Patent Publication Number: US-9412711-B2

Title: Electronic device

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an electronic device. 
     2. Description of Related Art 
     Heretofore, semiconductor devices are known (see JP-A-2002-76051, for example). The semiconductor device disclosed in this document is provided with a semiconductor element, bonding pads, wires, and a lead frame. The bonding pads are formed on the semiconductor element. The wires are bonded to the bonding pads and the lead frame. 
     SUMMARY OF THE INVENTION 
     The present invention has been proposed under the above circumstances, and a main object thereof is to provide an electronic device that is able to achieve an improvement in yield or an electronic device that is able to prevent sealing resin from exfoliating from a sub-electrode. 
     According to a first aspect of the present invention, an electronic device is provided that has an electronic element and a wire bonded to the electronic element, the electronic element including a first conductive layer, a second conductive layer and a third conductive layer, the first conductive layer having a bonding pad to which the wire is bonded, the second conductive layer having a buffer part and an interconnect portion that are disposed in the same plane as each other, the third conductive layer having a first interconnect region insulated from the bonding pad, and the buffer part being located between the bonding pad and the first interconnect region in a thickness direction of the bonding pad. 
     Preferably, the electronic device is further provided with an insulating layer, and the insulating layer has a region that is interposed between the first conductive layer and the second conductive layer. 
     Preferably, the insulating layer is made of SiO 2 . 
     Preferably, the wire includes a bonding portion bonded to the electronic element, and the buffer part has a region overlapping with the bonding portion as seen in the thickness direction. 
     Preferably, the bonding pad has a joining area joined to the bonding portion, and a periphery of the buffer part has a shape surrounding the joining area as seen in the thickness direction. 
     Preferably, the buffer part overlaps with an entirety of the joining area as seen in the thickness direction. 
     Preferably, the buffer part has a rectangular shape. 
     Preferably, the buffer part has a buffer part front surface and a buffer part back surface that face opposite sides to each other, and the buffer part front surface faces a side on which the bonding pad is located. 
     Preferably, the buffer part front surface and the buffer part back surface are both entirely covered by the insulating layer. 
     Preferably, the buffer part is a floating electrode. 
     Preferably, the insulating layer fills an entire area sandwiched between the buffer part and the bonding pad. 
     Preferably, the buffer part is covered by the insulating layer around an entire periphery thereof. 
     Preferably, the electronic element includes a support via extending in the thickness direction, the support via is interposed between the bonding pad and the buffer part, and the bonding pad and the buffer part are electrically connected to each other. 
     Preferably, a crack is formed in the bonding pad, and the crack is covered by the wire. 
     Preferably, the bonding pad has a pad front surface and the a pad back surface that face opposite sides to each other, and the wire is bonded to the pad front surface. 
     Preferably, the bonding pad includes an extended part extending from the pad front surface, and the extended part extends from the pad front surface along the bonding portion. 
     Preferably, the first conductive layer includes an interconnect metal, and the interconnect metal is connected to the bonding pad and overlaps with the interconnect portion as seen in the thickness direction. 
     Preferably, the interconnect metal has a region that overlaps with the interconnect portion as seen in the thickness direction, and is electrically connected to the interconnect portion. 
     Preferably, the electronic element includes a first via extending in the thickness direction, and the first via is interposed between the interconnect metal and the interconnect portion, and electrically connects the interconnect metal and the interconnect portion to each other. 
     Preferably, the first via overlaps with the interconnect metal and the interconnect portion as seen in the thickness direction. 
     Preferably, the insulating layer fills the entire area sandwiched between the third conductive layer and the buffer part. 
     Preferably, the third conductive layer has a second interconnect region disposed in the same plane as the first interconnect region, and the second interconnect region is electrically connected to the interconnect portion. 
     Preferably, the electronic element includes a second via extending in the thickness direction, and the second via is interposed between the second interconnect region and the interconnect portion, and electrically connects the second interconnect region and the interconnect portion to each other. 
     Preferably, the second via overlaps with the second interconnect region and the interconnect portion as seen in the thickness direction. 
     Preferably, the electronic element includes a fourth conductive layer, the third conductive layer is located between the second conductive layer and the fourth conductive layer in the thickness direction, and the fourth conductive layer has a region that overlaps with the buffer part as seen in the thickness direction. 
     Preferably, the fourth conductive layer has a first interconnect film and a second interconnect film, the first interconnect film overlaps with the buffer part as seen in the thickness direction, and the second interconnect film is electrically connected to the second interconnect region. 
     Preferably, the electronic element includes a third via extending in the thickness direction, and the third via is interposed between the first interconnect film and the first interconnect region, and electrically connects the first interconnect film and the first interconnect region to each other. 
     Preferably, the third via overlaps with the first interconnect film and the first interconnect region as seen in the thickness direction. 
     Preferably, the electronic element includes a fourth via extending in the thickness direction, and the fourth via is interposed between the second interconnect film and the second interconnect region, and electrically connects the second interconnect film and the second interconnect region to each other. 
     Preferably, the fourth via overlaps with the second interconnect film and the second interconnect region as seen in the thickness direction. 
     Preferably, the electronic element includes a semiconductor substrate having a semiconductor element, and the bonding pad overlaps with the semiconductor substrate as seen in the thickness direction. 
     Preferably, the semiconductor substrate is made of Si. 
     Preferably, the electronic element is further provided with a connecting part formed on the semiconductor substrate, and the bonding pad is electrically connected to the semiconductor element via the connecting part. 
     Preferably, the connecting part is interposed between the semiconductor substrate and the second interconnect film, and contacts the semiconductor substrate and the second interconnect film. 
     Preferably, taking the bonding pad as a first bonding pad, the first conductive layer includes a second bonding pad disposed in a different position from the first bonding pad as seen in the thickness direction, and the first interconnect region is electrically connected to the second bonding pad. 
     Preferably, the first conductive layer and the second conductive layer are made of at least one of Al and Cu. 
     Preferably, the first conductive layer has a greater maximum thickness than the second conductive layer. 
     Preferably, the first conductive layer has a maximum thickness of 1.0 to 3.0 μm, the second conductive layer has a maximum thickness of 0.1 to 0.5 μm, and the first conductive layer is separated from the second conductive layer by a distance of 0.1 to 0.5 μm. 
     Preferably, the first via is made of W. 
     Preferably, the wire is made of Cu, Au or Ag. 
     Preferably, the electronic element includes an insulating protective layer covering the first conductive layer, and the protective layer exposes the bonding pad. 
     Preferably, an opening is formed in the protective layer, and the bonding pad is exposed through the opening. 
     Preferably, the buffer part has a region that is located inside the opening and a region that is located outside the opening, as seen in the thickness direction. 
     Preferably, the inner edge of the opening is entirely surrounded by a peripheral edge of the buffer part as seen in the thickness direction. 
     Preferably, the protective layer has a passivation film, and the passivation film is made of at least one of SiN and SiO 2 . 
     Preferably, the passivation film has a SiN layer and a SiO 2  layer that are laminated one on the other. 
     Preferably, the protective layer has a polyimide layer covering the passivation film. 
     Preferably, the electronic device is further provided with a sub-electrode to which the wire is bonded. 
     Preferably, the electronic device is further provided with a sealing resin that seals the electronic element and the wire. 
     According to a second aspect of the present invention, an electronic device is provided that has an electronic element and a wire bonded to the electronic element, the electronic element including a bonding pad to which the wire is bonded, the wire including a bonding portion to which the electronic element is bonded, an outer surface of the bonding portion having a bottom surface, a lateral surface and a pressed surface, the bottom surface contacting the bonding pad, the lateral surface having a first curved surface part, the first curved surface part having a curved shape that, starting from a boundary between the bottom surface and the lateral surface, curves toward the pressed surface side as the first curved surface part extends outward as seen in the thickness direction, the pressed surface having a ring-shaped bent part and being located further inward than the lateral surface as seen in a thickness direction of the bonding pad, and the boundary being located further outward than the bent part as seen in the thickness direction. 
     Preferably, the bottom surface has a circular shape and faces in the thickness direction toward the bonding pad from the bonding portion. 
     Preferably, the lateral surface connects the pressed surface and the bottom surface. 
     Preferably, the lateral surface has an annular shape. 
     Preferably, a cross-section of the lateral surface in a plane orthogonal to the thickness direction has a circular shape whose diameter is defined as a ball diameter. 
     Preferably, the wire includes a bridging part, the bridging part is connected to the bonding portion, extends linearly, and has a circular shape in cross-section, the ball diameter is from 44 μm or more to 50 μm or less in the case where the bridging part has a diameter of less than 22.5 μm, the ball diameter is 59 μm or more in the case where the bridging part has a diameter from 22.5 μm or more to less than 27.5 μm, the ball diameter is 63 μm or more in the case where the bridging part has a diameter from 27.5 μm or more to less than 32.5 μm, and the ball diameter is 77 μm or more in the case where the bridging part has a diameter of 32.5 μm or more. 
     Preferably, the first curved surface part at least partially contacts the bonding pad. 
     Preferably, the lateral surface has a second curved surface part, and the second curved surface part has a curved shape that, starting from a boundary between the pressed surface and the lateral surface, curves toward the bottom surface side as the second curved surface part extends outward as seen in the thickness direction. 
     Preferably, the pressed surface has a first portion and a second portion that are each annular, the first portion is connected to the lateral surface, and the second portion is connected to the first portion via the bent part. 
     Preferably, the first portion and the second portion are both flat. 
     Preferably, the second portion slopes relative to the first portion, and forms an angle of 180 degrees or less with the first portion. 
     Preferably, the first portion is located between the lateral surface and the bent part as seen in the thickness direction, and the second portion is located further inward than the bent part as seen in the thickness direction. 
     Preferably, the second portion entirely overlaps with the bottom surface as seen in the thickness direction. 
     Preferably, the second portion slopes relative to the thickness direction, so as to extend outward as seen in the thickness direction as the second portion approaches the bottom surface in the thickness direction. 
     Preferably, an outer surface of the bonding portion has a peripheral surface, and the peripheral surface is connected to the pressed surface and stands up from the pressed surface. 
     Preferably, the peripheral surface has a circular shape in cross-section. 
     Preferably, the peripheral surface extends in the thickness direction. 
     Preferably, the peripheral surface is located further inward than the pressed surface as seen in the thickness direction. 
     Preferably, the electronic element includes a semiconductor substrate having a semiconductor element, and the bonding pad overlaps with the semiconductor substrate as seen in the thickness direction. 
     Preferably, the semiconductor substrate is made of Si. 
     Preferably, the bonding pad has a pad front surface and a pad back surface that face opposite sides to each other, and the wire is bonded to the pad front surface. 
     Preferably, the bonding pad includes an extended part that extends out from the pad front surface, and the extended part extends out from the pad front surface along the bonding portion. 
     Preferably, the extended part contacts the lateral surface. 
     Preferably, the wire is made of Cu, Au or Ag. 
     Preferably, the electronic element includes an insulating protective layer, and the protective layer exposes the bonding pad. 
     Preferably, an opening is formed in the protective layer, and the bonding pad is exposed through the opening. 
     Preferably, the protective layer has a passivation film, and the passivation film is made of at least one of SiN and SiO 2 . 
     Preferably, the passivation film has a SiN layer and a SiO 2  layer that are laminated one on the other. 
     Preferably, the protective layer has a polyimide layer covering the passivation film. 
     Preferably, the electronic device is further provided with a sub-electrode to which the wire is bonded. 
     Preferably, the wire includes a bonding region bonded to the sub-electrode, and a bridging part that is connected to the bonding portion and the bonding region. 
     Preferably, the bonding region is bonded after the bonding portion. 
     Preferably, the electronic device is further provided with a sealing resin that seals the electronic element and the wire. 
     Preferably, the sealing resin partially covers the lateral surface. 
     According to a third aspect of the present invention, a method for manufacturing an electronic device is provided that has a step of preparing a lead frame that includes a sub-electrode having an Ag layer, a step of holding the lead frame in an environment having a humidity of 40 to 50%, and a step of bonding the wire to the Ag layer, after the holding step. 
     Preferably, the holding step is performed for 1 to 168 hours. 
     Preferably, the environment in the holding step is an atmospheric pressure environment under an air or nitrogen atmosphere at 20 to 30° C. 
     Preferably, the lead frame includes a main electrode, and the method is further provided with a step of disposing an electronic element on the main electrode, before the holding step. 
     Preferably, the method is further provided with a step of bonding the wire to the electronic device, before the step of bonding the wire to the Ag layer. 
     Preferably, the method is further provided with a step of forming a sealing resin that covers the wire and the lead frame, after the step of bonding the wire to the Ag layer. 
     Preferably, the method is further provided with a step of holding the lead frame in an environment having a humidity of 40 to 50%, between the step of bonding the wire to the Ag layer and the step of forming the sealing resin that covers the wire and the lead frame. 
     Preferably, the method is further provided with a step of forming pieces by cutting the sealing resin and the lead frame, after the step of forming the sealing resin. 
     Preferably, the Ag layer has a thickness of 5 to 15 μm. 
     Preferably, the sub-electrode includes a Cu part on which the Ag layer is formed, and the Cu part is thicker than the Ag layer. 
     According to a fourth aspect of the present invention, an electronic device is provided that has an electronic element, a sub-electrode and a wire bonded to the electronic element and the sub-electrode, the sub-electrode including an Ag layer, the wire being bonded to the Ag layer, and the Ag layer being held at an environment having a humidity of 40 to 50%, before a step of bonding the wire to the Ag layer. 
     Preferably, the Ag layer has a thickness of 5 to 15 μm. 
     Preferably, the sub-electrode includes a Cu part on which the Ag layer is formed, and the Cu part is thicker than the Ag layer. 
     Preferably, the electronic device is further provided with a sealing resin that seals the electronic element and the wire. 
     Preferably, the Ag layer is covered by the sealing resin. 
     Preferably, the electronic element includes a semiconductor substrate having a semiconductor element. 
     Preferably, the semiconductor substrate is made of Si. 
     Preferably, the wire is made of Cu, Au or Ag. 
     Preferably, the electronic element includes an insulating protective layer, and the protective layer exposes the bonding pad. 
     Preferably, an opening is formed in the protective layer, and the bonding pad is exposed through the opening. 
     Preferably, the protective layer has a passivation film, and the passivation film is made of at least one of SiN and SiO 2 . 
     Preferably, the passivation film has a SiN layer and a SiO 2  layer that are laminated one on the other. 
     According to a fifth aspect of the present invention, an electronic device is provided that has an electronic element and a wire bonded to the electronic element, the electronic element including a bonding pad to which the wire is bonded, a main component of the bonding pad being Al, a mixed metal being mixed in the wire, and the mixed metal being one of Pt, Pd and Au. 
     Preferably, a main component of the wire is Cu or Ag. 
     Preferably, a main component of the wire is Cu. 
     Preferably, a concentration of the mixed metal in the wire is 0.5 to 5 wt %. 
     Preferably, the bonding pad includes a metal thin film layer, and the metal thin film layer is made of CuAl 2 . 
     Preferably, the metal thin film layer contacts the wire. 
     Preferably, the metal thin film layer has a thickness of 5 to 20 nm. 
     Preferably, the wire includes a bonding portion bonded to the electronic element, an outer surface of the bonding portion has a bottom surface, a lateral surface, and a pressed surface, the bottom surface contacts the bonding pad, the lateral surface connects the pressed surface and the bottom surface, the pressed surface has a ring-shaped bent part and is located further inward than the lateral surface as seen in a thickness direction of the bonding pad, the lateral surface has a first curved surface part, and the first curved surface part has a curved shape that, starting from a boundary between the bottom surface and the lateral surface, curves toward the pressed surface side as the first curved surface part extends outward as seen in the thickness direction. 
     Preferably, the bottom surface has a circular shape and faces in the thickness direction toward the bonding pad from the bonding portion. 
     Preferably, the lateral surface has an annular shape. 
     Preferably, the first curved surface part at least partially contacts the bonding pad. 
     Preferably, the lateral surface has a second curved surface part, and the second curved surface part has a curved shape that, starting from a boundary between the pressed surface and the lateral surface, curves toward the bottom surface side as the second curved surface part extends outward as seen in the thickness direction. 
     Preferably, the pressed surface has a first portion and a second portion that each has an annular shape, the first portion is connected to the lateral surface, and the second portion is connected to the first portion via the bent part. 
     Preferably, the first portion and the second portion are both flat. 
     Preferably, the second portion slopes relative to the first portion, and forms an angle of 180 degrees or less with the first portion. 
     Preferably, the first portion is located between the lateral surface and the bent part as seen in the thickness direction, and the second portion is located further inward than the bent part as seen in the thickness direction. 
     Preferably, the second portion entirely overlaps with the bottom surface as seen in the thickness direction. 
     Preferably, the second portion slopes relative to the thickness direction, so as to extend inwardly as seen in the thickness direction as the second portion is distanced further from the bottom surface in the thickness direction. 
     Preferably, an outer surface of the bonding portion has a peripheral surface, and the peripheral surface is connected to the pressed surface and stands up from the pressed surface. 
     Preferably, the peripheral surface has a circular shape in cross-section. 
     Preferably, the peripheral surface extends in the thickness direction. 
     Preferably, the peripheral surface is located further inward than the pressed surface as seen in the thickness direction. 
     Preferably, the electronic element includes a semiconductor substrate having a semiconductor element, and the bonding pad overlaps with the semiconductor substrate as seen in a thickness direction of the bonding pad. 
     Preferably, the semiconductor substrate is made of Si. 
     Preferably, the bonding pad has a pad front surface and a pad back surface that face opposite sides to each other, and the wire is bonded to the pad front surface. 
     Preferably, the bonding pad includes an extended part that extends out from the pad front surface, and the extended part extends out from the pad front surface along the bonding portion. 
     Preferably, the extended part contacts the lateral surface. 
     Preferably, the electronic element includes an insulating protective layer, and the protective layer exposes the bonding pad. 
     Preferably, an opening is formed in the protective layer, and the bonding pad is exposed through the opening. 
     Preferably, the protective layer has a passivation film, and the passivation film is made of at least one of SiN and SiO 2 . 
     Preferably, the passivation film has a SiN layer and a SiO 2  layer that are laminated one on the other. 
     Preferably, the protective layer has a polyimide layer covering the passivation film. 
     Preferably, the electronic device is further provided with a sub-electrode to which the wire is bonded. 
     Preferably, the wire includes a bonding region bonded to the sub-electrode, and a bridging part that is connected to the bonding portion and the bonding region. 
     Preferably, the bonding region is bonded after the bonding portion. 
     Preferably, the electronic device is further provided with a sealing resin that seals the electronic element and the wire. 
     Preferably, the sealing resin partially covers the lateral surface. 
     According to a sixth aspect of the present invention, an electronic device is provided that has an electronic element and a wire bonded to the electronic element, the electronic element including a bonding pad to which the wire is bonded, the wire including a bonding portion bonded to the electronic element, an outer surface of the bonding portion having a bottom surface, a lateral surface, a pressed surface and a peripheral surface, the bottom surface contacting the bonding pad, the pressed surface being located further inward than the lateral surface as seen in a thickness direction of the bonding pad, the peripheral surface being connected to the pressed surface, standing up from the pressed surface and having a circular shape in cross-section, the wire including a bridging part, the bridging part being connected to the bonding portion, extending linearly, and having a circular shape in cross-section, and a difference in diameter between the bridging part and the peripheral surface being 2 to 8 μm. 
     Preferably, a difference in diameter between the bridging part and the peripheral surface is 4 to 8 μm. 
     Preferably, the pressed surface has a ring-shaped bent part, and the bent part has a diameter of 46 to 54 μm in the case where the bridging part has a diameter from 27.5 μm or more to less than 32.5 μm. 
     Preferably, the bottom surface has a circular shape and faces in the thickness direction toward the bonding pad from the bonding portion. 
     Preferably, the lateral surface connects the pressed surface and the bottom surface. 
     Preferably, the lateral surface has an annular shape. 
     Preferably, a cross-section of the lateral surface in a plane orthogonal to the thickness direction has a circular shape. 
     Preferably, the pressed surface has a first portion and a second portion that each has an annular shape, the first portion is connected to the lateral surface, and the second portion is connected to the first portion via the bent part. 
     Preferably, the first portion and the second portion are both flat. 
     Preferably, the second portion slopes relative to the first portion, and forms an angle of 180 degrees or less with the first portion. 
     Preferably, the first portion is located between the lateral surface and the bent part as seen in the thickness direction, and the second portion is located further inward than the bent part as seen in the thickness direction. 
     Preferably, the second portion entirely overlaps with the bottom surface as seen in the thickness direction. 
     Preferably, the second portion slopes relative to the thickness direction so as to extend inwardly as seen in the thickness direction as the second portion is distanced further from the bottom surface in the thickness direction. 
     Preferably, the peripheral surface extends in the thickness direction. 
     Preferably, the peripheral surface is located further inward than the pressed surface as seen in the thickness direction. 
     Preferably, the electronic element includes a semiconductor substrate having a semiconductor element, and the bonding pad overlaps with the semiconductor substrate as seen in the thickness direction. 
     Preferably, the semiconductor substrate is made of Si. 
     Preferably, the bonding pad has a pad front surface and a pad back surface that face opposite sides to each other, and the wire is bonded to the pad front surface. 
     Preferably, the bonding pad includes an extended part that extends out from the pad front surface, and the extended part extends out from the pad front surface along the bonding portion. 
     Preferably, the extended part contacts the lateral surface. 
     Preferably, the wire is made of Cu, Au or Ag. 
     Preferably, the electronic element includes an insulating protective layer, and the protective layer exposes the bonding pad. 
     Preferably, an opening is formed in the protective layer, and the bonding pad is exposed through the opening. 
     Preferably, the protective layer has a passivation film, and the passivation film is made of at least one of SiN and SiO 2 . 
     Preferably, the passivation film has a SiN layer and a SiO 2  layer that are laminated one on the other. 
     Preferably, the protective layer has a polyimide layer covering the passivation film. 
     Preferably, the electronic device is further provided with a sub-electrode to which the wire is bonded. 
     Preferably, the wire includes a bonding region bonded to the sub-electrode, and a bridging part that is connected to the bonding portion and the bonding region. 
     Preferably, the bonding region is bonded after the bonding portion. 
     Preferably, the electronic device is further provided with a sealing resin that seals the electronic element and the wire. 
     Preferably, the sealing resin partially covers the lateral surface. 
     According to a seventh aspect of the present invention, an electronic device is provided that has an electronic element and a wire bonded to the electronic element, the electronic element including a bonding pad to which the wire is bonded, the bonding pad including Pd layer, and the Pd layer directly contacting the wire. 
     Preferably, the wire directly contacts a surface of the Pd layer. 
     Preferably, the surface of the Pd layer has a maximum height difference of 40 nm or less. 
     Preferably, the surface of the Pd layer has a maximum height difference of 30 nm or less. 
     Preferably, the surface of the Pd layer has a maximum height difference of 20 nm or less. 
     Preferably, the surface of the Pd layer has a maximum height difference of 10 nm or less. 
     Preferably, the Pd layer has a thickness of 0.1 to 1 μm. 
     Preferably, the bonding pad is further provided with a Ni layer, the Pd layer is located between the wire and the Ni layer, and the surface of the Ni layer contacts the Pd layer and has a maximum height difference of 40 nm or less. 
     Preferably, the Ni layer has a thickness of 1 to 5 μm. 
     Preferably, the bonding pad is further provided with a Cu layer, the Ni layer is located between the Pd layer and the Cu layer, and the surface of the Cu layer contacts the Ni layer and has a maximum height difference of 40 nm or less. 
     Preferably, the Cu layer has a thickness of 2 to 12 μm. 
     Preferably, the electronic device is further provided with a sealing resin that seals the electronic element and the wire. 
     Preferably, the electronic element includes a semiconductor substrate having a semiconductor element. 
     Preferably, the semiconductor substrate is made of Si. 
     Preferably, the wire is made of Cu, Au or Ag. 
     Preferably, the electronic element includes an insulating protective layer, and the protective layer exposes the bonding pad. 
     Preferably, an opening is formed in the protective layer, and the bonding pad is exposed through the opening. 
     Preferably, the protective layer has a passivation film, and the passivation film is made of at least one of SiN and SiO 2 . 
     Preferably, the passivation film has a SiN layer and a SiO 2  layer that are laminated one on the other. 
     Further features and advantages of the present invention will become apparent from the detailed description given below with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of an electronic device according to a first embodiment of the present invention. 
         FIG. 2  is a plan view of the electronic device shown in  FIG. 1  (sealing resin indicated with imaginary line). 
         FIG. 3  is a partially enlarged view in which a portion of  FIG. 1  is enlarged. 
         FIG. 4  is a partially enlarged view in which a portion of  FIG. 3  is enlarged. 
         FIG. 5  is a cross-sectional view along a line V-V in  FIG. 3 . 
         FIG. 6  is a cross-sectional view along a line VI-VI in  FIG. 3 . 
         FIG. 7  is a diagram in which a wire has been omitted from  FIG. 6  (joining area shown with hatching). 
         FIG. 8  shows a state where a bonding pad is cracked. 
         FIG. 9  is a partially enlarged view in which a portion of  FIG. 3  is enlarged. 
         FIG. 10  is a partially enlarged view in which a portion of  FIG. 1  is enlarged. 
         FIG. 11  is a partial cross-sectional view showing a step of a method for manufacturing the electronic device shown in  FIG. 1 . 
         FIG. 12  shows a step following  FIG. 11 . 
         FIG. 13  is a diagram looking at a capillary of  FIG. 12  from below. 
         FIG. 14  shows a step following  FIG. 12 . 
         FIG. 15  shows a step following  FIG. 14 . 
         FIG. 16  shows a step following  FIG. 15 . 
         FIG. 17  shows a step following  FIG. 16 . 
         FIG. 18  shows a step following  FIG. 17 . 
         FIG. 19  shows a step following  FIG. 18 . 
         FIG. 20  is a table showing test results of whether a wire is appropriately bonded to a bonding pad. 
         FIG. 21  is a partially enlarged cross-sectional view of an electronic device according to a first modification of the first embodiment of the present invention. 
         FIG. 22  is a cross-sectional view of an electronic device according to a second embodiment of the present invention. 
         FIG. 23  is a cross-sectional view of an electronic device according to a third embodiment of the present invention. 
         FIG. 24  is a partially enlarged view in which a portion of  FIG. 23  is enlarged. 
         FIG. 25  is a cross-sectional view of an electronic device according to a fourth embodiment of the present invention. 
         FIG. 26  is a partially enlarged view in which a portion of  FIG. 25  is enlarged. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. 
     &lt;First Embodiment&gt; 
     A first embodiment of the present invention will be described using  FIGS. 1 to 20 . 
       FIG. 1  is a cross-sectional view of an electronic device according to the first embodiment of the present invention. 
     An electronic device A 10  shown in  FIG. 1  is provided with an electronic element  1 , wires  3 , a main electrode  51 , sub-electrodes  52 , and a sealing resin  7 . 
       FIG. 2  is a plan view of the electronic device shown in  FIG. 1  (sealing resin indicated with imaginary line).  FIG. 3  is a partially enlarged view in which a portion of  FIG. 1  is enlarged  1 .  FIG. 4  is a partially enlarged view in which a portion of  FIG. 3  is enlarged.  FIG. 5  is a cross-sectional view along a line V-V in  FIG. 3 .  FIG. 6  is a cross-sectional view along a line VI-VI in  FIG. 3 . 
     The electronic element  1  is an element that achieves a desired function. In the present embodiment, the electronic element  1  consists of a semiconductor. As shown in  FIG. 4 , the electronic element  1  includes a semiconductor substrate  11 , a first conductive layer  13 , a second conductive layer  14 , a third conductive layer  15 , a fourth conductive layer  16 , first vias  171 , second vias  172 , third vias  173 , fourth vias  174 , connecting parts  177 , an insulating layer  18 , and a protective layer  19 . 
     The semiconductor substrate  11  shown in  FIG. 4  and the like is made of a semiconductor material. In the present embodiment, the semiconductor substrate  11  is made of Si. The semiconductor substrate  11  has a semiconductor element. Examples of such a semiconductor element include a diode, a transistor, and a capacitor. 
     The first conductive layer  13  shown in  FIG. 4  and the like is made of a conductive material. The first conductive layer  13  is made of at least one of Al and Cu, for example. In the present embodiment, the first conductive layer  13  is made of Al. The first conductive layer  13  has different thicknesses. The first conductive layer  13  has a maximum thickness (excluding an extended part  131 E discussed later) of 1.0 to 3.0 μm, for example. 
     The first conductive layer  13  has bonding pads  131  and an interconnect metal  133 . The bonding pads  131  and the interconnect metal  133  are disposed in the same plane as each other. 
     As shown in  FIG. 2 , in the present embodiment, the bonding pads  131  have a rectangular shape. The wires  3  are bonded to the bonding pads  131 . The bonding pads  131  overlap with the semiconductor substrate  11  as seen in a thickness direction Z of the bonding pad  131 . 
     As shown in  FIG. 7 , the bonding pads  131  have a joining area  131 R joined to the wire  3 . The bonding pads  131  have a pad front surface  131 A and a pad back surface  131 B that face opposite sides to each other. The wire  3  is bonded to the pad front surface  131 A. The pad front surface  131 A constitutes the joining area  131 R. The bonding pads  131  include an extended part  131 E that extends out from the pad front surface  131 A. The extended part  131 E extends out from the pad front surface  131 A along a bonding portion  31 . The extended part  131 E is formed as a result of a portion of the bonding pad  131  being pushed up by the wire  3 , when the wire  3  is bonded to the bonding pad  131 . 
     A crack  139  may be formed in the bonding pads  131  as shown in  FIG. 8 . The crack  139  is covered by the wire  3 . The crack  139  often forms an arc-like shape. Note that the crack  139  need not be formed in the bonding pads  131 . 
     The interconnect metal  133  shown in  FIG. 4  is connected to the bonding pads  131 . In the present embodiment, the interconnect metal  133  has a long rectangular shape, and has regions disposed at both ends of the bonding pads  131 . 
     Assuming that the abovementioned bonding pads  131  are first bonding pads  131 α (see  FIG. 2 ), the first conductive layer  13  has second bonding pads  131 β (see  FIG. 2 ). The second bonding pads  131 β are disposed in different positions from the first bonding pads  131 α as seen in the thickness direction Z. The second bonding pads  131 β are insulated from the first bonding pads  131 α. 
     The second conductive layer  14  shown in  FIG. 4  and the like is located between the first conductive layer  13  and the third conductive layer  15  in the thickness direction Z. The second conductive layer  14  is made of a conductive material. The second conductive layer  14  is made of at least one of Al and Cu, for example. In the present embodiment, the second conductive layer  14  is made of Al. The first conductive layer  13  has a greater maximum thickness (excluding the extended part  131 E) than the second conductive layer  14 . The second conductive layer  14  has a maximum thickness of 0.1 to 0.5 μm, for example. The first conductive layer  13  is separated from the second conductive layer  14  by a distance of 0.1 to 0.5 μm, for example. 
     The second conductive layer  14  shown in  FIG. 4  has a buffer part  141  and an interconnect portion  143  that are disposed in the same plane as each other. 
     The buffer part  141  shown in  FIGS. 4 to 6  and the like has a region that overlaps with the bonding portion  31  as seen in the thickness direction Z. A peripheral edge  141 C of the buffer part  141  has a shape that surrounds the joining area  131 R as seen in the thickness direction Z. The buffer part  141  overlaps with an entirety of the joining area  131 R as seen in the thickness direction Z. In the present embodiment, the buffer part  141  has a rectangular shape. The buffer part  141  is a floating electrode. That is, the buffer part  141  is insulated from all conductors apart from the buffer part  141 . 
     The buffer part  141  has a buffer part front surface  141 A and a buffer part back surface  141 B that face opposite sides to each other. The buffer part front surface  141 A faces a side on which the bonding pad  131  is located. 
     The interconnect metal  133  overlaps with the interconnect portion  143  shown in  FIG. 4  as seen in the thickness direction Z. The interconnect metal  133  has a region that overlaps with the interconnect portion  143  as seen in the thickness direction Z. The interconnect metal  133  is electrically connected to the interconnect portion  143 . 
     The third conductive layer  15  shown in  FIG. 4  is located between the second conductive layer  14  and the fourth conductive layer  16  in the thickness direction Z. The third conductive layer  15  is made of a conductive material. The third conductive layer  15  is made of at least one of Al and Cu, for example. In the present embodiment, the third conductive layer  15  is made of Al. The third conductive layer  15  has a maximum thickness of 0.1 to 0.5 μm, for example. The third conductive layer  15  is separated from the second conductive layer  14  by a distance of 0.1 to 0.5 μm, for example. 
     The third conductive layer  15  has a first interconnect region  151  and a second interconnect region  153  that are disposed in the same plane as each other. 
     The first interconnect region  151  is separated from the buffer part  141 . The first interconnect region  151  opposes the buffer part back surface  141 B. The first interconnect region  151  is insulated from the bonding pads  131 . The buffer part  141  is located between the first interconnect region  151  and the bonding pads  131  in the thickness direction Z. The first interconnect region  151  is electrically connected to the abovementioned second bonding pads  131 β. 
     The second interconnect region  153  is disposed in the same plane as the first interconnect region  151 . The second interconnect region  153  is electrically connected to the interconnect portion  143 . The second interconnect region  153  has a region that overlaps with the interconnect portion  143  as seen in the thickness direction Z. 
     The fourth conductive layer  16  shown in  FIG. 4  is made of a conductive material. The fourth conductive layer  16  is made of at least one of Al and Cu, for example. In the present embodiment, the fourth conductive layer  16  is made of Al. The fourth conductive layer  16  has a maximum thickness of 0.1 to 0.5 μm, for example. The third conductive layer  15  is separated from the fourth conductive layer  16  by a distance of 0.1 to 0.5 μm, for example. The fourth conductive layer  16  has a region that overlaps with the buffer part  141  as seen in the thickness direction Z. 
     The fourth conductive layer  16  has a first interconnect film  161 , a second interconnect film  163 , and a third interconnect film  165 . The first interconnect film  161 , the second interconnect film  163  and the third interconnect film  165  are disposed in the same plane as each other. 
     The first interconnect film  161  overlaps with the buffer part  141  as seen in the thickness direction Z. The first interconnect film  161  is electrically connected to the first interconnect region  151 . The second interconnect film  163  overlaps with the second interconnect region  153  as seen in the thickness direction Z. The third interconnect film  165  overlaps with the buffer part  141  as seen in the thickness direction Z. 
     The first vias  171  shown in  FIG. 4  extend in the thickness direction Z. The first vias  171  are interposed between the interconnect metal  133  and the interconnect portion  143 . The first vias  171  overlap with the interconnect metal  133  and the interconnect portion  143  as seen in the thickness direction Z. The first vias  171  electrically connect the interconnect metal  133  and the interconnect portion  143  to each other. The first vias  171  are made of a conductive material, such as W (tungsten), for example. 
     The second vias  172  shown in  FIG. 4  extend in the thickness direction Z. The second vias  172  are interposed between the second interconnect region  153  and the interconnect portion  143 . The second vias  172  overlap with the second interconnect region  153  and the interconnect portion  143  as seen in the thickness direction Z. The second vias  172  electrically connect the second interconnect region  153  and the interconnect portion  143  to each other. The second vias  172  are made of a conductive material, such as W (tungsten), for example. 
     The third vias  173  shown in  FIG. 4  extend in the thickness direction Z. The third vias  173  are interposed between the first interconnect film  161  and the first interconnect region  151 . The third vias  173  overlap with the first interconnect film  161  and the first interconnect region  151  as seen in the thickness direction Z. The third vias  173  electrically connect the first interconnect film  161  and the first interconnect region  151  to each other. The third vias  173  are made of a conductive material, such as W (tungsten), for example. 
     The fourth vias  174  shown in  FIG. 4  extend in the thickness direction Z. The fourth vias  174  are interposed between the second interconnect film  163  and the second interconnect region  153 . The fourth vias  174  overlap with the second interconnect film  163  and the second interconnect region  153  as seen in the thickness direction Z. The fourth vias  174  electrically connect the second interconnect film  163  and the second interconnect region  153  to each other. The fourth vias  174  are made of a conductive material, such as W (tungsten), for example. 
     The connecting parts  177  shown in  FIG. 4  are formed on the semiconductor substrate  11 . The bonding pads  131  are electrically connected to the semiconductor element via the connecting parts  177 . The connecting parts  177  are interposed between the semiconductor substrate  11  and the second interconnect film  163 , and contact the semiconductor substrate  11  and the second interconnect film  163 . The connecting parts  177  electrically connect the semiconductor element of the semiconductor substrate  11  to the second interconnect film  163 . 
     The insulating layer  18  shown in  FIG. 4  is formed between the first conductive layer  13  and the semiconductor substrate  11 . The insulating layer  18  has a region that is interposed between the first conductive layer  13  and the second conductive layer  14 , a region that is interposed between the second conductive layer  14  and the third conductive layer  15 , a region that is interposed between the third conductive layer  15  and the fourth conductive layer  16 , and a region that is interposed between the fourth conductive layer  16  and the semiconductor substrate  11 . In particular, the insulating layer  18  fills the entire area sandwiched between the buffer part  141  and the bonding pads  131 . The insulating layer  18  fills the entire area sandwiched between the third conductive layer  15  and the buffer part  141 . The insulating layer  18  covers the buffer part  141  around the entire periphery of the buffer part  141 . The insulating layer  18  entirely covers both the buffer part front surface  141 A and the buffer part back surface  141 B. The insulating layer  18  is made of SiO 2 , for example. 
     The protective layer  19  shown in  FIG. 4  has insulating properties, and covers the first conductive layer  13 . The protective layer  19  exposes the bonding pads  131 . An opening  19 A is formed in the protective layer  19 . The bonding pads  131  are exposed through the opening  19 A. The buffer part  141  has a region that is located inside the opening  19 A and a region that is located outside the opening  19 A as seen in the thickness direction Z. In the present embodiment, an inner edge  19 Aa of the opening  19 A is entirely surrounded by the peripheral edge  141 C of the buffer part  141  as seen in the thickness direction Z. 
     The protective layer  19  has a passivation film  191  and a polyimide layer  193 . 
     The passivation film  191  is made of at least one of SiN and SiO 2 . In the present embodiment, the passivation film  191  has a SiN layer  191 A and a SiO 2  layer  191 B that are laminated one on the other. The polyimide layer  193  covers the passivation film  191 . The passivation film  191  is interposed between the polyimide layer  193  and the first conductive layer  13 . 
     The wires  3  are bonded to the electronic element  1 . The wires  3  are bonded to the sub-electrodes  52 . The wires  3  are made of Cu, Au or Ag, for example. In the present embodiment, the wires  3  are made of Cu. 
     As shown in  FIG. 1 , the wires  3  include the bonding portion  31 , a bonding region  33 , and a bridging part  35 . 
     The bonding portions  31  are bonded to the electronic element  1 . Specifically, the bonding portions are electrically connected to the first conductive layer  13  (bonding pads  131 ) of the electronic element  1 . When manufacturing the electronic device A 10 , the bonding portions  31  are bonded before the bonding regions  33 . That is, the bonding portions  31  are first bonding parts. 
     As shown in  FIG. 9 , an outer surface of the bonding portions  31  has a bottom surface  311 , a lateral surface  312 , a pressed surface  314 , and a peripheral surface  316 . 
     The bottom surface  311  contacts the bonding pad  131 . The bottom surface  311  has a circular shape and faces in the thickness direction Z toward the bonding pad  131  from the bonding portion  31 . 
     The lateral surface  312  connects the pressed surface  314  and the bottom surface  311 . The lateral surface  312  has an annular shape. A cross-section of the lateral surface  312  in a plane orthogonal to the thickness direction Z has a circular shape whose diameter is defined as a ball diameter L 1  (see  FIG. 9 ). 
     The lateral surface  312  has a first curved surface part  312 A and a second curved surface part  312 B. 
     The first curved surface part  312 A has a curved shape that, starting from a boundary  313 A between the bottom surface  311  and the lateral surface  312 , curves toward the pressed surface  314  side as the first curved surface part  312 A extends outward as seen in the thickness direction Z. The first curved surface part  312 A at least partially contacts the bonding pad  131 . The first curved surface part  312 A partially contacts the sealing resin  7 . 
     The second curved surface part  312 B has a curved shape that, starting from a boundary  313 B between the pressed surface  314  and the lateral surface  312 , curves toward the bottom surface  311  side as the second curved surface part  312 B extends outward as seen in the thickness direction Z. The second curved surface part  312 B contacts the sealing resin  7 . 
     The pressed surface  314  is located further inward than the lateral surface  312  as seen in the thickness direction Z of the bonding pad  131 . The pressed surface  314  is formed by being pressed by a pressing part  82  of a capillary  8  which will be discussed later. 
     The pressed surface  314  has a first portion  314 A, a second portion  314 B, and a bent part  314 C. 
     The first portion  314 A has an annular shape. The first portion  314 A is connected to the lateral surface  312 . The first portion  314 A is flat. The first portion  314 A is located between the lateral surface  312  and the bent part  314 C as seen in the thickness direction Z. 
     The second portion  314 B has an annular shape. The second portion  314 B is connected to the first portion  314 A via the bent part  314 C. The second portion  314 B is flat. The second portion  314 B slopes relative to the first portion  314 A, and forms an angle of 180 degrees or less with the first portion  314 A. The second portion  314 B slopes relative to the thickness direction Z so as to extend outward as seen in the thickness direction Z as the second portion  314 B approaches the bottom surface  311  in the thickness direction Z. The second portion  314 B is located further inward than the bent part  314 C as seen in the thickness direction Z. The second portion  314 B entirely overlaps with the bottom surface  311  as seen in the thickness direction Z. 
     The bent part  314 C has a ring shape, and is located between the first portion  314 A and the second portion  314 B. The boundary  313 A is located further outward than the bent part  314 C as seen in the thickness direction Z. 
     The peripheral surface  316  is connected to the pressed surface  314 , and stands up from the pressed surface  314 . The peripheral surface  316  is located further inward than the pressed surface  314  as seen in the thickness direction Z. The peripheral surface  316  stands up from the second portion  314 B. The second portion  314 B slopes relative to the peripheral surface  316 . The peripheral surface  316  has a circular shape in cross-section. The peripheral surface  316  extends in the thickness direction Z. 
     The bonding regions  33  are bonded to the sub-electrodes  52 . When manufacturing the electronic device A 10 , the bonding regions  33  are bonded after the bonding portions  31 . That is, the bonding regions  33  are second bonding parts. The bonding regions  33  have a joining area with the sub-electrodes  52  in one direction. 
     The bridging part  35  is connected to the bonding portion  31  and the bonding region  33 . The bridging part  35  extends linearly, and has a circular shape in cross-section. 
     The sub-electrodes  52  shown in  FIG. 10  and the like are made of a conductive material. The sub-electrodes  52  originate from a lead frame. The sub-electrodes  52  have a Cu part  521  and an Ag layer  522 . 
     The Cu part  521  is made of Cu. The Ag layer  522  is formed on the Cu part  521 . The Cu part  521  is thicker than the Ag layer  522 . The Ag layer  522  is made of Ag. The wire  3  is bonded to the Ag layer  522 . The Ag layer  522  has a thickness of 5 to 15 μm, for example. 
     The main electrode  51  is made of a conductive material. The main electrode  51  originates from a lead frame. The main electrode  51  has a Cu part and an Ag layer, similarly to the sub-electrodes  52 , and description thereof will be omitted because of the similarly to the sub-electrodes  52 . The electronic element  1  is disposed on the main electrode  51  via an adhesive layer. 
     The sealing resin  7  seals the electronic element  1  and the wires  3 . Specifically, the sealing resin  7  covers the electronic element  1 , the wires  3 , the main electrode  51 , and the sub-electrodes  52 . The sealing resin  7  partially covers the lateral surface  312 . The sealing resin  7  is made of an epoxy resin, for example. An end face of the sub-electrodes  52  is exposed from the sealing resin  7 . This end face is the cut surface formed when the lead frame is cut. 
     Next, a method for manufacturing the electronic device A 10  will be described. 
     First, a lead frame  5  is prepared as shown in  FIG. 11 . The lead frame  5  has regions that will form the main electrode  51  and the sub-electrodes  52 . Also, the lead frame  5  has a Cu part  521 A and an Ag layer  522 A. Because the Cu part  521 A and the Ag layer  522 A are respectively similar to the Cu part  521  and the Ag layer  522 , description thereof will be omitted here. The lead frame  5  is sealed in a sealed housing body so as to not come in contact with the outside air. 
     Next, although not illustrated, the sealed housing body is opened and the lead frame  5  is removed. Once the lead frame  5  has been removed, the electronic element  1  is disposed on the main electrode  51 . In disposing the electronic element  1  on the main electrode  51 , a joining material such as silver paste or solder, for example, is used. Next, oxide and sulfide formed by a cure that is used when disposing the electronic element  1  are eliminated. 
     Next, although not illustrated, the lead frame  5  is housed in a container. Inside the container, the lead frame  5  is held in an environment having a humidity of 40 to 50%, for example. The environment is preferably an atmospheric pressure environment under an air or nitrogen atmosphere at 20 to 30° C. The step of holding the lead frame  5  inside the container is carried out for 1 to 168 hours, for example. 
     Next, the lead frame  5  is removed from the container and the wires  3  are bonded to the electronic element  1  using the capillary  8  shown in  FIGS. 12 and 13  (first bonding step). The capillary  8  has a hole inner surface  81  and the pressing part  82 . 
     The hole inner surface  81  is the inner surface of a through hole that extends in one direction. In the present embodiment, the hole inner surface  81  has a circular shape in cross-section. The pressing part  82  is connected to the hole inner surface  81 . The pressing part  82  is a region for pressing the wires  3  against a joining target when bonding the wires  3 . In the present embodiment, the pressing part  82  has a first pressing area  821  and a second pressing area  822 . The first pressing area  821  is connected to the second pressing area  822  and the hole inner surface  81 , and slopes relative to the second pressing area  822  and the hole inner surface  81 . The first pressing area  821  and the second pressing area  822  both have an annular shape. The boundary between the first pressing area  821  and the second pressing area  822  has a circular shape. 
     In performing the first bonding step, the wire  3  is inserted into the through hole in the capillary  8  as shown in  FIG. 12 , and the wire  3  is passed through to the outside of the through hole. Next, the tip of the wire  3  is melted by means such as directing sparks onto the tip of the wire  3 . A ball  319  is thereby formed. Next, as shown in  FIG. 14 , the capillary  8  is positioned above the electronic element  1  (specifically, above the bonding pad  131  of the first conductive layer  13 ). Next, the ball  319  is adhered to the electronic element  1 , as shown in  FIG. 15 . Vibrations produced by ultrasonic waves are applied to the ball  319 , while pressing the ball  319  against the electronic element  1  using the capillary  8  in this state. The ball  319  is thereby joined to the electronic element  1 . The capillary  8  is then separated from the electronic element  1 , as shown in  FIG. 16 . 
     The abovementioned bonding portion  31  is formed as a result of the ball  319  being pressed by the capillary  8 . The pressed surface  314  of the bonding portion  31  is formed as a result of being pressed by the pressing part  82  of the capillary  8 . Specifically, the second portion  314 B of the pressed surface  314  is formed as a result of being pressed by the first pressing area  821  of the pressing part  82 , and the first portion  314 A of the pressed surface  314  is formed as a result of being pressed by the second pressing area  822  of the pressing part  82 . A diameter L 3  of the boundary between the second pressing area  822  and the first pressing area  821  coincides with a diameter L 3  of the bent part  314 C of the bonding portion  31 . 
     Also, when the ball  319  is pressed by the capillary  8 , the ball  319  partially enters inside the through hole in the capillary  8 . Thus, the peripheral surface  316  having a shape corresponding to the hole inner surface  81  is formed in the bonding portion  31 . Therefore, the inner diameter of the hole inner surface  81  coincides with a diameter L 2  of the peripheral surface  316 . 
     The ball diameter L 1  of the bonding portion  31  can be adjusted by adjusting the strength with which the wire is pressed against the electronic element  1  by the capillary  8  and the size of the ball  319 . 
     In firmly joining the wire  3  to the electronic element  1 , the following relationships preferably exist between the ball diameter L 1  and a diameter L 4  (coincides with a diameter L 4  of the abovementioned bridging part  35 ) of the wire  3 . 
     If the bridging part  35  has a diameter L 4  of less than 22.5 μm, the ball diameter L 1  is preferably from 44 μm or more to 50 μm or less, if the bridging part  35  has a diameter L 4  from 22.5 μm or more to less than 27.5 μm, the ball diameter L 1  is preferably 59 μm or more, if the bridging part  35  has a diameter L 4  from 27.5 μm or more to less than 32.5 μm, the ball diameter L 1  is preferably 63 μm or more, and if the bridging part  35  has a diameter L 4  of 32.5 μm or more, the ball diameter L 1  is preferably 77 μm or more. Note that if the bridging part  35  has a diameter L 4  of 20 μm, the bent part  314 C has a diameter L 3  of 35 μm, for example, if the bridging part  35  has a diameter L 4  of 25 μm, the bent part  314 C has a diameter L 3  of 48 μm, for example, if the bridging part  35  has a diameter L 4  of 30 μm, the bent part  314 C has a diameter L 3  of 50 μm, for example, and if the bridging part  35  has a diameter L 4  of 35 μm, the bent part  314 C has a diameter L 3  of 64 μm, for example. 
     Next, although not illustrated, the capillary  8  is moved while letting out the wire  3  to form a wire loop, and the wire  3  is pressed into the sub-electrode  52  (in the present embodiment, the Ag layer  522 A). 
     Next, the second bonding step is performed. In the second bonding step, when the wire  3  has been pressed into the sub-electrode  52  (in the present embodiment, the Ag layer  522 A), the wire  3  is fixed to the sub-electrode  52  (in the present embodiment, the Ag layer  522 A) by applying a load to the capillary  8  together with applying ultrasonic vibrations. The ultrasonic vibrations are applied in a similar manner to the application of ultrasonic vibrations in the first bonding step. When the wire  3  has been fixed to the sub-electrode  52  (in the present embodiment, the Ag layer  522 A), the capillary  8  is raised with the wire  3  inserted into the capillary  8  in a clamped state, and the wire  3  is cut (not shown). The electronic element  1  and the sub-electrode  52  are thereby electrically coupled by the wire loop formed by the wire  3  (see  FIG. 17 ). A plurality of wires  3  are bonded in this way. 
     Next, when the bonding of the wires  3  has finished, the lead frame  5  to which the electronic elements  1  and the wires  3  are bonded is housed in a container. Inside the container, the lead frame  5  is held in an environment having a humidity of 40 to 50%, for example. The environment is preferably an atmospheric pressure environment under an air or nitrogen atmosphere at  20  to ° C. The step of holding the lead frame  5  inside the container is carried out for 1 to 168 hours, for example. 
     Next, the lead frame  5  is removed from the container, and the sealing resin  7  that covers the wires  3  and the lead frame  5  is formed, as shown in  FIG. 18 , using a desired metal mold. 
     Next, after forming the sealing resin  7 , pieces are formed by cutting the sealing resin  7  and the lead frame  5 , as shown in  FIG. 19 . A plurality of electronic devices A 10  are thereby manufactured. 
     Next, the operation and effects of the present embodiment will be described. 
     In the case where the crack  139  is formed in the bonding pads  131 , the conductive material constituting the bonding pads  131  moves downward. In the present embodiment, the second conductive layer  14  has the buffer part  141 . The buffer part  141  is located between the bonding pads  131  and the first interconnect region  151  in the thickness direction Z. According to such a configuration, even if the crack  139  is formed in the bonding pads  131 , the crack  139  is prevented from expanding by the buffer part  141 . Therefore, even if the crack  139  is formed in the bonding pads  131 , the problem of an electrical connection being established between the bonding pads  131  and the first interconnect region  151  can be avoided. An improvement in the yield of the electronic device A 10  can thereby be achieved. 
     In the first conductive layer  13 , the crack  139  tends to form in the portion that overlaps with the bonding portion  31  as seen in the thickness direction Z. In the present embodiment, the wires  3  include the bonding portion  31  bonded to the electronic element  1 . The buffer part  141  has a region that overlaps with the bonding portion  31  as seen in the thickness direction Z. According to such a configuration, even if the crack  139  forms in the bonding pads  131 , the crack  139  is more reliably prevented from expanding by the buffer part  141 . Therefore, even if the crack  139  forms in the bonding pads  131 , the problem of an electrical connection being established between the bonding pads  131  and the first interconnect region  151  can be more suitably avoided. Further improvement in the yield of the electronic device A 10  can thereby be achieved. 
     In the present embodiment, the insulating layer  18  fills the entire area sandwiched between the buffer part  141  and the bonding pads  131 . According to such a configuration, the crack  139  can be prevented from expanding to the buffer part  141 , between the bonding pads  131  and the buffer part  141 . 
     In the present embodiment, the boundary  313 A is located further outward than the bent part  314 C as seen in the thickness direction Z. According to such a configuration, the area of the bottom surface  311  of the bonding portion  31  can be enlarged. The impulse per unit area applied to the bonding pad  131  from the wire  3  can thereby be reduced at the time that the wire  3  is pressed by the capillary  8 . The wires  3  can thereby be firmly bonded to the bonding pads  131 , while preventing the crack  139  from forming in the bonding pads  131 . 
     Test results as to whether the wire  3  is appropriately bonded to the bonding pad  131  are shown in  FIG. 20 . After bonding the wire  3  to the bonding pad  131 , a pull test that involves pulling the wire  3  from the bonding pad  131  was carried out. The tests were each carried out a plurality of times, and the number of times that the wire  3  detached from the bonding pad  131  before the wire  3  broke between the bonding portion  31  and the bridging part  35  was investigated. For example, 2/12 shows that the wire  3  detached from the bonding pads  131  two out of 12 times. 
     As shown in  FIG. 20 , the wire  3  became detached from the bonding pad  131 , in the case where the wire  3  had a diameter L 4  (coincides with the diameter L 4  of the bridging part  35 ) of 20 μm and the ball diameter L 1  was 39 μm, 41 μm, 43 μm or 51 μm. On the other hand, the wire  3  did not become detached from the bonding pad  131 , in the case where the wire  3  had a diameter L 4  (coincides with the diameter L 4  of the bridging part  35 ) of 20 μm and the ball diameter L 1  was 45 μm or 47 μm. Therefore, in the case where the bridging part  35  has a diameter L 4  of less than 22.5 μm, the ball diameter L 1  is preferably from 44 μm or more to 50 μm or less. 
     As shown in  FIG. 20 , the wire  3  became detached from the bonding pad  131 , in the case where the wire  3  had a diameter L 4  (coincides with the diameter L 4  of the bridging part  35 ) of 25 μm and the ball diameter L 1  was 54 μm, 56 μm or 58 μm. On the other hand, the wire  3  did not become detached from the bonding pad  131 , in the case where the wire  3  had a diameter L 4  (coincides with the diameter L 4  of the bridging part  35 ) of 25 μm and the ball diameter L 1  was 60 μm, 62 μm or 64 μm. Therefore, in the case where the bridging part  35  has a diameter L 4  from 22.5 μm or more to less than 27.5 μm, the ball diameter L 1  is preferably 59 μm or more. 
     As shown in  FIG. 20 , the wire  3  became detached from the bonding pad  131 , in the case where the wire  3  had a diameter L 4  (coincides with the diameter L 4  of the bridging part  35 ) of 30 μm and the ball diameter L 1  was 58 μm or 62 μm. On the other hand, the wire  3  did not become detached from the bonding pad  131 , in the case where the wire  3  had a diameter L 4  (coincides with the diameter L 4  of the bridging part  35 ) of 30 μm and the ball diameter L 1  was 64 μm or more. Therefore, in the case where the bridging part  35  has a diameter L 4  from 27.5 μm or more to less than 32.5 μm, the ball diameter L 1  is preferably 63 μm or more. 
     As shown in  FIG. 20 , the wire  3  became detached from the bonding pad  131 , in the case where the wire  3  had a diameter L 4  (coincides with the diameter L 4  of the bridging part  35 ) of 35 μm and the ball diameter L 1  was 72 μm, 74 μm or 76 μm. On the other hand, the wire  3  did not become detached from the bonding pad  131 , in the case where the wire  3  had a diameter L 4  (coincides with the diameter L 4  of the bridging part  35 ) of 35 μm and the ball diameter L 1  was 78 μm, 80 μm or 82 μm. Therefore, in the case where the bridging part  35  has a diameter L 4  of 32.5 μm or more, the ball diameter L 1  is preferably 77 μm or more. 
     In the present embodiment, the lead frame  5  is held in an environment having a humidity of 40 to 50%, and thereafter the wires  3  are bonded to the Ag layer  522 A. According to such a configuration, the Ag layer  522 A of the lead frame  5  can be prevented from sulfurizing before the wires  3  are bonded to the lead frame  5 . According to such a configuration, the wires  3  and the lead frame  5  (Ag layer  522 A) can be more firmly joined. An improvement in the yield of the electronic device A 10  can thereby be achieved. 
     In the present embodiment, the lead frame  5  is held in an environment having a humidity of 40 to 50%, between the step of bonding the wires  3  to the Ag layer  522 A and the step of forming the sealing resin  7  that covers the wires  3  and the lead frame  5 . According to such a configuration, the Ag layer  522 A of the lead frame  5  can be prevented from sulfurizing before the sealing resin  7  is formed. According to such a configuration, the sealing resin  7  can be prevented from exfoliating from the sub-electrode  52 . 
     Note that, unlike the abovementioned electronic device A 10 , the electronic element  1  may include support vias  170  that extend in the thickness direction Z, as shown in  FIG. 21 . The support vias  170  are interposed between the bonding pads  131  and the buffer part  141 , and electrically connect the bonding pads  131  and the buffer part  141  to each other. According to such a configuration, the support vias  170  supports the bonding pads  131 , enabling the crack  139  in the bonding pads  131  to be prevented from occurring. 
     &lt;Second Embodiment&gt; 
     A second embodiment of the present invention will be described using  FIG. 22 . 
     Note that, in the following description, the same reference signs are given to configuration that is the same as or similar to the above, and description will be appropriately omitted. 
     An electronic device A 11  of the present embodiment differs from the abovementioned electronic device A 10  in that the peripheral surface  316  has a comparatively small diameter L 2 . In the present embodiment, the difference between the diameter L 4  (coincides with the diameter L 4  of the bridging part  35 ) of the wire  3  and the diameter L 2  of the peripheral surface  316  is 2 to 8 μm, for example. It becomes difficult to smoothly insert the wire  3  inside the through hole of the capillary  8  when the difference between the diameter L 4  (coincides with the diameter L 4  of the bridging part  35 ) of the wire  3  and the diameter L 2  of the peripheral surface  316  is 2 μm or less. More preferably, the difference between the diameter L 4  (coincides with the diameter L 4  of the bridging part  35 ) of the wire  3  and the diameter L 2  of the peripheral surface  316  is 4 to 8 μm, for example. Even more preferably, the difference between the diameter L 4  (coincides with the diameter L 4  of the bridging part  35 ) of the wire  3  and the diameter L 2  of the peripheral surface  316  is 5 to 7 μm, for example. 
     In the present embodiment, in the case where the bridging part  35  has a diameter L 4  from 27.5 μm or more to less than 32.5 μm, for example, the bent part  314 C has a diameter L 3  of 46 to 54 μm, for example. The diameter L 4  of the bridging part  35  and the diameter L 3  of the bent part  314 C are not limited thereto, and may take values mentioned in relation to the electronic device A 10 . 
     Next, the operation and effects of the present embodiment will be described. 
     In the present embodiment, the difference between the diameter L 4  of the bridging part  35  and the diameter L 2  of the peripheral surface  316  is 2 to 8 μm. This is due to the hole inner surface  81  having a small diameter. In the case where the hole inner surface  81  has a small diameter, the area of the pressing part  82  of the capillary  8  as seen from the bottom surface can be enlarged. A larger area of the ball  319  as seen in the thickness direction Z can thereby be pressed by the pressing part  82 . As a result, the area of the bottom surface  311  that effectively applies force to the bonding pad  131  can be enlarged. Therefore, the wires  3  can be firmly bonded to the bonding pads  131 , while preventing the crack  139  from forming in the bonding pads  131 . Accordingly, an improvement in the yield of the electronic device A 11  can be achieved. 
     &lt;Third Embodiment&gt; 
     A third embodiment of the present invention will be described using  FIGS. 23 and 24 . 
     An electronic device A 12  of the present embodiment differs from the abovementioned electronic device A 10  in that a mixed metal  39  is mixed in the wires  3 . A main component of the wires  3  is Cu or Ag, and, in the present embodiment, the main component of the wires  3  is Cu. The mixed metal  39  is one of Pt, Pd and Au. A concentration of the mixed metal  39  in the wires  3  is 0.5 to 5 wt %, for example. 
     In the present embodiment, the bonding pads  131  include a metal thin film layer  131 M. The metal thin film layer  131 M is made of CuAl 2 , for example. The metal thin film layer  131 M contacts the wire  3 . The metal thin film layer  131 M has a thickness of 5 to 20 nm, for example. 
     Note that the features of the electronic device A 12  may be combined with the electronic device A 11 . 
     Next, the operation and effects of the present embodiment will be described. 
     in the present embodiment, the mixed metal  39  is mixed in the wires  3 . The mixed metal  39  is one of Pt, Pd and Au. According to such a configuration, the formation of a Cu 9 Al 4  layer that contacts the bonding portion  31  on the bonding pads  131  can be suppressed. A Cu 9 Al 4  layer tends to react with the chlorine (Cl) in the sealing resin  7  and chemically change to alumina (Al 2 O 3 ). Since alumina is an insulator, an electrical connection between the bonding portions  31  and the bonding pads  131  will be difficult to establish if alumina is formed. Furthermore, alumina cracks easily, and there is also the possibility of the wires  3  detaching from the bonding pads  131 . Therefore, according to the present embodiment which can suppress the formation of a Cu 9 Al 4  layer on the bonding pads  131 , the above problems caused by the formation of alumina can be avoided. 
     Furthermore, the operation and effects mentioned in relation to the electronic device A 10  are attained by the electronic device A 12 . 
     &lt;Fourth Embodiment&gt; 
     A fourth embodiment of the present invention will be described using  FIGS. 25 and 26 . 
     An electronic device A 13  of the present embodiment differs from the electronic device A 10  in that the bonding pads  131  include a Pd layer  21 . The Pd layer  21  directly contacts the wire  3 , and, specifically, the wire  3  directly contacts a surface  211  of the Pd layer  21 . In the present embodiment, an alloy of the material constituting the Pd layer  21  and the material constituting the wire  3  is not formed between the Pd layer  21  and the wire  3 . The Pd layer  21  has a thickness of 0.1 to 1 μm, for example. 
     In the present embodiment, the bonding pads  131  include an Ni layer  22  and a Cu layer  23 . 
     The Pd layer  21  is located between the Ni layer  22  and the wire  3 . The Ni layer  22  has a thickness of 1 to 5 μm, for example. The Ni layer  22  is located between the Cu layer  23  and the Pd layer  21 . The Cu layer  23  has a thickness of 2 to 12 μm, for example. 
     In the present embodiment, the Pd layer  21 , the Ni layer  22 , and the Cu layer  23  are formed on the Al layer  29  (a similar configuration to the bonding pads  131  of the electronic device A 10 ). 
     The surface  211  of the Pd layer  21  is preferably smooth. The smoothness of the surface  211  of the Pd layer  21  depends on the smoothness of a surface  221  of the Ni layer  22 . Thus, the surface  221  of the Ni layer  22  is preferably smooth. The smoothness of the surface  221  of the Ni layer  22  is dependent on the smoothness of a surface  231  of the Cu layer  23 . Therefore, the surface  231  of the Cu layer  23  is preferably smooth. 
     Preferably, a maximum height difference L 5  of the surface  211  of the Pd layer  21 , a maximum height difference L 6  of the surface  221  of the Ni layer  22 , and a maximum height difference L 7  of the surface  231  of the Cu layer  23  are 40 nm or less. More preferably, the maximum height difference L 5  of the surface  211  of the Pd layer  21 , the maximum height difference L 6  of the surface  221  of the Ni layer  22 , and the maximum height difference L 7  of the surface  231  of the Cu layer  23  are 30 nm or less more. Even more preferably, the maximum height difference L 5  of the surface  211  of the Pd layer  21 , the maximum height difference L 6  of the surface  221  of the Ni layer  22 , and the maximum height difference L 7  of the surface  231  of the Cu layer  23  are 20 nm or less, and more preferably, the maximum height difference L 5  of the surface  211  of the Pd layer  21 , the maximum height difference L 6  of the surface  221  of the Ni layer  22 , and the maximum height difference L 7  of the surface  231  of the Cu layer  23  are 10 nm or less. The maximum height differences L 5 , L 6  and L 7  are the values measured on a line having a length of 80 μm, for example. 
     Unlike the present embodiment, the bonding pads  131  need not include the Cu layer  23 . Also, the configuration of the present embodiment may be combined with the configuration of the electronic device A 11  or the electronic device A 12 . Note that the maximum height differences L 5 , L 6  and L 7  may also be called surface morphologies. 
     The following results were obtained through tests conducted into the relationship between the maximum height difference L 5  of the Pd layer  21  and the viability of the join of the wire  3  to the Pd layer  21 . In the case where the maximum height difference L 5  was 10 nm or less, the wire  3  joined to the Pd layer  21  thirteen out of 13 times. On the other hand, in the case where the maximum height difference L 5  was any of 51 nm, 55 nm, 64 nm or 68 nm, it was not possible to join the wire  3  to the Pd layer  21 , and the wire  3  immediately detached from the Pd layer  21  despite having been pressed against the Pd layer  21  by the capillary  8 . Therefore, in joining the wire  3  to the Pd layer  21 , a maximum height difference L 5  of 40 nm or less is considered preferable, and a maximum height difference L 5  of 30 nm or less is considered more preferable, a maximum height difference L 5  of 20 nm or less is considered even more preferable, and a maximum height difference L 5  of 10 nm or less is considered still more preferable. 
     The present invention is not limited to the abovementioned embodiments. Various design modifications can be made to the specific configurations of the respective parts of the present invention.