Sheet-shaped inductor, printed wiring board, module, and method for using conductive adhesive layer

Abstract

In the present invention, a mold release film (13) in a sheet-shaped inductor product (1A) is peeled off and used as a sheet-shaped inductor (10A). The sheet-shaped inductor (10A) is provided with at least a conductive adhesive layer (11). The conductive adhesive layer (11) functions as an inductance by connecting a first conductive pattern and a second conductive pattern, which are formed on a printed wiring board and are separated from each other, without being connected to a conductive pattern for grounding formed on the printed wiring board.

Description

Method of using a sheet-shaped inductor, a printed wiring board, a module, and a conductive adhesive layer

[0001] The present disclosure relates to a method of using a sheet-shaped inductor, a printed wiring board, a module, and a conductive adhesive layer.

[0002] Inductors used in various circuits typically have a coil shape. An inductor having a coil shape is used by being soldered to a circuit board.

[0003] Japanese Patent Application Laid-Open No. 2007-150179 Japanese Patent Application Laid-Open No. 2013-243330

[0004] An inductor having a coil shape is difficult to miniaturize and, of course, cannot be thinned. Patent Documents 1 and 2 describe a sheet-shaped inductor. However, the sheet-shaped inductors described in Patent Documents 1 and 2 have a magnetic core and a coil in the substrate or a spiral wiring pattern that functions as an inductor in the substrate, so they cannot be substantially thinned.

[0005] One or more embodiments provide a sheet-shaped inductor capable of being thinned, a printed wiring board and a module that can solve the problems of an inductor having a coil shape by including the thinned sheet-shaped inductor, and a method of using a conductive adhesive layer that can function as a sheet-shaped inductor.

[0006] A first aspect of one or more embodiments provides a sheet-shaped inductor including at least a conductive adhesive layer, the conductive adhesive layer functioning as an inductance by connecting a first conductive pattern and a second conductive pattern spaced apart from each other formed on the printed wiring board without being connected to a ground conductive pattern formed on the printed wiring board.

[0007] A second aspect of one or more embodiments provides a printed circuit board comprising: a first conductive pattern formed on a base film; a second conductive pattern formed on the base film so as to be separated from the first conductive pattern; an opening formed to expose the first end of the first conductive pattern on the side of the second conductive pattern and the second end of the second conductive pattern on the side of the first conductive pattern; a coverlay bonded to cover the first conductive pattern excluding the first end, the second conductive pattern excluding the second end, and the base film; and a sheet-like inductor of the first aspect bonded to the coverlay by the conductive adhesive layer, wherein the conductive adhesive layer bonds to the first and second ends exposed in the opening, thereby connecting the first conductive pattern and the second conductive pattern and forming an inductance between the first end and the second end.

[0008] A third aspect of one or more embodiments provides a module comprising a circuit board on which a predetermined circuit is mounted, and a printed wiring board of a second aspect connected to the circuit board.

[0009] A fourth aspect of one or more embodiments is a method for using a conductive adhesive layer, which provides a method for using a conductive adhesive layer to function as a sheet-like inductor by bonding the conductive adhesive layer to the first end of a first conductive pattern and the second end of a second conductive pattern that are spaced apart from each other and formed on the printed circuit board, without connecting the conductive adhesive layer to a conductive pattern for ground formed on the printed circuit board, thereby connecting the first end and the second end.

[0010] According to one or more embodiments of the sheet-like inductor, it is possible to make it a thin film. According to one or more embodiments of the printed circuit board and module, by providing a thin-film sheet-like inductor, the problems that have been present in inductors having a coil shape can be eliminated. According to one or more embodiments of the method of using the conductive adhesive layer, the conductive adhesive layer can be made to function as a sheet-like inductor.

[0011] Figure 1 is a diagram showing a sheet-type inductor product including a sheet-type inductor according to the first or second embodiment. Figure 2 is a perspective view showing a sheet-type inductor product including a sheet-type inductor according to the first or second embodiment, wound in a roll. Figure 3 is a diagram showing a sheet-type inductor product including a sheet-type inductor with a different configuration according to the first or second embodiment. Figure 4 is a partial plan view showing a base film with a conductive pattern formed thereon, which constitutes a printed circuit board according to the first, second, or third embodiment. Figure 5 is a partial plan view showing a coverlay with a rectangular opening formed thereon, bonded to the base film shown in Figure 4. Figure 6 is a partial plan view showing a printed circuit board according to the first to third embodiments, with a sheet-type inductor according to the first, second, or third embodiment attached to the coverlay shown in Figure 5. Figure 7 is a cross-sectional view taken along line A-A of Figure 6 when Figure 6 is a printed circuit board according to the first or second embodiment. Figure 8 is a perspective view showing the printed circuit board shown in Figure 6 with the base film, coverlay, and sheet-type inductor (conductive adhesive layer) shifted in the height direction. Figure 9 is a characteristic diagram showing the relationship between frequency and transmission loss in the conductive adhesive layer when an AC signal with frequencies from 0 GHz to 20 GHz is passed through a pair of conductive patterns formed on the printed circuit board shown in Figure 6. Figure 10A is an enlarged view of the portion from 0.0 GHz to 0.5 GHz in Figure 9. Figure 10B is an enlarged view of the portion from 1 GHz to 10 GHz in Figure 9. Figure 11 is a partial plan view showing the inductance region and capacitance region formed on the printed circuit board according to the first, second, or third embodiment. It is a circuit diagram showing a low-pass filter composed of the inductance region and capacitance region shown in Figure 11. Figure 13A is a partial perspective view showing a pair of conductive patterns connected by a short sheet-shaped inductor. Figure 13B is a partial perspective view showing a pair of conductive patterns connected by a long sheet-shaped inductor. Figure 14 is a characteristic diagram showing the relationship between frequency and impedance when a sheet-shaped inductor is set to a predetermined width, and the length of the conductive path formed by the conductive adhesive layer connecting the conductive patterns is varied to 50 mm, 100 mm, 150 mm, 200 mm, and 250 mm.Figure 15 is a perspective view showing a module according to the first, second, or third embodiment. Figure 16A is a partial perspective view showing a pair of conductive patterns connected by a thin sheet-like inductor. Figure 16B is a partial perspective view showing a pair of conductive patterns connected by a thick sheet-like inductor. Figure 17 is a characteristic diagram showing the relationship between frequency and impedance when the sheet-like inductor is of a predetermined length and the width of the conductive path formed by the conductive adhesive layer connecting the conductive patterns is varied to 2 mm, 5 mm, 10 mm, 15 mm, and 20 mm. Figure 18 is a diagram showing a sheet-like inductor product including a sheet-like inductor according to the third embodiment. Figure 19 is a perspective view showing a sheet-like inductor product including a sheet-like inductor according to the third embodiment wound in a roll. Figure 20 is a diagram showing a sheet-like inductor product including a sheet-like inductor with a different configuration according to the third embodiment. Figure 21 is a cross-sectional view taken along line A-A of Figure 6 when Figure 6 is a printed circuit board according to the third embodiment. Figure 22 is a partial perspective view showing an example of a shape other than rectangular that a sheet-like inductor according to the first, second, or third embodiment may have.

[0012] The following describes the methods of using the sheet-like inductor, printed circuit board, module, and conductive adhesive layer according to the first to third embodiments, with reference to the attached drawings.

[0013] [First Embodiment] <Sheet-shaped Inductor> Figure 1 shows a sheet-shaped inductor product 1A in the form in which the sheet-shaped inductor according to the first embodiment is sold to the user. A release film 13 is attached to the conductive adhesive layer 11.

[0014] As shown in Figure 2, the sheet-shaped inductor product 1A is wound into a roll. The release film 13 is a protective film for the conductive adhesive layer 11 of the roll-shaped sheet-shaped inductor product 1A. As will be described later, the conductive adhesive layer 11 functions as a sheet-shaped inductor. The sheet-shaped inductor product 1A is cut to a predetermined size and shape, and the release film 13 is peeled off from the conductive adhesive layer 11 to be used as a sheet-shaped inductor. The conductive adhesive layer 11 will be referred to as the sheet-shaped inductor 10A according to the first embodiment. The thickness of the conductive adhesive layer 11 is about 3 to 20 μm.

[0015] As shown in Figure 3, the sheet-shaped inductor product 1A', the metal layer 15 may be laminated on the side of the conductive adhesive layer 11 opposite to the side in contact with the release film 13. The laminated conductive adhesive layer 11 and metal layer 15 will be referred to as the sheet-shaped inductor 10A'. The metal of the metal layer 15 is a conductive metal such as gold, silver, copper, iron, aluminum, or nickel. As can be seen from Figures 1 and 3, the sheet-shaped inductor according to the first embodiment only needs to include the conductive adhesive layer 11.

[0016] As described later, the sheet-type inductor 10A or 10A' is used by being attached to a printed circuit board. If necessary, a protective layer may be provided on the side of the sheet-type inductor 10A or 10A' that is opposite to the side in contact with the printed circuit board to protect the sheet-type inductor 10A or 10A'.

[0017] The base film of the printed circuit board has a first conductive pattern and a second conductive pattern formed on it, spaced apart from each other. The conductive adhesive layer 11 functions as an inductance by connecting the first conductive pattern and the second conductive pattern. Details of how the conductive adhesive layer 11 functions as an inductance and details of the printed circuit board will be described later.

[0018] The length L of the conductive path formed by the conductive adhesive layer 11 connecting the first conductive pattern and the second conductive pattern is preferably in the range of 10 mm or more and 1000 mm or less, and more preferably in the range of 30 mm or more and 800 mm or less. If the length L of the conductive path is shorter than 10 mm, the conductive adhesive layer 11 becomes difficult to handle and difficult to attach to the printed circuit board. If the length L of the conductive path is longer than 1000 mm, the printed circuit board needs to be made larger, and the module described later also becomes larger.

[0019] The conductive adhesive layer 11 contains a resin component for adhering the conductive adhesive layer 11 to the first and second conductive patterns, and conductive powder for conducting electricity between the first and second conductive patterns. The proportion of conductive powder contained in the conductive adhesive layer 11 is preferably 40% by weight or more and 70% by weight or less. If it is less than 40% by weight, the conductive adhesive layer 11 will hardly function as an inductance. If it exceeds 70% by weight, the peak of the frequency-impedance characteristic shifts too far to the high-frequency side, making it difficult to block the desired frequency components. Details of the frequency-impedance characteristic peak will be described later.

[0020] The conductive powder may be dendritic, leaf-shaped, flake-shaped, plate-shaped, needle-shaped, or grape-shaped. The conductive adhesive layer 11 preferably does not contain spherical conductive powder. If the conductive powder is spherical, the conductive adhesive layer 11 will not function as an inductor but will instead function as a capacitor.

[0021] For example, thermoplastic resins or thermosetting resins can be used as the resin component. Examples of thermoplastic resins include polyolefin resins, vinyl resins, styrene-acrylic resins, diene resins, terpene resins, petroleum resins, cellulose resins, polyamide resins, polyurethane resins, polyester resins, polycarbonate resins, polyimide resins, liquid crystal polymers, and fluororesins.

[0022] The thermosetting resin may be any resin having one or more functional groups in one molecule that can be used in crosslinking reactions by heating, such as hydroxyl groups, phenolic hydroxyl groups, methoxymethyl groups, carboxyl groups, amino groups, epoxy groups, oxetanyl groups, oxazoline groups, oxazine groups, aziridine groups, thiol groups, isocyanate groups, blocked isocyanate groups, blocked carboxyl groups, silanol groups, etc. Examples of thermosetting resins include acrylic resins, maleic acid resins, polybutadiene resins, polyester resins, polyurethane resins, epoxy resins, oxetane resins, phenoxy resins, polyimide resins, polyamide resins, phenolic resins, alkyd resins, amino resins, polylactic acid resins, oxazoline resins, benzoxazine resins, silicone resins, and fluororesins. In addition to the above resins, the thermosetting resin preferably contains a curing agent such as a resin or low molecular weight compound that crosslinks with the above functional groups, as needed.

[0023] It is necessary to appropriately configure the conductive adhesive layer 11 in both the sheet-shaped inductor 10A, which consists of a conductive adhesive layer 11, and the sheet-shaped inductor 10A', which has a metal layer 15 superimposed on the conductive adhesive layer 11. The proportion and shape of conductive powder contained in the conductive adhesive layer 11, or both, should be appropriately set for the sheet-shaped inductor 10A and the sheet-shaped inductor 10A'.

[0024] Since the thickness of the sheet-shaped inductor 10A or 10A' is several micrometers to several tens of micrometers, the sheet-shaped inductor 10A or 10A' makes it possible to make the inductor thinner. The sheet-shaped inductor 10A or 10A' can also be made significantly lighter compared to a coil-shaped inductor.

[0025] <Printed Wiring Board> Figures 4 to 8 will be used to explain how the sheet-type inductor 10A or 10A' is used in a printed wiring board. Here, the case in which the sheet-type inductor 10A is used in a flexible printed wiring board is used as an example. The printed wiring board is not limited to a flexible printed wiring board, but may also be a rigid printed wiring board. Figure 4 partially shows a base film 20 that constitutes a part of the printed wiring board. The base film 20 is made of, for example, a polyimide film. On the base film 20, a first conductive pattern 21 made of, for example, copper, and a second conductive pattern 22 are formed at a predetermined distance from the first conductive pattern 21.

[0026] Furthermore, a third conductive pattern 23 for grounding, formed of, for example, copper, is formed on the base film 20.

[0027] As shown in Figure 5, a coverlay 24 is bonded to the base film 20 on which the first conductive pattern 21, the second conductive pattern 22, and the third conductive pattern 23 are formed. The coverlay 24 has, for example, a rectangular opening 240. The opening 240 exposes the first end 210 of the first conductive pattern 21 on the side of the second conductive pattern 22, and the second end 220 of the second conductive pattern 22 on the side of the first conductive pattern 21. Therefore, the coverlay 24 is bonded so as to cover the first conductive pattern 21 excluding the first end 210, the second conductive pattern 22 excluding the second end 220, the third conductive pattern 23, and the base film 20.

[0028] As shown in Figures 7 and 8 described later, the coverlay 24 has a laminated structure of an adhesive sheet 241 and a polyimide film 242. The coverlay 24 is bonded by the adhesive sheet 241 to the base film 20 on which the first conductive pattern 21, the second conductive pattern 22, and the third conductive pattern 23 are formed. The coverlay 24 functions as a circuit protective film.

[0029] As shown in Figure 6, a sheet-shaped inductor 10A of a predetermined size is attached to the coverlay 24. Here, the shape of the sheet-shaped inductor 10A is rectangular. The sheet-shaped inductor 10A is larger than the opening 240 and is bonded to the first end 210 and the second end 220 where the conductive adhesive layer 11 is exposed to the opening 240. The sheet-shaped inductor 10A covers the coverlay 24 beyond both the first end 210 and the second end 220. The sheet-shaped inductor 10A is also attached to the coverlay 24 so as to partially cover the third conductive pattern 23 via the coverlay 24.

[0030] A printed circuit board in the state shown in Figure 6 can be constructed as follows: The sheet-shaped inductor product 1A shown in Figures 1 and 2 is cut to a predetermined size and shape. The release film 13 is peeled off the cut sheet-shaped inductor product 1A and attached to the coverlay 24 in the position shown in Figure 6. The printed circuit board with the sheet-shaped inductor product 1A attached to the coverlay 24 is heated and pressure is applied using a hot press machine. As a result, the conductive adhesive layer 11 adheres firmly to the printed circuit board, resulting in the printed circuit board in the state shown in Figure 6.

[0031] Figure 7 shows the A-A cross-section of Figure 6. The sheet-shaped inductor 10A is in close contact with the base film 20, the first end 210 and the second end 220, and the coverlay 24. Since the conductive adhesive layer 11 is in close contact with the first end 210 and the second end 220, the conductive adhesive layer 11 connects the first conductive pattern 21 and the second conductive pattern 22. As shown by the dashed line, when current flows through the first conductive pattern 21, the first conductive pattern 21 and the second conductive pattern 22 become conductive through the conductive adhesive layer 11, and the current flows to the second conductive pattern 22.

[0032] Figure 8 shows the printed circuit board shown in Figure 6, with the base film 20, coverlay 24, and conductive adhesive layer 11 (which functions as a sheet-like inductor 10A) shifted in the height direction. The current flowing through the first conductive pattern 21, shown by the dashed line, flows to the conductive adhesive layer 11 because an opening 240 is formed in the coverlay 24, and then flows from the conductive adhesive layer 11 to the second conductive pattern 22.

[0033] Figure 9 shows the relationship between frequency and transmission loss in the conductive adhesive layer 11 when an AC signal with frequencies from 0 GHz to 20 GHz is passed between the first conductive pattern 21 and the second conductive pattern 22 formed on a printed circuit board as shown in Figure 6. Figure 10A is an enlarged view of the portion from 0.0 GHz to 0.5 GHz in Figure 9, and Figure 10B is an enlarged view of the portion from 1 GHz to 10 GHz in Figure 9.

[0034] As can be seen from Figures 9 to 10B, the transmission loss in the conductive adhesive layer 11 increases as the frequency increases, so the conductive adhesive layer 11 has the characteristic of not passing AC signals as the frequency increases. In other words, the sheet-shaped inductors 10A and 10A' can be used as low-pass filters that block the high-frequency components of AC signals and allow the DC components or low-frequency components of AC signals to pass through. Also, as can be seen from Figures 9 to 10B, the conductive adhesive layer 11 functions as an inductance in which signals flow more easily at lower frequencies and more difficult to pass at higher frequencies.

[0035] Therefore, as shown in Figure 11, the area between the first conductive pattern 21 and the second conductive pattern 22 in the conductive adhesive layer 11 becomes an inductance region 25L where inductance is formed. It is not essential, but it is preferable, for the sheet-shaped inductor 10A or 10A' to partially cover the third conductive pattern 23 via the coverlay 24. When the sheet-shaped inductor 10A or 10A' covers the third conductive pattern 23 via the coverlay 24, the dielectric coverlay 24 exists between the third conductive pattern 23 and the conductive adhesive layer 11. Therefore, the area between the third conductive pattern 23 and the conductive adhesive layer 11 becomes a capacitance region 26C where capacitance is formed.

[0036] If the sheet-shaped inductor 10A or 10A' does not cover the third conductive pattern 23 via the coverlay 24, the printed circuit board will have only an inductance region 25L. If the sheet-shaped inductor 10A or 10A' covers the third conductive pattern 23 via the coverlay 24, the printed circuit board will have both an inductance region 25L and a capacitance region 26C.

[0037] The inductance region 25L and the capacitance region 26C constitute the low-pass filter shown in Figure 12. While the inductance provided by the inductance region 25L alone provides a high-frequency noise reduction effect, the low-pass filter shown in Figure 12 provides a greater high-frequency noise reduction effect than the inductance alone. The low-pass filter shown in Figure 12 can attenuate AC signals by rapidly reducing the gain above a predetermined cutoff frequency.

[0038] Figures 13A and 13B show two types of sheet-shaped inductors 10A with the same width but different conductive path lengths L. The width of the sheet-shaped inductor 10A is the dimension in the direction perpendicular to the direction connecting the first conductive pattern 21 and the second conductive pattern 22. The conductive path is formed by a conductive adhesive layer 11 connecting the first conductive pattern 21 and the second conductive pattern 22, and its length L is determined by the distance between the first conductive pattern 21 and the second conductive pattern 22 and the shape of the sheet-shaped inductor 10A. Since the sheet-shaped inductor 10A shown in Figures 13A and 13B is a straight, elongated rectangle, the length L of the conductive path is the distance between the ends of the first conductive pattern 21 and the second conductive pattern 22.

[0039] Figure 14 shows the relationship between frequency and impedance when the length L of the conductive path is varied to 50 mm, 100 mm, 150 mm, 200 mm, and 250 mm, while the sheet-shaped inductor 10A has a predetermined width. Increasing the length L shifts the characteristic peak to the lower frequency side. This is also true when using the sheet-shaped inductor 10A'.

[0040] As can be seen from Figure 14, by using a sheet-shaped inductor 10A or 10A', the characteristics of the low-pass filter can be changed simply by changing the length L of the conductive path formed by the conductive adhesive layer 11. When using a conventional inductor with a coil shape, one must select one of several types of inductors depending on the required low-pass filter characteristics. With the sheet-shaped inductor 10A or 10A', the length L can be set appropriately according to the required low-pass filter characteristics, thus significantly reducing the complexity of inductor selection.

[0041] When the proportion of conductive powder contained in the conductive adhesive layer 11 described above exceeds 70 weight percent, it becomes difficult to block the desired frequency components. This is because the peak of the characteristic shown in Figure 14 shifts too far to the high-frequency side.

[0042] <Module> Figure 15 shows a module 100 which is an example of the module according to the first embodiment. The module 100 is a battery module as an example. The module according to the first embodiment is not limited to the battery module. The module according to the first embodiment is an arbitrary module including a circuit board on which a predetermined circuit is mounted and a printed wiring board connected to the circuit board. The printed wiring board is a flexible printed wiring board or a rigid printed wiring board.

[0043] As shown in FIG. 15, the module 100 includes battery cells 30a to 30h, a circuit board 32, and a printed wiring board 200. The number of battery cells included in the module 100 is not limited to eight. Conductive patterns 21a to 21h formed on the printed wiring board 200 are connected to terminals 31a to 31h provided corresponding to the battery cells 30a to 30h respectively. The conductive patterns 21a to 21h correspond to the first conductive patterns 21 shown in FIG. 11. In FIG. 15, the illustration of the coverlay 24 and the third conductive pattern 23 is omitted.

[0044] Conductive patterns 22a to 22h are connected to the circuit board 32. The conductive patterns 22a to 22h correspond to the second conductive patterns 22 shown in FIG. 11. The conductive patterns 21a to 21h and the conductive patterns 22a to 22h facing them are separated by a predetermined distance. Sheet inductors 10a to 10h are provided so as to connect the conductive patterns 21a to 21h and the conductive patterns 22a to 22h respectively. The sheet inductors 10a to 10h correspond to the sheet inductors 10A shown in FIG. 11. The sheet inductors 10a to 10h may be the sheet inductors 10A'.

[0045] As an example, the circuit board 32 is a control board that controls the voltage of the module 100. The voltage monitoring signals for monitoring the voltages of the battery cells 30a to 30h respectively are supplied to a control circuit formed on the circuit board 32 via the conductive patterns 21a to 21h, the sheet inductors 10a to 10h, and the conductive patterns 22a to 22h.

[0046] In FIG. 15, assume that module 100 does not include sheet inductors 10a to 10h and a conductive pattern for connecting terminals 31a to 31h to circuit board 32 is formed. In this case, a coil-shaped inductor needs to be mounted on the circuit formed on circuit board 32. That is, a typical circuit board has a soldered coil-shaped inductor. The soldered inductor may have its solder damaged and fall off due to vibrations applied to the circuit board over time. As described above, since sheet inductors 10a to 10h (sheet inductor 10A or 10A') are firmly adhered to printed wiring board 200 by conductive adhesive layer 11, there is almost no risk of falling off.

[0047] Thus, according to module 100 including sheet inductors 10a to 10h, since it does not include a coil-shaped inductor, it is possible to eliminate the problems of a coil-shaped inductor. According to module 100, the adhesion reliability during vibration can be significantly improved.

[0048] Printed wiring board 200 included in module 100 includes sheet inductors 10a to 10h instead of a coil-shaped inductor mounted on circuit board 32. Therefore, by using printed wiring board 200 in module 100, it is possible to eliminate the problems caused by mounting a coil-shaped inductor on circuit board 32.

[0049] Generally, in a circuit board on which a coil-shaped inductor is mounted, the inductor is larger than other circuit components and has the largest size in the height direction. Thus, the size of the module in the height direction increases due to the height of the inductor. In contrast, since module 100 includes circuit board 32 on which a coil-shaped inductor is not mounted, the size in the height direction can be reduced.

[0050] [Second Embodiment] <Sheet-shaped Inductor> Figure 1 shows a sheet-shaped inductor product 1B in the form in which the sheet-shaped inductor according to the second embodiment is sold to the user. A release film 13 is attached to the conductive adhesive layer 11. As shown in Figure 2, the sheet-shaped inductor product 1B is wound into a roll. Similar to the first embodiment, the conductive adhesive layer 11 functions as a sheet-shaped inductor. The conductive adhesive layer 11 will be referred to as the sheet-shaped inductor 10B according to the second embodiment. As shown in the sheet-shaped inductor product 1B' in Figure 3, a metal layer 15 may be laminated on the side of the conductive adhesive layer 11 opposite to the side in contact with the release film 13. The laminated conductive adhesive layer 11 and metal layer 15 will be referred to as the sheet-shaped inductor 10B'.

[0051] The sheet-like inductors 10B and 10B' according to the second embodiment have the same configuration as the sheet-like inductors 10A and 10A' according to the first embodiment, except for the width of the conductive path formed by the conductive adhesive layer 11 connecting the first conductive pattern 21 and the second conductive pattern 22. Therefore, the width of the conductive path in the sheet-like inductors 10B and 10B' according to the second embodiment will be explained, and the explanation of the common parts will be omitted.

[0052] The width W of the conductive path formed by the conductive adhesive layer 11 connecting the first conductive pattern and the second conductive pattern is preferably in the range of 1 mm or more and 40 mm or less, and more preferably in the range of 2 mm or more and 30 mm or less. If the width W of the conductive path is narrower than 1 mm, the conductive adhesive layer 11 becomes difficult to handle, making it difficult to attach to the printed circuit board. If the width W of the conductive path is wider than 40 mm, the printed circuit board needs to be made larger, and the module 100, which will be described later, also becomes larger.

[0053] <Printed Wiring Board> The method of using the sheet-type inductor 10B or 10B' on the printed wiring board is the same as in Figures 4 to 8. Figures 6 and 7 show a printed wiring board according to the second embodiment with the sheet-type inductor 10B attached. The sheet-type inductor 10B' may be used instead of the sheet-type inductor 10B. The explanation of Figures 9 to 12 in the first embodiment also applies to the second embodiment.

[0054] Figures 16A and 16B show two types of sheet-shaped inductors 10B of the same length but with different conductive path widths W. The conductive path width W is the dimension perpendicular to the conductive path length L, as explained in Figures 13A and 13B. Figure 17 shows the relationship between frequency and impedance when the sheet-shaped inductor 10B is of a predetermined length and the width W is varied to 2 mm, 5 mm, 10 mm, 15 mm, and 20 mm. The narrower the width W of the sheet-shaped inductor 10, the lower the frequency peak of the characteristic can be shifted. This is also true when using sheet-shaped inductor 10B'.

[0055] As can be seen from Figure 17, by using a sheet-shaped inductor 10B or 10B', the characteristics of the low-pass filter can be changed simply by changing the width W of the sheet-shaped inductor 10B. When using a conventional inductor with a coil shape, one must select one of several types of inductors depending on the required low-pass filter characteristics. With the sheet-shaped inductor 10B or 10B', the width W can be set appropriately according to the required low-pass filter characteristics, thus significantly reducing the complexity of inductor selection.

[0056] <Module> The module 100 shown in Figure 15 is an example of a module according to the second embodiment. In module 100, sheet-shaped inductors 10a to 10h correspond to sheet-shaped inductors 10B or 10B'. The description of Figure 15 in the first embodiment also applies to the second embodiment.

[0057] [Third Embodiment] <Sheet-shaped Inductor> Figure 18 shows a sheet-shaped inductor product 1C, which is the form in which the sheet-shaped inductor according to the third embodiment is sold to the user. As shown in Figure 18, an insulating layer 12 is superimposed on a conductive adhesive layer 11. A release film 13 is attached to the conductive adhesive layer 11, and a release film 14 is attached to the insulating layer 12. For example, the release film 13 is a transparent release film, and the release film 14 is a white release film. The insulating layer 12 is, for example, a black insulating layer. The adhesive force of the release film 13 to the conductive adhesive layer 11 is weaker than the adhesive force of the release film 14 to the insulating layer 12.

[0058] As shown in Figure 19, the sheet-like inductor product 1C is wound into a roll. The release films 13 and 14 are protective films that prevent contact between the conductive adhesive layer 11 and the insulating layer 12 of the roll-like sheet-like inductor product 1C. As will be described later, the release films 13 and 14 are peeled off from the conductive adhesive layer 11 and the insulating layer 12, respectively. The laminated conductive adhesive layer 11 and insulating layer 12 will be referred to as the sheet-like inductor 10C. In the third embodiment as well, strictly speaking, the conductive adhesive layer 11 functions as the sheet-like inductor. The insulating layer 12 functions as a protective layer for the conductive adhesive layer 11. The thickness of the conductive adhesive layer 11 and the insulating layer 12 is about 20 μm.

[0059] As shown in Figure 20, a sheet-like inductor product 1C' may have a metal layer 15 placed between the conductive adhesive layer 11 and the insulating layer 12. The laminated conductive adhesive layer 11, metal layer 15, and insulating layer 12 will be referred to as a sheet-like inductor 10C'. Similar to the first and second embodiments, the metal of the metal layer 15 is a conductive metal such as gold, silver, copper, iron, aluminum, or nickel. As can be seen from Figures 18 and 20, the sheet-like inductor according to the third embodiment is a laminate comprising a conductive adhesive layer 11 and an insulating layer 12 directly or indirectly superimposed on the conductive adhesive layer 11.

[0060] The sheet-type inductors 10C and 10C' according to the third embodiment have the same configuration as the sheet-type inductors 10A and 10A' according to the first embodiment or the sheet-type inductors 10B and 10B' according to the second embodiment, except that they are equipped with an insulating layer 12. Therefore, the description of the common parts will be omitted.

[0061] <Printed Wiring Board> The method of using the sheet-type inductor 10C or 10C' on the printed wiring board is the same as in Figures 4 to 8. The explanation of Figures 9 to 12 in the first embodiment also applies to the third embodiment. Figure 6 shows a printed wiring board according to the third embodiment with the sheet-type inductor 10C attached.

[0062] The printed circuit board according to the third embodiment shown in Figure 6 can be constructed as follows. The sheet-shaped inductor product 1C shown in Figures 18 and 19 is cut to a predetermined size and shape. The release film 13 is peeled off the cut sheet-shaped inductor product 1C and attached to the coverlay 24 in the position shown in Figure 6. The printed circuit board with the sheet-shaped inductor product 1C attached to the coverlay 24 is heated and pressure is applied by a hot press machine. This causes the conductive adhesive layer 11 to adhere firmly to the printed circuit board. Finally, the release film 14 is peeled off, resulting in the printed circuit board in the state shown in Figure 6.

[0063] Figure 21 shows a cross-section along line A-A when Figure 6 is a printed circuit board according to the third embodiment. The sheet-like inductor 10C is in close contact with the base film 20, the first end 210 and the second end 220, and the coverlay 24. Since the conductive adhesive layer 11 is in close contact with the first end 210 and the second end 220, the conductive adhesive layer 11 connects the first conductive pattern 21 and the second conductive pattern 22. Similar to Figure 7, when current flows through the first conductive pattern 21 as shown by the dashed line, the first conductive pattern 21 and the second conductive pattern 22 become conductive through the conductive adhesive layer 11, and the current flows to the second conductive pattern 22.

[0064] <Module> The module 100 shown in Figure 15 is an example of a module according to the third embodiment. In module 100, sheet-shaped inductors 10a to 10h correspond to sheet-shaped inductors 10C or 10C'. The description of Figure 15 in the first embodiment also applies to the third embodiment.

[0065] The present invention is not limited to the first to third embodiments described above, and can be modified in various ways without departing from the spirit of the invention. The shape of the sheet-like inductors 10A, 10B, 10C, 10A', 10B', and 10C' is not limited to a rectangle. As shown in Figure 22, the base film 20 has a first portion 201, a second portion 202, and a third portion 203. A first conductive pattern 21 is provided at the end of the first portion 201, and a second conductive pattern 22 is provided at the end of the third portion 203. The first portion 201 and the second portion 202 are connected at a 90-degree angle, and the second portion 202 and the third portion 203 are connected at a 90-degree angle. The corners between the first portion 201 and the second portion 202, and between the second portion 202 and the third portion 203 are rounded (R-shaped).

[0066] The sheet-shaped inductors 10A, 10B, and 10C shown in Figure 22 have a first straight section 101, a second straight section 102, and a third straight section 103, corresponding to the shape of the base film 20. The first straight section 101 and the second straight section 102 are connected at a 90-degree angle, and the second straight section 102 and the third straight section 103 are also connected at a 90-degree angle. The corners between the first straight section 101 and the second straight section 102, and the corners between the second straight section 102 and the third straight section 103 are rounded (R-shaped). In this way, the sheet-shaped inductors 10A, 10B, and 10C have a bent shape that is not a straight line, and connect the first conductive pattern 21 and the second conductive pattern 22.

[0067] The length L of the conductive path of the sheet-shaped inductors 10A, 10B, and 10C having the shape shown in Figure 22 is the length along the first straight section 101, the second straight section 102, and the third straight section 103. More specifically, it is the sum of the length of the first straight section 101 from the end of the first conductive pattern 21 to the second straight section 102, the length of the second straight section 102, and the length of the third straight section 103 from the second straight section 102 to the end of the second conductive pattern 22.

[0068] Thus, the sheet-shaped inductors 10A, 10B, 10C, 10A', 10B', and 10C' can be any shape, such as a straight line, a curved line, or a combination of a straight line and a curved line.

[0069] Furthermore, the present invention is not limited to the individual embodiments of the first to third embodiments described above. The first embodiment and the second embodiment can be combined. That is, a sheet-shaped inductor can be made in which the length L of the conductive path formed by the conductive adhesive layer 11 is 10 mm or more and 1000 mm or less, and the width W is 1 mm or more and 40 mm or less. The first embodiment and the third embodiment can be combined, and the second embodiment and the third embodiment can be combined. That is, the length L of the conductive path formed by the conductive adhesive layer 11 provided in the sheet-shaped inductor 10C or 10C' is preferably 10 mm or more and 1000 mm or less. The width W of the conductive path formed by the conductive adhesive layer 11 provided in the sheet-shaped inductor 10C or 10C' is preferably 1 mm or more and 40 mm or less.

[0070] This application claims priority based on Japanese Patent Application No. 2024-220620, filed with the Japan Patent Office on 17 December 2024, and Japanese Patent Application Nos. 2025-067900 and 2025-067901, filed with the Japan Patent Office on 17 April 2025, all of which are incorporated herein by reference.

Claims

1. A sheet-shaped inductor comprising at least a conductive adhesive layer, wherein the conductive adhesive layer functions as an inductance by connecting a first conductive pattern and a second conductive pattern, which are spaced apart from each other and formed on the printed circuit board, without being connected to a conductive pattern for ground formed on the printed circuit board.

2. The sheet-like inductor according to claim 1, further comprising an insulating layer laminated on the side of the conductive adhesive layer opposite to the side in contact with the printed circuit board.

3. The sheet-like inductor according to claim 1, further comprising a metal layer laminated on the side of the conductive adhesive layer opposite to the side in contact with the printed circuit board.

4. The sheet-like inductor according to claim 3, further comprising an insulating layer laminated on the metal layer.

5. The sheet-like inductor according to any one of claims 1 to 4, wherein the length of the conductive path formed by the conductive adhesive layer connecting the first conductive pattern and the second conductive pattern is 10 mm or more and 1000 mm or less.

6. The sheet-like inductor according to any one of claims 1 to 5, wherein the width of the conductive path formed by the conductive adhesive layer connecting the first conductive pattern and the second conductive pattern is 1 mm or more and 40 mm or less.

7. The sheet-like inductor according to any one of claims 1 to 6, wherein the conductive adhesive layer comprises a resin component for adhering the conductive adhesive layer to the first and second conductive patterns, and a conductive powder for providing electrical conductivity between the first and second conductive patterns.

8. The sheet-like inductor according to claim 7, wherein the proportion of the conductive powder contained in the conductive adhesive layer is 40% by weight or more and 70% by weight or less.

9. The sheet-like inductor according to claim 7 or 8, wherein the conductive powder is dendritic, leaf-like, flake-like, plate-like, needle-like, or grape-like in shape.

10. A printed circuit board comprising: a first conductive pattern formed on a base film; a second conductive pattern formed on the base film so as to be separated from the first conductive pattern; a coverlay bonded to cover the first conductive pattern excluding the first end of the first conductive pattern on the side of the second conductive pattern and the second end of the second conductive pattern on the side of the first conductive pattern, with an opening formed therein that exposes the first conductive pattern excluding the first end, the second conductive pattern excluding the second end, and the base film; and a sheet-like inductor according to any one of claims 1 to 9, which is attached to the coverlay by the conductive adhesive layer, wherein the conductive adhesive layer bonds to the first and second ends exposed in the opening, thereby connecting the first conductive pattern and the second conductive pattern and forming an inductance between the first end and the second end.

11. The printed circuit board according to claim 10, further comprising a third conductive pattern for ground formed on the base film, wherein the coverlay is bonded to cover the third conductive pattern, the sheet-like inductor is bonded to the coverlay via the conductive adhesive layer so as to partially cover the third conductive pattern, and a capacitance is formed between the third conductive pattern and the conductive adhesive layer.

12. A module comprising: a circuit board on which a predetermined circuit is mounted; and a printed wiring board according to claim 10 or 11, connected to the circuit board.

13. A method for using a conductive adhesive layer, wherein the conductive adhesive layer is bonded to the first end of a first conductive pattern and the second end of a second conductive pattern, which are spaced apart from each other and formed on a printed circuit board, without connecting the conductive adhesive layer to a conductive ground pattern formed on the printed circuit board, thereby connecting the first end and the second end, and thereby causing the conductive adhesive layer to function as a sheet-like inductor.

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