A soldering device for IGBT module and vacuum reflow soldering method

Abstract

The application belongs to the technical field of IGBT module welding and relates to a vacuum reflow welding device and a use method thereof, in particular to an IGBT module welding device and a vacuum reflow welding method thereof. By increasing the heated area of the copper bottom plate, the cavity rate of the copper bottom plate and the mother copper-clad ceramic substrate welding is reduced, the consistency of the welding layer thickness is ensured, and the reliability of the IGBT module is improved. The copper bottom plate and the mother copper-clad ceramic substrate are pressed tightly during welding by setting the spring assembly, so that the stability of the device during welding is maintained. The copper bottom plate and the mother copper-clad ceramic substrate are closely attached during welding by setting the fixing pin, so that cavities are prevented. The baffle is arranged between adjacent sub copper-clad ceramic substrates to prevent the adjacent sub copper-clad ceramic substrates from sticking during welding. The plastic column is arranged around the placement area of the mother copper-clad ceramic substrate on the positioning plate to prevent the copper-clad ceramic substrate from being scratched or damaged during installation or disassembly.

Description

Technical Field

[0001] This invention belongs to the field of IGBT module welding technology, and relates to a vacuum reflow welding device and its usage method, specifically to a welding device and vacuum reflow welding method for IGBT modules. Background Technology

[0002] IGBT (Insulated Gate Bipolar Transistor) modules feature high frequency, high voltage, high current, and easy turn-on and turn-off characteristics, and have been widely used in locomotive traction, industrial control, wind power generation, automotive power and other fields.

[0003] The copper base plate is the main heat dissipation channel for IGBT modules. However, existing copper base plates cannot be used in IGBT modules for railway locomotives due to the harsh operating environment, where the thermal cycle count of the copper base plate cannot meet the requirements. Therefore, copper base plates are generally used in medium and low voltage IGBT modules. In soldered IGBT packaging processes, the copper-clad ceramic substrate (DBC) and the copper base plate are usually packaged using a high-temperature soldering method. Due to the significant difference in their coefficients of thermal expansion, the copper base plate deforms after soldering, leading to poor contact with the heat sink and increased thermal resistance. Therefore, traditional technology often pre-bends the IGBT copper module base plate. After high-temperature soldering, the copper base plate still retains a certain curvature, ensuring full contact between the copper base plate and the heat sink when the IGBT module is mounted on the heat sink surface, which is beneficial for heat dissipation.

[0004] In the existing technology, there are two shapes of copper base plates: (1) double-arched copper base plates, with the welding surface concave inward and the cooling surface convex outward; (2) single-arched copper base plates, with the welding surface being flat and the cooling surface convex outward. In the reflow soldering process of IGBT modules, heat is conducted from the heating plate to the copper base plate to achieve the welding of the copper base plate and the DBC. However, regardless of the shape of the copper base plate, the cooling surface is always convex outward, so that the cooling surface of the copper base plate only contacts the heating plate at the center. This causes the heat from the heating plate to be conducted from the center of the base plate to the surrounding area, resulting in uneven heating of the base plate. This affects the flow of solder, thereby increasing the void rate at each welding position and reducing the reliability of the IGBT module.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a welding device and a vacuum reflow welding method for IGBT modules.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] On one hand, the present invention provides a welding device for IGBT modules, which can be used in conjunction with a welding furnace to weld a copper base plate with an anti-arch structure to a copper-clad ceramic substrate in an IGBT module. The welding device includes a heating plate, which has at least one anti-arch groove for placing the copper base plate. A positioning plate with a copper-clad ceramic substrate is placed above the copper base plate. A welding sheet is laid between the copper base plate and the copper-clad ceramic substrate. A cover plate is provided above the positioning plate, and the two are pressed and fixed by at least two spring assemblies.

[0009] When the welding furnace is in operation, the cover plate and the positioning plate are pressed together by the spring assembly, thereby pressing the copper base plate and the heating plate together.

[0010] Specifically, the heating plate is also provided with at least two positioning posts. One end of the positioning post is fixed to the heating plate, and the other end passes through the copper base plate and the positioning plate in sequence and is exposed on the upper surface of the positioning plate.

[0011] Specifically, the positioning plate has a placement area for placing the mother copper-clad ceramic substrate, and several plastic pillars are evenly arranged around the placement area to prevent damage to the mother copper-clad ceramic substrate.

[0012] Specifically, the cover plate is provided with several fixing pins, the top of the fixing pin is provided with a first limiting head, and the bottom end passes through the cover plate downward and abuts against the mother copper-clad ceramic substrate.

[0013] Specifically, each of the mother copper-clad ceramic substrates includes several daughter copper-clad ceramic substrates, and a baffle is provided between adjacent daughter copper-clad ceramic substrates to prevent them from sticking together during welding; the baffle is vertically disposed on the copper base plate, with one end embedded in the positioning plate.

[0014] Specifically, the spring assembly includes a support column, a pressure-bearing shaft, and a sleeve;

[0015] One end of the pressure bearing shaft is provided with a second limiting head, and the sleeve is provided with a limiting step that matches the limiting head. The other end of the pressure bearing shaft passes vertically downward through the sleeve and the spring in sequence and then fits with the blind hole at the top of the support column.

[0016] The support column includes a third shaft at the top, a fourth shaft in the middle, and a fifth shaft at the bottom. The third shaft passes through the cover plate and abuts against the first shaft. The upper end of the fourth shaft abuts against the lower surface of the cover plate, and the lower end abuts against the upper surface of the positioning plate. The fifth shaft passes through the positioning plate and is exposed outside the positioning plate, with the exposed height being less than or equal to the thickness of the copper base plate.

[0017] Specifically, the other end of the pressure-bearing shaft includes a first shaft and a second shaft. The first shaft abuts against the top of the support column, and the second shaft is in clearance fit with the blind hole at the top of the support column.

[0018] Specifically, a washer is provided between the cover plate and the spring.

[0019] On the other hand, the present invention also provides a vacuum reflow soldering method for an IGBT module soldering apparatus, the specific method of which is as follows:

[0020] 1) Preheating: After the welding device is assembled, it is sent into the preheating chamber of the welding furnace by conveyor belt. The spring assembly presses the cover plate and positioning plate together, thereby pressing the copper base plate and heating plate together. Then, the preheating chamber is evacuated and the IGBT module is heated for the first time. When the temperature of the IGBT module reaches 150°C, formic acid is filled in. The IGBT module is heated for the second time in the formic acid environment. When it is heated to a certain temperature, nitrogen is filled in to remove the H2O generated by the reaction in the preheating chamber.

[0021] 2) Reflow: First, the preheated welding device is sent into the reflow chamber. Then, the reflow chamber is evacuated, and the IGBT module is heated for the third time. When the product temperature reaches 200℃, formic acid is introduced. When the formic acid pressure in the reflow chamber reaches a certain value, the introduction of formic acid is stopped. Then, the reflow chamber is evacuated to remove the H2O and CO2 generated in the reaction. Next, the IGBT module is heated for the fourth time in a vacuum environment. After heating to the peak temperature for a certain period of time, nitrogen is introduced into the reflow chamber to change the pressure in the reflow chamber, squeeze the copper-clad ceramic substrate, and increase the wettability of the copper layer and the copper base plate welding area under the copper-clad ceramic substrate. Finally, the reflow chamber is evacuated again to degas the solder and reduce welding voids.

[0022] 3) Cooling: The welding device with the reflowed solder is fed into the cooling chamber via a conveyor belt. The nitrogen filling rate and cooling rate are controlled to complete the reflow welding.

[0023] Specifically, the cooling rate is 20°C / min.

[0024] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0025] This invention reduces the void rate during welding between the copper base plate and the mother copper-clad ceramic substrate by increasing the heat-receiving area of ​​the copper base plate, ensuring the consistency of the weld layer thickness and improving the reliability of the IGBT module. Furthermore, by incorporating a spring assembly, the copper base plate and the mother copper-clad ceramic substrate are pressed together during welding, maintaining the stability of the welding device. Fixing pins ensure a tight fit between the copper base plate and the mother copper-clad ceramic substrate during welding, preventing voids. Baffles are placed between adjacent daughter copper-clad ceramic substrates to prevent them from sticking together during welding. Plastic pillars around the placement area of ​​the mother copper-clad ceramic substrate on the positioning plate prevent scratches and damage to the copper-clad ceramic substrate during installation or removal. Attached Figure Description

[0026] The accompanying drawings are incorporated in and form part of this specification, and together with the description serve to explain the principles of the invention.

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a front view of the welding apparatus for IGBT modules of the present invention;

[0029] Figure 2 for Figure 1 Top view;

[0030] Figure 3 for Figure 1 A three-dimensional image;

[0031] Figure 4 This is a perspective view of the welding device for the IGBT module of the present invention with the cover plate removed;

[0032] Figure 5 This is a schematic diagram of the baffle distribution of the welding device for the IGBT module of the present invention;

[0033] Figure 6 This is a schematic diagram of the copper base plate of the welding device for the IGBT module of the present invention;

[0034] Figure 7 This is a schematic diagram of the spring assembly of the welding device for the IGBT module of the present invention;

[0035] Figure 8 This is a schematic diagram of the pressure bearing shaft of the welding device for the IGBT module of the present invention;

[0036] Figure 9 This is a schematic diagram of the support column of the welding device for the IGBT module of the present invention.

[0037] Wherein: 1 is heating plate; 2 is positioning plate; 3 is cover plate; 4 is spring assembly; 41 is sleeve; 42 is spring; 43 is bearing shaft; 431 is limiting head; 432 is first shaft; 433 is second shaft; 44 is washer; 45 is support column; 451 is third shaft; 452 is fourth shaft; 453 is fifth shaft; 5 is copper base plate; 6 is positioning column; 7 is fixing pin; 8 is plastic column; 9 is baffle. Detailed Implementation

[0038] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples consistent with some aspects of the invention as detailed in the appended claims.

[0039] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0040] Example 1

[0041] This embodiment provides a welding device for IGBT modules, which can be used in conjunction with a welding furnace to weld a copper base plate 5 with an inverted arch structure to a copper-clad ceramic substrate in an IGBT module. The welding device includes a heating plate 1, which has at least one inverted arch groove for placing the copper base plate 5. A positioning plate 2 with a copper-clad ceramic substrate is placed above the copper base plate 5. A welding sheet is laid between the copper base plate 5 and the copper-clad ceramic substrate. A cover plate 3 is provided above the positioning plate 2. The two are pressed and fixed together by at least two spring assemblies 4.

[0042] During operation, the welding furnace uses spring assembly 4 to press the cover plate 3 and positioning plate 2 together, thereby pressing the copper base plate 5 and heating plate 1 together. (See [link]) Figure 1-4 As shown.

[0043] Specifically, the heating plate 1 is also provided with at least two positioning posts 6. One end of the positioning post 6 is fixed to the heating plate 1, and the other end passes through the copper base plate 5 and the positioning plate 2 in sequence, and is exposed on the upper surface of the positioning plate 2. See [reference needed]. Figure 5-6 As shown.

[0044] Specifically, the positioning plate 2 has a plurality of plastic pillars 8 evenly arranged around the circumference of the placement area for the mother copper-clad ceramic substrate to prevent damage to the mother copper-clad ceramic substrate, see [reference]. Figure 4-5 As shown.

[0045] Specifically, the cover plate 3 is provided with a plurality of fixing pins 7, the top of each fixing pin 7 is provided with a first limiting head, and the bottom end passes downward through the cover plate 3 and abuts against the mother copper-clad ceramic substrate, see [reference]. Figure 3-4 As shown.

[0046] Specifically, each of the mother copper-clad ceramic substrates includes several daughter copper-clad ceramic substrates, and a baffle 9 is provided between adjacent daughter copper-clad ceramic substrates to prevent them from sticking together during soldering; the baffle 9 is vertically disposed on the copper base plate 5, and one end is embedded in the positioning plate 2, see [reference]. Figure 5 As shown.

[0047] Specifically, the spring assembly 4 includes a support column 45, a pressure bearing shaft 43, and a sleeve 41;

[0048] One end of the pressure bearing shaft 43 is provided with a second limiting head, and the sleeve 41 is provided with a limiting step that matches the limiting head. The other end of the pressure bearing shaft 43 passes vertically downward through the sleeve 41 and the spring 42 in sequence and then fits with the blind hole at the top of the support column 45.

[0049] The support column 45 includes a third shaft 451 at the top, a fourth shaft 452 in the middle, and a fifth shaft 453 at the bottom. The third shaft 451 passes through the cover plate 3 and abuts against the first shaft 432. The upper end of the fourth shaft 452 abuts against the lower surface of the cover plate 3, and the lower end abuts against the upper surface of the positioning plate 2. The fifth shaft 453 passes through the positioning plate 2 and is exposed outside the positioning plate 2, with the exposed height being less than or equal to the thickness of the copper base plate 5. (See [reference]) Figure 7-9 As shown.

[0050] Specifically, the other end of the pressure-bearing shaft 43 includes a first shaft 432 and a second shaft 433. The first shaft 432 abuts against the top of the support column 45, and the second shaft 433 is in clearance fit with the blind hole at the top of the support column 45. (See [reference]) Figure 9 As shown.

[0051] Example 2

[0052] Based on Example 1, this example provides another welding device for IGBT modules, which can be used in conjunction with a welding furnace to weld the copper base plate 5 with an inverted arch structure to the mother copper-clad ceramic substrate in the IGBT module.

[0053] The difference from Embodiment 1 is that the welding device in this embodiment has two arched grooves on the heating plate 1 for placing the copper base plate 5. A positioning plate 2 with two mother copper-clad ceramic substrates is placed above the copper base plate 5. Welding sheets are laid between the copper base plate 5 and the mother copper-clad ceramic substrates. A cover plate 3 is provided above the positioning plate 2. The two are pressed and fixed by four spring assemblies 4.

[0054] During operation, the welding furnace uses four spring assemblies 4 to press the cover plate 3 and the positioning plate 2 together, thereby pressing the copper base plate 5 and the heating plate 1 together. (See attached image) Figure 1-4 As shown.

[0055] Specifically, the heating plate 1 is also provided with four positioning posts 6. Each copper base plate 5 is fixed by two diagonally arranged positioning posts 6. One end of each positioning post 6 is fixed to the heating plate 1, and the other end passes through the copper base plate 5 and the positioning plate 2 in sequence, and is exposed on the upper surface of the positioning plate 2. See [reference needed]. Figure 5-6 As shown.

[0056] Specifically, the positioning plate 2 has a rectangular placement area for placing the mother copper-clad ceramic substrate. Around the rectangular placement area are several plastic pillars 8 to prevent damage to the mother copper-clad ceramic substrate. Four plastic pillars 8 are evenly spaced along the length of the rectangular placement area, and two plastic pillars 8 are evenly spaced along the width of the rectangular placement area. Each plastic pillar 8 is embedded in the positioning plate 2, and the exposed side of the plastic pillar 8 separates the positioning plate 2 from the copper-clad ceramic substrate. (See [reference]) Figure 4-5 As shown.

[0057] Specifically, the cover plate 3 is provided with a plurality of fixing pins 7. Preferably, the area on the cover plate 3 corresponding to the rectangular placement area of ​​the mother copper-clad ceramic substrate is the rectangular distribution area of ​​the fixing pins 7. Each mother copper-clad ceramic substrate is composed of three sub-copper-clad ceramic substrates. Each sub-copper-clad ceramic substrate is provided with a fixing pin 7 at the four corners and the center of the rectangular area corresponding to the rectangular area.

[0058] Preferably, the fixing pin 7 has a first limiting head at its top end, and its bottom end passes downward through the cover plate 3 and abuts against the copper-clad ceramic substrate. The bottom end of the fixing pin 7 also has a retaining ring, which effectively prevents the fixing pin 7 from falling off when the cover plate 3 is flipped. (See [reference]) Figure 3-4 As shown.

[0059] Preferably, two baffles 9 are provided between adjacent copper-clad ceramic substrates to prevent them from sticking together during welding.

[0060] Preferably, a washer 44 is provided between the cover plate 3 and the spring 42, which is used to receive the elastic force of the spring 42 and transmit the force to the cover plate 3.

[0061] Example 3

[0062] Based on Example 1, this example also provides a vacuum reflow soldering method based on a welding device for IGBT modules, the specific method of which is as follows:

[0063] Vacuum reflow soldering is used for welding, and lead-free solder of tin-antimony alloy or tin-silver-copper alloy is selected. The process is divided into three stages: preheating, reflow, and cooling. Atmosphere and gas pressure design for reduction reaction are carried out.

[0064] 1) Preheating: After assembling the welding device, it is conveyed into the preheating chamber of the welding furnace via a conveyor belt. The spring assembly 4 presses the cover plate 3 and the positioning plate 2 together, thereby pressing the copper base plate 5 and the heating plate 1 together. Then, the preheating chamber is evacuated before the IGBT module is heated for the first time. When the IGBT module temperature reaches 150℃, formic acid (flow rate: 15Sl / min) is introduced. Formic acid begins to decompose at low temperatures (150℃~200℃) and has good hydrogen-like reduction ability. The reaction equation is:

[0065] CuO+2HCOOH=Cu(COOH)2+H2O↑(1)

[0066] The formic acid reacts with the solder, the copper base plate, and the metal oxides on the surface of the copper-clad ceramic substrate. The IGBT module is then heated a second time in the formic acid environment. The heating temperature is 20°C to 30°C lower than the melting point of the solder, the holding time is 120s to 240s, the pressure in the preheating chamber is 300mbar to 500mbar, nitrogen is introduced, and the H2O generated in the reaction in the preheating chamber is removed.

[0067] 2) Reflow: First, the preheated welding device is sent into the reflow chamber. Then, the reflow chamber is evacuated, and the IGBT module is heated for the third time. When the product temperature reaches 200℃, formic acid is introduced. The reaction equation for formic acid is:

[0068] Cu(COOH)2=Cu+2CO2↑+H2↑(2)

[0069] H2 + CuO = Cu + H2O↑ (3)

[0070] The formic acid further reduces the metal oxides on the surfaces of the solder, copper base plate, and copper-clad ceramic substrate, exposing the pure metal surfaces of all three. The formic acid flow rate in the reflow chamber is 15 μL / min. When the pressure in the reflow chamber reaches 300 mbar to 500 mbar, the formic acid flow is stopped, and the reflow chamber is evacuated to remove the H2O and CO2 generated during the reaction. Then, the IGBT module is heated for the fourth time under vacuum. When the peak temperature is 30°C to 40°C higher than the solder melting point, and the welding time is 40 to 240 seconds, nitrogen is then introduced into the reflow chamber to bring the pressure to 300 to 500 mbar, compressing the copper-clad ceramic substrate and increasing the wettability of the copper layer under the substrate and the welding area of ​​the copper base plate. Finally, the reflow chamber is evacuated again to degas the solder and reduce welding voids.

[0071] 3) Cooling: The welding device with the reflowed welding liquid is fed into the cooling chamber through a conveyor belt. The nitrogen filling rate and cooling rate are controlled to complete the reflow welding. The nitrogen filling rate is 50Sl / min and the cooling rate is 20℃ / min.

[0072] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention.

[0073] It should be understood that the present invention is not limited to the content already described above, and various modifications and changes can be made without departing from its scope. The scope of the present invention is limited only by the appended claims.

Claims

1. A vacuum reflow soldering method for an IGBT module soldering apparatus, characterized in that, The welding device for the IGBT module includes a welding furnace capable of welding a copper base plate (5) with an inverted arch structure to a copper-clad ceramic substrate in the IGBT module. The welding device includes a heating plate (1) with at least one inverted arch groove for placing the copper base plate (5). A positioning plate (2) with a copper-clad ceramic substrate is placed above the copper base plate (5). A welding sheet is laid between the copper base plate (5) and the copper-clad ceramic substrate. A cover plate (3) is provided above the positioning plate (2). The two are pressed and fixed by at least two spring assemblies (4). When the welding furnace is in operation, the cover plate (3) and the positioning plate (2) are pressed together by the spring assembly (4), thereby pressing the copper base plate (5) and the heating plate (1). The positioning plate (2) has a placement area for placing the mother copper-clad ceramic substrate, and several plastic pillars (8) are evenly arranged around the placement area to prevent damage to the mother copper-clad ceramic substrate. Each of the mother copper-clad ceramic substrates includes several daughter copper-clad ceramic substrates, and a baffle (9) is provided between adjacent daughter copper-clad ceramic substrates to prevent them from sticking together during welding; the baffle (9) is vertically arranged on the copper base plate (5), and one end is embedded in the positioning plate (2); The vacuum reflow soldering method is as follows: 1) Preheating: First, after assembling the welding device, it is sent into the preheating chamber of the welding furnace by conveyor belt. The spring assembly (4) is pressed to press the cover plate (3) and the positioning plate (2), thereby pressing the copper base plate (5) and the heating plate (1). Then, after evacuating the preheating chamber, the IGBT module is heated for the first time. When the temperature of the IGBT module reaches 150°C, formic acid is filled in. The IGBT module is heated for the second time in the formic acid environment. When it is heated to a certain temperature, nitrogen is filled in to remove the H2O generated by the reaction in the preheating chamber. 2) Reflow: First, the preheated welding device is sent into the reflow chamber, then the reflow chamber is evacuated and the IGBT module is heated for the third time. When the product temperature reaches 200℃, formic acid is filled in. When the formic acid pressure in the reflow chamber reaches a certain value, the filling of formic acid is stopped. Then the reflow chamber is evacuated to remove the H2O and CO2 generated in the reaction. Then the IGBT module is heated for the fourth time in a vacuum environment. After heating to the peak temperature for a certain time, nitrogen is filled into the reflow chamber to change the pressure in the reflow chamber, squeeze the copper-clad ceramic substrate, and increase the wettability of the copper layer and copper base plate (5) welding area under the copper-clad ceramic substrate. Finally, the reflow chamber is evacuated again to degas the solder and reduce the welding voids. 3) Cooling: The welding device with the reflowed solder is fed into the cooling chamber via a conveyor belt. The nitrogen filling rate and cooling rate are controlled to complete the reflow welding.

2. The vacuum reflow soldering method according to claim 1, characterized in that, The heating plate (1) is also provided with at least two positioning posts (6). One end of the positioning post (6) is fixed on the heating plate (1), and the other end passes through the copper base plate (5) and the positioning plate (2) in sequence and is exposed on the upper surface of the positioning plate (2).

3. The vacuum reflow soldering method according to claim 1, characterized in that, The cover plate (3) is provided with several fixing pins (7). The top of the fixing pin (7) is provided with a first limiting head, and the bottom end passes through the cover plate (3) downward and abuts against the mother copper-clad ceramic substrate.

4. The vacuum reflow soldering method according to claim 1, characterized in that, The spring assembly (4) includes a support column (45), a pressure bearing shaft (43), and a sleeve (41). One end of the pressure bearing shaft (43) is provided with a second limiting head, and the sleeve (41) is provided with a limiting step that matches the second limiting head. The other end of the pressure bearing shaft (43) passes vertically downward through the sleeve (41) and the spring (42) in sequence and then cooperates with the blind hole at the top of the support column (45) with a gap. The support column (45) includes a third shaft (451) at the top, a fourth shaft (452) in the middle, and a fifth shaft (453) at the bottom. The third shaft (451) passes through the cover plate (3) and abuts against the first shaft (432). The upper end of the fourth shaft (452) abuts against the lower surface of the cover plate (3) and the lower end abuts against the upper surface of the positioning plate (2). The fifth shaft (453) passes through the positioning plate (2) and is exposed outside the positioning plate (2), and the exposed height is less than or equal to the thickness of the copper base plate (5).

5. The vacuum reflow soldering method according to claim 4, characterized in that, The other end of the pressure bearing shaft (43) includes a first shaft (432) and a second shaft (433). The first shaft (432) abuts against the top of the support column (45), and the second shaft (433) is in clearance fit with the blind hole at the top of the support column (45).

6. The vacuum reflow soldering method according to claim 4, characterized in that, A washer (44) is also provided between the cover plate (3) and the spring (42).

7. The vacuum reflow soldering method according to claim 1, characterized in that, The cooling rate is 20°C / min.

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