EP0018885A1 - Manufacturing process for microwave cavities, cores utilised in this process and cavities obtained by this process - Google Patents

Abstract

Method permitting simultaneous fabrication, by electroforming, of a cavity and the integrated parts (partitions, membranes, rods, etc...) which it contains Onto a core (4) whose external surface reproduces the internal surface of the cavity to be made and in which are hollowed out holes corresponding to the integrated parts to be made in the cavity, are deposited successively an adhering sub-layer, a sub-layer conductive under high frequency, and a copper layer. The core (4) which can consist of several elements (40, 41, 42) is disengaged from the cavity by simple extraction in the case of the elements whose position and shape thus permit (41, 42), and by dissolving in the case of the other elements (40). Application to microwave cavities. <IMAGE>

Description

The present invention relates to a method for manufacturing, by electroforming, microwave cavities comprising integral parts integral with the internal walls of the cavity.

• - l'ensemble des pièces intégrantes qui sont des pièces rapportées en laiton ou en un autre métal cuivreux, ne forme pas un tout absolument homogène avec le reste du métal constituant les parois de la cavité proprement dite,
• - la mise en place des pièces intégrantes n'atteint pas toujours la précision désirable, tout au moins par un moyen simple de positionnement, car il faut prévoir un jeu suffisant pour pouvoir introduire ces pièces,
• - une fois mises en place, les pièces intégrantes doivent être maintenues de manière qu'elles ne puissent glisser hors de leur emplacement.

Microwave cavities often have internal parts, such as partitions, irises or rods, which must have excellent electrical continuity with the internal wall of the cavity itself. In what follows and in the claims, these internal parts will be called integral parts in abbreviation of integral parts of the cavity. The conventional method of manufacturing such cavities by electroforming consists of inserting the integral parts into the core used for electroforming the cavity. These integral parts form a block with the copper electrolytically deposited during electroforming. This process already represents progress compared to an assembly produced by brazing, but it still has drawbacks:

• - all of the integral parts which are added parts made of brass or another copper metal, do not form an absolutely homogeneous whole with the rest of the metal constituting the walls of the cavity proper,
• the fitting of the integral parts does not always reach the desired precision, at least by a simple positioning means, since there must be sufficient clearance to be able to introduce these parts,
• - once installed, the integral parts must be maintained so that they cannot slide out of their location.

The present invention aims to avoid the above drawbacks and relates not only to a manufacturing process but also to the cores for the implementation of this process and to the cavities obtained by this process.

This is obtained, in particular, by producing, by a single electroforming, the cavity proper and the integral parts. Such a method is made possible by the process and the nuclei used.

• - réalisation d'un noyau dont la surface externe correspond à la surface interne de la cavité à fabriquer,
• - décapage du noyau,
• - dépôt par voie chimique d'une sous-couche métallique d'adhérence,
• - dépôt par voie électrolytique d'une sous-couche métallique conductrice en haute fréquence,
• - dépôt par voie électrolytique d'une couche de cuivre, effectué dans un bain acide à grande pénétration, comportant des agents organiques destinés à favoriser la formation de couches de structure compacte et homogène,
• - extraction du noyau,
• - dissolution de la sous-couche d'adhérence,
• - nettoyage de la cavité obtenue.

According to the invention, a manufacturing process of the type described at the beginning of this text is characterized by the following series of operations:

• - production of a core whose external surface corresponds to the internal surface of the cavity to be manufactured,
• - stripping of the core,
• - chemical deposition of a metallic adhesion underlay,
• - electrolytic deposition of a metallic conductive sublayer at high frequency,
• - electrolytic deposition of a copper layer, carried out in an acid bath with high penetration, comprising organic agents intended to promote the formation of layers of compact and homogeneous structure,
• - core extraction,
• - dissolution of the adhesion undercoat,
• - cleaning of the cavity obtained.

• - les figures 1, 3, 5 des cavités selon l'invention,
• - les figures 2, 4, 6, 7 des noyaux selon l'invention.

The invention will be better understood and other characteristics will appear from the following description and the figures relating thereto which represent:

• - Figures 1, 3, 5 of the cavities according to the invention,
• - Figures 2, 4, 6, 7 of the cores according to the invention.

• - réaliser un noyau dont la surface externe correspond à la surface interne de la cavité (cette réalisation sera décrite plus loin à l'aide des figures 1 à 7),
• - décaper le noyau en milieu fluo-nitrique,
• - déposer une sous-couche d'adhérence constituée d'un premier dépôt de zinc (ou de nickel), d'environ 1 micron d'épaisseur, obtenu par voie chimique et d'un second dépôt d'une épaisseur de 2 à 3 microns, réalisé en laiton, en cuivre ou en nickel, et obtenu par voie électrolytique,
• - déposer une sous-couche métallique, conductrice en haute fréquence, d'environ 20 microns d'épaisseur, constituée d'argent ou d'or électrolytique,
• - déposer, par voie électrolytique, du cuivre jusqu'à l'épaisseur désirée pour les parois de la cavité à fabriquer,
• - extraire le noyau (l'extraction du noyau sera décrite à l'aide des figures 1 à 7),
• - nettoyer la pièce obtenue après extraction du noyau, en milieu de persulfate d'ammonium à 50°C en solution à 50 grammes par litre de persulfate d'ammonium,
• - rincer en eau déminéralisée froide,
• - dépassiver à l'aide d'acide chlorhydrique à 10% ,
• - rincer à nouveau en eau déminéralisée froide,
• - réaliser une argenture électrolytique de finition sur une épaisseur de 7 microns, afin d'obtenir une couche interne homogène du point de vue de ses caractéristiques en haute fréquence,
• - rincer en eau déminéralisée froide,
• - procéder à une passivation de l'argent par voie électrolytique,
• - rincer en eau déminéralisée sous ultrasons.

An example of the manufacturing process according to the invention comprises the following steps:

• - produce a core whose external surface corresponds to the internal surface of the cavity (this embodiment will be described later using Figures 1 to 7),
• - pickling the nucleus in fluo-nitric medium,
• - deposit an adhesion sublayer consisting of a first deposit of zinc (or nickel), about 1 micron thick, obtained by chemical means and a second deposit with a thickness of 2 to 3 microns, made of brass, copper or nickel, and obtained by electrolytic means,
• - deposit a metallic underlay, conductive at high frequency, about 20 microns thick, made of silver or electrolytic gold,
• - deposit, electrolytically, copper up to the desired thickness for the walls of the cavity to be manufactured,
• - extract the core (the extraction of the core will be described using Figures 1 to 7),
• - clean the part obtained after extraction of the core, in the middle of ammonium persulfate at 50 ° C in solution at 50 grams per liter of ammonium persulfate,
• - rinse with cold demineralized water,
• - deactivate using 10% hydrochloric acid,
• - rinse again with cold demineralized water,
• - achieve a finishing electroplating on a thickness of 7 microns, in order to obtain a homogeneous internal layer from the point of view of its characteristics at high frequency,
• - rinse with cold demineralized water,
• - passivate the silver electrolytically,
• - rinse with demineralized water under ultrasound.

In the process which has just been described, the baths making it possible to make the various deposits are commercial baths.

By way of example, the following details are given on the baths used for implementing the process which has just been described.

The chemical deposition of a metallic adhesion sublayer is obtained by chemical displacement of the metal dissolved in the bath; the good adhesion of this deposit depends on the chemical composition of the bath. These baths are commercially available and are widely used in the electrolytic treatment of alloys.

For the electrolytic adhesion deposits of brass, copper or nickel, the baths must have a composition such that the metal undercoat obtained by chemical means is not attacked, which would cause a defective adhesion of the electrolytic adhesion deposit. . These baths are in common use for the electrolytic treatment of light alloys.

The high frequency conductive metal undercoat is obtained using the baths marketed for coating the electronic cavities; these are generally cyanide baths.

The baths used for depositing copper up to the desired thickness for the walls of the cavity are acid baths with high penetration, comprising organic agents intended to promote the formation of layers of compact and homogeneous structure. These types of bath are in common use in the technique of printed circuits; they are based on copper sulphate and sulfuric acid; with this type of bath and the process used, correct deposits of copper are obtained in the angles, even when these angles are equal to or slightly less than 90 °.

For finishing electroplating, baths of the type discussed for the high frequency conductive metal underlay can be used.

The bath used for the electrolytic passivation of the finishing silver deposit is a commercial bath of common use in electrolytic treatments of surfaces.

The cores mentioned above are produced so as to electroform the integral parts of the cavity at the same time as the cavity itself. For this, the shapes of integral parts are hollowed out in the cores, with tolerances on their dimensions corresponding to the desired tolerances for the integral parts to be produced. To obtain precise dimensions, the cores are made entirely of metal.

Figures 1, 3, 5 show partially cut cavities so that the integral parts appear which have been inserted therein by electroforming. These three cavities have the form of waveguides and one of the cutouts intended to show their integral parts, is produced according to a longitudinal median plane.

Figure 1 is a partial view of a cavity, 1, comprising two rods 10, 11. This cavity, like besides the cavities shown in Figures 3 and 5, was produced by electroforming according to the method described above.

The core used to manufacture the cavity of FIG. 1 is shown in FIG. 2. FIG. 2 shows a core 2 whose position has been shown in dotted lines to reveal two holes 20, 21 intended to give the rods 10 and 11 of the cavity according to FIG. 1.

The core 2 of FIG. 2 is a core of light aluminum alloy (AU4G: aluminum alloy with 4% copper and 1% magnesium), produced by machining. The extraction of this core, after the electrolytic copper layer has been deposited, is done by dissolving in a hot 10% sodium hydroxide solution, under current. air and at a temperature of around 70 ° C. The duration of solubilization of a core under such conditions depends, of course, on the thickness of metal to be dissolved and on the contact surface between the metal and the dissolving liquid.

• - les éléments 41, 42 en acier inoxydable sont retirés et peuvent être réutilisés pour réaliser une autre cavité,
• - l'élément 40 est dissous de la même façon que le noyau de la figure 2.

Figure 3 is a partial view of a cavity having two irises 30 and 31. Figure 4 shows the core 4 which was used for the realization of this cavity. This core has three elements 40, 41, 42. Elements 41 and 42 are identical and are made of 18-8 stainless steel; they form a parallelepiped with, on one face of the parallelepiped, a cylindrical patch such as 43. The element 40 is a parallelepiped made of the same material as the core of FIG. 2. The three elements 40, 41, 42 are assembled using a cyanoacrylate type adhesive which, deposited locally in a very thin layer, ensures a good bond between the elements. The extraction of this nucleus, after deposition of the electrolytic copper layer, is done in two stages:

• the elements 41, 42 made of stainless steel are removed and can be reused to make another cavity,
• - element 40 is dissolved in the same way as the core of Figure 2.

FIG. 5 is a partial view of a cavity 5 comprising three internal partitions 51, 52, 53. The core, 6, having been used to manufacture this cavity is shown in FIG. 6; it is formed by a cylinder in which notches such as 60 are made; it is these notches which, during electroforming, give the internal partitions of the cavity. The core 6 is a core of light aluminum alloy (AG5: aluminum alloy with 5% magnesium), it is obtained by foundry with "lost wax". This core is dissolved, after use, in the same way as the core of Figure 2.

FIG. 7 represents a core 7 intended to allow the manufacture, according to the method described above, of a quadruplexer for reuse of frequencies; the ^q uadruplexer is intended for an antenna. This core comprises a cross element 70 and, on either side of this element, two other elements 71 and 72 bonded to the cross at the intersection of its two branches. It should also be noted that the core 7 comprises, at the intersection of the cross, a metallic piece of brass 73, which crosses the cross; this part is hollow and has partitions which, because of their position, could not be obtained by electroforming at the same time as the rest of the quadruplexer.

The partial views 1, 3, 5 do not show the flanges of the cavities, used for fixing in the microwave assemblies for which these cavities are intended; Similarly, on the partial views of cores 2, 4, 6, 7, the parts of the core on which, during electroforming, the deposits which constitute the flanges are not shown. This omission is voluntary because on the one hand it makes it possible to better highlight on the drawings the integral parts and the shapes of cores leading to obtaining such integral parts, and on the other hand the obtaining of flanges does not pose any problems from the moment when it is known to manufacture a cavity with internal integral parts. In the cavities according to the examples described, the flanges are obtained by stainless steel parts bonded to the rest of the core and whose faces which must not receive metallic deposits are covered with a layer of air-drying vinyl paint, or plastic tape, or plastic covers.

Of course, the invention is not limited to the examples described; thus the cohesion of the cores can be increased by mechanical means, metallic or non-metallic, which are removed once the electroforming is completed. Likewise, variants within the reach of those skilled in the art can be found in the example of the manufacturing process which has been described, in particular as regards the types of metals deposited, the thicknesses of the deposits and the number of deposits; this is how, in certain cases, the second silver plating, that is to say that produced after the core has been removed, can be avoided.

Claims (7)

1. A method of manufacturing, by electroforming, microwave cavities comprising integral parts integral with the internal walls of the cavity, characterized by the following operations: - production of a core whose external surface corresponds to the internal surface of the cavity to be manufactured, - stripping of the core, - chemical deposition of a metallic adhesion underlay, - electrolytic deposition of a metallic conductive sublayer at high frequency, - electrolytic deposition of a copper layer, carried out in an acid bath with high penetration, comprising organic agents intended to promote the formation of layers of compact and homogeneous structure, - core extraction, - dissolution of the adhesion undercoat, - cleaning of the cavity obtained. 2. Method according to claim 1, characterized in that it comprises, after cleaning, a silver plating, electrolytically, of the cavity. 3. Method according to any one of the preceding claims, characterized in that the pickling is carried out in a fluo-nitric medium. 4. Method according to any one of the preceding claims, characterized in that the adhesion sublayer consists of a first deposit of zinc and a second deposit of brass. 5. Core used (2,4,6) for implementing the method according to any one of the preceding claims, characterized in that it has a volume of which at least part corresponds to the internal volume of the cavity to be manufactured . 6. The core as claimed in claim 5, intended to allow the obtaining, during manufacture, of integral parts internal to the cavity, characterized in that holes (20, 21, 60) are dug there, the volume of which corresponds to the volume of the integral parts to be obtained. 7. Microwave cavity (1, 3, 5, 7), characterized in that it is obtained by a method according to any one of claims 1 to 4, using a core (2, 4, 6 ) according to any one of claims 5 and 6.

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