US20200378028A1

US20200378028A1 - Electrolytic Preparation Of A Metal Substrate For Subsequent Electrodeposition

Info

Publication number: US20200378028A1
Application number: US16/869,014
Authority: US
Inventors: Maria E. Inman; Jing Xu; Timothy D. Hall; Earl Jennings Taylor; Alan Bonifas; Rajeswaran Radhakrishnan
Original assignee: Faraday Technology Inc
Current assignee: Faraday Technology Inc
Priority date: 2019-05-30
Filing date: 2020-05-07
Publication date: 2020-12-03

Abstract

A method of plating a workpiece, the method includes electrochemically removing any oxide on the surface of the workpiece by applying a first waveform to the workpiece and a cathode both placed in a first electrolyte solution, and electroplating the workpiece surface by applying a second waveform to the workpiece and an anode both placed in a second electrolyte solution including a plating material.

Description

RELATED APPLICATIONS

This application claims benefit of and priority to U.S. Provisional Application Ser. No. 62/854,635 filed May 30, 2019, under 35 U.S.C. §§ 119, 120, 363, 365, and 37 C.F.R. § 1.55 and § 1.78, which is incorporated herein by this reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made in part with U.S. Government support from U.S. Air Force SBIR Contract No. FA8501-16-P-0047 and U.S. Department of Energy Grant No. DE-SC0017751 and U.S. Department of Energy Grant No. DE-SC0015201. The U.S. Government may have certain rights in the invention.

FIELD OF THE INVENTION

This invention relates to a new process to directly deposit a metallic coating onto a metal substrate while minimizing the number of surface pretreatment steps, and may in one embodiment particularly relate to a new process to directly deposit a metallic coating onto a passive oxide-forming metal substrate while minimizing the number of surface pretreatment steps.

BACKGROUND OF THE INVENTION

A need derives from the responsibility the US Air Force Air Logistics Complexes has for corrosion control and improved lifecycle sustainability of aircraft parts. A specific material that has been used for decades due to its excellent corrosion resistance, lubricity, electrical conductivity, and ability to be conversion coated and ability to withstands thermal and electrical shock is cadmium. Cadmium plating offers an effective barrier protection to the substrate, especially in the marine environment. Cadmium also offers sacrificial protection to the steel components under corroding conditions.
However, cadmium deposition from cyanide baths gives rise to unacceptably high hydrogen intake by plated components of high strength, leading to hydrogen embrittlement. Also cyanide waste treatment is very expensive and the cadmium is often conversion coated with hexavalent chromium—also highly toxic. Furthermore, cadmium and its salts are known carcinogens and were part of the Annex XVII REACH list as well as Executive Order 13431.
Therefore, the US Air Force and others desires replacement of cadmium plating with zinc-nickel alloy (Zn—Ni), specifically for steel and aluminum electrical connectors, back-shells, components on aircraft, and propeller system components. Corrosion resistant alloys such as Zn—Ni (10-15% Ni) offer low susceptibility to stress-corrosion cracking and good abrasion resistance, formability, weldability, paint adhesion, and corrosion resistance. The corrosion resistant Zn—Ni coating must adhere strongly to the aluminum substrate with the ability to resist delamination in order to maintain strong electrical connection during operation. The challenge in plating on aluminum is the tenacious oxide-forming passive film that readily forms on the surface. This is overcome in current practice through a large number of aggressive precleaning steps that include hydrofluoric acid or zincating.
Another interest is the direct deposition of nickel onto aluminum during manufacturing of neutrino focusing horns for the Department of Energy (DOE). The DOE requires novel coating technologies and processes for neutrino focusing horns that are cost effective, less complex and use a smaller volume of chemicals to replace the most successful functional coating thus far—an electroless nickel coating.
Another interest is electrodeposition of copper onto niobium for fabrication of copper-niobium superconducting radio frequency (SRF) cavities. The DOE seeks SRF cavity fabrication techniques that reduce use of expensive metals such as niobium while achieving equivalent performance as bulk niobium cavities. One approach is to electroform copper onto a thin niobium cavity shell. Electroforming is a well-established industrial processing technology, and is not only low cost, but is also flexible and adaptable to many cavity sizes and shapes. The challenge in plating copper on niobium is the tenacious oxide-forming passive film that readily forms on the niobium surface. This is overcome in current practice through a large number of aggressive precleaning steps.
Another interest is the plating of coatings such as nickel on oxide-forming passive substrates such as titanium. Another interest is the plating of coatings such as nickel on oxide-forming passive substrates such as silicon.

BRIEF SUMMARY OF THE INVENTION

Featured, in one aspect, is an environmentally benign pretreatment and deposition process to clean and prepare the aluminum surface and subsequently directly electrodeposit nickel or a nickel alloy onto the aluminum surface. In another example, disclosed is an environmentally friendly pretreatment and deposition process to clean, prepare and de-passivate a titanium surface and subsequently directly electrodeposit nickel on the titanium surface. In still another example, disclosed is an environmentally friendly pretreatment and deposition process to clean, prepare and de-passivate a niobium surface and subsequently directly electrodeposit copper on the niobium surface. In still another example, disclosed is an environmentally friendly pretreatment and deposition process to clean, prepare and de-passivate a silicon surface and subsequently directly electrodeposit nickel on the silicon surface.
Finally, disclosed is an environmentally friendly pretreatment and deposition process to clean, prepare and de-passivate an oxide-forming passive surface and subsequently directly electrodepositing a metal or metal alloy on the surface.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Other objects, features and advantages will occur to those skilled in the art from the following description of a preferred embodiment and the accompanying drawings, in which:

FIG. 1 generally depicts the steps for pretreating and plating on an oxide-forming passive substrate used in the prior art;

FIG. 2 generally depicts the primary steps for pretreating and plating on an oxide-forming passive substrate in one embodiment;

FIG. 3 generally depicts a plating line for pretreating and plating on an oxide-forming passive substrate;

FIG. 4 depicts a generalized pulse reverse waveform of the instant invention; and

FIGS. 5A and 5B illustrates an adhesion scratch test for a nickel coated titanium substrate.

DETAILED DESCRIPTION OF THE INVENTION

One challenge in plating a metal coating directly onto metal substrates including aluminum, titanium, niobium, silicon and the like is the tenacious passive oxide film that readily forms on the surface when it is exposed to air. If the oxide film is not removed prior to plating, the plated deposit generally demonstrates poor performance characteristics such as corrosion resistance, wear and adhesion. Consequently, plating lines generally include various pretreatment processes to prepare and remove oxide from the oxide-forming substrate prior to plating illustrated in the process flow in FIG. 1. While the instant invention is not bound by theory, the rationale and types of pretreatments used for aluminum has been reviewed by D. S. Lashmore, Plating on Aluminum: A Review, Plating & Surface Finishing 72(6) pp. 36-9 Jun. 1985, which is incorporated in its entirety by reference. Another exemplary pretreatment process for brush plating of porous aluminum castings is described in U.S. Pat. No. 4,346,128 which is incorporated in its entirety by reference. Initially the substrate is subjected to cleaning/degreasing immersion step 100 for a particular time and at a particular temperature followed by water rinse step 200. One skilled in the art understands that water rinse step 200 may be repeated multiple times prior to the next pretreatment step. After water rinse step 200 the substrate is subjected to an immersion etch step 300 for a predetermined time and at a predetermined temperature to roughen the surface. The immersion etch step 300 may employ an alkaline or acid solution and often contains hydrofluoric acid depending on the substrate. The immersion etch step 300 is followed by another water rinse step 200 which may be repeated multiple times. After water rinse step 200 the substrate is subjected to an immersion desmut step 400 for a predetermined time and at a predetermined temperature. The immersion desmut step 400 removes the native oxide formed on the oxide-forming passive substrate and generally uses strong acids such as nitric acid, hydrofluoric acid, sulfuric acid or mixtures thereof for a predetermined time and at a predetermined temperature. The immersion desmut step 400 is followed by another water rinse step 200 which may be repeated multiple times. After water rinse step 200 the substrate is subjected to an immersion zincate strip step 500 for a predetermined time and at a predetermined temperature. The zincate strip step 500 is generally repeated multiple times. The immersion zincate strip step 500 dissolves atoms from the substrate and replaces the dissolved atoms with zinc atoms. After multiple immersion zincate strip steps 500 a layer of zinc is deposited on the substrate and protects the substrate from further smut of oxide formation. The zincate strip step 500 often contains harsh chemicals such as nitric acid and cyanide. The immersion zincate strip step 500 is followed by another water rinse step 200 which may be repeated multiple times. After water rinse step 200 the substrate is subjected to an immersion electroless metal deposition step 600 which permanently protects the oxide-forming passive substrate from extensive oxide film formation. The immersion electroless metal deposition step 600 is followed by another water rinse step 200 which may be repeated multiple times. After water rinse step 200 the substrate is subjected to electrolytic metal plating step 700 to deposit the coating of interest on the oxide-forming passive substrate. The electrolytic metal plating step 700 is followed by another water rinse step 200 which may be repeated multiple times. As is evident from the process flow of the prior art illustrated in FIG. 1, the pretreatments steps for plating on oxide-forming passive substrates are somewhat complex, numerous, generally involve harsh chemicals and are costly. There is a need for a simpler, less complex and economical pretreatment process.
FIG. 2 presents one new process flow for pretreatment and subsequent plating oxide-forming substrate. Initially, the substrate may be subjected to cleaning/degreasing immersion step 100 for a particular time and at a particular temperature followed by water rinse step 200. One skilled in the art understands that water rinse step 200 may be repeated multiple times prior to the next pretreatment step. After water rinse step 200, the substrate may be subjected to electrolytic activation step 800 for a predetermined time and at a predetermined temperature. The electrolytic activation step 800 is preferably followed by another water rinse step 200 which may be repeated multiple times. After water rinse step 200 the substrate is preferably subjected to an electrolytic metal plating step 700 to deposit the coating of interest on the oxide-forming passive substrate. The electrolytic metal plating step 700 may be followed by another water rinse step 200 which may be repeated multiple times.
As evident from the process flow of the instant invention in FIG. 2 compared to the process flow of the prior art in FIG. 1, the preferred process flow of the instant invention eliminates several process steps. In particular, the process flow steps of the instant invention may not require immersion etch step 300 and the associated alkaline or acid solution or the associated alkaline or acid solution and subsequent multiple water rinse step 200. Further, the process flow steps of the instant invention may not require an immersion desmut step 400 or the associated strong acids such as nitric acid, hydrofluoric acid, sulfuric acid or mixtures thereof and subsequent multiple water rinse step 200. Further, the process flow steps of the instant invention may not require multiple immersion zincate strip step 500 or subsequent multiple water rinse step 200. Further, the process flow steps of the instant invention may not require immersion electroless metal deposition step 600 or subsequent multiple water rinse step 200. While the instant invention does not prohibit an immersion clectroless metal deposition step, some embodiments of the instant invention may benefit from an immersion electroless metal deposition step 600, FIG. 1 either as a final step or as a prior step to electrolytic metal plating step 700, FIG. 2.
An exemplary functional process flow is presented in FIG. 3. The process generally begins with a cleaning/degreasing immersion step 100. The cleaning/degreasing immersion step 100 generally removes dirt and grease from the workpiece 50. The cleaning/degreasing immersion step 100 may comprise a tank 120 containing a cleaning/degreasing electrolyte 150 at a predetermined temperature. The workpiece 50 is immersed in the cleaning/degreasing electrolyte 150 for a predetermined time. The workpiece 50 may then subjected to water rinse step 200. The water rinse step 200 removes residual cleaning/degreasing solution from previous cleaning/degreasing immersion step 100 from the workpiece 50. The water rinse step 200 may comprise a tank 220 containing water 250 generally at ambient temperature. The workpiece 50 is immersed in the water 250 for a predetermined time. The water rinse step 200 may generally repeated one or more times. Preferably, the workpiece 50 is next subjected to electrolytic activation step 800. The electrolytic activation step 800 removes the passive oxide film from the workpiece 50. The electrolytic activation step 800 may comprise a tank 820 containing an activation electrolyte 850 at a predetermined temperature. The electrolytic activation step 800 may further comprises a pulse reverse power supply 880 and a counter electrode 870. The workpiece 50 is connected to the opposite pole of the pulse reverse power supply and immersed in the activation electrolyte 850. A pulse reverse waveform may be applied to workpiece 50 for a predetermined time. In some embodiments, the pulse reverse waveform applied to the workpiece 50 is of net cathodic character and thereby the counter electrode experiences an opposite waveform of net anodic character. In other embodiments, the pulse reverse waveform applied to the workpiece 50 is of net anodic character and thereby the counter electrode experiences an opposite waveform of net cathodic character. In the electrolytic actuator step, any oxidation on the workpiece is removed or at least decreased. The workpiece 50 may then be subjected to water rinse step 200. The water rinse step 200 removes residual electrolytic activation solution from previous electrolytic activation step 800 from the workpiece 50. The water rinse step 200 comprises a tank 220 containing water 250 generally at ambient temperature. The workpiece 50 is immersed in the water 250 for a predetermined time. The water rinse step 200 is generally repeated one or more times. The workpiece 50 is next preferably subjected to an electrolytic metal plating step 700 to deposit the coating of interest on the oxide-forming passive substrate. The electrolytic metal plating step 700 applies the selected metal coating to the workpiece 50. The electrolytic metal plating step 700 may comprise a tank 720 containing a plating electrolyte 750 at a predetermined temperature. The electrolytic plating step 700 further comprises a power supply 780 and an anode 770. The power supply 780 may be capable of delivering a direct voltage/current, a pulse voltage/current, a pulse reverse voltage/current or combinations thereof as is required by the specific plated metal. The workpiece 50 is connected to cathodic pole of power supply 780 and immersed in the plating electrolyte 750. A net cathodic current is applied to workpiece 50 for a predetermined time resulting in the desired metal coating. The workpiece 50 may then be subjected to water rinse step 200. The water rinse step 200 removes residual electrolytic metal plating solution from previous electrolytic metal plating step 700 from the workpiece 50. The water rinse step 200 may comprise a tank 220 containing water 250 generally at ambient temperature. The workpiece 50 is immersed in the water 250 for a predetermined time. The water rinse step 200 is generally repeated one or more times.
As noted in the discussion, electrolytic activation step 800 may include a pulse reverse waveform and electrolytic metal plating step 700 may use a direct current, pulse current, pulse reverse current. A depiction of a general pulse reverse current waveform of the instant invention is shown in FIG. 4. Pulse current or pulse voltage, or pulse reverse current or pulse reverse voltage waveforms are interrupted, asymmetric waveforms characterized by an anodic or cathodic period and optionally followed by an off time and optionally followed by a cathodic or anodic period and optionally followed by an off time. Some preferred waveform parameters are: (1) the anodic pulse current density, i_anodic, (2) the anodic on-time, t_anodic, (3) the anodic off-time, t_{off, anodic}(4) the cathodic pulse current density, i_cathodic, (5) the cathodic on-time, t_cathodic, and (6) the cathodic off-time, t_{off, cathodic}. In some embodiments all of these parameters are used to generate the appropriate electrolytic activation or electrolytic metal plating waveforms. In other embodiments, one or more of the off-time parameters may be absent. In still other embodiments the waveform parameters may consist of only anodic or cathodic pulses. One of skill in the art realizes that applying a pulse waveform to one electrode in an electrochemical cell automatically applies a waveform of opposite polarity to the other electrode in the electrochemical cell. By convention, the electrode which experiences the net anodic waveform is designated the anode and the electrode which experiences the net cathodic waveform is designated the cathode. The sum of the cathodic and anodic on-times and the off times is the period, T, of the waveform. The inverse of the period is the frequency, f, of the waveform. The cathodic, λ_c, and anodic, λ_a, duty cycles are the ratios of their respective on-times to the waveform period. The average current density (i_avg) is given by:
i _avg =i _cλ_c −i _aλ_a (1)
In pulse/pulse reverse process there are numerous combinations of peak current densities, duty cycles, and frequencies to obtain a given average current. These parameters provide the potential for much greater process control compared to direct current (DC).
The instant invention preferably comprises a pretreatment/plating process for an oxide-forming substrate. As illustrated, the pretreatment/plating process is simpler, contains fewer processing steps, and eliminates the need for hazardous and difficult to control chemicals including hydrofluoric acid, nitric acid, sulfuric acid and cyanide containing solutions.
In one embodiment, the process reduces and eliminates the need for aggressive chemical precleaning steps to prepare a passive metal substrate for deposition of another metallic coating. The process includes applying a pulse reverse waveform that removes the native oxide film prior to deposition of the desired metallic coating. See also U.S. Pat. Nos. 6,080,504 and 5,084,144 incorporated herein by this reference.

Example I: Nickel Coating on Titanium

Titanium is an oxide-forming substrate and usually requires extensive pretreatment similar to that depicted in FIG. 1 to remove the oxide prior to metal plating. To compare the efficacy of the methods depicted in FIGS. 2 and 3, we plated nickel on titanium without the prior surface pretreatments and instead with the surface pretreatment of the instant invention. A titanium coupon was plated with nickel without any pretreatment from a Woods nickel plating bath. The Woods nickel plating bath included of 10% hydrochloric acid (HCl), 25% nickel chloride (NiCl₂), and 65% distilled water. The plating bath temperature was maintained at ambient temperature for the duration of the plating process. The plating was conducted under direct current conditions at a current density of 13 A/dm²and a cell voltage of 2.6 V for 12 minutes. A diamond scribe was used to create a scratch through the nickel coating to the titanium substrate and was observed optically. In FIG. 5A is presented the area containing the diamond scribe scratch. Delamination of the nickel coating from the titanium substrate is evident and indicative of poor adhesion.
In the next experiment, a nickel coating was applied to a titanium substrate after the electrolytic pretreatment (800, FIG. 3). Specifically, an aqueous salt solution consisting of sodium chloride (NaCl 180 g/L), sodium bromide (NaBr 60 g/L) and sodium fluoride (NaF 2.4 g/L) at ambient temperature was used as the electrolytic activation electrolyte. The electrolytic activation step employed a pulse reverse waveform consisting of 4 V cathodic for 50 msec followed by 0.5 V anodic for 50 msec applied to the titanium substrate. After the electrolytic activation step, nickel was plated onto the titanium coupon from a Woods nickel bath 700, FIG. 2 using the same conditions as described above, 13 A/dm²for 12 minutes. In FIG. 5B is presented the area containing the diamond scribe scratch. In contrast to the untreated titanium coupon, there is no delamination of the nickel coating from the titanium substrate.

Example II: Nickel and Nickel-Phosphorous Coating on Aluminum

Aluminum is an oxide-forming passivating substrate and usually requires extensive pretreatment similar to that depicted in FIG. 1 to remove the oxide prior to metal plating. To compare the efficacy of processes depicted in FIGS. 2 and 3, we directly plated nickel and nickel-phosphorous using commercial protocols onto aluminum (Al) T6061 alloy coupons after the electrolytic activation surface pretreatment of the instant invention. After degreasing/cleaning the Al T6061 coupon, steps 100 and 100, FIG. 3 the surfaces were electrolytically activated, step 800 using pulse reverse waveform in aqueous 10% H₂SO4 plus 100 g/L Na₂SO₄at 50 C. The electrolytic activation waveform was 1 V anodic for 0.2 msec followed by an off-time of 1 msec followed by 11 V cathodic for 0.9 msec followed by another off-time of 0.1 msec. The waveform was repeated for 5 minutes followed by a water rinse step 200. The electrolytically activated Al T6061 coupons were kept wet and immediately transferred to the nickel or nickel phosphorous plating tank step 700.
The nickel (Ni) coating was directly deposited onto the electrolytically activated Al T6061 coupons from a Watts nickel plating bath. The Watts nickel bath contained nickel sulfate (NiSO₄300 g/L), nickel chloride (NaCl 60 g/L) and boric acid (H₃BO₃45 g/L) in water. In this Ni deposition trial, a nickel anode was spaced 4″ from the electrolytically activated Al T6061 substrate. The plating bath temperature was maintained at 80° F. and the substrate was plated under direct current conditions for 35 minutes at a current density of 4 A/dm².
The nickel-phosphorous (Ni—P) was directly deposited onto the electrolytically activated Al T6061 coupons from a Umicore NIPHOS 968 plating bath obtained from UYEMURA Corp. The anode was nickel sulfide pellets in a titanium basket and was spaced 4″ from the Al T6061 substrate. The plating bath temperature was maintained at 140° F. and the substrate was plated under direct current conditions for 35 minutes at a current density of 4 A/dm.
As a baseline for comparison, a high phosphorous (9 to 10%) electroless nickel coating was obtained from a commercial surface finishing facility, Techmetals Inc. Prior to applying the electroless nickel coating, the Al T6061 substrates were subjected to the standard pretreatment as generally depicted in FIG. 1.
As measures and indicators of adhesion and therefore indicators of the effectiveness of the electrolytic activation pretreatment process, the samples and baseline were evaluated using 1) Tape Adhesion Test according to ASTM D3359 Tape Adhesion Test, 2) Bend Test around a 0.5″ radius, 3) Bend Test around a 0.25″ radius, and 4) Taber Wear Test according to ASTM D4060. The data are presented in TABLE I.


				Taber Wear
	Tape	0.5″	0.25″	Index
Sample	Test	Bend Test	Bend Test	(mg/1000 cycles)

Electro-	PASSED	PASSED	PASSED	23.6
less Ni
Watts Ni	PASSED	PASSED	PASSED	NOT TESTED
Ni—P	PASSED	PASSED	PASSED -	22.7 to 23.2
			slight edge
			blisters

Both the Watts nickel and nickel-phosphorous coatings on the electrolytically activated Al T6061 substrates exhibited comparable adhesion to the baseline electroless nickel coating on the standard pretreated Al T 6061 substrate. While the nickel-phosphorous coating exhibited slight edge blistering in the 0.25″ bend test, this may be attributed to the lack of plating uniformity on the Al T6061 edge. The Taber Wear Index is a measure of the wear resistance of the coating and is indirectly related to coating adhesion to the substrate. Specifically, if the coating does not exhibit good adhesion to the substrate, then the coating will spall during the Taber Wear Test and the resulting Index will be extremely high. The Taber Wear Index of the nickel-phosphorous coating on the electrolytically activated Al T6061 is comparable to the baseline electroless nickel high phosphorous. Since the nickel coating is different than the nickel-phosphorous coating, the nickel sample was not tested for Taber Wear.

Example III: Zinc-Nickel Coating on Aluminum

Aluminum is an oxide-forming substrate and usually requires extensive pretreatment similar to that depicted in FIG. 1 to remove the oxide prior to metal plating. To compare the efficacy of the processes depicted in FIGS. 2 and 3, we directly plated nickel-zinc coatings using commercial protocols onto aluminum (Al) T6061 alloy coupons after the electrolytic activation surface pretreatment of the instant invention. After degreasing/cleaning the Al T6061 coupon, steps 100 and 200, FIG. 3 the surfaces were electrolytically activated, step 800 using pulse reverse waveform in aqueous 10% H₂SO4 plus 100 g/L Na₂SO₄at 50° C. The electrolytic activation waveform was 1 V anodic for 0.2 msec followed by an off-time of 1 msec followed by 11 V cathodic for 0.9 msec followed by another off-time of 0.1 msec. The waveform was repeated for 5 minutes followed by a water rinse. The electrolytically activated Al T6061 coupons were kept wet and immediately transferred to the zinc nickel plating tank, step 700.
The zinc-nickel (Zn—Ni) coating was directly deposited onto the electrolytically activated Al T6061 coupons from a Dipsol IZ-C17+ plating bath obtained from DIPSOL OF AMERICA, Inc. The plating bath temperature was maintained at 80° F. and the substrate was plated under direct current conditions at a current density of 5.09 A/dm². The plating times were 15, 25 and 40 minutes resulting in coating thicknesses of 10, 20 and 28 μm, respectively. All direct current plated coatings the electrolytically activated passed the ASTM D3359 Tape Adhesion Test.
Finally, zinc-nickel (Zn—Ni) coatings were directly deposited onto the electrolytically activated Al T6061 coupons from the Dipsol IZ-C17+ plating bath using cathodic pulse currents at frequencies of 1, 100 and 1000 Hz and duty cycles of 25, 50 and 75%. The average current density for all nine samples was 5.09 A/dm². The plating duration was 25 minutes. All pulse current plated coatings on the electrolytically activated Al T6061 substrates passed the ASTM D3359 Tape Adhesion Test.

Example IV: Nickel Coating on Silicon

Silicon is an oxide-forming substrate and usually requires extensive pretreatment similar to that depicted in FIG. 1 to remove the oxide prior to metal plating. To compare the efficacy of the processes depicted in FIGS. 2 and 3, we directly plated nickel coatings using commercial protocols onto boron doped silicon (<0.005 W-cm obtained from Addison Engineering, Inc.) wafers of 2″ diameter after the electrolytic activation surface pretreatment of the instant invention. The boron doped silicon wafer was cleaned/degreased followed by the electrolytic activation step of the instant invention. The electrolytic activation step 800 was conducted in 20% KOH for 2 hours using the pulse reverse waveform parameters, 1 V anodic for 1 msec, 5 msec off-time, 11 V cathodic 9 msec. After electrolytic activation and water rinse, nickel was plated onto the silicon wafer from a Watts plating bath step 700 including 322 g/L NiSO₄.6H₂O, 45 g/L NiCl₂.6H₂O, and 37.5 g/L H₃BO₃. During plating the silicon wafer was rotated at 1000 rpm with the following pulse reverse waveform sequence: 1) 0.25 A cathodic for 9 msec, 1 msec off-time, 0.1 A anodic for 1 msec for 5 minutes, 2) 0.5 A cathodic for 9 msec, 1 msec off-time, 0.1 A anodic for 1 msec for 20 minutes, 3) 0.3 A cathodic for 9 msec, 1 msec off-time, 0.1 A anodic for 1 msec for 95 minutes. After the deposition process, the nickel coating was 22 μm in thickness.
Aside from the preferred embodiment or embodiments disclosed below, this invention is capable of other embodiments and of being practiced or being carried out in various ways. Thus, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. If only one embodiment is described herein, the claims hereof are not to be limited to that embodiment. Moreover, the claims hereof are not to be read restrictively unless there is clear and convincing evidence manifesting a certain exclusion, restriction, or disclaimer.
Although specific features of the invention are shown in some drawings and not in others, this is for convenience only as each feature may be combined with any or all of the other features in accordance with the invention. The words “including”, “comprising”, “having”, and “with” as used herein are to be interpreted broadly and comprehensively and are not limited to any physical interconnection. Moreover, any embodiments disclosed in the subject application are not to be taken as the only possible embodiments. Other embodiments will occur to those skilled in the art and are within the following claims.
In addition, any amendment presented during the prosecution of the patent application for this patent is not a disclaimer of any claim element presented in the application as filed: those skilled in the art cannot reasonably be expected to draft a claim that would literally encompass all possible equivalents, many equivalents will be unforeseeable at the time of the amendment and are beyond a fair interpretation of what is to be surrendered (if anything), the rationale underlying the amendment may bear no more than a tangential relation to many equivalents, and/or there are many other reasons the applicant cannot be expected to describe certain insubstantial substitutes for any claim element amended.

Claims

What is claimed is:

1. A method of plating a workpiece, the method comprising:

electrochemically removing any oxide on the surface of the workpiece by applying a first waveform to the workpiece and a cathode both placed in a first electrolyte solution; and

electroplating the workpiece surface by applying a second waveform to the workpiece and an anode both placed in a second electrolyte solution including a plating material.

2. The method of claim 1 further including cleaning the workpiece surface prior to electrochemically removing any oxide on the workpiece surface.

3. The method of claim 1 further including rinsing the workpiece between electrochemically removing any oxide on the workpiece surface and electroplating the workpiece surface.

4. The method of claim 1 further including rinsing the workpiece surface after electroplating.

5. The method of claim 1 in which the first waveform is a pulsed reverse waveform.

6. The method of claim 1 in which the workpiece is aluminum, titanium, silicon, or other oxide forming conductive materials/alloys.

7. The method claim 1 in which the plating material is a zinc-nickel alloy, nickel, nickel phosphorus, or other platable elements/alloys.

8. The method of claim 1 in which the first electrolyte solution includes sodium chloride, sodium bromide, sulfuric acid, sodium sulfate, potassium hydroxide, and/or other water-soluble salts.

9. The method of claim 1 in which the second electrolyte solution includes hydrochloric acid, water, and/or boric acid or other constituents required to electrodeposit a given material.

10. A system for plating a workpiece, the system comprising:

an electrochemical tank including an electrolyte solution about the workpiece and a cathode;

a first power supply for applying a first waveform to the workpiece and the cathode to electrochemically remove any oxide on the surface of the workpiece;

an electrochemical plating tank including an electrolyte solution including a plating material about the workpiece and an anode; and

a second power supply for applying a second waveform to the workpiece and the anode to electroplate the workpiece with the plating material.

11. The system of claim 10 further including a cleaning station for the workpiece for cleaning the workpiece surface prior to electrochemically removing any oxide on the workpiece surface.

12. The system of claim 10 further including a first rinsing station for rinsing the workpiece between electrochemically removing any oxide on the workpiece surface and electroplating the workpiece surface.

13. The system of claim 10 further including a second rinsing station for rinsing the workpiece surface after electroplating.

14. The system of claim 10 in which the first waveform is a pulsed reverse waveform.

15. The system of claim 10 in which the workpiece is aluminum, titanium, silicon, or other oxide forming conductive materials/alloys.

16. The system of claim 10 in which the plating material is a zinc-nickel alloy, nickel, nickel phosphorus, or other platable elements/alloys.

17. The system of claim 10 in which the first electrolyte solution includes sodium chloride, sodium bromide, sodium fluoride, sulfuric acid, sodium sulfate, and/or potassium hydroxide, and/or other water-soluble salts.

18. The system of claim 10 in which the second electrolyte solution includes hydrochloric acid, water, and/or boric acid or other constituents required to deposit a given material.