the fuse portion 31 can be improved while maintaining a structure in which the fuse portion 31 generates heat well, so that a printed circuit board 100 can be realized in which the fuse portion 31 dissipates heat well while a current within the rated current flows, and the fuse portion 31 melts more reliably within the melting time when a current equal to or greater than the melting current flows.

[0033] In this embodiment, each conductive pattern 20 includes an underlying pattern 25 made of copper foil, and a plating layer 50 is formed on the surface (upper surface) of the underlying pattern 25 opposite the base substrate 10 side. 5(a) and 5(b), the plating layer 50 is formed in a portion of the base pattern 25 corresponding to the non-fuse portion 36. The plating layer 50 is formed, for example, over the entire non-fuse portion 36 (the portion of the base pattern 25 corresponding to the non-fuse portion 36). The plating layer 50 is made of copper, for example. However, the material that makes up the plating layer 50 is not particularly limited, and may be any material that is at least conductive.

[0034] As shown in FIG. 5(b), in this embodiment, the plating layer 50 is also formed at the boundary portion 32 between the fuse portion 31 and the non-fuse portion 36, and at the boundary portion 32, the plating layer 50 becomes gradually thinner from the non-fuse portion 36 toward the fuse portion 31. In the following description, the portion in each boundary portion 32 where the thickness of the plating layer 50 gradually decreases from the non-fuse portion 36 toward the fuse portion 31 is referred to as a slope portion 53. Note that, although Fig. 6(a) and Fig. 6(b) illustrate an example in which the thickness of the conductor pattern 20 decreases at a constant rate in each slope portion 53, for example, the thickness of the conductor pattern 20 may change in a curved manner in each slope portion 53.

[0035] More specifically, in a slope portion 53 of the boundary portion 32 on the left side of the fuse portion 31, the film thickness of the conductive pattern 20 gradually decreases from the left side toward the fuse portion 31 side (right side). Similarly, in a slope portion 53 of the boundary portion 32 on the right side of the fuse portion 31, the film thickness of the conductive pattern 20 gradually decreases from the right side toward the fuse portion 31 side (left side). As a first arrangement, in the example shown in Figures 5(a) and 5(b), in the extension direction (left-right direction) of the straight portion 21, the position P1 where the slope portion 53 of the left-side boundary portion 32 terminates on the fuse portion 31 side coincides with the position of the left end of the left-side tapered portion 33. However, in the present invention, as a second arrangement, position P1 where slope portion 53 of left boundary portion 32 terminates on the fuse portion 31 side may be located, for example, to the left (non-fuse portion 36 side) of the left end of left tapered portion 33. By doing so, slope portion 53 and tapered portion 33 are configured to be spaced apart from each other in the extension direction of straight portion 21, so that when the plate surface of printed circuit board 100 is bent, the stress concentration point is more reliably located in non-fuse portion 36 which is wide and has a constant width dimension, rather than in tapered portion 33 which gradually narrows, and the structural strength of printed circuit board 100 can be improved. In addition, in the present invention, as a third arrangement, position P1 where slope portion 53 of left-side boundary portion 32 terminates on the fuse portion 31 side may be located, for example, to the right (fuse portion 31 side) of the left end of left-side tapered portion 33. By doing so, a sufficient film thickness of conductor pattern 20 in tapered portion 33 can be ensured, thereby improving the structural strength of tapered portion 33 and its vicinity. According to the first arrangement (position P1 coincides with the position of the left end of the left taper portion 33), the respective advantages of the second and third arrangements can be realized in a well-balanced manner. In the third arrangement, in the extension direction (left-right direction) of straight portion 21, start position P2 of slope portion 53 of left-side boundary portion 32 may be closer to the non-fuse portion 36 (left side) than left-side tapered portion 33, or may be located in said tapered portion 33. That is, in the third arrangement, left-side tapered portion 33 may include all or a part of slope portion 53. Similarly, in the example shown in Figures 5(a) and 5(b), as a first arrangement, in the extension direction of the straight portion 21 (the left-right direction in Figures 5(a) and 5(b)), position P3 where the slope portion 53 of the right-side boundary portion 32 terminates on the fuse portion 31 side coincides with the position of the right end of the right-side tapered portion 33. However, in the present invention, the position P3 where the slope portion 53 of the right-side boundary portion 32 terminates on the fuse portion 31 side may be, for example, located to the right of the right end of the right-side taper portion 33 as a second arrangement, or may be located to the left of the right end as a third arrangement. In the third arrangement, in the extension direction (left-right direction) of the straight portion 21, the start position P4 of the slope portion 53 of the right-side boundary portion 32 may be closer to the non-fuse portion 36 (to the right) than the right-side tapered portion 33, or may be located in the tapered portion 33. That is, in the third arrangement, the right-side tapered portion 33 may include the entirety or a part of the slope portion 53.

[0036] The maximum thickness of the plating layer 50 (T3 shown in FIG. 6B) is not particularly limited. For example, 6 It is preferable that the thickness of the second insulating film 34 is set to be 1.5 to 6 times the thickness T2 of the fuse portion 31. In this embodiment, the film thickness (T4 shown in FIG. 6(b)) of the non-fuse portion 36 excluding the plating layer 50 is set to be substantially equal to the film thickness T2 of the fuse portion 31.

[0037] 5(a) and 5(b), in the present embodiment, the fuse portion 31 is formed in a meandering shape in plan view, which ensures a sufficient length of the fuse portion 31 and increases the electrical resistance. In this embodiment, the fuse portion 31 may also be formed, for example, in a substantially linear shape in plan view, similarly to the first embodiment.

[0038] An example of a method for forming the conductor pattern 20 will be described below with reference to Figures 7(a) to 7(e). Figures 7(a) to 7(e) are cross-sectional views taken along a line corresponding to line AA shown in Figure 5(a). First, as shown in FIG. 7(a), a copper-clad board is prepared by laminating copper foil 110 on one main surface 10a of a base material 10. Next, as shown in Fig. 7(b), a masking 130 is applied to the portion of the copper foil 110 (later base pattern 25) that will become the fuse portion 31. Then, as shown in Fig. 7(c), a plating layer 50 is formed on the upper surface of the copper foil 110. In this manner, the plating layer 50 can be selectively formed on the non-fuse portion 36 out of the fuse portion 31 and the non-fuse portion 36. The method for forming the plating layer 50 is not particularly limited, but as an example, it can be formed by a wet plating method such as electrolytic plating. Next, as shown in Fig. 7(d), a resist material is applied to one main surface 10a of the base substrate 10, and the copper-clad substrate is exposed to light to create a resist pattern 120 having a planar shape and planar arrangement corresponding to the conductor pattern 20. The copper-clad substrate is then immersed in an etching solution to form the conductor pattern 20 (base pattern 25). Then, as shown in Fig. 7(e), the resist pattern 120 is removed from the conductor pattern 20.

[0039] Third Embodiment Next, a third embodiment will be described with reference to FIG. 8(a) to FIG. 10(e).

[0040] In this embodiment, the printed circuit board 100 further includes a second conductor pattern 40 formed on the other main surface 10b of the base substrate 10. Therefore, as shown in Fig. 9, the base substrate 10 is interposed between the conductor pattern 20 and the second conductor pattern 40 in the up-down direction. A through hole 15 is formed in the base substrate 10, and a plating layer 50 is also formed within the through hole 15, so that the conductor pattern 20 and the second conductor pattern 40 are electrically connected to each other via the plating layer 50 within the through hole 15. With this configuration, a sufficient heat dissipation area for heat generated in the fuse portion 31 can be secured, so that even if the resistance value of the fuse portion 31 is increased, a configuration can be realized in which the fuse portion 31 will not melt as long as a current within the rated current flows.

[0041] As shown in FIG. 8(a), the second conductor pattern 40 is formed, for example, in a shape that does not overlap the fuse portion 31 in a plan view. More specifically, as shown in FIG. 8(a) and FIG. 8(b), the second conductor pattern 40 includes, for example, a plurality of first portions 41 extending linearly in a first direction (the left-right direction in FIG. 8(a) and FIG. 8(b)) and a second portion 42 extending linearly in a second direction perpendicular to the first direction. In the example shown in FIG. 8(a) and FIG. 8(b), the second portion 42 extends from the left end of one of the first portions 41 toward one side in the second direction. Also, each of the first portions 41 is disposed apart from each other in the second direction. Then, each of the plurality of first portions 41 and the second portion 42 is disposed at a position not overlapping with the fuse portion 31 (a position avoiding the fuse portion 31) in a plan view. This allows the fuse portion 31 to be reliably melted when a current equal to or greater than the melting current flows while ensuring a sufficient heat dissipation area for heat generated in the fuse portion 31. As another example, the second conductor pattern 40 may be formed in a mesh shape in a plan view, which can ensure a sufficient radiation area for the heat generated in the fuse portion 31. In this embodiment, the width dimension of each of the first portions 41 and second portions 42 of the second conductor pattern 40 is constant regardless of the position in the extension direction. In the present embodiment, the conductor pattern 20 is also formed in the same shape as in the second embodiment. Therefore, in the conductor pattern 20, a plating layer 50 is selectively formed in the non-fuse portion 36 out of the fuse portion 31 and the non-fuse portion 36, and the film thickness of the non-fuse portion 36 is thicker than the film thickness of the fuse portion 31. The conductor pattern 20 includes a base pattern 25 and a plating layer 50. Meanwhile, as one example, a plating layer 50 is formed on the entire surface (lower surface) of the second conductor pattern 40 opposite to the base substrate 10. More specifically, the second conductor pattern 40 includes a base pattern 45 made of copper foil, and a plating layer 50 formed on the lower surface of the base pattern 45. This can improve the heat capacity when the fuse portion 31 dissipates heat. However, in the present invention, the second conductive pattern 40 does not necessarily have to have the plating layer 50 formed thereon, for example. Also in this embodiment, the fuse portion 31 is formed in a meandering shape in plan view, as in the second embodiment. However, also in this embodiment, the fuse portion 31 may be formed in, for example, a substantially linear shape in plan view, as in the first embodiment. In addition, in FIGS. 8(a) and 8(b), straight line portions 21 of two of the plurality of conductor patterns 20 are selectively illustrated.

[0042] As shown in FIGS. 8(a) and 8(b), the conductor pattern 20 and the second conductor pattern 40 each have portions that are arranged to overlap each other in a plan view (hereinafter, overlapping portions 24, 44). In this embodiment, the conductor pattern 20 has two overlapping portions 24. Similarly, the second conductor pattern 40 has two overlapping portions 44, and each overlapping portion 44 is arranged to overlap one overlapping portion 24 in a plan view. Each overlapping portion 44 and the corresponding overlapping portion 24 are connected to each other via a through hole 15. More specifically, in the case of the present embodiment, in the straight portion 21, portions on both ends with respect to the fuse portion 31 are respectively overlapping portions 24. In the extension direction of the straight portion 21, one fuse portion 31 is disposed between two overlapping portions 24.

[0043] In each overlapping portion 24 of the conductor pattern 20, a through hole 24a is formed penetrating the conductor pattern 20 (the base pattern 25 and the plating layer 50) in the thickness direction. The planar shape of each through hole 24a is not particularly limited, but in this embodiment, it is, for example, circular. However, in the present invention, the shape of the through hole 24a may be rectangular or may be another shape such as a polygonal shape other than a rectangle.

[0044] As shown in FIG. 9, the through-hole 15 penetrates the base material 10 in the thickness direction. In the present embodiment, one through hole 15 is formed in each overlapping portion 24 in a portion corresponding to the through hole 24a (the overlapping portion and the portion directly below in plan view). The planar shape of each through hole 15 is not particularly limited, but in this embodiment, it is, for example, circular. The outer diameter of each through hole 15 is set to be, for example, approximately equal to the outer diameter of the through hole 24a. In addition, in a plan view, the center position of each through hole 15 coincides with the center position of the corresponding through hole 24a. However, in the present invention, the shape of the through-hole 15 may be rectangular, or may be any other shape, such as a polygonal shape other than a rectangle.

[0045] As shown in FIG. 9, the plating layer 50 formed on the base pattern 25 is formed continuously over, for example, substantially the entire upper surface of the conductive pattern 20 and within the through-hole 15. More specifically, a portion of the plating layer 50 formed on the conductive pattern 20 is formed along the inner circumferential surface of the corresponding through hole 24a and the inner circumferential surface of the through hole 15, and has a generally cylindrical shape with an axis in the vertical direction. The lower end of the portion of the plating layer 50 formed in the through hole 15 (the generally cylindrical portion) reaches the surface of the second conductive pattern 40 on the base substrate 10 side (the upper surface in FIG. 9), and each overlapping portion 44 is electrically connected to the corresponding overlapping portion 24 via the through hole 15. In this embodiment, the plating layer 50 formed on the upper surface of the conductor pattern 20, the plating layer 50 formed in the through hole 15, and the plating layer 50 of the second conductor pattern 40 are made of the same type of conductive material. However, for example, the plating layer 50 formed on the upper surface of the conductor pattern 20, the plating layer 50 formed in the through hole 15, and the plating layer 50 of the second conductor pattern 40 may be made of materials having different conductive properties. In this embodiment, as an example, the plating layer 50 formed on the upper surface of the conductor pattern 20, the plating layer 50 formed in the through hole 15, and the plating layer 50 of the second conductor pattern 40 are made of copper.

[0046] An example of a method for forming the conductive pattern 20 will be described below with reference to FIGS. 10(a) to 10(e). First, as shown in FIG. 10(a), a copper-clad substrate is prepared by laminating copper foil 110 (later underlying patterns 25, 45) on both one main surface 10a and the other main surface 10b of a base material 10. 10(b), for example, two through holes penetrating the copper-clad substrate in the thickness direction are formed in the copper foil 110 (undercoat pattern 25) on one main surface 10a side, and through holes 15 are formed in the base material 10. The method for forming the through holes 24a and the through holes 15 is not particularly limited, and may be, for example, formed by etching, drilling, or laser processing. Then, the copper-clad substrate is subjected to a conductive treatment. Next, as shown in Fig. 10(c), a masking 130 is applied to the portion of the copper foil 110 on one principal surface 10a that will become the fuse portion 31. Then, as shown in Fig. 10(d), a plating layer 50 is formed on the upper surface of the copper foil 110 on one principal surface 10a and on the lower surface of the copper foil 110 (later to become the second conductor pattern 40) on the other principal surface 10b. At this time, the plating layer 50 is also formed on the inner circumferential surfaces of the corresponding through holes 24a and through holes 15. As described above, in this embodiment, the plating layer 50 is formed on the entire underside of the copper foil 110 (second conductor pattern 40) on the other principal surface 10b, so there is no need to apply masking 130 to the copper foil 110 on the other principal surface 10b, and manufacturing costs can be further reduced. 10(e), a resist material is applied to one main surface 10a of the base substrate 10, and the copper-clad substrate is exposed to light to create a resist pattern 120 that matches the conductor pattern 20. Similarly, a resist material is applied to the other main surface 10b of the base substrate 10, and the copper-clad substrate is exposed to light to create a resist pattern 120 that matches the second conductor pattern 40. The copper-clad substrate is then immersed in an etching solution to form the conductor pattern 20 and the second conductor pattern 40, respectively. The resist pattern 120 is then removed from the conductor pattern 20 and the second conductor pattern 40, respectively.

[0047] Although the embodiments have been described above with reference to the drawings, these are merely examples of the present invention, and various configurations other than those described above can also be adopted.

[0048] The above embodiment encompasses the following technical ideas. (1) a flexible film-like base material; A conductor pattern formed on one main surface of the base material; Equipped with a portion of the conductor pattern in an extending direction thereof is a fuse portion, A printed circuit board in which the fuse portion is thinner than a non-fuse portion, which is a portion of the conductor pattern other than the fuse portion. (2) The printed circuit board according to (1), wherein a plating layer is selectively formed on the non-fuse portion between the fuse portion and the non-fuse portion, so that the thickness of the non-fuse portion is thicker than the thickness of the fuse portion. (3) A second conductor pattern is formed on the other main surface of the base material, A through hole is formed in the base material, The plating layer is also formed in the through hole, The printed circuit board according to (2), wherein the conductor pattern and the second conductor pattern are electrically connected to each other via the plating layer in the through hole. (4) A printed circuit board according to any one of (1) to (3), wherein at the boundary between the non-fuse portion and the fuse portion, the film thickness of the conductor pattern is gradually thinner from the non-fuse portion toward the fuse portion. (5) The printed circuit board according to any one of (1) to (4), wherein the fuse portion has a width dimension narrower than a width dimension of the non-fuse portion. (6) The printed circuit board according to (5), wherein at the boundary between the non-fuse portion and the fuse portion, the width dimension of the conductor pattern gradually narrows from the non-fuse portion toward the fuse portion. [Explanation of symbols]

[0049] 10 Base Material 10a One main surface 10b Other main surface 15 through hole 20 Conductor Pattern 21 Straight section 24 Overlapping Parts 24a through hole 31 Fuse section 32 Boundary 33 Tapered section 34 Slope section 36 Non-fuse section 40 Second conductor pattern 41 Part 1 42 Part 2 44 Overlap 50 plating layer 53 Slope section 61 Reinforcement film 66 1st adhesive layer 71 Protective Film 76 2nd adhesive layer 100 Printed Circuit Boards 110 Copper foil 120 Resist Pattern 130 Masking

Claims

1. A flexible film-like base material; A conductor pattern formed on one main surface of the base material; Equipped with a portion of the conductor pattern in an extending direction thereof is a fuse portion, a thickness of the fuse portion is smaller than a thickness of a non-fuse portion, which is a portion of the conductor pattern other than the fuse portion; A printed circuit board having a plating layer selectively formed on the non-fuse portion out of the fuse portion and the non-fuse portion, so that the film thickness of the non-fuse portion is greater than the film thickness of the fuse portion.

2. Further, a second conductor pattern is formed on the other main surface of the base material, A through hole is formed in the base material, The plating layer is also formed in the through hole, The printed circuit board according to claim 1 , wherein the conductor pattern and the second conductor pattern are electrically connected to each other via the plating layer in the through hole.

3. 3. The printed circuit board according to claim 1, wherein the thickness of the conductor pattern at the boundary between the non-fuse portion and the fuse portion is gradually reduced from the non-fuse portion toward the fuse portion.

4. 4. The printed circuit board according to claim 1, wherein a width dimension of the fuse portion is narrower than a width dimension of the non-fuse portion.

5. 5. The printed circuit board according to claim 4, wherein at a boundary between the non-fuse portion and the fuse portion, a width dimension of the conductor pattern gradually narrows from the non-fuse portion toward the fuse portion.

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