CN107710394B

CN107710394B - Welding chopper

Info

Publication number: CN107710394B
Application number: CN201680038201.8A
Authority: CN
Inventors: 冈总一郎; 大西惇平; 石塚祐司; 本村研一
Original assignee: Toto Ltd
Current assignee: Toto Ltd
Priority date: 2015-07-03
Filing date: 2016-07-01
Publication date: 2020-05-19
Anticipated expiration: 2036-07-01
Also published as: KR20180011249A; PH12017502415B1; CN107710394A; TW201701982A; KR101907906B1; JP2017017306A; TWI562847B; JP2017041657A; JP6064308B2; PH12017502415A1

Abstract

The invention provides a welding chopper, which is provided with a body part and is provided with: a through hole penetrating the filament; a1 st pressing surface that presses the filament, the 1 st pressing surface being provided around the through hole and having a1 st inclined surface that is inclined with respect to a direction in which the through hole extends; and a2 nd pressing surface for pressing the filament, the pressing surface having a tapered surface provided between the 1 st inclined surface and the through hole, and a2 nd inclined surface provided between the tapered surface and the 1 st inclined surface, wherein a square mean square root slope of a roughness curve element of the 2 nd inclined surface is smaller than a square mean square root slope of a roughness curve element of the 1 st inclined surface.

Description

Welding chopper

Technical Field

The present invention relates generally to a weld chopper.

Background

In a manufacturing process of a semiconductor device, wire bonding for connecting a semiconductor element and a lead frame with a bonding wire (hereinafter, referred to as a "filament") is performed. In wire bonding, one end of a filament is bonded to an electrode pad of a semiconductor element by a wire bonding chopper (first bonding). The filament is then pulled to bond the wire (second bond). When joining the filaments, ultrasonic waves are applied in a state where the filaments are pressed by a welding chopper.

For example, in the second weld: the main joint part (stitch welding part) of the thin wire and the lead wire; and a temporary bonding portion (tail bonding portion) of the filament and the lead. After such second welding, the filaments extending from the tail weld are cut (severed). After that, the semiconductor element and the lead frame connected by the filament are sealed with a sealing resin, thereby manufacturing a semiconductor device.

In recent years, semiconductor devices are used in, for example, in-vehicle electronic devices and are used under severe temperature cycle environments. When a semiconductor device is used under a severe temperature cycle environment, there is a possibility that the sealing resin may peel off or crack due to a difference in thermal expansion between the sealing resin and the metal. Therefore, the semiconductor device manufactured as described above is required to have high environmental reliability (temperature cycle reliability).

In recent years, attempts have been made to use copper, which is lower in cost than gold, as a material for the filament. When the material of the filament is changed from the viewpoint of adhesion between the metal and the sealing resin, the material of the sealing resin is also changed. However, when copper is used for the filament, further improvement is required in order to satisfy the requirement for higher environmental reliability.

In this regard, for example, a method using a lead frame called a roughened lead frame is proposed. A thick plating layer containing nickel or the like is formed on the surface of the roughened lead frame, and the surface of the plating layer is subjected to roughening treatment. Since the surface is rough, the adhesion between the lead frame and the sealing resin can be improved.

However, if such a roughened lead frame is used, a filament containing harder copper will be pressed against the thicker plating when the second bond is made. In this case, the filament may be embedded in a thick plating layer, and the bondability between the filament and the lead may be reduced. Also, the cutting property of the filament after the second welding is deteriorated. If the cutting property of the filament is deteriorated, there is a problem that a defect (peeling defect) in which the joint portion is peeled off at the time of cutting the filament occurs. Further, since the weld chopper is pressed against the plating layer having a rough surface, the weld chopper is easily worn. The life of the weld chopper may be degraded.

Patent document 1: japanese patent application laid-open No. 2009-540624

Patent document 2: japanese unexamined patent publication Hei 2-163951

Disclosure of Invention

The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a welding chopper capable of improving the joining strength, improving the cutting performance of a wire, and suppressing abrasion.

The invention of claim 1 is a welding chopper including a main body portion, including: a through hole penetrating the filament; a1 st pressing surface that presses the filament, the 1 st pressing surface being provided around the through hole and having a1 st inclined surface that is inclined with respect to a direction in which the through hole extends; and a2 nd pressing surface for pressing the filament, the pressing surface having a tapered surface provided between the 1 st inclined surface and the through hole and a2 nd inclined surface provided between the tapered surface and the 1 st inclined surface, wherein a square mean square root slope of a roughness curve element of the 2 nd inclined surface is smaller than a square mean square root slope of a roughness curve element of the 1 st inclined surface,

the square mean square root slope is calculated according to equation (1),

where l is the reference length and Z (x) is the roughness curve upper value.

According to this welding chopper, the wire can be pressed by the relatively rough 1 st inclined surface at the time of the main joining, and the joining strength of the stitch-type welded portion can be ensured. In addition, when the temporary joining is performed, since the filaments are pressed by the 2 nd inclined surface and the tapered surface, the contact area between the welding chopper and the filaments is increased, and the joining strength of the tail wire welding portion can be improved. In addition, when the filaments are cut after the joining, a large tensile force is generated in the filaments due to the 1 st inclined surface having a large square average square root inclination. On the other hand, by the 2 nd inclined surface having a smaller square average square root inclination, it is difficult to generate a tensile force on the filament. By this action, the stress is maximized at the filament-cutting portion (for example, the portion where the filament is thinnest) located in the vicinity of the boundary between the 1 st inclined surface and the 2 nd inclined surface. Therefore, the generation of the micro-cracks is promoted, and the deformation form of the micro-cracks is a mode I (open mode), and the cracks progress. This can improve the filament cutting performance. Further, the stress generated when the filament is pressed is dispersed on the 2 nd inclined surface having a square average square root slope smaller than that of the 1 st inclined surface, and the abrasion of the welding chopper can be suppressed.

The invention of claim 2 is the welding chopper of claim 1, wherein the slope of the square average square root of the roughness curve element of the 1 st inclined surface is 8 ° or more, and the slope of the square average square root of the roughness curve element of the 2 nd inclined surface is 5 ° or less.

According to this welding chopper, since the square average square root slope of the 1 st inclined surface is 8 ° or more, a large tensile force can be generated in the filament by the 1 st inclined surface when the filament is cut. Further, since the inclination of the square average square root of the 2 nd inclined surface is 5 ° or less, a small tensile force can be generated in the filament by the 2 nd inclined surface when the filament is cut. Therefore, the deformation form of the micro cracks generated at the filament cutting portion is a mode I (open mode), and cracks progress. This can improve the filament cutting performance.

The invention of claim 3 is the welding chopper of

claim

1 or 2, wherein the slope of the square average square root of the roughness curve element of the 1 st inclined surface is 11 ° or more, and the slope of the square average square root of the roughness curve element of the 2 nd inclined surface is 2 ° or less.

According to this welding chopper, since the square average square root slope of the 1 st inclined surface is 11 ° or more and the square average square root slope of the 2 nd inclined surface is 2 ° or less, even if the welding chopper is worn, the difference between the square average square root slope of the 1 st inclined surface and the square average square root slope of the 2 nd inclined surface is easily kept constant or more. Therefore, a decrease in the difference between the tensile force generated by the 1 st inclined surface to the filament and the tensile force generated by the 2 nd inclined surface to the filament can be suppressed. Thus, even if the welding chopper is worn, the deformation form of the micro cracks generated at the filament cutting portion is the mode I, and the cracks progress. Thus, the filament cutting performance can be improved.

The 4 th aspect of the present invention is the welding chopper of any one of 1 st to 3 rd aspects of the present invention, wherein a width of the 2 nd inclined surface is 2% to 8% of an outer diameter of the 1 st pressing surface when viewed in the axial direction.

According to this welding chopper, since the width of the 2 nd inclined surface is 2% or more of the outer diameter of the 1 st pressing surface when viewed in the axial direction, the maximum stress generated at the tip of the welding chopper can be made lower than the critical stress at which the material of the welding chopper is worn. Thereby, the abrasion of the welding chopper can be restrained in a large width. Further, since the width of the 2 nd inclined surface is 8% or less of the outer diameter of the pressing surface when viewed in the axial direction, stress that can obtain sufficient joining strength of the tail wire welded portion can be generated.

The 5 th invention is the welding chopper according to any 1 of the 1 st to 4 th inventions, wherein a maximum height Rz of the 1 st inclined surface is 0.2 μm or more, and a maximum height Rz of the 2 nd inclined surface is 0.16 μm or less.

According to this solder cleaver, since the maximum height Rz of the 1 st inclined surface is 0.2 micrometers (μm) or more, the wire can be pressed by the 1 st inclined surface, and therefore, sufficient bonding strength can be obtained. In addition, the maximum height Rz of the 2 nd inclined surface is 0.16 μm or less, and therefore, the sliding of the wire and the welding chopper is promoted. This can improve the filament cutting performance. This can suppress the occurrence of peeling failure.

The 6 th aspect of the present invention is the welding chopper of any 1 of the 1 st to 5 th aspects of the present invention, wherein a maximum height Rz of the 1 st inclined surface is 0.3 μm or more, and a maximum height Rz of the 2 nd inclined surface is 0.10 μm or less.

According to this welding-type chopper, since the maximum height Rz of the 1 st inclined surface is 0.3 μm or more, even if the welding-type chopper is worn, the maximum height Rz of the 1 st inclined surface can be kept constant or more. Therefore, even if the welding chopper is worn, the wire is pressed by the 1 st inclined surface, and therefore, sufficient bonding strength can be obtained. Even if the welding chopper is worn, the maximum height Rz of the 2 nd inclined surface is 0.10 μm or less, and therefore, the sliding between the wire and the welding chopper is promoted. This can improve the filament cutting performance.

The 7 th invention is the welding chopper wherein, in any 1 st invention from 1 st to 6 th inventions, an angle formed by a surface perpendicular to the axial direction and the 2 nd inclined surface is smaller than an angle formed by the surface perpendicular to the axial direction and the 1 st inclined surface.

According to this welding riving knife, the wire is pressed by the 2 nd inclined surface at the time of temporary joining, so the joining strength of the tail wire welding portion can be improved.

The 8 th invention is the welding chopper wherein, in any 1 st invention from 1 st to 7 th inventions, an angle formed by a plane perpendicular to the axial direction and the 2 nd inclined plane is 11 degrees or less.

According to this welding riving knife, since the angle formed by the surface perpendicular to the axial direction and the 2 nd inclined surface is 11 degrees or less, stress (force with which the 2 nd pressing surface presses the filament) that can obtain sufficient bonding strength of the tail wire welding portion at the time of temporary bonding can be generated.

The 9 th aspect of the present invention is the welding chopper of any one of 1 st to 8 th aspects of the present invention, wherein a boundary between the 1 st inclined surface and the 2 nd inclined surface is saw-toothed as viewed in the axial direction.

According to this welding chopper, since the boundary between the 1 st inclined surface and the 2 nd inclined surface is formed in a zigzag shape, stress is repeatedly generated in the wire during the welding operation. This makes the filaments likely to have micro cracks. Thus, the filament cutting performance can be improved, and the occurrence of defective peeling can be suppressed.

The 10 th aspect of the present invention is the welding chopper of any 1 of the 1 st to 9 th aspects of the present invention, wherein a skewness of the 1 st inclined surface is-0.3 or less, and an average height of the 1 st inclined surface is 0.06 to 0.3 μm.

According to the welding chopper, the shape change caused by abrasion in use can be reduced. Even if welding is repeated, the initial filament cutting property and the bonding strength can be maintained for a long period of time.

The 11 th invention is the welding chopper wherein, in any 1 of the 1 st to 10 th inventions, a crest of the 2 nd inclined surface is 5.0 or less.

According to this welding chopper, since the crest of the 2 nd inclined surface is 5.0 or less, the sliding between the wire and the welding chopper is promoted, and the cutting performance of the wire can be improved.

Drawings

Fig. 1 is a schematic diagram illustrating a weld chopper according to the present embodiment.

Fig. 2 is a schematic enlarged view illustrating the tip end of the weld chopper according to the present embodiment.

Fig. 3 is a schematic enlarged view illustrating the tip end of the weld chopper according to the present embodiment.

Fig. 4(a) and 4(b) are schematic sectional views illustrating the tip end of the weld chopper according to the present embodiment.

Fig. 5 is a schematic cross-sectional view illustrating a distal end of the weld chopper according to the present embodiment.

Fig. 6 is a schematic cross-sectional view illustrating a state of wire bonding.

Fig. 7(a) and 7(b) are photographs illustrating the bonding wires and the leads.

Fig. 8(a) and 8(b) are schematic views for explaining the cutting of the wire by the weld chopper according to the present embodiment.

Fig. 9 is a diagram illustrating the evaluation results of the welding chopper.

Fig. 10 is a diagram illustrating the evaluation results of the welding chopper.

Fig. 11 is a diagram illustrating the evaluation results of the welding chopper.

Fig. 12 is a diagram illustrating the evaluation results of the welding chopper.

Fig. 13(a) and 13(b) are diagrams illustrating the distal end of the weld chopper according to the present embodiment.

Fig. 14 is a diagram illustrating the evaluation results of the welding chopper.

Fig. 15 is a diagram illustrating the evaluation results of the welding chopper.

Description of the symbols

10-a body portion; 11-a cylindrical portion; 12-a conical section; 13-a bottle neck; 20-through holes; 20 a-a central axis; 21-tapered pores; 22-linear holes; 51-the 1 st pressing surface; 51-inclined plane 1; 52-2 nd pressing surface; 52 f-2 nd inclined surface; 52 t-conical surface; 110-welding a chopper; 200-a lead; A. b, C, D-area; b1-boundary; f1, F11, F12, F2, F21, F22-vector; BW-filament; cr-imaginary circle; da-axial direction; dc-circumferential; d1-outer diameter; d2-inner diameter; p1-side; SB-stitch bond; TB-tail welds; t-tip diameter; w1-width; theta 1-6-degree

Detailed Description

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same components are denoted by the same reference numerals, and detailed description thereof will be omitted as appropriate.

Detailed description of the preferred embodiments

Fig. 2 is a schematic enlarged view illustrating a shape of a tip of the weld chopper according to the present embodiment.

The entirety of the weld chopper 110 is shown in FIG. 1. A diagram enlarging the area a shown in fig. 1 is shown in fig. 2.

As shown in fig. 1, a welding chopper (hereinafter, also referred to as "chopper") 110 has a body portion 10. The main body 10 is a cylindrical member having a through hole 20. The through hole 20 is a through hole extending in the axial direction Da of the main body 10. When using a chopper, a filament is passed through the through-going hole 20.

The main body 10 is provided with: a cylindrical portion 11; a conical portion 12 provided on the distal end side of the cylindrical portion 11; and a bottleneck portion 13 provided on the tip end side of the conical portion 12. The through hole 20 is provided to penetrate the cylindrical portion 11, the conical portion 12, and the neck portion 13.

In the present specification, the distal side or the distal direction refers to a direction from the end on the cylindrical portion 11 side toward the end on the neck portion 13 side. The top end of the riving knife (body portion) means the end portion on the side of the bottle neck portion 13.

The cylindrical portion 11 has a diameter for mechanically securing the riving knife 110 to a welding device.

The diameter of the conical portion 12 decreases toward the tip end side. The conical portion 12 has, for example, a truncated cone shape. The diameter of the end portion of the conical portion 12 on the cylindrical portion 11 side is substantially equal to the diameter of the cylindrical portion 11.

The diameter of the neck portion 13 is smaller than the diameter of the conical portion 12. For example, the diameter of the bottle neck portion 13 is tapered in the tip direction. By reducing the diameter of the bottle neck portion 13, it is possible to perform wire bonding at a predetermined position while avoiding adjacent filaments to which wiring has been already applied.

The riving knife 110 is made of, for example, ceramic. As a material of the riving knife 110, for example, alumina or the like can be used. Alternatively, a composite material containing at least one of alumina, zirconia, and chromia, or the like may be used as the material of the riving knife 110.

Fig. 3 is a schematic enlarged view illustrating the tip end of the weld chopper according to the present embodiment. Fig. 3 is a perspective view of the top end of the riving knife shown in fig. 2 viewed obliquely from below.

As shown in fig. 3, the main body 10 is provided at an end in the axial direction and has a1 st pressing surface 51 and a2 nd pressing surface 52.

The 1 st pressing surface 51 is provided around the through hole 20 at the tip of the main body 10. The 1 st pressing surface 51 is a part of the surface of the bottle neck portion 13, and is, for example, curved.

The 2 nd pressing surface 52 is provided between the through hole 20 and the 1 st pressing surface 51. The 2 nd pressing surface 52 is a part of the surface of the bottle neck portion 13, and is continuous with the 1 st pressing surface 51.

As described later, the 1 st pressing surface 51 and the 2 nd pressing surface 52 are surfaces for pressing the filament against the lead frame in wire bonding. For example, the 1 st pressing surface 51 is a pressing surface on which the main joint is formed, and the 2 nd pressing surface 52 is a pressing surface on which the temporary joint is formed.

The shape of the 1 st pressing surface 51 and the 2 nd pressing surface 52 will be described in more detail.

Fig. 4(a), 4(b), and 5 are schematic cross-sectional views illustrating the tip end of the weld chopper according to the present embodiment.

FIG. 4(a) shows a cross section on the line A1-A2 shown in FIG. 3. That is, fig. 4(a) shows a cross section on a plane parallel to the axial direction Da. Fig. 4(B) illustrates a cross section enlarging a region B shown in fig. 4 (a).

As shown in fig. 4(b), the through hole 20 has a tapered hole 21 and a linear hole 22. The tapered hole 21 is provided on the tip end side of the linear hole 22 and connected to the linear hole 22. The diameter of the tapered hole 21 increases toward the distal end side.

The 1 st pressing surface 51 has a1 st inclined surface 51s provided around the through hole 20. The 1 st inclined surface 51s is inclined with respect to the axial direction Da and the radial direction (the direction perpendicular to the axial direction Da). The diameter of the 1 st inclined surface 51s decreases toward the distal end of the main body 10. That is, the distance between the central axis 20a of the through hole 20 and the 1 st inclined surface 51s becomes shorter in the distal direction. In this example, the cross-sectional shape of the 1 st inclined surface 51s in fig. 4(b) includes a curved portion, but may be linear or may be composed of a straight line and a curved line.

The 2 nd pressing surface 52 has a tapered surface 52t and a2 nd inclined surface 52 f.

The tapered surface 52t is provided around the through hole 20 between the 1 st inclined surface 51s and the through hole 20. The tapered surface 52t is a portion of the 2 nd pressing surface 52 that faces the tapered hole 21. The tapered surface 52t has a tapered shape expanding toward the tip. That is, the distance between the central axis 20a of the through hole 20 and the tapered surface 52t becomes longer in the distal direction.

The 2 nd inclined surface 52f is provided between the tapered surface 52t and the 1 st inclined surface 51 s. The 2 nd inclined surface 52f is a surface continuous with the tapered surface 52t and the 1 st inclined surface 51s, and is located on the tip end side of the neck portion 13. In this example, the 2 nd inclined surface 52f extends along a plane perpendicular to the axial direction Da (that is, θ 1, which will be described later, is 0 °). However, the 2 nd inclined surface 52f may also be slightly inclined from a plane perpendicular to the axial direction Da (θ 1 > 0).

In the present embodiment, the surface of the 1 st pressing surface 51 is formed to be rougher than the surface of the 2 nd pressing surface 52. That is, the 2 nd inclined surface 52f and the tapered surface 52t are smoother than the 1 st inclined surface 51 s. The uneven shape of the surface of the 2 nd inclined surface 52f is smaller than the uneven shape of the surface of the 1 st inclined surface 51s, and the uneven shape of the surface of the tapered surface 52t is smaller than the uneven shape of the surface of the 1 st inclined surface 51 s. Specifically, the square average square root slope (R Δ q) of the roughness curve element of the 2 nd inclined surface 52f is smaller than the square average square root slope (R Δ q) of the roughness curve element of the 1 st inclined surface 51 s. For example, the square average square root slope (R Δ q) of the roughness curve element of the tapered surface 52t is smaller than the square average square root slope (R Δ q) of the roughness curve element of the 1 st inclined surface 51 s. The square average square root slope (R Δ q) of the roughness curve element represents the surface roughness, and is a parameter corresponding to the magnitude of the slope of the roughness.

Fig. 5 illustrates a further enlarged view of the cross-section of fig. 4 (b). In the example shown in fig. 5, the diameter of the 2 nd inclined surface 52f becomes smaller toward the tip end side of the main body 10. That is, the distance between the central axis 20a of the through hole 20 and the 2 nd inclined surface 52f becomes shorter in the distal direction. For example, the intersection (intersection) of the tapered surface 52t and the 2 nd inclined surface 52f is located at the uppermost end of the main body 10.

As shown in fig. 5, the angle θ 1 is smaller than the angle θ 2. Here, the angle θ 1 is an angle formed by the plane P1 perpendicular to the axial direction Da and the 2 nd inclined surface 52 f. The angle θ 2 is an angle formed by a plane P1 perpendicular to the axial direction Da and the 1 st inclined plane. The angle θ 1 is preferably 0 degree or more and 11 degrees or less. The angle θ 2 is preferably 2 degrees or more and 45 degrees or less, for example.

Next, the joining using the welding chopper (second welding) will be described.

The filament BW passing through the through hole 20 of the chopper 110 is first soldered to an electrode or the like of a semiconductor element not shown. Thereafter, the chopper 110 is pulled to the lead wire 200 along a predetermined trajectory to form the loop filament BW. Next, second bonding for bonding the filament BW to the lead 200 is performed. A second soldering state of bonding the lead 200 of the lead frame and the filament BW is shown in fig. 6.

The lead frame used in this embodiment is, for example, a roughened lead frame. That is, the surface of the lead 200 is provided with a thick Ni plating layer or the like subjected to roughening treatment. The thickness of the plating layer is, for example, about 20 μm. In addition, copper is used as the filament BW material, for example.

In the second bonding, the riving knife 110 is pressed onto the lead 200. Thereby, the filament BW is sandwiched between the 1 st pressing surface 51 (the 1 st inclined surface 51s) and the lead 200. The filament BW is sandwiched between the 2 nd pressing surface 52 and the lead 200.

Since the 1 st inclined surface 51s is inclined toward the 2 nd inclined surface 52f, the interval between the 1 st inclined surface 51s and the lead wire 200 is narrowed in a direction toward the inside of the riving knife 110. Thus, the thickness of the filament BW sandwiched between the 1 st inclined surface 51s and the lead wire 200 becomes thinner in the direction toward the inside of the riving knife 110.

Also, the thickness of the filament BW is thinnest between the 2 nd inclined surface 52f and the lead wire 200. Since the tapered surface 52t has a tapered shape, the interval between the tapered surface 52t and the lead wire 200 is widened toward the inside of the riving knife 110. Accordingly, the thickness of the filament BW sandwiched between the tapered surface 52t and the lead wire 200 becomes thicker in a direction toward the inside of the riving knife 110.

In this way, ultrasonic waves, for example, are applied to the riving knife 110 in a state where the thin wire BW is sandwiched between the riving knife 110 and the lead wire 200. Thereby, the filament BW is crimped to the lead 200. The present joint (stitch bond SB) is formed between the 1 st pressing surface 51 (1 st inclined surface 51s) and the lead 200, and the temporary joint (tail bond TB) is formed between the 2 nd pressing surface 52 (2 nd inclined surface 52f and tapered surface 52t) and the lead 200.

After the crimping of the filament BW, the chopper 110 is raised in a state where the filament BW is held by the chopper 110. Thus, the filament BW is cut off from the tail weld TB. For example, since the intersection (intersection) of the 2 nd inclined surface 52f and the tapered surface 52t is formed to be relatively sharp, the filament BW is cut at a portion pressed by the intersection.

Fig. 7(a) and 7(b) are photographs illustrating the bonding wire and the lead wire 200. Fig. 7(a) and 7(b) show the joint portion after the second welding.

As shown in fig. 7(a), after the second welding using the riving knife 110 according to the present embodiment, the wire BW is joined to the lead 200 and cut from the tail welding portion TB.

In such second bonding, when a roughened lead frame is used, the filament is easily embedded in the lead when the riving knife is pressed against the lead. Therefore, the bonding strength may be deteriorated and the filament cutting property may be deteriorated.

Fig. 7(b) illustrates a problem occurring when the cuttability of the filament is deteriorated. When the cutting property of the filament is deteriorated, as shown in a region C of fig. 7(b), a part of the joint portion (for example, a stitch-type welded portion SB) may be peeled off at the time of cutting the filament, and a defect called fishtail welding may occur.

In contrast, in the riving knife 110 according to the present embodiment, the 1 st inclined surface 51s having a rough surface state is provided at the tip end of the riving knife 110. Therefore, the filament BW can be efficiently pressed against the lead 200 by the 1 st inclined surface 51 s. Accordingly, the joint strength of the stitch-bonding portion SB can be ensured.

In the riving knife 110 according to the present embodiment, the top end of the riving knife 110 is provided with the smooth 2 nd inclined surface 52f and the tapered surface 52 t. The filament BW is pressed against the lead wire 200 by the 2 nd inclined surface 52f and the tapered surface 52 t. Therefore, compared to the case where the 2 nd inclined surface 52f is not provided, the contact area between the riving knife 110 and the filament BW is increased, and the joining strength of the tail welding portion TB can be improved.

In addition, when the filament is cut after the joining, the filament BW is pressed by the rough 1 st inclined surface 51s, and the sliding of the filament BW and the riving knife 110 is promoted by the smooth 2 nd inclined surface 52 f. This can improve the filament cutting performance.

Fig. 8(a) is a conceptual diagram illustrating the cleaver action when cutting a filament. Fig. 8(a) shows an enlarged cross section of the contact area of the riving knife 110 and the filament BW in the vicinity of the boundary between the 1 st inclined surface 51s and the 2 nd inclined surface 52 f. This region corresponds to a filament cut portion of the filament BW, that is, the thinnest portion of the filament BW.

The left side of the riving knife 110 in the figure corresponds to the 1 st inclined surface 51s having a larger R Δ q (square mean square root slope) and the right side corresponds to the 2 nd inclined surface 52f having a smaller R Δ q. The larger the R Δ q of the concave-convex shape, the larger the concave-convex gradient with respect to the filament surface. That is, for example, the angle θ 3 shown in fig. 8(a) is larger than the angle θ 4.

When cutting the filament BW, ultrasonic waves are applied in a state where the chopper 110 is in contact with the filament BW as shown in fig. 8 (a). Thereby applying a force to the riving knife 110. For example, a horizontal force (vector F1) is applied to the 1 st inclined surface 51s, and a horizontal force (vector F2) is applied to the 2 nd inclined surface 52F. Here, for convenience of explanation, the magnitude and direction of the vector F1 are the same as those of the vector F2.

For example, vector F2 can be decomposed into vector F21 and vector F22. The vector F21 is a vector in the direction toward the surface of the 2 nd inclined surface 52F. Vector F22 is a vector perpendicular to the direction of vector F21. Here, the smaller R Δ q, the larger vector F21. That is, the smaller R Δ q, the larger the upward component as the vector F21. Therefore, the force transmitted from the surface of the riving knife 110 to the filament BW becomes small. Accordingly, the tensile force FT2 generated by the 2 nd inclined surface 52f having a small R Δ q against the filament BW is small.

Similarly, vector F1 can be decomposed into vector F11 and vector F12. The vector F11 is a vector in the direction toward the surface of the 1 st inclined surface 51 s. Vector F12 is a vector perpendicular to the direction of vector F11. Since R Δ q is large on the 1 st inclined surface 51s, the component biased upward is small as the vector F11. Therefore, the tensile force FT1 generated by the 1 st inclined surface 51s having a large R Δ q against the filament BW is relatively large.

In the riving knife 110 according to the present embodiment, the 1 st inclined surface 51s having a large R Δ q and the 2 nd inclined surface 52f having a small R Δ q are provided adjacent to each other. Therefore, a large stress is generated in the filament-cut portion located in the vicinity of the boundary between the 1 st inclined surface 51s and the 2 nd inclined surface 52f due to the difference between the tension FT1 and the tension FT 2. Therefore, as shown in fig. 8(a), the generation of micro cracks is promoted in the vicinity of the boundary between the 1 st inclined surface 51s and the 2 nd inclined surface 52 f. Among the generated micro cracks, the deformation form of the micro cracks is a pattern I (open pattern) as shown in fig. 8 b. As a result, cracks develop in the region D of fig. 8(a), and the cutting performance of the filament can be improved. As a result, the occurrence of defects such as peeling can be suppressed.

Further, since the surface of the roughened lead frame is relatively rough, the tip of the riving knife is easily worn by the pressing of the riving knife. In contrast, the 2 nd inclined surface 52f is provided substantially parallel to the surface of the lead 200. Since R Δ q of the 2 nd inclined surface 52f is small, the tip angle θ 5 of the convex portion of the 2 nd inclined surface 52f is large as shown in fig. 8 (a). For example, the tip angle θ 5 is larger than the tip angle θ 6 of the convex portion of the 1 st inclined surface 51 s. Therefore, stress concentration at the tip of the riving knife 110 can be suppressed, and abrasion of the riving knife can be suppressed.

Hereinafter, an example of the chopper 110 according to the present embodiment will be described with reference to the evaluation results of the welding chopper.

In the present specification, the uneven shape (R Δ q, Rz, Rc, Rsk, Rp, Rku, etc.) of the surface of the chopper is calculated according to JIS (japanese industrial standards) B0601-2001. In each evaluation, the roughness curve was measured under the following conditions. The roughness was calculated from the measurement result of the roughness curve.

The measuring instrument: laser microscope (OLS 4000, manufactured by Olympus of Japan)

Measurement magnification: 50 times of

Evaluation length: 125-400 mu m

Cutoff (phase compensation type high-pass filter) λ c: 25 μm

Fig. 9 is a diagram illustrating the evaluation results of the welding chopper.

Fig. 9 shows evaluation results of examples (comparative examples 1 to 4 and examples 1 to 8) in which combinations of the square average square root slopes R Δ q (°) of the roughness curve elements of the 1 st inclined surface 51s and the square average square root slopes R Δ q (°) of the roughness curve elements of the 2 nd inclined surface 52f are different. In this evaluation, R Δ q of the 1 st inclined surface 51s was set to 5.4 ° to 12.4 °. The R.DELTA.q of the 2 nd inclined surface 52f is set to 1.8 DEG to 13.4 deg. R Δ q of the tapered surface 52t is made the same as R Δ q of the 2 nd inclined surface 52 f.

The square average square root slope R Δ q of the roughness curve element can be calculated by the following formula (1). l is the reference length and Z (x) is the roughness profile upper value.

Formula 1

in comparative examples 1 to 4 and examples 1 to 8 shown in fig. 9, the number of samples was made 32 or 128 "○" indicating that peeling occurred in 32 samples, that is, "○" indicating that peeling did not occur in 32 samples ". ◎" indicating that peeling did not occur in 32 samples, but if the number of samples was increased, ". ◎" indicating that peeling occurred was 1/127 or more and less than 1/32 ". x" indicating that peeling did not occur in 128 samples, that is, "-" indicating that peeling occurred in less than 1/128.

As in comparative examples 1 to 3, it is known that peeling is likely to occur when both R Δ q of the 1 st inclined surface 51s and R Δ q of the 2 nd inclined surface 52f are relatively large or small.

On the other hand, as in examples 1 to 8, when R Δ q of the 1 st inclined surface 51s is 8 ° or more and R Δ q of the 2 nd inclined surface 52f is 5 ° or less, the frequency of occurrence of peeling is low. In addition, as in examples 7 and 8, when R Δ q of the 1 st inclined surface 51s is 11 ° or more and R Δ q of the 2 nd inclined surface 52f is 2 ° or less, the occurrence of peeling can be further suppressed. This is considered because, as described with reference to fig. 8(a) and 8(b), the tensile force of the 1 st inclined surface 51s is large and the tensile force of the 2 nd inclined surface 52f is small. At the filament-cutting portion, the generation of micro-cracks is promoted, and the deformation form of the micro-cracks is a mode I (open mode), and cracks develop. This improves the filament cutting performance.

Further, when R Δ q of the 1 st inclined surface 51s is 11 ° or more and R Δ q of the 2 nd inclined surface 52f is 2 ° or less, even if the welding chopper is worn, it is easy to keep the difference between R Δ q of the 1 st inclined surface 51s and R Δ q of the 2 nd inclined surface 52f constant or more. Therefore, the stress generated in the filament BW due to the difference in the tensile force can be maintained.

Fig. 10 is a diagram showing the evaluation results when the width W1 of the 2 nd inclined surface 52f changes with respect to the top end diameter T of the riving knife 110.

Here, the width W1 of the 2 nd inclined surface 52f is the width of the 2 nd inclined surface 52f when the riving knife 110 is viewed in the axial direction. The 2 nd inclined surface 52f has an annular shape having an outer diameter D1 and an inner diameter D2 when viewed in the axial direction (see fig. 4 a and 4 b). At this time, the width W1 is 1/2 times the difference between the outer diameter D1 and the inner diameter D2. When the outer diameter varies in the circumferential direction, the average value of the outer diameter D1 in the circumferential direction may be used. When the inner diameter varies in the circumferential direction, the average value in the circumferential direction may be used as the inner diameter D2.

The top end diameter T of the riving knife 110 is the outer diameter of the annular 1 st inclined surface 51s (the 1 st pressing surface 51) when viewed in the axial direction. Specifically, for example, the outer diameter of the 1 st inclined surface 51s is the diameter of an imaginary circle Cr formed by the intersection of an extension of the outer peripheral surface of the neck portion 13 and a plane including the 2 nd inclined surface 52f (see fig. 4 a and 4 b).

in the present evaluation, regarding the ratio of the width W1 with respect to the tip diameter T shown in fig. 10, the number of samples was made 32 "○" indicating that peeling did not occur, that is, "○" indicating that peeling occurred less than 1/32. "x" indicating that peeling occurred, that is, ". x" indicating that peeling occurred at a frequency of 1/32 or more, and a filament having a diameter of 25 μm was used for the evaluation, the tip diameter T of the cleaver 110 was 75 μm.

As is clear from the evaluation results shown in fig. 10, when the ratio of the width W1 to the tip diameter T is 2% or more and 8% or less, peeling does not occur. That is, the width W1 of the 2 nd inclined surface 52f is preferably 2% to 8% of the tip diameter T. When the ratio of the width W1 to the tip diameter T is greater than 8%, it is difficult to generate sufficient stress at the tip of the riving knife 110, and the joining strength is reduced. On the other hand, when the ratio of the width W1 to the tip diameter T is less than 2%, the stress generated at the tip of the riving knife 110 is large, and the tip of the riving knife 110 is easily worn. In the embodiment, the ratio of the width W1 to the tip diameter T is 2% or more and 8% or less, whereby sufficient bonding strength can be obtained while suppressing wear of the riving knife 110.

Fig. 11 shows the evaluation results of examples (comparative examples 5 to 9 and examples 9 to 14) of different combinations of the maximum height Rz of the 1 st inclined surface 51s and the maximum height Rz of the 2 nd inclined surface 52 f. The maximum height Rz of the tapered surface 52t is set to be the same as the maximum height Rz of the 2 nd inclined surface 52 f. The maximum height Rz is the sum of the maximum value of the peak height and the maximum value of the valley depth at the reference length.

fig. 11 shows the evaluation result of the occurrence frequency of the peeling failure, and the term "peeling occurrence frequency" shows the occurrence frequency of peeling after the second welding, that is, in each example (each condition), "○" shows that peeling did not occur in 128 samples, "o" shows that peeling did not occur in 32 samples, and "x" shows that peeling occurred in 32 samples.

as is clear from the evaluation results shown in fig. 11, when the maximum height Rz of the 1 st inclined surface 51s is 0.2 μm or more and the maximum height Rz of the 2 nd inclined surface 52f is 0.16 μm or less, the frequency of occurrence of peeling is ". o", and, as in examples 13 and 14, when the maximum height Rz of the 1 st inclined surface 51s is 0.3 μm or more and the maximum height Rz of the 2 nd inclined surface 52f is 0.10 μm or less, the frequency of occurrence of peeling is "◎".

Since the maximum height Rz of the 1 st inclined surface 51s is 0.2 μm or more, the filaments BW can be suppressed by the 1 st inclined surface 51s, and therefore, sufficient bonding strength can be obtained. Further, since the maximum height Rz of the 2 nd inclined surface 52f and the maximum height Rz of the tapered surface 52t are 0.16 μm or less, respectively, the sliding of the wire BW and the weld chopper is promoted. This can improve the cutting property of the filament BW. This can suppress the occurrence of peeling failure. Further, when the maximum height Rz of the 1 st inclined surface 51s is 0.3 μm or more and the maximum height Rz of the 2 nd inclined surface 52f is 0.10 μm or less, the maximum height Rz can be maintained at a constant value or more even if the riving knife is worn. Thus, as described above, the filament cutting performance can be improved.

Fig. 12 shows the evaluation results when the angle θ 1 of the 2 nd inclined surface 52f (see fig. 5) is changed. In this evaluation, the angle θ 1 was set to 0.5 degrees or more and 17 degrees or less. The angle θ 2 of the 1 st inclined surface was set to 20 degrees, and the width W1 of the 2 nd inclined surface 52f was set to 4 μm.

similarly to the description of fig. 9, the term "frequency of occurrence of peeling" in fig. 12 indicates the frequency of occurrence of peeling after the second welding, that is, when the number of samples for each condition of the angle θ 1 was evaluated as 32, a "○" indicates that peeling did not occur, and an "x" indicates that peeling occurred.

Preferably, the angle θ 1 is smaller than the angle θ 2. This enables the 2 nd inclined surface 52f to press the filament during temporary joining, thereby improving the joining strength of the tail welding portion. As is clear from the evaluation results shown in fig. 12, when the angle θ 1 is 0.5 degrees or more and 11 degrees or less, no peeling failure occurs. If the angle θ 1 is 11 degrees or less, the filament can be pressed by the 2 nd inclined surface 52f at the time of temporary bonding. This can generate stress that can obtain sufficient bonding strength of the tail wire welding portion. Thus, the occurrence of peeling failure can be suppressed.

Fig. 13(a) and 13(b) are diagrams illustrating a weld chopper according to the embodiment.

Fig. 13(a) and 13(b) show the tip (the 1 st pressing surface 51 and the 2 nd pressing surface 52) of the weld chopper 110 as viewed in the axial direction. Fig. 13(a) is a laser microscope image, and fig. 13(b) is a plan view corresponding to fig. 13 (a).

As shown in fig. 13(B), a boundary B1 between the 1 st inclined surface 51s and the 2 nd inclined surface 52f is, for example, a substantially circular shape centered on the central axis 20 a. However, the shape of the boundary B1 is not a perfect circle (or an ellipse) but a zigzag (zigzag, zigzag line) when viewed in the axial direction. That is, the distance L1 from the center axis 20a to a point on the boundary B1 changes along the circumferential direction Dc. Specifically, the points on the boundary B1 are dispersed within a range of, for example, 1.5 μm from a circle (or ellipse) approximated (or smoothed) to the shape of the boundary B1.

As described with reference to fig. 8(a) and 8(B), the filament BW receives a large stress from the riving knife in the vicinity of the boundary B1 where the 1 st inclined surface 51s and the 2 nd inclined surface 52f contact. As shown in fig. 13(a) and 13(B), since the boundary B1 is zigzag, the boundary B1 further contacts the filament BW. That is, the contact portion of the boundary B1 with the filament BW, which generates a large stress on the filament BW, increases. As a result, for example, when an ultrasonic wave is applied, stress is repeatedly generated in the filament BW. This makes it easy to cause micro cracks, and improves the ability to cut the filaments.

Fig. 14 shows the results of the determination of the bonding strength in examples (comparative examples 10 to 12, examples 15 to 20) in which the uneven shape of the 1 st inclined surface 51s is different. In this evaluation, the 1 st inclined surface 51s had an uneven shape, and the average height Rc of the roughness curve element, the skewness Rsk of the roughness curve, and the maximum peak height Rp of the roughness curve were changed.

The average height Rc is obtained by the following formula (2). The skewness Rsk is obtained by the following equation (3).

Formula 2

Formula 3

In the formula (2), m is the number of contour curve elements, and Zti is the average value of the heights of the contour curve elements. In the formula (3), Zq is the square average square root height, and Zn is the height value on the roughness curve. The maximum peak height Rp is the maximum of the height on the roughness curve.

The skewness Rsk represents the symmetry between the peaks (projections) and the valleys (depressions) of the concave-convex shape. If the concavo-convex shape is a sine distribution, the skewness Rsk becomes 0. A negative skewness Rsk indicates that the area of the peak (convex) is larger than the area of the valley (concave) (the sharpness of the convex is smaller than that of the concave).

Fig. 14 shows the average height Rc, skewness Rsk, and maximum peak height Rp in each example (each condition). In this evaluation, the bonding strength was determined from the process capability index Cpk of the bonding strength. In each example shown in fig. 14, when the average bonding strength of the filament BW is Ave and the lower limit criterion of the bonding strength is 3 gram weight (gf), the calculation is performed by Cpk ═ (Ave-3gf)/3 σ. The joint strength is the strength of the tensile test in the second weld. The number of samples was 30. Generally, Cpk of bonding strength in wire bonding is required to be 1.67 or more.

In the term "bonding strength determination" in fig. 14, "yes" indicates that Cpk is 1.67 or more, and "no" indicates that Cpk is less than 1.67. In each example (each combination of Rc, Rsk, and Rp), the determination was initially made after 50 ten thousand, 100 ten thousand, and 150 ten thousand wire bonds.

In examples 15 to 20 and comparative examples 10 to 12, the initial bonding strength determinations were all yes. After 50 ten thousand wire bonds, although examples 15 to 20 were "yes", comparative examples 10 to 12 were all "no". After 100 ten thousand wire bonds, examples 15 to 17, 19 and 20 were "yes", and example 18 and comparative examples 10 to 12 were "no". After 150 ten thousand wire bonds, examples 19 and 20 are "yes" and examples 15 to 18 and comparative examples 10 to 12 are "no".

From the above results, it is preferable that the skewness Rsk of the 1 st inclined surface 51s is about-1.2 or more and-0.3 or less, and the average height Rc of the 1 st inclined surface 51s is 0.06 μm or more and 0.3 μm or less. If the average height Rc is less than 0.06 μm, the clamping force is small, and sufficient bonding strength cannot be obtained particularly when the filament BW of a copper wire is used. In addition, if the average height Rc exceeds 0.3. mu.m, it becomes difficult to form irregularities of-0.3 or less as the skewness Rsk. More preferably, the skewness Rsk of the tip surface 50 is about-1.2 or more and-0.43 or less, and the average height Rc of the tip surface 50 is 0.16 μm or more and 0.3 μm or less. Thus, the initial bonding strength can be maintained even after 150 ten thousand times from the initial welding.

The maximum peak height Rp of the 1 st inclined surface 51s is preferably 0.9 times or less (Rp/Rc. ltoreq.0.9) the average height Rc. In addition, Rp/Rc may be 0.5 times or more. When Rp/Rc exceeds 0.9, it is difficult to maintain the initial bonding strength for a long period of time. On the other hand, if Rp/Rc is 0.9 or less, the shape change accompanying wear during use is small, and the initial bonding strength can be maintained for a long period of time.

Fig. 15 shows the evaluation results of examples (comparative examples 13 and 14, and examples 21 to 23) in which the crest factor Rku of the roughness curve of the 2 nd inclined surface 52f is different. The kurtosis Rku was obtained by the following formula (4).

Formula 4

Rq is the square average square root height of the roughness curve, lr is the base length, and Z (x) is the roughness curve (height of the peak). That is, kurtosis (Rku) is a value of a quad-mean of Z (x) over a reference length divided by a quad-mean of square root of the square mean. Kurtosis Rku represents the "sharpness" of the roughness curve. The larger Rku is, the sharper the surface irregularities are.

similarly to the description of fig. 9, the term "frequency of occurrence of peeling" in fig. 15 indicates the frequency of occurrence of peeling after the second welding, that is, when the number of samples in each example was evaluated as 32, a "○" indicates that peeling did not occur, and an "x" indicates that peeling occurred.

As is clear from the results of fig. 15, the 2 nd inclined surface 52f preferably has a kurtosis Rku of 5.0 or less, more preferably 3.0 or less. Since the crest factor Rku of the 2 nd inclined surface 52f is 5 μm or less, the slippage of the filament BW and the 2 nd inclined surface 52f is promoted when the filament is cut. This can improve the filament cutting performance.

The embodiments of the present invention have been described above. However, the present invention is not limited to these descriptions. The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention. For example, the shape, size, material, arrangement, and the like of each element provided in the through hole, the 1 st pressing surface, the 2 nd pressing surface, and the like are not limited to those exemplified, and can be appropriately modified. In addition, each element included in each of the above embodiments may be combined as long as the technical feasibility is achieved, and a technique of combining these elements is included in the scope of the present invention as long as the feature of the present invention is included.

According to the aspect of the present invention, it is possible to provide a welding chopper which can improve the joining strength, improve the cutting performance of the wire, and suppress the abrasion.

Claims

1. A welding chopper is provided with a body part and is provided with:

a through hole penetrating the filament;

a1 st pressing surface that presses the filament, the 1 st pressing surface being provided around the through hole and having a1 st inclined surface that is inclined with respect to an axial direction in which the through hole extends;

and a2 nd pressing surface for pressing the filament, the pressing surface having a tapered surface provided between the 1 st inclined surface and the through hole, and a2 nd inclined surface provided between the tapered surface and the 1 st inclined surface,

the square average square root slope of the roughness curve element of the 2 nd inclined plane is smaller than the square average square root slope of the roughness curve element of the 1 st inclined plane,

the square mean square root slope is calculated according to equation (1),

where l is the reference length and Z (x) is the roughness curve upper value.

2. The weld chopper of claim 1,

the inclination of the square average square root of the roughness curve element of the 1 st inclined surface is 8 DEG or more,

the slope of the square average square root of the roughness curve element of the 2 nd inclined surface is 5 ° or less.

3. The weld chopper of claim 1 or 2,

the inclination of the square average square root of the roughness curve element of the 1 st inclined surface is 11 DEG or more,

the slope of the square average square root of the roughness curve element of the 2 nd inclined surface is 2 ° or less.

4. The weld riving knife of claim 1 or 2 wherein the width of the 2 nd inclined surface is 2% or more and 8% or less of the outer diameter of the 1 st pressing surface when viewed in the axial direction.

5. The weld chopper of claim 1 or 2,

the maximum height Rz of the 1 st inclined surface is 0.2 μm or more,

the maximum height Rz of the 2 nd inclined surface is 0.16 μm or less.

6. The weld chopper of claim 1 or 2,

the maximum height Rz of the 1 st inclined surface is 0.3 μm or more,

the maximum height Rz of the 2 nd inclined surface is 0.10 μm or less.

7. The weld chopper of claim 1 or 2, wherein an angle formed by a perpendicular surface perpendicular to the axial direction and the 2 nd inclined surface is smaller than an angle formed by the perpendicular surface perpendicular to the axial direction and the 1 st inclined surface.

8. The weld chopper of claim 1 or 2, wherein an angle formed by a plane perpendicular to the axial direction and the 2 nd inclined plane is 11 degrees or less.

9. The weld riving knife of claim 1 or 2 wherein the boundary of the 1 st inclined surface and the 2 nd inclined surface is serrated when viewed along the axial direction.

10. The weld chopper of claim 1 or 2,

the skewness of the 1 st inclined surface is less than-0.3,

the 1 st inclined surface has an average height of 0.06 to 0.3 μm.

11. The weld chopper of claim 1 or 2, wherein the 2 nd inclined surface has a kurtosis of 5.0 or less.