Solder flux cracking method

Abstract

This invention discloses a flux pyrolysis method to solve the problems of frequent maintenance, secondary pollution, and insufficient furnace purification caused by traditional condensation recovery methods. The method introduces waste gas containing flux volatiles into a pyrolysis system, where large particles are filtered to intercept them. The filtered waste gas is then preheated by indirect heat exchange with the clean gas to be discharged after pyrolysis. The preheated waste gas is then heated to the catalytic pyrolysis reaction temperature. The waste gas is then brought into contact with a catalyst for catalytic oxidation pyrolysis in an oxygen-containing atmosphere, generating harmless gases. The high-temperature harmless gas generated by pyrolysis is used as clean gas and indirectly exchanged with the unpyrolyzed waste gas to recover heat. The harmless gas after heat recovery is discharged or recycled to the welding equipment as a protective atmosphere. This solution pyrolyzes pollutants into harmless gases online at the source, eliminating condensate accumulation, achieving maintenance-free or extremely low-frequency maintenance, maintaining a continuously clean furnace atmosphere, eliminating secondary pollution, and significantly reducing maintenance costs.

Description

Technical Field

[0001] This invention relates to the field of reflow soldering processes, and in particular to a flux decomposition method. Background Technology

[0002] In the reflow soldering process of the electronics manufacturing industry, soldering flux volatilizes in large quantities at high temperatures, forming waste gas containing various organic compounds. If these volatiles are not effectively treated, they will condense and accumulate inside the equipment as solid or sticky residues, contaminating the furnace, blocking gas passages, and adhering to the surface of the products to be soldered, thus seriously affecting the soldering quality and equipment stability.

[0003] Therefore, existing reflow soldering equipment is generally equipped with a flux management system, with the mainstream technology being condensation recovery. This involves forcibly cooling the high-temperature waste gas stream, causing the flux volatiles to change from a gaseous phase to a liquid or solid phase, and then separating them from the gas stream using filtration or collection structures. While this phase change cold recovery method is structurally intuitive and has a certain collection effect initially, its inherent drawbacks are significant. As the equipment continues to operate, the viscous substances condensed and precipitated quickly adhere to the surface of the heat exchanger and the inner walls of the pipes, leading to a sharp decline in heat exchange efficiency and a continuous increase in airflow resistance, resulting in a significant decrease in collection efficiency. To restore processing capacity, frequent shutdowns and disassembly of the pipes and heat exchangers for manual cleaning are necessary, resulting in high maintenance intensity and costs. Furthermore, the waste residue generated during cleaning is a secondary pollutant and must be disposed of as hazardous waste, placing a heavy burden on environmental compliance.

[0004] In addition, condensation recovery can only intercept substances with high boiling points and easy condensation. Its ability to capture low-boiling-point components and fine aerosols is limited, making it difficult to maintain a high level of cleanliness in the furnace atmosphere, which affects the process stability of high-end precision welding. Summary of the Invention

[0005] The technical solution of this invention aims to at least partially solve one of the technical problems in related technologies. Therefore, the main objective of this invention is to provide a flux pyrolysis method to fundamentally solve the problems of frequent maintenance, secondary pollution, and insufficient furnace purification caused by traditional condensation and recovery methods.

[0006] To achieve the above objectives, the present invention provides a flux pyrolysis method, comprising the following steps: introducing a waste gas stream containing flux volatiles generated during the operation of the welding equipment into a flux pyrolysis system; filtering the waste gas stream to intercept large particulate matter entrained therein; performing an indirect heat exchange between the filtered waste gas stream and a clean gas stream to be discharged after pyrolysis to preheat the waste gas stream; heating the preheated waste gas stream to the temperature required for the catalytic pyrolysis reaction; contacting the waste gas stream that has reached the reaction temperature with a catalyst to catalytically oxidize and pyrolyze the flux volatiles in an oxygen-containing atmosphere to generate harmless gas; using the high-temperature harmless gas stream generated after pyrolysis as the clean gas stream and performing the indirect heat exchange with the unpyrolyzed waste gas stream to complete heat recovery; and after completing heat recovery, discharging the harmless gas stream or recovering the harmless gas stream into the welding equipment as part of the protective atmosphere.

[0007] This method transforms traditional cooling and collection into online catalytic pyrolysis, converting flux volatiles into harmless gases at their source, eliminating reliance on phase change interception and fundamentally preventing condensate accumulation and secondary pollution. The exhaust gas itself, after filtration and preheating, enters the catalytic reaction zone, where the heat released from pyrolysis provides energy for preheating subsequent exhaust gases, forming a highly efficient heat circulation system. Simultaneously, the system achieves maintenance-free or extremely low-frequency maintenance with virtually no solid-liquid residue, keeping the furnace atmosphere clean for extended periods and significantly improving the stability of welding quality.

[0008] Furthermore, the catalyst contains at least one noble metal component selected from platinum and palladium to achieve efficient oxidative cracking at a lower ignition temperature.

[0009] Furthermore, the temperature required for the catalytic cracking reaction is controlled between 300°C and 400°C to ensure a better match between catalyst activity and system thermal efficiency.

[0010] Furthermore, in the heating step, the waste gas stream is precisely heated to the catalytic cracking reaction temperature by an independently temperature-controlled heating element, and the temperature fluctuation is maintained within a preset range.

[0011] Furthermore, the primary filter in the filtration step intercepts large particles of foreign matter to prevent the catalyst bed from becoming clogged or poisoned.

[0012] Furthermore, the indirect heat exchange is achieved through a gas-to-gas heat exchanger, enabling the high-temperature clean gas discharged from the pyrolysis to complete the heat transfer with the low-temperature waste gas to be treated without mixing.

[0013] Furthermore, the exhaust gas containing flux volatiles comes from the welding chamber of the vacuum reflow soldering equipment, and the temperature of the exhaust gas when it enters the flux decomposition system is 100°C to 150°C.

[0014] Furthermore, the harmless gas generated by pyrolysis includes at least carbon dioxide and water, and the emission concentration of the resulting harmless gas stream meets the environmental protection standards for direct emissions.

[0015] Furthermore, the flux volatiles contain rosin, organic acids, activators, and solvents, and the catalyst breaks down the hydrocarbon chains and converts them into carbon dioxide and water through an oxidation reaction.

[0016] The beneficial effects of this invention are as follows:

[0017] The flux pyrolysis method proposed in this invention first filters the waste gas containing flux volatiles to intercept large particles, then performs indirect heat exchange with the clean gas to be discharged after pyrolysis to achieve preheating, and then heats it to the temperature required for catalytic pyrolysis reaction. In an oxygen-containing atmosphere, the waste gas comes into contact with the catalyst to undergo catalytic oxidation pyrolysis to generate harmless gas. The high-temperature harmless gas generated by pyrolysis is then used as a clean gas to perform indirect heat exchange with the unpyrolyzed waste gas to complete heat recovery. Finally, the harmless gas is discharged or recovered into the welding equipment as a protective atmosphere.

[0018] Unlike traditional condensation and collection methods, this solution catalytically decomposes pollutants into harmless gases online at the source, fundamentally eliminating the problem of condensate accumulation and blockage on the inner walls of heat exchangers and pipelines. This allows the system to operate continuously without the need for waste cleaning, achieving maintenance-free or very low-frequency maintenance, significantly reducing downtime and maintenance costs. Preheating the waste gas stream with clean air effectively recovers the heat released by the pyrolysis reaction, greatly improving overall thermal efficiency. Since it no longer relies on phase change interception, low-boiling-point components can also be completely oxidized, maintaining a high level of cleanliness inside the furnace for extended periods, providing strong assurance for the consistency and reliability of welding quality. The pyrolysis products are mainly carbon dioxide and water, and the exhaust gas meets direct emission environmental standards, with no secondary pollutants generated. This eliminates the additional burden of hazardous waste disposal found in traditional solutions, significantly improving environmental safety. Attached Figure Description

[0019] To more clearly illustrate the technical solutions 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, the drawings described below are only some embodiments of the technical solutions of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0020] Figure 1 This is a schematic block diagram illustrating the main implementation process of the present invention. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] The term "one embodiment" or "implementation" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. In the description of the present invention, it should be understood that the terms "upper," "lower," "left," "right," "top," "bottom," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are used only for the convenience of describing the present invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" and "second" may explicitly or implicitly include one or more of that feature. Moreover, the terms "first," "second," etc., are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the present invention described herein can be implemented in orders other than those illustrated or described herein.

[0023] as follows:

[0024] Please see the appendix Figure 1 ,

[0025] One specific implementation of this solution is...

[0026] During vacuum reflow soldering, printed circuit board assemblies undergo preheating, heating, reflow, and cooling stages within the soldering chamber. During this process, a large amount of flux in the solder paste volatilizes under high temperatures, forming a waste gas stream containing rosin, organic acids, activators, and various solvents. The temperature of this waste gas stream is typically between 100 and 150 degrees Celsius. To maintain a clean atmosphere within the soldering chamber and prevent the deposition of volatiles inside the equipment, the waste gas stream is piped to a flux decomposition system for treatment.

[0027] Furthermore, the exhaust gas first enters the primary filter unit, which uses a heat-resistant metal wire mesh or a porous ceramic structure to intercept larger particulate foreign objects that may be carried in the exhaust gas, such as solder beads, flux clumps and debris, and other mechanical impurities that may be brought out during the soldering process.

[0028] The primary filter is designed with a pore size that effectively traps particles that could clog or cover the downstream catalyst bed while ensuring low airflow resistance, thus protecting the catalyst and extending its effective service life.

[0029] The waste gas stream, after passing through the primary filter, enters the cold side channel of the gas-to-gas heat exchanger. Simultaneously, the high-temperature, clean gas stream from the subsequent catalytic cracking reaction enters the hot side channel of the same gas-to-gas heat exchanger. The two gases transfer heat through the partition wall within the heat exchanger without mixing, thus achieving the purpose of preheating the waste gas stream.

[0030] Understandably, after the exhaust gas is preheated, its temperature increases significantly from the original 100 to 150 degrees Celsius. The specific final preheating temperature is determined by the heat exchange area of ​​the heat exchanger, the flow rate matching, and the inlet temperature of the clean gas flow on the hot side. It can usually be increased to over 200 degrees Celsius, thereby significantly reducing the energy input requirements of the subsequent heating units.

[0031] Furthermore, the preheated waste gas continues to flow downstream, entering a heating section equipped with independently temperature-controlled heating elements. This heating section contains electric heating wires or ceramic heating rods, and is equipped with temperature sensors and a closed-loop control unit. By precisely adjusting the heating power, the temperature of the waste gas is continuously raised to the temperature range required for the catalytic cracking reaction, while maintaining temperature fluctuations within a narrow preset range. The temperature required for the catalytic cracking reaction is preferably controlled between 300 degrees Celsius and 400 degrees Celsius.

[0032] It is easy to understand that in this scheme, the temperature range of 300-400 degrees Celsius can ensure that the catalyst has sufficient activity to achieve deep oxidation of organic matter, without causing energy waste or excessive heat load on equipment materials due to excessive temperature.

[0033] Furthermore, once the waste gas stream reaches the aforementioned suitable reaction temperature, it is introduced into the catalytic reaction chamber and comes into full contact with the catalyst. The catalytic reaction chamber is filled with a catalyst, which uses at least one noble metal, such as platinum or palladium, as the active component, supported on a honeycomb ceramic carrier or metal mesh carrier to provide a large gas-solid contact area. Under the combined action of the catalyst surface and the oxygen-containing atmosphere, the hydrocarbons, organic acids, rosin acids, and other organic molecules contained in the flux volatiles in the waste gas stream undergo catalytic oxidation and cracking reactions. Their hydrocarbon chains break and combine with oxygen, ultimately converting into harmless carbon dioxide and water vapor. Because the introduction of the catalyst significantly lowers the activation energy of the oxidation reaction, the cracking reaction can proceed efficiently at a relatively low temperature of 300 to 400 degrees Celsius, avoiding the high-temperature conditions required for conventional thermal combustion and further reducing the system's operating energy consumption.

[0034] After the pyrolysis reaction is complete, the gas stream discharged from the catalytic reaction chamber is a high-temperature, harmless gas stream. Its main components are carbon dioxide, water vapor, nitrogen, and unreacted residual oxygen. Almost all organic matter has been completely decomposed, and it contains no solid or liquid harmful residues requiring further treatment. This high-temperature, harmless gas stream is still at a relatively high temperature. It is sent back to the hot side channel of the aforementioned gas-to-gas heat exchanger as a clean gas stream, where it undergoes indirect heat exchange with the low-temperature waste gas stream to be treated. It transfers its sensible heat to the waste gas stream, thus cooling itself while recovering heat. This heat recovery process constitutes a positive feedback heat cycle within the system, requiring only a relatively small amount of external heat to maintain the continuous stability of the pyrolysis reaction temperature.

[0035] After heat recovery, the temperature of the harmless gas flow has been significantly reduced. At this point, depending on the actual process requirements, it can be either directly discharged into the external environment or recycled and introduced into the welding chamber or related atmosphere protection area of ​​the welding equipment for reuse as part of the protective atmosphere.

[0036] For example, when direct emission is selected, the pollutant concentration of the harmless airflow has already decreased to within the range allowed by the environmental standards for direct emission, thus meeting environmental regulations without the need for additional end-of-pipe purification devices. When recycling is selected, the returned airflow, having undergone deep purification and with controllable temperature, helps to better maintain the uniformity of the temperature field and the cleanliness of the atmosphere within the welding chamber, further reducing the overall gas consumption and operating costs of the equipment.

[0037] Overall, during the continuous operation of the flux cracking system, since flux volatiles are directly converted into gaseous products such as carbon dioxide and water vapor in the catalytic reaction chamber, no liquid condensate or solid deposits are produced in the system. Therefore, unlike traditional condensation collection methods, there is no need for frequent disassembly and cleaning of collectors, heat exchangers, and pipelines. Although the primary filter will gradually accumulate intercepted particles over long-term use, the initial contamination rate is very slow due to the extremely low content of large particles in the exhaust gas. In actual use, it can be inspected and replaced or flushed and regenerated annually. The catalyst in the catalytic reaction chamber operates at a moderate temperature and the exhaust gas has already been pretreated, resulting in extremely low rates of poisoning and carbon buildup deactivation. Annual catalytic activity assessment and maintenance are sufficient.

[0038] In this way, the entire decomposition module achieves the operating characteristics of requiring no daily maintenance or very low-frequency maintenance, which greatly reduces downtime and labor costs caused by cleaning up waste residue and replacing consumables, while eliminating the generation of secondary pollutants and hazardous waste at the source.

[0039] The following points need to be explained:

[0040] (1) The accompanying drawings of the embodiments of this disclosure only involve the structures involved in the embodiments of this disclosure. Other structures can be referred to the general design.

[0041] (2) Where there is no conflict, features of the same embodiment and different embodiments of this disclosure can be combined with each other.

[0042] The above are merely specific embodiments of this disclosure, but the scope of protection of this disclosure is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this disclosure should be included within the scope of protection of this disclosure. Therefore, the scope of protection of this disclosure should be determined by the scope of the claims.

Claims

1. A method for pyrolysis of flux, characterized in that, Includes the following steps: S1. Introduce the waste gas containing flux volatiles generated during the operation of the welding equipment into the flux pyrolysis system; S2. Filter the waste gas to intercept large particulate matter entrained therein; S3. Indirectly exchange heat between the filtered waste gas and the clean gas to be discharged after pyrolysis to preheat the waste gas; S4. Heat the preheated waste gas to the temperature required for the catalytic pyrolysis reaction. S5. The waste gas flow that has reached the reaction temperature is brought into contact with the catalyst to catalytically oxidize and decompose the flux volatiles in an oxygen-containing atmosphere to generate harmless gas; S6. The high-temperature harmless gas flow generated after decomposition is used as the clean gas flow and is used to perform indirect heat exchange with the undecomposed waste gas flow in step S3 to complete heat recovery; S7. The harmless gas flow after heat recovery is discharged or the harmless gas flow is recycled into the welding equipment as part of the protective atmosphere.

2. The flux pyrolysis method according to claim 1, characterized in that, The catalyst described in step S5 contains at least one noble metal component selected from platinum and palladium.

3. The flux pyrolysis method according to claim 1, characterized in that, The temperature required for the catalytic cracking reaction in step S4 is controlled between 300°C and 400°C.

4. The flux pyrolysis method according to claim 1, characterized in that, In step S4, the waste gas flow is precisely heated to the catalytic cracking reaction temperature by an independently temperature-controlled heating element, and the temperature fluctuation is maintained within a preset range.

5. The flux pyrolysis method according to claim 1, characterized in that, In step S2, large particles are intercepted by a primary filter to prevent subsequent catalyst bed blockage or poisoning.

6. The flux pyrolysis method according to claim 1, characterized in that, The indirect heat exchange described in steps S3 and S6 is achieved through a gas-to-gas heat exchanger, where the high-temperature clean gas discharged from the pyrolysis process and the low-temperature waste gas to be treated complete the heat transfer without mixing.

7. The flux pyrolysis method according to claim 1, characterized in that, The waste gas containing flux volatiles in step S1 comes from the welding chamber of the vacuum reflow soldering equipment, and the temperature of the waste gas when it enters the flux decomposition system is 100°C to 150°C.

8. The flux pyrolysis method according to claim 1, characterized in that, The harmless gas generated by pyrolysis in step S5 includes at least carbon dioxide and water, and the emission concentration of the harmless gas stream discharged or recovered in step S7 meets the environmental protection standards for direct emission.

9. The flux pyrolysis method according to claim 1, characterized in that, The exhaust gas containing flux volatiles contains rosin, organic acids, activators and solvents. In step S5, the catalyst breaks down the hydrocarbon chains and converts them into carbon dioxide and water through an oxidation reaction.

10. The flux pyrolysis method according to any one of claims 1 to 9, characterized in that, The decomposition module of the flux cracking system does not require waste removal during continuous operation and is maintained annually.

Images