US20160177455A1

US20160177455A1 - Single Solution for Electro-Electroless Deposition of Metals

Info

Publication number: US20160177455A1
Application number: US14/909,552
Authority: US
Inventors: Mordechay Schlesinger; Robert PETRO
Original assignee: University of Windsor
Current assignee: University of Windsor
Priority date: 2013-08-09
Filing date: 2014-06-02
Publication date: 2016-06-23
Also published as: EP3041975A1; CA2919877A1; WO2015017913A1

Abstract

A hybrid electro-electroless deposition process whereby multiple metal films layers are deposited from a single plating solution which includes both electroless and electroplating components. The article to be plated is immersed in the solution, and electric current is selectively applied at determined voltages for predetermined times, at selected intervals to effect electroplating in conjunction with electroless deposition. Electroplated metal layers are interspersed with electroless deposited metal layers.

Description

RELATED APPLICATIONS

This application claims priority and the benefit of 35 USC §119(e) to U.S. Provisional Patent Application No. 61/864135, filed Aug. 9, 2013.

SCOPE OF THE INVENTION

The present invention provides for a single solution for use in a combined process for electroplating and electroless deposition of metal coatings as part of a hybrid deposition process.

BACKGROUND OF THE INVENTION

The current methods of depositing electroless gold use cyanide for the reason that cyanide baths are stable and relatively easy to use in both electroplating and electroless plating processes. For example, while Au(I) sulfite has been used in commercial baths, the complex is susceptible to disproportionation, forming Au(III) and metallic gold. This spontaneous decomposition of the bath has led commercial baths to use proprietary stabilizing additives.
Electroless deposition processes have been combined with the deposit of other non-conductive and semi-conductive materials such as Teflon™, diamond dust and sulfur suspended as a powder in the electroless solutions, and which carried with the metal to the surface being coated to provide unique properties to the coating process.

SUMMARY OF THE INVENTION

The present invention provides a hybrid deposition process which uses both electroplating and electroless deposition to co-deposit metals, or deposit metal coatings or layers, and most preferably differing metal coatings on layers, on a substrate.
More preferably, in one non-limiting embodiment, the process is used to deposit metallic gold layers using a sulfite bath without any breakdown, in place of a cyanide bath. This is environmentally beneficial, and minimizes cost for waste treatment/removal.
In another embodiment, simple electro-electroless deposition baths are provided for the deposition of different metal layers including, for example, nickel and Ni—Zn—P coatings, and Cu and Ni coatings. More preferably, the electro-electroless deposition baths are used in a multi metal hybrid electro-electroless coating process to selectively coat one metal using an electro-plating process, then turning off the electroplating process and activating the plating of a second different metal which then coats the article using the electroless process.
In another embodiment, the electro-electroless deposition is provided a hybrid deposition process, whereby multiple layers of thin metal films, or multi-layers, are deposited from a single solution by interspacing electroplated layers of a first metal or alloy, within a constant electroless deposition of a second different metal or alloy. The electro-electroless deposition process may provide a range of possible deposits characterized by two or more streams, multi-layers and, optionally, alloying. Most preferably, the process allows for control over the degree of alloying of electro-deposited layer, and/or even electro-doping of the electroless deposit for alloy creation.
For the formation of electro/electroless multi-layer deposits, it has been appreciated a constant slower deposit occurs for the metal or alloy which is to be formed by way of electroless deposition, such as nickel phosphorus [Ni—P], while a current or electric pulses are only required for the deposition of a second other metal to be formed by electrodeposition. Some alloying may further be expected during the electroplating phase. The degree of alloying and/or layer formation may be controlled by varying the deposition rate of the electroplated layer, compared to the constant electroless deposition rate. Alloying is dependent on the overlap, or lack of overlap, of the electroplating windows of the metal ions. If the window is sufficiently narrow, minimal alloying is to be expected, as only the targeted species would be deposited.
In cases where a large over-potential would deposit some of the metal to be electrolessly deposited, it is expected that following criteria from electroplated multi-layers would lead to best results. Namely, it is expected the more noble metals, such as Cu, at a lower concentration may be electrolessly deposited, while a less noble metal present at a higher concentration, such as Ni, is electroplated. Without being limited to a particular process or theory, preferably, multi-layer deposition is performed using a plating bath solution having an electroless plating ion metal source, and either an anion or electroplating metal ion source in solution. Most preferably, the electroplated metal ions are selected not to interfere with, and act purely as ‘spectators’, to the electroless deposition process.
In another possible embodiment, copper/nickel [Cu/Ni] multi-layer metal thin films are deposited from a single solution. Cu is present at a lower concentration and deposited at a lower potential around 0.17V, whilst Ni is typically present at a higher concentration, several thousand times higher, and deposited at the higher potential, around 1.19V. As such, at 0.17V Cu alone is deposited, while at 1.19V a small amount of Cu is included in the Ni deposit. The higher concentration of the Ni salt is so that during Ni phase of the deposit, minimal Cu is co-deposited. Additionally, the Ni phase is deposited faster, using shorter pulses than the Cu phase.
In addition to the potential for multi-layer deposition, it has been appreciated that by providing a single electroless electrodeposition solution, voltage pulses that are sufficiently short and frequent may provide a means to dope the electroless deposit, creating an alloy. By providing knowledge of the electroless deposition rate, highly precise alloys can be created allowing for precise control over the deposit properties, such as hardness. In another preferred embodiment, a hybrid deposit technique further has the possibility of being further combined with existing electroplated multi-layers to provide more complex alloys of multiple, or even three or more, components.
The process temperatures, for such hybrid deposition process using aqueous deposition baths, are primarily those needed for the electroless deposition bath. In most cases this will be anywhere from room temperature to just below the boiling point, generally around 95-98° C. However, in some instances, such as in depositing Ni—Zn—P coatings, temperatures below 60° C. may be less preferred. In particular, the lower temperatures may slow or hinder deposition as the Zn interferes with the deposition (the presence of Zn contaminates and slows the deposit) however, in such cases the maximum temperature would remain the same. In cases of non-aqueous media, such as ionic liquids, the process temperature range may tend to become narrower in the case of electroless deposition. In general, the deposition temperature is based on the stability of the electroless process.
As for voltage ranges, it has been recognized that regions of maximum efficiency may be ascertained, such as those established with voltammograms. In the case of electroplating Ni coatings, the deposit does not typically suffer from over potential, and it has even been suggested to use 9V batteries as Ni solutions have a wide potential window for deposition. The final chemistry of solution will vary and voltammograms may be undertaken to determine the optimum plating window, voltage/current of maximum efficiency, and the like.
Accordingly, in one aspect, the present resides in a process for the deposition of multiple layers of thin metal films on a substrate comprising: preparing a plating bath comprising an electroless plating metal component and electroplating metal component; and immersing the substrate in a plating bath to effect electroless plating of the electroless plating metal component; and with said substrate remaining immersed in said bath, selectively apply a selected voltage over a predetermined interval or series of intervals to effect electroplating of the electroplating metal component thereon.
The present invention also resides in various further non-limiting aspects, and which include:

1. A process for deposition of a multi-layer metal coating on a metal substrate to be plated, the process comprising, at least partially immersing said substrate into a plating bath, the plating bath comprising a reducing agent, and a source of metal plating ions, the plating ions comprising one or more from the grouping consisting of copper ions, gold ions, nickel ions, zinc ions, silver ions, boron ions, cobalt ions and phosphorous ions, providing a sacrificial metal anode and cathode in said plating bath, and electrically connecting said anode and cathode, selectively supplying power to said anode, wherein said power is supplied in a pulsed time-wise manner to alternately effect anode oxidation and the formation of an electro-deposition plating layer of metal ions from the anode on the substrate, and the formation of an electroless deposition plating layer of the plating ions from the bath solution.
2. A process for alternatively depositing metal coatings on a substrate, the process comprising, immersing a portion of the substrates to be plated in a plating bath, the plating bath including a least one source of plating ions selected from the group consisting of sodium tetrachloroaurate, nickel sulfate heptahydrate, zinc sulfate heptahydrate, boric acid, cobalt chloride heptahydrate, nickel chloride hexahydrate, providing a metal anode and a cathode in said plating bath, said anode being in electrical communication with said cathode, selectively supplying power to said anode in a pulsed time-wise manner to form on the portion of the substrate to be plated, alternating electro-deposited metal layers and electroless deposited metal layers.
3. A process for the deposition of multiple layers of thin metal films on a substrate comprising: preparing a plating bath comprising an electroless plating metal component and electroplating metal component; and immersing the substrate in a plating bath to effect electroless plating of the electroless plating metal component; and with said substrate remaining immersed in said bath, selectively apply a selected voltage over a predetermined interval or series of intervals to effect electroplating of the electroplating metal component thereon.
4. An aspect according to any of the foregoing 1 to 3, further comprising maintaining the plating bath at a temperature of up to 120° C., preferably between about 40° C. to less than about 99° C., and more preferably from about 95° C. to about 98° C.
5. An aspect according to any of the foregoing 1 to 4, wherein said plating ions are gold ions, and said anode comprises a metal selected from the group consisting of nickel, and cobalt.
6. An aspect according to any of the foregoing 1 to 4, wherein said substrate comprises magnesium or a magnesium alloy, said anode comprises zinc, and said plating ions comprise nickel, zinc and phosphorous ions in relative amounts selected to form an electroless Ni—Zn—P plating layer.
7. An aspect according to any of the foregoing 1 to 6, wherein power is supplied to said anode from a power source as alternating current.
8. An aspect according to any of the foregoing 1 to 7, wherein said power is supplied to said anode at up to 120 minute intervals, and preferably at 5 to 45 minute intervals, for a period of time selected at up to sixty minutes, preferably between about 30 and 600 seconds, and more preferably between about 120 and 300 seconds.
9. An aspect according to any of the foregoing 1 to 8, wherein said power is supplied in a pulsed time-wise manner at a voltage of up to 240 volts, preferably t between about 1 and 120 volts, and preferably between about 2 and 24 volts.
10. An aspect according to any of the foregoing 1 to 9, wherein the plating bath solution is a two part solution comprising, a first part comprising: 1 to 4 grams, and preferably about 2 grams per litre sodium tetrachloroaurate as an electroless plating metal component; 5 to 15 grams, and preferably about 10 grams per litre boric acid; and up to 2 grams and preferably about 1 gram per litre sodium hydroxide; and a second part comprising: 7 to 12 grams, and preferably about 9.5 grams per litre sodium thiosulfate; 2 to 5 grams, and preferably about 3.75 grams per liter sodium sulfite; and 7.5 to 15 grams, and preferably about 10 grams per liter of boric acid.
11. An aspect according to any of the foregoing 1 to 10, wherein the plating bath further comprises a dopant solution comprising: up to 70 grams and preferably 25 to 50 grams per litre cobalt chloride heptahydrate; and up to 75 grams, and preferably 25 to 50 grams per litre nickel chloride hexahydrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1, 2 a, and 2 b show macroscopic photographs showing plating samples formed by the electroless gold-electroplated nickel deposition process, illustrating the alternate deposition of gold and nickel layers on test substrates;

FIG. 3 shows a macroscopic photograph showing the further formation of sulfur/oxide complexes on the plating samples in accordance with FIGS. 2a and 2 b;

FIGS. 4a and 4b show photographs illustrating the anode used in electrodeposition of the coatings of FIG. 1;

FIGS. 5a to 5b illustrate photographs of a plating sample and EDS analysis after electroless Ni—Zn—P and electro-Zn deposition on a substrate according to the invention thereon;

FIGS. 6a and 6b show macroscopic photographs of an electroless gold and electroplated cobalt/nickel deposition on sample nickel substrate;

FIGS. 7 a, 7 b and 7 c illustrate microscopic (SEM) image and electron diffraction x-ray spectroscopy (EDS) results showing the electroless gold deposition on the nickel substrate of FIG. 5 and the co-deposition of nickel/cobalt at the plating boundary regions;

FIG. 8 shows a macroscopic scanned image of a gold/nickel deposited nickel substrate sample illustrating the electroless gold and electroplated-Ni deposition of a four layer test strip in accordance with the present invention;

FIGS. 9 a, 9 b and 9 c illustrate SEM microscopic image and electron diffraction x-ray spectroscopy (EDS) results showing the electroless gold deposition on the nickel substrate of FIG. 8 and the co-deposition of nickel at the plating boundary regions;

FIGS. 10 a, 10 b and 10 c shows SEM microscopic image and electron diffraction x-ray spectroscopy (EDS) results showing the electroless gold deposition on a copper substrate and the co-deposition of electroplated nickel thereon; and

FIG. 11 shows a macroscopic scan illustrating a copper substrate showing an electroless gold deposited layer thereon as a gold/nickel electroless-electro deposition.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An electro-electroless deposition is provided as a hybrid deposition process, whereby multiple layers of metal films are deposited from a single plating solution having both electroless and electroplating components. An article to be plated is immersed in the solution. Electric current is then selectively applied at fixed or variable voltages. The current is supplied for predetermined times, and at selected intervals depending on the desired electroplated layer thickness. The application of the current effects electroplating to thereby form interspaced electroplated layers of a first metal or alloy, and electroless deposited layers and/or alternatively with the constant electroless deposition of a second different metal and alloy. The electro-electroless deposition process provides a range of possible deposits characterized by two or more streams, multi-layers and, optionally, alloying.
Most preferably, the process allows for control over the degree of alloying of electro-deposited layer, and/or even electro-doping of the electroless deposit for alloy creation. The solution chemistry and/or plating temperature may be tailored, whereby the initiation of electroplating by the application of current effects the electrodeposition of the electroplating component to the substantially relative exclusion of the electroless bath component, and whereby the bath chemistry allows for electroplating to effectively be turned on or off.
The applicant has appreciated various potential applications for the use of electroless/electro hybrid deposition of the present invention. Applications include without limitation, the deposition of cobalt [Co] and hardened gold [Au] on suitable substrates for electronics. In particular, in one preferred embodiment co-depositing Co with Au coating layers may provide increased strength to electronic components by mixing face centered cubic (fcc) and hexagonal close packed (hcp) crystal structures of Au and Co, respectively.
Alternatively, the formation of multilayers, which are traditionally harder than either constituent metal, may be used to achieve a comparatively hardened gold deposit or layer on a suitable substrate.
In an alternate possible embodiment, the electroless/electro hybrid deposits may be used to provide corrosion resistance to Mg alloys or substrates. For example, by providing an electroplated layer of Zn from a nickel zinc phosphorus Ni—Zn—P deposition bath, after the electroless deposition of a Ni—Zn—P coating layer may provide still enhance corrosion resistance in addition to the galvanic corrosion resistance provided by the Ni—Zn—P coating.
It is envisioned that other electroless/electroplating deposit applications also remain possible and will now become apparent.

Test Sample—Electroless Gold and Electro-Plated Nickel Deposition

FIG. 1 shows an example test strip showing an electro-electroless deposition coating which is formed as a multiple layer structure of alternating gold and nickel films. The alternating metal layers illustrated in FIG. 1 were formed using a plating solution providing a suitable deposit source of gold ions for electroless deposition, such as sodium tetrachloroaurate. As will be discussed, the metal, gold and nickel layer were alternately deposited as sample strips, and are first shown in FIGS. 2a and 2 b.
The alternating layering shown in FIGS. 1, 2 a and 2 b was achieved by raising the sample substrate in the plating bath a short distance after each stage, in an effort to show the alternating layers provided by the process and deposition bath. Shedding in the first two layers is due to rising of the sample to see each layer. The exposure of the gasses of the bath and heat of the sample coupled with the smoothness of the polishing and stresses in the deposit are believed the cause of the shedding. The last two layers of the test strips have no shedding, as the exposure to the environment was minimal. The thick gold layers were deposited over 45 minutes each, while the electroplated nickel was deposited over 5 minutes using pulse plating. A cross-sectional view is difficult as the gold is soft and care must be taken to ensure minimal delamination.
The darker second gold deposits shown are due to pulse plating not being used in the deposit. Without pulse plating sulfur/oxide complexes are created and the affinity of gold for sulfur incorporates them into the deposit. This phenomenon, when shown, persists in the deposition bath once it has occurred (see FIG. 3).

Test Sample—Electroless Ni—Zn—P and Electroplated Zn or (Ni)

In a further test sample Zn (or Ni) layers were electrodeposited formation with electroless formed layers Ni—Zn—P on Mg/Mg Alloy
The application of the present hybrid electro-electroless deposit (HEED) coating process allows for improvement of corrosion protecting properties of Ni—Zn—P coating on Mg or Mg alloys. In particular, the application of an electroplating step to deposit Zn or (Ni) after initial coating formation allows for the deposition of Ni or Zn rich layers on top of the electroless deposited Ni—Zn—P layers.
Initial electroless deposition of Ni—Zn—P is performed to provide a continuous coating over the substrate surface, accessing recessed areas. The coating of recessed areas, which is difficult using standard electroplating techniques, prevents the formation of a galvanic cell between uncoated and coated regions of the coated part. Secondary or pulsed electroplating then may provide for a reinforcement or outer cladding layers of Ni or Zn. The electroplated reinforcing layers thus allow for greater corrosion protection, and in the case of multi-layers, greater wear protection of the Mg/Mg alloy substrate.
With the formation of electroless Ni—Zn—P coatings and multi-layers produced therein, Zn enrichment of the coatings provides a more anodic layer, relative to the remainder of the coating. The arrangement of such layers produces a sacrificial multi-layer structure which protects the coating from corrosion by forming corrosion to propagate along the coating surface, rather than through the coating to the substrate. The formation of sacrificial multi-layer coatings has previously been suggested for Ni/Zn layers, with layers deposited from separate electrolytes. Using the current process, electroplating in place of a two bath system produces some alloying of the Zn layer, as would be expected when depositing the less noble metal of a binary multi-layer electrolyte.
Applying electro-electroless plating techniques to increase the Zn content deposited for a Ni—Zn—P electrolyte bath (see for example the following Table) on Mg alloys, a deposit darker in colour than the typical Ni—Zn—P coating was obtained.
In experimental examples shown in FIGS. 5a to 5 d, zinc deposition was effected using the electro-electroless hybrid deposition process to achieve alternating zinc and Ni—Zn—P layers. An 80° C. plating bath with a pH of 11 (at 20° C. before use) used in electro-electroless deposition was prepared as follows:


Component	Chemical	Formula	g/L

1)	Nickel Sulfate	NiSO₄•6H₂O	5.2495 to 6.5715
	Hexahydrate
2)	Zinc Sulfate	ZnSO₄•7H₂O	5.7425 to 7.1885
	Heptahydrate
3)	Sodium Citrate	Na₃C₆H₅O₇•2H₂O	23.5 to 25.3
	Tribasic
	Dihydrate
4)	Sodium	NaPH₂O₂•H₂O	17.5
	Hypophosphite
	Hydrate
5)	Ammonium	NH₄OH	25 to 62.5
	Hydroxide*

*NH₄OH in mL/L

The initial results showed a darker color and more metallic finish of the parts post electro-Zn deposition, as compared to post-electroless Ni—Zn—P deposition. Preliminary testing showed a higher concentration of Zn in the outer layers. This deposit has been performed on magnesium [Mg] alloys, and shows promise in providing developments for corrosion resistance.
Analysis of the composition using EDS determined that while electroless Ni—Zn—P struggles to obtain Zn content within the coating above 24% wt, or 20% at, Zn content within the final electrodeposited layer was around 37% wt, or 32% at within the HEED coating (FIGS. 5b to 5d ).
Alternating the layers of Ni—Zn—P and Zn is likely to provide increased corrosion protection at a level robust enough so that the coating not only resists galvanic corrosion but also overall, normal corrosion. This scheme can be adjusted to provide a low Zn Ni—Zn—P layer, ˜2-5% Zn, followed by an electroplated-Zn layer essentially making Ni—P/Zn multilayer coatings. As Zn is more anodic than Ni and would act as a sacrificial layer, provided the coating is not severely damaged, to the point of exposing the Mg substrate.

Test Sample—Electroless Au-Electroplated Co—Ni Deposition

In a further example, electroless gold-electro-cobalt nickel hybrid deposition was achieved using a two-component plating bath, in combination with a dopant solution as follows:

Deposition Bath & Conditions:

Bath A

Component	Chemical	Formula	mol/L	g/mol	g/L

1)	Sodium	Na(AuCl₄)	0.005	397.8	1.9890
	tetrachloroaurate
2)	Boric Acid	H₃BO₃	0.16	61.83	9.8928
3)	Sodium	NaOH	0.0275	40	1.1000
	Hydroxide*

*pH of Bath A should be adjusted to around 7

Bath B

Component Chemical Formula mol/L g/mol g/L

1) Sodium Na₂S₂O₃ 0.06 158.11 9.4866

Thiosulfate

2) Sodium Sulfite Na₂SO₃ 0.03 126.04 3.7812

3) Boric Acid H₃BO₃ 0.16 61.83 9.8928

In preparing the plating bath solution, Bath A was added to B slowly at room temperature, mixed, then let stand for 24 hours. After 24 hours, the additives and dopant metal were added to the solution, with the creation of a dopant solution as follows.

Additives

Chemical	Formula	mol/L	g/mol	g/L

Sodium Hypophosphite*	NaH₂PO₂	0.25	87.98	21.995
Sodium Citrate Tribasic	Na₃C₆H₅O₇	0.25	294.1	73.525

*Sodium Hypophosphite was not added in the initial experiment but can be optionally added to increase the deposition rate of Au.

Dopant Solution

Deposition

	Dopant	Bath	Dopant	g/L
	Solution	Volume	Volume	(for

Chemical	Formula	g/L	g/mL	Used [mL]	[mL]	60 mL)

Cobalt	CoCl₂•7H₂O	120.0	0.12	60	15	30
Chloride
Heptahydrate
Nickel	NiCl₂•6H₂O	120.0	0.12	60	15	30
Chloride
Hexahydrate

*Excess liquid volume was removed by evaporation during heating to deposition temperature.

To ensure best deposition conditions, the pH of the deposition was adjusted with NaOH to be above 8. In this example the pH of the 60 mL deposition bath was adjusted with 0.25 g of NaOH and 0.8 mL of NH₄OH to a final pH of 10.23. Both electrodeposition and electroless deposition were performed at 60° C. Nickel electrodes measuring 25 mm×90 mm×3 mm were used as both the anode and cathode.
Stability of the deposition bath in the presence of Co and Ni was found to be achieved with the formulation.
The foregoing test samples are not intended to be limiting. The electroless gold deposition from the borohydride system may be achieved on a number of noble metals such as Pd, Rh, Ag, and Au itself; as well as on substrates comprising active metals such as Cu, Ni, Co, Fe, and their alloys. The initial reactions on these two classes of metals are understood as different. On noble metals the reaction is catalytic from the very beginning, whereas the gold deposition on the active metals is initiated by galvanic displacement, which results in accumulation of ions of those metals in the bath. No adverse effect occurs with copper, whereas the introduction of ions of Ni, Co, and Fe into the solution may prove detrimental-bath as decomposition may set in when these metals are present at a concentration as low as 10⁻³M (see Electroless Plating, Chapter 15: Electroless Plating Of Gold and Gold Alloys, Yutaka Okinak).
FIGS. 6a and 6b shows macroscopic scans of the resulting nickel substrate test strips illustrating the formation gold, cobalt-nickel layer deposits thereon. In FIG. 6 a, shedding is believed due to smooth polished surface and excessive deposition time causing stress in the coating. It should be noted that the stress may be overcome by the electroplating indicating the robustness of the present process.
As shown in FIG. 6 a, the use of a Ni anode contributed to an increased Ni signal, as both Co and Ni were co-deposited. This can be remedied using a Co anode. Electron Diffraction X-ray Spectroscopy (EDS) provides a means of analysis that penetrates the coating; hence the Au signal remains visible in the electroplated Ni—Co region. Beam spread is believed the reason for Cobalt appearing in the upper, electroless Au region.
FIG. 8 shows a scan of nickel substrate illustrating electroless deposition of gold and electrodeposition of Ni as deposits thereon. In the illustrated figure, shedding is due to prolonged deposition on a smooth surface and resulting stress of the deposit. Again, in exemplary testing, four layers were successfully deposited from a single deposition bath.
As shown in FIGS. 7 a, 7 b, and 7 c, penetration of the EDS produces a Ni signal from the substrate through the gold layer (top analysis); while a small part of the Ni signal and a slight Au signal persist in Ni electroplated region (bottom analysis) as shown in FIGS. 9 a, 9 b and 9 c.
FIGS. 10 a, 10 b and 10 c illustrate scans showing the electroless deposition gold and electro-Ni deposition on a copper substrate.
In FIG. 11 the thin electroless gold appears thin or discontinuous, this colour is accentuated by the Cu substrate.
Accordingly it is believed that the present invention provides for a variety of non-limiting possible applications in coating and plating processes. In one possible application, it is envisioned that the hybrid deposition process of the present application may prove highly suitable for use in the coating medical implants with biomerit materials. In particular, in a non-limiting example, gold and tin may be recognized as metals which are suitable for deposition and which are bio-compatible. In addition, other possible alloys which may be suitable for possible deposition could include, without restriction, titanium as well as cobalt and chromium, depending on the implant composition.
In an alternate embodiment, the hybrid deposition process of the present invention could be used to effect the application of conducting coatings on plastics as either a final layer or an intermediate layer for subsequent metal plating. In a preferred application, the coatings of the present application may be effected in a single deposition bath. In alternate embodiments, it is envisioned that certain “additives” may be used to increase deposition rates, and which in accordance with preferred aspects would include nickel/gold deposition systems, as well as Ni—Zn—P deposition systems.
A further application of the present system may include, without restriction, the manufacture of magnets; and most preferably magnets using electroless Ni—Fe—P deposition which may contain up to 25% Fe.
In yet another manufacturing method, the hybrid deposition process of the present invention may be used in the manufacture of high-wear conductive contact points, as for example, are used in electronics and electronic systems. The applicant has appreciated that early experimental results have shown the successful formation of multi-layer nickel-gold deposits. It is further envisions that the deposition of alloys could equally be achieved by slowing the electroplating rate. Further, as the gold bath in questions is initiated by tandem electroless deposit and simple displacement reaction, nickel may be electroplated to achieve an Au/Ni hardened alloy.
In addition, the hybrid deposition process of the present invention further may advantageously provide enhanced adhesive surfaces for metal adhesive bonding or welding in combination or tandem with the deposition of different metals.
While the description describes various preferred embodiment of the invention, the invention is not restricted to the specific constructions which are disclosed. Many modifications and variations will now occur to persons skilled in the art. For a definition of the invention, reference may be made to the appended claims.

Claims

1. A process for deposition of a multi-layer metal coating on a metal substrate to be plated, the process comprising,

at least partially immersing said substrate into a plating bath, the plating bath comprising a reducing agent, and a source of metal plating ions, the plating ions comprising one or more from the grouping consisting of copper ions, gold ions, nickel ions, zinc ions, silver ions, boron ions, cobalt ions and phosphorous ions,

providing a sacrificial metal anode and cathode in said plating bath, and electrically connecting said anode and cathode,

selectively supplying power to said anode, wherein said power is supplied in a pulsed time-wise manner to alternately effect anode oxidation and the formation of an electro-deposition plating layer of metal ions from the anode on the substrate, and the formation of an electroless deposition plating layer of the plating ions from the bath solution.

2. The process of claim 1, wherein said substrate is provided as said cathode.

3. The process of claim 1, wherein the plating ions comprise gold and/or copper ions.

4. The process of claim 1, further comprising maintaining the plating bath at a temperature of between about 40° C. to less than about 99° C., and preferably from about 95° C. to about 98° C.

5. The process of claim 1, wherein said plating ions are gold ions, and said anode comprises a metal selected from the group consisting of nickel, a nickel alloy and cobalt.

6. (canceled)

7. The process as claimed in claim 1, wherein said substrate comprises magnesium or a magnesium alloy, said anode comprises zinc, and said plating ions comprise nickel, zinc and phosphorous ions in relative amounts selected to form an electroless Ni—Zn—P plating layer.

8. The process as claimed in claim 1, wherein power is supplied to said anode from a power source as alternating current.

9. The process as claimed in claim 8, wherein said power is supplied to said anode at 5 to 45 minute intervals, for a period of time selected at between about 30 and 600 seconds.

10. The process as claimed in claim 9, wherein power is supplied to said anode at a voltage between about 8 and 80 volts, and preferably at about 9 and 50 volts.

11. The process as claimed in claim 1, wherein said reducing agent comprises sodium hypophosphite, and the source of metal plating ions is selected from the group consisting of sodium tetrachloroaurate, nickel sulfate heptahydrate, zinc sulfate heptahydrate, boric acid, cobalt chloride heptahydrate, and nickel chloride hexahydrate.

12. A process for forming multiple metal coatings on a substrate, the process comprising:

providing a portion of the substrate to be plated in a plating bath, the plating bath comprising a reducing agent and sodium tetrachloroaurate as a source of gold ions,

introducing a nickel or nickel alloy anode into said plating bath,

electrically connecting said anode to said substrate as a cathode,

selectively supplying power to said anode in a pulsed time-wise manner to alternately form on the portion of the substrate to be plated, layer of the an electro-deposited nickel and electroless deposited layers of gold.

13. The process as claimed in claim 12, wherein the substrate comprises a metal selected from the group consisting of Mg, Pd, Rh, Au, Ag, Cu, Ni, Co, Fe, and their alloys.

14. The process as claimed in claim 13, wherein said power is supplied to said anode at 5 to 45 minute intervals, for a period of time selected at between about 30 and 600 seconds, and preferably between about 120 and 300 seconds.

15. The process as claimed in claim 12, wherein

said power is supplied in a pulsed time-wise manner at a voltage selected at between about 1 and 120 volts, and further comprising maintaining said plating bath at a temperature between about 90° C. and 99° C.

16. (canceled)

17. A process for alternatively depositing metal coatings on a substrate, the process comprising,

immersing a portion of the substrates to be plated in a plating bath, the plating bath including a least one source of plating ions selected from the group consisting of sodium tetrachloroaurate, nickel sulfate heptahydrate, zinc sulfate heptahydrate, boric acid, cobalt chloride heptahydrate, nickel chloride hexahydrate,

providing a metal anode and a cathode in said plating bath, said anode being in electrical communication with said cathode,

selectively supplying power to said anode in a pulsed time-wise manner to form on the portion of the substrate to be plated, alternating electro-deposited metal layers and electroless deposited metal layers, said power being supplied to said anode from a power source as alternating current.

18. The process as claimed in claim 17, wherein said substrate is provided as said cathode, said substrate being selected from the group consisting of Mg, Pd, Rh, Au, Ag, Cu, Ni, Co, Fe, and their alloys.

19. The process as claimed in claim 18, wherein the plating bath further includes sodium hypophosphite as a reducing agent.

20. (canceled)

21. The process as claimed in claim 17, wherein said power is supplied to said anode at 5 to 45 minute intervals, for a period of time selected at between about 30 and 600 seconds, and preferably between about 120 and 300 seconds, and wherein power is supplied to said anode at a voltage of between about 40 and 120 volts, and preferably at about 60 and 70 volts.

22. (canceled)

23. A process for the deposition of multiple layers of thin metal films on a substrate comprising:

preparing a plating bath comprising an electroless plating metal component and electroplating metal component; and

immersing the substrate in a plating bath to effect electroless plating of the electroless plating metal component;

with said substrate remaining immersed in said bath, selectively apply a selected voltage over a predetermined interval or series of intervals to effect electroplating of the electroplating metal component thereon; and

wherein the plating bath solution is a two part solution comprising,

a first part comprising:

1 to 4 grams, and preferably about 2 grams per litre sodium tetrachloroaurate as said electroless plating metal component:

5 to 15 grams, and preferably about 10 grams per litre boric acid; and

up to 2 grams, and preferably about 1 gram per litre sodium hydroxide,

a second part comprising:

7 to 12 grams, and preferably about 9.5 grams per litre sodium thiosulfate;

2 to 5 grams, and preferably about 3.75 grams per liter sodium sulfite, and

7.5 to 15 grams, and preferably about 10 grams per liter of boric acid.

24. (canceled)

25. The process as claimed in claim 23, wherein the plating bath further comprises a dopant solution comprising:

25 to 50 grams per litre cobalt chloride heptahydrate; and

25 to 50 grams per litre nickel chloride hexahydrate.

26. The process as claimed in claim 23, wherein the plating bath solution has a pH of at least 8.

27. The process as claimed in claim 23, wherein plating bath solution further includes up to 25 grams per litre sodium hypophosphite, and optionally up to 100 grams per litre sodium citrate tribasic.

28. The process as claimed in claim 23, wherein both electroless and electroplating are effected at a temperature of up to 99° C. and preferably between about 50° C. and 80° C.

29. The process as claimed in claim 23, wherein the substrate comprises a nickel substrate or a copper substrate.

30. The process as claimed in claim 23, wherein the electroless plating metal component comprises gold, and the electroplating metal component is selected from the group consisting of nickel, cobalt and nickel/cobalt alloys.