JP2003188213A - Ultrasonic welding apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic welding apparatus having high connection reliability. <P>SOLUTION: In the ultrasonic welding apparatus, a plurality of components to be welded are overlapped one another for pinching, press due to the pinching and ultrasonic vibration that is generated in a vibrator and is transmitted via an ultrasonic horn are simultaneously added, thus achieving the non-dissolution junction of the junction section of the components to be joined that are mutually aligned. An electrode is connected to two points, where an IC chip retention section 101 of an ultrasonic horn 108 is pinched each, and a current is allowed to flow between the two points, thus heating an IC chip 204 by utilizing the electric resistance of the IC chip retention section 101 itself. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an IC among flip chip mounting for mounting an electronic component such as an IC chip as a single body (bare chip) on a printed circuit board for electronic circuits.
A metal block (hereinafter referred to as a bump) is formed on the chip electrode,
The present invention relates to an ultrasonic flip-chip mounting method in which the bumps are aligned with the electrodes of the circuit board with this surface facing the circuit board, the IC chip is pressed against the circuit board, and heat and ultrasonic vibrations are applied to bond them.

[0002]

2. Description of the Related Art In recent years, there has been a strong demand for mobile information communication-related products and the like to have circuit packaging boards that are smaller and lighter, have higher performance by higher frequencies, and cost reductions. Therefore, flip-chip mounting, which enables direct mounting of the IC and the circuit board, is effective. Among them, solid-phase diffusion bonding using ultrasonic vibration is attracting more and more attention because of its features such as low connection resistance, high bonding strength and short-time bonding.

Here, a conventional ultrasonic flip chip mounting method will be described with reference to FIGS. 3, 4 and 5. FIG. 3 shows a forming method using a wire bonding method as an example of a bump forming method for electrodes of an IC chip. First, in FIG. 3A, a ball 203 is formed on the tip of the gold wire 202 held by the capillary 201 by an electric discharge action, and the capillary 201 is moved in the direction of arrow A to move the ball 203 to the electrode of the IC chip 204. 205 is pressed and joined.

For this joining, there is a method of thermocompression bonding or a method of applying ultrasonic vibration thereto. Further, as shown in FIG. 3B, by moving the capillary 201 together with the gold wire 202 in the direction of arrow a, the gold wire 202 is torn off and bumps 206 are formed on the electrodes 205. The bump 206 thus formed has a rivet-like shape with a sharp tip 206A.

Next, FIG. 4 shows a main part of a conventional general ultrasonic bonding apparatus. First, the IC chip 204 on which the bumps 206 are formed by the above-described method is placed with the surface on which the bumps 206 are formed facing down, and the IC chip holding unit 1 that is the bonded component holding unit.
01 is sucked and held by the negative pressure generated by using the air flow path 10.

Further, a circuit board 104 is mounted on the stage 103.
And the bump 206 formed on the IC chip 204
After aligning the electrode 105 on the circuit board 104 with the electrode 105, the IC chip holding portion 101 is lowered in the direction of arrow d. As a result, the tips 206A of the bumps 206 have the electrodes 105
And the tip 206A is slightly crushed. Here, the electric energy generated by the oscillator 106 is transmitted to the vibrator 107, and the vibrator 107 converts the electric energy into physical ultrasonic vibration.

Further, the ultrasonic vibration is generated by the ultrasonic horn 10.
8 is transmitted as a longitudinal wave in the direction of arrow c, and a predetermined ultrasonic vibration is applied to the IC chip holding portion 101 provided therein. In this way, ultrasonic vibration in the direction parallel to the upper surface of the circuit board 104 is applied to the joint portion, and at the same time, a load in the direction of arrow D that presses the upper surface of the circuit board 104 vertically by the pressing means 1 is applied. Further, by heating this bonding portion to a predetermined temperature, the bump 206 is bonded to the electrode 105 while being deformed as shown in FIGS. 5A and 5B.
Here, this joining is a non-melting joining by a solid phase diffusion action.

[0008]

The above-mentioned joining is generally called diffusion joining, and has also been realized by a thermocompression joining method from before. This thermocompression bonding method realizes diffusion bonding by applying heat and load to the bonding surface, but by applying ultrasonic vibration in a direction parallel to the bonding surface to this, an oxide film or impurities at the interface between both bonding parts is obtained. The ultrasonic bonding method is capable of significantly reducing the heat and load, which have been required in the thermocompression bonding method until then, by removing the heat and promoting the diffusion action by the friction energy.

As described above, according to the ultrasonic bonding method, since the heating temperature can be set low, the residual stress due to the difference in the coefficient of thermal expansion of both objects to be bonded when the temperature returns to room temperature can be reduced. Further, since the load can be set to be small, it is possible to reduce damage caused by the pressure applied to the electrodes of the objects to be joined. Therefore, in ultrasonic bonding, it is ideal that bonding is possible at room temperature.
However, in reality, ultrasonic bonding at room temperature has a problem in connection reliability, and ultrasonic bonding is generally performed in a heating environment.

As a heating method in this case, a method of heating a stage on which a circuit board is mounted, a method of heating an ultrasonic horn having an IC chip holding portion, and a method of using both of them are considered. In the method of heating the stage, the material of the circuit board often has a low thermal conductivity, and in that case, heating the electrode on the opposite surface of the circuit board is very inefficient. Further, when the circuit board is in the form of a thin film, the heating temperature of the stage is limited in order to avoid deformation due to heat.

For the above reasons, it is a general idea among those skilled in the art that it is desirable to use the heating of the stage and the heating of the ultrasonic horn together. However, according to the prior art, as one of the methods of heating the ultrasonic horn, a method of contacting or embedding the electric heater in the ultrasonic horn is adopted. In this case, the method of heating by heating a heater wire or the like around an ultrasonic horn to bring them into contact with each other is not very efficient because the heat except for a slight contact portion of the heater wire is released into the air and wasted.

A method of embedding an electric heater in an ultrasonic horn in order to eliminate the inefficiency (Patent No. 30)
No. 78231), the nodal point (minimum amplitude point) distant from the IC chip holding part must be selected as the position of the electric heater in order to take measures to affect the acoustic characteristics of the ultrasonic horn that is buried. I have to. Therefore, even if the electric heater is brought into contact with the surface of the ultrasonic horn or is embedded at the nodal point,
In order to raise the temperature of the IC chip holding portion, it is necessary to rely on the heat conduction of the ultrasonic horn itself.

Various materials such as stainless steel and titanium are adopted as the material of the ultrasonic horn, but the rigidity and vibration characteristics are the most important selection conditions for the selection, so that a large temperature gradient occurs in heat conduction. The reality is that it cannot be avoided. The present invention has been made to solve the above problems, and by connecting an electrode to a position sandwiching an IC chip holding portion on the surface of an ultrasonic horn and energizing the ultrasonic horn, the electric resistance of the material of the ultrasonic horn itself is reduced. It is an object of the present invention to provide an ultrasonic bonding apparatus having a heating unit that guides the generation of Joule heat and heats the IC chip holding unit itself.

[0014]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention sandwiches a plurality of parts to be joined together and sandwiches them, and the pressing force generated by this sandwiching and the vibrator generate ultrasonic waves through an ultrasonic horn. An ultrasonic bonding apparatus for non-melt-bonding the bonded parts of the parts to be bonded, which are aligned with each other, by simultaneously applying the transmitted ultrasonic vibrations. As a first aspect, an IC chip holding part of an ultrasonic horn. There is provided an ultrasonic bonding apparatus, characterized in that electrodes are respectively connected to two points sandwiching and a current is passed between the two points to heat the parts to be bonded holding part.

As a second aspect, there is provided the ultrasonic bonding apparatus according to the first aspect, characterized in that at least one of the two points is divided into a plurality of sections and a current is passed in parallel.

As a third mode, there is provided the ultrasonic bonding apparatus as the first or second mode, wherein the heating is performed during the bonding operation and during a time period other than the bonding operation.

In a fourth aspect, the heating is carried out at least during the time when ultrasonic vibrations contribute to the joining action. The ultrasonic joining apparatus according to the first or second aspect. I will provide a.

As a fifth mode, the ultrasonic bonding apparatus according to any one of the first to third modes is characterized in that, as a form of the electrode, a tip of a wire is fixed to an ultrasonic horn to conduct electricity. provide.

In a sixth aspect, a movable electrode is used as the electrode, and the movable electrode can be brought into contact with or separated from the ultrasonic horn. The ultrasonic bonding apparatus according to the above aspect is provided.

As a seventh aspect, there is provided the ultrasonic bonding apparatus according to any one of the first to sixth aspects, wherein the heating is a pulse heating method.

As an eighth aspect, there is provided the ultrasonic bonding apparatus as described in any one of the first to seventh aspects, characterized in that the heating of the parts to be joined holding part is heating accompanied by temperature control. .

As a ninth aspect, there is provided the ultrasonic bonding apparatus according to the eighth aspect, wherein the temperature control is performed based on an output from a thermocouple attached to the heating section.

[0023]

1 is a perspective view of an ultrasonic bonding apparatus showing an embodiment of the present invention, and FIG. 2 is a perspective view of an ultrasonic bonding apparatus showing another embodiment of the present invention. First, Fig. 1
An embodiment will be described based on. In FIG. 1, 10
Reference numeral 1 denotes an IC chip holding portion provided on the ultrasonic horn 108. The IC chip holding unit 101 sucks and holds the IC chip 204 by the negative pressure of air generated by the air flow path 10 provided inside the ultrasonic horn. Where IC
Bumps (not shown) are formed on the lower surface of the chip 204.

The circuit board 10 is placed on the stage 103.
4 is placed and held by holding means (not shown).
Electrodes 105 are formed on the upper surface of the circuit board 104, and the electrodes 105 are bonded to the bumps (not shown) on the lower surface of the IC chip described above. At the time of joining, the pulse current generated by the pulse heat power source 6 is applied to the ultrasonic horn 108 through the pair of wires 3A and 3B between the both side surfaces of the IC chip holding portion 101 (between 4A and 4B).
Be washed away. In 4A and 4B, the tips of the wires 3A and 3B are fixed by screwing bolts.

The pulse current flowing between both side surfaces 4A, 4B acts on the electric resistance of the IC chip holding portion 101 itself to generate Joule heat, and heats the IC chip holding portion 101. Here, the pulse current is the IC chip holding unit 101.
IC chip holding part 101 obtained from thermocouple 5 attached to
The temperature is controlled by the control unit 2 based on the feedback value of the temperature. Further, at this time, if necessary, a heater stage is used as the stage 103 and the circuit board 10 is used.
4 may be heated.

In the present embodiment, the pulse heating method is used as the heating method. However, this pulse heating method is not the method capable of rapid heating for a short time, but if time restrictions permit,
A normal heating method (constant heating method) that achieves a predetermined temperature rise for a long time may be used.

Next, the bumps (not shown) on the lower surface of the IC chip 204 are relatively aligned with the electrodes 105 on the upper surface of the circuit board 104, and when the alignment is completed, the pressing means 1 moves the ultrasonic horn 108 in the direction of arrow A. Then, the bump is brought into contact with the electrode 105. Further, under the control of the control unit 2, the pressurizing means 1 applies a load to the joint portion, and at the same time, the oscillator 106 also generates electric energy of ultrasonic vibration under the control of the control unit 2.

The electric energy is converted into physical ultrasonic vibration by the vibrator 107, and is applied to the joint through the ultrasonic horn 108 and the IC chip 204 main body. Thus, the load, the ultrasonic vibration, and the heat are simultaneously applied to the joint portion in a predetermined time zone during the joint operation, so that the diffusion joint is performed.

Further, in the description of this embodiment, the pair of wires 3A and 3B are fixed to the IC chip holding portion 101 at one place, but the respective wires 3A and 3B may be fixed from the root or from the root. Alternatively, the wires may be separated from the middle to form a plurality of finer wires, which may be fixed at a plurality of positions on the side surface of the IC chip holding unit 101. This makes the wire more flexible and can reduce the attenuation of ultrasonic vibrations to be applied to the joint.

Next, another embodiment of the present invention will be described. In FIG. 2, the IC chip 204 and the circuit board 10
The holding method of No. 4, the pressing method by the pressing unit 1, and the method of applying ultrasonic vibration are the same as the description based on FIG. 1 described above, and thus detailed description thereof will be omitted in the description of the present embodiment.

In this embodiment, the output of the pulse heat power source 6 is connected to the movable electrodes 8A and 8B via a pair of conducting means 7A and 7B such as wires. The movable electrodes 8A and 8B are moved by drive means 9A and 9B such as an air cylinder based on a command from the control unit 2, and come into contact with both side surfaces of the IC chip holding unit 101 provided on the ultrasonic horn 108. To be separated. Therefore, the movable electrode 8
When A and 8B are in contact with both side surfaces of the IC chip holding portion 101, a pulse current can be passed between these electrodes.

The pulse current flowing between the two side surfaces is IC
It acts on the electric resistance of the chip holding unit 101 itself to generate Joule heat, and heats the IC chip holding unit 101. Here, the pulse current is controlled by the control unit 2 based on the feedback value of the temperature of the IC chip holding unit 101 obtained from the thermocouple 5 attached to the IC chip holding unit 101.

However, since the movable electrodes 8A and 8B are separated from the both side surfaces at least while the ultrasonic vibration contributes to the bonding action between the bump and the electrode 105,
No heating is done. That is, the present embodiment has the movable electrode 8
The time during which the IC chip holding portion 101 is heated to a predetermined temperature by the pulse current while the A and 8B are in contact with the both side surfaces and ultrasonic vibration is applied to the joint portion (usually less than 1 second). Is for obtaining a predetermined temperature by the residual heat.

Here, the movable electrodes 8A and 8B may be separated from both side surfaces of the IC chip holding portion 101 only while the ultrasonic vibration contributes to the bonding action of the bumps and the electrodes 105, or the pressing means. 1 may be separated while the load is applied to the joint, or may be separated for a longer time. At this time, if necessary, a heater stage may be used as the stage 103 to heat the circuit board. Thus, the load, the ultrasonic vibration, and the heat are simultaneously applied to the joint portion in a predetermined time zone during the joint operation, so that the diffusion joint is performed.

The pulse heating method is also used in this embodiment as the heating method. However, this is not the pulse heating method that enables rapid heating for a short time, and if the time constraint permits, a predetermined temperature rise can be achieved for a long time. A normal constant heating method to be realized may be used. However, in the case of the present embodiment, since there is a time zone in which the movable electrodes are separated and the temperature cannot be controlled, it is necessary to use the pulse heating method capable of rapid heating after this time zone because the time required for the entire connection work is long. Leads to shortening.

Further, although the movable electrodes 8A and 8B described above each have a pair of electrodes, each of them is composed of a plurality of electrodes, each of which is elastic in a direction substantially perpendicular to the contact surface. In the case of having the above, more reliable contact can be obtained even if the flatness of both side surfaces of the IC chip holding portion 101 is not sufficiently secured.

[0037]

According to the present invention, the IC chip holding portion 10
By connecting electrodes to both side surfaces of 1 and energizing them, the IC chip holding portion 101 itself generates Joule heat, and it becomes possible to directly raise the temperature of the IC chip 204. Therefore, it is possible to eliminate the inefficiency of heating a place other than the IC chip holding unit 101 and raising the temperature of the IC chip 204 by the heat reaching the IC chip holding unit 101 due to the effect of heat conduction, and further reducing the time. Temperature control with little delay becomes possible. As a result, the connection reliability of ultrasonic bonding can be improved. (Claim 1)

Here, by performing the heating during the bonding operation and also during the time other than the bonding operation, it becomes easy to control the heating temperature during the bonding. Therefore, when the electrodes for heating are the tips of the wires 3A and 3B, the attenuation of the ultrasonic vibration energy to be applied to the IC chip 204 can be suppressed small. (Claim 3,
5)

Further, the heating is performed excluding the time during which the ultrasonic vibration contributes to the bonding action, and the time during which the ultrasonic vibration contributes to the bonding action is the IC chip holding portion 1.
When the joint portion is kept at a predetermined temperature by the residual heat of 01, the movable electrodes 8A and 8B are connected to the IC chip holding portion 101.
It is possible to separate from both side surfaces, and it is possible to completely eliminate the adverse effect on ultrasonic vibration due to the connection of the electrodes. (Claims 4 and 6)

When the method of fixing the tips of the wires 3A, 3B as the electrodes is selected, if the wires are separated into a plurality of wires and fixed at a plurality of locations and a current is passed in parallel, the wires become thinner and more flexible, and ultrasonic vibrations occur. The energy attenuation of is also small. Further, the movable electrodes 8A and 8B are used as the electrodes.
When contacting / separating from the IC chip holding part 101 by using, each electrode can be separated into a plurality of parts and contacted with elasticity substantially perpendicular to the contact surface for more reliable contact. Therefore, the contact resistance can be reduced. (Claim 2)

If the heating is the pulse heating method, it is not necessary to keep the high temperature of the IC chip holding portion 101 for a long time,
Rapid heating can create a high temperature environment for a short period of time. Further, when the heating time is a critical factor in the joining work, the time required to reach the predetermined temperature is short, and therefore the time required for the entire joining work can be shortened. (Claim 7)

If the heating is heating accompanied by temperature control,
The temperature of the IC chip holder 101 can be controlled stably. (Claim 8)

A thermocouple 5 attached to the heating section for the temperature control.
If it is performed on the basis of the output from, the temperature of the heating portion can be directly fed back accurately, and accurate and fast response temperature control becomes possible. (Claim 9)

[Brief description of drawings]

FIG. 1 is a perspective view of an ultrasonic bonding apparatus showing an embodiment of the present invention.

FIG. 2 is a perspective view of an ultrasonic bonding apparatus showing another embodiment of the present invention.

FIG. 3 is a cross-sectional view showing a method for forming bumps on electrodes of an IC chip.

FIG. 4 is a side view showing a main part of a conventional ultrasonic bonding apparatus.

FIG. 5 is a side view of an IC chip and a circuit board showing a state of ultrasonic bonding.

[Explanation of symbols]

1 Pressurizing means 2 control unit 3A, 3B wire 4A, 4B Both sides of IC chip holding part 5 thermocouple 6 pulse heat power supply 7A, 7B conduction means 8A, 8B movable electrode 9A, 9B drive means 10 air flow paths 101 IC chip holder 103 stage 104 circuit board 105 electrode 106 oscillator 107 oscillator 108 Ultrasonic horn 204 IC chip

Claims (9)

[Claims] 1. A plurality of parts to be joined are sandwiched by being overlapped with each other, and the pressing force by the sandwiching and the ultrasonic vibration generated by the vibrator and transmitted through the ultrasonic horn are simultaneously applied to position the parts to each other. An ultrasonic joining device for non-melt-joining the joined parts of the joined parts to be joined together, wherein in the ultrasonic horn, electrodes are respectively provided at two points sandwiching the joined part holding part provided in the ultrasonic horn. An ultrasonic bonding apparatus, characterized in that the parts to be bonded are heated by connecting them and applying a current between the two points. 2. The ultrasonic bonding apparatus according to claim 1, wherein at least one of the two points is divided into a plurality of sections and a current is passed in parallel. 3. The heating is performed during the bonding operation and in a time period other than the bonding operation.
Alternatively, the ultrasonic bonding apparatus according to 2. 4. The ultrasonic bonding apparatus according to claim 1, wherein the heating is performed at least during a time when ultrasonic vibration contributes to the bonding action. 5. The ultrasonic bonding apparatus according to claim 1, wherein, as a form of the electrode, a tip of a wire is fixed to an ultrasonic horn and is energized. 6. The ultrasonic wave according to claim 1, 2 or 4, wherein a movable electrode is used as the electrode, and the electrode can be brought into contact with or separated from the ultrasonic horn by this movement. Joining device. 7. The ultrasonic bonding apparatus according to claim 1, wherein the heating is a pulse heating method. 8. The ultrasonic bonding apparatus according to claim 1, wherein the heating of the parts to be bonded holding part is heating accompanied by temperature control. 9. The ultrasonic bonding apparatus according to claim 8, wherein the temperature control is performed based on an output from a thermocouple attached to the heating unit.