Process for making an assembly of electrically conductive patterns on an insulating surface of complex form

The present invention relates to a process for making an assembly of electrically conductive patterns (9, 16) on an electrically insulating surface (20) of complex shape. According to the invention: PA0 said assembly of patterns (16) is formed on a face of a plastically deformable flat support (10); PA0 said flat support (10) is applied, by being deformed, against said surface (20) of complex shape; and PA0 said deformed flat support is connected to said surface (20) of complex shape. The invention finds an advantageous application in the production of reflectors for antennas.

The present invention relates to processes for making an assembly of 
conductive patterns on an insulating surface of complex form and, in 
particular, for making printed circuits presenting a complex surface 
which, a priori, is not developable, for example those which are used for 
making reflectors of antennas with discrete resonant elements distributed 
over surfaces of conical, parabolic, hyperbolic, etc . . . type, or those 
which enter in the structure of complex antennas comprising primary 
reflectors and secondary reflectors, as in the assemblies known to 
technicians under the names of Newton, Cassegrain, etc. assemblies. 
Several processes to that end already exist. One of them consists in making 
conductive patterns on a supple, flat support, for example an elastomer. 
This supple support is then drawn then glued on a form identical to that 
which is to be obtained. Another process consists in making the conductive 
patterns on a rigid support, for example a strip of a film of material 
known under the name KAPTON. This support is then cut out into strips or 
sectors of reduced width, thus more easily deformable. These strips are 
then glued on a substrate having the definitive form chosen. Finally, the 
process is known which consists in machining a metallized surface coated 
with a protecting varnish and superficially engraved mechanically along 
the contour of the desired patterns. Those parts which are not operative 
are then eliminated, like a skin, this operation generally being carried 
out manually. 
It is obvious that these processes present drawbacks, for example, for the 
first process, a poor resistance of the conductive patterns, particularly 
in the event of considerable variations in temperature. The other two 
processes seem more reliable, but the complexity of their embodiment does 
not render them industrializable and they can only be used punctually. 
The present invention has for its object a process for making printed 
circuits presenting a complex surface which is non-developable or 
developable only with great difficulty, which overcomes the drawbacks of 
the known processes, whilst conserving certain of their qualities. 
More precisely, the present invention has for its object a process for 
making an assembly of electrically conductive patterns on an electrically 
insulating surface of complex form, noteworthy in that: 
said assembly of patterns is formed on a face of a plastically deformable 
flat support; 
said flat support is applied, by being deformed, against said surface of 
complex form; and 
said deformed flat support is connected with said surface of complex form.

The present invention concerns a process for making printed circuits 
presenting complex surfaces which are non-developpable or at least fairly 
difficult to develop. These circuits are of very great importance in 
modern techniques and are in particular currently used in reflectors of 
antennas 1 such as the one illustrated in FIG. 1. This reflector 1 is 
mounted on a support 2, which cooperates with a support surface 3 via arms 
4. The reflector 1 presents a surface which is non-developpable in shape, 
for example paraboloid 5. The surface 6 of this paraboloid is constituted 
by a support 7 made of an electrically insulating material comprising on 
its surface 8 patterns 9 which, themselves, are electrically conductive. 
By way of example, patterns in the form of crosses have been shown, but it 
is obvious that these patterns may be in any other shapes necessary for 
the technicians. 
In order to make such electrically conductive patterns, the process as 
described hereinafter is advantageously used, which, with respect to the 
processes of the prior art, gives very good results, but which presents 
the additional advantage of being able to be industrialized for 
large-scale production. 
The different principal phases of the process are shown in FIGS. 2 to 7. 
The process consists, in a first stage, in making a first flat support 10 
whose dimensions are close to those which must be obtained for making the 
complex surface (FIG. 2). This first support must be deformable and, if it 
is made of a metallic material, must be able to be annealed. It may thus 
be constituted by a copper foil having a thickness of the order of 10 to 
40 microns. 
In a second step (FIG. 3), there is then deposited on this first support 10 
a layer of a first given material 11, for example a varnish, defining, in 
this first material, zones 12 corresponding to the shape of a giver 
circuit. In order to obtain these zones 12, it is possible to deposit the 
first material over the whole surface of the first support and then to 
define the zones therein, for example by photo-engraving or silk-screen 
process. 
By way of example, the shape of the circuit illustrated is a cross, but it 
is obvious that it may be any other: circular, elliptic, square, etc . . . 
When this second step is terminated, in a third step, a second material 13 
is deposited in these zones in order to cover the whole bottom thereof, 
over a thickness smaller than that of the first material 11 (FIG. 4). By 
way of example, this second material may be gold, silver, nickel, 
aluminium or tin, which are good electrically conductive materials and 
among those which are most advantageously used for the application 
mentioned hereinbefore, and the thickness may be of some microns. 
Moreover, if the second material 13 is one of the three mentioned 
previously, it may advantageously be deposited by an electro-chemical 
process presenting the advantage, at the same time, of connecting the 
layer of this second material with the surface of the first support 10. 
Having arrived at this stage, the process then consists, in a fourth phase, 
in eliminating the layer of the first material 11, without eliminating the 
second material 13 (FIG. 5). To that end, the two materials are chosen to 
be respectively attackable and non-attackable by a certain product. If the 
first material is a varnish and the second gold, the layer 11 may easily 
be eliminated by the action of a solvent not attacking the gold. This 
technique is, moreover, well known per se and will therefore not be 
described in greater detail. 
At this stage, a still flat support 10 is therefore obtained which 
comprises, in relief on a face 15, all the patterns 16 having the shape of 
the zones which had been defined in the layer of the first material 11 
originally deposited on this face 15. 
In a fifth stage, the edges 17 of the first support 10 comprising the 
patterns 16 are gripped firmly in a frame 18 (FIG. 6) and the assembly of 
these two elements, support 10 and patterns 16, is applied on a second 
support 19, for example a substrate of composite material reinforced with 
glass fibers or aramide fibers such as those known under the trade name 
KEVLAR. This support 19 is such that its face 20 has the profile of the 
complex shape of the surface of the printed circuit having to be finally 
obtained. On the frame 18 are then applied efforts shown schematically by 
arrows 21, in order to deform the first support 10 and to give it the 
shape of this complex surface 20, by applying it against the face 20 of 
the second support 19. 
The assembly of the two elements, first support and patterns, is, of 
course, connected by any means, for example glue previously spread over 
the face 20 of the second support 19. 
In the example illustrated, the complex shape is a convex surface but it 
may be of any other shape. 
When this fifth step is terminated, the material of the first support 10 is 
eliminated, so as to conserve on the second support of non-electrically 
conductive material, only the predetermined patterns 16 made of conductive 
material. If the first support is made of copper and the patterns of gold, 
the copper is eliminated by chemical attack with a solution of iron 
perchloride or an alkali solution. This operation may also be used with a 
first support made of aluminium. 
FIGS. 8, 9 and 10, 11 show two modes of application of the first support 10 
supporting the patterns 16 on the second support 19 made of non-conductive 
material. 
FIGS. 8 and 9 show a first mode of application. The assembly comprising the 
first support 10 with the patterns 16 is applied on the face 20 of the 
second support, so that the patterns 16 are in contact with this face, for 
example glued thereon (FIG. 8). In that case, the first support is 
attacked by the chemical product and, finally, there remain only patterns 
16 on the face 20 of the second support (FIG. 9). 
FIGS. 10 and 11 show another mode of application, in which the assembly of 
the support 10 and the patterns 16 is disposed on the second support 19 so 
that the first support 10 is itself directly glued on the face 20 of this 
second support. The material of the first support is then chemically 
attacked in the same manner as hereinabove. However, in this case, the 
patterns 16 remain located on columns 21 of material of the first support 
coming from parts of this first support which were not attacked 
chemically, since they were protected by the material of the patterns 16 
which is itself non-attackable by the chemical product chosen for 
eliminating the material of the first support. 
It should be specified that the Figures have been elaborated only to 
illustrate the different steps of carrying out the process and to enable 
it to be more readily understood, but that in no way do they intend to 
give a perfect representation, to scale, of the different thicknesses of 
the different layers of materials. 
In the embodiment given hereinabove, and up to the final result as 
illustrated in FIGS. 8 and 9, it is sometimes advantageous to choose the 
first support in a material of organic type, such as a thermoplastics 
resin. In that case, the assembly of the first support 10 and patterns 16 
is advantageously disposed on the second support 19 in accordance with the 
mode of application illustrated in FIG. 8. In fact, the material 
constituting the first support not being electrically conductive, it is 
not necessary to eliminate it and if, in addition, the second support is 
chosen to be made of this same material (FIG. 12), adherence of the 
patterns may be obtained by simultaneous heating of the two supports until 
at least a partial fusion 22 is obtained therebetween, the patterns 16 
then being imprisoned in this non-conductive material protecting them from 
any action of outside agents, which enables them to be made of any 
conductive material, even oxidizable. 
The foregoing description shows all the advantages of the process according 
to the invention, in particular the fact that it makes it possible to 
solve the problems raised in modern technology for obtaining industrial 
production of printed circuits disposed on complex surfaces which are very 
difficult to develop, in particular for making reflectors of antennas of 
which one has been chosen, in the description, by way of example of 
application.