Patent Publication Number: US-2021185828-A1

Title: Flux transfer apparatus

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a structure of a flux collecting apparatus. More specifically, the present invention relates to a structure of a flux collecting apparatus used in a flux transfer apparatus that transfers flux to a protruding electrode of an electronic component. 
     Description of Related Art 
     In recent years, a flip chip bonding method in which a protruding electrode (e.g., a solder bump) is formed in an electronic component such as a semiconductor, the electronic component is picked up to be reversed, the protruding electrode is placed on an electrode pad of a printed substrate, heating to a high temperature is performed to melt the solder of the protruding electrode, and the electronic component is bonded to the printed substrate, has been more and more broadly used. In the flip chip bonding method, in order to facilitate the bonding property between the solder and the electrode pad, a method of transferring flux (oxide film remover or surfactant) to the top surface of the protruding electrode (solder bump) and then placing the protruding electrode on the electrode pad is used. 
     At the time of transfer of the flux to the protruding electrode of the electronic component, an apparatus that dips the protruding electrode of the electronic component into a thin flux layer collected in a recessed portion to transfer the flux to the tip of the protruding electrode is used. The apparatus includes a stage provided with the recessed portion that collects the flux and a flux pot having a through hole into which the flux is introduced, makes the flux pot reciprocate along the top surface of the stage to supply the flux to the recessed portion of the stage and make the liquid surface of the flux collected in the recessed portion smooth using the bottom surface of the flux pot (for example, see Patent Document 1). 
     PRIOR ART DOCUMENTS 
     Patent Documents 
     Patent document 1: WO 2016/075982 
     SUMMARY OF THE INVENTION 
     Issue(s) to be Solved by the Invention 
     However, it is known that flux may change in quality, such as being solidified, if the temperature rises. Therefore, at the time when the protruding electrode of the electronic component is dipped into the flux collected in the recessed portion of the stage, it is necessary to cool down the electronic component, a bonding tool to which the electronic component is attached and fixed, a heater, etc., to a temperature at which the flux in standby in the flux pot does not change in quality, and suppress the rise of temperature of the flux in standby in the flux pot at the time of dipping. However, since it takes time to cool down the temperature of the bonding tool, the heater, etc., from the temperature at the time of bonding, there is an issue that the lower the temperature of the bonding tool and the heater at the time of dipping, the lower the productivity has become. 
     Therefore, the objective of the present invention is to suppress the rise of the temperature of the stage in the flux collecting apparatus. 
     Means for Solving the Issue 
     A flux collecting apparatus according to the present invention includes: a stage having a recessed portion for collecting flux; a flux pot, which is an annular member having a through hole into which the flux is introduced, reciprocates along a top surface of the stage to supply the flux having been introduced into the through hole into the recessed portion, and levels off a top surface of the flux using a bottom surface; and a cooling mechanism for cooling the stage. 
     In the flux collecting apparatus, the cooling mechanism may be a Peltier element. 
     Inventive Effect 
     The present invention is capable of suppressing the rise of the temperature of the stage in the flux collecting apparatus. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a plan view illustrating a configuration of a flux collecting apparatus in an embodiment of the present invention. 
         FIG. 1B  is a plan cross-sectional view illustrating a configuration of a flux collecting apparatus in an embodiment of the present invention. 
         FIG. 2A  is a plan view illustrating an operation of the flux collecting apparatus illustrated in  FIG. 1A . 
         FIG. 2B  is a plan cross-sectional view illustrating an operation of the flux collecting apparatus illustrated in  FIG. 1B . 
         FIG. 3  is an explanatory diagram illustrating a state in which a bonding tool at a high temperature is lowered to the flux collecting apparatus illustrated in  FIGS. 1A and 1B . 
         FIG. 4  is a graph illustrating changes of height and temperature of the bonding tool over time during the time of performing flip chip bonding using a bonding apparatus including the flux collecting apparatus illustrated in  FIGS. 1A and 1B . 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     In the following, a flux collecting apparatus  100  of the embodiment is described with reference to the drawings. As shown in  FIG. 1A  and  FIG. 1B , the flux collecting apparatus  100  includes a stage  12  having a recessed portion  13  that collects flux, a flux pot  20  which supplies flux  51  to the recessed portion  13  and levels off a top surface of the flux using a bottom surface  22  thereof, and a cooling mechanism  30  for cooling the stage  12 . The flux pot  20  moves reciprocally in the X direction by a driving mechanism not shown herein. The descriptions in the following are made with the reciprocal movement direction of the flux pot  20  as the X direction, a perpendicular direction thereof as the Y direction, and an up-down direction as the Z direction. 
     As shown in  FIG. 1A  and  FIG. 1B , the stage  12  has the recessed portion  13  which is recessed from a top surface  14  to collect the flux. The flux  13  has a width W and extends along the reciprocal movement direction (X direction). The depth of the recessed portion  13  is a depth in which a protruding electrode of an electronic component such as a semiconductor can be dipped into, and may be about 10 to 20 μm, for example. 
     As shown in  FIGS. 1A and 1B , the flux pot  20  is an annular member having a through hole  21  penetrating in the Z direction along which the flux  51  is introduced, supplies the flux  51  having been introduced into the through hole  21  to the recessed portion  13  from a stage side opening of the through hole  21 , and levels off the top surface of the flux using the bottom surface  22  thereof. The through hole  21 , like the recessed portion  13 , is a rectangular hole with the width W. 
     In addition, on the lower side of the stage  12 , the cooling mechanism  30  is installed. The cooling mechanism  30 , for example, may be a heat dissipating fan, and may be one using a Peltier element. 
     In the following, the operating of the flux collecting apparatus  100  with such configuration will be described with reference to  FIG. 2A  and  FIG. 2B . As shown in  FIG. 2A  and  FIG. 2B , in an initial state, the flux pot  20  is located at the upper side of the cooling mechanism  30  on the X direction plus side of the recessed portion  13 . In such state, the flux  51  is filled into the through hole  21  of the flux pot  20 . Since the bottom surface  22  of the flux pot  22  is in close contact with the top surface  14  of the stage  12 , the flux  51  does not flow to the outside from the through hole  21 , but is maintained in an inner side space of the through hole  21 . 
     Then, the flux pot  20  is moved by the driving mechanism not shown herein toward the X direction minus side. When the through hole  21  of the flux pot  20  comes above the recessed portion  13 , the flux  51  filled in the through hole  21  falls into the recessed portion  13  of the stage  12 . The top surface of flux  51  having fallen into the recessed portion  13  levels off by the bottom surface  22  of the flux pot  20  and becomes flux  53  whose depth is substantially the same as the depth of the recessed portion  13 . The flux pot  20  moves reciprocally in the X direction above the recessed portion  13  for several times, so that the entire recessed portion  13  is filled by the flux  53  with a uniform thickness. 
     As shown in  FIG. 3 , if the recessed portion  13  is filled by the flux  53 , the flux pot  20  is returned to the initial position by the driving mechanism not shown herein. 
     If the flux pot  20  returns to the initial position, a bonding head  41  is moved above the recessed portion  13  by the driving mechanism not shown herein. On the lower surface of the bonding head  41 , a heater  44  and a bonding tool  44  sandwiching a heat insulating material  42  are installed. In addition, a semiconductor die  10  is attached and fixed to the lower surface of the bonding tool  44 . A solder bump  11  is configured on the lower surface of the semiconductor die  10 . At this time, the temperature of the bonding tool  44  and the heater  43  becomes about 100° C., and the temperature of the semiconductor die  10  and the solder bump  11  also becomes about 100° C. 
     The bonding head  41  is lowered by a driving apparatus not shown herein, the solder bump  11  dipped into the flux  53  in the recessed portion  13 , and the flux  53  is transferred to the top surface of the solder bump  11 . At this time, the stage  12  is heated by radiant heat from the semiconductor die  10 , the bonding tool  44 , and the heater  43  at about 100° C. The heat that heats the stage  12 , as indicated by arrows  35  and  36  shown in  FIG. 3 , flows from the lower portion of the recessed portion  13  toward the cooling mechanism  30  and is discharged to the outside from the cooling mechanism  30 . 
     Accordingly, since the flux collecting apparatus  100  of this embodiment discharges the radiant heat received from the semiconductor die  10 , the bonding tool  44 , and the heater  43  at the time when these components approach the surface  14  of the stage to the outside from the cooling mechanism  30 , even if the temperature of the bonding tool  44  and the heater  43  becomes about 100° C., which is higher than the conventional 60° C., the flux collecting apparatus  100  can suppress the flux  51  filled in the flux pot  21  from changing in quality due to an excessive rise of the temperature of the stage  12 . 
     In addition, since the heating temperature at the time of bonding is a temperature of about 250° C. that melts the solder bump  11 , in the case where flip chip bonding is performed using the flux collecting apparatus  100  of the embodiment, the dipping into the flux  53  can be performed with the temperature of the bonding tool  44  and the heater  43  being about 100° C., which is higher than the conventional 60° C. Therefore, the time for cooling the bonding tool  44  and the heater  43  (time t 4 −time t 3 , as shown in  FIG. 4 ) is shorter than the time (time t 8 −time t 7 , as shown in  FIG. 4 ) in the case where a flux collecting apparatus  100  of the conventional technology is used. Accordingly, the cycle time of bonding can be significantly shortened to AT 1  from AT 2  of the conventional technology shown in  FIG. 4 . 
     As described above, since the flux collecting apparatus  100  of the embodiment can suppress the rise of the temperature of the stage  12  at the time when the bonding tool  44  and the heater  43  of a high temperature approach the stage  12 , the cooling temperature of the bonding tool  44  and the heater  43  can be higher than the conventional technology, so the cooling time of the bonding tool  44  and the heater  43  can be reduced and the tact time can be reduced. 
     DESCRIPTION OF REFERENCE SYMBOLS 
     
         
         
           
               10 : semiconductor die;  11 : solder bump;  12 : stage;  13 : recessed portion;  14 : top surface;  20 : flux pot;  21 : through hole;  22 : bottom surface;  30 : cooling mechanism;  35 ,  36 : arrows;  41 : bonding head;  42 : heat insulating material;  43 : heater;  44 : bonding tool;  51 ,  53 : flux.