Patent Publication Number: US-2015062220-A1

Title: Liquid ejecting apparatus, print head unit, and drive substrate

Description:
The entire disclosures of Japanese Patent Application Nos. 2013-179665, filed Aug. 30, 2013 and No. 2014-131048, filed Jun. 26, 2014 are expressly incorporated by reference herein. 
     BACKGROUND 
     1. Technical Field 
     The present invention relates to a liquid ejecting apparatus, a print head unit including an ejection unit that is provided to the liquid ejecting apparatus, and a drive substrate that drives the ejection unit. 
     2. Related Art 
     As a liquid ejecting apparatus such as an ink jet printer, there is known a liquid ejecting apparatus that uses a piezoelectric element as an actuator that ejects ink droplets. To drive the piezoelectric element, it is necessary to apply a drive signal having a vibration range of several tens of volts as a peak value. In the related art, an analog amplifier, in which a bipolar transistor is push-pull connected, is mounted on a drive substrate that generates the driving signal. In the bipolar transistor, when a collector current increases, heat is generated in proportion to the increase. Therefore, in the liquid ejecting apparatus in which a large current and a high voltage are applied between an emitter and a collector to drive multiple capacitive loads, power conversion efficiency is poor and an amount of heat generation is large, and thus there is a problem in that a heat sink for heat dissipation is necessary. 
     In consideration of the above-described problem, the present inventors suggest employing a digital amplification that uses a metal-oxide-semiconductor field-effect transistor (MOSFET) that is more excellent in power conversion efficiency in comparison to the analog amplifier (for example, JP-A-2011-5733). In the digital amplifier using the MOSFET, a pulse modulation technology is used, and thus the power conversion efficiency is more excellent in comparison to the analog amplifier, and thus heat generation can also be suppressed. The reason of using the MOSFET instead of the bipolar transistor is that it is possible to cope with a high-speed switching operation demanded for the digital amplifier. For example, it is necessary to reduce a base width so as to switch the bipolar transistor at a high speed. However, the reduction of the base width is apt to lead to a deterioration in withstanding pressure due to punch-through, and thus it is difficult to apply a high voltage for sufficient liquid ejection between an emitter and a connector. That is, the reduction of the base width is poor in feasibility, and thus it is difficult to employ the bipolar transistor. 
     However, to realize stable liquid droplet ejection by using the digital amplifier, there is demanded a high resolution for amplifying a modulation signal including a frequency component that is several tens of times a frequency component included in a drive signal that is applied to the piezoelectric element for ejection of the liquid droplets. Therefore, a high-frequency operation is necessary, and thus there is a problem in that heat generation at a considerable level is apt to occur. An amount of heat generation in the digital amplifier is caused by switching loss accompanying the high-frequency operation for realizing the high resolution. In a case of only ejecting liquid droplets, the amount of heat generation is at a level in which it is not necessary to use a heat sink. However, in a case of constantly stabilizing an amount of the liquid droplets that are ejected while securing a stable circuit operation, it can be said that the amount of heat generation is at a level for which an arbitrary heat dissipation countermeasure is necessary. Actually, when consideration is given based on a drive signal for ejecting an ink, a modulation single becomes a signal in the order of MHz, and thus it is also necessary for the digital amplifier to be driven in the order of MHz. Due to the high-frequency operation, there is a problem in that heat generation due to a switching loss of a switching element occurs at a considerable level. 
     In addition, there is a demand for miniaturization of the liquid droplet ejecting apparatus, and thus an arbitrary heat dissipation countermeasure is necessary, but there is a problem in that addition of a dedicated heat dissipation component or an increase in the size of the dedicated heat dissipation component is difficult. 
     SUMMARY 
     The invention can be realized in the following forms or application examples. 
     APPLICATION EXAMPLES 
     According to an aspect of the invention, there is provided a liquid ejecting apparatus including an A/D converter that performs pulse modulation of an original drive signal at a high frequency region to generate a modulation signal, a transistor that amplifies the modulation signal to generate an amplified modulation signal, a filter circuit that smooths the amplified modulation signal to generate a drive signal, an ejection unit that is subjected to an ejection operation by the drive signal to eject liquid droplets, and a substrate on which at least the transistor is disposed. Through-holes are formed in the substrate in a region in which the transistor is disposed. 
     According to this configuration, even though including a drive circuit that performs a high-frequency operation, it is possible to secure an expected heat dissipation performance with a simple configuration in which through-holes are formed in a region in which a transistor is disposed without using a dedicated heat dissipation component such as a heat sink. Accordingly, it is possible to constantly stabilize an amount of liquid droplets to be ejected while securing operation stability of the drive circuit. 
     Accordingly, it is possible to provide a liquid ejecting apparatus which realizes stabilization in an amount of liquid droplets that are ejected and operation stability with a simple configuration without using a dedicated heat dissipation component. 
     In addition, the original drive signal represents a signal that is a source of a drive signal that drives an ejection unit to eject a liquid droplet, that is, a reference signal before modulation. The modulation signal represents a digital signal that is obtained by subjecting the original drive signal to pulse modulation (for example, pulse width modulation, pulse density modulation, and the like). The amplified modulation signal represents a modulation signal that is amplified by an amplification circuit including a transistor. The drive signal represents a signal which is obtained by smoothing the amplified modulation signal by using a coil and which is applied to an ejection unit. 
     In addition, it is preferable that a frequency band of an AC component included in the modulation signal or the amplified modulation signal be 1 MHz or higher. 
     In the liquid ejecting apparatus of this application example, the amplified modulation signal is smoothed to generate a drive signal, and a liquid is ejected from a nozzle based on deformation of a piezoelectric element to which a drive signal is applied. Here, when a waveform of a drive signal used by the liquid ejecting apparatus to eject a small dot is subject to frequency spectrum analysis, it can be seen that a frequency component of 50 kHz or lower is included. To amplify an original drive signal including the frequency component of 50 kHz with the digital amplifier, a modulation signal including a frequency component of 1 MHz or higher is necessary. When reproducing the original drive signal only with a frequency component of 1 MHz or lower, an edge of a waveform becomes dull and is rounded. In other words, a waveform in which a corner is removed becomes dull. When the waveform of the drive signal becomes dull, movement of the piezoelectric element that operates along with a rising edge and a falling edge of a waveform gradually occurs, and thus an unstable operation such as tailing during ejection and an ejection failure is apt to occur. In the liquid ejecting apparatus of this application example, since the frequency band of the AC component of the amplified modulation signal is set to 1 MHz or higher, an unstable operation such as the tailing during ejection and the ejection failure does not occurs, and thus it is possible to realize a liquid ejecting apparatus capable of obtaining a high-resolution product. 
     In addition, it is preferable that the frequency band of the AC component included in the modulation signal or the amplified modulation signal be lower than 8 MHz. 
     A high frequency of 8 MHz or higher is supported as a frequency of the amplified modulation signal, resolution of a waveform of the drive signal increases, but a switching frequency in a digital amplifier is raised along with an improvement in the resolution. When the switching frequency is raised, switching loss increases. Therefore, power saving properties and low heat-generation properties of the digital amplifier which are superior to that of an analog amplifier (AB-grade amplifier) may be damaged, and thus amplification by the AB-grade amplifier may be superior to that of the digital amplifier in some cases. In the liquid ejecting apparatus of this application example, the frequency band of the AC component of the amplified modulation signal is set to be lower than 8 MHz, it is possible to maintain the superiority in the power saving properties and the low heat-generation properties in comparison to a case of using the AB-grade amplifier. 
     In addition, it is preferable that the number of the through-holes be more than the number of mounting terminals that mount the transistor one the substrate. 
     According to simulation results obtained by the present inventors, it can be seen that the more the number of the through-holes is, the higher the heat dissipation effect becomes. Accordingly, in a circuit scale of a drive circuit provided with a switching circuit including a switching transistor, and a filter circuit, heat dissipation through-holes are additionally provided even in an interconnection scale capable of being interconnected in a single-sided substrate in which the through-holes are not necessary, thereby securing an expected heat dissipation performance. In other words, through-holes are formed in the number more than necessary in the interconnection scale to increase heat dissipation properties, thereby securing an expected heat dissipation performance. 
     In addition, it is preferable that the number of the through-holes be more than the number of through-holes that are necessary to interconnect the transistor and the filter circuit to the substrate. 
     According to simulation results obtained by the present inventors, it can be seen that the more the number of the through-holes is, the higher the heat dissipation effect becomes. Accordingly, when providing more through-holes, it is possible to increase a heat dissipation effect. 
     In addition, it is preferable that the number of the through-holes be 10 or more. 
     According to simulation results obtained by the present inventors, it can be seen that the more the number of the through-holes is, the higher the heat dissipation effect becomes. Accordingly, when providing more through-holes, it is possible to increase a heat dissipation effect. 
     In addition, it is preferable that the through-holes be formed in a first interconnection that extends from each of the mounting terminals in the transistor. 
     To form the through-holes in the first interconnection that extends from the mounting terminal in the transistor, it is necessary to increase an area of the first interconnection. As the area increases, a surface area of the first interconnection formed from metal foil increases. Accordingly, the first interconnection itself also functions as a heat dissipation plate (heat sink). Accordingly, a heat dissipation effect can be increased. 
     In addition, it is preferable that a solid pattern region, which is broader than the mounting terminal, be formed in the first interconnection, and the through-holes be formed in the solid pattern region. 
     The broader an area of the first interconnection is, the broader a surface area is. Accordingly, it is possible to increase a heat dissipation effect to the air. According to this, it is possible to further increase the heat dissipation effect. 
     In addition, it is preferable that an area of the solid pattern region be broader than a plane area of the transistor. 
     The broader the area of the first interconnection is, the further the surface increase. Accordingly, it is possible to increase the heat dissipation effect to the air. According to this, it is possible to further increase the heat dissipation effect. 
     In addition, it is preferable that the substrate be a double-sided substrate, the transistor and the filter circuit be mounted on a first surface of the substrate, and a second interconnection, which is connected to the first interconnection through the through-holes, be formed on a second surface that is opposite to the first surface. 
     In a case of the double-sided substrate, the second interconnection is also formed on the second surface in addition to the first interconnection that is a heat dissipation plate of the first surface, and the second interconnection also functions as a heat dissipation plate. Accordingly, it is possible to further increase the heat dissipation effect. 
     In addition, it is preferable that an area of the second interconnection be broader than the plane area of the transistor. 
     The broader the area of the second interconnection is, the broader a surface area is. Accordingly, it is possible to increase a heat dissipation effect to the air. According to this, it is possible to further increase the heat dissipation effect. 
     In addition, it is preferable that the liquid ejecting apparatus further include a casing body and a frame of the casing body, the substrate be mounted on the frame in a state in which the second surface faces the frame, and a heat transfer member be interposed between the frame and the substrate. 
     According to this configuration, the substrate is mounted on the frame of the casing through the heat conductive member. That is, the substrate is thermally coupled to a metal frame, and thus heat generated in the substrate is effectively transferred to the frame and is dissipated. Accordingly, it is possible to further increase the heat dissipation effect. 
     In addition, it is preferable that the ejection unit include a piezoelectric element, a pressure chamber which is filled with a liquid and in which an inner pressure increases or decreases due to displacement of the piezoelectric element, and a nozzle which communicates with the pressure chamber and ejects the liquid as the liquid droplet due to the increase and decrease in the pressure inside the pressure chamber. 
     A liquid ejection type is largely classified into a thermal type in which a liquid filled in the pressure chamber is heated by allowing a current to flow through a resistive element such as a heater, and the liquid is ejected by transferring the thermal energy to the liquid, a piezo type in which at least a part of a wall surface inside the pressure chamber is designed to be displaceable, and a volume inside the pressure chamber is caused to vary by displacing the wall surface using displacement of a piezoelectric element that displaces when a voltage is applied thereto, thereby ejecting the liquid filled in the pressure chamber, and the like. However, heat generation in an amplification circuit including a transistor is larger in the piezo type in comparison to the thermal type when considering that a large voltage variation accompanied by ejection of the liquid is necessary, and thus it is possible to strongly have the effect of the invention. 
     According to another aspect of the invention, there is provided a drive substrate including an A/D converter that performs pulse modulation of an original drive signal at a high frequency region to generate a modulation signal, a transistor that amplifies the modulation signal to generate an amplified modulation signal, a filter circuit that smooths the amplified modulation signal to generate a drive signal, and a substrate on which at least the transistor is disposed. Through-holes are formed in the substrate in a region in which the transistor is disposed. 
     According to still another aspect of the invention, there is provided a printer head unit including an A/D converter that performs pulse modulation of an original drive signal at a high frequency region to generate a modulation signal, a transistor that amplifies the modulation signal to generate an amplified modulation signal, a filter circuit that smooths the amplified modulation signal to generate a drive signal, an ejection unit that is subjected to an ejection operation by the drive signal to eject liquid droplets, and a substrate on which at least the transistor is dispose. Through-holes are formed in the substrate in a region in which the transistor is disposed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
         FIG. 1  is a perspective view illustrating an overview of a liquid ejecting apparatus according to Embodiment 1. 
         FIG. 2  is a view schematically illustrating a printing mechanism. 
         FIG. 3  is a plan view of a nozzle plate; 
         FIG. 4  is a cross-sectional view taken along line IV-IV in  FIG. 3 . 
         FIG. 5  is a block diagram illustrating a configuration of a control circuit of a printer. 
         FIG. 6  is a block diagram illustrating a configuration a drive circuit. 
         FIG. 7  is a view illustrating an example of a drive signal and printing data. 
         FIG. 8  is a spectrum analysis diagram of an original drive signal. 
         FIG. 9  is a circuit block diagram of a head substrate; 
         FIG. 10  is a plan view of a surface of a drive circuit region in a main substrate. 
         FIG. 11  is a plan view illustrating an interconnection scale of the drive circuit. 
         FIG. 12  is a plan view illustrating a heat generation distribution of the drive circuit. 
         FIG. 13  is a view illustrating a substrate setting in a simulation. 
         FIG. 14  is a graph illustrating heat dissipation characteristics with respect to a rear surface of a substrate. 
         FIG. 15  is an enlarged view of a switching circuit mounting region in  FIG. 10 . 
         FIG. 16  is a plan view of a rear surface in a main substrate. 
         FIG. 17  is a cross-sectional view illustrating an aspect of a heat dissipation structure to a frame. 
         FIG. 18  is a schematic configuration view of a different ejection unit. 
         FIG. 19  is a schematic configuration view of a different ejection unit. 
         FIG. 20  is a schematic configuration view of a different ejection unit. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Hereinafter, embodiments of the invention will be described with reference to the attached drawings. In addition, in the respective drawings, reduced scales of respective layers or respective portions are made to be different from actual scales so as to make the respective layers or the respective portions have a recognizable size in the drawings. 
     Embodiment 1 
     Overview of Liquid Ejecting Apparatus 
       FIG. 1  is a perspective view illustrating an overview of a liquid ejecting apparatus according to Embodiment 1. First, an overview of a printer  100  as the liquid ejecting apparatus according to this embodiment will be described. 
     The printer  100  is an ink jet type printer that performs printing by using a print head unit  20  with respect to a sheet of paper  1  as a printing medium fed from a paper feeding tray  2  on a rear surface side, and discharges the sheet of paper  1  toward a paper discharging tray  6  on a front surface side. In addition, in the following description, a direction in which the sheet of paper  1  is transported is referred to as a transportation direction  4 , and a direction (a width direction of the sheet of paper  1 ) intersecting the transportation direction is referred to as a paper width direction  5 . In addition, in the transportation direction  4 , a paper feeding tray  2  side is referred to as an upstream side, and a discharge (front surface) side is referred to as a downstream side. 
     The print head unit  20  is provided with a line head, and can complete the printing with a so-called single pass in which scanning (reciprocal operation) in the paper width direction  5  is not performed and the printing is performed only with a sheet of paper  1  transporting operation to the transportation direction  4 . On the print head unit  20 , a black ink is also mounted in addition to three columns of line heads corresponding to a plurality of colors (cyan, magenta, yellow, light cyan, light magenta, and the like) of inks, and thus the print head unit  20  is provided with a total of four line heads. Although details will be described later, a plurality of print head modules are disposed at each of the line heads at a constant pitch across the width direction (paper width direction  5 ) of the sheet of paper  1 . 
     A plurality of flexible printed circuits (FPC)  51  are connected to the print head unit  20 . The FPC  51  supplies a control single such as a drive signal for an ejection operation of a plurality of ejection units and a timing signal to the print head unit  20  from a main substrate  50 . Here, a drive circuit that generates the drive signal is mounted on the main substrate  50 . The drive circuit employs a digital amplifier (amplification circuit) excellent in power conversion efficiency, but heat generation due to switching loss of a switching element is apt to occur at a considerable level. In the printer  100 , a plurality of through-holes are formed in a drive circuit region of the main substrate  50  to dissipate the generated heat. In addition, the main substrate  50  is fixed to a metal frame (not shown) of a case  3  to increase a heat dissipation effect, thereby realizing a stable operation. Hereinafter, these configurations will be described in detail. 
       FIG. 2  is a view schematically illustrating a printing mechanism. 
     Subsequently, an overview of the printing mechanism and a printing flow will be described. 
     The printing mechanism of the printer  100  includes the paper feeding tray  2 , a paper feeding roller  7 , a transportation unit  10 , the print head unit  20 , the paper discharging tray  6 , and the like. 
     The paper feeding roller  7  represents a pair of rollers provided on a downstream side of the paper feeding tray  2 , and feeds the sheet of paper  1  on the paper feeding tray  2  one by one to the transportation unit  10 . 
     The transportation unit  10  includes a transportation drive roller  11 , a transportation belt  12 , a driven roller  13 , and the like. The transportation belt  12  is wound (stretched) between (at the outer periphery of) the transportation drive roller  11  and the driven roller  13 . The transportation belt  12  is a strip-shaped belt. As indicated by an arrow, the transportation belt  12  mounts the sheet of paper  1  supplied from the paper feeding roller  7  thereon, and transmits the sheet of paper  1  to a downstream side along with rotation of the transportation drive roller  11 . 
     The transportation belt  12  is provided with a suction device that suctions the sheet of paper  1  on a surface of the transportation belt  12 , a position detection device that detects a position of the sheet of paper  1  in the transportation direction  4  (all of these are not shown), and the like. As the suction device, an air suction device that suctions the sheet of paper  1  by using a negative pressure of air, an electrostatic suction device that suctions the sheet of paper  1  by using an electrostatic force, and the like are used. As the position detection device, a linear encoder and the like are used. 
     An electric motor (not shown) is connected to the transportation drive roller  11 . The electric motor rotates in response to a control signal transmitted from a control unit to be described later, and moves the transportation belt  12 . The driven roller  13  rotates along with movement of the transportation belt  12 . 
     The print head unit  20  ejects inks with respect to the sheet of paper  1  on the transportation belt  12  at a timing synchronized with transportation movement (including a stationary state) to performs printing. Specifically, the print head unit  20  ejects inks from nozzles of a plurality of ejection units disposed on a head disposition surface  27  on a transportation unit  10  side in the print head unit  20 . The printed-out sheet of paper  1  is fed to the paper discharging tray  6  on a downstream side by the transportation belt  12 . 
       FIG. 3  is a plan view of the head disposition surface. Specifically,  FIG. 3  is a plan view of the head disposition surface  27  when observing the print head unit  20  from a transportation unit  10  side. 
     As described above, a plurality of columns of line heads  22  corresponding to inks of a plurality of colors such as cyan, magenta, yellow, and black are formed in the print head unit  20 . When being observed from the head disposition surface  27  side, a line head  22 (C) for cyan, a line head  22 (M) for magenta, a line head for yellow (not shown), a line head for black (not shown), . . . are disposed in this order from an upstream side to a downstream side in the transportation direction  4 . A basic configuration of the line heads is common regardless of ink colors, and thus hereinafter, a description will be made by representatively referring to the line head  22 (C) for cyan as the “line head  22 ”. 
     The line head  22  includes a plurality of print head module  23  that are disposed in a zigzag manner in the paper width direction  5 . 
     Each of the print head modules  23  has an elongated rectangular shape, and is disposed in a state in which a long side direction is set as the paper width direction  5 . In other words, two columns of print head modules  23 , which are parallel with each other in the transportation direction  4 , are disposed in the line head  22 , and the print head modules  23  in each column are alternately disposed in the paper width direction  5 . A reference hole  24  is respectively formed in both ends (short-side side) of the rectangular print head module  23 . 
     In the head disposition surface  27 , the print head module  23  is disposed with the the two reference holes  24  made as a planar position reference. The plurality of print head modules  23  are disposed in this manner, thereby constituting the line head  22  in which ejection units (ejection heads) are disposed at a constant pitch across the paper width direction  5 . That is, an ejection unit column (nozzle column) across the paper width direction  5  which is constituted by the plurality of print head modules  23  instead of an independent constituent unit is referred to as the line head  22 . 
     Each of the print head modules  23  is provided with two nozzle columns  26  each including a plurality of nozzles  25  disposed at a constant pitch in the paper width direction  5 . The two nozzle columns  26  in the paper width direction  5  are disposed between the two reference holes  24 . The two nozzle columns  26  are parallel with each other in the transportation direction  4 , but are disposed to deviate (shift) by a half pitch in the paper width direction  5 . In other words, the two nozzle columns  26  are disposed in a zigzag manner in such a manner that a nozzle  25  of an adjacent nozzle column is disposed at a half position of an arrangement pitch in the nozzle columns  26  in the transportation direction  4 . This disposition is also referred to a zigzag disposition. According to this configuration, a printing dot density (resolution) in the paper width direction  5  increases. In addition, a nozzle length by the two nozzle columns  26  in the paper width direction  5  is also referred to as a “band length”. In the line head  22 , the band length is continuously disposed in the paper width direction  5 , thereby constituting the line head  22 . In addition, although details will be described later, an ejection operation including an operation of a drive circuit is performed per unit of the print head module  23 . 
     Configuration of Ejection Unit 
       FIG. 4  is a cross-sectional view taken along IV-IV line in  FIG. 3 . Specifically,  FIG. 4  is a side cross-sectional view of the nozzle columns  26  (ejection unit) in the transportation direction  4  of the print head modules  23 . 
     Here, a single-component structure of the ejection units  30  that constitute the print head module  23 , and an ink ejecting operation will be described. 
     Each of the ejection units  30  is an ink jet type recording head (ejection head) that ejects (sprays) an ink, and has a configuration in which a flow passage unit  28  and a drive unit  29  are stacked in this order from a nozzle plate  21  side. 
     The flow passage unit  28  includes the nozzle plate  21 , a reservoir plate  31 , a sealing plate  32 , and the like. 
     In the nozzle plate  21 , each ejection nozzle  25  of each of the ejection units is formed in a depth direction (paper width direction  5 ) of the drawing (paper surface). 
     The reservoir plate  31  is disposed on the nozzle plate  21  in an overlapping manner and includes a second communication hole  39  and a common ink chamber  93 . The second communication hole  39  is a penetration hole that is formed at a position overlapping the nozzle  25 . The common ink chamber  93  is a common ink chamber that is formed an upstream side in the transportation direction  4 , and is also referred to as a reservoir. The common ink chamber  93  is formed across the ejection units that are continuous in the depth direction (the paper width direction  5 ) of the drawing. An ink is supplied to the common ink chamber  93  from an ink tank (not shown) through a supply passage (not shown) such as a tube. 
     The sealing plate  32  is a member that becomes a lid of the reservoir plate  31 , and has a common supply port  34  and a first communication hole  38 . The common supply port  34  is an ink supply port of the common ink chamber  93 , and is formed in a slit shape along the common ink chamber  93  in the depth direction (the paper width direction  5 ) of the drawing. The first communication hole  38  is a penetration hole formed at a position overlapping the second communication hole  39 . 
     The drive unit  29  includes a pressure chamber substrate  40 , a vibrating plate  41 , a head substrate  15 , and the like. A pressure chamber  36  constituted by an elongated rectangular groove in the transportation direction  4  is formed in the pressure chamber substrate  40 . The pressure chamber  36  is formed for each ejection unit, and thus in a plan view, a plurality of the pressure chambers  36  are formed in the pressure chamber substrate  40  in a comb tooth shape in the paper width direction  5 . On an upstream side of the pressure chamber  36 , a supply hole  35  constituted by a penetration hole is formed at a position overlapping the common supply port  34 . On a downstream side of the pressure chamber  36 , a communication hole  37  constituted by a penetration hole is formed at a position overlapping the first communication hole  38 . In addition, the pressure chamber  36  is also referred to as a cavity. 
     The vibrating plate  41  is a member that becomes a lid of the pressure chamber substrate  40  (pressure chamber  36 ), and a piezoelectric element  33  as an actuator is attached onto a surface (top surface) that is opposite to the pressure chamber  36 . 
     The head substrate  15  is disposed on an upper side of the drive unit  29 , and selectively supplies a drive signal to the piezoelectric element  33 . Although details will be described later, a switch selection circuit that sequentially and selectively supplies the drive signal with respect to the plurality of ejection units  30  (piezoelectric elements  33 ) is mounted on the head substrate  15 . One sheet of the head substrate  15  is mounted with respect to the print head module  23  ( FIG. 3 ). In other words, one sheet is set with respect to (over) the plurality of ejection units  30  that constitute the print head module  23 . An FPC  51  is connected to the head substrate  15 . 
     Continuously, an ink ejection operation will be described. 
     First, as an initial state of each of the above-described ejection units  30 , the common ink chamber  93 , the common supply port  34 , the supply hole  35 , the pressure chamber  36 , the communication hole  37 , the first communication hole  38 , and the second communication hole  39  communicate with each other, and enter a state of being filled with an ink set to the same hydraulic pressure. 
     When a drive signal is applied to the piezoelectric element  33 , the piezoelectric element  33  is contraction-vibrated. When the vibrating plate  41  is bent according to the contraction vibration and a volume of the pressure chamber  36  decreases, an ink is extruded and is ejected from the nozzle  25  as an ink droplet. In addition, when the volume of the pressure chamber  36  returns to an original state after the ink is ejected, a negative pressure is generated, and thus an ink corresponding to an amount of ejected ink is sucked into the pressure chamber  36  from the common ink chamber  93 . 
     Configuration of Control Circuit 
       FIG. 5  is a block diagram illustrating a configuration of a control circuit of the printer. 
     Here, a configuration of the control device (circuit) that controls the printer  100  will be described. The control device of the printer  100  is constituted by a plurality of circuit units mounted on the main substrate  50  ( FIG. 1 ). Accordingly, hereinafter, an overview of the control device will be described with reference to a circuit block configuration diagram of the main substrate  50  in  FIG. 5 . 
     On the main substrate  50  (control device), an interface circuit  42 , a control circuit  43 , a head drive circuit  44 , a paper feeding roller drive circuit  45 , a transportation roller drive circuit  46 , and the like are mounted. The interface circuit  42  trims printing data  17  input from an external apparatus such as a personal computer (PC) to data capable of being processed in the control circuit  43 , and transmits the trimmed data to the control circuit  43  as printing data  18 . 
     The control circuit  43  is a central processing unit (CPU) and controls respective units such as the head drive circuit  44 , the paper feeding roller drive circuit  45 , and the transportation roller drive circuit  46 . A read-only memory (ROM)  47 , and a random access memory (RAM)  48  are annexed to the control circuit  43  as a storage unit. Various control programs that control an operation of the printer  100 , data accompanying the various control programs, and the like are stored in the ROM  47 . In addition, the accompanying data also includes a data table of drive signal data  61  that drives the piezoelectric element  33  ( FIG. 4 ) of the ejection unit  30 . A plurality of pieces of drive signal data in accordance with a resolution (dot size), a gradation, a color tone, and the like are stored in the table. 
     Printing data that is input, processing data that is necessary when printing the printing data, and the like are temporarily stored in the RAM  48 . In addition, a program for a printing process and the like may be temporarily developed in some cases. In addition, there is no limitation to this configuration, and a one-chip dedicated system integrated circuit (IC) such as a micro controller unit (MCU) including a ROM and a RAM may be used. 
     In addition, the control circuit  43  distinguishes the printing data  18  input through the interface circuit  42  into printing data  60  and drive signal data  61  (generates the printing data  60  and the drive signal data  61 ), transmits the printing data  60  to the head substrate  15 , and transmits the drive signal data  61  to the drive circuit  44 . The printing data  60  is information about ON/OFF switching of the ejection unit  30  ( FIG. 4 ) and control of an ejection timing in the print head. The drive signal data  61  is information about a voltage (drive signal) that is applied to the piezoelectric element  33  ( FIG. 4 ) of the ejection unit  30 . 
     The head drive circuit  44  will be described later. In addition, in  FIG. 5 , the drive circuit  44  that drives one of the print head modules  23  ( FIG. 3 ) is illustrated for simplification. However, actually, the drive circuit  44  is mounted on the main substrate  50  in a number corresponding to the number of the print head modules  23  (head substrates  15 ). 
     The paper feeding roller drive circuit  45  is a drive circuit of a motor that rotates the paper feeding roller  7  ( FIG. 2 ), and drives the paper feeding roller motor  52  based on a control signal transmitted from the control circuit  43 . 
     The transportation roller drive circuit  46  is a drive circuit of a motor that rotates the transportation drive roller  11  ( FIG. 2 ), and drives the transportation roller motor  53  based on a control signal transmitted from the control circuit  43 . 
     Configuration of Head Drive Circuit 
       FIG. 6  is a block diagram illustrating a configuration of the head drive circuit. 
     Continuously, a circuit configuration of the drive circuit  44  will be described in detail. 
     The drive circuit  44  is a so-called D-grade amplifier (digital amplifier) that is constituted by a drive IC  54  a switching circuit  55 , a filter circuit  56 , and the like. 
     The drive IC  54  D/A converts the digital drive signal data  61  supplied from the control circuit  43  to generate original drive signal  62 , performs pulse density modulation, and switches the switching circuit  55  based on the modulated data. 
     The drive IC  54  is constituted by a storage unit  57 , a control unit  58 , a D/A conversion unit  59 , a triangular wave oscillator  63 , a comparator  64 , a gate drive circuit  65 , and the like. 
     The storage unit  57  is a RAM and stores drive signal data  61  constituted by digital electric potential data and the like. 
     The control unit  58  converts drive signal data fetched from the storage unit  57  into a voltage signal, and holds the voltage data for a predetermined sampling period. In addition, the control unit  58  gives an instruction for a frequency of a triangular signal, a drive signal, a drive signal output timing, and the like to a triangular wave oscillator  63  to be described later. In addition, the control unit  58  also outputs an operation stopping signal  66  (on operation: high level) that stops an operation of the gate drive circuit  65 . 
     The D/A conversion unit  59  converts the voltage signal output from the control unit  58  into an analog signal, and outputs the converted signal as the original drive signal  62 . That is, the storage unit  57 , the control unit  58 , and the D/A conversion unit  59  function as an original drive signal generating circuit. 
     The triangular wave oscillator  63  outputs a triangular wave signal that becomes a reference signal in accordance with the frequency, the drive signal, and the drive signal output timing based on the instruction of the control unit  58 . 
     The comparator  64  compares the original drive signal  62  output from the D/A conversion unit  59  and the triangular wave signal output from the triangular wave oscillator  63  with each other, and outputs a pulse-duty modulation signal (high frequency) that becomes an on-duty when the original drive signal  62  is larger than the triangular wave signal. As described above, the triangular wave oscillator  63  and the comparator  64  function as a modulation circuit (A/D converter). 
     The gate drive circuit  65  selectively turns on any of two transistors  68  and  71  of the switching circuit  55  to be described later based on the modulation signal transmitted from the comparator  64 . In other words, the gate drive circuit  65  alternately switches (ON/OFF) the transistors  68  and  71  for switching. In addition, in a case where the operation stopping signal  66  transmitted from the control unit  58  is in a low level, the gate drive circuit  65  turns off all of the two transistors  68  and  71 . 
     The switching circuit  55  is constituted by the two transistors  68  and  71 , a capacitor  72 , a resistor  73 , a capacitor  74 , a resistor  75 , and the like. In addition, the gate drive circuit  65  and the switching circuit  55  function as a digital power amplification circuit. 
     The transistor  68  is a metal oxide semiconductor field effect transistor (MOSFET). In the transistor  68 , a gate terminal is connected to a high-side output terminal GH of the gate drive circuit  65 , a source terminal is connected to an intermediate node  69  (also, referred to as an intermediate electric potential  69 ) that becomes a half bridge output terminal, and a drain terminal is connected to a VDD. As an appropriate example, a resistor  67  is inserted (interposed) between the output terminal GH and the gate terminal. 
     The transistor  71  is a MOSFET. In the transistor  71 , a gate terminal is connected to a low-side output terminal GL of the gate drive circuit  65 , a source terminal is connected to a GND, and a drain terminal is connected to the intermediate node  69 . As an appropriate example, a resistor  70  is inserted (interposed) between the output terminal GL and the gate terminal. In addition, the resistors  67  and  70  are overcurrent preventing resistors that prevent an overcurrent to the gate terminal. 
     In addition, as an appropriate example, the capacitor  72  and the resistor  73  are serially connected in this order between the source terminal and the drain terminal of the transistor  68 . Similarly, the capacitor  74  and the resistor  75  are serially connected in this order between the source terminal and the drain terminal of the transistor  71 . The capacitors and the resistors constitute a circuit that reduces a high frequency noise during switching. In addition, there is no limitation to this configuration, and a configuration by only the two transistors  68  and  71  is also possible. 
     An output signal of the switching circuit  55  is output from the intermediate node  69  to the filter circuit  56 . The output signal is an amplified modulation signal obtained by amplifying a modulation signal, and becomes a high-frequency pulse signal in which pulses (rectangular waves) of a VDD electric potential (wave height) are continuous with the GND set as a reference. 
     The filter circuit  56  is a low-pass filter constituted by a coil  76 , a capacitor  77 , and the like. 
     One end of the coil  76  is connected to the intermediate node  69 , and the other end is connected to one end of the capacitor  77 . The other end of the capacitor  77  is connected to the GND. In addition, the other end of the coil  76  becomes an output line of a drive signal  78 . Specifically, in an amplified modulation signal that is input to the filter circuit  56  from the switching circuit  55 , a high-frequency region is cut out and is demodulated to an analog signal obtained by amplifying the original drive signal  62 . The analog signal becomes the drive signal  78  and is supplied to the head substrate  15  through the FPC  51 . 
     Details of Drive Signal (Waveform) 
       FIG. 7  is a view illustrating an example of a drive signal and printing data. 
     Here, a drive signal (waveform) that is generated by the drive circuit  44  will be described. 
     Similar to a waveform PCOM 2 , a representative drive signal  78  is a waveform which rises from the intermediate electric potential  69 , retains a high electric potential (VDD) for a little while, falls under the intermediate electric potential  69 , retains a low electric potential (GND) for a little while, rises again to the intermediate electric potential  69 , and retains the intermediate electric potential  69  for a little while. In addition, similar to a waveform PCOM 1 , a waveform which rises from the intermediate electric potential  69 , retains the high electric potential VDD for a little while, falls (returns) to the intermediate electric potential  69 , and retains the intermediate electric potential  69  is also a drive waveform. That is, the drive signal  78  is constituted by the unit waveform PCOM 1 , PCOM 2 , PCOM 3 , . . . which are continuous in time series. 
     In the case of the waveform PCOM 2 , a rising portion is a step of expanding a volume of the pressure chamber  36  ( FIG. 4 ) that communicates with the nozzle  25  ( FIG. 4 ) to draw an ink (to pull in a meniscus in consideration of an ink ejection surface) into the pressure chamber  36 , and the falling portion is a step of reducing the volume of the pressure chamber  36  to extrude the ink (to extrude the meniscus). According to this operation, an ink droplet is ejected from the nozzle. In addition, the waveform PCOM 1  is a unit waveform that is called minute vibration, and is a waveform that allows an ink in the vicinity of the nozzle to fluctuate at a level in which the ink is not ejected (takes in and out the meniscus) to stir the ink, thereby suppressing thickening of the ink. 
     In addition, an ink droplet may be ejected by only a single waveform PCOM 2 . It is possible to change a pull-in amount of the ink, a pull-in speed of the ink, an ejected amount of the ink, or an ejection speed of the ink by changing a voltage increase and decrease inclination or a wave height value of the waveform PCOM 2  constituted by a trapezoidal voltage waveform in various manners, thereby obtaining ink droplets having sizes different from each other. 
     As is the case with the drive signal  78  in  FIG. 7 , when a plurality of drive waveforms are connected in time series, it is possible to impact next ink droplet to the same position before previously impacted ink is dried, and thus it is also possible to make a printing dot size large. Also, it is possible to realize multi-gradation in combination with this technology. 
     Continuously, a waveform quality of the drive signal  78  and the like will be described with reference to  FIG. 6 . 
     As described above, the drive signal  78  is a signal obtained by amplifying the original drive signal  62  generated by the D/A conversion unit  59 . Specifically, the drive signal  78  is a signal obtained by amplifying the original drive signal  62  in which a vibration range (peak to peak) is several volts (for example, approximately 3 V) to a signal having a vibration range of several tens volts (for example, approximately 42 V). For example, the waveform PCOM 2  is a waveform obtained by amplifying a waveform COMA (an enlarged view on an upper side of  FIG. 7 ) in the original drive signal  62 . 
     Here, with regard to a waveform quality (degree of similarity before and after amplification) of the drive signal  78 , the waveform of the original drive signal  62  is reproduced in an approximately reliable manner by suppressing jaggies. 
     The reason of the approximately reliable reproduction is that a pulse density modulation method is employed. Specific reasons are as follows. For example, a power supply voltage is set to 42 V, it is necessary for a vibration range of the drive signal  78  to be as wide as approximately 2 V to 37 V. To perform pulse modulation while securing a waveform quality, operation with a high-frequency modulation signal in the order of MHz is necessary. However, according to experiment results obtained by the present inventors, the pulse density modulation method is more appropriate for high-frequency operation in comparison to a pulse width modulation method in which a period is constant. In addition, in a typical audio apparatus, a frequency of approximately 32 kHz to 400 kHz is used. In addition, there is no limitation to the pulse density modulation method, and a modulation method compatible with a high-frequency operation on the order of MHz is also possible. 
       FIG. 8  is a spectrum analysis diagram of an original drive signal. Specifically,  FIG. 8  is a view obtained by performing frequency spectrum analysis with respect to the waveform COMA (waveform PCOM 2  after amplification) in the original drive signal in  FIG. 7 . As shown in a graph  95 , it can be seen that a frequency of approximately 10 kHz to 400 kHz is included in the original drive signal COMA that is subjected to the frequency spectrum analysis. 
     To amplify a drive signal by a digital amplifier, it is necessary to drive the digital amplifier with a switching frequency at least 10 or more times that of a frequency component included in the drive signal before amplification. If the switching frequency of the digital amplifier is less than 10 times in comparison to a frequency spectrum included in the drive signal, it is difficult to perform amplification by modulating a high-frequency spectrum component included in the drive signal, and thus a corner (edge) of the drive signal becomes dull and is rounded. When the drive signal becomes dull, movement of the piezoelectric element that operates along with a rising edge and a falling edge of a waveform gradually occurs, and thus an ejected amount may be unstable, or ejection may not occur. That is, there is a concern that an unstable operation may occur. 
     In this embodiment, as shown in a graph  95  in  FIG. 8 , a peak is present at approximately 60 kHz, and many components are less than 100 kHz, an thus it is preferable that the digital amplifier be operable at a switching frequency of approximately 1 MHz that is at least 10 times the 100 kHz. 
     Here, a frequency component included in the original drive signal is different depending on a waveform of the original drive signal in accordance with the size of an ink droplet to be ejected or the size of a printing dot. For example, the waveform COMA is an original drive signal for ejecting an ink droplet having a size smaller than a standard size, and thus as shown in  FIG. 8 , a vibration range is made to be as small as approximately 2 V. As described above, to eject a small-sized ink droplet, it is necessary to allow the piezoelectric element to sharply move so as to eject a small amount of ink droplet. Therefore, it is necessary for the drive signal to include many high-frequency spectrum components. In addition, it is necessary to quickly move the piezoelectric element so as to perform high-speed printing, and thus it is necessary for the drive signal to include many high-frequency spectrum components. That is, the further high-speed and high image quality printing is tried, the higher a demanded minimum frequency becomes. 
     In addition, the drive signal in this embodiment is designed for use in typical homes and offices, and thus the drive signal is designed on the assumption that a A4-size printed material having a resolution of approximately 5760×1440 dpi is obtained at a printing speed of 5 sheets per minute by using 180 piezoelectric elements. 
     In addition, even in a case where the switching frequency is high, a different problem occurs. When performing switching with a high voltage and a high frequency for driving the piezoelectric element, a junction capacity increases due to a switching transistor structure, and thus various problems such as occurrence of noise caused by the increase in the junction capacity, and an increase in a switching loss due to the high-frequency operation are apt to occur. Particularly, the increase in the switching loss may be a significant problem in the digital amplifier. The reason of the significance is that the increase in the switching loss may damage a merit relating to power saving properties and low heat-generation properties of the digital amplifier which are superior to that of an AB-grade amplifier (analog amplifier). 
     In this embodiment, when being compared with the analog amplifier (AB-grade amplifier) that has been used in the related art, it can be seen that the following results are obtained. That is, the digital amplifier is superior to the analog amplifier up to 8 MHz, but in a case of driving the transistor at a frequency higher than 8 MHz, the AB-grade amplifier may be superior to the digital amplifier. 
     In consideration of these situations, it is preferable that the frequency of the modulation signal be equal to or higher than 1 MHz and lower than 8 MHz. In this embodiment, the frequency of the modulation signal may be set to a range of equal or higher than 1 MHz and lower than 8 MHz in accordance with specifications of the ejection unit (piezoelectric element), or an ejection quality. 
     Method of Selecting (Switching) Ejection Unit 
       FIG. 9  is a circuit block diagram of the head substrate. 
     Continuously, a circuit configuration of the head substrate  15 , and a switching method of sequentially selecting the plurality of ejection units  30  (piezoelectric elements  33 ) of the print head module  23  ( FIG. 3 ) will be described. 
     In  FIG. 7 , an example of the printing data  60  is shown on a lower side of the drive signal  78 . The printing data  60  is a signal for performing ON/OFF switching of the ejection units and control of an ejection timing in the print head, and examples thereof include a drive pulse selection signal SI&amp;SP, a latch signal LAT, a channel signal CH, a clock signal (not shown), and the like. 
     As shown in  FIG. 9 , as is case with the drive signal  78 , the printing data  60  is supplied to the head substrate  15  through the FPC  51 . 
     The head substrate  15  is constituted by a shift register  79 , a latch circuit  80 , a level shifter  81 , a selection switch  82 , and the like. 
     The drive pulse selection signal SI&amp;SP is sequentially input to the shift register  79 , and a storage region thereof is sequentially shifted from an initial stage to a subsequent stage in accordance with an input pulse of the clock signal (not shown). After the drive pulse selection signal SI&amp;SP is stored in the shift register  79  in a number corresponding to the number of nozzles, the latch circuit  80  latches each output signal of the shift register in response to the latch signal LAT that is input. A signal retained in the latch circuit  80  is converted by the level shifter  81  into a signal having a voltage level capable of turning ON/OFF a subsequent-stage selection switch  82 . The reason of the voltage conversion is that the drive signal  78  is set to a voltage higher than an output voltage of the latch circuit  80 , and thus an operation voltage of the selection switch  82  is also set to be high in accordance with the level. In addition, the channel signal CH is also input to the latch circuit  80 . The channel signal CH latches an individual waveform PCOM of the drive signal  78 . That is, serial drive signals  78  start to be output with the latch signal LAT, and an individual waveform PCOM is output for each channel signal CH. 
     In this manner, the drive signal  78  is supplied to the piezoelectric element  33  of an ejection unit, in which a corresponding individual switch is turned on, at a connection timing of the drive pulse selection signal SI&amp;SP. 
     In addition, after the drive pulse selection signal SI&amp;SP of the shift register  79  is retained in the latch circuit  80 , subsequent printing information is input to the shift register  79 , and retention data of the latch circuit is sequentially updated in accordance with the ejection timing of an ink droplet. 
     Interconnection Aspect of Drive Circuit in Main Substrate 
       FIG. 10  is a plan view of a drive circuit region in the main substrate. 
     First, basic specifications of the main substrate  50  will be described. 
     In this embodiment, as an appropriate example of the main substrate  50 , a double-sided substrate that is a glass epoxy substrate (for example, FR4) is employed. In an initial state, copper foil is bonded to the entirety of a front surface and a rear surface, and the copper foil is patterned by a known method such as an etching method or a photolithography method to form a necessary interconnection pattern. 
     Here, a plurality of through-holes  85  (hereinafter, also referred to as THs  85 ), which penetrate between the front surface and the rear surface and establish electrical connection between interconnections on the front surface and interconnections on the rear surface, are formed in the main substrate  50 . In addition, in this embodiment, “through-hole” is a via in Japanese Industrial Standard Printed Circuit terminology (JIS C5603-1993), and is a hole that is used for interlayer connection. Each of the THs  85  is formed by boring a hole in the substrate and plating an inner wall of the hole. 
       FIG. 10  illustrates a mounting region in which the drive circuit  44  is mounted (disposed) on the front surface (first surface) of the main substrate  50 . The drive circuit is mounted across three regions in which a drive IC mounting region  154 , a switching circuit mounting region  155 , and a filter circuit mounting region  156  are continuous. In addition, in this embodiment, the main substrate  50  is also referred to as a drive substrate. 
     The drive IC  54  is mounted in the drive IC mounting region  154 . The switching circuit mounting region  155  is disposed on a right side of the drive IC mounting region  154  on the paper (drawing). 
     The resistors  67  and  70 , the transistors  68  and  71 , the capacitor  72 , the resistor  73 , the capacitor  74 , and the resistor  75  are mounted in the switching circuit mounting region  155 . The filter circuit mounting region  156  is disposed on a right side of the switching circuit mounting region  155 . 
     The coil  76  and the capacitor  77  are mounted in the filter circuit mounting region  156 . In this manner, all components that constitute the drive circuit  44  are mounted on the surface, but many THs  85  are disposed at a region centering around the switching circuit mounting region  155 , and the THs  85  are used for electrical connections of these components. 
       FIG. 11  is a plan view illustrating an interconnection scale of the drive circuit and corresponds to  FIG. 10 . 
       FIG. 11  is a view obtained by extracting the components of the drive circuit  44  from  FIG. 10 , and by connecting terminals of respective components with solid lines similar to circuit interconnections in  FIG. 6 . As can be seen from the drawing, a portion in which solid lines intersect each other is not present, and the interconnections are completed on a single surface (front surface). That is, it can be seen that the drive circuit  44  has an interconnection scale that can be mounted on a single-sided substrate without providing the TH  85 . 
     On the other hand, as described above, an expensive double-sided substrate is used as the actual main substrate  50 , and many THs  85  are formed in the main substrate  50 . The reason of this configuration is that the THs  85  are used for heat dissipation. According to experiment results obtained by the present inventors, it is can be seen that when the THs  85  are formed in a heat generation portion, a heat dissipation effect is obtained. Details will be described below. 
     Heat Generation Distribution 
       FIG. 12  is a plan view illustrating a heat generation distribution of the drive circuit and corresponds to  FIG. 10 . 
     To examine a heat generation distribution of the drive circuit  44 , the present inventors mounted the drive circuit  44  on a glass epoxy substrate for evaluation, and a temperature distribution was examined with a thermography in a state in which a load was applied to the drive circuit  44  under substantially the same test conditions as that in actual operation. In addition, an interconnection pattern of the substrate for evaluation was made to be different from that of the actual main substrate  50  ( FIG. 10 ) and was set to have simple specifications in which through-holes for heat dissipation were not provided, and electrical interconnections and interconnections necessary for evaluation were formed. 
       FIG. 12  illustrates results of the above-described test. A portion in which a temperature was the highest was the switching circuit mounting region  155 . In the switching circuit mounting region  155 , a heat generation region  97  indicated by a shadow ellipse centering around the two transistors  68  and  71  was at a high temperature. Specifically, a temperature of the package of the transistors  68  and  71  was the highest and the temperature was approximately 70° C., and a temperature of patterns at the periphery of a drain terminal of each of the transistors was 65° C. to 70° C. Even in a region in which the temperature was the highest among other regions, the temperature was lower than 50° C. With regard to ranking, the filter circuit mounting region  156  ranked second and the drive IC mounting region  154  ranked third (the temperature was the lowest among the three regions). 
     With regard to determination whether or not the heat generation of approximately the highest temperature of 70° C. obtained from the experiment results is a temperature level that becomes a problem, a configuration including only one drive circuit  44  may not cause a problem. However, actually, a plurality of the drive circuits  44  are mounted on the main substrate  50  adjacently to each other as described above. Therefore, the present inventors made the following determination. Although a heat sink is not necessary, an arbitrary countermeasure for heat dissipation is necessary in consideration of the following situations and the like. That is, the main substrate  50  is mounted on a bottom side in a casing  3  ( FIG. 1 ) and thus heat is likely to be shut, and in addition to heat generation in the plurality of drive circuits  44  adjacent to each other, heat from other heat generation sources such as a power supply circuit is applied to the main substrate  50 . 
     With regard to a situation in which the two transistors  68  and  71  themselves become the biggest heat generation portion, a main cause of the situation is considered due to a switching loss. Specifically, power at on-resistance inside a transistor is consumed as heat due to a current flowing between a drain and a source during switching. Particularly, the switching loss occurs for each switching, and thus in the drive circuit  44  that operates with a high-frequency in the order of MHz that is 10 or more times that of an audio apparatus and the like, a considerable amount of heat generation occurs. 
     Simulation of Through-Hole for Heat Dissipation 
       FIG. 13  is a view illustrating a substrate setting in a simulation.  FIG. 14  is a graph illustrating heat dissipation characteristics with respect to the rear surface of the substrate. 
     When finding various countermeasures for heat dissipation on the basis of the above-described heat generation distribution results, the present inventors thought up provision of the through-holes for heat dissipation in the substrate, and performed a simulation with respect to a heat dissipation effect in the through-holes. In the simulation, conditions of a simulation substrate are set as shown in  FIG. 13 . 
     In the simulation substrate in  FIG. 13 , the THs  85  are disposed in a manner of 4(row)×4(column) (totally, sixteen). A length in the disposition region is set as “L”. In addition, in the simulation, to change the number of the THs  85 , the length L is also changed in accordance with the number of THs  85 . At this time, an arrangement pitch of the THs  85  is set to be constant. 
     In addition, the number of the THs  85  is set as “N”, a diameter of (hole diameter) is set as φ, and the thickness of plating is set as “t”. In addition, the thickness of the substrate is set as “H”. 
     A thermal conductivity of copper that constitutes interconnections and plating is set as “Ka”, and a thermal conductivity of a resin in the glass epoxy substrate is set as “Kb”. 
     The following theoretical formulae are derived based on the above-described setting conditions. 
     First, a thermal resistance Ra of a through-hole portion is obtained by the following Expression (1). 
     
       
         
           
             
               
                 
                   Ra 
                   = 
                   
                     H 
                     
                       Ka 
                       × 
                       N 
                       × 
                       π 
                       × 
                       φ 
                       × 
                       t 
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     Similarly, a thermal resistance Rb of a resin portion in the substrate is obtained by the following Expression (2). 
     
       
         
           
             
               
                 
                   Rb 
                   = 
                   
                     H 
                     
                       Kb 
                       × 
                       
                         ( 
                         
                           
                             L 
                             2 
                           
                           - 
                           
                             N 
                             × 
                             π 
                             × 
                             φ 
                             × 
                             t 
                           
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     In addition, a thermal resistance R from the front surface to the rear surface of the substrate is obtained by the following Expression (3). 
     
       
         
           
             
               
                 
                   R 
                   = 
                   
                     1 
                     
                       
                         1 
                         Ra 
                       
                       + 
                       
                         1 
                         Rb 
                       
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
     A graph  86  in  FIG. 14  is a result obtained by simulating a variation in the thermal resistance R from the front surface to the rear surface of the substrate by using Expression (1) to Expression (3) in a case of changing the number of THs  85 . The horizontal axis represents the number of through-holes, and the vertical axis represents the thermal resistance R. In addition, in the simulation, the diameter (hole diameter) φ of the THs  85  is set to 0.75 mm, and the thickness t of the plating is set to 35 μm. The arrangement pitch of the THs  85  is set to 1.4 mm. Accordingly, in  FIG. 13 , the length L of the arrangement region in which four THs  85  are arranged in a row is approximately 5 mm (4.95 mm), but as described above, the length L varies in accordance with the number of the THs  85 . In addition, the thickness H of the substrate is set to 1 mm. The simulation is performed in a state in which the thermal conductivity Ka of copper is set to 380 W/mK and the thermal conductivity Kb of the resin in the glass epoxy substrate is set to 0.3 W/mK. 
     As can be seen from the graph  86 , in a case where only one TH  85  is provided, the thermal resistance R becomes 32° C./W, and thus a heat dissipation effect is hardly expected. However, in a case where the number of the THs  85  is set to 10, the thermal resistance R becomes 3.2 ° C./W that is 1/10 times that of the case in which one TH  85  is provided, and thus a considerable heat dissipation capacity can be obtained. In addition, from the simulation, it can be seen that as the number of the THs  85  increases, the thermal resistance decreases. In addition, the graph  86  is obtained by performing calculation using the above-described simulation conditions (the size of the TH  85  and the like), but there is no limitation to the conditions. Even when the size of the TH  85 , the arrangement pitch, and the like vary, the characteristic (tendency) of the graph in that as the number of THs  85  increases, the thermal resistance decreases is maintained. In other words, when the size of the THs  85 , the arrangement pitch, and the like vary, the inclination (variation) of the graph is changed. However, the fact in that the heat dissipation effect increases by increasing the number of THs  85  is also true of this case. 
     The reason that the through-holes show a heat dissipation operation is considered due to thermal conduction provided by the copper plating (metal) formed mainly on the inner wall of the TH  85 . Specifically, heat of the front surface pattern migrates (conducts) to the rear surface pattern through the copper plating of the TH  85 . In addition, although not considered in the simulation, in a case of forming a hollow (penetration) through-hole such as a large-sized through-hole in which the inside is empty, a heat dissipation effect due to convection of the air may be further expected. 
     Detailed Arrangement Aspect of Through-Hole 
       FIG. 15  is an enlarged view of the switching circuit mounting region in  FIG. 10 . In addition, a scale of the entirety of the drawing is enlarged, but a relative scale between components and a pattern size (including the TH) maintains a ratio of design values. This is also true of in respective drawings subsequent to  FIG. 10 . In addition, the following description will be made on the assumption that in the drawing, a drive IC mounting region  154  side is set as a left side, a filter circuit mounting region  156  side set as a right side, and a right and left direction is set as a horizontal direction with the switching circuit mounting region  155  made as the center. Similarly, the following description will be made on the assumption that a transistor  71  side is set a lower upper side, a side opposite to the transistor  71  side is set as an upper side, and an upper and lower direction is set as a vertical direction with the transistor  68  set as the center. In addition, in  FIG. 15 , the external shape (package) of electronic components is indicated by a dotted line for easy visibility of interconnections (pattern). 
     An interconnection layout (pattern, TH arrangement) of the drive circuit  44  is designed based on findings obtained from the above-described examination about heat generation distribution and the above-described simulation about the through-holes for heat dissipation. 
     Here, an interconnection layout at the periphery of mounting terminals of transistors will be described. First, a description will be made starting from an interconnection (first interconnection) that is connected to the drain terminal of the transistor  68 . The drain terminal ranks second to transistor package as a portion in which an amount of heat generation is large. 
     As shown in  FIG. 15 , a drain terminal D of the transistor  68  is disposed along two short sides of horizontally elongated rectangular package. The drain terminal D is respectively disposed at the right side and the left side in a division manner. However, the drain terminals D are the same electrical terminals, and thus a solid pattern that expands to an upper side of the package connects to the right and left drain terminals D in a state of surrounding three sides of the package. In addition, for example, a typical interconnection pattern is linear member (interconnection line) having a width of approximately 0.5 mm, and electrical connection is sufficiently performed with this width. However, in this embodiment, a region (solid pattern) broader than an electrically necessary line width is provided as a through-hole forming (arranging) region to obtain a heat dissipation function from the front surface. In addition, an interconnection that is directly connected to each terminal of transistors is referred to as the first interconnection. The solid pattern is a high electric potential VDD ( FIG. 6 ) interconnection in a power supply electric potential. In addition, in the following description, the solid pattern (region) is also referred to as solid pattern VDDa. 
     Here, in the solid pattern VDDa, eighteen THs  85  are formed even in the switching circuit mounting region  155 . Specifically, fifteen THs  85  are formed in the vicinity of a left drain terminal D, and three THs  85  are formed in a portion ranging through the resistor  73  from the right drain terminal D. In addition, the three THs  85  on a resistor  73  side are parts of a group of the THs  85  which are also continuous to the filter circuit mounting region  156  side, and thus when adding the number (6 pieces) of the THs in the group, a total number of the THs becomes  24 . That is, a large number of THs  85  are formed in comparison to the number of terminals (totally four; the gate G, the source S, and the drain D×2) necessary for mounting of the transistor  68 . In addition, in the drawing, mounting terminals for the gate terminal G, the source terminal S, and the drain terminal D of the transistor  68  are hatched, and this hatching illustrates a recommended land (pattern) size in component specifications. A land size of the drain terminal D is 1.3 mm (vertical)×1.0 mm (horizontal). In addition, as shown in the drawing, a recommended land of the drain terminal D is vertically divided into two pieces, but a drain terminal on a package side is one (integrated), and thus the number of necessary terminals is set to four. Even assuming that the portions divided into two are counted, the number of the terminals is six, and thus the number of the THs  85  is larger than the number of terminals. In addition, as an appropriate example, the diameter φ of the TH  85  is set to 0.75 mm, and the thickness t of the plating is set to 35 μm. A basic arrangement pitch of the TH  85  is set to 1.4 mm. 
     In addition, an area of the solid pattern VDDa as the first interconnection is set to be broader (larger) than the land size of the drain terminal D. This is also obvious when considering that lands of all of the drain terminals D are included in the region of the solid pattern VDDa. In addition, in an actual substrate, an insulating resist layer is formed on approximately the entire surface of the solid pattern VDDa, and the resist is opened in an amount corresponding to the mounting terminals including the land of the drain terminal D, and thus a copper pattern is exposed. That is, the resist is arranged across a region other than the mounting terminal (land) portions indicated by hatching in the drawing. In addition, in  FIG. 15 , hatching of mounting terminals in components other than the transistor is omitted, but this arrangement is also true of components other than the transistor. In addition, an area of the solid pattern VDDa is set to be broader than the package size (plane area) of the transistor  68 . Even in the switching circuit mounting region  155 , the area of the solid pattern VDDa is approximately two times the area of the package. 
     Next, an interconnection (first interconnection) that is connected to the source terminal S of the transistor  68  will be described. The source terminal S is formed on a bottom surface (bottom portion) of the package. A land size of the source terminal S is set to 1.0 mm (vertical)×0.7 mm (horizontal). The first interconnection that is led-out from the source terminal S has a solid pattern shape broader than the land size from the starting point, and is largely expanded toward a transistor  71  side to form a solid pattern  169   a  including the drain terminal D of the transistor  71 . In other words, the solid pattern  169   a  is an intermediate node  69  ( FIG. 6 ) interconnection, and electrically connects between the source terminal S of the transistor  68 , and the drain terminal D of the transistor  71 . 
     Here, twenty six THs  85  are formed in the solid pattern  169   a.  Specifically, six THs  85  are formed between the transistor  68  and the transistor  71 , six THs  85  are formed on a lower-right side of the transistor  68 , and fourteen THs  85  are formed on a left side of a package of the transistor  71 . That is, a large number of THs  85  are formed in comparison to the number of terminals necessary for mounting of the transistor  68 . 
     In addition, an area of the solid pattern  169   a  as the first interconnection is set to be broader (larger) that the land size of the source terminal S (drain terminal D). This is also obvious when considering that the land of the source terminal S (drain terminals D) is included in the region of the solid pattern  169   b.  In addition, an area of the solid pattern  169   a  is set to be broader than a package size (plane area) of the transistor  68 . Specifically, the area of the solid pattern  169   a  is approximately two times the area of the package. 
     Next, an interconnection (first interconnection) that is connected to the gate terminal G of the transistor  68  will be described. In addition, as described above, the gate terminal is not a heat generation source. However, the gate terminal is a terminal of the transistor  68 , and thus the gate terminal is collectively described. The gate terminal G is also formed on the bottom surface (bottom portion) of the package. A land size of the gate terminal G is set to 0.7 mm (vertical)×0.7 mm (horizontal). The first interconnection that is led-out from the gate terminal G has a solid pattern shape broader than the land size from the starting point, is largely expanded toward a lower-left side, and is connected to the other end of the resistor  67 . 
     Continuously, the transistor  71  will be described. In addition, the transistor  71  is the same component as the transistor  68 , and thus a description of a terminal position, a land size, and the like will not be repeated. 
     An interconnection that is connected to the drain terminal D of the transistor  71  is the same as the solid pattern  169   a  of the source terminal S of the transistor  68 . As described above, twenty six THs  85  are formed in the solid pattern  169   a,  and the majority of the THs  85  are disposed in the vicinity of the drain terminal D of the transistor  71 . 
     A first interconnection that is led-out from the source terminal S of the transistor  71  has a solid pattern shape broader than the land size from the starting point, and is largely expanded toward a lower side. The first interconnection is divided into a right region and a left region in the middle of the expansion toward the lower side, but the first interconnection respectively forms further broader solid pattern GNDa on the right region and the left region. The solid pattern GNDa is low electric potential GND ( FIG. 6 ) interconnection in the power supply electric potential. Even in the switching circuit mounting region  155 , twenty two THs  85  are formed in the solid pattern GNDa. Specifically, eleven THs  85  are formed on a lower side immediately close to the source terminal S, six THs  85  are formed on the region that is divided as a lower-right region, and five THs  85  are formed on the region that is divided as a lower-left region. That is, a large number of THs  85  are formed in comparison to the number of terminals necessary for mounting of the transistor  71 . In addition, the solid pattern GNDa is also a power supply electric potential, and thus the solid pattern GNDa is further expanded toward left and right sides. Therefore, when the TH is formed in the further expanded portions, the number of the THs further increases. 
     In addition, an area of the solid pattern GNDa as the first interconnection is set to be broader (larger) that the land size of the source terminal S. This is also obvious when considering that the land of the source terminal S is included in the region of the solid pattern GNDa. In addition, an area of the solid pattern GNDa is set to be broader than a package size (plane area) of the transistor  71 . Specifically, the area of the solid pattern GNDa 9  is approximately five or more times the area of the package even in the switching circuit mounting region  155 . 
     Next, an interconnection (first interconnection) that is connected to the gate terminal G of the transistor will be described. The first interconnection that is led-out from the gate terminal G has a solid pattern shape broader than the land size from the starting point, is largely expanded toward lower-left side, and is connected to the other end of the resistor  70 . The interconnection is substantially the same interconnection aspect as the gate terminal G of the transistor  68 . 
     Continuously, an interconnection aspect of components at the periphery of the transistors  68  and  71  will be described. 
     The capacitor  72  and the resistor  73 , which are connected between the source terminal S and the drain terminal D of the transistor  68 , are disposed in a state of being surrounded by the solid pattern  169   a  and the solid pattern VDDa. That is, the capacitor  72  and the resistor  73  are disposed in a state of being surrounded by a plurality of the THs  85  that are formed in the solid pattern  169   a  and the solid pattern VDDa. 
     Similarly, the capacitor  74  and the resistor  75 , which are connected between the source terminal S and the drain terminal D of the transistor  71  are also disposed in a state of being surrounded by the solid pattern GNDa and the solid pattern  169   a.  That is, the capacitor  74  and the resistor  75  are disposed in a state of being surrounded by a plurality of THs  85  that are formed in the solid pattern GNDa and the solid pattern  169   a.    
     Interconnection Aspect of Filter Circuit 
     A description will be made with reference to  FIG. 10 . 
     Continuously, an interconnection aspect of the filter circuit mounting region  156  that ranks second to the switching circuit mounting region  155  in the amount of heat generation will be described. 
     The coil  76  has an approximately square package, and input terminal  76   a  and an output terminal  76   b  are provided on a left side (left-hand side). In addition, a mounting terminal is provided on a right side (right-hand side). A package size is larger than the area of two transistors  68 . 
     The input terminal  76   a  that is located on an upper side of the left-hand side is electrically connected to the solid pattern  169   a  through a plurality of THs  87 . Each of the THs  87  is a through-hole having a diameter larger than that of the TH  85 , and the inside is empty (air can pass through the inside). As an appropriate example, the diameter φ of the TH  87  is set to 1.5 mm, and the thickness t of plating is set to 35 μm. An arrangement pitch of the TH  87  is set to 2.0 mm. 
     A mounting land of the input terminal  76   a  is included in a corner of an approximately square solid pattern in which the TH  87  is formed. In other words, the corner of the approximately square solid pattern becomes the mounting land. In addition, ten THs  87  are formed in the solid pattern. 
     A plurality of THs  87  are formed in the vicinity of the output terminal  76   b.  A mounting land of the output terminal  76   b  is included in a corner of the approximately rectangular solid pattern in which the TH  87  is formed. A mounting land for one end of the capacitor  77  is formed on a lower side of the solid pattern. In the solid pattern, in addition to the ten THs  87 , two THs  85  are formed in the vicinity of the capacitor  77 . 
     A mounting land for other end of the capacitor  77  is formed in the solid pattern GNDa. Ten or more THs  85  are also formed at a portion close to the mounting land for the other end of the capacitor  77 . 
     Interconnection Aspect of Substrate Rear Surface 
       FIG. 16  is an enlarged plan view of a mounting region in which the drive circuit  44  is mounted on a rear surface (second surface) of the main substrate  50 , and FIG.  16  corresponds to  FIG. 10 . In addition, for easy comprehension of a relationship with component arrangement on the front surface,  FIG. 16  is drawn as a perspective view in which an interconnection on the rear surface is drawn in a perspective manner from a front surface side. An external shape of components is indicated by a dotted line. 
     Components are not mounted in the mounting region of the drive circuit  44  on the rear surface as the second surface, and the mounting region is formed as an approximately flat surface. First, a description will be made starting from a solid pattern  169   b  as a second interconnection that is formed between the two transistors and  71  in a horizontally elongated shape. The solid pattern  169   b  is an interconnection (second interconnection) that is electrically connected to the solid pattern  169   a  ( FIGS. 10 and 15 ) on the front surface through the plurality of THs  85 . The solid pattern  169   b  is disposed in a horizontally elongated manner from the vicinity of the drive IC  54  to an intermediate portion of the coil  76 . At a portion overlapping the coil  76 , connection is established with the mounting land of the input terminal  76   a  of the coil  76  by the plurality of THs  87 . 
     Here, an area of the solid pattern  169   b  is set to be broader than the package (external) size of the transistor  68  ( 71 ). Specifically, the solid pattern  169   b  has an area approximately six to seven times that of the package. 
     On an upper side of the solid pattern  169   b,  a solid pattern VDDb as the second interconnection is formed. The solid pattern VDDb is an interconnection (second interconnection) that is connected to the solid pattern VDDa ( FIG. 10 ) on the front surface through the plurality of THs  85 . The solid pattern VDDb is disposed in a horizontally elongated shape from the vicinity of the drive IC  54  to a region ranging to a part of the filter circuit mounting region  156 . An area of the solid pattern VDDb is set to be broader than the package size of the transistor  68 . Specifically, the solid pattern VDDb has an area approximately three times that of the package. 
     On a lower side of the solid pattern  169   b,  a solid pattern GNDb as a second interconnection is formed. The solid pattern GNDb is an interconnection (second interconnection) that is connected to the solid pattern GNDa ( FIG. 10 ) on the front surface through the plurality of THs  85 . The solid pattern GNDb is disposed in a horizontally elongated shape across a wide range from the vicinity of the drive IC  54  to a region exceeding the filter circuit mounting region  156 . An area of the solid pattern GNDb is set to be broader than the package size of the transistor  68 . Specifically, the solid pattern GNDb has an area approximately ten times that of the package. 
     Heat Dissipation Structure to Frame 
       FIG. 17  is a cross-sectional view illustrating an aspect of a heat dissipation structure to a frame. 
     As also illustrated in  FIG. 1 , the main substrate  50  is mounted on the frame of the printer  100 . The frame is a metal frame, and is formed by subjecting a metal plate to press working or thin plate working. 
     As shown in  FIG. 17 , the main substrate  50  is mounted on the frame  90  in a state in which the rear surface (second surface) faces the frame  90 . The main substrate  50  is attached to a metal plate surface portion that is flat in a structure of the frame  90 . The main substrate  50  is tightly fixed to frame  90  by fastening a screw  91  through a screw hole  88  ( FIG. 10 ). In addition, the screw fastening is performed at a plurality of sites at a peripheral portion of the main substrate  50 . 
     Here, a heat transfer member  89  is disposed (interposed) between the main substrate  50  and the frame  90 . The heat transfer member  89  is sheet-shaped member having flexibility, heat transfer properties, and insulating properties. In an appropriate example, a heat dissipation sheet formed from a silicone rubber to which a ceramic-based material having excellent thermal conductivity is mixed is used as the heat transfer member  89 . In addition, there is no limitation to this member, and an arbitrary sheet-shaped member having the flexibility, the heat transfer properties, and the insulating properties may be used. 
     In an approximate example, the heat transfer member is disposed across the entire surface of the main substrate  50 . In addition, there is no limitation to this configuration, and the heat transfer member  89  may be disposed across a region including a portion overlapping the mounting region of the drive circuit  44 . 
     As described above, according to the printer  100  according to this embodiment, the following effects can be obtained. 
     As a countermeasure for heat generation accompanying the high-frequency operation, the present inventors repeated the examination and simulation about the heat generation distribution of the drive circuit  44 , and repeated trial and error. Then, the present inventions thought up a configuration in which a double-sided substrate is used in spite of an interconnection scale capable of being interconnected with a single-sided substrate, and through-holes for heat dissipation are formed in a transistor arranging region. According to this, it is possible to stabilize the operation of the drive circuit  44  that performs high-frequency operation without using a large-sized (expensive) heat dissipation component such as a heat sink. In other words, it is possible to improve reliability of the drive circuit  44 . Specifically, in the heat generation distribution examination in  FIG. 12 , a temperature of the package of the transistors is the highest and the temperature is approximately 70° C. However, according to the interconnection aspect (including arrangement of the through-holes) of the main substrate  50 , the temperature becomes approximately 60° C., and thus it is possible to accomplish a temperature falling (heat dissipation effect) by approximately 10° C. Similarly, it is also realize temperature falling by approximately 10° C. in patterns at the periphery of the drain terminal. 
     Accordingly, it is possible to provide the main substrate  50  (drive substrate) which has a simple configuration and in which operation stability is realized (secured) even though including the drive circuit  44  that performs high-frequency operation without using a dedicated heat dissipation component such as a heat sink. In other words, it is possible to provide the main substrate  50  (drive substrate) which has a small size and which is excellent in reliability. 
     Accordingly, it is possible to provide the printer  100  which has a simple configuration and which realizes operation stability without using a dedicated heat dissipation component. 
     As a specific through-hole arrangement aspect, the TH  85  is formed in a region of the main substrate  50  in which the switching transistors  68  and  71  are disposed. That is, the TH  85  is formed in a main heat generation region. As illustrated in  FIG. 10 , it is not necessary to provide a through-hole in consideration of an interconnection scale of the drive circuit  44 , but the TH  85  is formed for heat dissipation. In other words, a large number of THs  85  are formed in comparison to the number of through-holes that are necessary for interconnection of the drive circuit  44  in the substrate. According to this configuration, it is possible to improve heat dissipation performance of the drive circuit  44 . The reason of employing this configuration is as follows. Specifically, as illustrated in  FIG. 14 , as the number of the THs  85  for heat dissipation increases, the heat dissipation effect can be raised. 
     As the number of THs  85  increases, the higher heat dissipation effect can be expected. However, generally, as the number of the THs  85  increases, man-hours taken to manufacture the substrate increase and the cost increases, and there is a restriction on a forming space. Therefore, a constant index is necessary. According to experiment results obtained by the present inventors, the number of the mounting terminals of a switching transistor becomes one index, and it can be seen that when forming a large number of through-holes than the number of the mounting terminals, a constant heat dissipation effect is obtained. With regard to a through-hole forming site, it is preferable that the through-hole be formed in an interconnection that is connected to each terminal of the transistors  68  and  71 , but the through-hole may be formed in a region at the periphery of the transistor. In the case of the transistors  68  and  71  that is used in this embodiment, the number of mounting terminals is four (six including divided portions). However, in a case of using three-terminal type, three becomes an index. More preferably, as illustrated in  FIG. 14 ,  10  or more through-holes are formed. In this embodiment, in the switching circuit mounting region  155 , eighteen THs  85  are provided in the solid pattern VDDa, twenty six THs  85  are provided in the solid pattern  169   a,  and twenty two THs  85  are provided in the solid pattern GNDa. In this manner, the above-described index is satisfied only with the solid pattern VDDa in the switching circuit mounting region  155 , and thus it is possible to obtain a sufficient heat dissipation effect. 
     In addition, in an interconnection design of a typical substrate, an interconnection that is led-out from a land of a component is typically formed from a conductive line (pattern) that is narrower than the land. The reason is that a narrow pattern is sufficient to satisfy electrical connection specifications. On the other hand, in this embodiment, the lead-out line from the gate terminal G of the transistor, in which the amount of heat generation is relatively small, is also formed from a solid pattern broader than a land size (0.7 mm) from the starting point. With regard to the source terminal S and the drain terminal D, a further broader solid pattern is used. The reason is that the solid pattern is used for not only electrical interconnection but also heat dissipation. Specifically, the solid patterns come into contact with the air, and thus as the area increases, it is possible to expect heat dissipation due to the air. As the solid pattern is broader, the heat dissipation effect can be expected. However, there is a restriction on a forming space. Therefore, a constant index is necessary. As illustrated in  FIG. 12 , a portion in which the amount of heat generation is the largest is the package of the transistors  68  and  71 , but when a heat sink is mounted to the package, the number of components increases, and an increase in a size is caused. Accordingly, in this embodiment, the periphery of the transistor is formed as a solid pattern, and thus an alternate function of the heat sink is realized. Accordingly, the package size (plane area) of the transistors is set as an index. 
     In this embodiment, the solid pattern VDDa is set to have an area approximately two times that of the package of the transistors. The solid pattern VDDb is set to have an area approximately three times that of the package. Similarly, the solid pattern  169   a  is set to have an area approximately two time that of the package. The solid pattern  169   b  is set to have an area approximately six to seven times that of the package. In addition, the solid pattern GNDa is set to have an area approximately five times the package. The solid pattern VDDb is set to have an area approximately ten or more times that of the package. In this manner, all of the solid patterns on the front and rear surfaces satisfy the above-described index, and thus a sufficient heat dissipation effect can be obtained. Specifically, the periphery of the transistors  68  and  71  is surrounded by the solid patterns, and thus the entirety of the mounting region is allowed to function as a heat dissipation plate. In addition, solid patterns broader than that on the front surface are also formed on the rear surface to which heat is transferred through a plurality of through-holes, and thus the rear surface is also allowed to function as a heat dissipation plate. 
     In addition, the method of forming (designing) the through-holes for heat dissipation and the solid patterns is also applied to interconnection patterns of resistors  73  and  75  and the capacitors  72  and  74  which are components at the periphery of the transistors. In addition, the method is also applied to the filter circuit  56  and the interconnection pattern of the drive IC  54 . That is, the method is applied to the entirety of the mounting region of the drive circuit  44 , and thus a sufficient heat dissipation function is provided. Particularly, the TH  87  in which the inside is empty and which has a large diameter is formed at the periphery of the input terminal  76   a  and the output terminal  76   b  of the coil  76  of the filter circuit  56 . According to the TH  87 , the air can pass through the inside, and thus an air flow occurs between the front and rear surfaces, thereby further increasing the heat dissipation effect. 
     In addition, as illustrated in  FIG. 17 , the main substrate  50  is mounted on the frame  90  in a state in which the rear surface faces the frame  90 , and the heat transfer member  89  is disposed (interposed) between the main substrate  50  and the frame  90 . According to this configuration, it is possible to reliably dissipate heat of the main substrate  50  to the frame  90 . The frame  90  has a large heat capacity, and an area exposed to the air of the outside is also broad, and thus the frame  90  can sufficiently function as the heat dissipation plate. 
     In addition, generally, it is said that man-hours increase in the double-sided substrate having the through-holes due to an increase in man-hours taken for through-hole punching or man-hours taken for plating in comparison to a single-sided substrate. In addition, in addition to the increase in the man-hours, a raw material is also more expensive than that of the single-sided substrate, and thus it is said that the cost increases (two times or four times). This embodiment employs a configuration in which the drive circuit  44  is mounted on the main substrate  50  on which the control circuit  43  is mounted without constituting the drive circuit  44  as an independent substrate, and thus the cost is suppressed. Specifically, the main substrate  50  including the CPU uses a double-sided substrate in consideration of an interconnection scale, and the drive circuit  44  is mounted by increasing an area of the substrate. Accordingly, a great reduction effect is obtained in consideration of the number of components and main-hours in comparison to a case of separately providing an independent substrate. 
     In addition, the invention is no limited to the above-described embodiment, and various changes and modification can be made with respect to the above-described embodiment. Modification Examples will be described below. 
     MODIFICATION EXAMPLE 1 
     A description will be made with reference to  FIG. 13 . 
     In Embodiment 1, the description has been made with respect to a configuration in which the glass epoxy substrate is used as the main substrate  50 . However, there is no limitation to this configuration, and an arbitrary substrate is also possible as long as the through-holes can be formed in the substrate. For example, a ceramic substrate, a Teflon (registered trade mark) substrate, a glass composite substrate, a paper epoxy substrate, a flexible substrate, and the like may be used. 
     In addition, there is no limitation to the double-sided substrate, and the invention may be applied to a multi-layer substrate. In this case, it is not necessary for the through-holes to penetrate the substrate from a front surface to a rear surface, and for example, connection may be established from through-holes in the front surface to through-hole in the rear surface through an intermediate layer (solid) pattern. In other words, there is no problem as long as a heat transfer route from the front surface to the rear surface is formed. 
     In addition, there is no limitation to a through-hole (plated through-hole) in which an plated interconnection is formed on an inner wall, and an arbitrary through-hole is possible as long as the through-hole can transfer heat from the front surface to the rear surface. For example, a through-hole filled with conductive paste is possible, and a through-hole in which solder plating is formed on an inner wall is also possible. In addition, there is no limitation to the size or the arrangement pitch of the through-holes described in an appropriate example of the embodiment. The size or arrangement pitch of the through-holes may be appropriately changed in accordance with a substrate that is used, and design specifications such as a circuit scale and a substrate mounting type to a casing, a frame, and the like. 
     Even in this configuration, the above-described heat dissipation operation effect is also obtained, and thus the same effect as the above-described embodiment can be obtained. 
     MODIFICATION EXAMPLE 2 
     A description will be made with reference to  FIG. 16 . 
     In Embodiment 1 and Modification Example 1, the description has been made with respect to a configuration in which the drive circuit  44  is mounted on the main substrate  50 . However, there is no limitation to this configuration, and a single configuration (substrate) is possible as long as a double-sided through-hole substrate is used. For example, it is possible to employ a configuration in which an independent drive substrate (on which the drive circuit  44  is mounted) is built-in in the print head unit  20  in  FIG. 1 . In this configuration, the drive substrate is mounted on a metal component of the print head unit  20 . In addition, it is also possible to employ a configuration in which a circuit of the head substrate  15  is also mounted on the drive substrate and thus the head substrate  15  and the substrate are integrated is built-in in the print head unit  20 . 
     Even in this configuration, the above-described heat dissipation operation effect is also obtained, and thus the same effect as the above-described embodiment and modification examples can be obtained. 
     MODIFICATION EXAMPLE 3 
     A description will be made with reference to  FIG. 1 . 
     In the embodiment and modification examples, the printer  100  has been described as a line printer that performs printing with a single pass in the transportation direction  4  (sub-scanning direction). However, there is no limitation to this configuration, and an arbitrary printer is possible as long as this printer is provided with the print head module  23 . For example, a so-called carriage type ink jet printer provided with a carriage that performs printing while reciprocally moving in the paper width direction  5  (main scanning direction) is also possible. In this case, an ink cartridge and the print head module  23  are mounted on the carriage. An extension direction of the nozzle column (band length) in the print head module  23  becomes the transportation direction  4 , and feeding of the sheet of paper  1  is performed per band length unit. In addition, with regard to a printing medium, there is no limitation to a single sheet (sheet of paper), and a rolled sheet of paper or a continuous sheet of paper is possible. In addition, a material of the printing medium is not limited to the sheet of paper, and texture or a film is possible. 
     Even in this configuration, the above-described heat dissipation operation effect is also obtained, and thus the same effect as the above-described embodiment and modification examples can be obtained. 
     MODIFICATION EXAMPLE 4 
       FIG. 18  is a schematic configuration view of an ejection unit with a different vibration mode. 
     In the above-described embodiment and modification examples, the description has been made with respect to a type in which the vibration mode of the piezoelectric element  33  of the ejection unit  30  ( FIG. 4 ) uses a bending mode. However, there is no limitation to this configuration, and any ejection unit is possible as long as this ejection unit uses vibration of the piezoelectric element. For example, similar to an ejection unit  280  in  FIG. 18 , a head using a vertical mode is also possible. Specifically, in the ejection unit  280 , an ink inside a pressure chamber  245  is ejected from a nozzle  241  due to operation of a piezoelectric element  200 . The ejection unit  280  includes a nozzle plate  240  in which the nozzle  241  is formed, a cavity plate  242 , a vibrating plate  243 , and a stacked piezoelectric element  201  constituted by stacking a plurality of the piezoelectric elements  200 . 
     The cavity plate  242  is shaped into a predetermined shape (shape in which a concave portion is formed), and thus the pressure chamber  245  and a reservoir  246  are formed. The pressure chamber  245  and the reservoir  246  communicate with each other through an ink supply port  247 . In addition, the reservoir  246  communicates with an ink cartridge  312  through an ink supply tube  311 . 
     A lower end of the stacked piezoelectric element  201  is bonded to the vibrating plate  243  through an intermediate layer  244 . A plurality of outer electrodes  248  and a plurality of inner electrodes  249  are bonded to the stacked piezoelectric element  201 . That is, the outer electrodes  248  are bonded to the outer surface of the stacked piezoelectric element  201 , and each of the inner electrodes  249  is respectively provided between the piezoelectric elements  200  that constitute the stacked piezoelectric element  201  (or, at the inside of each of the piezoelectric elements). In this case, the outer electrodes  248  and the inner electrodes  249  are arranged in such a manner that a part of each of the outer electrodes  248  and a part of each of the inner electrodes  249  alternately overlap each other in a thickness direction of the piezoelectric element  200 . In addition, when a drive signal is applied between the outer electrode  248  and the inner electrode  249  from the drive circuit  44  (head substrate  15 ), the stacked piezoelectric element  201  is deformed as indicated by an arrow in the drawing and vibrates, and the vibrating plate  243  vibrates due to the vibration. Due to the vibration of the vibrating plate  243 , the volume of the pressure chamber  245  (pressure inside the pressure chamber) varies, and thus an ink (liquid) that is filled in the pressure chamber  245  is ejected from the nozzle  241  as a liquid droplet. Due to the ejection of the liquid droplet, an amount of liquid that is reduced in the pressure chamber  245  is refilled by supply of the ink from the reservoir  246 . In addition, the ink is supplied to the reservoir  246  from the ink cartridge  312  through the ink supply tube  311 . 
       FIG. 19  is a schematic configuration view of an ejection unit with a different vibration mode.  FIG. 20  is a schematic configuration view of an ejection unit with a different vibration mode. 
     In addition, there is no limitation to the configuration ( FIGS. 4 and 18 ) in which the piezoelectric element is attached to the vibrating plate, and a configuration in which the piezoelectric element also functions as the vibrating plate is also possible. In other words, a configuration in which a dedicated vibrating plate is not provided is also possible. 
     In addition, an ejection unit  281  in  FIG. 19  also has a configuration that an ink (liquid) inside a pressure chamber  221  is ejected from a nozzle due to operation of a piezoelectric element  200 . The ejection unit  281  includes a pair of opposing substrates  220 , and a plurality of the piezoelectric elements  200  are intermittently provided between both of the substrates  220  with a predetermined interval. A pressure chamber  221  is formed between the piezoelectric elements  200  adjacent to each other. In the drawing, a plate (not shown) is provided in front of the pressure chamber  221 , the nozzle plate  222  is formed behind the pressure chamber  221 , and a nozzle (hole)  223  is formed in the nozzle plate  222  at a position corresponding to each of the pressure chamber  221 . 
     A pair of electrodes  224  is respectively provided on one surface and the other surface of each of the piezoelectric elements  200 . That is, four electrodes  224  are bonded to one of the piezoelectric elements  200 . When a predetermined drive voltage waveform is applied between predetermined electrodes among the electrodes  224 , the piezoelectric element  200  is subjected to share mode deformation and vibrates (indicated by an arrow in the drawing). Due to the vibration, the volume (pressure in a cavity) of the pressure chamber  221  varies, and thus an ink (liquid) that is filled in the pressure chamber  221  is ejected from the nozzle  223  as a liquid droplet. That is, in the ejection unit  281 , the piezoelectric element  200  itself functions as a vibrating plate. 
     An ejection unit  282  illustrated in  FIG. 20  also has a configuration that an ink (liquid) inside a pressure chamber  233  is ejected from a nozzle  231  due to operation of a piezoelectric element  200 . The ejection unit  282  includes a nozzle plate  230  in which the nozzle  231  is formed, a spacer  232 , and a piezoelectric element  200 . The piezoelectric element  200  is provided to be spaced away from the nozzle plate  230  by a predetermined distance through a spacer  232 , and a pressure chamber  233  is formed in a space surround by the nozzle plate  230 , the piezoelectric element  200 , and the spacer  232 . 
     A plurality of electrodes are bonded to an upper surface of the piezoelectric element  200  in the drawing. Specifically, a first electrode  234  is bonded to approximately the central portion of the piezoelectric element  200 , and a second electrode  235  is respectively bonded to both side portions of the central portion. When a predetermined drive voltage waveform is applied between the first electrode  234  and the second electrode  235 , the piezoelectric element  200  is subjected to share mode deformation and vibrates (indicated by an arrow in the drawing). Due to the vibration, the volume (pressure in a cavity) of the pressure chamber  233  varies, and thus an ink (liquid) that is filled in the pressure chamber  233  is ejected from the nozzle  231  as a liquid droplet. That is, in the ejection unit  282 , the piezoelectric element  200  itself functions as a vibrating plate. 
     In addition, hereinbefore, the description has been made by using the piezoelectric element as an actuator. However, there is no limitation to this configuration, and the invention may be applied to various actuators. For example, the actuator may be a so-called electrostatic actuator which includes a first electrode bonded to an outer side (vibrating plate) of a pressure chamber and a second electrode that is spaced away from the first electrode and faces the first electrode, and a drive voltage is applied to both of the electrodes to generate Coulomb&#39;s force, thereby bending the pressure chamber. 
     In addition, as the actuator, an actuator using electro-thermal conversion by a heater (resistor) is also known. However, when using electromotive conversion by a piezoelectric element, power consumption per one actuator is large. Accordingly, with regard to use of the drive circuit  44  using a digital amplifier, the drive circuit  44  is particularly effective for a piezo-type liquid ejecting apparatus in which consumption of much power is necessary. 
     MODIFICATION EXAMPLE 5 
     A description will be made with reference to  FIG. 1 . 
     In the above-described embodiment and modification examples, the main substrate  50  (drive substrate) is used for ejection of a printing ink. However, there is no limitation to the use, and the main substrate  50  may be applied to a liquid spraying apparatus that sprays other liquids (including fluidal substance such as a liquid substance and gel in which a functional material particles are dispersed in addition to the liquids) other than the ink, or a fluid (a solid capable of being sprayed as a fluid, and the like) other than a liquid. For example, the main substrate  50  may be used in a liquid substance spraying apparatus that sprays liquid substance containing materials such as an electrode material and a coloring material, which are used for manufacturing of a liquid crystal display, an electroluminescence (EL) display, a surface light-emitting display, a color filer, and the like, in a dispersion manner or a dissolution manner, a liquid spraying apparatus that sprays living body organic materials that are used for manufacturing of biochips, and a liquid spraying apparatus that sprays a liquid that is used as a precision pipette and becomes a sample. In addition, the main substrate  50  may be applied to a liquid spraying apparatus that sprays a lubricant to a precision machine such as a timepiece and a camera as a pinpoint, a liquid spraying apparatus that sprays a transparent resin liquid such as a ultraviolet curable resin, which is used to form a micro hemispheric lens (optical lens) that is used in an optical communication element and the like, to a substrate, a liquid spraying apparatus that sprays an etchant such as an acid and an alkali to etch a substrate and the like, a fluidal substance spraying apparatus that sprays a gel, and a fluid spraying type recording device that sprays a solid such as a powder including a toner. 
     Even in a case of being applied to these apparatuses, the above-described heat dissipation operation effect is also obtained, and thus the same effect as the above-described embodiment and modification examples can be obtained.