Semiconductor device and method for manufacturing semiconductor device

Abstract

The present invention relates to a semiconductor device and a method for manufacturing the same. In wire bonding using ultrasonic bonding, the stability of the thickness of the wire at the joint between the wire and the lead frame is improved. The semiconductor device comprises: a lead frame (8) on which a semiconductor element (6) is mounted; and a metal wire (3) joined to the lead frame (8). The lead frame (8) has a step portion (11) on the surface to which the wire (3) is joined, i.e., the first main surface, and the step portion (11) has a height greater than or equal to 5 μm and less than or equal to 20 μm relative to the joining position of the wire (3).

Description

Technical Field

[0001] The present invention relates to a semiconductor device and a method for manufacturing the same, and in particular, to a semiconductor device having a structure in which a metal wire is bonded to a lead frame on which a semiconductor element is mounted. Background Art

[0002] In the manufacture of semiconductor devices such as power semiconductor devices, wire bonding by ultrasonic bonding is performed as a wiring method between a semiconductor element and a lead frame or between different semiconductor elements. This ultrasonic bonding is performed by applying ultrasonic waves (US) while applying heat and load to a wire made of a metal such as gold, silver, or copper, thereby bonding the wire to a component to be bonded (for example, Patent Document 1 listed below).

[0003] Ultrasonic bonding is performed by bringing the wire extending from the capillary mounted on the ultrasonic horn into contact with the joined part and vibrating the ultrasonic horn in an arc motion. For example, the wiring between a semiconductor element and a lead frame is performed by the following process. First, the first (1st) bonding is performed, that is, a free air ball (FAB) is formed by discharge at the front end of the wire passing through the capillary, and the free air ball is bonded to the chip of the semiconductor element, thereby forming a ball bond. Next, the second (2nd) bonding is performed, that is, while the wire is extended from the capillary, the capillary is moved onto the lead frame, and the wire is bonded to the lead frame, thereby forming a seam weld bond. Finally, the capillary is lifted and the wire is pulled up, thereby pulling off the wire at the part where the thickness of the wire is thinned by the load during the second bonding and cutting it. At this time, in order to form a free air ball used in the first bonding of the next wiring, a certain length of wire called the tail remains in the capillary.

[0004] Patent Document 1: Japanese Patent Application Publication No. 2001-144132

[0005] As described above, the wire is cut in the wire bonding using ultrasonic bonding by pulling off the wire at the portion where the thickness of the wire becomes thinner due to the second bonding. Therefore, the quality of the seam weld bond formed in the second bonding is affected by the thickness of the wire in the bonding portion formed by the second bonding. Therefore, it can be considered that in order to improve the quality of the seam weld bond, it is effective to improve the stability of the thickness of the wire in the bonding portion formed by the second bonding. If the quality of the seam weld bond deteriorates, not only will the seam weld bond be poorly bonded, but the length of the tail will also become unstable, which will also have an adverse effect on the quality of the ball bond formed in the first bonding of the next wiring. Therefore, improving the quality of the seam weld bond is an important issue. Summary of the invention

[0006] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to improve the stability of the thickness of the wire at the bonding portion between the wire and the lead frame in wire bonding using ultrasonic bonding.

[0007] The semiconductor device involved in the present invention comprises: a lead frame, which is equipped with a semiconductor element; and a metal wire, which is joined to the lead frame, and the lead frame has a step portion on the surface to which the wire is joined, that is, the first main surface, and the step portion has a height greater than or equal to 5μm and less than or equal to 20μm relative to the joining position of the wire.

[0008] Effects of the Invention

[0009] According to the present invention, in wire bonding using ultrasonic bonding, bonding between the wire and the lead frame is performed with the tip of the capillary in contact with the step portion, thereby improving the stability of the thickness of the wire at the bonding portion. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is a diagram for explaining the wire bonding process.

[0011] Figure 2 This is a diagram showing an example of wiring between a semiconductor element and a lead frame.

[0012] Figure 3 This is a diagram for explaining tail molding after the second bonding.

[0013] Figure 4 This is a diagram for explaining the structure and manufacturing method of the semiconductor device according to the first embodiment.

[0014] Figure 5 This is a diagram for explaining the structure and manufacturing method of the semiconductor device involved in the second embodiment.

[0015] Figure 6 This is a diagram showing a structural example of the vicinity of a wire bonding position on the first main surface of a lead frame of a semiconductor device according to the second embodiment.

[0016] Figure 7 is a cross-sectional view of the front end of the capillary.

[0017] Figure 8 This is a diagram showing a structural example of the vicinity of a wire bonding position on the first main surface of a lead frame of a semiconductor device according to the second embodiment.

[0018] Fig. 9 It is a plan view of the lead frame of the semiconductor device according to the second embodiment, and the vicinity of the wire bonding position.

[0019] Fig.10This is a diagram for explaining the structure and manufacturing method of the semiconductor device involved in the third embodiment.

[0020] Fig.11 This is a diagram showing a structural example of the vicinity of a wire bonding position on the second main surface of a lead frame of a semiconductor device according to a third embodiment.

[0021] Fig.12 This is a diagram showing a structural example of the vicinity of a wire bonding position on the first main surface of a lead frame of a semiconductor device according to a fourth embodiment.

[0022] Fig.13 It is a plan view of the lead frame of the semiconductor device according to the fourth embodiment, and the vicinity of the wire bonding position. DETAILED DESCRIPTION

[0023] <Implementation method 1>

[0024] First, the bonding process of metal wires by ultrasonic bonding is described. Figure 1 As shown, the wire 3 to be bonded passes through the capillary 2 attached to the front end of the ultrasonic horn 1 and extends from the front end of the capillary 2. In addition, a spark rod 5 extending toward the wire 3 extending from the capillary 2 is provided.

[0025] Before the first bonding, the spark rod 5 is ignited toward the front end of the wire 3, and discharge is performed at the front end of the wire 3, thereby forming a free air ball 4 at the front end of the wire 3. Then, the ultrasonic horn 1 and the capillary 2 are moved in the vertical direction (Z direction) to press the free air ball 4 against the semiconductor element 6 ( Figure 2 ). Then, by applying ultrasonic waves from the ultrasonic horn 1 to the free air ball 4 in a state where the semiconductor element 6 is sufficiently heated, the first bonding of the wire 3 to the semiconductor element 6 is performed. At this time, a ball bond is formed at the bonding portion between the wire 3 and the semiconductor element 6. In addition, in this embodiment, as Figure 2 As shown, the semiconductor element 6 is bonded to the lead frame 8 via the die bonding material 7. The lead frame 8 may have a metal plating layer 8a formed on its upper surface as needed from the viewpoint of ensuring bonding with the die bonding material 7.

[0026] Next, while the wire 3 is extended from the capillary 2, the ultrasonic horn 1 and the capillary 2 are moved, a wire loop is formed through the wire 3, and the wire 3 is pressed to the lead frame 8, which is the object of the second bonding. Then, ultrasonic waves are applied to the wire 3 from the ultrasonic horn 1 in a state where the lead frame 8 is sufficiently heated, thereby performing the second bonding of the wire 3 to the lead frame 8 having the metal plating layer 8a. Here, the surface of the lead frame 8 to which the wire 3 is bonded is defined as the "first main surface", and the surface on the back side of the first main surface is defined as the "second main surface".

[0027] After the second bonding, Figure 3 As shown in FIG. 1 , the capillary 2 is raised to pull the wire 3 upward, and the wire 3 is pulled off starting from the portion 3a where the thickness of the wire 3 is reduced by the second bonding, thereby cutting the wire 3. At this time, a crescent-shaped seam weld bond called a new moon is formed at the bonding portion between the wire 3 and the lead frame 8. In addition, the wire 3 remaining on the capillary 2 side (the portion of the wire 3 extending from the capillary 2) becomes the tail 9.

[0028] Through the above bonding process, Figure 2 As shown, wiring between the semiconductor element 6 and the lead frame 8 is formed.

[0029] Figure 4 FIG. 1 is a diagram for explaining the structure and manufacturing method of a semiconductor device according to Embodiment 1. Figure 4 As shown, in the vicinity of the bonding position 10 between the lead frame 8 and the wire 3 during the second bonding, a metal plating layer 8b is further partially formed on the metal plating layer 8a of the lead frame 8, and a step portion 11 is formed at the end of the metal plating layer 8b. The thickness of the metal plating layer 8b is set to be greater than or equal to 5μm and less than or equal to 20μm. That is, the lead frame 8 has a step portion 11 near the bonding position 10 of the wire 3 on the first main surface, and the step portion 11 has a height greater than or equal to 5μm and less than or equal to 20μm relative to the bonding position 10.

[0030] Then, if Figure 4 As shown in FIG. 1 , the second bonding of the wire 3 and the lead frame 8 is performed with the tip of the capillary 2 abutting against the step 11. Thus, during the second bonding, the distance between the lead frame 8 and the capillary 2 at the bonding position 10 of the wire 3 is maintained at a constant value corresponding to the thickness of the metal plating layer 8b.

[0031] Therefore, according to the semiconductor device and the manufacturing method thereof involved in the first embodiment, the following effect is obtained, that is, the stability of the thickness of the wire 3 of the bonding portion formed by the second bonding (the thickness of the thinned portion 3a) is improved, and the quality of the second bonding is improved. In addition, since the quality of the second bonding is stable, the length of the tail portion 9 formed after the second bonding is stabilized, which can also help improve the quality of the ball bond formed in the first bonding of the next wiring.

[0032] In addition, as the material of the capillary 2 used in the present embodiment, alumina or alumina to which zirconium oxide is added is preferable. In addition, the tip of the capillary 2 may be subjected to a polishing finish or a matte finish.

[0033] In the first embodiment, the metal plating layer 8b is partially formed on the first main surface of the lead frame 8, thereby forming the step portion 11 near the bonding position 10 between the lead frame 8 and the wire 3, but the method for forming the step portion 11 is not limited to this. For example, instead of providing the metal plating layer 8b, the metal plating layer 8a at the bonding position 10 of the wire 3 may be partially thinned by etching or cutting to form the step portion 11.

[0034] <Implementation method 2>

[0035] In implementation mode 2, Figure 5 As shown in the figure, at least one groove 12 is formed by stamping near the bonding position 10 between the lead frame 8 and the wire 3 on the first main surface, and the convex parts formed by the bulging of both sides of the groove 12 during the stamping are used as the step part 11. That is, in the second embodiment, the step part 11 is formed on both sides of the groove 12 formed on the first main surface of the lead frame 8. As for the method of forming the groove 12, etching or cutting may be used in addition to stamping.

[0036] The shape of the groove 12 formed on the first main surface of the lead frame 8 when viewed from above may be any shape. Figure 6 As shown, if the groove 12 is formed to be linear in a plan view, the process of forming the groove 12 can be simplified, and the step portion 11 can be formed at low cost.

[0037] The number of grooves 12 may be any number. When a plurality of grooves 12 are formed, the grooves 12 are not overlapped (intersected). The intervals between the grooves 12 may be unequal, but equal intervals are preferred because they suppress the fluctuation in the height of the step portion 11. Figure 7 As shown in FIG. 1 , if the inner diameter of the front end of the capillary 2 is CD and the outer diameter of the front end of the capillary 2 is T, then the interval P1 of the groove 12 preferably satisfies

[0038] (T-CD)×30%≤P1≤(T-CD)×40%···(1)

[0039] relationship.

[0040] In the second embodiment as well, the second bonding of the wire 3 and the lead frame 8 is performed in a state where the tip of the capillary 2 is in contact with the step 11 , thereby obtaining the same effects as those of the first embodiment.

[0041] Here, when bonding wires, the bonded surface (the surface bonded to the wire) needs to be fixed. This is because if the bonded surface is not fixed, the bonded surface will follow the movement of the ultrasonic horn, and the bonding energy cannot be smoothly transmitted to the bonded surface. Usually, the bonded surface is fixed by pressing the bonded component with a clamp, but in recent years, with the miniaturization of products, the wiring of the lead frame has become complicated, and it is sometimes difficult to press the lead frame stably.

[0042] In the second embodiment, the step portion 11 is linear along the groove 12, so the contact between the capillary 2 and the lead frame 8 is linear contact, and the friction between the capillary 2 and the lead frame 8 is reduced compared to the case of the first embodiment. Therefore, when the ultrasonic wave is applied for the second bonding, the following effect can be expected, that is, the movement of the lead frame 8 following the capillary 2 is suppressed, and the reliability of the bonding is further improved.

[0043] exist Figure 6 In the embodiment, the groove 12 formed in the lead frame 8 is shown as a straight line when viewed from above, but for example, it may be Figure 8 As shown, the groove 12 is formed in a circular arc shape (here, a semicircular shape) surrounding the bonding position 10 of the wire 3 when viewed from above. The step portion 11 is formed on both sides of the groove 12, so the shape of the step portion 11 is also in a circular arc shape surrounding the bonding position 10 when viewed from above. When a plurality of grooves 12 are formed, it is preferable to make the arcs of the plurality of grooves 12 concentric and to make the intervals between the grooves 12 equal because the fluctuation in the height of the step portion 11 is suppressed.

[0044] When the grooves 12 are formed into an arc shape, it is also preferable that the interval P1 of the grooves 12 satisfies the relationship of the above-mentioned formula (1). Furthermore, it is preferable that the diameter H1 of the arc formed by the grooves 12 satisfies

[0045] CD×80%+T×15%≤H1≤CD×85%+T×20%···(2)

[0046] relationship.

[0047] Fig. 9 FIG. 1 is a top view of the vicinity of the bonding position 10 of the wire 3 in the lead frame 8 after the second bonding. When the groove 12 is set to an arc shape, it is preferred that the arc is as follows: Fig. 9 The wiring direction of the wire 3 is equivalent to the extension direction of the wire 3 from the first bonding position to the second bonding position. Fig. 9 Indicated by arrows.

[0048] When the groove 12 formed in the lead frame 8 is set to an arc shape, in addition to the same effect as the straight line, the groove 12 can also be used as an identification pattern for the position of the bonding position 10, and the effect of improving the alignment accuracy between the bonding position 10 of the capillary 2 and the wire 3 can also be expected.

[0049] <Implementation method 3>

[0050] In implementation mode 3, Fig.10 As shown, at least one groove 13 is formed by stamping near the bonding position 10 with the wire 3 on the second main surface of the lead frame 8, and the convex portion formed by the back side (second main surface side) of the groove 13 during the stamping is used as the step portion 11. That is, in the second embodiment, the step portion 11 is formed at a position corresponding to the groove 13 formed on the second main surface of the lead frame 8.

[0051] This embodiment is effective when the lead frame 8 is thin (for example, 1 mm or less). Alternatively, the lead frame 8 may be processed to be thin by etching or cutting, and then the groove 13 may be formed by punching.

[0052] In implementation mode 3, Fig.11 As shown, a plurality of arc-shaped (semicircular) grooves 13 are formed on the second main surface of the lead frame 8 so as to surround the bonding position 10 of the wire 3 when viewed from above. However, the shape of the grooves 13 when viewed from above may be any shape such as a straight line. Fig.11 This is a plan view of the vicinity of the bonding position 10 of the wire 3 in the lead frame 8 as seen from the second main surface side.

[0053] The step portion 11 is formed on the back side of the groove 13, so the shape of the step portion 11 is also an arc shape that surrounds the bonding position 10 when viewed from above. When a plurality of grooves 13 are formed, the grooves 13 do not overlap (do not cross) each other. In addition, if the arcs of the plurality of grooves 13 are concentric and the intervals between the grooves 13 are equal, the fluctuation of the height of the step portion 11 is suppressed, which is preferred.

[0054] In addition, if Figure 7 As shown in the figure, the inner diameter of the front end of the capillary 2 is set to CD, and the outer diameter of the front end of the capillary 2 is set to T. Then, the interval P2 of the groove 13 preferably satisfies

[0055] (T-CD)×30%≤P2≤(T-CD)×40%···(3)

[0056] Furthermore, when the groove 13 is set to an arc shape, it is preferred that the diameter H2 of the arc formed by the groove 13 satisfies

[0057] CD×80%+T×15%≤H2≤CD×85%+T×20%···(4)

[0058] relationship.

[0059] In the third embodiment, the same effect as in the second embodiment is obtained. In addition, by forming the step portion 11 by stamping the second main surface of the lead frame 8, the second main surface of the lead frame 8 is prevented from rising. As a result, the second main surface of the lead frame 8 can be brought into contact with the heating portion during the second bonding, and the lead frame 8 can be easily raised to an appropriate temperature. In addition, when the groove 13 is formed into an arc shape, it is preferable that the arc and the lead frame 8 are aligned. Fig. 9 The groove 12 is similarly opened in the opposite direction to the wiring direction of the conductive wire 3 .

[0060] <Implementation method 4>

[0061] In the case of a semiconductor device in which a large current of 3A to 10A or more flows, a plurality of wires 3 may be arranged on one lead frame 8. In the fourth embodiment, it is assumed that a plurality of wires 3 are arranged on one lead frame 8, and the step portions 11 shown in the second or third embodiment are provided at the bonding positions of the plurality of wires 3 in the lead frame 8. In other words, the step portions 11 are provided at a plurality of locations on one lead frame 8, and the second bonding process for bonding the wires 3 to the lead frame 8 is performed at the positions corresponding to the step portions 11 at the plurality of locations. Therefore, the lead frame 8 of the semiconductor device of the fourth embodiment has a structure in which the wires 3 are bonded at the positions corresponding to the step portions 11 at the plurality of locations.

[0062] For example, when the arc-shaped step portions 11 shown in the second embodiment are provided at a plurality of locations of the lead frame 8, as shown in FIG. Fig.12 As shown in FIG. 1 , arc-shaped grooves 12 are provided at a plurality of locations on the first main surface of the lead frame 8. Fig.12 When the arc-shaped slots 12 are arranged in a matrix, the wiring direction of the conductors 3 is set as the column direction (Y direction) of the matrix, and the direction perpendicular to it is set as the row direction (X direction) of the matrix, so that the arc of each slot 12 is open in the column direction (Y direction). Alternatively, in order to prevent interference between the conductors 3, Fig.13 As shown, the wiring direction of the conductor 3 is inclined at about 30 degrees with respect to the opening direction of the groove 12.

[0063] If Figure 7 As shown, the inner diameter of the front end of the capillary 2 is set as CD, and the outer diameter of the front end of the capillary 2 is set as T. It is preferred that the interval P1 of the grooves 12 provided at the bonding position 10 of one wire 3 satisfies the relationship of the above formula (1), and it is preferred that the diameter H1 of the arc formed by the grooves 12 satisfies the relationship of the above formula (2). In addition, it is preferred that the interval P3 between the grooves 12 provided at the bonding positions 10 of two wires 3 adjacent in the X direction (direction perpendicular to the opening direction of the arc formed by the grooves 12) is greater than or equal to 100 μm. It is preferred that the interval P4 between the grooves 12 provided at the bonding positions 10 of two wires 3 adjacent in the Y direction (opening direction of the arc formed by the grooves 12) is greater than or equal to the diameter H1 of the arc formed by the grooves 12.

[0064] exist Fig.12 and Fig.13 , an example is shown in which the step portions 11 shown in the second embodiment (the step portions 11 formed on both sides of the groove 12 on the first main surface) are provided at multiple locations on the lead frame 8, but the step portions 11 shown in the third embodiment (the step portions 11 formed on the back side of the groove 13 on the second main surface) may be provided at multiple locations on the lead frame 8. When the step portions 11 shown in the third embodiment are provided at multiple locations on the lead frame 8, it is preferred that the interval P2 of the grooves 13 provided at the bonding position 10 of one wire 3 satisfies the relationship of the above-mentioned formula (3), and it is preferred that the diameter H2 of the arc formed by the grooves 13 satisfies the relationship of the above-mentioned formula (4). In addition, it is preferred that the interval P3 between the grooves 13 provided at the bonding positions 10 of two wires 3 adjacent to each other in the X direction (the direction perpendicular to the opening direction of the arc formed by the grooves 13) is greater than or equal to 100 μm. Preferably, the interval P4 between the grooves 13 provided at the joining positions 10 of two adjacent conductors 3 in the Y direction (the opening direction of the circular arc formed by the grooves 13 ) is greater than or equal to the diameter H2 of the circular arc formed by the grooves 13 .

[0065] In this way, the lead frame 8 having the step portions 11 at multiple locations can be applied to a semiconductor device in which multiple wires 3 are arranged on one lead frame 8. In addition, the wires 3 do not need to be joined at all positions corresponding to the step portions 11 provided at multiple locations. That is, the wire 3 only needs to be joined at a position corresponding to at least one step portion 11. For example, only one wire 3 can be arranged on the lead frame 8 having the step portions 11 at multiple locations. In this case, the options for the position where the wire 3 is joined to the lead frame 8 are increased, and the restrictions on the position where the wire 3 is joined can be reduced.

[0066] In addition, the various embodiments can be freely combined, or the various embodiments can be appropriately modified or omitted.

[0067] Description of the label

[0068] 1 ultrasonic welding head, 2 capillary, 3 wire, 3a portion where the thickness of the wire becomes thinner, 4 free air ball, 5 ignition rod, 6 semiconductor element, 7 chip bonding material, 8 lead frame, 8a, 8b metal plating, 9 tail, 10 bonding position of the wire, 11 step portion, 12, 13 grooves.

Claims

1. A semiconductor device comprising: a lead frame on which a semiconductor element is mounted; and A metal wire bonded to the lead frame, The lead frame has a step portion on a first main surface to which the wire is bonded, the step portion having a height of 5 μm or more and 20 μm or less relative to a bonding position of the wire. The step portions are formed on both sides of the groove formed on the first main surface, The bonding position of the wire does not overlap with the slot.

2. The semiconductor device according to claim 1, wherein The step portion is formed at a position corresponding to a groove formed on a second main surface which is a rear surface of the first main surface.

3. The semiconductor device according to claim 1 or 2, wherein: The groove and the step portion are linear in a plan view.

4. The semiconductor device according to claim 1 or 2, wherein: The groove and the step portion are in an arc shape surrounding a joining position of the wire in a plan view.

5. The semiconductor device according to claim 1 or 2, wherein: The lead frame is provided with the step portions at a plurality of locations. The wire is joined to a position corresponding to at least one of the step portions.

6. A method for manufacturing a semiconductor device, comprising the following steps: bonding a metal wire passing through a capillary installed at an ultrasonic horn to a lead frame; and After the wire is bonded to the lead frame, the wire is cut by lifting the capillary. The lead frame has a step portion on a first main surface to which the wire is bonded, and the step portion has a height of 5 μm or more and 20 μm or less relative to a bonding position of the wire. The step of bonding the wire to the lead frame is performed in a state where the tip of the capillary is in contact with the step portion.

7. The method for manufacturing a semiconductor device according to claim 6, wherein: The step portions are formed on both sides of the groove formed in the first main surface.

8. The method for manufacturing a semiconductor device according to claim 6, wherein: The step portion is formed at a position corresponding to a groove formed on a second main surface which is a rear surface of the first main surface.

9. The method for manufacturing a semiconductor device according to claim 7 or 8, wherein: The groove and the step portion are linear in a plan view.

10. The method for manufacturing a semiconductor device according to claim 7 or 8, wherein: The groove and the step portion are in an arc shape surrounding a joining position of the wire in a plan view.

11. The method for manufacturing a semiconductor device according to any one of claims 6 to 8, wherein: The lead frame is provided with the step portions at a plurality of locations. The step of bonding the wire to the lead frame is performed at a position corresponding to at least one of the step portions.

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