Abstract:
A semiconductor device of the present invention includes a chip which has a pad; a bump electrode formed on the pad; and a wire whose stitch bonding is made on the bump electrode. The wire satisfies a condition: (modulus-of-elasticity/breaking strength per unit area) ≧400.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a semiconductor device having a chip which has a pad, a bump electrode formed on the pad, and a wire whose stitch bonding is performed on the bump electrode, and its manufacturing method. 
     2. Background Art Background Art 
     When performing stitch bonding of a gold wire on an aluminum pad on a chip directly, load of a capillary concentrates and a crack enters into SiO2 interlayer insulation film under the aluminum pad. For this reason, a bump electrode is used for the wire bonding between a chip and a chip (chip-to-chip) (for example, refer to Japanese Unexamined Patent Publication No. 2001-15541). Further, in a thin package, in order to make the height of a gold wire low, reverse bonding using a bump electrode is performed. 
       FIGS. 10A and 10B  are sectional views showing the state of conventional bump electrode formation. First, as shown in  FIG. 10A , bump electrode  14  is formed on aluminum pad  11  of a chip with gold wire  13  discharged from capillary  12 . Then, as shown in  FIG. 10B , gold wire  13  is cut by pulling upward, while holding both sides of gold wire  13  by clamper  15 . 
       FIGS. 11A and 11B  are sectional views showing the state of conventional stitch bonding of a gold wire onto a bump electrode. First, as shown in  FIG. 11A , gold wire  13  is crushed by pushing and pressing gold wire  13  to bump electrode  14  and applying supersonic vibration by capillary  12 , and gold wire  13  is joined to bump electrode  14 . Then, as shown in  FIG. 11B , gold wire  13  is cut by pulling upward, while holding both sides of gold wire  13  by clamper  15 . 
     However, since the gold wire used as a material of bump electrode  14  is soft in the conventional formation of a bump electrode with a gold wire and conventional stitch bonding of a gold wire onto a bump electrode, crush of gold wire  13  held by capillary  12  and bump electrode  14  becomes insufficient, so that gold wire  13  cannot become sufficiently thin. Hereby, since the strength of gold wire  13  becomes high, the distortion of gold wire  13  by the reaction at the time of cutting gold wire  13 , and the peeling of bump electrode  14  from aluminum pad  11  occur. The same phenomenon is generated also in the conventional bump electrode formation. As a result, there was a problem of gold wires having electrically short-circuited with S character deflection of gold wire  13  resulting from distortion, and opening electrically by peeling of bump electrode  14 . 
     What is necessary is just to use the soft type gold wire cut by lower load, in order to solve this problem. However, since the modulus of elasticity is low, the such soft type gold wire had the problem that a gold wire flowed when sealing resin was poured, and gold wires electrically short-circuited. 
     SUMMARY OF THE INVENTION 
     The present invention was made in order to solve the above problems. A purpose is to obtain the semiconductor device and its manufacturing method which can protect electric short circuit of wires and peeling of a bump electrode, and can be stably manufactured. 
     A semiconductor device according to Claim  1  comprises a chip which has a pad; a bump electrode formed on the pad; and a wire whose stitch bonding is made on the bump electrode; wherein the wire satisfies a condition: (modulus-of-elasticity/breaking strength per unit area) ≧400. 
     A manufacturing method of a semiconductor device according to claim  3  comprises the steps of: forming a bump electrode on a pad with a wire passed to a capillary; operating the capillary in a horizontal direction with an amplitude at least more than a clearance between the wire, and an inner wall of the capillary after the step of forming the bump electrode; and cutting the wire by pulling upward, holding both sides of the wire by a clamper after the step of operating the capillary in a horizontal direction; wherein as the wire, what satisfies a condition: (modulus-of-elasticity/breaking strength per unit area) ≧400 is used. 
     A manufacturing method of a semiconductor device according to Claim  4  comprises the steps of: performing stitch bonding of a wire on a bump electrode using a capillary; operating the capillary in a horizontal direction with an amplitude at least more than a clearance between the wire, and an inner wall of the capillary after the step of performing stitch bonding; and cutting the wire by pulling upward, holding both sides of the wire by a clamper after the step of operating the capillary in a horizontal direction; wherein as the wire, what satisfies a condition: (modulus-of-elasticity/breaking strength per unit area) ≧400 is used. 
     The features and advantages of the present invention may be summarized as follows. 
     The features and advantages of the present invention may be summarized as follows. Since a wire can be cut with a low load, maintaining the modulus of elasticity of the wire, electric short circuit of wires and peeling of a bump electrode are prevented, so that the highly integrated semiconductor device can be stably manufactured. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a sectional view showing an example of the semiconductor device concerning First Embodiment of the present invention. 
         FIG. 1B  is a top view showing an example of the semiconductor device concerning First Embodiment of the present invention. 
         FIGS. 2A-2C  are sectional views showing the step which forms a bump electrode. 
         FIGS. 3A and 3B  are sectional views showing the step which performs stitch bonding of a gold wire on a bump electrode; 
         FIG. 4  is a drawing showing the relation between an elongation percentage of a gold wire, and the stress. 
         FIGS. 5A and 5B  are drawings showing the elongation percentage of a gold wire, and the flow curvature of a gold wire. 
         FIG. 6A  is a sectional view showing another example of the semiconductor device concerning First Embodiment of the present invention. 
         FIG. 6B  is a top view showing another example of the semiconductor device concerning First Embodiment of the present invention. 
         FIG. 7A  is a sectional view showing still another example of the semiconductor device concerning First Embodiment of the present invention. 
         FIG. 7B  is a top view showing still another example of the semiconductor device concerning First Embodiment of the present invention. 
         FIGS. 8A-8D  are sectional views showing the manufacturing method of the semiconductor device concerning Second Embodiment of the present invention. 
         FIGS. 9A-9D  are sectional views showing the manufacturing method of the semiconductor device concerning Third Embodiment of the present invention. 
         FIGS. 10A and 10B  are sectional views showing the state of conventional bump electrode formation. 
         FIGS. 11A and 11B  are sectional views showing the state of conventional stitch bonding of a wire onto a bump electrode. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
       FIG. 1A  is a sectional view showing an example of the semiconductor device concerning First Embodiment of the present invention, and  FIG. 1B  is the top view. Chip  22  and chip  23  are mounted on die pad  21 , being put in order. These chips  22  and  23  and lead  24  are connected by gold wire  13 . Further, bump electrode  14  is formed on aluminum pad  11  of chip  23 . And ball bonding of the gold wire  13  is performed on the aluminum pad of chip  22 , and the stitch bonding is performed on bump electrode  14 . Furthermore, the whole is sealed with sealing resin  25 . 
       FIGS. 2A-2C  are sectional views showing the step which forms a bump electrode. First, as shown in  FIG. 2A , gold ball  32  with a larger diameter than gold wire  13  is formed by melting the tip of gold wire  13  discharged from capillary  12  by discharge from blowpipe  31 . Then, as shown in  FIG. 2B , gold ball  32  is pushed and pressed by capillary  12  on aluminum pad  11  of chip  23  arranged on a stage. And the interface of aluminum pad  11  is joined to gold ball  32  by applying load, heat, supersonic wave, etc. Then, as shown in  FIG. 2C , by holding both sides of gold wire  13  above capillary  12  and pulling by clamper  15 , gold wire  13  is cut above gold ball  32 . Thus, bump electrode  14  is formed on aluminum pad  11  with gold wire  13  discharged from capillary  12 . 
       FIGS. 3A and 3B  are sectional views showing the step which performs stitch bonding of a gold wire on a bump electrode. First, gold ball  32  is formed at the tip of gold wire  13  discharged from capillary  12  like  FIG. 2A , and as shown in  FIG. 3A , ball bonding (first bonding) of the gold ball  32  at the tip of gold wire  13  is performed on an aluminum pad of chip  22  using capillary  12 . Then, gold wire  13  prolonged from gold ball  32  is discharged from capillary  12 , and lengthened onto bump electrode  14 . And the stitch bonding (second bonding) of a part of gold wires  13  prolonged from gold ball  32  is performed on bump electrode  14 , pushing and pressing gold wire  13  for 10 ms (milli seconds) to bump electrode  14  by capillary  12 , and applying supersonic vibration. And as shown in  FIG. 3B , gold wire  13  is cut (tail cut) by pulling upward, holding both sides of gold wire  13  by clamper  15 . Thus, gold wire  13  which electrically connects the aluminum pad of chip  22  with bump electrode  14  is formed with gold wire  13  discharged from capillary  12 . 
     Here, in the present invention, in order to prevent electric short circuit of wires, and peeling of the bump electrode, a material of gold wire  13  is set up as follows. First,  FIG. 4  is a drawing showing the relation of elongation percentage and stress of a gold wire. When tensile stress is applied in the length direction, gold wire A is cut when an elongation percentage becomes 4%, and the stress at that time (breaking strength) is 12.4 gf. Similarly, when an elongation percentage is 7% with gold wire B, breaking strength is 9.5 gf, when an elongation percentage is 11% with gold wire C, breaking strength is 8.8 gf, and with gold wire D, when an elongation percentage is 15%, breaking strength is 8.3 gf. And gold wire E is a soft type gold wire, and its breaking strength is low compared with hard type gold wire A-D. 
     When the stress is applied, at first, a gold wire will perform elastic deformation and will perform plastic deformation after that. The inclination in the case of this elastic deformation is equivalent to the modulus of elasticity of a gold wire. And the moduli of elasticity of hard type gold wire A-D are 9.4, 9.3, 9, and 8.5 (x103 kgf/mm2), respectively, and soft type gold wire E has a low modulus of elasticity compared with these. 
     In order to prevent the distortion (deformation) of a gold wire by the reaction at the time of cutting the gold wire, and the peeling from aluminum pad  11  of bump electrode  14 , it is preferred to use a gold wire with low breaking strength. This is because the maximum load which will be applied by the time of fracture is small and the energy released as reaction at the time of fracture is small with a wire with low breaking strength. In order to prevent deformation of a gold wire, a gold wire with a high modulus of elasticity is preferred. This is because the wire with a high modulus of elasticity can more suppress the deformation at the time of energy being applied. Therefore, the one where the ratio of a modulus of elasticity to the breaking strength per unit area, i.e., (the modulus of elasticity (kgf/mm2)/breaking strength per unit area (kgf/mm2)) is higher is preferred. However, there is an inclination for the wire with a high modulus of elasticity to have high breaking strength like the above-mentioned gold wire A, and for the wire with low breaking strength to have a low modulus of elasticity like the above-mentioned gold wire E. Then, what fulfills the following condition as a gold wire is used.
 
(A modulus of elasticity (kgf/mm2)/breaking strength per unit area (kgf/mm2))≧400
 
     Since a wire can be cut by low load by this, maintaining the modulus of elasticity of a wire, the electric short circuit of the wires accompanying deformation of a wire and the peeling of a bump electrode are prevented, so that the highly integrated semiconductor device can be stably manufactured. In particular, in material with as high elongation percentage of the wire at the time of fracture as at least 6% or more, more preferably 10% or more, it becomes easy to obtain the characteristics of the rate of high elasticity and low breaking strength like gold wire B, C, and D. 
     Further, in the present invention, in order to prevent gold wires from electrically short-circuiting with flowing when sealing resin is poured, the material of sealing resin is set up as follows. First,  FIGS. 5A and 5B  are the drawings showing the relation between the elongation percentage of a gold wire, and the flow curvature of a gold wire. The flow curvature of a gold wire is the curvature of the gold wire flowed, when sealing with sealing resin.  FIG. 5A  is a case where the resin whose spiral flow is less than 110 cm and whose viscosity is 10 Pa·S or more is used.  FIG. 5B  is a case where the resin whose spiral flow is 110 cm or more and whose viscosity is less than 10 Pa·S is used. 
     Here, the measurement of melt viscosity is based on JIS K7210, and as a measurement condition, the amount of a sample shall be 3 g, a temperature level shall be 175±2° C., and a nozzle dimension shall be (1.00±0.02) mm φ×10 mm. Spiral flow is a length which resin reaches, when resin is filled up under certain conditions into the flow test metal mold having a spiral shape. This spiral flow can estimate the fluidity of the resin in injection molding. 
     The metal mold specified to EMMI-1-66 and a transfer-molding machine are used for measurement of spiral flow as a measuring apparatus. Further, a test sample is measured after being taken out from a preservation warehouse, leaving as it is under a room temperature for 2 hours being unopened, and opening after that. And the test is completed within 2 hours after opening. Further, as measurement conditions, an amount of a sample is set as about 15 g, setting cull thickness as about 3 mm, injection pressure as 6.9±0.5 MPa, molding time as 120±5 seconds, preheating as off, and temperature level as 175±2° C. Under these conditions, a sample is inserted after checking having reached the prescribed temperature level, a plunger is dropped promptly, and application of pressure is started within 10 seconds. And a metal mold is disassembled after termination of a prescribed period, and spiral flow is measured by reading the flow length (cm) of resin. 
     Compared with  FIG. 5A , the flow curvature of a gold wire is small in  FIG. 5B . Therefore, in order to prevent gold wires from electrically short-circuiting with a gold wire&#39;s flowing when sealing resin is poured, it is preferred to use the resin whose spiral flow is 110 cm or more and whose viscosity is less than 10 Pa·S. 
       FIG. 6A  is a sectional view showing another example of the semiconductor device concerning First Embodiment of the present invention, and  FIG. 6B  is the top view. On glass epoxy wiring substrate  41 , chip  42 , spacer chip  43 , chip  44 , and chip  45  are mounted. Bump electrodes  14  are formed on aluminum pads  11  of chips  44  and  45 . And ball bonding of gold wire  13  is performed on lead  46 , and the stitch bonding is performed on bump electrode  14 . The whole is sealed with sealing resin  47  and solder balls  48  are formed on the bottom face of glass epoxy wiring substrate  41 . 
       FIG. 7A  is a sectional view showing still another example of the semiconductor device concerning First Embodiment of the present invention, and  FIG. 7B  is the top view. Chip  52  is mounted on die pad  51 . And a plurality of aluminum pads  11  are formed at the center of chip  52  at one row. Bump electrode  14  is formed on this aluminum pad  11 . And ball bonding of the gold wire  13  is performed on lead  53 , and the stitch bonding is performed on bump electrode  14 . Further, the whole is sealed with sealing resin  54 . 
     Second Embodiment 
       FIGS. 8A-8D  are sectional views showing a manufacturing method of the semiconductor device concerning Second Embodiment of the present invention. First, as shown in  FIG. 8A , bump electrode  14  is formed by joining the gold ball at the tip of gold wire  13  discharged from capillary  12  on aluminum pad  11  of chip  23 , However, the thing of the material same as gold wire  13  as First Embodiment is used. 
     And as shown in  FIG. 8B , capillary  12  is raised by 15 μm. Here, since the height of bump electrode  14  is 15 μm, capillary  12  is evacuated above bump electrode  14 . In the dimension of capillary  12  and gold wire  13  which are used in the embodiment, the inside diameter of capillary  12  is 30 μm, and the diameter of gold wire  13  is 23 μm. 
     Capillary  12  is made to reciprocate in a horizontal direction after that, as shown in  FIG. 8C . However, the operational amplitude of capillary  12  is more than the clearance between gold wire  13 , and the inner wall of capillary  12  at least. Since the diameter of gold wire  13  is 23 μm and the inside diameter of capillary  12  is 30 μm concretely, the clearance between both is 3.5 μm at one side, when it is averaged, and when both sides are put together, it is 7 μm. It is necessary to be more than 3.5 μm which is the one side clearance between capillary  12  inner wall and gold wire  13  at worst as an amplitude of operation. In order to give sufficient stress to the tail cut portion of gold wire  13  and to reduce cut strength, it is more preferred to be as an amplitude of operation more than 7 μm which is the sum of the both sides of clearance between capillary  12  inner wall and gold wire  13 . Then, for example, after performing 30 μm horizontal displacement of the capillary  12  to one way, a counter direction is made to perform 65 μm horizontal displacement. Hereby, stress can be given to tail cut portion of gold wire  13 , and cut strength can be reduced. It is also possible to cut gold wire  13  from bump electrode  14  by horizontal displacement depending on the size of horizontal displacement. 
     After that, as shown in  FIG. 8D , gold wire  13  is cut by pulling upward, holding both sides of gold wire  13  by clamper  15 . On this occasion, since the strength of gold wire  13  is decreasing with the reciprocating motion of capillary  12 , reaction of a cut of gold wire  13  can be reduced and S character deflection of gold wire  13  and peeling of bump electrode  14  can be further suppressed rather than First Embodiment. 
     Bump electrode  14  contacting capillary  12  and bump electrode  14  receiving a damage can be prevented in the case of a reciprocating motion, by evacuating capillary  12  above bump electrode  14  before the reciprocating motion of capillary  12 . 
     The circular motion may be performed to a horizontal direction, instead of making capillary  12  reciprocate to a horizontal direction. In addition, what is necessary is just the action comprising movement in a horizontal direction, when decomposing into vectors. Although limited for neither the frequency of an oscillation, nor an operation means in particular, since the amplitude of supersonic vibration is generally less than 1 μm, it is difficult to obtain amplitude sufficient as an action of capillary  12  for reducing the strength of gold wire  13 . In this embodiment, the horizontal displacement action of the above-mentioned capillary  12  was generated by making it operate, performing position control of the motor mechanically as the source of power. 
     Third Embodiment 
       FIGS. 9A-9D  are sectional views showing a manufacturing method of a semiconductor device concerning Third Embodiment of the present invention. First, as shown in  FIG. 9A , after performing ball bonding of the gold ball at gold wire  13  tip on the aluminum pad of chip  22  using capillary  12 , stitch bonding of the gold wire  13  is performed on bump electrode  14  formed on aluminum pad  11  of chip  23 . Concretely speaking, gold wire  13  is crushed pushing and pressing gold wire  13  for 10 ms to bump electrode  14  by capillary  12 , and applying supersonic vibration, and gold wire  13  is joined to bump electrode  14 . However, as gold wire  13 , the thing of the same material as First Embodiment is used. 
     After that, as shown in  FIG. 9B , capillary  12  is evacuated more than half of the amplitude of the horizontal direction action of capillary  12  of later process in the loop advancement direction of gold wire  13 . For example, horizontal displacement of the capillary  12  is performed by 30 μm. 
     Capillary  12  is made to reciprocate in a horizontal direction like Second Embodiment after that, as shown in  FIG. 9C . However, the amplitude of capillary  12  of operation is made at least to more than the clearance between gold wire  13 , and the inner wall of capillary  12 . That is, it is necessary to be more than 3.5 μm which is a one side clearance between capillary  12  inner wall and gold wire  13  at worst as an amplitude of operation. Further, in order to give sufficient stress to tail cut portion of gold wire  13  and to reduce cut strength, it is more preferred to be as amplitude of operation more than 7 μm which is the sum of both sides of the clearance between capillary  12  inner wall and gold wire  13 . The amplitude of operation in this embodiment is 40 μm. 
     After that, as shown in  FIG. 9D , gold wire  13  is cut by pulling upward, holding both sides of gold wire  13  by clamper  15 . On this occasion, since the cut strength of gold wire  13  is reduced with the reciprocating motion of capillary  12 , reaction of a cut of gold wire  13  can be reduced. S character deflection of gold wire  13  and peeling of bump electrode  14  can be further suppressed rather than First Embodiment. It is also possible to cut gold wire  13  with a reciprocating motion depending on the amplitude of a reciprocating motion of operation. In this case, S character deflection of a wire by reaction of a cut of gold wire  13  can be suppressed to the minimum. 
     Since capillary  12  is separated from the location which started stitch bonding, i.e., the location where gold wire  13  is contacting bump electrode  14  by more than half of the amplitude of a both-way action before the reciprocating motion of capillary  12 , in the reciprocating motion of capillary  12 , giving of the stress to joining portion of gold wire  13  and bump electrode  14 , and the portion of the root of gold wire  13  can be reduced, and sharp strength lowering and an open circuit of a gold wire can be prevented. 
     Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described. 
     The entire disclosure of a Japanese Patent Application No. 2005-147674 filed on May 20, 2005 including specification, claims, drawings and summary, on which the Convention priority of the present application is based, are incorporated herein by reference in its entirety.