MXPA00000212A - Method and apparatus for treating metal surfaces by dry process - Google Patents

Abstract

The invention concerns a dry process surface treatment method for treating at least a metal surface portion, wherein the portion is treated at a pressure close to atmospheric pressure with a treating gas stream comprising excited and unstable species, which consists in locally increasing the treating gas pressure on the metal surface portion so as to force the l species to move along a direction substantially perpendicular to the surface. The invention is useful for wave brazing electronic components on printed circuit wafers.

Description

METHOD AND APPARATUS FOR TREATING METALLIC SURFACES BY DRY ROAD The present invention relates to a method for treating a surface by the dry route of at least a portion of the metal surface, of the kind in which such portion is treated at a pressure close to atmospheric pressure with a treatment gas which includes excited or unstable species. Such surface treatments can intervene, for example, in the course of the production or evaluation procedures of flat products or hollow bodies, in the production of electronic circuits such as printed circuit boards for performing functions of cleaning or application of flow, of defatting or also activation of the surface, often before carrying out a further process, which may be for example an annealing, electro deposit of zinc, aluminum, tin or its alloys, a welding (for example of electronic components) on the printed circuit board), or also the deposit of organic coatings such as varnishes or paints, or inorganic as nitrides or films based on. silicon. In the field of manufacture of printed circuit boards or boards, these steps of metal surface treatment are especially pickling, cleaning, deburring of connection holes ("desmearing") or also the application of flow before tinning or welding. Examples of such dry surface treatment methods have been reported in the following documents: EP-658391 and EP-658637. As regards the welding of electronic components in an electronic circuit, especially in printed circuit boards or plates, the two most frequently used methods for carrying out such a welding operation are "wave soldering" and "reflow soldering". The technique of reflow soldering, a solder paste containing a mixture of metal alloy and fluxes is deposited on the printed circuit at those connection sites of the components and then the components are placed on the plate. The plate provided with the components is then inserted in a reflow oven to thereby provide a certain amount of heat necessary to obtain the fusion of the metal alloy, as well as the activation of the flow-applying element contained in the paste. Wave soldering consists, as such, of placing the plates or boards carrying the electronic components subject to welding, in contact with one or several waves of liquid solder alloy obtained by circulation of a solder bath contained in a tank, or by means of of a bushing. Generally the circuits are treated with flow in advance in an area upstream of the wave welding machine with the aid of a flow spray or a flow foam and then the material is preheated to activate the previously deposited flows to clean the surfaces that must be welded, in order to eliminate oxides and organic pollutants. As in the case of reflow soldering, in order that the alloy can soften the metallizations and form the connections, it is necessary to proceed from a pickling of the metallizations, that is to say the printed circuit board and the components it bears. This pickling is generally carried out by an agent that can be presented in liquid or gas form. ~ A gas flow containing excited or unstable chemical species can be used to proceed with gas pickling, and this flow is directed to the printed circuit. This flow manages to strip the metallizations before the welding step is taken to the tail.

In this field of dry flow application of metal surfaces before welding or bursting, the work carried out by the Applicant has shown that to obtain an effective pickling, it is necessary that the chemical species arrive to treat all metallizations including the holes "made in the connection sites of the plate and on the other hand those legs of the inserted components" throug hole components "(in English) It is then that according to the methods currently available for the treatment by the dry route, although the gas flow is treating the printed circuit board is generally emitted in a direction basically perpendicular to it, the flow naturally tends to fractionate in such a way that the particles and in particular the particles located in the periphery have a tendency to move tangentially to the surface of the plate. It is inferred from the above that there is a need to improve this type of pickling technique, especially with the purpose of ensuring in a more efficient and systematic way the pickling of the holes made in the splint or plate for the insertion of the so-called legs. electronic components called "wire" or "insertable".

One of the objects of the present invention is to propose such improvements. This object is achieved in accordance with the present invention because the excited or unstable species have a velocity component that is basically perpendicular to the surface. The invention therefore relates to a method for treating a surface by the dry route of at least a portion of the metal surface, according to which the portion is treated at a pressure close to atmospheric pressure with a gas flow of treatment including excited or unstable species, characterized in that the pressure of the treatment gas is locally increased on the metal surface to thereby force the chemical species that move in a direction substantially perpendicular to the aforementioned surface. The process according to the invention can also entail one or more of the following characteristics: the treatment gas is essentially devoid of electrically charged species; the treatment gas is obtained from a primary gas mixture and according to the case of an adjacent gas mixture, the primary gas mixture being obtained at the exit of the gas from at least one apparatus for the formation of excited or unstable gaseous species in which an initial gaseous mixture comprising an inert gas and / or a reducing gas and / or oxidizing gas has been transformed, while the adjacent mixture did not pass through the apparatus; The flow of treatment gas is emitted in the direction of the surface in a direction substantially perpendicular to it and because the flow carries in the periphery of the excited or unstable particles. driven by movements in a direction substantially tangential to the surface, thereby increasing the pressure of the treatment gas flow on the surface, to the periphery of the flow; The pressure of the treatment gas on the surface is increased by at least one flow of entrained gas perpendicular to the surface; the trailing gas carries nitrogen; As a variant, as long as the portion of surface to be treated is arranged in a treatment chamber, the pressure of the treatment gas on the surface is increased by at least one fan turned towards the surface to force the flow of gas for treatment so that it meets the surface in a "direction fundamentally perpendicular to the latter, the excited or unstable chemical species are obtained by the passage of an initial gas in an electric discharge, and the treatment gas carries species Excited or unstable chemical species are produced from an initial reducing gas mixture comprising nitrogen and hydrogen An example of an apparatus for the formation of the aforementioned excited or unstable gaseous species has been described in European document EP-658391 The invention also relates to a wave soldering process, with electronic components. In an electronic circuit, in whose course: it is placed in the components in connection points practiced in the circuit, an operation of application of flow in the circuit is carried out by treating the latter, at a pressure close to atmospheric, through a flow of treatment gas carrying excited or unstable chemical species, and the circuit leading to the components is brought into contact with at least one wave of a solder alloy, characterized in that in the course of the flow application operation of the electronic circuit, the pressure of the treatment gas is locally increased over the circuit to force the chemical species to move in a direction essentially perpendicular to the circuit. The invention also has for its object an apparatus for the treatment of at least one portion of metal surface by the dry route, for the practical application of a method as defined above., characterized in that it carries a source of treatment gas comprising excited or unstable chemical species, a device for moving the parts bearing at least a portion of the metal surface and thus allowing the parts to be brought into contact with a gas flow. of treatment, characterized in that it contains auxiliaries to locally increase the pressure of the treatment gas in each piece to thereby force the chemical species to move in a direction substantially perpendicular to the latter. Another subject of the invention is a wave soldering apparatus of electronic components in an electronic circuit for carrying out a method as defined above, characterized in that it carries a device for transporting or moving circuits through at least one device of circuit flow application, by treatment of the latter with a flow of treatment gas containing excited or unstable chemical species, these circuits carrying on at least one of their faces the welding components in the connection sites of these last, and then the material is moved through a deposit containing a solder alloy to achieve the welding of the components and is also characterized because at least one of the flow application devices carries elements to locally increase the pressure of the treatment gas flow in each circuit to thus force the chemical species to move in a direction virtually perpendicular to the latter. Other features and advantages will be apparent from the following description which is presented by way of example only and with reference to the accompanying drawings in which: Figure 1 is a schematic representation of a wave soldering apparatus according to the present invention . - Figure 2 is a schematic representation in section of a device for forming excited or unstable chemical species that enter into the constitution of the flow application device of the wave soldering device according to Figure 1. - Figure 3 represents a first embodiment of the elements for locally increasing the pressure of the treatment gas in one piece; and Figure 4 illustrates a second embodiment of the elements for locally increasing the pressure of the treatment gas in one piece. With reference to Figure 1, a wave soldering apparatus according to the present invention carries for the represented embodiment a device 10 for the displacement of the circuits 12 (here, for example, printed circuit boards), of a first position 14 for the preheating of the plates, towards a device 16 for the treatment of the plates 12 before welding, by treating the latter with excited or unstable chemical species and then towards a welding station on wave 18 at which level they are placed the plates that lead to the electronic components subject to welding, in contact with at least one wave of a welding alloy. As seen in Figure 1, the displacement device 10 carries one or more transfer mats, such as for example 20, illustrated in dotted and dashed lines in this figure and in which the printed circuit boards 12 are arranged. Each plate 12 carries here a set of continuous holes in which the legs of the electronic components 22 and 24 are inserted, which must be welded. As can be seen in Figure 1, the mat 20 extends between two guide rollers, such as 26, of which at least one is driven. The plates 12, arranged in the mat 20 are first transferred from the first preheating station 14 at which level a device for the appropriate heat treatment 28 is arranged, and then to the second station 16 which serves for "the application of flow and in whose level the plates undergo a decontaminating and deoxidizing operation by contacting the plates with excited or unstable gaseous species.The plates thus treated with flow are then brought into contact with at least one wave 30 of alloy solder, at the level of the welding station 18. This wave 30 is obtained by pumping a welding bath contained in a tank 32 through a bushing or nozzle 34. The excited or unstable gaseous species, which serve to treat the plates 12 at the level of the post of flow application 16, are obtained here by passing an appropriate initial gas, for example a gaseous reducing mixture containing for example nitrogen and hydrogen no, through a device such as 36 for the formation of excited or unstable chemical species by the passage of the initial gas in an electric discharge. As shown in Figure 2, each device 36 for the formation of the excited or unstable chemical species carries, for the embodiment represented, a first tubular electrode 36, formed for example by an internal face of a metal block 38, and in ~~ that is concentrically arranged an assembly consisting of a tube of dielectric material 40, for example ceramic, on whose inner face is metallized, a second electrode 41 exaggeratedly enlarged in Figure 2, in order to achieve a greater clarity. The dielectric tube 40 and the second electrode 41 define with the first electrode 37 a tubular passage for the gas 42 and internally an internal volume 44 where a cooling fluid is circulated. The block 38 carries, diametrically opposite, two longitudinal grooves 46 and 48 which respectively form the inlet for the initial gas to be excited in the passage 42 and the treatment gas flow outlet carrying the excited or unstable gaseous species. The slits 46 and 48 extend over the entire axial length of the cavity 42. In addition, the block 38 advantageously brings to the periphery of the first electrode 37 a plurality of conduits, such as 50, for the passage of a cooling fluid, for example water. It is also seen in Figure 2 that the gas inlet slit 46 communicates with a "homogenization chamber 52 formed in a box 54 connected to the block 38 and carrying a branch pipe 56 for driving the initial gas.This module is completed. with an electric generator 58 high voltage and high frequency, intended to generate a discharge in the gaseous mixture circulating through the gas passage 42 to cause an excitation of the gaseous molecules that enter its constitution to thereby generate at exit 48, a gaseous treatment mixture carrying excited chemical species or unstable but which is virtually devoid of electrically charged species, which have the purpose of deoxidizing and decontaminating the external surface of the printed circuit boards 20 (Figure 1). As will be clear to the expert, the plates are here in a post-discharge state. Thus, each device 36 for the formation of excited or unstable chemical species generates at the outlet a gas flow carrying chemical species emitted in a direction generally perpendicular to the surface of the plates 12, subject to treatment. As can be seen in Figures 3 and 4, the flow of gas carrying chemical species intended to ensure the application of flow to the platelet by its nature tends to widen so that the particles located at the periphery of the flow have a tendency to move in a direction virtually parallel to the surface of the plate. As mentioned above, this flow portion has a lower efficiency for the treatment of the holes made in the plate for the assembly of the components. To remedy this drawback and in accordance with the present invention, the excited particles are forced to propagate virtually perpendicular to the plate to enter the holes. To achieve this operation, the pressure on each plate 12 of the gas flow containing the chemical species is locally increased. More preferably, and to the extent that the incriminated particles are located at the periphery of the treatment flow, the pressure of the treatment flow is increased to the periphery of the flow. According to a first embodiment, visible in Figure 3, the pressure of the activated gas flow is increased by using a jet of auxiliary gas (which does not pass through the electric discharge), such as nitrogen or a gas identical to that used to generate the excited particles, for example an amount of nitrogen mixed with hydrogen and, depending on the case, water vapor.

As can be seen in Figure 3, the jet of drag gas is generated by means of a dragging device 60, adapted to project the dragging gas, drawn from an enclosure 62, in a direction virtually parallel to the axis of the holes, that is to say perpendicular to the surface subject to treatment, as indicated by the arrows F, and all this with a relatively high speed, comprised for example between 10 and 100 m / s. The elements 60 may be constituted, for example, by a blade with a venturi effect or by a flow amplifier. Under the action of this jet of entrained gas, the excited or unstable particles are forced to be directed parallel to the axis of the holes to be treated. In this way the width of the treated zone is conrably improved with the flow of the excited particles. According to another embodiment shown in Figure 4, each plate, which is located at the level of the station 16 of the flow application, in a preferably hermetically sealed enclosure, increases the pressure of the treatment gas on the plate by means of at least one fan 64 turned towards the plate and arranged at the level of the periphery of the gas flow to thereby force in this zone the flow of treatment gas to be directed in a direction virtually perpendicular to the plate. It is noted that in this embodiment the entrainment gas is extracted from the treatment gas present in the enclosure. As in the embodiment described above, with reference to FIG. 3, there is thus the possibility of conrably increasing, with the aid of this driving device, the surface treated with the gas flow containing the excited or unstable species. Although the present invention has been described in relation to particular embodiments, it is by no means limited by such examples but is susceptible to modifications which will be suggested to the skilled person within the framework of the following claims. In this way the invention has been exemplified particularly in the above, in the case of a wave welding based on components that are applied in electronic circuits, and consequently it is understood that it can be applied in a much more "broad" sense. to other surface treatments, in the case of systems applied in the manufacture of printed circuits, single layers or multiple layers (operations of pickling, cleaning, deburring of connection holes, in English "desmearing" or also the application of a flow before performing tinning or another deposit of metallic layers) as well as in other industries that carry out the realization of other types of metallic surfaces.

Claims (21)

1. CLAIMS: 1. A method for treating a surface by the dry route, of at least a portion of the metal surface, according to which the portion is treated at a pressure close to atmospheric with a flow of treatment gas that it comprises excited or unstable species, characterized in that the pressure of the treatment gas is locally increased in the portion of the metal surface to thereby force the chemical species to move in a direction virtually perpendicular to the aforementioned surface. The method according to claim 1, characterized in that the excited or unstable chemical species are obtained by the passage of an initial gas in an electric discharge. 3. The process according to claim 1 or 2, characterized in that the treatment gas is virtually devoid of electrically charged species. 4. The process according to claim 3, characterized in that the treatment gas is obtained from a primary gas mixture and according to the case of an adjacent gas mixture, obtaining the primary gas mixture at the exit of the gas from at least one apparatus formator of excited or unstable gas species, where an initial gas mixture including an inert gas and / or a reducing gas and / or an oxidizing gas has been transformed, while this adjacent mixture mentioned does not pass through the apparatus in question. The method according to any one of claims 1 to 4, characterized in that the flow of treatment gas is emitted in the direction of said surface portion in a direction generally perpendicular to it, and that leads excited particles to the periphery. or unstable, subject to a movement in a direction virtually tangential to the surface portion, and that the pressure of the treatment gas on the surface portion is increased to the periphery of the flow: 1. The method according to any of claims 1 to 5, characterized in that the pressure of the treatment gas on the related surface portion is increased by at least one flow of entrained gas perpendicular to the aforementioned surface portion 7. The method according to claim 6, characterized in that the gas of nitrogen entrainment 8. The process according to any of claims 1 to 5, characterized Because the surface portion is arranged in a treatment chamber and thus the pressure of the treatment gas is increased on this surface portion by at least one fan turned towards said surface to thereby force the flow of treatment gas to bump into the surface. portion of the surface in question, in a direction virtually perpendicular to the latter. The method according to any of claims 1 to 5, characterized in that the metal surface portion is present on a printed circuit board and that said surface treatment performs one or several of the following functions on the surface in question: cleaning , defatting, surface activation, deburring, flow application before welding or tinning. 10. The wave soldering process with electronic components (22, 24) in an electronic circuit in the course of which: - the components (22, 24) are placed in the connection points made in the circuit, -7"- is made a flow application of the circuit (12) by treating the latter with a pressure close to atmospheric by a flow of treatment gas using the surface treatment method according to any of claims 1 to 9; circuit (12) carrying the components (22, 24) in contact with a wave (30) of a welding alloy 11. The method according to claim 10, characterized in that the flow of treatment gas is emitted in the direction of the circuit (12) according to a direction generally perpendicular to it, and because on the surface it carries excited or unstable particles driven with a movement that goes in a direction virtually tangential to the surface of the circuit (12), whereby the operation of increasing the pressure of the flow of treatment gas in the circuit is carried out. (12), to the periphery of the flow. 12. The process according to any of claims 10 or 11, characterized by the pressure of the treatment gas in the circuit being increased by at least one flow of entrained gas perpendicular to the circuit. The method according to claim 12, characterized in that the entrained gas carries nitrogen. The method according to any of claims 10 or 11, characterized in that during the course of the flow application step, the circuit that is arranged in a treatment chamber is subjected to an increase in the treatment gas pressure by means of at least one fan (64) turned towards the circuit to force the flow of treatment gas to run into the circuit (12) in a direction virtually perpendicular to the latter. 15. The method according to any of claims 10 to 14, characterized in that the excited or unstable chemical species are obtained by the passage of an initial gas within an electric discharge. 16. The process according to any of claims 10 to 15, characterized in that the treatment gas carried by the excited or unstable chemical species is produced from a reducing gas mixture containing nitrogen and hydrogen. The method according to any of claims 10 to 16, characterized in that the treatment gas is virtually devoid of electrically charged species. 18. The procedure according to the claim 17, characterized in that the treatment gas is obtained from a primary gas mixture and according to the case of an adjacent gas mixture, the primary gas mixture being obtained at the outlet of the gas from at least one apparatus forming excited or unstable gaseous species. , in which an initial gaseous mixture comprising an inert and / or reducing gas and / or an oxidizing gas was transformed, while the adjacent mixture did not pass through the apparatus. 19. The method according to any of claims 10 to 18, characterized in that the treated electronic circuit is a printed circuit board. 20. A treatment apparatus for at least a portion of metal surface by the dry route, in order to apply a method indicated in any of claims 1 to 9, characterized in that it carries a source of treatment gas containing excited chemical species or unstable as a part displacement device carrying at least one portion of metal surface, to thereby allow the parts to be contacted with a flow of treatment gas, characterized in that it contains elements for locally increasing the pressure of the treatment gas in each piece to force the chemical species to move in a direction virtually perpendicular to the latter. 21. The wave soldering apparatus of electronic components (22, 24) on a printed circuit board, for carrying out a method according to any of claims 10 to 19, characterized in that it carries a device (10) for the displacement of plates through at least one flow applicator device (36) for the plates, by treating the latter with a flow of treatment gas containing excited or unstable chemical species, carrying these plates (12) in at least one of their faces the components (22, 24) that must be welded, in those sites of the connections of the latter, and then pass the material through a deposit (32) containing a solder alloy to achieve the welding of the components , and because he or each flow application device (36) carries elements (60, 62; 64) to locally increase the pressure of the treatment gas in each plate (12) to thereby force the chemical species so that they move in a direction that is virtually perpendicular to the latter.