Printed circuit with a layer of gold-substitute alloy and method for manufacturing such a printed circuit

Abstract

Printed circuit (5) comprising a dielectric substrate (4) comprising a first and a second main face, with at least one first sheet (10) of a first electrically conductive material at least on a portion of the first main face, at least one layer (12) of a second electrically conductive material on at least one area of the first sheet (10). The at least one layer (12) of at least one second electrically conductive material is formed of an alloy comprising at least 50% by weight of copper, less than 20% by weight of tin and more than 5% by weight of zinc. The invention also relates to a method for producing said printed circuit.

Description

Description Title of the invention: Printed circuit with a gold-substituting alloy layer and method of manufacturing such a printed circuit Technical field

[0001] The invention relates to the field of printed circuits, for example printed circuits for chip card connectors or for devices intended for medical applications (e.g. blood glucose detection) or for the production of antennas for example for the connection of objects via the internet (IoT or "Internet of Things" in English). State of the art

[0002] For example, printed circuits according to the invention may comprise conductive tracks and / or electrical contact pads etched in a sheet of electrically conductive material previously deposited and fixed (for example by lamination and / or bonding) on ​​a dielectric substrate (for example by implementing a photo-litho etching technology), or circuits comprising one or more connection grids, each consisting of a sheet of electrically conductive material cut, then co-laminated with a dielectric substrate (for example by implementing a connection grid technology, called "leadframe" technology in English). Such printed circuits are used for example for producing contacts for electronic chip card modules, for producing antennas, for producing mixed circuits comprising both contacts and an antenna, for producing electrodes, etc.

[0003] As an illustration, if we take the example of smart cards, these are generally made up of a rigid support, for example made of plastic, constituting the main part of the card, in which is incorporated a separately manufactured electronic module. This electronic module comprises a printed circuit, generally flexible (for example in comparison with the rigid support constituting the body of the card), provided with an electronic chip (integrated circuit) and means for connecting the chip to a device making it possible to read and / or write data in the electronic chip. These connection means - or connectors - are for example formed of contacts made up of conductive metal tracks flush with the electronic module, on the surface of the support. In addition to the need for excellent mechanical strength and corrosion resistance of the contacts, on the one hand, and a good electrical connection between the contacts and a reading / writing device on the other, smart card manufacturers want to achieve certain contact colors. To this end, the contacts are coated, for example, with a layer of gold, to obtain a gold finish, or with a layer of silver or palladium, to obtain a silver finish. However, this type of finish poses problems. For example, palladium is a relatively expensive metal; as for gold, which is also a relatively expensive metal, it has the disadvantage of having to be deposited on a layer of nickel.But nickel has magnetic properties that present disadvantages for radio frequency applications (for example, for contactless data exchange with the chip and / or a card / antenna connection by inductive effect) and / or for other applications requiring an absence of magnetic properties. Nickel is also problematic in the medical field if it must be placed in contact or near the skin, etc.

[0004] An aim of the invention is to produce printed circuits in which gold is not used or is used little, that is to say less used than in the prior art for equivalent applications, while possibly retaining a golden appearance and electrical and mechanical properties suitable for their use in particular (but not exclusively as indicated above) in contact modules for smart cards. In other words, an aim of the invention is to find an at least partial substitute for certain layers of gold used in printed circuits.

[0005] For this purpose, a printed circuit comprising a dielectric substrate is described below. This dielectric substrate has a flat shape with a first and a second main face delimiting this substrate according to its thickness. At least said first main face supports, at least on a portion thereof, a first sheet of a first electrically conductive material. In addition, at least one layer of at least one second electrically conductive material is deposited on at least one area of ​​the first sheet.

[0006] Further, said at least one layer of at least one second electrically conductive material is formed from an alloy comprising at least 50% by weight of copper, less than 20% by weight of tin and more than 5% by weight of zinc.

[0007] Thus, with a relatively high copper concentration and a relatively low tin concentration, the layer of second conductive material does indeed have a color gold-plated, similar or close to that of a gold layer, while the mechanical properties, corrosion resistance and electrical properties meet the requirements for the intended applications and in particular for the production of smart card connectors. For example, the printed circuit has a contact resistance (CRM: Contact Resistance Measurement) of less than 500m0hm before and after being subjected to a 24-hour salt spray test, in accordance with ISO 10373.

[0008] The printed circuit mentioned above optionally advantageously comprises one or other of the following characteristics considered independently of each other or in combination with one or more others:

[0009] - it comprises a second sheet of electrically conductive material on at least a portion of the second main face of the dielectric substrate, and at least one layer of the second electrically conductive material is deposited on at least one area of ​​the second sheet; in other words, the first sheet is supported by the first main face of the substrate, or front face, and the second sheet is supported by its second main face, or rear face, and a layer of the second electrically conductive material is deposited on at least one area of ​​each of these faces;

[0010] - it comprises at least one layer of at least one third electrically conductive material intercalated, on at least one area of ​​the first sheet or the second sheet, between the first material and the second material, this third electrically conductive material being chosen from the list comprising nickel and a nickel phosphorus alloy; it will be noted that the use of the coordinating conjunction “or” is inclusive in this context (“of the first sheet or the second sheet”); in other words, it must be understood as meaning “and / or”;

[0011] - it comprises a protective layer formed of at least one self-assembled monolayer (“SAM” or Self-Assembled Monolayer in English);

[0012] - it comprises on the side of the first main face, a layer of gold between the layer of third material and the layer of second material;

[0013] - it comprises on the side of the second main face, a layer of gold on at least one area of ​​the layer of second material;

[0014] - the layer of second material has a thickness of between 0.1 and 3 micrometers, and more preferably between 0.1 and 2 micrometers;

[0015] - the second material is a ternary alloy comprising between 70 and 80% by weight of copper, between 5 and 12% by weight of zinc and between 10 and 20% by weight of tin; alternatively the second material is a binary alloy comprising between 50 and 85% by weight of copper and between 15 and 50% by weight of zinc;

[0016] - it comprises connection wells at the bottom of which is arranged at least one layer of second material; more particularly, for example, the bottom of these connection wells corresponds to the face of the first sheet facing the dielectric substrate.

[0017] According to another aspect, the invention relates to a method for manufacturing a printed circuit. This then comprises: a supply or provisioning step during which a dielectric substrate is at least partially immersed in at least one electrochemical deposition bath, this substrate comprising a first and a second main face, with at least a first sheet of a first electrically conductive material at least on a portion of the first main face, this first sheet comprising current leads and at least one pattern also produced in the first sheet, an electrochemical deposition step during which at least one layer of a second electrically conductive material is electrodeposited on at least one area of ​​the pattern.

[0018] Further, the layer of second electrically conductive material electrodeposited on the pattern is formed from an alloy comprising at least 50% by weight of copper, less than 20% by weight of tin and more than 5% by weight of zinc.

[0019] Due to the presence of the second material layer, this process may possibly make it possible to avoid depositing nickel (whereas nickel is essential in the layer underlying a gold layer, for example).

[0020] This process, as well as all operations described in this document, can be implemented reel-to-reel.

[0021] Other characteristics and advantages of the invention will appear on reading the detailed description and the attached drawings in which: - FIG. 1 schematically represents in perspective a smart card comprising an example of a module according to the invention; - FIG. 2 schematically represents a top view of a portion of an example of a printed circuit according to the invention, comprising several connectors for a smart card module; - FIG. 3 shows in section, partially and schematically, an example of a single-sided printed circuit, for example for a smart card module connector such as that shown in FIG. 1; - FIG. 4 shows in section, partially and schematically, an example of a double-sided printed circuit, for example for a smart card module connector, for a smart card such as that shown in FIG. 1; - FIG. 5 shows in section, partially and schematically, an example of a double-sided printed circuit such as that of figure 4, on which several layers are electrodeposited; as well as its single-sided variant, if we ignore the sheets and layers located under the dotted lines; - FIG. 6 shows in section, partially and schematically, another example of a double-sided printed circuit such as that of figure 4, on which several layers are electrodeposited; as well as its single-sided variant, if we ignore the sheets and layers located under the dotted lines; - FIG. 7 shows in section, partially and schematically, yet another example of a single-sided printed circuit, on which several layers are electrodeposited; - FIG. 8 shows in section, partially and schematically, yet another example of a single-sided printed circuit, on which several layers are electrodeposited.

[0022] A first example of application of the printed circuit according to the invention is taken from the field of smart cards, but those skilled in the art will be able to transpose this example to other applications of printed circuits (contacts for USB sockets, antennas, devices for medical applications such as pressure sensors in contact with the skin, strips for detecting glucose or other compounds in the blood, electrodes for producing encephalograms, etc.).

[0023] Therefore, according to an example of application of the printed circuit according to the invention, illustrated by figure 1, a smart card 1 comprises a module 2 with a connector 3. According to this example, the smart card 1 is a bank card in ID-1 format. The module 2 is for example a banking type module (also called “EMV” module for Europay Mastercard Visa) meeting the ISO 7810 standard. The module 2 is generally produced in the form of a separate element which is inserted into a cavity provided in the card. This element comprises a dielectric substrate 4 (see Fig. 2) of PET or polyimide or glass-epoxy, etc., the thickness of which is for example between 25 and 150 micrometers (it is therefore sufficiently thin to have a flexibility suitable for its use in a continuous process). On the dielectric substrate 4 is produced the connector 3. An electronic chip (not shown) is subsequently attached to the module 2 (either on the substrate 4 or in a cutout 15 made therein). The electronic chip is connected to the connector 3.

[0024] Figure 2 thus illustrates an example of a portion of printed circuit 5, with six connectors 3. Each connector 3 comprises a contact pad 8. This contact pad 8 comprises conductive pads 6. Among these conductive pads 6, some are intended to form electrical contacts 7. In the example illustrated here, eight of the conductive pads 6 are intended to form the electrical contacts 7 identified from C1 to C8 as defined by the ISO 7816-2 standard. The contact pads 8, the conductive pads 6 and the contacts 7 correspond for example to patterns etched in a first sheet 10 of a first electrically conductive material.

[0025] The connector 3 may be formed from a single-sided structure (with a sheet of electrically conductive material on only one of the main faces of the dielectric substrate 4) or a double-sided structure (with a sheet of electrically conductive material on each of the two main faces of the dielectric substrate 4).

[0026] An example of a single-sided structure is illustrated in Figure 3. This single-sided structure is, for example, produced according to the following method: a dielectric substrate 4 is provided, which is coated on one of its main faces with a layer of adhesive 9; then, the dielectric substrate 4 provided with the layer of adhesive 9 is perforated in order to produce connection wells 14 and possibly a cavity 15 in which an electronic chip will subsequently be housed; the dielectric substrate 4 provided with the layer of adhesive 9 is then complexed (laminated) with a first sheet 10 of a first electrically conductive material such as a sheet of copper, aluminum, or one of their alloys, or even steel, etc., before possibly undergoing hot crosslinking of the layer of adhesive 9.Alternatively, it is possible to directly use a laminate (“clad” in English), but in this case, the connection wells 14 and / or the cavity 15 are formed for example using a laser configured to perforate only the dielectric substrate 4 and to stop at the interface between the dielectric substrate 4 and the first sheet 10 of a first electrically conductive material. In all cases, the bottom of the connection wells 14 and / or of the cavity 15 is thus made up of an electrically conductive surface, on which layers of conductive materials may possibly be electrodeposited, for the purpose of an electrical connection, for example using a wire bonding technology. passing through the dielectric substrate 4 through the connection wells 14, or using flip chip technology via metallized connection wells for example.

[0027] An example of a double-sided structure is illustrated in Figure 4. This double-sided structure is for example produced according to the following method: a dielectric substrate 4 is provided already supporting, on a first of its main faces (which will correspond to the so-called “back face”), a second sheet 11 of a first conductive material such as a sheet of copper, aluminum, or one of their alloys, or even steel, etc.; it is then a laminate for example; the other of its main faces (which will correspond to the face called "front face") is coated with a layer of adhesive 9; then, this laminate provided with the layer of adhesive 9 is possibly perforated in order to produce connection wells 14 and possibly a cavity 15 in which an electronic chip will subsequently be housed; the laminate provided with the layer of adhesive 9 is then complexed (laminated) with a first sheet 10 of conductive material (for example also made of the same conductive material as the first conductive material, even if the respective thicknesses of the first 10 and second 11 sheets may be different; it will also be noted that the first 10 and second 11 sheets may be made of different electrically conductive materials).The bottom of the connection wells 14 and / or of the cavity 15 is thus made up of an electrically conductive surface, on which layers of conductive materials may possibly be electrodeposited, for the purpose of an electrical connection, for example using a wire bonding technology, or using a flip chip technology via metallized connection wells for example.

[0028] Alternatively, it is possible to use double-sided laminate directly ("double-sided clad" in English), but in this case, the connection wells 14 and / or the cavity 15 are formed for example using a laser configured to perforate only the dielectric substrate 4 and the second sheet 11 of electrically conductive material, and to stop at the interface between the dielectric substrate 4 and the first sheet 10 of a first electrically conductive material.

[0029] For example, as shown in section in Figures 5 and 6, a connector 3 (i.e. essentially a module 2 without an electronic chip) has a multilayer structure formed from the dielectric substrate 4, an adhesive layer 9 (optional and not shown in Figures 5 and 6), and a first 10, and possibly a second 11, sheets made of an electrically conductive material on which at least one layer 12 of a second electrically conductive material is electrochemically deposited. In the figures, the horizontal dotted line indicates the limit of a so-called single-sided connector 3, which then corresponds to the part above this dotted line, while these figures represent a double-sided structure if the dotted line is ignored.

[0030] For example, the first electrically conductive material is made of copper or a copper alloy. The layer 12 of second electrically conductive material is made of an alloy comprising at least 50% by weight of copper, less than 20% by weight of tin and more than 5% by weight of zinc.

[0031] The respective compositions of the layer 12 of the second electrically conductive material are not necessarily the same on the first 10 and the second sheet 11. The composition of the layer 12 of the second electrically conductive material deposited on the second sheet 11 can in fact be determined by the desire to obtain better weldability thereon.

[0032] Layer 12 of the second electrically conductive material is deposited for example from a bath supplied by the company UMICORE or the company MACDERMID or the company KIESOW, at a temperature between 20 and 60°C for example, with a current density between 0.2 and 4 A / dm 2The operating conditions may differ depending on the type of composition desired to form the layer 12 of the second electrically conductive material. For example, for a ternary alloy, comprising between 70 and 80% by weight of copper, between 5 and 12% by weight of zinc and between 10 and 20% by weight of tin, the bath temperature may be for example between 55 and 58°C and the current density may be between 2 and 4 A / dm 2 . Whereas for example for a binary alloy, comprising between 50 and 85% by weight of copper and between 15 and 50% by weight of zinc, the bath temperature can be for example between 20 and 50°C and the current density can be between 0.3 and 2 A / dm 2 .

[0033] The layer 12 of the second electrically conductive material can be used, at least on one of the faces of the first sheet 10 and / or the second sheet 11, to replace all or part of the thickness of gold which would have been deposited without this replacement.

[0034] In the example illustrated in Figure 5, the multilayer structure is a double-sided structure. It comprises a dielectric substrate 4 whose nature and thickness correspond for example to those already mentioned above. This dielectric substrate 4 is perforated (as explained above) for example to form connection wells 14 allowing to electrically connect a chip located on the rear side (rear side or bonding side in English) to contact pads 8 located on the front side (front side or contact side in English). This dielectric substrate 4 comprises on each of its main faces, respectively a first 10 and a second 11 sheets both formed of a first electrically conductive material, for example copper or a copper alloy (alternatively, the first electrically conductive material can be aluminum, or one of its alloys, steel, etc.).

[0035] A layer 12 of a second electrically conductive material is deposited on at least one area of ​​the first sheet 10 and on at least one area of ​​the second sheet 11.

[0036] This embodiment is particularly advantageous for replacing nickel and precious metals, particularly on the front face. It is also advantageous in terms of production costs because it is obtained using a reduced number of electrolytic deposition operations.

[0037] A protective layer 20 formed from at least one self-assembled monolayer can be deposited on at least one area of ​​the layer 12 of second electrically conductive material, itself deposited on the front face on at least one area of ​​the first sheet 10. But this protective layer 20 is optional and according to a variant (not illustrated) of the embodiment illustrated by FIG. 5, the layer 12 of second electrically conductive material is bare.

[0038] According to another variant (not illustrated) of the embodiment illustrated by FIG. 5, a protective layer 20 formed of at least one self-assembled monolayer is deposited on at least one area of ​​the layer 12 of second electrically conductive material, on the front face and on the rear face.

[0039] According to another variant (not shown) of the embodiment illustrated by FIG. 5, the front face is treated as indicated above, while the rear face is treated as in the prior art (for example, with a stack of electrodeposited layers of nickel, nickel-phosphorus and gold), i.e. without the layer 12 of second electrically conductive material electrodeposited.

[0040] According to another variant (not shown) of the embodiment illustrated by Figure 5, the front face is treated as indicated above, while the rear face comprises on the second sheet 11, a layer 12 of second electrically conductive material electrodeposited, then a surface layer containing gold (for example like the surface layer 19 mentioned below, itself deposited on a layer in the form of a “flash” or gold primer 18).

[0041] According to another variant (not shown) of the embodiment illustrated by FIG. 5, the front face and the rear face further comprise a surface layer containing gold (for example like the surface layer 18 in the form of a “flash” mentioned below).

[0042] According to another variant of the embodiment illustrated by figure 5, the rear face of the dielectric substrate 4 is left bare (without the second sheet 11 and without the layer 12 of second electrically conductive material electrodeposited thereon), and at the bottom of the connection wells 14, there is a stack comprising the layer 12 of second electrically conductive material and possibly the optional protective layer 20. This is then a single-sided structure.

[0043] The table below summarizes examples of characteristic thicknesses of each of the layers of the structure illustrated in Figure 5.

[0044] According to other embodiments of the printed circuit according to the invention, it may have a more complex multilayer structure. Thus, in addition to the layer 12 of the second electrically conductive material, one or more layers may be deposited on and / or under the layer 12 of the second electrically conductive material. For example, layers of electrically conductive materials may be deposited electrochemically on at least certain areas of each of the two sheets 10, 11 of first electrically conductive material.

[0045] Thus, in the example illustrated in Figure 6, the multilayer structure is a double-sided structure. It comprises a dielectric substrate 4 as mentioned above. As in the previous example, the dielectric substrate 4 is perforated and comprises on each of its main faces, respectively a first 10 and a second 11 sheets, both formed of a first electrically conductive material consisting, for example, as previously mentioned, of copper or a copper alloy. The first 10 and second 11 sheets are fixed to the dielectric substrate 4 using one of the methods described above for example.

[0046] In the example illustrated by figure 6, the first sheet 10 receives, in order from the first sheet 10, possibly a layer of nickel 16, possibly a layer of nickel-phosphorus 17, possibly a thin layer in the form of a “flash” or gold primer 18, a layer 12 of the second electrically conductive material and possibly a protective layer 20 formed of a self-assembled monolayer.

[0047] Still according to this example, the second sheet 11 receives, in order from the second sheet 11, possibly a layer of nickel 16, possibly a layer of nickel-phosphorus 17, possibly a layer 12 of the second electrically conductive material, possibly a thin layer in the form of a “flash” or gold primer 18, and possibly a layer of gold 19.

[0048] The table below summarizes examples of characteristic thicknesses of each of the layers of the structure illustrated in Figure 6.

[0049] It should be noted that each of the layers of nickel 16, nickel-phosphorus 17, the second electrically conductive material 12 on the rear face, the thin layer of gold 18 and the surface layer containing gold 19 can be considered as optional. However, the addition of certain layers of precious metal on the rear face can improve the welding quality of connection wires for example.

[0050] According to this example, the stacking of the layers on the rear face is the same whether at the bottom of the connection wells 14 or on the second sheet 11. But, it is possible to obtain different stacks using masking techniques for example.

[0051] According to a variant of the embodiment illustrated by Figure 6, the rear face of the dielectric substrate 4 is left bare (without the second sheet 11 and without the layers electrodeposited thereon); on the other hand, at the bottom of the connection wells 14, there is a stack comprising a layer of nickel 16, a layer of nickel-phosphorus 17, a layer 12 of the second electrically conductive material, a thin layer 18 of gold in the form of a “flash” or primer and a surface layer containing gold 19. This is then a single-sided structure.

[0052] According to another variant (not shown) of the embodiment illustrated by FIG. 6, the front face is treated as indicated above, while the rear face is treated as in the prior art (for example, with a stack of electrodeposited layers of nickel, nickel-phosphorus and gold), i.e. without the layer 12 of second electrically conductive material electrodeposited.

[0053] For example, a smart card module comprising a stack consisting of a dielectric 4 covered with a copper foil 10 on which are electrodeposited a nickel layer 16, a nickel phosphorus layer 17, a gold flash 18 and a layer 12 of second electrically conductive material of 0.5 micrometer comprising at least 50% by weight of copper, less than 20% by weight of tin and more than 5% by weight of zinc (structure of figure 6), has a contact resistance of less than 500m0hm before and after being subjected to a 24h salt spray test, in accordance with the ISO 10373 standard.

[0054] In the exemplary embodiment of the printed circuit according to the invention illustrated in Figure 7, the multilayer structure of this printed circuit is a single-sided structure. A layer 12 of second electrically conductive material is deposited on at least one area of ​​the first sheet 10. Optionally, the front face can then receive a protective layer 20. This type of printed circuit can be used for applications where nickel is prohibited, for example for medical applications.

[0055] In the exemplary embodiment of the printed circuit according to the invention illustrated in Figure 8, the multilayer structure of this printed circuit is a single-sided structure. It comprises a dielectric substrate 4 as mentioned above. On the front side, the first sheet 10 made of the first electrically conductive material is fixed to the dielectric substrate 4 in one of the ways described above.

[0056] Several layers of electrically conductive materials are deposited electrochemically on at least certain areas of the free surface of the first sheet 10. In the example illustrated by FIG. 8, the front face receives a layer 12 of second electrically conductive material, then possibly a thin layer 18 in the form of a “flash” or primer of one of the metals chosen from gold, silver and palladium, and finally at least one surface layer 19 comprising a metal from the following list: gold, silver, palladium, rhodium, ruthenium. Optionally, the front face then receives a protective layer 20. This type of printed circuit can be used for applications where nickel is prohibited, for example for medical applications.

[0057] The table below summarizes examples of characteristic thicknesses of each of the layers of the structure illustrated in Figure 8.

[0058] In the embodiments presented above with their variants, when a protective treatment 20 is carried out, this may correspond, in a non-exhaustive manner, to the passage in:

[0059] - an organic solderability preservative bath, such as benzotriazole or an imidazole (for example an alkyl benzimidazole, an aryl benzimidazole, etc.);

[0060] - a bath suitable for forming a self-organized monolayer, such as a mixture of polyethylene glycol ether and propylene glycol, or a mixture of polyglycolether and isopropyl glycol, or a mixture of octylphenoxyethanol and octadecane-1-thiol or polyoxyethylene sorbitan monooleate (Polysorbate 80, CAS number 9005-65-6), or a mixture of propoxylated ethoxylated (C12-18) alcohols (CAS number 69227-21-0) with poly(oxyethylene) lauryl ether (CAS number 9002-92-0) and 1-octadecanethiol (CAS 2885-00-9).

Claims

Claims

1. Printed circuit (5) comprising: a dielectric substrate (4) comprising a first and a second main face, with at least one first sheet (10) of a first electrically conductive material at least on a portion of the first main face, at least one layer (12) of a second electrically conductive material on at least one area of ​​the first sheet (10), characterized in that said at least one layer (12) of at least one second electrically conductive material is formed from an alloy comprising at least 50% by weight of copper, less than 20% by weight of tin and more than 5% by weight of zinc.

2. Printed circuit (5) according to claim 1, comprising a second sheet (11) of electrically conductive material on at least a portion of the second main face of the dielectric substrate (4), at least one layer (12) of the second electrically conductive material being deposited on at least one area of ​​the second sheet (11).

3. Printed circuit (5) according to claim 1 or 2, comprising at least one layer (16, 17) of at least one third electrically conductive material interposed, on at least one area of ​​the first sheet (10) or of the second sheet (11), between the first and second materials, this third electrically conductive material being chosen from the list comprising nickel and a nickel phosphorus alloy.

4. Printed circuit (5) according to the preceding claim, comprising on the side of the first main face, a layer of gold (18) between the layer (16, 17) of third material and the layer (12) of second material.

5. Printed circuit (5) according to one of the preceding claims, comprising a protective layer (20) formed of at least one self-assembled monolayer.

6. Printed circuit (5) according to one of the preceding claims, comprising, on at least one of the two sides corresponding respectively to the first main face and to the second main face, a layer of gold (19) on at least one area of ​​the layer (12) of second material.

7. Printed circuit according to one of the preceding claims, in which the layer (12) of second material has a thickness of between 0.1 and 3 micrometers.

8. Printed circuit (5) according to one of the preceding claims, in which the second material is a ternary alloy comprising between 70 and 80% by weight of copper, between 5 and 12% by weight of zinc, and between 10 and 20% by weight of tin.

9. Printed circuit (5) according to one of claims 1 to 7, in which the second material is a binary alloy comprising between 50 and 85% by weight of copper and between 15 and 50% by weight of zinc.

10. Printed circuit according to one of the preceding claims, comprising connection wells (14) at the bottom of which is arranged at least one layer (12) of second material.

11. A method of manufacturing a printed circuit comprising: a supply step during which a dielectric substrate (4) is at least partially immersed in at least one electrochemical deposition bath, this dielectric substrate (4) comprising a first and a second main face, with at least a first sheet (10) of a first electrically conductive material at least on a portion of the first main face, this first sheet (10) comprising current leads and at least one pattern (6) also produced in the first sheet (10), an electrochemical deposition step during which at least one layer (12) of a second electrically conductive material is electrodeposited on at least one area of ​​the pattern (6), characterized in that the layer (12) of second electrically conductive material electrodeposited on the pattern (6) is formed of an alloy comprising at least 50% by weight of copper,less than 20% by weight of tin and more than 5% by weight of zinc.,

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