Ultrasonic bonding

Abstract

To solve a problem in which, currently, the energy sources used at the bonding site for ultrasonic bonding are ultrasound, pressure, and heat.SOLUTION: There is provided a method for passing an electric current to the joining points of members to be ultrasonically bonded when performing ultrasonic bonding.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to a method for ultrasonically joining components. [Background technology]

[0002] The TEM image in Figure 2.1(b) of [Non-Patent Document 1] shows a lattice image of Au metal bonding by surface atomic diffusion when the metals are in contact with each other at room temperature. It is described that Au metal can be atomically bonded at room temperature without melting at high temperatures. It also states that when force is applied, the free electrons move along with the atoms, and the free electrons act as a glue between the atoms, giving the material ductility to deform 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 a device that joins 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 is estimated that when a method of applying a load in addition to ultrasonic waves is used, the temperature rise (energy) at the ultrasonic bonding location is suppressed, and the effect of the applied ultrasonic waves is reduced.

[0004] FIG. 8 of [Non-Patent Document 3] shows a cross-sectional observation image of an ultrasonic bond between Au and aluminum. It is described that since the bonding between Au and aluminum progresses through an intermetallic compound, heating at 150 to 200° C. is required as the activation energy for forming an intermetallic compound layer. However, although the intermetallic compound layer improves the strength of the joint, Figure 9 shows that if the intermetallic compound layer becomes too thick, the strength in the shear direction decreases. In addition, since the heating heats the entire semiconductor chip, the transistors of the integrated circuits formed on the semiconductor chip and the wiring that runs throughout the chip are also heated, which is thought to cause thermal damage.

[0005] In the crystal orientation analysis using an EBSD device in Figure 7 of "3. Ultrasonic bonding of multi-wire and substrate" in [Non-Patent Document 4], after ultrasonic bonding, the crystal grains in most areas were <110> It is reported that the grains are oriented in the direction of shear and that shear texture is formed. In addition, in the section "4. In-situ observation experiment," it is described 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 around between the two stacked thin aluminum samples.

[0006] FIG. 1 of [Non-Patent Document 5] shows a crystal orientation map near the joint 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 describes {111} pole figures obtained from crystal orientation maps obtained by cross-sectional observation of the aluminum alloy and the contact area between the aluminum alloy and SUS304 steel. It also describes that in the pole figures near the joint interface, 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 stated that the {111} pole figures suggest that the {111} faces of the crystal grains, which are the slip planes, are parallel to the joint surface.

[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, that is, a bonding method that uses only heat and pressure, is described. In the case of the "thermocompression bonding method" which does not use ultrasound, bonding is carried out at a high temperature (300°C), which means that there is a possibility that the chip, the chip mount, and other semiconductor materials may be destroyed. It is also described that by using "Hot Work Ultrasonic Bonding" (1970), a bonding method developed by A. Coucoulas that combines ultrasonic bonding and thermocompression bonding, rather than the "thermocompression bonding" method, the bonding temperature can be lowered to 125-220°C.

[0008] In [Non-Patent Document 7], in the section "III. Experimental Results and Discussions", under "1. Void formation at the joint", Fig. 3 shows that when ultrasonically joining dissimilar metals Au and Al, if there is an oxide film on the surface of the Al pad, the joint will not be good. Additionally, in the same section "III. Experimental results and discussion," under "1. Void formation at the joint," it is also stated that the natural oxide film or thermal oxide film formed on the aluminum surface is destroyed by the load deformation and ultrasonic application during ball joint joining, exposing the newly formed aluminum surface, thereby enabling a good metal joint to be obtained.

[0009] In "7-1 Generation of high-intensity ultrasonic waves" in [Non-Patent Document 8], a method of generating ultrasonic waves by applying an AC voltage to piezoelectric ceramics is described. In addition, the configuration of an ultrasonic welding device is shown in Figures 7-14(a), (b), and (c) of "7-4 Ultrasonic Welding" and "7-4-1 Basic Configuration of Ultrasonic Welding Device." [Prior art documents] [Non-patent literature]

[0010] [Non-Patent Document 1] Japan Institute of Metals, Japan Institute of Metals Bulletin "Materia" Vol. 57, No. 10 (2018), "Diffusion bonding, Part 2: Joining metals, bonding equipment, increasing process of bonding area, behavior of coating on bonding surface" WELLBOND Representative (Visiting Professor, Tokyo University of Science) Osamu Ohashi [Non-Patent Document 2] General Incorporated Association, Production Technology Promotion Association, Osaka University Production Technology Promotion Association, Quarterly Magazine "Production and Technology" Vol. 14, No. 8 (1962), "About Ultrasonic Welding Method" by Shigeo Arata, Doctor of Engineering, Department of Welding Engineering, Osaka University [Non-Patent Document 3] Journal of the Japan Institute of Electronics Packaging, Vol. 5, No. 4 (2002), Basic Materials Lectures, 5th Lecture, "Wire Bonding Technology for Semiconductor Devices", Jin Ohnuki, Department of Electronics and Information Systems, Faculty of Systems Science and Technology, Akita Prefectural University [Non-Patent Document 4] Journal of Surface Analysis, Vol. 28, No. 2 (2022), "Microstructure of Ultrasonic Bonding Interface" Tomohiro Iwamoto, Department of Quantum Beam Science, Graduate School of Science and Engineering, Ibaraki University [Non-Patent Document 5] 21st Aoba Engineering Research Encouragement Award, "Elucidation of the joining function in ultrasonic joining of metal materials" Assistant Professor Hiromichi Fujii, Department of Materials Systems Engineering, Graduate School of Engineering, Tohoku University [Non-Patent Document 6] Doctoral thesis, Osaka University (January 2022), "Research on highly reliable ultrasonic bonding technology for high current power modules," by Fumitaka Kawashiro, Department of Environmental and Energy Engineering, Graduate School of Engineering, Osaka University [Non-Patent Document 7] 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, Kohei Tatsumi, Advanced Technology Research Laboratories, Nippon Steel Corporation [Non-Patent Document 8] "Knowledge Base" of the Institute of Electronics, Information and Communication Engineers (2014) 1st Gun-10th Edition-7th Chapter "7-1 Generation of High-Power Ultrasonic Waves" by Kentaro Nakamura (September 2010), "7-4 Ultrasonic Welding" by Yuji Watanabe (July 2009) Summary of the Invention [Problem to be solved by the invention]

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

[0012] In addition, there is a method of applying 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, causing the attractive forces between the metal atoms to act, joining the components (3) below their melting points (solid state).

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

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

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

[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. Effect of the Invention

[0018] When using the conventional ultrasonic thermocompression bonding method, the transistors and wiring that make up the integrated circuit, which do not need to be heated, are heated and thermally damaged. When the method of the present invention of applying electric current to the points to be ultrasonically bonded is used, in a state in which bonded points and unbonded points are mixed during the ultrasonic bonding process, thermal energy is supplied from the bonded points to the unbonded points, making it possible to lower the temperature at which the points to be bonded are heated or to eliminate the need to heat them, thereby making it possible to reduce or eliminate thermal damage to transistors, wiring, etc. that make up the integrated circuit and that do not need to be heated. [Brief description of the drawings]

[0019] [Figure 1] Bonding by metal atomic attraction [Diagram 2] Face-centered cubic (fcc) structure [Diagram 3] (100) face of face-centered cubic lattice [Figure 4] (111) face of face-centered cubic lattice [Diagram 5] Changes in the bonding condition between components [Figure 6] A state in which joined parts and parts that have not yet been joined are mixed together. [Figure 7] A method of passing an electric current through the area to be ultrasonically joined [Figure 8] Locations that act as antennas emitting electromagnetic noise [Figure 9] AC electromagnetic noise generated by a capacitor [Figure 10] How to block electromagnetic noise [Figure 11] Methods for eliminating antennas that emit high-frequency electromagnetic noise [Figure 12] Equipment configuration and circuit configuration when changing to DC power supply [Figure 13] A method of passing current through the area to be ultrasonically bonded using an inductor [Figure 14] AC electromagnetic noise generated by inductors [Figure 15] Methods for shielding against electromagnetic noise from magnetic fields DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

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

[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) for applying 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 load application jig (23) to the jig (21) that applies 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 the flow of current. Furthermore, the receiving jig (17) for the members (1) to be ultrasonically joined has a screw hole drilled, 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) to which the round crimp terminal is not connected is connected to a capacitor (27).

[0031] A high-frequency current of commercial frequency 13.56 MHz is applied from the high-frequency power supply (26) to the capacitor (27), and the high-frequency current is applied to the members (1) through the displacement current and the 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 applied 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) has a resistor (28) for preventing short circuits connected to 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 Fig. 7 make it possible to apply a current to the ultrasonically bonded parts of the members to be ultrasonically bonded when performing ultrasonic bonding according to the present invention. Note that the device configuration and circuit configuration shown in Fig. 7 are only one example.

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

[0035] Figure 2 shows the face-centered cubic (fcc) crystal structure of metals such as Au and aluminum. 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] FIG. 3 shows the crystal structure of the face-centered cubic (100) plane of the metal Au or aluminum crystal structure when viewed from the vertical direction. FIG. 3 also illustrates an atom (61) that is not on the (100) plane of the face-centered cubic lattice, but that blocks the flow of electric current when the direction in which the (100) plane of the face-centered cubic lattice is viewed perpendicularly coincides with the direction in which the electric current flows.

[0037] FIG. 4 shows the crystal structure of the (111) plane of a face-centered cubic lattice, which is the crystal structure of metals such as Au and aluminum, viewed from the vertical direction. FIG. 4 also illustrates an atom (62) that is not on the (111) plane of the face-centered cubic lattice, but which blocks the flow of electric current when the direction in which the (111) plane of the face-centered cubic lattice is viewed perpendicularly coincides with the direction in which the electric current flows.

[0038] When viewed from the direction of current flow, the crystal structure is formed so that the plane orientation is the (100) plane shown in FIG. 3 or the (111) plane shown in FIG. 4. Compared to this, when the crystal structure is formed in an arbitrary direction as shown in FIG. 2, there are 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 ultrasonically bonded parts, the crystal structure of the ultrasonically bonded parts is formed so that the (100) and (111) planes are 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 current flow, in other words, a crystal structure that allows electrons to move easily, and the resistance value decreases.

[0041] In the following, when the word "electron" is used, it refers to a free electron.

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

[0043] Figure 5 shows, as an example, a schematic diagram of the transition of the joining state between the members (1) when ultrasonic joining is performed while applying a current using the method of the present invention for the metals Au and aluminum, including (4) before ultrasonic joining while applying a current, (6) when the members (1) are in local contact (5), (9) when ultrasonic waves (7) are applied laterally to the contact points, the contact points are plastically deformed (8) while destroying the oxide film on the surface of the members, and (10) when ultrasonic joining is completed, i.e., when solid-state joining (joining is performed below the melting point of the members). Note that in Figure 5, the application of ultrasonic waves (7) laterally is shown by arrows.

[0044] In Fig. 6, when ultrasonic bonding of the present invention is performed by using a method of passing an electric current through the bonding points, the oxide film (11) on the surface of the member (1) is destroyed by ultrasonic waves (7) while the contact points are plastically deformed (8) and bonding progresses (9). In other words, when the bonded points (12), the not yet bonded points (13), and the oxide film (11) on the surface of the member are mixed, the current flow (15) concentrates (14) on the bonded points (12) according to the natural principle that current flows through areas with low resistance. The current flow (15) is diagrammatically shown by arrows in Fig. 6. The ultrasonic waves (7) are also diagrammatically shown by arrows being applied laterally to the bonding points of the members (1).

[0045] Since the current is alternating current, the current flow (15) shown in FIG. 7 when reversed is shown diagrammatically in FIG. 16 as current flow (58) using arrows.

[0046] An example will be described in which the members to be joined (1) are metals such as Au and aluminum, with reference to Fig. 6. When ultrasonically joining the parts to be joined by applying a current to the parts to be joined according to the present invention, the resistance value 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.

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

[0049] As shown in FIG. 6, when a method of passing an electric current through the parts to be joined is used for ultrasonic bonding of the present invention, in a state in which joined parts (12) and parts that have not yet been joined (13) are mixed, the flow of electric current (15) concentrates (14) at the joined parts, generating heat at the joined parts (12).

[0050] The heat generated from the joined portion becomes thermal energy supplied to the unjoined portions in order to join them.

[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. The heat generated at the joined portion (12) is conducted to the unjoined portion (13) and becomes the thermal energy required for joining.

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

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

[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 members (1) to be joined using the method of applying a current to the parts to be ultrasonically joined.

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

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

[0057] Figure 8 shows, as a simplified equivalent circuit diagram, how the receiving jig (15) for the members (1) to be ultrasonically joined, the members (1) to be ultrasonically joined, and the jig (19) that applies voltage to the members (1) to be ultrasonically joined function as an antenna (32) that emits high-frequency electromagnetic noise. Note that the lightning bolt-shaped diagram (30) in the diagram is a schematic representation of the electromagnetic waves emitted from the 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 support jig (17) for the parts to be ultrasonically joined (1), to the parts to be ultrasonically joined (1), or to the jig (21) that applies ultrasonic waves to the parts to be ultrasonically joined (1).

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

[0060] Since it is a floating circuit part floating above the GND potential, 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 the ultrasonic waves become an antenna (32) that emits high-frequency electromagnetic noise.

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

[0062] FIG. 10 shows a method for shielding the electromagnetic noise generated from the capacitor (27) by surrounding the area that serves as an antenna (32) that emits high-frequency electromagnetic noise, including the capacitor (27), with 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 from the conductive case (31) surrounding the area that serves as the antenna (32) that emits high-frequency electromagnetic noise to the external surrounding environment.

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

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

[0066] FIG. 11 shows an example of another method for passing current through the members (1) to be ultrasonically joined, in which, in the device configuration and circuit configuration shown in FIG. 10, a screw hole is drilled into the jig (21) for applying ultrasonic waves, a round crimp terminal is attached to one side of a bend-resistant robot cable (39), and the round crimp terminal is screwed (40) into the jig (21) for applying ultrasonic waves that has a screw hole drilled therein, and the opposite side of the robot cable, the side to which the round crimp terminal is not crimped, is grounded to GND (29) through a short-circuit prevention resistor (41), eliminating the floating circuit part that is floating above the GND potential and eliminating any part that acts as an antenna that emits high-frequency electromagnetic noise.

[0067] FIG. 11 shows an example of a method of passing current through the members (1) to be ultrasonically joined. The members (1) to be ultrasonically joined, and a jig (19) that applies ultrasonic waves to the members (1) to be ultrasonically joined are connected to GND, and as shown in FIG. 10, a floating circuit section that is floating above the GND potential, i.e., connected to GND (29) so that there are no parts that can become antennas that emit electromagnetic waves, and is an example of a method of passing current through the members (1) to be ultrasonically joined.

[0068] FIG. 12 shows an example of another method for passing a current through the members (1) to be ultrasonically joined, which shows the configuration of an apparatus and a circuit when the high-frequency power supply (26) used in FIG. 11 is changed to a DC power supply, and shows a method of 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 source (44), and the side of the AC power source (44) that is 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) that is not connected to the receiving jig (17) is grounded to the 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). Note that in Figure 13, the magnetic field coupling (45) between the inductor (43) and the inductor (46) is shown diagrammatically enclosed in a box.

[0073] As for 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 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] Fig. 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) intensity (51) in the vicinity of the source (49) of the electromagnetic wave emission is greater than the electric field (52) intensity (53).

[0075] As shown in Figure 15, the case (55) used to shield the electromagnetic noise emitted from the circuit (54) using the AC magnetic field is made of a material that conducts electricity easily, 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 leaks out, making it difficult to prevent external devices from malfunctioning. Note that the magnetic flux (56) leaking out is shown as a schematic image with an arrow in Figure 15.

[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 to use magnetic materials, i.e., materials 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 high-frequency magnetic fields, 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 directing the generated eddy currents to the GND. However, in the case of electromagnetic noise caused by medium-frequency magnetic fields 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 if the material used for the enclosing case (55) for shielding electromagnetic noise is magnetic, 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 prevent it from leaking to the outside, it is necessary to make the enclosing case (55) for shielding electromagnetic noise thicker. [Explanation of symbols]

[0079] 1. Materials 2 atoms 3. Junction 4 Before ultrasonic bonding 5 Local contact 6 When parts are in local contact with each other 7. Ultrasound 8 Plastic Deformation 9 When plastic deformation occurs and joining progresses 10 Ultrasonic bonding is completed 11 Oxide film on the surface of components 12 Joint 13 Parts that have not yet been joined 14 Current flow is concentrated 15 Current Flow 16 Insulators 17. Jig for holding components to be ultrasonically joined 18 Ultrasonic transducer 19. Power supply that outputs medium frequency AC voltage 20. Horn 21 Jig for applying ultrasonic waves to the parts to be ultrasonically joined 22 Insulators 23 Load application jig 24 Arrow 25 Insulators 26 High frequency power supply 27 Capacitor 28 Resistors to prevent short circuits 29 GND 30 Lightning Shape 31 Conductive case 32 Antennas that emit high-frequency electromagnetic noise 33 Direction of electromagnetic waves 34 Source of electromagnetic radiation 35 Electric Field 36 Electric field strength 37 Magnetic Field 38 Magnetic Field Strength 39 Robot Cable 40 Screw fastening 41 Short circuit prevention resistor 42 DC power supply 43 Inductor 44 AC power supply 45 Magnetic Field Coupling 46 Inductor 47 Short circuit prevention resistor 48 Direction of electromagnetic waves 49 Source of electromagnetic radiation 50 Magnetic Field 51 Magnetic Field Strength 52 Electric Field 53 Electric Field Strength 54 Circuit for the method using AC magnetic field 55 Enclosure to block electromagnetic noise 56 Leaking magnetic flux 57 Short circuit prevention resistor 58 Current Flow 59 Cable 60 Screw fastening 61 Atoms that Block Electric Current 62 Atoms that Block Electric Current

Claims

[Claim 1] A method of ultrasonic joining in which an electric current is passed through the joint between the parts to be ultrasonically joined.

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