FR2536944A1 - Device for the reflow of electrolytic coatings on boards, especially printed-circuit boards - Google Patents

Abstract

The invention relates to the techniques of applying electrolytic coatings. The device forming the subject of the invention is characterised in that the system 7 ensuring the desired direction of the flow of heat-transfer fluid 2 is constituted by a closed chamber 8 comprising inlet and outlet nozzles for the heat-transfer fluid and openings 13, for the passage of boards to be treated, made in mutually opposing walls 11, 12 of the chamber 8, transversely to the direction of the flow of heat-transfer fluid, the mechanism for transporting the said boards being placed inside the chamber 8. The invention is particularly applicable to the reflow of the electrolytic coatings on printed-circuit boards in radioelectric installations.

Description

 The present invention relates to the field of radio equipment technology and in particular relates to a device for the remelting of electrolytic coatings on printed circuits.

 The invention can be applied with maximum effectiveness to the remelting of electrolytic coatings on printed circuit boards used in radioelectric assemblies. In addition, the invention can be applied to the remelting of electrolytic coatings on flat elements of apparatus structures in front of between welded during their subsequent assembly.

 A device is known for the reflow of electrolytic coatings on printed c # rwit plates comprising a tank containing a coolant, a mechanism creating in the tank a current of said coolant, a system ensuring the desired direction of flow of the current coolant and a plate transport mechanism through this system.

 The system ensuring the desired direction of flow of the coolant stream is produced in the form of a pair of superposed pipes, mounted horizontally and communicating with each other, these pipes being fitted with coolant outlet pipes, oriented one towards the 'other.

 The mechanism creating the coolant current in the tank is a pump comprising a impeller and an electric motor.

 The plate transport mechanism is a grid conveyor provided with stops for the plates.

The upper strand of the conveyor is located between the lines mentioned, and the lower strand passes under the tank.

 The plate on which the electrolytic coating must be remelted is placed on the conveyor after having placed the stops in the desired positions as a function of the length of the plates to be treated. During its movement by the conveyor, the plate arrives in the area of action of the coolant discharged into the lines by the pump by firing from the tank. Passing through the pipes, the heat carrier heated in the tank is sprayed on the upper and lower surfaces of the plate, in the direction of its movement on the conveyor, and it melts the electrolytic coating of said plate.

 However, such a device does not ensure a high quality of the reflow, because it does not stabilize the temperature parameters of the coolant over time during the treatment of the plates.

 Spraying the coolant on the plate during its treatment causes the coolant to cool rapidly, which means that the operation of the device must be interrupted from time to time to equalize the temperature of the coolant in the tank to the prescribed value.

 During operation, the coolant undergoes intense oxidation by the oxygen in the air, and the solidification process is not stabilized, since the design of the device does not prevent the coolant from dripping onto the already treated plate.

 In addition, the transition to processing plates of other standard dimensions means that the device must be stopped to change the setting of the stops on the conveyor.

 In addition, the design of the known device does not allow reflow on the flexible or flexible plates without using additional means for fixing them during treatment, nor the treatment of plates of different dimensions and configurations in a single technological cycle.

 It is therefore proposed to create a device for the reflow of electrolytic coatings on plates, in which the design of the system ensuring the desired direction of the coolant current makes it possible to obtain a high quality of the reflow of electrolytic coatings on plates of various configuration and thickness.

 This problem is solved by the fact that the device for the reflow of electrolytic coatings on plates of the type comprising a tank containing a coolant, a mechanism creating in the tank a current of said coolant, a system ensuring the required direction of flow of the coolant, and a mechanism for transporting the plates through this system, is characterized, according to the invention, in that the system ensuring the desired direction of flow of the coolant is constituted by a closed chamber comprising pipes for the inlet and the outlet of the coolant and the openings for the passage of the plates, formed in the mutually opposite walls of the chamber, transversely to the direction of the coolant current, the plate transport mechanism being placed inside said chamber.

 The high quality of the reflow of the electrolytic coating on the plates, that is to say the obtaining of a shiny, uniform coating, with a structure without pores, results from the fact that the temperature parameters of the coolant over time , created in the closed chamber, are optimal for the simultaneous treatment of both sides of the plates while ensuring an intense circulation of the coolant. In the device according to the invention, the continuous uniformization of the temperature of the coolant in the volume of the chamber is effected by virtue of the arrangement of the mechanism for transporting the plates in a stream of undivided coolant inside the bedroom.

 The minimum flow of the coolant on the plate when entering and leaving the chamber is due to the fact that the direction of movement of the plate in the chamber and the direction of admission of the coolant into the chamber are perpendicular to it. one to the other, which excludes the thermal action of the coolant on the already treated plate and thus stabilizes the solidification process of the coolant on the plate.

 It is advantageous to make the plate transport mechanism in the form of pairs of rollers placed one above the other, the lower rollers being motor and ensuring the movement of the plates transversely to the heat transfer stream, and the rollers upper ones being mounted so that they can move vertically forming a spacing for the passage of plates of different thicknesses between the rollers.

 Such a design of the plate transport mechanism enables continuous uniformization of the temperature of the coolant in the volume of the chamber, due to the arrangement of the rollers in an undivided coolant stream and the accumulation of heat by the 'rollers. In addition, such a design allows reflow on flexible or flexible plates, not fixed in position during transport.

 The stabilization of the thermal regime in the reflow chamber is also favored by the fact that the first and last rolls, in the direction of movement of the plate in the chamber, limit the zone of thermal action on the plate.

 It is advantageous to make in the mutually opposite walls of the chamber- vertical grooves receiving the axes of the upper rollers so that they can rotate and move there vertically. This makes it possible to process plates of different thicknesses in a single technological cycle without further changing the adjustment of the plate transport mechanism.

 It is also advantageous for the upper rollers to be composite, by being made up of washers mounted so that they can move vertically with respect to one another for the passage of plates having different thicknesses. Such a design of the upper rollers eliminates the escape of the coolant from the chamber during the treatment of plates whose width is much smaller than the width of the openings for the passage of said plates.

 The washers constituting the upper rollers are advantageously freely mounted on the axes of said rollers, which makes it possible to process in a single technological cycle plates of different thicknesses, widths and configurations without vertical displacement of the upper rollers, since the rise of the washers does not is effected only under the action of the plate, the value of the interval between the axes of the upper rollers and the bore of the washers corresponding to the maximum thickness of the plate to be treated.

 In addition, it is advantageous for the openings made in the walls of the chamber for the passage of the plates to coincide with the plane passing through the line of contact of the rollers with one another.

 Such an embodiment of the openings eliminates the need to fix the plates on the conveyor during their treatment in the chamber, because, regardless of its thickness, the plate to be treated is positioned on the lower rollers, which have no vertical movement and are rigorously positioned relative to the chamber openings.

The invention will be better understood and other objects, details and advantages thereof will appear better in the light of the explanatory description which will follow of different embodiments given only by way of nonlimiting examples, with references to the drawings. nonlimiting annexed in which
- Figure 1 schematically shows an overall view of a device for the reflow of electrolytic coatings on plates, according to the invention, cross section;
- Figure 2 shows a sectional view along II-II of Figure 1 ;;
- Figure 3 shows an overview of the system ensuring the desired direction of flow of the coolant, consisting, according to the invention, by a closed chamber (axometric view on a larger scale)
- Figure 4 shows a following sectional view
IV-IV of Figure 3, showing the interaction of the upper roller, consisting of washers, the lower roller and the plate to be treated.

 The device for the reflow of electric, trolytic coatings on plates comprises a tank 1 (FIG. 1) containing a coolant 2 and a heating element 3.

The device also includes a tunnel 4 (Figure 2) creating in the tank a coolant stream, shown in Figures 2 and 3 by arrows "a". This mechanism 4 is constituted by an electric motor 5 and a impeller 6 with fins. In addition, the device which is the subject of the invention comprises a system 7 (FIGS. 1,2) ensuring the desired direction of flow of the coolant, and a mechanism for transporting the plates through the system 7.

 The system ensuring the desired direction of flow of the coolant consists of a chamber 8 closed on all sides, comprising pipes 9 and 10, for, respectively, the inlet and the outlet of the coolant, as well as openings 13 (figures 1,3) practiced in the mutually opposite walls 11 and 12 of the chamber 8, transvervffes ment to the direction of the coolant current, for the passage of the plates, for example printed circuit boards like that shown at 14 in Figures 3 , 4.

 The plate transport mechanism is mounted inside the chamber 8. It comprises lower rollers 15 and upper rollers 16, arranged in pairs, one above the other.

 The lower rollers 15 are motor, the rotation being transmitted to them from the chaste wheel 17, by the shaft 18 and the toothed wheels 19, 20, 21, 22, 23, 24, 25, 26, 27. The wheels mounted on the lower rollers 15 are integral with it. The rotation is transmitted to the chain wheel 17 by a chain driven by a motor system (not shown).

 The upper rollers 16a = tmc # fted so that they can move vertically, forming a spacing for the passage of plates 14 of different thicknesses between the rollers 15 and 16. For this we have achieved in the mutually opposite walls 28 (Figure 3) and 29 of the chamber 8 of the vertical grooves 30, in which are engaged the axes 31 of the upper rollers 16, so that they can rotate and move there vertically.

 The openings 13 of the chamber 8 coincide with the plane passing through the contact line of the rollers 15 and 16. In front of the openings 16d 'entne'et # s: rtLesoetmonté # s' a conveyor 32 (Figure 1) supplying the chamber 8 in plates 14 and a conveyor 33 for discharging the plates 14 from chamber 8.

 Each upper roller 16 is composite (FIG. 4), constituted by washers 34 which are mounted on the axis 31 with a clearance 35 allowing the washers 34 to carry out relative vertical displacements for the passage of plates 14 of different thicknesses.

 The device operates as follows.

 The plate 14, previously fluxed, is placed on the feed conveyor 32, which moves it towards the opening 13 of the chamber 8 entrance. The plate 14 engaged in the chamber 8 is clamped there by the first pair of rotating rollers 15 and 16, which advances it to the next pair of rolls. The upper rollers 16 then rise in the grooves 30 of the walls 28 and 29, by a value equal to the thickness of the plate 14. The first upper roller 16 (in the direction of movement of the plate) is applied to the surface thereof, thus preventing the coolant 2 from flowing towards the part of the plate which has not yet entered the chamber 8.

 The coolant 2 being permanently in the chamber 8 uniformly and simultaneously licks the plate 14 on both sides larsdesandéfilemenrt between the rollers 15 and 16. Inside the chamber 8, the temperature field is uniform throughout the volume, because the coolant circulates there constantly and its contact with air is minimal.

In addition, as the rollers 15 and 16 are permanently in the zone of the heat transfer fluid 2, they play the role of heat accumulators, by standardizing its temperature.

 The rollers 15 and 16 scroll the plate across the undivided stream of coolant 2, transversely to the direction of its circulation, then they take it out of the chamber by presenting it to the conveyor 33 for discharging the plates. Once the plate 14 has left the chamber 8, the last upper roller -16 (in the direction of movement of the plate) descends on the roller 15 closing the opening 13 and thus preventing the coolant 2 from flowing on the plate 14 having just been treated, which contributes to the stabilization of the solidification process of the recast coating.

 After having traversed the chamber 8, the current "a" of coolant 2 passes through the tube 10 and returns to the tank 1.

 When there are no plates 14 to be treated in the chamber 8, the end rollers 15 and 16 come into intimate contact and the coolant can practically not escape to the outside through the opening 13, because the current "a" of the coolant 2 flows in the chamber 8 along the rollers 15 and 16.

 In the case where the plate 14 (Figure 4) to be treated located in the chamber 8 has a width much smaller than the width of the opening 13, the washers 34 are lifted above the plate 14, the axis 31 remaining stationary thanks to the play 35, while the washers 34 located beyond the plate 14 remain intimately applied to the lower roller 15 under the action of their own weight.

 This also contributes to limiting the quantity of coolant 2 escaping from the chamber 8.

 The device for the rejection of electrolytic coatings on plates is a device with extended functional possibilities, because, for the first time in the art, it provides high-quality reflow on thin multilayer and monolayer plates (0.1 3 mm), including flexible or flexible plates of any length and configuration.

 In addition, the device has a high efficiency, because it operates in a continuous cycle, the stops for setting changes and the uniformization of the temperature of the coolant being eliminated.

Claims (6)

 1. Device for the remelting of electrolytic coatings on plates such as, for example, printed circuit boards, of the type comprising a tank (1) containing a coolant (2), a mechanism (4) creating in the tank a current of said coolant, a system (7) ensuring the direction of flowreqns McozEnSde coolant, and a mechanism for transporting the plates through said system, characterized in that the system (7) ensuring the desired direction of the coolant stream (21) is constituted by a closed chamber (8) comprising pipes (9, 10) for the entry and exit of the coolant and openings (13) for the passage of the plates to be treated, formed in mutually opposite walls (11, 12) of the chamber (8), transverse to the direction of the coolant current, the transport mechanism of said plates being placed inside the closed chamber (8).  2. Device according to claim 1, characterized in that the plate transport mechanism is constituted by pairs of superimposed rollers (15, 16), the lower rollers (15) being motors and ensuring the displacement of the plates to be treated transversely to the direction of the coolant current, and the upper rollers (16) being mounted so that they can move vertically and thus form a gap for the passage of plates (14) of different thicknesses between the rollers (15,16).  3. Device according to one of claims 1 and 2, characterized in that in the mutually opposite walls (28, 29) of the chamber (8) are formed vertical grooves (30) receiving the ends of the axes (31) of upper rollers (16) so that they can rotate and sty move vertically.  4. Device according to one of claims 1, 2 and 3, characterized in that the upper rollers! 16) are constituted by washers (34) mounted so that they can move vertically relative to each other to allow the passage of plates (14) of different thicknesses.  5. Device according to claim 4, characterized in that the washers (34) constituting the upper rollers (16) are freely mounted on the axes (31) of these rollers.  6. Device according to one of claims 1, 2, 3 and 4, characterized in that the openings (13) of the chamber (8) for the passage of the plates (14) coincide with the plane passing through the contact line rollers (15, 16) therebetween.