Bonding tools

Abstract

To provide a bonding tool that can ensure uniformity of bonding within the chip surface. [Solution] The bonding tool for ultrasonic bonding comprises a core block 4, a horn 1 including a first side block 5 provided on the first side surface of the core block 4 and a second side block 6 provided on the second side surface on the opposite side, and an ultrasonic transducer 2 provided on the first side block 5. A nozzle 10 for adsorbing semiconductor elements 9 is provided on the bottom surface of the core block 4. A dummy nozzle 11 is provided on the side opposite the bottom surface of the core block 4. The nozzle 10 is made of a material with higher hardness than the core block 4.

Description

Technical Field

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

Background Art

[0002] As one method of bonding a chip to a substrate via bumps, there is an ultrasonic bonding method.

[0003] This is a type of solid-phase bonding in which bumps formed on one of the chip and the substrate are pressed against an electrode formed on the other, and minute ultrasonic vibrations are applied in the plane direction of the electrode surface for bonding. At this time, plastic deformation of the bumps and the electrode is promoted by the ultrasonic waves, and these newly formed surfaces are bonded by coming into close contact with each other.

[0004] The bonding tool used in this method has an ultrasonic vibrator that is a 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 resonate mechanically with the vibrations of the vibrator so that a longitudinal vibration mode appears in the longitudinal direction. The nozzle is provided at a position corresponding to the antinode where the vibration of the horn is the largest.

[0006] The ultrasonic vibrations and the pressing load are applied to the chip via the nozzle. At this time, minute slippage repeatedly occurs between the nozzle and the chip. In order to prevent wear of the nozzle due to this, there is a bonding tool that uses a super-hard material such as cemented carbide, which has a higher hardness than the material of the horn, as the material of the nozzle (Patent Document 1).

Prior Art Documents

Patent Documents

[0008] When bonding was performed using the bonding tool described in Patent Document 1, the bumps located on the central side of the chip sometimes deformed less than the bumps located on the edges of the chip. As a result, the contact area between the bumps and electrodes on the central side of the chip became smaller than on the edges, reducing the bonding strength. This tendency became more pronounced with larger chip sizes, making it difficult to ensure uniformity of bonding on the inner surface of the chip.

[0009] The object of this disclosure is to provide a bonding tool that can ensure uniformity of bonding within the chip surface. [Means for solving the problem]

[0010] The bonding tool of this disclosure is a bonding tool for bonding a semiconductor element and a substrate via bumps by ultrasonic bonding, and comprises 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 opposite to the first side surface of the core block, and an ultrasonic transducer provided on the first side block. A nozzle for adsorbing the semiconductor element is provided on the bottom surface of the core block. A dummy nozzle is provided on the side opposite to the bottom surface of the core block. The nozzle is made of a material with a higher hardness than the core block. [Effects of the Invention]

[0011] The bonding tool of this disclosure has a dummy nozzle on the opposite side of the nozzle in the core block, which suppresses lateral vibration of the bonding tool, thereby enabling a uniform load to be applied to the bonding surface and improving the uniformity of the bond. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a schematic side view showing a bonding tool according to the first embodiment. [Figure 2] Figure 2 is a schematic perspective view showing a bonding tool according to the first embodiment. [Figure 3] Figure 3 is a schematic cross-sectional view showing the horn in the bonding tool of the first embodiment. [Figure 4] Figure 4 shows the amplitude distribution of longitudinal vibration in the horn of the first embodiment. [Figure 5] Figure 5 shows the state of the horn in the first embodiment during vibration. [Figure 6] Figure 6 shows the strain distribution during vibration of the horn in the first embodiment. [Figure 7] Figure 7 is a schematic diagram showing the horn in the bonding tool of the second embodiment. [Modes for carrying out the invention]

[0013] The embodiments will be described below with reference to the drawings. However, the following description is illustrative and not limiting. Furthermore, modifications can be made as appropriate within the scope of achieving the desired effect.

[0014] (First embodiment) Figure 1 is a schematic side view of the bonding tool 101 in the first embodiment, and Figure 2 is a schematic perspective view of the bonding tool 101. Note that the dimensions of each part in Figure 1 and Figure 2 do not necessarily match.

[0015] As shown in Figure 1, the bonding tool 101 is equipped with ribs 3, which are used to fix it to the head 102 of the mounting machine.

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

[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 electrode 16 provided on the substrate 14 via the bump 15.

[0018] Hereinafter, in each figure, the X-axis, Y-axis, and Z-axis are defined so as to correspond to the three axes of the orthogonal coordinate system. The X-axis is the longitudinal direction of the horn 1 (the left-right direction in FIG. I), 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. I), with the head 102 side being positive, and the Y-axis is the direction perpendicular to both the X-axis and the Z-axis. Also, in each figure, it is described assuming that the Z-axis is the vertical direction and the X-axis and Y-axis are the horizontal directions.

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

[0020] The horn 1 has an elongated shape and includes a core block 4, a first side block 5 provided on its first side surface (the right surface in FIG. 2) via a first connection portion 7, and a second side block 6 provided on the second side surface (the left surface in FIG. 2) opposite to the first side surface via a second connection portion 8. A fastening hole 12 is provided on the side of the first side block 5 opposite to the core block 4. The ultrasonic vibrator 2 is connected to the first side block 5 using the fastening hole 12.

[0021] ​​​​​​​

[0023] The core block 4, the first side block 5, the second side block 6, the first connecting portion 7, and the second connecting portion 8 are preferably formed as a single, seamless piece. However, it is also possible to form them individually and then join them. Furthermore, metal materials with low vibration damping and high toughness are preferred for these components. Examples include stainless steel, aluminum alloys, and titanium alloys, with stainless steel being particularly preferred due to its high workability and strength.

[0024] (Regarding the reason for the unevenness of the joint) Here, we will explain the inventors' findings regarding the reason why the uniformity of bonding within the tip surface decreases when ultrasonic bonding is performed using conventional bonding tools.

[0025] Conventional bonding tools have a similar configuration to the bonding tool 101 of this embodiment, but differ in that they do not include a dummy nozzle 11. Since the nozzle is made of a high-hardness material with a density about twice that of the horn material, the center of gravity of the nozzle and horn is shifted towards the nozzle side with respect to the longitudinal axis center of the horn (similar to the axis shown as O-O' in Figure 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. As a result, in addition to the force that tries to expand and contract the horn in the longitudinal direction, a rotational force is generated.

[0027] Due to this rotational force, the vibration modes of the ultrasonic vibrations generated in the bonding tool consist of longitudinal vibrations intended to be generated by the ultrasonic transducer, superimposed with transverse vibrations whose amplitude is in a direction shifted from the center of gravity.

[0028] In this vibration mode, the nozzle does not vibrate parallel to the bonding surface, but rather vibrates in an alternating, pendulum-like motion. Consequently, the semiconductor element, vibrating with the nozzle, is pressed against the substrate while alternatingly tilting. As a result, a large local load is applied to the bumps located at both ends of the semiconductor element, and bonding proceeds in this state. The bumps near the center of the semiconductor element experience less load compared to the bumps at both ends, resulting in less deformation. This reduces the contact area between the bumps and electrodes, and thus the bonding force decreases.

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

[0030] The nozzle 10 adsorbs the semiconductor element 9 on the adsorption surface 10a opposite to the core block 4. The adsorption surface 10a is set to approximately the same size as the semiconductor element 9. The bonding surface between the nozzle 10 and the core block 4 may differ slightly in dimensions from the adsorption surface 10a depending on the bonding method, but it is 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, in the example of Figure 3, the bottom surface of the core block 4 is at the same level as the bottom surfaces of the first side block 5 and the second side block 6, but the bottom surface of the core block 4 may be recessed. In this case, the thickness t is made greater than the difference between the bottom surface of the core block 4 and the bottom surfaces of the first side block 5 and the second side block 6.

[0032] In this way, interference between the first side block 5 and the second side block 6 and the substrate 14 is prevented during ultrasonic bonding.

[0033] Furthermore, the nozzle 10 is made of a metal material with higher hardness than the core block 4, preferably a cemented carbide, for example. This makes it possible to suppress wear even when ultrasonic bonding is performed repeatedly.

[0034] Next, it is preferable that the dummy nozzle 11 is made of the same material as the nozzle 10, or a material having a similar density.

[0035] Furthermore, it is preferable that the area of ​​the opposing surface 11a of the dummy nozzle 11, which is opposite to the core block 4, is greater than or equal to the area of ​​the suction surface 10a of the nozzle 10, and that it fits within the upper surface of the core block 4. The joining surface between the dummy nozzle 11 and the core block 4 may differ slightly in dimensions from the opposing surface 11a depending on the joining method, but it is approximately the same shape.

[0036] The thickness t' of the dummy nozzle 11 is preferably set such that the mass of the dummy nozzle 11 is greater than the mass of the nozzle 10.

[0037] The nozzle 10 and the dummy nozzle 11 are connected to the core block 4 by means of adhesive, fastening, brazing, welding, etc. Brazing is particularly preferred as it provides high joint strength and minimal thermal deformation.

[0038] In this embodiment having the configuration described above, 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 toward the dummy nozzle 11 than the longitudinal axis O-O' connecting the end face center of the first side block 5 and the end face center 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] Furthermore, the ultrasonic transducer 2 is configured so as not to affect the center of gravity in the Z-axis direction.

[0040] Furthermore, when ultrasonic vibrations are applied to the core block 4, deformation occurs due to compressive or tensile strain, but this deformation is suppressed because it is joined to the dummy nozzle 11 or 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 on the dummy nozzle 11 side of the core block 4 more than on the nozzle 10 side.

[0041] As described above, the differences in the position of the center of gravity G of the horn 1, including the nozzle 10 and the dummy nozzle 11, and the effect of deformation suppression, make it possible to suppress lateral vibrations generated in the bonding tool 101 and improve the uniformity of the bond. This will be explained further below.

[0042] (Vibration mode of Horn 1) The ultrasonic transducer 2 generates longitudinal ultrasonic vibrations in the longitudinal direction of the horn 1. These ultrasonic vibrations are transmitted to the horn 1.

[0043] Horn 1 resonates mechanically with ultrasonic transducer 2, and a standing wave with longitudinal vibration appears in the longitudinal direction.

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

[0045] Ribs 3 (see Figures 1 and 2) are provided at the first connection point 7 and the second connection point 8, which are vibration nodes. Therefore, ribs 3 allow the bonding tool 101 to be fixed to the head 102 of the mounting machine without hindering longitudinal vibration. For this reason, ribs 3 and the fixing provided by ribs 3 can be considered negligible in the following discussion.

[0046] Next, Figure 5 shows the state of the horn 1 during vibration in the bonding tool 101 of this embodiment. In Figure 5, the deformation of the horn 1 due to vibration is emphasized. Furthermore, Figure 6 shows the distribution of strain ε in the X-axis direction during vibration of the horn 1. Note that Figures 4 to 6 show the same moment.

[0047] When longitudinal vibrations propagate from the ultrasonic transducer 2 to the core block 4 via the first side block 5 and the first connection part 7, a translational force F is generated in the core block 4 that tends to translate in the positive X-axis direction. In Figure 6, the force F is acting in the positive X-axis direction.

[0048] In addition, longitudinal vibrations propagated from the ultrasonic transducer 2 generate a rotational force T in the core block 4 that causes it to rotate 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 located on the dummy nozzle 11 side of the central axis O-O', the sum of the clockwise moment and the counterclockwise moment in Figure 6 is not zero when using any point on the central axis O-O' as a reference. As a result, at the moment shown in Figure 6 (the moment when a translational force F in the positive X-axis direction is generated), a rotational force T is generated that causes the core block 4 to rotate clockwise.

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

[0050] In this case, deformation is suppressed by the nozzle 10 near the connection point between the core block 4 and the nozzle 10. Similarly, deformation is suppressed by the dummy nozzle 11 near the connection point between the core block 4 and the dummy nozzle 11. Furthermore, the contact area between the core block 4 and the dummy nozzle 11 (approximately equal to the area of ​​the opposing surface 11a) is larger than the contact area between the core block 4 and the nozzle 10 (approximately equal to the area of ​​the suction surface 10a). As a result, the amount of deformation d' in the X-axis direction on the dummy nozzle 11 side is smaller than the amount of deformation d in the X-axis direction on the nozzle 10 side (Figure 6).

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

[0052] The magnitudes of the rotational force T that attempts to rotate the core block 4 clockwise, and the rotational force T' that attempts to rotate it counterclockwise, are determined by the position of the center of gravity G, the area of ​​the contact surfaces between the nozzle 10 and the dummy nozzle 11 and the core block 4, and so on. Therefore, by setting these parameters, the rotational force T and the rotational force T' can be canceled out, preventing any force from being generated that attempts to rotate the core block 4 around the Y axis.

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

[0054] In the above explanation, we described the case where the center of horn 1 is displaced to the positive side of the X-axis due to longitudinal vibration. However, even in the case where it is displaced to 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, in this case as well, only the force that tries to translate core block 4 acts. At any point in the longitudinal vibration, only the translational force F acts.

[0055] As described above, using the configuration of this embodiment, even when the nozzle 10 is made from a material that is harder than the core block 4 and therefore normally denser, the vibration mode of the horn 1 will be a mode consisting only of longitudinal vibration without superposition of transverse vibration. In other words, the nozzle 10 can vibrate parallel to the bonding surface between the substrate 14 and the semiconductor element 9. This allows ultrasonic bonding to be performed while applying a uniform load within the surface of the semiconductor element 9, and the amount of deformation of the bump 15 can be made uniform regardless of its position. Therefore, the uniformity of bonding within the surface of the semiconductor element 9 can be improved.

[0056] Furthermore, longitudinal vibration modes without transverse vibration superposition exhibit improved transmission efficiency of ultrasonic energy for wave bonding compared to vibration modes with transverse vibration superposition. As a result, the time required for bonding can be reduced.

[0057] Conversely, it is also possible to make the mass of nozzle 10 greater than the mass of dummy nozzle 11, and to make the area of ​​the joint surface between nozzle 11 and core block 4 greater than the area of ​​the joint surface between dummy nozzle 11 and core block 4. In this case, the center of gravity G is located in a position shifted toward nozzle 10, and the deformation of core block 4 is suppressed more 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, making the horn 1 a mode of longitudinal vibration without superposition of lateral vibration.

[0058] However, when fixing the bonding tool 101, including the horn 1, to the head 102 of the mounting machine, it is desirable that the dummy nozzle 11 be positioned between the core block 4 and the head 102. Furthermore, it is 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 protrudes beyond the bottom surfaces of the first side block 5 and the second side block 6. To address these requirements, the configuration described in detail in this embodiment is desirable.

[0059] Furthermore, the above assumes that the center of gravity of the horn 1 alone, excluding the nozzle 10 and dummy nozzle 11, is located on the central axis O-O'. Therefore, by using the dummy nozzle 11, which 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 from the central axis O-O' towards the dummy nozzle 11.

[0060] In contrast, depending on the configuration of horn 1, it is conceivable that the center of gravity of horn 1 alone may be offset from the central axis O-O'. However, even in this case, it is possible to set the mass of nozzle 10 and dummy nozzle 11 and the area of ​​the joint surface with 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 core block 4, cancel each other out.

[0061] (Second embodiment) Next, a second embodiment will be described. Figure 7 is a schematic cross-sectional view illustrating the horn 1a of the bonding tool in the second embodiment. Note that, apart from the horn 1a, the bonding tool in this embodiment is the same as that of the bonding tool 101 in the first embodiment.

[0062] The horn 1a also comprises a core block 4, a first side block 5 provided on the core block 4 via a first connecting portion 7, and a second side block 6 provided on the core block 4 via a second connecting portion 8, similar to the first embodiment. Furthermore, the first side block 5 is provided with fastening holes 12 for connecting the ultrasonic transducer 2.

[0063] Furthermore, the core block 4 is equipped with a nozzle 10b on its bottom surface and a dummy nozzle 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. Therefore, the nozzle 10b and the dummy nozzle 11b also have the same mass.

[0065] As a result, the center of gravity G of the horn 1a lies on the longitudinal axis O-O' 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, since the shape and dimensions of the nozzle 10b and the dummy nozzle 11b are identical, the area of ​​the bonding surface to the core block 4 can also be made identical. Therefore, unlike the first embodiment, deformation due to compressive or tensile strain when ultrasonic vibration is applied to the core block 4 is suppressed to the same extent on both the nozzle 10b side and the dummy nozzle 11b side. As a result, since the same amount of deformation occurs on both the nozzle 10b side and the dummy nozzle 11b side, unlike the first embodiment, no rotational force T' is generated due to differences in the amount of deformation.

[0067] As described above, in the horn 1a of this embodiment, when longitudinal vibration is transmitted from the ultrasonic transducer 2, no force is generated that would cause the horn 1a to rotate. In other words, the horn 1a operates in a mode of longitudinal vibration without the superposition of transverse vibration. As a result, the uniformity within the 9 surfaces of the semiconductor element can be improved.

[0068] The embodiments described above may be modified in form and detail, provided that they do not deviate from the spirit of the claims. Furthermore, the contents of each embodiment can be combined and substituted as appropriate, as long as they do not impair the functions covered by this disclosure. [Industrial applicability]

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

[0070] 1, 1a Horn 2. Ultrasonic transducer 3 Ribs 4 core blocks 5. First side block 6. Second side block 7. First connection section 8. Second connection section 9 Semiconductor elements 10, 10b nozzle 10a Adsorption surface 11, 11b Dummy nozzle 11a Opposite side 12 fastening holes 13 Adsorption holes 14 circuit boards 15 Bump 16 electrodes 101 Bonding Tools 102 (head of the mounting machine) 103 Stages

Claims

1. A bonding tool that joins a semiconductor element and a substrate via bumps using ultrasonic bonding, 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 opposite to the first side surface of the core block, The first side block comprises an ultrasonic transducer, A nozzle for adsorbing 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 to the bottom surface. A bonding tool characterized in that the nozzle is made of a material with higher hardness than the core block.

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

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

4. In claim 1, If the combined center of gravity of the horn, nozzle, and dummy nozzle is located on the dummy nozzle side of the longitudinal central axis of the horn, then the contact surface area between the nozzle and the core block is smaller than the contact surface area between the dummy nozzle and the core block. If 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. 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. A bonding tool characterized by the following features.

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

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

Images