Soldering device and manufacturing method for joined body

Abstract

To provide a soldering device that can accurately control heating-intensity that is required in soldering, so that high-quality soldering can be performed.SOLUTION: A soldering device 100 described in the disclosure, which joins two or more members to be joined with solder 21, comprises: a heating part 1 that heats soldering sites P of the members to be joined; a resistance measuring part 3 that measures resistance between the members to be joined and the solder 21; and a control part 5 that controls heating-intensity of the heating part 1. When resistance measured by the resistance measuring part 3 falls below a certain value, the control part 5 increases the heating-intensity of the heating part 1.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a soldering apparatus and a method for manufacturing a joint. [Background technology]

[0002] Soldering, which melts solder to join components, is used, for example, to connect the terminals of electronic components or to mount electronic components on a circuit board. Heating methods for melting solder include flow, reflow, and laser. When soldering electronic components with low heat resistance, laser soldering devices are used, which are capable of localized heating. Laser soldering devices often include a non-contact temperature sensor to control the laser beam output based on temperature changes at the soldered portion of the components. However, variations in the measured temperature due to various factors make it difficult to precisely control the laser beam output to match the target temperature. If the soldered portion is not heated to the appropriate temperature, poor solder joints can occur, resulting in reduced durability and short circuits.

[0003] For example, Patent Document 1 discloses a method for precisely controlling the output of a laser beam so that the soldering portion is heated to a target temperature. In Patent Document 1, the soldering process is divided into a process of controlling the output of a laser beam in accordance with a control waveform, and a process of controlling the output of a laser beam based on the temperature of the soldering portion measured by a radiation thermometer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-176246 Summary of the Invention [Problem to be solved by the invention]

[0005] When supplying solder to the soldering area, the area is heated before the solder reaches it (hereinafter referred to as the preheating process). Then, once the solder reaches the soldering area, the laser output is increased to melt the solder (hereinafter referred to as the main heating process). When transitioning from the preheating process to the main heating process, if the output of the laser light cannot be accurately controlled based on the measured temperature of the soldering area, the soldering performance will not be stable. In other words, it is necessary to detect when the solder reaches the soldering area and control the increase in laser output at that timing.

[0006] The present disclosure has been made to solve these problems, and provides a soldering apparatus and a method for manufacturing a joint that can accurately control the heating intensity required for soldering and perform high-quality soldering. [Means for solving the problem]

[0007] The soldering apparatus according to the present disclosure is a soldering apparatus for joining two or more workpieces with solder, and includes a heating unit for heating the soldering points of the workpieces, a resistance measuring unit for measuring the resistance between the workpieces and the solder, and a control unit for controlling the heating intensity of the heating unit, wherein the control unit increases the heating intensity of the heating unit when the resistance measured by the resistance measuring unit falls below a certain value. This allows the soldering apparatus to detect when the solder has reached the soldering points and increase the laser output at that timing.

[0008] The heating unit may also be configured to include a laser oscillator that outputs laser light, and an irradiation head that irradiates the laser light output from the laser oscillator toward the soldering area, and to heat the soldering area by irradiating the laser light.

[0009] The soldering device may further include a temperature measuring unit that measures the temperature of the soldering portion, and the control unit may be configured to determine the heating intensity of the heating unit based on the temperature measured by the temperature measuring unit when the resistance measured by the resistance measuring unit falls below a certain value.

[0010] The method for manufacturing a joined body according to the present disclosure is a method for manufacturing a joined body in which two or more members to be joined are joined with solder, and includes a preheating step of heating the soldering portions of the members to be joined at a predetermined heating intensity, and a main heating step of heating the soldering portions at a heating intensity greater than that of the preheating step, in which the preheating step supplies solder to the soldering portions after a predetermined time has elapsed since the start of heating, and transitions to the main heating step after the resistance between the members to be joined and the solder falls to a certain value or less. This allows the soldering device to detect when the solder has reached the soldering portions and increase the laser output at that timing.

[0011] Furthermore, the pre-heating process may be configured to determine the heating intensity in the main heating process based on the temperature of the soldering area after the resistance between the workpiece and the solder falls below a certain value, and then transition to the main heating process. [Effects of the Invention]

[0012] The present disclosure makes it possible to provide a soldering apparatus and a method for manufacturing a bonded body that can accurately control the heating intensity required for soldering and perform high-quality soldering. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is an explanatory diagram of a soldering apparatus according to the present disclosure. [Figure 2] 2A and 2B are explanatory diagrams of a method for producing a bonded body according to the present disclosure, in which Fig. 2A is an explanatory diagram showing a preheating step, Fig. 2B is an explanatory diagram showing a main heating step, and Fig. 2C is an explanatory diagram showing a postheating step. [Figure 3]FIG. 3 is a flowchart of the method for manufacturing the bonded body according to the first embodiment. [Figure 4] 4A shows the change in output of the heating unit over time in the soldering apparatus of the present embodiment 1, FIG. 4B shows the change in temperature of the soldering portion over time, and FIG. 4C shows the change in resistance between the workpiece and the solder over time. [Figure 5] FIG. 5 is a flowchart of a method for manufacturing a bonded body according to the second embodiment. [Figure 6] 6A and 6B are diagrams showing the change in output of the heating section over time in the soldering apparatus of the second embodiment, FIG. 6A shows the change in temperature of the soldering portion over time, and FIG. 6C shows the change in resistance between the member to be joined and the solder over time. DETAILED DESCRIPTION OF THE INVENTION

[0014] Embodiment 1 The soldering apparatus according to the present disclosure will be described below with reference to the drawings.

[0015] <Configuration of soldering equipment> First, the configuration of the soldering apparatus according to the present disclosure will be described with reference to Fig. 1. Fig. 1 is an explanatory diagram of the soldering apparatus according to the present disclosure.

[0016] As shown in FIG. 1, a soldering apparatus 100 includes a heating unit 1, a solder supply unit 2, a resistance measurement unit 3, a temperature measurement unit 4, and a control unit 5. The soldering apparatus according to the present disclosure manufactures a joined body by joining two or more members to be joined with solder. In the first embodiment, the soldering apparatus 100 joins two members to be joined, that is, a substrate 6 and an electronic component 7, with solder. More specifically, the soldering apparatus 100 solders an annular terminal 61 formed on the substrate 6 to a lead 71 extending from the electronic component 7 to manufacture a joined body. Note that the members to be joined are not limited to these.

[0017] The heating unit 1 heats the soldering portion P of the workpiece. The heating unit 1 changes the heating intensity based on a command signal from the control unit 5. In the present embodiment 1, a laser irradiation unit is used as the heating unit 1, and the heating unit 1 includes a laser oscillator 11 and an irradiation head 12. The heating unit 1 is not limited to this, and other heating means may be used.

[0018] The laser oscillator 11 emits laser light L output by oscillation to the irradiation head 12. In response to an output command signal from the control unit 5, the laser oscillator 11 changes the output of the laser light L. As the light source of the laser oscillator 11, for example, a solid-state laser light source, a gas laser light source, a fiber laser light source, or the like can be used.

[0019] The irradiation head 12 irradiates the soldering area P with the laser light L output from the laser oscillator 11. The irradiation head 12 is equipped with an optical system and protective glass (not shown). The optical system focuses and refracts the laser light L transmitted from the laser oscillator 11 via an optical fiber cable so that it can be irradiated onto the soldering area P. The optical system includes, for example, a lens, a reflecting mirror, a filter, etc. The protective glass is provided on the irradiation head 12 to prevent dirt and the like generated during soldering from adhering to the optical system.

[0020] Here, the soldering area P will be described. The soldering area P differs depending on the soldering process. Before supplying the solder 21, the soldering area P includes an annular terminal 61 formed on the substrate 6 and a lead 71 extending from the electronic component 7. After supplying the solder 21, the soldering area P includes the terminal 61, the lead 71, and also the solder 21.

[0021] The solder supply unit 2 supplies solder 21 to the soldering portion P. The solder supply unit 2 may include, for example, a controller. The solder supply unit 2 may control the timing of supplying the solder 21, the amount and speed of supplying the solder 21, etc., based on a command signal received from the controller.

[0022] The resistance measuring unit 3 measures the resistance between the joined member and the solder 21. More specifically, in the first embodiment, the resistance measuring unit 3 measures the resistance between the solder 21 and a lead 71 extending from the electronic component 7. The resistance measuring unit 3 is connected to each of the lead 71 and the solder 21 by, for example, wiring for resistance measurement, and measures the resistance between the lead 71 and the solder 21 based on the value of the current flowing through the wiring for resistance measurement. Note that the connection point of the joined member with the resistance measuring unit 3 is not particularly limited; for example, the terminal 61 of the substrate 6 and the resistance measuring unit 3 may be connected by wiring. In this case, the resistance measuring unit 3 measures the resistance between the terminal 61 and the solder 21. The resistance measuring unit 3 transmits information indicating the measured resistance to the control unit 5.

[0023] The temperature measurement unit 4 measures the temperature of the soldering area P. The temperature measurement unit 4 is equipped with a non-contact temperature sensor. The temperature sensor is preferably a non-contact temperature sensor that measures temperature using infrared rays, but is not particularly limited to this. The temperature measurement unit 4 transmits information indicating the measured temperature to the control unit 5.

[0024] The control unit 5 controls the heating intensity of the heating unit 1. The control unit 5 is connected to the heating unit 1, the resistance measurement unit 3, and the temperature measurement unit 4. The control unit 5 receives information indicating the resistance between the joined members and the solder 21 from the resistance measurement unit 3, and information indicating the temperature of the soldering area P from the temperature measurement unit 4. The control unit 5 then monitors the change in the resistance between the joined members and the solder 21 over time, and the change in the temperature of the soldering area P over time.

[0025] The control unit 5 detects that the solder 21 has reached the soldering portion P based on a decrease in resistance between the workpieces and the solder 21. When the solder 21 has reached the soldering portion P, the resistance measured by the resistance measuring unit 3 decreases, for example, from several MΩ (open state) to several Ω. When the control unit 5 detects this decrease in resistance, it determines that the solder 21 has reached the soldering portion P. Then, after detecting the decrease in resistance, the control unit 5 increases the heating intensity of the heating unit 1.

[0026] <Method of manufacturing the bonded body> Next, a method for manufacturing the bonded body according to the first embodiment will be described.

[0027] First, an overview of a method for manufacturing a bonded body according to the present disclosure will be described with reference to Fig. 2. The method for manufacturing a bonded body according to the present disclosure includes a preheating step, a main heating step, and a postheating step. Fig. 2 is an explanatory diagram of the method for manufacturing a bonded body according to the present disclosure. Fig. 2(a) is an explanatory diagram showing the preheating step, Fig. 2(b) is an explanatory diagram showing the main heating step, and Fig. 2(c) is an explanatory diagram showing the postheating step.

[0028] In the preheating step, the heating unit 1 heats the soldering area P of the workpiece with a predetermined heating intensity. In the present embodiment 1, as shown in FIG. 2(a), the irradiation head 12 of the heating unit 1 irradiates the soldering area P with laser light L output by the laser oscillator 11. Then, after a predetermined time has elapsed since the start of heating, the solder supply unit 2 begins to supply solder 21 to the soldering area P. When the solder 21 reaches the soldering area P, the process transitions from the preheating step to the main heating step.

[0029] In the main heating step, the heating unit 1 heats the soldering area P with a heating intensity greater than that in the pre-heating step. As a result, as shown in Fig. 2(b), the solder 21 melts and diffuses into the soldering area P. When the solder supply unit 2 supplies a predetermined amount of solder, the main heating step transitions to the post-heating step.

[0030] In the post-heating step, the heating unit 1 heats the soldering area P with a heating intensity lower than that in the main heating step. As a result, the solder 21 diffused in the soldering area P is formed into a shape suitable for joining the members to be joined, as shown in FIG. 2(c).

[0031] Next, a method for manufacturing a bonded body according to the first embodiment will be described in detail with reference to Fig. 3 and Fig. 4. Fig. 3 is a flowchart of the method for manufacturing a bonded body according to the first embodiment. In Fig. 3, steps S101 to S104 correspond to a preheating process, steps S105 to S106 correspond to a main heating process, and steps S107 to S109 correspond to a postheating process. Fig. 4(a) shows the change in output of the heating unit over time, Fig. 4(b) shows the change in temperature of the soldering portion over time, and Fig. 4(c) shows the change in resistance between the members to be joined and the solder over time.

[0032] First, the heating unit 1 starts the preheating step by heating the soldering portion P of the member to be joined with a predetermined heating intensity based on a command signal from the control unit 5 (step S101).

[0033] The heating intensity in the preheating step is preferably set to a level that does not overheat the soldering area P. When soldering is performed multiple times, the time it takes for the solder 21 to reach the soldering area P may vary. This is because there is variation in the amount of unmelted solder 21 when the previous soldering was completed. In other words, the position of the tip of the solder 21 supplied from the solder supply unit 2 varies. Because the solder supply unit 2 supplies the solder 21 to the soldering area P at a constant speed, if the position of the tip of the solder 21 varies, the time it takes for the solder 21 to reach the soldering area P will vary.

[0034] For example, if the time it takes for the solder 21 to reach the soldering area P is longer than desired, the time it takes to heat the soldering area P will also be longer, resulting in an overheating of the soldering area P. Therefore, in the preheating step, it is preferable to set the heating intensity to a level that will prevent the soldering area P from overheating if the time it takes for the solder 21 to reach the soldering area P is longer than desired. Here, an overheating refers to a temperature at which the members to be joined, that is, the objects to be soldered, will be burned. In the first embodiment, the heating intensity may be set based on the heat resistance temperatures of other electronic components already mounted on the substrate 6, the electronic component 7 to be soldered, and the like.

[0035] Next, the solder supply unit 2 waits to supply solder 21 until a preset time has elapsed since the start of the preheating step (NO in step S102), and once the preset time has elapsed (YES in step S102), the solder supply unit 2 starts to supply solder 21 to the soldering area P (step S103). It is preferable that the solder supply unit 2 supplies solder 21 to the soldering area P at a constant speed.

[0036] Next, the control unit 5 continues the preheating step until the resistance measured by the resistance measuring unit 3 becomes equal to or less than a certain value (NO in step S104). When the control unit 5 detects that the resistance measured by the resistance measuring unit 3 becomes equal to or less than the certain value (YES in step S104), the heating unit 1 increases the heating intensity based on a command signal from the control unit 5 and starts the main heating step (step S105).

[0037] As shown in FIG. 4(c), when the solder 21 reaches the soldering portion P, the resistance measured by the resistance measuring portion 3 decreases, for example, from several MΩ (open state) to several Ω. The control portion 5 detects from this decrease in resistance that the solder 21 has reached the soldering portion P. The control portion 5 then transmits a command signal to the heating portion 1 to change the heating intensity. Furthermore, in the present embodiment 1, the heating intensity in this heating step is a preset heating intensity, and is preferably a heating intensity sufficient to melt the solder 21.

[0038] In the main heating step, the heating unit 1 maintains the set heating intensity until the amount of solder 21 supplied from the solder supply unit 2 reaches the set value (NO in step S106). When the amount of solder 21 supplied from the solder supply unit 2 reaches the set value (YES in step S106), the heating unit 1 reduces the heating intensity based on a command signal from the control unit 5 and starts the post-heating step (step S107). In the present embodiment 1, the heating intensity in the post-heating step is a preset heating intensity, and is preferably lower than the heating intensity in the main heating step.

[0039] In step S106, the control unit 5 may determine whether the amount of solder 21 supplied from the solder supply unit 2 has reached the set value based on, for example, the resistance measured by the resistance measurement unit 3. When the amount of solder 21 supplied from the solder supply unit 2 reaches the set value, the solder supply unit 2 stops supplying the solder 21. As a result, as shown in FIG. 2(c), the solder 21 diffused to the soldering area P separates from the solder 21 from the solder supply unit 2. Therefore, as shown in FIG. 3(c), the resistance measured by the resistance measurement unit 3 increases, for example, from several ohms to several megohms (open state). Therefore, the control unit 5 can determine that the amount of solder 21 supplied from the solder supply unit 2 has reached the set value by detecting that the resistance measured by the resistance measurement unit 3 has reached a certain value or greater. Alternatively, the resistance measurement unit 3 may determine that the amount of solder 21 supplied has reached the set value by, for example, the solder supply unit 2 transmitting a signal indicating that the amount of solder 21 supplied has reached the set value to the control unit 5.

[0040] Next, the set heating intensity is maintained until a preset time has elapsed since the start of the post-heating step (NO in step S108), and once the preset time has elapsed (YES in step S108), heating unit 1 stops heating (step S109). Finally, solder supply unit 2 returns the solder 21 from solder supply unit 2 by, for example, several mm into solder supply unit 2, and soldering apparatus 100 completes soldering (step S110).

[0041] In the present embodiment 1, the control unit 5 can detect that the solder 21 has reached the soldering area P by detecting a decrease in resistance between the workpieces and the solder 21. Therefore, when transitioning from pre-heating to main heating, the control unit 5 can increase the heating intensity at the timing when the solder 21 reaches the soldering area P. In other words, the heating intensity required for soldering can be controlled with precision, enabling high-quality soldering.

[0042] Embodiment 2 The second embodiment will be described, focusing on the differences from the first embodiment. The configuration of the soldering apparatus according to the second embodiment is the same as the configuration of the soldering apparatus according to the first embodiment, and therefore a description thereof will be omitted.

[0043] In the first embodiment, in the main heating step, the heating unit 1 heats the soldering area P with a preset heating intensity. On the other hand, in the second embodiment, before moving from the preheating step to the main heating step, the control unit 5 determines the heating intensity for the main heating step from a plurality of preset heating intensities based on the temperature of the soldering area P. Then, the heating unit 1 heats the soldering area P with the heating intensity determined by the control unit 5.

[0044] <Method of manufacturing the bonded body> Next, a method for manufacturing the bonded body according to the second embodiment will be described.

[0045] A method for manufacturing a bonded body according to the second embodiment will be described with reference to Fig. 5 and Fig. 6. Fig. 5 is a flowchart of the method for manufacturing a bonded body according to the second embodiment. The method for manufacturing a bonded body according to the second embodiment further includes steps S112 and S113 between steps S104 and S105 in the first embodiment. Steps S101 to S107 are the same as those in the first embodiment, and therefore their explanation will be omitted where appropriate. Fig. 6(a) shows the change in output of the heating unit over time, Fig. 6(b) shows the change in temperature of the soldering portion over time, and Fig. 6(c) shows the change in resistance between the members to be joined and the solder over time.

[0046] First, similarly to the first embodiment, the heating unit 1 starts the preheating step by heating the soldering portion P of the members to be joined with a predetermined heating intensity based on a command signal from the control unit 5 (step S101).

[0047] Next, as in the first embodiment, the solder supply unit 2 waits until a preset time has elapsed since the start of the preheating step (NO in step S102) before supplying solder 21. Once the preset time has elapsed (YES in step S102), the solder supply unit 2 starts supplying solder 21 to the soldering area P (step S103).

[0048] Next, control unit 5 continues the preheating step until the resistance measured by resistance measurement unit 3 falls below a certain value (NO in step S104). When control unit 5 detects that the resistance measured by resistance measurement unit 3 has fallen below a certain value (YES in step S104), control unit 5 acquires the temperature of the soldering area P measured by temperature measurement unit 4 at the timing when it detects that the resistance measured by resistance measurement unit 3 has fallen below the certain value (step S112). The temperature of the soldering area P acquired in step S112 is the temperature when the resistance measured by resistance measurement unit 3 falls below the certain value (when solder 21 reaches the soldering area P).

[0049] Next, the control unit 5 determines the heating intensity for the main heating step based on the acquired temperature of the soldering area P (step S113). A plurality of heating intensities to be switched in the next step S105 are set in advance. As shown in FIG. 6, the control unit 5 selects one of the plurality of heating intensities set in advance based on the temperature of the soldering area P when the resistance falls below a certain value (when the solder 21 reaches the soldering area P). The control unit 5 then transmits a command signal for the determined heating intensity to the heating unit 1.

[0050] As explained in the first embodiment, when soldering is performed multiple times, the time it takes for the solder 21 to reach the soldering area P may vary. If the time it takes for the solder 21 to reach the soldering area P varies, the temperature of the soldering area P at the start of the main heating process will vary. In the main heating process, if the soldering area P is not heated with a heating intensity appropriate for the temperature of the soldering area P at the start of the main heating process, the quality of the soldering will not be stable. In the second embodiment, the appropriate heating intensity for the main heating process can be determined based on the temperature of the soldering area P when the resistance measured by the resistance measurement unit 3 falls below a certain value (when the solder 21 reaches the soldering area P).

[0051] As a method for determining the heating intensity, the control unit 5 reduces the heating intensity in the main heating step as the temperature of the soldering area P when the solder 21 reaches the soldering area P increases. On the other hand, the control unit 5 increases the heating intensity in the main heating step as the temperature of the soldering area P when the solder 21 reaches the soldering area P decreases. For example, the control unit 5 may determine the heating intensity to be 50 W when the temperature of the soldering area P is 250 to 300°C, 45 W when the temperature is 300 to 350°C, and 40 W when the temperature is 350 to 400°C.

[0052] Next, similarly to the first embodiment, the heating unit 1 increases the heating intensity based on the command signal from the control unit 5, and starts the main heating step (step S105).

[0053] Next, as in embodiment 1, in this heating process, the heating unit 1 maintains the set heating intensity until the amount of solder 21 supplied from the solder supply unit 2 reaches the set value (NO in step S106), and when the amount of solder 21 supplied from the solder supply unit 2 reaches the set value (YES in step S106), the heating unit 1 reduces the heating intensity based on a command signal from the control unit 5 and starts the post-heating process (step S107).

[0054] Next, as in the first embodiment, when a preset time has elapsed since the start of S107 (step S108), the heating unit 1 stops heating (step S109). Finally, the solder supply unit 2 returns the solder 21 from the solder supply unit 2, for example, by several mm, into the solder supply unit 2, and the soldering apparatus 100 finishes soldering (step S110).

[0055] In the second embodiment, as in the first embodiment, the control unit 5 detects that the solder 21 has reached the soldering area P by detecting a decrease in resistance between the workpiece and the solder 21. Therefore, when transitioning from preheating to main heating, the control unit 5 can increase the heating intensity at the timing when the solder 21 reaches the soldering area P. Furthermore, in the second embodiment, the heating intensity in the main heating step can be determined based on the temperature of the soldering area P when the resistance measured by the resistance measurement unit 3 falls below a certain value (when the solder 21 has reached the soldering area P). Because the appropriate heating intensity in the main heating step can be determined based on the temperature of the soldering area P, the heating intensity required for soldering can be accurately controlled, enabling high-quality soldering.

[0056] The present invention is not limited to the above-described embodiment, and can be modified as appropriate within the scope of the invention. [Explanation of symbols]

[0057] 1 Heating section 2 Solder supply section 3 Resistance measurement section 4 Temperature measurement part 5. Control section 6 PCB 7. Electronic Components 11 Laser oscillator 12 irradiation head 61 terminals 71 leads 100 soldering equipment L laser light P Soldering area

Claims

1. A soldering apparatus for joining two or more members to be joined together with solder, a heating unit that heats the soldering portion of the workpiece; a resistance measuring unit for measuring the resistance between the workpiece and the solder; a control unit that controls the heating intensity of the heating unit, the control unit increases the heating intensity of the heating unit when the resistance measured by the resistance measuring unit becomes equal to or less than a certain value. Soldering equipment.

2. The heating unit is a laser oscillator that outputs laser light; an irradiation head that irradiates the laser light output from the laser oscillator toward the soldering portion, The soldering portion is heated by irradiating the laser light.

2. The soldering apparatus according to claim 1.

3. a temperature measuring unit for measuring the temperature of the soldering portion; the control unit determines the heating intensity of the heating unit based on the temperature measured by the temperature measuring unit when the resistance measured by the resistance measuring unit becomes equal to or less than a certain value.

3. The soldering apparatus according to claim 1 or 2.

4. A method for manufacturing a joined body in which two or more members to be joined are joined by solder, comprising the steps of: a preheating step of heating the soldering portion of the workpiece with a predetermined heating intensity; a main heating step of heating the soldering portion with a heating intensity greater than that of the preheating step, In the preheating step, solder is supplied to the soldering portion after a predetermined time has elapsed since the start of heating, and the process proceeds to the main heating step after the resistance between the workpiece and the solder becomes equal to or less than a certain value. A method for manufacturing a bonded body.

5. In the preheating step, after the resistance between the workpieces and the solder becomes equal to or less than a certain value, a heating intensity in the main heating step is determined based on the temperature of the soldering portion, and the main heating step is started. The method for producing the bonded body according to claim 4 .

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