Abstract:
A semiconductor device including a die pad having a front surface made of Cu; a semiconductor chip disposed so as to be opposed to the front surface of the die pad; a bonding layer provided between the die pad and the semiconductor chip; and a plurality of leads disposed around the die pad, wherein the die pad and the plurality of leads make up a lead frame in cooperation with each other, a cavity is fabricated on the surface of the plurality of leads, and a projecting portion is fabricated next to the cavity.

Description:
TECHNICAL FIELD 
     The present invention relates to a semiconductor device and a method for manufacturing the same. 
     BACKGROUND ART 
     Conventionally, a reduction in the amount of lead to be used in semiconductor devices has been demanded from the viewpoint of environmental load. 
     In the semiconductor device, for example, lead has been used for outside components to be used outside the device, such as an exterior plating of an outer lead in an SOP (Small Outline Package) or a QFP (Quad Flat Package) and a solder ball in a BGA (Ball Grid Array). Lead has also been used for an inside component to be used inside the device such as a bonding material between a semiconductor chip and lead frame in the inside of the package. 
     Lead-freeing to make the content of lead to a fixed ratio or less has almost been achieved for the outer components through research of substitute materials. On the other hand, there is no material suitable as a substitute for the inside components. Therefore, for example, Pb-xSn-yAg (x and y are positive numbers), a lead-containing metal has been used. 
     PRIOR ART 
     Patent Document 
     Patent Document 1: Japanese Published Unexamined Patent Application No. 2007-67158 
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     Bi easily reacts with metallic elements such as Au, Ag, and Ni normally contained in a metal layer formed at a bonding part to the bonding material in the semiconductor chip and lead frame. Bi forms compounds with the metallic elements or forms a eutectic composition. 
     Therefore, if the metallic elements such as Au, Ag, and Ni are exposed on an outermost surface of the metal layer, when Bi is used as the bonding material, an alloy layer (intermetallic compound) of Bi and the metallic elements is sometimes formed in the vicinity of an interface with the metal layer in the bonding material as a result of Bi contacting the metallic elements. Moreover, the bonding material as a whole is sometimes formed into a eutectic composition of Bi and the metallic elements. 
     The intermetallic compound of Bi and the metallic elements is hard and fragile and may thus serve as a starting point of fracture in a temperature cycle test (TCY test) of the semiconductor device. 
     Moreover, the melting point of a eutectic composition of Bi and the metallic elements is lower than that of Bi alone. For example, the melting point of Bi alone is approximately 271° C., while the melting point of a eutectic composition of Bi and Au is approximately 241° C., and the melting point of a eutectic composition of Bi and Ag is approximately 262° C. The bonding material may melt again in reflow (having a peak temperature of approximately 260° C.) for mounting the semiconductor device. 
     It is an object of the present invention to provide a semiconductor device for which lead-freeing can be achieved by using a Bi-based material for a bonding layer between a semiconductor chip and lead frame, and further, the melting point of the bonding layer can be maintained high while the temperature cycle resistance of the bonding layer can be improved and a method for manufacturing the same. 
     Means for Solving the Problems 
     A semiconductor device of the present invention to achieve the above-described object includes a die pad having a front surface made of Cu, a semiconductor chip disposed so as to be opposed to the front surface of the die pad, the semiconductor chip having a Cu layer forming a back surface thereof, and a bonding layer provided between the die pad and the semiconductor chip, and the bonding layer includes a Bi-based material layer and Cu alloy layers not containing Pb that sandwich the Bi-based material layer from both sides in an opposing direction of the die pad and the semiconductor chip with respect to the Bi-based material layer. 
     According to this configuration, since the bonding layer that bonds the die pad and the semiconductor chip is made of a Cu alloy not containing Pb and a Bi-based material, lead-freeing of the bonding layer can be achieved. 
     Moreover, the Bi-based material layer in the bonding layer is in contact with Cu alloy layers not containing Pb as a result of being sandwiched by the alloy layers from both sides in the opposing direction of the die pad and the semiconductor chip. 
     The Bi-based material layer is in contact with the Cu alloy layers, but since Cu hardly reacts with Bi, there is little possibility of the melting point of the bonding layer lowering or the temperature cycle resistance decreasing due to contact between these layers. 
     Moreover, even when there is formed a metal layer containing inhibitory metallic elements, such as Au, Ag, and Ni, that may degrade the characteristics of the Bi-basedmaterial layer in the die pad or semiconductor chip, contact of the Bi-based material layer with the metal layer can be prevented by the Cu alloy layers. As a result, the formation of intermetallic compounds of Bi and the inhibitory metallic elements and the formation of eutectic compositions of Bi and the inhibitory metallic elements can be prevented. Consequently, not only can the temperature cycle resistance of the bonding layer be improved, but the melting point of the bonding layer can also be maintained high. 
     The semiconductor device described above can be manufactured, for example, by a method for manufacturing a semiconductor device of the present invention. That is, the semiconductor device described above can be manufactured by a method for manufacturing a semiconductor device including a step of preparing a semiconductor chip having a back surface made of a Cu layer, a step of bonding the semiconductor chip to a die pad having a front surface made of Cu via a bonding material containing a dissimilar metal not containing Cu and Pb and a Bi-based material so that the Cu layer and the bonding material come into contact with each other, and a step of heat-treating the die pad after bonding the semiconductor chip. 
     According to this method, the semiconductor chip is bonded to the die pad so that the Cu layer of the semiconductor chip and the bonding material come into contact with each other, and thereafter, the die pad is heat-treated. Accordingly, each of the Cu layers of the semiconductor chip and Cu forming the front surface of the die pad and the dissimilar metal (metal not including Cu and Pb) in the bonding material react with each other to form Cu alloy layers in the vicinities of the Cu layer and the front surface of the die pad. On the other hand, the component other than the dissimilar metal in the bonding material hardly reacts with Cu, and thus remains, between the alloy layers, as a Bi-based material layer sandwiched by these layers. 
     In formation of the bonding layer, the components (Bi-based material and dissimilar metal) in the bonding material do not contact metallic elements other than Cu, and further, the alloy layers are formed on both sides of the Bi-basedmaterial layer in the opposing direction of the die pad and the semiconductor chip. Therefore, even when there is formed a metal layer containing inhibitory metallic elements, such as Au, Ag, and Ni in the die pad or semiconductor chip, contact of the Bi-based material layer with the inhibitory metallic elements can be prevented. 
     Further, when Sn is contained as the dissimilar metal in the bonding material, at least one of the Cu alloy layers can be formed as a Cu—Sn alloy layer. Moreover, when Zn is contained as the dissimilar metal in the bonding material, at least one of the Cu alloy layers can be formed as a Cu—Zn alloy layer. 
     Neither of the Cu—Sn alloy and Cu—Zn alloy is a hard and fragile metal like a Bi—Au alloy, a Bi—Ag alloy, or the like, but both are high-strength metals. Therefore, the bonding strength of the semiconductor chip and die pad and the bonding layer can be improved by these alloy layers. 
     Moreover, when the semiconductor chip includes a Si substrate on a back surface side of which the Cu layer is formed, it is preferable that a metal layer capable of making ohmic contact with a Si semiconductor is formed between the Si substrate and the Cu layer. Accordingly, the Cu layer and the Si substrate can be made conductive with each other via the metal layer. As a result, the Si substrate and the die pad can be electrically connected with each other. 
     Further, a semiconductor device in such a mode can be manufactured, for example, in the step of preparing a semiconductor chip of the method for manufacturing a semiconductor device of the present invention described above, by carrying out a step of forming a metal layer capable of making ohmic contact with a Si semiconductor at a back surface of the Si substrate and a step of forming the Cu layer on the metal layer. 
     Moreover, in the semiconductor device of the present invention, the die pad in cooperation with leads disposed therearound may make up a lead frame. That is, the die pad may be a part of the lead frame. 
     Moreover, when the semiconductor device of the present invention is a resin-encapsulated semiconductor device having a resin package, it is preferable that a back surface of the lead frame is provided as an exposed surface exposed from the resin package, a front surface of the lead frame is encapsulated by the resin package, and the die pad and/or the lead of the lead frame includes a deformed portion formed as a result of the encapsulated surface being deformed by a peripheral edge portion of the encapsulated surface being pressed from the encapsulated surface side and a projecting portion formed lateral to the deformed portion, projecting from a side surface of the die pad and/or the lead of the lead frame inside the resin package. 
     According to this configuration, to the inside of the resin package that encapsulates the side surface of the lead frame, a projecting portion projects from the side surface of the lead frame, and the projecting portion bites into the resin package. Therefore, when a force toward the lower surface side of the package (exposed surface side of the lead frame) is applied to the lead frame in an opposing direction of the encapsulated surface (front surface of the lead frame) and exposed surface (back surface of the lead frame), the projecting portion biting into the resin package is caught therein. As a result, the lead frame can be prevented from coming off. 
     Moreover, the encapsulated surface of the lead frame is not the same plane in its entire region, but has a deformed portion in its peripheral edge portion. Therefore, depending on the shape of the deformed portion, when a force is applied to the lead frame in a horizontal direction perpendicular to the opposing direction of the encapsulated surface and exposed surface, the peripheral edge portion of the encapsulated surface serves as resistance against the horizontal force. As a result, horizontal shifting of the lead frame can be suppressed as compared with when the entire region of the encapsulated surface of the lead frame is the same plane. 
     That is, this configuration can provide a semiconductor device capable of suppressing horizontal shifting of the lead frame while preventing the lead frame from coming off the resin package. 
     The deformed portion may be a recess formed as a result of the encapsulated surface being recessed in a thickness direction of the lead frame. In this case, since the recess is formed in the encapsulated surface, the resin package is fitted in part with the recess as a result of the resin package entering inside the recess. Therefore, when the horizontal force is applied to the lead frame, the recess is caught on the resin package inside the recess. As a result, horizontal shifting of the lead frame can be prevented. 
     Moreover, it is preferable that a peripheral portion of the recess in the encapsulated surface is raised. In this case, as a result of the peripheral portion of the recess rising, the encapsulated surface is bulging in part in the opposing direction. Therefore, when the horizontal force is applied to the lead frame, the bulging part serves as resistance to horizontal shifting. As a result, horizontal shifting of the lead frame can be prevented more reliably. 
     Moreover, it is preferable that a protrusion is formed inside the recess. In this case, since the protrusion is formed inside the recess, the protrusion projects to the inside of the resin package within the recess. The protrusion allows, inside the recess, the lead frame to bite into the resin package. Therefore, a complicated fitting structure between the recess and resin package can be provided. As a result, the fitting strength of the resin package with respect to the recess can be improved. 
     Moreover, the lead frame may be made of Cu. In that case, the front surface of the lead frame may be an uncoated surface that is not coated with a metal layer through a process such as plating or sputtering. That is, Cu that forms the lead frame may be exposed on the whole of the front surface of the lead frame. Accordingly, it is unnecessary, in manufacturing of the semiconductor device, to apply a process such as plating or sputtering to the lead frame, so that the cost can be reduced. 
     Moreover, in the lead frame made of Cu, the die pad on which the semiconductor chip is mounted may have a stacked structure including a metal layer not containing Cu and a frame-side Cu layer that are stacked in order toward the front surface side of the die pad. 
     Examples of the metal layer include an Ag layer, an Au layer, and a Ni layer. In that case, in a plurality of leads disposed around the die pad, it is preferable that the metal layer is exposed on an outermost surface of the lead. By appropriately selecting the type of the metal layer, various wires such as an Au wire and a Cu wire can be used as a bonding wire to be connected to the lead. 
     Moreover, in the method for manufacturing a semiconductor device of the present invention, the step of bonding the semiconductor chip may include a step of bonding the semiconductor chip to the die pad of a lead frame including the die pad and a plurality of leads disposed around the die pad. 
     In that case, the method for manufacturing a semiconductor device of the present invention may further include a step of forming a deformed portion and a projecting portion projecting from a side surface of the lead frame, to be carried out prior to the step of bonding the semiconductor chip, by pressing, from a front surface side of the die pad and/or the lead of the lead frame, a peripheral edge portion of the front surface with a capillary of a wire bonder or a stamping tool fitted to the wire bonder in place of the capillary to deform the front surface and a step of, after heat treatment of the lead frame, encapsulating the front surface side of the lead frame by a resin package so that the back surface of the lead frame is exposed. 
     According to this method, the deformed portion and projecting portion are formed by pressing the peripheral edge portion of the front surface of the lead frame with the stamping tool. Therefore, even when the back surface (surface to be exposed from the resin package) of the lead frame is covered and etching from the back surface side is difficult, the projecting portion (retaining structure) to prevent the lead frame from coming off can be reliably formed. Moreover, since the lead frame is pressed by using a capillary of a wire bonder or a stamping tool fitted to the wire bonder in place of the capillary, the lead frame can be simply and accurately deformed focusing on the peripheral edge portion of the lead frame. 
     That is, this configuration can provide a method for manufacturing a semiconductor device capable of simply and accurately forming a retaining structure in the lead frame even when it is difficult to form the retaining structure by etching. 
     Moreover, in the semiconductor device of the present invention, an electrode pad may be formed on a front surface of the semiconductor chip. In this case, the electrode pad may be made of a metallic material containing Al. 
     Moreover, in the semiconductor device of the present invention, the metal layer formed between the Si substrate and the Cu layer may be an Au layer. In that case, it is preferable to further include a Ni layer formed between the Si substrate and the Au layer. Moreover, the Si substrate may have a thickness of 220 μm to 240 μm. 
     Moreover, in the semiconductor device of the present invention, it is preferable that the lead frame is formed by a plating method. In that case, the lead frame may have a thickness of 10 μm to 50 μm. 
     Moreover, in the semiconductor device of the present invention, the die pad may have a quadrilateral shape in a plan view, and the leads may be disposed so as to surround the four sides of the die pad. That is, the semiconductor device of the present invention may be a semiconductor device to which a QFN (Quad Flat Non-leaded) package is applied. 
     In that case, it is preferable that the die pad has a quadrilateral shape larger than the semiconductor chip in a plan view, and the peripheral edge portion of the encapsulated surface of the die pad surrounds the semiconductor chip. 
     Moreover, in the semiconductor device of the present invention, the bonding layer may have a total thickness of 12 μm to 36 μm, the total thickness being a total of a thickness of the Bi-based material layer and thicknesses of the Cu alloy layers. Moreover, the thickness of the Bi-based material layer may have a thickness of 10 μm to 30 μm. Moreover, the Cu alloy layer may have a thickness of 1 μm to 3 μm. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic plan view of a semiconductor device according to a first embodiment of the present invention. 
         FIG. 2  is a schematic sectional view of the semiconductor device according to the first embodiment of the present invention, showing a section taken along a cut line A-A of  FIG. 1 . 
         FIG. 3  is an essential-part enlarged view of a part surrounded by a dashed line circle B of  FIG. 2 . 
         FIG. 4  is an essential-part enlarged view of a part surrounded by a dashed line circle C of  FIG. 2 . 
         FIG. 5  is an essential-part enlarged view of a part surrounded by a dashed line circle D of  FIG. 2 . 
         FIG. 6A  is a schematic sectional view showing a part of a manufacturing process of the semiconductor device shown in  FIG. 1  and  FIG. 2 . 
         FIG. 6B  is a schematic sectional view showing a next step of  FIG. 6A . 
         FIG. 6C  is a schematic sectional view showing a next step of  FIG. 6B . 
         FIG. 6D  is a schematic sectional view showing a next step of  FIG. 6C . 
         FIG. 6E  is a schematic sectional view showing a next step of  FIG. 6D . 
         FIG. 6F  is a schematic sectional view showing a next step of  FIG. 6E . 
         FIG. 6G  is a schematic sectional view showing a next step of  FIG. 6F . 
         FIG. 7  is a view showing a first modification of the lead shown in  FIG. 3 . 
         FIG. 8  is a view showing a second modification of the lead shown in  FIG. 3 . 
         FIG. 9  is a view showing a third modification of the lead shown in  FIG. 3 . 
         FIG. 10  is a view showing a fourth modification of the lead shown in  FIG. 3 . 
         FIG. 11  is a view showing a modification of the layout pattern of pin recesses shown in  FIG. 1 . 
         FIG. 12  is a schematic plan view of a semiconductor device according to a second embodiment of the present invention. 
         FIG. 13  is a schematic sectional view of the semiconductor device according to the second embodiment of the present invention, showing a section taken along a cut line A′-A′ of  FIG. 12 . 
         FIG. 14  is a view showing a modification of the lead frame shown in  FIG. 13 . 
         FIG. 15  is an essential-part enlarged view of a part surrounded by a dashed line circle F of  FIG. 14 . 
         FIG. 16  is an essential-part enlarged view of a part surrounded by a dashed line circle G of  FIG. 14 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
     &lt;First Embodiment&gt; 
       FIG. 1  is a schematic plan view of a semiconductor device according to a first embodiment of the present invention.  FIG. 2  is a schematic sectional view of the semiconductor device according to the first embodiment of the present invention, showing a section taken along a cut line A-A of  FIG. 1 .  FIG. 3  is an essential-part enlarged view of a part surrounded by a dashed line circle B of  FIG. 2 .  FIG. 4  is an essential-part enlarged view of a part surrounded by a dashed line circle C of  FIG. 2 .  FIG. 5  is an essential-part enlarged view of a part surrounded by a dashed line circle D of  FIG. 2 . In addition,  FIG. 1  shows a state where a resin package has been removed. 
     The semiconductor device  1  is a semiconductor device to which a QFN (Quad Flat Non-leaded) package is applied. The semiconductor device  1  includes a semiconductor chip  2  having a front surface  21  and a back surface  22 , a die pad  3  on which the semiconductor chip  2  is mounted, a plurality of electrode leads  4  disposed around the die pad  3 , a bonding wire  5  that electrically connects the semiconductor chip  2  and the electrode lead  4 , and a resin package  6  for encapsulating these elements. 
     The semiconductor chip  2  includes a Si substrate  7  having a quadrilateral shape (for example, a quadrilateral of approximately 2.3 mm×2.3 mm) in a plan view. The thickness of the Si substrate  7  is, for example, 220 μm to 240 μm (preferably, approximately 230 μm). On an upper surface of the Si substrate  7 , a multilayer wiring structure (not shown) formed of a plurality of wiring layers stacked via an interlayer insulating film is formed, and an outermost surface of the multilayer wiring structure is covered with a surface protective film (not shown). 
     In the surface protective film, a plurality of pad openings  8  to expose an uppermost wiring layer in the multilayer wiring structure are formed. The pad openings  8  are quadrilateral in a plan view, and are provided in the same number (in  FIG. 1 , four each) for edges of the semiconductor chip  2 . The pad openings  8  are disposed at equal intervals along the sides of the semiconductor chip  2 . The wiring layer is exposed in part, as electrode pads  9  of the semiconductor chip  2 , from the pad openings  8 . The surface with the pad openings  8  formed forms the front surface  21  of the semiconductor chip  2 . 
     The uppermost wiring layer exposed as the electrode pads  9  is made of, for example, a metallic material containing Al (aluminum), and specifically, made of a metallic material (for example, an Al—Cu alloy) composed mainly of Al. 
     On the other hand, on a lower surface (opposing surface to the die pad  3 ) of the Si substrate  7 , a back metal  10  is formed. The back metal  10  forms the back surface  22  of the semiconductor chip  2 . 
     The back metal  10  has a three-layer structure in which, as shown in  FIG. 3 , in order from the side of the Si substrate  7 , an Au layer  11 , a Ni layer  12 , and a Cu layer  13  are stacked. The Au layer  11  is capable of making ohmic contact with a Si semiconductor, and is in contact with the lower surface of the Si substrate  7 . The Ni layer  12  is formed closer to the Si substrate  7  side than the Cu layer  13  that forms an outermost surface of the back metal  10 , and is a layer to prevent a Si nodule where Si in the Si substrate  7  precipitates on the outermost surface of the back metal  10 . 
     The die pad  3  and the electrode leads  4  are formed as a lead frame  14  made of the same metal thin plate. The lead frame  14  is formed by, for example, a plating method. Examples of a metallic material to be used for plating growth include Cu-based raw materials mainly containing Cu, specifically, high purity copper with a purity of 99.9999% (6N) or more and a purity of 99.99% (4N) or more and an alloy (for example, a Cu—Fe—P alloy) of Cu and a dissimilar metal and Fe-based raw materials such as a 42 alloy (Fe-42% Ni). Moreover, the thickness of the lead frame  14  is, for example, less than 100 μm, and preferably, 10 μm to 50 μm. 
     The die pad  3  has a quadrilateral shape (for example, an approximately 2.7 mm square in a plan view) larger than the semiconductor chip  2  in a plan view, in which a quadrilateral annular peripheral edge portion  33  surrounds the semiconductor chip  2 . 
     A front surface  31  (encapsulating surface to be encapsulated by the resin package  6 ) of the die pad  3  is an uncoated surface that is not coated with a metal thin film through a process such as plating or sputtering, and a Cu-based raw material that forms the lead frame  14  is exposed on the whole of the front surface  31 . 
     In the peripheral edge portion  33  of the die pad  3 , as shown in  FIG. 4 , a plurality of minute pin recesses  34  (deformed portions) are formed for which the front surface  31  of the die pad  3  is recessed in the thickness direction of the lead frame  14 . 
     The pin recesses  34  on the die pad  3  side are provided in the same number (in  FIG. 1 , six each) for straight portions of the peripheral edge portion  33 . The pin recesses  34  are disposed at equal intervals along the sides of the peripheral edge portion  33 . Each pin recess  34  has a tapered, substantially bowl shape in a sectional view whose diameter is reduced in the depth direction, and has, for example, a maximum diameter of 10 μm to 50 μm and a depth of 5 μm to 25 μm. In the front surface  31  of the die pad  3 , a peripheral surface  35  having a circular annular shape in a plan view that surrounds each pin recess  34  is raised with respect to a mounting surface  36  on which the semiconductor chip  2  is mounted in the front surface  31 . The mounting surface  36  is a surface parallel to a back surface  32  (mounting surface onto a wiring board) of the die pad  3 . 
     Moreover, in a side surface  37  of the die pad  3 , retainer portions  38  (projecting portions) that project in a direction perpendicular to the thickness direction of the lead frame  14  are formed at positions opposed to the pin recesses  34  of the peripheral edge portion  33 , respectively. Each retainer portion  38  is formed at an upper side in the thickness direction of the lead frame  14 , and is, in a sectional view, adjacent to each pin recess  34 . 
     The semiconductor chip  2  and the die pad  3  are bonded to each other, with the lower surface (back surface  22  of the semiconductor chip  2 ) of the Si substrate  7  and the front surface  31  (mounting surface  36 ) of the die pad  3  opposed to each other as bonding surfaces, by interposing a bonding layer  15  between the back surface  22  and the front surface  31 . Accordingly, the semiconductor chip  2  in a position where the front surface  21  is facing upward is supported on the die pad  3 . 
     The bonding layer  15 , as shown in  FIG. 3 , includes a Bi-based material layer  16  as a relatively thick main layer and Cu—Sn alloy layers  17 ,  18  as relatively thin sublayers. 
     The Bi-based material layer  16  contains Bi as a main component, and may contain accessory components such as Sn, Zn, and Co of such amounts so as not to have effect on the properties of Bi. 
     The Cu—Sn alloy layers  17 ,  18  are made of an alloy of Cu and Sn that is a dissimilar metal not containing Cu and Pb, and in which Cu is contained as a main component. 
     The Cu—Sn alloy layer  17  on the semiconductor chip  2  side is, in the vicinity of an interface with the Cu layer  13  of the back metal  10  in the bonding layer  15 , formed across its entire region. Accordingly, the Cu—Sn alloy layer  17  is in contact with the Cu layer  13  of the back metal  10 . The Cu—Sn alloy layer  17  has, for example, a stacked structure represented by Cu6Sn5/Cu3Sn, in the opposing direction of the die pad  3  and the semiconductor chip  2 , from the side of the Bi-based material layer  16  toward the semiconductor chip  2  side. 
     The Cu—Sn alloy layer  18  on the die pad  3  side is, in the vicinity of an interface with the front surface  31  of the die pad  3  in the bonding layer  15 , formed across its entire region. Accordingly, the Cu—Sn alloy layer  18  is in contact with the front surface  31  of the die pad  3 . The Cu—Sn alloy layer  18  has, for example, a stacked structure represented by Cu6Sn5/Cu3Sn, in the opposing direction of the die pad  3  and the semiconductor chip  2 , from the side of the Bi-based material layer  16  toward the die pad  3  side. 
     The Cu—Sn alloy layers  17 ,  18  may be partially formed in the vicinity of an interface with the front surface  31  of the die pad  3  in the bonding layer  15  and the vicinity of an interface with the Cu layer  13  of the back metal  10  in the bonding layer  15 , respectively. 
     The Bi-based material layer  16  and the Cu—Sn alloy layers  17 ,  18 , between the front surface  31  of the die pad  3  and the Cu layer  13  of the back metal  10 , form a three-layer structure (Cu—Sn alloy layer  17 /Bi-based material layer  16 /Cu—Sn alloy layer  18 ) in which the Bi-based material layer  16  is sandwiched, from both sides in the opposing direction of the die pad  3  and the semiconductor chip  2 , by the Cu—Sn alloy layers  17 ,  18 . 
     The melting point of the bonding layer  15  as described above is, for example, 260° C. to 265° C., and preferably, 265° C. to 271° C. Moreover, in a state where the semiconductor chip  2  and the die pad  3  are bonded, the total thickness T (total of the thickness of the Bi-based material layer  16  and the thicknesses of the Cu—Sn alloy layers  17 ,  18 ) of the bonding layer  15  is, for example, 12 μm to 36 μm. As the thicknesses of the respective layers, for example, the thickness of the Bi-based material layer  16  is 10 μm to 30 μm, and the thicknesses of the Cu—Sn alloy layers  17 ,  18  are 1 μm to 3 μm. 
     The back surface  32  (mounting surface onto a wiring board) of the die pad  3  is exposed from the resin package  6 . On the exposed back surface  32 , for example, a die pad back surface plating  19  made of a metallic material such as tin (Sn) or a tin-silver alloy (Sn—Ag) is formed. 
     The electrode leads  4  are, as shown in  FIG. 1 , as a result of being disposed at both sides in directions perpendicular to the side surfaces  37  of the die pad  3 , disposed around the die pad  3 . The electrode leads  4  opposed to the side surfaces  37  of the die pad  3  are disposed at equal intervals in directions parallel to their opposing side surfaces  37 . Each electrode lead  4  is formed to have a rectangular shape in a plan view that is longer in a direction perpendicular to the side surface  37  of the die pad  3  (direction opposed to the die pad  3 ), and its length in the opposing direction (length at a back surface  42  side) is, for example, approximately 450 μm. 
     A front surface  41  (connecting surface of the bonding wire  5 ) of the electrode lead  4  is, as shown in  FIG. 5 , an uncoated surface that is not coated with a metal thin film through a process such as plating or sputtering, and a Cu-based raw material that forms the lead frame  14  forms the whole of the front surface  41 . 
     At edge portions  43  on the die pad  3  side in the electrode leads  4 , a plurality of minute pin recesses  44  (deformed portions) are formed, respectively, for each of which the front surface  41  (encapsulating surface to be encapsulated by the resin package  6 ) of the electrode lead  4  is recessed in the thickness direction of the lead frame  14 . 
     The pin recess  44  on the electrode lead  4  side has a substantially bowl shape in a sectional view whose diameter is reduced in the depth direction, and has, for example, a maximum diameter of 10 μm to 50 μm and a depth of 5 μm to 25 μm. In the front surface  41  of the electrode lead  4 , a peripheral surface  45  having a circular annular shape in a plan view that surrounds each pin recess  44  is raised with respect to a connecting surface  46  to which the bonding wire  5  is connected in the front surface  41 . The connecting surface  46  is a surface parallel to the back surface  42  (mounting surface onto a wiring board) of the electrode lead  4 . 
     Moreover, in a side surface  47  of the electrode lead  4 , a retainer portion  48  (projecting portion) that projects in a direction perpendicular to the thickness direction of the lead frame  14  is formed so as to surround the pin recess  44  at the edge portion  43  in a plan view. Each retainer portion  48  is formed at an upper side in the thickness direction of the lead frame  14 , and is adjacent to the pin recess  44  in a sectional view. 
     The back surface  42  (mounting surface onto a wiring board) of the electrode lead  4  is exposed from the resin package  6 . On the exposed back surface  42 , for example, a lead back surface plating  20  made of a metallic material such as tin (Sn) or a tin-silver alloy (Sn—Ag) is formed. 
     The bonding wire  5  is made of, for example, copper (for example, high purity copper with a purity of 99.9999% (6N) or more and a purity of 99.99% (4N) or more, in which a minute amount of impurities is sometimes contained.) The bonding wire  5  connects a single electrode pad  9  and a single electrode lead  4  one to one. 
     The resin package  6  defines an external form of the semiconductor device  1 , and is formed to have a substantially rectangular parallelepiped shape. In terms of the size of the resin package  6 , its planar size is, for example, an approximately 4 mm square, and its thickness is approximately 0.85 mm. The resin package  6  is made of, for example, a publicly known molding resin such as an epoxy resin, and encapsulates the semiconductor chip  2 , the bonding wires  5 , and the lead frame  14  so as to cover the front surfaces  31 ,  41  and side surfaces  37 ,  47  of the lead frame  14  and expose the back surfaces  32 ,  42 . The resin package  6 , in each of the peripheral edge portion  33  of the die pad  3  and the edge portions  43  of the electrode leads  4 , enters in the pin recess  34  or the pin recess  44 . 
       FIG. 6A  to  FIG. 6G  are schematic sectional views showing a manufacturing process in the order of steps of the semiconductor device shown in  FIG. 1  and  FIG. 2 . 
     For manufacturing the semiconductor device  1  described above, for example, as shown in  FIG. 6A , the lead frame  14  is formed by making a material of the lead frame  14  grow by a plating method, on a stainless steel substrate  23 , in a pattern with a plurality of units including the die pads  3  and the electrode leads  4 . In  FIG. 6A  to  FIG. 6G , an overall view of the lead frame  14  is omitted, and only the die pad  3  and electrode leads  4  for a single unit necessary for mounting a single semiconductor chip  2  are shown. 
     Then, as shown in  FIG. 6B , a stamping tool  24  is driven into the edge portion  43  on the die pad  3  side of the electrode lead  4  vertically with respect to the front surface  41 . The stamping tool  24  is fitted, to a wire bonder to be used for wire bonding to be described later, in replacement of its capillary. By driving of the stamping tool  24 , the pin recess  44  on the electrode lead  4  side is formed at the edge portion  43  of the electrode lead  4  as a dent of the stamping tool  24 . Simultaneously with the formation of the pin recess  44 , as a result of the periphery of the pin recess  44  in the electrode lead  4  being pressed and expanded by the stamping tool  24 , the peripheral surface  45  of the electrode lead  4  surrounding the pin recess  44  rises, and the retainer portion  48  projects from the side surface  47  of the electrode lead  4  adjacent to the pin recess  44 . 
     A load to be applied to the electrode lead  4  by the stamping tool  24  varies depending on the depth of the pin recess  44  aimed at, but is, for example, approximately 200 g/mm 2  to 400 g/mm 2 . As the stamping tool  24 , for example, a stamping capillary without a hole through which a wire or the like is inserted (for example, manufactured by TOTO company) can be applied. 
     Thereafter, as shown in  FIG. 6C , as a result of the same step as  FIG. 6B  being performed for the remaining electrode leads  4 , the pin recesses  44  are formed at the edge portions  43  of all electrode leads  4 . 
     Then, as shown in  FIG. 6C , by the same step as  FIG. 6B , the stamping tool  24  is driven in order into the peripheral edge portion  33  of the die pad  3  along its sides. Accordingly, the pin recess  34  on the die pad  3  side is formed, the peripheral surface  35  of the die pad  3  surrounding the pin recess  34  rises, and the retainer portion  38  projects from the side surface  37  of the die pad  3  adjacent to the pin recess  34 . 
     On the other hand, as shown in  FIG. 6D , as a result of the Au layer  11 , the Ni layer  12 , and the Cu layer  13  being stacked in order on the lower surface of the Si substrate  7 , the back metal  10  is formed. Accordingly, the semiconductor chip  2  with the back metal  10  is prepared. 
     Then, as shown in  FIG. 6E , a bonding paste  25  as a bonding material made of a Bi-based material containing Sn is applied to the front surface  31  of the die pad  3 . 
     The content of Sn in the bonding paste  25  is preferably, for example, an amount that can be dispersed in full amount for Cu of the Cu layer  13  of the back metal  10  and the front surface  31  of the die pad  3 , and is, for example, 4 wt % or less, preferably, 1 to 3 wt %, and more preferably, 1.5 to 2.5 wt %. 
     After applying the bonding paste  25 , as shown in  FIG. 6F , the bonding paste  25  is sandwiched by the semiconductor chip  2  and the die pad  3  so that the Cu layer  13  of the back metal  10  contacts the bonding paste  25 . Subsequently, for example, reflow (heat treatment) is carried out at 290° C. to 300° C. 
     Accordingly, as shown in  FIG. 6G , each of the Cu layer  13  of the back metal  10  and Cu of the front surface  31  of the die pad  3  and Sn in the bonding paste  25  react with each other to form the Cu—Sn alloy layers  17 ,  18  in the vicinities of the Cu layer  13  and front surface  31 . On the other hand, Bi in the bonding paste  25  hardly reacts with Cu, and thus remains, between the Cu—Sn alloy layers  17 ,  18 , as the Bi-based material layer  16  sandwiched by these layers. 
     Thereafter, the electrode pads  9  of all semiconductor chips  2  and the electrode leads  4  corresponding to the electrode pads  9  are connected by the bonding wires  5 , respectively. 
     After completion of the wire bonding, the lead frame  14  is set in a mold, and all semiconductor chips  2  are collectively encapsulated together with the lead frame  14  by the resin package  6 . 
     After the encapsulation by the resin package  6 , the stainless steel substrate  23  and the lead frame  14  are peeled away. Then, the die pad back surface plating  19  is formed on the back surface  32  of the die pad  3  exposed from the resin package  6 , and simultaneously, the lead back surface plating  20  is formed on the back surface  42  of the electrode lead  4 . Finally, by using a dicing saw to cut the lead frame  14  together with the resin package  6  into pieces of the size of semiconductor devices  1 , the piece of the semiconductor device  1  shown in  FIG. 1  is obtained. 
     As in the above, according to the method described above, the bonding paste  25  applied to the front surface  31  of the die pad  3  is sandwiched by the semiconductor chip  2  and the die pad  3  so as to contact the Cu layer  13  of the back metal  10 . Thereafter, as a result of reflow (heat treatment) being carried out, the bonding layer  15  including the Bi-based material layer  16  and the Cu—Sn alloy layers  17 ,  18  is formed. 
     In formation of the bonding layer  15 , the components (Bi-based material and Sn) in the bonding paste  25  do not contact metallic elements other than Cu, and further, the Cu—Sn alloy layers  17 ,  18  are formed on both sides of the Bi-based material layer  16  in the opposing direction of the semiconductor chip  2  and the die pad  3 . 
     Therefore, contact between inhibitory metallic elements, such as Au in the Au layer  11  and Ni in the Ni layer  12  of the back metal  10 , which may degrade the characteristics of the Bi-based material layer  16 , and the Bi-based material layer  16  can be prevented. As a result, the formation of intermetallic compounds of Bi and the inhibitory metallic elements and the formation of eutectic compositions of Bi and the inhibitory metallic elements can be prevented. Consequently, not only can the temperature cycle resistance of the bonding layer  15  be improved, but the melting point of the bonding layer  15  can also be maintained high. 
     On the other hand, the Bi-based material layer  16  is in contact with the Cu—Sn alloy layers  17 ,  18 , but since Cu hardly reacts with Bi, there is little possibility of the melting point of the bonding layer  15  lowering or the temperature cycle resistance decreasing due to contact between these layers. 
     Moreover, since the bonding layer  15  is made of the Bi-based material layer  16  and the Cu—Sn alloy layers  17 ,  18 , lead-freeing of the bonding layer  15  can be achieved. 
     Moreover, the Cu—Sn alloy is not a hard and fragile metal like a Bi—Au alloy, a Bi—Ag alloy, or the like, but a high-strength metal. Therefore, the bonding strength of the semiconductor chip  2  and lead frame  14  and the bonding layer  15  can be improved by the Cu—Sn alloy layers  17 ,  18 . 
     Moreover, since the Au layer  11  is in contact with the lower surface of the Si substrate  7 , the Cu layer  13  and the Si substrate  7  can be made conductive with each other via the Au layer  11 . Accordingly, the Si substrate  7  and the die pad  3  can be electrically connected with each other. 
     Moreover, since both of the front surface  31  of the die pad  3  and the front surface  41  of the electrode lead  4  are uncoated surfaces not coated with a metal thin film through a process such as plating or sputtering, it is unnecessary, in manufacturing of the semiconductor device  1 , to apply a process such as plating or sputtering to the lead frame  14 , so that the cost can be reduced. 
     Moreover, the configuration of the semiconductor device  1  according to the present embodiment can solve the following problem. 
     As the problem, conventionally, a package for high-density mounting has been used for which, in order to mount semiconductor devices at high density on a wiring board, extension of leads from a resin package is eliminated and lead thermals (terminal parts electrically connected with a semiconductor chip) of a lead frame are exposed on a lower surface of the package to allow surface mounting on the wiring board. Known examples of such a package for high-density mounting include leadless packages such as a QFN (Quad Flat Non-leaded Package) and an SON (Small Outlined Non-leaded Package). 
     In such a semiconductor package, further, a package (for example, HQFN: Heat sink Quad Flat Non-leaded Package) having a structure where the die pad (support portion on which the semiconductor chip is mounted) of the lead frame is exposed on the lower surface of the package so as to enhance heat radiation from the semiconductor chip has also been put into practical use. 
     In these modes of packages, a mounting surface of the lead frame to be packaged by a molding resin together with the semiconductor chip is exposed on the lower surface of the package. Therefore, there is a drawback that the lead terminals and die pad easily come off the package. For example, in a board bending test after packaging, the lead terminal and die pad may come off when an external force is applied to the package. 
     By making the lead terminals and die pad have substantially reverse tapered sectional shapes, their side surfaces are made to bite into the molding resin so as to prevent the lead terminals and die pad from coming off. 
     The sectional shapes as described above are formed by, for example, prior to packaging of the semiconductor chip and lead frame, etching the lead frame from its mounting surface side (back surface side) to remove the side surfaces of the lead terminals and die pad in part. 
     As the lead frame, a metal thin plate of approximately 100 μm to 200 μm has conventionally been used, but recently, a lead frame formed by a plating method has come to be used. For example, a method for forming a lead frame, on a substrate, by performing plating growth with a predetermined pattern has been studied. In such a method, since the thickness of the lead frame can be accurately controlled, a lower profile package may be realized by forming the lead frame thin. 
     However, the timing of peeling of the lead frame and substrate is after the lead frame has been packaged together with the semiconductor chip. Therefore, before packaging, the mounting surface of the lead frame (lead terminals and die pad) is covered with the substrate, and it is thus difficult to press the lead frame from its mounting surface side by etching. On the other hand, after packaging, even when the substrate is peeled away, the side surfaces of the lead frame have already been covered with the molding resin, it is thus difficult to process the side surfaces by etching. 
     For the above reason, when a lead frame is formed by a plating method, there is a drawback that forming a retaining structure of the lead frame is difficult. 
     Moreover, in the conventional lead frame, the entire region of its encapsulating surface at the opposite side to the mounting surface is the same plane, and is in planar contact with the molded resin, and thus there is also a drawback that the lead frame easily shifts horizontally with respect to the molding resin. 
     In the present embodiment, each of the side surfaces  37  of the die pad  3  and the side surfaces  47  of the electrode leads  4  is encapsulated by the resin package  6 , and to the inside of the resin package  6  that encapsulates the side surfaces  37 ,  47 , the retainer portions  38  on the die pad  3  side project from the side surfaces  37  and the retainer portions  48  on the electrode lead  4  side project from the side surfaces  47 . 
     The retainer portions  38 ,  48  bite into the resin package  6  in horizontal directions perpendicular to the thickness direction of the lead frame  14 . Therefore, when a force toward the lower surface side of the resin package  6  (exposed surface side of the lead frame  14 ) is applied to the lead frame  14  in the thickness direction of the lead frame  14 , the retainer portions  38 ,  48  biting into the resin package  6  are caught therein. As a result, the lead frame  14  can be prevented from coming off. 
     Moreover, the front surface  31  of the die pad  3  is not the same plane in its entire region, but pin recesses  34  are formed in its peripheral edge portion  33 , and the resin package  6  enters inside the pin recesses  34 . Accordingly, the resin package  6  is fitted in part with the pin recesses  34 . Moreover, similar to the front surface  31  of the die pad  3 , the front surface  41  of the electrode lead  4  is not the same plane in its entire region, but a pin recess  44  is formed in its edge portion  43 , and the resin package  6  enters inside the pin recess  44 . Accordingly, the resin package  6  is fitted in part with the pin recess  44 . 
     Therefore, when a force is applied to the lead frame  14  in the horizontal directions, the pin recesses  34 ,  44  are caught on the resin package  6  inside the pin recesses  34 ,  44 . As a result, horizontal shifting of the lead frame  14  can be prevented. 
     Moreover, as a result of the peripheral surface  35  of the pin recess  34  rising in the front surface  31  of the die pad  3 , the front surface  31  is bulging in part. Moreover, as a result of the peripheral surface  45  of the pin recess  44  rising in the front surface  41  of the electrode lead  4 , the front surface  41  is bulging in part. Therefore, when the horizontal force is applied to the lead frame  14 , the bulging peripheral surfaces  35 ,  45  serve as resistance to horizontal shifting. As a result, horizontal shifting of the lead frame  14  can be prevented more reliably. 
     Moreover, according to a method for manufacturing the semiconductor device  1 , the pin recess  44  and the retainer portion  48  are formed, as shown in  FIG. 6B , in the electrode lead  4 , by driving the stamping tool  24  into the edge portion  43  of the front surface  41  at the opposite side to the back surface  42  to be exposed from the resin package  6 . Moreover, as shown in  FIG. 6C , in the same manner as in the electrode lead  4 , the pin recess  34  and the retainer portion  38  are formed in the die pad  3 . 
     Therefore, for example, even when the exposed surface (back surfaces  32 ,  42 ) of the lead frame  14  is covered with the stainless steel substrate  23  as a result of the lead frame  14  being formed by plating growth and etching from the back surface  32 ,  42  side is difficult, the retainer portions  38 ,  48  (retaining structure) can be reliably formed. 
     Moreover, since the lead frame  14  is pressed by using the stamping tool  24  that can be replaced with a capillary of a wire bonder, the pin recesses  34 ,  44  can be simply and accurately formed focusing on the peripheral edge portion  33  of the die pad  3  and the edge portions  43  of the electrode leads  4 . 
     Further, since the lead frame  14  is formed by a plating method, the lead frame  14  can be formed thin by controlling the time of plating growth. As a result, a lower profile package can be realized. 
     In the first embodiment, for example, the deformed part formed as a result of the electrode lead  4  being deformed by driving of the stamping tool  24  is not limited to a minute circular pin recess, and may be, for example, a linear recess. 
     Moreover, in the case of being a pin recess, its shape is not limited to that shown in  FIG. 4  and  FIG. 5 . 
     For example, as shown as a first modification in  FIG. 7 , a pin recess  29  formed inside with a single protrusion  28  may be formed by vertically driving a capillary  26  (capillary  26  formed at its center with a single minute hole  27 ) to be used for wire bonding into the edge portion  43  on the die pad  3  side of the electrode lead  4 . 
     Moreover, for example, as shown as a second modification in  FIG. 8 , a pin recess  53  formed inside with a plurality of protrusions  52  may be formed by vertically driving a stamping tool  51  formed at its tip with a plurality of minute holes  50  into the edge portion  43  on the die pad  3  side of the electrode lead  4 . 
     In the first modification and second modification of the lead shown in  FIG. 7  and  FIG. 8 , since the protrusions  28 ,  52  are formed inside the pin recesses  29 ,  53 , the protrusions  28 ,  52  project to the inside of the resin package  6  within the pin recesses  29 ,  53 . The protrusions  28 ,  52  allow, inside the pin recesses  29 ,  53 , the electrode lead  4  (lead frame  14 ) to bite into the resin package  6 . Therefore, a complicated fitting structure between the pin recesses  29 ,  53  and the resin package  6  can be provided. As a result, the fitting strength of the resin package  6  with respect to the pin recesses  29 ,  53  can be improved. 
     Moreover, the pin recess is not necessarily in a tapered shape whose diameter is reduced in the depth direction, and may be in a reverse tapered shape whose diameter is increased in the depth direction. 
     Moreover, for example, as shown as a third modification in  FIG. 9 , the electrode lead  4  may be pressed and expanded to the side surface  47  side to form the retainer portion  48  by driving the stamping tool  24  at an acute angle with respect to the front surface  41 , so as not to raise the front surface  41 , into the edge portion  43  on the die pad  3  side of the electrode lead  4 . 
     In that case, by adjusting the angle of the stamping tool  24  with respect to the front surface  41  to be small, as shown as a third modification in  FIG. 9 , a slope  49  (deformed portion) can be formed in the front surface  41  of the electrode lead  4  so that a dent of the stamping tool  24  does not bulge there. 
     On the other hand, as shown as a fourth modification in  FIG. 10 , a recess  54  can be formed in the front surface  41  of the electrode lead  4  by adjusting the angle of the stamping tool  24  with respect to the front surface  41  to be large. 
     The shapes of the first to fourth modifications of the lead shown in  FIG. 7  to  FIG. 10  can be applied also when the retainer portion  38  is formed in the side surface  37  of the die pad  3 . 
     Moreover, the number of pin recesses  44  to be formed in each electrode lead  4  is not limited to one, and may be a plural number. In that case, the plurality of pin recesses  44  may be disposed spaced from each other along the sides of the edge portion  43  of each electrode lead  4 , as shown as a modification in  FIG. 11 . 
     Moreover, a description has been given that the back metal  10  has a three-layer structure in which the Au layer  11 , the Ni layer  12 , and the Cu layer  13  are stacked one each, but without limitation hereto, for example, at least one type of these layers may be stacked in a plurality of layers. In that case, the plurality of layers may be stacked successively, and another or other types of layers may be interposed between the layers. 
     Moreover, the back metal  10  may include layers different from an Au layer, a Ni layer, and a Cu layer. For example, the back metal  10  may include an Ag layer, a Ti layer, and the like. A Ti layer is capable of making ohmic contact with a Si semiconductor, and can thus be applied in place of the Au layer  11 . 
     &lt;Second Embodiment&gt; 
       FIG. 12  is a schematic plan view of a semiconductor device according to a second embodiment of the present invention.  FIG. 13  is a schematic sectional view of the semiconductor device according to the second embodiment of the present invention, showing a section taken along a cut line A′-A′ of  FIG. 12 . In  FIG. 12  and  FIG. 13 , the configuration described in the foregoing first embodiment is denoted by the same reference signs, and description thereof is omitted. 
     The semiconductor layer  61  of the second embodiment includes a lead frame  62  made of a metal thin plate. The metal thin plate that forms the lead frame  62  is made from a Cu-based raw material mainly containing Cu, and specifically, made from, for example, high purity copper with a purity of 99.9999% (6N) or more or a purity of 99.99% (4N) or more or an alloy (for example, a Cu—Fe—P alloy) of Cu and a dissimilar metal. The metal thin plate may be made from, for example, an Fe-based raw material such as a 42 alloy (Fe-42% Ni). Moreover, the thickness of the lead frame  62  (metal thin plate) is, for example, 190 μm to 210 μm (preferably, approximately 200 μm). 
     Moreover, a die pad  63  and electrode leads  64  that form the lead frame  62  have, as their respective front surfaces  65  and  66 , flat surfaces with no recesses formed, which is unlike the first embodiment. Other aspects of the configuration are the same as those of the first embodiment, and the advantageous effects are also the same. 
     In the first and second embodiments, for example, the sublayers of the bonding layer  15  are not necessarily the Cu—Sn alloy layers  17 ,  18 , and may be Cu—Zn alloy layers made of an alloy of Cu and Zn that is a dissimilar metal not containing Cu and Pb, in which Cu is contained as a main component. 
     Moreover, for example, the front surface (front surface  65  of the die pad  63  and front surface  66  of the electrode lead  64 ) of the lead frame  62  is not necessarily an uncoated surface. As an example thereof, as shown as a modification of the second embodiment in  FIG. 14 , a coating layer  67  may be formed by a plating or sputtering process applied. 
     The coating layer  67 , on the front surface  65  of the die pad  63 , has a two-layer structure in which, as shown in  FIG. 15 , an Ag layer  68  and a frame-side Cu layer  69  are stacked in order from the die pad  63  side. By stacking the frame-side Cu layer  69  on the Ag layer  68 , Cu can be exposed on the whole of the opposing surface (front surface  65 ) to the semiconductor chip  2  in the die pad  63 . 
     On the other hand, the coating layer  67 , on the front surface  66  of the electrode lead  64 , has a single layer structure in which, as shown in  FIG. 16 , only an Ag layer  68  is formed. Accordingly, Ag can be exposed on the whole of the connecting surface of the bonding wire  5 . Therefore, as the bonding wire  5  to be connected to the electrode lead  4 , various wires such as not only a Cu wire but also an Au wire can be used. 
     In the case of the modification, for example, the frame-side Cu layer  69  may be used as an example of the die pad of the present invention. Accordingly, the lead frame  62  can be omitted (flameless). In the above, a description has been given of embodiments of the present invention, but the present invention can also be carried out in other modes. 
     For example, QFN type semiconductor devices have been mentioned in the foregoing embodiments, but the present invention can also be applied to semiconductor devices of other package types such as a QFP (Quad Flat Package) and an SOP (Small Outline Package). 
     The embodiments of the present invention are merely specific examples used to clarify the technical contents of the present invention, and the present invention should not be interpreted as being limited to only these specific examples, and the spirit and scope of the present invention shall be limited only by the accompanying claims. 
     Moreover, the components mentioned in the embodiments of the present invention can be combined in the scope of the present invention. 
     The present application corresponds to Japanese Patent Application No. 2009-241550 filed on Oct. 20, 2009 in the Japan Patent Office and Japanese Patent Application No. 2009-241551 filed on Oct. 20, 2009 in the Japan Patent Office, and the entire disclosures of these applications are herein incorporated by reference. 
     DESCRIPTION OF THE NUMERALS 
       1 : Semiconductor device,  2 : Semiconductor chip,  3 : Die pad,  4 : Electrode lead,  6 : Resin package,  7 : Si substrate,  9 : Electrode pad,  10 : Back metal,  11 : Au layer,  12 : Ni layer,  13 : Cu layer,  14 : Lead frame,  15 : Bonding layer,  16 : Bi-based material layer,  17 : Cu—Sn alloy layer,  18 : Cu—Sn alloy layer,  21 : Front surface (of semiconductor chip),  22 : Back surface (of semiconductor chip),  24 : Stamping tool,  25 : Bonding paste,  26 : Capillary,  28 : Protrusion,  29 : Pin recess,  31 : Front surface (of die pad),  32 : Back surface (of die pad),  33 : Peripheral edge portion (of die pad),  34 : Pin recess,  35 : Peripheral surface (of die pad),  37 : Side surface (of die pad),  38 : Retainer portion (of die pad),  41 : Front surface (of electrode lead),  42 : Back surface (of electrode lead),  43 : Edge portion (of electrode lead),  44 : Pin recess,  45 : Peripheral surface (of electrode lead),  47 : Side surface (of electrode lead),  48 : Retainer portion (of electrode lead),  49 : Slope,  51 : Stampingtool,  52 :Protrusion,  53 : Pin recess:  54 : Recess,  61 : Semiconductor device,  62 : Lead frame,  63 : Die pad,  64 : Electrode lead,  65 : Front surface (of die pad),  66 : Front surface (of electrode lead),  67 : Coating layer,  68 : Ag layer,  69 : Frame-side Cu layer