Abstract:
An electronic component is equipped with electrode protrusions that make it possible to mount the electronic component without covering connection pads of a circuit board with solder and to dispose the connection pads of the circuit board with a narrow pitch while preventing electrical shorting of the connection electrodes during mounting. A method of manufacturing an electronic component equipped with connection electrodes, where electrode protrusions are covered with solder, includes a step of heating a solder sheet to a semi-molten state and pressing the electronic component onto the solder sheet to place the electrode protrusions in contact with the solder sheet and a step of retracting the electronic component from a position where the electrode protrusions contact the solder sheet to transfer solder onto outside surfaces of the electrode protrusions that contacted the solder sheet.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an electronic component equipped with connection electrodes where electrode protrusions are covered with solder and a method of manufacturing the same, and also to an electronic device produced by mounting such electronic component on a circuit board or the like and a method of manufacturing the same. 
     2. Related Art 
     Methods of mounting a semiconductor chip on a circuit board by flip-chip bonding include a method of forming solder bumps used for connecting on electrodes of the semiconductor chip to bond the semiconductor chip to the circuit board and a method that covers connection pads formed on the circuit board with solder and aligning and bonding the electrodes of the semiconductor chip and the connection pads. 
     Methods of forming solder bumps on the electrodes of a semiconductor chip include a method that forms a solder layer in the form of dots on a carrier chip and transfers the solder layer onto the electrodes of the semiconductor chip (see Patent Document 1) and a method that forms solder bumps by placing a solder sheet in contact with the electrodes of the semiconductor chip in a state where the electrodes are heated so as to melt the solder and cause the solder to adhere to the electrodes (see Patent Document 2). 
     Methods of covering connection pads of a circuit board with solder include solder cream printing and solder plating. Among methods for covering connection pads of a circuit board with solder and bonding the circuit board to a semiconductor chip, for cases where the electrodes of the semiconductor chip have an extremely narrow pitch, there is a method that forms protruding stud bumps (“electrode protrusions”) on the electrodes of the semiconductor chip, sticks fine solder powder onto the connection pads of the circuit board, and melts the solder on the connection pads to bond the electrode protrusions and the connection pads (see Patent Document 5).
     Patent Document 1   

     Japanese Laid-Open Patent Publication No. H10-229087
     Patent Document 2   

     Japanese Laid-Open Patent Publication No. H8-203904
     Patent Document 3   

     Japanese Laid-Open Patent Publication No. H11-163199
     Patent Document 4   

     Japanese Laid-Open Patent Publication No. H10-70153
     Patent Document 5   

     Japanese Laid-Open Patent Publication No. 2000-77471 
     SUMMARY OF THE INVENTION 
     As described earlier, with a method that covers the connection pads of a circuit board with solder in advance, it is necessary to carry out a process such as solder cream printing or solder plating on the substrate, which raises the manufacturing cost. Also, when the electrodes of a semiconductor chip have an extremely narrow pitch, the connection pads of the circuit board will also have a narrow pitch, which increases the likelihood of the connection pads being electrically shorted by the solder. 
     Also, the semiconductor chip is heated when the semiconductor chip is bonded to the circuit board. Since the semiconductor chip has a high thermal conductivity compared to the circuit board, there is the problem of solder flowing up onto the electrode protrusions when the solder supplied onto the connection pads of the circuit board melts, which makes the bonding of the semiconductor chip unreliable. 
     The present invention was conceived in view of the problems described above, and it is an object of the present invention to provide an electronic component equipped with electrode protrusions that are formed at a narrow pitch, that make a process of covering connection pads of a circuit board with solder unnecessary, and enable the connection pads of the circuit board to be disposed at a narrow pitch, and is an electronic component that can be mounted while avoiding electrical shorting between the connection electrodes. It is also an object of the present invention to provide a method of manufacturing such electronic component, an electronic device that uses such electronic component, and a method of manufacturing such electronic device. 
     To achieve the stated object, a method of manufacturing according to the present invention manufactures an electronic component equipped with connection electrodes where electrode protrusions are covered with solder, including steps of: heating a solder sheet to a semi-molten state and pressing an electronic component onto the solder sheet to place the electrode protrusions in contact with the solder sheet; and retracting the electronic component from a position where the electrode protrusions contact the solder sheet to transfer solder onto outer surfaces of the electrode protrusions that contacted the solder sheet. 
     Here, the solder sheet may be supported by a heating stage, the electronic component may be supported by a heating head, and the solder sheet and the electronic component may be pressed together by the heating stage and the heating head to press the electrode protrusions onto the solder sheet and thereby favorably transfer solder from the solder sheet to the electrode protrusions. 
     The heating stage and the heating head may heat the solder sheet to a temperature where a semi-molten state is achieved and a heating temperature of the heating stage may be set higher than a heating temperature of the heating head. By doing so, it is possible to reliably cover the electrode protrusions with solder. 
     Also, ultrasound may be applied to the electronic component when the electrode protrusions are pressed onto the solder sheet. By doing so, it is possible to transfer solder onto the electrode protrusions without raising the heating temperature of the solder sheet. 
     A method where the solder sheet is supported by a heating stage, the electronic component is supported by an ultrasonic head, the solder sheet and the electronic component are pressed together by the heating stage and the ultrasonic head, and the electrode protrusions are pressed onto the solder sheet while ultrasound is applied to the electronic component using the ultrasonic head is also effective. 
     Also, by carrying out an operation that presses the electrode protrusions onto the solder sheet with the ultrasound being applied to the electronic component in a nitrogen atmosphere, it is possible to prevent fretting corrosion of the solder formed on the electrode protrusions. 
     For a method of manufacturing an electronic device by mounting an electronic component equipped with connection electrodes, where electrode protrusions are covered with solder, onto a circuit board on which connection pads are formed by bonding the connection electrodes to the connection pads, the electronic component is formed by heating a solder sheet to a semi-molten state and pressing the electronic component onto the solder sheet to place the electrode protrusions in contact with the solder sheet and then retracting the electronic component from a position where the electrode protrusions contact the solder sheet to transfer solder onto outer surfaces of the electrode protrusions that contacted the solder sheet, and the method of manufacturing an electronic device includes a step of aligning the connection electrodes of the electronic component with the connection pads of the circuit board and heating to a temperature where the solder melts to bond the electronic component and the circuit board. 
     It is effective to use an electronic component where the solder has been transferred from the solder sheet to the electrode protrusions by applying ultrasound to the electronic component when the electrode protrusions were pressed onto the solder sheet as the electronic component. 
     The circuit board may be supported on a heating stage, the electronic component may be supported on a mounting heating head, the heating stage may be heated to at least a melting point of the solder, and a heating temperature of the mounting heating head may be set lower than a temperature of the heating stage to bond the electronic component and the circuit board. By doing so, it is possible to prevent the solder from flowing up onto the electrode protrusions and thereby reliably bond the electrode protrusions and the connection pads. 
     Flux fill may be applied in advance onto a region of the circuit board where the electronic appliance will be mounted, the connection electrodes of the electronic component and the connection pads of the circuit board may be aligned, the electronic component and the circuit board may be heated to a temperature where the solder melts, and the flux fill may be thermally cured to bond the electronic component and the circuit board. By doing so, it is possible to reliably bond the electrode protrusions and the connection pads, to seal the bonded part of the electronic component and the circuit board, and to reliably support the bonded part of the electronic component and the circuit board. 
     As the electronic component equipped with connection electrodes where electrode protrusions are covered with solder, an electronic component that has been formed by a method of manufacturing including steps of: heating a solder sheet to a semi-molten state and pressing an electronic component onto the solder sheet to place the electrode protrusions in contact with the solder sheet; and retracting the electronic component from a position where the electrode protrusions contact the solder sheet to transfer solder onto outer surfaces of the electrode protrusions that contacted the solder sheet can be favorably used. 
     For an electronic device formed by mounting an electronic component equipped with connection electrodes, where electrode protrusions are covered with solder, onto a circuit board on which connection pads are formed by bonding the connection electrodes to the connection pads, it is favorable for the electronic component to be formed by heating a solder sheet to a semi-molten state and pressing the electronic component onto the solder sheet to place the electrode protrusions in contact with the solder sheet and then retracting the electronic component from a position where the electrode protrusions contact the solder sheet to transfer solder onto outer surfaces of the electrode protrusions that contacted the solder sheet, and for the electronic device to be formed by a method of manufacturing including a step of aligning the connection electrodes of the electronic component with the connection pads of the circuit board and heating to a temperature where the solder melts to bond the electronic component and the circuit board. 
     With a method of manufacturing an electronic component and an electronic device according to the present invention, by transferring solder from a solder sheet to electrode protrusions of the electronic component to form connection terminals for mounting on the electronic component, connection electrodes can be easily formed on the electronic component. It is also possible to prevent electrical shorting of the electrode protrusions, so that even an electronic component on which the electrode protrusions have been formed with an extremely narrow pitch can be mounted reliably. Also, by forming the connection electrodes on the electronic component, it is possible to easily manufacture a circuit board on which connection pads are formed with a high density while preventing electrical shorting of the connection pads. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A to 1C  are schematic diagrams showing a manufacturing process according to a first embodiment of a method of manufacturing an electronic component; 
         FIGS. 2A to 2C  are schematic diagrams showing a manufacturing process in a second embodiment of a method of manufacturing an electronic component; 
         FIGS. 3A to 3C  are schematic diagrams showing one example of where fretting corrosion of electrode protrusions is prevented; and 
         FIGS. 4A to 4C  are schematic diagrams showing a method of manufacturing an electronic device. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Method of Manufacturing an Electronic Component 
     First Embodiment 
       FIGS. 1A to 1C  show a process that manufactures an electronic component on which connection electrodes are formed by covering the outer surfaces of electrode protrusions of a semiconductor chip with solder.  FIG. 1A  shows a state where electrode protrusions  12  have been formed on electrodes of the semiconductor chip  10 . The electrode protrusions  12  are formed by a method called “ball bonding”. Ball portions  12   a  are formed by melting metal wire using a bonding tool, the respective electrodes (not shown) of the semiconductor chip  10  are pressed into contact with the ball portions  12   a , and protruding parts  12   b  are formed by cutting the metal wires while pulling on the wires. The protruding parts  12   b  are formed in peaks on the ball portions  12   a  that are slightly flattened. 
     In the method of manufacturing an electronic component according to the present invention, connection electrodes are formed by covering the outer surfaces of the electrode protrusions  12  formed on the semiconductor chip  10  with solder using a solder sheet  20 .  FIG. 1A  schematically shows the semiconductor chip  10 , on which the electrode protrusions  12  have been formed, and the solder sheet  20 . As the solder sheet  20 , products of a variety of thicknesses are provided as mill rolls. Here, a solder sheet  20  of a suitable thickness should be selected in accordance with the height of the parts of the electrode protrusions  12  to be covered with solder. 
     Since the height of the electrode protrusions  12  of the semiconductor chip  10  in the present embodiment is around 30 μm, a sheet with a thickness of 50 μm is used as the solder sheet  20 . The solder sheet  20  used in the present embodiment is made of Sn—Ag (tin-silver) solder, and the melting point thereof is 220° C. 
       FIG. 1B  shows a process where the semiconductor chip  10  is pressed onto the solder sheet  20  so that the protruding parts  12   b  of the electrode protrusions  12  penetrate and become buried in the solder sheet  20 . The solder sheet  20  is supported and heated on a heating stage  30  and the semiconductor chip  10  is held by suction on a mounting/heating head  32 . The surface of the semiconductor chip  10  on which the electrode protrusions  12  are formed is disposed in parallel with the surface of the solder sheet  20  supported on the heating stage  30  and the mounting/heating head  32  is pressed toward the solder sheet  20 . 
     The semiconductor chip  10  and the solder sheet  20  are pressed together by the mounting/heating head  32  and the heating stage  30  and the protruding parts  12   b  of the electrode protrusions  12  on the semiconductor chip  10  are pressed into the solder sheet  20 . Since the electrode protrusions  12  are formed so that the protruding parts  12   b  project outward from the ball portions  12   a , the insertion positions of the electrode protrusions  12  are restricted when the protruding parts  12   b  are buried in the solder sheet  20 . 
     In the process shown in  FIG. 1B , the heating stage  30  and the mounting/heating head  32  are heated and controlled so that the solder sheet  20  becomes semi-molten. Here, “semi-molten” refers to a temperature range that is at or below the melting temperature and is where the solder sheet  20  becomes soft. This is an intermediate state between where the solder is completely hard and where the solder is a liquid, or in other words where solid-phase solder and liquid-phase solder coexist. In this semi-molten phase, the solder sheet remains in a sheet-like state. The melting point for the Sn—Ag solder used in the present embodiment is 220° C., and the semi-molten state starts at around 170° C. 
     To place the solder sheet  20  in a semi-molten state and transfer the solder from the solder sheet  20  to the electrode protrusions  12 , the temperature of the mounting/heating head  32  in the present embodiment is set at around 150° C. and the temperature of the heating stage  30  is set at around 190° C. The temperature of the mounting/heating head  32  is set lower than the temperature of the heating stage  30  so that solder is not excessively transferred to the electrode protrusions  12 . If the temperature of the mounting/heating head  32  rises to around the melting point of the solder, when the electrode protrusions  12  are in contact with the solder sheet  20 , the solder will rise up onto the outer surfaces of the electrode protrusions  12 , resulting in an increase in the amount of transferred solder adhering to the electrode protrusions  12 . Accordingly, the heating temperature of the mounting/heating head  32  should be set at a low end of the semi-molten temperature range of the solder sheet  20  or slightly below the semi-molten temperature range. On the other hand, the heating stage  30  is set at a high end of the semi-molten temperature range of the solder. By doing so, it becomes easier for the electrode protrusions  12  to penetrate the solder sheet  20 , so that the solder can easily adhere to the electrode protrusions  12 . 
       FIG. 1C  shows a state where the semiconductor chip  10  has been separated from the solder sheet  20  after the process in  FIG. 1B . Solder  20   a  covers the outer surfaces of the protruding parts  12   b  of the electrode protrusions  12  on the semiconductor chip  10  that were inserted into the solder sheet  20 , thereby producing an electronic component where connection electrodes  14  used for connecting the electronic component are formed. Concave parts  21  where the protruding parts  12   b  of the electrode protrusions  12  were inserted are formed in the solder sheet  20 . 
     The thickness of the solder  20   a  that covers the protruding parts  12   b  of the electrode protrusions  12  is 2 to 3 μm on average, and has a maximum of around 5 μm. By causing the solder  20   a  to adhere with this thickness on the electrode protrusions  12 , connection pads formed on a circuit board can be reliably soldered to the electrode protrusions  12 . 
     This method of the present embodiment where the solder sheet  20  is placed in a semi-molten state and solder is transferred from the solder sheet  20  to the electrode protrusions  12  to form the connection electrodes  14  has an advantage in that it is possible to easily form connection electrodes on the semiconductor chip  10 . Since the electrode protrusions  12  are thinly covered with the solder  20   a , compared to a method where solder is melted and attached to electrodes to form solder bumps, there is the advantage that it is possible to form connection electrodes without electrically shorting the electrode protrusions  12 , even when the electrode protrusions  12  are formed with an extremely narrow pitch. 
     Method of Manufacturing an Electronic Component 
     Second Embodiment 
       FIGS. 2A to 2C  show a second embodiment where solder is transferred onto the electrode protrusions  12  provided on the electrodes of the semiconductor chip  10  using the solder sheet  20 . 
     In the present embodiment, the semiconductor chip  10  is held by suction on an ultrasonic head  40  and when solder is transferred from the solder sheet  20  onto the electrode protrusions  12  of the semiconductor chip  10 , ultrasound is applied to the semiconductor chip  10  to transfer the solder onto the electrode protrusions  12 . 
       FIG. 2A  shows a state where the solder sheet  20  is supported on the heating stage  30  and the semiconductor chip  10  is held by suction on the ultrasonic head  40  with the electrode protrusions  12  facing the solder sheet  20 .  FIG. 2B  shows a state where the semiconductor chip  10  is pressed on the solder sheet  20  supported on the heating stage  30  and ultrasound is applied by the ultrasonic head  40  in a state where the protruding parts  12   b  of the electrode protrusions  12  have penetrated the solder sheet  20 . Here, around 0.5 seconds is sufficient as the time for which ultrasonic vibration is applied in a state where the protruding parts  12   b  have penetrated the solder sheet  20 . 
     In the same way as in the first embodiment, the solder sheet  20  is heated to a semi-molten state by the heating stage  30  and the semiconductor chip  10  is heated by the ultrasonic head  40 , so that solder is transferred from the solder sheet  20  to the electrode protrusions  12 . When solder is transferred by applying ultrasound to the semiconductor chip  10  like in the present embodiment, compared to the case where ultrasonic vibration is not used, it is possible to transfer solder with the heating temperature of the heating stage  30  set lower. For example, when the solder sheet  20  is made of the Sn—Ag solder used in the present embodiment, the heating temperature of the heating stage  30  may be set at around 170° C. Here, it is believed that when the electrode protrusions  12  are placed in contact with the solder sheet  20  and ultrasonic vibration is applied to the semiconductor chip  10 , the temperature will rise due to friction at the parts where the electrode protrusions  12  contact the solder sheet  20 . 
     Since it is possible to lower the heating temperature of the solder sheet  20  with a method where solder is transferred from the solder sheet  20  to the electrode protrusions  12  by applying ultrasound to the semiconductor chip  10  like in the present embodiment, there is the advantage that the solder sheet  20  retains its shape more favorably than in the first embodiment, which makes it easier to handle the solder sheet  20 . When ultrasonic vibration is applied to the semiconductor chip  10 , the protruding parts  12   b  of the electrode protrusions  12  that have penetrated the solder sheet  20  rub against the solder sheet  20 , so that solder can be reliably transferred to the parts of the protruding parts  12   b  that contact the solder sheet  20 . 
       FIG. 2C  shows an electronic component where solder  20   a  has been transferred from the solder sheet  20  to the protruding parts  12   b  of the electrode protrusions  12  to form the connection electrodes  14  and also shows the solder sheet  20  after the solder has been transferred. In the present embodiment also, since the electrode protrusions  12  are covered with the solder  20   a  with the solder sheet  20  in a semi-molten state, the solder  20   a  only thinly adheres to the outer surfaces of the protruding parts  12   b , and therefore electrical shorting of the electrode protrusions  12  can be prevented, even if the electrode protrusions  12  are disposed at a narrow pitch. 
     However, when ultrasound is applied to the semiconductor chip  10  to transfer the solder from the solder sheet  20  to the electrode protrusions  12 , there are cases where the friction between the electrode protrusions  12  and the solder sheet  20  causes fretting corrosion which produces an oxide film on the contacting parts of the electrode protrusions  12  and the solder. It is possible to easily tell whether an oxide film has been produced on the solder  20   a  transferred onto the electrode protrusions  12  since the solder becomes blackened when an oxide film is formed. 
     To prevent fretting corrosion from occurring, the operation that applies ultrasound to the semiconductor chip  10  and transfers solder onto the electrode protrusions  12  from the solder sheet  20  should be carried out in a non-oxygenated atmosphere. More specifically, the area where the solder is transferred may be closed off from the outside and the operation carried out with such area in a nitrogen atmosphere. As a simple method, when ultrasound is applied by the ultrasonic head  40  and the semiconductor chip  10  is pressed onto the solder sheet  20 , nitrogen gas may be blown toward the contacting parts of the semiconductor chip  10  and the solder sheet  20 . 
       FIG. 3A  shows a state where ultrasonic vibration is applied onto the electrode protrusions  12  in a state where the protruding parts  12   b  of the electrode protrusions  12  have penetrated the solder sheet  20 .  FIG. 3B  schematically shows a state where fretting corrosion has occurred and the solder  20   a  covering the protruding parts  12   b  of the electrode protrusions  12  has been oxidized. On the other hand,  FIG. 3A  shows a state where the solder  20   a  has been transferred without the solder  20   a  being blackened and an oxide film being produced by transferring the solder  20   a  onto the electrode protrusions  12  in a nitrogen atmosphere. 
     In this way, according to a method that applies ultrasound to the semiconductor chip  10  to transfer solder onto the electrode protrusions  12  from the solder sheet  20  in a nitrogen atmosphere, it is possible to suppress oxidization of the solder  20   a  that covers the electrode protrusions  12 , which means that soldering can be carried out reliably when mounting the electronic component. 
     Note that although examples of electronic components where the electrode protrusions  12  are formed by ball bonding on the electrodes of the semiconductor chip  10  have been described in the above embodiments, the present invention is not limited to the electrode protrusions  12  formed on the electrodes of the semiconductor chip  10  being formed by ball bonding. Also, although examples where the electrode protrusions  12  are formed of the ball portions  12   a  and the protruding parts  12   b  have been described in the above embodiments, the form of the electrode protrusions formed on the electrodes of the semiconductor chip  10  is not limited to the form described in the above embodiments. However, in the method of manufacturing an electronic component according to the present invention, since the solder is transferred to the electrode protrusions in a state where at least the front end portions of the electrode protrusions have penetrated the solder sheet  20 , it is effective for the front ends of the protruding portions of the electrode protrusions to be formed in peaked shapes. 
     Method of Manufacturing an Electronic Device 
     Third Embodiment 
       FIGS. 4A to 4C  show an example of a manufacturing process that mounts an electronic component where connection electrodes  14  have been formed by covering electrode protrusions  12  with solder  20   a  on a circuit board to assemble an electronic device. The electronic device according to the present embodiment is formed by flip-chip bonding the semiconductor chip  10  to a circuit board  50  and sealing the bonded part of the semiconductor chip  10  and the circuit board  50  using resin to fix the semiconductor chip  10  on the circuit board  50 . 
     A method of manufacturing an electronic device according to the present embodiment mounts the semiconductor chip  10  on the circuit board  50  by flip-chip bonding after applying flux fill  60  in advance to a region of the circuit board  50  where the semiconductor chip  10  will be mounted. 
       FIG. 4A  shows a state where the flux fill  60  has been applied onto the region of the circuit board  50  where the semiconductor chip  10  will be mounted. Connection pads  52  are formed at the position of the circuit board  50  where the semiconductor chip  10  is mounted so that the positions of the connection pads  52  match the planar arrangement of the electrode protrusions  12  that are the connection portions formed on the semiconductor chip  10 . 
     The flux fill  60  acts as flux that ensures sufficient bonding between the electrode protrusions  12  and the connection pads  52  when the semiconductor chip  10  is mounted on the circuit board  50  and, after the semiconductor chip  10  has been mounted on the circuit board  50 , also acts as underfill resin that fills the gap between the semiconductor chip  10  and the circuit board  50  and fixes and supports the semiconductor chip  10  on the circuit board  50 . 
       FIG. 4B  shows a state where the circuit board  50  is set on a heating stage  70  and the semiconductor chip  10  is held by suction on a heating head  80  used for mounting and is positioned on and bonded to the circuit board  50 . The electrode protrusions  12  of the semiconductor chip  10  and the connection pads  52  formed on the circuit board  50  are aligned and the semiconductor chip  10  is bonded to the circuit board  50  by applying pressure and heat. 
       FIG. 4C  shows a state where the semiconductor chip  10  has been bonded to the circuit board  50  to assemble an electronic device. The electrode protrusions  12  formed on the semiconductor chip  10  are respectively soldered to the connection pads  52  formed on the circuit board  50 , the gap between the semiconductor chip  10  and the circuit board  50  is filled with the flux fill  60 , and the bonded part of the semiconductor chip  10  and the circuit board  50  is sealed. 
     By pressing the semiconductor chip  10  onto the circuit board  50  and heating to the temperature at which the solder  20   a  melts, the solder can spread out between the electrode protrusions  12  and the connection pads  52  and solder the electrode protrusions  12  and the connection pads  52  together. By maintaining the pressure and heat in this state, the flux fill  60  is cured to firmly fix the semiconductor chip  10  to the circuit board  50 . 
     When heat and pressure are applied to the semiconductor chip  10  on the circuit board  50 , the temperature of the heating head  80  that applies heat and pressure to the semiconductor chip  10  should be set lower than the temperature of the heating stage  70  that supports the circuit board  50 . By doing so, the solder  20   a  that covers the electrode protrusions  12  on the semiconductor chip  10  spreads from the electrode protrusions  12  onto the connection pads  52  of the circuit board  50 , so that the electrode protrusions  12  and the connection pads  52  are reliably soldered together. 
     Here, by setting the heating temperature of the semiconductor chip  10  lower than the melting point of the solder  20   a  and setting the heating temperature of the circuit board  50  higher than the melting point of the solder  20   a , it is possible to prevent solder from flowing up from the connection pads  52  to the electrode protrusions  12 , so that the semiconductor chip  10  and the circuit board  50  can be soldered together more reliably. 
     Note that although a method where the semiconductor chip  10  is mounted with the flux fill  60  having been applied in advance onto the circuit board  50  has been described in the above embodiment, it is also possible to produce an electronic device by injecting underfill resin into the bonded part between the semiconductor chip  10  and the circuit board  50  after the semiconductor chip  10  has been bonded to the circuit board  50 . A method that mounts the semiconductor chip  10  by supplying the flux fill  60  onto the circuit board  50  in advance can be effectively used when manufacturing an electronic device where the electrode protrusions  12  have an extremely narrow pitch, which makes underfilling difficult. 
     With the method of manufacturing an electronic device according to the present embodiment, since the solder  20   a  covers the electrode protrusions  12  of the semiconductor chip  10  and solder is not supplied to the connection pads  52  of the circuit board  50 , the processing of the circuit board  50  is simple. Even if the connection pads  52  are formed with a minute pitch, it is possible to avoid the electrical shorting of adjacent connection pads  52  due to supplied solder, which means it is possible to form the circuit board  50  in an extremely fine pattern. 
     For the semiconductor chip  10  also, since transferring the solder  20   a  to the electrode protrusions  12  from the solder sheet  20  makes it possible to form a semiconductor chip (electronic component) with electrode protrusions  12  formed with a narrow pitch, reliable mounting on a circuit board is possible, even for a semiconductor chip with electrodes disposed with a high density. 
     Note that although a semiconductor chip has been given as an example of an electronic component in the above embodiments, in some cases it is also possible to apply the method according to the present invention to mounting a semiconductor package on which a semiconductor chip has been mounted. In such cases, the semiconductor package corresponds to the “electronic component” and a product where the semiconductor package has been mounted on a mounting board corresponds to the “electronic device”.