Abstract:
An exemplary grinding machine includes a grinding unit and a receiving unit. The grinding unit includes a rotor, a first spindle, and a first driver unit connected in series. The first spindle has a first end coupled to the rotor. The first driver unit is coupled to an opposite second end of the first spindle and configured for driving the rotor to rotate relative to a first axis. The receiving unit includes a container configured for receiving the rotor therein. The container has an inner spherical grinding surface defining a central second axis. The first axis is parallel to and spaced from the second axis.

Description:
FIELD OF THE INVENTION 
   The present invention relates to grinding machines, and more particularly to a grinding machine for grinding for example a thermal interface material. 
   DESCRIPTION OF RELATED ART 
   Electronic components such as semiconductor chips are becoming progressively smaller, while at the same time heat dissipation requirements are increasing. Commonly, a thermal interface material (hereafter called TIM) is applied between the electronic component and a heat sink in order to fill air space therebetween thereby promoting efficient heat transfer. Nevertheless, the thermal conductivity of TIM is typically in the range of 0.15 W/mK (watts/mill Kelvin) to 0.30 W/mK. 
   TIMs are generally made of matrix material and thermally conductive fillers. The matrix material is selected from the group consisting of organic silicon and multi-hydroxyl radical esters. The fillers are chosen from the group consisting of metal powder, boron nitride (BN), alumina (Al 2 O 3 ), and zinc oxide (ZnO). With the development of the nano-technology, nano-fillers have become widely used in TIMs. 
   However, nano-particles may easily conglomerate under the influence of Van der Waal&#39;s forces. Therefore, the nano-fillers and the matrix material of the conventional TIM are difficult to mix uniformly. Generally, the TIM with high content of the nano-fillers has a relatively high thermal conductivity. However, the greater the number of the filler-particles in the TIM, the higher viscosity of the TIM. As a result the fillers and the matrix material are more difficult to mix uniformly. An external force is usually used to spread the fillers through the matrix material uniformly. One method of doing this is grinding. However, grinding cannot sufficiently disperse the nano-fillers in a high viscosity TIM. 
   What is needed, therefore, is a grinding machine that can mix the matrix material uniformly with the nano-fillers having larger mass than that of the matrix material. 
   SUMMARY OF THE INVENTION 
   In a preferred embodiment, a grinding machine includes a grinding unit and a receiving unit. The grinding unit includes a rotor, a first spindle, and a first driver unit connected in series. The first spindle has a first end coupled to the rotor. The first driver unit is coupled to an opposite second end of the first spindle and configured for driving the rotor to rotate relative to a first axis. The receiving unit includes a container configured for receiving the rotor therein. The container has an inner spherical grinding surface defining a central second axis. The first axis is parallel to and spaced from the second axis. 
   In another preferred embodiment, a grinding machine includes a grinding member, a first driving unit, a container, and a second driving unit. The grinding member is configured for driving the grinding member to rotate relative to a first axis in a first direction. The container is configured for receiving the grinding member therein. The second driving unit is configured for driving the container to rotate relative to a second axis in a second direction opposite to the first direction. The second axis is parallel to and spaced from the first axis. 
   Other advantages and novel features will become more apparent from the following detailed description of the present grinding machine when taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Many aspects of the grinding machine can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present invention. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
       FIG. 1  is a schematic view of a grinding machine, in accordance with a first preferred embodiment; and 
       FIG. 2  is a schematic view of a grinding machine, in accordance with a second preferred embodiment. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Reference will now be made to the drawing figures to describe the preferred embodiments of the present grinding machine in detail. 
   Referring to  FIG. 1 , a grinding machine  100  in accordance with a first preferred embodiment is shown. The grinding machine  100  includes a grinding unit  10 , a receiving unit  20 , a transmission unit  30 , a base stage  40 , and a hydraulic unit  50 . 
   The grinding unit  10  and the receiving unit  20  press against each other and the grinding unit  10  grinds a mixture  60 , for example, matrix material and fillers, inside the receiving unit  20 . The base stage  40  is configured for supporting the receiving unit  20  and the transmission unit  30 . 
   The grinding unit  10  includes a rotor  12 , a first spindle  14 , and a first driver  16 . The rotor  12  is connected fixedly with the first spindle  14 . The rotor  12  has a smooth grinding surface  122  thus preventing the mixture  60  from adhering thereto. The first driver  16  is connected fixedly with the first spindle  14 . The first driver  16  drives the rotor  12  to rotate along the first spindle  14 . In this embodiment, the rotor  12  only can rotate along an axis labeled with a character b in a first direction. 
   The receiving unit  20  includes a container  22 , a second spindle  24 , and a first loading element  26 . The second spindle  24  connects fixedly with the container  22  and the second spindle  24  connects fixed with the first loading element  26 . The first loading element  26  is cylindrically shaped. 
   The container  22  includes a heating element  222  contained in a cavity  224  defined by walls of the container  22 . The bottom of the wall has a smooth grinding face  226 . The grinding surface  122  of the rotor  12  is spherical and has a first curvature. The container  22  has an inner spherical grinding surface with a second curvature. The first curvature is generally configured to be less than the second curvature. 
   The container  22  receives the rotor  12  therein. The mixture  60  can move to the center of the container  22  under the gravity. The rotor  12  can sufficiently grind the mixture  60  in the container  22 . The heating element  222  is arranged in the cavity  224  and is used to heat the internal portion of the container  22  during grinding. Therefore, the mixture  60  may become more viscous, and cannot adhere to the rotor  12 . The heating element  222  can be a thermal element (i.e. a resistance wire). 
   The transmission unit  30  is configured for driving the receiving unit  20  to rotate in a second direction opposite the first direction. The transmission unit  30  includes a second driver  32 , a third spindle  34 , a second loading element  36 , and a transmission belt  38 . The third spindle  34  is connected fixedly with the second driver  32  and the second loading element  36 . The second loading element  36  is cylindrically shaped. The second loading element  36  is connected with the first loading element  26  through the transmission belt  38 . The second driver unit  32  can drive the third spindle  34  to rotate along with the second loading element  36 . The transmission belt  38  is driven by the second loading element  36  and thus drives the first loading element  26 . The second spindle  24  is driven by the transmission belt  38  and rotates along an axis labeled with a character c in the second direction. The axis c is not coaxially aligned with the axis b. Therefore, the rotor  12  is arranged with its axis offset to the container  22 . The transmission belt  38  is a component chosen from the group consisting of a belt and a chain. 
   The base stage  40  defines a first recess  42  and a second recess  44 . The first recess  42  receives the first loading element  26 . The radius of the first loading element  26  is smaller than that of the first recess  42 . Therefore a ring region is defined between the first recess  42  and the first loading element  26 . A number of ball bearings  46  are placed in the ring region to smooth the rotation of the first loading element  26 . The second recess  44  is used to receive the second loading element  36 . A number of ball bearings  46  are placed between the second recess  44  and the second loading element  36  to smooth the rotation of the second loading element  36 . 
   The hydraulic unit  50  is located at a bottom of the base stage  40 . The hydraulic unit  50  can support the receiving unit  20 , the transmission unit  30 , and the base stage  40  and also can adjust the position of the receiving unit  20  relative to the grinding unit  10  in a direction parallel to the direction of gravity. 
   The operation of the grinding machine  100  is described in detail below. The second driver unit  32  drives the third spindle  34  and the second loading element  36  to rotate and the first loading element  26 , the second spindle  24 , and the container  22  rotate along the axis c accordingly. The first driver unit  16  drives the first spindle  14  and the rotor  12  to rotate, the rotor  12  rotates along the axis b. The heating unit  222  heats the container  22 , and the mixture  60  is melted. In operation of the grinding machine  100 , the hydraulic unit  50  adjusts the position of the rotor  12  and the container  22 . The rotor  12  and the container  22  press against each other and the mixture  60  is ground uniformly. The nano-fillers embedded in mixture  60  are mixed until it is evenly distributed throughout the mixture  60 . After a period, the grinding machine  100  stops working, the ground mixture  60  is collected, and a next grinding process begins. In the grinding, in order to grind the mixture  60  more uniformly, one of the rotor  12  and container  22  is configured for rotating at a speed of less than 50 revolutions per minute. 
   Referring to  FIG. 2 , an grinding machine  200  in accordance with a second preferred embodiment is shown. The structure of the grinding machine  200  is similar to that of the grinding machine  100 . The grinding machine  200  includes a grinding unit  10 , a receiving unit  20 , a base stage  40 , and a hydraulic unit  50 . 
   The base stage  40  is horizontally movable. The receiving unit  20  mounted on the base stage  40  is horizontally movable, accordingly. The second spindle  24  is connected with the container  22  and the first loading element  26 . The container  22  is configured for containing the rotor  12  of the grinding unit  10  and the rotor  12  is arranged with its axis offset from that of the container  22 . The rotor  12  can rotate in the container  22  and the container  22  cannot rotate around the second spindle  24 . The hydraulic unit  50  is configured for moving the container  22  in the direction of the axis c. 
   Although the present invention has been described with reference to specific embodiments, it should be noted that the described embodiments are not necessarily exclusive, and that various changes and modifications may be made to the described embodiments without departing from the scope of the invention as defined by the appended claims.