Printed Circuit Board

Abstract

To prevent static electricity from entering a ground region on which a connector is mounted.SOLUTION: A front layer of a printed circuit board 100 includes: frame ground regions 102a, 102b on which connectors 202, 203 to be connected with external apparatuses or communication cables are mounted and which are connected with a ground; a signal ground region 101 which is separated from the frame ground regions 102a, 102b at the front layer, on which electronic devices 200, 201 configured to receive signals from the connectors 202, 203 are mounted, and which is connected with the ground; and a static electricity removal ground region 103 separated from the frame ground regions 102a, 102b and the signal ground region 101 at the front layer, situated outside the frame ground regions 102a, 102b, and connected with the ground.SELECTED DRAWING: Figure 3

Description

[Technical field]

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

[0002] An electronic device has a built-in printed circuit board (PCB), which is fixed to a housing, etc. Passive components such as resistors and capacitors, and active components such as ICs (Integrated Circuits) are mounted on the printed circuit board.

[0003] In recent years, the size of printed circuit boards has been shrinking due to the trend toward miniaturization of electronic devices. In addition, ICs mounted on printed circuit boards are becoming more miniaturized and highly integrated in order to reduce power consumption and improve performance.

[0004] As board sizes become smaller, the area of ​​the ground that serves as the reference potential on printed circuit boards becomes smaller, making it difficult for static electricity and other noise to escape and making it more difficult to stabilize voltage levels. In addition, as ICs become smaller and more highly integrated, their electrostatic resistance has decreased, making them more susceptible to malfunctions and destruction due to external noise such as static electricity.

[0005] In the control board 5 described in Patent Document 1, a frame ground area 53 and a signal ground area 52 are provided with an insulation distance ΔL2 between them. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2018-117131 A Summary of the Invention [Problem to be solved by the invention]

[0007] In Patent Document 1, since the frame ground area 53 and the signal ground area 52 are separated by an insulation distance ΔL2, it is possible to suppress the propagation of signals from the frame ground area 53 to the signal ground area 52. However, it is not possible to suppress the intrusion of static electricity into the frame ground area 53. For example, when a connector for connecting a cable or an external device is mounted in the frame ground area 53, static electricity charged on the hand of a person holding the cable or the external device, the cable, or the external device will intrude into the frame ground area 53. In Patent Document 1, it is possible to suppress the propagation of signals from the frame ground area 53 to the signal ground area 52, but it is not possible to prohibit the propagation of all static electricity. Therefore, it is better to suppress the intrusion of static electricity into the frame ground area 53 to suppress the intrusion of static electricity into the signal ground area 52.

[0008] Therefore, the present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a printed circuit board that can suppress the intrusion of static electricity into the ground area where the connector is mounted. [Means for solving the problem]

[0009] In order to achieve the above-mentioned object, the printed circuit board of the present invention has a surface layer including a first ground area on which a connector to which an external device or a communication cable is connected is mounted and which is connected to ground, a second ground area on the surface layer separated from the first ground area, on which an electronic device that receives a signal from the connector is mounted and which is connected to ground, and a third ground area on the surface layer separated from the first ground area and the second ground area, provided outside the first ground area, and connected to ground. Effect of the Invention

[0010] According to the present invention, it is possible to prevent a return from the power saving state due to information held in the second control means immediately after transition to the power saving state. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 illustrates a structure of an image forming apparatus. [Diagram 2] FIG. 2 is a block diagram showing a controller. [Diagram 3] FIG. 2 is a diagram showing details of a printed circuit board. [Figure 4] FIG. 2 is an enlarged view of a portion of the printed circuit board. [Diagram 5] FIG. 4 is a cross-sectional view taken along line AA' in FIG. [Figure 6] FIG. 1 is a diagram showing paths along which static electricity propagates. [Figure 7] 11 is a diagram showing the relationship between the resonance frequency and gain of a signal layer and a ground layer. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, the embodiments of the present invention will be described with reference to the drawings. Note that the following embodiments do not limit the invention according to the claims, and all of the combinations of features described in the embodiments are not necessarily essential to the solution of the invention. EXAMPLES

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0014] <Overall configuration of image forming apparatus> 1 is a diagram showing the structure of an image forming apparatus according to a first embodiment of the present invention. As shown in Fig. 1, an image forming apparatus 10 includes a scanner unit 12 which is an image input device, and a printer unit 13 which is an image output device.

[0015] The scanner unit 12 is a device that reads an image formed on a document and acquires image data. The reflected light of light irradiated onto the image formed on the document is input to a CCD, and the image information is converted into an electrical signal. This electrical signal is converted into a luminance signal consisting of R, G, and B colors, and is output to the controller 11, which will be described later.

[0016] The originals set on the tray 1250 of the scanner unit 12 are fed one by one by the original feeder 1260 to a reading position of the optical unit 1213 on the platen glass 1211. The originals read by the optical unit 1213 are discharged to a discharge tray 1219. Light irradiated from a lamp 1212 of the optical unit 1213 and reflected by the original is input to a CCD image sensor 1218 via mirrors 1214, 1215, 1216 and a lens 1217. The original may be read by scanning a carriage on which the optical unit 1213 is mounted with respect to the original placed on the platen glass 1211, instead of the automatic feeding method by the original feeder 1260. In the first embodiment, the image forming apparatus 10 capable of monochrome printing is described, but the image forming apparatus 10 may be capable of color printing.

[0017] The printer unit 13 is a device that forms an image on paper using input image data. Note that the image forming method of the printer unit 13 in this embodiment is an electrophotographic method using a photosensitive drum or a photosensitive belt, but the present invention is not limited to this. For example, the printer unit 13 may be an inkjet method that ejects ink from a minute nozzle array to print on paper.

[0018] The image forming apparatus 10 also has a plurality of paper cassettes 1311, 1312, 1313, and 1314 that store paper on which an image is formed by the printer unit 13, and a manual feed tray 1315. A laser driver 1321 of the printer unit 13 drives a laser emitting unit 1322. The laser driver 1321 causes the laser emitting unit 1322 to emit a laser beam corresponding to image data output from the controller 11. The laser beam is irradiated onto a photosensitive drum 1323, and a latent image corresponding to the laser beam is formed on the photosensitive drum 1323. A developer is applied to the latent image portion of the photosensitive drum 1323 by a developing unit 1324. A transfer unit 1325 transfers the developer applied to the photosensitive drum 1323 to a recording paper that has passed through a conveying path 1331. The recording paper on which the developer is applied is conveyed to a fixing unit 1327 by a conveying belt 1326. The fixing device 1327 fixes the developer to the recording paper by heat and pressure. The recording paper that has passed through the fixing device 1327 passes through a conveying path 1335 and a conveying path 1334, and is discharged to a paper discharge tray 1328. Alternatively, when the printed surface is to be inverted and discharged to the paper discharge tray 1328, the recording is led to a conveying path 1336 and a conveying path 1338, and then passes through a conveying path 1337 and a conveying path 1334.

[0019] When double-sided printing is performed, the recording paper is guided from the fixing unit 1327 to a conveying path 1336, and then to a conveying path 1333 by a flapper 1329. The recording paper is then conveyed in the reverse direction, and is guided by the flapper 1329 to a conveying path 1338 and a re-feed conveying path 1332. The recording paper guided to the re-feed conveying path 1332 passes through a conveying path 1331 and is fed to the transfer unit 1325.

[0020] <Explanation of the Controller 11 of the Image Forming Apparatus 10> 2 is a block diagram showing a controller that controls the entire operation of the image forming apparatus 10. The controller 11 that controls the entire operation of the image forming apparatus 10 will be described in detail with reference to FIG.

[0021] As shown in FIG. 2, the controller 11 is electrically connected to the scanner unit 12, the printer unit 13, and the operation unit 12. Each device of the controller 11 in this embodiment is mounted on one printed circuit board. Each device of the controller 11 may be separately mounted on two or more printed circuit boards. For example, the controller 11 may be configured by a printed circuit board on which the operation unit I / F 1105 and the human sensor 1110 are mounted, and a printed circuit board on which the CPU 1101 and the like are mounted. This controller 11 includes the CPU 1101, the RAM 1102, the ROM 1103, the operation unit I / F 1105, the LAN controller 1106, the human body detection sensor 1110, the paper detection sensor 1112, and the power supply control unit 1114. The CPU 1101, RAM 1102, ROM 1103, operation unit I / F 1105, LAN controller 1106, human body detection sensor 1110, paper detection sensor 1112, and power supply control unit 1114 are connected to a system bus 1107. The controller 11 also includes a HDD 1104, an image processing unit 1109, a scanner I / F 1111, and a printer I / F 1113. The HDD 1104, the image processing unit 1109, the scanner I / F 1111, and the printer I / F 1113 are connected to an image bus 1108.

[0022] The CPU 1101 performs overall control of access to various connected devices based on a control program stored in a ROM 1103 , and also performs overall control of various processes executed by the controller 11 .

[0023] The RAM 1102 is a system work memory for the operation of the CPU 1101. The RAM 1102 is also a memory for temporarily storing image data. The RAM 1102 has an SRAM capable of retaining stored contents even when the power is off, and a DRAM from which stored contents are erased when the power is off. The ROM 1103 stores a boot program for the device, etc. The HDD 1104 is a hard disk drive, and stores programs for controlling the image forming apparatus 10 and image data.

[0024] The operation unit I / F 1105 is an interface unit for connecting the system bus 1107 and the operation unit 12. This operation unit I / F 1105 receives image data to be displayed on the operation unit 12 from the system bus 1107 and outputs it to the operation unit 12, and also outputs information input from the operation unit 12 to the system bus 1107.

[0025] The LAN controller 1106 controls the input and output of information between the image forming apparatus 10 and an external device 50 connected to the network 60 .

[0026] The human body detection sensor 1110 is an infrared sensor array in which infrared sensors that receive infrared rays are arranged in a matrix. The human body detection sensor 1110 detects the approach of a person to the image forming apparatus 10 by receiving infrared rays emitted from a person or the like. Note that, in this embodiment, an example in which the human body detection sensor 1110 detects a person will be described, but any object that emits infrared rays can be detected by the human body detection sensor 1110. Note that the human body detection sensor is not limited to the infrared sensor described above. Any device that can detect the approach of an object to the image forming apparatus 10 (such as an optical sensor that detects light, a strain sensor that deforms due to physical force, a magnetic sensor that detects magnetism, or a temperature sensor that detects temperature) other than an infrared sensor may be used.

[0027] A paper detection sensor 1112 detects that paper has been set on the manual feed tray 1315 .

[0028] The power supply control unit 1114 controls the power supply to each unit of the image forming apparatus 10. The power supply control unit 1114 will be described in detail later.

[0029] An image bus 1108 is a transmission path for exchanging image data, and is composed of a PCI bus, IEEE1394 or other bus.

[0030] An image processing unit 1109 is for performing image processing, reading out image data stored in the RAM 1102, and performing image processing such as enlargement or reduction of JPEG, JBIG, etc., and color adjustment.

[0031] The scanner unit 12 has a scanner control unit 1201 and a scanner driving unit 1202. The scanner driving unit 1202 is a device that physically drives the scanner unit 12, including a paper transport motor for transporting a document set on a tray 1250 to a reading position of the scanner unit 12. The scanner control unit 1201 controls the operation of the scanner driving unit 1202. The scanner control unit 1201 receives setting information set by a user when performing scanner processing through communication with the CPU 1101, and controls the operation of the scanner driving unit 1202 based on the setting information.

[0032] The printer unit 13 has a printer control unit 1301 and a printer driving unit 1302. The printer driving unit 1302 is a device that physically drives a motor that rotates a photosensitive drum 1323, a motor that rotates a fixing unit 1327, a paper conveying motor, etc. The printer control unit 1301 controls the operation of the printer driving unit 1302. The printer control unit 1301 receives setting information set by a user when performing print processing through communication with the CPU 1101, and controls the operation of the printer driving unit 1302 based on the setting information.

[0033] <Explanation of printed circuit board> 3 and 4 are diagrams showing the details of the printed circuit board. The printed circuit board 100 is fixed to a metallic housing 300 by metallic screws 20 to 24. An IC 200 and an IC 201 are mounted on the printed circuit board 100. The IC 200 is the above-mentioned CPU 1101, and the IC 201 is the above-mentioned LAN controller 1106. The printed circuit board 100 is mounted with a connector 202 to which an external device or a cable (for example, a USB device or a USB cable) is connected, and a connector 203 to which a cable (for example, an Ethernet cable) is connected. The IC 200 is connected to the connector 202 via signals 110, 111, 112, and 113. The IC 201 is connected to the connector 203 via signals 114 and 115. The IC 200 can communicate with an external device via the connector 202. The IC 201 can communicate with an external device via the connector 203. The signals 110 to 115 may transmit a clock signal, may transmit a data signal, may supply power, or may be connected to the ground. In this embodiment, the connector 202 is a 4-pin (pins 400, 401, 402, 403) connector, and the connector 203 is a 2-pin (pins 405, 405) connector. The number of pins of the connectors 202 and 203 is not limited to 4 pins or 2 pins.

[0034] The IC200 may be a PGA (Prigrammable Gate Array) or an ASIC (Application Specific Integrated Circuit). The power supply control unit 1114 is a PGA, and the image processing unit 1109 is an ASIC. The IC200 and IC201 are highly integrated, and the semiconductor process thereof is on the order of nanometers. The smaller the semiconductor process, the lower the electrostatic resistance, and therefore the higher the probability of malfunction due to external noise such as static electricity.

[0035] The connector 202 is fixed to the printed circuit board 100 by lock pins 406 and 407. The connector 203 is fixed to the printed circuit board 100 by lock pins 408 and 409. If the connector 202 is a surface mounted type (SMD: Surface Mounted Device) connector, the lock pins 406 and 407 are joined to the surface layer (signal layer 30) of the printed circuit board 100 by solder. If the connector 202 is an insertion mounted component (DIP: Dual In-line Package), the lock pins 406 and 407 penetrate from the surface layer (signal layer 30) to the back layer (signal layer 36) of the printed circuit board 100, and are also joined by solder. The same applies to the connector 203, so a description thereof will be omitted.

[0036] The surface layer (signal layer 30) of the printed circuit board 100 of this embodiment has three ground areas separated by slits. The three ground areas are a signal ground area 101, a frame ground area 102b, and a ground area 103 for removing static electricity.

[0037] The signal ground area 101 is an area in which IC200 and IC201 that receive signals from connectors 202 and 203 are mounted. This signal ground area 101 is connected to the ground via an inner ground layer 32. The potential of the inner ground layer 32 serves as the reference potential of signals 110 to 115 and the reference potential of the power supply supplied to IC200 and IC201. This signal ground area 101 is provided outside frame ground areas 102a and 102b.

[0038] The frame ground area 102a has the connector 202 mounted thereon and is electrically connected to the metal housing 300. The frame ground area 102a is connected to the metal frame of the connector 202.

[0039] The frame ground area 102b has a connector 203 mounted thereon and is electrically connected to the metal housing 300. The frame ground area 102b is connected to the metal frame of the connector 203.

[0040] In this embodiment, in addition to the signal ground area 101, the frame ground area 102a, and the frame ground area 102b, a ground area 103 for removing static electricity is formed on the signal layer 30 of the printed circuit board 100. The ground area 103 for removing static electricity is provided on the periphery of the printed circuit board 100. The ground area 103 for removing static electricity is formed in an uninterrupted ring shape. The ground area 103 for removing static electricity is provided so as to surround the signal ground area 100 without interruption. The ground area 103 for removing static electricity is provided so as to surround the frame ground area 102a without interruption. The ground area 103 for removing static electricity is provided so as to surround the frame ground area 102b without interruption. In this embodiment, the ground area 103 for removing static electricity is provided so as to surround the signal ground area 101 without interruption.

[0041] The ground area 103 for static electricity evacuation is provided outside the frame ground area 102a at a position corresponding to at least an insertion opening 202a through which an external device or a cable of the connector 202 is inserted. The ground area 103 for static electricity evacuation is provided outside the frame ground area 102b at a position corresponding to at least an insertion opening 203a through which a cable of the connector 203 is inserted.

[0042] The ground area 103 for discharging static electricity is connected to the ground layer 32. The frame ground area 102a, the frame ground area 102b, and the signal ground area 101 are also connected to the ground layer 32. In other words, the ground area 103 for discharging static electricity is connected to the frame ground area 102a, the frame ground area 102b, and the signal ground area 101 in the ground layer 32.

[0043] The static electricity escape ground area 103 has through holes through which the screws 20 to 23 pass. The screws 20 to 23 fix the printed circuit board 100 to the metal housing 300. The through holes may be cutouts. The screws 20 to 23 are made of metal, and are connected to the ground when the printed circuit board 100 is fixed to the metal housing 300.

[0044] The ground area 103 for removing static electricity is completely separated from the frame ground area 102a, the frame ground area 102b, and the signal ground area 101 by a slit 502 in the signal layer 30. The slit 502 is provided only in the signal layer 30 and does not reach the ground layer 32.

[0045] The static electricity escape ground area 103 is provided on the signal layer 30 and the signal layer 36. The static electricity escape ground area 103 on the signal layer 30 and the static electricity escape ground area 103 on the signal layer 36 are provided on the periphery of the printed circuit board 100. In this embodiment, no frame ground area is present on the signal layer 36. Naturally, a frame ground area may be provided on the signal layer 36.

[0046] In this embodiment, a signal ground area 101 is disposed between the static electricity escape ground area 103 and the frame ground area 102a. Also, a signal ground area 101 is disposed between the static electricity escape ground area 103 and the frame ground area 102b. Note that the signal ground area 101 does not have to be provided between the static electricity escape ground area 103 and the frame ground area 102a. Also, the signal ground area 101 does not have to be provided between the static electricity escape ground area 103 and the frame ground area 102b.

[0047] A via 107 is formed in the ground area 103 for removing static electricity, and the ground area 103 for removing static electricity is connected to the ground layer 32 .

[0048] The slits 502 prevent static electricity that has entered the peripheral portion of the printed circuit board 100 from propagating to the signal ground area 101 and the frame ground areas 102a and 102. The static electricity that has entered the peripheral portion of the printed circuit board 100 propagates to the metal housing 300 through the vias 107 and the screws 20 to 23 in the ground area 103 for static electricity evacuation. Static electricity that is generated by discharge from a person when inserting or removing a device or cable into or from the connector 202 or the connector 203 can be prevented from penetrating inside the ground area 103 for static electricity evacuation. The static electricity discharged around the connector 202 or the connector 203 can be prevented from penetrating into the active elements (ICs 200 and 201) that operate at high frequencies and are mounted on the printed circuit board 100.

[0049] The frame ground area 102a is connected to the ground area 103 for static electricity evacuation of the ground layer 32 and the signal layer 36 through the vias 103 from the signal layer 30. Static electricity discharged to the frame of the connector 202 is propagated to the frame ground area 102a through the lock pins 406 and 407. The static electricity is then propagated through the vias 103 to the ground area 103 for static electricity evacuation of the signal layer 36, and escapes to the metal housing 300.

[0050] Moreover, the frame ground area 102a is separated from the signal ground area 101 by a slit 500. Moreover, the frame ground area 102b is separated from the signal ground area 101 by a slit 501. Moreover, in this embodiment, the static electricity escape ground area 103 and the frame ground area 102a are separated by the slits 502 and 500. Moreover, the static electricity escape ground area 103 and the frame ground area 102b are separated by the slits 502 and 501. Moreover, the static electricity escape ground area 103 and the signal ground area 101 are separated by the slit 502. The slit is a groove for physically separating the conductor (copper film) constituting the signal layer 30 of the printed circuit board 100 and making it electrically non-conductive. That is, in the signal layer 30, the signal ground 100 and the frame ground 101 are separated by the slit 500. In addition, in the signal layer 30 , the signal ground 100 and the frame ground 102 are separated by a slit 501 .

[0051] The connector 202 is connected to the ground layer 32 of the printed circuit board 100 through the via 103. The via in this embodiment is a through via. A through via is a hole that penetrates from the front layer to the back layer. A through via is connected to multiple layers by drilling a hole from the front layer to the back layer and coating the hole with a conductor. Pins 400 to 403 of the connector 202 are connected to the outside of the frame ground area 102a, that is, to the signal ground 100. This is to prevent signals 110 to 113 from straddling two different ground areas.

[0052] Fig. 5 is a cross-sectional view of the printed circuit board taken along the line AA' in Fig. 3. In Fig. 5, the shaded area is the signal ground area, the vertical line area is the frame ground area, and the dotted area is the power supply layer.

[0053] The printed circuit board 100 of this embodiment has a four-layer structure. The number of layers of the printed circuit board 100 is not limited to four. The printed circuit board 100 may have six or eight layers.

[0054] The signal layer 30 and the signal layer 36 are provided to transmit signals output from the IC 200 or the IC 201 to other ICs, etc. The signals output from the IC 200 or the IC 201 may be transmitted to the signal layer 36 or may be transmitted within the signal layer 30.

[0055] The above-mentioned signals 110-115 and the like are wired on the signal layer 30. In addition to the signal lines 110-115 and the like, a power plane and ground areas 101-103 are provided on the signal layer 30. A frame ground area 102a provided on the signal layer 30 is connected to the ground layer 32 and the signal ground 100 of the signal layer 36 by a via 103.

[0056] The ground layer 32 stabilizes the voltage level of the ground. In this embodiment, the entire ground layer 32 serves as a signal ground area 101.

[0057] The power supply layer 34 is provided with planes of power supplies of multiple systems used by the IC 200, the IC 201, the connector 202, and the connector 203. The power supply plane of the power supply layer 34 supplies power to the IC mounted on the signal layer 30 through the via 105. The via 105 has the same potential as the power supply plane, and is therefore not connected to the signal layer 30, the ground layer 32, or the ground of the signal layer 36. The via 103 is not connected to the power supply plane of the power supply layer 34.

[0058] The material of each layer is a conductor such as copper. In addition, prepregs 31, 35, and a core material 33 are arranged between each layer. Prepregs 31 and 35 are base materials made by impregnating glass cloth with a resin such as epoxy and semi-hardening it, and are used for insulation between each layer when the copper and core material 33 of each layer are layered to form the printed circuit board 100.

[0059] The screws 20 are fixed to the metal housing 300 .

[0060] When inserting or unplugging a cable or the like into connector 202 or 203, static electricity is discharged from the charged human body, device, cable, etc., and there is a possibility that static electricity may enter the frame of connector 202 or 203 that it comes into contact with, or signal 110 wired from connector 202 or 203, etc.

[0061] FIG. 6 is a diagram showing the path along which static electricity propagates.

[0062] When a device or cable is inserted or removed from connector 202 or connector 203, due to the close physical distance, there is a high possibility that a charged human body or device will discharge to ground area 103 for removing static electricity, which is provided on the insertion opening side of connector 202. The static electricity discharged to ground area 103 for removing static electricity propagates through vias 107 to ground layer 32 and signal layer 36. The static electricity then propagates through screws 20 to metal housing 300 (path 2000).

[0063] Furthermore, static electricity that has entered the frame of connector 202 propagates through lock pins 406 and 407 to frame ground area 102a, and then through vias 103 to ground layer 32 and signal layer 36. Since vias 103 are connected to ground area 103 for static electricity evacuation in signal layer 36, static electricity escapes to metal housing 300 through screws 20. (Path 2001) It should be noted that noise that has entered the signals 110 to 113 connected to the connector 202 may reach the IC 200. (Path 2002) There is a path (path 2003) through which static electricity that has entered the ground area 103 for static electricity evacuation and the frame ground 101 propagates to the signal ground area 101 via the parasitic capacitance formed in the slits 500 and 502. In this embodiment, the ground area 103 for static electricity evacuation is provided on the outside of the connector 202, and further, two slits 500 and 502 are formed up to the signal ground area 101, so that static electricity is less likely to propagate to the signal connector.

[0064] As shown in Fig. 7, the signal layer 30 and the ground layer 32 of the printed circuit board 100 have different frequencies that tend to vibrate. This is because the signal layer 30 has three ground areas separated by slits, whereas the ground layer 32 does not have the above-mentioned slits, and the shapes of the signal layer 30 and the ground layer 32 are significantly different. Even if the static electricity propagated through the path 2003 causes a resonance phenomenon in the signal ground area 101 of the signal layer 30, the ground layer 32 is less likely to cause a resonance phenomenon of the same intensity as that of the signal layer 30. Therefore, the static electricity propagated to the signal layer 30 attenuates based on the frequency characteristics as it propagates to the ground layer 32 and the signal layer 36. Therefore, it becomes less likely to be superimposed as noise as it propagates to the inner layers.

[0065] In this embodiment, the slits 502 allow the ground area 103 for static electricity evacuation, which is separated from the signal ground area 101, the frame ground 101 area, and the frame ground area 102b, to be provided on the periphery of the printed circuit board 100. This allows static electricity to concentrate on the ground area 103 for static electricity evacuation, which is on the periphery of the printed circuit board 100. This allows static electricity charged to people, cables, and devices to escape to the metal housing 300.

[0066] In addition, by making the shapes of the surface signal layer 30 and the inner ground layer 32 different, the resonance frequency can be shifted, and the static electricity propagating to the inner layer is attenuated. As a result, the electrostatic resistance of electronic devices such as printing devices incorporating the printed circuit board 100 is improved, and the possibility of malfunction of the mounted ICs 200 and the like is reduced.

[0067] <Modification> In the above embodiment, an example in which the printed circuit board of the present invention is mounted on an image forming apparatus has been described, but the apparatus in which the printed circuit board of the present invention is mounted is not limited to an image forming apparatus. For example, the printed circuit board of the present invention can be mounted on various devices such as a notebook PC, a tablet PC, a desktop PC, a smartphone, an automobile, an air conditioner, a gaming machine, and a robot. [Explanation of symbols]

[0068] 1. Image forming device 100 Printed Circuit Boards 101 Signal Ground Area 102a Frame ground area 102b Frame ground area 103 Ground area for static electricity evacuation 200 IC 201 IC 202 Connector 203 Connector

Claims

1. The surface of the printed circuit board is a first ground area on which a connector to be connected to an external device or a communication cable is mounted and which is connected to ground; a second ground area on the surface layer, the second ground area being separated from the first ground area, the second ground area being connected to ground and having an electronic device mounted thereon that receives a signal from the connector; a third ground area that is separated from the first ground area and the second ground area on the surface layer, is provided outside the first ground area, and is connected to ground.

2. 2. The printed circuit board according to claim 1, wherein the third ground area is provided so as to surround the first ground area.

3. 3. The printed circuit board according to claim 2, wherein the third ground area is provided so as to surround the first ground area without interruption.

4. 4. The printed circuit board according to claim 1, wherein the third ground area is provided so as to surround the second ground area.

5. 5. The printed circuit board according to claim 4, wherein the third ground area is provided so as to surround the second ground area without interruption.

6. 6. The printed circuit board according to claim 1, wherein the second ground area is provided outside the first ground area.

7. 7. The printed circuit board according to claim 1, wherein the second ground area is provided outside the first ground area, and the third ground area is provided outside the second ground area.

8. The printed circuit board according to any one of claims 1 to 7, characterized in that the third ground area is provided outside the first ground area and at a position corresponding to at least an insertion port of the connector into which the external device and the communication cable are inserted.

9. The surface layer is 9. The printed circuit board according to claim 1, further comprising a fourth ground area on the surface layer, the fourth ground area being separated from the first ground area, the second ground area, and the third ground area, the fourth ground area being mounted with another connector to which an external device or a communication cable is connected, and being connected to ground.

10. 10. The printed circuit board according to claim 1, wherein the printed circuit board is a multi-layer printed circuit board having at least a signal layer, a power layer, and a ground layer.

11. the first ground area, the second ground area, and the third ground area are connected in the ground layer; The printed circuit board according to claim 10 .

12. 12. The printed circuit board according to claim 1, wherein the first ground area is connected to a metallic housing of the connector.

13. 13. The printed circuit board according to claim 1, wherein the third ground area has a hole or a notch through which a fixing member for fixing the printed circuit board to a housing passes.

14. The fixing member and the housing are made of metal.

14. The printed circuit board according to claim 13.

15. 15. The printed circuit board according to claim 1, wherein the printed circuit board is a printed circuit board for a printing device.

16. A printed circuit board according to any one of claims 1 to 15; A printing device comprising: a printing means for printing an image on a sheet of paper.

Images