METHOD FOR PRODUCING A NICKEL-PHOSPHORUS COATING ON A LAMINATE OF POLYMER AND ALUMINUM MATERIAL

Abstract

------ METHOD FOR PRODUCING A NICKEL-PHOSPHORUS COATING ON A LAMINATE OF POLYMER MATERIAL AND ALUMINUM Method for producing a nickel-phosphorus coating on a laminate comprising a heat-sensitive polymer substrate and an aluminum layer. Figure to be published with the abstract: Figure 1

Description

Title of the invention: METHOD FOR PRODUCING A NICKEL-PHOSPHORUS COATING ON A LAMINATE OF POLYMER AND ALUMINUM MATERIAL

[0001] The present patent application relates to a method for producing a Nickel-Phosphorus coating on a laminate of polymer and aluminum material in order to guarantee effective electrical contact.

[0002] Processes are known for the metallic coating of metallic substrates by galvanic as well as chemical means. In particular, one of these known type of metallic coating processes is nickel plating, which is generally used on metallic mechanical parts (steels, aluminum alloys or copper) when it is necessary to protect these parts against oxidation and against corrosion by external agents.

[0003] As is known, in fact, metallic materials, exposed to the atmosphere and at room temperature, tend to corrode, forming oxides. The stability of these oxides decreases as the temperature increases. This is because at room temperature, almost all metals have a positive chemical affinity for oxygen, that is, they tend to react with oxygen by oxidizing. This oxidation process causes the metallic material to become covered with a very resistant oxide layer, which alters the conductivity of the metallic material.

[0004] Nickel plating increases the corrosion resistance of metallic materials thanks to the chemical resistance of the nickel-phosphorus layer deposited on the metallic material.

[0005] This nickel-phosphorus layer, in fact, protects against corrosion because it acts as a barrier and isolates the underlying metallic material from external aggressive agents, preventing, delaying or limiting points of corrosive attack.

[0006] Nickel plating is therefore very important, for example to protect against oxidation the electrical contact points of precision mechanical parts or industrial machine parts, in order to prevent the conductivity of these electrical contact points from being compromised by the formation of an oxide layer.

[0007] One of the metals that benefits most from nickel plating is aluminum, which represents a valuable resource used today in a wide range of industrial and non-industrial sectors. Indeed, aluminum is valued for its many properties, including its lightness, electrical conductivity and non-magnetic character, but it is also easily deformable and can be quickly affected by corrosive processes.

[0008] Indeed, nickel plating of an aluminum substrate presents critical problems linked to a difficulty of adhesion between nickel and aluminum, by electrolytic as well as chemical means, precisely because of the rapid formation of an oxide layer above the aluminum substrate.

[0009] Currently, there are preparatory treatments on the market such as deoxidizers and zinc-coated adhesion agents, which allow nickel to adhere to the aluminum substrate at the level of a few microns. However, the methods using these preparatory treatments have usage constraints linked to a very high operating temperature which does not allow their application on materials having a low heat distortion temperature. Consequently, the methods using such preparatory treatments cannot be used to treat laminates comprising, for example, aluminum and a substrate made of heat-sensitive material, such as, for example, a polymer material with a low heat distortion temperature.

[0010] Alternatively, the nickel-aluminum contact can be obtained by mechanical preparation of the aluminum substrate, which however involves physical aggression of the aluminum substrate.

[0011] In the field of RFID antenna printed circuits, traditional methods are known for generating aluminum conductive tracks on a plastic substrate, using printing and chemical etching. In this case, a plastic film is used with an aluminum top layer coupled to the plastic film. On the aluminum top layer, a resist film is deposited by printing in the areas where the tracks are to be obtained. The aluminum top layer is etched by etching where there is no resist film and the resist film is removed. However, these methods do not provide for the possibility of applying a protective Nickel-Phosphorus coating to the aluminum conductive tracks. The resulting printed circuit therefore has the disadvantage that after a certain time, oxide forms on the aluminum, which compromises the operation of the printed circuit.

[0012] Starting from this state of the art, the objective technical problem to be solved is that of protecting the aluminum, avoiding the formation of oxide on the aluminum of the printed circuit.

[0013] There are, however, other technical problems to be solved which are closely related to the objective technical problem. These additional technical problems are: • allow, following the protection of the aluminum, electrical conduction of the aluminum tracks with electrical contacts of electronic components, • avoid heat treatments for the protection of the aluminum so as not to melt the plastic film coupled with the aluminum, • avoid mechanical treatments on the aluminum layer to avoid damaging it.

[0014] In other sectors, very different from that of printed circuits, processes are known for chemically plating a Nickel-Phosphorus alloy on generic metal objects, with the aim of improving their resistance to wear and corrosion. However, this state of the art does not provide any instructions on the question of whether the Nickel-Phosphorus plating can be applied to conductive tracks of a printed circuit board and be suitable for electrical conduction from the track to the electronic component mounted on the track, nor does it teach how to carry out cold plating so as not to damage a polymer film. Indeed, the generic object to be plated does not have a polymer film and has an aluminum layer having a very high thickness.Moreover, these known techniques do not exclude physical treatment of the aluminum substrate, since the aluminum substrate is not thin (12 to 25 pm) nor intended to generate conductive tracks.

[0015] The aim of the present invention is to overcome the drawbacks of the known art by providing a method for producing a nickel-phosphorus coating on a laminate comprising a heat-sensitive polymer substrate and an aluminum layer which is reliable, efficient, simple to implement and, above all, capable of ensuring the maintenance of optimal electrical conductivity of the aluminum.

[0016] These aims are achieved in accordance with the invention with the characteristics listed in the attached independent claim 1.

[0017] The present invention therefore relates to a method for producing a nickel-phosphorus coating on a laminate comprising a heat-sensitive polymer substrate and an aluminum layer; said method comprising the following steps: • preparing a polymer and aluminum laminate comprising a substrate made of heat-sensitive polymer material and an aluminum (Al) layer, arranged above the substrate made of heat-sensitive polymer material; • identifying, on the aluminum (Al) layer of the polymer and aluminum laminate, operational portions, intended to become conductive tracks, with electrical contact points, and non-operational portions, intended not to support any electronic component; where said step of identifying the operational portions of the aluminum (Al) layer provides for carrying out a first impression on specific areas of the aluminum (Al) layer, intended to become said operational portions, so as to protect the tracks conductive of the aluminum (Al) layer of the polymer and aluminum laminate; • remove the non-operational portions, i.e. the portions not protected by the first impression, of the aluminum (Al) layer from the polymer and aluminum laminate; • removing said first impression of the aluminum (Al) layer of the polymer and aluminum laminate, so as to leave the conductive tracks uncovered; • subject the polymer and aluminum laminate to nickel plating, so as to form, on the aluminum conductive tracks, a protective layer of Nickel-phosphorus;

[0018] where said step of forming said protective layer of Nickel-phosphorus on the aluminum conductive tracks provides for subjecting the polymer and aluminum laminate to a treatment capable of depositing Nickel-phosphorus on the aluminum conductive tracks by chemical reaction.

[0019] Advantageous embodiments appear from the dependent claims.

[0020] Said step of carrying out said first printing on said specific areas of the aluminum layer (Al), intended to become said operational portions, may provide for the use of an ink resistant to acidic or basic chemical agents.

[0021] Said first printing may be carried out by contact type printing techniques such as flexographic, offset and rotogravure printing, or by non-contact type printing techniques such as screen, inkjet and slot die printing.

[0022] Said step of carrying out said first printing on said specific areas of the aluminum layer (Al), intended to become said operational portions, may provide the following steps: • deposit a photosensitive layer on the entire aluminum (Al) layer of the polymer and aluminum laminate, • exposing, to UV or laser light, specific areas of the photosensitive layer, arranged to cover said parts of the aluminum (Al) layer intended to become conductive tracks, causing the polymerization and hardening of said specific areas of the photosensitive layer.

[0023] Said step of removing the non-operational portions of the aluminum (Al) layer from the polymer and aluminum laminate may provide for the use of a mixture of acids or bases capable of attacking the aluminum and dissolving it, without affecting said first impression.

[0024] Said treatment capable of depositing Nickel-phosphorus on the conductive tracks (P) made of aluminum, by chemical reaction, may provide for subjecting the polymer and aluminum laminate to a series of washes carried out in sequence on a vertical galvanic installation, consisting of a series of tanks containing sulfuric deoxidizer, an adhesion agent based on zinc oxide and an ammoniacal mixture. This treatment may be carried out at a temperature of 20 to 30 °C and the protective layer of Nickel-phosphorus generated on the conductive tracks made of aluminum has a thickness of 0.2 to 0.7 μm.

[0025] The heat-sensitive polymer material substrate (2) may be made of a polymer material with a thermal deformation temperature of 40 to 80°C, and

[0026] the aluminum (Al) layer can have a thickness of 12 to 25 pm and can be made with an aluminum alloy 1200 or 8079.

[0027] After the step of removing said first impression of the aluminum (Al) layer from the polymer and aluminum laminate and before the nickel plating step, a step of masking parts of the conductive tracks which do not require said protective layer of Nickel-phosphorus may be provided; said masking step may provide for: • produce a cover, using photosensitive ink, with UV polymerization or hot air baking, exclusively on the conductive tracks of the aluminum (Al) layer, leaving uncovered the electrical contact points of the conductive tracks; and • place, in a UV or hot air oven, the polymer and aluminum laminate, with the cover on the conductive tracks of the aluminum (Al) layer, so as to harden the ink of the cover and ensure effective coverage of the conductive tracks, with the exception of the electrical contact points of the conductive tracks.

[0028] Said step of producing said cover may be carried out by film application, by contact type printing techniques such as flexographic, offset and rotogravure printing, or by non-contact type printing techniques such as screen printing, inkjet and slot die printing.

[0029] For greater clarity of explanation, the description of the method according to the invention continues with reference to the attached drawing, which has only an illustrative and non-limiting value, in which:

[0030] [Fig.l] is a functional diagram illustrating the steps of the method according to the invention.

[0031] With reference to the attached Fig., the method according to the invention firstly provides for preparing a polymer and aluminum laminate (1) comprising a substrate made of heat-sensitive polymer material (2) and a layer of aluminum (Al) (3), arranged above the substrate made of heat-sensitive polymer material (2).

[0032] The thermosensitive polymer material substrate (2) is made of a polymer material with a heat deformation temperature of 40 to 80 °C. Preferably, the thermosensitive polymer material substrate (2) is made of polypropylene (PP), having a heat deformation temperature of about 50 °C, and has a thickness of 220 to 280 μm. The aluminum (Al) layer (3) advantageously has a thickness of 12 to 25 μm and is preferably made of aluminum alloys 1200 and 8079.

[0033] The polymer and aluminum laminate (1) is capable of supporting or connecting electronic components. Thus, the method according to the invention provides for identifying, on the aluminum (Al) layer (3) of the polymer and aluminum laminate (1), operational portions (30), intended to become conductive tracks (P), with electrical contact points (PI), and non-operational portions (31), intended not to support any electronic components.

[0034] This phase of identifying the operational portions (30) of the aluminum (Al) layer (3) provides for carrying out a first print (4) on specific areas of the aluminum (Al) layer (3), intended to become said operational portions (30), so as to protect the conductive tracks (P) of the aluminum (Al) layer (3) of the polymer and aluminum laminate (1). The production of this first print (4) can be carried out using a roller or in sheets and advantageously provides for the use of an ink resistant to acidic or basic chemical agents. This first print (4) can be carried out either by contact type printing techniques such as, for example, flexographic, offset and rotogravure printing, or by non-contact type printing techniques such as, for example, screen printing, inkjet and slot die printing.

[0035] Alternatively, the production of this first impression (4) can be done by a photolithographic process. In this case, the production of this first impression (4) provides for depositing a photosensitive layer on the entire aluminum (Al) layer (3) of the polymer and aluminum laminate (1), then exposing, to UV or laser light, specific areas of the photosensitive layer, arranged to cover parts of the aluminum (Al) layer (3) intended to become conductive tracks (P), causing their polymerization and, consequently, their hardening.

[0036] Then, the method according to the invention provides for removing from the aluminum (Al) layer (3) of the polymer and aluminum composite (1) the non-operational portions (31), i.e. the portions not protected by the first impression (4). In this way, all the aluminum that is not necessary for the production of the conductive tracks (P) is removed from the aluminum (Al) layer (3) of the polymer and aluminum laminate (1). This removal phase provides for the use of a mixture of acids or bases capable of attacking aluminum and dissolving it, without in any way damaging the ink or the photosensitive layer of the first print (4).

[0037] At this stage, on the aluminum (Al) layer (3) of the polymer and aluminum laminate (1) only the conductive tracks (P) remain, which are however covered by the first print (4). Thus, the method according to the invention provides for removing, from the aluminum (Al) layer (3) of the polymer and aluminum laminate (1), the ink or the photosensitive layer used for producing the first print (4), so as to leave the conductive tracks (P) uncovered.

[0038] At this stage, the polymer and aluminum laminate (1) is formed exclusively by the substrate made of heat-sensitive polymer material (2) and the conductive tracks (P) made of aluminum.

[0039] The polymer and aluminum laminate (1) is then subjected to a nickel plating phase capable of forming, on the aluminum conductive tracks (P), a protective layer (6) of Nickel-phosphorus. This nickel plating phase consists of a treatment capable of depositing Nickel-phosphorus on the aluminum conductive tracks (P) by chemical reaction. This treatment is based on a sulfuric deoxidizer, an adhesion agent based on Zinc oxide and an ammoniacal mixture and provides for subjecting the polymer and aluminum laminate (1) to a series of washes carried out in sequence on a vertical galvanic installation, consisting of a series of tanks containing the sulfuric deoxidizer, the adhesion agent based on Zinc oxide and the ammoniacal mixture. In particular, the polymer and aluminum laminate (1) is introduced into special frames and moved between the tanks of the vertical galvanic installation via an overhead crane.This treatment is carried out at a temperature of 20 to 30 °C and the protective layer (6) of Nickel-phosphorus generated on the aluminum conductive tracks (P) has a thickness of 0.2 to 0.7 pm.

[0040] With reference to [Fig. 1], if the polymer and aluminum laminate (1) is intended to give rise to a product requiring selective coverage of the conductive tracks (P), then, before the nickel plating phase, the parts of the conductive tracks (P) which do not require said protective layer (6) of Nickel-phosphorus are masked. For this purpose, a cover (5) is produced exclusively on the conductive tracks (P) of the aluminum (Al) layer (3), while leaving the electrical contact points (PI) of the conductive tracks (P) uncovered. This cover (5) can be produced by applying films, by contact-type printing techniques such as, for example, flexographic, offset and rotogravure printing, or by non-contact-type printing techniques such as, for example, screen printing, inkjet and slot die printing.The ink used to produce this cover (5) can be photosensitive, UV-cured or hot air cured.

[0041] Depending on the type of cover chosen, the polymer and aluminum laminate (1), with the cover (5) on the conductive tracks (P) of the aluminum (Al) layer (3), can be placed in a UV or hot air oven, in order to harden the ink of the cover (5) and ensure effective coverage of the conductive tracks (P), with the exception of the electrical contact points (PI) of the conductive tracks (P).

[0042] At this stage, the nickel plating phase described above is carried out, which will however generate the protective layer (6) of Nickel-phosphorus exclusively on the electrical contact points (PI) of the conductive tracks (P), not protected by the cover (5).

Claims

1. Claims - Method for producing a nickel-phosphorus coating on a laminate comprising a heat-sensitive polymer substrate and an aluminum layer; said method comprising the following steps: • prepare a polymer and aluminum laminate (1) comprising a substrate made of thermosensitive polymer material (2) and an aluminum (Al) layer (3), arranged above the substrate made of thermosensitive polymer material (2); • identifying, on the aluminum (Al) layer (3) of the polymer and aluminum laminate (1), operational portions (30), intended to become conductive tracks (P), with electrical contact points (PI), and non-operational portions (31), intended not to support any electronic component; wherein said step of identifying the operational portions (30) of the aluminum (Al) layer (3) provides for carrying out a first impression (4) on specific areas of the aluminum (Al) layer (3), intended to become said operational portions (30), so as to protect the conductive tracks (P) of the aluminum (Al) layer (3) of the polymer and aluminum laminate (1); • removing the non-operational portions (31), i.e. the portions not protected by the first impression (4), of the aluminum (Al) layer (3) of the polymer and aluminum laminate (1); • removing said first impression (4) from the aluminum layer (Al) (3) of the polymer and aluminum laminate (1), so as to leave the conductive tracks (P) uncovered; • subjecting the polymer and aluminum laminate (1) to nickel plating, so as to form, on the aluminum conductive tracks (P), a protective layer (6) of Nickel-phosphorus; where said step of forming said protective layer (6) of Nickel-phosphorus on the conductive tracks (P) made of aluminum provides for subjecting the polymer and aluminum laminate (1) to a treatment capable of depositing Nickel-phosphorus on the conductive tracks (P) made of aluminum by chemical reaction.

2. - Method according to claim 1, characterized in that said step of carrying out said first printing (4) on said specific areas of the aluminum layer (Al) layer (3), intended to become said operational portions (30), provides for the use of an ink resistant to acidic or basic chemical agents.

3. - Method according to claim 2, characterized in that said first printing (4) is carried out by contact type printing techniques such as flexographic, offset and rotogravure printing, or by non-contact type printing techniques such as screen printing, inkjet and slot die printing.

4. - Method according to claim 1, characterized in that said step of carrying out said first printing (4) on said specific areas of the aluminum layer (Al) (3), intended to become said operational portions (30), provides the following steps: • depositing a photosensitive layer on the entire aluminum layer (Al) (3) of the polymer and aluminum laminate (1), • exposing, to UV or laser light, specific areas of the photosensitive layer, arranged to cover said parts of the aluminum layer (Al) (3) intended to become conductive tracks (P), causing the polymerization and hardening of said specific areas of the photosensitive layer.

5. - Method according to any one of claims 1 to 4, characterized in that said step of removing the non-operational portions (31) of the aluminum (Al) layer (3) of the polymer and aluminum laminate (1) provides for the use of a mixture of acids or bases capable of attacking the aluminum and dissolving it, without affecting said first impression (4).

6. - Method according to any one of claims 1 to 5, characterized in that said treatment capable of depositing Nickel-phosphorus on the conductive tracks (P) in aluminum, by chemical reaction, provides for subjecting the polymer and aluminum laminate (1) to a series of washes carried out in sequence on a vertical galvanic installation, consisting of a series of tanks containing sulfuric deoxidizer, an adhesion agent based on Zinc oxide and an ammoniacal mixture.

7. - Method according to claim 6, characterized in that said treatment is carried out at a temperature of 20 to 30 °C and the protective layer (6) of Nickel-phosphorus generated on the conductive tracks (P) made of aluminum has a thickness of 0.2 to 0.7 pm.

8. - Method according to any one of claims 1 to 7, characterized in that the substrate made of heat-sensitive polymer material (2) is made of a polymer material with a thermal deformation temperature of 40 to 80 °C, and the aluminum (Al) layer (3) has a thickness of 12 to 25 pm and is made with an aluminum alloy 1200 or 8079.

9. - Method according to any one of claims 1 to 8, characterized in that, after the step of removing said first impression (4) from the aluminum (Al) layer (3) of the polymer and aluminum laminate (1) and before the nickel plating step, a step of masking parts of the conductive tracks (P) which do not require said protective layer (6) of Nickel-phosphorus is provided; said masking step provides for:

10. • producing a cover (5), using photosensitive ink, with UV polymerization or hot air baking, exclusively on the conductive tracks (P) of the aluminum layer (Al) (3), leaving uncovered the electrical contact points (PI) of the conductive tracks (P); and • placing, in a UV or hot air oven, the polymer and aluminum laminate (1), with the cover (5) on the conductive tracks (P) of the aluminum (Al) layer (3), so as to harden the ink of the cover (5) and ensure effective coverage of the conductive tracks (P), with the exception of the electrical contact points (PI) of the conductive tracks (P). - Method according to claim 9, characterized in that said step of producing said cover (5) is carried out by application of film, by contact type printing techniques such as flexographic, offset and rotogravure printing, or by non-contact type printing techniques such as screen printing, inkjet and slot die printing.

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