Reflow oven

Abstract

This application provides a reflow oven, comprising: a soldering section for processing circuit boards to be soldered, the soldering section having N soldering sub-regions; a purification section including M purification sub-regions, wherein each of the M purification sub-regions is connected to one of the N soldering sub-regions, where M is less than or equal to N; a controllable discharge pipe and K discharge branches, each of the K discharge branches connecting one of the M purification sub-regions to the controllable discharge pipe; and a valve device, the inlet end of the valve device being connected to the outlet of the controllable discharge pipe for controlling the connection or disconnection of the controllable discharge pipe from the outside environment. The reflow oven provided in this application can operate in air mode and inert gas mode.

Description

Technical Field

[0001] This application relates to reflow ovens, and more particularly to reflow ovens capable of operating in air and inert gas modes. Background Technology

[0002] In the fabrication of printed circuit boards (PCBs), electronic components are typically mounted onto the board using a process known as "reflow soldering." In a typical reflow soldering process, solder paste (e.g., solder grease) is deposited onto selected areas of the PCB, and the leads of one or more electronic components are inserted into the deposited solder paste. The PCB is then passed through a reflow oven, where the solder paste is reflowed in a heated zone (i.e., heated to a melting or reflow temperature) and then cooled in a cooling zone to electrically and mechanically connect the leads of the electronic components to the PCB. The term "PCB" as used herein includes any type of substrate assembly for electronic components, such as a wafer substrate.

[0003] Typically, solder paste includes not only solder but also flux that wets the solder and provides a good solder joint. Other additives, such as solvents and catalysts, may also be included. After the solder paste is deposited on the circuit board, the board is conveyed on a conveyor through multiple heating zones of a reflow oven. The heat in the heating zones melts the solder paste and simultaneously vaporizes the volatile organic compounds (VOCs) in the flux and other additives in the solder paste, forming vapors. These vapors are referred to below as "volatile contaminants."

[0004] These volatile contaminants can accumulate in the reflow oven and cause several problems. If the temperature of these contaminants decreases, they may condense on the circuit boards, contaminating them and requiring subsequent cleaning steps. Volatile contaminants can also condense on the surfaces of the reflow oven's coolers, clogging pores. The condensate may also drip onto subsequent circuit boards, damaging them or requiring further cleaning.

[0005] In reflow ovens, air or an inert gas (such as nitrogen) is typically used as the working atmosphere, with different atmospheres employed for circuit boards with varying process requirements. The oven chamber is filled with this working atmosphere, and the circuit boards undergo soldering within it as they are conveyed through the chamber. For reflow ovens using air as the working atmosphere, fresh air is typically introduced from both ends of the oven, flowing in a specific manner to heat or cool the circuit boards. This air, along with volatile contaminants, is then exhausted from the interior of the reflow oven. Furthermore, the precise temperature distribution required for reflow processing must be maintained when handling volatile contaminants. Summary of the Invention

[0006] This application provides a reflow oven that more effectively handles volatile contaminants, thereby reducing the frequency of subsequent maintenance and upkeep.

[0007] The reflow oven is capable of operating in inert gas mode and air mode. The reflow oven includes: a welding section for processing circuit boards to be welded, the welding section having N welding sub-regions; a purification section including M purification sub-regions, wherein each of the M purification sub-regions is connected to a corresponding welding sub-region among the N welding sub-regions, where M is less than or equal to N; a controllable discharge pipe and K discharge branches, each of the K discharge branches connecting one of the M purification sub-regions to the controllable discharge pipe, where K is less than or equal to M; and a valve device, the inlet end of the valve device being connected to the outlet of the controllable discharge pipe for controlling the connection or disconnection of the controllable discharge pipe from the outside environment.

[0008] As described above, the reflow oven operates in air mode when the valve device is open and in inert gas mode when the valve device is closed.

[0009] In the reflow oven described above, the outlet end of the valve device is connected to the exhaust device.

[0010] The reflow oven as described above further includes:

[0011] An inlet area and an outlet area are respectively located at both ends of the welded part; a pair of inlet area isolation pipes are respectively connected to the upper and lower sides of the inlet area; a pair of outlet area isolation pipes are respectively connected to the upper and lower sides of the outlet area.

[0012] In the reflow oven as described above, the first end of each of the pair of inlet area isolation pipes is connected to the upper and lower sides of the inlet area, the second end of one of the pair of inlet area isolation pipes is connected to the controllable discharge pipe, and the second end of the other of the pair of inlet area isolation pipes is connected to one of the N welding sub-regions.

[0013] As described above, in the reflow oven, the welding section includes a heating zone and a cooling zone, and each welding sub-region in the heating zone is connected to a corresponding purification sub-region.

[0014] As described above, in the reflow oven, each welding sub-region in the heating zone and a purification sub-region connected to it form a heating working unit. The heating working unit includes an inner circulation unit and an outer circulation unit. Each of the purification sub-regions has a purification airflow inlet and a purification airflow outlet. The purification airflow inlet and purification airflow outlet of the purification sub-region of the inner circulation unit are both connected to the corresponding welding sub-region. The purification airflow inlet of the purification sub-region of the outer circulation unit is connected to the corresponding welding sub-region. The purification airflow outlet of the purification sub-region of the outer circulation unit is connected to the controllable discharge pipeline through one of the K discharge branch pipes.

[0015] In the reflow oven described above, the external circulation unit is located near the front and rear ends of the heating zone.

[0016] As described above, in the reflow oven, each of the N welding sub-regions includes a flow guiding device that can guide a portion of the gas in the welding sub-region to a corresponding purification sub-region.

[0017] As described above, in the reflow oven, each of the M purification sub-regions includes a catalytic device and a heating device; the heating device has a catalytic operating mode and a maintenance operating mode.

[0018] The reflow oven of this application, through the above improvements to the exhaust pipes and valve devices, can effectively perform soldering operations in both air and inert gas operating modes using a single set of equipment. In inert gas operating mode, only a small amount of inert gas needs to be replenished, saving inert gas consumption. In air operating mode, the yield of processed circuit boards still meets requirements. Switching between operating modes is simple and easy, requiring only the opening or closing of the valve device. Both operating modes reduce the frequency of subsequent maintenance and upkeep of the reflow oven. Attached Figure Description

[0019] The reflow oven of this application will become more readily understood when read in conjunction with the accompanying drawings, in which the same reference numerals represent the same parts throughout the drawings, wherein:

[0020] Figure 1 A simplified schematic diagram of one embodiment of the reflow oven of this application is shown;

[0021] Figure 2 It shows Figure 1 A schematic diagram of the gas flow direction for intake and exhaust when the reflow oven is operating in inert gas mode;

[0022] Figure 3 It shows Figure 1 A schematic diagram showing the gas flow direction of the inlet and outlet when the reflow oven is operating in air mode. Detailed Implementation

[0023] Various specific embodiments of this application will now be described with reference to the accompanying drawings, which form part of this specification. It should be understood that although directional terms such as "front," "rear," "upper," "lower," "left," "right," "inner," "outer," "top," and "bottom" are used in this application to describe various exemplary structural parts and elements, their use is merely for ease of description and is based on the exemplary orientations shown in the accompanying drawings. Since the embodiments disclosed in this application can be arranged in different orientations, these directional terms are for illustrative purposes only and should not be considered limiting. Where possible, the same or similar reference numerals used in this application refer to the same parts.

[0024] Figure 1 A simplified schematic diagram of one embodiment of the reflow oven 100 of this application is shown. The reflow oven 100 can be used as an air / inert gas switchable reflow oven, which can use either air or an inert gas as the working atmosphere, thus allowing the reflow oven 100 to operate in either air mode or inert gas mode. The inert gas is, for example, nitrogen. The operation of the reflow oven 100 in inert gas mode will be described below using nitrogen as an example. However, it should be noted that the reflow oven 100 of this application is not limited to using nitrogen as the inert gas, but can use any inert gas.

[0025] like Figure 1 As shown, the reflow oven 100 includes a welding section 101, a purification section 102, and a furnace chamber 104. It should be noted that... Figure 1 The view shown is taken from the side of the reflow oven 100. For ease of explanation, the reflow oven 100 is shown in the image below. Figure 1 The outer casing used to cover the front and rear sides of the furnace 104 was removed.

[0026] The furnace chamber 104 extends through the welding section 101 and includes a furnace inlet 142 and a furnace outlet 144. The reflow oven 100 is also provided with a conveying device 105, which extends through the furnace chamber 104 and is used to feed the circuit board to be processed into the furnace chamber 104 from the furnace inlet 142, and to output the circuit board processed by the reflow oven 100 from the furnace chamber 104 through the furnace outlet 144.

[0027] The welding section 101 includes a heating zone 110 and a cooling zone 120. A barrier exhaust zone 130 is also provided between the heating zone 110 and the cooling zone 120. The furnace chamber 104 extends through the heating zone 110, cooling zone 120, and barrier exhaust zone 130, and these zones are in fluid communication through the furnace chamber 104. Furthermore, each region of the heating zone 110, cooling zone 120, and barrier exhaust zone 130 is also in fluid communication with the furnace chamber 104. The barrier exhaust zone 130 extracts or discharges gas from the furnace chamber 104, thereby preventing or reducing the entry of gases containing volatile pollutants from the heating zone 110 into the cooling zone 120. In addition, by extracting or discharging gas from the furnace chamber 104, the barrier exhaust zone 130 can also serve as an insulation zone, separating the high-temperature heating zone 110 from the low-temperature cooling zone 120.

[0028] The heating zone 110 and the cooling zone 120 may each include multiple welding sub-regions. Figure 1 In the illustrated embodiment, the heating zone 110 includes 12 soldering sub-regions Z1-Z12, which are continuously connected and gradually increase in temperature. Each soldering sub-region is connected to its adjacent sub-region only through the furnace chamber 104. When the circuit board is fed into the heating zone 110 by the conveyor 105, the circuit board is heated, and some contaminants in the flux of the solder paste dispensed on the circuit board vaporize. The cooling zone 120 includes four soldering sub-regions C1-C4. After the circuit board is conveyed from the heating zone 110 into the cooling zone 120, the solder paste is cooled and solidified on the soldering areas of the circuit board, thereby connecting the electronic components to the circuit board. It is worth noting that the number of soldering sub-regions in the heating zone 110 and cooling zone 120 of the reflow oven can be configured according to the required process requirements, and is not limited to... Figure 1 The example shown.

[0029] The purification unit 102 includes multiple purification sub-regions (P1-P14), each connected to a corresponding soldering sub-region, used to purify the gas within the soldering sub-region. Each purification sub-region is equipped with a catalytic device and a heating device (not shown in the figure). The catalytic device contains a catalyst that catalyzes the decomposition of volatile contaminants in the flux into non-condensable components, thereby maintaining the cleanliness of the furnace 104 for a longer period and preventing circuit board contamination. The heating device has a catalytic operating mode and a maintenance operating mode. In the catalytic operating mode, the temperature setting of the heating device is suitable for the catalytic device to decompose contaminants in the flux; in the maintenance operating mode, the temperature setting of the heating device is sufficient to activate the catalyst in the catalytic device.

[0030] The total number of purification sub-regions in the heating device can be equal to or less than the total number of welding sub-regions. In this application, there are 16 welding sub-regions and 14 purification sub-regions.

[0031] The reflow oven 100 also includes a controllable exhaust pipe 108, several exhaust branches 2, and a valve device 150 for venting gas from the heating zone 110 of the reflow oven 100. One end of each of the several exhaust branches 2 is connected to a corresponding purification sub-zone, and the other end is connected to the controllable exhaust pipe 108, allowing gas from the corresponding purification sub-zone to enter the controllable exhaust pipe 108. The number of exhaust branches 2 is less than or equal to the number of purification sub-zones; in this application, the number of exhaust branches 2 is four. The controllable exhaust pipe 108 has an outlet 153, which is connected to the inlet end of the valve device 150, thereby connecting the controllable exhaust pipe 108 to the outside via the valve device 150. By controlling the opening or closing of the valve device 150, the connection or disconnection between the controllable exhaust pipe 108 and the outside can be controlled.

[0032] See still Figure 1Each of the 12 welding sub-regions (Z1-Z12) in the heating zone 110 is provided with a heating zone airflow outlet 8, and some of the welding sub-regions (e.g., Z2, Z3, Z11, Z12) are provided with a heating zone airflow inlet 6. Some of the welding sub-regions in the four welding sub-regions of the cooling zone (e.g., C1, C3, C4) are provided with a cooling zone airflow outlet 7, and one welding sub-region C1 is provided with a cooling zone airflow inlet 9. A flow guiding device (not shown in the figure) is provided in each welding sub-region to guide a portion of the gas inside the welding sub-region to flow out from the heating zone airflow outlet 8 or the cooling zone airflow outlet 7. The flow guiding device ensures continuous gas flow within the welding sub-region to guarantee a uniform temperature distribution inside the welding sub-region. Each of the 14 purification sub-regions (P1-P14) in the purification section 102 is provided with a purification zone airflow outlet 5 and a purification zone airflow inlet 3. Each welding sub-region (Z1-Z12) in the heating zone 110 and a corresponding purification sub-region in the purification section 102 form a heating working unit. The heating working unit includes an inner circulation unit 181 and an outer circulation unit 182. In the inner circulation unit 181, the purification zone airflow inlet 3 and purification zone airflow outlet 5 of the purification sub-region are connected to the welding sub-region via corresponding purification branch pipes 1, allowing gas in the welding sub-region of the inner circulation unit 181 to enter the purification zone airflow inlet 3 of the purification sub-region from the heating zone airflow outlet 8. After purification in the purification sub-region, the clean gas flows out from the purification zone airflow outlet 5 and re-enters the welding sub-region. In the outer circulation unit 182, the purification zone airflow inlet 3 of the purification sub-region is connected to the welding sub-region via a corresponding purification branch pipe 1, and the purification zone airflow outlet 5 is connected to a controllable discharge pipe 108 via a corresponding discharge branch pipe 2, allowing gas in the welding sub-region of the outer circulation unit 182 to be discharged through the controllable discharge pipe 108. In cooling zone 120, a portion of the welding sub-areas and a corresponding purification sub-area form a cooling working unit, while another portion of the welding sub-areas form a separate cooling working unit. Each cooling working unit includes an internal circulation unit, such as the unit consisting of welding sub-area C1 and purification sub-area P13. The purification zone airflow inlet 3 and purification zone airflow outlet 5 of purification sub-area P13 are connected to welding sub-area C4 via corresponding purification branch pipes 1, allowing gas in welding sub-area C4 to enter the purification zone airflow inlet 3 of purification sub-area P13 from the cooling zone airflow outlet 7. After purification in purification sub-area P13, the clean gas flows out from the purification zone airflow outlet 5 and re-enters welding sub-area C4 through the cooling zone airflow inlet 9. Each heating working unit is connected to adjacent heating working units only through the furnace chamber 104, ensuring that most of the gas within each heating working unit flows within its own unit, with only a small amount flowing through the furnace chamber 104 to adjacent heating working units.Similarly, each cooling working unit is connected to its adjacent cooling working unit only through the furnace 104, so that most of the gas inside each cooling working unit flows within its own unit, and only a small amount of gas flows through the furnace 104 to the adjacent cooling working unit.

[0033] The reflow oven 100 also includes an inlet zone B1 and an outlet zone B2, which are respectively located at both ends of the welding section 101. The inlet zone B1 and outlet zone B2 are used to form an air curtain by providing airflow towards the furnace inlet 142 and furnace outlet 144 of the furnace chamber 104 in nitrogen mode. This air curtain prevents air from the external environment from entering the furnace chamber 104, thereby maintaining the cleanliness of the inert working atmosphere in the reflow oven 100. For this purpose, a pair of connecting ports 171a and 171b are respectively provided on the upper and lower sides of the inlet zone B1, and a pair of connecting ports 173a and 173b are respectively provided on the upper and lower sides of the outlet zone B2.

[0034] The reflow oven 100 also includes a pair of inlet zone isolation pipes 175a and 175b, and a pair of outlet zone isolation pipes 176a and 176b. One end of the inlet zone isolation pipe 175a is connected to the connection port 171a of the inlet zone B1, and the other end is connected to the welding sub-area C3 of the cooling zone. One end of the inlet zone isolation pipe 175b is connected to the connection port 171b of the inlet zone B1, and the other end is connected to the controllable discharge pipe 108. The connection between the inlet zone isolation pipe 175b and the controllable discharge pipe 108 is close to the valve device 150 and is located downstream of the connection between the discharge branch pipe 2 and the controllable discharge pipe 108. One end of the outlet zone isolation pipe 176a is connected to the welding sub-area C4 of the cooling zone, and the other end is connected to the outlet zone connection port 173a. One end of the outlet zone isolation pipe 176b is connected to the exhaust zone 130, and the other end is connected to the outlet zone connection port 173b. The outlet isolation pipe 176b includes a front section 11 and a rear section 12, which are connected by a purification sub-region P14 so that the gas in the blocked exhaust zone 130 can be purified by the purification sub-region P14 and then passed to the outlet zone B2.

[0035] The outlet end of valve device 150 is connected to the plant's exhaust system, such as a plant fan, so that when valve device 150 is opened, the fan draws air from inside the plant to the outside, accelerating the discharge of gas in the controllable exhaust pipe 108. The reflow oven 100 includes gas accelerating devices 20, 21, 22, and 23 respectively installed on the controllable exhaust pipe 108, the inlet isolation pipe 175a, and the outlet isolation pipes 176a and 176b. Gas accelerating devices 20, 21, 22, and 23 are used to guide the flow of gas and accelerate its flow. Gas accelerating device 20 causes the gas in the controllable exhaust pipe 108 to flow towards valve device 150. Gas accelerating device 21 causes gas to flow from the welding sub-region C3 of the cooling zone to the upper side of the inlet region B1. Gas acceleration device 22 causes gas to flow from exhaust zone 130 through purification sub-region P14 to the lower side of outlet zone B2, and gas acceleration device 23 causes gas to flow from welding sub-region C4 of cooling zone to the upper side of outlet zone B2.

[0036] Still as Figure 1 As shown, the furnace inlet 142 and furnace outlet 144 are connected to a nitrogen source (not shown) or directly to the outside atmosphere, respectively. When the reflow oven 100 operates in nitrogen mode, it receives clean nitrogen from the nitrogen source. When operating in air mode, it obtains clean air directly from the atmosphere. In each soldering sub-region of the heating zone 110 of the reflow oven 100, the temperature of the gas inside the furnace 104 gradually increases from left to right. Different regions have different requirements for the temperature of the gas inside the furnace 104 to meet the temperature requirements of circuit board processing. Supplying clean gas to the reflow oven 100 from a position near the furnace inlet 142 and furnace outlet 144 allows clean gas at room temperature to enter the soldering sub-region of the heating zone with the lowest temperature, thus avoiding a significant impact on the temperature of the gas in the soldering sub-region of the heating zone with higher temperature. Because the exhaust zone 130 and welding sub-regions Z2, Z3, Z11, Z12, C3, and C4 are blocked from exhausting outwards, and because the gas is heated in the heating zone 110, the gas pressure in the middle of the furnace 104 is lower than the gas pressure at the furnace inlet 142 and the furnace outlet 144. Therefore, supplying clean gas to the reflow oven 100 from the position near the furnace inlet 142 and the position near the furnace outlet 144 makes it easier for the gas to enter the furnace 104 under pressure.

[0037] Figure 2 and Figure 3 They are shown respectively Figure 1 The diagram shows the gas flow direction of the reflow oven 100 when it is operating in nitrogen and air modes, where the arrows indicate the flow direction of the airflow.

[0038] like Figure 2 As shown, the reflow oven 100 operates in nitrogen mode. At this time, the valve device 150 of the reflow oven 100 is closed. The nitrogen source (not shown) is opened to supply clean nitrogen to the reflow oven 100. In the inner circulation unit 181 of the heating zone 110, the flow guide device in the welding sub-zone allows gas to enter the corresponding welding sub-zone's purification zone flow inlet 3 from the heating zone gas outlet 8 through the purification branch pipe 1. In the welding sub-zone, volatile pollutants in the gas are catalytically decomposed, thereby purifying the gas. The purified gas returns to the welding sub-zone from the purification zone gas outlet 5 through the purification branch pipe 1 and the heating zone gas inlet 6. Thus, nitrogen is internally circulated in the inner circulation unit 181. In the outer circulation unit 182 of the heating zone 110, the flow guide device in the welding sub-zone allows gas to enter the corresponding welding sub-zone's purification zone flow inlet 3 from the heating zone gas outlet 8 through the purification branch pipe 1. In the purification sub-zone, volatile pollutants in the gas flow are catalytically decomposed, thereby purifying the gas. The purified gas enters the controllable discharge pipe 108 from the airflow outlet 5 of the purification zone through the discharge branch pipe 2. The airflow in the controllable discharge pipe 108 flows towards the valve device 150. Since the valve device 150 is closed, the gas in the controllable discharge pipe 108 passes through the inlet isolation pipe 175b and enters the lower side of the inlet zone B1. In the external circulation unit 182, the welding sub-regions continuously receive fresh nitrogen from the furnace inlet 142 and furnace outlet 144 through the furnace 104. The external circulation unit 182 is located at the front and rear ends of the heating zone 110. In one embodiment of this application, the external circulation unit 182 is the heating working unit where the welding sub-regions Z2, Z3, Z11, and Z12 are located, that is, the second, third, and penultimate heating working units of the welding section 101. The gas in the internal circulation unit 181 is circulated internally, requiring only a small amount of new nitrogen to be replenished from the outside, or almost no replenishment at all. The external circulation unit 182 needs to be replenished with fresh nitrogen from a nitrogen source; therefore, minimizing the number of external circulation units reduces nitrogen consumption. It should be noted that this application is an example; in other embodiments, the arrangement of the internal and external circulation units can be tailored to actual process conditions.

[0039] In cooling zone 120, the temperature of welding sub-regions C1-C4 gradually decreases. The cooling working unit formed by the higher-temperature welding sub-region C1 and the corresponding purification sub-region P13 is an internal circulation unit. The purification sub-region P13 can purify the airflow in welding sub-region C1. The welding sub-regions C2-C4 have lower temperatures and produce fewer volatile pollutants, so they do not need to be connected to the purification sub-region.

[0040] The inlet isolation duct 175a is connected to the cooling zone airflow outlet 7 of the welding sub-region C3, thereby providing airflow to the upper side of the inlet zone B1 via the gas acceleration device 21. With the valve device 150 closed, the airflow in the controllable discharge duct 108 is provided to the lower side of the inlet zone B1 via the inlet isolation duct 175b. The inlet zone B1 is configured such that the airflow provided by the inlet isolation duct 175a flows downwards perpendicular to the conveying direction of the conveying device 105, and the airflow in the inlet isolation duct 175b flows upwards perpendicular to the conveying direction of the conveying device 105, thereby forming an air curtain in the inlet zone B1 to prevent outside air from entering the furnace inlet 142.

[0041] One end of the outlet isolation pipe 176a is connected to the cooling zone airflow outlet 7 of the welding sub-region C4, and the other end is connected to the upper side of the outlet region B2. With the assistance of the gas acceleration device 23, the outlet isolation pipe 176a provides airflow to the upper side of the outlet region B2. One end of the outlet isolation pipe 176b is connected to the barrier exhaust zone 130 through a purification sub-region P14, and the other end is connected to the lower side of the outlet region B2. Thus, with the assistance of the gas acceleration device 22, the outlet isolation pipe 176a provides airflow to the lower side of the outlet region B2. The outlet region B2 is configured such that the airflow provided by the outlet isolation pipe 176a flows downward perpendicular to the conveying direction of the conveying device 105, and the airflow in the outlet isolation pipe 176b flows upward perpendicular to the conveying direction of the conveying device 105, thereby forming an air curtain in the outlet region B2 to prevent outside air from entering the furnace outlet 144. The purification sub-region P14 can purify the gas from the barrier exhaust zone 130, resulting in a lower content of easily condensable volatile pollutants in the airflow entering the lower side of the outlet zone B1.

[0042] In nitrogen working mode, the catalyst in the purification sub-regions P1-P14 can maintain good activity and have a long maintenance cycle. The air curtains in the inlet zone B1 and outlet zone B2 can prevent outside air from entering the furnace 104 to ensure the working atmosphere inside the reflow oven 100.

[0043] like Figure 3 As shown, the reflow oven 100 operates in air mode. At this time, the valve device 150 of the reflow oven 100 is open. Figure 2The operation is similar in nitrogen mode, except that the airflow in the controllable exhaust pipe 108 and the inlet isolation pipe 175b is discharged outside the reflow oven 100 by opening valve device 150. The furnace inlet 142 and furnace outlet 144 are connected to the air source, continuously providing clean air to the reflow oven 100. In air mode, the purification sub-regions P1-P14 also play a certain purification role, but compared with nitrogen mode, the catalyst in purification sub-regions P1-P14 is relatively easy to deactivate, resulting in relatively low catalytic efficiency. Therefore, it is necessary to promptly discharge some of the airflow containing high levels of non-condensable volatile pollutants to the outside of the reflow oven to extend the maintenance and cleaning cycle.

[0044] In this application, the heating working units where the welding sub-regions Z2, Z3, Z11, and Z12 are located, namely the second, third, and penultimate heating working units of the welding section 101, are set as external circulation units 182 to ensure that the reflow oven 100 can work normally in air mode.

[0045] Through repeated observation and experimentation, the inventors discovered that soldering sub-regions Z2, Z3, Z11, and Z12 are areas where flux generates a significant amount of volatile pollutants. This is because the volatile pollutants originate from the flux on the circuit board. While the temperature of soldering sub-region Z1, near the furnace inlet 142, is relatively low, the flux has not yet reached the temperature required to generate a large amount of volatile pollutants. Z2 and Z3 are where the circuit board has just entered the heating unit of the soldering section 101 and has been heated through soldering sub-region Z1. At this point, the flux on the circuit board is just beginning to be heated to a temperature that easily generates volatile pollutants, resulting in a significant amount of volatile pollutants. Therefore, the heating unit containing soldering sub-region Z1 is designated as an internal circulation unit, and the heating units containing soldering sub-regions Z2 and Z3 are designated as external circulation units. Soldering sub-regions Z11 and Z12 are relatively high-temperature areas in the heating zone 110, where flux easily generates a large amount of volatile pollutants. Therefore, the heating units containing Z11 and Z12 are also designated as external circulation units. Therefore, in air mode, timely exhaust of gas from welding sub-regions Z2, Z3, Z11, and Z12 can keep the gas in furnace 104 clean for a long time, reducing the frequency of maintenance.

[0046] The reflow oven described in this application requires regular maintenance and cleaning. During regular maintenance, the heating device in the cleanroom sub-area needs to be adjusted to a maintenance mode to activate the catalyst in the catalytic converter. In nitrogen mode, the catalyst maintains good activity for a longer period, resulting in a longer maintenance cycle. In air mode, the catalyst is more susceptible to reduced activity due to oxygen in the air, leading to a shorter maintenance cycle. Maintenance is typically performed before switching from air mode to nitrogen mode to ensure good catalyst activity under nitrogen operation.

[0047] Through observation, analysis, and research, the applicant discovered that in a reflow oven using nitrogen as the working atmosphere, the gas inside the reflow oven is separated from the outside environment, and the reflow oven is sealed by air curtains formed in the inlet and outlet zones. For each internal circulation unit in the heating zone, the gas circulates within the internal circulation unit, and the airflow inside the internal circulation unit is cleaned by the purification function of the purification unit, thereby reducing nitrogen consumption. However, this type of reflow oven using nitrogen as the working atmosphere is not suitable for using air as the working atmosphere. If the existing nitrogen reflow oven is not modified, and only the furnace ends of the existing nitrogen reflow oven are connected to the atmosphere, the existing nitrogen reflow oven does not meet the welding process requirements of air reflow ovens.

[0048] If an additional air circulation pipeline and control device are added to an existing nitrogen reflow oven in accordance with the existing air reflow oven, valves and pipelines for venting air will need to be added to each welding sub-area to allow the gas in each welding sub-area to be collected together and then discharged to the designated area. At the same time, without affecting the performance of the existing nitrogen reflow oven after the modification, a large number of pipelines and valves will be required. The pipelines are complex, the structure of the existing nitrogen reflow oven is significantly modified, and the cost is high.

[0049] In this invention, existing nitrogen reflow ovens still largely configure the welding sub-areas of the heating zone as internal circulation units, selectively configuring welding sub-areas with higher volatile pollutant content as external circulation units. In air mode, this allows for timely removal of volatile pollutants, thus meeting the process requirements in air mode. Furthermore, the reflow oven in this application utilizes its purification unit to purify the air in air mode, resulting in lower levels of volatile pollutants in the exhaust gas. The reflow oven with purification unit in this application can simultaneously meet the process requirements of both nitrogen and air modes.

[0050] The reflow oven of this application, through the above improvements to the exhaust pipes and valve devices, enables efficient soldering in both air and nitrogen operating modes using a single equipment. In nitrogen operating mode, the yield of processed circuit boards meets requirements. By incorporating a purification section, the nitrogen inside the reflow oven can be recycled, requiring only a small amount of nitrogen to be replenished from the nitrogen source, thus saving nitrogen consumption. In air operating mode, gases containing more volatile pollutants are discharged to the outside of the reflow oven, preventing accumulation inside, and the yield of processed circuit boards still meets requirements. Switching between operating modes is simple and easy, requiring only the opening or closing of the valve device.

[0051] This specification uses examples to disclose this application, one or more of which are illustrated in the accompanying drawings. Each example is provided for the purpose of explaining this application and not for limiting it. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made to this application without departing from the scope or spirit of this application. For example, features illustrated or described as part of one embodiment may be used with another embodiment to obtain further embodiments. Therefore, it is intended that this application cover modifications and variations made within the scope of the appended claims and their equivalents.

Claims

1. A reflow oven, the reflow oven being capable of operating in inert gas mode and air mode, characterized in that, The reflow oven includes: A welding section for processing circuit boards to be welded, the welding section having N welding sub-regions; The purification section includes M purification sub-regions, wherein each of the M purification sub-regions is connected to a corresponding welding sub-region in N welding sub-regions, and M is less than or equal to N. A single controllable discharge pipe and K discharge branches, each of the K discharge branches connecting one of M purification sub-regions to the single controllable discharge pipe, where K is less than or equal to M; and A single valve device, the inlet of which is connected to the outlet of a single controllable discharge pipe, is used to control the connection or disconnection of the single controllable discharge pipe with the outside world; wherein, the single valve device is configured to connect the outlet of the single controllable discharge pipe with the outside world when air is flowing in the single controllable discharge pipe so that air is discharged to the outside world, and to disconnect the outlet of the single controllable discharge pipe from the outside world when inert gas is flowing in the single controllable discharge pipe so that inert gas returns to the reflow oven.

2. The reflow oven as described in claim 1, characterized in that: Each of the purification sub-regions has a purification zone airflow inlet and a purification zone airflow outlet. All of the purification zone airflow inlets are connected to a corresponding welding sub-region. The first part of the purification zone airflow outlets are connected to a corresponding welding sub-region, while the second part of the purification zone airflow outlets are connected to the single controllable discharge pipe through the corresponding discharge branch pipe. Specifically, the air or inert gas discharged from the airflow outlet of the first part of the purification zone returns to the corresponding welding sub-area, while the air or inert gas discharged from the airflow outlet of the second part of the purification zone enters the single controllable discharge pipe.

3. The reflow oven as described in claim 2, characterized in that: The outlet end of the valve device is connected to the exhaust device.

4. The reflow oven as described in claim 1, characterized in that, The reflow oven also includes: An inlet area and an outlet area are respectively located at both ends of the welded part; A pair of entrance area isolation pipes, the pair of entrance area isolation pipes being connected to the upper and lower sides of the entrance area respectively; A pair of outlet area isolation pipes, wherein the pair of outlet area isolation pipes are respectively connected to the upper and lower sides of the outlet area.

5. The reflow oven as described in claim 4, characterized in that: The first end of each of the pair of inlet area isolation pipes is connected to the upper and lower sides of the inlet area, the second end of one of the pair of inlet area isolation pipes is connected to the controllable discharge pipe, and the second end of the other of the pair of inlet area isolation pipes is connected to one of the N welding sub-regions.

6. The reflow oven as described in claim 1, characterized in that: The welding section includes a heating zone and a cooling zone, and each welding sub-region in the heating zone is connected to a corresponding purification sub-region.

7. The reflow oven as described in claim 6, characterized in that: Each welding sub-region in the heating zone and a purification sub-region connected thereto form a heating working unit. The heating working unit includes an inner circulation unit or an outer circulation unit, wherein at least one heating working unit includes an outer circulation unit. Each of the purification sub-regions has a purification zone airflow inlet and a purification zone airflow outlet. The purification zone airflow inlet and purification zone airflow outlet of the purification sub-region of the inner circulation unit are both connected to the corresponding welding sub-region. The purification zone airflow inlet of the purification sub-region of the outer circulation unit is connected to the corresponding welding sub-region. The purification zone airflow outlet of the purification sub-region of the outer circulation unit is connected to the controllable discharge pipeline through one of the K discharge branch pipes.

8. The reflow oven as described in claim 7, characterized in that: The external circulation unit is located at the front and rear ends near the heating zone.

9. The reflow oven as described in claim 3, characterized in that: Each of the N welding sub-regions includes a flow guiding device, which can guide a portion of the gas in the welding sub-region to the corresponding purification sub-region.

10. The reflow oven as described in claim 1, characterized in that: Each of the M purification sub-regions includes a catalytic device and a heating device; the heating device has a catalytic working mode and a maintenance working mode.

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