Patent Application
20060024514
Spontaneous decomposition (seeding) is a problem in the electroless plating industry. Seeding reduces production throughput by limiting the length of time a production-plating tank can be used. When seeding occurs, the plating bath must be removed and the “seeded-out” residue chemically stripped and/or mechanically removed from the plating tanks. This removal, or “clean-out”, normally occurs after every 3-5 days of use. Some applications, especially in the electronics industry where the plated surface must be free of any inclusions, roughness or pits, it is common to remove the plating bath after one day of use. The plating tank is treated with nitric acid to dissolve the debris. Some shops use disposable tank liners to avoid using acids for cleaning. By improving tank and filter designs, some shops are able to increase the length of time between “clean-outs”. Because of the seeding problem associated with electroless plating, plating shops usually employ two production plating tanks so while one is being used for production work, the other is being cleaned by filling with a suitable acid, typically nitric acid, to dissolve the seeded residue.
After the nitric acid is removed and stored away, the tank and filter systems are normally purged with a suitable acid neutralizer such as ammonium hydroxide before the plating bath is returned to the clean plating tank. This operation protects the chemical-plating bath from reacting with the nitric acid, which can severally damage the plating solution.
The nitric acid and ammonium hydroxide solutions are usable for several cycles. However, both require eventual replacement with fresh solutions and both are considered hazardous waste. This waste stream is damaging to the environment.
Nickel boron (NIB) plating is known in the art to be especially troublesome with seeding due to the aggressive nature of sodium borohydride as a reducing agent. Electroless plating baths that use comparatively less aggressive reducing agents such as sodium hypophosphite or dimethylamine borane (DMAB do not suffer as much from seeding as NiB plating baths however seeding does occur even in those baths
The prior art has added DLC (carbonaceous) nanometer particles to electro chemical baths for chrome plating. These nanometer particles do not codeposit into the chrome coating. In electroless plating the nanometer particles codeposit in the coating. U.S. Pat. No. 6,156,390 to Henry et al, teaches adding DLC like particles to an electroless nickel bath using sodium hypophosphite as the reducing agent.
Nanometer diamond-like carbon (here to fore known as DLC) is a product sold by NanoBlox Inc. in Boco Raton, Fla., having a diameter between about 2-8 nanometer. The DLC can be manufactured according to U.S. Pat. Nos. 5,861,349 and 5,916,955. Aqueous dispersions containing an about 10% concentration of these DLC particles are available from Moyco Industries Inc. in Philadelphia, Pa.
The addition of nanometer particles to electroless plating baths reduces or eliminates seeding in electroless plating baths. In nickel boron baths, the maintenance and frequent tank-cleaning schedule can be increased beyond the normal 2-3 day interval. In this work twelve (12) days or more of successful plating were accomplished before tank clean-out was required
An objective of the invention is to add nanometer sized particles to electroless metal plus phosphorus plating baths to reduce or eliminate seeding. By doing so this reduced the quantity of inclusions and pitting in the coating.
An objective of this invention is to improve the properties of the coating.. Properties such as hardness, corrosion resistance, and wear resistance were improved.
The co-deposition of nanometer particles with the nickel boron affects the physical structure of all plated samples compared to the microstructure of NIB coatings that did not utilize nanometer particles. The degree of change appears to depend on the aggressive nature of the different reducing agents. The test panels coated from baths reduced with sodium borohydride realized the most significant change to its physical structure while the panels from the DMAB bath resulted in the least change of structure, although still apparent.
The effective size of the nanometer particles is that size that reduces seeding in the bath. The size of the nanometer particles added to an electroless bath should be less than 100 nanometer in diameter in order to reduce seeding or to improve the properties of the coating. The effective size would most likely depend on the chemical composition of the particle and the compositional makeup of the bath. For zirconium oxide the effective size would be less than 40 nanometer. For silicon carbide the size would be less than 30 nanometer. The preferred size appears to be less than 25 nanometer. More preferably the size should be less than 10 nanometer.
The nanometer particles can be added to the bath as dispersion or in solid form. The particle can have functional groups attached to the surface of the particles. When the particles are added in solid form the bath should be sufficiently agitated to ensure that there is a good dispersion. It is expected that a percentage of the particles will agglomerate in the bath or in a dispersing liquid. These agglomerations could possibly reach sizes greater than 5 microns
The presence of nanometer sized particles is believed to prevent localized cells of metal ions and the chemical reducing agent from initiating autocatalytic reduction and forming solid particles that, over time, increase in mass and eventually settle to the plating tank floor and/or the work item surface causing an undesirable roughness and/or wasted chemicals used to plate the plating tank and associated plumbing.
The “effective size” of the nanometer particles is that size that reduces seeding in the bath and/or improves the properties of the coating When an excess amount of nanometer particles is added to the tank, this additional quantity may settle to the bottom of the tank. For example, the addition of greater than 7.5 grams of DLC particles per gallon of plating bath results in some excess DLC material settling to the bottom of the plating tank. The addition of 0.75 gram of DLC (10% of above) per gallon is insufficient to reduce seeding or improve the coating. The preferred amount is about 3-4 grams of DLC per gallon of plating bath.
The properties of the coating deposit are also significantly changed/improved by the utilization of the DLC particles. As a result of adding nm size particles of diamond or “diamond like carbon” to the bath, (all of the following examples were performed using the lead-tungstate stabilized baths) DLC particles are co-deposited into the coating.
Microhardness of the coating changes from about 850-950 (non-DLC coating) up to 1000-1100 (DLC coating) Knoop (25 g, 10 sec) but when heat-treated the microhardness increases from about 1400 (non-DLC coating) up to 1800 (DLC coating) Knoop. The columnar structure becomes more spatially dense with less porosity between columns.
The improvements to the physical properties of the coating deposit by adding nanometer size DLC particles to a typical electroless nickel boron plating bath using lead tungstate as a stabilizer are shown by the following examples.
Two separate 15-gallon electroless nickel (NiB) baths were prepared according to U.S. Pat. No. 6,066,406 to McComas using lead tungstate as a stabilizer. One bath was labeled as Bath-1 and the second labeled as Bath-2-DLC.
The Plating Baths were made as follows:
One gallon of Reducer solution was made as follows;
1. About 1100 grams of sodium hydroxide was added to DI water, thoroughly mixed and allowed to cool to room temperature
A separate Stabilizing Solution was made as follows;
1. 10 grams of Lead tungstate was added to a solution of DI water, EDA, EDTA and sodium hydroxide.
2. The solution was allowed to thoroughly mix and cool to room temperature.
3. The solution was topped-off to the one gallon level with water and labeled as “Stabilizer Solution”
Preparing the Baths For Use;
Both plating solutions were placed in 15 gallon plating tanks with constant mechanical agitation due from a pump and filter system that was constantly run while containing the plating solutions. The solutions were heated by electric resistance type heaters. The thermostats were set and confirmed at 192° F.±2° F.
Five (5) minutes prior to placing prepared coupons in each bath, 120 mls of each reducer and stabilizer solution were added to the plating baths. This addition was repeated every 30 minutes of plating.
Preparing the Coupons/Blank Test Specimens;
Twenty (20) 2×3 inch, mild steel test coupons and 6 medium steel Falex Pins were prepared for plating as follows:
1, Soaked in a detergent cleaner at 160° F. for 5 minutes followed by a thorough rinse
2. Placed in a solution of 30% hydrochloric acid for 2 minutes followed by a rinse.
3. Thoroughly rinsed using DI water.
The Plating;
The coupons and Falex pins coated from Bath-2-DLC were immediately noticed as much smoother.
Half of the 20 coupons and half of the 6 Falex pins were randomly selected for heat treatment at 725° F. for 90 minutes. Half were left in the “as plated” condition. The platings were tested and the DLC particles were codeposited into the nickel boron coating.
The Effect on Hardness was Shown by the Following Tests:
The effects of DLC on the Physical Structure of the nickel boron deposit was shown by the following tests.
The corrosion resistance of a nickel boron coating is only as good and effective as its ability to seal the surface completely from the corrosive environment. Nickel boron coatings are typically columnar in structure and normally require an underlayer of a barrier coating such as copper or electrolytic nickel to first seal the surface before the nickel boron is applied. Early generations of nickel boron had very little corrosion protection value because of a lack of bath stability that resulted in frequent voids between column boundaries. As new methods of stabilizing the autocatalytic nickel boron deposition reaction occurred, corrosion resistance improved. The addition of DLC reduced porosity, thereby further improving corrosion resistance. This was shown by placing one coupon from each group in a salt spray chamber according to ASTM B-117. The four coupons remained in the salt spray test until surface oxidation (red rust) was visible.
A second set of Corrosion Samples coated with Nickel, Boron and Thallium according to U.S. Pat. No. 6,183,546 to McComas were corrosion tested using the same salt spray chamber in accordance with ASTM B-117 specification.. This was compared to an identical bath containing DLC. The results are as follows (time indicates time to failure);
1. Baseline; Nickel, boron & thallium, as plated; less than 24 hours
2. Nickel boron thallium, heat treated; less than 24 hours
3. Nickel, boron thallium plus DLC, as plated, 280 hours
4. Nickel, boron thallium plus DLC heat treated 320 hours
The following tests showed the wear resistance:
The Falex Pin and Vee Accelerated Wear and Friction Machine were used to measure the wear resistance of typical nickel boron sample (using a lead tungstate bath). Coated pins are mounted into a device that rotates the pins at a constant angular velocity regardless of applied load. A pair of Vee blocks is affixed in such a manor that applies equal and constant pressure or load to both sides of the pin while in motion. As the test continues, the load from each Vee block also increases equally on both sides causing a “squeezing effect” to the pin that increases until eventual failure occurs by either the pin fracturing or the failing of the shear pin that holds the pin in place. The test received ASTM approval in the mid-1950's however, for the last 20 years, the metal finishing industry has adopted the test for determining the wear resistance of functional coatings. A coated pin from each of the four groups was tested by allowing the pins to run until failure. The Vee blocks were ASTM standard Falex 1095 high carbon tool steel, heat treat hardened to 52 Rc. White mineral oil, which effectively removed debris but does not offer significant lubrication, was used to isolate the lubricity properties of the coating itself. (All times and pressures indicate failure point).
The addition of nanometer size DLC particles add significant improvements to hardness, compressive strength, corrosion resistance and wear resistance of any nickel boron deposit. The significant increase in corrosion resistance of the nickel, boron & thallium coating clearly demonstrates that the addition of these nanometer particles have a large effect on physical structure and mechanical properties of columnar coatings.
The effects of adding nanometer particles to electroless plating bath to reduce seeding or pitting of the coating were shown by the following examples.
A one gallon plating bath of electroless nickel boron with and without DLC was made as follows to compare a nickel boron coating
The bath makeup solution without DLC
A one-gallon plating bath of electroless nickel boron and with 2-8 nanometer DLC was made as follows;
The total solution level was raised to the 1 gallon level (3783 mls) with DI water. The Reducer solution was made up as follows.
The bath stabilizer solution;
3000 mls of DI water was added to a 4 liter beaker with magnetic stirring rod.
To water, about 25 grams of sodium hydroxide was added To the solution above, 10 grams of lead tungstate (PbWO4) was added while stirring and allowed to thoroughly mix for 10 minutes.
To the solution above, about 80 mls of ethylenediamine (EDA) was added and allowed to mix until the solution became clear in appearance.
Panel Preparation
The panels were then placed in the center of the one-gallon plating bath void of nanometer particles as made above and time noted. Prior (3-4 minutes) to placing the panels into the plating bath, 10 mls of the Reducer Solution and 10 mls of the Stabilizer Solution were thoroughly mixed together and slowly added to the plating bath. This was repeated every 30 minutes until the desired coating thickness was obtained, about 0.003 inches thick.
The panels were thoroughly rinsed of plating solution and dried using forced air. The plating bath was carefully siphoned/decanted from the top into a clean storage container
Upon examination of the beaker from the bath that did not use DLC, as expected after >5 hours of continuous plating, about 8 grams of solid particles and residue were present at the bottom of the beaker. Some were attached to the Teflon coated magnetic stirring rod but generally dispersed across the bottom of the beaker with a larger amount located at the outer rim of the beaker as would be expected due to the clockwise rotation of the solution.
The control panels had about 0.003 of an inch of nickel boron plating per surface. As expected with electroless plating baths used in a glass beaker without constant filtration, one side of each panel had more surface roughness than the other because one side would be facing the oncoming rotation of the solution.
The solid particles were analyzed by ICP and determined to be about 95% nickel and 5% boron by weight. This would be indicative of a nickel boron deposit as described in U.S. Pat. No: 6,066,406
Using SEM-EDAX to examine the solid debris, residue and particles located at the bottom of the beaker; no center of any particle was visually obvious even under high magnification supporting random nucleation of each particle. In addition, no other elements were found within the solid debris particles supporting the fact that the solid particles are the result of spontaneous decomposition and not the result of another element entering the bath and initiating the decomposition.
The same experiment as in example 2 was repeated using the nickel boron bath made up with the about 2-8 nanometer particles
The panels were thoroughly rinsed of plating solution and dried using forced air. The plating bath was carefully siphoned/decanted from the top into a clean storage container Upon examination of the beaker after >5 hours of continuous plating, less than 1 gram of solid nickel born particles and residue were present at the bottom of the beaker. Only a slight amount, less than 0.05 grams were attached to the magnetic stirring rod, with even less located at the outer rim of the beaker.
Examining the plated panels, they had about 0.003 of an inch of nickel boron plating per surface. After plating for 5 hours without filtration a very rough surface would normally be expected, especially on the surface that is facing the flow of the bath however all panels were very smooth with no pits, attached particles or debris.
The following example contrasts the effect of using 2-8 nanometer diamond like particles codeposited with Nickel Boron and Thallium when thallium compounds are used as a stabilizer
1. The nickel boron bath makeup bath was the same bath as used in example 2 without nanometer particles;
2 The Reducer solution was the same as in in example 2
3. The bath stabilizer solution;
The panels were prepared as in example 2
The panels were thoroughly rinsed of plating solution and dried using forced air. The plating bath was carefully siphoned/decanted from the top into a clean storage container.
Upon examination of the beaker, as expected after >5 hours of continuous plating, about 7 grams of particles and residue were present at the bottom of the beaker. Some were attached to the Teflon coated magnetic stirring rod but generally dispersed across the bottom of the beaker with a larger amount located at the outer rim of the beaker as would be expected due to the clockwise rotation of the solution.
Examining the plated panels, they had about 0.0029 of an inch of nickel boron plating per surface. As expected with electroless plating baths used in a glass beaker without constant filtration, one side of each panel had more surface roughness than the other because one side would be the facing the oncoming rotation of the solution.
The solid particles were analyzed by ICP and determined to be about 93% nickel and 4% boron and 3% thallium by weight. This would be indicative of a nickel boron thallium deposit as described in U.S. Pat. No. 6,183,546
This example is identical to example 4 except the plating nickel boron make up bath has having about 2-8 nanometer DLC used in the example 2.
The panels were thoroughly rinsed of plating solution and dried using forced air. The plating bath was carefully siphoned/decanted from the top into a clean storage container. Upon examination of the beaker after >5 hours of continuous plating, less than 1 gram of solid nickel born particles and residue were present at the bottom of the beaker. Only a slight amount, less than 0.05 grams were attached to the magnetic stirring rod, a even less located at the outer rim of the beaker.
Examining the plated panels, they had about 0.003 of an inch of nickel boron plating per surface. After plating for 5 hours without filtration, a very rough surface would normally be expected, especially on the surface that is facing the flow of bath however, all panels were very smooth with no pits, attached particles or debris. This is the exact opposite result of Bath #1 that did not contain 2-8 nm particles.
The effect of DLC particles on a DMAB Electroless Nickel Boron Plating Bath is shown by the following comparative example.
A bath was made up according to McDermid Specifications without DLC particles using a McDermid bath (niklad-752).
Bath Make-Up, One Gallon;
1. To 2000 mls of DI water, 85 grams of Nickel Sulfate was mixed.
2. To the solution, 50 grams of Sodium Acetate was added and mixed.
3. While mixing, 13.5 grams of Dimethylamine Borane (DMAB) was added and mixed.
4. As a stabilizer, 6.8 milligrams of Lead Acetate was added and topped-off to 1 gallon level.
5. The pH was adjusted to 6.1
6. The temperature was set at 160° F.
The Panels Were Prepared as in Example 2
The panels were then placed in the center of the plating bath and the time noted. The panels were thoroughly rinsed of plating solution and dried using forced air.
The plating bath was carefully siphoned/decanted from the top into a clean storage container and labeled.
DMAB plating baths are known in the art to deposit slowly as a result of a less aggressive reduction reaction compared to sodium borohydride. Even still, after examination of the beaker, as expected after >5 hours of continuous plating, about 2 grams of particles and residue were present at the bottom of the beaker. Some were attached to the Teflon coated magnetic stirring rod but generally dispersed across the bottom of the beaker with a larger amount located at the outer rim of the beaker as would be expected due to the clockwise rotation of the solution.
Examining the plated panels, they had about 0.00035 of an inch of nickel boron plating per surface. As expected with electroless plating baths used in a glass beaker without constant filtration, one side of each panel had more surface roughness than the other because one side would be the facing the oncoming rotation of the solution. 5 of 7 panels had pitting on one or both sides in a random pattern.
The solid particles were analyzed by ICP and determined to be about 98% nickel and 2% boron by weight. This would be indicative of a nickel boron deposit.
Using SEM-EDAX to examine the solid debris, residue and particles located at the bottom of the beaker no center of any particle was visually obvious even under high magnification supporting random nucleation of each particle. In addition, no other elements were found within the solid debris particles supporting the fact that the solid particles are the result of spontaneous decomposition and not the result of another element entering the bath and initiating the decomposition.
The example is identical to example 6 except the make up bath has DLC particles as shown below.
Bath Make-up, one gallon;
The panels were thoroughly rinsed of plating solution and dried using forced air.
The plating bath was carefully siphoned/decanted from the top into a clean storage container.
Upon examination of the beaker, no plate-out or other debris was found at the bottom or sides of the beaker.
Examining the plated panels, they had about 0.00032 of an inch of nickel boron plating per surface.
The coating was smooth and pit free on all sides.
The effect of DLC particles on a Standard Electroless Nickel High-Phosphorus plating bath is shown by the following comparative examples.;
Bath Make-up; (one gallon)
The panels were prepared as in example 2.
The panels were thoroughly rinsed of plating solution and dried using forced air.
The plating bath in the beaker was carefully siphoned/decanted from the top into a clean storage container. Upon examination of the beaker, as expected after >5 hours of continuous plating, about 2 grams of solid nickel-phosphorus particles and residue were present at the bottom of the beaker. Some were attached to the Teflon coated magnetic stirring rod but generally dispersed across the bottom of the beaker with a larger amount located at the outer rim of the beaker as would be expected due to the clockwise rotation of the solution.
The plated panels measured about 0.0026 of an inch of nickel-phosphorus plating per surface. As expected with electroless plating baths used in a glass beaker without constant filtration, one side of each panel had more surface roughness than the other because one side would be the facing the oncoming rotation of the solution. Both panels had pits. The solid particles were analyzed by SEM-EDAX and determined to be about 89% nickel and 11% phosphorus by weight. This would be indicative of a “high-phoss” electroless nickel phosphorus deposit.
Using SEM-EDAX to examine the solid debris, residue and particles located at the bottom of the beaker no center of any particle was visually obvious even under high magnification supporting random nucleation of each particle. In addition, no other elements were present within the solid debris particles supporting the fact that the solid particles are the result of spontaneous decomposition and not the result of another element entering the bath and initiating the decomposition.
The effect of the addition of DLC on Standard Electroless Nickel High-Phosphorus plating bath is shown by this example. The same procedure was used as in example 8 except the addition of DLC to the make up bath.
Bath Make-up; (one gallon)
The panels were thoroughly rinsed of plating solution and dried using forced air.
The plating bath was carefully siphoned/decanted from the top into a clean storage container and labeled. Upon examination of the beaker, no debris was present on the beaker sides or bottom. One particle of unknown origin measuring about 0.001 inch was attached to the Teflon coated magnet.
Examining the plated panels, they measured to indicate about 0.0027 of an inch of nickel-phosphorus plating per surface. All panels were identical in smoothness and no pits or other imperfections were found.
One single particle was found but did not have enough mass for analysis.
The effect of the addition of DLC on Standard Electroless Nickel Medium-Phosphorus plating bath is shown by this example. The same procedure was used as in examples 8 and 9 except the make up bath and the addition of DLC to the make up bath is different.
A one-gallon plating bath was made as follows;
The panels were prepared as in example 2
The thickness of the panel was measured in the center of the panel, about 1 inch from the drilled end. The panels were thoroughly rinsed of plating solution and dried using forced air.
The plating bath in the beaker was carefully siphoned/decanted from the top into a clean storage container and labeled as Bath #2.
Upon examination of the beaker, as expected after >5 hours of continuous plating, about 1.4 grams of solid nickel-phosphorus particles and residue were present at the bottom of the beaker. Some were attached to the Teflon coated magnetic stirring rod but generally dispersed across the bottom of the beaker with a larger amount located at the outer rim of the beaker as would be expected due to the clockwise rotation of the solution.
The plated panels had about 0.0022 of an inch of nickel-phosphorus plating per surface. As expected with electroless plating baths used in a glass beaker without constant filtration, one side of each panel had more surface roughness than the other because one side would be the facing the oncoming rotation of the solution.
The solid particles at the bottom of the bath were analyzed by SEM-EDAX and determined to be about 94% nickel and 6% phosphorus by weight. This would be indicative of a “medium-phoss” electroless nickel phosphorus deposit. Using SEM-EDAX to examine the solid debris, residue and particles located at the bottom of the beaker for other than nickel phoss compound resulted in no visually observed particles even under high magnification supporting random nucleation no such particle was seen.
Standard Electroless Nickel-Medium-Phosphorus Plating bath; with DLC particles;
One gallon make-up
The thickness of the panel was measured in the center of the panel, about 1 inch from the drilled end. The thickness was recorded.
The panels were thoroughly rinsed of plating solution and dried using forced air. The plating bath was carefully siphoned/decanted from the top into a clean storage container.
Upon examination of the beaker, no plate-out or other debris was present at the bottom or sides of the beaker.
The plated panels measured about 0.0022 of an inch of nickel-phosphorus plating per surface. The coating was smooth and pit free on both sides.
This is a continuation in part of U.S. patent application Ser. No. 10/903687 filed Aug. 2, 2005. This invention relates to the addition of nanometer particles to an electroless-plating bath. The nanometer particles provide beneficial results for the coating and the process of electroless coating.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10903687 | Aug 2004 | US |
| Child | 11193533 | Aug 2005 | US |
