Patent Application
20060024447
This invention relates to the addition of nanometer particles in an electroless-plating bath. The nanometer particles provide beneficial results for the coating and the process for electroless coating.
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. The plating bath must be removed from the plating tanks and the “seeded-out” residue chemically stripped and/or mechanically removed. This removal, “clean-out” normally occurs after every 3-5 days of use. Some applications, especially in the electronic 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 this seeding problem associated with electroless plating, plating shops usually employ two production plating tanks so while one is being used to produce production work, the other is being cleaned by filling with a suitable acid, typically nitric acid to dissolve the seeded residue.
Normally, after the nitric acid is removed and stored away, the tank and filter systems are 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 that 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 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 less aggressive reducing agents do not suffer as much from seeding as NiB plating baths. However seeding does occur. And some of the problem associated with seeding such as pitting or surface inclusions can be seen in some highly sensitive applications. For example, electroless plating for printed circuit boards cannot tolerate surface inclusions or pitting. Likewise in a DMAB (dimethylamine borane) reduced nickel boron bath which is a less aggressive bath, seeding can occur.
The prior art has added DLC 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.
Nanometer diamond like carbon (here to fore known as DLC) is a product sold by Odyssey Consultants, LLC 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.
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. Twelve 12 days or more were experienced before tank clean-out was required
An objective of the invention is to add nanometer sized particles to electroless metal phosphorus plating baths to reduced or eliminated seeding. This resulted in less inclusions or pitting.
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 effects the physical structure of all plated samples. The degree of change appears to depend on the aggressiveness 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 present.
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 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.
he presence of nanometer particles is believed to prevent localized cells of metal ions and the chemical reducing agent from initiating autocatalytic reduction and forming a solid particle that over time, increase in mass and eventually fall to the plating tank floor and/or the work item causing an undesirable roughness and/or wasted chemicals used to plate the plating tank and associated plumbing.
The effective amount of nanometer particles to add to the bath is that amount that reduces seeding or improves the coating. When an excess amount is added, the additional amount needed to reduce seeding or improve the coating falls 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 the excess falling to the bottom of the plating tank. Also 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 coating deposit is also significantly changed/improved. As a result of adding Nm size particles of diamond or “diamond like carbon”, (all of the following examples were performed using the lead-tungstate stabilized baths); We are sure the DLC is co-depositing into the coating. Hardness jumps from about 850-950 up to 1000-1100 but when heat-treated, it jumps even farther from about 1400 up to 1800 knoop using a 25 gram weight. The columnar structure becomes much tighter, less porosity between columns.
The improvements to the physical properties of the coating deposit by adding nanometer size DCL particles to a typical electroless nickel boron plating bath using an electroless nickel boron bath and or coating using Lead Tungstate as a stabilizer is 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;
A separate Stabilizing Solution was made as follows;
Both plating solutions were placed in 15 gallon plating tanks that have constant mechanical agitation due to a pump and filter system that is allowed to 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, 8 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:
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 complete surface from the corrosive environment. Because nickel boron coatings are typically columnar in structure, they normally require an underlayment 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 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-17. The four coupons were allowed to stay 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;
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 speed regardless of load, RPM. 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 duration increases, 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 of 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. Only white mineral oil was used for lubrication so only the lubricating properties of the coating could be tested.
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 to physical structure 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 with out DLC
A one-gallon plating bath of electroless nickel boron and with 2-8 nanometer DLC was made as follows;
The Reducer solution was made up as follows.
The bath stabilizer solution;
Panel Preparation
The panels were then placed in the center of the one-gallon plating bath void of nanometer particles as made above, the time noted. Just 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-plus 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.
These control panel measured about 0.003 of an inch of nickel boron plating per surface. As excepted 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 95% nickel and 5% boron. 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 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-plus 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 measured to indicate about 0.003 of an inch of nickel boron plating per surface. After plating for 5 hours without filtration, normally a very rough surface would 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.
The following examples 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
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-plus 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 measured to indicate about 0.0029 of an inch of nickel boron plating per surface. As excepted 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. 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 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-plus 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 measured to indicate about 0.003 of an inch of nickel boron plating per surface. After plating for 5 hours without filtration, normally a very rough surface would 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.
Bath was made up according to McDermid Specifications without s DLC particles using a McDermid bath (niklad-752.
Bath Make-Up, One Gallon;
The panels were prepared as in example 2
The panels were then placed in the center of the plating bath, 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 be slow in deposition as a result of a less violent reduction reaction. Even still, after examination of the beaker, as expected after 5-plus 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 all measured to indicate about 0.00035 of an inch of nickel boron plating per surface. As excepted 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 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. 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 measured to indicate 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-plus 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 excepted 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 98% nickel and 11% phosphorus. 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, no pits or other imperfections were found.
One single particle wss 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 perpared 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-plus 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 measured about 0.0022 of an inch of nickel-phosphorus plating per surface. As excepted 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. 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.
