FR2564763A1 - APPARATUS AND METHOD FOR WELDING, IN PARTICULAR FOR PRINTED CIRCUITS - Google Patents

Abstract

THIS APPARATUS IS OF THE TYPE INCLUDING AN ENCLOSURE 10 DELIMING A CHAMBER FOR STEAM PHASE, MEANS 12, 14 ALLOWING TO PROVIDE A SATURATED INERT STEAM IN THIS CHAMBER, AT A TEMPERATURE ALLOWING TO HEAT A PRODUCT 27 BEFORE APPLYING WELDING, MEANS 22 ENABLING THIS PRODUCT TO BE TRANSPORTED TO AND OUT OF THE SAID CHAMBER. THE PROBLEM CONSISTS OF REMOVING THE DISADVANTAGES OF THE PREVIOUS WAVES OF WELDING AND DRIVE WELDING. FOLLOWING THE INVENTION, THE APPARATUS IS CHARACTERIZED IN THAT IT FURTHER INCLUDES A SOURCE OF WELDING 30 AND AT LEAST ONE NOZZLE 24, 26 WHICH IS CONNECTED TO THIS SOURCE 30 AND IS PROVIDED INSIDE THE SAID CHAMBER, THIS CHAMBER. NOZZLE SERVING TO DIRECT A JET OF WELDING ON THE HEATED PRODUCT 27. THE INVENTION FINDS AN ADVANTAGEOUS APPLICATION IN THE WELDING OF PRINTED CIRCUIT BOARDS.

Description

The present invention relates to welding apparatus, allowing more

  particularly the vapor phase heating of a product and the separate application of solder to the product thus heated, of the type comprising an enclosure defining a vapor phase chamber, means for supplying a saturated inert vapor in this chamber, at a temperature of temperature to heat a product before the application of solder

  and means for conveying this product into said chamber

  and out of it. The invention also relates to the methods of

corresponding age.

  Welding is widely used for manufacturing

  many different products, especially products from the tech-

  electronics, and in particular printed circuit boards. For the mass production of such printed circuit boards and similar products, solder wave apparatuses have been widely used. These devices comprise a molten soldering tank which is pumped in the form of a wave, the circuit board being carried in contact with this wave in order to cause the wetting of the desired zones of this card. The solder wave serves as a heat source for heating the circuit board, and also a solder source for the solder application on the board. Such a welding wave apparatus is relatively complex and it

  must be carefully designed and constructed to provide a wave of

  a hard-wearing machine having the proper dimensions and characteristics, providing the desired heating and soldering application to the particular products being treated. The length of the wave must be

  sufficient to provide sufficient contact time to heat the sur-

  face soldering. This design of the wave is critical in connection with the nature of the product and the speed of it through the wave. It exists

  indeed a maximum speed beyond which we can not transport

  ter a product through a particular weld wave while maintaining

  enough heat, because for higher speeds the wave should be redrawn, which would require a whole new design

of the device.

  The height of the weld wave is also a factor

  a critical factor and may be a factor limiting the size of

  to be treated. For example, in a printed circuit board in which through-conductor components are inserted, the length of these conductors can not be greater than the depth -2 of the solder wave, because in otherwise, the card could not be housed in a weld wave apparatus determined because of the obstacle that the elongated conductors of the components would encounter. In this way, it is necessary to monitor the assembly of the components on a circuit board, to ensure that the length

  conductors is less than the depth of the weld wave

  both in a particular welding apparatus to use. Since the solder wave serves both as a solder source and as a heating source, the dynamics of the whole becomes complex when designing a

  welding wave apparatus for particular applications. In addition

  same dynamic makes it difficult to change the characteristics of

  ticks the weld wave in order to adapt it to different types of products.

  Another type of series welding apparatus is the drive type in which a welding reservoir is provided in which a product is dipped and immersed, partially or totally, in order to apply this weld to this product. Here again, the molten solder serves both as a source of heat for heating the product to a temperature

  welding, and solder applicator.

  US Reissue Patent No. Re 30,399 discloses a wave flow welding apparatus in which the weld wave is created at the base of an enclosure containing saturated and heated steam. The

  product is transported through the steam chamber and is heated

  by immersion in the vapor phase, being welded by passing through

  the welding wave. The weld is applied in an anaerobic atmosphere

  which is provided by the vapor phase, but placing the weld wave apparatus in the chamber provides a poor improvement

  the control and performance of the welding operation. The cri-

  the relative complexity of the weld wave remain the same

  as indicated above, while the presence of the weld wave in the

  interior of heated steam does not alter critical considerations

  of the design of the wave apparatus.

  An article entitled "A New Welding Process" by WR George, Brazing & Soldering No. 5, Fall 1983, presents a drag welding apparatus in which the product is initially placed inside an Inert vapor phase. and heated, before immerslon

in the molten solder bath.

  U.S. Patent No. 3,825,164 discloses a welding apparatus having a reservoir which contains a molten weld pool which is

  located at its base and is covered by a bath of liquid

  positive welding spray being disposed within this flux bath. A flux circuit board is placed vertically in this flux bath for fluxing and preheating purposes, and solder is sprayed onto one or both surfaces of the circuit board.

  printed circuit board at the time when this card is removed from the tank.

  Therefore, given the state of the art

  The object of the invention is an apparatus of the aforementioned type, characterized in that it further comprises a welding source and at least one nozzle which is connected to this source and is disposed inside said chamber,

  this nozzle serving to direct a weld jet on the heated product.

  fe. The invention also relates to a corresponding method.

  Thus, the invention provides an apparatus for welding circuit boards and other products in which the product is located.

  heated with an independently controlled vapor phase system.

  te, while the weld is applied using an applicator device

  nozzle which is controlled separately and is used to

  nis and controlled welding on the product. It is foreseen a speaker

  to include a saturated and heated inert vapor, into which the product is introduced before the application of solder and by means of which the product is heated up to the welding temperature. Inside this chamber is one or more nozzles used to direct a

  or several weld jets melted on the heated product, the weld

  which is retained by the areas of the surfaces of the product on which the weld must adhere. Thus, in the case of a circuit board, the solder adheres to the conductive paths of the circuit, to the metallized holes from one side to the other which may be present in this circuit board, and to the conductors or bonding pads of the components. who are assembled on the

  card or inserted through it.

  The heating of the product is essentially provided by

  the heated vapor phase atmosphere inside the

  surrounded, while establishing and controlling this atmosphere of

  steam are separately supplied by the vapor phase apparatus. The applicable

  welding cation is carried out by the applicator nozzles which, with

  the welding pump and the associated welding source, provide, for

  independent market, the desired weld jets for the particular product

  re. In this way, the heating of the product and the application of solder to 4 - these constitute operations which are controlled separately, and these operations are substantially independent of each other. The product can be introduced into the treatment chamber and extracted in any suitable manner for the application in question. Thus, typically, for a continuous production process, the product is carried on a conveyor into the treatment chamber, for heating and welding application, and is then carried by this

  carrier out of this enclosure.

  Other features and advantages of the invention

  out of the following description, as non-limiting examples

  and with reference to the appended drawings in which: FIG. I is a schematic elevational view of a welding apparatus according to the present invention;

  - fig. 2 is a schematic elevational view of a vault

  the embodiment of the apparatus of FIG. 1, having a single nozzle disposed below the product; - fig. 3 is a schematic view in elevation of another

  variant embodiment of the apparatus of FIG. 1, comprising a single nozzle

that arranged above the product;

  - fig. 4 is a schematic elevational view of the apparatus

  in a preferred detailed embodiment; - fig. 5 is a top view and partially broken away from the apparatus of FIG. 4; - fig. 6 is a perspective view and broken away

  partial of a set of welding nozzles.

  Fig. 1 represents a preferred embodiment of a

  welding apparatus according to the invention, this embodiment being particularly suitable for

  particularly to the welding of electronic circuit boards. A closed enclosure 10 defines an interior vapor phase chamber in which there is provided an inert saturated vapor zone at a predetermined elevated temperature for heating a product to be welded. Heating members 12 are arranged at the bottom of the enclosure 10 and they serve to heat a vapor phase liquid 14, for example Fluorinert FC-70, to a temperature sufficient to supply the interior of the chamber

  a saturated and heated vapor of this liquid. Cooling coils

  16 may be placed along the walls of the enclosure, in one

  location which delimits the upper part of the steam zone

  inside the room. Products such as circuit boards 27 are carried within the vapor phase chamber via an inlet chute 18, and out of this chamber via a chute. 20, each chute extending outwardly from opposite side walls of the enclosure 10. A conveyor 22 extends through this inlet chute 18, the inner chamber of

  enclosure 10 and outlet channel 20, and serves to

  to see or transport the circuit boards into and out of the vapor phase chamber. This carrier can have any suitable form that can receive the particular product to be treated. Thus, for circuit boards, this carrier may include frames to maintain the edges of the cards leaving the surfaces thereof exposed for welding. A pair of welding nozzles 24 and

  26 is located in the vapor phase chamber, each in one

  placement for applying a weld jet to the respective opposing surfaces of the circuit boards that are transported past these nozzles along the path of product movement within the chamber. A soldering pump 28 is disposed inside the enclosure 10, in a bowl 30 which contains molten solder, this pump making it possible to supply solder to the nozzles 24 and 26. The bowl 30 collects the solder excess that drips or drips cards after the application of welding from the nozzles. This bowl also serves as a source or welding supply for the pump 28 and the nozzles. In

  Alternatively, a separate weld source can be provided. As an alternative

  Alternatively, the solder pump may be disposed externally to the enclosure.

  The configuration of the inlet and outlet chutes is preferably provided in combination with that of the enclosure to reduce

  a minimum of the external vapor flow from this chamber to the atmosphere.

  phere. This configuration may be as disclosed in US Pat. No. 4,389,797 in the name of the present applicant. However, the use of the present invention is not limited to such input chutes

  and exit, since many different forms can be foreseen.

  fent product input to the enclosure and output out of that-

  ci, adaptable to particular product configurations and specific operating requirements. For continuous treatment,

  it is preferable to have a gear with continuous traverse, or sensitive-

  continuously in which the product can be continuously conveyed through this apparatus for welding operations. The inlet and outlet chutes 18 and 20 may be placed in a substantially horizontal arrangement, or they may be inclined upward or downward to provide a desired transport path and realize the a desired minimum for the loss of steam from the chutes to the atmosphere. The heating of a product which enters the chamber of the enclosure, and the application of welding on the product thus heated, are controllable separately and the control of each is substantially independent of that of the other. The product that enters the chamber is heated by the vapor phase atmosphere that is inside this chamber. Establishment and control of this atmosphere of

  heated vapor are provided by the vapor phase apparatus which

  takes the heating elements 12 and the vapor phase liquid 14, as well as the associated setting of the heating elements. The welding application is carried out by the applicator nozzles 24 and 26 as well as by the source 30 and the pump 28 associated therewith, these nozzles being constructed and adjusted so as to provide the desired weld jets intended for the

  product which, before the application of welding, was heated to a temperature

  desired by the vapor phase apparatus of the assembly.

  If you only have to deal with one side of the circuit boards

  27, the apparatus can be realized in practice with a single lower nozzle.

  26, as shown in FIG. 2, or with only one upper nozzle 24,

as shown in fig. 3.

  A practical implementation typical of the apparatus of FIG. 1 is shown in FIGS. 4 and 5. There is provided a pair of conveyor chains 30 and 32 to which frames 34 are coupled.

  spaces along these chalnes and which serve to retain the cir-

  Each of these frames 34 is coupled at its forward end, by means of a coupling 35, to the drive chains 30 and 32, and includes lateral elements or shoes 36 which slide along guide surfaces 38 provided inside the enclosure 10. These guide surfaces located inside the enclosure, follow a downward path, represented by the reference 40, at the inlet portion of the enclosure, then they follow through this enclosure a uniform path upwardly which is substantially collinear with the outlet channel 20. It is provided inside the enclosure , and for the respective chains 30 and 32, a pair of return wheels 42 and 44 which change the direction of movement 7 - of these chains, as shown. Once a frame and the circuit board that it has entered into the enclosure, this frame and this circuit board follow the path of the guide surfaces 38 and adopt an upwardly inclined orientation, as shown in FIG. 4, for linear upward movement through the processing chamber.

  ment. Thanks to these means, the circuit board is transported following

  in a uniform orientation and past the welding nozzles, so that there can be maintained between the board surfaces and the facing nozzles a desired relative arrangement which is located within the the shortest suitable speaker length, in order to minimize the time during which the circuit board is subjected to the high temperatures of the zone

  treatment that is inside the enclosure.

  Above the conveyor there is disposed a pair of downward holding plates 64 which resiliently urge the lateral pads 36 of the carrier frame into contact with the guide surfaces 38, these plates holding the frame and the card. circuit that it contains applied down against these guide surfaces. The circuit board is thus held in a precise, guided position and orientation along the path in front of it.

welding nozzles.

  These welding nozzles 24 and 26 are provided on the respective sides of the card which is transported together, on either side of the path of movement, and each nozzle is adjustable with respect to the angular orientation of its orifice. relative to the circuit board, as well as with respect to the offset or spacing of this nozzle relative to the facing surfaces of the card. Typically, these nozzles are angularly adjustable over a range of 45 on either side of an axis perpendicular to the surface of the card, and they are adjustable in offset from the card surfaces, in a area from 0.64 to 2.54 cm. The lower nozzle 26 is shown in a more

  detailed in fig. 6 on which we can see that it includes a tuition

  substantially cylindrical and elongate bole 50 having, according to its length,

  A straight elongate orifice 52 is provided, the length of which is sufficient to provide a weld jet across the width of the circuit board. This piece 50 has a lip 54 which is adjustable relative to a lip 56 so as to constitute an adjustable orifice. Typically, this orifice has an opening in the range of 0.254 to 0.762 mm. This same cylindrical part 50 can be rotated about its axis so as to make an angular adjustment of the orifice 52 according to the desired angle of incidence of the weld jet applied to the surface opposite the card. A

  linkage 58 is coupled to the part 50 for the purpose of adjusting the

  ci up and down, which allows to choose the distance between

  the nozzle and the surface facing the map. The upper nozzle 24 is

  glable in an analogous manner both offset from the surface facing the map in angular orientation. The molten solder is

  pumped to the nozzles via piping 60 which is

  coupled to a supply manifold 62 which is itself connected to the bowl

or melted solder source.

  Each of the nozzles is adjustable to have an angular orientation that can be selected for that nozzle relative to the

  the surface opposite the map, and in order to choose the interval or

  tance existing between this nozzle and this surface facing the card. The possibility of angular adjustment of each nozzle makes it possible to give a given angle of incidence to the incident weld jet, which may be normal to the surface of the card or to make a certain angle with the direction of

  moving the map in the same direction or in the opposite direction. We determine

  mine the angular orientation of each nozzle as well as the distance between this nozzle and the surface of the card so that we obtain the desired amount of welding and the desired profile for the weld jet, in correspondence with the product particular to be treated. Welding jets

  are controlled separately, so that the application can be

  desired cation of welding. Since before welding, the product was heated up to the soldering temperature using the

  the vapor phase inside the enclosure, the spray nozzles

  soldering need only be controlled to provide the proper application of welding, and not to heat

the product.

  The device is usable for soldering a wide variety of circuit board types. This is how the device can be used for so-called bare cards which are printed circuit boards presenting

  on one or both of the circuit layouts, without any

  on these surfaces, these cards may include holes through them.

  across the board to connect circuit layouts. The apparatus may also be used for circuit boards containing on one or both of the surface mount components, conductor components traversing the board from one side or a mixture of components.

  surface mounting and through conductors. You can use the appa-

  corresponding to the embodiment shown, with one or other of the

  welding nozzles, or both, in service for a particular cycle of

  ment. In some cases, it is necessary to apply the solder only on a single surface of the board, in which case the other welding nozzle can be deactivated by suitably cutting the solder supply of

this nozzle.

  It is also possible to use the apparatus for the application of solder jets using a nozzle and on a single card surface, with

  a re-flow welding provided on the opposite surface of this card.

  In some types of circuit boards, it is preferable to attach components to a board surface using a re-flow welding technique, such as applying solder paste, for example.

  on the map, and then heat the map so as to provoke

  to re-flow this solder paste to form a bond between

  the associated component and the conductive areas of the map surface.

  Such rewind welding can be performed in a known manner and using the present apparatus, by introducing the circuit board into the heated saturated vapor in the enclosure. We

  can weld the opposite surface of the board with a weld jet

  coming from the corresponding nozzle. Thus, the present apparatus is universal and serves to provide both a weld jet and a possibility of soldering by re-flow, this inside a single device, all in

  the atmosphere of the heated vapor phase.

  Typically, the atmosphere of the vapor phase in chamber 10 is brought to a temperature in the range of 213 to 232 ° C. Also typically, the welding source is maintained in the same atmosphere. temperature range. Melt is also maintained in the molten state which is in the bowl 30, using the heated atmosphere contained in the enclosure. Alternatively, separate heating means may be provided in or around the bowl to maintain the weld at the desired temperature. The atmosphere of the vapor phase is therefore at a temperature sufficient to heat the circuit boards to the soldering temperature, so that prior to the application of the solder jet using the welding nozzles, the product is already at this welding temperature. We define the weld jet of each nozzle taking into account the viscosity of the weld weld,

- 10 -

  the pressure supplied by the pump 28 and the dimensions of the orifice of the nozzle, so that one obtains the desired configuration for the jet so that the incidence of welding on the card is suitable. We move

  the product through the apparatus at a speed sufficient to obtain

  keep the board warm from the vapor phase atmosphere

  inside the enclosure 10, as well as an application

  venable of welding on the product thus heated. In a typical practical embodiment, the circuit boards are moved through the enclosure to

  a speed of 1.20 to 3.05 meters per minute.

- 11 -

R EV IN DI C A T I 0 N S

  1. Welding apparatus, of the type comprising an enclosure

  (10) defining a vapor phase chamber, means (12, 14)

  to provide saturated inert vapor in this chamber at a

  structure for heating a product (27) before the application of solder, and means (22) for transporting said product into and out of said chamber, characterized in that it further comprises a source of welding (30) and at least one nozzle (24, 26) which is connected to this source (30) and is disposed inside said chamber,

  this nozzle serving to direct a weld jet on the heated product.

fairy (27).

  2. Apparatus according to claim 1, characterized in that the welding is continuous, in that the means for supplying the steam

  are means (12, 14) for producing an inert saturated vapor and heating

  in that the nozzle (24, 26) faces the path of the product (27) through

  to the chamber, and in that this nozzle directs the jet of solder during

  that the product is transported through this chamber.

  3. Apparatus according to claim 1, characterized in that it allows to weld circuit boards (27), in that the steam supply means (12, 14) provide a saturated and heated inert vapor, in that it carries the circuit boards (27) up to the welding temperature, before the soldering application, in that the transport means (22) carries the circuit boards through the vapor phase chamber, and in that the nozzle (24, 26) directs a weld jet

  melted on the heated circuit boards (27).

  4. Apparatus according to claim 1, characterized in that the steam supply means (12, 14) provide a saturated and heated inert vapor, and this at a controlled temperature, the transport means (22) carries the product (27). ) through the vapor phase chamber, the welding source (30) is a molten solder source, and there is provided one or more nozzles (24, 26) directing respective streams of molten solder on the heated product (27) .

  5. Apparatus according to claim 4, characterized in that the welding source (30) is arranged inside the phase chamber

steam.

  6. Apparatus according to claim 4, characterized in that

  the enclosure (10) comprises an inlet chute (18) and a chute of

  tie (20) each extending outwardly from side walls

- 12 -

  opposing this enclosure (10) and through which the product (27) is transported into the vapor phase chamber for heating

and welding application.

  7. Apparatus according to claim 2, characterized in that at least one nozzle (24, 26) is adjustable with respect to its distance from the surface facing the product (27) which is transported through the chamber of vapor phase, and with respect to the angle of the jet of

  soldering that is projected onto the surface of this product.

  8. Apparatus according to claim 4, characterized in that said steam supply means (12, 14) comprise means for controlling the temperature of the steam, in order to achieve, prior to the application of welding, heating of the product ( 27) has a temperature at least equal to

  the welding temperature of this product.

  9. Apparatus according to claim 4, characterized in that it comprises means (38, 64) for holding the product (27) in a predetermined orientation during its displacement in front of the

or the nozzles (24, 26).

  Apparatus according to claim 9, characterized in that

  the holding means comprise guiding means (38) which are disengaged

  placed in the enclosure (10) and means (64) pushing the product (27) in contact with these guide means (38) during the transportation of the product to

through this enclosure (10).

  11. Apparatus according to claim 9, characterized in that said holding means comprise guide means (38) which are arranged in the enclosure (10) and have a downwardly inclined path (40) in the part of input of this enclosure (10), and a rectilinear trace upwards through the remaining part of this enclosure (10),

  the nozzle or nozzles (24, 26) being arranged along this straight line.

line up.

  Apparatus according to claim 4, characterized in that

  the means of transport (22) comprise a pair of transport chains

  (30, 32) which are arranged along a conveyor path located at

  through the enclosure (10), and a series of frames (34) each of which is

  abutting these conveyor chains (30, 32) with a spacing relative to the adjacent frames (34), each of which frames (34) serves to retain on

him the product (27).

  Apparatus according to claim 4, characterized in that

  the nozzle or nozzles (24, 26) are each adjustable with respect to their

- 13 -

  relative to the surface facing the product (27) being transported

  through the vapor phase chamber.

  Apparatus according to any of claims 4 and

  13, characterized in that the nozzle or nozzles (24, 26) are each adjustable with respect to the angle of the weld jet which is projected onto the surface

of the product (27).

  Apparatus according to claim 1, characterized in that it is applied to the soldering of circuit boards (27), the steam supply means (12, 14) provides a saturated and heated inert vapor carrying these circuit boards ( 27) at the welding temperature, there is provided an inlet chute (18) and an outlet chute (20) each extending outwardly from opposite side walls of the enclosure (10), the transport means carry the circuit boards (27) through this inlet trough (18), the vapor phase chamber of the enclosure (10) and the outlet trough (20), the source of the

  solder (30) is a source of molten solder, one or more

  a plurality of nozzles (24, 26) directing respective molten weld jets on the heated circuit boards (27), and the inlet and outlet chutes.

  output (18, 20) provide a transport path through which

  sibly continues through the enclosure (10) and these inlet and outlet chutes (18, 20), for the purpose of heating the circuit boards (27) and

  the application of solder inside the vapor phase chamber.

  Apparatus according to claim 15, characterized in that the steam supplying means comprise heating means (12) arranged at the bottom of the enclosure (10) and serving to heat the vapor phase liquid (14) in order to to supply said saturated inert vapor to

  inside the vapor phase chamber.

  Apparatus according to claim 16, characterized in that said enclosure (10) comprises cooling coils (16) disposed along the walls of said enclosure at a location defining the upper limit of the vapor within the chamber vapor phase. Apparatus according to claim 15, characterized in that each of the nozzles (24,26) comprises an elongate tubular piece (50) having an elongated straight orifice (52) of sufficient length to provide a weld jet over the entire width of the circuit board (27), and a pipe (60, 62) coupling said tubular piece (50) to the weld source (30) to provide molten solder to that piece

- 14 -

  tubular (50) and the orifice (52).

  Apparatus according to claim 18, characterized in that

  that each elongate rectilinear orifice (52) is adjustable in a direction

  normal length, to provide additional control of the weld jet. Apparatus according to claim 1, characterized in that the steam supplying means (12, 14) provide, within the chamber, a saturated inert vapor zone at a selected high temperature for heating the product ( 27) at a predetermined temperature, the transport means (22) transports the product to this vapor zone

  and out of it, along a path of travel, the source of

  hard (30) is a molten solder source, and there is provided one or more nozzles (24, 26) which are disposed in said vapor zone and each serving to direct a weld jet melted on the heated product (27) to

  to apply solder on this product.

  21. Apparatus according to claim 20, characterized in that at least one pair of nozzles (24, 26) are arranged on either side of the product displacement path in order to direct the weld jets.

  melted on opposite surfaces of the heated product (27).

  22. Apparatus according to claim 20, characterized in that the heating of the product (27) before the application of welding, and the same welding application, are controllable separately, and the

  control of each is substantially independent of that of the other.

  Apparatus according to claim 20, characterized in that each nozzle (24, 26) is controllable separately to provide

the desired application of welding.

  Apparatus according to claim 20, characterized in that

  that it includes means to refer to the source of

  lasts (30) the excess solder which does not adhere to the product (27).

  Apparatus according to claim 20, characterized in that

  that the welding source (30) is disposed within the range of

  fear. Apparatus according to claim 20, characterized in that

  that the product displacement path (27) is a continuous path with

wise substantially continuous.

  27. A method of welding a product, such as establishing a zone of inert saturated vapor at a selected elevated temperature, transporting the product along a path of travel in the direction of

- 15 -

* this area of steam and out of it, and to bring this product to a predetermined temperature by exposing it to the vapor that is in

  said vapor zone, characterized in that it consists, after heating

  the product at said predetermined temperature and before transporting this product out of the vapor zone, applying solder to this product by directing one or more molten solder streams onto the product so heated. 28. The method of claim 27, characterized in that

  the travel path is a continuous path with substantially

tinu.

  29. The method of claim 27, characterized in that the predetermined temperature at which the product is worn is equal

  or greater than the re-flow temperature of the weld that is applied

  on the product before the transport of this product into the vapor zone, and in that it further consists in causing the solder thus pre-applied to be re-discharged by exposing it to the vapor which is in said zone of steam. 30. The method of claim 27, characterized in that it consists of controlling separately each weld jet so

  to obtain the desired application of welding.