Abstract: A process chamber for carrying out thermal processes in the manufacture of an electronic assembly with at least one opening for moving in and/or removing the electronic assembly; a supply of a protective gas; a controllable protection device arranged at the opening to reduce escape of the protective gas from the process chamber; and a control that can control the protection device such that, when the electronic assembly passes through the opening, an opening cross section of the opening is provided, which corresponds to the cross section of the electronic assembly.

Abstract: A purge system useful in welding applications to provide a shielding or purging gas to a weld site, preferably of a tube, pipe or construction, while also providing controlled release of an exhaust gas and pressure relief through the use of a permeable body. The purge system is also flame resistant allowing use in close proximity to the weld site. The design facilitates ease of insertion, holding and retraction in a tube, pipe or other construction.

Abstract: A bonding system for bonding a semiconductor element to a substrate is provided. The bonding system includes a substrate oxide reduction chamber configured to receive a substrate. The substrate includes a plurality of first electrically conductive structures. The substrate oxide reduction chamber is configured to receive a reducing gas to contact each of the plurality of first electrically conductive structures. The bonding system also includes a substrate oxide prevention chamber for receiving the substrate after the reducing gas contacts the plurality of first electrically conductive structures. The substrate oxide prevention chamber has an inert environment when receiving the substrate. The bonding system also includes a reducing gas delivery system for providing a reducing gas environment during bonding of a semiconductor element to the substrate.

Abstract: The method for heating a metal component to a target temperature, in which the component has a preliminary coating and is passed through a furnace that has at least four zones, which can be respectively adjusted to an individual zone temperature, wherein the component is passed successively through at least an initial heating zone, a plateau zone, a peak heating zone and an end zone and wherein the initial heating zone is adjusted to an initial heating temperature, the plateau zone is adjusted to a plateau temperature, the peak heating zone is adjusted to a peak temperature and the end zone is adjusted to the target temperature, the plateau temperature being chosen such that the temperature of the component in the plateau zone lies in a band around a melting temperature of the preliminary coating which is characterized in that the peak temperature lies by at least 100 K above the target temperature.

Abstract: A vehicle in which separation of airflow from a vehicle surface can be prevented without causing disfigurement is provided. A vehicle body is insulated from a road surface, and positive static charges accumulate on the vehicle body during propulsion. The vehicle comprises a charge control device adapted to decrease the positive potential of a separation point at which positively charged airflow flowing along a vehicle surface deviates from the vehicle surface during propulsion by applying negative ions to an inner surface of the separation point.

Abstract: Method for cooling soldered printed circuit board modules in a cooling zone of a soldering system, wherein at least one cooling gas comprising inert gas is introduced into the cooling zone, wherein the printed circuit boards are conveyed continuously from a soldering zone of the soldering system into the cooling zone, wherein the cooling gas is generated using liquid cooling gas. The method according to the invention and the device (1) according to the invention advantageously permit highly efficient cooling of printed circuit board modules after the soldering process. The cooling gas may advantageously be used for inerting the soldering system (2) after extraction from the cooling zone (15).

Abstract: Embodiments of a thermal compression bonding (TCB) process cooling manifold, a TCB process system, and a method for TCB using the cooling manifold are disclosed. In some embodiments, the cooling manifold comprises a pre-mixing chamber that is separated from a mixing chamber by a baffle. The baffle may comprise at least one concentric pattern formed through the baffle such that the primary cooling fluid in the pre-mixing chamber is substantially evenly distributed to the mixing chamber. The pre-mixing chamber may be coupled to a source of primary cooling fluid. The mixing chamber may have an input configured to accept the primary cooling fluid and an output to output the primary cooling fluid.

Abstract: An inflatable purge dam apparatus for use with pipes of different nominal pipe size (NPS) includes first and second inflatable purge bladders, and an intermediate bridge conduit. In a first aspect, the purge bladders each comprise an expandable inner purge gas retaining liner and a heat-resistant stretchable outer protective cover. The protective covers comprise a heat-resistant stretchable material that is constructed to undergo variable stretching to increase the size of the purge bladders as they are inflated with purge gas to a desired sealing pressure, thereby allowing the purge bladders to form an effective weld zone seal in pipes of different NPS. In a second aspect, an air vent conduit extends between first and second ports located proximate to a longitudinal centerline of the first purge bladder. The air vent conduit provides a vent pathway for venting air from the weld zone through the first purge bladder.

Abstract: A reflow oven includes a chamber housing including surfaces that are in contact with heated air mixed with contaminants, including flux, and a water-soluble layer selectively applied to the surfaces of the chamber housing. Embodiments of the reflow oven include an acrylic-based layer, such as an acrylic paint. In one embodiment, the acrylic paint includes a water-soluble polymer, a polymer emulsion, and water. The water-soluble polymer includes butyl benzyl phthalate. In some embodiments, the acrylic paint includes 1-10% by weight butyl benzyl phthalate, 30-55% by weight acrylic polymer emulsion, and balance water. In a certain embodiment, the acrylic paint includes 1-5% by weight butyl benzyl phthalate, 35-50% by weight acrylic poly emulsion, and balance water. Methods of treating surfaces of the reflow oven are further disclosed.

Abstract: A die attachment apparatus for attaching a semiconductor die onto a substrate having a metallic surface comprises a material dispensing station for dispensing a bonding material onto the substrate and a die attachment station for placing the semiconductor die onto the bonding material which has been dispensed onto the substrate. An activating gas generator positioned before the die attachment station introduces activated forming gas onto the substrate in order to reduce oxides on the substrate.

Abstract: This disclosure describes a method and apparatus for controlling the temperature of a welding zone for welding together pipe sections. The temperature is controlled by a flow of inert gas through the pipes. The inert gas flow is cooled and acts as a heat sink to remove heat from the weld zone thereby controlling the weld zone temperature.

Abstract: A method of forge welding includes placing at least two components for welding together, adjacent each other and with an exothermic flux mixture placed between the components. The exothermic flux mixture is heated to initiate an exothermic reaction and the faying surfaces of the two components are pressed together. The components being welded may be tubular, in particular pipes. Apparatus for the method of forge welding and exothermic flux mixtures for the method of forge welding are also provided.

Abstract: An inflatable purge dam apparatus includes first and second inflatable purge bladders defining a weld-zone therebetween. A purge gas discharge port is adapted to deliver a purge gas into the weld zone. A purge gas diffuser is in fluid communication with the gas discharge port. The purge gas diffuser is operable to diffuse the purge gas as it enters the weld zone.

Abstract: A flip chip assembly apparatus includes at least one warpage-suppressor assembly. Each warpage-suppressor assembly can include a side heater, a deformable material pad, and an actuator assembly for moving the side heater and the deformable material pad. Each side heater provides additional heat to peripheral solder balls during bonding of two substrates, thereby facilitating the reflow of the peripheral solder balls. Each deformable material pad contacts, and presses down on, a surface of one of the two substrates under bonding. The deformable material pad(s) can prevent or minimize warpage of the contacted substrate.

Abstract: Provide is an apparatus for thermal melting processes that is capable of directly cooling the process object without requiring a separate cooling plate. The apparatus for thermal melting process according to the present invention is an apparatus 1 for thermal melting process that thermally melts objects 100 including solder in an atmosphere containing carbonic acid vapor, and the hand part 4 for carrying and transferring the thermally melted process objects 100 is used as a cooling plate as well.

Abstract: In certain embodiments, a system includes a deposition system and a plasma/bonding system. The deposition system deposits a solder outwardly from a substrate of a number of substrates. The plasma/bonding system comprises a plasma system configured to plasma clean the substrate and a bonding system configured to bond the substrates. The plasma/bonding system at least reduces reoxidation of the solder. In certain embodiments, a method comprises depositing solder outwardly from a substrate, removing metal oxide from the substrate, and depositing a capping layer outwardly from the substrate to at least reduce reoxidation of the solder.

Abstract: A reflow oven includes a chamber housing including surfaces that are in contact with heated air mixed with contaminants, including flux, and a water-soluble layer selectively applied to the surfaces of the chamber housing. Embodiments of the reflow oven include an acrylic-based layer, such as an acrylic paint. In one embodiment, the acrylic paint includes a water-soluble polymer, a polymer emulsion, and water. The water-soluble polymer includes butyl benzyl phthalate. In some embodiments, the acrylic paint includes 1-10% by weight butyl benzyl phthalate, 30-55% by weight acrylic polymer emulsion, and balance water. In a certain embodiment, the acrylic paint includes 1-5% by weight butyl benzyl phthalate, 35-50% by weight acrylic poly emulsion, and balance water. Methods of treating surfaces of the reflow oven are further disclosed.

Abstract: Disclosed herein is a solder ball supplying apparatus including: a cartridge formed in a box shape and having a plurality of solder balls embedded therein; a vibration unit coupled to a lower portion of the cartridge; and a metal mask coupled integrally with a lower portion of the vibration unit and having a plurality of holes formed over the entire surface thereof.

Abstract: An ultrasonic bonding system is provided. The system includes: a) a bond head assembly carrying an ultrasonic bonding tool; b) a conductive material supply; c) a conductive material feeding system for guiding a length of the conductive material supply to a position proximate the ultrasonic bonding tool; and d) a vapor generation system for supplying a vapor proximate the ultrasonic bonding tool, the vapor including a carrier gas and a lubricating vapor.

Abstract: A purge dam for retaining a purge gas around a weld zone includes a purge dam structure configured to substantially obstruct an air passage leading to the weld zone. The purge dam includes a main blocking portion configured to substantially block the air passage. The purge dam structure further includes a wall portion configured to engage the air passage for attachment. Adhesive can be optionally provided on the wall portion to facilitate the air passage attachment. Some or all of the purge dam structure may be formed as a multi-layer structure that includes one or more layers of water degradable paper and one or more layers of water degradable polymer. If present, the optional adhesive may be applied to the water degradable polymer layer. The purge dam may be installed by placing the purge dam in the air passage and adhering the wall portion thereto.

Abstract: A water-degradable purge dam apparatus for purging a weld zone of a pipe assembly comprising first and second pipes having respective first and second ends. A first purge dam subassembly adapted for installation in the first pipe end has a hollow first conduit defining a first air flow pathway. A second purge dam subassembly adapted for installation in the second pipe end has a hollow second conduit defining a second air flow pathway. Each subassembly has one or more air flow blocking plates. A hollow third conduit, defining a third air flow pathway, is interconnectable to the first and second conduits members to span the weld zone. The first, second and third air flow pathways allow pressurized air within the pipes to pass through the purge dam apparatus and the weld zone in a sequestered by-pass zone defined by the first, second and third conduits.

Abstract: A flip chip assembly apparatus includes at least one warpage-suppressor assembly. Each warpage-suppressor assembly can include a side heater, a deformable material pad, and an actuator assembly for moving the side heater and the deformable material pad. Each side heater provides additional heat to peripheral solder balls during bonding of two substrates, thereby facilitating the reflow of the peripheral solder balls. Each deformable material pad contacts, and presses down on, a surface of one of the two substrates under bonding. The deformable material pad(s) can prevent or minimize warpage of the contacted substrate.

Abstract: A reflow oven used to join electronic components to a substrate includes a chamber housing having surfaces that are in contact with heated air mixed with contaminants, including flux, and an intermediate layer selectively applied to the surfaces of the chamber housing. The reflow oven may include fabricating the intermediate layer with a foam material, including foaming polymers, e.g., epoxy, polyurethane, polyester, and silicone, or a non-foam material, including non-foaming polymers, e.g., polytetrafluoroethylene and polyimide. A method of treating surfaces of a reflow oven exposed to contaminants, including flux, is further disclosed.

Abstract: A water-degradable welding purge dam for purging a weld zone of a pipe assembly comprising first and second pipes having respective first and second ends to be welded together at a root gap. The purge dam includes a blocking plate comprising one or more plate members. The one or more plate members include a friction plate member having a plurality of flexible members on its periphery adapted to flexibly engage an inside wall of one of the first or second pipe ends in a self-retaining manner. The purge dam comprises one or more water degradable materials so that it can be flushed from the pipe assembly following welding.

Abstract: Provided are: a method for brazing an aluminum alloy, which is characterized in that brazing is carried out by heating an aluminum brazing sheet without using flux in a furnace that is in an argon gas-containing atmosphere, said aluminum brazing sheet comprising a core material that is composed of aluminum or an aluminum alloy and a brazing filler material that is composed of an aluminum alloy and clad on one surface or both surfaces of the core material, and said core material and/or said brazing filler material containing Mg; and a brazing apparatus which is used in the method for brazing an aluminum alloy. The brazing method has good and stable brazing properties and is applicable in industrial practice.

Abstract: In the present invention, when a power module is soldered to a heatsink, steam which is temperature-adjusted to at least the melting point of a solder is introduced from a steam generating tank into the flow path provided in the heatsink, the heatsink is heated and the solder is melted. Inert gas is introduced into a soldering tank from another route so as not to mix with the steam supplied to the heatsink. Voids in the solder are reduced and condensed by pressure regulation and as a result the negative impact of voids is eliminated.

Abstract: A reflow apparatus, where formic acid is used for cleaning a surface of a solder electrode on a processing target, is disclosed. The reflow apparatus includes a processing chamber, a formic acid introduction mechanism for supplying an atmosphere gas containing formic acid to the processing chamber, and a shielding member that is made of a material having corrosion resistance against formic acid. The shielding member is arranged between a reflow processing section of the processing chamber and an inner wall of the processing chamber. In place of or in addition to the shielding member, the reflow apparatus may include a heater for decomposing residual formic acid.

Abstract: A reflow soldering system wherein a heating oven is provided with a contact heating unit which has a transport rail and a top heat transfer heater, and with a hot gas blowing heating unit, the transport rail and top heat transfer heater are respectively provided with heaters which heat the outer edge part of the printed circuit board, and the transport rail or top heat transfer heater moves in an up-down direction so that the transport rail and top heat transfer heater clamp and heat the outer edge part of the printed circuit board.

Abstract: Described herein is an apparatus and method for providing an inerting gas during the application of soldering to a work piece. In one aspect, there is provided an enclosure for providing an inerting gas into an atmosphere above a solder reservoir during soldering of a work piece comprising: a tube in fluid communication with an inerting gas source wherein the tube comprises one or more openings for the flow of the inerting gas therethrough, a base wherein the tube resides in therein and comprises an interior volume, a neck comprising an opening and an interior volume in fluid communication with the interior volume of the base, and a cap proximal to the opening wherein the inerting gas source travels through the tube into the interior volume and into the atmosphere through the opening defined by the neck and cap.

Abstract: The invention relates to a device for supplying inert gas in order to protect the surface of a solder bath in a wave soldering installation and the components to be soldered against oxidation. Wave soldering installations form solder waves over which parts to be soldered are transported. The parts to be soldered are generally electronic printed circuit boards which have electronic components soldered onto their undersides by the solder wave making contact with the printed circuit board.

Abstract: A purge plug for welding applications is provided that can be interchangeably used to seal tubing, pipes, or the like of various diameter or cross-sectional area. The purge plug has a central body with a male connector and a diffuser disposed on the end portions. The purge plug also includes one or more flexible seals annularly disposed around the central body. In some implementations, the diameter of the flexible seals is slightly larger than the diameter of the tubing or pipe. When the purge plug is inserted into the tubing or pipe, the resiliency of the seal allow the seal to expand mechanically and flex against the inner walls of the tubing, thus sealingly engage with the inner walls.

Abstract: Reflow soldering apparatus comprising a vapour chamber in communication with a reservoir of heat transfer fluid such that a volume of vaporised heat transfer fluid is created and held in the vapour chamber by heating of the heat transfer fluid. A heating chamber is provided for receiving a board and a transportation mechanism is provided to transport vapour, and condensate formed from the vapour, from the volume of vaporised heat transfer fluid to the heating chamber. The transported vapour and condensate applies heat to the heating chamber for the reflow soldering process.

Abstract: A brazing system for brazing component members of a workpiece has a brazing chamber an inside of which is made a heating space of a volume corresponding to the workpiece, a radiant heating means provided with a plurality of heating sources which are positioned so as to correspond to a plurality of regions into which two facing surfaces of the workpiece are respectively divided, a convection heating means for circulating a heated inert gas to the heating space so as to heat the workpiece, and a control means for controlling the operation of the heating sources and the circulation of the inert gas. Each heating source is independently controlled by the control means, and the convection heating means circulates the inert gas so as to reduce a temperature difference of the workpiece caused by the heating sources.

Abstract: A reflow apparatus, where formic acid is used for cleaning a surface of a solder electrode on a processing target, is disclosed. The reflow apparatus includes a processing chamber, a formic acid introduction mechanism for supplying an atmosphere gas containing formic acid to the processing chamber, and a shielding member that is made of a material having corrosion resistance against formic acid. The shielding member is arranged between a reflow processing section of the processing chamber and an inner wall of the processing chamber. In place of or in addition to the shielding member, the reflow apparatus may include a heater for decomposing residual formic acid.

Abstract: The invention relates to a device and method for selective soldering, including at least one nozzle and a soldering channel surrounded by a vertically moveable hood, which immerses in a soldering bath or which is sealed against a surface of the soldering bath. The hood includes a passage for each nozzle, at least one gas feeding device for providing protective and/or active gas underneath the hood, and flow plates which are attached to the hood to extend substantially downward in the direction of the soldering bath from the hood.

Abstract: A novel inert environment enclosure includes an object inlet where production objects enter the enclosure and an object outlet where the production objects exit. At least one of the object inlet and the object outlet includes both a top-side flow obstructer and a bottom-side flow obstructer for preventing air from entering the enclosure. In a particular embodiment, the top-side flow obstructer and the bottom-side flow obstructer each include a curtain constructed from a flexible fabric having a plurality of individual adjacent fingers. In another particular embodiment, the inert environment enclosure is a nitrogen hood that houses a wave soldering machine. A inert gas nozzle is mounted at or near the inlet and/or the outlet. The inert environment enclosure maintains a positive pressure with respect to the surrounding environment when production objects are passed through the enclosure.

Abstract: A device for assembling components having metal bonding pads includes plates that can move relative to each other, bearing metal components respectively and leaving between them a flat chamber surrounding the components when the latter are in contact with each other. The flat chambers can be saturated with deoxidizing gaseous fluid.

Abstract: Apparatus and method for purging atmospheric air from a chamber with a gas including means for generating a substantially non-turbulent, laminar flow front of the gas into the chamber with minimal turbulence to displace the atmospheric air in the chamber, the chamber having exhaust means associated therewith to permit the displaced atmospheric air to exit the chamber. The chamber is preferably a welding chamber and the gas is preferably argon.

Abstract: There is provided a bonding apparatus for holding a semiconductor chip by using a bonding head and bonding the semiconductor chip onto a substrate. The bonding head includes: a holding part for holding the semiconductor chip; gas exhausting means for surrounding the holding part and exhausting gas toward the holding part; and an elevator means for lifting down/up the gas exhausting means to a lift-down state, in which at least a portion of the gas exhausting means protrudes downward from the bottom face of the holding part, and a lift-up state, in which any portion of the gas exhausting means does not protrude downward from the bottom face of the holding part. When the bonding apparatus holds and conveys the semiconductor chip by using the bonding head, the bonding apparatus brings the gas exhausting means to the lift-down state and exhausts the gas toward the semiconductor chip.

Abstract: Described herein is an apparatus and method for providing an inerting gas during the application of soldering to a work piece. In one aspect, there is provided an apparatus that is placed atop of a solder reservoir and comprises a plurality of porous tubes that are in fluid communication with an inerting gas. In another aspect, there is provided a method for providing an inerting gas to a wave soldering apparatus comprising the steps of, among other things, placing an apparatus atop at least one edge of the solder reservoir wherein the apparatus comprises a plurality of tubes comprising one or more openings in fluid communication with an inerting gas source. In a further aspect, at least one of the tubes comprises a non-stick coating or is comprised of a porous non-stick material such as a sleeve.

Abstract: This disclosure describes a method and apparatus for controlling the temperature of a welding zone for welding together pipe sections. The temperature is controlled by a flow of inert gas through the pipes. The inert gas flow is cooled and acts as a heat sink to remove heat from the weld zone thereby controlling the weld zone temperature.

Abstract: A main body of an apparatus for delivering shielding gas during wire bonding of an electronic device has a through-hole in the main body which is sized for allowing a capillary tip of a bonding tool to be insertable through the main body when performing wire bonding. At least one gas outlet located on a bottom surface of the main body adjacent to the through-hole is operative to direct an inert gas in a direction towards the electronic device. At least one gas inlet in the main body is operative to supply the inert gas to the through-hole and to the gas outlet.

Abstract: A reflow oven chamber assembly that is configured to be installed within a reflow oven chamber of a reflow oven includes a chamber housing disposed within the reflow oven chamber, one or more heating elements disposed in the chamber housing, and one or more compression box assemblies disposed in the chamber housing. The compression box assembly includes a compression box housing having an intake port located adjacent the heating element, an intake duct disposed in the compression box, and a diffuser plate disposed above the intake duct. The intake duct has an inlet opening in fluid communication with the intake port of the compression box housing and an outlet opening. The compression box assembly is configured to draw heated air into the compression box housing from the reflow oven chamber through the intake port and into the inlet opening of the intake duct and exhaust air out of the outlet opening of the intake duct to the diffuser plate.

Abstract: A main body of an apparatus for delivering shielding gas during wire bonding of an electronic device has a through-hole in the main body which is sized for allowing a capillary tip of a bonding tool to be insertable through the main body when performing wire bonding. At least one gas outlet located on a bottom surface of the main body adjacent to the through-hole is operative to direct an inert gas in a direction towards the electronic device. At least one gas inlet in the main body is operative to supply the inert gas to the through-hole and to the gas outlet.

Abstract: A novel inert environment enclosure includes an object inlet where production objects enter the enclosure and an object outlet where the production objects exit. At least one of the object inlet and the object outlet includes both a top-side flow obstructer and a bottom-side flow obstructer for preventing air from entering the enclosure. In a particular embodiment, the top-side flow obstructer and the bottom-side flow obstructer each include a curtain constructed from a flexible fabric having a plurality of individual adjacent fingers. In another particular embodiment, the inert environment enclosure is a nitrogen hood that houses a wave soldering machine. A inert gas nozzle is mounted at or near the inlet and/or the outlet. The inert environment enclosure maintains a positive pressure with respect to the surrounding environment when production objects are passed through the enclosure.

Abstract: A novel inert environment enclosure includes an object inlet where production objects enter the enclosure and an object outlet where the production objects exit. At least one of the object inlet and the object outlet includes both a top-side flow obstructer and a bottom-side flow obstructer for preventing air from entering the enclosure. In a particular embodiment, the top-side flow obstructer and the bottom-side flow obstructer each include a curtain constructed from a flexible fabric having a plurality of individual adjacent fingers. In another particular embodiment, the inert environment enclosure is a nitrogen hood that houses a wave soldering machine. A inert gas nozzle is mounted at or near the inlet and/or the outlet. The inert environment enclosure maintains a positive pressure with respect to the surrounding environment when production objects are passed through the enclosure.

Abstract: A wire-bonding machine includes a main body, a fixture block, a mounting block, a gas supply tube, a cover-gas supply device, a capillary tool and an electrode. The fixture block is provided with a chamber defined therein and a central bore formed at one side wall of the fixture block communicating the chamber. The mounting block has a fixture member extending upwards for being mounted to the main body and an electrode clamping member extending downwards into the chamber of the fixture block. The cover-gas supply device has a continuous gas passage and an orifice defined therein. The protection gas flows in a steady flow field around the orifice in the continuous gas passage of the cover-gas supply device so as to result in better ball formation during the ball formation and ball-bonding process.

Abstract: The instant invention relates to a device for wave soldering workpieces, encompassing means for moving the workpiece, which is to be soldered, along a specific path across at least one solder wave generated above a solder reservoir, with a protective and/or active gas atmosphere of a first composition being located above the solder reservoir so as to exclude oxygen and with means for introducing the protective and/or active gas as well as an enclosure being provided, with the enclosure being configured in such a manner that it encloses at least the essential parts of a solder zone.

Abstract: A device for purging gas comprises a conduit assembly defining an interior volume. The conduit assembly comprises a first conduit portion having an open first end and an open second end and a second conduit portion having an open first end and a closed second end. The open second end of the first conduit portion is disposed proximate to the open first end of the second conduit portion to define a weld region. The device further comprises a supply element supplying a gas to the interior volume at a substantially constant rate and a vent element venting the gas from the interior volume at a rate that maintains the gas in the interior volume within a pressure range suitable to hold a weld bead in the weld region in equilibrium during formation of a weld to join the first conduit portion and the second conduit portion.

Abstract: A reflow furnace using a conventional heater for blowing hot air has difficulty in reducing ?t and in stabilizing the oxygen concentration at a low level. In addition, it is difficult to uniformly discharge hot air from the discharge holes in a perforated plate of a conventional heater for blowing hot air. In a reflow furnace according to the present invention, the total area per unit area of discharge holes formed in a perforated plate in a heater for blowing hot air installed in a main heating zone is 1.5-5 times the total area per unit area of the discharge holes formed in a perforated plate of a heater for blowing hot air installed in a preheating zone. A heater for blowing hot air has a body divided into three chambers by partitions.