Abstract:
A plasma-processing apparatus providing a resin mold domed enough to allow no bonding wires to be exposed is presented. The plasma-processing apparatus cleans a board including a chip mounted thereon and a disposing area for a pad formed around the chip. The apparatus includes a chamber for accommodating the board; an electrode mounted to the chamber for generating plasma in the chamber with a voltage applied thereto, a table for supporting the board in the chamber, and a masking member which is provided above the board. The masking member has an opening for exposing the chip and the disposing area to the plasma.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to plasma-processing apparatus and method for plasma-cleaning pads on a chip and pads on a board to which chips are mounted, and a plasma-processed board, and further relates to a chip mounting method employing the plasma-processing method and a chip mounted assembly.  
         BACKGROUND OF THE INVENTION  
         [0002]    A plasma-cleaning process, which is known, removes a dirt on a pad at the sides of a position for mounting a chip on a printed circuit board or on a pad on the upper surface of the chip prior to a wire bonding to the pad. In the plasma-cleaning process, the board including the chip mounted thereon is placed in a chamber of a plasma-processing apparatus, in which plasma is generated, and ions and neutral particles called radicals collide with the surface of the chip to remove the dirt on the board. After the plasma-cleaning process, the pad on the chip and the board are connected with wires by a wire bonding apparatus. Finally, the chip and the wires are covered with a resin by mold sealing.  
           [0003]    [0003]FIG. 7 is a side view of a board including a conventional resin mold  6 ′. A chip  2  is mounted on a chip-mounting position  1 ′ of a board  1 . A Pad  3  at the side of the position  1 ′ is connected to a pad  4  on the upper surface of the chip  2  with a wire. The resin mold  6 ′ is provided for protecting the chip  2  and the wire  5  by mold sealing.  
           [0004]    As denoted by the real line in FIG. 7, the resin mold  6 ′ flows wide and flatten around the chip  2  but not domed. This causes the top of the wire  5  to be exposed out of the resin mold  6 ′. A desired shape of the resin mold  6  is denoted by the dotted line keeping a dome shape to encapsulate the chip  2  and wire  5 .  
           [0005]    The reason why the resin mold  6 ′ is not domed but flatten is explained below. In a conventional plasma-processing apparatus, the board  1  has an entire surface exposed for plasma for the plasma-cleaning. As being plasma-cleaned, the entire surface has an increasing wetting property. Accordingly, the resin, the material of the resin mold  6 ′, has adhesivity increased. And therefore, the molded form of the resin may thus flow extensively around the chip and flatten over the upper surface of the board  1  before being cured down. As a result, the resin bold  6 ′ has a flat shape as denoted by the real line in FIG. 7.  
         SUMMARY OF THE INVENTION  
         [0006]    A plasma-processing apparatus for plasma-cleaning a board having a chip and a pad-disposed area around the chip includes a chamber for accommodating the board, an electrode disposed at the chamber for generating plasma in the chamber by a high frequency voltage applied to the electrode; a table for supporting the board in the chamber, and a masking member provided above the board and having an opening for exposing the chip and the pad-disposed area to the plasma.  
           [0007]    A plasma-processing method using the plasma-processing apparatus includes a process of applying a voltage to the electrode to generate plasma in the chamber; and a process of exposing the chip and the pad area to the plasma through the opening of the masking member for performing the plasma-process.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIGS. 1A to  1 E illustrate a procedure of mounting a chip according to Embodiment 1 of the present invention.  
         [0009]    [0009]FIG. 2 is a perspective view of a plasma-processing apparatus according to Embodiment 1.  
         [0010]    [0010]FIG. 3 is a cross sectional view of the plasma-processing apparatus according to Embodiment 1.  
         [0011]    [0011]FIG. 4 is a plan view of the plasma-processing apparatus according to Embodiment 1.  
         [0012]    [0012]FIG. 5 is a partial plan view of a board according to Embodiment 1.  
         [0013]    [0013]FIGS. 6A to  6 D illustrate a chip mounting method according to Embodiment 2 of the invention.  
         [0014]    [0014]FIG. 7 is a side view of a board having a resin mold provided thereon according to Embodiment 1 and a prior art. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     Embodiment 1  
       [0015]    [0015]FIGS. 1A to  1 E illustrate a procedure of mounting a chip according to Embodiment 1 of the present invention. FIG. 2 is a perspective view of a plasma-processing apparatus according to Embodiment 1. FIG. 3 is a cross sectional view of the plasma-processing apparatus. FIG. 4 is a plan view of the plasma-processing apparatus. FIG. 5 is a partial plan view of a board according to Embodiment 1. FIG. 7 is a side view of the board having a resin mold provided thereon according to Embodiment 1.  
         [0016]    A procedure of mounting a chip will be described in steps. FIG. 1A illustrates a die bonding process. A chip  2  is mounted on a chip mounting position  1 ′ of the upper surface of a board  1 . Pads  3  of a circuit pattern are formed around the position  1 ′, and a pad  4  is formed on the upper surface of the chip  2 . The chip  2  is sucked with a nozzle  41  of a head  40  and placed on the board  1 . In this embodiment, the board  1  is a multi-board sheet, which is separated into small board units at a later step.  
         [0017]    [0017]FIG. 1B illustrates a plasma-cleaning process. A masking member  33  is placed above the board  1 . The board  1  and the chips  2  have a portion exposed through openings  34  provided in the masking member  33  and cleaned with plasma applied on the portion.  
         [0018]    [0018]FIG. 1C illustrates a wire bonding process. The pads  3  and  4  cleaned by the plasma-process are connected to each other with wires  5  released from a capillary tool  42  of a wire bonding apparatus.  
         [0019]    [0019]FIG. 1D illustrates a resin-applying process. Drops of sealing resin  6 , e.g. epoxy resin, are applied from a nozzle  43  of a resin applying apparatus for encapsulating the chips  2  and the wires  5 . The sealing resin  6  are then cured at a curing process. The wires  5  is prevented from being exposed out of the sealing resins  6  flowing extensively and flattening due to the plasma-process for the surface of the board  1 .  
         [0020]    [0020]FIG. 1E illustrates a separating process. The board  1  is separated by a cutting device such as a cutter (not shown) into small board units  1 A, which become chip mounted assemblies  7 .  
         [0021]    An overall arrangement of the plasma-processing apparatus will be described with referring to FIG. 2. A guide rail  11  for conveying the board  1  are provided on a table  10 . A loader  12  and an unloader  13  are provided at both ends of the guide rail  11 . The loader  12  and the unloader  13  have heights capable of being adjusted with elevators  14  and  15 , respectively. The loader  12  holds a stack of the boards  1  in shelves. The boards  1  can be transferred to the guide rail  11  one at a time by a pusher  16 . The board  1  carries plural chips  2  mounted thereon at the process shown in FIG. 1A.  
         [0022]    A top cover  21  of a chamber  28  is bridged over a central region of the guide rail  11 . The top cover  21  is supported by an arm  22  and can be lifted up and down for opening and closing with the arm  22 . A transfer finger  17  forwards the board  1  from the loader  12  to the unloader  13  along the guide rail  11 . The transfer finger  17  can be lifted up and down with a cylinder  18 . The transfer finger  17  and cylinder  18  move in pitches by an endless belt  19 , which is driven by a motor  20 .  
         [0023]    The plasma-processing apparatus will be described in more detail with referring to FIGS. 3 and 4. FIG. 3 is a cross sectional view at a line  3 - 3  in FIG. 4. As shown in FIG. 3, the top cover  21  capable of moving upward and downward is disposed over a support  23 . A lower electrode  24  is provided beneath the top cover  21 . A table  25  is disposed over the lower electrode  24 . The lower electrode  24  is electrically connected to a high-frequency power supply  26 , and the top cover  21  is grounded to a grounding port  27 . The top cover  21  and lower electrode  24  form the chamber  28  for generating plasma. A sealing member  29  is also provided on the support  23 . The interior of the chamber  28  is evacuated by a vacuum sucking apparatus  30  such as a vacuum pump. The chamber  28  is filled with a gas for generating the plasma provided by a gas feeder  31 . The lower electrode  24  and bed  25 , as being connected to the power supply  26 , can function as a single electrode.  
         [0024]    In FIG. 3, a masking member  33  is provided over the bed  25 . The masking member  33  may be made of electrically insulating, hard material such as ceramic. The masking member  33  has an opening  34  provided therein for exposing the chip  2  and its peripheral region to the plasma.  
         [0025]    As shown in FIG. 5, the pad  4  is provided on the upper surface of the chip  2 , and the pad  3  is provided in a circuitry pattern on the upper surface of the board  1 . That is, the chip  2  is mounted on a chip-mounting position  1 ′ of the board  1 . The pad  2  is formed to surround the chip  2  beside the position  1 ′ of the board  1 . As the opening  34  of the masking member  33  has a width L 1  sized to expose the chip  2  and a disposing area E 1  of the pad  3 . The disposing area E 1  has a width L 1  between the inner edge at the opening  34  of the masking member  33  and the outer edge of the chip  2 . In an area E 2 , which is covered with the making member over the board  1 , the resin is prevented from flowing extensively. In FIG. 3, two boards  1  placed on the table  25  are separated by a partition  35  at the center of the table. An insulating member  36  is provided between the lower electrode  24  and the support  23 .  
         [0026]    An operation of the plasma-processing apparatus will be explained. In FIG. 2, the board  1  released from the loader  12  by the pusher  16  is conveyed by the transfer finger  17  to the table  25  shown in FIG. 3. At the moment, the top cover  21  remains at an upper position to clear the upper surface of the table  25 . Then, the top cover  21  is fallen down to the support  23  to shut off the chamber  28 . At the moment, the chip  2  on the board  1  is located just beneath the opening  34  of the masking member  33 .  
         [0027]    Then, the chamber  28  is evacuated by the vacuum sucking apparatus  30 , and the gas feeder  31  fills the chamber  28  with plasma gas such as argon gas. Then, the lower electrode  24  is fed with a high-frequency voltage from the power supply  26 . The plasma generated in the chamber  28  passes through the opening  34  and strikes against the upper surfaces of the chip  2  and the board  1  to clean the upper surfaces with an etching effect or the like.  
         [0028]    In FIG. 3, the pad  3  of the board  1  and the pad  4  of the chip  2  are exposed through the opening  34 . Dirt on the pads  3  and  4  can thus be removed by the etching effect of the plasma. Simultaneously, the upper surface of the board  1  exposed through the opening  34  is etched and activated by the plasma to have an increased wetting property. The increased wetting property increases the adhesivity of the resin mold  6 .  
         [0029]    After the plasma-processing is completed, the top cover  21  is lifted up, and the (plasma-processed) board  1  on the bed  25  is conveyed by the transfer finger  17  to the unloader  13  unloading the board. By repeating the foregoing processes, the boards  1  in the loader  12  are plasma-processed and received by the unloader  13 .  
         [0030]    The unloader  13  is then transferred to the wire bonding apparatus connecting the pads  3  of the board  1  to the corresponding pads  4  of the chip  2  with the wire  5  as shown in FIG. 1C. The pads  3  and  4 , as being cleaned by the plasma etching, can be bonded with each other easily with the wires  5 .  
         [0031]    After the wire bonding process, the boards  1  are transferred to a resin applying apparatus. The board  1  has the surface coated with the rein  6  to encapsulate the chip  2  and wire  5  to form a resin mold as shown in FIG. 1D.  
         [0032]    As a result, the resin mold  6  in FIG. 7 provided on the plasma-processed board  1  has a domed shape and is not flattened. In FIG. 5, the area E 1  of the board  1  including the pad  3  is exposed to the plasma through the opening  34  having the width L 1  of the masking member  33 , and therefore, has an improved wetting property. This allows the resin mold  6  to be securely adhered to the upper surface of the board  1  in the exposed area E 1 . The resin-flow-protecting area E 2  (denoted by the hatching in FIG. 5) around the exposed area E 1  including the pad  3  is covered with the masking member  33  and protected from the plasma, and has a low wetting property. Under the low wetting property, the resin mold on the board  1  does not flow extensively and stays tenacious unlike that in the prior art process. The rein mold  6  is domed but not flattened as shown in FIG. 7, hence having a raised shape for encapsulating the chip  2  and wire  5  completely. The resin mold  6  may have a width L 1  equal to or slightly greater than the width L 1  of the opening  34 . Then, the board  1  is separated into small board units  1 A, which become chip-mounted assemblies  7 , as shown in FIG. 1E.  
       Embodiment 2  
       [0033]    [0033]FIGS. 6A to  6 D illustrates processes of a chip mounting method according to Embodiment 2 of the present invention. In this embodiment, a chip  53  having a bump  54  is mounted on the board. At a chip-mounting position  1 ′, pads  3  where the bump  54  is jointed are formed. That is, The chip-mounting position is a disposing area E 3  of the pads  3 .  
         [0034]    [0034]FIG. 6A illustrates a plasma-cleaning process substantially identical to that explained in Embodiment 1. A chip is not mounted on the board  1 . The upper surface of the board and the pads  3  in the disposing area E 3  exposed through an opening  34  of a masking member  33  are plasma-cleaned. The disposing area E 3  to which plasma is applied through the opening  34  is processed by a plasma-process with in a width L 1 .  
         [0035]    Then, an under-fill resin  51  is released from a nozzle  50  of a resin coating apparatus and applied to the disposing are E 3  as shown in FIG. 6B. A resin-flow-protecting area E 2  prevents a resin  51  form flowing extensively on the board  1 , and therefore, the resin stays within the disposing area E 3  where the plasma is collided. The reason is described previously.  
         [0036]    Then, as shown in FIG. 6C, a tool  52  of a bonding apparatus holds a chip  53  having a bump such as a flip-chip, and positions the bump  54  directly on the pad  3  on the board  1 . In this embodiment, the tool  52 , which also functions as a heater, heats up the chip  53  to bond the bump  54  to the pad  3 . As being lifted down and placed directly on the resin mold  51 , the chip  53  has a lower surface closely adhered to the resin mold  51 . The resin mold  51  is then cured at a curing process, and then, the board  1  is separated into small board units  1 A, which become chip mounted assemblies  7 ′ as shown in FIG. 6D.  
         [0037]    According to the method of this embodiment, a chip mounted assembly is provided, which has the resin mold  51  prevented from flowing extensively, and an increased bonding effect between the bumps  54  and the pad  3 .