Printed circuit board and printing device

Abstract

Printed circuit board (100) having a front layer (30) comprising: a first ground region (102a, 102b) to which a connecting device (202, 203) to be connected to an external device or a communication cable is attached and which is connected to a ground; a second ground region (101) separated from the first ground region (102a, 102b) at the front layer (30), to which an electronic device (200, 201) configured to receive a signal from the connecting device (202, 203) is attached and which is connected to ground; and a third mass region (103) separated from the first mass region (102a, 102b) and the second mass region (101) at the front layer (30), located outside the first mass region (102a, 102b) and connected to the mass wherein the third mass region (103) is accommodated to surround the first mass region (102a, 102b) without interruption, wherein the printed circuit board (100) is a multi-layer printed circuit board comprising at least a signal layer (30) formed by the front layer (30), a power layer (34), and a ground layer (32). wherein the first mass region (102a, 102b), the second mass region (101) and the third mass region (103) are connected to the mass layer (32).

Description

BACKGROUND OF THE INVENTIONField of the InventionThe present disclosure relates to printed circuit boards and printing devices.Description of Related ArtAn electronic device includes a built-in printed circuit board (PCB) fixed to a housing. Passive components such as a resistor and a capacitor, and active components such as an integrated circuit (IC) are mounted on the printed circuit board.Recently, the sizes of printed circuit boards have been reduced due to an effect of size reduction of electronic devices. Further, downsizing and high integration of ICs to be mounted on printed circuit boards have been developed to reduce power consumption and improve performance.As a result of board size reduction, the area of a ground to be a reference potential of a printed circuit board is reduced, noise such as static electricity becomes difficult to leak, and a voltage level becomes difficult to stabilize. Further, as a result of downsizing and high integration of ICs, antistatic properties are decreased, and erroneous operations and damage resulting from disturbance noise such as static electricity often occur.Japanese Patent Laid-Open No. JP 2018-117 131 A discusses a control board 5 in which a frame ground region 53 and a signal ground region 52 are housed with an isolation distance ΔL2 therebetween.In Japanese Patent Laid-Open No. JP 2018-117 131 A, since the frame ground region 53 and the signal ground region 52 are separated by the isolation distance ΔL 2, signal transmission from the frame ground region 53 to the signal ground region 52 is prevented. However, it is difficult to prevent static electricity from entering the frame mass region 53. For example, in a case where a connector to be connected to a cable or an external device is attached to the frame ground region 53, static electricity charged on the cable or the external device by a hand of a person holding the cable or the external device enters the frame ground region 53. In Japanese Patent Laid-Open No. JP 2018-117 131 A prevents signal transmission from the frame ground region 53 to the signal ground region 52, but it is difficult to prevent transmission of all static electricity. Thus, when intrusion of static electricity into the frame ground region 53 is prevented, intrusion of static electricity into the signal ground region 52 is also prevented.The document JP 2014-36 138 A describes a printed circuit board in which the propagation of electromagnetic extraneous noise (e.g. electrostatic noise) to circuit components is reduced. The printed circuit board includes: a main frame grounding unit connected to an external interface connector mounting wiring portion to which an external interface connector is mounted; a protective frame grounding wiring disposed to oppose the main frame grounding unit with a space therebetween; and a circuit body having a circuit component mounted thereon and spaced from the external interface connector mounting wiring portion, a main frame grounding wiring, and the protective frame grounding wiring. The main frame grounding unit and the guard frame grounding wiring each include a grounding portion connected to a stable potential.Document US 2019 / 0 223 287 A1 describes an in-vehicle electronic device. A fourth-layer outer frame protection pattern of a multilayer printed circuit board accommodated in a conductive base and a non-conductive cover is in contact with an inner surface of the base via a selection layer and is connected to a second-layer planar ground pattern via a coupling capacitor, outer peripheral portions of respective layer patterns including first-layer and third-layer ring ground patterns are overlapped with each other, and the planar ground pattern is wire-connected to a reference ground point of a vehicle body. When the base is conductively attached to the vehicle body, a selection layer is a solder resist film, and when it is non-conductively attached, the selection layer is a solder film so that the planar ground pattern does not conduct with the base at the time of short-circuit abnormality of the coupling capacitor.SUMMARYIt is an object of the invention to solve the above-described problem, to provide a printed circuit board configured to prevent static electricity from entering a ground region to which a connector is attached.This object is achieved by a printed circuit board according to claims 1 and 2. There is further provided a printing apparatus according to claim 11. Advantageous further developments are specified in the dependent patent claims.Further features of the present disclosure will become apparent from the following description of exemplary embodiments with reference to the accompanying drawings.BRIEF DESCRIPTION OF THE DRAWINGFIG. 1 illustrates a configuration of an image forming apparatus. FIG. 2 is a block diagram illustrating a control device. FIG. 3 illustrates a printed circuit board in detail. FIG. 4A is an enlarged view of a portion of a printed circuit board. Fig. 4B shows an enlarged view of another portion of the printed circuit board. FIG. 5 is a cross-sectional view along A-A' specified in FIG. 3. FIG. 6 illustrates a static electricity transmission path. FIG. 7 illustrates a relationship between a resonant frequency of a signal layer and a gain, and a relationship between a resonant frequency of a ground layer and a gain.DESCRIPTION OF THE EMBODIMENTSIt should be noted that the following embodiments are merely for illustrative purposes and are not intended to limit the scope of the claimed invention, and that not every combination disclosed in the embodiments is always essential for a technical solution of the present disclosure. The present invention is also not limited to the configurations shown in the drawings. Each of the embodiments of the present invention described below may be implemented alone or as a combination of a plurality of the embodiments. Features of different exemplary embodiments can likewise be combined where necessary or where the combination of elements or features from individual exemplary embodiments is advantageous in a single exemplary embodiment.[First Embodiment]Embodiments of the present disclosure will be described below with reference to the drawings.< Configuration of Image Forming Apparatus>FIG. 1 illustrates a configuration of an image forming apparatus according to a first embodiment of the present disclosure. As illustrated in FIG. 1, an image forming apparatus 10 includes a sensing unit 12 and a printer unit 13. the sensing unit 12 is an image input device, and the printer unit 13 is an image output device.The sensing unit 12 is a device configured to read an image formed on a document and acquire image data. A reflection light of a light with which an image formed on a document is irradiated is input to a charge coupled device (CCD) image sensor, so that information about the image is converted into an electric signal. The electric signal is converted into luminance signals R, G and B, and the luminance signals R, G and B are output to a controller 11 which will be described below with reference to Fig. 2.Documents set on a tray 1250 of the scanning unit 12 are fed one by one by a document feeder 1260 to a reading position of an optical unit 1213 on an original glass 1211. Then, each document read by the optical unit 1213 is discharged onto a sheet discharge tray 1219. Light output from a lamp 1212 of the optical unit 1213 and reflected by a document is input to a CCD image sensor 1218 via mirrors 1214, 1215, and 1216 and a lens 1217. As for the document reading method, and as an alternative to an automatic feeding method by the document feeder 1260, a method of scanning a document on the document glass 1211 with a carriage to which the optical unit 1213 is attached may be employed. While the image forming apparatus 10 is configured to perform monochrome printing in the first embodiment, it may also be configured to perform color printing.The printer unit 13 is an apparatus configured to form an image on a sheet using input image data. While an image forming method of the printer unit 13 according to the present embodiment is an electrophotographic method using a photosensitive drum or a photosensitive belt, the present disclosure is not limited to this method. For example, the printer unit 13 may employ an ink jet method in which an ink is ejected from a micro nozzle array to print an image on a sheet.The image forming apparatus 10 further comprises a plurality of sheet cassettes 1311, 1312, 1313, and 1314, and a manual sheet feeding tray 1315. Sheets on which an image is to be formed by the printer unit 13 are stored in the plurality of sheet cassettes 1311, 1312, 1313, and 1314. A laser driver 1321 of the printer unit 13 drives a laser light emitting unit 1322. The laser driver 1321 irradiates laser light corresponding to image data output from the controller 11 by the laser light irradiation unit 1322. The laser light is irradiated onto a photosensitive drum 1323, and a latent image corresponding to the laser light is formed on the photosensitive drum 1323. A developing device 1324 applies a developing agent to the latent image portion of the photosensitive drum 1323. A transfer unit 1325 transfers the developing agent applied to the photosensitive drum 1323 to a recording sheet which has been conveyed by a sheet conveyance path 1331. The recording sheet having the developing agent thereon is conveyed to a fixing device 1327 by a sheet conveying belt 1326. The fixing device 1327 fixes the developing agent on the recording sheet with heat and pressure. The recording sheet conveyed by the fixing device 1327 is conveyed by sheet conveying paths 1335 and 1334, and then discharged to a sheet discharge tray 1328. In a case where a printed surface is to be reversed and the reversed recording sheet is to be ejected to the sheet ejection tray 1328, the recording sheet is guided to sheet conveyance paths 1336 and 1338, and thereafter conveyed through a sheet conveyance path 1337 and the sheet conveyance path 1334.Further, in a case of two-sided printing, a recording sheet is sent from the fixing device 1327 through the sheet conveyance path 1336, and then sent to a sheet conveyance path 1333 through a folder 1329. Thereafter, the recording sheet is conveyed in the reverse direction and guided to the sheet conveying path 1338 and a return conveying path 1332 by the folder 1329. The recording sheet guided to the return conveyance path 1332 is conveyed by the sheet conveyance path 1331 and fed to the transfer unit 1325.< Of Controller 11 of Image Forming Apparatus 10>Fig. 2 is a block diagram illustrating a control means which controls the entire image forming apparatus. The controller 11 configured to control all operations of the image forming apparatus 10 will be described in detail below with reference to FIG. 2.As illustrated in FIG. 2, the controller 11 is electrically connected to the sensing unit 12, the printer unit 13, and an operation unit 14. The devices of the controller 11 according to the present embodiment are mounted on a single printed circuit board. Alternatively, the devices of the controller 11 may be separately mounted on two or more printed circuit boards. For example, the controller 11 may include a printed circuit board on which an operation unit interface (operation unit I / F) 1105 and a human body detection sensor 1110 are mounted, and another printed circuit board on which a central processing unit (CPU) 1101 is mounted. The controller 11 includes the CPU 1101, a random access memory (RAM) 1102, a read only memory (ROM) 1103, the operation unit I / F 1105, a local area network (LAN) controller 1106, the human body detection sensor 1110, a sheet detection sensor 1112, and a power control unit 1114. 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 sheet detection sensor 1112, and the power control unit 1114 are connected to a system bus 1107. The controller 11 further includes a hard disk drive (HDD) 1104, an image processing unit 1109, a scanner interface (scanner I / F) 1111, and a printer interface (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.The CPU 1101 comprehensively controls access to / from each connected device on the basis of a control program stored in the ROM 1103. The CPU 1101 also controls various types of processing performed by the controller 11 in a comprehensive manner.The RAM 1102 is a system memory for the CPU 1101 to operate. The RAM 1102 is also a memory for temporarily storing image data. The RAM 1102 includes a static RAM (SRAM) and a dynamic RAM (DRAM). Data stored on the SRAM is retained even when the power is turned off, whereas data stored on the DRAM is erased when the power is turned off. The ROM 1103 stores a device boot program. The HDD 1104 is a hard disk drive and stores a program for controlling the image forming apparatus 10 and image data.The operation unit I / F 1105 is an interface unit for connecting the system bus 1107 and the operation unit 14. the operation unit I / F 1105 receives image data to be displayed on the operation unit 14 from the system bus 1107, outputs the received image data to the operation unit 14, and outputs information input from the operation unit 14 to the system bus 1107.The LAN controller 1106 controls input and output of information between the image forming apparatus 10 and an external device 50 connected to a network 60.The human body detection sensor 1110 is an infrared sensor array in which infrared sensors configured to receive infrared rays are arranged in a matrix. The human body detection sensor 1110 receives infrared rays radiated from a person, thereby detecting the person who has approached the image forming apparatus 10. While an example in which the human body detection sensor 1110 detects a person is described in the present example, any objects that emit infrared rays may be detected by the human body detection sensor 1110. The human body detection sensor is not limited to the infrared sensor described above. Any devices other than an infrared sensor, which are sensors (an optical sensor configured to detect light, a deformation sensor configured to be deformed by a physical force, a magnetic sensor configured to detect magnetism, and a temperature sensor configured to detect temperature) configured to detect an object that has come close to the image forming device 10 may be employed.The sheet detection sensor 1112 detects a placement of a sheet on the manual sheet supply tray 1315.The power control unit 1114 controls power supply to the components of the image forming apparatus 10.The image bus 1108 is a transmission path for exchanging image data, and is a peripheral component interconnect (PCI) bus, an Institute of Electrical and Electronics Engineers (IEEE)1394 bus, or the like.The image processing unit 1109 performs image processing. The image processing unit 1109 reads out image data stored in the RAM 1102, and performs image processing such as enlargement or reduction based on, for example, joint photographic experts group (JPEG) or joint bi-level image experts group (JBIG), and color adjustment on the read-out image data.The sensing unit 12 includes a sensing device control unit 1201 and a sensing device driving unit 1202. The scanner driving unit 1202 is an apparatus that includes a motor for conveying a document set on the tray 1250 to a reading position of the scanner unit 12 and performs physical driving. The scanner control unit 1201 controls operations of the scanner driving unit 1202. The scanner control unit 1201 receives setting information set by a user at the time of execution of scan processing via communication with the CPU 1101, and controls the operations of the scanner drive unit 1202 based on the setting information.The printer unit 13 includes a printer control unit 1301 and a printer drive unit 1302. The printer driving unit 1302 is an apparatus which comprises a motor for rotating the photosensitive drum 1323, a motor for rotating the fixing device 1327, and a sheet conveying motor and performs physical driving. The printer control unit 1301 controls operations of the printer drive unit 1302. The printer control unit 1301 receives setting information set by the user at the time of execution of print processing via communication with the CPU 1101, and controls the operations of the printer drive unit 1302 based on the setting information.< Of Printed Circuit Board>FIGS. 3, 4A and 4B illustrate a printed circuit board in detail. A printed circuit board 100 is fixed to a metallic case 600 with metallic screws 20 to 24. Integrated circuits (ICs) 200 and 201 are mounted on the printed circuit board 100. The IC 200 is the CPU 1101, and the IC 201 is the LAN controller 1106. Further, connectors 202 and 203 are mounted on the printed circuit board 100. An external device and a cable (for example, a universal serial bus (USB) device, a USB cable) are connected to the connector 202, and another external device and a cable (for example, an Ethernet router, an Ethernet cable) are connected to the connector 203. Signals 300, 301, 302 and 303 are transmitted between the IC 200 and the connector 202. Signals 304 and 305 are transmitted between the IC 201 and the connector 203. The IC 200 communicates with the external device via the connector 202. The IC 201 communicates with an external device via the connector 203. Each of the signals 300 to 305 may be a signal configured to transmit a clock signal, a data signal, a supply power, or a signal connected to the ground. In the present embodiment, connector 202 is a four-contact connector (contacts 400, 401, 402, and 403), and connector 203 is a two-contact connector (contacts 404 and 405). The numbers of contacts of the connectors 202 and 203 are not limited to four and two.The IC 200 may be a programmable gate array (PGA) or an application specific integrated circuit (ASIC). The power control unit 1114 is a PGA, and the image processing unit 1109 is an ASIC. The ICs 200 and 201 are highly integrated, wherein semiconductor processes of the ICs 200 and 201 are on the order of nanometers. The smaller the semiconductor process, the lower the antistatic property becomes, so that the probability of erroneous operation resulting from exogenous noise such as static electricity increases.The connector 202 is fixed to the printed circuit board 100 with retaining pins 406 and 407. The connector 203 is fixed to the printed circuit board 100 with retaining pins 408 and 409. In a case where the connector 202 is a surface mount device (SMD) type connector, the support pins 406 and 407 are soldered to a front layer (signal layer 30 shown in FIG. 5 ) of the printed circuit board 100. In a case where the connector 202 is a double row housing (DIP), the support pins 406 and 407 pass through the printed circuit board 100 from the front layer (the signal layer 30) to a rear layer (a signal layer 36 shown in FIG. 5 ) of the printed circuit board 100, and are also soldered to the printed circuit board 100. The same applies to the connector 203, so a description thereof will be omitted.The front layer (signal layer 30) of the printed circuit board 100 according to the present embodiment includes three ground regions separated by slits. The three mass regions are a signal mass region 101, a frame mass region 102 (a or b), and a static electricity removal mass region 103.The signal ground region 101 is a region where the ICs 200 and 201 configured to receive signals from the connectors 202 and 203 are mounted. The signal ground region 101 is connected to ground via an internal ground layer 32. The potential of the internal ground layer 32 is a reference potential for the signals 300 to 305, and a reference potential for the power to be supplied to the ICs 200 and 201. The signal ground region 101 is located outside the frame ground region 102 aand the frame ground region 102 b.The connector 202 is attached to the frame ground region 102 a, and the frame ground region 102 ais electrically connected to a metal case 600. The frame ground region 102 ais connected to a metallic frame of the connector 202.The connector 203 is mounted on the frame ground region 102 b, and the frame ground region 102 bis electrically connected to the metal case 600. The frame ground region 102 bis connected to a metallic frame of the connector 203.In the present embodiment, a static electricity removal ground region 103 is provided in addition to the signal ground region 101 and the frame ground regions 102 aand 102 bin the signal layer 30 of the printed circuit board 100. The static electricity removal ground region 103 is a peripheral portion of the printed circuit board 100. Further, the static electricity removal mass region 103 forms a mass loop without interruption. Further, the static electricity removal ground region 103 surrounds the frame ground region 102 awithout a break, the frame ground region 102 bwithout a break, and the signal ground region 101 without a break in the present embodiment, respectively.Further, the static electricity removal mass region 103 is respectively accommodated at a position that is outside the frame mass region 102 aand corresponds to (in other words, faces) at least one insertion opening 202 aof the connector 202 into which an external device or a cable is inserted, and accommodated at a position that is outside the frame mass region 102 band corresponds to (in other words, faces) at least one insertion opening 203 aof the connector 203 into which a cable is inserted.The static electricity removal mass region 103 is connected to the mass layer 32. Frame ground regions 102 aand 102 band signal ground region 101 are also connected to ground layer 32. In other words, the static electricity removal ground region 103 is connected to the frame ground regions 102 aand 102 band the signal ground region 101 at the ground layer 32.The static electricity removal mass region 103 includes through holes through which the screws 20 to 23 are passed. The screws 20 to 23 fix the printed circuit board 100 to the metal case 600. The through holes may be cuts. The screws 20 to 23 are metallic screws and are connected to the ground, and the printed circuit board 100 is fixed to the metal case 600.The static electricity removal ground region 103 is completely separated from the frame ground regions 102 aand 102 band the signal ground region 101 in the signal layer 30 by a slot 502. The slot 502 is only in the signal layer 30 and does not reach the ground layer 32.The static electricity removal mass region 103 is accommodated in the signal layers 30 and 36. The static electricity removal mass region 103 of the signal layer 30 and the static electricity removal mass region 103 of the signal layer 36 are accommodated in the peripheral portion of the printed circuit board 100. In the present embodiment, the signal layer 36 does not include a frame ground region. Alternatively, the signal layer 36 may include a frame ground region.In the present embodiment, the signal ground region 101 is accommodated between the static electricity removal ground region 103 and the frame ground region 102 a, and between the static electricity removal ground region 103 and the frame ground region 102 b. However, the signal ground region 101 has not been accommodated between the static electricity removal ground region 103 and the frame ground region 102 a, nor between the static electricity removal ground region 103 and the frame ground region 102 b.The static electricity removal mass region 103 includes a through hole 107, and is connected to the mass layer 32.The slot 502 prevents static electricity that has entered the peripheral portion of the printed circuit board 100 from being transmitted to the signal ground region 101 and the frame ground regions 102 aand 102 b. Static electricity that has entered the peripheral portion of the printed circuit board 100 is transmitted to the metal housing 600 via the through hole 107 of the static electricity removing mass region 103 and the screws 20 to 23. Intrusion of static electricity discharged from a person when a device or a cable is attached to or removed from the connector 202 or 203 into the inside of the static electricity removal mass region 103 is prevented. Intrusion of static electricity discharged near the connector 202 or 203 into active elements (ICs 200 and 201) mounted on the printed circuit board 100 and operating at high frequencies is prevented.The frame ground region 102 ais connected to the ground layer 32 and the static electricity removal ground region 103 of the signal layer 36 via a through hole 106 from the signal layer 30. Static electricity discharged onto the frame of the connector 202 is transmitted to the frame ground region 102 avia the support pins 406 and 407. Then, the static electricity is transmitted to the static electricity removing ground region 103 of the signal layer 36 via the through hole 107, and escapes to the metal case 600.Further, frame ground region 102a is separated from signal ground region 101 by a slot 500. Further, frame ground region 102b is separated from signal ground region 101 by a slot 501. Further, in the present embodiment, the static electricity removal mass region 103 and the frame mass region 102 aare separated by the slits 502 and 500. Further, the static electricity removal mass region 103 and the frame mass region 102 bare separated by the slits 502 and 501. Further, the static electricity removal ground region 103 and the signal ground region 101 are separated by the slit 502. The term "slot" refers to a groove that physically separates a conductor (e.g., a film-like copper layer) of the signal layer 30 of the printed circuit board 100 such that the signal layer 30 is in an electrically non-conductive state. Specifically, in the signal layer 30, the signal ground region 101 and the frame ground 102 aare separated by the slot 500. Further, in the signal layer 30, the signal ground region 101 and the frame ground 102 bare separated by the slot 501.The connector 202 is connected to the ground layer 32 of the printed circuit board 100 via the through hole 106. The through hole 106 according to the present embodiment is a through hole. Similarly, the connector 203 is connected to the ground layer 32 of the printed circuit board 100 via the through hole 206 (shown in FIG. 4B ). A through hole is a through hole from a front layer to a back layer. A through hole is formed by making a hole from a front layer to a rear layer with a drill and coating the hole with a conductor to connect a plurality of layers. The contacts 400 to 403 of the connector 202 are connected to the outside of the frame ground region 102 a, i.e., the signal ground region 101, so that the signals 300 to 303 are prevented from being transmitted via two different ground regions. The same applies to the connector 203, so a description thereof will be omitted.FIG. 5 is a cross-sectional view illustrating the printed circuit board 100 along a line A-A' specified in FIG. 3. In FIG. 5, each diagonal line region is a ground region (except for ICs 200 and 202), and each dotted region is a power layer.The printed circuit board 100 according to the present embodiment includes four layers. However, the number of layers of the printed circuit board 100 is not limited to four. The printed circuit board 100 may include a different number of layers and include, for example, six or eight layers.The signal layers 30 and 36 are provided to transmit signals output from the ICs 200 and 201 to another IC. A signal output from the IC 200 or 201 is transmitted to the signal layer 36 in some cases, or is transmitted within the signal layer 30 in some cases.The signal layer 30 comprises signal lines for the signals 300 to 305. The signal layer 30 includes a power supply plane and the ground regions 101 to 103 in addition to signal lines for the signals 300 to 305. The frame ground region 102 aof the signal layer 30 is connected to the ground layer 32 and the signal ground region 101 of the signal layer 36 via the through hole 106.The ground layer 32 serves to stabilize the voltage level of the ground.A power layer 34 includes a power supply plane of a plurality of systems for use by the ICs 200 and 201 and the connectors 202 and 203. The power supply plane of the power layer 34 supplies power to the ICs mounted on the signal layer 30 via a through hole 105. Since the potential of the through hole 105 is the same as the potential of the power supply plane, the through hole 105 is not connected to the ground of the signal layer 30, the ground layer 32, and the ground of the signal line 36. The through hole 106 is not connected to the power supply plane of the power layer 34.A material of each layer is a conductor such as copper. Furthermore, prepregs 31 and 35 and a core material 33 are provided between layers. The prepregs 31 and 35 are base materials which are prepared by impregnating a glass fiber cloth with a resin such as epoxy and then partially curing the glass fiber cloth. The prepregs 31 and 35 are used to insulate layers when the copper of the layers and the core materials 33 are laminated to form the printed circuit board 100.The screw 20 is fixed to the metal case 600.When a cable is inserted into or removed from the connector 202 or 203, static electricity may be discharged from a charged human body, a charged device, or the charged cable, and may enter the frame of the connector 202 or 203 that is in contact or the signal lines for the signals 300 to 305 from the connector 202 or 203.FIG. 6 illustrates a static electricity transmission path.When a device or a cable is inserted into or removed from the connector 202 or 203, since the physical distance is small, there is a high possibility that a charged human body or a charged device discharges static electricity to the static electricity removal mass region 103 housed close to the insertion opening 202 a(shown in FIG. 4A ) of the connector 202. Static electricity discharged to the static electricity removing ground region 103 is transmitted to the ground layer 32 and the signal layer 36 via the through hole 107. Then, the static electricity is transmitted to the metal case 600 via the screw 20 (path 2000).Further, static electricity that has entered the frame of the connector 202 is transmitted to the frame ground region 102 avia the support pins 406 and 407, and is transmitted to the ground layer 32 and the signal layer 36 via the through hole 106. The through hole 106 is connected to the static electricity removing ground region 103 of the signal layer 36, so that the static electricity escapes to the metal case 600 through the screw 20 (path 2001).Noise that has entered the signal lines for the signals 300 to 303 connected to the connector 202 can reach the IC 200 (path 2002).There is a path (path 2003) through which static electricity that has entered the static electricity removal ground region 103 and the frame ground region 102 ais transmitted to the signal ground region 101 via a parasitic capacitor of the slots 500 and 502. In the present embodiment, the static electricity removing ground region 103 is accommodated outside the connector 202, and further the two slits 500 and 502 are formed up to the signal ground region 101, so that it is difficult for the static electricity to be transmitted to the connector.As illustrated in FIG. 7, frequencies at which the signal layer 30 and the ground layer 32 of the printed circuit board 100 are likely to vibrate differ because, while the signal layer 30 includes the three ground regions 101, 102, 103 separated by the slits 500 and 502, the ground layer 32 does not include such slits, and the shapes of the signal layer 30 and the ground layer 32 are significantly different. Also, in a case where static electricity transmitted through the path 2003 causes a resonance phenomenon at the signal ground region 101 of the signal layer 30, a resonance phenomenon of an intensity the same as that at the signal layer 30 is less likely to occur at the ground layer 32. Thus, static electricity transmitted to the signal layer 30 is attenuated based on a frequency characteristic because the static electricity is transmitted to the ground layer 32 and the signal layer 36. Consequently, the static electricity is less likely to become superimposed noise when the static electricity is transmitted into the internal layer.According to the present embodiment, the static electricity removal ground region 103 separated from the signal ground region 101 and the frame ground regions 102 aand 102 bby the slot 502 is accommodated in the peripheral portion of the printed circuit board 100. Accordingly, static electricity is concentrated in the static electricity removal mass region 103 in the peripheral portion of the printed circuit board 100. Thus, static electricity charged to a person, a cable, or a device can leak into the metal housing 600.Further, since the front layer signal layer 30 and the internal layer ground layer 32 have different shapes, the resonant frequencies are shifted, so that static electricity transmitted to the internal layer is attenuated. Accordingly, antistatic properties of an electronic device such as a printing device including the printed circuit board 100 installed therein improve, thereby decreasing the possibility of erroneous operations of mounted components such as the IC 200.< Embodiments>While the example in which the printed circuit board according to the present disclosure is mounted on the image forming apparatus is described in the above-described embodiment, an apparatus in which the printed circuit board according to the present disclosure is to be mounted is not limited to an image forming apparatus. For example, the printed circuit board according to the present disclosure may be mounted on various devices such as notebook personal computers (notebook PCs), tablet PCs, desktop PCs, smart phones, vehicles, air conditioners, game machines, and robots.While the present invention has been described with reference to embodiments, it will be understood that the invention is not limited to the disclosed embodiments, but is defined by the scope of the following claims.A printed circuit board (100) includes a front layer (30) including frame ground regions (102a, 102b) to which connection devices (202, 203) to be connected to external devices or communication cables are attached and which are connected to a ground, a signal ground region (101) separated from the frame ground regions at the front layer to which electronic devices (200, 201) configured to receive signals from the connection devices are attached and which is connected to a 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, accommodated outside the frame ground regions (102a, 202b), and connected to a ground.

Claims

A printed circuit board (100) having a front layer (30), comprising: a first ground region (102a, 102b) to which a connector (202, 203) to be connected to an external device or a communication cable is attached and which is connected to a ground; a second ground region (101) separated from the first ground region (102a, 102b) at the front layer (30) to which an electronic device (200, 201) configured to receive a signal from the connector (202, 203) is attached and which is connected to the ground; and a third ground region (103) separated from the first ground region (102a, 102b) and the second ground region (101) at the front layer (30), accommodated outside the first ground region (102a, 102b), and connected to the ground, the third ground region (103) being accommodated to surround the first ground region (102a, 102b) without a break, wherein the printed circuit board (100) is a multilayer printed circuit board comprising at least a signal layer (30) formed by the front layer (30), a power layer (34), and a ground layer (32), wherein the first ground region (102a, 102b), the second ground region (101), and the third ground region (103) are connected at the ground layer (32).A printed circuit board (100) having a front layer (30), comprising: a first ground region (102a, 102b) to which a connector (202, 203) to be connected to an external device or a communication cable is attached and which is connected to a ground; a second ground region (101) separated from the first ground region (102a, 102b) at the front layer (30) to which an electronic device (200, 201) configured to receive a signal from the connector (202, 203) is attached and which is connected to the ground; and a third ground region (103) separated from the first ground region (102a, 102b) and the second ground region (101) at the front layer (30), accommodated outside the first ground region (102a, 102b), and connected to the ground, the third ground region (103) accommodated to surround the second ground region (101) without a break, wherein the printed circuit board (100) is a multilayer printed circuit board comprising at least a signal layer (30) formed by the front layer (30), a power layer (34), and a ground layer (32), wherein the first ground region (102a, 102b), the second ground region (101), and the third ground region (103) are connected at the ground layer (32).The printed circuit board (100) according to claim 1 or 2, wherein the second ground region (101) is accommodated outside the first ground region (102a, 102b).The printed circuit board (100) according to claim 3, wherein the second ground region (101) is accommodated outside the first ground region (102a, 102b), and the third ground region (103) is accommodated outside the second ground region (101).The printed circuit board (100) according to any one of claims 1 to 4, wherein the third ground region (103) is at a position that is outside the first ground region (102a, 102b) and corresponds to at least one insertion opening (202a, 203a) of the connector (202, 203) into which the external device or the communication cable is to be inserted.The printed circuit board (100) according to any one of claims 1 to 5, wherein the front layer (30) further comprises a fourth ground region separated from the first ground region (102a, 102b), the second ground region (101), and the third ground region (103) at the front layer (30), to which another connector (202, 203) to be connected to another external device or another communication cable is attached, and which is connected to the ground.The printed circuit board (100) according to any one of claims 1 to 6, wherein the first ground region (102a, 102b) is connected to a metallic housing (600) of the connector (202, 203).The printed circuit board (100) according to any one of claims 1 to 7, wherein the third ground region (103) comprises a hole (107) or a cut through which a fixing member (20 to 24) configured to fix the printed circuit board (100) to a housing (600) is passed.The printed circuit board (100) according to claim 8, wherein the fixing member (20 to 24) is a metallic fixing member, and the housing (600) is a metallic housing (600).The printed circuit board (100) according to any one of claims 1 to 9, wherein the printed circuit board (100) is a printed circuit board (100) of a printing device.A printing apparatus comprising: a printed circuit board (100) according to any one of claims 1 to 10; and a printer unit (13) configured to print an image on a sheet.

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