A nitrogen protection sensing system applied to a vacuum reflow soldering device

Abstract

The application relates to a nitrogen protection sensing system applied to a vacuum reflow soldering device, which is assembled on a vacuum chamber and connected with a gas supply device and a sensor host, belongs to the technical field of vacuum reflow soldering devices, and comprises a nitrogen gas spraying pipeline and a sensor assembly. One end of the nitrogen gas spraying pipeline is connected with the gas supply device, nitrogen gas sprayed by the gas supply device is distributed through a control valve block at the other end of the nitrogen gas spraying pipeline to form primary nitrogen gas and secondary nitrogen gas, the sensor assembly comprises a protective cover, a fiber probe and a fiber line, the fiber probe is coaxially arranged in the protective cover, the protective cover is communicated with the nitrogen gas spraying pipeline, one end of the fiber line is connected with the fiber probe, the other end of the fiber line penetrates through a throttling pipeline and is connected with the sensor host, a plurality of spiral shunt channels are circumferentially arranged on the inner wall of the protective cover and are used for shunting the secondary nitrogen gas to form straight-flow nitrogen gas and rotational-flow nitrogen gas. Two gas flows are distributed in the protective cover, the fiber probe is ensured to be wrapped in nitrogen gas, and heat and pollutants are prevented from accumulating.

Description

Technical Field

[0001] This application relates to the field of vacuum reflow soldering equipment technology, and in particular to a nitrogen protection sensing system for use in vacuum reflow soldering equipment. Background Technology

[0002] In existing technologies, vacuum reflow soldering technology effectively reduces the formation of oxides by placing the welding environment in a vacuum state, thereby significantly improving the quality and reliability of the solder joints. In vacuum reflow soldering equipment, fiber optic sensors are typically used to monitor temperature changes and positional accuracy in real time during the welding process, and their performance directly affects the stability of the welding quality.

[0003] Existing technology involves a conveying system for a vacuum reflow oven, including an in-furnace conveying device, a vacuum device, and a track width adjustment device. The in-furnace conveying device includes at least one in-furnace conveying track. The vacuum device includes a housing, a vacuum conveying module, a front door connecting shaft, a rear door connecting shaft, a first connecting shaft, a second connecting shaft, and several transition shafts. The vacuum conveying track and the in-furnace conveying track are collinearly corresponding. The track width adjustment device connects each conveying chain in the in-furnace conveying track and each vacuum conveying chain in the vacuum conveying track. The spacing between two conveying chains in the in-furnace conveying track and the spacing between two vacuum conveying chains in the collinear vacuum conveying track are adjusted synchronously.

[0004] In the aforementioned and existing vacuum reflow soldering equipment, sensors are generally used to monitor the parameters of the entire reflow soldering process in real time. However, since the flux evaporates during soldering, if the existing single-blowing air supply continues during the vacuum evacuation stage, it will increase the pump load. If the air supply is stopped, the flux will instantly back-spread and contaminate the lens, thereby affecting the sensor monitoring and readings, and thus affecting the control of heating time and temperature rise. Maintaining the lens clean will also increase the equipment maintenance cost and downtime. Summary of the Invention

[0005] This application provides a nitrogen protection sensing system for vacuum reflow soldering equipment, which can solve the problems of existing single gas supply methods in vacuum reflow soldering process, which can cause flux volatilization, resulting in blurred sensor probes, leading to sensor performance degradation or even failure. At the same time, maintaining lens cleanliness also increases equipment maintenance costs and downtime.

[0006] The technical solution of this application is as follows: A nitrogen protection sensing system applied to a vacuum reflow soldering apparatus, assembled on a vacuum chamber and connected to a gas supply device and a sensor host, comprising: A nitrogen gas ejection pipeline, one end of which is connected to a gas supply device, and the other end of which distributes the nitrogen gas ejected from the gas supply device through a control valve block to form primary nitrogen gas and secondary nitrogen gas; The sensor assembly includes a protective cover, an optical fiber probe, and an optical fiber cable. The optical fiber probe is coaxially disposed inside the protective cover. The protective cover is connected to the nitrogen gas ejection pipeline. One end of the optical fiber cable is connected to the optical fiber probe, and the other end is connected to the sensor host. The inner wall of the protective cover is provided with multiple spiral-shaped diversion channels to divert the secondary nitrogen gas into direct flow nitrogen gas and swirling flow nitrogen gas. The control valve block is configured to control the on / off state of the main nitrogen gas to control the evacuation or pressure maintenance of the vacuum chamber; and The control valve block is configured to control the flow rate of the secondary nitrogen gas and continuously supply the secondary nitrogen gas into the protective cover.

[0007] By adopting the above scheme, a dual-path distribution of a single gas source is achieved using a control valve block. During operation, secondary nitrogen continuously enters the protective cover and is distributed into two airflows inside the cover: one airflow forms a downward-flowing DC through the gap between the fiber optic probe and the protective cover, scouring the probe end face and ensuring that the fiber optic probe is encased in nitrogen to prevent the accumulation of heat and contaminants; the other airflow is accelerated through a spiral channel and forms a circumferentially rotating vortex outside the DC, using centrifugal force to throw the suspended flux particles around the lower periphery of the protective cover outward, thereby reducing the occurrence of weak crosswind resistance or easy formation of backflow zone contamination of the lens under the single airflow mode.

[0008] In one embodiment of this application, a displacement pipeline and a throttling pipeline are further included. One end of the displacement pipeline and the throttling pipeline is connected to the nitrogen injection pipeline through a control valve block. The other end of the displacement pipeline is connected to the vacuum chamber through a jet pipe. The other end of the throttling pipeline is connected to the protective cover.

[0009] By adopting the above scheme, the gas delivery path is separated into a displacement pipeline for high-flow gas filling and a throttling pipeline for protecting the sensor probe. A control valve block is set to regulate the on / off state and flow state of the two paths. This ensures that the throttling pipeline can maintain a normally open gas supply state through the control valve block, whether the vacuum chamber is in the vacuuming, pressure holding, or gas filling and back pressure stage. This ensures that the protective cover always maintains a positive pressure environment relative to the vacuum chamber and prevents the dirty gas of the flux from flowing back into the protective cover.

[0010] In one embodiment of this application, a throttling channel is provided inside the control valve block. One end of the throttling channel is connected to the gas supply device, and a throttling valve is provided on the inner wall of the other end. A main channel is provided inside the control valve block on one side of the throttling channel. One end of the main channel is connected to the middle of the throttling channel, and a solenoid valve is provided on the inner wall of the other end. The other end of the throttling channel is connected to the throttling pipeline, and the other end of the main channel is connected to the displacement pipeline.

[0011] By adopting the above scheme, the flow rate of secondary nitrogen is preset to be limited by a throttle valve, the main nitrogen is controlled to be quickly switched on and off by a solenoid valve, and the flow resistance is preset by a physical throttle valve. This ensures that even when the main channel is opened and seizes the gas source, the throttle channel can still maintain a minimum airflow, thus avoiding the interruption of gas supply to the protective cover due to the pressure drop in the main pipeline.

[0012] In one embodiment of this application, the protective cover includes: The main body of the cover is assembled vertically onto the vacuum chamber; A connecting pipe, one end of which is fitted onto the upper end of the cover body, and the other end of which is connected to the throttling pipe.

[0013] By adopting the above scheme, the assembly difficulty is reduced by assembling the main body of the cover inside the vacuum chamber. At the same time, the connecting pipe extends to the outside of the vacuum chamber to connect with the throttling channel.

[0014] In one embodiment of this application, the main body of the cover is provided with an air intake section, a throat section and a diffuser section along the air intake direction. The air intake section, throat section and diffuser section are interconnected to form a DC channel for the flow of DC nitrogen, and the other end is connected to the diffuser section.

[0015] By adopting the above scheme, nitrogen accumulates pressure in the inlet section, reduces the flow cross-section and increases the flow velocity when flowing through the throat section, and diffuses in a controlled manner in the diffuser section. Combined with the shape of the fiber optic probe, the constriction design of the throat section can straighten the airflow direction and eliminate turbulence caused by pipe bends, making the nitrogen blown directly onto the probe surface more stable and uniform. At the same time, the negative pressure zone and high flow resistance established in the throat section also provide a basis for some of the secondary nitrogen in the subsequent inlet section to be diverted into the swirl channel.

[0016] In one embodiment of this application, the inner wall of the air intake section is provided with a plurality of intercepting pipes that correspond one-to-one with the diversion channel. One end of the diversion channel is connected to the intercepting pipe to form a swirling channel for the flow of swirling nitrogen.

[0017] By adopting the above scheme, a portion of the high-pressure gas is introduced into the spiral channel on the side wall through a choke pipe on the inner wall of the inlet section. The pressure difference between the inlet section and the throat section is used to drive the gas into the spiral channel without the need for an additional power source. The choke pipe ensures that the gas obtains a predetermined tangential entry angle before entering the spiral section, thus guaranteeing the angular velocity of the swirling flow and enhancing the centrifugal shielding effect of the nitrogen swirling flow.

[0018] In one embodiment of this application, the cross-sectional area of ​​the intake section is defined as S1, the cross-sectional area of ​​the throat section is defined as S2, and the total cross-sectional area of ​​the plurality of cut-off pipes is defined as S3. The cross-sectional area S1 of the intake section, the cross-sectional area S2 of the throat section, and the total cross-sectional area S3 of the plurality of cut-off pipes satisfy: S1>S2+S3.

[0019] By adopting the above scheme, by limiting the upstream air inlet cross-sectional area of ​​the protective cover to be greater than the sum of the cross-sectional areas of all downstream outlets, and by constructing a flow resistance difference through the ratio of S2 to S3, the device ensures that there is always sufficient static pressure in the air inlet section. This forces the gas to overcome the friction resistance along the spiral channel and spray it out evenly from each branch channel, ensuring that the central direct current and the external vortex can be formed simultaneously and that the intensity meets the design expectations, thus ensuring the integrity of the composite flow field.

[0020] In one embodiment of this application, the sensor assembly further includes a positioning rod, and multiple positioning rods are provided and located on the air intake section. The multiple positioning rods are circumferentially spaced outside the fiber optic probe. One end of the positioning rod is connected and fixed to the fiber optic probe, and the other end is slidably connected to the inner wall of the protective cover.

[0021] By adopting the above scheme, the positioning rod is used to constrain the relative position of the fiber optic probe and the inner wall of the protective cover in the radial direction, keeping them coaxial. This allows the direct current of nitrogen to flow in the annular flow field between the fiber optic probe and the protective cover, enveloping the sensor probe and flowing out in direct current. This improves the protection effect of the sensor probe and reduces the occurrence of air curtain rupture caused by uneven strength on both sides of the direct current nitrogen.

[0022] In one embodiment of this application, the jet pipe is mounted vertically on the vacuum chamber, the upper end of the jet pipe is connected to the replacement pipeline, and the lower end extends into the vacuum chamber. The height of the lower end of the jet pipe is defined as h1, and the height of the lower end of the protective cover is defined as h2. The heights h1 and h2 of the lower end of the jet pipe and the lower end of the protective cover satisfy h2>h1.

[0023] By adopting the above scheme, the outlet of the jet pipe responsible for high-flow inflation is set below the outlet of the protective cover. By placing the jet nozzle below, gravity and airflow are used to guide the flow, avoiding direct impact of the inflation jet on the sensor area. At the same time, the high-velocity jet pipe can form a negative pressure zone on one side below the protective cover, thereby reducing the risk of flux particles rising and contaminating the lens.

[0024] In one embodiment of this application, a telescopic seal is further included, the telescopic seal comprising: A fixed tube is provided vertically through the connecting tube, and the inner wall of the fixed tube is threaded. A threaded cylinder, one end of which is threaded to the inner wall of the fixed tube, and the other end extends to the outside of the fixed tube; A rotating ring is coaxially fixedly connected to the optical fiber line, and the outer wall of the rotating ring is coaxially rotatably connected to the inner wall of the threaded cylinder.

[0025] By adopting the above scheme, the axial position of the fiber optic probe inside the protective cover can be continuously fine-tuned through the cooperation of the rotating ring and the threaded cylinder, while maintaining a sealed state during the adjustment process. In particular, by fine-tuning the probe height, the size of the annular gap in the throat section can be directly changed, thereby enabling the flow distribution ratio of the central DC and the external vortex to be adjusted without replacing parts, in order to adapt to different welding process pressures.

[0026] In summary, this application includes at least one of the following beneficial technical effects: The diversion structure inside the protective cover creates a direct current of nitrogen gas flowing along the axial direction of the fiber optic probe, effectively eliminating the gas stagnation dead zone on the probe end face and continuously pushing flux particles outward while carrying away accumulated heat. At the same time, a high-speed rotating swirling air curtain is formed around the direct current, using centrifugal effect to throw suspended flux particles around the protective cover outward. This ensures the cleanliness of the core detection area and effectively blocks the intrusion of external lateral airflow and contaminants, improving the protection capability of the sensor probe lens.

[0027] 2. By pre-setting the flow resistance on the throttle valve, the protective cover is kept at a slightly positive pressure relative to the chamber environment during the process cycle of vacuum chamber evacuation, pressure holding, and high-flow gas charging back pressure. Especially when the main channel is opened for high-flow gas charging, it effectively prevents the interruption of protective airflow due to pressure diversion in the main pipeline and reduces the possibility of flux waste gas flowing back into the protective cover during pressure fluctuations.

[0028] 3. By strictly limiting the area ratio between the upstream inlet section and the downstream outlet section, and constructing a throttling back pressure at the throat section, the secondary nitrogen entering the protective cover is forced to overcome the friction resistance along the flow channel to be diverted, thus avoiding the situation where the gas only flows out from the middle gap. This ensures that the central direct current and the external vortex can be formed simultaneously and that the intensity meets the design expectations. Combined with the positioning component's constraint on the probe's coaxiality, this ensures the uniformity and integrity of the protective gas field. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the pipeline of a nitrogen protection sensing system for a vacuum reflow soldering apparatus during venting, provided in an embodiment of this application. Figure 2This is a schematic diagram of the pipeline of a nitrogen protection sensing system applied to a vacuum reflow soldering apparatus during pressure holding, provided in an embodiment of this application. Figure 3 This is a perspective view of a protective cover for a nitrogen protection sensing system applied to a vacuum reflow soldering apparatus, provided in an embodiment of this application. Figure 4 This is a front sectional view of a protective cover for a nitrogen protection sensing system applied to a vacuum reflow soldering apparatus, provided in an embodiment of this application. Figure 5 This is a top sectional view of a protective cover for a nitrogen protection sensing system applied to a vacuum reflow soldering apparatus, provided in an embodiment of this application. Figure 6 This is a planar sectional view of a control valve block for a nitrogen protection sensing system applied to a vacuum reflow soldering apparatus, as provided in an embodiment of this application. Figure 7 This is a planar sectional view of a telescopic seal for a nitrogen protection sensing system used in a vacuum reflow soldering apparatus, as provided in an embodiment of this application.

[0030] Explanation of reference numerals in the attached diagram: 1. Nitrogen ejection pipeline; 2. Control valve block; 21. Throttling channel; 22. Throttling valve; 23. Main channel; 24. Solenoid valve; 3. Sensor assembly; 31. Protective cover; 311. Diverting channel; 312. Main body of the cover; 3121. Inlet section; 3122. Throat section; 3123. Diverter section; 3124. Cut-off pipe; 313. Connecting pipe; 32. Fiber optic probe; 33. Fiber optic cable; 34. Positioning rod; 4. Replacement pipeline; 5. Throttling pipeline; 6. Telescopic seal; 61. Fixed pipe; 62. Threaded cylinder; 63. Rotating ring; 7. Jet pipe; 8. Vacuum chamber. Detailed Implementation

[0031] The following is in conjunction with the appendix Figure 1 -Appendix Figure 7 This application provides a more detailed description of a nitrogen protection sensing system for use in a vacuum reflow soldering apparatus.

[0032] This application provides a nitrogen protection sensing system for a vacuum reflow soldering apparatus, which is mounted on a vacuum chamber 8 and connected to a gas supply device and a sensor host, including a nitrogen ejection pipeline 1 and a sensor assembly 3.

[0033] Please see Figure 1 , Figure 2 and Figure 3One end of the nitrogen ejection pipe 1 is connected to the gas supply equipment, and the other end distributes the nitrogen ejected from the gas supply equipment through the control valve block 2 to form primary nitrogen and secondary nitrogen. The sensor assembly 3 includes a protective cover 31, an optical fiber probe 32, and an optical fiber cable 33. The optical fiber probe 32 is coaxially disposed inside the protective cover 31, and the protective cover 31 is connected to the nitrogen ejection pipe 1. One end of the optical fiber cable 33 is connected to the optical fiber probe 32, and the other end passes upward through the connecting pipe 313 and the throttling pipe 5 and extends to the outside of the vacuum chamber 8 to connect with the sensor host. The inner wall of the protective cover 31 is circumferentially provided with multiple spiral-shaped... The diversion channel 311 is used to split the secondary nitrogen gas into direct nitrogen gas and swirling nitrogen gas. The control valve block 2 is configured to control the on / off of the main nitrogen gas to control the vacuum chamber 8 to be emptied or pressurized. The control valve block 2 is also configured to control the flow rate of the secondary nitrogen gas and continuously introduce the secondary nitrogen gas into the protective cover 31. By dividing the secondary nitrogen gas into two streams, direct nitrogen gas and swirling nitrogen gas, inside the protective cover 31, the direct nitrogen gas protects the sensor probe while the centrifugal force of the swirling nitrogen gas throws the suspended flux particles around the lower periphery of the protective cover 31 outward, thereby improving the protection capability of the sensor probe lens.

[0034] In this embodiment, the inlet of the diversion channel 311 can be tangentially located on the inner wall of the protective cover 31.

[0035] Please see Figure 1 , Figure 2 and Figure 6 It also includes a displacement pipeline 4 and a throttling pipeline 5. One end of the displacement pipeline 4 and the throttling pipeline 5 are connected to the nitrogen injection pipeline 1 through the control valve block 2. The other end of the displacement pipeline 4 is connected to the vacuum chamber 8 through the jet pipe 7. The other end of the throttling pipeline 5 is connected to the protective cover 31. The control valve block 2 has a throttling channel 21 inside. One end of the throttling channel 21 is connected to the gas supply equipment, and the inner wall of the other end is equipped with a throttling valve 22. The control valve block 2 has a main channel 23 on one side of the throttling channel 21. One end of the main channel 23 is connected to the middle of the throttling channel 21, and the inner wall of the other end is equipped with a solenoid valve 24. The other end of the throttling channel 21 is connected to the throttling pipeline 5, and the other end of the main channel 23 is connected to the displacement pipeline 4. By setting the control valve block 2 to adjust the on / off state and flow state of the two paths, the vacuum chamber 8 can maintain a normally open gas supply state through the flow resistance of the preset throttling valve 22, whether it is in the vacuuming, pressure holding or gas filling back pressure stage.

[0036] In this embodiment, the gas supply device is an air pump, which can provide constant pressure or sufficient flow. At the same time, by pre-setting the diameter of the main channel, even if the main channel is open, the throttling channel can still maintain a minimum amount of secondary nitrogen. Specifically, the air pump provides a constant gas source pressure of 0.4MPa-0.6MPa. Meanwhile, in order to ensure the stability of dual-path gas supply, the inner diameter of the main channel 23 is designed to be 8mm-12mm, and the throttling orifice diameter or equivalent flow diameter of the throttling valve 22 is preset to 1.5mm-2.5mm. By setting the ratio of the flow cross-sectional area of ​​the main channel 23 to the throttling channel 21 to be greater than 10:1, even if the solenoid valve 24 is fully opened for high-flow gas filling, the pressure drop in the main pipeline will not cause the parallel throttling channel 21 to be interrupted, thereby ensuring that the throttling channel 21 can still maintain a minimum amount of secondary nitrogen continuously flowing into the protective cover 31 to maintain positive pressure protection.

[0037] Please see Figure 4 The protective cover 31 includes: a cover body 312 and a connecting pipe 313. The cover body 312 is vertically mounted on the vacuum chamber 8. One end of the connecting pipe 313 is mounted on the upper end of the cover body 312, and the other end of the connecting pipe 313 is connected to the throttling pipe 5. Inside the cover body 312, along the air intake direction, there are an air intake section 3121, a throat section 3122, and a diffuser section 3123, which are interconnected to form a protective cover. The intake section 3121 has a direct current channel for the flow of nitrogen, and the other end is connected to the diffuser section 3123. The inner wall of the intake section 3121 is provided with multiple cut-off pipes 3124 that correspond one-to-one with the diversion channel 311. One end of the diversion channel 311 is connected to the cut-off pipe 3124 to form a swirling channel for the flow of swirling nitrogen. The negative pressure zone and high flow resistance established in the throat section 3122 provide a basis for the diversion of some secondary nitrogen in the subsequent intake section 3121 into the swirling channel.

[0038] Please continue reading. Figure 4 The cross-sectional area of ​​the intake section 3121 is defined as S1, the cross-sectional area of ​​the throat section 3122 is defined as S2, and the total cross-sectional area of ​​the multiple cut-off pipes 3124 is defined as S3. The cross-sectional areas S1 of the intake section 3121, S2 of the throat section 3122, and S3 of the multiple cut-off pipes 3124 satisfy: S1>S2+S3. The device constructs a flow resistance difference through the proportional distribution of S2 and S3, ensuring that there is always sufficient static pressure in the intake section 3121, thereby forcing the gas to overcome the friction resistance of the spiral channel and uniformly eject from each branch channel 311, ensuring that the central direct current and the external vortex can be formed simultaneously and the intensity meets the design expectations.

[0039] Please see Figure 4 and Figure 5The sensor assembly 3 also includes positioning rods 34. Multiple positioning rods 34 are provided and located on the air inlet section 3121. The multiple positioning rods 34 are circumferentially spaced outside the fiber optic probe 32. One end of the positioning rod 34 is connected and fixed to the fiber optic probe 32, and the other end is slidably connected to the inner wall of the protective cover 31. The positioning rods 34 constrain the fiber optic probe 32 and the protective cover 31 to keep them coaxial in the radial direction, so that the nitrogen direct current can flow in the annular flow field between the fiber optic probe 32 and the protective cover 31, wrap the sensor probe, and flow out as direct current, thereby improving the protection effect of the sensor probe.

[0040] Please see Figure 2 The jet pipe 7 is mounted vertically on the vacuum chamber 8. The upper end of the jet pipe 7 is connected to the replacement pipe 4, and the lower end extends into the vacuum chamber 8. The height of the lower end of the jet pipe 7 is defined as h1, and the height of the lower end of the protective cover 31 is defined as h2. The heights h1 and h2 of the lower end of the jet pipe 7 and the lower end of the protective cover 31 satisfy h2>h1. The outlet of the jet pipe 7, which is responsible for high-flow-rate inflation, is located below the outlet of the protective cover 31. By placing the jet outlet below, gravity and airflow guidance are used to avoid the inflation jet directly impacting the sensor area. At the same time, a negative pressure zone can be formed on one side below the protective cover 31, thereby reducing the risk of flux particles rising and contaminating the lens.

[0041] Please see Figure 7 It also includes a telescopic seal 6, which includes a fixed tube 61, a threaded cylinder 62, and a rotating ring 63. The fixed tube 61 is vertically inserted into the connecting tube 313. The inner wall of the fixed tube 61 is threaded. One end of the threaded cylinder 62 is threaded to the inner wall of the fixed tube 61, and the other end extends to the outside of the fixed tube 61. The rotating ring 63 is coaxially fixedly connected to the optical fiber 33. The outer wall of the rotating ring 63 is coaxially rotatably connected to the inner wall of the threaded cylinder 62. Through the cooperation of the rotating ring 63 and the threaded cylinder 62, the axial position of the optical fiber probe 32 inside the protective cover 31 can be continuously finely adjusted, and the sealing state is maintained during the adjustment process.

[0042] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A nitrogen protection sensing system for use in a vacuum reflow soldering apparatus, mounted on a vacuum chamber and connected to a gas supply device and a sensor host, characterized in that, include: Nitrogen gas ejection pipeline (1), one end of which is connected to the gas supply equipment, and the other end is distributed by the control valve block (2) to form primary nitrogen and secondary nitrogen; The sensor assembly (3) includes a protective cover (31), an optical fiber probe (32), and an optical fiber line (33). The optical fiber probe (32) is coaxially disposed inside the protective cover (31). The protective cover (31) is connected to the nitrogen gas ejection pipe (1). One end of the optical fiber line (33) is connected to the optical fiber probe (32), and the other end is connected to the sensor host. The inner wall of the protective cover (31) is provided with multiple spiral-shaped diversion channels (311) to divert the secondary nitrogen gas into direct current nitrogen gas and swirling nitrogen gas. The control valve block (2) is configured to control the on / off state of the main nitrogen gas to control the evacuation or pressure maintenance of the vacuum chamber; and The control valve block (2) is configured to control the flow rate of the secondary nitrogen and continuously supply the secondary nitrogen into the protective cover (31).

2. The nitrogen protection sensing system for a vacuum reflow soldering apparatus according to claim 1, characterized in that: It also includes a displacement pipeline (4) and a throttling pipeline (5). One end of the displacement pipeline (4) and the throttling pipeline (5) are connected to the nitrogen injection pipeline (1) through a control valve block (2). The other end of the displacement pipeline (4) is connected to the vacuum chamber through a jet pipe (7). The other end of the throttling pipeline (5) is connected to the protective cover (31).

3. The nitrogen protection sensing system for a vacuum reflow soldering apparatus according to claim 2, characterized in that: The control valve block (2) has a throttling channel (21) inside. One end of the throttling channel (21) is connected to the gas supply equipment, and the inner wall of the other end is provided with a throttling valve (22). The control valve block (2) has a main channel (23) inside on one side of the throttling channel (21). One end of the main channel (23) is connected to the middle of the throttling channel (21), and the inner wall of the other end is provided with a solenoid valve (24). The other end of the throttling channel (21) is connected to the throttling pipeline (5), and the other end of the main channel (23) is connected to the displacement pipeline (4).

4. A nitrogen protection sensing system for a vacuum reflow soldering apparatus according to claim 3, characterized in that, The protective cover (31) includes: The main body of the cover (312) is assembled on the vacuum chamber in a vertical direction; A connecting pipe (313) is attached at one end to the upper end of the cover body (312), and the other end of the connecting pipe (313) is connected to the throttling pipe (5).

5. A nitrogen protection sensing system for a vacuum reflow soldering apparatus according to claim 4, characterized in that: The main body of the cover (312) is provided with an air intake section (3121), a throat section (3122) and a diffuser section (3123) respectively along the air intake direction. The air intake section (3121), the throat section (3122) and the diffuser section (3123) are interconnected to form a DC channel for direct flow of nitrogen gas, and the other end is connected to the diffuser section (3123).

6. A nitrogen protection sensing system for a vacuum reflow soldering apparatus according to claim 5, characterized in that: The inner wall of the air intake section (3121) is provided with a plurality of intercepting pipes (3124) that correspond one-to-one with the diversion channel (311). One end of the diversion channel (311) is connected to the intercepting pipe (3124) to form a swirling channel for the flow of swirling nitrogen.

7. A nitrogen protection sensing system for a vacuum reflow soldering apparatus according to claim 6, characterized in that: The cross-sectional area of ​​the intake section (3121) is defined as S1, the cross-sectional area of ​​the throat section (3122) is defined as S2, and the total cross-sectional area of ​​the plurality of cut-off pipes (3124) is defined as S3. The cross-sectional area S1 of the intake section (3121), the cross-sectional area S2 of the throat section (3122), and the total cross-sectional area S3 of the plurality of cut-off pipes (3124) satisfy: S1>S2+S3.

8. A nitrogen protection sensing system for a vacuum reflow soldering apparatus according to claim 1, characterized in that: The sensor assembly (3) also includes a positioning rod (34), a plurality of which are provided and located on the air intake section (3121). The plurality of positioning rods (34) are circumferentially spaced outside the fiber optic probe (32). One end of the positioning rod (34) is connected and fixed to the fiber optic probe (32), and the other end is slidably connected to the inner wall of the protective cover (31).

9. A nitrogen protection sensing system for a vacuum reflow soldering apparatus according to claim 2, characterized in that: The jet pipe (7) is mounted vertically on the vacuum chamber. The upper end of the jet pipe (7) is connected to the replacement pipe (4), and the lower end extends into the vacuum chamber. The height of the lower end of the jet pipe (7) is defined as h1, and the height of the lower end of the protective cover (31) is defined as h2. The heights h1 and h2 of the lower end of the jet pipe (7) and the lower end of the protective cover (31) satisfy h2>h1.

10. A nitrogen protection sensing system for a vacuum reflow soldering apparatus according to claim 4, characterized in that, It also includes a telescopic seal (6), which comprises: A fixed tube (61) is vertically inserted through the connecting tube (313), and the inner wall of the fixed tube (61) is threaded. A threaded cylinder (62) has one end threadedly connected to the inner wall of the fixed tube (61) and the other end extending to the outside of the fixed tube (61); A rotating ring (63) is coaxially fixedly connected to the optical fiber (33), and the outer wall of the rotating ring (63) is coaxially rotatably connected to the inner wall of the threaded cylinder (62).

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