Abstract:
A vacuum pump including a pump main unit and a control unit is disclosed. The control unit includes a substrate having electronic elements mounted thereon and terminal pins soldered to the substrate at a first end edge of the substrate. The substrate is mounted to a plate via an attachment near a second end edge opposing the first end edge and the plate is mounted to the pump main unit. The terminal pins extend through the plate. Upon linear thermal expansion of the terminal pins, by reason of the location of the terminal pins near the first end edge and the attachment near the second end edge, stresses in the soldered pin connections are reduced. A molding material having a Shore hardness of less than 50, is molded around the electronic elements on the substrate in one embodiment.

Description:
TECHNICAL FIELD 
     The present invention relates to a vacuum pump, and particularly relates to a vacuum pump reducing the influence of thermal expansion of connector pins to prevent cracks in soldered parts while preventing damage to electronic elements. 
     BACKGROUND ART 
     As a result of the recent development of electronics, there is a rapid increase in the demand for semiconductor devices such as memories and integrated circuits. 
     Such a semiconductor device is manufactured by doping impurities into a highly pure semiconductor substrate to impart electrical properties thereto, and forming a minute circuit on the semiconductor substrate by etching, for example. 
     Such operations must be performed in a chamber in a high-vacuum state to avoid the influence of dust or the like in the air. A vacuum pump is generally used to evacuate the chamber. In particular, a turbo-molecular pump, which is a kind of vacuum pump, is widely used since it involves little residual gas and is easy to maintain. 
     When manufacturing a semiconductor, these are many steps for making various process gases act on a semiconductor substrate, and the turbo-molecular pump is used not only to create a vacuum in a chamber, but also to discharge these process gases from the chamber. 
     This turbo-molecular pump consists of a pump main unit and a control device for controlling the pump main unit. As a method for simplifying wiring between substrates by reducing the number of pins of connector plugs for connecting the pump main unit and the control device, Patent Literature 1 suggests that a control substrate for a motor and a magnetic bearing should be arranged on the vacuum side. 
     CITATION LIST 
     Patent Literature 
     [Patent Literature 1] Japanese Unexamined Patent Pub. No, 2007-508492 
     SUMMARY OF INVENTION 
     Technical Problem 
     In the case of Patent Literature 1, a cable is used to connect a substrate having electronic elements thereon to a connector. In order to further simplify the wiring, it is desirable to connect the substrate directly to the connector through soldering, without using the cable. 
     However, when connecting the substrate directly to the connector through soldering, heat is easily accumulated in the pump main unit since the inside thereof is in a vacuum state and it is difficult to release heat through conduction. Accordingly, connector pins linearly expand greatly with the accumulated heat, which leads to possible cracks in solder connection parts. 
     Further, it is required to prevent the electronic elements mounted on the substrate from damage due to the linear expansion of the connector pins. 
     The present invention has been made in view of these conventional problems, and an object thereof is to provide a vacuum pump reducing the influence of thermal expansion of connector pins to prevent cracks in soldered parts while preventing damage to electronic elements. 
     Solution to Problem 
     Accordingly, the present invention is characterized in including: a substrate on which electronic elements are mounted; a plurality of pins soldered to the substrate so that the pins are arranged near one end edge apart from the center of the substrate; a plate having the pins; and an attachment for attaching the substrate to the plate, in which 5 the attachment is arranged near the other end edge apart from the center of the substrate. 
     The pins may be retained by the plate by being fixed while directly penetrating the plate, instead of by being inserted into the plate through the body of the terminal. When the pins are fixed while directly penetrating the plate, it is desirable that the parts where the pins are in contact with the plate are insulated depending on the material of the plate. 
     The pins are arranged near one end edge apart from the center of the substrate. A group of pins functions as a connector. An attachment such as a screw is arranged near the other end edge apart from the center of the substrate, the one end edge and the other end edge facing each other with the center of the substrate therebetween. 
     Since an attachment is arranged only on the other end side of the substrate and the one end side of the substrate is released from attachments, the bend angle of the substrate can be kept small even when the pins expand with heat, which makes it possible to reduce the stress applied on solder connection parts. Accordingly, the possibility of causing cracks in the solder connection parts is extremely small. Since deforming pressure of the substrate is reduced, influence on the electronic elements can be reduced correspondingly. 
     Further, the present invention is characterized in that a ratio of a distance from the center of the group of pins to the attachment to a distance from the center of the group of pins to the center of the substrate is 1.5 or greater. 
     Furthermore, the present invention is characterized in including: a substrate on which electronic elements are mounted; a plurality of pins soldered to the substrate so that the pins are arranged near one end edge apart from the center of the substrate; a plate having the pins; an attachment for attaching the substrate to the plate; and a molding material for molding the electronic elements on the substrate, in which the molding material has a Shore D hardness of less than 50. 
     The electronic element on the substrate is molded with a molding material such as resin. When the substrate bends, the molding material  243 , if having high hardness, is deformed corresponding to the deformation of the substrate. At this time, pressure of the molding material is applied to a fixing leg etc. of the electronic element. When the molding material has high hardness, the electronic element is possibly destroyed when reaction force of the electronic element is not great enough to resist the deforming pressure. 
     Accordingly, a molding material having a Shore D hardness of less than 50 is selected. Since the molding material flexibly follows the deformation of the substrate, load applied to the electronic element is reduced and reaction force of the electronic element can resist the deforming pressure of the molding material. Therefore, the electronic element cannot be easily destroyed. 
     Advantageous Effects of Invention 
     As explained above, according to the present invention, since the attachment is arranged near the other end edge apart from the center of the substrate, the bend angle of the substrate can be kept small even when the pins expand with heat, which makes it possible to reduce the stress applied on solder connection parts. Accordingly, the possibility of causing cracks in the solder connection parts is extremely small. Since deforming pressure of the substrate is reduced, influence on the electronic elements can be reduced correspondingly. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  A block diagram according to an embodiment of the present invention; 
         FIG. 2  Terminal structure; 
         FIG. 3  A diagram showing a pin soldered to a substrate; 
         FIG. 4  A diagram showing a bend amount when a screw is arranged near the center of an AMB control substrate; 
         FIG. 5  A diagram showing a method for reducing a bend angle; 
         FIG. 6  A diagram showing an electronic element when a molding material having high hardness is used; and 
         FIG. 7  A diagram showing the electronic element when a molding material having low hardness is used. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments of the present invention will be explained.  FIG. 1  shows a block diagram according to an embodiment of the present invention. In  FIG. 1 , a turbo-molecular pump  10  consists of a pump main unit  100  and a control unit  200  integrated with each other while sandwiching an aluminum plate  201  therebetween. 
     The plate  201  functions both as the bottom face of the pump main unit  100  and the top face of the control unit  200 . However, the plate  201  may be replaced with two plates. 
     The pump main unit  100  has an inlet port  101  formed at the upper end of an outer cylinder  127 . Inside the outer cylinder  127 , there is provided a rotor  103  having in its periphery a plurality of rotary blades  102   a ,  102   b ,  102   c , . . . formed radially in a number of stages and constituting turbine blades for sucking and exhausting gas. 
     A rotor shaft  113  is mounted at the center of the rotor  103 , and is levitated and supported in the air and controlled in position by a so-called 5-axis control magnetic bearing, for example. 
     Four upper radial electromagnets  104  are arranged in pairs in the X and Y axes which are perpendicular to each other and serve as the radial coordinate axes of the rotor shaft  113 . An upper radial sensor  107  formed of four electromagnets is provided in close vicinity to and in correspondence with the upper radial electromagnets  104 . The upper radial sensor  107  detects a radial displacement of the rotor  103  and transmits the detection result to a control device  300  (mentioned later.) 
     Based on the displacement signal from the upper radial sensor  107 , the control device  300  controls the excitation of the upper radial electromagnets  104  through a compensation circuit having a PID adjusting function, thereby adjusting the upper radial position of the rotor shaft  113 . 
     The rotor shaft  113  is formed of a material having a high magnetic permeability (e.g., iron), and is attracted by the magnetic force of the upper radial electromagnets  104 . Such adjustment is performed independently in the X- and Y-axis directions. 
     Further, lower radial electromagnets  105  and a lower radial sensor  108  are arranged similarly to the upper radial electromagnets  104  and the upper radial sensor  107  to adjust the lower radial position of the rotor shaft  113  similarly to the upper radial position thereof. 
     Further, axial electromagnets  106 A and  106 B are arranged with a metal disc  111  vertically sandwiched therebetween, the metal disc  111  having a circular plate-like shape and arranged at the bottom of the rotor shaft  113 . The metal disc  111  is formed of a material having a high magnetic permeability, such as iron. An axial sensor  109  is arranged to detect an axial displacement of the rotor shaft  113 , and its axial displacement signal is transmitted to the control device  300 . 
     The axial electromagnets  106 A and  106 B are excitation-controlled based on this axial displacement signal through a compensation circuit having a PID adjusting function in the control device  300 . The axial electromagnet  106 A and the axial electromagnet  106 B attract the metal disc  111  upward and downward respectively by their magnetic force. 
     In this way, the control device  300  appropriately adjusts the magnetic force exerted on the metal disc  111  by the axial electromagnets  106 A and  106 B to magnetically levitate the rotor shaft  113  in the axial direction while supporting it in space in a non-contact state. 
     A motor  121  has a plurality of magnetic poles circumferentially arranged around the rotor shaft  113 . Each magnetic pole is controlled by the control device  300  to rotate and drive the rotor shaft  113  through the electromagnetic force acting between the rotor shaft  113  and the magnetic pole. 
     A plurality of stationary blades  123   a ,  123   b ,  123   c , . . . are arranged apart from the rotary blades  102   a ,  102   b,  102 c , . . . with small gaps therebetween. The rotary blades  102   a ,  102   b ,  102   c , . . . are inclined by a predetermined angle from a plane perpendicular to the axis of the rotor shaft  113  in order to transfer the molecules of exhaust gas downward through collision. 
     Similarly, the stationary blades  123  are inclined by a predetermined angle from a plane perpendicular to the axis of the rotor shaft  113 , and arranged alternately with the rotary blades  102  so as to extend toward the inner side of the outer cylinder  127 . 
     One ends of the stationary blades  123  are supported while being fitted into the spaces between a plurality of stationary blade spacers  125   a ,  125   b ,  125   c , . . . stacked together. 
     The stationary blade spacers  125  are ring-like members which are formed of, e.g., aluminum, iron, stainless steel, copper, or an alloy containing some of these metals. 
     The outer cylinder  127  is fixed on the outer periphery of the stationary blade spacers  125  with a small gap therebetween. A base portion  129  is arranged at the bottom of the outer cylinder  127 , and a threaded spacer  131  is arranged between the lower end of the stationary blade spacers  125  and the base portion  129 . An exhaust port  133  is formed under the threaded spacer  131  in the base portion  129 , and communicates with the exterior. 
     The threaded spacer  131  is a cylindrical member formed of aluminum, copper, stainless steel, iron, or an alloy containing some of these metals, and has a plurality of spiral thread grooves  131   a  in its inner peripheral surface. 
     The direction of the spiral of the thread grooves  131   a  is determined so that the molecules of the exhaust gas moving in the rotational direction of the rotor  103  are transferred toward the exhaust port  133 . 
     At the lowest end of the rotary blades  102   a ,  102   b ,  102   c , . . . of the rotor  103 , a rotary blade  102   d  extends vertically downward. The outer peripheral surface of this rotary blade  102   d  is cylindrical, and extends toward the inner peripheral surface of the threaded spacer  131  so as to be close to the inner peripheral surface of the threaded spacer  131  with a predetermined gap therebetween. 
     The base portion  129  is a disc-like member constituting the base portion of the turbo-molecular pump  10 , and is generally formed of a metal such as iron, aluminum, and stainless steel. 
     Further, the base portion  129  physically retains the turbo-molecular pump  10  while functioning as a heat conduction path. Thus, it is desirable that the base portion  129  is formed of a metal having rigidity and high heat conductivity, such as iron, aluminum, and copper. 
     In this configuration, when the rotor shaft  113  is driven by the motor  121  and rotates with the rotary blades  102 , exhaust gas from the chamber is sucked in through the inlet port  101  by the action of the rotary blades  102  and the stationary blades  123 . 
     The exhaust gas sucked in through the inlet port  101  flows between the rotary blades  102  and the stationary blades  123  to be transferred to the base portion  129 . At this time, the temperature of the rotary blades  102  increases due to frictional heat generated when the exhaust gas comes into contact with or collides with the rotary blades  102 , and conductive heat and radiation heat generated from the motor  121 , for example. This heat is transmitted to the stationary blades  123  through radiation or conduction by gas molecules of the exhaust gas etc. 
     The stationary blade spacers  125  are connected together in the outer periphery and transmit, to the outer cylinder  127  and the threaded spacer  131 , heat received by the stationary blades  123  from the rotary blades  102 , frictional heat generated when the exhaust gas comes into contact with or collides with the stationary blades  123 , etc. 
     The exhaust gas transferred to the threaded spacer  131  is transmitted to the exhaust port  133  while being guided by the thread grooves  131   a.    
     Further, in order to prevent the gas sucked in through the inlet port  101  from entering an electrical component section formed of the motor  121 , the lower radial electromagnets  105 , the lower radial sensor  108 , the upper radial electromagnets  104 , the upper radial sensor  107 , etc., the electrical component section is covered with a stator column  122 , and the inside of this electrical component section is kept at a predetermined pressure by a purge gas. 
     Next, configuration of the control device  300  will be explained. Electronic elements constituting the control device  300  are stored separately in a bottom space  301  formed between the plate  201  and the base  129  of the pump main unit  100  and in the control unit  200 . The inside of the bottom space  301  is set at a vacuum atmosphere, and the inside of the control unit  200  is set at an air atmosphere. 
     A hole is arranged in a part of the plate  201 , and a body  205  of a terminal  210  as shown in  FIG. 2  is fixed while penetrating this hole. The body  205  of the terminal  210  has a columnar shape and protrudes from the top face of a roughly-quadrangular bottom plate  203 , and many straight pins  207  are fixed while penetrating the body  205  and the roughly-quadrangular bottom plate  203 . 
     The pins  207  may be retained by the plate  201  by being fixed while directly penetrating the plate  201 , instead of by being inserted into the plate  201  through the body  205  of the terminal  210 . In this case, it is desirable that the parts where the pins  207  are in contact with the plate  201  are insulated depending on the material of the plate  201 . 
     The upper parts of the pins  207  are exposed upward from the plate  201  and penetrate pinholes  212  of an AMB control substrate  209 . As shown in  FIG. 3 , the upper parts of the pins  207  are soldered to the AMB control substrate  209  through the pinholes  212  of the AMB control substrate  209 . Accordingly, no cable is required between the substrate and the pins, differently from the conventional techniques. Electronic elements for controlling the magnetic bearing are mounted on the AMB control substrate  209 . 
     The pins  207  and the electronic elements on the AMB control substrate  209  are electrically connected through the soldered parts. 
     On the other hand, the lower parts of the pins  207  are exposed downward from the plate  201  and penetrate the pinholes  212  of an aerial connection substrate  211 . As shown in  FIG. 3 , the lower parts of the pins  207  are soldered to the aerial connection substrate  211  through the pinholes  212  of the aerial connection substrate  211 . Electronic elements for controlling the motor  121  are mounted mainly on the aerial connection substrate  211 . The pins  207  and the electronic elements on the aerial connection substrate  211  are electrically connected through the soldered parts. 
     An electrolytic capacitor  213  is arranged near the pins  207  on the aerial connection substrate  211  with its elements facing the plate  201 . A heat sink  215  is arranged between the aerial connection substrate  211  and the plate  201 . As a result, the AMB control substrate  209 , the plate  201 , and the aerial connection substrate  211  are integrated into one structure. 
     Some electronic elements which are not used for controlling the magnetic bearing and the motor are mounted on bottom control substrates  217  and  219 . However, instead of arranging the substrates depending strictly on the intended use, electronic elements excepting the electrolytic capacitor  213  may be arbitrarily mounted on the AMB control substrate  209  in the vacuum atmosphere. 
     In order to achieve drip-proof performance, an O-ring  221  is embedded between the plate  201  and the base  129  while surrounding the bottom space  301 , and an O-ring  223  is embedded between the plate  201  and a wall  225  forming the housing of the control unit  200 . 
     Further, a water-cooling pipe is arranged in the base portion  129  near the plate  201  (see a water-cooling pipe  149  in  FIG. 1 ), which makes it possible to cool the plate  201  through the base portion  129 . 
     Next, operation of the control device  300  will be explained. 
     A substrate unit structure is formed by covering the opening of the casing of the pump main unit  100  with the plate  201  functioning also as the casing of the control unit  200 . The pins  207  of the terminal  210  fixed while penetrating the plate  201  are soldered directly to the AMB control substrate  209  and the aerial connection substrate  211  in order to integrate these components. Therefore, only one plate  201  is arranged between the pump main unit  100  and the control unit  200 . 
     By integrating the pump main unit  100  with the control unit  200 , the casing and sealing structures can be made simple, differently from the conventional techniques requiring each of the pump main unit  100  and the control unit  200  to have a casing and a sealing member. 
     Further, by cooling the plate  201  by the water-cooling pipe  149 , electronic components mounted respectively on the AMB control substrate  209  in the vacuum atmosphere and the aerial connection substrate  211  in the air atmosphere can be cooled simultaneously. Therefore, the cooling structure can be simplified. 
     The AMB control substrate  209  is arranged in the bottom space  301  set at the vacuum atmosphere, and electronic elements difficult to place in the vacuum atmosphere are arranged on the aerial connection substrate  211 . Since the AMB control substrate  209 , the plate  201 , and the aerial connection substrate  211  are integrated into one structure through the pins  207 , no extra wiring work is required for the substrates. 
     Since electronic elements for controlling the magnetic bearing are arranged in the bottom space  301  set at the vacuum atmosphere, there is no need to lead the lines of the electromagnets and sensors to the outside, which makes it possible to reduce the number of lines between the AMB control substrate  209  and the aerial connection substrate  211  and the number of pins  207  as much as possible. 
       FIG. 4  is a diagram showing the area including the AMB control substrate  209 , the plate  201 , and the aerial connection substrate  211 . A recess  233  is formed on the plate  201  around the upper parts of the pins  207 , corresponding to the shape of the AMB control substrate  209 . The AMB control substrate  209  is fixed to the plate  201  at several points by screws  235 A,  235 B, and  235 C serving as attachments. 
     In  FIG. 4 , the screws  235 A,  235 B, and  235 C are arranged only on the left of the pins  207 . The screw  235 A is arranged near the left edge of the AMB control substrate  209 , and the screw  235 C is arranged approximately at the center of the AMB control substrate  209 . 
     In the configuration of  FIG. 4 , there is a fear that the pins  207  linearly expands with the heat accumulated in the bottom space  301  and makes the AMB control substrate  209  suddenly bend by an angle θ 1  from the screw  235 C as a fulcrum. The bottom space  301  is heated quite easily since it is in the vacuum environment. In this case, the distance between the center of the group of pins  207  and the screw  235 C is defined as L 1 . 
     As shown in  FIG. 5 , the bend angle of the AMB control substrate  209  is reduced by omitting the screw  235 B and  235 C while keeping only the screw  235 A. Since no screw is arranged on the right of the screw  235 A, the AMB control substrate  209  is released toward the right. 
     In this case, the AMB control substrate  209  bends by an angle θ 2  from the screw  235 A as a fulcrum, but this bend angle is gradual, which means that the possibility of causing cracks in the solder connection parts is extremely small. Here, the distance between the center of the group of pins  207  and the screw  235 A is defined as L 2 . Both in  FIG. 4  and  FIG. 5 , the pins  207  linearly expand with the heat accumulated in the bottom space  301 , similarly. Therefore, the relationship as shown in Formula 1 is established.
 
 L 1×tan θ1= L 2×tan θ2  [Formula 1]
 
     Here, a bend reduction α is defined as θ 1 /θ 2 . When the angle θ is tiny, the bend reduction α can be expressed as in Formula 2. 
     
       
         
           
             
               
                 
                   α 
                   = 
                   
                     
                       
                         θ 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                       
                       
                         θ 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                       
                     
                     ⁢ 
                     ⁢ 
                     
                       
                         L 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                       
                       
                         L 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Formula 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     2 
                   
                   ] 
                 
               
             
           
         
       
     
     The bend reduction α is effective when it is 1.5 or greater. It is more desirable that the bend reduction α is 1.7 or greater, and still more desirably, 2 or greater. 
     A recess  253  is expanded to the left beyond the left edge of the recess  233 , to have a larger area than the recess  233 . 
     By making the recess  253  broader, the AMB control substrate  209  bends smoothly since the AMB control substrate  209  can be prevented from adhering to the plate  201  due to any deposit etc. 
     Next, influence of the bend on the electronic elements mounted on the AMB control substrate  209  will be discussed. 
     As shown in  FIG. 6 , an electronic element  241  on the AMB control substrate  209  is molded with a molding material  243  such as resin. As stated above, when the AMB control substrate  209  bends, the molding material  243 , if having high hardness (e.g., as when using Araldite  2012  (trade name) produced by Huntsman), is largely deformed corresponding to the deformation of the substrate. At this time, great deforming pressure of the molding material is applied to a fixing leg etc. of the electronic element  241 , as shown with a thick arrow in the drawing. When the molding material  243  has high hardness, the electronic element  241  is possibly destroyed when reaction force of the electronic element  241  is not great enough to resist the deforming pressure. 
     Accordingly, as shown in  FIG. 7 , a molding material  245  having low hardness (e.g., DELO-DUOPDX CR804 (trade name) having a Shore D hardness of 43) is selected. It is desirable that the molding material  245  has a Shore D hardness of less than 50. 
     In this case, since load applied to the electronic element  241  is reduced as shown with a thick arrow in the drawing, reaction force of the electronic element  241  can resist the deforming pressure of the molding material  245 . Therefore, the electronic element  241  cannot be easily destroyed. 
     REFERENCE SIGNS LIST 
     
         
         
           
               10 : Turbo-molecular pump 
               100 : Pump main unit 
               102 : Rotary blades 
               104 : Upper radial electromagnets 
               105 : Lower radial electromagnets 
               106 A, B: Axial electromagnets 
               107 : Upper radial sensor 
               108 : Lower radial sensor 
               109 : Axial sensor 
               111 : Metal disc 
               113 : Rotor shaft 
               121 : Motor 
               122 : Stator column 
               123 : Stationary blades 
               125 : Stationary blade spacers 
               127 : Outer cylinder 
               129 : Base portion 
               131 : Spacer 
               133 : Exhaust port 
               149 : Water-cooling pipe 
               200 : Control unit 
               201 : Plate 
               203 : Roughly-quadrangular bottom plate 
               205 : Body 
               207 : Pins 
               209 : AMB control substrate 
               210 : Terminal 
               211 : Aerial connection substrate 
               212 : Pinholes 
               213 : Electrolytic capacitor 
               215 : Heat sink 
               221 ,  223 : O-rings 
               233 ,  253 : Recesses 
               235 A,  235 B,  235 C: Screws 
               241 : Electronic element 
               243 ,  245 : Molding material 
               300 : Control device 
               301 : Bottom space