JPH0945737A - Ultrasonic bonding method and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonic bonding method and apparatus whereby a good bonding condition can be ensured, with avoiding defects due to excessive ultrasonic vibration energy applied to workpieces to be bonded. SOLUTION: Ultrasonic bonding process is to bond one work 3 pressed to another work piece 2 through a press tool 4 connected to an ultrasonic source 6. The ultrasonic vibration by the source 6 stops or slows down, depending on the vibrating condition of the workpiece 2 or its support member.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an ultrasonic bonding method and apparatus, which are improved so that a suitable bonding state between a bonding member and a member to be bonded can be obtained.

[0002]

2. Description of the Related Art A case where metal plates are joined together by an ultrasonic joining method will be described with reference to FIG. A metal plate 2a serving as a member 2 to be joined is placed on a suitable supporting base 1, and a metal plate 3a serving as a joining member 3 is superposed on the upper surface thereof. Reference numeral 4 indicates a pressing tool connected to the ultrasonic wave generation source 6 via the ultrasonic horn 5, so that the lower end surface 4a thereof can come into contact with the upper surface of the upper metal plate 3a with a predetermined pressure. It has become. When the ultrasonic generator 6 is driven in a state where the pressing tool 4 is in pressure contact with the upper surface of the upper metal plate 3a, the horizontal component of ultrasonic vibration is transmitted to the upper metal plate 3a via the pressing tool 4. To be done. Both metal plates 2a which receive the pressing force by the pressing tool 4,
Local frictional heat is generated at the interface of 3a, and by the cooperative action of this frictional heat and the pressure of the pressing tool, both metal plates 2
a and 3a are joined to each other by the joining portion 7 formed on the pressing interface.

[0003]

By the way, the both metal plates 2a and 3a described above behave in the following manner in the process of ultrasonic bonding. That is, in the initial stage of application of ultrasonic vibration, the upper metal plate 2a as a joining member vibrates relative to the lower metal plate 3a as a joined member, but as time passes, As the accumulated ultrasonic vibration energy increases, the lower metal plate 3a, which is the member to be joined, also starts to vibrate, and the vibration gradually increases and eventually becomes synchronized with the vibration of the upper metal plate 2a. Become. Finally 2
This is because the joining that integrates the metal plates is gradually completed.

If the ultrasonic vibration is continuously applied even after the joining is completed in this way, various problems may occur depending on the form of the member 3 to be joined, and conversely, the ultrasonic vibration may be generated before the joining is completed. If the application is interrupted, the joining between both members will be insufficient.

For example, as shown in FIG. 11, in the manufacture of a semiconductor device, an ultrasonic bonding method may be used together with wire bonding between the semiconductor chip 8 and the lead 9, especially second bonding. In this case, The capillary 10 is connected to the ultrasonic wave generation source 6 via the ultrasonic horn 5. In this case, when ultrasonic vibration is applied while the capillary 10 presses the wire 11 against the lead 9, the lead 9 synchronizes with the vibration of the capillary 10 as the bonding between the wire 11 and the lead 9 approaches completion. And start oscillating. If this state is left as it is, the ultrasonic vibration applied to the lead may spread over the entire lead frame, and the miniaturized lead may be broken.

[0006] It is very difficult to control such as setting the drive time of the ultrasonic wave generation source by predicting such a defect that may occur in the members to be joined. There is a tendency to try to apply the ultrasonic vibration energy exceeding the above.

The present invention has been devised under such circumstances, and in the case of joining two members by an ultrasonic joining method, the members to be joined are joined members after the completion of joining. It is an object of the present invention to eliminate the inconvenience caused by vibrating in synchronization and to obtain an appropriate joined state of the two members.

[0008]

DISCLOSURE OF THE INVENTION In order to solve the above problems, the present invention employs the following technical means.

According to the first aspect of the present invention, a new ultrasonic bonding method is provided, which is a method in which a bonding member is pressed against a member to be bonded by a tool connected to an ultrasonic source. An ultrasonic bonding method by applying ultrasonic vibration to the bonding member via the tool, wherein ultrasonic vibration by the ultrasonic source is stopped according to a vibration state of the bonded member or its supporting member. Characterized or reduced.

Such a method can be applied to wire bonding in which a pad and a lead on the upper surface of a semiconductor chip are connected by a wire in the manufacture of a semiconductor device using a lead frame. In this case, the tool is a capillary for wire bonding, the bonding member is a wire inserted in the capillary, and the bonded member is a lead frame or a semiconductor chip bonded on the lead frame.

The method of the present invention can also be applied to the case of joining a metal radiator plate to the lower surface of a die pad in the manufacture of a semiconductor device. In this case, the bonding member is a die pad in the lead frame, and the member to be bonded is a metal heat dissipation plate arranged on the lower surface of the die pad.

According to the method of the present invention, the vibration state of the members to be joined is directly detected and fed back to the drive control of the ultrasonic wave generation source. More specifically, as the ultrasonic bonding progresses, the members to be bonded start to vibrate in synchronization with the bonding members, but this state is directly detected and more ultrasonic vibration energy than necessary is applied. I am trying not to Further, by detecting the vibration state of the members to be joined, it is possible to determine whether or not the proper joining state is obtained. Therefore, even if the joining member and the joined member are variously changed, it is possible to obtain a proper joining state without causing a defect in the joining member.

As described above, when the method of the present invention is applied to the wire bonding in the manufacture of the semiconductor device, particularly the second bonding, the fine-pitched leads are damaged by the application of ultrasonic vibration energy more than necessary. It is possible to obtain an appropriate wire bonding state while surely avoiding such problems.

According to a second aspect of the present invention, there is provided a new ultrasonic bonding apparatus, the ultrasonic bonding apparatus being driven and controlled by the control means and being connected to the ultrasonic generation source. And a vibration sensor that detects the vibration state of the member to be joined or its supporting member, and the control means is the vibration sensor. The ultrasonic wave generation source is controlled in accordance with the vibration state of the joined member or its supporting member detected by.

Specifically, this control stops the ultrasonic vibration by the ultrasonic source when the vibration of the member to be joined or its supporting member detected by the vibration sensor reaches a predetermined state. Or to reduce.

Obviously, the same advantages as described above can be obtained also in ultrasonic bonding using this ultrasonic bonding apparatus.

As the vibration sensor for detecting the vibration state of the members to be joined, a contact type pressure sensor capable of detecting high frequency vibration can be used, or an electromagnetic wave emitted toward the vibrating body or It is also possible to employ a non-contact type that detects the vibration state by analyzing the Doppler phenomenon seen in the reflection of sound waves.

Other features and advantages of the present invention will become more apparent from the detailed description given below with reference to the accompanying drawings.

[0019]

1 is a schematic diagram of an apparatus for carrying out the method of the present invention. A first metal plate 2a, which is a member 2 to be joined, is placed on the upper surface of a suitable support 1.
The second metal plate 3a, which is the joining member 3, is stacked so as to be overlapped with this. Reference numeral 4 denotes a pressing tool, and as shown in FIG. 1, it is possible to select a state in which the lower end comes into contact with the surface of the second metal plate 3a with a predetermined pressure and a state in which the lower end is separated from the upper side. The pressing tool 4 is also connected to an ultrasonic wave generation source 6 via an ultrasonic horn 5. The ultrasonic generator 6 is drive-controlled by the control means 12.

On the other hand, a vibration sensor 13 for detecting the vibration state of the first metal plate 2a as the member 2 to be joined is arranged. The vibration sensor 13 can select a state in which it contacts the appropriate portion of the first metal plate 2a as shown by the solid line in FIG. 1 and a state in which it is separated from the first metal plate 2a as shown by the phantom line. Is attached to a support member (not shown).

When the ultrasonic wave generating source 6 is driven, the pressing tool 4 vibrates in the horizontal direction due to its horizontal component. The amplitude of this vibration may be, for example, about 20 μm. In the application start state of ultrasonic vibration, only the second metal plate 3a pressed by the pressing tool 4 vibrates relatively to the first metal plate 2a. Since a predetermined pressure is applied by the pressing tool 4, frictional heat due to the relative vibration is locally generated at the interface between the metal plates 2a and 3a affected by this pressure. The heat thus generated and the pressure of the pressing tool 4 cooperate to advance the joining of the two metal plates 2a and 3a. As the joining progresses, the lower first metal plate 2a also starts vibrating in synchronization with the upper second metal plate 3a. When the joining of the two metal plates 2a and 3a is completed, this first
The vibration state of the metal plate 2a is synchronized with the vibration state of the second metal plate 3a. That is, the kinetic energy per unit time by the ultrasonic waves given to the first metal plate 2a as the member to be joined 2 through the upper second metal plate 3a is as shown in FIG. Increased,
It approaches a certain value. Such a change in the kinetic energy of the first metal plate 2a is found by processing the detection signal from the vibration sensor 13.

For example, in the range shown by reference character A in the graph of FIG. 2, it is considered that the two metal plates are sufficiently joined. Therefore, the control means 12 stops or reduces the ultrasonic vibration of the ultrasonic wave generation source 6 in the range indicated by the symbol A in FIG. 2, that is, at a certain point in time when the kinetic energy of the first metal plate 2a approaches the asymptotic value. Let
If the application of ultrasonic vibration is continued even after reaching the area indicated by the symbol A in FIG. 2, this may have an adverse effect on the state of the member 2 to be joined, but according to the method of the present invention, It is possible to avoid adverse effects on the members to be joined.

The vibration sensor indicated by reference numeral 13 in FIG. 1 is a contact type pressure sensor capable of detecting high frequency vibrations, or a Doppler phenomenon observed in reflection of sound or electromagnetic waves from a vibrating body to analyze non-contact. What can detect the vibration state of the vibrating body can be adopted.

The ultrasonic bonding method or ultrasonic bonding apparatus of the present application can be suitably applied in the process of manufacturing a semiconductor device using the lead frame 30, as described below.

In FIG. 3, the metal plate 21 for heat dissipation is package 2
2 shows the structure of the quat type semiconductor device 20 incorporated in the device 2. Inside the resin package 22 formed of epoxy resin or the like and having a rectangular shape in a plan view, the semiconductor chip 24 bonded on the die pad 23, bonded at the center of the lower surface of the die pad 23, and having a predetermined planar shape. The metal heat dissipation plate 21 and the like that it has are incorporated. The die pad 23 has a rectangular shape in plan view, and the suspension leads 25 remaining in the resin package 22 extend from the four corners thereof.

The die pad 23 and the metal heat dissipation plate 21 can be joined by the ultrasonic joining method according to the present invention, as will be described later.

A plurality of inner leads 26, the inner ends of which are arranged at regular intervals on the four circumferences of the die pad 23 or the semiconductor chip 24 mounted thereon, are extended outward in the horizontal direction, Each of them is connected to the external leads 27 protruding from the four side surfaces of the resin package 22.

The bonding pads on the upper surface of the semiconductor chip 24 and the upper surfaces of the tips of the internal leads 26 are connected by wire bonding 11. This wire bonding, especially the other end of the wire 11 whose one end is connected to the upper surface pad of the semiconductor chip 24 is connected to the internal lead 26.
The ultrasonic bonding method of the present invention can also be preferably applied to so-called second bonding, in which the upper surface of the substrate is bonded.

The quad type semiconductor device 20 shown in FIG.
Is manufactured using a lead frame 30 as shown in FIG. Components of the semiconductor device 20 in a rectangular region 33 surrounded by the side frame portions 31 on both sides in the width direction and the cross frames 32 formed so as to span the side frame portions at equal intervals in the longitudinal direction. Leads 26, 27 or die pad 23 to be
Etc. are punched out. Quadrilateral frame-shaped tie bar 3
4 is formed so that its four corners are connected to the side frame 31 and the cross frame 32 by the support leads 35. The rectangular die pad 23 is supported by four suspension leads 25 extending inward from the four corners of the quadrilateral frame-shaped tie bar 34. The above-mentioned quadrilateral frame-shaped tie bar 3 divided by the adjacent suspension leads 25, 25
In each trapezoidal region within 4, a plurality of internal leads 26 are formed, the base ends of which are connected to the tie bars 34 and which extend toward one side of the die pad 23. On the outer side of the tie bar 34, a plurality of outer leads 27 that continuously extend to the inner leads 26 are formed. The outer end portion of each outer lead 27 is connected to the side frame 31 or the cross frame 32 via the support lead 36. The metal heat dissipation plate 21 is bonded to the lower surface of the die pad 23 of the lead frame 30. The ultrasonic bonding method of the present invention is applied to this bonding method.

That is, as shown in FIG. 5, the lead frame 30 is provided on the upper surface of the metal heat dissipation plate 21 placed on the support 1.
The die pad 23 is overlapped, and the pressing tool 4 connected to the ultrasonic horn 5 is pressed against the central portion of the upper surface of the die pad 23 to supply ultrasonic vibration of the pressing tool 4. For example, ultrasonic vibration having a horizontal component with an amplitude of about 20 μm is applied from the pressing tool 4 to the die pad 23, and due to the frictional heat generated at the contact interface with the metal heat dissipation plate 21 and the pressing force by the pressing tool 4, The die pad 23 and the metal radiating plate 21 are bonded to each other with the bonding portion 7 in a limited area.

In this case, the vibration state of the metal heat sink 21 is detected by the vibration sensor 13, and when the vibration state of the metal heat sink 21 reaches a predetermined state, that is, as described above, At the time when the kinetic energy reaches the area indicated by the symbol A in the graph shown in FIG. 2, the control means 12 stops or reduces the drive of the ultrasonic wave generation source 6.

Next, as shown in FIGS. 6 and 7, the semiconductor chip 24 is bonded to the upper surface of the die pad 23, and then the bonding pad on the upper surface of the semiconductor chip 24 and the internal lead 26 corresponding thereto are bonded. The upper surfaces of the tip portions are connected by wire bonding 11. In this case, the method of the present invention is preferably applied to the second bonding, in which the other end of the wire 11 whose one end is connected to the upper surface of the semiconductor chip 24 is pressed against the upper surface of the internal lead 26 by the capillary 10 for connection. You can

That is, as shown in FIG. 8, an ultrasonic wave generation source 6 is connected to the capillary 10 via an ultrasonic horn 5, while a vibration sensor 13 for detecting the vibration state of an appropriate portion of the lead frame 30 is used. Is inputted to the control means 12, and the control means 12 stops driving the ultrasonic wave generation source 6 when the vibration state of the lead frame 30 reaches a predetermined state.

Such wire bonding is performed with the entire lead frame 30 placed on the heat block 37 and the lead frame being heated. In the example shown in the figure, when the capillary 10 presses the wire 11 against the upper surface of the tip of the inner lead 26, the inner lead 26 is elastically deformed and pressed against the peripheral edge of the upper surface of the metal heat dissipation plate 21. Since the metal radiator plate 21 is in contact with the heat block, the heat from the heat block 37 is transferred to the internal lead 26,
The other end of the wire 11 is connected to the upper surface of the inner lead 26 by this heat and the ultrasonic vibration energy applied from the ultrasonic generator 6 through the capillary 10. Even in this case, as the joining of the wire 11 and the inner lead 26 due to ultrasonic vibration progresses, the inner lead 2
6 also starts vibrating in synchronization with the ultrasonic vibration of the wire 11 or the capillary 10. Such vibration of the inner lead 26 affects the entire lead frame 30. Therefore, it is possible to substantially know the vibration state of the inner lead 26 by detecting the vibration state of the appropriate portion of the lead frame 30, and in this case also, in the same manner as described above, the vibration state of the lead frame 30. When the vibration energy of the inner lead 26 estimated from the state reaches the range indicated by the symbol A in the graph shown in FIG. 2, the control means 12 stops or reduces the drive of the ultrasonic wave generation source 6. Of.

By doing so, not only the second bonding is properly and surely performed, but also the situation where the internal lead 26 or the lead frame 30 is damaged by the excessive vibration energy applied can be effectively avoided. it can. When such a second bonding is completed and the capillary 10 is retracted upward, each internal lead 26 returns to a natural state in which it is separated from the upper surface of the metal heat dissipation plate 21 by its elastic restoring force.

Next, as shown in FIG. 9, the semiconductor chip 2
4. Wrap the wire bonding part 11
The resin package 22 is formed by a transfer molding method using a thermosetting resin such as epoxy.

Then, the unit semiconductor device shown in FIG. 3 is obtained through steps such as solder plating on the lead frame 30, marking on the resin package 22, tie bar cutting, lead cutting, and lead forming.

The present invention is not limited to the embodiment shown in the drawings and described above. In short, the ultrasonic bonding method of the present invention is intended to directly detect a change in the kinetic energy of a member to be connected in real time and feed back this as a stop condition for the ultrasonic wave generation source. The target of ultrasonic bonding is not limited to the bonding of various members to the lead frame in the manufacture of semiconductor devices as described above. All modifications within the inventive concept described in the claims are included in the scope of the present invention.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an apparatus for carrying out the method of the present invention.

FIG. 2 is a graph showing a change in vibration energy transmitted to a member to be joined during ultrasonic joining.

FIG. 3 is a cross-sectional view showing an example of a resin semiconductor device bonded by the method of the present invention.

4 is a partial cross-sectional view of an example of a lead frame used for manufacturing the resin package type semiconductor device shown in FIG. 3, showing a state in which a metal heat dissipation plate is joined to the lower surface of the die pad.

5 is a cross-sectional view taken along the line VV of FIG. 4, showing a state in which a metal heat dissipation plate is bonded to the lower surface of the die pad by the method of the present invention.

6 is a partial cross-sectional view of an example of a lead frame used for manufacturing the resin package type semiconductor device shown in FIG. 3, showing a bonding pad on the upper surface of a semiconductor chip and an upper surface of a tip portion of each internal lead. It shows a state in which the spaces are connected by wire bonding.

FIG. 7 is a sectional view taken along line VII-VII in FIG. 6;

FIG. 8 is a side sectional view showing a state in which wire bonding is performed between the upper surface of the semiconductor chip and the internal lead by the method of the present invention.

9 is a side sectional view showing a state in which a resin package is formed on the lead frame shown in FIG.

FIG. 10 is a cross-sectional view showing a conventional joining method.

FIG. 11 is a cross-sectional view showing a conventional joining method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Support base 2 Joined member 3 Joining member 4 Pressing tool 5 Ultrasonic horn 6 Ultrasonic wave generation source 7 Joining part 8 Semiconductor chip 9 Lead 10 Capillary 11 Wire 12 Control means 13 Vibration sensor

Claims (5)

[Claims] 1. An ultrasonic joining method comprising applying ultrasonic vibration to the joining member through the tool in a state where the joining member is pressed against the members to be joined by a tool connected to an ultrasonic wave generation source. An ultrasonic bonding method is characterized in that the ultrasonic vibration generated by the ultrasonic source is stopped or reduced according to the vibration state of the member to be bonded or its supporting member. 2. The tool is a capillary for wire bonding, the bonding member is a wire inserted through the capillary, and the bonded member is a lead frame or a semiconductor chip bonded on the lead frame. The ultrasonic bonding method according to claim 1, wherein: 3. The ultrasonic bonding method according to claim 1, wherein the bonding member is a die pad in a lead frame, and the member to be bonded is a metal heat dissipation plate disposed on a lower surface of the die pad. 4. An ultrasonic wave generation source which is controlled and driven by a control means, a pressing tool which is connected to the ultrasonic wave generation source, and can press the bonding member against the member to be bonded, A vibration sensor for detecting a vibration state of the member or its supporting member; and the control means according to the vibration state of the joined member or its supporting member detected by the vibration sensor,
An ultrasonic bonding apparatus, which is configured to control the ultrasonic vibration source. 5. The control means stops or reduces the ultrasonic vibration generated by the ultrasonic source when the vibration of the member to be joined or its supporting member detected by the vibration sensor reaches a predetermined state. The ultrasonic bonding apparatus according to claim 4, wherein: