Circuit board, and image forming apparatus

Abstract

To provide a circuit board that can prevent an increase in the temperature of an electronic component.SOLUTION: A circuit board 300 is provided with a mounting area 512 where a motor driver IC 406 is mounted, and a mounting area 513 where a motor driver IC 416 is mounted which has higher heat radiation properties than the motor driver IC 406 and has the same function as the motor driver IC 406. The motor driver IC 406 and the motor driver IC 416 are mounted exclusively on the circuit board 300. The mounting area 512 is provided on a mounting surface 501a, and the mounting area 513 is provided on a mounting surface 504a different from the mounting surface 501a. The heat radiation properties of the mounting surface 501a are higher than the heat radiation properties of the mounting surface 504a.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to a circuit board on which electronic components are mounted, and to an image forming apparatus, such as a printer, a copier, or a multifunction peripheral, that includes such a circuit board. [Background technology]

[0002] The image forming apparatus includes a plurality of circuit boards for controlling a plurality of components for image formation. The control circuit boards include a circuit board having a function of controlling image processing and a circuit board having a function of controlling paper transport. On each control circuit board, a plurality of electronic components are mounted according to the functions to be realized, such as electronic components for performing logical operations, electronic components for performing drive control, and electronic components for generating power supply voltage. The electronic components on the circuit boards are connected by conductors such as printed wiring. Each electronic component constitutes an electronic component component that realizes a predetermined function, including peripheral electronic components. For example, an electronic component component is constituted by an integrated circuit and peripheral electronic components such as resistors, capacitors, and inductors that are connected to input / output terminals of the integrated circuit.

[0003] Furthermore, the image forming apparatus prints an image on paper through multiple processes such as paper transport, image formation, image transfer onto paper, and fixing of the image onto the paper. To achieve this, the image forming apparatus needs to control a wide variety of actuators such as optical sensors, temperature sensors, motors, and solenoids. A control circuit board mounted on the image forming apparatus has multiple electronic components mounted thereon for actuator control. For example, a driver board that drives a motor has an integrated circuit (motor driver IC) for generating a drive signal for the motor based on a control signal input from a controller in order to appropriately control the motor (Patent Document 1). Furthermore, multiple control circuit boards themselves are provided within the image forming apparatus. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2022-6639 Summary of the Invention [Problem to be solved by the invention]

[0005] The present inventors have devised a method of providing mounting areas for mounting electronic components on both sides of a substrate. However, in the prior art, sufficient consideration has not been given to heat dissipation when providing mounting areas on both sides of a substrate. When electronic components are mounted exclusively on the front and back sides of a circuit board, the electronic components mounted on the side with poor heat dissipation are at high risk of malfunction, such as thermal shutdown or failure. Methods for suppressing temperature rise include increasing the number of layers on the circuit board and adding fans. However, these methods lead to increased complexity and cost of the device.

[0006] In view of the above-mentioned problems, a main object of the present invention is to provide a circuit board capable of suppressing a rise in temperature of electronic components. [Means for solving the problem]

[0007] The circuit board of the present invention is a circuit board comprising a first mounting area for mounting a first electronic component having at least a first function, and a second mounting area for mounting a second electronic component having higher heat dissipation properties than the first electronic component and at least the first function, wherein the first mounting area is provided on a first mounting surface of the circuit board, the second mounting area is provided on a second mounting surface of the circuit board different from the first mounting surface, and the heat dissipation properties of the first mounting surface are higher than the heat dissipation properties of the second mounting surface. Effect of the Invention

[0008] According to the present invention, it is possible to suppress the temperature rise of electronic components and thereby suppress the occurrence of operational malfunctions. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a system configuration diagram of an image forming apparatus. [Diagram 2]FIG. 1 is a diagram illustrating the configuration of an image forming apparatus. [Diagram 3] FIG. [Figure 4] FIG. 1 is an illustration of an electronic component. [Diagram 5] FIG. 3 is a diagram illustrating the configuration of a circuit board 300 when a motor driver IC is mounted. [Figure 6] FIG. 3 is a diagram illustrating the configuration of a circuit board 300 when a motor driver IC is mounted. [Figure 7] An explanatory diagram of the temperature of a motor driver IC. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

[0011] (Configuration of Image Forming Apparatus) 1 is a system configuration diagram of an image forming apparatus having a circuit board according to the present embodiment. Unless otherwise specified, it goes without saying that the image forming apparatus 100 may be a system made up of multiple devices connected via a network, as long as the functions of the image forming apparatus 100 are executed.

[0012] The image forming apparatus 100 of this embodiment is communicatively connected to a host computer 101 via a network 105. The network 105 is configured with communication lines such as a local area network (LAN), a wide area network (WAN), and a public line. A plurality of image forming apparatuses 100 and a plurality of host computers 101 may be connected to the network 105. The host computer 101 generates a print job based on input information from a user acquired by an input device (not shown), and transmits the generated print job to the image forming apparatus 100 via the network 105.

[0013] The image forming apparatus 100 includes a controller board 110, a storage 115, a paper feed unit 140, a printer engine 150, and an operation panel 180. The controller board 110, the storage 115, the paper feed unit 140, the printer engine 150, and the operation panel 180 are connected to each other via a system bus 116 so as to be able to communicate with each other.

[0014] The controller board 110 includes an I / O control unit 111, a Read Only Memory (ROM) 112, a Random Access Memory (RAM) 113, and a Central Processing Unit (CPU) 114. The I / O control unit 111, the ROM 112, the RAM 113, and the CPU 114 are electronic components mounted on a circuit board. The controller board 110 functions as a main control unit of the image forming apparatus 100, performs various data processing, and controls the operation of the entire image forming apparatus 100. The circuit board is, for example, a printed wiring board on which printed wiring is formed.

[0015] The I / O control unit 111 controls communication with external devices such as the host computer 101 via the network 105. The CPU 114 controls operations such as image formation processing by the image forming apparatus 100 by executing computer programs stored in the ROM 112 and the storage 115. The RAM 113 provides a working area when the CPU 114 executes processing, and stores temporary data. The storage 115 stores large-capacity data such as image data and print data temporarily or for a long period of time. For example, the storage 115 stores image data for generating an adjustment image for adjusting image formation conditions. The storage 115 is a large-capacity storage device such as an HDD (Hard Disk Drive) or an SSD (Solid State Drive). Computer programs such as a boot program, a control program, and an operating system executed by the CPU 114 are stored in the ROM 112 and the storage 115.

[0016] Operation panel 180 is a user interface equipped with an input interface and an output interface. The input interface is, for example, a key button, a touch panel, etc. The output interface is a display, a speaker, etc. Operation panel 180 accepts instructions and the like by user operation and inputs them to CPU 114. CPU 114 controls the operation of image forming apparatus 100 in response to the instructions. Operation panel 180 also displays the status of image forming apparatus 100 and various setting screens in response to instructions from CPU 114.

[0017] The paper feed unit 140 includes a paper feed device including one or more paper feed stages and a transport unit that transports paper from the paper feed stages to a paper discharge unit. The paper feed unit 140 feeds paper one sheet at a time from the paper feed stages in response to an instruction from the CPU 114.

[0018] Printer engine 150 includes image forming section 152, print position control section 153, image position detection section 154, fixing section 260, and image reading section 290. Image forming section 152 forms an image (toner image) on paper fed by paper feed section 140. Fixing section 260 fixes the image (toner image) on the paper. Image reading section 290 reads the adjustment image printed on the paper. Image position detection section 154 detects the position of the image printed on the paper based on the result of reading the adjustment image by image reading section 290. Print position control section 153 controls the position of the image printed on the paper based on the position of the image detected by image position detection section 154.

[0019] 2 is a configuration diagram of image forming apparatus 100. Image forming apparatus 100 has an operation panel 180 on the top of a housing 201. Inside housing 201, controller board 110, storage 115, paper feed unit 140, and printer engine 150 shown in FIG. 1 are provided. Printer engine 150 includes each mechanism constituting the engine unit and an engine control unit that controls the processing by each mechanism. Each mechanism constituting the engine unit includes an optical processing mechanism for forming an electrostatic latent image, visualizing the electrostatic latent image, and transferring the visual image to paper S, and a fixing processing mechanism for fixing the toner image transferred to paper S.

[0020] The image forming unit 152 of the printer engine 150 corresponds to an optical processing mechanism, and includes a Y station 220, an M station 221, a C station 222, a K station 223, an intermediate transfer belt 252, and a secondary transfer outer roller 251. The Y station 220, the M station 221, the C station 222, and the K station 223 have the same configuration, and only the colors of the images they form are different. The Y station 220 forms a yellow image. The M station 221 forms a magenta image. The C station 222 forms a cyan image. The K station 223 forms a black image. Here, the configuration of the Y station 220 will be described, and the configurations of the M station 221, the C station 222, and the K station 223 will not be described.

[0021] The Y station 220 includes a photosensitive drum 205, a charger 211, an exposure unit 207, and a developing unit 212. The photosensitive drum 205 is a drum-shaped photoconductor having a photosensitive layer on its surface. The charger 211 uniformly charges the surface of the photosensitive drum 205, which rotates around the drum axis. The exposure unit 207 scans the charged surface of the photosensitive drum 205 with a laser beam modulated according to image data.

[0022] The exposure unit 207 includes a laser driver that controls the emission of a semiconductor laser (not shown) in accordance with image data obtained from the printer controller 203 (CPU 114), a rotating polygon mirror 208, and a reflecting mirror 209. The laser light emitted from the semiconductor laser moves in the main scanning direction in accordance with the rotation of the rotating polygon mirror 208, and is guided to the surface of the photosensitive drum 205 by the reflecting mirror 209. As a result, the laser light scans the surface of the photosensitive drum 205 in the drum axial direction. An electrostatic latent image is formed on the photosensitive drum 205 by exposing the surface to light.

[0023] The developing unit 212 visualizes the electrostatic latent image with toner of a corresponding color, forming a toner image on the surface of the photosensitive drum 205. A yellow toner image is formed on the photosensitive drum 205 of the Y station 220. A magenta toner image is formed on the photosensitive drum 205 of the M station 221. A cyan toner image is formed on the photosensitive drum 205 of the C station 222. A black toner image is formed on the photosensitive drum 205 of the K station 223.

[0024] The intermediate transfer belt 252 is wound around rollers such as the inner secondary transfer roller 240, and rotates in a clockwise direction in the figure. The toner images of each color formed on each photosensitive drum 205 are transferred to the rotating intermediate transfer belt 252 so as to be superimposed on each other. The toner images are transferred from the photosensitive drums 205 to the intermediate transfer belt 252 by applying a bias voltage having opposite characteristics to the toner images to the intermediate transfer belt 252. As a result, the intermediate transfer belt 252 carries a full-color toner image. The intermediate transfer belt 252 conveys the carried toner image to a secondary transfer section composed of the inner secondary transfer roller 240 and the outer secondary transfer roller 251 as it rotates.

[0025] The paper feed unit 140 corresponds to a feeding mechanism for the paper S, and includes a storage 210 which is a paper feed stage that stores the paper S, a transport path, transport rollers, etc. The paper feed unit 140 transports the paper S one by one from the storage 210 to the secondary transfer unit. The secondary transfer unit sandwiches and transports the intermediate transfer belt 252 and the paper S between the secondary transfer inner roller 240 and the secondary transfer outer roller 251. At this time, a bias voltage of the opposite polarity to the toner image is applied to the secondary transfer outer roller 251, so that the toner image is transferred from the intermediate transfer belt 252 to the paper S.

[0026] The paper S onto which the toner image has been transferred is transported to the fixing unit 260, which is a fixing processing mechanism. The fixing unit 260 includes a fixing roller 261 having an internal heat source, a pressure roller 262 that is biased toward the fixing roller 261, and a circuit board 300 that controls the fixing processing by the fixing unit 260. The fixing unit 260 fixes the toner image onto the paper S by sandwiching and transporting the paper S onto which the toner image has been transferred between the fixing roller 261 and the pressure roller 262. At that time, the fixing roller 261 heats and melts the toner image, and presses the paper S between the fixing roller 261 and the pressure roller 262.

[0027] In this manner, an image is printed on the paper S. In the case of double-sided printing, the paper S with an image printed on its first side (front side) is transported again to the secondary transfer unit via reversal path 270. By being transported to the secondary transfer unit via reversal path 270, the image-formed side of the paper S is reversed. After the image-formed side of the paper S has been reversed, an image is printed on its second side (back side), which is different from the first side, by the secondary transfer unit and fixing unit 260.

[0028] The paper S on which the image is printed passes through an image reading unit 290 provided downstream of the fixing unit 260 in the paper transport direction, and is discharged to the outside of the image forming apparatus 100. When the image formed on the paper S is an image for adjusting image formation conditions, the image reading unit 290 is used to read the image for adjusting the image formation conditions.

[0029] (Circuit board) In order to perform the image formation process as described above, the image forming apparatus 100 includes various actuators such as motors and sensors. The actuators are connected to a circuit board on which electronic components for control are mounted. The electronic components mounted on the circuit board are connected by conductors. The circuit board of this embodiment is, for example, a printed wiring board using printed wiring as the conductors.

[0030] The electronic components control the operation of the actuators. To this end, a large number of circuit boards are provided in the image forming apparatus 100 corresponding to the actuators. One or more actuators are controlled by one circuit board. The circuit boards are controlled by a CPU 114. Note that the controller board 110 on which the CPU 114 is mounted is also an example of a circuit board.

[0031] FIG. 3 is a configuration diagram of a circuit board 300 provided in the fixing unit 260. A plurality of motors 309-311 in the fixing unit 260 and a plurality of sensors 312-314 in the fixing unit 260 are electrically connected to the circuit board 300. The motor 309 is a drive source for driving the fixing roller 261, which is a rotating body. The motor 310 is a drive source for urging the pressure roller 262 toward the fixing roller 261. The motor 311 is a drive source for driving a roller, which is a rotating body, that transports the paper S after the fixing process to a subsequent stage. The sensor 312 is a detector for detecting the paper S transported to the fixing unit 260. The sensor 313 is a temperature detector for detecting the temperature of the fixing roller 261. The sensor 314 is a detector for detecting the paper S after the fixing process.

[0032] The circuit board 300 realizes various functions by using a plurality of electronic components. In the example of Fig. 3, the circuit board 300 includes an ACDC converter 302 used to generate a predetermined DC voltage from an AC voltage, and a DCDC converter 303 that converts the voltage value of the DC voltage. The circuit board 300 further includes a CPU 304, an ASIC (Application Specific Integrated Circuit) 305, and motor driver ICs 306 to 308 used to control the actuator. The circuit board 300 is mounted with the above-mentioned plurality of integrated circuits (hereinafter referred to as "ICs") as electronic components, and peripheral electronic components corresponding to the ICs.

[0033] The ACDC converter 302 generates a DC power supply voltage having a predetermined voltage value based on the AC power supplied from the commercial power supply 301. The DCDC converter 303 generates a DC power supply voltage having a voltage value different from the power supply voltage supplied from the ACDC converter 302 based on the power supply voltage. The power supply voltage generated by the DCDC converter 303 is supplied to the CPU 304, the ASIC 305, etc. The CPU 304 and the ASIC 305 operate by the power supply voltage supplied from the DCDC converter 303. The power supply voltage output from the ACDC converter 302 is also supplied to electronic components and motors 309 to 311 that operate at a voltage value different from that of the CPU 304 and the ASIC 305.

[0034] The CPU 304 is connected to the motor driver ICs 306-308 and the sensors 312-314 via the ASIC 305. The CPU 304 acquires detection results from the sensors 312-314, and detects the state of the fixing unit 260 based on the detection results. The CPU 304 controls the motor driver ICs 306-308 via the ASIC 305 in accordance with the detected state of the fixing unit 260, thereby controlling the driving of the motors 309-311. In this manner, the CPU 304 and the ASIC 305 control the operation of the fixing unit 260.

[0035] Since circuit board 300 is provided in fixing unit 260, it controls the operation of fixing unit 260, but other circuit boards provided in image forming apparatus 100 also control the operation of corresponding components. Each circuit board (including circuit board 300 and other circuit boards) in image forming apparatus 100 is communicatively connected to controller board 110. Each circuit board can communicate with each other via controller board 110. Each circuit board appropriately controls the components in image forming apparatus 100 while sharing information related to the detection results of each sensor and the control state of the motors with each other.

[0036] A large number of electronic components are mounted on the circuit board. In response to such demand, it is possible that some or all of the electronic components may become difficult to procure due to various reasons, including distribution, the environment, and accidents. To deal with situations in which electronic components are difficult to procure, electronic components with the same or similar shapes and specifications as each electronic component may be prepared as substitutes. If a specific component cannot be procured, the production of the circuit board 300 can be continued by mounting the substitute on the circuit board.

[0037] However, for example, in the circuit board 300, specific ICs such as the IC of the DC-DC converter 303 and the motor driver ICs 306, 307, and 308 may require specific peripheral components when used. Also, the number, arrangement, and layout of terminals of the ICs, or electrical specifications, may differ, and there may be no substitute IC. In such a case, in order to deal with the situation in which it is difficult to procure each IC, another electronic component that can achieve the same function as the electronic component consisting of the IC and peripheral components is prepared. These electronic components are exclusively mounted on the circuit board. With this method, it is possible to continue manufacturing the circuit board 300 in order to mount ICs that can be procured depending on the availability of mounting components.

[0038] The circuit board 300 of this embodiment has a configuration that can cope with situations where parts procurement is difficult, does not impair the heat dissipation performance of electronic parts, and can further reduce the area required for mounting. A specific circuit configuration and wiring (wiring pattern) of the circuit board 300 will be described below. Note that in this embodiment, the configuration of a motor driver IC that controls a two-phase bipolar drive stepping motor will be used for the description.

[0039] (Electronic Components) 4 is an explanatory diagram of an electronic component including a motor driver IC and its peripheral components. The electronic component includes a first electronic component 410 including a motor driver IC 406, and a second electronic component 420 including a motor driver IC 416 that is a substitute for the motor driver IC 406. The first electronic component 410 and the second electronic component 420 have similar functions and are mounted exclusively on the front and back surfaces of the circuit board 300.

[0040] The first electronic component 410 includes resistors R11, R12, and R13, and capacitors C11, C12, and C13 in addition to the motor driver IC 406. The resistors R12 and R13 are detection resistors for detecting current. The resistor R11 is a resistor for determining a chopping frequency of constant current PWM (Pulse Width Modulation) control when controlling the motor current. The capacitors C11, C12, and C13 are provided for noise removal.

[0041] Similarly, the second electronic component 420 includes resistors R21, R22, and R23, and capacitors C21, C22, and C23, in addition to the motor driver IC 416. The resistors R22 and R23 are detection resistors for detecting current. The resistor R21 is a resistor for determining the chopping frequency of constant current PWM control when controlling the motor current. The capacitors C21, C22, and C23 are provided for noise removal.

[0042] The motor driver ICs 406 and 416 receive control signals branched from the ASIC 305 via damping resistors R1 to R6. The control signals include an ENABLE signal, a CLK signal, a VREF signal, a MODE signal (a MODE_1 signal and a MODE_2 signal), and a DIR signal. The ENABLE signal is a control signal that enables the output of the motor driver ICs 406 and 416. The CLK signal is a control signal that controls the speed of the motor. The VREF signal is a control signal that controls the current value flowing through the motor. The MODE signal controls the excitation pattern of the motor. The DIR signal is a control signal that controls the rotation direction of the motor. The motor driver ICs 406 and 416 can drive the motor in response to commands from these control signals. The phase output signals (OUTA, OUTA*, OUTB, OUTB*) output from the motor driver ICs 406 and 416 are input to the motor connected via vias at the shortest distance. The operation of the motor is controlled by these signals input from the motor driver ICs 406 and 416.

[0043] As described above, the first electronic component 410 and the second electronic component 420 are mounted exclusively on the front and back surfaces of the circuit board 300. By allowing them to be mounted exclusively on the front and back surfaces, it is possible to minimize the distance from the terminals of the motor driver ICs 406, 416 to the common signal lines for the phase output signals (OUTA, OUTA*, OUTB, OUTB*) and the like.

[0044] Furthermore, the circuit board 300 may be configured such that ICs are mounted exclusively, rather than electronic component units. For example, the motor driver IC 406 and the motor driver IC 416 may be mounted exclusively on the front and back surfaces of the circuit board 300. In this case, for example, the resistors R11, R12, and R13 and the capacitors C11, C12, and C13 may be shared by the motor driver IC 416, and the resistors R21, R22, and R23 and the capacitors C21, C22, and C23 may be unnecessary.

[0045] The motor driver IC 406 and the motor driver IC 416, which are exclusively mounted, may have different package sizes. In this embodiment, a case in which the package size of the motor driver IC 416 is larger than that of the motor driver IC 406 will be described.

[0046] The circuit board 300 of this embodiment has a multi-layer structure. Here, a four-layer circuit board 300 will be described, but any number of layers may be used. The four-layer circuit board 300 is double-sided reflowable, and electronic components can be mounted on one of the outermost layers (first layer) and the other layer (fourth layer). The motor driver IC 406 and the motor driver IC 416 are mounted exclusively on the first layer, which is the first surface (front side), and the fourth layer, which is the second surface (back side). The second layer is a power supply layer, and includes load driving power supply wiring that supplies power to the motor driver ICs 406 and 416, logic power supply wiring that supplies low voltage to the CPU 304, ASIC 305, etc. The third layer is a ground layer, and is connected to the ground patterns of the first and fourth layers through vias.

[0047] The motor driver ICs 306 to 308 and the ICs of the DCDC converter 303 are electronic components that tend to generate heat due to the large current flowing through them. In general, a motor driver IC may cause malfunctions such as thermal shutdown or failure when its temperature rises to about 150° C. For this reason, when designing the motor driver IC, a thermal design is performed that defines an upper limit temperature (100° C. in this embodiment) that allows some margin to avoid the risk of malfunction. The circuit board 300, which has ICs mounted exclusively on the front and back sides, is also designed so that the temperature rise of the ICs is below the upper limit temperature defined in the design.

[0048] Fig. 5 is a diagram illustrating the configuration of circuit board 300 when motor driver ICs 406, 416 are mounted. Fig. 5 is a cross-sectional view of circuit board 300. Circuit board 300 has a four-layer structure consisting of a first layer 501, a second layer 502, a third layer 503, and a fourth layer 504.

[0049] The mounting surface 501a of the first layer 501 is provided with a mounting area 512 in which the motor driver IC 416 can be mounted. The mounting surface 504a of the fourth layer 504 is provided with a mounting area 513 in which the motor driver IC 406 can be mounted. The motor driver IC 416 includes an IC chip 416c therein. The motor driver IC 406 includes an IC chip 406c therein. A die pad 416d for conducting heat to the circuit board 300 is provided on the rear surface of the motor driver IC 416. A die pad 406d for conducting heat to the circuit board 300 is provided on the rear surface of the motor driver IC 406. As with the package sizes of the motor driver ICs 406 and 416, the size of the die pad 416d is larger than the size of the die pad 406d.

[0050] When the motor driver IC 406 is mounted, the die pad 406d is soldered to the mounting area 513. Heat from the IC chip 406c is conducted to the mounting area 513 via the die pad 406d and diffused into the circuit board 300. When the motor driver IC 416 is mounted, the die pad 416d is soldered to the mounting area 512. Heat from the IC chip 416c is conducted to the mounting area 512 via the die pad 416d and diffused into the circuit board 300.

[0051] The leads of the motor driver IC 416 are connected to an output signal line 505. The leads of the motor driver IC 406 are connected to an output signal line 506. The output signal lines 505 and 506 are connected by vias 507 that penetrate the circuit board 300 from the first layer 501 to the fourth layer 504. The output signal line 505 is connected to a connector 508 that is provided on the mounting surface 501a.

[0052] The circuit board 300 is attached inside the housing 201 of the image forming apparatus 100 or inside the housing of the fixing unit 260. Here, an example of attachment inside the housing of the fixing unit 260 will be described. The circuit board 300 is fixed to the metal plate 509 so that the fourth layer 504 faces the metal plate 509 side inside the housing of the fixing unit 260. The metal plate 509 is an example of a support member that supports the circuit board 300. In this configuration, the distance (spatial distance 511) from the mounting surface 501a of the first layer 501 to the surface of the metal plate of the housing of the fixing unit 260 that faces the normal direction of the mounting surface 501a is larger than the distance (spatial distance 510) from the mounting surface 504a of the fourth layer 504 to the surface of the metal plate 509. Therefore, the spatial distance 511 in the vertical direction of the first layer 501 is larger than the spatial distance 510 in the vertical direction of the fourth layer 504. A fan 514 is disposed on the first layer 501 side of the circuit board 300. The fan 514 blows air toward the mounting area 512, thereby cooling the entire circuit board 300.

[0053] The mounting surface 504a of the fourth layer 504 has a smaller spatial distance 510 than the mounting surface 501a of the first layer 501, and has a low heat dissipation performance because of less convection (forced convection when the fan 514 is present, and natural convection when the fan 514 is not present). Therefore, the motor driver IC 406 mounted on the fourth layer 504 has a higher risk of malfunction, such as thermal shutdown or failure due to temperature rise, than the motor driver IC 416 mounted on the first layer 501.

[0054] In the example of FIG. 5, a motor driver IC 416 with a large package size can be mounted on the first layer 501, and a motor driver IC 406 with a small package size can be mounted on the fourth layer 504. The larger the package size, the higher the heat dissipation of the IC. This is because the larger the package size, the greater the amount of heat conducted from the IC to the circuit board via the die pad on the back side of the IC and the greater the amount of heat dissipated by convection on the surface of the package. Conversely, the smaller the package size, the lower the heat dissipation. In other words, in FIG. 5, the motor driver IC 406 with a small package size and low heat dissipation is configured to be mounted on the fourth layer 504, which is relatively easy to heat up.

[0055] FIG. 6 is a diagram illustrating the configuration of the circuit board 300 when the motor driver ICs 406 and 416 are mounted, taking into consideration the heat dissipation of the ICs. In FIG. 6, the motor driver IC 406 with a small package size can be mounted on the mounting surface 501a of the first layer 501, and the motor driver IC 416 with a large package size can be mounted on the mounting surface 504a of the fourth layer 504. For this reason, the area of ​​the mounting region 512 on the mounting surface 501a of the first layer 501 is smaller than the area of ​​the mounting region 513 on the mounting surface 504a of the fourth layer 504. As described above, due to the difference between the spatial distances 510 and 511, the heat dissipation of the mounting region 512 on the mounting surface 501a is higher than the heat dissipation of the mounting region 513 on the mounting surface 504a. In addition, the fan 514 further improves the heat dissipation of the mounting region 512 on the mounting surface 501a.

[0056] Mounting area 512 of mounting surface 501a has a size corresponding to the package size of motor driver IC 406. Mounting area 513 of mounting surface 504a has a size corresponding to the package size of motor driver IC 416. For this reason, mounting area 512 of mounting surface 501a is configured to be smaller than mounting area 513 of mounting surface 504a.

[0057] An IC with a small package size has a smaller surface area of ​​the package and die pad than a large IC, and therefore the thermal resistance of the heat dissipation path to the circuit board 300 and the surrounding air is high and the temperature rises easily. In other words, the motor driver IC 406 with a small package size has relatively low heat dissipation, while the motor driver IC 416 with a large package size has relatively high heat dissipation.

[0058] In this embodiment, the motor driver IC 406, which has a relatively low heat dissipation property, can be mounted in a mounting area 512 provided on the mounting surface 501a of the first layer 501, which has a relatively high heat dissipation property. The motor driver IC 416, which has a relatively high heat dissipation property, can be mounted in a mounting area 513 provided on the mounting surface 504a of the fourth layer 504, which has a relatively low heat dissipation property. Therefore, the temperature rise of the motor driver IC 406 can be suppressed.

[0059] Fig. 7 is an explanatory diagram of the temperatures of the motor driver ICs 406, 416 when the image forming apparatus 100 is continuously operated with the configurations of Fig. 5 and Fig. 6. The bar graph labeled "Comparative Example" in Fig. 7 shows the temperature rise results with the configuration of Fig. 5. The bar graph labeled "Present Embodiment" in Fig. 7 shows the temperature rise results with the configuration of Fig. 6.

[0060] In the configuration of Fig. 5, the motor driver IC 416 is 68[°C], which satisfies the condition of being equal to or lower than the design target upper limit temperature of 100[°C]. However, the motor driver IC 406 is 110[°C], which exceeds the design target upper limit temperature of 100[°C]. Therefore, when the motor driver IC 406 is mounted, there is a possibility that malfunction such as thermal shutdown or failure of the motor driver IC 406 may occur.

[0061] It is possible to suppress the temperature rise by adding a fan 514, increasing the airflow, or increasing the number of layers of the circuit board 300, but this leads to the complication of the device and an increase in costs. For this reason, the configuration shown in FIG. 6 is used in this embodiment. The configuration shown in FIG. 6 allows thermal design so that the temperature of the mounted IC is equal to or lower than the upper limit temperature of the design target, without adding a fan 514 or increasing the number of layers. This makes it possible to suppress the risk of thermal shutdown or failure due to a rise in temperature of the IC.

[0062] As shown in Fig. 6, the motor driver IC 416, which has a large package size and high heat dissipation, is mounted on the fourth layer 504, which has low heat dissipation. As a result, the temperature of the motor driver IC 416 increases from 68[°C] to 87[°C] (see Fig. 7), but is kept below the upper limit temperature of the design target. The motor driver IC 406, which has a small package size and low heat dissipation, is mounted on the first layer 501, which has high heat dissipation. As a result, the temperature of the motor driver IC 406 decreases from 110[°C] to 91[°C] (see Fig. 7), and is kept below the upper limit temperature of the design target.

[0063] As described above, in the circuit board 300 on which two or more electronic components capable of realizing the same function can be exclusively mounted, an electronic component with relatively low heat dissipation is mounted in a mounting area of ​​the mounting surface 501a of the circuit board 300 with relatively high heat dissipation. Conversely, an electronic component with relatively high heat dissipation is mounted in a mounting area of ​​the mounting surface 504a of the circuit board 300 with relatively low heat dissipation. In the above example, the motor driver IC 406 with a small package size and relatively low heat dissipation is mounted in a mounting area 512 provided on the mounting surface 501a of the first layer 501 with relatively high heat dissipation of the circuit board 300. The motor driver IC 416 with a large package size and relatively high heat dissipation is mounted in a mounting area 513 provided on the mounting surface 504a of the fourth layer 504 with relatively low heat dissipation of the circuit board 300. With such a configuration, it is possible to suppress the risk of malfunction such as thermal shutdown or failure of electronic components with relatively low heat dissipation.

[0064] In addition, although FIG. 6 shows an example in which the circuit board 300 is arranged horizontally, even when the circuit board 300 is arranged vertically, electronic components with relatively low heat dissipation are mounted in an area of ​​the circuit board 300 with relatively high heat dissipation. For example, when the spatial distance 511 of the first layer 501 is larger than the spatial distance 510 of the fourth layer 504 as in FIG. 6, the heat dissipation of the mounting surface 501a of the first layer 501 is higher than the heat dissipation of the mounting surface 504a of the fourth layer 504. In this case, the mounting area of ​​the motor driver IC 406 with low heat dissipation is provided on the mounting surface 501a of the first layer 501. As a result, even when the circuit board 300 is arranged vertically, the risk of malfunction such as thermal shutdown or failure of electronic components with relatively low heat dissipation can be suppressed.

[0065] Although the circuit board 300 described above is four-layered, even if it is a two-layered, six-layered, or other multi-layered board, electronic components with relatively low heat dissipation are mounted in the mounting area of ​​the mounting surface with relatively high heat dissipation, and electronic components with relatively high heat dissipation are mounted in the mounting area of ​​the mounting surface with relatively low heat dissipation, thereby obtaining the same effect as a four-layered circuit board.

[0066] In the present embodiment, the motor driver ICs 406 and 416 are described as examples of electronic components, but the electronic components are not limited to these. The functions of the electronic components are not limited as long as they are configured to be mounted exclusively on the front and back surfaces of the circuit board 300. For example, the electronic components may be switching ICs, FETs (Field effect transistors), etc.

[0067] Also, an example in which the motor driver IC 416 is an alternative component has been described. However, the effects obtained by this embodiment are not limited to such an example. For example, the circuit board 300 may be designed as a common platform for a plurality of devices. In this case, in one model, a first electronic component having a first function is mounted on a first mounting surface, while in another model, a second electronic component having a different specification from the first electronic component but similarly having the first function is mounted on a second mounting surface. Even in such a case, the effects described in this embodiment can be obtained.

Claims

1. a first mounting area for mounting a first electronic component having at least a first function; a second mounting area for mounting a second electronic component having a higher heat dissipation property than the first electronic component and having at least the first function, the first mounting area is provided on a first mounting surface of the circuit board, the second mounting area is provided on a second mounting surface of the circuit board that is different from the first mounting surface, The heat dissipation of the first mounting surface is higher than the heat dissipation of the second mounting surface. Circuit board.

2. The circuit board is attached to a predetermined device, a distance between the first mounting surface and a surface of the device facing the first mounting area is greater than a distance between the second mounting surface and a surface of the device facing the second mounting area. The circuit board according to claim 1.

3. a package size of the first electronic component is smaller than a package size of the second electronic component, and an area of ​​the first mounting region is smaller than an area of ​​the second mounting region. The circuit board according to claim 1.

4. Further comprising a fan for blowing air to the first mounting surface. The circuit board according to claim 1.

5. a via for connecting an output signal line of the first electronic component and an output signal line of the second electronic component, The circuit board according to claim 1.

6. a connector to which the output signal line of the first electronic component is connected is provided on the first mounting surface, The circuit board according to claim 5.

7. The circuit board has a multi-layer structure, and the first mounting area is provided in one of the outermost layers, and the second mounting area is provided in the other of the outermost layers. The circuit board according to claim 1.

8. A circuit board according to claim 1; a component that forms an image under the control of either the first electronic component or the second electronic component mounted on the circuit board, Image forming device.

9. A circuit board; a support member for supporting the circuit board, the circuit board includes a first mounting area for mounting a first electronic component having at least a first function, and a second mounting area for mounting a second electronic component having at least the first function; the first mounting area is provided on a first mounting surface of the circuit board, the second mounting area is provided on a second mounting surface of the circuit board that is different from the first mounting surface, the circuit board is supported by the support member such that the second mounting surface faces the support member; a package size of the first electronic component is smaller than a package size of the second electronic component, The area of ​​the first mounting area is smaller than the area of ​​the second mounting area. Image forming device.

10. Further comprising a fan for blowing air to the first mounting surface.

10. The image forming apparatus according to claim 9.

11. a via for connecting an output signal line of the first electronic component and an output signal line of the second electronic component, 10. The image forming apparatus according to claim 9.

12. a connector to which the output signal line of the first electronic component is connected is provided on the first mounting surface, The image forming apparatus according to claim 11.

13. The circuit board has a multi-layer structure, and the first mounting area is provided in one of the outermost layers, and the second mounting area is provided in the other of the outermost layers.

10. The image forming apparatus according to claim 9.

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