Plating bath solutions

Abstract

The present invention is directed to compositions for electroless plating baths and their use, and more particularly to different solutions each usable to both make up an original bath and to replenishment of the original bath.

Claims

1. A single plating solution for use as both an initial and a replenishment solution for the same plating bath, comprising, in defined concentrations: a metal salt selected from a group where the metal consists of nickel, cobalt, and copper; a complexer, said complexer selected from the group consisting of lactic acid, malic acid, maleic anhydride, glycine, citric acid, citrates, glycolic acid or salts, succinic acid or salts, beta-alanine, EDTA, ammonium carbonate, ammonium chloride, propionic acid, tetra potassium pyrophosphate, and boric acid; a reducing agent; at least one pH adjuster; and at least one stabilizer for stabilizing a plating reaction; wherein said plating solution is mixable with water to form said bath and is also usable in the same defined concentrations for replenishing said bath.

2. The plating solution of claim 1, further comprising at least one type of particulate matter.

3. The plating solution of claim 2, further comprising at least one type of particulate matter stabilizer.

4. The plating solution of claim 1, wherein a pH of the bath formed using the initial solution is in a specified range and a pH of said bath is in the same range after replenishment.

5. The plating solution of claim 1, wherein said stabilizer is selected from the group consisting of lead, bismuth, tin, copper, antimony, sulfur, and non-metal stabilizers.

6. The plating solution of claim 1 further comprising at least one selected from the group consisting of a brightener, a buffer, or an accelerator.

7. The plating solution of claim 1, wherein the solution is conformant to RoHS, ELV, and WEEE regulations.

8. The plating solution of claim 1, wherein a nickel concentration of the initial bath and the bath upon replenishment is six grams per liter or less.

9. The plating solution of claim 1 further comprising at least one of diamond, silicon carbide, boron nitride, PTFE, graphite, carbides, oxides, fluorides, and visually detectable particles, wherein said detectable particles include at least one of the group consisting of insoluble, fluorescent, or otherwise visually detectable particles, and said visual detectability is related to at least one from the group consisting of phosphorescent, fluorescent, chemically, and electronically detectable.

10. The plating solution of claim 1, wherein said plating bath is an electroless nickel plating bath.

11. The plating solution of claim 1, wherein said solution includes ammonium hydroxide.

12. The plating solution of claim 1, wherein said at least one pH adjuster is selected from the group consisting of potassium carbonate, ammonium carbonate, potassium hydroxide, sodium hydroxide, or other ammonium, or hydroxide or carbonate compound.

13. The plating solution of claim 1, wherein said plating solution is usable for at least 8 metal turn overs of said bath.

14. The plating solution of claim 1, wherein said plating solution is not formed through regeneration of a plating bath.

15. The plating solution of claim 1 wherein said plating bath is directed to commercial use.

16. A plating solution concentrate for a replenishment plating process comprising, in defined concentrations: a complexer; at least one pH adjuster, said pH adjuster selected from the group consisting of potassium carbonate, ammonium carbonate, potassium hydroxide, sodium hydroxide, ammonium hydroxide, or carbonate compound; and at least one stabilizer for stabilizing a plating reaction; wherein said plating solution concentrate is mixable with at least one of the group consisting of a metal salt, and a reducing agent to form a plating bath, and said plating solution concentrate in the same defined concentrations is usable to replenish said plating bath, and said plating bath is used for plating objects.

17. The plating solution concentrate of claim 16, wherein said complexer is selected from the group consisting of lactic acid, malic acid, maleic anhydride, glycine, citric acid, citrates, glycolic acid or salts, succinic acid or salts, beta-alanine, EDTA, ammonium carbonate, ammonium chloride, ammonium hydroxide, propionic acid, tetra potassium pyrophosphate and boric acid.

18. A plating solution concentrate for a replenishment plating process, comprising: a complexer, selected from the group consisting of lactic acid, malic acid, maleic anhydride, glycine, citric acid, citrates, glycolic acid or salts, succinic acid or salts, beta-alanine, EDTA, ammonium carbonate, ammonium chloride, ammonium hydroxide, propionic acid, tetra potassium pyrophosphate, and boric acid; at least one pH adjuster, said pH adjuster selected from the group consisting of potassium carbonate, ammonium carbonate, potassium hydroxide, sodium hydroxide, or other ammonium, or hydroxide or carbonate compound; and at least one stabilizer for stabilizing a plating reaction; wherein said plating solution concentrate is formed in defined concentrations, is mixable with at least one of the group consisting of a metal salt and a reducing agent in defined concentrations to form a plating solution, and wherein said plating solution is added to water to form an initial plating bath usable for plating objects and said plating solution is also usable in the same defined concentrations for replenishing said bath.

19. The plating solution concentrate of claim 18 further comprising at least one of diamond, silicon carbide, boron nitride, PTFE, graphite, carbides, oxides, fluorides, and visually detectable particles, wherein said detectable particles include at least one of insoluble, fluorescent or otherwise visually detectable particles, and said visually detectability is related to at least one from the group consisting of phosphorescent, fluorescent, chemically, and electronically detectable.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIGS. 1A-E include a chart (Chart 1) showing various combinations of components and their concentrations and operating ranges in single solutions of the present invention.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

(2) The present invention is directed to a single solution useful for the make-up and replenishment of a plating bath that is useful and economical on a commercial basis, as well as to its use.

(3) The present invention is directed to a single solution and its use for both make up and replenishment of an electroless plating bath, thereby replacing the two, three or four solution systems traditionally used in the field. Auxiliary solutions may still be used with the single solution of the present invention, similarly to how they may be used in the prior art systems with two, three, four, or more solutions.

(4) The present invention is also directed to a bath using the aforementioned solution as well as plated articles plated using the aforementioned solution.

(5) Though the present invention primarily focuses on some electroless nickel phosphorus plating systems other plating systems fall within the spirit of this invention. Other examples include, but are not limited to: All electroless plating baths All electroless nickel plating baths All nickel-phosphorous alloy ratios Electroless nickel-boron Poly alloys Electroless cobalt EN systems with different levels of brightness EN plating that is subsequently blackened Non-metal stabilized plating systems Metal stabilized plating systems Heavy metal stabilized plating systems Composite plating systems Electroless copper, palladium, gold, and/or silver Alloys/combinations thereof

(6) The solution of the present invention may contain some quantity of one or more of the materials that are ordinarily added to the plating bath as auxiliary solutions. For example, it is within the scope of the present invention to have a single solution used for the make up and replenishment of the plating bath where this solution contains insoluble particulate matter, and additional quantities of particulate matter may be added to the plating bath during make up and/or replenishment as an auxiliary material or dispersion.

(7) Although the present invention may include components for stability, brightness, fume control, pit reduction, or other alterations to the properties of the coatings, in some situations, platers may add additional auxiliary solutions to the plating bath for modified stability, brightness, fume control, pit reduction, or other alterations to the properties of the coatings resulting from the plating baths.

(8) The present invention includes embodiments directed to similar practices and solutions used for electroless nickel phosphorous, nickel boron, nickel boron phosphorous, nickel tungsten phosphorous, cobalt boron, cobalt phosphorous, copper phosphorous, and other plating baths.

(9) Typically the plater (the end user of the plating bath) buys the solutions needed to make up and replenish the plating baths from a supplier (a manufacturer or distributor) of such solutions.

(10) There are numerous shortcomings to this decades old practice on how to make up and replenish and use electroless plating baths.

(11) First, the need to use multiple solutions for bath make up and replenishment involves significant logistics, including shipping, storage, labeling, material safety data sheets (MSDS) and other product information. These excessive logistics add complexity to both the manufacturer of the solutions, any distributors that may be involved, transportation companies, compliance companies, emergency response organizations, and naturally the end user of the solutions.

(12) Second, the use of multiple solutions requires the packaging and shipping of excess deionized water. This causes excessive packaging materials such as totes, drums, buckets, etc. It also causes excess shipping of water that means higher costs to the manufacturer and end user, as well as a waste of energy by the transport company.

(13) Third, the use of multiple solutions increases the opportunity for error by the end user. There exists the opportunity, as is known to occur periodically, for an end user to mistakenly use a C solution during bath make up instead of the correct B solution, or mistakenly use a B solution for replenishment of a bath instead of the correct C solution. When these mistakes occur, made more likely by the presence of multiple solutions, the composition of the bath will certainly be out of balance, and there is a strong likelihood that the bath will be rendered useless for proper plating.

(14) Fourth, even though the manufacturers of solutions to be used by platers formulate their solutions to work in relatively convenient formulations so they can be used in a certain ratio, these practices and the formulations still have shortcomings. A typical plating system may use A, B, and C solutions whereby the bath is made up with 5% by volume of the A solution plus 15% by volume of the B solution plus water as the balance. Such baths are then typically replenished during use with a ratio of 1 part of the A solution to 2 parts of the C solution. This means that one metal turnover (MTO) would involve the cumulative addition of another 5% by volume of the A solution plus 10% by volume of the C solution. The shortcoming of this system is that while the solutions are formulated for use in this or another designated ratio, in practice, it is difficult for many platers to accurately make the required additions of the multiple solutions so as to assure proper ratios and pH. Use of improper ratios or pH can impact the coverage of the article being plated as well as have other non-desirous consequences. Through manual pouring/measuring of the individual solutions and adding each to the bath, there are numerous opportunities for the user to add the wrong amount of one or more of these solutions and thereby cause the ingredients in the plating bath to become out of balance, which can lead to one or more of the problems in the plating bath, and/or the plating disclosed in the course of this present invention, and/or possibly, the need to dispose of the bath unnecessarily prematurely. While some platers use automated pumping systems to make the additions of the replenishment solutions, and some include automated analysis equipment to determine the quantities of replenishment solutions required, malfunctions and other issues can occur which can lead to the wrong amount of one or more of these solutions being added to the plating bath and thereby cause the ingredients in the plating bath to become out of balance.

(15) Fifth, when using multiple solutions for the make up and/or replenishment of a plating bath, there exists an opportunity for contamination of one solution to the next if pumps, containers, and the like are shared between two or more of the solutions.

(16) There exists, therefore, an unmet need for a novel electroless plating bath formulation and system of make up and replenishment.

(17) The present invention meets this need with a novel single solution that is useful for both plating bath make up as well as replenishment.

(18) As will become evident in the examples below, the present invention includes multiple combinations of ingredients in various ranges of quantities/percentages in a single solution useful to both make up and maintain the composition of ingredients in the plating bath. In general, the present invention is comprised of a family of solutions each of which affords an improved ease of use with less room for error and may also extends the life of typical plating baths.

(19) The present invention solves the aforementioned deficiencies and other deficiencies in conventional electroless plating bath systems by overcoming a number of factors which have limited manufacturers and users of plating baths to use plating bath systems with multiple solutions instead of a single solution. These factors include, but are not limited to, the following:

(20) 1. Keeping the metal salt(s) and reducing agent(s) in separate solutions to avoid any possible reaction between these ingredients before they are introduced to the plating bath.

(21) 2. Keeping all ingredients stable and free from precipitation while in solution. If a material precipitates out of a solution, it will not get properly added to the plating bath and therefore cause performance problems at least at certain pH levels. Replenishment solutions (like a typical C solution) generally have a pH that is higher than the pH of a solution containing metal salts in high concentrations such as a typical A solution or the single solution of the present invention.

(22) 3. The usage ratios of each ingredient are ordinarily different in make up and replenishment. When making an electroless plating bath, certain ingredients are included in specified quantities required for the bath to work properly. As parts are plated in this bath, each of the bath ingredients is consumed at different rates. Some ingredients are consumed faster, some slower, and some essentially not at all. It is for this reason that the C solution typically has different concentrations of ingredients than the corresponding B solution used to make up the plating bath. In addition, it is possible to have some ingredients in a C solution that are not in the corresponding B solution that can improve the performance of the plating bath as it is used.

(23) 4. Proper stabilizer content is critical for the performance of a plating bath. Achieving this content is especially challenging as these stabilizer ingredients (such as those listed in this disclosure, and others) are used in very small amounts relative to the other ingredients. Stabilizers are typically used in parts per million whereas other ingredients are used in grams per liter.

(24) 5. If any or all ingredients are not added and maintained in the proper concentrations in the plating bath, the resulting deficiencies can range from instability, overstability, precipitation, shortened bath life, and plating defects (including pits, nodules, edge problems, skip plating, streaks, inconsistent finish, deficient performance, and others).

(25) A key measure of the quality and suitability of solutions for making up and replenishing electroless plating baths is the resulting plating rate and lifetime of the plating bath.

(26) The plating rate represents the thickness of the coating achieved from a plating bath over a period of time. For example, microns of thickness per hour is a typical measure of plating rate. There are generally accepted ranges of plating rates for various types of plating baths and these rates might differ based on the articles being plated. For example, a typical low to medium phosphorous plating bath typically plates at a rate of 15 to 25 microns per hour. A typical high phosphorous electroless nickel plating bath plates at a rate of 7 to 12 microns per hour. The plating rate of a given plating bath depends upon operating temperature, bath loading, pH, agitation, age of the bath, and other factors.

(27) The bath life is typically measured in metal turn-overs or MTOs. Different baths can have different MTO lifetimes depending on a number of factors such as but not limited to the type of plating bath, the operation and maintenance of the plating bath, the quantity and types of articles plated, the base metal of the articles being plated, and other factors. One MTO represents the use of a plating bath over a period of time where parts are plated, the cumulative quantity of the metal salt in the bath at make up is used (deposited onto parts immersed in the plating bath) and replenished into the plating bath. For example, if a one liter electroless nickel plating bath is made up with 6 grams of nickel metal (coming from a metal salt like nickel sulfate), parts are plated therein until 0.6 grams of nickel are depleted, the bath is replenished with 0.6 grams of nickel, and this process is repeated 9 more times for a total depletion and replenishment of 6 grams of nickel, then this bath has achieved one MTO. Of course it is not only the nickel salt that is consumed and replenished in the course of usage. Any and all reducing agent(s), stabilizer(s), brightener(s), and all other ingredients must be maintained in proper concentration in the plating bath, otherwise plating bath performance, life, and resulting plating quality will suffer. Adding too much or too little of certain ingredients can also reduce the bath life. Another factor influencing the bath life is the gradual build up of byproducts in the plating bath as a result of the plating reaction. A maximum bath life is important to the plater since the solutions used for plating baths are a significant cost to the plater; it is time consuming, inconvenient, and costly for the plater to dispose of a used bath and replace it with a new bath; treatment of a used bath is costly and can have environmental implications. Therefore it is important to the plater that the solutions used for bath make up and replenishment are formulated in a way as to maximize bath life and performance.

(28) When evaluating solutions for the make up and replenishment of an electroless plating bath, achieving at least one MTO with proper performance and results is a significant threshold to validate the composition(s) of the solution(s). Although some plating bath systems exist for the perpetual use of the plating bath, accomplished by removal of byproducts from the bath and replenishment with select materials, such baths are generally not considered practical nor economical for widespread commercial use, and therefore the life of an electroless plating bath in terms of the number of MTOs achievable is an important factor in the utility of an electroless plating bath.

(29) When evaluating solutions for the make-up and replenishment of an electroless plating bath, verification of the physical properties of the coatings resulting from this plating bath is significant to validate the composition(s) of the solution(s). Such physical properties of the coatings include, but are not limited to, composition, hardness, corrosion resistance, thickness, uniformity, electrical conductivity and resistivity, porosity, appearance, brightness, reflectivity, adhesion, stress, elasticity, tensile strength, elongation, density, coefficient of thermal expansion, wear resistance, coefficient of friction, and/or other properties.

(30) Ingredients typical in electroless plating and useful in the present invention include, but are not limited to: Acetic Acid, Glacial Ammonium Bicarbonate Ammonium Carbonate Ammonium Hydroxide, Reagent Ammonium Hydroxide, Technical Borax Boric Acid Caustic Potash Caustic Soda Caustic Soda Beads Citric Acid DMAB Glycerine Glycine Hydroxyacetic Acid Lactic Acid Malic Acid Nickel Sulfate Liquid Nickel Sulfate Crystal Propionic Acid Sodium Glucoheptonate Sodium Hypophosphite Sodium Isothionate Succinic Acid Sulfamic Acid Sulfuric Acid, Reagent Tartaric Acid, NF Granular

(31) Once the bath has been prepared, it is ready for use in the electroless plating process of the present invention. This involves contacting the surface of an article with the electroless metallizing bath. However, the article to be coated may require preliminary preparation prior to this contact in order to enable the autocatalytic plating deposition on the surface of the article. This preparation includes the removal of surface contaminants. For example, this process may involve any of, but not limited to, degreasing, alkaline cleaning, electrocleaning, zincating, water or solvent rinsing, acid activation, pickling, ultrasonic cleaning, physical modification of the surface, vapor or spray treatments, etc.

(32) An electroless plating bath is typically operated according to the following practices related to the equipment, and operation of the bath.

(33) The plating tank is typically constructed of polypropylene, stainless steel or mild steel with a suitable tank liner depending on bath in use and other considerations. Stainless steel tanks may be anodically protected. In laboratory testing and small scale plating, beakers made of Pyrex and the like are used, often on a hot plate with a magnetically driven PTFE coated stir bar at the bottom of the beaker.

(34) Filtration of electroless plating baths through a 10-micron or finer rated polypropylene filter bag or wound cartridge system is common. The filtering pump system typically turns the bath over at a rate of at least 10 times per hour. The filtration method and rate are often different for composite electroless plating and determined according to the specific composite electroless plating bath system being used.

(35) Agitation is useful in maintaining bath homogeneity and consistent finish. Air spargers with air from a high volume, low-pressure air blower is common. Compressed air is not recommended due to potential oil contamination. Other types of agitation, may also be used.

(36) Heating of the bath may be accomplished by various methods including heat exchangers and immersion heaters. The bath temperature should be monitored and maintained closely. Cooling of the bath with an appropriate cooling apparatus should be done rapidly at the end of a shift or any time the bath will not be used for an extended period of time.

(37) Rack, barrel, and fixturing devices to hold the parts, workpieces, or articles being coated in an electroless plating bath are typically constructed of compatible materials such as polypropylene, chlorinated polyvinyl chloride, stainless steel, PTFE, synthetic rubber/fluoropolymer elaster, silicone rubber, and other materials that can withstand the chemicals and temperature of the plating bath and pretreatment process. Maskants may be used to protect portions of fixtures and/or articles from being plated. Masking is typically accomplished with compatible materials such as certain vinyl tapes, stop-off paints, plugs and gaskets made of synthetic rubber/fluoropolymer elaster, silicone rubber, and others that can withstand the chemicals and temperature of the plating bath and pretreatment process.

(38) The plating tank should be clean and passivated prior to use and periodically during use generally depending on usage rates and conditions. The most common method is with a solution of 40-50% nitric acid for 1-4 hours at room temperature, followed by rigorous rinsing and verification that no nitrate contamination remains.

(39) The plating bath is typically maintained to be within 80% and 100% concentration of nickel, hypophosphite, stabilizers, or other chemicals based on the initial make up concentration of these ingredients. Tighter control further helps performance. Titration of the plating bath to ascertain the metal concentration in the plating bath is typically before and after every batch of parts that is plated. Replenishing is normally done during and/or between plating cycles. Analysis of the reducing agent concentration is typically performed much less frequently or not at all in commercial use of electroless plating baths. When making up and replenishing a plating bath with a solution from the present invention, the need to analyze for the reducing agent concentration in the bath will be even less necessary as the reducing agent and the metal salt will be continually added in proper ratio when they are contained in a solution from the present invention, and not added separately in two different solutions.

(40) Continual and accurate measurement of bath temperature, pH, and bath solution volume level is important and typically done. Evaporation will reduce bath volume level and give false indication of actual concentration if this factor is not accounted for when analyzing the plating bath for the concentration of any ingredients. Adding water (typically deionized) as needed during the plating cycle is useful to keep solution at the proper level which is the volume level at which the plating bath was originally made up.

(41) The plating baths made from the solution of the present invention are suitable for use according to the above generally accepted procedures and equipment, and no unique equipment or accommodations are anticipated for the use of the single solution of the present invention in comparison to the multiple solutions of the current practice in the field.

(42) An electroless plating bath is typically operated generally according to the following practices related to the equipment, and operation of the bath. The plating tank is typically constructed of polypropylene, stainless steel (Type 316) or mild steel with a suitable tank liner depending on bath in use and other considerations. Stainless steel tanks may be anodically protected. Filtration through a 10-micron or finer rated polypropylene filter bag system is suggested. Polypropylene wound cartridge filters are also permissible, but are not as easy to use as filter bags. The filtering pump system should turn the bath over at a rate of at least 10 times per hour. Agitation is useful in maintaining bath homogeneity and consistent finish. Air spargers with air from a high volume, low-pressure air blower is recommended. Compressed air is not recommended due to potential oil contamination. Other types of agitation, may also be used. Heating of the bath may be accomplished by various methods including heat exchangers and immersion heaters. The bath temperature should be monitored and maintained closely. Cooling of the bath with an appropriate cooling apparatus should be done rapidly at the end of a shift or any time the bath will not be used for an extended period of time. Rack, barrel, and fixturing devices are typically constructed of compatible materials such as polypropylene, CPVC, stainless steel, PTFE, Viton, silicone rubber, and others that can withstand the chemicals and temperature of the plating bath and pretreatment process. Maskants may be used to protect fixtures from being plated. Masking is typically accomplished with compatible materials such as certain vinyl tapes, stop-off paints, plugs and gaskets made of Viton, silicone rubber, and others that can withstand the chemicals and temperature of the plating bath and pretreatment process. The plating tank should be clean and passivated. The most common method is with a solution of 40-50% nitric acid for 2-3 hours at room temperature, followed by rigorous rinsing and neutralizing of the tank and verification that no nitrate contamination remains. The plating bath is typically maintained to be within 80% and 100% concentration of nickel, hypophosphite, stabilizers, or other chemicals based on the initial make up concentration of these ingredients. Tighter control further helps performance. Titration of the plating bath is typically before and after every batch of parts that is plated. Replenishing is normally done during plating cycles if the workload will lower the nickel concentration to 90% or less. Continual and accurate measurement of bath temperature, pH, and bath solution level is important and typically done. Evaporation will reduce bath volume and give false indication of actual concentration. Adding DI water as needed during the plating cycle is useful to keep solution at proper level. The deposition rate of a given plating bath depends upon operating temperature, bath loading, pH, agitation, age of the bath, and other factors.

(43) The technique of blackening electroless nickel coatings is known in the industry. A number of methods have been developed to produce black electroless nickel. The most common process is generally characterized by the oxidation or etching of an electroless nickel coating. Oxidizing materials that can be used include acids, metal chlorides, peroxides and other oxidizing agents.

(44) Another method involves adding materials to the electroless nickel plating bath similar to what can be used in black electrolytic nickel plating baths. Such ingredients may include zinc and/or sulfur. Such materials may be included in the solutions of the present invention.

(45) These and other objects of the present invention together with the advantages over the existing prior art and method will become apparent from the following specification and the method described herein.

(46) The present invention is directed to processes and product related to a single solution for both the make-up and replenishment of an electroless plating bath.

(47) In describing the preferred embodiments of the present invention, specific terminology will be resorted to for the sake of clarity. However, the invention is not intended to be limited to the specific terms so selected, and is to be understood that each specific term includes all technical equivalence which operate in a similar manner to accomplish a similar purpose.

(48) The preferred embodiment of the present invention is detailed in the examples.

(49) Though the present invention primarily focuses on some electroless plating systems other plating systems fall within the spirit of this invention. Other examples include, but are not limited to: all electroless plating baths, all electroless nickel plating baths including any content of phosphorous and/or boron, poly alloy plating baths, electroless cobalt plating baths, EN systems with different levels of brightness, EN plating that is subsequently blackened, plating systems stabilized with heavy metals, toxic, non heavy metals, non toxic metals, or no metals, plating baths including nickel hypophosphite, composite plating systems, electroless cobalt, copper, palladium, gold, and/or silver plating baths, plating baths that are made up with or without ammonium hydroxide, plating baths that may be replenished and maintained with or without ammonium hydroxide, plating baths that are made up with or without ammonium hydroxide, and plating baths that may be replenished and maintained with or without ammonium hydroxide.

(50) The present invention encompasses all varieties of electroless nickel coatings with varying concentrations or freedom from various materials such as, but not limited to, lead, cadmium, heavy metals, toxic metals, PFOA, PFOS and others that are subject of environmental and related regulations such as Restriction of Hazardous Substance Directive (RoHS), Directive on Waste Electrical and Electronic Equipment (WEEE), End of Life Vehicle Directive (ELV), ammonia, and the like.

(51) The more recent use of stabilizers other than lead in electroless nickel plating baths has enabled the utility of the present invention. Lead, the traditional stabilizer in electroless nickel systems, works in the plating bath in a very tight range of about 1 to 3 parts per million. Too little lead and the bath will produce plating defects, become over active, and/or decompose. Too much lead and the bath will produce plating defects, plate too slowly, and/or stop plating. Keeping the lead stabilizer within the tight range required for proper bath operation, proper plating quality and proper bath life is one of the reasons why a single solution useful for the make up and replenishment of an electroless plating bath was not possible until the present invention. In a preferred embodiment of the present invention, the single solution useful for the make up and replenishment of an electroless plating bath uses materials other than lead, and these other materials are able to stabilize the plating bath within a much broader range than the traditional lead stabilizers. Such non-lead stabilizers include, but are not limited to bismuth, copper, antimony, and non-metal stabilizers either individually or in combination. For example, lead is generally effective in the range of only about 1 to 3 parts per million in an electroless nickel plating bath, whereas bismuth is effective in the range of about 1 to 50 parts per million in an electroless nickel plating bath.

(52) Similarly, thiourea has been widely accepted and used as a traditional sulfur compound stabilizer in electroless nickel plating baths. Sulfur functions in an electroless nickel system mainly as stabilizer, the ratio of sulfur to the lead or other metal stabilizer in the plating bath can affect the performance of the plating bath and the properties of the plating itself. And similar to lead, thiourea works in the plating bath in a very tight range. Too little thiourea and the bath will produce plating defects and/or decompose. Too much thiourea and the bath will produce plating defects and/or stop plating. In a preferred embodiment of the present invention, the single solution useful for the make up and replenishment of an electroless plating bath can use materials other than thiourea, and these other materials are able to function in the plating bath within a much broader range than the traditional thiourea. Such non-thiourea sulfur compounds include, but are not limited to thiosalicylic acid, thiodipropionic acid, and the like. For example, thiourea is generally effective in the range of only about 1 to 5 parts per million in an electroless nickel plating bath, whereas thiosalicylic acid is effective in the range of about 1 to 30 parts per million in an electroless nickel plating bath, and thiodipropionic acid is effective in the range of about 1 to 300 parts per million in an electroless nickel plating bath.

(53) In one preferred embodiment of the present invention, the solution useful for both the make up and replenishment of an electroless plating bath will contain one or more of the following ingredients: metal salt, reducing agent, complexer, pH adjuster, and stabilizer.

(54) Although the examples detailed below depict specific combinations of components, time, and control, the reader should recognize that the present invention is not limited to the specific materials and metrics in the examples. For example, plating different goods may require different quantities or combinations. The pH of the plating bath can vary by application but is preferably in a range of 4.0 to 9.0. The plating bath temperatures can preferably be in the range of 20 to 100 degrees Celsius. The duration of the cycle times can be in any range required to provide the coating thickness and properties desired.

(55) The present invention is directed to a single solution useful for the make-up and replenishment of a plating bath that is useful and economical on a commercial basis. The present invention is further directed towards a single solution that is useful for the make-up and replenishment of a plating bath that is capable of producing plating performance and coatings that are free of problems in the deposit being caused by the solution. Such problems include, but are not limited to skip plating, pitting, edge pull-back, step plating, dark or laminar deposit, roughness in deposits, streaks in deposit, dull or matte deposits, poor adhesion of the deposit to the substrate, poor corrosion and/or chemical resistance of the deposit.

(56) The single solution of the present invention can take any of several forms, such as but not limited to the forms described in Chart 1 (in FIGS. 1A-1E, referred heretofore as FIG. 1). In general, these solutions include one or more metal salts, complexers, reducing agents, pH adjusters, and stabilizers, and may also contain one or more forms of particulate matter and particulate matter stabilizers. In the preferred embodiment, the single solution is used for formulating a bath further comprising water, where the bath is carefully controlled with respect to pH and temperature, and the plating rate is also carefully controlled.

(57) The solution of the present invention's contents will vary based on the plating needs, such as but not limited to, the type of plating necessary, and the types of objects being plated. Preferably, the solution is directed to electroless nickel plating, but other types of plating may also lend themselves to a single solution.

(58) Again, the initial solution and the replenishment solution of the present invention are the same. In general, during plating, the individual contents of the single solution will deplete from the bath, and the introduction of replenishment solution may change the overall mix in some ways (consequential to variation in the depletion rates of the various component elements), but the overall ability to plate and for the bath to remain usable will not be impacted by the introduction of replenishment solution.

EXAMPLES

(59) A solution as listed in each of the columns D through AR in Chart 1 (in FIG. 1) was prepared with quantities recorded of the ingredients as in rows 7 through 44 of Chart 1 (in FIG. 1) by dissolving these ingredients in water. Each of these examples describes a solution usable as both an initial solution where water is added and is also usable as a replenishment solution, typically without the need to add additional water. All of these solutions have been tested in controlled environments where the environment is described in the bottom rows. Of course, different of these examples might be applicable to different plating situations, however, each has been shown to be usable in the single solution composition described in this application. In the solutions listed in each of the columns Q through AA and AC through AE, insoluble particulate matter was also added as listed in rows 41 through 44. Column C in Chart 1 (in FIG. 1) discloses the units of measurement of each ingredient added to each solution.

(60) Each of the above solutions was stored at room temperature of 20 degrees Celsius for 15 days and inspected for precipitation or other degradation. The same solutions were then stored in a 5 degree Celsius environment for 30 days, removed from this environment and inspected for precipitation or other degradation, then stored in a 40-45 degree Celsius environment for 30 days, removed from this environment, and inspected to for precipitation or other degradation.

(61) A quantity of each of the above solutions was diluted to one liter with deionized water to form an electroless plating bath. The quantity of the solution that was diluted to a one liter plating bath is listed in row 47 of Chart 1 (in FIG. 1). Mild agitation was introduced to the bath. The pH of this bath may have then been adjusted with an auxiliary solution to achieve the pH listed in row 48 of Chart 1 (in FIG. 1) for each plating bath. The bath was then heated to the operating temperature listed in row 49 of Chart 1 (in FIG. 1) for each plating bath.

(62) Substrates made of steel, stainless steel, copper and aluminum alloys were cleaned and otherwise pretreated and immersed in the plating baths listed in Chart 1 (in FIG. 1). The substrates were left in the plating baths for cycle times from 15 to 240 minutes, during which time the pH, temperature and agitation of the plating baths were maintained. The substrates were removed and both the substrates and plating baths were analyzed.

(63) Each of the plating baths were analyzed by titration for the metal salt concentration and replenished with the required quantity of the exact same solution used in the make up of the respective plating bath to return metal salt concentration of the plating bath to the same starting concentration as its initial make up. The solution as used for replenishment was the exact same as used for make up of the plating bath in each example as on Chart 1 (in FIG. 1). The replenishment of the plating bath was made before, during and after the substrates were being plated in the plating bath.

(64) This process of plating substrates, analyzing the substrates, analyzing the baths, and replenishing the baths was continued until the baths reached at least one metal turnover. This process was implemented at timing consistent with conventional plating practice in order to maintain the concentration of materials in the plating bath in a useful range. Throughout the process, the pH, temperature and agitation were maintained, and the plating reaction was observed by the bubbles evolving from the substrates. Throughout the process, the plating rates were measured and recorded in row 50 of Chart 1 (in FIG. 1) for each respective plating bath. This process was performed on each of the plating baths in Chart 1 (in FIG. 1) over the course of a number of days with the baths cooled at the end of use on one day and reheated to the operating temperature on the following day. This process is representative of the typical usage of a plating bath in a commercial practice.

(65) The electroless platings produced by each of the plating baths made from each of the solutions in Chart 1 (in FIG. 1) were analyzed. In those examples, where insoluble particulate matter was included in the solution used in each of these plating baths, the resulting platings were analyzed by cross sectional examination to verify the incorporation of these particulate materials in the plating.

ADDITIONAL EXAMPLES

Example 1

(66) An aqueous solution was prepared with: nickel sulfate, sodium hypophosphite and other ingredients useful in electroless nickel plating.

(67) 200 ml of the above solution was diluted to one liter with deionized water to form an electroless plating bath. Mild agitation was introduced to the bath. The pH of this bath was adjusted to with ammonium hydroxide. The bath was then heated to an operating temperature. Titration analyses indicated a nickel concentration of 6 grams per liter and a hypophosphite concentration of 30 grams per liter.

(68) A substrate was pretreated and immersed in the plating bath. The substrate was left in the plating bath for 60 minutes, during which time the pH, temperature and agitation maintained, and the plating reaction remained evident from the bubbles evolving from the substrate.

(69) After 60 minutes of plating time, the substrate was removed and both the substrate and bath were analyzed.

(70) The substrate exhibited a uniform 20 microns thick nickel-phosphorous layer free of irregularities.

(71) The bath was analyzed by titrations to contain a nickel concentration of 5.52 grams per liter and a hypophosphite concentration of 27.6 grams per liter, therefore demonstrating an 8% depletion of the initial content of these ingredients. The bath was replenished to 100% concentration with an addition of 16 ml of the solution prepared above. This cycle thereby representing 8% of one metal turn-over (MTO).

(72) This process of plating substrates, analyzing the substrates, analyzing the bath, and replenishing the bath was continued until the bath reached a cumulative one MTO. Throughout the process, the pH, temperature and agitation were maintained, and the plating reaction remained evident from the bubbles evolving from the substrate. The substrates exhibited a uniform nickel-phosphorous layer free of irregularities achieved at a plating rate between 17 and 22 microns per hour. This process was performed on this plating bath over the course of a number of days with the bath cooled at the end of use on one day and reheated to the operating temperature on the following day. This process is representative of the typical usage of a plating bath in a commercial practice.

Example 2

(73) An aqueous solution was prepared with: nickel sulfate, sodium hypophosphite and other ingredients useful in electroless nickel plating.

(74) 200 ml of the above solution was diluted to one liter with deionized water to form an electroless plating bath. Mild agitation was introduced to the bath. The pH of this bath was adjusted to with ammonium hydroxide. The bath was then heated to an operating temperature. Titration analyses indicated a nickel concentration of 3 grams per liter and a hypophosphite concentration of 30 grams per liter.

(75) A substrate was pretreated and immersed in the plating bath. The substrate was left in the plating bath for 60 minutes, during which time the pH, temperature and agitation maintained, and the plating reaction remained evident from the bubbles evolving from the substrate.

(76) After 60 minutes of plating time, the substrate was removed and both the substrate and bath were analyzed.

(77) The substrate exhibited a uniform 19 microns thick nickel-phosphorous layer free of irregularities.

(78) The bath was analyzed every 20 minutes during the course of this 60 minute plating cycle by titrations and each time found to contain a nickel concentration of about 2.7 grams per liter, therefore demonstrating a 10% depletion of the initial content of these ingredients. Each time, the bath was replenished to 100% concentration with an addition of 20 ml of the solution prepared above. This cycle thereby representing 10% of one metal turn-over (MTO) every 20 minutes or 30% of one MTO every 60 minute plating cycle.

(79) This process of plating substrates, analyzing the substrates, analyzing the bath, and replenishing the bath was continued until the bath reached a cumulative one MTO. Throughout the process, the pH, temperature and agitation were maintained, and the plating reaction remained evident from the bubbles evolving from the substrate. The substrates exhibited a uniform nickel-phosphorous layer free of irregularities achieved at a plating rate between 17 and 22 microns per hour. This process was performed on this plating bath over the course of a number of days with the bath cooled at the end of use on one day and reheated to the operating temperature on the following day. This process is representative of the typical usage of a plating bath in a commercial practice.