EP0100203A1 - Vorrichtung und Verfahren für das stromlose Plattieren - Google Patents

Vorrichtung und Verfahren für das stromlose Plattieren Download PDF

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Publication number
EP0100203A1
EP0100203A1 EP83304214A EP83304214A EP0100203A1 EP 0100203 A1 EP0100203 A1 EP 0100203A1 EP 83304214 A EP83304214 A EP 83304214A EP 83304214 A EP83304214 A EP 83304214A EP 0100203 A1 EP0100203 A1 EP 0100203A1
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EP
European Patent Office
Prior art keywords
solution
plating
plating metal
nickel
content
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Application number
EP83304214A
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English (en)
French (fr)
Inventor
Serge Leroy
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Chemetall Ltd
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Brent Chemicals International PLC
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Filing date
Publication date
Application filed by Brent Chemicals International PLC filed Critical Brent Chemicals International PLC
Publication of EP0100203A1 publication Critical patent/EP0100203A1/de
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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
    • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
    • C23C18/1601—Process or apparatus
    • C23C18/1617—Purification and regeneration of coating baths

Definitions

  • This invention relates to the electroless plating of articles by nickel, cobalt or alloys containing nickel or cobalt.
  • the invention is particularly of use in the plating of nickel or nickel alloys and so will primarily be discussed with reference to nickel.
  • Nickel can be plated onto an article, either by Lectroplating or by electroless plating.
  • electroplating the article is immersed in a solution containing a dissolved nickel compound and an electric potential is applied that is sufficient to cause electrolysis and the deposition of nickel in,accordance with Faradays Laws.
  • the thickness of the coating tends to vary according to the radius of curvature of the surface.
  • the article In electroless plating the article is immersed in a solution of a nickel salt and a reducing agent and coating occurs primarily as a result of chemical reduction of the nickel,as compared to electrochemical deposition in accordance with Faradays Laws.
  • Some electric potential may be applied in the apparatus during the electroless process, but the potential does not result in deposition in accordance with Faradays Laws and instead may be present, for instance, to prevent unwanted plating on the apparatus being used.
  • the reducing agent is often hypophosphite.
  • the increase in the phosphite content will be accompanied by an increase in the content of sodium sulphate.
  • boron-based reducing agents they lead to an increase in the concentration of borate.
  • a typical plating solution initially contains 7.5 g/1 nickel (as salt), 30 g/1 hypophosphite and 0 g/1 phosphite and has a specific gravity of about 1060. This will typically give a plating rate of about 30 microns per hour and will consume hypophosphite at the rate of about 4.12 grams per gram nickel. After consumption of 1 gram of nickel the bath will therefore contain about 6.5 g/1 nickel, 25 to 26 g/l hypophosphite and 4 to 5 g/l phosphite.
  • the bath will rapidly become exhausted. It is therefore standard practice to replenish nickel and hypophosphite during use.
  • the nickel content of the solution may be monitored by observing the light absorption of the solution and the solution automatically replenished with nickel, and possibly also hypophosphite, in accordance with the recorded absorption.
  • Such a process is described in, for instance, U.S. Patent Specification 4229218 and in an article by Nuzzi published in Metal Finishing, May, 1983, page 31, after the priority date of this Application.
  • a succession of articles are plated by.a plating metal selected from nickel, cobalt, alloys of nickel and alloys of cobalt by contact with a ; plating solution containing plating metal (as salt) and reducing agent and the solution is maintained for prolonged use by replenishing with plating metal to maintain the plating metal concentration substantially constant, and by replenishing with reducing agent to maintain the reducing agent concentration substantially constant, and by observing the content of dissolved solids and, upon observing an increase in the content of dissolved solids, automatically diluting the solution and thereby maintaining substantially constant the concentration of oxidation products formed from the reducing agent.
  • a plating metal selected from nickel, cobalt, alloys of nickel and alloys of cobalt by contact with a ; plating solution containing plating metal (as salt) and reducing agent and the solution is maintained for prolonged use by replenishing with plating metal to maintain the plating metal concentration substantially constant, and by replenishing with reducing agent to maintain the reducing agent concentration substantially constant, and by observing the content of
  • the reducing agent is preferably hypophosphite, in which event the oxidation product whose concentration is held constant by the invention is phosphite.
  • Boron-based reducing-agents for instance dimethyl (or diethyl) amine borane or BH 4 may be used, in which event the product whose concentration is held constant is one or more borates (tetra - or meta-borate) and possibly amines. Hydrazine or other reducing agents may also be used.
  • the process can be continued, with appropriate replenishment, and maintenance of a constant volume of plating solution, during the formation of more than 250 grams phosphite per litre of plating solution and generally during formation of more than 1,000 and often more than 5,000 grams phosphite per litre plating solution (or during the formation of equivalent amounts of other oxidation products).
  • the ratio of nickel or other plating metal to reducing agent should be within about 10% of the stoichiometric amount, typically about 7.5 nickel: 40 hypophosphite.
  • a surprising advantage of the invention is that we find the plating is not adversely affected even though the proportions may vary widely and the concentration may be very low.
  • the dilution of the solution is normally effected by automatically removing solution in response to an increase in the observed content of dissolved solids of the plating solution, and automatically replacing the removed solution with diluent selected from water and aqueous solutions containing plating metal (as salt) and/or reducing agent.
  • the diluent is preferably water, since this minimises the amount of solution that has to be rejected.
  • Replenishment of nickel and reducing agent (to maintain those concentrations constant) is then preferably made using a solution, or solutions, having a higher concentration of nickel and reducing agent than the working bath.
  • the diluent can be a solution, or solutions, containing nickel and reducing agent, generally more diluent than the working bath.
  • the process is generally conducted at an elevated temperature in the range of 60 to 95°C, for instance around 90°C, and this results in evaporation of water during the process, Increase in dissolved solids content due to evaporation should be compensated for by adding water since other replacement of evaporated water by replenishment may result in an increase in the concentration of plating metal and hypophosphite even though it may have the desired effect of reducing dissolved solids.
  • the amount of hypophosphite that is replenished is from 4 to 6.5, preferably 5 to 5.5, grams hypophosphite per gram plating metal.
  • the replenishment is provided as a single solution containing both the plating metal (as salt) and hypophosphite, and generally has a concentration of from 5 to 30, preferably 10 to 20 1/g of the plating metal(introduced as salt) and the replenishment is normally free of phosphite.
  • the replenishment is generally much more dilute then the replenishment conventionally used in electroless nickel plating which typically contained 67 g/l nickel and 400 g/1 hypophosphite.
  • the observation of the plating metal content may be conducted by calculation from the throughput of articles or, more usally, by occasional titration of the solution.
  • the plating solution may be analysed for its plating metal content, and the dissolved solids content::recorded and water, plating metal and hypophosphite added to produce a solution having the desired plating metal and dissolved solids content.
  • the solution may then be operated for, for instance, 2 to 10 hours with replenishments of plating metal and hypophosphite in accordance with the calculated consumption (based on throughput of surfaces) and with frequent or continuous observation of the dissolved solids content, and consequential removal of solution and replenishment with water whenever necessary to effect dilution.
  • the plating metal content of the solution is observed automatically and plating metal (as salt) is added to the solution automatically in response to the observed value so as to maintain the value substantially constant.
  • the content of plating metal is observed by light absorption.
  • a colorimeter may be used to observe the concentration of plating metal and for generating a signal in response to a predetermined decrease in concentration.
  • the apparatus may include a light source and a photocell or other light receiver positioned a predetermined distance from the source, whereby the electrical signal generated by the light receiver will vary according to the plating metal content of the solution. When the content falls below a predetermined value the signal will be such as to activate a pump for adding plating metal salt solution (and generally hypophosphite) to the bath.
  • the colorimeter must be designed so that it records the concentration of the plating metal and not of other components in the bath. For instance, although nickel is often observed using light-of wave length 390nmthis wave length also records the concentration of other components in the bath and so in the invention the wave length should preferably be in the range 660 to 720nm.unless the apparatus includes conventional comparative means for eliminating interference by other components in the solution.
  • the preferred process therefore comprises observing the content of plating metal in the solution by light absorption and, in response to a decrease in the concentration, automatically replenishing the solution with plating metal (as salt),and a substantially stoichiometric amount of hypophosphite and thereby maintaining the concentrations of plating metal and hypophosphite substantially constant, and observing the dissolved solids content of the solution and , in response to a decrease in the observed dissolved solids content, automatically removing solution and automatically replacing the removed solution with water, and thereby maintaining the phosphite concentration substantially constant.
  • the phosphite concentration must be below 150 g/1 and the nickel and hypophosphite concentrations should be maintained around 7.5 and 40 g/1 respectively, in the invention we deliberately aim at keeping the phosphite level, for best results, at 200 to 250 g/l. At initial startup it may be lower, for instance, as low as 50 g/l and occasionally it may rise to about 275 g/l, but during prolonged use it is preferably held in the range 200 to 250 g/l, by the removal and dilution technique described above.
  • the content of plating metal is generally in the range 1 to 10 preferably 2 to 8 g/l, and the content of hypophosphite is generally from 5 . to 70 9/ 1, typically being present in an amount of from 4 to 8 times the amount of plating metal.
  • the content of dissolved solids may be observed by observing any meaningful property which in practice means observing the density, conductivity or retractive index of the solution. Apparatus for observing these physical properties in a solution, and for utilising the observed value to control a pump, is well known.
  • the preferred property is specific gravity (or density) and this is preferably observed by an adjustable float whereby, when the density increases above a predetermined value, the float operates a switch that causes dilutionof the solution in the bath when the specific gravity exceeds the desired value, which is generally in the range 1100 to 1200, preferably being in the range 1130 to 1170..
  • the bath is usually equipped for automatic addition of deionised water through a constant level devioewhenever the solution level in the bath falls, and so preferably the dilution is effected by the switch activating a pump to remove solution from the bath and by the addition of deionised water to the bath through the constant level device.
  • the invention is of particular value for processes in which the plating metal is nickel or a blend of nickel with chromium or tungsten and the quantities quoted above are calculated for processes when nickel is the sole coating metal, but are also applicable with the other coating metals and combinations.
  • the process can also be used for other alloys of nickel and also for cobalt or alloys of cobalt.
  • the plating solution will normally have a conventional acidic pH, generally in the range of 3 to 6, and preferably in the range of 4 to 5, but alkaline pH is operable, for instance at values up to 10.
  • the plating solution can include a dispersion of metallic or non metallic particles that are to be incorporated into the metal plate coating.
  • the invention includes also apparatus for the control of an electroless plating solution for such processes and comprises means for observing the dissolved solids content of the solution and for automatically diluting the solution in response to an increase in the dissolved solids content.
  • the apparatus generally includes a tank in which the articles to be plated are immersed, and is provided with means for pumping the solution from the tank in response to an increase in the content of dissolved solids and means for flowing water into the tank in response to a decrease in the volume of solution in the tank.
  • the apparatus of the invention is preferably provided as a monitoring unit through which plating solution from the tank is pumped continuously or intermittently
  • the plating solution is preferably brought to a standard temperature, generally around 15 to 25°C, before it is monitored. It is necessary that these should be excluded from means for determining specific gravity or light absorption or otherwise it will distort the values. Accordingly an appropriate filter should be included.
  • Figure 1 diagrammatically illustrates a monitoring unit according to the invention
  • Figure 2 diagrammatically illustrates a coating plant according to the invention.
  • the monitoring unit in Figure 1 comprises a vessel 1, a pipe 2 leading to an inlet 3 for receiving solution from the bath and an outlet 4 for returning the solution to the bath.
  • the total apparatus will also include a pump for adding nickel salt solution to the bath, a pump for adding hypophosphite solution to the bath, and a pump for removing plating solution from the bath, and a constant level apparatus for adding a volume of deionised water that is the same as the volume of plating solution that is removed.
  • the monitor apparatus includes a colorimeter 6a and 6b, and a float 7.
  • the colorimetric nickel measuring device 6a and 6b includes a light source 6a and a receiver 6b and is provided with appropriate electrical connections 9 leading through an amplifier to the pump for nickel salt solution, whereby nickel salt is added to the plating solution only when the nickel concentration in the vessel 1 falls below a predetermined value. Hypophosphite is added with nickel salt.
  • the float 7 is connected to a switch 10 provided with appropriate electrical connections 11 which lead through an amplifier to the pump for removing solution. from the bath, whereby the pump is operated only when the density is above a predetermined value, such that the float rises.
  • the float 7 may be provided with an , . adjustment nut 12 such that it is possible easily to adjust the density at which the float rises sufficiently to operate the switch 10 and hence the pump for removing solution from the bath.
  • a heat -exchanger 13 may be provided in the inlet pipe 2 for bringing the solution to a constant temperature, typically about 50°C.
  • the heat exchanger may be provided with inlet 14 and outlet 15 for circulating cooling fluid.
  • a sheet 16 or other suitable baffle may be provided over the inlet 3 so as to minimise upward fluid flow velocity adjacent the float.
  • a standard solution of known nickel, hypophosphite and phosphite content may be introduced from pipe 17 through valve 18 into the inlet 3.
  • the apparatus in Figure 2 comprises a plating tank 20 provided with a conventional conveyor 21 for immersing articles 22 in solution 23 in the tank for the duration necessary for appropriate plating of them.
  • a pump 24 is provided to withdraw solution from outlet 25 continuously or intermittently and through a cooling vessel 26 containing a coil 27 through which is passed tap water at ambient temperature.
  • the cooled plating solution is then forced by the pump 24 through a device 28 in which its specific gravity is continuously monitored, for instance including the parts 7, 10, 11 and 12 in Figure 1. It then passes through a device 29 in which the concentration of plating solution is determined optically, for instance including the parts 6a, 6b and 9 of Figure 1.
  • the parts 28 and 29 may be combined into a single monitoring unit, as in Figure 1.
  • the plating solution contains dispersed solids filters will be provided in the devices 28 and 29 to divert solids away from the apparatus for observing specific gravity and optical absorption.
  • the monitored liquid is returned to the plating solution via line 30.
  • the specific gravity recording device 28 When the specific gravity recording device 28 records that the specific gravity has risen above a predetermined value, generally around 1150, if activates a pump 31 that draws plating solution from the apparatus and runs it to reject via pipe 32. This rejected solution may be drawn from the tank 20 as shown, or from elsewhere.
  • level sensor 33 records this and automatically activates a pump 34 by which water, generally deionised water, is added to the plating solution via pipe 35 in order to replace the volume of solution withdrawn by pump 31.
  • pump 36 by which a solution of plating metal, as salt, is added to the bath by line 37.
  • pump 38 by which hypophosphite is added to the bath by line 39 in an amount proportion to the amount of plating metal.
  • this device can be replaced by conventional devices for recording refractive index or electrical conductivity.
  • the bath is initially made up with a solution having pH 4 to 5, specific gravity 1150 and containing 7.5 g/l nickel (as nickel sulphate) 40 g/1 hypophosphite and 150 g/1 phosphite.
  • the temperature is about 90°C.
  • Plating proceeds in conventional manner and plating liquid is continuously withdrawn by pump 24 at about 1 litre per minute. Air bubbles in the solution are removed by the pump, and the specific gravity device 28 is set to activate the pump 31 when the specific gravity exceeds 1150 and the optical device 29 is set to activate the pump 36 when the nickel content falls below 7.5 g/l.
  • Pump 38 is related to pump 36 so as to replenish at the rate of about 5.3 grams hypoposphite per gram nickel. Instead of using separate pumps 36 and 38 a single replenishment solution of 15 g/1 nickel (as sulphate) and 80 g/1 hypophosphite can be used.
  • the process can continue for several days or weeks. It may be desirable to analyse for hypophosphite from time to time, and activate the replenishment pump 38 if the ratio nickel: hypophosphite is deviating too far from the optimum, but generally this is unnecessary.
  • Solution rejected by pump 31,or plating solution 23 rejected when it has been used for so long that it is no longer convenient or possible to maintain concentrations constant, may be dumped (after appropriate effluent treatment) but when the surface being plated is aluminium it is convenient to pretreat it with a dilute plating bath, termed a nickel strike process, and preferably the rejected solution is used for making up the nickel strike solution.
  • the overall plating process typically involves 3 to 5 minutes immersion in this or some other strike solution followed by 1 hour in the plating solution 23, followed by a first rinse in water and then a second rinse in water.
  • the water for replenishment of the tank by pump 34 may be drawn from the first rinse.

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  • Chemical & Material Sciences (AREA)
  • General Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Chemically Coating (AREA)
EP83304214A 1982-07-23 1983-07-20 Vorrichtung und Verfahren für das stromlose Plattieren Withdrawn EP0100203A1 (de)

Applications Claiming Priority (2)

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GB8221414 1982-07-23
GB8221414 1982-07-23

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EP0100203A1 true EP0100203A1 (de) 1984-02-08

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6524642B1 (en) 2001-04-21 2003-02-25 Omg Fidelity, Inc. Electroless metal-plating process

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1816237A1 (de) * 2006-02-02 2007-08-08 Enthone, Inc. Verfahren und Vorrichtung zur Beschichtung von Substratoberflächen

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3043066A1 (de) * 1979-11-14 1981-05-21 C. Uyemura & Co., Ltd., Osaka Verfahren und vorrichtung zur steuerung eines bades zur stromlosen plattierung
US4324589A (en) * 1979-02-05 1982-04-13 Shipley Company Inc. Solute monitoring process

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4324589A (en) * 1979-02-05 1982-04-13 Shipley Company Inc. Solute monitoring process
DE3043066A1 (de) * 1979-11-14 1981-05-21 C. Uyemura & Co., Ltd., Osaka Verfahren und vorrichtung zur steuerung eines bades zur stromlosen plattierung

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
PATENT ABSTRACTS OF JAPAN, unexamined applications, C Field, vol. 4, no. 151, October 23, 1980 THE PATENT OFFICE JAPANESE GOVERNMENT page 93 C 28 & JP-A-55 097 463 ( OKI DENKI KOGYO K.K. ) *
PATENTS ABSTRACTS OF JAPAN, unexamined applications, C Field, vol. 3, no. 43, April 13, 1979 THE PATENT OFFICE JAPANESE GOVERNMENT page 113 C 42 & JP-A-54 017 333 ( CANON K.K. ) *

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6524642B1 (en) 2001-04-21 2003-02-25 Omg Fidelity, Inc. Electroless metal-plating process

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JPS59173259A (ja) 1984-10-01

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