TWI401131B - Apparatus and method for providing an inerting gas during soldering - Google Patents

Description

Apparatus and method for providing inert gas during soldering Cross-reference to related applications

The priority of the following application is as follows: U.S. Provisional Patent Application Serial No. 61/313,376, filed on March 12, 2010, and U.S. Provisional Patent Application Serial No. 61/313,372, filed on March 12, 2010; U.S. Provisional Patent Application Serial No. 61/321,011, filed on Apr. 5, 2010; U.S. Provisional Patent Application Serial No. 61/320,939, filed on Apr. 5, 2010; Application Serial No. 61/323,607; and U.S. Provisional Patent Application Serial No. 61/365,607, filed on Jul. 19, 2010.

Described herein are apparatus and methods for providing inert gas during soldering. More specifically, what is described herein is an apparatus and method for providing an inert gas when using nitrogen and/or other inert gas welding.

Workpieces such as printed wiring boards or circuit boards have increasingly smaller wettable surfaces that must be coated and bonded with solder. Typical wave soldering operations involve solder baths that can be soldered through the solder bath during transport. Conventional automatic wave soldering equipment includes fluxing devices, preheaters, and solder stations that are provided to handle printed circuit boards. The printed circuit boards are transported along a moving track or conveyor belt and their side edges are supported by grip fingers. A glidant can contact the plate with a foam or spray of a glidant. The board is then passed through a preheating zone to enable the flow aid to reduce oxides on the metal surface to be soldered. The board is then contacted with a single or multiple wave of molten solder in air or in an inerting atmosphere.

The inerting atmosphere is typically nitrogen (N ₂ ) and/or other inerting gases and is often referred to as N ₂ inerting. Soft soldering in an inert gas and/or nitrogen atmosphere minimizes the formation of scum or oxide on the surface of the solder. It is known that the presence of a scum or oxide layer can cause jumps, bridges or other defects in the solder joint. The solder wave is generated by the wave soldering device during operation - the proximal end is a porous tube that runs parallel to the solder wave and is used to deliver the inert gas and/or N ₂ gas to provide Relatively low oxygen atmosphere, especially under the workpiece to be soldered.

Regarding lead-free wave soldering, the value of the inerting atmosphere containing N ₂ is further improved for the following reasons. The processing temperatures using conventional lead-free solders are significantly higher than the processing temperatures of conventional tin-lead solders due to the increased melting point of conventional lead-free solders. This increase in processing temperature contributes to the formation of scum. Moreover, the cost of lead-free solder is generally much higher than the cost of conventional tin-lead solder, and the economic loss associated with solder waste due to scum formation is more pronounced than that of lead-free wave soldering. In addition, the wettability of lead-free solders is inherently inferior to conventional tin-lead solders. Therefore, the quality of the solder joint formed is more sensitive to the oxidation state on the surface of the lead-free solder.

It is well known that inertization during wave soldering significantly reduces scum formation on the surface of the molten solder. Reducing scum formation not only saves solder and reduces maintenance requirements, but also improves solder wetting and ensures the quality of the solder joints formed. In order to apply an inerting atmosphere to current wave soldering machines, a common method is to insert a cage-like protective housing with an internally mounted diffuser into the molten solder reservoir. An inert gas blanket can be formed across the solder reservoir, thus reducing the tendency of the solder to oxidize.

These diffusers are often made of a perforated tube to introduce an inerting gas such as N ₂ and/or other inerting gas into the soldering station. However, the porous tubes become susceptible to blockage by solder splashing or flux vapor condensation during the wave soldering process. Once the diffuser is blocked, the efficiency of inertization will be greatly reduced. Modern cleaning of such diffusing tubes, for example, using an ultrasonic bath filled with a cleaning solution, is extremely difficult and time consuming. The cleaning of these tubes must be carried out regularly and can cause physical damage to such tubes. To avoid these problems, the diffusers are typically replaced once they are blocked rather than being cleaned. This increases the overall cost of the end user.

Accordingly, in order to facilitate the application of inertization by N ₂ and/or other inerting gases during wave soldering, we desire at least one or more of the following devices, methods, or both. First, we intend to reduce the N ₂ or other inert gas consumption for the inerting apparatus and method such as, but not limited to, 12 cubic meters per hour (m ³ /hr) or less to meet the cost benefit of applying the technology. Secondly, it is desirable for the inerting apparatus and method to reduce the O ₂ concentration above the surface of the molten solder, for example, but not limited to, 2500 parts per million (ppm) or less. Thirdly, we intend to use equipment that is easy to set up and that still minimizes the cost of trimming for the inerting equipment and method. Furthermore, it is desirable for the apparatus or method to reduce or avoid clogging of the porous diffuser to ensure stable and long lasting inertization performance.

The apparatus and methods described herein accomplish at least one or more of the inactivation of nitrogen and/or other inerting gases, which may be more cost effective and user friendly than similar methods and equipment currently in use. .

In one embodiment, an apparatus for providing an inert gas during soldering of a workpiece is provided, the apparatus comprising: at least one recess in the bottom of the apparatus, the at least one recess for placing a solder containing molten solder At least one edge of the sump, wherein at least one side wall of the groove and at least one wall of the device define a chamber outside the solder sump; at least one opening from the top surface of the device, at least one emitted from the solder sump a solder wave passing through the at least one opening and touching the workpiece as it travels on the moving track; and a plurality of tubes including one or more openings in fluid communication with the source of inerting gas, wherein at least the tubes are One of the devices is present in the chamber; wherein the device is located above the solder reservoir and below the workpiece to be soldered to form an atmosphere and substantially no between the workpiece to be soldered and the apex of the at least one solder wave gap. The apparatus is located above the solder reservoir and below the workpiece to be soldered to form an atmosphere and substantially no gap between the workpiece to be soldered and the apex of the at least one solder wave. In a particular embodiment, the apparatus additionally includes a thermally conductive projection, wherein at least a portion of the projection contacts the molten solder and the at least one tube. In this or another embodiment, an optional cover is placed on top of the apparatus through which the workpiece passes, wherein the cover additionally includes a vent that communicates with the ventilation system.

In another aspect, a method for providing an inerting atmosphere for workpiece wave soldering is provided, the method comprising: providing a wave soldering machine comprising: a solder reservoir containing molten solder, at least one nozzle, at least one pump Ejecting at least one solder wave from the molten solder bath upwardly through the nozzle; placing a device on top of at least one edge of the solder reservoir, wherein the device includes at least one opening on the top surface, on top of at least one edge of the solder reservoir At least one groove and a plurality of tubes comprising one or more openings, the plurality of tubes being in fluid communication with a source of inert gas, wherein the workpiece to be soldered and the top surface of the molten solder define an atmosphere and the soft to be softened There is substantially no gap between the soldered workpiece and the apex of the at least one solder wave; the workpiece is passed along a path such that at least a portion of the workpiece touches at least one solder wave emitted through the opening of the device; through the porous tube Introducing an inerting gas and entering the atmosphere, wherein at least one of the tubes touches a portion of the thermally conductive protrusion inserted into the molten solder to thereby At least one of the molten solder is heated to a temperature above the melting point or. In a particular embodiment, at least one of the tubes further comprises a non-stick coating or a porous sleeve comprising a non-stick material.

At least one or more of the objects of the art can be accomplished by the methods and apparatus described herein for inertial protection during soldering. The apparatus and methods described herein provide for inertial protection during soldering, particularly those embodiments where significant movement and rotation of the solder, such as printed circuit board soldering, and enhanced oxidation of the solder surface may occur. It is contemplated that the apparatus and methods described herein can be used, for example, to trim existing wave soldering machines. In a particular embodiment, the apparatus described herein is placed over the solder sump and below the moving track or other transport mechanism for transporting the workpiece to be soldered. In a particular embodiment, there is substantially no gap between the workpiece to be soldered and the apex of the at least one solder wave. In other embodiments, there is a gap between the workpiece to be soldered and the apex of the at least one solder wave. The majority of the diffusion tubes placed in the apparatus are fluidly connected to an inert gas source such as nitrogen, an inert gas (eg, helium, neon, argon, neon, xenon, and combinations thereof), generating gas (eg, containing up to 5% by weight) A mixture of nitrogen and hydrogen of hydrogen, or a combination thereof, to provide an inerting atmosphere. One of the devices and methods described herein is for reducing the concentration of oxygen (O ₂ ) in the atmosphere defined by the surface of the workpiece to be soldered and the surface of the molten solder contained in the solder reservoir, for example, but not limited to, per million 2500 parts (ppm) or less.

The apparatus and method described herein are intended to be placed on top of a molten solder bath containing molten solder that is maintained at or above the melting point of the solder (e.g., up to 50 ° C). The apparatus described herein has an internal volume disposed atop the solder reservoir to define an atmosphere between the workpiece to be soldered and the surface of the molten solder that are transported in a direction above the solder track above the solder reservoir. In a particular embodiment, the workpieces support the side edges by moving the track or belt fingers and passing the fingers through the solder waves. In other embodiments, the workpieces are supported on pallets, locators or shelves when the workpieces are transported through the wave soldering machine. The solder reservoir has one or more nozzles that discharge one or more solder waves generated by the solder pump. The solder pump is typically a variable speed pump that allows the end user to control the flow of solder from the solder wave and increase or decrease the apex or peak of the solder wave to suit the processing conditions. The one or more solder waves impinge on the surface of the workpiece to be soldered through one or more openings in the top surface of the apparatus described herein. During this process, the apparatus stores a plurality of diffusing tubes comprising openings, orifices, slits, perforations or pores in fluid communication with an inert gas source such as N ₂ , the source of gas passing through the internal volume of the tube and passing through the tubes The opening or pores of the tube enter the atmosphere. In doing so, the lower surface, the front green, the back green, and the side edges of the workpiece are uniformly covered by the inert gas when the workpiece passes the solder wave.

In a particular embodiment of the apparatus and method described herein, the size of the device placed on top of the solder reservoir is minimized to enhance inerting efficiency around the moving solder waves. In various embodiments, the static molten solder surface, or regions outside of the device path in the solder reservoir, may be covered by a high temperature material that can withstand the temperature of the molten solder contained in the solder reservoir.

The apparatus and method described herein comprise a plurality of diffusion tubes having an internal volume and one or more openings, which may be, but are not limited to, pores, holes, slots, vents, orifices, perforations or other A means for allowing nitrogen and/or other inerting gas to pass through the internal volume of the tube and exit through the opening of the tube. In a particular embodiment, the tubes are porous and comprise an average pore size of about 0.2 micrometers (μm) or less to provide a laminar flow of inerting or N ₂ gas exiting the porous tube. In various embodiments, the tubes are in fluid communication with a source of inert gas that supplies the inerting gas through the internal volume of the tube, such as, for example, N ₂ and openings or fines through the tubes The aperture exits into the surface of the molten solder of the sump and within the area defined by the transport operation.

As previously mentioned, the apparatus described herein includes a housing containing a plurality of diffuser tubes and an internal volume. In a particular embodiment, the tubes may be located between the plurality of solder waves, the board entry side of the solder sump, the workpiece exit side of the solder sump, perpendicular to the direction of the solder wave, or a combination thereof. In these embodiments, there is substantially no gap between the surface of the workpiece to be soldered and the surface of the solder waves. In a particular embodiment, one or more of the tubes, such as those in which one or more of the tubes are present between a plurality of solder waves, may additionally comprise a metal protrusion or fin a sheet, wherein at least a portion of the protrusion touches the molten solder and is thermally conducted with the tube. In this regard, the metal tab or fin allows the tube temperature to which it is attached to become higher than the melting point of the solder to avoid, for example, clogging caused by soldering splashes and/or flux vapor condensation. In a particular embodiment, the metal protrusions or fins that touch the one or more tubes and the molten solder can be a component of the vertical wall of the device. In various embodiments, another tube may be disposed on the inside and/or outside of the solder bath. The use of one or more metal protrusions that conduct heat between at least one tube and the molten solder bath avoids the problems associated with prior art and impregnation and/or contacting the porous tube with the solder bath.

In a particular embodiment of the apparatus and method described herein, the plurality of diffusers, such as, but not limited to, a central diffuser between a plurality of solder waves, one or more comprising a non-stick coating . An example of a non-stick coating is a polytetrafluoroethylene (PTFE) coating, which can be registered under the trademark Teflon. A non-stick coating (Teflon manufactured by DuPont, Inc. of Wilmington, Delaware) was found. To maintain the inert gas through the surface of the diffuser, a porous Teflon non-adhesive sleeve can be applied to at least a portion of the surface of the tube. In various embodiments, the selected non-stick coating should maintain its integrity at or above the molten solder temperature typically used in lead-free wave soldering processes (e.g., up to about 260 ° C). In a more specific embodiment, the coating comprises a non-adhesive coating cohesionless Thermolon ^TM, manufactured by South Korea Thermolon Ltd., at 450 deg.] C and can maintain its integrity and avoids toxic vapor to increase the temperature Inorganic (mineral-based) coating. In a specific embodiment in which the central porous tube is present between one or more pairs of solder waves, the flux dissolved in the solder reservoir will be in direct contact with and located in the first and second due to the continuous dynamic movement of the molten solder. The center of the diffuser surface between the waves. When the liquid flux on the surface of the diffuser evaporates or thermally decomposes, solid flux residues may remain on the diffuser surface, thus causing the diffuser to clog. To remedy this, a non-stick coating or a porous, non-adhesive sleeve or a metal shell made of a slit-free coated non-stick coating can be applied to the porous tube or can cover at least a portion of the porous tube. Adding a non-adhesive coating or a porous non-adhesive sleeve or a metal shell made of an elongated hole coated with a non-adhesive coating to at least one of the porous diffusion tubes prevents the porous tube from being The central tube is blocked by solid flux residues. The non-stick coating can also be applied to at least a portion of the inner surface of the device or the inner surface of the cap for ease of cleaning.

In still another embodiment of the apparatus and method described herein, the apparatus additionally includes any cover mounted on the moving track to form a tunnel through which the workpieces pass. The optional cover additionally includes a venting opening in fluid communication with the venting vent line of the wave soldering machine, the venting aperture permitting collection of flux vapor from the atmosphere below the cover. In one embodiment, the optional cover is made from a single layer of metal cover with a central aperture to the venting line of the machine. In another embodiment, the optional cover is comprised of a double layer of metal sheet and the double layer spacing is coupled to the venting venting line of the furnace thereby forming a boundary gas trap. In a particular embodiment, the distance between the two metal sheets can be between about 1/8" to about When a workpiece or circuit board passes under the cover, the flux vapor generated in the soldering zone can be collected through the boundary well, and the air surrounding the solder tank is trapped in the double layer interval, thereby Ensuring good inertization performance. In the case where there is no workpiece or circuit board on top of the solder tank, the inert gas generated by the majority of the diffuser of the inerting device can be pumped to the volume below the double layer spacing of the lid. Internally, a boundary gas inerting is formed to minimize air entering the volume.

Figure 1 provides a specific embodiment of a porous tube or diffuser of the apparatus and method described herein. The perforated tube 10 is depicted as a cylindrical tube having an internal volume 15 that allows for inerting gases such as nitrogen and/or other gases such as, but not limited to, inert gases (eg, argon, helium, neon, etc.) The hydrogen, or a combination thereof, flows through and is in communication with an inerting gas source fluid (not shown). In one embodiment of the perforated tube 10, the perforated tube is made of stainless steel. However, materials for other porous tubes 10 are also applicable as long as the materials are not reactive to the solder. The perforated tube 10 is in fluid communication with the source of inerting gas through a gas conduit or other means (not shown). The perforated tube 10 additionally includes a plurality of perforations 20, pores or holes that allow gas to pass from the interior volume 15 through the perforations 20 from the surface of the solder bath, the molten solder (not shown), and the workpiece to be soldered ( The atmosphere defined below, or a combination thereof, flows out. While the porous tube 10 is shown to be cylindrical and has a circular cross-section, other geometries are contemplated, such as, but not limited to, circular, square, rectangular, elliptical, and the like, all of which may be used. The perforations 20 are designed such that, for example, a circular aperture as shown in the particular embodiment of Figure 1 will direct the airflow in a narrower manner and fill the full length of the solder reservoir (not shown). In another embodiment, the perforations 20 can be elongated holes or slits. In various embodiments, the perforations 20 can be truncated or angled to further introduce gas flow from the interior volume 15 into the solder bath (not shown) and/or the gap between the solder bath and the workpiece. The perforations 20 may have an average pore size of from 0.05 microns to 100 microns, or from 0.1 to 10 microns, or from 0.2 to 5.0. In a particular embodiment, the perforations 20 have an average pore size of about 0.2 microns or less. So that pore size and porosity of the porous tube 10 on the perforated optimized, to seek to leave the porous tube laminar gaseous N _2. In various embodiments, in order to minimize intrusion of air from the boundary of the soft pad (e.g., workpiece, conveyor belt, etc.) to be inertized, a layer of N ₂ and/or other inert gas is preferred. flow.

With respect to an alternative embodiment of the porous diffuser, one or more of the plurality of diffusers, such as, but not limited to, a central diffuser between a plurality of solder waves, may be formed into concentric slits Made of tube. Examples of such specific embodiments are provided in Figures 23a (side view) and 23b (section). In this particular embodiment, the diffuser tube 1100 has one or more elongated holes 1110 and is surrounded by a concentric cover 1120. The lid 1120 has one or more openings or slits 1130 that face downward and allow inert gas to pass. It is believed that the downward structure of the elongated holes minimizes the chance of liquid flux entering the tube and blocking the one or more openings. In a particular embodiment, the concentric cover 1120 has a non-stick coating applied to at least a portion of its surface, such as any of the coatings described herein. Although the diffuser tube 1100 and its surrounding cover 1120 are shown to be cylindrical in shape and have a circular cross-section, other geometries are contemplated, such as, but not limited to, circular, square, rectangular, elliptical, and the like.

Figures 3a and 4 provide top and isometric views of one embodiment of the apparatus 30 described herein. Referring to Figure 3a, device 30 is placed on wave soldering apparatus 70 to provide an inerting atmosphere during the wave soldering operation. Wave soldering apparatus 70 includes a solder sump 75 containing molten solder 80 and one or more nozzles 85 that discharge one or more solder waves (not shown) produced by a solder pump (not shown). Referring to both Figures 3a and 4, the device 30 has a top surface 35 that is removable from the carrier of the device to make it easier for the end user to complete the scum removal. The top surface 35 additionally includes at least one opening 40 through which at least one solder wave radiated from the molten solder 80 contained in the solder reservoir 75 passes through the nozzle 85 and contacts a workpiece passing along a moving rail (not shown). Referring to Figures 3a and 4, device 30 is additionally included in at least one recess 45 (shown in phantom in Figure 3) on the bottom of device 30, which is placed atop the edge of solder reservoir 75. In a particular embodiment, device 30 can include more than one recess that enables device 30 to be placed atop solder reservoir 75, as shown in Figures 3a and 4. The other specific embodiments described herein have only one recess 245 such as the specific embodiment depicted in Figures 7 and 8. Yet another embodiment of the apparatus described herein does not have one or more grooves but a plurality of flanges that allow the apparatus to be placed or placed on a solder reservoir, such as the specific embodiment depicted in Figures 11 and 14. . Referring again to Figures 3a and 4, the side walls of the recess 45 and the front or rear wall 33 or rear wall 37 define a compartment 50 that allows the perforated tube 55 (shown in phantom in Figure 3) to be placed within the apparatus 30. Perforated tube 55 is in fluid communication with inerting gas source 65 via tube 60. As previously mentioned, the inerting gas used in conjunction with the apparatus and methods described herein may comprise nitrogen, hydrogen, an inert gas (e.g., helium, argon, neon, xenon, krypton, etc.) or combinations thereof. In a particular embodiment, the inerting gas is preheated prior to introduction into the porous tube 55. It will be appreciated that the specific embodiment illustrated in Figures 3a and 4 can vary with the structure of the wave soldering machine. Referring now to Figure 4, apparatus 30 additionally includes an interior volume 69 defined by the molten solder surface (not shown), the workpiece (not shown), front wall 33, back wall 37, and side walls 43 and 47. Apparatus 30 additionally includes at least one metal fin 57 in contact with the molten solder sump and at least one porous tube for heating the center of the porous tube 55 to a temperature above the melting point of the molten solder.

Figure 3b provides a top view of a particular embodiment of the apparatus 30' described herein in which the porous diffuser 55' is oriented perpendicular to the width of the solder wave. Referring to Figure 3b, device 30' is placed on wave soldering apparatus 70' to provide an inerting atmosphere during the wave soldering operation. The wave soldering apparatus 70' includes a solder reservoir 75' containing molten solder 80', and one or more nozzles 85' that discharge one or more solder waves (not shown) generated by a solder pump (not shown). The device 30' has a top surface 35' that is removable from the carrier of the device to make it easier for the end user to complete the scum removal. The top surface 35' additionally includes at least one opening 40' through which at least one solder wave radiated from the molten solder 80' contained in the solder sump 75' passes through the at least one opening 40' and passes along the moving track (not Show) the workpiece passed. In other embodiments, the apparatus described herein includes a plurality of flanges that allow the apparatus to be placed or placed on a solder reservoir. Perforated tube 55' is in fluid communication with inerting gas source 65' via tube 60'. As previously mentioned, the inerting gas used in conjunction with the apparatus and methods described herein may comprise nitrogen, hydrogen, an inert gas (e.g., helium, argon, neon, xenon, krypton, etc.) or combinations thereof. In a particular embodiment, the inerting gas is preheated prior to introduction into the porous tube 55'. It is understood that the specific embodiment shown in Figure 3b can vary with the structure of the wave soldering machine.

Figure 5 provides an isometric view of any cover 90 placed over the apparatus 30 and moving track (not shown) such that the workpiece can travel. It is shown that any cover 90 has a glazing 95 that can be viewed. Any cover 90 additionally has a vent 97 in fluid communication with a venting line (not shown) of the wave soldering machine to remove any flux vapor within the atmosphere of the soldering station.

Figure 6 provides a side view of a particular embodiment of the device 130 as defined herein. As illustrated in Figure 6, device 130 is placed atop wave soldering apparatus 170 by mounting recess 145 on at least one edge of solder reservoir 175 as shown. The solder reservoir 175 has a molten solder 180 contained therein. The moving track (not shown) transports the workpiece 100 to be soldered in the upward direction indicated by the arrow 105 shown. At least one or more solder pumps (not shown) are used to generate a plurality of solder waves 115 through the nozzles 185. The majority of the solder wave 115 strikes the underside of the workpiece 100 through the opening 107 in the device 130. The inert gas is introduced into the perforated tube 155 in the tank 150 outside the solder tank 175. In the particular embodiment illustrated in FIG. 6, a porous tube 155 is located at the inlet and outlet of the solder reservoir 175. In yet another embodiment, the porous tube 155 is oriented perpendicular to the direction of the solder waves (not shown). At least one of the porous tubes 155 is connected to the metal protrusion 157 contacting the molten solder 180. The inerting gas fills under the workpiece 100 and is depicted in cross-parallel hatching and the area or atmosphere indicated by 120 above the surface of the molten solder 180. In the particular embodiment illustrated in FIG. 6, the apparatus has substantially no gap between the workpiece 100 and the apex of the solder wave 115.

Figures 7 and 8 provide an alternate embodiment of apparatus 230 in which only one recess 245 is placed over the edge of a solder reservoir (not shown). At least one side wall and front wall 233 of the recess 245 of the device 230 defines a pod 250 containing a perforated tube 255 (shown in phantom in Figure 8). Apparatus 230 additionally includes an interior volume 269 defined by the molten solder surface (not shown), the workpiece (not shown), front wall 233, back wall 237, and side walls 243 and 247. Referring to Figure 8, device 230 additionally includes at least one metal fin 257 in contact with at least one of the molten solder reservoir (not shown) and the plurality of porous tubes 255 (shown in phantom) for use of the metal fin 257 The center of the porous tube 255 is heated to a temperature higher than the melting point of the molten solder.

Figures 9 through 13 provide a number of different embodiments of the apparatus described herein, including a plurality of porous tubes. Figure 9 provides a specific embodiment in which one of the porous tubes 355 is located in a recess 350 outside the solder reservoir 375, and the second porous tube 355' interposed between the solder waves comprises a thermally conductive material 357, for example Metal fins, the thermally conductive material 357 touches the molten solder 380 and the second porous tube 355' and heats the second porous tube to a temperature higher than the melting point of the solder, and the third porous tube 355" touches the The wall of device 330, which is thermally conductive or extends into molten solder 380. Device 330 additionally contains a flange that facilitates placement of device 330 on top of solder reservoir 375.

Figure 10 provides a specific embodiment of apparatus 430 in which the first porous tube 455 is located within a recess 450 outside the solder reservoir 475, and the second porous tube 455' and the third porous tube 455" comprise a thermally conductive material. For example, a metal fin 457 that touches the molten solder 480 and the second porous tube 455' and the third porous tube 455" and heats the porous tubes to a temperature above or above the melting point of the solder.

Figure 11 provides a specific embodiment wherein the first porous tube 555, the second porous tube 555' and the third porous tube 555" are attached to the inside of the solder reservoir 575, and each porous tube comprises a thermally conductive material such as a metal. Fin 557, the thermally conductive material contacts the molten solder 580 and heats each porous tube to a temperature above the melting point of the solder. Device 530 does not have a recess for placing the device on top of solder reservoir 575. Rather, device 530 has a majority A flange 567 that holds the device 530 on top of the solder reservoir 575.

Figure 12 provides a specific embodiment of an apparatus 630 having a plurality of grooves 645, wherein at least one side wall of the recess and the front wall 633 or rear wall 637 of the apparatus 630 define a compartment 650 having perforated tubes 655 and 655". Also included is a porous tube 655' that is in contact with a thermally conductive material, such as metal fin 657, that contacts the molten solder 680 and heats the porous tube 655' to a temperature above the melting point of the solder.

Figure 13 provides a specific embodiment of an apparatus 730 having a plurality of grooves 745, wherein at least one side wall of the recess and the front wall 733 or rear wall 737 of the apparatus 730 define a compartment 750 having perforated tubes 755 and 755". Also included is an inner flange 752 extending from the sidewall of the recess 745 into the solder reservoir 780, which facilitates placement of the device 730 on top of the solder reservoir 775.

Figure 14 provides a specific embodiment of the apparatus 930 described herein, wherein the first porous tube 955, the second porous tube 955', and the third porous tube 955" are attached to the inside of the solder reservoir 975, and the porous One of the tubes or 955' additionally includes a thermally conductive material, such as metal fins 957, that contacts the molten solder 980 and heats the porous tube 955' to a temperature above the melting point of the solder. Device 930 does not place the device on the solder Instead, the container 930 has a plurality of flanges 967 that can place the device 930 on top of the solder reservoir 975. The device 930 is shown to be comprised of a double wall of a material such as metal, which The double wall defines at least one compartment 950 that houses at least one of the illustrated perforated tubes, such as 955 and 955'. The workpiece 923 travels over the apparatus 930 in the direction indicated by arrow 925 and is in contact with most of the molten solder waves emitted from the nozzle 985. the majority of perforated pipe 955,955 'and 955 "in fluid communication with a source of an inert gas such as N ₂ (not shown), the inert gas source to provide an inert atmosphere of a N ₂ atmosphere, or through the pipe, to the tank 950, to Device 930 The volume defined by the bilayer of material is in the interior volume 969 defined by the molten solder surface 980, the workpiece 923, and the wall of the apparatus 930.

15 through 17 provide a specific embodiment of apparatus 830 that additionally includes any cover 890 on top of the solder reservoir 870 to form a tunnel through which workpiece 905 held on moving rail 900 passes. Figure 15 provides an end view and Figures 16 and 17 provide side views of device 830. In specific In a particular embodiment, any cover 890 is in fluid communication with a vent tube of a wave soldering machine (not shown). Any cover 890 is constructed of a two-layer sheet that is attached to the venting exhaust pipe 897 of the furnace to form a boundary gas trap. The optional cover 890 can be made from a double sheet of sheet metal or other suitable material. In a particular embodiment, the distance between the two metal sheets can be between, but not limited to, from 1/8" to about 1⁄4". In the particular embodiment illustrated in Figures 15 through 17, any cover 890 can include an inerting gas inlet 895 that is in fluid communication with an inert gas source (not shown) to facilitate cleaning away from the soft pad. Flux vapor and air. As shown in FIG. 16, when a circuit board passes under the cover 890, the flux vapor generated in the soldering zone can be collected through the boundary well, and the air surrounding the solder tank 870 can also be trapped under the cover 890. In the double layer spacing, it helps to ensure a good inerting atmosphere. In the example where the solder reservoir 870 is not covered by the workpiece 905 shown in FIG. 17, the inerting gas generated by the plurality of porous tubes 855 can be sucked into the double-layered space of the cover 890, thereby forming a boundary inert gas. The mist minimizes air entering the atmosphere 920 above the solder reservoir 870 from the external environment.

In another embodiment of the apparatus and method described herein, such as the embodiment illustrated in Figure 21, an inert aerosol 1010, such as N ₂ and/or other inerting gases as described herein, is applied to the solder. The inlet, outlet or both the inlet and outlet of the sump 1020 further minimizes intrusion of air from around the solder sump. The salty gas mist 1010 will block the gap on either the top or bottom or the top and bottom of the workpiece 1005 to be treated (note: 1005 should be implied on the straight line of the workpiece and the small rectangle should be removed). The workpiece 1005 enters the solder reservoir 1020 using a device 1030 placed on top of the solder reservoir 1020 and a top cover 1040 disposed at the top. In the embodiment or other embodiments illustrated in Figure 21, the aerosol may be produced by one or more diffusion tubes having one or more openings containing elongated holes or perforations, wherein tubes, boxes, triangles or The combination has a length parallel to the width of the solder waves and an inert gas flowing from one or both ends. A narrow slit or small perforation allows for strong gas jets to form an aerosol containing the inert gas. In various embodiments, the narrowed or perforated diffuser tube can comprise a porous tube or a porous layer within the tube to minimize pressure drop along the length of the diffuser making the elongated holes or perforations. Referring now to Figure 22a, the diffuser tube 1050 is formed with one or more openings or slits 1060 that can be used alone (as shown) or inserted into a porous diffuser (not shown) to create an aerosol. . With respect to an alternative example, Figure 22b shows a cross section of a diffusion box 1070 with its top surface 1075 made of a perforated plate and the other three surfaces made of a solid plate 1078. Figure 22b also shows a cross-section of a triangular gas guide 1080 having an open elongated aperture in the bottom and top edges 1090 of the triangle 1080. The bottom surface of the triangular gas director 1080 is in direct contact with the pores contained in the surface 1075 to be in fluid communication with the diffusion cell 1070 and to uniformly inject gas along the length of the diffuser.

Although the device and method have been described in detail and in detail with reference to the specific embodiments and embodiments thereof, those skilled in the

Example Example 1: Effect of pore size of porous tube on gas flow diagram

The three diffusers or perforated tubes with three different grades listed in the table below were tested. A lower rating indicates that the diffuser has a smaller pore size and porosity. This test was carried out by flowing N _{2 in} the hood into each of the seamless porous tubes and measuring the pressures upstream (P _up ) and downstream (P _down ) of each diffuser to obtain a specific N ₂ flow rate. The pressure drop (ΔP) along the diffuser is determined as follows:

ΔP=P _up -P _down

Then calculate the average pressure along the diffuser:

P _ave =(P _up +P _down )/2

When ΔP/P _{ave is} much smaller than 1, the gas flowing out of the diffusion tube can be regarded as a laminar flow pattern. Conversely, when ΔP/P _{ave is} close to 1, the turbulent gas flow is usually dominant. With respect to particular embodiments, it is preferred that the porous tube provides a laminar gas flow pattern.

As shown in Table I and Figure 2, the ΔP/P _{ave of the} 0.2-stage diffuser or porous tube is minimal and well below 1 at the relevant N ₂ flow rate. Based on this result, a 0.2-stage diffuser was selected. The 0.2 stage diffuser has an average pore size of about 0.2 μm. Figure 2 shows that a porous tube having an average pore size of 0.2 μm or the 0.2 diffuser grade is most desirable at an associated N ₂ flow rate (e.g., 6 m ³ /hr/diffuser). In contrast, U.S. Patent No. 6,234,380 teaches that a diffuser for N ₂ inertization during wave soldering preferably has a pore size range of 0.3 to 2 μm or 0.4 to 0.6 μm beyond the optimum pore size of the layered layer.

Example 2: Effect of heated diffuser on N ₂ inertization during wave soldering

In this embodiment, at least one of the plurality of porous tubes is located between the two solder waves and has a metal fin extending into the molten solder sump so that the temperature of the porous tube diffuser can be kept higher than The melting point of the solder. This heated diffuser avoids potential blockage problems such as splashing/solidification by solder and condensation by flux vapor on the diffuser surface. Figure 9 shows an example of the structure used in this experiment.

Figure 19 provides O ₂ concentration results around the solder reservoir at positions 1 through 8 indicated in Figure 18 with a static plate on top of the solder reservoir and without the top cover (e.g., as shown in Figure 5), and FIG 20 is repeated by O and the cap above the ventilation device (e.g., that shown in FIG. 5) analysis of _2. It was visually observed that any soldering splash on the surface of the perforated tube would not cure in the second case. The solder droplets splashed on the surface of the central diffuser will automatically drip due to their high surface tension and the intrinsic properties of the diffuser surface. Furthermore, there is no way to prove that the flux vapor condenses on the surface of the diffuser. Figure 19 shows that the O ₂ concentration near the molten solder waves is very low for very small amounts of N ₂ flow rate, and this performance can be maintained over time as the diffuser blockage has been eliminated. Similarly, Figure 20 shows that even with a venting device, the O ₂ concentration near the molten solder waves is low for a very small amount of N ₂ flow rate, and the performance can be maintained over time because the diffuser has blocked Was eliminated. Due to the presence of the metal fins, the diffuser tube can be disposed closer to the molten solder surface for more efficient cleaning of the air exiting the solder reservoir.

Example 3: Application of a non-viscous porous casing to a central diffuser

In this embodiment, at least one of the plurality of porous tubes is located between the two solder waves and has a metal fin inserted into the molten solder sump such that the temperature of the porous tube diffuser can be maintained higher than the The melting point of the solder. This heated diffuser avoids potential blockage problems such as splashing/solidification by solder and condensation by flux vapor on the diffuser surface. Figure 9 shows an example of the structure used in this experiment.

The central diffuser is covered with a sleeve made of ePTFE (expanded polytetrafluoroethylene). The Eptfe is formed into a tubular shape and white, which is made by Phillips Scientific Ltd. under the part number TB3000. The perforated tube can only expand along the length of the tube, but does not expand in the diametrical direction. The material withstood the test at 315 ° C and had an average pore size of about 2 to 10 microns. The tube may have a wall thickness of between 0.001" and 0.002".

The ePTFE sleeve on the porous diffusion tube was immersed in a molten solder bath at 260 °C. The sleeve did not show a visible change.

The 12 "ePTFE on long diffusion cannula connected to the source 85 psig of N _2. N ₂ flow rate of supply 4 NM ³ / Hr from the diffuser and there is no problem on the surface of the sleeve.

A diffuser (12" length and 3/8" outer diameter (OD) with ePTFE sleeve was set up as the central diffuser in the equipment described herein, and there is 4 NM ³ /Hr on the center diffuser N ₂ flow rate. The device was then mounted on a 260 ° C molten solder bath and the passing two solder waves touched the hot fins of the center diffuser. A liquid flux is continuously sprayed onto the surface of the ePTFE of the central diffuser. It was found through visual inspection that the ePTFE was completely non-tacky to the liquid flux, and the molten solder sprayed on the ePTFE sleeve of the center diffuser could be easily dropped into the solder bath.

10. . . Porous tube

15. . . Internal volume

20. . . perforation

30. . . device

30’. . . device

33. . . Front wall

35. . . Top surface

35’. . . Top surface

37. . . Back wall

40. . . Opening

40’. . . Opening

43. . . Side wall

45. . . Groove

47. . . Side wall

50. . . cabin

55. . . Porous tube

55’. . . Porous diffuser

57. . . Metal fin

60. . . tube

60’. . . tube

65. . . Inert gas source

65’. . . Inert gas source

69. . . Internal volume

70. . . Wave soldering equipment

70’. . . Wave soldering equipment

75’. . . Solder tank

75. . . Solder tank

80’. . . Molten solder

80. . . Molten solder

85. . . nozzle

85’. . . nozzle

90. . . Optional cover

95. . . Glass window

97. . . Vent

100. . . Workpiece

105. . . arrow

107. . . Opening

115. . . Solder wave

120. . . Atmosphere

130. . . device

145. . . Groove

150. . . cabin

155. . . Porous tube

157. . . Metal protrusion

170. . . Wave soldering equipment

175. . . Solder tank

180. . . Molten solder

185. . . nozzle

230. . . device

233. . . Front wall

237. . . Back wall

243. . . Side wall

245. . . Groove

245. . . Groove

247. . . Side wall

250. . . cabin

255. . . Porous tube

257. . . Metal fin

269. . . Internal volume

330. . . device

350. . . Pocket

355. . . Porous tube

355’. . . Second porous tube

355"...the third porous tube

357. . . Thermally conductive material

375. . . Solder tank

380. . . Molten solder

430. . . device

450. . . Pocket

455. . . First porous tube

455’. . . Second porous tube

455"...the third porous tube

457. . . Metal fin

475. . . Solder tank

480. . . Molten solder

530. . . device

555. . . First porous tube

555’. . . Second porous tube

555"...the third porous tube

557. . . Metal fin

567. . . Flange

575. . . Solder tank

580. . . Molten solder

630. . . device

633. . . Front wall

637. . . Back wall

645. . . Groove

650. . . cabin

655. . . Porous tube

655’. . . Porous tube

655"...porous tube

657. . . Metal fin

680. . . Molten solder

730. . . device

733. . . Front wall

737. . . Back wall

745. . . Groove

750. . . cabin

752. . . Internal flange

755. . . Porous tube

755"...porous tube

775. . . Solder tank

780. . . Solder tank

830. . . device

855. . . Porous tube

870. . . Solder tank

880. . . Solder tank

890. . . Optional cover

895. . . Inert gas inlet

897. . . Ventilation exhaust pipe

900. . . Moving track

905. . . Workpiece

920. . . Atmosphere above the solder tank

923. . . Workpiece

925. . . arrow

930. . . device

950. . . cabin

955. . . First porous tube

955’. . . Second porous tube

955"...the third porous tube

957. . . Metal fin

967. . . Flange

969. . . Internal volume

975. . . Solder tank

980. . . Molten solder

985. . . nozzle

1005. . . Pending workpiece

1010. . . Inert aerosol

1020. . . Solder tank

1030. . . device

1040. . . Top cover

1050. . . Diffusion tube made of narrow holes

1060. . . Long hole

1070. . . Diffusion box

1075. . . Top surface

1078. . . Solid board

1080. . . Triangular gas director

1090. . . Top edge

1100. . . Diffusion tube

1110. . . Long hole

1120. . . Concentric cover

1130. . . Long hole

Figure 1 provides an isometric view of a particular embodiment of a diffuser or porous tube comprising pores as described herein.

Figure 2 is a graph showing the relationship between the pressure drop along the porous tube affected by the pore size or grade of the diffusion tube of Example 1 and the nitrogen (N ₂ ) flow rate per cubic meter (m ³ /hr). .

Figure 3a provides a top view of one embodiment of the apparatus described herein.

Figure 3b provides a top view of another embodiment of the apparatus described herein.

Figure 4 provides an isometric view of a particular embodiment of the apparatus illustrated in Figure 3a.

Figure 5 provides an isometric view of any cover that can be placed on top of the moving track.

Figure 6 provides a side view of the embodiment illustrated in Figure 3a mounted on a solder sump.

Figure 7 provides an isometric view of a particular embodiment of the apparatus described herein.

Figure 8 provides an isometric view of the embodiment illustrated in Figure 7 additionally comprising a plurality of tubes (shown in phantom), wherein at least one of the plurality of tubes comprises a fin-like projection, wherein at least a portion of the fin-like projection Contact with the molten solder.

Figure 9 provides the text for the particular side view of N ₂ inertization device of the embodiment, which comprises a plurality of tubes comprising one or more openings, wherein at least one of these tubes contain molten solder into contact with the Fin-like projections.

FIG 10 described provides a side view of the embodiment in particular N ₂ inertization device of the embodiment.

Venturi 11 provides a side view of the embodiment in N ₂ specific inertization device of the embodiment.

FIG 12 described provides a side view of the embodiment in particular N ₂ inertization device of the embodiment.

Venturi 13 provides a side view of the embodiment in N ₂ specific inertization device of FIG.

FIG 14 described provides a side view of the embodiment of N ₂ inertization device of the particular embodiment.

Figure 15 provides an end view of any of the covers that can be set up on the moving track, in the particular embodiment the workpiece travels on the moving track.

Figure 16 provides a side view of the embodiment illustrated in Figure 15 illustrating the passage of a workpiece or printed circuit board beneath the cover.

Figure 17 provides a side view of the embodiment illustrated in Figure 15 with no circuit board passing underneath the cover.

Figure 18 provides a picture demonstrating eight locations for measuring the O ₂ concentration in Example 2.

Figure 19 provides the O ₂ concentration results for positions 1 through 8 of the apparatus of Fig. 18 for a device having a plurality of porous diffusion tubes, wherein one of the plurality of tubes has a metal protrusion in contact with the solder bath of embodiment 2 and Wherein any of the covers is not located on the moving track and the top of the workpiece.

Figure 20 provides the O ₂ concentration results for positions 1 through 8 of the apparatus of Figure 18 for a device having a plurality of porous diffusion tubes, wherein one of the plurality of tubes has a metal protrusion in contact with the solder bath of Embodiment 2 and The position of any device connected to the ventilating device on the moving track and the top of the workpiece.

Figure 21 provides a specific embodiment of an aerosol that can be used in conjunction with the methods and apparatus described herein.

22a and 22b respectively provide a specific embodiment of a diffusion tube and a diffusion box as described herein, wherein the diffusion tube includes a plurality of elongated holes and is housed in a diffusion box, the diffusion box including a plurality of openings to allow inert gas Pass through the openings.

Figures 23a and 23b provide side and cross-sectional views, respectively, of an alternate embodiment of a diffuser tube.

30. . . device

35. . . Top surface

40. . . Opening

45. . . Groove

50. . . cabin

55. . . Porous tube

60. . . tube

65. . . Inert gas source

70. . . Wave soldering equipment

75. . . Solder tank

80. . . Molten solder

85. . . nozzle

Claims (26)

An apparatus for providing an inert gas during soldering of a workpiece, the apparatus comprising: at least one opening on a top surface of the apparatus, at least one solder wave emitted from a solder reservoir containing molten solder passes through the at least one opening and Touching the workpiece; a plurality of tubes comprising one or more openings, the tubes being in fluid communication with a source of inerting gas, wherein at least one of the tubes is present in a chamber located outside the solder reservoir, a thermally conductive projection At least a portion of the protrusion contacts the molten solder and the at least one tube; wherein the device is located above the solder reservoir and under the workpiece to be soldered to form an atmosphere and the workpiece to be soldered and the at least one There is substantially no gap between the apexes of the solder wave. The device of claim 1, further comprising: at least one groove at the bottom of the device, the at least one groove for placing on at least one edge of the solder sump containing molten solder, wherein the recess At least one sidewall of the slot and at least one wall of the device define a pod outside the solder reservoir. The device of claim 2, wherein the thermally conductive protrusion comprises a metal fin. The device of claim 2, wherein the at least one tube is present at a proximal end of the at least one solder wave. The apparatus of claim 1, further comprising a cover placed on top of the moving rail for passing the workpiece therethrough, wherein the cover additionally includes a vent that communicates with the ventilation system. The apparatus of claim 5, wherein the cover comprises a plurality of sheets defining an interior volume and wherein the interior volume is in fluid communication with a venting exhaust line of the soldering furnace. The apparatus of claim 6 wherein the lid further comprises an inlet in fluid communication with the source of inerting gas. The apparatus of claim 1, wherein the openings in the tubes are fine pores and the porous tube has an average pore diameter of 0.2 μm or less. The apparatus of claim 1, wherein the apparatus comprises a plurality of grooves, wherein the grooves define a plurality of compartments having the perforated tubes. The apparatus of claim 1, wherein the solder reservoir generates a plurality of solder waves and at least one tube is interposed between the solder waves. The apparatus of claim 1, wherein the inert gas comprises nitrogen. The apparatus of claim 11, wherein the inerting gas additionally contains 5% by weight or less of hydrogen. The apparatus of claim 1, wherein the inerting gas comprises a gas selected from the group consisting of nitrogen, hydrogen, helium, neon, argon, xenon, krypton, and combinations thereof. The apparatus of claim 8 wherein at least a portion of one of the porous tubes comprises a non-stick material. A method for providing an inerting atmosphere for workpiece wave soldering, the method comprising: providing a wave soldering machine comprising: a solder reservoir containing molten solder, at least one nozzle, at least one pump to pass upward from the molten solder bath The nozzle generates at least one solder wave; placing a device on top of at least one edge of the solder reservoir, wherein the device includes at least one opening on the top surface, at least one groove on the top of at least one edge of the solder reservoir, and a plurality of a tube comprising one or more openings, the plurality of tubes being in fluid communication with a source of inert gas, wherein the workpiece to be soldered and the top surface of the molten solder define an atmosphere and the workpiece to be soldered and the at least one There is substantially no gap between the apexes of the solder wave; the workpiece is passed along a path such that at least a portion of the workpiece touches And at least one solder wave emitted through the opening of the device; and introducing an inert gas through the tubes and entering the atmosphere, wherein at least one of the tubes contacts a portion of the thermally conductive protrusion inserted into the molten solder The at least one tube is heated to a temperature above the melting point of the molten solder. The method of claim 15, wherein the thermally conductive protrusion comprises a metal fin. The method of claim 15, wherein the at least one tube is present at a proximal end of the at least one solder wave. The method of claim 15, further comprising a cover through which the workpiece passes, wherein the cover additionally includes a vent that communicates with the ventilation system. The method of claim 18, wherein the cover comprises a plurality of sheets defining an interior volume and wherein the interior volume is in fluid communication with a venting exhaust line of the soldering furnace. The method of claim 19, wherein the lid further comprises an inlet in fluid communication with the source of inerting gas. The method of claim 15, wherein the opening comprises a fine hole And the porous tube thereof has an average pore diameter of 0.2 μm or less. The method of claim 15 wherein the apparatus comprises a plurality of grooves, wherein the grooves define a plurality of compartments having the tubes. The method of claim 15, wherein the solder reservoir generates a plurality of solder waves and at least one tube is interposed between the solder waves. The method of claim 15, wherein the inerting gas comprises nitrogen. The method of claim 24, wherein the inerting gas further comprises 5% by weight or less of hydrogen. The method of claim 15, wherein the inerting gas comprises a gas selected from the group consisting of nitrogen, hydrogen, helium, neon, argon, xenon, krypton, and combinations thereof.