Reflow oven with flux reactor and method of operation

Abstract

A reflow oven according to some embodiments includes a process chamber configured to perform reflow soldering on circuit assemblies, and a flux reactor configured to receive flux-laden gas transferred from one or more first regions of the process chamber and to output cleaned gas for returning to one or more second regions of the process chamber. The flux reactor includes a heating assembly configure to heat the flux-laden gas to a predetermined temperature significantly above temperature in any of the one or more first regions and to output heated gas, a catalytic trap configured receive the heated gas and to output pre-cleaned gas after trapping large molecule species and / or particulates in the heated gas, and a catalytic filter configured to receive the pre-cleaned gas and to output cleaned gas after converting long-chain hydrocarbons in the pre-cleaned gas into CO2, CO, water, and / or organics having lower molecular weight than the long-chain hydrocarbons.

Description

Reflow Oven with Flux Reactor and Method of OperationCROSS REFERENCE TO REACTED APPLICATIONS

[0001] The present application claims priority to US Provisional Application No. 64077382, filed January 24, 2024, entitled “Reflow Oven with Flux Reactor and Method of Operation,” which is incorporated herein by reference in its entirety.TECHNICAL FIELD

[0002] The present disclosure is related to the field of semiconductor manufacturing, and in particular to a reflow oven with flux reactor and method of operation.BACKGROUND

[0003] Soldering is the process of using a metal alloy with a low melting temperature (solder) to fuse electrical contacts of one electronic component (e.g., an integrated circuit chip) to corresponding solder pads of another component (e.g., a circuit board). Various soldering methods have been developed to meet the needs of specific applications. For example, reflow soldering is often used to surface mount electronic components on circuit boards, which can be any type of substrate for mounting electronic components.

[0004] In a typical reflow soldering process, a circuit board with one or more electronic components placed thereon is passed through a series of zones in a reflow oven, such as one or more heating zones and a cooling zone. The circuit board has pads and solder paste deposited on the pads, and the leads of the one or more electronic components are inserted into the deposited solder paste on the circuit board. The solder paste is heated to a melting or reflow temperature in the one or more heating zones and then solidifies after being cooled in the cooling zone, as the circuit board passes through the reflow oven. The solidified solder paste electrically and mechanically connect the leads of each electronic component to the corresponding pads on the circuit board.

[0005] Solder paste typically contains soldering flux (or flux), which is used to remove oxidation from the metal surfaces to be soldered, and to aid in solder flow. If metal oxidation is not removed, solder does not adhere well to the solder pad, resulting in poor connections, higher resistance, and failure of the component. Solder paste may also include other constituents, such as adhesives, binders, etc. The presence of flux and these other constituents in a reflow oven, however, can cause a slew of problems when heating vaporizes these materials and the vapors thus generated (collectively called “flux vapors”) migrate to the cooling zone and condense on the circuit boards, contaminating the boards and requiring subsequent cleaning steps. The flux vapors can also condense on cooler surfaces inside the oven, causing damage to equipment and creating hazard to the working environment.

[0006] Flux accumulation and dripping inside the oven also require frequent maintenance, increasing the cost and reducing the yield of a reflow process. What is needed is an advanced flux management system that safeguards the quality of products from flux vapors, and eliminates or significantly reduces the downtime for maintenance in high volume electronics manufacturing.SUMMARY

[0007] According to some embodiments, a solder reflow oven includes a flux reactor, which comprises a catalytic trap and a catalytic filter. The catalytic trap includes one or more wire mesh traps coated with one or more first catalysts, and the catalytic filter includes a support or substrate (e.g., ceramic honeycomb) coated and / or infused with one or more second catalysts .

[0008] In some embodiments, a flux-laden gas is exhausted from a process chamber of the reflow oven. The flux-laden gas is then heated to an elevated temperature (e.g., ~ 500 °C) before passing through the catalytic trap and subsequently the catalytic filter, where the fluxladen gas is filtered and chemically altered. The catalytic trap traps large molecule species (e.g., aromatic, benzene rings, etc.) and / or particulates (e.g., liquid phase carbon) in the flux-laden gas to reduce the chemical load on the catalytic filter. In some embodiments, oxidation also occurs at the trap, utilizing the small amount of oxygen included in the flux-laden gas. At the catalytic filter, the flux-laden gas undergoes pyrolysis (hydrocarbon combustion or cracking at a high-temperature and low oxygen environment) and some oxidation, aided by the one or more second catalysts in the filter. Thus, the catalytic filter or the flux reactor is also referred to herein as a pyrolysis reactor. The cleaned gas exiting the flux reactor is cooled and then returned to the chamber. In some embodiments, the cleaned gas at an outlet of the flux reactor includes CO2, CO, water, and some organics having lower molecular weight than the long-chain hydrocarbons in the flux-laden gas at an inlet of the reactor. Intermittent regeneration with 02 at temperature would mitigate this problem. The small amount of oxygen in the flux-laden gas is largely used up in the reactor, and thus is not returned to the chamber.

[0009] In some embodiments, a reflow oven comprises a process chamber configured to perform reflow soldering on circuit assemblies; and a flux reactor configured to receive fluxladen gas transferred from one or more first regions of the process chamber and to output cleaned gas for returning to one or more second regions of the process chamber. The flux reactor including a heating assembly configure to heat the flux-laden gas to a predetermined temperature significantly above temperature in any of the one or more first regions and to output heated gas, a catalytic trap configured receive the heated gas and to output pre-cleaned gas after trapping large molecule species and / or particulates in the heated gas, and a catalytic filter configured to receive the pre-cleaned gas and to output cleaned gas after converting certain long-chain hydrocarbons in the pre-cleaned gas into CO2, CO, water, and / or organics having lower molecular weight than the long-chain hydrocarbons.

[0010] In some embodiments, the catalytic trap includes one or more wire meshes, a respective wire mesh of the one or more wire meshes being coated with one or more first catalysts, and the one or more first catalysts include copper and alumina oxide.

[0011] In some embodiments, the catalytic filter includes a monolithic substrate coated and / or infused with one or more second catalysts, and the one or more second catalysts include one or more zeolites with one or more base metal promoters.. In some embodiments, the substrate is a wall-flow substrate. In some embodiments, the one or more second catalysts include copper chabazite. In some embodiments, the one or more second catalysts include copper or platinum.

[0012] In some embodiments, the predetermined temperature is about 500 or higher, the system further comprising a cooling assembly between an outlet of the flux reactor and the one or more second regions of the process chamber, and configured to cool the cleaned gas output from the reactor before returning the cleaned gas to the one or more second regions of the process chamber.

[0013] In some embodiments, the system further comprises an ambient blower configured to blow ambient air into at least some of the one or more first regions.

[0014] In some embodiments, a method of carrying out a reflow process comprises processing electronic assemblies in a process chamber of a solder reflow oven, exhausting flux-laden gas from one or more first regions of the process chamber, transferring the fluxladen gas to a flux reactor through a manifold, heating up the flux-laden gas to an elevated temperature significantly above temperature in any of the one or more first regions, flowing the flux-laden gas through a catalytic trap and a catalytic filter after heating the flux-laden gas to the elevated temperature. The catalytic trap is configured to trap large molecule species and / or particulates in the flux-laden gas, and the catalytic filter is configured to convert certain long-chain hydrocarbons flowing through the catalytic filter into CO2, CO, water, and / or organics having lower molecular weight than the long-chain hydrocarbons and to output cleaned gas. The method further comprises returning the cleaned gas output from the reactor to one or more second regions in the process chamber.BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG. l is a schematic diagram of a reflow oven including a flux reactor according to some embodiments.

[0016] FIG. 2 is a cross-sectional diagram showing a few main components of the flux reactor according to some embodiments.

[0017] FIG. 3 is an exploded view drawing showing various parts of the flux reactor according to some embodiments.

[0018] FIG. 4 is a photograph of a mesh trap coated with one or more first catalysts according to some embodiments.

[0019] FIG. 5A is a photograph of several ceramic substrates coated or infused with one or more second catalysts according to some embodiments.

[0020] FIG. 5B is a schematic diagram showing some of the channels in a catalytic filter according to some embodiments.

[0021] FIG. 6 shows examples of chemical reactions at the inlet of the flux reactor according to some embodiments.

[0022] FIG. 7 is a chart of Fourier-transform infrared spectroscopy (FTIR) results showing gas compositions at the inlet (red) and outlet (blue) of the flux reactor.

[0023] FIG. 8 is a photograph of wire meshes used in a wire mesh catalyst trap showing carbon capture by the wire meshes according to some embodiments.

[0024] FIG. 9A is a photograph of an aged catalytic filter showing evenly distributed contamination according to some embodiments.

[0025] FIG. 9B is a photograph of an aged conventional filter made of zeolite extrudate showing poorly distributed contamination.

[0026] FIG. 10A is a photograph of an interior of a reflow oven having a conventional flux filter made of zeolite extrudate after a 10KG flux test.

[0027] FIG. 1 OB is a photograph of an interior of a reflow oven including the flux reactor according to some embodiments after a 10KG flux test.DETAILED DESCRIPTION OF THE EMBODIMENTS

[0028] As shown in FIG. 1, a reflow oven 10 according to some embodiments includes a chamber in the form of a thermally insulated tunnel 11 defining a passage between a top 1 and a bottom 2 for pre-heating, reflowing and then cooling solder on a circuit board passing therethrough. A series of temperature control components 12a at the top and a series of corresponding components 12b at the bottom of the chamber 11 define a plurality of zones along the passage, including, for example, one or more pre-heat zones 13, followed by one or more heat-absorption (or thermal soak) zones 14, which are followed by one or more reflow (or spike) zones 15 and subsequently one or more cooling zones 16.

[0029] The reflow oven 10 further includes a reactor blower 3, a cooling assembly including, e.g., a water jacket 5, a flux reactor (e.g., a pyrolysis reactor) 100 having an inlet 110 in fluid communication with the reactor blower 3, and an outlet 120 in fluid communication with the cooling assembly 5. In some embodiments, the blower 3 is in fluid communication with one or more first regions 1 la in the reactor chamber via exhaust(s) 6 and manifold 17, and is configured to draw flux-laden gas from the one or more first regions I la and blow the flux-laden gas toward the inlet 110 of the flux reactor 100 via piping 18. The one or more first regions are, for example, a region I la between the one or more pre-heat zones 13 and the one or more heat-absorption or thermal soak zones 14, and / or a region 1 lb between the one or more heat-absorption or thermal soak zones 14 and the one or more reflow (or spike) zones 15, where flux vapors are more concentrated. The outlet 120 of the flux reactor 100 is in fluid communication with one or more second regions (e.g., region(s) in the one or more reflow (or spike) zones 15) further down the passage via the coolingassembly 5 and manifold 19. In some embodiments, the one or more second regions may have higher temperature than the one or more first regions.

[0030] FIG. 2 is a cross-sectional diagram showing a few main components of the flux reactor 100 according to some embodiments. As shown in FIG. 2, in some embodiments, the flux reactor 100 includes a heater 130 disposed in a heating tube 132, which is in fluid communication with the inlet 110. The heater is configured to heat up the flux-laden gas entering the flux reactor 100 via the inlet 110. The flux reactor 100 further includes a catalytic trap 140 and a catalytic filter 150 in a main reactor cavity 160, which has an inlet 160a in fluid communication with the heating tube 132 via a tunnel 134 on one side and an outlet 160b in fluid communication with the outlet 120 on the other side via a funnel passageway 170. The catalytic trap 140 includes one or more wire mesh traps 142 coated with one or more first catalysts (e.g., a Cu and alumina oxide composite), and the catalytic filter 150 includes a support or substrate (e.g., a ceramic honeycomb substrate) coated and / or infused with one or more second catalysts with base metal promoters (e.g., Cu chabazite), as described in further details below.

[0031] As shown in FIG. 3, which is an exploded view showing various components of the flux reactor 100 according to some embodiments, the reactor 100 includes a reactor pipe weldment 300 including the heating tube 132, the main reactor cavity 160 and the tunnel 134, which fit inside a reactor housing 101. The catalytic trap 140 and the catalytic filter 150 are disposed inside the main reactor cavity 160 of reactor pipe weldment 300. In some embodiments, the catalytic filter 150 is fit inside a pyrolysis cage assembly, which is disposed inside the main reactor cavity 160 of reactor pipe weldment 300. Gaskets 136 and 162 are provided for high temperature sealing to ensure that the flux-laden gas goes through the catalytic trap 140 and the catalytic filter 150, instead of around them. The reactor 100 further includes a heater including the heating tube 132 and a heater coil 130a inside the heating tube 132, which is in fluid communication with the main reactor cavity 160 via the tunnel 134. In some embodiments, after being exhausted from the chamber 11 of the reflowoven 10, the flux-laden gas enters the heater 130 through the inlet 110 of the flux reactor 100 and gets heated up in the heater 130 to an elevated temperature of, for example, 300 °C to 850 °C, which is significantly higher than the gas temperature of, for example, 160 °C to 240 °C, in the one or more first regions in the reflow oven 10. In some embodiments, the elevated temperature is about 450 °C or higher (e.g., ~ 500 °C). After the flux-laden gas goes through the heater 130, it enters the main reactor cavity 160 of the reactor pipe weldment 300 through the tunnel 134 of the reactor pipe weldment 300, where the heated flux-laden gas is filtered through the catalytic trap 140 and the catalytic filter 150. The cleaned gas exits the reactor 100 through the outlet 120 of the reactor and is returned to the oven through the cooler 5, which is in fluid communication with the main reactor cavity 160 via the outlet 120. The reactor 100 further includes a drip pan or base plate at the bottom of the reactor housing 101, which collects liquid or dust from the filters. With the filters and catalyst used in some embodiments, very little residue has been collected at the base plate during practical operation of the reflow oven 10 with the flux reactor 100.

[0032] In some embodiments, as shown in FIG. 1, the flux-laden gas is drawn from the chamber of the reflow oven toward the reactor 100 by the reactor blower 3, and includes at least one processing gas (e.g., nitrogen) mixed with a small amount of oxygen from the environment (e.g., 30-40 parts per million oxygen) due to, for example, imperfect sealing of the chamber, or cold ambient air being blown into the regions where the flux-laden gas is drawn from. The flux-laden gas also includes flux vapors (evaporated constituents of the flux applied to the circuits being processed). The flux-laden gas exiting a particular region in the chamber is at approximately the temperature of that region (e.g., 160 °C at the region I la between the one or more pre-heat zones 13 and the one or more heat-absorption or thermal soak zones 14, and 180-240 C at the region 1 lb between the one or more heat-absorption or thermal soak zones 14 and the one or more reflow (or spike) zones 15). Thus the flux-laden gas at the inlet 110 of the reactor 100 can be, for example, at a temperature of about 200 °C. In some embodiments, the heater 130 in the reactor 100 is configured to heat the flux-laden gas received from the reactor blower 3 to an elevated temperature (e.g., ~ 500 °C) to facilitatethe hydrocarbon combustion reactions that crack certain long-chain chemicals in the fluxladen gas as it is forced through low-oxygen environment in the flux reactor by the blower 3.

[0033] The flux typically includes a vehicle, solvent, activators and other additives. The vehicle is a solid or nonvolatile liquid that coats the surface to be soldered and can include rosin, resins, glycols, polyglycols, polyglycol surfactants, and glycerine. The solvent, which evaporates during the pre-heat and soldering process, serves to dissolve the vehicle activators, and other additives. Typical solvents include alcohols, glycols, glycol esters and / or glycol ethers and water. The activator enhances the removal of metal oxide from the surfaces to be soldered. Common activators include amine hydrochlorides, dicarboxylic acids, such as adipic or succinic acid, and organic acids, such as citric, malic or abietic acid. Other flux additives can include surfactants, viscosity modifiers and additives for providing low slump or good tack characteristics for holding the components in place before reflow.

[0034] In some embodiments, , as shown in FIGS. 2 and 4, the catalytic trap 140 includes one or more layers of wire mesh 140a. Each wire mesh 140a is about 15% - 50% (e.g., ~ 25%) volume, and is coated with a Cu-based catalyst. As an example, each wire mesh 140a can be knitted from DIN 0Cr25A15 wires having a diameter of 0.35 + / - 0.02 mm, and is about 142 mm in diameter, about 12.7 mm in thickness, about 1.15 G / cm3in density, about 235 G in weight, and about 203 cm3in volume. The knitted wires are washed in nonionic cleaner to rid surfaces of forming oils physical debris, and then thermally oxidized at about 920 °C for about 2 hours in air followed by a passive cool down period.

[0035] The knitted wire is coated with a catalyst, e.g., a copper-based catalyst. For example, the Cu-based catalyst can be made by ion-exchanging Cu into alumina oxide to form a Cu / alumina oxide composite having 5% - 20% Cu (e.g., 10% Cu and 90% alumina) in a large pore alumina oxide slurry state having particles sizes large than, for example, a tenth of a micron. The coated wire is then dipped into the slurry having solids level or dispersion at, for example, 30 grams alumina oxide in 70 grams of water. Key parameters of the slurry including, for example, pH level, particle size distribution, solids level, GSA of supports andviscosity, etc., can be varied to achieve the wet gain for better adherence to metal surfaces. The wire mesh coated with the slurry is then dried and calcined. The metal alloy coating thus formed on the wire mesh is unique (e.g., a high-temperature Aluchrom-based alloy), which allows the alumina in the alloy to migrate to the surface of the coating, where large-chain hydrocarbons or even particulates in the flux-laden gas form particles that dry out so that the trap can keep functioning. Oxidation also goes on at the trap - utilizing the oxygen that is available in the flux-laden gas.

[0036] In some embodiments, the wire mesh (e.g., 20-30% volume wire mesh) is coated with a zeolite pre catalyst including, e.g., 1-30% copper and 70-95% alumina, plus a small amount of binder including, for example, a more active, specific transition phase of alumina with a particle size much smaller than gamma alumina. In some embodiments, the zeolite pre catalyst includes 5-15% (e.g., 10%) copper. The zeolite pre catalyst with more copper tend to be more active. The binder is to promote adhesion (to metal surface of wire mesh) and cohesion, so the particle themselves stay together. The binder can include chrome alloy alumina (iron chrome alumina) with some rare earth oxide (REO) in it (e.g., Fecralloy®, which is an industry standard material used mostly in mobile applications), which imparts heat resistance and durability. In some embodiments, the coated wire mesh is heat treated or oxidized at 900 °C in air to force at least some of the alumina to migrate to the surface, forming an in-situ fine layer of alumina oxide that helps to anchor the alumina alloy (e.g., gamma alumina) and to enhance cohesion. In some embodiments, the amount of the binder is controlled to not exceed what is needed for its purpose, e.g., less than 5% weight, or 2-3% weight. In some embodiments, the binder (e.g., alumina sol) has a particle size of about 40 nm, which is significantly smaller than the particle size of 5-20 microns (after milling) for typical commercial gamma alumina.

[0037] In some embodiments, after exiting the oven chamber, some of the reactants in the flux-laden gas can form large chain hydrocarbons, e.g., Promyristyl-PM-3 (or C23, e.g., C23H48O4), at the inlet of the catalytic filter 150 or in the transfer manifold. Some largemolecule species (e.g., large-chain hydrocarbons) and / or particulates (e.g., liquid phase carbon) in the flux-laden gas are trapped in the catalytic trap 140, so the chemical load on the catalytic filter 150 is reduced. Oxidation may also occur at the trap, utilizing the small amount oxygen in the flux-laden gas.

[0038] Compared to the catalytic filter 150, there is less surface area for reaction chemistry at the trap 140, but it provides sufficient turbulence to help to collect particulate (liquid phase carbon) and large molecule species, to lower the chemical load on the filter. The wire meshes 140a in the catalytic trap 140 can be easily cleaned with thermal treatment, during which the particles adhering to the meshes simply fall off.

[0039] The catalytic filter 150 includes a monolithic substrate 500 (e.g., a ceramic honeycomb substrate shown in FIG. 5A). In general, the monolithic substrate can be any of a metallic honeycomb, a cordierite straight channel honeycomb, a Gas Particulate Filter (GPF) cordierite filter, a Diesel Particulate Filter (DPF) cordierite filter, etc. FIG. 5 illustrates a portion of a monolithic substrate 500 for the catalytic filter 150 according to certain embodiments. As shown in FIG. 5B, the monolithic substrate 500 according to some embodiments has a honeycomb structure therein, which has many small, parallel channels 501 running axially. In some embodiments, the catalytic filter 150 is a wall-flow filter, where the channels 501 are not entirely flow-through (e.g., each channel having an inlet 510 or an outlet 520, but not both, or, each channel having a plug 540 plugging one of its inlet 510 or outlet 520), forcing the flux-laden gas entering one channel 501 to flow through the porous walls 530 surrounding the channel to exit via neighboring channels with outlets 520. This also forces the flux-laden gas to make contact with the one or more catalysts deposited on the channel walls 530 and diffuse into the porous channel walls 530. Thus, the hydrocarbon combustion occurs not only on the surfaces of the substrate but inside the porous material as well. Major advantages of such a monolithic substrate include high geometric surface area (GSA) per unit volume (compactness), large open frontal area (low pressure drop), and excellent attrition resistance.

[0040] In the cross-section perpendicular to the direction of the channels, the number of channels or cells can vary between 100 to over 1000 cells per square inch (cpsi) (e.g., 200 and 600 cpsi, or about 400 cpsi) to facilitate chemical reactions for cleaning the flux vapors in the flux-laden gas. Compared to the catalyst materials, the walls of ceramic honeycombs have large pores and very low specific surface areas (e.g., about 0.3 m / g). Foils used for metal substrates have no porosity and have flow-through channels. Since hydrocarbon combustion is a function of geometrical surface area, a high surface area coating (e.g., washcoat) can be applied to the channel walls, so that the flux-laden gas entering some of the channels can diffuse through the washcoat pore structure to the catalytic sites where catalytic reactions occur.

[0041] As an example, the substrate for the catalytic filter 150 can have the shape of a cylinder with a cross-sectional area of about 162 cm2and a volume of about 2.5 liter. The substrate can weigh about 640-780 g / PC, with a porosity of about 63+ / -3%, and an average hole diameter of about 19 pm + / - 3 pm. The substrate can be coated with one or more catalysts, such as Cu-SCR containing Zeolite Cha (Chabazite, 85% SiCh, 12% AI2O3, 3% CuO).

[0042] The monolithic substrate 500 can be coated or infused with one or more catalysts using, for example, a meter charge coater. The catalysts can be anchored to perimeters of the monolithic substrate. The catalytic filter 150 thus forces the gas to the reactive sites to induce pyrolysis, breaking down the long-chain hydrocarbons in the flux-laden gas that have entered the reactor. In some embodiments, the one or more catalysts include one or more zeolites with base metal promoters, e.g., 75% volume ion-exchanged / impregnated Cu Chabazite, which is a Zeolite having about 5-15% (e.g., 10%) Cu content and a pore size around 1 nm (e.g., 1.4 nm). For example, Cu-SCR containing Zeolite Cha (Chabazite having 85% SiCh, 12% AI2O3, 3% CuO). Such pore size is about the size of some large-chain hydrocarbon molecules (e.g., C2H6, CeHe, CioHs, etc.). Cu Chabazite is found to be effective in destroying flux and has a secondary effect in reducing oxygen in the gas.

[0043] In some embodiments, the catalytic filter 150 includes one or more coated GPF filters. The dimensions of the GPF filters can be, for example, ~ 5.65”(143.5mm)D x 6.0”(152.4mm)L, with a volume of, for example, -2.47L. Each filter is charged with 100.0- 120.0g / L of coating on a dry weight basis. So, the approximate loading of Cu-Chabazite for each filter is 275.0 of Cu-Zeolite. About 10% of the coating is Cu metal, while the remaining balance is the zeolite Chabazite. In some embodiments, the coating on the inner wall can be, for example, between 20-40 microns thick, while the fillets are around, for example, 150-170 microns thick.

[0044] Alternatively, or additionally, the one or more catalysts may include one or more other types of Diesel Oxidation Catalyst (DOC) with or without platinum, Selective Catalytic Reduction (SCR) catalyst, Zeolite, and / or Three-Way Conversion Catalyst (TWC). In some embodiments, types of substrates suitable for the catalytic filter 150 include monolithic substrate, gas particulate filter (GPF), wall-flow filter, diesel particulate filter (DPF). In some embodiments, the catalytic filter 150 includes Cu chabazite on a GPF. Alternatively, the catalytic filter 150 includes silicon carbide and / or a platinum-based catalyst on a DPF. The platinum-based catalyst from, for example, DOC technology, can do cracking and keep surfaces clean. Catalysts from precious metal technologies are also options.

[0045] Following are further examples of catalyst technologies for the catalytic filter 150 according to some embodiments: (1) DOC with 3O.gPt / ft3 on GPF substrate with higher content for oxygen storage capacity (OSC) (e.g., 1 : 1) to provide substantial O2 catalyst capacity with moderate filtration efficiency and particulate matter conversion (PM); (2) DOC with 3O.gPt / ft3 on DPF substrate with higher OSC content (e.g., 1 : 1) to provide substantial O2 catalyst capacity with high filtration efficiency and particulate matter conversion (PM);(3) 10% Cu-Chabazite on SiC DPF substrate with standard catalyst loading (e.g., zeolite with Cu and relatively high catalyst loading, with / without PM); (4) TWC-like catalyst with 3O.gPt / f3 on 400 cpsi straight channel cordierite (which is a robust option for more O2 catalyst capacity and base metals promoting both cracking and oxidation); and (5) TWC-likecatalyst with 3O.gPt / f3 on SiC DPF substrate (which is a robust option for more O2 catalyst capacity and base metals with high filtration efficiency and PM).

[0046] FIG. 9A is a photograph of an aged catalytic filter 150 according to some embodiments showing evenly distributed contamination. As comparison, FIG. 9B is a photograph of an aged conventional filter made of zeolite extrudate showing poorly distributed contamination.

[0047] In some embodiments, the gas flow rate in the reflow oven 10 is relatively low (e.g., 20 CFM). Thus, back pressure is usually not of concern. As a result, the restrictions by the wall-flow filter does not affect the operation of reflow oven. The relatively low flow rate also ensures sufficient residence time of the flux molecules in the catalytic filter 150 for the chemistry to happen. Thus, the catalytic filter 150 can have a relatively low-filtration efficiency, e.g., 70% filtration efficiency, although higher filtration efficiency may lead to better chemistry. Even with the relatively low filtration, the catalytic filter 150 according to some embodiments is still better than the extrudate filter in conventional flux reactors, which is mostly for water absorption and CO2 capture.

[0048] Inside the chamber 11 of the reflow oven 10, the flux includes different materials. In the beginning of the oven, at lower temperature, solvent will boil off at 100 °C. As the gas moves further down the machine at higher temperatures, the rosin in the flux becomes active. The rosin is acidic and is used to strip away oxide to make the soldering process more efficient. The larger-chain molecules in the rosin end up in the cloud in the oven 10 in the form of vapor, which, if not drawn out and filtered, condense on the interior of the reflow oven 10 and the condensation is very difficult to clean off. Other large-chain hydrocarbons (e.g. C23) can also be in the flux-laden gas entering the reactor. For example, C23 has been detected in an experimental set up simulating the reflow oven and the flux reactor. The additives used to make the flux can come off in the oven, some of which could polymerize and form large-chain hydrocarbons such as the C23. Thus, the C23 compound could be in the flux or could form at the inlet 110 of the reactor 100 or in the transfer manifold on the wayfrom the oven 10 to the reactor 100 as the temperature drops from about 240 °C to about 200 °C. At 200 °C, there is not enough energy to break up the large-chain hydrocarbons such as the C23 compound.

[0049] Thus, the flux-laden gas entering the flux reactor 100 includes mostly long-chain hydrocarbons (e.g. , C23), small chain hydrocarbons, liquid phase carbon, benzene, aromatics. In some embodiments, the flux reactor 100 first heats up the flux-laden gas and then breaks down the larger-chain molecules into smaller-chain molecules that are easier to clean. The catalyst trap traps some large-chain molecules (aromatics, benzene rings) and some particulates (liquid phase carbon, dry soot, etc.). The coated wire mesh traps also collect soluble organic fraction (SOF, in partial vapor / partial solid phase) in the flux-laden gas. The copper in the catalytic trap 140 could use oxygen to decompose the soot. FIG. 8 is a photograph of five aged Cu-LPA wire mesh catalyst traps that has been used in the gas inlet position. The black deposits indicate carbon capture by the wire mesh traps, which remain open and not blocked despite the build-up of the deposits.

[0050] In the catalytic filter 150, pyrolysis occurs and breaks down the large-chain hydrocarbons. Pyrolysis can sometimes also create large chain hydrocarbons, e.g., Char, particularly in the absence of 02. With the small amount of oxygen available in the flux- laden-gas, however, this is less of a problem. Copper-zeolite catalyst helps with the cracking and seems to have the ability to store oxygen. On the filter exit, the oxygen content goes to zero over time (even when higher level of oxygen is being fed to the filter by, for example, one or more ambient blower that blow ambient air into the one or more first regions in the process chamber, where the flux-laden gas is exhausted, as shown in FIG. 1).

[0051] If there is oxygen available, in the presence of platinum, the catalytic filter 150 is even more capable in producing very small chain hydrocarbons, Co or CO2, from the flux- laden gas, as platinum is a lot more active than copper.

[0052] Below are several competing chemical reactions in the reflow oven according to some embodiments:1. Steam reforming - production of H2 and CO by reacting HC with H2O at temperatures above 400C (strongly endothermic)CH4 + H2O (steam) CO + 3H22. Water-gas shift (WGSR) - the reaction of carbon monoxide CO and water vapor H2O (steam) to form carbon dioxide CO2 and hydrogen H2 (mildly exothermic)CO + H2O (steam) CO2 + H23. Partial oxidation with limited 02 in the feed (exothermic)4. Condensation (polymerization) when small hydrocarbons from the oven chamber forming larger hydrocarbons on their way to the reactor as the molecules lose potential and kinetic energy (exothermic). For example, FIG. 6 illustrates a possible reaction, showing the formation of Promyristyl - PM-3 C23H48O4, a compound identified at reactor inlet. Other reactions are also possible.5. Oxidation of Hydrocarbons in the production of CO2 and H2O (exothermic)CxH4 + (2x) 02 (x) CO2 + (2x) H2O6. Pyrolysis (HC cracking), primarily endothermic that involves exothermic and endothermic processes with little or no 02, which cracks certain long-chain hydrocarbons to smaller species but can also create char, which are larger hydrocarbon species.

[0053] In some embodiment, the heated flux-laden gas is converted to a cleaned gas as the flux vapors in the heated flux-laden gas are filtered and chemically altered in the flux reactor 100. In some embodiments, at least some or most of the long-chain molecules in the fluxladen gas undergo pyrolysis (cracking at a low oxygen environment), aided by the one or more catalysts in the filter. As a result, the cleaned gas reaching the outlet 120 of the flux reactor 100 includes largely CO, CO2, water, and other smaller molecular weight species. The cleaned gas is output through the outlet 120 of the flux reactor. FIG. 7 shows the FTIR results of the gas compositions at the inlet 110 and the outlet 120 of the flux reactor 100 including a Cu-Chabazite (10% Cu -zeolite) filter and wire mesh Cu coating on pre-catalysts, showing that water as well as CO2 and some hydrocarbons are detected at the inlet, CO is forming and increasing and CO2 is increasing at the outlet 120, and more CO, CO2 and water are at the outlet 120 compared to the inlet 110. A new (unknown) hydrocarbon at 1300 cm-1 is also detected at the outlet 120.

[0054] As shown in FIG. 1, the cleaned gas exiting the flux reactor 100 is cooled as it goes through the water jacket 5 to about the same temperature as the temperature in the one or more second regions (e.g., in the spike zone(s) 15) in the process chamber 11, and the cooled gas is subsequently returned to the chamber 11. In some embodiments, the cleaned gas at an outlet 120 of the flux reactor 100 includes CO2, CO, water, and some organics having lower molecular weight than the long-chain compound in the flux-laden gas at an inlet 110 of the reactor, as shown in the FTIR results in FIG. 6. The lower molecular weight species may condense on cooler surfaces after entering the reflow oven (if they have not been converted to CO, CO2 and H2O or possibly stored on the catalytic filter temporarily), but they are much easier to clean. Intermittent regeneration with 02 at temperature would mitigate this problem. The small amount of oxygen in the flux-laden gas is largely used up in the reactor, and thus is not returned to the chamber.

[0055] FIG. 10A is a photograph of an interior of a reflow oven having a conventional flux filter made of zeolite extrudate after a 10KG flux test, showing very contaminated surfacesinside the oven chamber. In comparison, FIG. 1 OB is a photograph of an interior of a reflow oven including the flux reactor 100 according to some embodiments after a 10KG flux test, showing much cleaner surfaces inside the oven chamber.

[0056] The terminology used in the description of the various described embodiments herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used in the description of the various described embodiments and the appended claims, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that the term “and / or” as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items. It will be further understood that the terms “includes,” “including,” “comprises,” and / or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0057] The foregoing description, for purpose of explanation, has been described with reference to specific embodiments. However, the illustrative discussions above are not intended to be exhaustive or to limit the scope of the claims to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings. The embodiments were chosen in order to best explain the principles underlying the claims and their practical applications, to thereby enable others skilled in the art to best use the embodiments with various modifications as are suited to the particular uses contemplated.

Claims

WHAT IS CLAIMED IS:

1. A system, comprising: a process chamber configured to perform reflow soldering on circuit assemblies; and a flux reactor configured to receive flux-laden gas transferred from one or more first regions of the process chamber and to output cleaned gas for returning to one or more second regions of the process chamber, the flux reactor including a heating assembly configure to heat the flux-laden gas to a predetermined temperature significantly above temperature in any of the one or more first regions and to output heated gas, a catalytic trap configured receive the heated gas and to output pre-cleaned gas after trapping large molecule species and / or particulates in the heated gas, the pre-cleaned gas including long-chain hydrocarbons, and a catalytic filter configured to receive the pre-cleaned gas and to output cleaned gas after converting at least some of the long-chain hydrocarbons in the pre-cleaned gas into CO2, CO, water, and / or organics having lower molecular weight than the at least some of the long-chain hydrocarbons.

2. The system of claim 1, wherein the catalytic trap includes one or more wire meshes, a respective wire mesh of the one or more wire meshes being coated with one or more first catalysts.

3. The system of claim 2, wherein the one or more first catalysts include copper and alumina oxide.

4. The system of claim 1, wherein the catalytic filter includes a monolithic substrate coated and / or infused with one or more second catalysts.

5. The system of claim 4, wherein the substrate is a wall-flow substrate.

6. The system of claim 4, wherein the one or more second catalysts include one or more zeolites with one or more base metal promoters.

7. The system of claim 6, wherein the one or more second catalysts include copper chabazite.

8. The system of claim 6, wherein the one or more second catalysts include copper or platinum.

9. The system of claim 1, wherein the predetermined temperature is about 500 or higher, the system further comprising a cooling assembly between an outlet of the flux reactor and the one or more second regions of the process chamber, and configured to cool the cleaned gas output from the reactor before returning the cleaned gas to the one or more second regions of the process chamber.

10. The system of claim 1, further comprising an ambient blower configured to blow ambient air into at least some of the one or more first regions.

11. A method, comprising: processing electronic assemblies in a process chamber of a solder reflow oven; exhausting flux-laden gas from one or more first regions of the process chamber; transferring the flux-laden gas to a flux reactor through a manifold; heating up the flux-laden gas to an elevated temperature significantly above temperature in any of the one or more first regions; flowing the flux-laden gas through a catalytic trap and a catalytic filter after heating the flux-laden gas to the elevated temperature, wherein the catalytic trap is configured to trap large molecule species and / or particulates in the flux-laden gas and to output pre-cleaned gas including long-chain hydrocarbons, and the catalytic filter is configured to convert at least some of the long-chain hydrocarbons in the pre-cleaned gas into CO2, CO, water, and / or organics having lower molecular weight than the at least some of the long-chain hydrocarbons; and returning the cleaned gas output from the reactor to one or more second regions in the process chamber.

12. The method of claim 11, wherein the catalytic trap includes one or more wire meshes, a respective wire mesh of the one or more wire meshes being coated with one or more first catalysts.

13. The method of claim 12, wherein the one or more first catalysts include copper and alumina oxide.

14. The method of claim 11, wherein the catalytic filter includes a monolithic substrate coated and / or infused with one or more second catalysts.

15. The method of claim 14, wherein the substrate is a wall-flow substrate.

16. The method of claim 14, wherein the one or more second catalysts include one or more zeolites with one or more base metal promoters.

17. The system of claim 6, wherein the one or more second catalysts include copper chabazite.

18. The method of claim 6, wherein the one or more second catalysts include copper and / or platinum.

19. The method of claim 11, wherein the predetermined temperature is about 500 or higher, the method further comprising cooling the cleaned gas output from the reactor before returning the cleaned gas to one or more second regions in the process chamber.

20. The method of claim 11, further comprising blowing ambient air into at least some of the one or more first regions.

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