KR20220158765A - Method for electrodeposition of gray or black layers on electrical circuits and electrical circuits for electronic modules of chip cards comprising such layers - Google Patents

Abstract

The present invention relates to a method for electrodepositing a gray or black layer onto an electrical circuit. An electrical circuit is, for example, a printed circuit-type electrical circuit for producing a module intended to be integrated into a card, such as a chip card. The module contains electrical contact pads - or connections (3) - which allow the chip to connect to and communicate with the read/write system. To provide an electrical contact pad with a black or nearly black color, the electrical contact pad is at least partially covered with a surface layer 13 containing ruthenium. This surface layer is electrodeposited from an electrolyte bath containing at least ruthenium and an agent that inhibits the kinetics of deposition. The invention similarly relates to electrical circuits obtained using this method.

Description

Method for electrodeposition of gray or black layers on electrical circuits and electrical circuits for electronic modules of chip cards comprising such layers

The present invention relates to the field of electrical circuits comprising surfaces intended to form connections and low-resistance electrical contacts.

For example, an electrical circuit produced in accordance with the present invention may be an etched printed circuit or circuits comprising one or more lead frames made of sheets of conductive material cut out and co-laminated with an insulating substrate. Such electrical circuits are used, for example, to produce contacts for connections, for example contacts for electronic modules of chip cards, contacts of memory sticks (USB sticks or others), and the like. More specifically, an electrical circuit produced according to the present invention, when intended to be at least partially visible in its present use, has certain advantages.

The present invention is described below using examples of electrical circuits intended to form contacts of connections of chip cards, but such examples should not be construed as limiting and, in general, the deposition methods described below may be of any type. It can be applied to the metal conductive base of

Taking a chip card as an example, a chip card generally consists of a rigid base, eg made of plastic, which constitutes the main part of the card, into which a separately manufactured electronic module is integrated. Such electronic modules generally include a flexible printed circuit, which includes a chip (integrated circuit) and means for connecting the chip to a device that allows data to be read and/or written to/from the chip. do. These connecting means (or connecting parts) mean contacts made of conductive metal tracks flush with the electronic module, for example on the surface of the base of the card. Apart from the need for good conduction of electricity between the chip and the contact on the one hand and between the contact and the read/write device on the other hand, manufacturers of chip cards are encouraged to match the color of the contacts to one or more colors on the card. want. To this end, the contact is typically covered with a layer of gold to obtain a gold finish, or a layer of silver or palladium to obtain a silver finish.

To obtain more colors, a method as described in document US6259035B1 can be used. This method is based on using gold-based, palladium-based or silver-based solutions to obtain a broader spectrum of colors. However, this type of method cannot obtain a specific color, particularly a color of black or a color close to black. Document WO2014064278A1 discloses a method for obtaining a black color from a layer comprising ruthenium deposited with thiourea. However, thiourea is an organic molecule that oxidizes the deposited layer and lowers its corrosion resistance. The resulting layer does not provide completely satisfactory corrosion resistance. Conversely, document FR3074193A1 discloses a method which makes it possible to obtain a contact of a chip card on which is deposited a layer comprising essentially rhodium, which has satisfactory corrosion resistance. However, the color obtained is white or a color close to white.

It is an object of the present invention to achieve a black or black color that is visible in the final product while simultaneously retaining the appropriate electrical and mechanical properties for use as a contact intended to be electrically connected to a joint, in particular over the course of numerous connect and disconnect cycles. To obtain a printed circuit containing conductive tracks of a color close to black.

To this end, a method for electrodepositing a gray or black layer onto an electrical circuit is presented. As mentioned above, this method can be used in particular to produce modules of chip cards. This method includes providing a dielectric substrate having a sheet of electrically conductive material disposed on the dielectric substrate. For example, the substrate is an epoxy glass substrate, and the sheet of electrically conductive material is made of copper or a copper alloy.

Advantageously, the assembly comprising the substrate and the sheet of electrically conductive material is flexible (this allows the assembly to be used in a reel-to-reel or roll-to-roll method). Sheets of electrically conductive material can be attached to the dielectric substrate with or without (eg, thermal lamination) layers of adhesive material between them (adhesive bonding and lamination). This sheet of electrically conductive material includes at least one electrical contact. These electrical contacts have an inner side facing the dielectric substrate and an outer side opposite the inner side. The outer side has a contact surface intended to form an electrical connection with the connector. Before (eg, in the context of the lead frame technology described above) or after (eg, using photolithography techniques) transferring the sheet of electrically conductive material onto the dielectric substrate, one or more contacts are placed within the sheet of electrically conductive material. can be created

The method also includes electrochemically depositing at least one layer of electrically conductive material onto the sheet of electrically conductive material. This deposition can be done either before or after the sheet of electrically conductive material is transferred onto the dielectric substrate. The one or more layers of electrically conductive material so deposited on the sheet of electrically conductive material include a surface layer covering at least one region of the contact surface of the at least one electrical contact. Thus, the sheet of electrically conductive material may include one or more electrochemically deposited metallization layers below the electrochemically deposited surface layer. This or these metallization layers are, for example, layers of nickel, gold, silver, palladium, or alloys thereof.

The surface layer is electrochemically deposited from an electrolyte bath comprising at least ruthenium and an inhibitor of the electrochemical kinetics of deposition of the surface layer. The role of inhibitors is to slow down the electrochemical reaction rate of deposition. The electrochemical reaction rate is, by definition, related to the redox reaction at the interface between the electrode and the electrolyte. Such redox reactions can only lead to deposition or decomposition. In this case, the inhibitor affects the kinetics of the deposition.

In this specification, the expression “deposition of ruthenium” refers to the deposition of metal ruthenium, as well as other compounds comprising ruthenium, and in particular ruthenium oxide or ruthenium chloride.

The function of the inhibitor is to slow down the deposition of ruthenium and to alter the morphology of the surface of this deposition. Light reflection is thereby altered, which also affects the perception of black color.

Metallic ruthenium has very good electrical conductivity (13.7 × 10 ⁶ S·m ^-1 ). Ruthenium dioxide has a black appearance. The presence of ruthenium and ruthenium oxide in the surface layer makes it possible to obtain both a black colored surface layer and a low contact resistance.

Thus, a surface layer is obtained which has both the expected black (or close to black) color and conductivity suitable for a good connection through the contact between the surface layer and the reader (eg a connection in a read/write device for a chip card).

The method of electrodepositing a gray or black layer onto an electrical circuit can potentially include one or another of the following features, each considered independently of the other features or in combination with one or more other features:

- the thickness of the surface layer is advantageously between 5 nanometers and 3 micrometers. A minimum thickness of 25 nanometers is useful for obtaining a uniform dark color (black or near black); At a ruthenium thickness of less than 25 nanometers, a rainbow effect can be obtained; In contrast, depositing more than 3 microns of ruthenium into the conductive layer has little or no benefit;

- inhibitors of the electrochemical kinetics of the deposition of the surface layer are not deposited together with ruthenium; Thus, as is the case with certain sulfur compounds (see below), the inhibitor itself does not directly produce black particles;

- inhibitors of the electrochemical kinetics of surface layer deposition are organic molecules; For example, it includes amines with carboxylic acid functional groups; For example, such a carboxylic acid amine is N-carboxymethyliminobis(ethylenenitrilo)tetraacetic acid;

- at least one step of rinsing the surface layer comprising electrodeposited ruthenium is carried out in an alkaline solution; The surface layer is electrochemically deposited in an acid bath; The rinsing step significantly improves the corrosion resistance properties of the surface layer comprising electrodeposited ruthenium (this step allows better removal and/or neutralization of acid compounds trapped in the deposited surface layer);

- electrochemically depositing at least one layer of electrically conductive material onto a sheet of electrically conductive material, prior to deposition of a surface layer, included in the list of copper, nickel, nickel alloys, gold, silver, palladium, and white bronze depositing at least one layer below the surface layer, made of at least one of the following materials;

- at least one of the layers comprising the sheet of electrically conductive material and the layer below the surface layer is a gloss layer; For example, the sheet of electrically conductive material is a sheet of copper or a copper alloy, the surface of which has a luster (either by manufacture or by a polishing treatment after manufacture);

- carrying out a step of polishing or electropolishing at least one layer made of a material included in the list of copper, nickel, nickel alloys and white bronze to form a lustrous layer;

Alternatively, at least one step of gloss depositing at least one layer of a material included in the copper, nickel, nickel alloys and white bronze inventories is performed.

The invention also relates to an electrical circuit for producing modules of chip cards, in particular:

- a flexible dielectric substrate;

- a sheet of copper-based electrically conductive material placed on a dielectric substrate, the sheet of electrically conductive material comprising at least one electrical contact having an inner side facing the dielectric substrate and an outer side opposite to the inner side; a sheet of electrically conductive material, the outer side having a contact surface intended to form an electrical connection with the connector;

- at least one layer of electrically conductive material laid directly on a sheet of electrically conductive material, which layer of electrically conductive material is among the materials included in the list of copper, nickel, nickel alloys, gold, silver, palladium and white bronze at least one electrically conductive material comprising a potentially shiny lower layer comprising at least one and a surface layer electrochemically deposited on the lower layer and covering at least one region of the contact surface of the at least one electrical contact; contains a layer

In this electrical circuit, the surface layer is produced using the method for electrodepositing a gray or black layer as described above.

Other features, objects and advantages of the foregoing electrical circuit will become apparent upon reading the following detailed description in conjunction with the accompanying drawings, given by way of non-limiting example.
1 shows schematically and in perspective a chip card comprising an example of a module having an electrical circuit according to the invention.
2 shows schematically and from above a part of an electrical circuit according to the invention.
Figure 3 schematically and in cross section shows an example of a stack of layers as obtainable with the method according to the invention.
Figures 4a to 4k schematically show the steps of an example of an embodiment of the method according to the present invention.

An example of embodiment of an electric circuit according to the present invention is described below. Although these examples are from the chip card field, a person skilled in the art, without training in the techniques of the present invention, will be able to apply these examples to other applications of electrical circuitry. In particular, the present invention is particularly advantageous in all cases where creating black-colored contacts or conductive tracks, for example for SD memory cards or USB sticks, can add aesthetic value.

As shown in FIG. 1 , the chip card 1 comprises a module 2 having, for example, a connection part 3 . The module 2 is usually produced in the form of a separate element that is inserted into a cavity made in the card 1 . This element comprises a generally flexible substrate 4 (see FIG. 2 ) made of PET, epoxy glass or the like, on which a connection 3 , to which chips (not shown) are subsequently connected, is created.

2 shows an example of a part of an electrical circuit, here a printed circuit 5 , with six connections 3 . Each connecting portion 3 includes a contact pad 8 formed of a conductive track 6 . In the example shown, eight electrical contacts 7 are created from the conductive tracks 6 .

More particularly, as shown in cross section in FIG. 3 , the connection 3 (i.e. essentially a chipless module) comprises, for example, a substrate 4, a layer of adhesive 9, (e.g., made of copper or copper alloy), and a multilayer structure formed from a stack of layers (A, B, C and/or D), which may be more or less.

Each electrical contact 7 of this connection 3 has an inner side 18 facing the dielectric substrate and an outer side opposite to this inner side. The inner side 18 is exposed at the lower end of the connection well 14 to form an electrical connection with a chip that can be received within the cavity 15. The outer side has contact surfaces intended to form electrical connections with other connectors. The layers deposited on the inner and outer sides do not necessarily have the same properties or the same thickness.

The table below illustrates possible stacks:

It will be noted that by electrolytically depositing copper onto an electrically conductive sheet 10 that is already potentially composed of copper or a copper alloy, copper can be brightened.

It will be noted that the gold layer (C) is optional. It is deposited in the form of a flash, ie electrodeposited to a thickness of 0 nanometers to 15 nanometers. It may be free of palladium or replaced by palladium.

The presence of an (optional) gloss layer under the ruthenium deposits makes it possible to obtain an electrical circuit 3 with a glossier appearance and a deeper black color.

4a to 4k schematically show the different steps of an example of the method according to the invention for producing a connector 3 , the stack of layers of which connector is shown in FIG. 3 .

These steps are:

- providing a substrate 4 (Fig. 4a);

- coating the side surface of the substrate 4 with a layer 9 of adhesive (Fig. 4b);

- drilling the substrate 4 with a layer 9 of adhesive, in order to create potential cavities 15 and connection wells 14 in which the chip will subsequently be accommodated (Fig. 4c);

- complexing a sheet 10 of an electrically conductive material (eg a sheet of copper) with a substrate 4 with a layer 9 of adhesive and, under heat, a layer 9 of adhesive cross-linking and deoxidizing the resulting composite (FIG. 4d);

- depositing dry film photoresist 16 (Fig. 4e);

- exposing the film photoresist 16 to light through a mask (Fig. 4f);

- developing the film photoresist 16 (Fig. 4g);

- chemically etching the sheet 10 of electrically conductive material in areas not protected by the film photoresist 16, to form conductive tracks and/or contacts 17 (FIG. 4h);

- dissolving the film photoresist 16 (Fig. 4i);

- metallizing at least part of the tracks and/or at least part of the contacts 17 obtained after etching the sheet 10 of electrically conductive material, this metallization comprising a layer as described above with respect to FIG. 3 . may be performed in one or more steps, to form a stack of; For example, such a stack includes a layer 11 of nickel and a layer 12 of gold (FIG. 4j),

- metallization again to form a surface layer 13 of ruthenium (which also contains other compounds comprising ruthenium), and

- rinsing the surface layer 13 comprising electrodeposited ruthenium in an alkaline solution (eg NaOH).

3, to deposit only a layer 12 of gold (as in FIG. 4K) and/or a layer of nickel and/or another alloy (eg of nickel or platinum bronze) thereon, Sides 18 (ie, sides intended to be invisible in the final product) may be masked. In fact, in order to obtain better weldability of the connecting wire to the chip, during the step of depositing the surface layer 13 of ruthenium, a protective film (opposite to what is called the front side or contact side or outer side, and ruthenium It may be advantageous to apply to the inner side 18 of the conductive track 17 (which is intended to receive the surface), or to press the masking belt against this side.

A surface layer 13 of ruthenium is deposited electrochemically over a thickness of 5 nanometers to 3 micrometers, and more preferably over a thickness of 100 nanometers or nearer. The mass concentration of ruthenium in the electrochemical bath for the deposition of the surface layer 13 is between 1 and 15 grams per liter. A ruthenium solution enabling the deposition of the surface layer 13 is sold, for example, by Atotech ^® . Ruthenium is advantageously deposited at a pH of 0.1 to 2 and at a temperature of 65°C +/- 10°C. In order for the ruthenium solution to deposit the surface layer 13, an inhibitor of the electrochemical kinetics of the deposition of ruthenium is added.

The inhibitor of the electrochemical rate of deposition of the surface layer 13 is an organic molecule, for example an amine with a carboxylic acid functional group.

The color obtained for the surface layer 13 of ruthenium depends on the deposition conditions.

Therefore, the brightness measured by the L* index of the CIELab color space is less than about 64. Colorimetric measurements were performed in reflection, including specular reflection. We obtained a surface layer with an L* index of 56.1 to 63.3, but without inhibitors of the electrochemical kinetics of deposition, with an L* index greater than 71.3. Accordingly, the presence of an electrochemical kinetic inhibitor of deposition in the electrochemical bath for depositing the surface layer 13 makes it possible to obtain the electrical circuit 3 having a darker black appearance (shown in the table below). As can be seen, the coordinates a and b of the CIELab color space are very close to 0; thus there are practically no green, red, yellow or blue components; thus a black appearance is obtained).

In a bath for electrochemically depositing ruthenium, the concentration of the electrochemical kinetic inhibitor of this deposition affects the deposition rate. From some of the results obtained by the present inventors and summarized in the tables below, it is clear that at the same concentration (ie, about 6.5 grams per liter) of an electrolyte solution containing ruthenium, at the same current (ie, 1.5 A/dm ² ), and At the same deposition rate (i.e. 5 minutes), the higher the concentration of the electrochemical kinetic inhibitor, the thinner the surface layer obtained (whatever the pH of the bath).

The pH as well as the concentration of the inhibitor of the electrochemical kinetics of the deposition affect the color. Therefore, the color was measured using a spectroscopic colorimeter configured in the following manner (measuring device: X Rite SP62):

- Illuminant D65 (ie has a light corresponding to daylight at 6500 K);

- observation at an angle of 10 degrees;

− the spectrally diffused light involved in the measurement;

- incident light of light at reflection, of 8 degrees.

An electrical circuit 3 obtained under the conditions mentioned in relation to the table and having a surface layer thickness of more than 70 nanometers is, in particular, for application to payment chip cards (and in particular according to the ISO 10373 standard or the EMV ^® specification, It satisfies the force requirements (related to contact resistance measurement or CRM).

In particular, this electric circuit 3 satisfies the salt spray corrosion test, the two-gas (H ₂ S and SO ₂ ) industrial corrosion test, and the temperature humidity test (THT), and after performing these tests for 24 hours, a 500 Keep the contact resistance below milliohms.

Good contact resistance and good corrosion resistance are related in particular to the fact that inhibitors of the electrochemical kinetics of the deposition of ruthenium are not deposited together with ruthenium. In Table 4 below, values are expressed as atomic percent from high-resolution XPS spectra for the deposition of ruthenium on the connections of chip cards. Examples 1 and 2 were produced with two baths containing thiourea according to the disclosure of document WO2014064278A1. Examples 3 and 4 were produced with baths containing electrochemical kinetic inhibitors of amine-type deposition. From this table, it can be observed that when using a bath with thiourea, the presence of sulfur in the deposited layer is systematically detected, indicating that thiourea is co-deposited. In contrast, when using a bath with an inhibitor of the electrochemical kinetics of the deposition of ruthenium of the amine type, the XPS measurement cannot detect this agent in the layer. Potential detection would indicate an organic form of nitrogen originating from the inhibitor's amine functional group, which in this case was not the case.

The electric circuit 3 described above may be a one-sided type or a double-sided type circuit. Advantageously, in the case of a double-sided circuit, the surface layer 13 of ruthenium will be created only on the side with the contact 7 .

Claims (12)

As a method of electrodepositing a gray or black layer onto an electrical circuit, in particular to produce a module (2) of a chip card (1):
- providing a dielectric substrate (4) with a sheet (10) of an electrically conductive material placed on the dielectric substrate (4), the sheet (10) of this electrically conductive material having an inner side facing the dielectric substrate (4). (18) and at least one electrical contact (7) having an outer side opposite this inner side (18), which outer side has a contact surface intended to form an electrical connection with the connector,
- depositing at least one layer of electrically conductive material onto the sheet (10) of electrically conductive material, which layer of electrically conductive material covers at least one area of the contact surface of the at least one electrical contact (7). comprising an electrochemically deposited surface layer (13);
wherein the surface layer (13) is electrochemically deposited from an electrolyte bath comprising at least ruthenium,
The electrolyte bath comprising at least ruthenium contains an electrochemical kinetic inhibitor of the deposition of the surface layer 13, and this inhibitor of the electrochemical kinetic of the deposition of the surface layer 13 is not deposited together with the ruthenium, Characterized in that the layer (13) has a gray or black color not produced by sulfur compounds. According to claim 1,
A method comprising at least one step of rinsing the surface layer (13) comprising electrodeposited ruthenium in an alkaline solution. According to claim 1 or 2,
wherein the inhibitor of the electrochemical rate of deposition of the surface layer (13) is an organic molecule. According to any one of claims 1 to 3,
wherein the inhibitor of the electrochemical rate of deposition of the surface layer (13) comprises an amine having a carboxylic acid functional group. According to any one of claims 1 to 4,
Electrochemically depositing at least one layer of electrically conductive material onto the sheet of electrically conductive material 10 comprises, prior to deposition of the surface layer 13, copper, nickel, nickel alloys, gold, silver, palladium, and depositing at least one layer (A, B or C) below the surface layer (13), consisting of at least one of the materials included in the list of white bronzes. According to any one of claims 1 to 5,
wherein the sheet of electrically conductive material (10) is a sheet of copper or a copper alloy. According to claims 5 and 6,
wherein at least one of the layer comprising the sheet (10) of electrically conductive material and the layer (A, B or C) below the surface layer (13) is a gloss layer. According to claim 7,
A method comprising at least one step of gloss depositing at least one layer of a material included in the inventories of copper, nickel, nickel alloys, gold, silver, palladium and white bronze. According to claim 7,
A method comprising polishing or electropolishing at least one layer made of a material included in the list of copper, nickel, nickel alloys, gold, silver, palladium and white bronze to form a lustrous layer. According to claim 7,
The method of claim 1 , wherein the sheet of electrically conductive material (10) is a sheet of copper or copper alloy having a lustrous surface. In particular, an electrical circuit for producing a module 2 of a chip card 1:
- flexible dielectric substrate 4;
- a sheet 10 of copper-based electrically conductive material placed on a dielectric substrate 4, the sheet 10 of electrically conductive material having an inner side 18 facing the dielectric substrate 4 and opposite to this inner side a sheet (10) of copper-based electrically conductive material comprising at least one electrical contact (7) having an outer side surface which is the outer side surface having a contact surface intended to form an electrical connection with the connecting portion;
- at least one layer of electrically conductive material lying directly on the sheet 10 of electrically conductive material, which layer of electrically conductive material is included in the list of copper, nickel, nickel alloys, gold, silver, palladium and white bronze and a surface layer (13) electrochemically deposited on the lower layer and covering at least one area of the contact surface of the at least one electrical contact (7). at least one layer of material;
The surface layer (13) is produced using a method as claimed in any one of claims 1 to 10 and has a gray or black color not produced by sulfur compounds. A chip card (1) comprising a module (2) manufactured from an electrical circuit (5) as claimed in claim 11 and inserted into a cavity made in the card (1).

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