Abstract:
A pressure device for pressure bonding an IC chip on a circuit board includes an IC pressurizing member having a groove extending in a predetermined direction, and formed on a surface opposite to a surface abutting the IC chip. A columnar member is provided overlapped on the IC pressurizing member so as to bring an external surface thereof into contact within the groove of the IC pressurizing member. A pressure receiving member has a groove extending in a predetermined direction and overlapped on the IC pressurizing member so as to bring an external surface of the columnar member into contact within the groove thereof. An adjusting member adjusts parallelism between the IC pressurizing member and the pressure receiving member, and a fixing member fixes a relative position between the IC pressurizing member and the pressure receiving member.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a pressure device for pressure bonding an integrated circuit (IC) on a printed circuit board.  
           [0003]    2. Description of the Related Art  
           [0004]    Recently, in electrical circuit devices having IC chips mounted on circuit boards, advances have been achieved resulting in the increase in electrical signal velocity and integration density, and in the reduction in size. As a result, signal wiring is becoming fine in pitch and the number of pins is increasing. Along therewith, it has become more difficult to obtain positional accuracy and connection reliability in the process of bonding IC chips on a circuit board.  
           [0005]    As a method for mounting an IC chip on a circuit board such as a ceramic substrate for a micropattern, silicon substrate, and glass substrate for liquid crystal, at present, wire bonding, a solder bump, stud bump, anisotropic conductive film (ACF), anisotropic conductive paste (ACP), nonconductive film (NCF), and nonconductive paste (NCP) are combined. Also, in such a mounting method, a chip on board (COB) device is used. For example, as such a COB device, a device adaptable to work with a wide space between ICs is known, in which an IC chip is bonded with a melted solder bump. Since the solder bump has a self-alignment mechanism itself, an allowable range in parallelism between the substrate and IC chips is large in such a COB device.  
           [0006]    In the typical COB device, IC chips and the circuit board are sandwiched to perform heating and pressure bonding with a pair of tools arranged at the top and bottom. One such COB device is a one-position fixed type having one heating and bonding position with the tool. Another type of COB device is a plural-positions moving type, in which one of the tools arranged at the top and bottom (the top tool, for example) is fixed and the other (substrate-mounted stage) is moved. An example of the latter type COB device using the ACF is disclosed in Japanese Patent Laid-Open No. 2000-68633. In this disclosure, an elastic sheet is interposed therebetween, in order to reduce nonuniformity in pressure due to differences in height.  
           [0007]    However, the following problems have been encountered in the conventional mounting method. Like reference characters will be used to designate like members in FIGS.  1  to  8 .  
           [0008]    A COB device may be at the one-position fixed type, as shown in FIG. 1, and the plural-positions moving type, shown in FIG. 2, in which a stage with a circuit board  5  is moved. In either type, in order to uniformly pressurize bumps  4  (not visible in FIG. 2) and an IC chip  3  in the direction of arrow  8 , an upper tool  1  and a lower tool  2  are provided. A mechanism for adjusting parallelism between the tools  1  and  2  is provided in at least one of the tools (the upper tool in FIGS. 1 and 2). Referring to FIGS. 1 and 2, the upper tool  1  is slidable in directions of arrows  6  and  7 . FIG. 3 shows a one-position fixed type in a state that the IC chip  3  is press-bonded after the parallelism of the upper tool  1  is adjusted relative to inclination of the press-bonding surface of the lower tool  2 .  
           [0009]    However, the parallelism adjusting mechanism mentioned above is for adjusting the parallelism between the press-bonding surfaces of the tools and not for adjusting the parallelism relative to each IC chip and circuit board. Therefore, as shown in FIG. 4, there is a first problem that for fluctuations in thickness of individual circuit boards  5  and IC chips  3  and fluctuations in height of individual bumps  4 , uneven abutment and nonuniformity in a pressurization force are produced, and along therewith, nonuniformity in a connection resistance and instability in the connection reliability may be produced.  
           [0010]    In the plural-positions moving type of the lower tool  2  (substrate-mounted stage), the upper tool  1  is provided with the parallelism adjusting mechanism, the upper tool  1  being parallel-adjusted at a predetermined position corresponding to every press-bonding position of the lower tool  2 . Also, in this type, in addition to the same problem as in the one-position fixed type, errors are produced in a parallel-adjusted position due to fluctuations in positional accuracy of the reciprocating stage.  
           [0011]    A second problem is that if the IC chips to be connected are arranged at a small pitch, it may occur that a number of the IC chips cannot be connected, because of the size and shape of the upper tool  1  for heating and pressurizing the IC chips.  
           [0012]    A third problem is that when a plurality of the IC chips  3  are mounted on one circuit board  5  in the COB device as shown in FIG. 5, the circuit board  5  is warped in the longitudinal direction. This is significant in a silicon substrate with a thickness of 625 μm, length of 100 mm, and width of 7 mm having 8 to 9 thin bare IC chips with a thickness of 175 μm, length of 10 mm, and width of 2.5 mm mounted thereon, where it is confirmed that the substrate is warped by 40 to 50 μm.  
           [0013]    A fourth problem is that in a method for pressing the IC  3  with an elastic sheet interposed therebetween, disclosed in Japanese Patent Laid-Open No. 2000-68633, as shown in FIG. 6, when the back face of the IC chip  3  is inclined relative to the pressing direction, nonuniform distribution in the pressure is produced, resulting in nonuniformity of crush amounts of the bumps  4  and of a connection state.  
           [0014]    Furthermore, as shown in FIG. 7, there is also a problem that because the elastic sheet  9  pressurizes the back surface of the IC chip  3  with a uniformly distributed force, portions, particularly where the bumps  4  do not exist in the bump arrangement, cave in, resulting in a warp of the IC chip  3 . The warp of the IC chip  3  is significant especially in the case of a thin IC. When the warped IC is bonded and mounted, an ACF resin changes in quality and is softened while the warped IC chip is to get back, after a heating process performed thereafter or a reliability test. Then, as shown in FIG. 8, a largely crushed bump  4   a  is separated from the substrate  5 , resulting in defective bonding.  
           [0015]    Moreover, in the mounting method using the elastic sheet, it is difficult for the elastic sheet to follow the height differences and different force may be applied of the IC chips for adjacent chips. If there are differences in height, the elastic sheet follows the higher IC chips, so that the lower IC chips are not abutted by the elastic sheet and not subjected to a force.  
         SUMMARY OF THE INVENTION  
         [0016]    It is an object of the present invention to provide a pressure device capable of mounting IC chips on a circuit board with high reliability by solving the problems of conventional techniques described above.  
           [0017]    In order to achieve the object mentioned above, in accordance with a first aspect of the present invention, a pressure device for pressure bonding an IC chip on a circuit board comprises an IC pressurizing member having a groove extending in a predetermined direction, which is formed on a surface opposite to the surface abutting the IC chip; a columnar member overlapped on the IC pressurizing member so as to bring an external surface thereof into contact within the groove of the IC pressurizing member; a pressure receiving member having a groove extending in a predetermined direction and overlapped on the IC pressurizing member so as to bring an external surface of the columnar member into contact within the groove thereof; an adjusting member for adjusting parallelism between the IC pressurizing member and the pressure receiving member; and a fixing member for fixing a relative position between the IC pressurizing member and the pressure receiving member.  
           [0018]    In accordance with a second aspect of the present invention, a pressure device for pressure bonding an IC chip on a circuit board comprises an IC pressurizing member having a groove extending in a first direction, which is formed on a surface opposite to the surface abutting the IC chip; a first columnar member overlapped on the IC pressurizing member so as to bring an external surface thereof into contact within the groove of the IC pressurizing member; an intermediate member having first and second surfaces opposing each other, the first surface having a first groove formed thereon and extending in the first direction, the second surface having a second groove formed thereon and extending in a second direction perpendicular to the first direction, the intermediate member being overlapped on the first columnar member so as to bring an external surface of the first columnar member into contact within the first groove thereof; a first adjusting member for adjusting parallelism between the IC pressurizing member and the intermediate member; a first fixing member for fixing a relative position between the IC pressurizing member and the intermediate member; a second columnar member overlapped on the intermediate member so as to bring an external surface thereof into contact within the second groove of the intermediate member; a pressure receiving member having a groove extending in the second direction and overlapped on the second columnar member so as to bring an external surface of the second columnar member into contact within the groove thereof; a second adjusting member for adjusting parallelism between the intermediate member and the pressure receiving member; and a second fixing member for fixing a relative position between the intermediate member and the pressure receiving member.  
           [0019]    In accordance with a third aspect of the present invention, a pressure device for pressure bonding an IC chip on a circuit board and having a plurality of pressure mechanisms arranged close to each other, each of the pressure mechanisms comprises an IC pressurizing member having a groove extending in a first direction, which is formed on a surface opposite to the surface abutting the IC chip; a first columnar member overlapped on the IC pressurizing member so as to bring an external surface thereof into contact within the groove of the IC pressurizing member; an intermediate member having first and second surfaces opposing each other, the first surface having a first groove formed thereon and extending in the first direction, the second surface having a second groove formed thereon and extending in a second direction perpendicular to the first direction, the intermediate member being overlapped on the first columnar member so as to bring an external surface of the first columnar member into contact within the first groove thereof; a first adjusting member for adjusting parallelism between the IC pressurizing member and the intermediate member; a first fixing member for fixing a relative position between the IC pressurizing member and the intermediate member; a second columnar member overlapped on the intermediate member so as to bring an external surface thereof into contact within the second groove of the intermediate member; a pressure receiving member having a groove extending in the second direction and overlapped on the second columnar member so as to bring an external surface of the second columnar member into contact within the groove thereof; a second adjusting member for adjusting parallelism between the intermediate member and the pressure receiving member; and a second fixing member for fixing a relative position between the intermediate member and the pressure receiving member.  
           [0020]    Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]    [0021]FIG. 1 is a schematic perspective view of an example of a conventional pressure device.  
         [0022]    [0022]FIG. 2 is a schematic perspective view of another example of a conventional pressure device.  
         [0023]    [0023]FIGS. 3 and 4 are schematic sectional views showing pressurizing an IC chip using a conventional pressure device.  
         [0024]    FIGS.  5  to  8  are schematic sectional views showing a circuit board having the IC chips mounted thereon by a conventional pressure device.  
         [0025]    [0025]FIG. 9 is a schematic perspective view of a pressure device according to a first embodiment of the present invention showing only principal members of a parallelism adjusting mechanism.  
         [0026]    [0026]FIG. 10 is a schematic perspective view of a parallelism adjusting mechanism having adjusting pins and fixing screws in addition to the structure shown in FIG. 9.  
         [0027]    [0027]FIG. 11 is a plan view of the device shown in FIG. 10, in which the side indicated by arrow  32  is expressed on the bottom side.  
         [0028]    [0028]FIGS. 12A to  12 D are sectional views of the device shown in FIG. 10 at the respective different lines.  
         [0029]    [0029]FIG. 13 is a schematic view of a pressure device having the parallelism adjusting mechanism shown in FIG. 10 and assembled therein.  
         [0030]    [0030]FIG. 14 is a schematic side view of a structure combined by adjacent pressure rectangles having parallelism adjusting mechanisms assembled therein according to a second embodiment of the present invention.  
         [0031]    [0031]FIG. 15 is a schematic plan view of the structures shown in FIG. 14 and arranged in five lines.  
         [0032]    [0032]FIG. 16 is a schematic perspective view showing only the pressure rectangle of the structure shown in FIG. 14. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0033]    Embodiments according to the present invention will be described in detail below with reference to the drawings.  
       First Embodiment  
       [0034]    [0034]FIG. 9 is a schematic perspective view of a pressure device according to the present invention in which only principal members of a parallelism adjusting mechanism for pressurizing IC chips and a circuit board in parallel with each other are shown. Referring to FIG. 9, an IC pressing member  11 , an intermediate member  12 , and a pressure receiving member  13  are provided with V-shaped grooves (concave portions)  15  for receiving columnar members  14   a  and  14   b , respectively. Both ends of the V-shaped groove  15  may close up so as not to displace the columnar member. By fitting the columnar members  14   a  and  14   b  into the V-shaped grooves  15 , the rotational direction is restricted to one direction. In such a manner, combinations between the V-shaped groove and the columnar member are arranged to be out of alignment with each other by 90°, so that the columnar members can independently rotate about axes α and β, respectively. This structure is a basic pattern for adjusting the parallelism between the IC chip and circuit board about the axes α and β.  
         [0035]    [0035]FIG. 10 is a schematic perspective view of a parallelism adjusting mechanism in that adjusting pins and fixing screws are added to the structure shown in FIG. 9. FIG. 11 is a plan view of the parallelism adjusting mechanism in that the side indicated by the arrow  32  in FIG. 10 is expressed on the bottom side. FIGS. 12A to  12 D are sectional views at the lines  12 A- 12 A,  12 B- 12 B,  12 C- 12 C, and  12 D- 12 D of FIG. 11, respectively. In FIGS. 10 and 11, and FIGS. 12A to  12 D, like reference characters designate like members and like reference characters designate like members in FIG. 9, and the detailed description thereof is omitted.  
         [0036]    Referring to FIG. 10, the axis α denotes the imaginary rotational shaft about which the upper columnar member  14   a  rotates, and the axis β denotes the imaginary rotational shaft about which the lower columnar member  14   b  rotates. Therefore, FIGS. 12A and 12B show a structure for rotating and fixing the axis β, i.e., the lower columnar member  14   b . Also, FIGS. 12C and 12D show a structure for rotating and fixing the axis α, i.e., the upper columnar member  14   a.    
         [0037]    The parallelism adjusting method will be described about the axis α at first. The parallelism between the pressure receiving member  13  and the intermediate member  12  is adjusted with a pushing pin  16  for adjusting the axis α. The pushing pin  16  for adjusting the axis α uses M 1  fine pitch cast thread, and the adjustment is performed through an adjusting screw hole  17 . The position is fixed with screws  18  for fixing the axis α through fixing screw holes  19 . The screw  18  for fixing the axis α also uses M 1  fine pitch cast thread.  
         [0038]    Next, the parallelism adjustment is also performed on the axis β in the same way. The adjustment and fixing are performed using a pushing pin  20  for adjusting the axis β and screws  22  for fixing the axis β through an adjusting screw hole  21  and fixing screw holes  23 , respectively.  
         [0039]    [0039]FIG. 13 is a schematic view of a pressure device having a parallelism adjusting mechanism  24  assembled therein and shown in FIG. 10. The circuit board  5  on a base  26  is provided with an ACF bonded thereon, and the IC chip  3  positioned and mounted thereon is pressurized.  
         [0040]    Referring to FIG. 13, a pressure rectangle  25  having the parallelism adjusting mechanism  24  assembled at an end thereof is fitted to vertical guides  28  with oilless bearings  29  interposed therebetween. The pressure rectangle  25  floats in midair by support springs  27  before the pressure is applied. Upon receiving a press-eliminating pressure  30  from the above, the pressure rectangle  25  moves vertically in a rectangle-moving direction  31 . There are through-holes for operating adjusting and fixing screws of the parallelism adjusting mechanism  24  formed on the top surface of the pressure rectangle  25  corresponding to the respective holes. The parallelism adjustment is performed using such a mechanism.  
         [0041]    Using the pressure device shown in FIG. 13, the mounting of the IC chips was performed as follows. First, the IC chip  3  was mounted on the circuit board  5  after positioning the IC chip  3  in a state that an ACF  10  is not bonded on the board, or only part thereof is bonded. Then, the board was set in the pressure device shown in FIG. 13, and it was pressurized at a desired pressure to fix it at the state. Then, the circuit board  5  after being pressurized was removed therefrom so as to peel off the IC chip  3  for observing the indentation of the bumps. The axes α and β were adjusted so that the bumps were uniformly crushed.  
         [0042]    Consequently, on the bump-bonding portions on the circuit board  5 , the ACF  10  was again bonded after the adjustment was performed to a state that all of the bumps of the IC chip  3  were uniformly pressurized. After positioning and mounting the IC chip  3 , it is set in the pressure device shown in FIG. 13 so as to pressurize it at a desired pressure and is fixed at the state. For heat setting the ACF  10  disposed between the circuit board  5  and the IC chip  3 , the pressurized pressure device was put into a clean oven for heat setting. Once the pressure device was in the oven, the oven was heated from a room temperature to 170° C. When the temperature of the circuit board, IC chip, and pressure device reached 170° C., the power supply was turned off to cool them naturally. At the room temperature, the pressure device was removed and the pressure was released.  
         [0043]    A confirmation of the connection resistance values of the IC chips  3  mounted by the above-described process showed that the entire connection check portions of nine IC chips had an excellent resistance value of 60 mΩ.  
       Second Embodiment  
       [0044]    According to a second embodiment, adjacent IC chips to be connected are arranged in two rows. FIG. 14 is a schematic side view of a structure in that neighboring pressure rectangles, each having the parallelism adjusting mechanism  24  assembled therein, are combined. FIG. 15 is a schematic plan view showing a state that the combined structures shown in FIG. 14 are arranged in five lines. FIG. 16 is a schematic perspective view of the combined structure of FIG. 14 showing only the pressure rectangles. In FIGS.  14  to  16 , like reference characters designate like members common to FIG. 13, and the detailed description thereof is omitted.  
         [0045]    According to the embodiment, pressure rectangles  33  and  34  have the respective parallelism adjusting mechanisms  24 , and have a structure entangled with each other so as to be adjacently arranged. A planar portion  35  is for receiving pressure, and the same load can be applied on the same area in the respective pair of pressure rectangles. The basic structure of the pressure device is the same as that described in the first embodiment.  
         [0046]    Referring to FIGS. 15 and 16, through-holes  36  of the screws for adjusting parallelism and for fixture are formed in the respective pressure rectangles from the top. This structure enables each one IC chip to move independently so that differences in height can be absorbed to apply a uniform pressure.  
         [0047]    A mounting example will be described below using an aggregated pressure device having the parallelism adjusting mechanisms  24 , in which lines are arranged in two rows, each line having eight parallelism adjusting mechanisms  24  arranged at an interval of 0.77 mm.  
         [0048]    First, the indentation of the bumps was confirmed without the low-pressure and low-temperature ACF so as to adjust the parallelism by moving the screws back and forth. Then, eight IC chips, each having a size of 2.64 mm×10.11 mm×0.175 mm, were arranged in one line at an interval of 0.77 mm, and two lines are simultaneously heated and pressure bonded. As a result, excellent connection resistance values were obtained, enabling collective bonding of  16  chips to be performed.  
         [0049]    According to the embodiment, a silicon substrate with a thickness of 625 μm was used as the circuit board  5 . The thin IC chip  3  had a thickness of 175 μm, a length of 10.11 mm, and a width of 2.5 mm, and the number of bumps is 446. Nine of the IC chips were used. The gap between adjacent IC chips was 0.77 mm.  
         [0050]    The pressure rectangles  33  and  34  are provided with oilless bearings  29  built therein, thereby being vertically moved by following the vertical guides  28 . When the IC chips are not pressurized, the pressure rectangle is supported by the support springs  27  so as not to come into contact with the IC chips  3 . On the other hand, during the pressurization, the pressure rectangles  33  and  34  are downwardly pressurized with, for example, compressed air.  
         [0051]    For heat setting the ACF  10  disposed between the circuit board  5  and the IC chip  3 , which were heated and bonded, the pressure device in the pressurized state was heated in a clean oven. After putting the pressure device put into the clean oven, the clean oven was heated from a room temperature to 170° C. When the temperature of the circuit board, IC chip, and pressure device reached 170° C., the power supply was turned off to cool them naturally. At the room temperature, the pressure device was removed and the pressure was released.  
         [0052]    A confirmation of the connection resistance values of the IC chips  3  mounted by the process described above showed that the entire connection check portions of nine IC chips have an excellent resistance value of 60 mΩ. The amount of warp of the circuit board  5  in the longitudinal direction was reduced to be 10 μm or less, resulting in a marked improvement in comparison with 50 μm achieved by a conventional process.  
         [0053]    According to the present invention, in addition to the embodiments described above, various modifications may be made. For example, according to the above embodiments, the axes α and β are adjustable. Alternatively, one of the axes may be made adjustable. More specifically, referring to FIG. 10, if the longitudinal direction of the V-shaped groove of the pressure receiving member  13  is aligned in parallel with the axis β and the pressure receiving member  13  is directly overlapped on the columnar member  14   b  while the intermediate member  12  and the columnar member  14   a  are removed, a pressure device adjustable using only the axis β may be constructed.  
         [0054]    According to the embodiment described above, the ACF is used; alternatively, the ACP, NCF, and NCP may be used. Moreover, according to the embodiment, the oven is used for heat setting the ACF; alternatively, it may be performed by heaters built in the pressurizing unit and stage.  
         [0055]    Such modifications may incorporate the present invention within the scope of attached claims.  
         [0056]    While the present invention has been described with reference to what are presently considered to be the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, the invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.