Patent Publication Number: US-7222409-B2

Title: Method of manufacturing a small vibration motor

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This present application is a divisional application of patent application Ser. No. 10/624,603 filed on Jul. 23, 2003, now U.S. Pat. No. 7,157,822. 
   The present document is based on Japanese Priority Document JP2002-220889, filed in the Japanese Patent Office on Jul. 30, 2002, the entire contents of which being incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a small vibration motor for generating vibrations, which is built in an electronic apparatus, such as a mobile telephone, a PDA and the like, and to a method of manufacturing the same. 
   2. Description of Related Art 
   Conventionally, an electronic apparatus such as the mobile telephone, the PDA and the like includes a mechanism of a so-called silent mode to notify an incoming call through vibrations, and an alarm to notify a predetermined time through vibrations, and the like. As a mechanism for generating a vibration, a vibration actuator is built into such an electronic apparatus. 
     FIG. 14A  is a schematic view showing the inner structure of a mobile telephone in which a vibration motor serving as a conventional vibration actuator is built.  FIG. 14B  is a schematic view showing the appearance of the vibration motor. As shown in  FIG. 14A , printed circuit boards (motherboards)  101 ,  102  are mounted within the mobile telephone  100 . A speaker  103  and a vibration motor  104  are connected to the side of the printed circuit board  101 . The vibration motor  104  is driven by a driver IC  105  mounted on the printed circuit board  101 . On the other hand, a power supply IC  110 , a converter IC  111 , an MPU  112 , a memory IC  113  and the like are mounted on the side of the printed circuit board  102 . 
   The illustrated vibration motor  104  is a motor with a brush. As shown in  FIG. 14B , a weight  125  is fixed around an output shaft  120 . When the vibration motor  104  is driven, the output shaft  120  is rotated, and the weight  125  is eccentrically rotated. The eccentric rotation of the weight  125  causes rotationally unbalanced energy to be generated as a vibration component. 
   SUMMARY OF THE INVENTION 
   Conventionally, when a motor with a brush is used as the vibration motor, the rotational defect caused by a so-called slit-short can not be made zero. Thus, this is a problem with the reliability of a vibration generation operation. 
   Also, in view of the internal volume of a portable apparatus and the like, it is naturally desired to have a smaller vibration motor. A motor body can be reduced to, for example, a diameter of about 3.5 mm. However, a problem may occur if the diameter of the motor body is made smaller. That is, the diameter of the weight for generating the rotational unbalanced energy becomes too small to generate enough vibrations, and thus the vibration component decreases. In particular, recently, portable apparatuses, such as the mobile telephone, the PDA and the like tend to be thinned. Accordingly, this causes a problem that fitting a cylindrical vibration motor to such a thinned portable apparatus is difficult. 
   Further, from the viewpoint of the battery life of a portable apparatus such as the mobile telephone and the like, obviously it is desirable to lower the electric power consumption. However, this has a problem that miniaturization of the motor body brings about increases in the rotational number and the electric power consumption. 
   Moreover, the assembly of the conventional vibration motor into the electronic apparatus must rely on manpower. Thus, automation thereof is difficult. 
   Accordingly, there has been a need to provide a smaller vibration motor that may be miniaturized, thinned and automatically assembled into an electronic apparatus and a method of manufacturing the same. 
   In order to attain the above-mentioned subjects, a small vibration motor according to the present invention is characterized by including: a rotor yoke in which an unbalance weight and a magnet are placed and which is fixed to a shaft; a driving torque-generating coil that is placed on a substrate so as to face the magnet; driving electronic parts placed on the substrate, which includes an integrated circuit composed of non-molded bare chips, supply an alternating current to the driving torque generating coil to rotate the rotor yoke around the shaft; a bottom plate which supports the substrate and to which a radial bearing to which the shaft is engaged is fixed; and a cover for covering the rotor yoke, the driving torque-generating coil and the driving electronic parts, which is adhered to the bottom plate. 
   Also, as the preferable embodiment, in the small vibration motor, the substrate may be constituted by a flexible substrate, and the driving torque generating coil may be electrically connected to the flexible substrate through three terminals. 
   Also, as the preferable embodiment, the small vibration motor may include a terminal that is formed on a substrate protruded from the package and engaged with a connector mounted on a motherboard and thereby electrically connected. 
   Also, as the preferable embodiment, the small vibration motor may include a terminal that is placed in the cover or the bottom and engaged with a socket mounted on a motherboard and thereby electrically connected. 
   Also, as the preferable embodiment, the small vibration motor may include a land that is formed on a surface of the cover or the bottom in contact with a motherboard and electrically connected to another land formed on the motherboard. 
   In order to attain the above-mentioned subjects, a method of manufacturing a small vibration motor according to the present invention is characterized by including the steps of: mounting driving electronic parts and a driving torque-generating coil on a board; placing a magnet on a rotor yoke so as to face the driving torque-generating coil, in a rotor composed of the rotor yoke and a shaft; placing an unbalance weight at a part of the rotor yoke; fixing a radial bearing to a bottom plate; installing a bottom plate on which the radial bearing is placed to the substrate; installing the rotor to the radial bearing that is engaged with the shaft; and packaging by covering the substrate, the driving electronic parts and the rotor with a cover, and adhering the cover to the bottom plate. 
   Also, as the preferable embodiment, the method of manufacturing the small vibration motor may be characterized in that as the driving electronic parts, at least an integrated circuit composed of non-molded bare chips is mounted on the substrate. 
   Also, as the preferable embodiment, the method of manufacturing the small vibration motor may be designed such that the board is constituted by a flexible substrate and the driving torque generating coil is electrically connected to the flexible substrate through three terminals. 
   Also, as the preferable embodiment, the method of manufacturing the small vibration motor may include a step of forming a terminal on a substrate protruded from the package, which is engaged with a connector mounted on a motherboard and thereby electrically connected. 
   Also, as the preferable embodiment, the method of manufacturing the small vibration motor may include a step of placing a terminal, which is engaged with a socket mounted on a motherboard and thereby electrically connected, on the package. 
   Also, as the preferable embodiment, the method of manufacturing the small vibration motor may include a step of forming a land on a surface in contact with the motherboard of the package, which is electrically connected to another land formed on a motherboard. 
   In the present invention, the driving electronic parts and the driving torque generating coil are mounted on the board. In the rotor composed of the rotor yoke and the shaft, the magnets are placed so as to face the driving torque generating coil in the rotor yoke. The unbalance weight is placed at a part of the rotor yoke. The radial bearing is fixed to the bottom plate. The bottom plate on which the radial bearing is placed is installed to the board. The shaft is engaged with the radial bearing, and the rotor is also installed on the radial bearing. Moreover, the board, the driving electronic parts and the rotor are covered with the cover. Then, the cover is adhered to the bottom plate to be packaged. Thus, the vibration motor can be miniaturized and thinned. Moreover, it is possible to carry out automatically the manufacturing process for the vibration motor and mounting the motor to an electronic apparatus. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will become more apparent from the following description of the presently preferred exemplary embodiments of the present invention taken in conjunction with the accompanying drawings, in which: 
       FIGS. 1A ,  1 B are schematic views showing a structure of a small vibration motor according to an embodiment of the present invention; 
       FIGS. 2A to 2D  are conceptual views showing a process for manufacturing a driver IC  4 . 
       FIG. 3  is a flowchart showing a process for manufacturing a small vibration motor; 
       FIG. 4  is a flowchart showing a process for manufacturing a small vibration motor; 
       FIG. 5  is a flowchart showing a process for manufacturing a small vibration motor; 
       FIG. 6  is a flowchart showing a process for manufacturing a small vibration motor; 
       FIGS. 7A ,  7 B are schematic views explaining a process for manufacturing a small vibration motor; 
       FIGS. 8A to 8C  are schematic views explaining a process for manufacturing a small vibration motor; 
       FIGS. 9A to 9C  are schematic views explaining a process for manufacturing a small vibration motor; 
       FIGS. 10A to 10C  are schematic views explaining a process for manufacturing a small vibration motor; 
       FIGS. 11A to 11C  are schematic views explaining a process for manufacturing a small vibration motor; 
       FIGS. 12A to 12C  are schematic views showing an example of a method of mounting a small vibration motor  30  onto a motherboard; 
       FIG. 13  is a schematic view showing an example of a shipping/delivering method for the small vibration motor  30 ; and 
       FIGS. 14A ,  14 B are schematic views showing the inner structure of a mobile telephone in which a vibration motor serving as a conventional vibration actuator is built. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   An embodiment of the present invention will be described below with reference to the attached drawings. 
   A. Structure of Small Vibration Motor 
     FIGS. 1A ,  1 B are schematic views showing the structure of a small vibration motor according to the embodiment of the present invention. An FP (Flexible Printed) coil  1  and a magnet  2  are placed facing each other. The FP coil  1  is constituted by a wiring layer composed of a plurality of layers. A signal inputted through a flexible substrate  3  is converted into a three-phase voltage by a driver IC  4  so that a magnetic field is cyclically generated. The magnet  2  is linked to a yoke  6  having a shaft  5 . The rotational magnetic field of the FP coil  1  rotates the magnet  2  and the yoke  6 . An unbalance weight  7  is eccentrically installed to the yoke  6 . The rotation of the unbalance weight  7  generates an unbalanced component to thereby generate a vibration. 
   Notches  10  are formed at the four corners of the FP coil  1 , and the flexible substrate  3  is exposed there. The driver IC  4 , passive parts (C, R)  11  and the like are mounted on the notches  10 . The flexible substrate  3  is made of polyimide as the base material, and that wiring surface is treated with Cu+Ni+Au. 
   The shaft  5  is supported by a radial bearing  13  installed to a bottom plate  12 , a thrust bearing  14  and a thrust bearing holder  15 . The radial bearing  13  is made of sintered metal in which, for example, copper-based, iron-steel-based or iron-based oil is impregnated, and it is the cylindrical shaped member. Incidentally, the radial bearing  13  may be made of resin. 
   Also, a cover  16  is caulked and soldered and thereby fixed to the bottom plate  12 . The top surface of the cover  16  is flat such that the small vibration motor can be assembled (absorbed) by a robot arm and the like when it is mounted onto the motherboard. Also, a part of the flexible substrate  3  is protruded so as to be wired to the motherboard. However, having this protrusion is not the essential condition. 
   The small vibration motor according to this embodiment, as mentioned above, has the approximate dimension of 8.6×8.6 mm, the thickness of 1.9 mm, and the volume is about 140 mm 3 . The conventional motor with the brush has the dimension of about 300 to 500 mm 3 . Thus, as compared with the conventional motor, the small vibration motor according to this embodiment can have its volume reduced substantially equal to ½ to ⅓. 
   B. Process for Manufacturing Small Vibration Motor 
   The process for manufacturing the above-mentioned small vibration motor will be described below. Here,  FIGS. 2A to 2D  are conceptual views showing the process for manufacturing the driver IC  4 . Also,  FIGS. 3 to 6  are flowcharts showing the entire process for manufacturing the small vibration motor. Moreover,  FIGS. 7A to 11C  are schematic views explaining the process for manufacturing the small vibration motor. 
   B-1. Process for Manufacturing Driver IC 
   At first, as shown in  FIG. 2A , the necessary circuit is formed on a Si wafer  20  by a typical process such as a photo processing and the like. After that, as shown in  FIG. 2B , protrusion electrodes  21  are formed thereon. Next, as shown in  FIG. 2C , chips are diced one by one and made into pieces by an extension ring  22 , as shown in  FIG. 2D . The driver IC is not a typical package IC (an IC molded with resin and the like), but it is a so-called bare chip in which a circuit section is exposed. Also, the protrusion electrode  21  can be formed by an Au plating, a Ni plating, an Au stud bumping method, or a solder bumping method or the like. Such a protrusion electrode can be flexible about the supplying condition and the inspecting method of the wafer. 
   B-2. Flexible Substrate Process 
   On the other hand, a flexible substrate manufactured in a different step (not shown) is prepared (Step S 10  in  FIG. 3 ). At first, as shown in  FIG. 7A , the driver IC (bare chip)  4  and the passive elements (C, R)  11  are placed at predetermined positions on the flexible substrate  3 . Soldering (reflow) is performed thereon, and flux components contained in paste are washed. Then, underfill resin is coated to reinforce mechanically the driver IC  4 . Again, the resin is cured at a thermal curing process (Step S 112 ). Next, as shown in  FIG. 7B , the FP coil  1  manufactured in a different process is placed at a predetermined position, and soldering (reflow) is performed thereon (Step S 14 ). 
   There are three connection portions between the FP coil  1  and the flexible substrate  3 , and there are also only three connection terminals to the motherboard (not shown) through the flexible substrate  3 . Thus, although the vibrating section and the driver IC  4  are electrically connected, this is not a strong vibrator, and this has the action of attenuating the vibration generated by the flexible substrate  3  itself. Hence, it is possible to suppress the mechanical stress on the mounted portion. Then, the circuit is inspected (Step S 16 ). If the circuit contains any repairable defect, it is returned to the step S 12  in order to repair it by carrying out soldering and the like once again and then reinspected. On the other hand, if it contains any defect that can not be repaired, it is discarded (Step S 18 ). Also, if the inspected result is satisfactory, the operational flow proceeds to a next process, which will be described later. 
   B-3. Process for Installing Radial Bearing 
   A bottom plate is prepared in order to package the small vibration motor (Step S 20  in  FIG. 4 ). The bottom plate  12  is manufactured by performing a rolling process on an aluminum plate and the like. At first, as shown in  FIG. 8A , the radial bearing  13  is installed onto the bottom plate  12  (Step S 22 ). Then, as shown in  FIGS. 8B to 8C , the thrust bearing  14  and the thrust bearing holder  15  are installed (Step S 24 ) and caulked and thereby fixed (Step S 26 ). Next, whether or not the radial bearing  13 , the thrust bearing  14  and the thrust bearing holder  15  are rightly installed is inspected (Step S 28 ). Here, if any of them has a defect, it is discarded (Step S 30 ). On the other hand, if they have no defect, the operational flow proceeds to a next process which will be described later. 
   B-4. Rotor Yoke Process 
   The rotor yoke  6  is prepared (Step S 40  in  FIG. 5 ). As shown in  FIG. 9A , the magnets  2  are adhered (Step S 42 ). Then, the magnets  2  are magnetized (Step S 44 ). As shown in  FIG. 9B , the shaft  5  is pressed into the rotor yoke  6  (Step S 46 ). Then, as shown in  FIG. 9C , the unbalance weight  7  is adhered and caulked and thereby fixed to the rotor yoke  6  (Step S 48 ). 
   B-5. Assembling Process 
   Next, as shown in  FIGS. 10A and 10B , the flexible substrate  3  formed by the above-mentioned flexible substrate process, on which the parts are mounted, is adhered on the bottom plate  12  manufactured by the process for installing the radial bearing as mentioned above. (Step S 50  in  FIG. 6 ). Next, as shown  FIG. 10B , the shaft  5  and the rotor yoke  6  manufactured by the above-mentioned rotor yoke process are installed to the radial bearing  13  (Step S 52 ). Next, as shown in  FIG. 10C , the differently manufactured cover  16  is caulked and thereby fixed to the bottom  12  (Step S 54 ), and a terminal to be electrically connected to the motherboard is soldered to the protrusion portion of the flexible substrate  3  (Step S 56 ). Then, an appearance check and an electrical inspection are carried out (Step S 58 ). If there is any defect, the vibration motor is discarded (Step S 60 ). On the other hand, if there is no defect, the vibration motor is shipped (Step S 62 ). Manufacturing the small vibration motor  30  is completed as described above. 
   The small vibration motor  30  according to the above-described embodiment can be miniaturized and thinned. As compared with a conventional motor with a brush, the longitudinal and lateral dimension of the small vibration motor  30  is about 8.6×8.6 mm, and thickness is about 1.9 mm, and its volume is about 140 mm 3 . Thus, this motor has a volume substantially equal to ½ to ⅓ of the conventional motor. In addition, because the driver IC can be mounted as the bare chip, it is advantageous in that the chip manufacturing processes may be reduced. Further, the rotation of the rotor yoke  6  inside helps to increase the cooling efficiency. 
   Also, since the vibration motor  30  has the driver IC  4  therein, mounting on the motherboard (not shown) can be treated similarly to mounting the surface mount parts. At this time, the mounted direction of the small vibration motor  30  needs to be recognized. In order to indicate the mounting direction, a simple mark  31  may be printed as shown in  FIGS. 11A and 11B , or a part of the outer surface may be cut away as a notch  32 , as shown in  FIG. 11C . 
   In addition, as the methods of mounting the small vibration motor  30  on the motherboard, there are: a method of using an FPC (Flexible Printed Circuit Board) connector  40  electrically connected to the terminal formed on the protrusion section of the flexible substrate  3 , as shown in  FIG. 12A ; a method of using sockets  41  that are engaged with a terminal placed in a package to be electrically connected, as shown in  FIG. 12B ; and a method of forming lands  42  on the rear surface of the small vibration motor  30  to mount on the motherboard like the surface mount part. In these ways, it is possible to address flexibly a request from a client. 
   Also, as a parts shipment/delivery method for the vibration motor  30 , it is possible to pack it in a reel-shaped tape  50  as shown in  FIG. 13 , which enables easier management of parts. The small vibration motor  30  is stored in a small, vibration-motor storing portion  51  of the reel-shaped tape  50 , which has reel wheel holes  52 . 
   Finally, the embodiments and examples described above are only examples of the present invention. It should be noted that the present invention is not restricted only to such embodiments and examples, and various modifications, combinations and sub-combinations in accordance with its design or the like may be made without departing from the scope of the present invention.