METHOD OF METAL PLATING OF POLYMER-CONTAINING SUBSTRATES

Abstract

Method of forming a metallic plating (9) on a substrate (1), comprising the steps of: —providing a substrate (1) comprising a hydrocarbon-based polymer containing C—C and either or both of C—H and N—H bonds; —covalently bonding an azide-containing primer compound (3) to said substrate (1) by C—H and/or N—H insertion, said primer compound (3) comprising molecules each having at plurality of C—H and/or C—N insertion sites; —in the absence of in-situ polymerisation, covalently bonding a pre-synthesised chelating polymer (5) to said primer compound (3) by C—H and/or N—H insertion, said chelating polymer (5) being capable of forming ligand bonds with metal atoms or ions; —dispersing a plating catalyst (7) in said pre-synthesised polymer (5); —forming said metallic plating (9) on said pre-synthesised polymer (5) by means of electroless plating or electroplating

Claims

1.-15. (canceled)

16. A method of forming a metallic plating on a substrate, comprising the steps of: providing a substrate comprising a hydrocarbon-based polymer containing C—C and either or both of C—H and N—H bonds; covalently bonding an azide-containing primer compound to said substrate by C—H and/or N—H insertion, said primer compound comprising molecules each having at plurality of C—H and/or C—N insertion sites; in the absence of in-situ polymerisation, covalently bonding a pre-synthesised chelating polymer to said primer compound by C—H and/or N—H insertion, said chelating polymer being capable of forming ligand bonds with metal atoms or ions; dispersing a plating catalyst in said pre-synthesised polymer; forming said metallic plating on said pre-synthesised polymer by means of electroless plating or electroplating.

17. The method according to claim 16, wherein said azide-containing primer compound contains at least two, preferably at least ten, further preferably at least forty azide groups situated on side chains of a core polymeric chain.

18. The method according to claim 16, wherein said catalyst comprises metal ions and/or metal nanoparticles.

19. The method according to claim 16, wherein said catalyst is formed from metal ions which are subsequently reduced to metal by a reducing agent.

20. The method according to claim 18, wherein said ions are palladium ions, platinum ions, nickel ions, silver ions or copper ions.

21. The method according to claim 19, wherein said ions are palladium ions, platinum ions, nickel ions, silver ions or copper ions.

22. The method according to claim 16, wherein said primer compound and said pre-synthesised polymer are applied to said substrate simultaneously.

23. The method according to claim 16, wherein said pre-synthesised polymer is deposited on said substrate and is subjected to UV radiation or heat so as to cause the pre-synthesised polymer to bond covalently to said primer compound.

24. The method according to claim 16, wherein said metallic plating is applied by means of electroless plating or electroplating.

25. The method according to claim 24, wherein said electroless plating or electroplating is carried out in a pH range of 1-3 or 12-14.

26. The method according to claim 16, wherein said polymer has a molecular weight of at least 100,000 Daltons.

27. The method according to claim 26, wherein said polymer has a molecular weight of at least 500,000 Daltons.

28. The method according to claim 27, wherein said polymer has a molecular weight of at least 750,000 Daltons.

29. The method according to claim 28, wherein said polymer has a molecular weight of at least 1,000,000 Daltons.

30. The method according to claim 16, wherein said method does not include any in-situ polymerisation step.

31. The method according to claim 16, wherein said primer does not contain one or more of the following: a triazine ring; an alkylsilane group; a silanol group; a maleimide group; a complex compound based on aluminium or titanium; dextran.

32. The method according to claim 16, wherein said primer does not contain any of the following: a triazine ring; an alkylsilane group; a silanol group; a maleimide group; a complex compound based on aluminium or titanium; dextran.

33. A product comprising: a substrate comprising a hydrocarbon-based polymer containing C—C and C—H or N—H bonds; a metallic plating provided on a surface of said substrate; wherein said metallic plating is formed on said substrate by the method of claim 16.

34. A product according to claim 33, wherein said metallic plating is a composite between its constituent metal and said polymer in at least a part of its thickness.

35. A product according to claim 33, wherein said metallic plating comprises at least one of copper, nickel, silver, nickel phosphorous, nickel boron, cupronickel, platinum or palladium.

36. A product according to claim 33, wherein said metallic plating forms an antenna.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Further details of the invention will appear more clearly upon reading the description below, in connection with the following figures which illustrate:

[0030] FIG. 1: a schematic (not to scale) representation of a method of plating according to the invention;

[0031] FIG. 2: a schematic (not to scale) representation of a variant of a method of plating according to the invention;

[0032] FIG. 3: a schematic (not to scale) representation of how polymer molecules are bonded to the primer used in the method of FIG. 1; and

[0033] FIG. 4: a schematic view of a product wherein the plating forms an antenna.

EMBODIMENTS OF THE INVENTION

[0034] FIG. 1 illustrates a first embodiment of a method according to the invention.

[0035] In step 101, a substrate 1 is provided. This substrate 1 comprises a polymer intended to receive a metallic plating on at least one surface thereof. This polymer may be, for instance, polycarbonate (PC), poly methyl methacrylate (PMMA), polyethylene (PE), polyvinyl chloride (PVC), polystyrene (PS), polyamide, thermoplastic polyurethane (TPU), polyether ether ketone (PEEK), an epoxy-based polymer, an acrylate-based polymer, 3D-printed resins, polymer-based photoresists, printed circuit board (PCB) substrate materials, a glass-reinforced epoxy laminate material such as FR4, or any other suitable polymer. It may be fibre reinforced by means of glass fibres, carbon fibres, basalt fibres, natural fibres (hemp, cotton, etc.) and so on, and may contain other fillers. Furthermore, the substrate 1 may be monolithic, or may be made of another material (glass, metal, ceramic, silicon, silicon oxide, silicon nitride, silicon carbide or similar) provided with a polymeric layer on its surface.

[0036] Such a substrate may for instance be a printed circuit board (PCB) substrate, a housing for an electrical device such as a mobile telephone, smartphone, tablet computer, laptop computer, or any other electronic or mechanical device. It may be produced by moulding, 3D printing (additive manufacture), photolithography, stereolithography, LIGA, hot pressing, sintering (by laser or pressure), or any other convenient process appropriate for the material in question. It may have a simple, planar shape, or may have a complicated three-dimensional form.

[0037] Although the method of the invention is applicable to surfaces of any roughness, it is particularly suited for plating extremely smooth surfaces such as those with an R.sub.a roughness of 10 nm or less, more particularly 10 nm or less, 7 nm or less, or even 5 nm or less, as measured according to the ISO 4287:1997 standard. However, surfaces deliberately roughened during manufacture of the substrate, or in a separate chemical etching, plasma etching or mechanical roughening (e.g. sanding, bead blasting or similar) step are not excluded from the scope of application of the present invention. Furthermore, the method can be used with surfaces which are very difficult to etch chemically using industry-standard etchants such as a chromic etch, permanganate etch, acid etch, basic etch, etc. An example of a difficult-to-etch surface is Prototherm®, an epoxy-based polymer manufactured by Somos. Also, the surface may be activated e.g. by exposure to ultraviolet light, heat and/or plasma under atmospheric or (partial) vacuum conditions.

[0038] In step 102, the substrate 1 is treated with a primer compound 3 so as to form a coating thereupon, this primer compound being azide based and containing molecules each comprising a plurality of C—H and/or N—H insertion sites which can hence each covalently bond to at least one polymer molecule of the substrate 1 and to at least one polymer molecule of the pre-synthesised chelating polymer 5 (see below). Such primers have a polymer backbone which may be neutral or may contain various bonding groups such as amino groups, silane groups, thiol groups, phosphonates and so on, and which further comprise a plurality of C—H or N—H insertion groups, specifically two or more of azide groups situated on sidechains of the core polymeric chain constituting said polymer backbone. Ideally, the number of azide groups is at least ten, further preferably at least forty.

[0039] Specifically, such primers may incorporate for instance the compounds disclosed in EP2236524. To this end, this document is herein incorporated by reference in its entirety, but other azide-containing primers are of course possible. It should be noted that the discovery that the adhesion promoter of this document was particularly suitable for use as a primer in the specific plating process of the invention was entirely unexpected, since neither in this document, nor in the datasheet for the corresponding commercial product AziGrip4 (from Susos®), is there any suggestion at all that it would have the above-mentioned advantageous technical effects in this role. The standard primers to be experimented with are based on silanes, isocyanates, thiols, acrylates or hydroxyls. However, these are typically pH sensitive and are hence not suitable for plating at extremely low pH (1-3; typically associated with electroplating) or extremely high pH (12-14; typically associated with electroless plating) since they decompose under such conditions. Indeed, the pH insensitivity of azide-containing primers is not generally noted, making the unexpected technical effect of the invention all the more surprising.

[0040] The primer 3 is directly applied in a layer to a surface of the substrate 1 which is intended to be plated, for instance by dip-coating, drop-coating, spraying, bar-coating, brushing or any other method. To this end, the primer may be dissolved in a solvent such as toluene, chloroform, dichloromethane, an alcohol, particularly methanol, ethanol, isopropanol or a mixture of two or more thereof. It should be noted that the primer 3 is not synthesised in situ, nor is it synthesised immediately before use, since it is stable at room temperature.

[0041] The solvent is then allowed to evaporate under ambient conditions or in an oven set at a moderate temperature such as 20° C. to 100° C., leaving the layer of primer 3 on the surface of the substrate 1.

[0042] In step 103, a layer of pre-synthesised chelating polymer 5 is coated directly on the primer layer 3, in the absence of any preceding in-situ polymerisation-based step, and without the presence of a polymerisation-promoting agent such as a polymerisation initiator. Depending on the chosen polymer, this may be applied as a solution of the polymer in water or in an appropriate organic solvent. By “pre-synthesised”, it is meant that the polymer in question is applied in already-polymerised form, and is hence not synthesised in situ during execution of the method by means of monomers being joined together by a polymerisation agent such as a catalyst. In other words, the polymer molecules retain the same molecular weights and do not grow when applied to the substrate 1. The chelating polymer 5 is also bonded to the primer 3 by C—H or N—H insertion in a similar manner to the bonding between the primer 3 and the polymer of the substrate 1, C—H or N—H-insertable groups of the primer 3 again being inserted into C—H or N—H bonds of the chelating polymer 5.

[0043] The polymer in question is chosen for its interaction properties with metal ions and/or nonvalent metal particles. Examples of such polymers include polyacrylic acid, nitrogen-bearing polymers such as polyethyleneimine, polyvinylpyridine, polyvinylpyrolidone, polyacrylic acid, polyethylamine, poly(2-vinyl pyridine) (P2VP), poly(4-vinyl pyridine) (P4VP), polyaminophenylene (PAP) and so on. The important point is that the polymers in question can form ligand bonds with the catalysts mentioned in respect of step 104 below, and are hence chelating polymers, i.e. polymers which will bind to metals and/or to metal ions. Ligand bonds are by definition ionic and/or coordinate covalent bonds formed between the chelating polymer 5 and a metal atom or metal ion, as is generally known and understood from the relevant scientific literature, and all the example polymers given above are capable of forming such bonds. A logarithmic chelation stability constant log.sub.10 β of at least 5.0 is advantageous (and is fulfilled by all the above-mentioned polymers), and polymers capable of forming polydentate ligands are preferred in order to bond strongly to the metal ions. Ideally, the polymer molecules in question will have a high molecular weight, such as at least 100,000 Daltons, preferably 500,000 Daltons, preferably at least 750,000 Daltons. The larger the molecular weight of the polymer, the more chelation sites are present, leading to attachment of a greater number of metal ions to the polymer. Multiple layers of lower molecular weight chelating polymers are also possible, as are certain other lower molecular weight polymer molecules such as dendrimers (e.g. polyamidoamine, also known as PAMAM) and metal chelating hyperbranched polymers. The publication “Metal chelate dendrimer, star and hyperbranched polymers”, Uflyand Igor and Zhinzhilo Vladimir, LAP Lambert Academic Publishing, EAN 9786202013246 contains many examples of both of these types of polymers.

[0044] The polymer solution may be coated onto the primer layer 3 by dip-coating, drop-coating, spraying, bar-coating, brushing or any other method of thin film coating of the polymer in aqueous or alcohol-based solution.

[0045] The solvent is then allowed to evaporate under ambient conditions or in an oven set at a moderate temperature such as 20° C. to 100° C., leaving a layer of polymer 5 attached to the primer 3.

[0046] Subsequently, in step 103a, if required, the polymer 5 is reacted with the primer 3 so as to create covalent bonds between these two substances by means of e.g. UV light (such as UVC light), heating to a sufficient temperature (such as to above 120° C., preferably to above 125° C.), or by any other convenient method such as exposure to plasma, local heating with ultrasound or similar. If the polymer 5 has already sufficiently bonded to the primer 3 in step 103, e.g. during the evaporation of the solvent, this step is unnecessary.

[0047] Subsequent to this bonding step, and if required, excess polymer which has not bonded to the primer 3 can be rinsed off with an appropriate solvent and optionally also by sonication to agitate the unbonded polymer, and the substrate can then be dried again if required, for instance in the case in which the solvent used for rinsing is incompatible with the next step.

[0048] In step 104, a plating catalyst 7 is distributed throughout the polymer 5. This catalyst, which is chosen for its promotion of electroless plating and/or electroplating, may be formed of metallic ions, metallic nanoparticles, or similar. In the case of metallic ions, these may be Pd.sup.2+ ions, Cu.sup.2+ ions, Pt.sup.2+ ions, or any other suitable .sup.2+ valence metal ions provided as a solution of an appropriate metal salt. These ions are complexed by the molecules of polymer 5 and thus are anchored thereon. The catalyst 7 is applied by dip-coating, drop-coating, spraying, bar-coating, brushing or any other method of thin film coating of the catalyst 7 in aqueous solution in the case of ions, or as a suspension of metallic nanoparticles in water or an organic solvent such as ethanol. As a result, the ions or metallic nanoparticles diffuse into the polymer layer 5 and attach to the polymer molecules by ligand bonding, i.e. by ionic bonding and/or coordinate covalent bonding as appropriate, as mentioned above. Optionally, the in the case of metal ions, these may be reduced to zero-valence metal atoms by means of a redox reaction with another appropriate reducing agent such as formaldehyde or a salt such as sodium hypophosphite, sodium borohydride, ascorbic acid, dimethylamine borane, boric acid with an addition of acetic or sulphuric acid, or other suitable salt applied in a bath, by spray coating, bar coating, dip coating, drop coating, brushing, or any other suitable method. The excess reducing agent can then be removed by rinsing in water, with or without sonication. This reduction results in catalyst metal being intimately and strongly attached to the polymer layer 5

[0049] In step 105, the polymer-grafted, catalyst-containing substrate 1 is then subject to an electroless (autocatalytic) plating of copper, nickel, nickel-phosphorous, nickel boron, palladium, silver, cupronickel, platinum or other suitable metal in a plating bath comprising a suitable salt of the metal in question. Since the solution of metal salt penetrates through the polymer layer 5, the layer of metallic plating 9 which is formed reaches the primer 3 layer. Alternatively, the plating 9 can be applied by electroplating in a suitable electroplating bath, to the same effect.

[0050] Since the plating is formed not only on the surface of the polymer layer but is formed right throughout the polymer layer 5, including down to the primer layer 3, it is firmly anchored to the polymer molecules. These latter are themselves covalently bonded to the primer 3, which is itself covalently bonded to the substrate 1.

[0051] As a result, since the metal plating is intimately intermingled with the tangle of polymer molecules 5 which are covalently bonded to the substrate 1 via the primer 3, the adhesion between the metal plating 9 and the substrate 1 is significantly improved. This has been proven by the results of experimental tests, the results of which have been reproduced below.

[0052] Another way of looking at the resulting structure is that the portion of the plating layer 9 immediately adjacent to the primer 3 and substrate 1 is a metal-polymer composite with the metal filling up essentially all the space between the individual polymer molecules, these molecules being covalently bonded to the primer 3 and hence indirectly to the substrate 1. The portion of the metal plating 9 which grows beyond the extent of the polymer 5 molecules is monolithic. However, if the metal layer 9 is only as thick as the polymer layer 5, the entire plating is hence a metal-polymer composite.

[0053] The resulting plated substrate 1 forms at least part of a product 11, the plating forming e.g. the tracks of an electrical circuit, an antenna (such as a GHz or THz antenna in a wireless electronic device), a mirror, or any other product 11.

[0054] FIG. 2 illustrates schematically a variation on the method of FIG. 1, which differs from this latter in the following particulars.

[0055] Steps 101 and 102 are as in FIG. 1. However, steps 103 and 104 of FIG. 1 are combined in a single step 106, in which a mixture of polymer 5 and primer 3 in an appropriate solvent is coated onto the substrate 1 by dip-coating, drop-coating, spraying, bar-coating, brushing or any other method of thin film coating of the polymer in aqueous or alcohol solution.

[0056] The solvent is then allowed to evaporate under ambient conditions or in an oven set at a moderate temperature such as 20° C. to 100° C., leaving a layer of intermixed polymer 5 and primer 3 on the substrate 1, the primer molecules binding the polymer molecules to the substrate as before, but also with residual primer 3 distributed amongst the polymer 5. The block illustrating the primer 3 in this particular case is purely schematic and does not indicate a solid layer of primer 3, but rather the extent of its distribution throughout the polymer 5 once the solvent has evaporated. For this reason it has been illustrated with dashed lines.

[0057] If required, a step of irradiation or heating 106a can be carried out in identical fashion to step 103a described above.

[0058] Subsequently, steps 104 and 105 are carried out as above, with the metal plating 9 being formed through the intermingled polymer/primer layer, right down to the surface of the substrate 1, with the same effects as in the method of FIG. 1. Again, the extent of the dispersed primer compound 3 is illustrated with a dashed line, however this is again not a solid layer. In essence, the thickness between the dashed line and the surface of the substrate 1 comprises not only polymer 5 and metal 9, but also primer 3 dispersed therein.

[0059] FIG. 3 illustrates schematically an important aspect of the result of the method of the present invention. Since the polymer 5 used in the method of the invention is pre-synthesised, each molecule of polymer is covalently bonded to the primer 3 at one or more points along its length, indicated schematically by “X” symbols. For instance, polymer molecule 5a is covalently bonded to the primer 3 at one of its extremities. Polymer molecules 5b and 5e are covalently bonded to the primer 3 each at a single point along their lengths near one of their respective extremities. Polymer molecule 5c is covalently bonded at a plurality of points along its length, of which two are visible in the figure. Polymer molecule 5d is likewise covalently bonded to the primer 3 at a number of points. In the alternative case of a method according to FIG. 2, the only difference is that there is no discrete layer of primer compound 3, the individual molecules of primer compound being intermingled with the polymer 5.

[0060] This is distinct from a polymer synthesised in situ such as that disclosed in WO2017060656, which is only bonded to the underlying layer by a single extremity from which each individual molecule is grown. The bonding arrangement of the invention significantly increases the bonding strength between polymer 5 and primer 3 (and hence substrate 1) since many, if not most, polymer molecules will be bonded at multiple points and the angle made between the polymer molecule and the normal to the underlying layer will be typically greater. Since the metal plating 9 is intermingled with the polymer 5, its adhesion strength to the substrate will be significantly greater due to the larger number of covalent bonds present between the polymer and the primer (and hence with the substrate) in a given surface area.

[0061] Experimental tests carried out according to the strictest appropriate testing procedure, namely ASTM standard D3359-09, on a polymer substrate of surface roughness R.sub.a<5 nm using conventional plating methods and plated according to the invention showed an adhesion improvement from grade 0B (the lowest possible grade) to grade 5B (the highest possible grade).

[0062] As can be seen from the foregoing, the method of the invention is carried out entirely without any step of in-situ polymerisation, i.e. no polymer is grown from monomers or other polymer precursors on the substrate 1 or on the primer 3. The chelating polymer 5 is simply applied fully-formed thereupon, and retains its initial molecular weight. Indeed, the entire method can be carried out using readily-available off-the-shelf chemistry.

[0063] FIG. 4 illustrates schematically a product 1 in which the metal plating 9 is configured on the substrate 1 as an antenna, such as a GHz or THz antenna. The substrate 1 may be a printed circuit board, a casing for an electronic device, or similar, and the plating tracks may be structured by masking pre-deposition, or masking and subsequently etching the plating 9 after deposition by any convenient means.

[0064] Several concrete examples of tests were carried out, the details of which are as follows. For information, each example follows the method of FIG. 1.

Example 1

[0065] The substrate 1 is produced in step 101 by stereolithography from SOMOS® Prototherm 12120 epoxy-based resin without fillers, which is commercially available and has an unchanging formulation, ensuring reproducibility for the skilled person. The surface roughness of the substrate as measured by atomic force microscopy was between 3 nm and 7 nm, RMS (root mean square) value. After an atmospheric plasma surface activation, in step 102 the substrate 1 was drop-coated in the commercially-available azide-based polymeric adhesion promoter Azigrip4 (Susos®) (specifically product reference HVE256-3-1) which constitutes the primer 3, and the solvent is allowed to evaporate during a period of 30 minutes. This results in a N atom of the primer 3 inserting into a C—C or C—H bond of the polymer of the substrate 1.

[0066] In step 103, the substrate 1 was drop-coated in a 5 mg/mL aqueous solution of polyacrylic acid of molecular weight MW=3'000'000 Daltons, which constitutes the chelating polymer 5. The water was allowed to evaporate in an oven set at 40° C. for 2 h. The substrate 1 was then placed under UVC exposure in step 103a to ensure covalent grafting of the polymer 5 onto the substrate 1. The non-grafted polymer 5 was removed by sonication in water.

[0067] In step 104, the substrate 1 was immersed in a 5 mM solution of tetraaminepalladium (II) chloride monohydrate in water for 5 minutes. The substrate 1 was rinsed in water then placed in a 1M solution of sodium hypophosphite for 2 minutes in order to reduce the Pd.sup.2+ ions to Pd metal, which constitutes the plating catalyst 7. The substrate 1 was again rinsed in water, with sonication, so as to remove excess Pd metal and residual Pd.sup.2+ ions (if present).

[0068] In step 105, the coated substrate 1 was placed in an electroless copper bath from Dow (Circuposit™ 3350) at a temperature of 45° C. for 10 minutes in order to form the metallic plating 9. This particular bath is a copper chloride bath containing EDTA as a stabiliser, formaldehyde as a reducing agent, organic stabilisers and a high pH of 12-14.

[0069] After plating, the adhesion between the copper plating 9 and the substrate 1 was tested using the normalised test ASTM standard D3359-09 and improved from grade 0B when plated without the presence of the grafted polymer 5 to grade 5B when plated with the grafted polymer 5.

Example 2

[0070] In step 101, the substrate 1 was produced by stereolithography, again from SOMOS Prototherm 12120 resin. After an atmospheric plasma surface activation, in step 102 the substrate 1 was dip-coated the commercial azide-based adhesion promoter Azigrip4 (Susos) at 100 mm/minutes and the solvent was allowed to evaporate for 5 minutes. Again, the Azigrip4 constitutes the primer 3.

[0071] In step 103 the substrate 1 was similarly dip-coated in a 5 mg/mL solution of polyacrylic acid of molecular weight MW=3'000'000 Daltons in water, the polyacrylic acid constituting the chelating polymer 5. The water was then allowed to evaporate in an oven set at 40° C. for 2 h.

[0072] In step 103a the substrate was placed under UVC exposure to ensure covalent grafting of the polymer 5 onto the substrate 1. The non-grafted polymer was then removed by sonication in water.

[0073] In step 104, the coated substrate 1 was immersed in a 3 mM solution of palladium (II) chloride and 0.1M solution of NaCl in water for 5 minutes. The substrate 1 was then rinsed in water then placed in a 1M solution of sodium hypophosphite for 2 minutes to reduce the Pd.sup.2+ ions to Pd metal, which constitutes the plating catalyst 7. The substrate 1 was then rinsed in water, with sonication so as to remove excess Pd metal and residual Pd.sup.2+ ions (if present).

[0074] In step 105, the substrate 1 was placed in an electroless copper bath from Dow (Circuposit™ 3350) at a temperature of 45° C. for 10 minutes to form the metallic plating 9.

[0075] After plating, the adhesion of the metal plating 9 to the substrate 1 was tested using the normalized test ASTM standard D3359-09 and the test results improved from grade 0B when plated without the presence of the grafted polymer 5 to grade 5B when plated with the grafted polymer 5.

Example 3

[0076] In step 101, a commercial extruded polyethylene sheet of 1 mm thickness and dimensions of 25 mm by 75 mm was provided as substrate 1. After an atmospheric plasma surface activation, in step 102 the substrate 1 was dip-coated in the commercial adhesion promoter Azigrip4 (Susos) at 100 mm/minute and the solvent was allowed to evaporate for 5 minutes. Again, the Azigrip 4 constitutes the primer compound 3.

[0077] In step 103, the substrate 1 was dip-coated in a 5 mg/mL solution of polyacrylic acid of molecular weight 3'000'000 Daltons in water, the polyacrylic acid constituting the chelating polymer 5. The water was then allowed to evaporate in an oven set at 40° C. for 2 h.

[0078] In step 103a, the substrate was placed under UVC exposure to ensure covalent grafting of the polymer 5 onto the substrate. The non-grafted polymer was then removed by sonication in water.

[0079] In step 104, the substrate 1 was placed in a 5 mM solution of tetraaminepalladium (II) chloride monohydrate in water for 5 minutes. The substrate was rinsed in water and was then placed in a 1M solution of sodium hypophosphite for 2 minutes to reduce the Pd.sup.2+ ions to Pd metal and thereby to form the plating catalyst 7. The substrate was then rinsed in water, with sonication, so as to remove excess Pd metal and residual Pd.sup.2+ ions (if present).

[0080] In step 105, the substrate was placed in an electroless copper bath from Dow (Circuposit™ 3350) at a temperature of 45° C. for 10 minutes, so as to form the metallic plating 9.

[0081] After plating, the adhesion of the copper plating 9 was tested using the normalized test ASTM standard D3359-09 and was measured to be grade 4B with the grafted polymer.

Example 4

[0082] In step 101, the substrate was produced by stereolithography, again from SOMOS Prototherm 12120 resin. After an atmospheric plasma surface activation, the substrate was drop-coated in step 102 in the commercial adhesion promoter Azigrip4 (Susos) as before, and the solvent was allowed to evaporate for 30 minutes in air.

[0083] In step 103, the substrate was drop-coated in 25% solution of polyethyleneimine (PEI) of molecular weight 750'000 Daltons in water, the PEI constituting the chelating polymer 5. The water was allowed to evaporate in an oven set at 40° C. for 2 h.

[0084] In step 103a, the substrate was placed under UVC exposure to ensure covalent grafting of the polymer 5 onto the substrate. The non-grafted polymer was removed by sonication in water.

[0085] In step 104, the substrate was placed in a 5 mM solution of tetraaminepalladium (II) chloride monohydrate in water for 5 minutes. The substrate 1 was rinsed in water and then placed in a 1M solution of sodium hypophosphite for 2 minutes in order to reduce the Pd.sup.2+ ions to Pd metal to form the plating catalyst 7. The substrate was then rinsed in water, with sonication, so as to remove excess Pd metal and residual Pd.sup.2+ ions (if present).

[0086] In step 105, the substrate was placed in an electroless copper bath from Dow (Circuposit™ 3350) at a temperature of 45° C. for 10 minutes in order to deposit the metallic plating 9.

[0087] After plating, the adhesion between the plating layer 9 and the substrate 1 was tested using the normalized test ASTM standard D3359-09 and measured to be grade 5B with the grafted polymer.

[0088] As can be seen from the foregoing, the invention achieves the desired results of providing a metallic plating 9 on a polymer-containing substrate 1 with excellent adhesion. Furthermore, this is achieved using commercially-available products, and without resorting to complex processes or complex, bespoke chemistry. The invention is thus simple and economic to carry out on standard, existing equipment.

[0089] Although the invention has been described in terms of specific embodiments, variations thereto are possible without departing from its scope as defined in the appended claims. It is particularly noted that, although the tests were carried out forming electroless copper platings, nickel, palladium and other metallic platings such as platinum, silver, cupronickel, Ni—B and Ni—P are also possible using the same principles. Furthermore, electroplating may be carried out as an alternative to electroless plating.