Abstract:
An exemplary hot press ( 2 ) for bonding electronic devices ( 31, 32 ) includes a hot-head ( 24 ) and a control device ( 28 ). The hot-head includes a plurality of heating members ( 241 ). The hot-head includes a plurality of heating members ( 241 ) and a pressing end ( 243 ) joining same ends of the heating members. The pressing end is configured for pressing a bonding portion of one of the electronic devices. The heating members are configured for converting input electrical energy into heat and transferring the heat to the bonding portion of said one of the electronic devices via the pressing end. The control device is electrically connected with the heating members and configured for controlling the amount of the heat generated by each heating member.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a hot press which can for example be used to attach two electronic devices together, and a hot pressing method employing the hot press. 
       GENERAL BACKGROUND 
       [0002]    Various printed circuit boards (PCBs) have very complex wiring patterns and very high density wiring patterns. Typically, this is because of the need to provide patterns of complex wiring connections between electronic components that are fixed on the PCB in close proximity to one another. Thus in many cases, it is not possible to produce all the wiring patterns on a single piece of board material. In these cases, it is usual practice to divide the wiring pattern into a plurality of groups, and print the wiring pattern groups on respective substrate boards (hereinafter, “substrates”). Then the substrates are superposed one over another in a predetermined order and pressed together, to provide a single unified printed circuit board. This kind of printed circuit board is usually referred to as a multilayer printed circuit board (hereinafter, “multilayer board”). When the substrates are mechanically pressed together, the wiring pattern groups are simultaneously electrically connected to one another. Typically, the substrates are pressed together by means of a hot press machine (hereinafter, “hot press”). 
         [0003]    Referring to  FIG. 5 , a typical hot press  1  includes a working table  11 , a supporting plate  13 , and a hot-head  15 . The supporting plate  13  is disposed on the working table  11 , and can move relative to the working table  11 . The hot-head  15  is disposed above the supporting plate  13 . 
         [0004]    Referring also to  FIG. 6 , the hot-head  15  includes a heating body  151  and a pressing end  153 . The heating body  151  is configured to convert electrical energy to heat energy, and provide the heat to the pressing end  153 . The pressing end  153  is at a bottom end of the hot-head  15 . The pressing end  153  is configured to mechanically press on the top one of a stack of electronic devices, and transfer the heat to the electronic devices to bond the electronic devices together. 
         [0005]    Before operating the hot press  1 , two electronic devices are prepared. The electronic devices can for example be a printed circuit board  17  and a liquid crystal panel  19 . An anisotropic conductive adhesive layer  18  is sandwiched between the printed circuit board  17  and the liquid crystal panel  19 . The printed circuit board  17  and the liquid crystal panel  19  are fixed in position, with the liquid crystal panel  19  being supported by the supporting plate  13 . 
         [0006]    In operation of the hot press  1 , the supporting plate  13  having the printed circuit board  17  and the liquid crystal panel  19  fixed thereat is moved in a horizontal plane, so that bonding portions of the printed circuit board  17  and the liquid crystal panel  19  are aligned with the hot-head  15 . The hot-head  15  is moved vertically down until the pressing end  153  abuts and presses the bonding portion of the printed circuit board  17 . The heating body  151  is electrified, and converts the electrical energy to heat energy. The heat is transferred to the press portion  153 , and then is transferred to the bonding portions of the printed circuit board  17  and liquid crystal panel  19  and the adhesive layer  18 . Thereby, the adhesive layer  18  melts, and the printed circuit board  17  is mechanically and electrically connected with the liquid crystal panel  19  via the adhesive layer  18 . 
         [0007]    However, when the heat is provided by the heating body  151  to the pressing end  153 , the heat does not conduct to the pressing end  153  uniformly. In particular, there is a difference between the speed of heat transmission in a center portion of the heating body  151  and the speed of heat transmission at peripheral edge portions of the heating body  151 . Therefore a surface temperature of a bottom face of the pressing end  153  is liable to be non-uniform. This non-uniformity may bring about defects in the bonding between the two electronic devices  17 ,  19 . For example, unwanted protrusions or cold solder joints may occur. When this happens, the mechanical connection and the electrical connection between the two electronic devices  17 ,  19  may be impaired. 
         [0008]    Thus, a new hot press that can overcome the above-described problems is desired. A method employing such a hot press is also desired. 
       SUMMARY 
       [0009]    In one preferred embodiment, a hot press for bonding at least two electronic devices together includes a hot-head and a control device. The hot-head includes a plurality of heating members and a pressing end joining same ends of the heating members. The pressing end is configured for pressing a bonding portion of one of the electronic devices. The heating members are configured for converting input electrical energy into heat and transferring the heat to the bonding portion of said one of the electronic devices via the pressing end. The control device is electrically connected with the heating members and configured for controlling the amount of the heat generated by each heating member. 
         [0010]    Other novel features and advantages will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. In the drawings, all the views are schematic. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is an isometric view of a hot press according to an exemplary embodiment of the present invention, showing an electronic device assemblage mounted on the hot press. 
           [0012]      FIG. 2  is an enlarged, right side, partly cutaway view of certain parts of the hot press and the electronic device assemblage of  FIG. 1 , showing a temperature sensor of the hot press, and also showing aspects of a control device of the hot press. 
           [0013]      FIG. 3  is an enlarged view of a hot-head of the hot press of  FIG. 1 . 
           [0014]      FIG. 4  is a diagram showing electrical connectivity among the temperature sensor, the control device, and the hot-head of the hot press of  FIG. 1 . 
           [0015]      FIG. 5  is essentially a side view of a conventional hot press, showing an electronic device assemblage mounted on the hot press. 
           [0016]      FIG. 6  is an enlarged, isometric view of a hot-head of the hot press of  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0017]    Referring to  FIG. 1  and  FIG. 2 , aspects of a hot press  2  according to an exemplary embodiment of the present invention are shown. The hot press  2  is used to bond two electronic devices  31 ,  32  together via a piece of intervening bonding material  33 . In the illustrated embodiment, the electronic device  31  is a printed circuit board, and the electronic device  32  is a liquid crystal panel. The bonding material  33  can for example be solder or an anisotropic conductive adhesive layer. In the illustrated embodiment, the bonding material  33  is an anisotropic conductive adhesive layer. 
         [0018]    The hot press  2  includes a working table  21 , an X-Y platform  22 , a temperature sensor  23 , a hot-head  24 , a turret  25 , a movable head  26 , a frame  27 , and a control device  28 . 
         [0019]    The X-Y platform  22  is mounted on the working table  21 , and is configured to support the electronic devices  31 ,  32 . The X-Y platform  22  can move along an X axis or a Y axis in a horizontal plane. 
         [0020]    The temperature sensor  23  is disposed in the X-Y platform  22 . The temperature sensor  23  can for example be an infrared temperature sensor. The temperature sensor  23  is configured to measure a temperature of bonding portions of the electronic devices  31 ,  32 , and generate a temperature signal according to the measured temperature. Further, the temperature sensor  23  can measure more than one temperature corresponding to the bonding regions, in order to effectively deal with non-uniform temperature distribution at the bonding regions. In such case, the temperature sensor  23  can generate more than one temperature signal. 
         [0021]    The frame  27  is generally U-shaped, and is mounted on the working table  21 . The movable head  26  is mounted on the frame  27 , and can move along the strip-shaped frame  27 . The turret  25  is mounted on the movable head  26 . The turret  25  can for example include a piston cylinder or the like. The hot-head  24  is mounted at a bottom end of the turret  25 , and is used to press the electronic devices  31 ,  32  as well provide heat to the bonding portions of the electronic devices  31 ,  32 . The turret  25  can drive the hot-head  24  to move in vertical directions. Due to the movable engagement of the movable head  26  with the frame  27 , and the operation of the turret  25 , the hot-head  24  can move vertically and along a single horizontal axis. 
         [0022]    Referring also to  FIG. 3 , the hot-head  24  is a single piece, which includes a plurality of heating bodies  241  and a pressing end  243 . The heating bodies  241  are arranged parallel to one another, and are spaced apart from each other at a constant pitch. The heating bodies  241  can be made from high heat conductive material, such as iron, copper or aluminum. Each heating body  241  is in the shape of a plate, which has a wide main portion, a tapering neck portion extending down from the main portion, and a narrow bottom portion. The narrow bottom portions of the heating bodies  241  are joined together by the pressing end  243 . 
         [0023]    Referring also to  FIG. 4 , the control device  28  is used to generate control signals to control the hot-head  24 . The control device  28  includes a plurality of control units  281  and a comparator  283 . The control units  281  are electrically connected with the comparator  283 , and are electrically connected with the heating bodies  241  of the hot-head  24  respectively. The comparator  283  is electrically connected with the temperature sensor  23 . The control units  281  provide control signals and electrical energy to the heating bodies  241 . The comparator  283  is configured to receive information on the control signals from the control units  281  and the temperature signal(s) from the temperature sensor  23 , compare the information on the control signals and the temperature signal(s), generate adjusting signals, and provide the adjusting signals to the control units  281 . The adjusting signals adjust the control signals output by the control units  281 , and thereby adjust the amount of heat provided by the heating bodies  241 . 
         [0024]    In operation, the control device  28  provides control signals and electrical energy to the heating bodies  241 . The control signals can be pulse signals or constant voltage signals. The heating bodies  241  convert the electrical energy to heat energy under control of the control signals, and transmit the heat to the pressing end  243 . The pressing end  243  transmits the heat to the bonding portions of the electronic devices  31 ,  32  and the bonding material  33 . The temperature sensor  23  senses at least one temperature of the bonding portions of the electronic devices  31 ,  32 , and provides at least one temperature signal to the comparator  283  of the control device  28 . The comparator  283  compares the information on the control signals and the temperature signal(s), generates adjusting signals if and as necessary according to the results of the comparison, and provides the adjusting signals to the corresponding control units  281 . Thereby, the control units  281  respectively adjust the amount of heat provided by the heating bodies  241 , to make sure that a bottom face of the pressing end  243  has a substantially uniform surface temperature. Accordingly, the bonding portions of the electronic devices  31 ,  32  and the bonding material  33  have a substantially uniform temperature. 
         [0025]    In summary, the hot-head  24  of the hot press  2  includes the plurality of heating bodies  241 , with each heating body  241  being controlled by the respective control unit  281 . By adjusting the amount of heat provided from each heating body  241  to the pressing end  243 , the pressing end  243  can achieve a substantially uniform temperature. Thus, the bonding material  33  can be molten uniformly. Accordingly, the electronic devices  31 ,  32  can be bonded together via the bonding material  33  without defects. 
         [0026]    In addition, the control device  28  in cooperation with the temperature sensor  23  can adjust the control signals provided to the heating bodies  241  in order to overcome non-uniformity of the temperature of the bonding portions of the electronic devices  31 ,  32  where such non-uniformity is due to circuit design and/or construction aberrations. In this circumstance, the temperature sensor  23  sends at least one temperature signal to the control devices  28 , the at least one temperature signal relating to a temperature distribution of the bonding portions of the electronic devices  31 ,  32 . The control device  28  adjusts the control signals provided to the heating bodies  243  according to the at least one temperature signal, so that the bonding portions of the electronic devices  31 ,  32  achieve a substantially uniform temperature distribution. 
         [0027]    An exemplary hot pressing method employing the hot press  2  is as follows: 
         [0028]    Before the hot press  2  is operated, the electronic devices  31 ,  32  are fixed on the X-Y platform  22 , with the bonding material  33  being disposed between the bonding portions of the electronic devices  31 ,  32 . The temperature sensor  23  in the X-Y platform  22  is located directly beneath the bonding portions of the electronic devices  31 ,  32 . Either or both of the movable head  26  and the X-Y platform  22  are moved, so that the turret  25  and the hot-head  24  are aligned with the bonding portions of the electronic devices  31 ,  32 . The turret  25  moves the hot-head  24  down until the pressing end  243  presses on the bonding portion of the electronic device  31 . The control units  281  of the control device  28  respectively control the heating bodies  241  to convert electrical energy to heat energy, and transfer the heat to the pressing end  243 . Thereby, the bonding material  33  is melted. The temperature sensor  23  senses a temperature of the bonding portions of the electronic devices  31 ,  32 , and provides a temperature signal to the comparator  283  of the control device  28 . The comparator  283  compares the information on the control signals of the control units  281  with the temperature signal, generates adjusting signals according to results of the comparison, and provides the adjusting signals to the control units  281 . Thereby, the control units  281  control the heating bodies  241  such that the pressing end  243  has a uniform temperature. 
         [0029]    In an alternative method, the control units  281  of the control device  28  respectively control the heating bodies  241  to convert electrical energy to heat energy and transfer the heat to the pressing end  243  prior to the turret  25  moving the hot-head  24  down until the pressing end  243  presses on the bonding portion of the electronic device  31 . 
         [0030]    It is believed that the present embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the invention.