Methods for using sheet-type inductors, flexible printed circuit boards, modules, and laminates.
The sheet-like inductor, with a conductive adhesive layer connecting conductive patterns on a flexible printed circuit board, achieves thin-film inductance, overcoming the limitations of coil-shaped inductors by enabling miniaturization and reducing thickness.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- TOYO INK MFG CO LTD
- Filing Date
- 2024-12-17
- Publication Date
- 2026-06-29
AI Technical Summary
Inductors with a coil shape are difficult to miniaturize and thin, as exemplified by sheet inductors described in Patent Documents 1 and 2, which have a magnetic core and spiral wiring pattern that hinder substantial thinning.
A sheet-like inductor comprising a conductive adhesive layer and an insulating layer, directly or indirectly superimposed, where the conductive adhesive layer connects spaced-apart conductive patterns on a flexible printed circuit board to form an inductance, and a flexible printed circuit board with a conductive pattern configuration that includes a coverlay and a sheet-like inductor bonded by the adhesive layer.
The solution enables the inductor to be made into a thin film, addressing the challenges of miniaturization and thickness, and provides a flexible printed circuit board and module that eliminate the issues associated with coil-shaped inductors.
Smart Images
Figure 2026105977000001_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a sheet inductor, a flexible printed wiring board, and a module.
Background Art
[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.
Prior Art Documents
Patent Documents
[0003]
Patent Document 1
Patent Document 2
Summary of the Invention
Problems to be Solved by the Invention
[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 inductor. However, the sheet 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, and thus cannot be substantially thinned.
[0005] One or more embodiments provide a sheet inductor capable of being thinned, and a flexible printed wiring board and a module that can solve the problems of an inductor having a coil shape by including the thinned sheet inductor.
Means for Solving the Problems
[0006] A first aspect of one or more embodiments provides a sheet-like inductor comprising a conductive adhesive layer and an insulating layer directly or indirectly superimposed on the conductive adhesive layer, wherein the conductive adhesive layer functions as an inductance by connecting a first conductive pattern and a second conductive pattern that are spaced apart from each other and formed on a flexible printed circuit board.
[0007] A second aspect of one or more embodiments provides a flexible 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 a first end of the first conductive pattern on the side of the second conductive pattern and a second end of the second conductive pattern on the side of the first conductive pattern, the first conductive pattern excluding the first end, the second conductive pattern excluding the second end, and a coverlay bonded to cover 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 and second conductive patterns and forming an inductance between the first and second ends.
[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 flexible printed circuit board of a second aspect connected to the circuit board. [Effects of the Invention]
[0009] 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 flexible 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. [Brief explanation of the drawing]
[0010] [Figure 1] Figure 1 shows the stacked state of a sheet-type inductor product, including a sheet-type inductor according to one or more embodiments. [Figure 2] Figure 2 is a perspective view showing a sheet-type inductor product wound into a roll. [Figure 3] Figure 3 shows the stacked state of a sheet inductor product, including sheet inductors of other configurations according to one or more embodiments. [Figure 4] Figure 4 is a partial plan view showing a base film on which a conductive pattern is formed, which constitutes a flexible printed circuit board according to one or more embodiments. [Figure 5] Figure 5 is a partial plan view showing a coverlay with a rectangular opening bonded to the base film shown in Figure 4. [Figure 6] Figure 6 is a partial plan view showing a flexible printed circuit board according to one or more embodiments, in which a sheet-like inductor is attached to the coverlay shown in Figure 5. [Figure 7] Figure 7 is a cross-sectional view of AA in Figure 6. [Figure 8] Figure 8 is a perspective view showing the flexible printed circuit board shown in Figure 6, with the base film, coverlay, and sheet-like inductor (conductive adhesive layer) shifted in the height direction. [Figure 9] Figure 9 is a characteristic diagram showing the relationship between frequency and transmission loss in the conductive adhesive layer when an AC signal ranging from 0 GHz to 20 GHz is passed through a pair of conductive patterns formed on the flexible printed circuit board shown in Figure 6. [Figure 10A] Figure 10A is a magnified view of the portion of Figure 9 from 0.0 GHz to 0.5 GHz. [Figure 10B] Figure 10B is a magnified view of the portion of Figure 9 from 1 GHz to 10 GHz. [Figure 11]FIG. 11 is a partial plan view showing an inductance region and a capacitance region formed on a flexible printed wiring board according to one or more embodiments. [Figure 12] FIG. 3 is a circuit diagram showing a low-pass filter constituted by the inductance region and the capacitance region shown in FIG. 11. [Figure 13A] FIG. 13A is a partial perspective view showing a state in which a pair of conductive patterns are connected by a thin sheet-like inductor. [Figure 13B] FIG. 13B is a partial perspective view showing a state in which a pair of conductive patterns are connected by a thick sheet-like inductor. [Figure 14] FIG. 14 is a characteristic diagram showing the relationship between frequency and impedance when the width of a sheet-like inductor is changed to 2 mm, 5 mm, 10 mm, and 15 mm with a predetermined length. [Figure 15A] FIG. 15A is a partial perspective view showing a state in which a pair of conductive patterns are connected by a short sheet-like inductor. [Figure 15B] FIG. 15B is a partial perspective view showing a state in which a pair of conductive patterns are connected by a long sheet-like inductor. [Figure 16] FIG. 16 is a characteristic diagram showing the relationship between frequency and impedance when the length of a sheet-like inductor is changed to 5 cm, 10 cm, and 15 cm with a predetermined width. [Figure 17] FIG. 17 is a perspective view showing a module according to one or more embodiments.
Embodiments for Carrying Out the Invention
[0011] Hereinafter, a sheet-like inductor, a flexible printed wiring board, and a module according to one or more embodiments will be described with reference to the accompanying drawings.
[0012] <Sheet-like Inductor> Figure 1 shows a sheet-type inductor product 1 in the form in which a sheet-type inductor according to one or more embodiments is sold to a user. As shown in Figure 1, an insulating layer 12 is superimposed on a conductive adhesive layer 11. A transparent release film 13 is attached to the conductive adhesive layer 11, and a white release film 14 is attached to the insulating layer 12. The insulating layer 12 is, for example, a black insulating layer. The adhesive strength of the transparent release film 13 to the conductive adhesive layer 11 is weaker than the adhesive strength of the white release film 14 to the insulating layer 12.
[0013] As shown in Figure 2, the sheet-shaped inductor product 1 is wound into a roll. The transparent release film 13 and the white release film 14 are protective films that prevent contact between the conductive adhesive layer 11 and the insulating layer 12 of the roll-shaped sheet-shaped inductor product 1. As will be described later, the transparent release film 13 and the white release film 14 are peeled off from the conductive adhesive layer 11 and the insulating layer 12, respectively. What is necessary for a sheet-shaped inductor is the laminated conductive adhesive layer 11 and the insulating layer 12. The laminated conductive adhesive layer 11 and the insulating layer 12 will be referred to as the sheet-shaped inductor 10. The thickness of the conductive adhesive layer 11 and the insulating layer 12 is about 20 μm.
[0014] As shown in Figure 3, a sheet-like inductor product 1' 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 10'. 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, a sheet-like inductor according to one or more embodiments may be a laminate comprising a conductive adhesive layer 11 and an insulating layer 12 directly or indirectly superimposed on the conductive adhesive layer 11.
[0015] The sheet-shaped inductor 10 or 10' is used mounted on a flexible printed circuit board. The base film of the flexible 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 flexible printed circuit board will be described later.
[0016] 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 high-frequency components. Details of the frequency-impedance characteristic peak will be described later.
[0017] 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.
[0018] It is necessary to appropriately configure the conductive adhesive layer 11 in both sheet-shaped inductors 10, where an insulating layer 12 is directly superimposed on the conductive adhesive layer 11, and sheet-shaped inductors 10', where an insulating layer 12 is superimposed on the conductive adhesive layer 11 via a metal layer 15. The proportion and shape of conductive powder contained in the conductive adhesive layer 11, or both, should be appropriately set for sheet-shaped inductors 10 and sheet-shaped inductors 10'.
[0019] According to the sheet-shaped inductor 10 or 10', the thickness is about several tens of micrometers, making it possible to thin the inductor. According to the sheet-shaped inductor 10 or 10', the weight can also be significantly reduced compared to a coil-shaped inductor.
[0020] <Flexible Printed Circuit Board> Figures 4 to 8 illustrate how a sheet-type inductor 10 or 10' is used in a flexible printed circuit board. Here, we will use the case where a sheet-type inductor 10 is used as an example. Figure 4 partially shows a base film 20 that constitutes a part of a flexible printed circuit board. The base film 20 is made of polyimide film. On the base film 20, a first conductive pattern 21 formed of, for example, copper, and a second conductive pattern 22 are formed at a predetermined distance from the first conductive pattern 21.
[0021] Furthermore, a third conductive pattern 23 for grounding, formed, for example, of copper, is formed on the base film 20.
[0022] 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.
[0023] 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.
[0024] As shown in Figure 6, a sheet-shaped inductor 10 of a predetermined size is attached to the coverlay 24. The sheet-shaped inductor 10 is larger than the opening 240 and is bonded to the first end 210 and second end 220 where the conductive adhesive layer 11 is exposed to the opening 240. The sheet-shaped inductor 10 covers the coverlay 24 beyond both the first end 210 and the second end 220. The sheet-shaped inductor 10 is also attached to the coverlay 24 so as to partially cover the third conductive pattern 23 via the coverlay 24.
[0025] A flexible printed circuit board in the state shown in Figure 6 can be constructed as follows: The sheet-shaped inductor product 1 shown in Figures 1 and 2 is cut to a predetermined size. The transparent release film 13 is peeled off the cut sheet-shaped inductor product 1 and attached to the coverlay 24 in the position shown in Figure 6. The flexible printed circuit board with the sheet-shaped inductor product 1 attached to the coverlay 24 is heated and pressure is applied using a hot press machine. This firmly adheres the conductive adhesive layer 11 to the flexible printed circuit board. Finally, the white release film 14 is peeled off, resulting in the flexible printed circuit board in the state shown in Figure 6.
[0026] Figure 7 shows the AA cross-section of Figure 6. The sheet-shaped inductor 10 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.
[0027] Figure 8 shows the flexible printed circuit board shown in Figure 6, with the base film 20, coverlay 24, and sheet-shaped inductor 10 shifted in the height direction. In Figure 8, only the conductive adhesive layer 11 of the sheet-shaped inductor 10 is shown. 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.
[0028] 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 flexible 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.
[0029] 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 allowing AC signals to pass through as the frequency increases. In other words, the sheet-shaped inductors 10 and 10' 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 that allows signals to flow more easily at lower frequencies and more difficult to flow at higher frequencies.
[0030] 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 10 to partially cover the third conductive pattern 23 via the coverlay 24. When the sheet-shaped inductor 10 covers the third conductive pattern 23 via the coverlay 24, a dielectric polyimide film 242 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.
[0031] If the sheet-shaped inductor 10 does not cover the third conductive pattern 23 via the coverlay 24, the flexible printed circuit board will only have an inductance region 25L. If the sheet-shaped inductor 10 covers the third conductive pattern 23 via the coverlay 24, the flexible printed circuit board will have both an inductance region 25L and a capacitance region 26C.
[0032] The inductance region 25L and the capacitance region 26C constitute the low-pass filter shown in Figure 12. While the inductance of 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.
[0033] Figures 13A and 13B show two types of sheet-shaped inductors 10 with the same length but different widths. The length of the sheet-shaped inductor 10 is the dimension in the direction connecting the first conductive pattern 21 and the second conductive pattern 22, and the width of the sheet-shaped inductor 10 is the dimension in the direction perpendicular to the direction connecting the first conductive pattern 21 and the second conductive pattern 22. Figure 14 shows the relationship between frequency and impedance when the sheet-shaped inductor 10 is given a predetermined length and its width is changed to 2 mm, 5 mm, 10 mm, and 15 mm. The narrower the width of the sheet-shaped inductor 10, the more the peak of the characteristic can be shifted to the lower frequency side.
[0034] Figures 15A and 15B show two types of sheet-shaped inductors 10 with the same width but different lengths. Figure 16 shows the relationship between frequency and impedance when the sheet-shaped inductor 10 has a predetermined width and its length is changed to 5 cm, 10 cm, and 15 cm. The longer the length of the sheet-shaped inductor 10, the more the peak of the characteristic can be shifted to the lower frequency side.
[0035] As can be seen from Figures 14 and 16, using the sheet-shaped inductor 10, the characteristics of the low-pass filter can be changed simply by changing the length or width of the sheet-shaped inductor 10. When using conventional inductors 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 10, the length or width can be set appropriately according to the required low-pass filter characteristics, thus greatly improving the design flexibility.
[0036] The reason why the conductive powder content in the conductive adhesive layer 11 described above exceeds 70 weight percent makes it difficult to block high-frequency components is that the peak of the characteristic shown in Figure 14 or Figure 16 shifts too far towards the high-frequency side.
[0037] <module> Figure 17 shows module 100, which is an example of a module according to one or more embodiments. Module 100 is a battery module as an example. A module according to one or more embodiments is not limited to a battery module. A module according to one or more embodiments is any module comprising a circuit board on which a predetermined circuit is mounted and a flexible printed circuit board connected to the circuit board.
[0038] As shown in Figure 17, module 100 comprises battery cells 30a to 30h, a circuit board 32, and a flexible printed circuit board 200. The number of battery cells in module 100 is not limited to eight. Conductive patterns 21a to 21h formed on the flexible printed circuit board 200 are connected to terminals 31a to 31h, which are provided corresponding to each of the battery cells 30a to 30h. Conductive patterns 21a to 21h correspond to the first conductive pattern 21 shown in Figure 11. In Figure 17, the coverlay 24 and the third conductive pattern 23 are not shown.
[0039] Conductive patterns 22a to 22h are connected to the circuit board 32. Conductive patterns 22a to 22h correspond to the second conductive pattern 22 shown in Figure 11. Conductive patterns 21a to 21h and the corresponding conductive patterns 22a to 22h are separated by a predetermined distance. Sheet-shaped inductors 10a to 10h are provided to connect conductive patterns 21a to 21h and conductive patterns 22a to 22h, respectively. Sheet-shaped inductors 10a to 10h correspond to the sheet-shaped inductor 10 shown in Figure 11.
[0040] As an example, circuit board 32 is a control board that controls the voltage of module 100. Voltage monitoring signals, which monitor the voltage of each battery cell 30a to 30h, are supplied to a control circuit formed on circuit board 32 via conductive patterns 21a to 21h, sheet-shaped inductors 10a to 10h, and conductive patterns 22a to 22h.
[0041] In Figure 17, let's assume that module 100 does not have sheet-shaped inductors 10a to 10h, and that a conductive pattern is formed connecting terminals 31a to 31h to the circuit board 32. In this case, it is necessary to mount coil-shaped inductors in the circuit formed on the circuit board 32. That is, a typical circuit board has soldered coil-shaped inductors. Soldered inductors may detach due to damage to the solder caused by vibrations applied to the circuit board as it ages. As described above, since sheet-shaped inductors 10a to 10h (sheet-shaped inductors 10) are firmly bonded to the flexible printed circuit board 200 by the conductive adhesive layer 11, there is almost no risk of them detaching.
[0042] Thus, the module 100, which includes sheet-shaped inductors 10a to 10h, does not include coil-shaped inductors, thus eliminating the problems associated with coil-shaped inductors. The module 100 significantly improves the adhesive reliability during vibration.
[0043] The flexible printed circuit board 200 of module 100 is equipped with sheet-shaped inductors 10a to 10h instead of coil-shaped inductors mounted on the circuit board 32. Therefore, by using the flexible printed circuit board 200 in module 100, the problems caused by mounting coil-shaped inductors on the circuit board 32 can be eliminated.
[0044] Generally, in a circuit board with a coil-shaped inductor mounted on it, the inductor is larger than other circuit components and has the largest size in the height direction. Therefore, the height of the module increases due to the height of the inductor. In contrast, module 100 has a circuit board 32 that does not have a coil-shaped inductor mounted on it, so its height can be reduced.
[0045] The present invention is not limited to the one or more embodiments described above, and can be modified in various ways without departing from the spirit of the invention. [Explanation of symbols]
[0046] 1,1' Sheet-type inductor product 10,10',10a~10h Sheet-shaped inductor 11 Conductive adhesive layer 12 Insulating layer 13 Transparent release film 14 White release film 15 metal layer 20 base film 21 First conductive pattern Conductive patterns 21a~21h, 22a~22h 22 Second conductive pattern 23 Third conductive pattern 24 Coverlays 25L inductance range 26C capacitance region 30A~30H Battery Cell Terminals 31a~31h 32 Circuit boards 100 modules 200 Flexible Printed Circuit Boards 210 First end 220 Second end 240 aperture 241 Adhesive Sheet 242 Polyimide film
Claims
1. A conductive adhesive layer, An insulating layer directly or indirectly superimposed on the conductive adhesive layer, Equipped with, The conductive adhesive layer functions as an inductance by connecting the first and second conductive patterns, which are spaced apart from each other and formed on the flexible printed circuit board. Sheet-shaped inductor.
2. The conductive adhesive layer is A resin component for bonding the conductive adhesive layer to the first and second conductive patterns, A conductive powder for providing electrical conductivity between the first and second conductive patterns, Contains The sheet-shaped inductor according to claim 1.
3. The sheet-like inductor according to claim 2, 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.
4. The sheet-like inductor according to claim 2 or 3, wherein the conductive powder is dendritic, leaf-like, flake-like, plate-like, needle-like, or grape-like in shape.
5. The sheet-like inductor according to claim 1 or 2, further comprising a metal layer between the conductive adhesive layer and the insulating layer.
6. A first conductive pattern formed on the base film, A second conductive pattern is formed on the base film so as to be separated from the first conductive pattern, An opening is formed that exposes 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, and a coverlay is bonded to cover the first conductive pattern excluding the first end, the second conductive pattern excluding the second end, and the base film. A sheet-like inductor according to claim 1, which is attached to the coverlay by the conductive adhesive layer, Equipped with, The conductive adhesive layer adheres 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. Flexible printed circuit board.
7. The base film further comprises a third conductive pattern for grounding formed on the base film, The coverlay is bonded to cover the third conductive pattern, The sheet-like inductor is attached by the conductive adhesive layer so as to partially cover the third conductive pattern via the coverlay. A capacitance is formed between the third conductive pattern and the conductive adhesive layer. The flexible printed circuit board according to claim 6.
8. A circuit board equipped with a predetermined circuit, A flexible printed circuit board according to claim 6 or 7, connected to the circuit board, A module equipped with the following features.