JP4415294B2 - Bonding head - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improvement in a bonding apparatus that applies ultrasonic vibration to bond a chip to a substrate, and is specifically developed mainly for holding means for a bonding tool.
[0002]
[Prior art]
Due to the demand for lighter and smaller portable devices, the mounting area of semiconductor components has been reduced year by year, and mounting of CSP and bare chip flip chips is being realized at the mass production level. As a mounting technology that is considered promising in terms of mass productivity, there is a mounting technology using ultrasonic vibration. However, although the current ultrasonic vibration mounting technology is suitable for a small chip level with few pins, it is still not suitable for mounting a large chip with many pins.
[0003]
The reason is that the bonding tool cannot be vibrated efficiently, the second is that it is difficult to control the vibration attenuation time of the bonding tool, and the third is that the resonance frequency of the bonding tool is made constant by changing the chip size. It is difficult to do this, that is, the natural frequency for resonance changes because the weight of the ultrasonic bonding tool including the weight of the chip changes due to the change of the chip size. Fourth, it may be difficult to maintain mounting accuracy.
[0004]
[Problems to be solved by the invention]
The present invention supports the bonding tool by a floating structure, improves the vibration efficiency of the bonding tool, facilitates control of vibration damping time, and makes it possible to make the resonance frequency of the bonding tool constant by changing the chip size, It is another object of the present invention to provide a bonding head that can improve mounting accuracy.
[0005]
[Means for Solving the Problems]
In order to solve the above problems, the present invention employs the following means for the bonding head.
First, a bonding tool is mounted inside the housing of the bonding head via a gap.
Second, an ultrasonic vibration applying means for applying ultrasonic vibration to the bonding tool is provided.
Thirdly, a biasing means for biasing the bonding tool upward by magnetic force is provided. Fourthly, gas supply means for supplying gas to the gap between the top and side surfaces of the bonding tool and the inside of the housing is provided.
Fifth, the bonding tool is held in a floating state inside the housing by the above means.
[0006]
Furthermore, as a second invention, a bonding head is provided in which a sensor for measuring a gap between the top surface of the bonding tool and the inside of the housing is provided on the bonding head.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described together with examples according to the drawings. FIG. 1 is an explanatory view showing an outline of attachment of an ultrasonic bonding head that is a characteristic part of the present invention, in which 1 is an ultrasonic bonding head, and 31 is a substrate stage holding a substrate 30.
[0008]
The ultrasonic bonding head 1 is attached and fixed to the lower surface of a head support bracket 3 that is passed to two guide rails 2 that are vertically attached. The ultrasonic bonding head 1 is attached by a Z-axis drive mechanism (not shown). The head support bracket 3 and the head support bracket 3 are moved up and down along the guide rail 2, and ultrasonic vibration is applied to the chip 20 by an ultrasonic vibration applying means to be described later and bonded to the substrate 30.
[0009]
The head support bracket 3 is brought into contact with the load cell 4 at one place (upper position in FIG. 1) so that the mounting load can be monitored. The load cell 4 is supported by a separate load cell support plate 5.
[0010]
In FIG. 1, only the vertical movement is shown as the movement of the ultrasonic bonding head 1, but the whole mechanism shown in FIG. 1 can be moved in the horizontal direction or the like, or the whole mechanism can be used. Can be fixed, and the chip supply and substrate supply can be performed by another mechanism.
[0011]
FIG. 2 is an explanatory cross-sectional view showing the configuration of the ultrasonic bonding head 1. The ultrasonic bonding head 1 includes an ultrasonic bonding tool 6 serving as a bonding tool body, a suction plate 7 serving as a bonding tool top surface, and a tool holder. 8 and a top cover 9.
[0012]
The top cover 9 constituting the upper part of the ultrasonic bonding head 1 and the tool holder 8 constituting the side peripheral surface are the housing of the bonding head in the present invention.
[0013]
A predetermined gap (a gap in which air gaps 41 and 42 to be described later can be secured) is provided in the housing space inside the bonding head surrounded by the top cover 9 and the tool holder 8, and the suction plate 7 and the lower surface of the suction plate 7. The ultrasonic bonding tool 6 fixed to is attached.
[0014]
As shown in FIG. 1, the top cover 9 is fixed to the head support bracket 3, and a permanent magnet 21 is embedded inside. The permanent magnet 21 serves as a biasing unit that biases the bonding tool in the present invention upward by a magnetic force.
[0015]
That is, the permanent magnet 21 biases the suction plate 7 constituting the top surface of the ultrasonic bonding tool 6 located in the housing space below the top cover 9 upward. By urging the suction plate 7 upward, the ultrasonic bonding tool 6 fixed to the lower surface of the suction plate 7 is also urged toward the top cover 9 side.
[0016]
The adsorption plate 7 constituting the ultrasonic bonding tool 6 is a flat plate, and in order to maintain the vertical air gap 41, dry air is ejected upward from the center of the adsorption plate 7 through the pipe 27, and a permanent magnet. 21 prevents the suction plate 7 from being sucked, and the air gap 41 between the inside of the top cover 9 and the suction plate 7 (5 to 10 microns) is kept constant.
[0017]
With this structure, the ultrasonic bonding tool 6 can be levitated in the air against gravity. Note that the load applied to the chip 20 can be finely controlled by finely adjusting the pressure of the dry air supplied to the suction plate 7.
[0018]
A non-contact type gap sensor 22 is embedded in the top cover 9, and an air gap 41 between the top cover 9 and the suction plate 7 which will be described later is observed, and the pressure of dry air supplied to the suction plate 7 is controlled. The air gap 41 is controlled.
[0019]
The air gap 41 serves as a buffer mechanism that softens the mechanical impact on the chip 20 when the chip 20 contacts the substrate 30 at a high speed during mounting, and damage to the chip 20 can be prevented.
[0020]
As will be described later, since the ultrasonic bonding tool 6 and the suction plate 7 supply air not only to the top surface side of the suction plate 7 but also to the side surface side of the ultrasonic bonding tool 6, the ultrasonic bonding tool 6 may tilt. There is no such thing. In the embodiment, a groove is not provided on the opposing surfaces of the top cover 9 and the suction plate 7, but a groove may be provided so that air is evenly supplied.
[0021]
The tool holder 8 has a rectangular frame shape that surrounds the four sides of the ultrasonic bonding tool 6, and air supply ports 18 are provided in the four directions. Dry air is supplied from the four air supply ports 18, and ultrasonic bonding is performed. The tool 6 can be fixed in a horizontal plane with air. The horizontal air gap 42 in the exemplary embodiment is 5 to 10 microns.
[0022]
The tool holder 8 is made of a rigid material, and the inner surface facing the ultrasonic bonding tool 6 is finished with high accuracy. By supplying dry air between the ultrasonic bonding tool 6 and the tool holder 8 at a predetermined pressure with an electropneumatic valve (not shown), this gap can be kept at 5 to 10 microns. This is very important for three reasons.
[0023]
First, the vibration attenuation time of the ultrasonic bonding tool 6 can be controlled. For example, the decay time can be shortened by setting the air pressure to high with an electropneumatic valve.
[0024]
Secondly, the resonance frequency of the ultrasonic bonding tool 6 due to the change in the size of the chip 20 can be made constant. That is, since the weight of the ultrasonic bonding tool 6 including the weight of the chip changes as the size of the chip 20 changes, the natural frequency for resonance changes. Therefore, the air pressure is adjusted to a predetermined pressure with an electropneumatic valve in order to make the natural frequency constant.
[0025]
Third, the mounting accuracy can be improved. Since the ultrasonic bonding tool 6 is supported by air bearings from four directions, the position where vibration is attenuated and stopped can always be held within ± 5 microns.
[0026]
The ultrasonic bonding tool 6 includes a chip suction means, and a chip vacuum suction hole 19 is formed in the center of the tip 24 as shown in FIG.
[0027]
As shown in FIG. 6, the vacuum pressure is supplied to the chip vacuum suction hole 19 from the vacuum suction line 25 connected to a vacuum pump or the like installed outside, inside the suction plate 7 and the ultrasonic bonding tool 6. This is done through the pipe 26. The pipe 26 is a flexible tube so as not to hinder the movement of the ultrasonic bonding tool 6. The chip 20 is sucked and held on the tip 24 of the ultrasonic bonding tool 6 by the vacuum pressure supplied to the chip vacuum suction hole 19.
[0028]
Further, as shown in FIG. 5, the tip 24 of the ultrasonic bonding tool 6 is finished in a concave curved surface shape in order to increase the friction coefficient of the contact portion with the chip 20. As a result, the chip 20 is slightly deformed when the chip 20 is sucked. This can be expected to prevent tip displacement and improve the transmission efficiency of ultrasonic vibration.
[0029]
The ultrasonic bonding tool 6 is a bonding tool having a built-in ultrasonic vibration applying means, and two sets of elastic frames 10 and 11 having two rectangular shapes and two ultrasonic transducers 12 inside the ultrasonic bonding tool 6. 13 are built in. The elastic frames 10 and 11 and the ultrasonic transducers 12 and 13 are configured in pairs, and are arranged at orthogonal positions as shown in FIGS. 1, 3, and 4.
[0030]
As a result, the ultrasonic transducer 12 built in the upper part of the ultrasonic bonding tool 6 imparts vibration in the left-right direction in FIG. 3, while the ultrasonic transducer 13 imparts vibration in the vertical direction in FIG. ing. If the vibration period of the two ultrasonic transducers 12 and 13 is relatively shifted by 90 degrees as in the embodiment, the ultrasonic bonding tool 6 generates elliptical vibration. is doing. Furthermore, if the mutual amplitude is made equal, the ultrasonic bonding tool 6 becomes a circular motion. By causing the ultrasonic bonding tool 6 to perform a substantially circular motion such as an elliptical motion or a circular motion, the friction distance between the tip 20 adsorbed on the tip of the ultrasonic bonding tool 6 and the substrate 30 is simply compared to the case of a reciprocating motion. Thus, the maximum is π times the maximum, and the thermal efficiency can be improved and the time required for bonding can be shortened.
[0031]
As shown in FIGS. 3 and 4, the elastic frames 10 and 11 include vibration transmitting portions 14 and 14 ′, weight portions 15 and 15 ′, spring portions 16 and 16 ′, and an outer peripheral housing portion 17. Each spring portion 16, 16 ′ is connected to the portion 17. The ultrasonic transducers 12 and 13 are attached to the outer peripheral housing portion 17 and a vibration generating portion side end is in contact with the vibration transmitting portions 14 and 14 '. In the embodiment, the tip 24 serving as the suction portion of the chip 20 is held below the outer peripheral housing portion 17.
[0032]
With the elastic frames 10 and 11 having the above-described structure, the ultrasonic vibrations of the ultrasonic vibrators 12 and 13 are transmitted from the vibration transmitting portions 14 and 14 'to the weight portions 15 and 15', and further through the spring portions 16 and 16 '. The ultrasonic bonding tool 6 is vibrated by being transmitted to the outer peripheral housing portion 17. When the elastic frames 10 and 11 have the above structure, they resonate with the ultrasonic vibration, and the ultrasonic bonding tool 6 can be vibrated efficiently, and the vibration can be transmitted to the chip 20 with low loss.
[0033]
The power supply to the two ultrasonic transducers 12 and 13 is wired from the suction plate 7 to the inside of the outer peripheral housing portion 17 of the ultrasonic bonding tool 6 as shown in FIG. By wiring 23 connected to the sound wave vibrators 12 and 13.
[0034]
【The invention's effect】
The present invention relates to an ultrasonic bonding tool provided in a housing of a bonding head via a gap, biasing means for biasing the bonding tool upward by magnetic force, a top surface and a side surface of the bonding tool, and the inside of the housing. And a gas supply means for supplying gas to the gap between the two, and the bonding tool is characterized by holding the bonding tool in a floating state inside the housing. The vibration of the child can be efficiently transmitted to the bonding tool, the vibration attenuation time of the bonding tool can be easily controlled, the resonance frequency of the bonding tool can be made constant by changing the chip size, and the mounting accuracy can be improved. It became a bondin head.
[0035]
Although it is an effect of invention of Claim 2, by providing the sensor which measures the clearance gap between the top | upper surface of a bonding tool, and the inside of a housing, this clearance gap can be observed and the pressure of the gas supplied to a clearance gap is determined from the result. It is possible to easily control the gap (air gap).
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing an outline of attachment of an ultrasonic bonding head. FIG. 2 is a cross-sectional explanatory diagram showing a configuration of an ultrasonic bonding head. FIG. Cross-sectional explanatory diagram of the lower part of the bonding tool [Fig. 5] Enlarged explanatory diagram of the tip of the ultrasonic bonding tool [Fig. 6] Vacuum piping diagram for chip adsorption of the ultrasonic bonding tool [Fig. 7] Electrical wiring diagram of the ultrasonic bonding tool [Code] Explanation of]
1. . . . . . 1. Ultrasonic bonding head . . . . . Guide rail 3. . . . . . 3. Head support bracket . . . . . 4. Load cell . . . . . 5. Load cell support plate . . . . . 6. Ultrasonic bonding tool . . . . . Suction plate 8. . . . . . Tool holder 9. . . . . . Top cover 10,11. . Elastic frame 12,13. . Ultrasonic transducers 14, 14 '. Vibration transmitting portions 15, 15 '. Weight part 16, 16 '. Spring part 17. . . . . Outer peripheral housing part 18. . . . . Air supply port 19. . . . . Chip vacuum suction hole 20. . . . . Chip 21. . . . . Permanent magnet 22. . . . . Gap sensor 23. . . . . Wiring 24. . . . . Tip 25. . . . . Vacuum suction lines 26, 27. . Piping 30. . . . . Substrate 31. . . . . Substrate stages 41, 42. . Air gap

Claims (2)

Bonding tool provided inside the housing of the bonding head via a gap, ultrasonic vibration applying means for applying ultrasonic vibration to the bonding tool, biasing means for biasing the bonding tool upward by magnetic force, and bonding tool And a gas supply means for supplying gas to a gap between the top and side surfaces of the housing and the inside of the housing, and holding the bonding tool in a floating state inside the housing. The bonding head according to claim 1, further comprising a sensor that measures a gap between the top surface of the bonding tool and the inside of the housing.

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