Bonding tool

Abstract

This bonding tool for ultrasonic bonding comprises: a horn (1) including a core block (4), a first side block (5) provided on a first lateral surface of the core block (4), and a second side block (6) provided on a second lateral surface which is on the opposite side of the core block; and an ultrasonic vibrator (2) provided at the first side block (5). A nozzle (10) for picking up a semiconductor element is provided on the bottom surface of the core block. A dummy nozzle (11) is provided on the surface of the core block opposite the bottom surface.

Description

Bonding Tools

[0001] The present disclosure relates to a bonding tool.

[0002] One method for bonding a chip to a substrate via bumps is ultrasonic bonding.

[0003] This is a type of solid-state bonding in which bumps formed on one side of the chip or the substrate are pressed against electrodes formed on the other side and minute ultrasonic vibrations are applied in the planar direction of the electrode surfaces. During this process, the ultrasonic waves induce plastic deformation of the bumps and electrodes, bringing these newly formed surfaces into close contact, resulting in a bond.

[0004] The bonding tool used in this method has an ultrasonic vibrator that is the source of ultrasonic vibrations, an elongated horn that transmits the vibrations, and a nozzle that is integrated with the horn and holds the chip.

[0005] The horn is mainly made of stainless steel, aluminum alloy, titanium alloy, etc. and is designed to mechanically resonate with the vibration of the vibrator, producing a longitudinal vibration mode in the longitudinal direction. The nozzle is located at the position corresponding to the antinode, where the vibration of the horn is strongest.

[0006] Ultrasonic vibrations and pressure are applied to the tip through the nozzle. During this process, minute slippage occurs repeatedly between the nozzle and the tip. To prevent this wear on the nozzle, there are bonding tools that use an ultra-hard material, such as a cemented carbide, for the nozzle, which is harder than the material of the horn (Patent Document 1).

[0007] Patent No. 5426762

[0008] When bonding is performed using the bonding tool of Patent Document 1, bumps located near the center of the chip are sometimes crushed less than bumps located near the edges of the chip. As a result, the contact area between the bumps and electrodes near the center of the chip is smaller than that near the edges, resulting in a decrease in bonding strength. This tendency becomes more pronounced as the chip size increases, making it difficult to ensure uniform bonding on the inner surface of the chip.

[0009] An object of the present disclosure is to provide a bonding tool that can ensure uniformity of bonding within the chip surface.

[0010] The bonding tool disclosed herein is a bonding tool that bonds a semiconductor element and a substrate via bumps by ultrasonic bonding, and includes a horn including a core block, a first side block provided on a first side surface of the core block, and a second side block provided on a second side surface of the core block opposite the first side surface, and an ultrasonic vibrator provided on the first side block. A nozzle that adsorbs the semiconductor element is provided on the bottom surface of the core block. A dummy nozzle is provided on the surface of the core block opposite the bottom surface. The nozzle is made of a material that is harder than the core block.

[0011] The bonding tool of the present disclosure is provided with a dummy nozzle on the surface of the core block opposite the nozzle, which suppresses lateral vibration of the bonding tool, thereby applying a uniform load to the bonding surface and improving the uniformity of the bonding.

[0012] FIG. 1 is a side view schematically showing a bonding tool of the first embodiment. FIG. 2 is a perspective view schematically showing the bonding tool of the first embodiment. FIG. 3 is a cross-sectional view schematically showing a horn in the bonding tool of the first embodiment. FIG. 4 is a diagram showing the distribution of amplitude of longitudinal vibration in the horn of the first embodiment. FIG. 5 is a diagram showing the state of the horn of the first embodiment when vibrating. FIG. 6 is a diagram showing the distribution of strain when the horn of the first embodiment vibrates. FIG. 7 is a diagram schematically showing a horn in a bonding tool of a second embodiment.

[0013] Hereinafter, embodiments will be described with reference to the drawings. Note that the following description is merely an example and is not intended to be limiting. Furthermore, appropriate modifications can be made within the scope of the present invention.

[0014] (First embodiment) Fig. 1 is a side view that schematically shows a bonding tool 101 in a first embodiment, and Fig. 2 is a perspective view that schematically shows the bonding tool 101. Note that the dimensions of the various parts in Fig. 1 and Fig. 2 do not necessarily match.

[0015] As shown in FIG. 1, the bonding tool 101 has ribs 3 and is fixed to a head 102 of a mounting machine by the ribs 3 .

[0016] The bonding tool 101 also includes a horn 1 and an ultrasonic vibrator 2 that generates ultrasonic vibrations. The horn 1 includes a core block 4, and a nozzle 10 for suctioning a semiconductor element 9 on the side of the core block 4 opposite to the head 102 of the mounting machine. A dummy nozzle 11 is provided on the side of the core block 4 opposite to the nozzle 10 (i.e., on the head 102 side).

[0017] Using such a bonding tool 101, the semiconductor element 9 is bonded to the substrate 14 placed on the stage 103. More specifically, the semiconductor element 9 is bonded to the electrodes 16 provided on the substrate 14 via the bumps 15.

[0018] Hereinafter, in each figure, the X-axis, Y-axis, and Z-axis are defined to correspond to the three axes of a Cartesian coordinate system. The X-axis is the longitudinal direction of the horn 1 (the left-right direction in FIG. 1 ), with the first side block 5 side being positive; the Z-axis is the direction connecting the head 102 and the stage 103 (the up-down direction in FIG. 1 ), with the head 102 side being positive; and the Y-axis is the direction perpendicular to both the X-axis and the Z-axis. In addition, in each figure, the Z-axis will be described as being vertical, and the X-axis and Y-axis will be described as being horizontal.

[0019] Next, FIG. 3 is a schematic cross-sectional view further illustrating the horn 1 of the bonding tool 101.

[0020] Horn 1 has a long, slender shape and includes a core block 4, a first side block 5 attached to a first side surface (the right side in FIG. 2 ) of core block 4 via a first connecting portion 7, and a second side block 6 attached to a second side surface (the left side in FIG. 2 ) opposite the first side surface via a second connecting portion 8. A fastening hole 12 is provided in first side block 5 on the side opposite core block 4. Ultrasonic vibrator 2 is connected to first side block 5 using fastening hole 12.

[0021] A nozzle 10 for suctioning a semiconductor element 9 is provided on the bottom surface of the core block 4. A dummy nozzle 11 is provided on the surface opposite the bottom surface of the core block 4. A suction hole 13 is provided so as to penetrate the core block 4, the nozzle 10, and the dummy nozzle 11. The semiconductor element 9 is suctioned by drawing air through the suction hole 13.

[0022] The nozzle 10 is, for example, a square plate-like shape corresponding to the semiconductor element 9 to be ultrasonically bonded. The dummy nozzle 11 is also, for example, a square plate-like shape.

[0023] The core block 4, first side block 5, second side block 6, first connecting portion 7, and second connecting portion 8 are preferably molded seamlessly as a single unit. However, they can also be formed individually and then joined. Furthermore, metal materials with low vibration damping and high toughness are preferred for these materials. Examples include stainless steel, aluminum alloys, and titanium alloys. Stainless steel is particularly preferred because of its high workability and strength.

[0024] (Reason for Uneven Bonding) Here, the inventors' findings regarding the reason why uniformity of bonding within the chip surface decreases when ultrasonic bonding is performed using a bonding tool of the prior art will be explained.

[0025] The bonding tool of the prior art has a similar configuration to bonding tool 101 of this embodiment, but differs at least in that it does not include dummy nozzle 11. The nozzle is made of a high-hardness material that is about twice as dense as the material of the horn, so the center of gravity of the nozzle and horn is shifted toward the nozzle side with respect to the axial center of the horn in the longitudinal direction (similar to the axis indicated as O-O' in FIG. 3).

[0026] When longitudinal vibrations are transmitted to such a horn, the moment around any point on the axis becomes unbalanced due to the shift in the center of gravity, resulting in a force that tries to rotate the horn in addition to a force that tries to expand and contract in the longitudinal direction.

[0027] Due to this rotational force, the vibration mode of the ultrasonic vibration generated in the bonding tool is a combination of the longitudinal vibration that the ultrasonic vibrator is trying to generate and a transverse vibration with an amplitude in the direction in which the center of gravity is shifted.

[0028] In this vibration mode, the nozzle does not vibrate parallel to the bonding surface, but instead vibrates by tilting alternately like a pendulum. As a result, the semiconductor element vibrating with the nozzle is pressed against the substrate while tilting alternately. As a result, a large load is applied locally to the bumps located at both ends of the semiconductor element, and bonding progresses in this state. The load applied to the bumps near the center of the semiconductor element is smaller than that to the bumps at both ends, so the amount of crushing is smaller. This reduces the contact area between the bump and the electrode, and the bonding force decreases.

[0029] (Configuration of this embodiment) In contrast to the above, as described above, the bonding tool 101 of the present disclosure is provided with the dummy nozzle 11 on the surface of the horn 1 opposite to the nozzle 10. The nozzle 10 and the dummy nozzle 11 will be further described below.

[0030] The nozzle 10 sucks the semiconductor element 9 on a suction surface 10a on the side opposite the core block 4. The suction surface 10a is set to be approximately the same size as the semiconductor element 9. Note that the joining surface between the nozzle 10 and the core block 4 may have slightly different dimensions from the suction surface 10a depending on the joining method, but they have approximately the same shape.

[0031] The thickness t of the nozzle 10 is set so that the suction surface 10a of the nozzle protrudes beyond the bottom surfaces of the first side block 5 and the second side block 6. In other words, although the bottom surface of the core block 4 and the bottom surfaces of the first side block 5 and the second side block 6 are flush with each other in the example of Figure 3, the bottom surface of the core block 4 may be recessed. In this case, the thickness t is set to be greater than the difference between the bottom surfaces of the core block 4 and the first side block 5 and the second side block 6.

[0032] In this way, the first side block 5 and the second side block 6 are prevented from interfering with the substrate 14 during ultrasonic bonding.

[0033] Furthermore, the nozzle 10 is preferably made of a metal material, such as a cemented carbide, that is harder than the material of the core block 4. This makes it possible to suppress wear even when ultrasonic welding is repeatedly performed.

[0034] Next, the dummy nozzles 11 are preferably made of the same material as the nozzles 10 or a material having the same density.

[0035] Furthermore, the area of ​​the opposing surface 11a of the dummy nozzle 11 opposite the core block 4 is preferably equal to or larger than the area of ​​the suction surface 10a of the nozzle 10 and is sized to fit within the upper surface of the core block 4. The joining surface between the dummy nozzle 11 and the core block 4 may have slightly different dimensions from the opposing surface 11a depending on the joining method, but they have approximately the same shape.

[0036] The thickness t′ of the dummy nozzle 11 is preferably set so that the mass of the dummy nozzle 11 is greater than the mass of the nozzle 10 .

[0037] The nozzles 10 and the dummy nozzles 11 are connected to the core block 4 by adhesive bonding, fastening, brazing, welding, etc. Brazing is particularly preferred because it provides high joint strength and little thermal deformation.

[0038] In this embodiment having the above-described configuration, the center of gravity G of the horn 1, nozzle 10, and dummy nozzle 11 is located in a position biased toward the dummy nozzle 11. More specifically, the center of gravity G is located closer to the dummy nozzle 11 than the longitudinal axis O-O' connecting the center of the end face of the first side block 5 and the center of the end face of the second side block 6. This is because the mass of the dummy nozzle 11 is set to be greater than the mass of the nozzle 10.

[0039] The ultrasonic transducer 2 is configured so as not to affect the center of gravity position in the Z-axis direction.

[0040] Furthermore, when ultrasonic vibration is applied to the core block 4, deformation due to compressive strain or tensile strain occurs, but this deformation is suppressed by being joined to the dummy nozzle 11 or the nozzle 10. The dummy nozzle 11 is joined to the core block 4 over a larger area than the nozzle 10. Therefore, deformation is suppressed more on the dummy nozzle 11 side of the core block 4 than on the nozzle 10 side.

[0041] As described above, the position of the center of gravity G of the horn 1 including the nozzle 10 and the dummy nozzle 11 and the difference in the effect of suppressing deformation can suppress lateral vibrations occurring in the bonding tool 101 and improve the uniformity of bonding. This will be further explained below.

[0042] (Vibration Mode of Horn 1) The ultrasonic vibrator 2 generates ultrasonic vibrations of longitudinal vibration in the longitudinal direction of the horn 1. The ultrasonic vibrations are transmitted to the horn 1.

[0043] The horn 1 mechanically resonates with the ultrasonic vibrator 2, and a standing wave of longitudinal vibration appears in the longitudinal direction.

[0044] Figure 4 shows the distribution of the amplitude of longitudinal vibration in the horn 1. A standing wave of one wavelength appears in the horn 1. The ends and center of the horn 1 correspond to the antinodes of the vibration, where the displacement due to the vibration is maximum. In addition, there are vibration nodes at the positions of the first connecting portion 7 and the second connecting portion 8, where the displacement due to the vibration is zero. The graph shows the displacement of each part when the center of the horn 1 is displaced to the positive side of the X-axis, that is, toward the first side block 5. For example, this can be considered the moment when the displacement reaches its maximum.

[0045] The ribs 3 (see FIGS. 1 and 2) are provided at the first connection portion 7 and the second connection portion 8, which are vibration nodes. Therefore, the ribs 3 can fix the bonding tool 101 to the head 102 of the mounting machine without interfering with the longitudinal vibration. Therefore, in the following, the ribs 3 and the fixation by the ribs 3 can be considered to be negligible.

[0046] Next, Fig. 5 shows the state of the horn 1 when vibrating in the bonding tool 101 of this embodiment. Fig. 5 emphasizes the deformation of the horn 1 due to vibration. Fig. 6 shows the distribution of strain ε in the X-axis direction when the horn 1 vibrates. Note that Figs. 4 to 6 show the same moment.

[0047] When longitudinal vibration is propagated from the ultrasonic vibrator 2 to the core block 4 via the first side block 5 and the first connection portion 7, a translational force F is generated in the core block 4, causing the core block 4 to translate in the positive direction of the X axis. In Figure 6, the force F is acting in the positive direction of the X axis.

[0048] In addition, the longitudinal vibration propagated from the ultrasonic vibrator 2 generates a rotational force T in the core block 4 that tends to rotate it around the Y axis. This is because the center of gravity G is positioned offset in the Z axis direction from the central axis O-O' of the horn 1. Since the center of gravity G is positioned closer to the dummy nozzle 11 than the central axis O-O', when any point on the central axis O-O' is used as the reference, the sum of the clockwise moment and counterclockwise moment in Figure 6 does not become zero. As a result, at the moment shown in Figure 6 (the moment when a translational force F in the positive direction of the X axis is generated), a rotational force T that tends to rotate the core block 4 clockwise is generated.

[0049] On the other hand, when a translational force is applied in the positive direction of the X-axis, deformation due to compressive strain occurs in region C on the first connecting portion 7 side of the core block 4, as shown in Fig. 7. At the same time, deformation due to tensile strain occurs in region C' on the second connecting portion 8 side of the core block 4.

[0050] At this time, deformation near the connection portion of the core block 4 with the nozzle 10 is suppressed by the nozzle 10. Similarly, deformation near the connection portion of the core block 4 with the dummy nozzle 11 is suppressed by the dummy nozzle 11. Furthermore, the bonding area between the core block 4 and the dummy nozzle 11 (substantially equal to the area of ​​the opposing surface 11a) is larger than the bonding area between the core block 4 and the nozzle 10 (substantially equal to the area of ​​the suction surface 10a). As a result, the deformation amount d' in the X-axis direction on the dummy nozzle 11 side is smaller than the deformation amount d in the X-axis direction on the nozzle 10 side ( FIG. 6 ).

[0051] Depending on the difference in the amount of deformation in the X-axis direction between the top surface side and the bottom surface side of the core block 4, a rotational force T' that tends to rotate the core block 4 counterclockwise around the Y-axis is generated.

[0052] The magnitudes of the rotational force T that tries to rotate the core block 4 clockwise and the rotational force T' that tries to rotate it counterclockwise are determined by the position of the center of gravity G, the area of ​​the joint surfaces of the nozzle 10 and the dummy nozzle 11 with the core block 4, etc. Therefore, by setting these, the rotational force T and the rotational force T' can be offset, and no force that tries to rotate the core block 4 around the Y axis can be generated.

[0053] As a result, only the translational force F acts on the core block 4 .

[0054] In the above, we have explained an example in which the center of the horn 1 is displaced toward the positive side of the X-axis due to longitudinal vibration. However, even in the opposite state in which the center is displaced toward the negative side, the translational force F, rotational force T, and rotational force T' all have opposite directions, and rotational force T and rotational force T' cancel each other out. Therefore, even in this case, only a force that tends to translate the core block 4 acts. At any point during longitudinal vibration, only the translational force F acts.

[0055] As described above, when the configuration of this embodiment is used, even when the nozzle 10 is made of a material that is harder than the core block 4 and therefore typically has a high density, the vibration mode of the horn 1 is a vertical vibration mode without superimposed horizontal vibration. In other words, the nozzle 10 can vibrate parallel to the bonding surfaces of the substrate 14 and the semiconductor element 9. This allows ultrasonic bonding while applying a uniform load across the surface of the semiconductor element 9, making the amount of crushing of the bumps 15 uniform regardless of their position. This improves the uniformity of bonding across the surface of the semiconductor element 9.

[0056] Furthermore, the longitudinal vibration mode without the superimposed lateral vibration has a higher transmission rate of ultrasonic energy for wave bonding than the vibration mode with the superimposed lateral vibration, which results in a reduction in the time required for bonding.

[0057] Conversely, it is also possible to make the mass of the nozzle 10 greater than the mass of the dummy nozzle 11 and to make the area of ​​the joint surface between the nozzle 11 and the core block 4 greater than the area of ​​the joint surface between the dummy nozzle 11 and the core block 4. In this case, the center of gravity G is shifted toward the nozzle 10, and deformation of the core block 4 is suppressed on the nozzle 11 side. As a result, the rotational force caused by the position of the center of gravity G and the rotational force caused by the difference in joint area are both in opposite directions. However, even in this case, the two rotational forces can be canceled out, allowing the horn 1 to vibrate in a longitudinal vibration mode without superimposition of lateral vibration.

[0058] However, when the bonding tool 101 including the horn 1 is fixed to the head 102 of the mounting machine, it is desirable that the dummy nozzle 11 fit between the core block 4 and the head 102. It is also desirable that the dimensions and shape of the nozzle 11 correspond to the dimensions of the semiconductor element 9 to be ultrasonically bonded, and that the suction surface 10a protrude beyond the bottom surfaces of the first side block 5 and the second side block 6. To address these needs, the configuration described in detail in this embodiment is desirable.

[0059] Furthermore, in the above, it is assumed that the center of gravity of the horn 1 alone, excluding the nozzle 10 and dummy nozzle 11, etc., is located on the central axis O-O'. Therefore, by using a dummy nozzle 11 that has a greater mass than the nozzle 10, the center of gravity G of the nozzle 10, dummy nozzle 11, and horn 1 combined will be shifted toward the dummy nozzle 11 from the central axis O-O'.

[0060] On the other hand, it is possible that the center of gravity of the horn 1 alone is shifted from the central axis O-O' depending on the configuration of the horn 1. However, even in this case, it is possible to set the masses of the nozzles 10 and dummy nozzles 11 and the area of ​​the joint surfaces with the core block 4 so that the rotational force T, which depends on the position of the center of gravity, and the rotational force T', which depends on the difference in the amount of deformation of the core block 4, cancel each other out.

[0061] Second Embodiment Next, a second embodiment will be described. Fig. 7 is a schematic cross-sectional view illustrating a horn 1a provided in a bonding tool according to the second embodiment. The configuration of the bonding tool of this embodiment, other than the horn 1a, is the same as that of the bonding tool 101 of the first embodiment.

[0062] Similarly to the first embodiment, the horn 1a also includes a core block 4, a first side block 5 provided to the core block 4 via a first connecting portion 7, and a second side block 6 provided to the core block 4 via a second connecting portion 8. Furthermore, the first side block 5 includes a fastening hole 12 for connecting the ultrasonic vibrator 2.

[0063] The core block 4 is also provided with nozzles 10b on its bottom surface and dummy nozzles 11b on its top surface.

[0064] In this embodiment, the nozzle 10b and the dummy nozzle 11b are made of the same material and have the same shape and dimensions, and therefore have the same mass.

[0065] As a result, the center of gravity G of the horn 1a is located on the axis O-O' in the longitudinal direction of the horn 1a. Therefore, unlike the first embodiment, no rotational force T is generated due to the center of gravity G being offset from the axis O-O'.

[0066] Furthermore, because the nozzles 10b and the dummy nozzles 11b have the same shape and dimensions, the areas of their bonding surfaces with respect to the core block 4 can also be made the same. Therefore, unlike the first embodiment, deformation due to compressive strain or tensile strain when ultrasonic vibration is applied to the core block 4 is suppressed to the same extent on the nozzle 10b side and the dummy nozzle 11b side. As a result, deformation to the same extent occurs on the nozzle 10b side and the dummy nozzle 11b side, and therefore, unlike the first embodiment, a rotational force T' due to the difference in the amount of deformation does not occur.

[0067] As described above, in the horn 1a of this embodiment, when longitudinal vibration is transmitted from the ultrasonic vibrator 2, no force is generated that tends to rotate the horn 1a. In other words, the horn 1a is in a longitudinal vibration mode without superimposed lateral vibration. As a result, uniformity within the surface of the semiconductor element 9 can be improved.

[0068] The above-described embodiments may be modified in form and detail without departing from the spirit of the claims. Furthermore, the contents of the embodiments may be combined and substituted as appropriate as long as the functions of the subject matter of the present disclosure are not impaired.

[0069] According to the present disclosure, uniform ultrasonic bonding is possible within the bonding surface, making it useful as a bonding tool used for bonding semiconductor elements to substrates via bumps, etc. It can also be applied to ultrasonic bonding of metal foils and plate materials such as electrodes.

[0070] REFERENCE SIGNS LIST 1, 1a Horn 2 Ultrasonic vibrator 3 Rib 4 Core block 5 First side block 6 Second side block 7 First connection portion 8 Second connection portion 9 Semiconductor element 10, 10b Nozzle 10a Suction surface 11, 11b Dummy nozzle 11a Opposing surface 12 Fastening hole 13 Suction hole 14 Substrate 15 Bump 16 Electrode 101 Bonding tool 102 (Mounting machine) head 103 Stage

Claims

1. A bonding tool that bonds a semiconductor element and a substrate via bumps by ultrasonic bonding, comprising: a horn including a core block, a first side block provided on a first side of the core block, and a second side block provided on a second side of the core block opposite the first side; and an ultrasonic vibrator provided on the first side block; a nozzle for adsorbing the semiconductor element is provided on the bottom surface of the core block; and a dummy nozzle is provided on the surface of the core block opposite the bottom surface, the nozzle being made of a material harder than the core block.

2. A dummy nozzle according to claim 1, characterized in that the area of ​​the contact surface between the nozzle and the core block is equal to or less than the area of ​​the contact surface between the dummy nozzle and the core block, and the mass of the nozzle is equal to or less than the mass of the dummy nozzle.

3. A bonding tool according to claim 1, characterized in that the nozzle and the dummy nozzle have the same shape and are made of the same material.

4. A bonding tool as claimed in claim 1, characterized in that when the center of gravity of the horn, nozzle and dummy nozzle combined is located on the dummy nozzle side of the longitudinal central axis of the horn, the area of ​​the contact surface between the nozzle and the core block is smaller than the area of ​​the contact surface between the dummy nozzle and the core block, when the center of gravity is located on the nozzle side of the central axis, the area of ​​the contact surface between the nozzle and the core block is larger than the area of ​​the contact surface between the dummy nozzle and the core block, and when the center of gravity coincides with the central axis, the area of ​​the contact surface between the nozzle and the core block is equal to the area of ​​the contact surface between the dummy nozzle and the core block.

5. A bonding tool according to claim 1, characterized in that said core block, said first side block and said second side block are integrally formed.

6. A bonding tool according to any one of claims 1 to 5, characterized in that the nozzle and the dummy nozzle are both made of a cemented carbide alloy.

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