Abstract: A solder jet apparatus is disclosed The solder jet apparatus is a continuous mode solder jet that includes a blanking system and raster scan system. The use of the raster scan and blanking systems allows for a continuous stream of solder to be placed anywhere on the surface in any desired X-Y plane. This allows for greater accuracy as well as greater product throughput. Additionally, with the raster scan system, repairs to existing soldered surfaces can be quickly and easily performed using a map of the defects for directing the solder to the defects.

Abstract: A solder immersion chamber in a solder crater/leveler includes a solder manifold having upper and lower solder chambers, from which solder is directed onto the top and bottom surfaces of printed circuit boards conveyed therebetween. The solder immersion chamber has a pair of driven rollers at either end thereof for conveying the printed circuit boards through the solder immersion chamber, and for damming and holding the molten solder within the solder immersion chamber. A pair of oil weirs is provided adjacent either side of the upper solder chamber for continuously flowing oil to flood the top surface of the molten solder in the solder immersion chamber. A skimmer skims oil from the top surface of the molten solder, and returns the separated oil to the pair of oil weirs.

Abstract: The linear motor pump for a wave soldering apparatus comprises in accordance with the invention several pumping channels arranged substantially parallel to each other and separate from each other. It includes preferably a multiply segmented stator. Each stator segment has one pumping channel allocated to same. By means of this a homogeneous pumping performance i.e. homogeneous pumping pressure distribution over a practically arbitrary width is achieved, which leads to a homogeneous solder wave. By the arrangement of the pumping channels and the design of the stator in accordance with the invention a turbulent whirling of the solder is made practically impossible.

Abstract: A method is provided for wave-soldering printed circuit boards. In order to obtain wave-soldered printed circuit boards with smallest possible number of solder globules, after the passage on the wave of solder, the printed circuit boards are further artificially cooled at an approximately constant time-temperature gradient of 20 K/sec.

Abstract: A method for wave soldering comprises the steps of providing a circuit board having a plurality of electronic components thereon and providing a pallet comprising a frame, first and second parallel rails attached to the frame, and third and fourth rails for receiving the circuit board. The third and fourth rails are attached to the first and second rails and the third and fourth rails form an angle of between about 30.degree. and 60.degree. with the first and second rails. Next, a solder wave is provided which generally flows in a first direction. Finally, the pallet is moved in a second direction generally perpendicular with the first direction across the solder wave. The components are therefore positioned at an angle with respect to the solder wave and solder-related electrical defects are reduced.

Abstract: A wave soldering machine welling up molten solder by means of a pump for soldering a printed circuit board. The wave soldering machine comprises a nozzle formed of an enclosure surrounded by a front upright, a rear upright and side plates, a rear baffle plate extended from the top edge of the rear upright in a manner that the height of the rear baffle plate is adjusted, and a generally L-shaped front baffle plate having a large radius of curvature pivotally attached to the top edge of the front upright, whereby a solder wave formed on the top end of the rear baffle plate by surface tension of molten solder flows along the top surface of the front baffle plate. The rear baffle plate is particularly shaped and a bypass is formed to present a stable solder wave.

Abstract: A method of wave-soldering assembled units which are conducted over a soldering unit by a transport device including propelling solder against the assembled units in a turbulent zone by a first turbulent soldering wave at an acute angle in the transport direction and subsequently by a quiet soldering wave approximately at right angles thereto. To avoid cold soldered spots and shadow regions, the method includes propelling solder against the assembled units by a second turbulent wave at an acute angle against the transport direction in the turbulent zone. A device for wave-soldering assembled units is also provided.

Abstract: A method is available for wave-soldering component groups, especially printed circuit boards with shielding from the environment, in which lead-free or at least low-lead solders, especially tin solders, with a melting point of more than 210.degree. C., are used. Since in wave soldering the solder bath temperature must usually be set considerably higher than the melting point of the solder, problems with overheating the components are encountered with higher-melting lead-free or low-lead solders. This problem is solved in accordance with the invention by setting a solder bath temperature which is only a few degrees Celsius above the melting point of the solder material, and performing the wave-soldering by the action of a plasma of a process gas atmosphere at low pressure.

Abstract: The invention relates to a soldering apparatus, comprising a solder vessel; at least one soldering tower located in said solder vessel; transport means for transporting objects to be soldered over said soldering tower; solder wave generating means for generating a solder wave emerging from the apex of the soldering tower and contacting the objects to be soldered, the soldering tower comprising a weir such that at least a part of the solder wave flows parallel to the direction of movement of the objects to be soldered over said weir; and guide means for guiding said part of the solder wave such that the solder wave leaves the soldered object substantially abruptly. As a consequence of said feature the stream of solder is abruptly guided away from the printed circuit board, so that the possibilities for developing short circuits on the printed circuit board are substantially reduced.

Abstract: The method and the device serve for soldering of workpieces, namely of pc boards and substrates, which are equipped with chip component parts and/or microelements and/or assemblies comprised thereof. Such boards are passed through a main solder bath or at least one main solder wave, and the workpiece is contacted with the surface of the wave. The solder wave has an imaginary break edge 2, i.e., a break edge at which the solder loses the contact with the workpiece in connection with an unwettable workpiece. The imaginary break edge 2 of the soldering device 1 extends not in a straight line and, viewed in the direction of conveyance 3, has at least one diminution 4, i.e., two edge parts ending in a point, i.e., the edges form a triangle.

Abstract: An arrangement of applying flux in solid, liquid or gaseous form directly to the solder wave avoids prefluxing of printed circuit boards or other elements to be soldered or solder wetted. The process for wave soldering an element comprises the steps of forming a solder wave above a solder reservoir, applying a flux directly to the solder wave separately from a shield gas delivery means to blanket the solder wave, and conveying the element through at least a portion of the solder wave. The process is applicable to wave soldering under a shroud wherein a gas shield is supplied by diffusers under the shroud, the flux being applied by at least one gas applicator directly to the solder wave.

Abstract: A lead oxide preventing apparatus for an automatic soldering device does not generate lead oxides around an impeller shaft inside a lead chamber. Industrial waste in the form of heavy-metal-contaminated material is reduced by installing a ring member and by placing an oxidation preventing agent into the ring members, or by installing a beating therein so that the molten lead does not contact portions of the impeller shaft.

Abstract: The present invention relates to a wave soldering process wherein an inert gas atmosphere is injected inside the wave soldering machine, the inert gas atmosphere having a temperature which might be controlled. Particularly, the atmosphere can be heated at the same or different temperatures before injection, for example in the preheating zones, in the machine. The atmosphere can also be cooled (or injected at ambient temperature) e.g. in the cooling zone. Various atmospheres can be used (similar or different from one zone to another). Also, maintaining the atmosphere under forced laminer flow conditions improves the quality of the solder joints. The thermal efficiency of the heat transfer between the atmosphere and the printed circuit boards is thus greatly enhanced, which means less solder defects, higher components density and decrease of energy consumption and inert gas flow rate.

Abstract: Methods of soldering circuit boards are provided in which a snap bar is provided on the conductor side of a printed circuit board for reducing defects, such as bridging, during mass soldering. This and other provided process and design techniques, such as lead lengths, orientation, mask finish, and the location of the leads on the board, have significantly reduced reworking and defective components and are especially effective when applied to 50 mil connector products.

Abstract: A wave soldering process and apparatus in which a localized low oxygen-containing atmosphere is provided at the point of contact of the solder wave and the substrate to be soldered by bubbling an inert gas through the solder wave.

Abstract: The invention relates to a soldering apparatus comprising: a vessel for liquid solder; at least one soldering tower placed in the vessel for causing liquid solder to leave the soldering tower on the upper side, wherein the soldering tower is adapted to cause the liquid solder to run off on all sides; a conveyor for carrying objects for soldering along the top side of the soldering tower such that the objects for soldering come into contact with the liquid solder; and a cover for maintaining an atmosphere with a reduced oxygen content at least in the surrounding area of the liquid solder.

Abstract: An apparatus and process prepares surfaces on components, boards and the like for assembly and solder joining. Oxides and other coatings can be removed from surfaces to be soldered without having to solder coat surfaces prior to joining. A polymer and an activator combination is applied to the surfaces, the polymer being thermally de-polymerizable and the combination removing oxides from the surfaces. The surfaces are heated after application of the polymer and activator to de-polymerize the polymer. Solder is then applied to solder join the surfaces.

Abstract: Printed circuit boards are wavesoldered by a method featuring the use of a plurality of elementary jets of molten solder to form a single flat soldering wave. Such a single flat wave is achieved by revolving those jets in an orbital motion such that the orbital motion is in a horizontal plane substantially parallel to the printed circuit board. Such a method allows the removal of air/gas bubbles during wavesoldering from any side of a component that is attached to a printed circuit board.

Abstract: A printed circuit board is provided with a solder pad configuration for wave soldering a surface mount device with its longitudinal axis in a direction perpendicular to the solder wave. A leading solder pad is not wider than the surface mount device. A trailing solder pad is wider than the surface mount device, thereby ensuring that the trailing pad is sufficiently wet by the solder wave.

Abstract: Wave soldering method and apparatus for fluxing a substrate in a low oxygen containing atmosphere, preheating the fluxed substrate at least partially in a non-low oxygen containing atmosphere, and soldering the preheated substrate in a low oxygen containing atmosphere.

Abstract: A fixture for positioning high density packaged integrated circuits for tinning which includes a clamp bar assembly pivotally attached to a base. The base includes recessed nests in which the high density packages are positioned. The high density packages are secured in the nests by the clamp bar assembly. The top surfaces of the high density packages are protected from the solder wave by the base. A predetermined spacing and orientation of the nests ensures proper tinning.

Abstract: A plated-through hole solder thief for inhibiting solder bridges between adjacent leads of an integrated circuit and simultaneously providing for electrical interconnection of certain leads of the integrated circuit other surfaces or layers of a printed wiring board. Plated-through holes are used as solder thieves and are located in the proximity of the last solder pad in a row of solder pads. The plated-through hole draws the solder from the last solder pad to fill the plated-through hole and inhibit bridging between functional leads of the integrated circuit as well as make an electrical interconnection between the last lead of the integrated circuit in each row and other surfaces or layers of the printed wiring board. The plated-through hole is located askew from the rows of solder pads so that functional use may be made of the plated-through hole once it is filled to provide a test point for testing the integrated circuit.

Abstract: Disclosed is a method and apparatus for applying flux and solder in order to attach connectors to printed circuit boards (PCBs). Flux is applied to the connector tails and the PCB pads by means of a roller mounted above a flux reservoir. The piece parts are then exposed to a solder wave such that the solder sticks only to the selected area to which the flux was applied.

Abstract: Provided is an apparatus for circulating a body of molten solder. An enclosure, attached to the base of an impeller motor extends downward into the body of molten solder. A rotatable shaft, advantageously attached to the impeller motor by a flexible coupling device, extends through the interior of the enclosure, terminating beyond the open end of the enclosure and connected at that end to an impeller. A seal between the rotatable shaft and the open end of the enclosure acts to prevent solder from entering the interior of the enclosure. The seal is comprised of a self-lubricating material which expands as the temperature of solder increases, forming a solder tight fit between the rotatable shaft and the seal and further securing the exterior of the seal to the interior wall of the enclosure while permitting shaft rotation. The self-lubricating and high temperature characteristics of the sealing material preclude the production of by-products from wear by the rotatable shaft.

Abstract: A soldering apparatus for selectively soldering designated areas on the surface of a printed circuit (PC) board for mounting multi-pin, through hole circuit components thereto includes a wave solder pot, a fixture for receiving and positioning the PC board over the solder pot, and a plurality of spaced nozzles disposed adjacent a lower surface, i.e., solder side, of the PC board. When actuated, the apparatus directs a solder flow through the nozzles to designated areas corresponding to the location of various components on the PC board. Each nozzle is configured and positioned to match the location and pin pattern of components to be soldered on the PC board for applying solder only to the local area, not affecting adjacent parts, and minimizing the amount of solder applied as well as limiting the temperatures to which the PC board is subjected. The apparatus may be used with either a foam or wave flux application to selected areas of the PC board.

Abstract: Two opposing hollow non-turbulent solder waves are provided which project inwards and solder is collected in a containment area. The two solder waves can have different flows and pressures, the first solder wave flooding the underside of a circuit board or other item and the second solder wave reducing a build up of solder. The soldering apparatus has a solder tank with a conveyor to convey items to a first solder wave and to a second solder wave. A solder containment area is provided between the two solder waves which receives solder from the solder waves and feeds the solder back into the solder tank.

Abstract: The selective wave soldering apparatus (101) of the present invention permits wave soldering of select components on a printed circuit board. This is accomplished by narrowing the flow of solder from the wave solder apparatus and creating the proper back pressure on two sides of the flow to form the proper height wave. The back pressure is created by an extended, angled lip (102) on one side and a trough (103) on the side opposite the lip. The trough (103) is open on top and has small openings in one end to slow the flow of molten solder from the trough (103).

Abstract: An automatic soldering method and the apparatus thereof is disclosed, wherein a transporting device progressively moves up a horizontal position of a base board as the latter is transported to be soldered in a direction from a base board entrance side to a soldered base board exit side of a base board transporting path. An elongated molten solder storing tank is arranged laterally of the base board transporting path. The solder storing tank has an elongated molten solder jetting nozzle located therein and is inclined in a horizontal plane with respect to a base board transporting direction. An operating device is provided to adjust an inclination of the base board in a vertical plane intersecting the base board transporting direction such that a distance between a lower side of the base board and a top end of the molten solder jetting nozzle is constant all through the length of the nozzle as the base board is transported past over the nozzle.

Abstract: Apparatus and method for foam fluxing and tinning the solder pads of a plurality of leadless ceramic chip packages wherein each package is held by suction on a carrier surface such that the pads are exposed to solder as the carrier is passed over a jet of solder. The devices are oriented on the carrier such that the leading edge of the devices is inclined at an angle to the direction of conveying. The conveying system includes an endless chain for passing the carrier in an endless loop through the various stations of loading, fluxing, tinning, cleaning and unloading.

Abstract: Fluxing station (34) has a flux dispenser (52) where liquid flux cascades down steps (88, 90). Circulating pump (46) draws liquid flux from a reservoir (54) below the steps and recirculates it to cascade down the steps. There is provision to add makeup flux from reservoir (38) or supply a cleaning liquid such as alcohol from reservoir (37) to clean the circulating system. A drain (62) is provided. Electrical components can be positioned with their leads on the steps so that liquid flux cascades thereover for accurately fluxing only the ends of the leads. Two or more pairs of steps, with different spacing, may be provided to accommodate components of different lengths.

Abstract: At least one chip type component is soldered to a printed circuit board by independent first and second nozzles which spout molten solder so as to form respective first and second solder waves, with the printed circuit board sequentially passed through the first and second nozzles. The first and second solder waves define therebetween a space and flow at least in a direction of movement of the printed circuit board and in a direction counter to the direction of movement of the printed circuit board, respectively. The second nozzle is disposed at a level higher than the first nozzle such that the printed circuit board is moved obliquely upwardly.

Abstract: This invention relates to an improved process for application of a metal-comprising coating to a metal-comprising surface without using a flux. The metal-comprising surface must be wettable by or become wettable upon contact with a bath of the metal-comprising coating. Application of the coating is carried out in an environment which is inert at least with respect to the coating material during the time period of its application to the metal-comprising surface, and preferably inert with respect to both the coating material and the metal-comprising surface. The inert environment temperature is sufficiently low that no damage is done to the metal-comprising surface and no damage is done to other materials adjacent to the metal-comprising surface.

Abstract: To match the soldering of an assembled printed-circuit board (13) to its assembly configuration, the circuit board (13) is brought in contact with a soldering wave (21) for a first time along a predetermined path (57, 58), and thereupon the circuit board is rotated about a vertical axis and is brought into contact, preferably with the same soldering save (21), a second time, along predetermined paths from the same direction during its motion along the paths (57, 58). The printed circuit board (13) may be rotated by an angle (.alpha.) depending on the assembly configuration relative to the direction of flow (56) of the soldering wave (21).

Abstract: A fountain-type soldering apparatus is disclosed, which comprises:an outer tank which contains molten solder;a nozzle which is immersed in said molten solder in said outer tank, said nozzle having a longitudinally-extending discharge port which extends above the surface of said molten solder and having two end panels at the opposite ends of said nozzle which form the end walls thereof, each of said end panels having a through opening formed therein;a moving body which is disposed in said discharge port and which extends for the length thereof, the opposite ends of said moving body passing loosely through said through openings in said end plates; andsupport means for supporting each end of said moving body such that said moving body can oscillate vertically therein.

Abstract: The present invention is directed to a method for soldering each of a plurality of members (40), arranged in one or more parallel rows, to a separate one of a plurality of metallized pads (42) on a substrate (10), each pad being contiguous with a corresponding member. The method is initiated by tilting the substrate so that one end of each row of members and the metallized pads contiguous therewith are at a higher elevation than the other end. A stream (80) of molten solder and a dripping stream (88) of flux droplets are directed onto the substrate into the regions where the members are contiguous with the metallized pads. Simultaneously, the substrate is displaced relative to the streams along a path (96) inclined with respect to the horizontal and parallel to the rows of members so that the members and the metallized pads are successively coated with solder and then flux.

Abstract: A system for the continuous production soldering of circuit boards and other products in which the product is heated by an independently controlled vapor phase system, and solder applied by a separately controlled application system operative to direct one or more controlled and defined streams of solder onto the product. A vessel is provided for containing a heated saturated inert vapor into which the product is introduced prior to solder application. One or more nozzles are disposed within the vessel for directing one or more streams of molten solder to the heated product. The heating and soldering operations are separately controllable and are each substantially independent of the control of the other.

Abstract: A soldering system is described in which a fluid stream is directed onto a solder board substantially immediately following the deposition of molten solder onto the boards. The impinging fluid stream is rapidly oscillated to create a plurality of different angles of impingement of the air on each area of the bottom surface of the circuit board.

Abstract: A soldering apparatus comprises a solder bath, an applicator for applying solder to a joint or the like to be soldered and a pump for pumping solder substantially continuously through the applicator. The applicator is movable vertically relative to the solder bath to solder a joint positioned above the bath.

Abstract: This is an article and process which provide the first essentially continuous high tin flow soldering method for attaching copper based fins to copper based tubing. This invention avoids sludge buildup in the reservoir and generally avoids lead carbonate formation when the heat exchanger is in service. In addition, a novel structure is produced having a braze like joint with eta phase layers adjacent to the copper based surfaces. The invention utilizes an essentially lead free, high tin solder cascade onto a preferably cool tube, generally with a limited time of contact between the liquid solder and the tube, and with a combination air quench and wipe to remove excess solder and solidify the remaining solder. Thus a braze like joint is achieved having better heat conduction and closer thermal expansion match. This finned heat exchanger tubing is generally useful for liquid to gas type heat exchangers and especially useful for hydrogen coolers for electrical generators.

Abstract: For protecting the surface of a soldering bath a covering means is used which comprises two phases (3,4), which are placed one on top of the other, are not soluble in each other and are liquid at the soldering temperature. The bottom phase (3) is produced by spreading over the top phase (4), which consists of a liquid synthetic polyalphaolefin, a powder of a chemically active component of sebacic acid and/or suberic acid which is solid at room temperature and liquid at the soldering temperature.

Abstract: A soldering apparatus has a base, and a solder tank and a nozzle arranged in tandem with the base. A partition plate is arranged in the solder tank. The partition plate, a bottom plate disposed at the bottom of the solder tank, and a lower plate covering the bottom of the solder tank define a channel communicating with a portion of the solder tank remote form the nozzle and the interior of the nozzle. A moving magnetic field generating mechanism for exerting a force toward the nozzle to a solder in the channel is arranged in the base to extend along the channel under the partition wall. That portion of the solder tank at the side of the nozzle constitutes a wide portion of the same width as that of the nozzle while the remaining portion of the solder tank constitutes a narrow portion.

Abstract: Wave soldering apparatus particularly adapted for soldering printed circuit boards which have closely packed chip components adhesively mounted on one side of the boards is described. A novel nozzle assembly is dimensioned to be mounted to the solder supply conduit of a conventional wave soldering reservoir. The nozzle assembly comprises a first nozzle which delivers a turbulent jet to the undersides of the printed circuit boards as they are conveyed over the nozzle assembly, and a second nozzle which delivers a smooth laminar wave through which the undersides of the printed circuit boards immediately subsequently pass. The turbulent jet forces solder into the restricted spaces at which chip component contact pads are located and the smooth wave completes this soldering action by building of additional solder in a manner which discourages the formation of solder "icicles" and bridging.

Abstract: Printed circuit boards bearing chip type electric parts on its underside surface and travelling along a predetermined path are soldered using first and second molten solder, successively. The first molten solder is forced to overflow from a nozzle member to form a wave of overflowing solder extending in the direction of the path of travel of the printed circuit board so that the lower side of the printed circuit board is brought into co-current contact with the upper surface of the solder wave for effecting both preheating and first soldering treatment by the first molten solder. A solder applicator is provided adjacent to and downstream of the nozzle member to effect a second soldering treatment by the second molten solder.

Abstract: An apparatus for wave soldering component leads to a conductor on a printed circuit board surface includes a fountain for forming a standing wave of hot molten solder. A pool of hot oil having a specific gravity lower than the solder floats in a depression in the surface of the solder adjacent to the standing wave. A printed circuit board whose surface is to be soldered is passed through the crest of the molten solder standing wave and then while the solder adhering to the component leads and conductor is still molten, into contact with the pool of hot oil.

Abstract: A solder or other liquid wave forming machine has a solder delivery chamber with a tapered depth profile to deliver solder uniformly from a horizontal stream to plural vertical chambers from which the upwardly flowing solder exits to form a solder wave. The wave has substantially uniform height and contour over its width. A slide valve cooperates with baffles that form the vertical chambers selectively to block flow from a prescribed number of chambers to adjust the width of the solder wave. Curved re-entry baffles direct the flow vector of the solder returning from the wave into a main solder supply tank in a horizontal direction to minimize turbulence at such surface and, thus, the formation and circulation of dross.

Abstract: The formation of dross in a molten solder bath (28) by surface agitation of the bath, and the adverse effects of dross on a solder pumping operation, are essentially eliminated by suspending a pump shaft (36) and an impeller (38) thereon for free rotation within a housing (96) in the molten solder bath so that solder in the solder bath is precluded from making any significant contact with the rotating shaft. To insure against binding between the impeller (38) and an opposed horizontal inner surface (132) of the housing (96), a small amount of solder is permitted to flow continuously between the impeller and the surface into contact with the rotating shaft (36) adjacent the impeller. The small solder flow then is exposed to the atmosphere to form a correspondingly small amount of light powdery solder dross (134).

Abstract: A solder mask (62) of special construction is mounted on each of a plurality of crystal filters (10) having continuous seams (16) defined by peripheral edges (20) of filter metal covers (14) and peripheral portions (18) of filter metal headers (12). The crystal filter-solder mask assemblies (10,62) then are passed over a solder wave (24) to solder the continuous seams (16) of the crystal filters (10) simultaneously. The crystal filters (10) are suspended on magnetic carriers (104) of an endless conveyor (106) as the filters pass over the solder wave. During the wave-soldering operation the solder masks (62) preclude solder from access to various critical areas of the crystal filters (10).

Abstract: A soldering system is described in which a freshly soldered board is heated substantially immediately following deposition of molten solder onto the board so as to maintain the freshly applied solder in molten condition, and a fluid stream is then directed onto the molten solder. Preferably, but not necessarily, the fluid, which may comprise a gas or mixture of gases, is heated prior to contacting the board. The impinging fluid stream relocates solder on, and/or blasts excess solder from the bottom of the board, and any interconnections, component leads and/or component bodies carried thereon before the solder solidifies as shorts, icicles or bridges. If desired, liquid droplets such as soldering oil may be included in the fluid stream.

Abstract: Soldering techniques, where a circuit component having a row of closely spaced leads (e.g., dual in-line packages) are to be soldered to a printed circuit board and the leads are oriented on the printed circuit board such that the row of leads is arranged parallel to the direction of motion of the printed circuit board through a wave solder pot, may effect a high incidence of soldering bridging. This bridging may form between the last few adjacent leads in the row which emerges from the solder pot. A printed circuit board is provided with an additional foil pad (or a pair of additional pads in the case of a dual in-line package) arranged in line with the row of leads. This additional foil pad tends to draw off any excess solder to reduce the solder bridging between adjacent leads during the soldering operation.

Abstract: A low-cost method of fabricating a solar absorber panel for use with a flat plate solar collector system is disclosed in which a plurality of formed elongated substantially U-shaped members are fixed in a predetermined configuration to the reverse side of a single sheet absorber member forming therewith hollow fluid passages or ducts. The fluid duct members are provided with a series of tabs which alternately protrude through spaced slits in the absorber panel such that when the tabs are folded over, a tight interlocking construction is produced. The ends of the single sheet absorber may then be folded to form inlet and outlet manifolds connecting the ends of the series of spaced ducts including closing end tabs or the manifolds may be fabricated of U-shaped tabbed members in the manner of the connecting passages. After the mechanical assembly, the entire unit is sealed as by pumping liquid solder under pressure through the unit.