MXPA99009952A - Apparatus and method for inerting a wave soldering installation - Google Patents

Abstract

The present invention relates to an apparatus and a method for inerting a wave soldering installation having a solder bath (19) and a conveying system for producing one or more solder waves (14, 15), in particular for soldering electric printed circuit boards, having an immersion box (1) which is closed on all sides, shaped like a frame, can be immersed in the solder bath (19) and which has porous pipes (2, 3, 4) to distribute nitrogen, said pipes being arranged inside the immersion box in cage-like housings (5, 6, 7) with outlet openings (8, 9, 10), the cage-like housings (5, 6, 7) being designed such that the porous pipes (2, 3, 4) are arranged therein in such a way that the porous pipes (2, 3, 4) are essentially not struck by solder splashes produced during the operation of the wave soldering installation. By means of the arrangement and shape of the outlet openings (8, 9, 10), very uniform inerting of the wave soldering installation under all operating states can be achieved, even without an inerting covering hood. The elimination of solder splashes, which can damage the porous pipes (2, 3, 4), permits long service times;the construction of the installation permits simple maintenance.

Description

APPARATUS AND METHOD TO MAKE AN INSTALLATION INERT OF WAVE WELDING The present invention relates to an apparatus for making an inert wave soldering installation, having a solder bath and a transport system, to produce one or more solder waves, as they are used, in particular, for welding boards d printed electrical circuits. Welding devices for welding waves for printed circuit boards with known ones, for example from U.S. Patent No. 5,121,874. In the case of the system described therein, the inertia of the atmosphere on the welding bath is achieved by a closed, elongated cover, inside which the printed circuit boards, which are to be welded, are transported and in which they are transported. It maintains an inert atmosphere, usually of nitrogen. In the vicinity of the welding waves, which is produced by the wave soldering installation, during the operation, there are porous tubes that run parallel to the waves and through which the inert gas emerges, d so that a particularly low atmosphere in oxygen can be achieved, in particular under the printed circuit board to be welded. In addition, U.S. Patent Nos. 5,411,200 5,409,159 teach the practice of encircling the distribution pipes for the inert gas, above the welding bath of a wave soldering installation, cage-like co-accommodations, which allow the inert gas emerge through numerous exit openings. In those documents, a description is also given of the possibility of operating such a wave soldering installation with only a short hood or even without a hood, producing an atmosphere with very low oxygen content under the circuit boards. printed, by means of the appropriate distribution of the inert gas above the welding bath, during the passage of the printed circuit boards to be welded, and then in the state when no printed circuit board passes through it, producing a protective layer of inert gas over the welding bath and welding waves.

In addition, U.S. Patent No. 5,361,969 also describes the practice of designing an apparatus for making a wave solder installation inert, such as an immersion box, which is closed on the sides and on which the tubes are mounted for the distribution of inert gas. However, in the case of a wave soldering installation, three different states of operation may occur, specifically state of rest of the installation (ie, the pumps turned off and, therefore, welding waves will not be present) , the state of operation of the installation, without a printed circuit board passing through it and the operation status of the installation with a printed circuit board passing through it. For all three states, it is necessary to ensure that oxygen goes to the surface of the weld pool and weld waves. In addition, when a printed circuit board passes through the installation, it must be ensured that a particularly inert atmosphere, with only very low oxygen proportions, less than 10 ppm, can be maintained below This printed circuit board, where the welding process tries to take place, since, otherwise, the quality of the welding joints becomes poor quality. Likewise, it is intended that such installation be operated for a period as long as possible, if maintenance and is as easy, as possible, to maintain. It is precisely at this point that the known installations have weaknesses, since, for example, weld spatter, which always occurs during the operation of a wave welding plant, may collide with the nitrogen distribution pipes and block them. in the course of time. This is critical, particularly when the pipes of the used distribution are porous tubes, with very fine pore sizes. The object of the present invention, therefore, is the provision of an apparatus that allows the inert state of the wave soldering installation under all operating conditions, with or even without a cover hood and which is designed to require little maintenance and be easy to maintain. In addition, suitable methods for the operation of such an apparatus will be specified.

In order to achieve this object, use is made of an apparatus according to claim 1 and methods according to claims 14 and 15. Advantageous and preferred refinements of the apparatus are specified in the dependent claims. An apparatus, according to the invention, for making a wave soldering installation inert, which has a welding bath and a transport system for producing one or more welding waves, in particular for soldering boards of printed electrical circuits, has an immersion box, which is closed on all sides, configured as a frame, which can be submerged in the welding bath and has porous tubes to distribute the nitrogen, these tubes are arranged inside the immersion box in housings With cage-type co-openings, these cage-type housings are designed so that the porous tubes are arranged in such a way that these porous tubes can not be hit by the weld spatter produced during the operation of the welding plant. waves. In accordance with the invention, the cage type accommodations, around the porous tubes, they are used not only to distribute the nitrogen in the desired regions, but, in particular, also to protect the porous tubes that perform a uniform distribution of nitrogen within their housing, In distinction from the prior art, the Cage-like elements are configured not only from the point of view of the arrangement of their exit openings, but also from the point of view of the possibility of preventing weld spatter from entering through the exit openings, reaching to the porous tubes. A particularly suitable arrangement for the exit openings has proven to be an arrangement of the exit openings which is directed only to the sides and / or downwards. Since the most important objective of all arrangements for inerting has always been to achieve an atmosphere with the lowest possible content under the printed circuit board during welding, the exit openings are mostly also directed upwards against the board. circuit. In addition, the exit openings are arranged in the entrance region and in the exit region of the arrangement and, when attempted the penetration of oxygen, particularly in the case of installations without an inert cover of large area. Surprisingly, however, the exit openings that are directed to the sides and / or downwards are sufficient to ensure that the wave solder installation becomes inert under all operating conditions. If there is no printed circuit board to be welded, then, in the case of this mode, the inert gas flows uniformly over the welding surface. If a printed circuit board is present, then the inert gas can, in any case, escape only in the input region and in the output region of the printed circuit board, below the last, so that the oxygen displacement, in In any case, it is assured there. The arrangement of the outlet openings, according to the invention, allows them to be arranged so that there is no straight line connection from the surface of the weld pool and the welding waves through the outlet openings to the porous tubes. , which meant that the probability that porous tubes can crashed with weld spatter is considerably reduced. As an alternative or supplementary measure, the porous tubes can be disposed in a non-centered manner within their cage-like housings, disposed farther from the respective outlet openings than from the walls of the cage-type housings, which are placed opposite from each other. exit openings. This also reduces the shock probability of weld spatter, with no disadvantages for inert gas distribution. For any weld spatter d welding that, nevertheless, penetrate through the exit openings, it is beneficial if these splashes can run outwards downwards inside the weld bath, through an intermediate space, inside the cage-like housings, which open at the bottom . For this purpose, it is also particularly advantageous if all the walls of the cage-like housings have an inclination with respect to the horizontal, so that the weld spatter that collides with the walls and the interior can run out and down, without crashes with the porous tubes. In particular, it is also impossible for any weld spatter to run along the walls above the porous tube and then fall on the tubes. In particular, for an arrangement without a cover, which can be made inert, it is beneficial if a first porous tube is arranged on the input side of the apparatus, parallel to the welding wave, and a second porous tube is disposed on the side of opposite output. If the wave soldering installation has two or more solder waves, then, according to the invention, a further porous tube is preferably disposed between each two welding waves and parallel thereto, the cage-type housing of the tube it is curved in a semicircular cross-section, above the further porous tube "and is carried down on the sides under the tube, with at least one outlet opening being just below the porous tubule, so that the porous tube can not virtually collide with the tube. all with weld spatter, allows the inert gas to flow out precisely where it needs, specifically in the flank region of the of welding. At those points where weld waves flow back into the weld pool, turbulence may occur, which is a particularly critical point for oxidation of the weld pool surface. Reliable inertia is achieved in this region by means of the arrangement according to the invention. For welding waves that are physically close together, the subsequent porous tube is selected to have a smaller cross section than the other porous tubes and is supplied with a cage type housing, which is located closely thereon, so there is a gap of 1 to 3 mm between this housing and the porous tube, through this gap the inert gas can flow uniformly. This arrangement is particularly compact and, in the case where the porous tube and the housing are suspended on the side walls of the immersion box, does not require any assembly of interference construction in the region, in which the weld waves flow again inside the welding bath. It is preferably used, in the present invention, of porous tubes having an average size of pores from 0.3 to 2 μm, in particular from 0.4 to 0.6 μm. In general, porous tubes made of sintered metal are used, which have a coefficient of expansion which is similar to that of the metal immersion box, so that it was fastened to the walls of the immersion box in a relatively simple manner. As a result of the reduced shock probability of weld spatter on the sintered metal tubes, according to the invention, it is also possible for very fine pore tubes to remain in use without maintenance for a prolonged period and can then be easily replaced. by simply assembling it in the immersion box. The fine pore tubes allow a very uniform distribution of the inert gas inside the cage-type housings, a very uniform flow of the inert gas through the openings d output occurs, which is a precondition for a good inert state of the surface of the welding bath, even when no printed circuit board is present. According to another aspect of the present invention, which is intended to be suitable, in particular, for wave soldering installations, without a cover hood made inert, at least one guide plate is additionally fastened to a cage-like housing in regions of turbulence in the weld pool or in regions where weld spatter is widely expected, the guide plate is capable of deflect weld spatter down and reduce turbulence as weld waves flow back into the weld pool. It is particularly preferred that there is an additional outlet opening for the inert gas, under such a guide plate, so that a turbulent region below the guide plate is particularly well covered by the inert gas. As already mentioned, in the case of the present invention, it is particularly important to achieve good inertia even in operating states where a printed circuit board is not present above the wave soldering installation. This is assisted if the outlet openings are configured so as to have a relatively large area and, as a result of their arrangement configuration, a very uniform flow is established on the surfaces of the weld pool and the weld waves.

It is particularly beneficial for the operation of the apparatus, according to the invention, if a larger flow of inert gas is guided through the second porous tube in the outlet side of the apparatus than through each of the other porous tubes. Typically, in the case of a wave soldering installation, the printed circuit boards are guided so that they rise slightly with respect to the horizontal, with the result that, in the exit region, there is a greater distance between the Welding bath and the printed circuit board or the upper edge of the immersion box on the side of the entrance. In addition, it exists in this region, because the welding ripple is present there, a region of increased turbulence, which is covered, for example, with a guide plate. An additional flow of inert gas in this region is, therefore, useful in order to configure the inertia as beneficially as possible in this region as well. It is particularly advantageous to supply the apparatus, according to the invention, with nitrogen at a temperature well below the bath temperature. welding, preferably 100 to 400 ° K below the temperature of the weld pool. In particular, nitrogen can be supplied at room temperature at about 20 ° C. This nitrogen initially occupies a low volume as supplied and as it emerges from the outlet openings, by which means low flow velocities of the outlet and thus a very uniform laminar flow is achieved. However, the nitrogen is heated in the region of the immersion box, above the weld pool, as a result of which its volume becomes significantly larger. As a consequence, it fills the whole system very uniformly and escapes to the sides and upwards and / or below the printed circuit board, on the sides of the latter, with a higher volume flow. This process may be somewhat less beneficial in the energy terms than supplying the previously heated nitrogen or nitrogen to the temperature of the weld pool, but it leads to a very good inert state. Since porous tubes will probably not collide with weld spatter, it is also not a disadvantage that These tubes are at a lower temperature, so weld spatter can stick to them. An exemplary embodiment of the invention, but which does not restrict it, will be described in detail below with reference to the drawing, in which: Figure 1 shows a schematic longitudinal section through an apparatus according to the invention, and Figure 2 shows a top view of the apparatus, according to Figure 1. The present exemplary embodiment relates to the general arrangement of a wave soldering installation, as described, for example, in US Pat. Nos. 5, 411 , 200 or 5,409,159, mentioned above, to which reference is made here in its entirety. The present invention is concerned only with the connection of such installation in order to make the surfaces inert. Figure 1 shows a longitudinal section, schematically, through the apparatus according to the invention. Mounted in an immersion box 1, which is closed on the sides, is a first tube pores 2, a second porous tube 3 and a subsequent porous tube 4. These tubes, in each case, are arranged inside the cage-like housings 5, 6, 7, these housings have exit openings, 8, 9, 10. The porous tubes 2, 3, 4 are not arranged centrally or symmetrically in the cage-like housing 5, 6, 7; instead they have the largest possible space from the respective outlet opening, 8, 9 or 10. The entire immersion box is placed on a wave soldering installation, part of the immersion box is immersed inside the bath 19 of welding, to be specific at a depth that, even in the case of fluctuations in the level of the weld pool, no gaps develop through which the ambient air could penetrate. During the operation of the wave soldering installation, the welding waves 14, 15 are located at the points indicated schematically in Figure 1. The openings 8, 9, 10, outlet and the arrangement of the porous tubes, 2, 3, 4, in the cage-like housings, 5, 6, 7, are selected so that weld spatter has only very little probability of being capable of colliding with the porous tubes, 2, 3, 4. In particular, there is a straight connection line from the welding bath 19 or the "welding waves, 14, 15, through the outlet openings, 8, 9, 10, to the porous tubes, 2, 3, 4. Any weld spatter that, however, penetrates through the outlet openings, 8, 9, 10, can flow out into the weld pool by means of of the intermediate spaces 11, 12, 13, which are open at the bottom.This is assisted by the fact that all the walls of the housings, 5, 6, 7, of cage type, go in an angle, and particularly in a An angle such that the weld can not fall on the porous tubes, 2, 3, 4. This is also assisted by the fact that the cage-like housings do not have openings in the upper side.For reasons of space, it is often it is possible to arrange, between two waves, 14, 15, d welding, a porous tube with a cage-like housing, the walls of which reach down into the sun bath 19 According to the present invention, therefore, a further porous tubing 4, preferably one with a smaller cross-section than the remaining porous tubing 2, 3, s disposes at such a point, so that it is surrounded by pox housing 7, which is curved in a semicircle above this further porous tube 4 and is further guided down to the sides of the cross section of the porous tube 4. Produced in this manner, there is at least one outlet opening 10, which it is directed downward and, at the same time, by means of an intermediate space 13 that opens at the bottom, it is removed away from the subsequent porous tube 4, so that the weld spatter can not reach it, but, if necessary, it can run outside downwards. A recess 16 with a width of 1 to 3 mm is located between the subsequent porous tube 4 and its cage-like housing 10. The porous tubes, by themselves, are preferably produced from sintered metal having a pore size between 0.3 and 2 μm, preferably from 0.4 to 0.6 μm. In regions of increased turbulence in the welding bath 19, ie, in the present example, where the welding waves 15 flow back into the welding bath 19, according to the invention, a guiding plate 17 is preferably disposed in the jaul-like housing 6 of the second porous tube 3. This guide plate 17 reduces l turbulence and deflects the weld spatter downwards, and, at the same time, guides the inert gas, which emerges from an outlet opening 18 below the guide plate 17, in the region of turbulence and thus effectively protects the surface, in particular against oxidation at that point. The outlet openings, 8, 9, 10 are configured in such a way that they produce a mu flow of uniform nitrogen in the direction of the interior of the immersion box 1 and / or along the waves, 14, 15, of welding. This is assisted if the nitrogen at room temperature, or, in any case, at a temperature well below the temperature of the welding bath 19, is introduced as the inert gas. The volume of the nitrogen is still relatively low when it is introduced, which favors the uniform flow without turbulence, the nitrogen is then heated above the weld pool and emerges in ascending or sideways form with a greater volume. As a result, in the case where a printed circuit board is present, the environmental oxygen remains reliably removed from the board of the printed circuit board, which is going to be soldered. If n there is printed circuit board axxiba of box 1 d immersion, the entire interior of the immersion box, however, remains in an inert state very greatly, specifically during the operation of the welding pumps and when they stop. A further view from above of the immersion box is illustrated schematically in Figure 2. The present invention is suitable, in particular, for compacting installations without an inert cover, and makes possible the welding of printed circuit boards with high quality, with very long service times of the installation and simple maintenance.

Claims (15)

1. CLAIMS 1. Apparatus for making a wave soldering installation inert, having a welding bath and a transport system to produce one or more welding waves, in particular for soldering boards of printed electrical circuits, having a dip box , which is closed on both sides, configured as a frame, can be submerged in the welding bath and has porous tubes for distributing nitrogen, these tubes are disposed inside the immersion box in cage-like housings, with the openings of In this case, the cage-type housings are designed so that the porous tubes are disposed there in such a way that these porous tubes can not be essentially shocked by the weld spatter produced during the operation of the wave solder installation.
2. 2. Apparatus, according to claim 1, and that the cage-like housings have exit openings, which are directed only to the sides and / or downwards.
3. 3. Apparatus, according to claim 1 or 2, in which the porous tubes are arranged not centrally within their cage-type housings, in particular farther from the respective outlet openings than from those walls of the cage-type housings, which they are opposite the exit openings.
4. 4. Apparatus, according to claim 1 or 2, in which there exists, in each case, between the outlet openings and the porous tubes, an intermediate space, which opens at the bottom inside the cage-type housings, and which allows that the weld spatter runs displaced downwards.
5. 5. Apparatus, according to claims 1 or 2, in which all the walls of the cage-type housings have an inclination with respect to the horizontal, so that weld spatter that collide against the walls inside can run displaced towards below, without hitting the porous tubes.
6. 6 Apparatus, according to claims 1 or 2, in which at least one first porous tube is disposed on a side of the apparatus, which is placed parallel to the welding wave, and a second porous tube is arranged on an opposite exit side, in each case with the upper region of the immersion box.
7. 7. Apparatus according to claim 6, which, in the case of a wave soldering installation, having at least two welding waves, a further porous tube is disposed between each two welding waves, parallel to these, the The cage-like housing of the tube is curved in a semicircular cross-section above the subsequent porous tube and is guided down the sides to be below the porous tube, and which has at least one outlet opening only below the subsequent pore tube.
8. 8. Apparatus according to claim 7, wherein the subsequent porous tube has a smaller cross section than the first and second porous tubes.
9. 9. Apparatus according to claim 7, wherein there is a gap of 1 to 3 mm in the interior, between the cage-type housing and the subsequent porous tube.
10. Apparatus according to one of claims 1 or 2, in which the porous tubes have an average pore size of 0.3 to 2 μm, in particular 0.4 to 0.6 μm.
11. 11. Apparatus according to one of claims 1 or 2, in which at least one guide plate is fastened to a cage-like housing, in the turbulence regions in the welding bath and / or in the regions in which the splashes of Welding is expected at an increased extension.
12. 12. Apparatus according to claim 11, in which there is at least one outlet opening for nitrogen, below the guide plate.
13. 13. Apparatus, according to one of claims 1 or 2, in which all the outlet openings are configured so that a more uniform nitrogen flow occurs with low turbulence.
14. 14. Method for operating an apparatus, according to claim 6, wherein the flow of nitrogen through the second porous tube in the outlet side is greater than the respective flow through each of the remaining porous tubes.
15. 15. Method for operating an apparatus, according to claim 1, wherein the nitrogen is supplied at a temperature well below the temperature of the welding bath, preferably from 100 to 400 ° K below, in particular at approximately an ambient temperature of about 20 ° C. SUMMARY OF THE INVENTION The present invention relates to an apparatus and method for rendering a wave soldering installation inert, having a welding bath (19) and a transport system for producing one or more welding waves (14, 15), in particular for welding "printed electrical circuit boards, it has an immersion box (1), closed on all sides, configured as a frame, which can be submerged in the bath (19) of welding and co-tubes (2, 3, 4) porous, to distribute the nitrogen, these tubes are arranged inside the immersion box and the cage-like housings (5, 6, 7), with exit openings (8, 9, 10 =, these housings ( 5, 6, 7) are designed so that the porous tubes (2, 3, 4) are disposed there in such a way that they essentially do not receive impacts from weld spatter produced during the operation of the wave soldering installation. By means of the arrangement and configuration of the exit openings (8, 9, 10), a very uniform inert state of the wave soldering installation can be achieved, under all operating conditions, even without a campan of cover with inert state. The elimination of said splashes, which can damage the porous tubes (2, 3, 4), allows long service times; The construction of this installation allows easy maintenance.