CA1171549A

CA1171549A - Printed circuits and methods of manufacturing same

Info

Publication number: CA1171549A
Application number: CA000385491A
Authority: CA
Inventors: Edouard Serras-Paulet
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-09-09
Filing date: 1981-09-09
Publication date: 1984-07-24
Also published as: WO1982000938A1; EP0059206A1; AU7537981A; NO821481L; BE890272A; ES8302403A1; JPS57501353A; DK204982A; FR2490059B1; FR2490059A1; IT8123851A0; IT1138586B; EP0059206B1; ES505299A0

Abstract

ABSTRACT OF THE DISCLOSURE
A printed circuit has at least two crossed or superimposed conductor path systems insulated from one another except at certain points of interconnection. The printed circuit comprises a support such as a polyester film, the upper face of which has a system of conductor paths and contact areas and the lower face of which also has a system of conductor paths, these systems being formed by serigraphic deposition of conductive ink and polymerization of these inks, with connections between the two systems being formed by holes in the support, the walls of which are at least partly covered by polymerized conductive ink. The invention is in particular concerned with flexible printed circuits and their methods of manufacture.

Description

FIELD OF THE INVENTION
The present invention relates to an electrical printed circuit of the type having at least two crossed or superimposed conductor systems separated by a dielectric.
DESC_IPTION OF THE PRIOR ART
Conventional printed circuits having a single face or a double face are well known, which comprise a dielectric support, usually of glass or epoxy resin, covered on one or both of its major surfaces with a thin copper layer, the major part of which is subsequently removed to leave remaining only a system or network of conductive paths and contact studs or lands of copper on one or both faces of the support.
These printed circuits have the basic disadvantage of having a high cos-t price due to the complexity of their method of manufacture and to the elimination of the large majority of the copper with which the supports are initially covered and of being, in general, rigid and thick. Furthermore, the upper contact studs or lands should be subjected to a supplementary treatment for resistance to oxidation.
Likewise, flexible printed circuits are known which are obtained by the same procedure and which difer from the above mentioned prior art printed circuits only by the nature of the support, which can be a sheet of flexible dielectric material.
However, the copper paths which these circuits comprise are fragile and are broken by bending or as a result of a ~`
~ - 2 -s~
substantial Elexure. They also have a high cost.
To mitigate these disadvantages, there has recently been developed a technique for the manufacture of flexible or rigid printed circuits which consists of depositing a conductive ink by serigraphy on a dielectric support to form a conductor system on one face of this support. After deposition on the support, the ink is polymerized by heating. In this way, printed circuits are obtained the cost price of which is much less than that of conventional printed circuits having copper paths and the conductive paths of which, formed by polymerized ink, are not broken by bending.
However, in practice this procedure is suitable only for the manufact~re of circuits having a single conductor system. Numerous attempts have been made to obtain printed circuits of this type but comprising two crossed or superimposed conductor systems which are electrically insulated from one another at certain points of connection. The previously proposed methods have consisted, in principle, of depositing a first layer of conductive ink by serigraphy on to the support to form a first system, polymerizing this layer to dry and harden it, depositing a layer of dielectric or insulating ink on parts of the first conductive system by serigraphy, polymerizing the dielectric layer to harden and dry it, subsequently depositing a second layer of conductive ink by serigraphy onto the support and onto certain parts of the first system and the layer of ~ 3 --dielectric ink and polymerizing, by heating, this second layer of conductive ink. In this way there is obtained a second conductor system insulated from the first at certain zones by the intermediate layer of dielectric ink and connected to the first system by the zones at which the second layer of conductive ink has been deposited directly onto the first layer ot conductive ink.
It has ~een established that the circuits obtained in this way present the following extreme disadvantages:
- the conductive particles which the layers of conductive ink contain migrate across the layer of dielectric ink and establish short circuits between the two conductor systems, - the layer of dielectric ink becomes fragile by polymerization and breaks when bent or substantially flexed, which causes rupture of the underlying adjacent conductive paths of the first system;
- the insulating ink undergoes substantial shrinkage on heating, which causes interruption of the overlying conductive paths;
- the heating of the insulating ink for polymerizing it is often accompanied by the formation of blisters, which make impossible the deposition of the second layer of conductive ink;
- insulating inks adhere poorly to certain supports such as, for example, a sheet of polyester;

:~7:~5~
- the thickness of the layer of insulating ink should be much greater than that of the layer of conductive ink which causes the formation by the insulating ink of shoulders or ledges on the support and the first conductive system. The conductive paths of the second system, deposited on these projections or protrusions, present cracks and/or microfissures and are not resistant to bending.
- the thickness of the layer of insulating ink diminishes during the polymerization heating and, at the zones where it is not ~ery substantial, allows the exposure of micro-points of the first layer of conductive ink, which causes short circuits between the two conductive systems;
- the dielectric capacity of the layer of insulating ink is not constant throughout the circuit due to variations in the thickness of this layer; and - the results obtained by utilization of the same inks are not reproducible.
SUMMAR~ OF T~IE INVENTION
It is an object of the present invention to eliminate or at least partially mitigate at least some of the above-mentioned disadvantages.
It is a further object of the present invention to provide a printed circuit having at least two crossed or superimposed conductor systems and Eormed by the deposition of conductive ink or inks by serigraphy, the circuit at least 1~7~5~1~
partially avoiding the above-mentioned disadvantages and being able to be made at a cost price which is three or four times less than that of an eq~ivalent circuit obtained by known serigraphic methods.
According to the present invention, there is provided a printed circuit comprising a dielectric support and at least two electrically conductive systems carried by the support, these systems being crossed or superimposed and electrically insulated from one another except at certain points of interconnection, the systems each preferably comprising paths of polymerized conductive ink and being formed on respective sides of the support so as to be electrically insulated from one another by said support, connections between the systems being established provided across the support by films of conductive ink.
ThUS, according to the invention, the two conductive systems of the printed circuit are perfectly separated from one another by the circuit support, which is of a constant thickness, which has a flat surface and which the conductive particles of the ink cannot traverse by migration.
~he connections between the systems may comprise holes extending through the support and having walls which are at least partially covered by a uniform layer of conductive ink.
In this way~ the desired connections between the two conductor systems are very easily obtained by means of the holes extending through the support and the walls covered at least ~:9.7~
partially with a film of conductive ink, which establishes homogeneous and reliable connections between the systems.
This type of connection differs totally from what is known from the prior art relating to conventional printed circuits with copper paths on both faces of a rigid and thick support of epoxy glass. In this prior technique, the two systems are connected together by 'metallized' holes in the support. These holes are perforated in the support at the desired locations after the complete manufacture of the two conductive systems of the circuit, and then their cylindrical internal walls are covered with a conductive metallic film by galvanization, which is a long and costly process which again increases the cost price of such a printed circuit.
In contrast thereto, the present connections between the two systems are formed at the same time as the conductive systems, in a single operation and without taking up the circuit again for corresponding processing.
The present invention also includes a multi-layer printed circuit assembly comprising a plurality of crossed or superimposed conductor systems which are electrically insulated from one another except at certain points of interconnection between certain zones of certain ones of at least the said systems, which assembly comprises a printed circuit the support of which is provided on its two faces with a conductive system formed by the serigraphic deposition of conductive ink or inks :~'7~
and in which at least one surface of the printed circuit is covered with a sheet or fil3n of dielectric material presenting an exterior surface which carries a conductor system formed by the serigraphic deposition of conductive ink or inks and having connection holes formed through said sheet or fllm and the walls of which are at least partly covered by conductive ink.
This multi-layer printed circuit assembly may comprise a stack of sheets or films of dielectric material, each of which comprises, on one face, a conductor system of the above-mentioned type and connection holes having walls at least partly covered by conductive ink.
Such a multi-layer printed circuit assembly may, for example, have a thickness between one and two millimeters, it can be pliant and comprise a large number of crossed or superimposed conductive systems, this number comprising, for example, between three and fifteen.
The present invention further provides a method of manufacturing a printed circuit, comprising the steps of:
forming holes in a flat support of dielectric material at predetermined points, formed preferably by depositing conductive ink by serigraphy onto the support, on each of its surfaces a conductor system, at least partly covering the walls of the holes by conductive ink and subsequently polymerizing the ink by heating.
The method may include depositing the conductive ink by '7~9 serigraphy simultaneously on tne two faces of the support or depositing a first system of conductive ink by serigraphy on a First face of the support, polymerizing the ink by heating, subseqllently depositing a second system of conductive ink by serigraphy on the second face of the support and polymerizing the second syste~ by heating.
For manufacturi.ng a multi-layer printed circuit assembly, the method may comprise subsequently fixing, on one face of the circuit thus obtained, a sheet or film of dielectric material perforated by holes at predetermined points in such a manner that these holes open onto conductive parts of the circuit, deposing by serigraphy on the exterior face of the sheet or film a layer of conductive ink in such a manner as to form on this face a conductor system and at least partially covering the walls of the holes with conductive ink and polymerizing by heating the ink thus deposited.
These operations may then be repeated to obtain a multi-layer printed circuit assembly comprising a stack of sheets or films of dielectric material each carrying on one face a conductor system of polymerized ink.
In the following description, given by way of example, references made to the accompanying drawings, in which:-Figure 1 shows an enlarged view in perspective of a part of a prior art printed circuit;
Figure 2 is a view in section of a part of the circuit;

~ g _ Figure 2A is an enlarged view o~ the detail encircled II-A in Figure 2;
Figure 3 is a diagrammatic enlarged view, in perspective, of a part of a printed circuit embodying the present invention;
Figure 4 is a view in section of a par-t of the circuit of Figure 3;
Figure 5 diagrammatically represents, in the form of blocks, the steps in a method of manufacture of a printed circuit embodying the invention;
Figure 6 digrammatically represents, in the form of blocks, the supplementary steps for the manufacture of a multi-layer printed circuit assembly; and Figure 7 is a view in section of a multi-layer printed circuit assembly embodying the invention.
Reference is made firstly to Figures 1, 2 and 2A, which represent a prior art printed circuit 10.
The printed circuit 10 comprises a flat support 11 of dielectric material which can be rigid and thick, but which advantageously is thin and flexible, such as a polyester film having a thickness, for example, about 0.1 millimeters. On the upper face 12 of the support 11 first conductive paths 13, 14 and 15 are formed by deposition by serigraphy of a conductive ink, which is then polymerized by heating.
There is then deposited, by serigraphy, on certain 5~3 parts of the upper face 12 of the support 11 and the conductive paths 13, 1~ and 15 a layer of insulating or dielectric ink with the form of bands 16, which is then polymerized by heating.
This insulating layer has a thickness greater than that of the conductive paths 13, 14 and 15.
Further conductive paths 17 are then formed, as previously, on the face 12 of the support 11, on the bands 16 of insulating ink and likewise on certain parts of the first conductive paths 13, 14 or 15 at regions where it is desired to obtain electrical connections between the first conductor system formed by the paths 13, 14 and 15 and the second conductor system formed by the conductive paths 17. By way of example, it is mentioned more specifically ~hat the conductive paths have a width of about 1 millimeter and a thickness comprising between 20 and 30 microns and that the bands 16 of insulating ink have a thickness and a width which are several times greater than those of the conductive paths.
Figure 2 is a view in section of the printed circuit 10 at the zone at which one of the conductive paths 17 of the second system crosses one of the conductive paths 15 of the first s~stem, being insulated therefrom by the one of the band 16 of dielectric ink. The edges of this band 16 form, on the upper surface 12 of the support 11, shoulders or ledges 18 and the thickness of the conductive path 17 deposited on these projections is much less than at the regions where it is S~9 deposited on a flat part, because of the fluidity of the conductive ink.
It has been found that cracks and/or micro-fissures are formed in this zone 19 of lesser thickness of the conductive path 17.
The essential disadvantages of this prior art printed circuit have been indicated hereinbefore. It is repeated only ~hat the conductive particles (for example gold) contained in the conductive paths have a tendency to migrate across the layer of dielectric ink and to establish short circuits between the two conductor systems. The dielectric layer 16 becomes fragile after heating and its rupture causes the rupture of the conductive paths which it covers. Furthermore, the dielectric and conductive inks are not very compatible one with the other and the conductive paths 17 of the second conductor system adhere poorly to the bands 16 of dielectric ink. For this reason, it is often necessary to deposit a new layer of insulating ink, on a part of the conductive path 17 deposited on a band 16 o insulating ink in an attempt to consolidate the assembly.
The method of manufacturing such a printed circuit 10 is relatively long and necessitates the use of Eour serigraphic screens, for depositing the conductive paths 13, 14 & 15 of the first conductor system, fox depositing the bands 16 of insulating ink, for depositing the conductive paths 17 of the ~'7~5~
second conductor system and for depositing a new layer of insulating ink 16 on certain parts of the paths of the second system and the first insulating layer. E~urthermore, a new ink layer cannot be deposited until after polymerization of the previously deposited ink layer, which results in a succession of operations of deposition by serigraphy and heating for polymerization.
The present invention mitigates these disadvantages and, furthermore, provides a substantial improvement of the quality of the printed circuit.
Reference is now made to Figures 3 and 4, which illustrate a printed circuit embodying the invention.
This printed circuit 30 comprises a flat support 31 of dielectric material, such as a polyester film having a thickness comprising between 15 and 1500 microns, for example, between 80 and 100 microns. One such film is known commercially under the name of "Mylar" (Trade Mark). me two faces 32 and 33 of the support 51 each comprise a conductor system formed by deposition by serigraphy of conductive ink, which is then polymerized by heating. The conductor system formed on the upper face 32 of the support 31 comprises conductive paths 34, 35, 36, 37, 38, etc., and contact areas 39 and 40 connected to the paths 37 and 38, respectively.
The conductor system formed on the lower face 33 of the support 31 comprises conductive paths 41, of which only one has been shown in Figure 3. The desired connections between the two ~7~
conductor systems are established by means of holes 42 in the support 31, which open at their upper extremities onto conductive paths of the first system and at their lower extremities onto conductive paths of the second system. The holes 42 may, for example, be at least partly filled with polymerized conductive ink. In the example illustrated in Figure 3, one extremity of the path 41 of the lower conductor system is connected by such a connection to the path 35 of the upper conductor system, and the other extremity of the path 41 is connected to the path 38 of the upper conductor system by a film 43 of conductive ink at least partly covering the wall of the hole 42 and terminating at each extremity of the hole in an annular land ~4 on the corresponding face of the support 31, this land having an exterior diameter greater than the diameter of the hole 42.
The thickness of the film 43 of conductive ink covering the wall of the hole is equal to the thickness of the path 41 or 38 of conductive ink formed on the face 33 or 32 of the ; support. In this way there is obtained, after polymerization of the ink, a conn~ction which is perfectly homogeneous and free of defects (such as cracks, fissures and variations of thickness at the extremities of this hole) which is essential when the support is a flexible film of plastic material having a small thickness of, for example, 80 to 100 microns~ The quality of the connection through the support is due to the formation of 5~ 3 the paths and the connections through the support in a single operation. When the holes are filled with conductive ink, they contain a relatively large amount of ink which is susceptible to producing shrinkages on polymerization, which causes risks of cracks at the edges of the holes.
The holes 42 may be of circular cross-section, as illustrated, in which case their cylindrical walls are completely covered with a film of conductive ink, or of square or rectangular section, in which case a single flat face of the hole is covered with ink or two opposed faces.
A connection between two conductive paths each formed on a different face of the support can equally be effected at the edge of the support, as indicated by reference numeral 43a in Figure 3.
A projecting tab formed by the support, such as that in Figure 3 carrying the extremities of the paths 34, 35, 36 and 37, can be utilized as the male part of the standard connector.
When the support is a flexible film of plastic material, this tab can be connected around a corresponding tab of a rigid support having the desired thickness.
If desired, the contact studs or lands 39, 40, like the extremities of the paths 34 - 37 which terminate at the edge 43 of the support 41 and which serves as paths of connection with a connector, may be formed by a conductive ink different from the ink utilized for the conductive paths and having, after .~'7~9 polymerization, a hardness or a mechanical resistance greater than that of the conductive paths. By way of non-limiting example, it is pointed out that the contact areas or lands can be formed with ink supplied by the SOCIETE EPOTECNY under Reference H20F-l and that the conductive paths can be formed with ink supplied by COMPTOIR LYON ALE~AND LOUYOT under Reference BF5 or by the SOCIETE DUPONT DE NEMOURS under Reference 4049.
Commercially available resistive, copacitive or inductive serigraphic inks may likewise be used to form by serigraphy a printed conductor system including resistors, capacitors and inductors, respectively.
It is possible to solder components, such as resistors, capacitors, conductors, transistors, integrated circuits, etc.
onto a circuit according to the invention, such as that of Figure 3.
In a modified embodiment, the flexible suppor-t 31, comprising, for example, a polyester film, can be replaced by a thicker sheet of dielectric material, such as, for example, a sheet of epoxy glass. In this way there is obtained a printed circuit which is rigid or semi-rigid, corresponding to the thickness of the support.
In all cases, the diameter of the connection holes 42 between the two conductive systems of the circuit should be determined such that the walls of the holes are partially or ~7~5~
totally covered with conductive ink when the conductor systems are formed on the support by serigraphic deposition of the conductive ink. This diameter is a function of the viscosity of the ink utilized and of the thickness of the support. It has been found that, for the majority of conductive inks, and when the support has a thickness of about 80 to 100 microns, the best results were obtained with holes having a mimimum diameter of approximately 0.8 millimeters.
Reference is now made to Figure 5, which diagrammatically represents the different steps of a method of manufacturing a printed circuit according to the invention. The first step 45 consists in perforation of the support 31 in such a way as to form therein holes of a predetermined size at the regions were it is desired to ensure connections between the two conductor systems. The next step 46 comprises depositing onto each face 32, 33 of the support 31 a system of conductive ink by means of two serigraphic screens containing the ink. This technique of printing or ~eposition by serigraphy is very well known and will not be described in greater detail. The walls of the holes 42 pierced in the support are covered, at least partly, with a film of conductive ink at the same time as the conductor systems are formed on the two faces of the support 31. The next step 47 consists in submitting the support, the two faces of which each caery a system of conductive ink, to heating in order to polymerize the ink. This heating is s~
effected in general in an oven, for example by infra-red or ultraviolet irradiation, at a temperature of 150C for a period of five to ten minutes.
The printed circuit is then finished and can be utilized. Possibly, if required, one and/or the o-ther of the conductor systems can be covered with a film of dielectric material such as an insulating varnish, in conventional fashion.
In a modification of this procedure, after the step 45 of the perforation of the support, a system of conductive ink is deposited by serigraphy on only one face of the support 31, and then the circuit is submitted to heating for polymerizing the ink, in the same manner as previously. Subsequently, as indicated by the broken-line arrow 48, another s~stem of conductive ink is deposited on the other face of the support, and this other system is then submitted, as indicated by the broken~line arrow 49, to a further heating for polymerizing this ink.
The contact areas or lands 39, 40 can be formed at the same time as the conductive paths of the corresponding conductive system, i~e. with the same conductive ink, or alternatively then they can be formed in a separate manner by a supplementary deposition by serigraphy of conductive ink which, after polymerization, presents a greater hardness or a greater mechanical resistence than the inks of the conductive paths.
In another variant of the performance of the invention, '7;~5~3 a flexible, semi-rigid or rigid support is used, of which the two faces already carry a conductor system, for example of copper. For this, one commences, as in the conventional technique, with a support the two faces of which are metalized, for example by a film of copper, a conductive system is formed on each of these faces by the conventional photogravure technique and holes are pierced in the support at the regions where it is desired to establish connections between the two conductive systems. It is then sufficient to deposit conductive ink by serigraphy in the zones comprising the holes, or on one or both faces of the support, and to submit the assembly to heating for polymerizing of the ink. The technique can likewise be used to form the contact areas or lands on the conductive system of copper. For this, a conductive ink can be used which contains particles of gold which, after polymerization of the ink, form the contact lands on the copper paths or connected to the copper paths.
Figure 6 diagrammatically represents another variant of the method according to the invention for the manufacture of a multi-layer printed circuit assembly illustrated in Figure 7.
This circuit 50 is made, for example, commencing with a printed circuit 51 obtained by the method of Figure 5. The circuit 51 then comprises a support 52, such as a polyester film having a thickness of 80 to 100 microns, of which the two faces each comprise a conductor system comprising conductive paths 53 and '7~5~
54, respectively, and connections between the two s~stems formed by holes 55 extending through the support 52 and having walls covered, at least partly, by polymerized inlc. On the upper face of the support 52 and on the upper conductor system comprising the paths 53, there is secured a support 56 such as a sheet or film of polyester having a thickness of between 15 and 100 microns and which, for e~ample, is less than the thickness of the support 52 of the circuit 51. On the upper face of this sheet 56 there is formed a conductor system comprising conductive paths 57. Holes 58 formed through the sheet 56 and provided with a polymerized film of ink ensure the desired connections between the conductive paths 57 formed on the upper face of the sheet 56 and the conductive paths 53 of the system formed on the upper face of the printed circuit 51. Another film or sheet 60 of dielectric material, for example polyester, which may be identical to the film or sheet 56, is then secured on the upper face of the sheet 56 and on the conductor system thereof and itself comprises, on its upper face, a conductor system comprising conductive paths 61. ~oles 62 formed through the f ilm 60 and provided with a film of polymerized conductive ink ensure the desired connections between the conductive paths 61 and the conductive paths 57. One hole 62 of the f ilm 60 can be vertically aligned with one hole 58 of the sheet 56, and in this case a connection is established between the paths 61, 57 and 53.

~ '7~5~9 In this way, a multi-layer printed circuit assembly can be produced by stacking films or sheets 56, 60, ~.. each having a conductor system and connection holes between these conductor systems.
The method oE manufacture of such a multi-layer printed circuit assemblyr starting for example with a printed circuit 51 obtained by the method of Figure 5, comprises, as illustrated in Figure 6, a first step 65 of perforation of the sheet or film 56 of dielectric material. The following step 66 comprises securing this sheet or film onto one face of the printed circuit 51, for example by glueing or heat pressing. The following step 67 consists in forming, by serigraphic deposition of conductive ink, a conductor system 57 on the upper or free face of the sheet or film 56. The following step 68 is a heating operation for polymerizing the deposited conductive ink. These operations are then repeated for the sheet or film 60.
The above-described embodiments of the present invention present very numerous advantages with respect to the prior art:-- the cost of a printed circuit embodying the invention may be about 80 times less than that of a conventional printed circuit having conductive paths of copper on a support of epoxy glass and three to four times less than that of a circuit such as that of Figures 1 and 2.
- the rate of rejec-ts in the manufacture of the printed s~
circuits embodying the invention is zero due to the possibility of retouching ~he conductor systems formed by deposition by serigraphy of polymerized conductive ink, while the rate of rejects in the manufacture of printed circuits such as those of Figure 1 and 2 is of the order of at least 25 to 30~.
- the insulation between the two conductor systems is guaranteed by the thickness of the support.
- the conductor systems are deposited on flat surfaces.
- in the method illustrated in Figure 5, only two serigraphic screens are utilized instead of the three or four which are utilized in the method of manufacture of the circuits of Figures 1 and 2.
- a printed circuit embodying the invention can be made by a single pass between the serigraphic screens, instead of the three or four passes in the prior art.
- according to the method of Figure 5, the circuit is passed only a single time into an oven, for the polymerization of ink, while the number of passes into an oven is three or four in the prior art.
- the reliability of a printed circuit according to the invention is much higher than that of a printed circuit represented in Figures 1 and 2 ! since the paths of conductive ink and the connections do not rupture even following substantial flexure o~ the support. The simultaneous deposition of the conductive ink on the two faces of the support, or the '7~5~
two succesive depositions of conductive ink firstly on one face and than on the other face of the support, ensure in all cases a good covering of walls of the holes of the connections by a uniform layer of a single inlc which is then polymerized by heating, which results in the provision o~ a connection which is homogeneous and lacking internal mechanical tension (which avoids expansion gradients, the appearance of microfi~sures, etc.) - the thickness of the film of conductive ink covering the walls of the connection holes is substantially equal to that of the conductive paths formed on the two faces of the support, which avoids risks of cracks or fissures at the edges of the holes following polymerization.
- the invention enables printed circuits to be provided which have at least two crossed or superimposed conductor systems and whicn are flexible, semi-rigid or rigid, in accordance with the type and the thickness of the support of dielectric material.
- the invention likewise enables the provision of printed circuits starting from polyester sheets the two faces of which are metalized, for example by a copper film, which are treated by photogravure to form conductor systems on the two faces and in which the connections between the two systems are provided by means of holes ex-tending through the support and of which the walls are covered, at least partly, with polymeri~ed .
. .

~1"7~5~3 conduc tive ink .

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS

1. A printed circuit comprising:-a dielectric support; and at least two electrically conductive path systems carried by the support;
said systems being crossed or superimposed and electrically insulated from one another except at certain points of interconnection;
said systems being formed respectively on one side and the other of the support so as to be electrically insulated from one another by said support; and connections between said systems being formed across said support by a uniform layer of polymerized conductive ink.

2. A printed circuit as claimed in claim l, wherein said systems comprise electrically conductive paths of polymerized conductive ink.

3. A printed circuit as claimed in claim 2, wherein said support is a flexible film or sheet, for example of polyester.

4. A printed circuit according to claim 3, wherein said film has a thickness of between approximately 50 and 1500 microns.

5. A printed circuit according to claim 2, wherein said connections between said systems are holes extending through said support, said holes having walls at least partly covered by a film of polymerized conductive ink.

6. A printed circuit as claimed in claim 5, wherein said layer of conductive ink at least partially covering the wall of said connection holes has the same thickness as said paths of conductive ink formed on the two faces of said support.

7. A printed circuit as claimed in claim 2, 3 or 4, wherein said systems of conductive ink comprise conductive connecting paths, contact areas and passive components such as resistors, capacitors and inductors.

8. A printed circuit according to claim 1, wherein 1 said systems are formed on said support by deposition by serigraphy of conductive ink which is subsequently polymerized by heating.

9. A printed circuit according to claim 2, 3 or 4, wherein some of said connections between said two faces of said support are formed by paths of conductive ink deposited on the edge of said support perpendicular to the place of said support.

10. A printed circuit as claimed in claim 5, wherein said holes have a diameter of the order of at least 0.8 millimeters.

11. A printed circuit according to claim 2, 3 or 4, wherein at least one of said conductive systems is covered over at least a major portion thereof with a very thin film of dielectric material.

12. A multi-layer printed circuit assembly, comprising a printed circuit as claimed in claim 1, at least one face of which is covered by a sheet or film of dielectric material presenting an exterior face having a conductor system formed by deposition by serigraphy of conductive ink and holes formed through said sheet or said film and having walls covered with ink for connecting each conductive zone of said system to a conductive zone of a conductor system formed on said face of said printed circuit.

13. A printed circuit as claimed in claim 12, wherein said exterior face of said sheet or film of dielectric material is itself covered with another sheet or film of dielectric material an exterior face of which has a conductor system formed by deposition by serigraphy of conductive ink and which comprises holes having walls covered with conductive ink connecting said conductor systems of said two sheets or films.

14. A printed circuit according to claim 12, comprising a stack of said sheets or films of dielectric material, each of said sheets of films comprising on one face a conductor system of the above-mentioned type and connection holes having walls covered with conductive ink.

15. A printed circuit according to claim 14, wherein some of said holes of said sheets are aligned and form a connection between a plurality of said conductor systems.

16. A printed circuit according to claim 12, 13 or 14, wherein each said sheet or film of dielectric material has a thickness comprising between approximately 15 and 1500 microns.

17. A printed circuit according to claim 12, 13 or 14, wherein each said sheet or film of dielectric material is secured to said circuit or to an adjacent one of said sheets or film by adhesive or by heat pressing.

18. A method of manufacturing a printed circuit, comprising forming holes in a flat support of dielectric material at predetermined points;
said support being formed on opposite faces thereof with a respective conductor path system;
covering at least the walls of said holes with a film of conductive ink to form connections to connect said conductor systems, and in polymerizing the ink by heating.

19. A method of manufacturing a printed circuit as claimed in claim 18, which includes forming said conductor systems and said connections on the walls of the holes by depositing conductive ink by serigraphy on said support and polymerizing said ink by heating.

20. A method as claimed in claim 19, further including depositing said conductive ink by serigraphy simultanteously on the opposite faces of said support.

21. A method as claimed in claim 19, further comprising depositing by serigraphy a first system of conductive ink on a first face of said support;
polymerizing said first system by heating;
subsequently depositing on a second face of said support a second system of conductive ink; and polymerizing said second system by heating.

22. A method as claimed in claim 19, comprising depositing by serigraphy, on at least one face of said support, areas of conductive ink and polymerizing said areas by heating so as to produce contact areas or zones.

23. A method as claimed in claim 22, further comprising employing, for said contact areas or zones, a conductive ink having, after polymerization, a hardness or mechanical resistence greater than that of the ink utilized for said conductive paths of said system.

24. A method according to claim 19 for the manufacture of a multi-layer printed circuit assembly, further comprising subsequently fixing, on a face of the printed circuit, a sheet or film of dielectric material perforated by holes at predetermined points so that said holes open onto conductive parts of said circuit;
depositing by serigraphy on the exterior face of said sheet or film a layer of conductive ink forming on said face a conductor system; and at least partly covering the walls of said holes with a conductive ink; and polymerizing the ink thus deposited by heating.

25. A method as claimed in claim 24, further comprising repeating the steps therein of claim 2 to produce a multi-layer printed circuit assembly, comprising a stack of said sheets or films of dielectric material each carrying on one face thereof a conductor system of polymerized ink.