JP2006066810A - Printed circuit board and image forming device provided therewith - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a printed circuit board having no wasteful energy loss, by simply restraining radiation using the resonance between the power supply layer and ground layer without large changes, in the substrate process of the prior art. <P>SOLUTION: The printed circuit board 100 includes signal wiring layers 1, 9 on which signal lines are wired, dielectric material layers 2, 5, 8, a power supply layer 3 forming the power supply region, thin films 4, 6 having anisotropic conductive property in the vertical direction to the surface of the printed circuit board, and a ground layer 7 forming the ground region. On the signal wiring layer 1, a dielectric material 2, a power supply layer 3, a thin film 4, a dielectric material layer 5, a thin film 6, a ground layer 7, a dielectric material layer 8, and a signal wiring layer 9, are laminated sequentially. The high-frequency current, flowing into the area near the opposing surfaces of the power supply layer 3 and the ground layer 7, is restrained with a conductive substance inside the thin films 4, 6. As a result, the current flowing in the surface direction of the thin films 4, 6 is significantly impeded. As a result, electromagnetic radiation by the high-frequency current can be controlled effectively. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a printed wiring board, and more particularly to a printed wiring board used in electronic equipment such as information equipment.

  Electromagnetic noise radiated from various electronic devices such as information devices, which has been a problem in the past, is mainly caused by clock signals on a printed circuit board and signal lines such as digital signals synchronized with the clock signals. It is considered. Therefore, various countermeasures against electromagnetic radiation have been taken for signal lines on a printed wiring board, wire harnesses connected to the signal lines, and the like. For example, a method of adding a damping resistor or filter to the signal output line to smooth the rise and fall of the output signal, a method of reducing the feedback current loop by arranging a guard pattern that is set to the ground potential near the signal line, etc. Is widely done.

  In addition, electromagnetic waves observed on the printed wiring board include electromagnetic waves that have a frequency distribution different from that predicted from the current distribution on the signal line and have a sharp peak at a specific frequency regardless of the nature of the signal line. As described in Patent Document 1, the main cause of the generation of the electromagnetic wave is not the signal line of the printed wiring board but the power supply system, and the electrical resonance generated in the opposing power supply layer and ground layer. It is known. In Patent Document 1, in order to reduce the reflectance of the resonance current at the end of the printed wiring board, a plurality of first capacitors are arranged at the end of the printed wiring board, and the first capacitor and the printed wiring board are arranged. Technology for connecting a second capacitor for suppressing a loop current flowing between an active element such as an IC mounted on the power supply terminal of the active element or between a power supply layer and a ground layer in the vicinity thereof Is disclosed.

  According to Patent Document 2, a radiation source of electromagnetic wave radiation caused by a power supply system of a printed wiring board flows through the power supply wiring of the digital IC when the digital IC mounted on the printed wiring board is driven. Since it is a current, for the purpose of separating the power supply surface of the printed wiring board and the digital IC at a high frequency, a branch wiring having a shape such as a zigzag shape or a cross shape is formed so as to increase the high frequency impedance, Furthermore, the high frequency power supply current flowing into the power supply surface is reduced by forming the insulating material on both the upper and lower sides of the power supply surface with a material containing a magnetic material.

  Further, according to Patent Documents 3 to 6, a voltage supply means for supplying power to the substrate, a loss material that attenuates a high-frequency current staying on one surface of the voltage supply means, and an insulation means applied to the loss material And a grounding conductive means applied to the insulating means, and a structure is proposed in which the surface portion of the power source / ground surface has a loss due to the skin effect.

Further, as described in Patent Document 7, a low conductivity region is further provided at the boundary, and the roughness of the interface between the low conductivity region and the insulating substrate is the skin depth at the highest frequency of the signal transmitted to the wiring substrate. The structure which makes it twice or more is proposed.
Japanese Patent No. 3036629 Japanese Patent No. 2734447 Japanese Patent Laid-Open No. 7-14018 JP 2001-102702 A JP 2003-283073 A JP 2003-283079 A JP 2001-244582 A

  However, the technique described in Patent Document 1 has a problem that it has no effect on a high-frequency resonance current whose frequency exceeds about 1 GHz, for example, because there is an inductance due to the capacitor itself and the mounting of the capacitor. . In addition, the resonance current cannot be completely eliminated even in a low frequency band, and there is a problem that electromagnetic waves radiated from the end of the printed wiring board cannot be completely suppressed.

  Moreover, in the technique described in Patent Document 2, as in the technique described in Patent Document 1, the high-frequency current flowing between the power supply surface and the ground surface cannot be completely suppressed, and the printed circuit board The electromagnetic waves radiated from the end cannot be completely suppressed. In addition, providing a decoupling capacitor on the sub power supply surface increases the impedance of the main power supply surface to the ground surface, which causes electromagnetic radiation, and thus a separate capacitor must be provided on the main power supply surface. As a result, the number of components increases, and a secondary problem occurs that the stability of the potential of the ground plane deteriorates.

  That is, by adding a large number of capacitors that couple the power supply surface and the ground surface, a large number of openings (clearances) are formed in the ground surface for passing through via holes connecting the capacitor pads and the power supply surface. Ideally, the ground plane does not have a potential difference at each location on the ground plane, but when multiple openings are provided close to each other, inductance is generated in a region between one opening and the other opening. Then, a potential difference is generated at both ends. Furthermore, since the metal region of the ground plane is reduced by providing a large number of openings, the stability of the potential of the entire ground plane is impaired.

  Furthermore, in the case of the noise suppression techniques described in Patent Documents 3 to 6, depending on Joule loss, problems such as waste of energy and heat generation may occur.

  Moreover, in the structure described in Patent Document 7, even if the maximum frequency component of the signal is 1 GHz, the copper skin depth is about 2 μm, and the roughness of the general copper foil interface excluding special electrolytic copper foil is one digit. It is rough and does not improve the current technology.

  As described above, in a printed wiring board having a configuration in which the power supply layer and the ground layer face each other and the facing area is large, electromagnetic wave radiation from the edge of the board caused by the resonance current that flows approximately symmetrically between the power supply layer and the ground layer. Becomes dominant. However, even if the techniques described in Patent Documents 1 to 7 are used, there is no effect on a high-frequency resonance current whose frequency exceeds 1 GHz, and the low-frequency resonance current is completely suppressed. I can't. On the other hand, the operation speed of digital circuits in recent years is increasing more and more, and problematic frequencies are becoming higher.

  In addition, in order to transmit a high-frequency signal on a printed wiring board, it is indispensable to lower the impedance of the signal wiring and ensure the stability of the potential of the power supply surface and the ground surface through which the return current to the signal wiring flows. .

  Here, in order to reduce the impedance of the signal wiring in the printed wiring board having a structure in which the power supply layer and the ground layer face each other and the inner layer is formed, the distance between the power supply layer and the ground layer is increased, It is necessary to provide a plurality of power supply layers and ground layers. In the former case, there is a problem that electromagnetic wave radiation due to the resonance current increases, and in the latter case, the cost increases. In addition, in the case of a structure that relies on Joule loss to suppress resonance current, there are problems such as waste of energy and heat generation.

  The present invention has been made to solve the above problem, and can easily suppress radiation caused by resonance between a power supply layer and a ground layer without greatly changing the conventional substrate process, and can be used without waste of energy. An object is to provide a wiring board and an image forming apparatus using the same.

  A printed wiring board according to the present invention is a printed wiring board in which a first dielectric layer, a ground layer, a second dielectric layer, and a signal wiring layer are sequentially stacked on a power supply layer. A thin film is formed between one dielectric layer and one or both of the first dielectric layer and the ground layer, and at least a part of the thin film is anisotropically conductive in a direction perpendicular to the printed circuit board surface. It has the characteristics.

  In the printed wiring board according to the present invention, the high-frequency current that tends to flow in the vicinity of the surfaces where the power supply layer and the ground layer face each other is bound to the thin film. Thereby, the current flowing in the plane direction of the thin film is significantly inhibited. As a result, electromagnetic radiation due to high-frequency current can be efficiently suppressed.

  In addition, since heat is not generated due to Joule loss unlike the prior art, electromagnetic wave radiation can be efficiently suppressed without wasting energy. Furthermore, by using a resin in which a conductive material similar to the anisotropic conductive resin used for connection of LCDs or the like is used, a low-noise printed wiring board can be manufactured without changing the conventional manufacturing process. it can. Further, even in a multilayer substrate having six or more layers, noise can be reduced by dispersing the conductive material in an arbitrary region.

  Furthermore, even when signal lines are wired to the inner layer of the printed wiring board according to the present invention, if signal lines are wired to a dielectric layer that does not have anisotropic conductivity, the signal integrity of high-speed signals flowing through the signal lines may be impaired. Absent.

  The end of the thin film may have anisotropic conductivity. In this case, even when the electromagnetic radiation due to the vertical electric field with respect to the substrate surface becomes a problem at the end as in the case of the patch antenna, the electromagnetic radiation can be efficiently prevented. Further, even if the high-speed signal wiring is arranged in the layer between the power supply layer and the ground layer inside the end portion of the thin film, the signal integrity of the signal flowing through the high-speed signal wiring is not impaired.

  The whole thin film may have anisotropic conductivity. In this case, the high-frequency current that tends to flow in the vicinity of the surfaces where the power supply layer and the ground layer face each other is bound to the entire thin film. Thereby, the current flowing in the plane direction of the thin film is significantly inhibited. As a result, it is possible to efficiently suppress electromagnetic radiation due to the high frequency current.

  The thin film may include a conductive material. In this case, the high-frequency current that tends to flow in the vicinity of the surfaces where the power supply layer and the ground layer face each other is bound by the conductive material in the thin film. Thereby, the current flowing in the plane direction of the thin film is significantly inhibited. As a result, it is possible to efficiently suppress electromagnetic radiation due to the high frequency current.

  The conductive material includes metal particles, and the diameter of the metal particles may be larger than the skin depth of the metal particles at the maximum frequency of the signal flowing through the signal line.

  In this case, a considerable part (at least 60%) of the high-frequency current that tends to flow in the vicinity of the surfaces where the power supply layer and the ground layer face each other is bound by the metal particles. Further, the harmonic component of the high-frequency current is more effectively bound (by a ratio greater than 60%) by the metal particles.

  The conductive material includes a metal line, and the thickness of the thin film may be greater than the skin depth of the metal line at the maximum frequency of the signal flowing through the signal line. In this case, the electric charge can be moved in the direction perpendicular to the thin film surface, but electrical conduction can be ignored in the thin film surface direction. As a result, the high-frequency current that tends to flow in the vicinity of the surfaces where the power supply layer and the ground layer face each other is bound to the metal wire in the thin film.

  The thin film may be an adhesive that is cured after the conductive material is dispersed. In this case, a thin film can be formed by dispersing metal particles in an adhesive and bonding the dielectric layer and the ground layer. Therefore, it is not necessary to go through a step of bonding a thin film in which a conductive material is dispersed in advance between the dielectric layer and the ground layer.

  The present invention also includes an image forming unit and a controller that controls the image forming unit, and the controller includes an image forming apparatus including the printed wiring board.

  According to the present invention, electromagnetic radiation due to a high frequency current can be efficiently suppressed. In addition, since heat is not generated due to Joule loss unlike the prior art, electromagnetic wave radiation can be efficiently suppressed without wasting energy. Furthermore, by using a resin in which a conductive material similar to the anisotropic conductive resin used for connection of LCDs or the like is used, a low-noise printed wiring board can be manufactured without changing the conventional manufacturing process. it can. Further, even in a multilayer substrate having six or more layers, it is possible to reduce noise by dispersing a conductive substance in an arbitrary region. Furthermore, even when signal lines are wired in the inner layer of the printed wiring board, signal integrity of high-speed signals flowing through the signal lines is not impaired if they are wired in a dielectric layer that does not have anisotropic conductivity.

  Hereinafter, the best mode for carrying out the present invention will be described.

  FIG. 1 is a cross-sectional view of a printed wiring board 100 according to a first embodiment of the present invention.

  As shown in FIG. 1, a printed wiring board 100 is formed with respect to signal wiring layers 1 and 9, dielectric layers 2, 5, and 8 on which signal lines are wired, a power supply layer 3 that forms a power supply region, and a printed wiring board surface. And thin films 4 and 6 having anisotropic conductivity in the vertical direction, and a ground layer 7 forming a ground region. On the signal wiring layer 1, a dielectric layer 2, a power supply layer 3, a thin film 4, a dielectric layer 5, a thin film 6, a ground layer 7, a dielectric layer 8 and a signal wiring layer 9 are sequentially laminated.

  The dielectric layer 5 has, for example, a structure in which an arbitrary number of cores and prepreg materials are stacked.

  For the thin films 4 and 6, for example, a dielectric film in which a conductive substance is sparsely dispersed can be used. A metal or the like can be used as the conductive substance. Specifically, it is possible to use a metal core such as nickel alone or gold-plated nickel, or a resin core such as styrene, acrylic, or silicon oxide that has been subjected to gold plating. Alternatively, an insulating film that is broken or melted by pressure or the like may be used. Various other conductive materials can also be used.

  Since the conductive material is dispersed in the thin films 4 and 6, the thin films 4 and 6 have anisotropic conductivity perpendicular to the surface of the printed wiring board 100. That is, in the thin films 4 and 6, the impedance in the direction perpendicular to the printed circuit board surface is sufficiently small, and the electrical conduction in the surface direction of the printed circuit board 100 can be ignored. Therefore, the high-frequency current that tends to flow in the vicinity of the surfaces where the power supply layer 3 and the ground layer 7 face each other is bound by the conductive substance in the thin films 4 and 6. Thereby, the current flowing in the plane direction of the thin films 4 and 6 is significantly inhibited. As a result, it is possible to efficiently suppress electromagnetic radiation due to the high frequency current.

  In addition, since heat is not generated due to Joule loss unlike the prior art, electromagnetic wave radiation can be efficiently suppressed without wasting energy. Furthermore, by using a resin in which a conductive material similar to the anisotropic conductive resin used for connection of LCDs or the like is used, a low-noise printed wiring board can be manufactured without changing the conventional manufacturing process. it can. Further, even in a multilayer substrate having six or more layers, noise can be reduced by dispersing the conductive material in an arbitrary region.

  The structure of the printed wiring board 100 is not limited to the above structure. For example, a structure without the signal wiring layer 1 and the dielectric layer 2 may be used. Moreover, the structure without any one of the thin films 4 and 6 may be sufficient. Furthermore, the thin films 4 and 6 need only have anisotropic conductivity in the direction perpendicular to the surface of the printed wiring board, and do not necessarily have a structure in which a conductive material is dispersed.

  FIG. 2 is a cross-sectional view for explaining the thin films 4a and 6a which are examples of the thin films 4 and 6 of FIG.

  As shown in FIG. 2, the thin films 4 a and 6 a have a structure including a plurality of substantially spherical metal particles 10 in a dielectric 11. The diameter of the metal particle 10 is set to be larger than the skin depth of the metal particle 10 at the maximum frequency of the signal flowing through the signal line.

  In this case, a substantial part (at least 60%) of the high-frequency current that tends to flow in the vicinity of the surfaces where the power supply layer 3 and the ground layer 7 face each other is bound by the metal particles 10. Further, the harmonic component of the high-frequency current is more effectively bound by the metal particles 10 (a proportion greater than 60%). As a result, the current flowing in the plane direction of the thin films 4a and 6a is significantly inhibited. As a result, it is possible to efficiently suppress electromagnetic radiation due to the high frequency current.

  The metal which comprises the metal particle 10 is copper, for example. In this case, if the maximum frequency component of the signal flowing through the signal line is, for example, 1 GHz, the diameter of the metal particles 10 may be 2 μm or more. As the dielectric 11, a dielectric adhesive can also be used. If the metal particles 10 are dispersed in the dielectric adhesive and the dielectric layer 5 and the ground layer 7 are adhered, the thin films 4a and 6a can be formed. In this case, it is not necessary to go through a step of bonding a prepreg material or the like in which a conductive material is dispersed in advance between the dielectric layer 5 and the power supply layer 3 or the ground layer 7 as the thin films 4a and 6a.

  The shape of the metal particles 10 is not limited to a spherical shape as long as the diameter of the metal particles 10 is larger than the skin depth. Moreover, the metal which comprises the metal particle 10 is not restricted to copper, You may use another metal.

  FIG. 3 is a cross-sectional view for explaining thin films 4b and 6b which are other examples of the thin films 4 and 6 of FIG. As shown in FIG. 3, the thin films 4 b and 6 b have a structure including a plurality of metal wires 12 made of a thin and short needle-like metal material in a dielectric 11. If the metal wire 12 is dispersed in the dielectric 11 and the substrate is formed by means such as heating, the thin films 4b and 6b can be formed.

  The length of the metal wire 12 is about the thickness of the thin films 4b and 6b. In this case, the electric charge can be moved in the direction perpendicular to the thin film surface, but electrical conduction can be ignored in the thin film surface direction. Thereby, the high-frequency current that tends to flow in the vicinity of the surfaces where the power supply layer 3 and the ground layer 7 of FIG. 1 face each other is bound to the metal wire 12 in the thin films 4b and 6b. Therefore, the current flowing in the surface direction of the thin films 4b and 6b is significantly inhibited. As a result, it is possible to efficiently suppress electromagnetic radiation due to the high frequency current. The thickness of the thin films 4b and 6b is preferably larger than the skin depth of the metal wire 12 at the maximum frequency of the signal flowing through the signal line.

  Next, simulation of the electromagnetic wave radiation preventing effect of the printed wiring board according to the present embodiment will be described.

  FIG. 4 is a diagram for explaining the effect of the printed wiring board according to the present embodiment. 4A is a cross-sectional view of the modeled printed wiring board 100a, and FIG. 4B is a bird's eye view of the modeled printed wiring board 100a.

  As shown in FIG. 4 (a), the modeled printed wiring board 100a has a dielectric layer 14 and a transmission line as a transmission line on a metal layer 13 as a transmission line for simple modeling of the printed wiring board 100 in FIG. The metal layer 15 has a laminated structure. Square-shaped metal 16 is embedded in stripes at equal intervals on the surface of the dielectric layer 14 on the metal layer 15 side. The thickness of the metal layers 13 and 15 is 25 μm, the thickness of the dielectric layer 14 is 100 μm, the dielectric constant of the dielectric layer 14 is 4.7, and the width and depth of the metal 16 is 25 μm. .

  FIG. 5 is a graph showing a result of FDTD (Finite-Difference Time Domain) method simulation performed on the modeled printed wiring board 100a of FIG. The vertical axis in FIG. 5 represents the transmission characteristic S21 (dB) of the modeled printed wiring board 100a, and the horizontal axis represents the frequency of the high-frequency current flowing through the signal line. An FDTD method simulation was performed with a mesh of 25 μm. As can be seen from FIG. 5, even with a model such as the modeled printed wiring board 100a of FIG. 4, high-frequency current is limited in a wide band and electromagnetic radiation is prevented. Therefore, it can be said that electromagnetic radiation can be prevented by finely dispersing the conductive material as the thin films 4 and 6 in FIG.

  FIG. 6 is a view showing a printed wiring board 100b according to the second embodiment of the present invention. 6A is a cross-sectional view of the printed wiring board 100b, and FIG. 6B is a bird's-eye view of the printed wiring board 100b.

  As shown in FIG. 6A, in the printed wiring board 100b, a power supply layer 22, a thin film 23, a dielectric layer 24, a thin film 25, a ground layer 26, and a dielectric layer 27 are sequentially laminated on a dielectric layer 21. Has a structure. As shown in FIG. 6B, conductive material dispersion regions 28 and 29 in which a conductive material is sparsely dispersed are formed at the ends of the thin films 23 and 25, respectively. The conductive substance dispersed regions 28 and 29 have anisotropic conductivity in the direction perpendicular to the printed wiring board surface.

  In this case, even when the electromagnetic radiation due to the vertical electric field with respect to the substrate surface becomes a problem at the end as in the case of the patch antenna, the electromagnetic radiation can be efficiently prevented. Further, even if the high-speed signal wiring is arranged in the layer between the power supply layer 22 and the ground layer 26 inside the conductive material dispersion regions 28 and 29, it is not affected by the conductive material dispersion regions 28 and 29. . Therefore, the signal integrity of the signal flowing through the high-speed signal wiring is not impaired.

  FIG. 7 is a view showing a printed wiring board 100c according to a third embodiment of the present invention. FIG. 7A is a cross-sectional view of the printed wiring board 100c, and FIG. 7B is a bird's-eye view of the printed wiring board 100c.

  As shown in FIG. 7A, the printed wiring board 100c has a structure in which a power supply layer 32, a dielectric layer 33, a thin film 34, a ground layer 35, and a dielectric layer 36 are sequentially laminated on a dielectric layer 31. Have. On the dielectric layer 36, digital elements 37 and 38 that operate at high speed are arranged. The thin film 34 includes an anisotropic conductive region 34a and a dielectric region 34b. A conductive substance is dispersed in the anisotropic conductive region 34a, and has anisotropic conductivity in a direction perpendicular to the surface of the printed wiring board. In the printed wiring board 100 c, similarly to the signal wiring board 100 of FIG. 1, electromagnetic radiation can be efficiently prevented by providing the anisotropic conductive region 34 a in the thin film 34.

  The digital element 37 and the digital element 38 are connected by a signal line 39 wired in the inner layer of the printed board 100c. The signal line 39 passes through the dielectric layer 33 in the dielectric layer 33 and below the dielectric region 34 b, the dielectric region 34 b, a through hole provided in the ground layer 35, and the dielectric layer 36. Thereby, the return current from the signal line 39 flowing in the ground layer 35 is not affected by the anisotropic conductive region 34a. As a result, the signal integrity of the signal flowing through the signal line 39 is not impaired.

  From the above, if the printed wiring board 100c according to the present embodiment is used, it is possible to efficiently prevent electromagnetic wave radiation due to a high-frequency current and not impair the signal integrity of the high-speed signal flowing through the inner layer.

  In this embodiment, a thin film having an anisotropic conductive region is not formed between the power supply layer 32 and the dielectric layer 33, but it may be formed.

  FIG. 8 is a view showing an image forming apparatus using the printed wiring board. In the figure, a document 42 placed on a document table 41 is R (red), G (green) by an image scanner having a color CCD sensor 43 via a scanning optical system including a light source and a scanning mirror. , B (blue) image signals. The R, G, B image signals read by the color CCD sensor 43 are fed into the image forming unit 45C for each color of Y (yellow), M (magenta), C (cyan), K (black) by the printer controller 44. , 45M, 45Y, and 45K ROS (Raster Output Scanner) 47C, 47M, 47Y, and 47K sequentially output image data of each color, and laser beams emitted from these ROS 47C, 47M, 47Y, and 47K in accordance with the image data However, the surface of each of the photosensitive drums 46C, 46M, 46Y, and 46K is scanned and exposed to form an electrostatic latent image. The electrostatic latent images formed on the photosensitive drums 46C, 46M, 46Y, and 46K are developed as toner images of C, M, Y, and K colors by the developing devices 48C, 48M, 48Y, and 48K, respectively. The printer controller unit 44 controls the entire image processing apparatus. The printer controller unit 44 includes a CPU, a memory, an image processing unit, an interface unit, and the like provided on the printed wiring board.

  Since the image processing apparatus uses the printed wiring board, electromagnetic waves radiated inside the apparatus are suppressed and can operate with low power consumption. The image forming apparatus of the present invention is not limited to the above-described configuration, and includes an apparatus such as a printer that does not have an optical scanning system.

It is sectional drawing of the printed wiring board by 1st Example of this invention. It is sectional drawing for demonstrating an example of the thin film of FIG. It is sectional drawing for demonstrating the other example of the thin film of FIG. (A) is sectional drawing of a modeled printed wiring board, (b) is a bird's-eye view of a modeled printed wiring board. It is a graph which shows the result of having performed the FDTD method simulation about the modeled printed wiring board of FIG. It is a figure which shows the printed wiring board by 2nd Example of this invention. (A) is sectional drawing of a printed wiring board, (b) is a bird's-eye view of a printed wiring board. It is a figure which shows the image forming apparatus using the printed wiring board of this invention.

Explanation of symbols

3, 22, 32 Power supply layer 4, 6 Thin film 7, 26, 35 Ground layer 10 Metal particle 12 Metal wire 28, 29 Conductive material dispersed region 34a Anisotropic conductive region 100, 100b, 100c Printed wiring board 100a Modeled print Wiring board

Claims (8)

A printed wiring board in which a first dielectric layer, a ground layer, a second dielectric layer, and a signal wiring layer are sequentially laminated on a power supply layer,
A thin film is formed between one or both of the power source layer and the first dielectric layer and between the first dielectric layer and the ground layer;
At least a part of the thin film has anisotropic conductivity in a direction perpendicular to the printed circuit board surface. The printed wiring board according to claim 1, wherein an end of the thin film has the anisotropic conductivity. The printed wiring board according to claim 1, wherein the entire thin film has the anisotropic conductivity. The printed wiring board according to claim 1, wherein the thin film contains a conductive substance. The conductive material includes metal particles,
The printed wiring board according to claim 4, wherein a diameter of the metal particles is larger than a skin depth of the metal particles at a maximum frequency of a signal flowing through the signal line. The conductive material includes a metal wire,
The printed wiring board according to claim 4, wherein the thickness of the thin film is larger than a skin depth of the metal line at a maximum frequency of a signal flowing through the signal line. The printed wiring board according to claim 4, wherein the thin film is an adhesive that is cured after the conductive material is dispersed. An image forming apparatus comprising: an image forming unit; and a controller that controls the image forming unit, wherein the controller includes the printed wiring board according to claim 1.

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