Ultrasonic bonding method

Abstract

For ultrasonic bonding, an energy source used for a bonding site is currently ultrasonic, pressure, and heating. Provided is a method for, when performing ultrasonic bonding, making a current flow through a bonding surface of two members to be ultrasonically bonded.

Description

Ultrasonic bonding method

[0001] The present invention relates to a method for ultrasonically joining members.

[0002] The TEM image in Figure 2.1(b) of [Non-Patent Document 1] shows a lattice image of Au metals bonding by surface atomic diffusion when they come into contact at room temperature. It describes how Au metal can be atomically bonded at room temperature without melting at high temperatures. It also describes how, when force is applied, free electrons move along with the atoms, acting as an adhesive between the atoms, providing ductility that allows deformation without breaking the bonds between the atoms.

[0003] Figures 28, 29, 30, and 31 of [Non-Patent Document 2] show graphs of the results of temperature measurements using a thermocouple in an apparatus for joining wires between a tip that applies ultrasonic waves and an anvil that applies a load to the tip. It is described that increasing the load applied to the tip reduces the amplitude (output) of the applied ultrasonic waves, thereby suppressing the temperature rise between the tip and the anvil. From this, it can be inferred that using a method that applies a load in addition to ultrasonic waves suppresses the temperature rise (energy) at the ultrasonic joining location, thereby reducing the effect of the applied ultrasonic waves.

[0004] Figure 8 of [Non-Patent Document 3] shows a cross-sectional image of an ultrasonically bonded area between gold and aluminum. Because the bonding of gold and aluminum occurs via an intermetallic compound, the publication describes heating at 150 to 200°C as the activation energy required to form the intermetallic compound layer. While the intermetallic compound layer improves the strength of the bond, Figure 9 shows that if the intermetallic compound layer becomes too thick, the strength in the shear direction decreases. Furthermore, because the heating heats the entire semiconductor chip, the transistors of the integrated circuits formed on the semiconductor chip and the extensive wiring are also heated, which may cause thermal damage.

[0005] In [Non-Patent Document 4], in "3. Ultrasonic bonding of multi-wire and substrate," the authors describe that, in the crystal orientation analysis using an EBSD device shown in Figure 7, after ultrasonic bonding, the crystal grains in most regions were oriented in the <110> direction, confirming the formation of a shear texture. Furthermore, in the section "4. In-situ observation experiment," they describe that a large number of nanoparticles were generated during ultrasonic bonding, and that by applying ultrasonic waves multiple times, these nanoparticles accumulated to form a fine-grained region, and that the nanocrystals were observed moving between the two stacked thin aluminum samples.

[0006] Figure 1 of [Non-Patent Document 5] shows a crystal orientation map near the bonded interface between 6061 aluminum alloy and 304 stainless steel. The crystal orientation map was obtained by observing a cross section parallel to the direction of current flow. The paper also shows {111} pole figures obtained from crystal orientation maps obtained by cross-sectional observation of the aluminum alloy and the contact region between the aluminum alloy and SUS304 stainless steel. It is described that the {111} pole figures near the bonded interface show that the strength is high at the pole center, i.e., the distribution is similar to that observed in shear bands of fcc (face-centered cubic) metals. It is also described that the {111} pole figures suggest that the {111} planes of the crystal grains, which are the slip planes, are parallel to the bonded interface.

[0007] In the section "1.3.1 Wire Bonding Process (Wedge, Ball)" of [Non-Patent Document 6], a "thermocompression bonding method" that does not use ultrasonic waves, i.e., a bonding method that uses only heat and pressure, is described. It is noted that in the case of "thermocompression bonding" that does not use ultrasonic waves, bonding is performed at a high temperature (300°C), which may destroy the chip, the chip mount, and other semiconductor materials. It is also noted that if "ultrasonic thermocompression bonding" (Hot Work Ultrasonic Bonding, 1970), a bonding method developed by A. Coucoulas that combines ultrasonic bonding and thermocompression bonding, is used instead of "thermocompression bonding," the bonding temperature can be lowered to 125 to 220°C.

[0008] In [Non-Patent Document 7], in the section "III. Experimental Results and Discussion," under "1. Void Formation at the Bonding Portion," Fig. 3 shows that when ultrasonically bonding dissimilar metals Au and Al, if there is an oxide film on the surface of the Al pad, the bonding will not be good. Furthermore, in the same section "III. Experimental Results and Discussion," under "1. Void Formation at the Bonding Portion," it is also described that the native oxide film or thermal oxide film formed on the Al surface is destroyed by the load deformation and ultrasonic application during ball bonding, exposing the newly formed Al surface, thereby achieving good metal bonding.

[0009] In Non-Patent Document 8, in "7-1 Generation of Powerful Ultrasonic Waves," a method of generating ultrasonic waves by applying an AC voltage to piezoelectric ceramics is described. Also, in "7-4 Ultrasonic Welding," in "7-4-1 Basic Configuration of an Ultrasonic Welding Device," Figures 7-14(a), (b), and (c) show the configuration of an ultrasonic welding device.

[0010] Japan Institute of Metals, Public Interest Incorporated Foundation, Journal of the Japan Institute of Metals, "Materialia," Vol. 57, No. 10 (2018), "Diffusion Bonding Part 2: Joining Metals, Bonding Equipment, Increasing the Bonding Area, and Behavior of the Coating on the Bonding Surface," WELLBOND Representative (Visiting Professor, Tokyo University of Science), Osamu Ohashi, General Incorporated Association, Production Technology Advancement Association, Osaka University Production Technology Advancement Association, Quarterly Journal "Production and Technology," Vol. 14, No. 8 (1962), "On Ultrasonic Bonding," Shigeo Arata, Doctor of Engineering, Department of Welding Engineering, Osaka University, Journal of the Japan Institute of Electronics Packaging, Vol. 5, No. 4 (2002), Fundamental Materials Lecture Series, 5th "Wire Bonding Technology for Semiconductor Devices," Jin Onuki, Department of Electronic and Information Systems, School of Systems Science and Technology, Akita Prefectural University, Journal of Surface Analysis, Vol. 28, No. 2 (2022), "Microstructure of Ultrasonic Welding Interface," Tomohiro Iwamoto, Department of Quantum Beam Science, Graduate School of Science and Engineering, Ibaraki University; 21st Aoba Engineering Research Encouragement Award; "Elucidation of the Joining Function in Ultrasonic Welding of Metallic Materials," Hiromichi Fujii, Assistant Professor, Department of Materials Systems Engineering, Graduate School of Engineering, Tohoku University; Doctoral Dissertation, Graduate School of Osaka University (January 2022); "Research on Highly Reliable Ultrasonic Welding Technology for High-Current Power Modules," Fumiyoshi Kawashiro, Department of Environmental and Energy Engineering, Graduate School of Engineering, Osaka University; Journal of the Japan Institute of Metals, Vol. 63, No. 7 (1999); "Growth of Intermetallic Compounds and Void Formation in Al / Au Joints," Tomohiro Uno and Kohei Tatsumi, Advanced Technology Research Laboratories, Nippon Steel Corporation; "Knowledge Base" (2014), Chapter 7, 1st Gun-10, Part 7, "7-1 Generation of High-Power Ultrasonic Waves," Kentaro Nakamura (September 2010); "7-4 Ultrasonic Welding," Yuji Watanabe (July 2009)

[0011] One method for applying energy necessary to join members is to apply ultrasonic waves to the members to be joined.

[0012] Another method is to apply a load to the members to be joined in order to obtain the energy required to join the members.

[0013] Figure 1 shows a schematic diagram of how, when a load is applied to a metal component (1), the metal atoms (2) of the component come close to each other, and the metal atoms are attracted to each other, resulting in a bond (3) below the melting point of the component (solid state).

[0014] However, when a load is applied to the members to be joined in addition to ultrasonic waves, the temperature rise (energy) at the ultrasonic joining location is suppressed, and the effect of the applied ultrasonic waves is reduced.

[0015] When applying a load in addition to ultrasonic waves to the parts to be joined, the temperature rise (energy) at the ultrasonic joining point is suppressed, and the effect of the applied ultrasonic waves is reduced. To compensate for this, there is an ultrasonic thermocompression method in which the joining point is heated.

[0016] However, when ultrasonic thermocompression bonding is applied to an integrated circuit, there is a concern that it may cause thermal damage to the transistors, wiring, and the like that constitute the integrated circuit, which do not need to be heated.

[0017] The present invention provides a method for applying an electric current to the joining points of members to be ultrasonically joined when ultrasonically joining the members.

[0018] When the conventional ultrasonic thermocompression bonding method is used, even the transistors and wiring that make up the integrated circuit, which do not need to be heated, are heated and thermally damaged. However, when the method of applying current to the points to be ultrasonically bonded of the present invention is used, when there is a mixture of bonded and unbonded points during the ultrasonic bonding process, thermal energy is supplied from the bonded points to the unbonded points, so the temperature to which the points to be bonded can be reduced or it becomes unnecessary to heat them at all. This makes it possible to reduce or even eliminate thermal damage to the transistors and wiring that make up the integrated circuit and which do not need to be heated.

[0019] Bonding due to the attractive force between metal atomsFace-centered cubic lattice (fcc) structureThe (100) face of a face-centered cubic latticeThe (111) face of a face-centered cubic latticeTransition of the bonding state between membersA state in which bonded areas and unbonded areas are mixedMethod of passing current through the area to be ultrasonically bondedA area that acts as an antenna emitting electromagnetic noiseAC electromagnetic noise generated from a capacitorMethod of shielding electromagnetic noiseMethod of eliminating an area that acts as an antenna emitting high-frequency electromagnetic noiseDevice configuration and circuit configuration when changing to a DC power supplyMethod of passing current through the area to be ultrasonically bonded using an inductorMethod of shielding AC electromagnetic noise generated from an inductorElectromagnetic noise from a magnetic field

[0020] FIG. 7 shows the configuration of a current-flowing device and a circuit configuration as a method of applying a current to the ultrasonically joined portions of members to be ultrasonically joined during ultrasonic bonding of the present invention.

[0021] FIG. 7 shows an example of the configuration of a device for passing a current through the ultrasonically joined portions of members to be ultrasonically joined, and an example of the circuit configuration.

[0022] The device for applying current to the members (1) to be ultrasonically joined shown in Figure 7 has a support jig (17) for the members (1) to be ultrasonically joined on a ceramic insulator (16). The support jig (17) for the members (1) to be ultrasonically joined is made of a conductive material.

[0023] For example, a medium frequency AC voltage of several hundred kilohertz is applied to an ultrasonic vibrator (18) made of piezoelectric ceramics from a power source (19) that outputs a medium frequency AC voltage of several hundred kilohertz.

[0024] When a medium-frequency AC voltage of several hundred kilohertz is applied to the ultrasonic vibrator (18) from a power source (19) that outputs a medium-frequency AC voltage of several hundred kilohertz, the ultrasonic vibrator (18) generates a mechanical deformation, i.e., vibration, of several hundred kilohertz, causing the ultrasonic vibrator (18) to vibrate at several hundred kilohertz, and ultrasonic waves of several hundred kilohertz are generated from the ultrasonic vibrator (18).

[0025] Ultrasonic waves of several hundred kilohertz generated from the ultrasonic vibrator (18) are transmitted through the horn (20) to the ultrasonic wave application jig (21) that is in contact with the horn (20). In Fig. 7, the ultrasonic wave application jig (21) applies ultrasonic waves in the lateral direction to the members (1) to be ultrasonically joined, based on the positions of the horn (20) and the ultrasonic wave application jig (21).

[0026] The horn (20) also has a ceramic insulator (22) that conducts ultrasonic waves but blocks the flow of electrical current.

[0027] The members (1) to be ultrasonically joined are placed between a jig (21) that applies ultrasonic waves to the members (1) and a receiving jig (17) for the members (1) to be ultrasonically joined.

[0028] A jig (21) for applying ultrasonic waves to members (1) to be ultrasonically joined is provided with a jig (23) for applying a load.

[0029] In FIG. 7, the load applied from the jig (23) for applying the load to the jig (21) for applying ultrasonic waves to the member (1) is shown by an arrow (24) as a schematic diagram.

[0030] Between the jig (23) that applies the load and the jig (21) that applies the load to the members (1) to be ultrasonically joined, there is a ceramic insulator (25) that prevents current flow. The receiving jig (17) for the members (1) to be ultrasonically joined has a screw hole, and a round crimp terminal is connected to one side of the cable (59). The round crimp terminal is screwed (60) to the receiving jig (17) for the members (1) to be ultrasonically joined, and the side of the cable (59) not connected to the round crimp terminal is connected to a capacitor (27).

[0031] A high-frequency current of 13.56 MHz, a commercial frequency, is passed from a high-frequency power supply (26) to a capacitor (27), and the high-frequency current is passed to the members (1) through a displacement current and a support jig (17) for the members (1) to be ultrasonically joined. Note that the support jig (17) for the members (1) to be ultrasonically joined is conductive. The frequency of the current passed from the high-frequency power supply (26) is not limited to 13.56 MHz. 13.56 MHz is just one example, and it may be, for example, 2.7 MHz.

[0032] The high frequency power supply (26) is connected to a resistor (28) for preventing short circuits on the side opposite to the side connected to the capacitor (27), and is grounded to GND (29) through the resistor (28) for preventing short circuits.

[0033] The device configuration and circuit configuration shown in Figure 7 make it possible to apply a current to the ultrasonically joined parts during ultrasonic bonding of the present invention. Note that the device configuration and circuit configuration shown in Figure 7 are just one example.

[0034] When ultrasonically bonding, if an electric current is applied to the ultrasonically bonded parts, the natural principle is that the electric current will try to pass through areas with low resistance, and the crystalline structure of the ultrasonically bonded parts will be one that allows the electric current to flow easily in the direction of the current flow, i.e., a crystalline structure that has low electrical resistance.

[0035] The face-centered cubic (fcc) lattice structure, which is the crystalline structure of the metals Au and aluminum, is shown in Figure 2. At room temperature, the lattice constant (a-axis) of Au is 4.0875 Å, and the lattice constant (a-axis) of aluminum is 4.0496 Å.

[0036] Figure 3 shows the crystal structure of the (100) plane of a face-centered cubic lattice, which is the crystal structure of metals Au and aluminum, when viewed from the vertical direction. Figure 3 also shows an atom (61) that is not on the (100) plane of the face-centered cubic lattice, but that blocks the flow of current when the direction in which the (100) plane of the face-centered cubic lattice is viewed from the vertical direction coincides with the direction in which the current flows.

[0037] Figure 4 shows the crystal structure of the (111) plane of a face-centered cubic lattice, which is the crystal structure of metals Au and aluminum, when viewed from the vertical direction. Note that Figure 4 also shows atoms (62) that are not on the (111) plane of the face-centered cubic lattice, but that obstruct the flow of current when the direction in which the (111) plane of the face-centered cubic lattice is viewed from the vertical direction coincides with the direction in which current flows.

[0038] When the crystal structure is formed so that the plane orientation of the crystal structure is the (100) plane shown in FIG. 3 or the (111) plane shown in FIG. 4 when viewed from the direction of current flow, if the crystal structure is formed in an arbitrary direction as shown in FIG. 2, there will be more atoms that obstruct the flow of current, making it difficult for the current to flow.

[0039] According to the natural principle that electric current tends to flow through areas with low resistance, when electric current is applied to the area to be ultrasonically bonded during ultrasonic bonding, the crystal structure of the area to be ultrasonically bonded is formed so that the (100) plane or (111) plane is perpendicular to the direction of the current flow, i.e., a crystal structure that allows electric current to flow easily, and the resistance value decreases.

[0040] Alternatively, based on the natural principle that when free electrons move, they tend to pass through areas where it is easier for them to move, when current is applied during ultrasonic bonding, the crystal structure at the bonding point is formed so that the (100) or (111) plane is perpendicular to the direction of the current flow, i.e., a crystal structure that allows electrons to move easily, and the resistance value decreases.

[0041] In the following, when simply referring to electrons, this refers to free electrons.

[0042] For example, if the components are metallic gold or aluminum, when the method of the present invention of applying an electric current to the joining points during ultrasonic bonding is used, the ultrasonically bonded points will have a crystalline structure that allows electrons to move easily, and the resistance value of the ultrasonically bonded points will be reduced.

[0043] Figure 5 shows a schematic diagram of the transition of the bonded state between metals (1) when ultrasonic bonding is performed while applying current using the method of the present invention for gold and aluminum metals, showing the transition before ultrasonic bonding while applying current (4), when the components (1) are in local contact (5) (6), when ultrasonic waves (7) are applied laterally to the contact points, destroying the oxide film on the surface of the components and causing plastic deformation (8) of the contact points as the bonding progresses (9), and when ultrasonic bonding is completed (10), i.e., when solid-state bonding (bonding below the melting point of the components) is achieved. Note that in Figure 5, the application of ultrasonic waves (7) laterally is schematically indicated by arrows.

[0044] Figure 6 shows the ultrasonic bonding method of the present invention, in which an electric current is passed through the joining points. The oxide film (11) on the surface of the components (1) is destroyed by ultrasonic waves (7) while the contact points undergo plastic deformation (8). As the joining progresses (9), i.e., when the joined points (12), unjoined points (13), and the oxide film (11) on the surface of the components are mixed, the current flow (15) concentrates (14) at the joining points (12) due to the natural principle that current tends to flow through areas of low resistance. The current flow (15) is also shown diagrammatically with arrows. The arrows also diagrammatically show the application of ultrasonic waves (7) laterally to the joining points of the components (1).

[0045] Since the current flow is AC, the current flow (58) in the case where the current flow (15) shown in FIG. 7 is reversed is shown schematically in FIG. 16 by an arrow as the current flow (58).

[0046] An example in which the members to be joined (1) are metals such as gold or aluminum will be described with reference to Figure 6. When ultrasonically joining the parts of the present invention, the resistance of the parts to be joined by applying a current to the parts to be joined decreases, as described in paragraphs

[0024] ,

[0025] , and

[0027] of the specification.

[0047] Power is the product of the square of the current and the resistance value.

[0048] Also, Joule heat is the product of power and time.

[0049] As shown in Figure 6, when ultrasonic bonding of the present invention is performed by passing an electric current through the joining points, if there are a mixture of joined points (12) and unjoined points (13), the flow of electric current (15) will concentrate (14) at the joined points, generating heat at the joined points (12).

[0050] The heat generated from the joined portion becomes thermal energy supplied to the unjoined portion for joining.

[0051] For example, when the members to be joined (1) are metals such as gold or aluminum, it is well known that they are thermally conductive, and the heat generated from the joined part (12) is conducted to the unjoined part (13) and becomes the thermal energy for joining.

[0052] That is, when the method of the present invention of applying an electric current to the parts to be ultrasonically bonded is used, the heat generated from the bonded parts (12) becomes thermal energy supplied to the parts (13) that have not yet been bonded in order to promote bonding.

[0053] That is, when the method of the present invention of applying an electric current to the parts to be ultrasonically bonded is used, in addition to the applied ultrasonic waves, energy for bonding is supplied to the parts (13) that have not yet been bonded, thereby promoting the bonding of the parts (13) that have not yet been bonded.

[0054] As an example, the present invention has been described with reference to a case where metals such as Au and aluminum are used as the members (1) to be joined using the method of applying a current to the parts to be ultrasonically joined.

[0055] The method of applying a current to the portion to be ultrasonically bonded according to the present invention can be applied to bonding dissimilar metals such as Au and aluminum, other metals such as copper and nickel, or conductive alloy materials.

[0056] FIG. 8 shows the configuration of the device shown in FIG. 7 and a simplified circuit diagram of the circuit configuration.

[0057] Figure 8 shows a simplified equivalent circuit diagram of the antenna 32 that emits high-frequency electromagnetic noise, consisting of a jig 15 for receiving the ultrasonically bonded components 1, the components 1, and a jig 19 for applying voltage to the components 1. The lightning bolt 30 in the diagram is a schematic representation of the electromagnetic waves emitted from a capacitor 27 that emits high-frequency electromagnetic noise.

[0058] In the simplified circuit diagram of FIG. 8, there are no connections to GND from the capacitor (27) to the jig (17) for receiving the members (1) to be ultrasonically joined, the members (1) to be ultrasonically joined, or the jig (21) for applying ultrasonic waves to the members (1) to be ultrasonically joined.

[0059] Since the capacitor (27) to the receiving jig (17) for the members (1) to be ultrasonically joined, the members (1) to be ultrasonically joined, and the jig (21) that applies ultrasonic waves to the members (1) to be ultrasonically joined are not connected to GND, the capacitor (27) to the jig (21) that applies ultrasonic waves to the members (1) to be ultrasonically joined form a floating circuit section that is floating above GND potential.

[0060] Since the circuit is a floating circuit floating above the GND potential, the support jig (17) for the members (1) to be ultrasonically joined, the members (1) to be ultrasonically joined, and the jig (21) that applies ultrasonic waves act as an antenna (32) that emits high-frequency electromagnetic noise.

[0061] FIG. 10 shows a method for shielding the capacitor (27) and the electromagnetic noise generated from the antenna (32) that emits high frequency electromagnetic noise.

[0062] FIG. 10 shows a method for shielding electromagnetic noise generated from a capacitor (27) by enclosing an area that serves as an antenna (32) that emits high-frequency electromagnetic noise, including the capacitor (27), in a conductive case (31), and the conductive case (31) is connected to GND (29).

[0063] The ceramic insulator (22) described in paragraph

[0048] and the ceramic insulator (25) described in paragraph

[0053] are intended to prevent high-frequency current from flowing into the external surrounding environment from the conductive case (31) surrounding the area that serves as the antenna (32) that emits high-frequency electromagnetic noise.

[0064] FIG. 9 shows that when AC electromagnetic noise generated from a capacitor propagates in the direction of electromagnetic wave propagation (33), the electric field (35) strength (36) near the source (34) of the electromagnetic wave radiation is greater than the magnetic field (37) strength (38).

[0065] Since AC electromagnetic noise generated from a capacitor is easier to shield than electromagnetic noise caused by a magnetic field (37), measures to prevent malfunction of external devices are easy to take.

[0066] Figure 11 shows an example of another method for passing current through the members (1) to be ultrasonically joined. In the device configuration and circuit configuration shown in Figure 10, a screw hole is drilled into the jig (21) that applies ultrasonic waves, a round crimp terminal is attached to one side of a flexible robot cable (39), and the round crimp terminal is screwed (40) into the jig (21) that applies ultrasonic waves and has a screw hole drilled into it. The other side of the robot cable, the side where the round crimp terminal is not crimped, is grounded to GND (29) through a short-circuit prevention resistor (41), eliminating the floating circuit part floating above GND potential and eliminating any part that could serve as an antenna for emitting high-frequency electromagnetic noise.

[0067] FIG. 11 shows an example of a method for passing current through the members (1) to be ultrasonically joined, in which a receiving jig (15) for the members (1) to be ultrasonically joined, the members (1) to be ultrasonically joined, and an applying jig (19) for applying ultrasonic waves to the members (1) to be ultrasonically joined are connected to GND, and a floating circuit section floating above GND potential, as in the circuit configuration shown in FIG. 10, i.e., connected to GND (29) so as not to have any portion that becomes an antenna that emits electromagnetic waves.

[0068] FIG. 12 shows an example of another method for passing a current through the members (1) to be ultrasonically joined. It shows the configuration of the device and the circuit configuration when the high frequency power supply (26) used in FIG. 11 is changed to a DC power supply, and shows a method for passing a DC current through the members (1) to be ultrasonically joined.

[0069] FIG. 13 shows an example of another method for passing a current through the members (1) to be ultrasonically joined. The device configuration and circuit configuration are shown in which an inductor (43) is used to pass a current from an AC power source (44) through the inductor (43), and the current generated in the inductor (46) by electromagnetic induction of the inductor (43) is passed through the members (1).

[0070] In the device configuration and circuit configuration shown in Fig. 13, an inductor (43) and an inductor (46) are connected instead of the capacitor (27) used in the example of the device configuration shown in Fig. 7. The inductor (43) is connected to an AC power supply (44), and the side of the AC power supply (44) not connected to the inductor (43) is grounded to GND (29) through a short-circuit prevention resistor (57).

[0071] The inductor (46) is connected to a receiving jig (17) for the members (1) to be ultrasonically joined, and the side of the inductor (46) not connected to the receiving jig (17) is grounded to GND (29) through a short-circuit prevention resistor (47). The inductor (43) and the inductor (46) are magnetically coupled (45).

[0072] When a current flows from the AC power supply (44) to the inductor (43), electromagnetic induction causes a current to flow in the inductor (46). In addition, in Figure 13, the magnetic field coupling (45) between the inductor (43) and the inductor (46) is shown schematically as a framed image.

[0073] Regarding the AC power supply (44) used in the configuration of the device shown in FIG. 13, when the frequency of the voltage and current applied to the inductor (43) is high, the reactance component (jωL) of the impedance (R+jωL) becomes large, resulting in a high impedance. Therefore, the AC power supply (44) applies a voltage and current of a medium frequency of several tens of kilohertz to several hundreds of kilohertz.

[0074] Figure 14 shows the propagation of AC electromagnetic noise when a magnetic field is generated from an inductor. When electromagnetic noise propagates in the direction of electromagnetic wave propagation (48), the magnetic field (50) strength (51) near the source (49) of the electromagnetic wave is greater than the electric field (52) strength (53).

[0075] As shown in Figure 15, the case (55) used to shield the electromagnetic noise emitted from the circuit (54) using an AC magnetic field is made of a material that conducts electricity, such as aluminum, and even if it is connected to GND (29), aluminum is not a magnetic material, so the magnetic flux cannot be passed through the magnetic material to GND (29) to shield the electromagnetic noise. In other words, if a non-magnetic material is used, the magnetic flux will leak out, making it difficult to prevent external equipment from malfunctioning. In Figure 15, the magnetic flux (56) leaking out is schematically represented by an arrow.

[0076] In the method using an AC magnetic field, the electromagnetic noise emitted from the circuit (54) has a magnetic field strength (51) greater than the electric field strength (53). Therefore, in order to shield the magnetic flux emitted from the magnetic field, there are many restrictions on the materials to be used, such as the need for a magnetic material, i.e., a material that can allow magnetic flux to flow and provide shielding, and the number of material options is limited.

[0077] In the case of electromagnetic noise caused by a high-frequency magnetic field, eddy currents are generated on the surface due to the skin effect of the metal, so even if a non-magnetic material such as aluminum is used, the electromagnetic noise can be shielded by flowing the generated eddy currents to GND. However, in the case of electromagnetic noise caused by a medium-frequency magnetic field of several hundred kilohertz, the skin effect decreases, so the effectiveness of shielding electromagnetic noise decreases when using a non-magnetic material such as aluminum.

[0078] Furthermore, even when the material used for the enclosing case (55) for shielding electromagnetic noise is magnetic in order to shield magnetic flux, if the enclosing case (55) for shielding electromagnetic noise is thin, there is a high possibility that the magnetic flux will not be able to flow through the magnetic material and be completely shielded, so in order to allow the magnetic flux to flow and shield it so that it does not leak to the outside, it is necessary to make the enclosing case (55) for shielding electromagnetic noise thicker.

[0079] 1 Members 2 Atoms 3 Bonding 4 Before ultrasonic bonding 5 Local contact 6 When members are in local contact with each other 7 Ultrasonic waves 8 Plastic deformation 9 When plastic deformation occurs and bonding is progressing 10 Completion of ultrasonic bonding 11 Oxide film on the surface of the members 12 Bonded area 13 Area not yet bonded 14 Current flow concentrates 15 Current flow 16 Insulator 17 Jig for holding members to be ultrasonically bonded 18 Ultrasonic vibrator 19 Power source that outputs medium-frequency AC voltage 20 Horn 21 Jig that applies ultrasonic waves to members to be ultrasonically bonded 22 Insulator 23 Jig that applies load 24 Arrow 25 Insulator 26 High-frequency power source 27 Capacitor 28 Resistor to prevent short circuits 29 GND 30 Lightning bolt diagram 31 Conductive case 32 Antenna that emits high-frequency electromagnetic noise 33 Direction of electromagnetic wave propagation 34 Source of electromagnetic wave radiation 35 Electric field 36 Electric field strength 37 Magnetic field 38 Magnetic field strength 39 Robot cable 40 Screw fastening 41 Resistor to prevent short circuits 42 DC power supply 43 Inductor 44 AC power supply 45 Magnetic field coupling 46 Inductor 47 Resistor to prevent short circuits 48 Direction of electromagnetic wave propagation 49 Source of electromagnetic wave radiation 50 Magnetic field 51 Magnetic field strength 52 Electric field 53 Electric field strength 54 Circuit using AC magnetic field 55 Enclosure to shield electromagnetic noise 56 Leaking magnetic flux 57 Resistor to prevent short circuits 58 Current flow 59 Cable 60 Screw fastening 61 Atom that obstructs current flow 62 Atom that obstructs current flow

Claims

1. When ultrasonically joining, one of the two components to be ultrasonically joined is connected to one side of a power supply, the other of the two components is connected to the other side of the power supply, and current is passed through the joining surfaces.

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