US3261711A - Electroless plating - Google Patents
Electroless plating Download PDFInfo
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- US3261711A US3261711A US245234A US24523462A US3261711A US 3261711 A US3261711 A US 3261711A US 245234 A US245234 A US 245234A US 24523462 A US24523462 A US 24523462A US 3261711 A US3261711 A US 3261711A
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- cobalt
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- 238000007772 electroless plating Methods 0.000 title description 14
- 238000007747 plating Methods 0.000 claims description 67
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 39
- 239000001301 oxygen Substances 0.000 claims description 39
- 229910052760 oxygen Inorganic materials 0.000 claims description 39
- 239000010941 cobalt Substances 0.000 claims description 28
- 229910017052 cobalt Inorganic materials 0.000 claims description 28
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 claims description 28
- 230000003197 catalytic effect Effects 0.000 claims description 16
- 238000000034 method Methods 0.000 claims description 14
- ACVYVLVWPXVTIT-UHFFFAOYSA-M phosphinate Chemical compound [O-][PH2]=O ACVYVLVWPXVTIT-UHFFFAOYSA-M 0.000 claims description 14
- 230000008569 process Effects 0.000 claims description 9
- 150000001768 cations Chemical class 0.000 claims description 5
- 150000001450 anions Chemical class 0.000 claims description 3
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 68
- 229910052759 nickel Inorganic materials 0.000 description 33
- 229910052751 metal Inorganic materials 0.000 description 23
- 239000002184 metal Substances 0.000 description 23
- UMGDCJDMYOKAJW-UHFFFAOYSA-N thiourea Chemical compound NC(N)=S UMGDCJDMYOKAJW-UHFFFAOYSA-N 0.000 description 22
- GQZXNSPRSGFJLY-UHFFFAOYSA-N hydroxyphosphanone Chemical compound OP=O GQZXNSPRSGFJLY-UHFFFAOYSA-N 0.000 description 17
- 229940005631 hypophosphite ion Drugs 0.000 description 17
- QXZUUHYBWMWJHK-UHFFFAOYSA-N [Co].[Ni] Chemical compound [Co].[Ni] QXZUUHYBWMWJHK-UHFFFAOYSA-N 0.000 description 13
- XSQUKJJJFZCRTK-UHFFFAOYSA-N Urea Natural products NC(N)=O XSQUKJJJFZCRTK-UHFFFAOYSA-N 0.000 description 11
- 238000000354 decomposition reaction Methods 0.000 description 10
- 230000008901 benefit Effects 0.000 description 8
- 238000006243 chemical reaction Methods 0.000 description 8
- 239000000203 mixture Substances 0.000 description 7
- WSFSSNUMVMOOMR-UHFFFAOYSA-N Formaldehyde Chemical compound O=C WSFSSNUMVMOOMR-UHFFFAOYSA-N 0.000 description 6
- ZGDWHDKHJKZZIQ-UHFFFAOYSA-N cobalt nickel Chemical compound [Co].[Ni].[Ni].[Ni] ZGDWHDKHJKZZIQ-UHFFFAOYSA-N 0.000 description 6
- 239000000463 material Substances 0.000 description 6
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 5
- 230000005587 bubbling Effects 0.000 description 5
- 239000003795 chemical substances by application Substances 0.000 description 5
- 229910052802 copper Inorganic materials 0.000 description 5
- 239000010949 copper Substances 0.000 description 5
- 229920006395 saturated elastomer Polymers 0.000 description 5
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 4
- KDLHZDBZIXYQEI-UHFFFAOYSA-N Palladium Chemical compound [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 description 4
- 238000002474 experimental method Methods 0.000 description 4
- 238000010438 heat treatment Methods 0.000 description 4
- 229910001453 nickel ion Inorganic materials 0.000 description 4
- 230000006911 nucleation Effects 0.000 description 4
- 238000010899 nucleation Methods 0.000 description 4
- 150000002926 oxygen Chemical class 0.000 description 4
- 239000002245 particle Substances 0.000 description 4
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 4
- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 description 3
- 229910000531 Co alloy Inorganic materials 0.000 description 3
- 239000003638 chemical reducing agent Substances 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 150000002500 ions Chemical class 0.000 description 3
- 230000006641 stabilisation Effects 0.000 description 3
- 238000011105 stabilization Methods 0.000 description 3
- 239000003381 stabilizer Substances 0.000 description 3
- 238000012360 testing method Methods 0.000 description 3
- KWSLGOVYXMQPPX-UHFFFAOYSA-N 5-[3-(trifluoromethyl)phenyl]-2h-tetrazole Chemical compound FC(F)(F)C1=CC=CC(C2=NNN=N2)=C1 KWSLGOVYXMQPPX-UHFFFAOYSA-N 0.000 description 2
- NLXLAEXVIDQMFP-UHFFFAOYSA-N Ammonia chloride Chemical compound [NH4+].[Cl-] NLXLAEXVIDQMFP-UHFFFAOYSA-N 0.000 description 2
- OAKJQQAXSVQMHS-UHFFFAOYSA-N Hydrazine Chemical compound NN OAKJQQAXSVQMHS-UHFFFAOYSA-N 0.000 description 2
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 2
- VEQPNABPJHWNSG-UHFFFAOYSA-N Nickel(2+) Chemical compound [Ni+2] VEQPNABPJHWNSG-UHFFFAOYSA-N 0.000 description 2
- 239000000654 additive Substances 0.000 description 2
- 238000013019 agitation Methods 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 229910052793 cadmium Inorganic materials 0.000 description 2
- BDOSMKKIYDKNTQ-UHFFFAOYSA-N cadmium atom Chemical compound [Cd] BDOSMKKIYDKNTQ-UHFFFAOYSA-N 0.000 description 2
- 229910001429 cobalt ion Inorganic materials 0.000 description 2
- XLJKHNWPARRRJB-UHFFFAOYSA-N cobalt(2+) Chemical compound [Co+2] XLJKHNWPARRRJB-UHFFFAOYSA-N 0.000 description 2
- 230000001419 dependent effect Effects 0.000 description 2
- 238000000151 deposition Methods 0.000 description 2
- 230000008021 deposition Effects 0.000 description 2
- 238000009713 electroplating Methods 0.000 description 2
- -1 hypophosphite ions Chemical class 0.000 description 2
- 239000003112 inhibitor Substances 0.000 description 2
- 229910052757 nitrogen Inorganic materials 0.000 description 2
- 229910052763 palladium Inorganic materials 0.000 description 2
- 229910001379 sodium hypophosphite Inorganic materials 0.000 description 2
- 239000000758 substrate Substances 0.000 description 2
- QGZKDVFQNNGYKY-UHFFFAOYSA-O Ammonium Chemical compound [NH4+] QGZKDVFQNNGYKY-UHFFFAOYSA-O 0.000 description 1
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 1
- KRKNYBCHXYNGOX-UHFFFAOYSA-K Citrate Chemical compound [O-]C(=O)CC(O)(CC([O-])=O)C([O-])=O KRKNYBCHXYNGOX-UHFFFAOYSA-K 0.000 description 1
- BDAGIHXWWSANSR-UHFFFAOYSA-M Formate Chemical compound [O-]C=O BDAGIHXWWSANSR-UHFFFAOYSA-M 0.000 description 1
- 229910000990 Ni alloy Inorganic materials 0.000 description 1
- VMHLLURERBWHNL-UHFFFAOYSA-M Sodium acetate Chemical compound [Na+].CC([O-])=O VMHLLURERBWHNL-UHFFFAOYSA-M 0.000 description 1
- 235000019270 ammonium chloride Nutrition 0.000 description 1
- 229910052785 arsenic Inorganic materials 0.000 description 1
- RQNWIZPPADIBDY-UHFFFAOYSA-N arsenic atom Chemical compound [As] RQNWIZPPADIBDY-UHFFFAOYSA-N 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000033228 biological regulation Effects 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 239000007795 chemical reaction product Substances 0.000 description 1
- 229910052804 chromium Inorganic materials 0.000 description 1
- 239000011651 chromium Substances 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- GFHNAMRJFCEERV-UHFFFAOYSA-L cobalt chloride hexahydrate Chemical compound O.O.O.O.O.O.[Cl-].[Cl-].[Co+2] GFHNAMRJFCEERV-UHFFFAOYSA-L 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 238000013500 data storage Methods 0.000 description 1
- 230000002939 deleterious effect Effects 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 1
- 229910052737 gold Inorganic materials 0.000 description 1
- 239000010931 gold Substances 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 150000002431 hydrogen Chemical class 0.000 description 1
- 239000004615 ingredient Substances 0.000 description 1
- 238000003780 insertion Methods 0.000 description 1
- 230000037431 insertion Effects 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 229910021645 metal ion Inorganic materials 0.000 description 1
- 238000001465 metallisation Methods 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- LAIZPRYFQUWUBN-UHFFFAOYSA-L nickel chloride hexahydrate Chemical compound O.O.O.O.O.O.[Cl-].[Cl-].[Ni+2] LAIZPRYFQUWUBN-UHFFFAOYSA-L 0.000 description 1
- RRIWRJBSCGCBID-UHFFFAOYSA-L nickel sulfate hexahydrate Chemical compound O.O.O.O.O.O.[Ni+2].[O-]S([O-])(=O)=O RRIWRJBSCGCBID-UHFFFAOYSA-L 0.000 description 1
- 229940116202 nickel sulfate hexahydrate Drugs 0.000 description 1
- 239000007800 oxidant agent Substances 0.000 description 1
- 238000006213 oxygenation reaction Methods 0.000 description 1
- 239000000047 product Substances 0.000 description 1
- 150000003839 salts Chemical class 0.000 description 1
- 239000001632 sodium acetate Substances 0.000 description 1
- 235000017281 sodium acetate Nutrition 0.000 description 1
- 239000001509 sodium citrate Substances 0.000 description 1
- NLJMYIDDQXHKNR-UHFFFAOYSA-K sodium citrate Chemical compound O.O.[Na+].[Na+].[Na+].[O-]C(=O)CC(O)(CC([O-])=O)C([O-])=O NLJMYIDDQXHKNR-UHFFFAOYSA-K 0.000 description 1
- 230000002269 spontaneous effect Effects 0.000 description 1
- 230000000087 stabilizing effect Effects 0.000 description 1
Images
Classifications
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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
- C23C18/48—Coating with alloys
- C23C18/50—Coating with alloys with alloys based on iron, cobalt or nickel
-
- 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
- C23C18/31—Coating with metals
- C23C18/32—Coating with nickel, cobalt or mixtures thereof with phosphorus or boron
- C23C18/34—Coating with nickel, cobalt or mixtures thereof with phosphorus or boron using reducing agents
- C23C18/36—Coating with nickel, cobalt or mixtures thereof with phosphorus or boron using reducing agents using hypophosphites
Definitions
- Electroless plating of nickel, cobalt and nickel-cobalt alloys has been utilized extensively in recent years due to the unique capabilities of electroless plating not found in ordinary electrolytic plating.
- electroless plating may be applied directly to nonconductive substrates and may also be used for plating the interior surfaces of parts without the necessity of using elaborate electroding of electrolytic plating.
- the present invention provides both increased stability for electroless nickel, cobalt or nickel-cobalt plating baths generally and further permits use of far higher concentration of hypophosphite ion than has heretofore been possible. Some attendant advantages of this higher hypophosphite concentration will be discussed hereinbelow.
- the preesnt invention resides in the maintaining of a saturated or near saturated concentration of oxygen within the bath during the plating period.
- FIGURE 1 is a schematic illustration of a plating bath in accordance with the present invention.
- FIGURE 2 is a schematic illustration of a second plating bath system in accordance with one modification of the present invention.
- FIGURE 3 is a plot of relative plating rate versus hypophosphite concentration in a plating bath of the present invention wherein the oxygen concentration is near saturation.
- the present invention utilizes an at or near saturated oxygen condition to provide a type of bath stability against decomposition which will be referred to as class I.
- Homogeneous decomposition is the formation of free metal within the body of the bath in accordance with the following idealized reactions. It should be appreciated that the precise reactions may differ from the following. However, these reactions do show one explanation for the phenomena observed.
- Heterogeneous decomposition is the formation of free metal at the surface of a catalytic metal in accordance with the following reaction:
- the H ion (or other reaction product) once formed is then capable of reacting with either water, to produce free hydrogen, or with the nickel ion to form nickel metal as in Equation II.
- the oxygen successfully competes with the metal as an oxidizing agent for H.
- the use of the saturated oxygen solution of the present invention will not serve to inhibit further reaction of the bath with the metal nucleation sites. The bath will only see the sites as additional catalytic surface.
- Inhibitors of the class II type reactions have been studied by previous investigators. These previous investigators have proposed the use of materials such as thiourea in minute quantities. These agents act to decrease the rate at which the plating can occur on minute particles of metal which are already formed in the body of the plating bath. These agents apparently are absorbed on the surface of the already formed particle. Of course, these agents must be present in minute quantities only or they will inhibit the plating from forming in the parts being plated as well as preventing spontaneous decomposition on the minute nucleation sites.
- the inhibitor agents which are beneficial in stabilizing against class II decomposition are ineifective against class I decomposition. Accordingly, they do not permit the use of high concentrations of reducing agent and the attendant advantages which the present invention allows. However, when these agents are used in combination (as will be explained herein) with the saturated oxygen solution of my invention, certain advantages result.
- An electroless nickel plating bath of the following composition was formulated.
- Nickel sulfate hexahydrate gm./l 17 Sodium hypophosphite gm./l 24 Sodium acetate gm./l 41 pH 4.5 Acetic acid gm./l 30 This bath was heated to 205 F. It is important to realize at this time that the solubility of oxygen in water varies very strongly with increasing temperature. For example, at room temperature (25 C.) the solubility is equivalent to .004 gram per 100 grams water. At 205 F. (96.1 C.) the solubility is approximately .0004 gram per 100 grams of water. It is thus apparent that as the bath is heated from room temperature to an elevated temperature, a considerable quantity of the dissolved oxygen will escape. A bath prepared as above and maintained at 205 without the insertion of any catalytic substrate for plating decomposed uncontrollably after a period of about minutes. At this time, interior deterioration of the bath was noted with the forming of nucleation sites.
- a second bath prepared in the same manner and maintained at the same temperature with the exception that oxygen was bubbled (including the heat-up period) through the bath at a rate of 15 to bubbles per minute per liter, was stable indefinitely. (This is 3-4 ml./minute oxygen.)
- Ammonium chloride 33.3 gm./l. (.62).
- Sodium hypophosphite 83.3 gm./l. (.78 M).
- Sodium citrate 100 gm./l. (.34). pH 7.5.
- a bath prepared according to the above schedule would decompose before the operating temperature of 200 F. had been reached. However, if oxygen was passed through the bath during the heating stage, this bath shows indefinite stability.
- FIGURE 1 there is shown one such scheme where 10 generally indicates a container for the particular solution 11 being used for plating. 12 designates a heating means which may be a glass coil heating element. 13 is a manifold pipe having a number of fine openings for allowing the oxygen to escape therefrom and pass through the solution. 14 designates a filter for removing oil and other materials carried by the gas stream which may be deleterious to the bath. 15 is an oxygen source which may be ordinary air or bottled oxygen.
- FIGURE 2 there is illustrated a second mode of operation of a plating bath in accordance with the present invention.
- this system while slightly more complicated, possesses advantages which are not found in the system shown schematically in FIGURE 1.
- the system of FIGURE 2 utilizes an oxygenation bath 11 in conjuntcion with an actual plating bath 21.
- Pump means 22 and return path means 23 serve to circulate the plating solution between the two baths.
- the minimum rate at which one will need to circulate the solution will be dependent upon the rate at which plating is occurring and the temperatures at which the baths are operated. Optimum rates can be determined readily for any particular system used.
- FIGURE 1 For most plating systems, the scheme of FIGURE 1 will suffice; however, I have found that in the plating of magnetic elements as will be described hereinbelow, uniformity is much more readily obtained through the system such as shown in FIGURE 2 due to the lack of agitation and solution nonconformity which tends to occur in the bath of FIG- URE 1.
- FIGURE 3 there is shown a plot of plating rate per unit time in arbitrary units versus increasing hypophosphite ion concentration in a mixed cobalt-nickel bath as described above. As can be seen, the plating rate increased on a linear scale with increasing concentration of hypophosphite ion.
- concentration limit of hypophosphite ion reaches approximately 30 gm./1., these baths spontaneously decompose within a very few minutes.
- hypophosphite ion When oxygen is bubbled through a bath at the rate of to bubbles per second per liter of solution, it has been found that hypophosphite ion can be increased to as high as 96 gm./ 1. Of course, as can be seen from the chart of FIGURE 3, the plating rate is no longer increased at concentrations above approximately 48 gm./l. However, the permissible increase concentration of hypophosphite ion above 48 gm./l. can still prove to be useful in view of the fact that this ion will not have to be replenished in the bath as frequently as has been required heretofore.
- Plating was done on nickel metal strips having a surface of 0.25 in. for a period of 30 minutes with oxygen passing through at 15 to 20 bubbles per second per liter of solution.
- FIG- URE 2 there is schematically illustrated a body to be plated 24 interposed between the poles of a strong magnet 25 to provide the orienting magnetic field.
- Cobalt content of the deposit decreases when oxygen is passed through the plating solution.
- class I and class II stabilizers may vary the ratio of cobalt to nickel in the deposit and thereby tailor the coercivity, within limits, to desired values.
- the process of chemically plating a non-magnetic 8 body of which at least surface portions are catalytic with a nickel-cobalt alloy possessing magnetic properties useful for memory units which comprises providing a hot aqueous plating bath including nickel ions, cobalt ions, hypophosphite ions, and from -500 ,ug./1. of thiourea, maintaining the oxygen content of said bath at near saturation level, placing said body in said plating bath, applying a magnetic field across the surface of said body greater than H the coercivity of the deposit, and allowing said body to remain in said bath until the desired thickness of metal is deposited thereon.
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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)
Description
July 19, 1966 J. s. SALLO 3,261,711
ELEGTROLESS PLATING Filed Dec. 17, 1962 j 0 SUPPLY'".
W0 SUPPLTIJII PLATING RATE 0 INVENTOR. INCREASING H2PO2 CONCENTRATION (eRAMs/uTER) JfPflME 354M ATTORNEY United States Patent 3,261,711 ELECTRULESS PLATING Jerome S. Sallo, St. Louis Park, Minn, assignor to Honeyweli Inc, a corporation of Delaware Filed Dec. 17, 1962, Ser. No. 245,234 8 (Iiaims. (CI. 117-931) The present invention is directed to improvements in the electroless plating of nickel, cobalt or mixtures thereof.
Electroless plating of nickel, cobalt and nickel-cobalt alloys has been utilized extensively in recent years due to the unique capabilities of electroless plating not found in ordinary electrolytic plating. For example, electroless plating may be applied directly to nonconductive substrates and may also be used for plating the interior surfaces of parts without the necessity of using elaborate electroding of electrolytic plating.
In addition to the nickel, cobalt and nickel-cobalt electroless plating to which the present invention is specifically directed, the literature reports a large number of other electroless plating systems. Among these are arsenic, chromium, cadmium, copper, gold, iron and palladium. Various reducing agents have been suggested for use with these materials including the hypophosphite of the present invention as well as formate or formaldehyde in the case of cadmium and copper and hydrazine in the case of palladium.
Although electroless nickel and cobalt have been plated for many years from hypophosphite baths, the commercially used baths have not been wholly satisfactory for several reasons. Among these are relatively slow deposition rate (generally less than 1 mil per hour) and bath instability. It has been shown that plating rate is dependent upon the concentration of hypophosphite (with the exception of diffusion controlled baths) and that increasing the hypophosphite concentration will increase the rate of metal deposition. However, with increasing hypophosphite concentration, the tendency of the bath to decompose uncontrollably is also increased. By decomposition is meant that the bath uncontrollably creates minute particles of metal in the solution rather than only on the catalytic surface to be plated. Once formed, these particles in the solution, which are catalytic themselves, act as nucleation sites and bring about the rapid decompo sition of the bath and produce a finely divided black metal deposit throughout the bath.
Even in baths of nickel or cobalt having what is considered normal hypophosphite concentration, it has been found that these baths have relatively short life at the high temperatures (approximately 200 F.) at which these baths must necessarily be used. Numerous schemes have been proposed for eliminating this problem or reducing it. While partially successful, the schemes have not provided the advantages of the present invention.
The present invention provides both increased stability for electroless nickel, cobalt or nickel-cobalt plating baths generally and further permits use of far higher concentration of hypophosphite ion than has heretofore been possible. Some attendant advantages of this higher hypophosphite concentration will be discussed hereinbelow. Briefly, the preesnt invention resides in the maintaining of a saturated or near saturated concentration of oxygen within the bath during the plating period.
The present invention can best be understood from a study of the following specification and drawings wherem:
FIGURE 1 is a schematic illustration of a plating bath in accordance with the present invention;
FIGURE 2 is a schematic illustration of a second plating bath system in accordance with one modification of the present invention; and
Fatentedl July I9, 196% FIGURE 3 is a plot of relative plating rate versus hypophosphite concentration in a plating bath of the present invention wherein the oxygen concentration is near saturation.
I am aware that other investigators have proposed the bubbling of oxygen through copper electroless plating baths containing formaldehyde for increasing the stability of these baths. However, the problems encountered in the electroless plating of copper and the decomposition of these baths are quite dissimilar from those problems encountered in the use of nickel and cobalt .in electroless plating systems. Further, it has been shown in published work of the previous investigators that increasing the concentration of their reducing agent lowers plating rate rather than increases it as is the case with the present in vention. Of course, the copper deposit does not show magnetic properties as do certain of the deposits in accordance with the present invention.
While I do not intend to be bound to any theory as to the manner in which the present invention operates, the following appears to provide a reasonable explanation of the phenomena observed.
The present invention utilizes an at or near saturated oxygen condition to provide a type of bath stability against decomposition which will be referred to as class I.
Previous investigators have utilized certain additives in electroless nickel plating baths to provide a degree of bath stability against decomposition. This type of bath stability will be referred to as class II.
Understanding of the above two types of decompositionhomogeneous and heterogeneous-will prove helpful in distinguishing the present inventions method of stabilization from those previously known.
Homogeneous decomposition is the formation of free metal within the body of the bath in accordance with the following idealized reactions. It should be appreciated that the precise reactions may differ from the following. However, these reactions do show one explanation for the phenomena observed.
Heterogeneous decomposition is the formation of free metal at the surface of a catalytic metal in accordance with the following reaction:
III.
In the homogeneous reaction I, the H ion (or other reaction product) once formed is then capable of reacting with either water, to produce free hydrogen, or with the nickel ion to form nickel metal as in Equation II. I'have found that if a plating solution of nickel, cobalt or nickel-cobalt mixtures is maintained saturated with oxygen that the H" ion (or its equivalent product) will be oxidized in the bulk of the solution Without interference with the heterogeneous reaction of Equation III taking place upon the catalytic surface. In effect the oxygen successfully competes with the metal as an oxidizing agent for H. Once elemental metal has been formed in the bulk of the bath, the use of the saturated oxygen solution of the present invention will not serve to inhibit further reaction of the bath with the metal nucleation sites. The bath will only see the sites as additional catalytic surface.
Inhibitors of the class II type reactions have been studied by previous investigators. These previous investigators have proposed the use of materials such as thiourea in minute quantities. These agents act to decrease the rate at which the plating can occur on minute particles of metal which are already formed in the body of the plating bath. These agents apparently are absorbed on the surface of the already formed particle. Of course, these agents must be present in minute quantities only or they will inhibit the plating from forming in the parts being plated as well as preventing spontaneous decomposition on the minute nucleation sites. The inhibitor agents which are beneficial in stabilizing against class II decomposition are ineifective against class I decomposition. Accordingly, they do not permit the use of high concentrations of reducing agent and the attendant advantages which the present invention allows. However, when these agents are used in combination (as will be explained herein) with the saturated oxygen solution of my invention, certain advantages result.
It is an object of the present invention to provide an electroless plating bath for the plating of nickel, cobalt or cobalt-nickel alloys which is more stable than baths known heretofore.
It is a further object of the present invention to provide a plating bath of the above enumerated type which is capable of plating at higher speeds than prior art plating baths of these types.
It is a still further object of the present invention to provide a method of plating nickel-cobalt alloys which possess unique magnetic properties for use in recording and data storage devices.
Other and further objects of the present invention will become apparent from a study of the specification and claims.
As illustrative of the results achieved through the use of a saturated oxygen bath in the systems electroless nickel, electroless cobalt and electroless cobalt-nickel, the following tests and data are supplied.
An electroless nickel plating bath of the following composition was formulated.
Nickel sulfate hexahydrate gm./l 17 Sodium hypophosphite gm./l 24 Sodium acetate gm./l 41 pH 4.5 Acetic acid gm./l 30 This bath was heated to 205 F. It is important to realize at this time that the solubility of oxygen in water varies very strongly with increasing temperature. For example, at room temperature (25 C.) the solubility is equivalent to .004 gram per 100 grams water. At 205 F. (96.1 C.) the solubility is approximately .0004 gram per 100 grams of water. It is thus apparent that as the bath is heated from room temperature to an elevated temperature, a considerable quantity of the dissolved oxygen will escape. A bath prepared as above and maintained at 205 without the insertion of any catalytic substrate for plating decomposed uncontrollably after a period of about minutes. At this time, interior deterioration of the bath was noted with the forming of nucleation sites.
A second bath, prepared in the same manner and maintained at the same temperature with the exception that oxygen was bubbled (including the heat-up period) through the bath at a rate of 15 to bubbles per minute per liter, was stable indefinitely. (This is 3-4 ml./minute oxygen.)
The above results clearly show that the greatly enhanced stability can be obtained through the use of oxygen in an electroless nickel plating system. Similar tests were run on plating baths of cobalt electroless systems and of mixed cobalt and nickel electroless plating systems. As an example of the type of mixed system showing the same efifect, a bath of the following composition was made and tested as indicated above.
Cobalt chloride hexahydrate 33.3 gm./l. (.25 M). Nickel chloride hexahydrate gm./l. (.23 M).
Ammonium chloride 33.3 gm./l. (.62). Sodium hypophosphite 83.3 gm./l. (.78 M). Sodium citrate 100 gm./l. (.34). pH 7.5.
A bath prepared according to the above schedule would decompose before the operating temperature of 200 F. had been reached. However, if oxygen was passed through the bath during the heating stage, this bath shows indefinite stability.
While the above examples are to specific electroless nickel-cobalt or mixture baths and composition, it will be recognized that the concentrations of the various ingredients may be varied over wide limits. Likewise, various additives of the prior art may also be used in conjunction with the present invention. The prime advantage of my invention is the greatly enhanced stability of electroless nickel-cobalt, nickel and cobalt baths coupled with the permissible increase in hypophosphite ion concentration in these baths. It will generally be advantageous to increase the concentration of metal ion when the hypophosphite ion concentration is increased.
Two separate techniques have been utilized for maintaining the baths of the present invention essentially saturated with oxygen. In FIGURE 1 there is shown one such scheme where 10 generally indicates a container for the particular solution 11 being used for plating. 12 designates a heating means which may be a glass coil heating element. 13 is a manifold pipe having a number of fine openings for allowing the oxygen to escape therefrom and pass through the solution. 14 designates a filter for removing oil and other materials carried by the gas stream which may be deleterious to the bath. 15 is an oxygen source which may be ordinary air or bottled oxygen. In a system of this type the rate of passage of oxygen which will sufiice to provide effective stabilization of a system is quite broad and depends to an extent on the concentration of hypophosphite ion in the solution as will be described. In a bath of the simple electroless nickel plating type discussed above, a few milliliters per minute per liter of solution is sufficient to maintain stability. Larger amounts of oxygen are permissible but will tend to react with the hypophosphite and lower plating rate and further, will lower the overall efficiency of the bath insofar as grams of deposited metal per grams of original salt used.
In FIGURE 2 there is illustrated a second mode of operation of a plating bath in accordance with the present invention. In certain respects, this system, while slightly more complicated, possesses advantages which are not found in the system shown schematically in FIGURE 1. The system of FIGURE 2 utilizes an oxygenation bath 11 in conjuntcion with an actual plating bath 21. Pump means 22 and return path means 23 serve to circulate the plating solution between the two baths. Of course, the minimum rate at which one will need to circulate the solution will be dependent upon the rate at which plating is occurring and the temperatures at which the baths are operated. Optimum rates can be determined readily for any particular system used. For most plating systems, the scheme of FIGURE 1 will suffice; however, I have found that in the plating of magnetic elements as will be described hereinbelow, uniformity is much more readily obtained through the system such as shown in FIGURE 2 due to the lack of agitation and solution nonconformity which tends to occur in the bath of FIG- URE 1.
As has already been noted, the use of oxygen in a plating bath in accordance with the above description permits increased hypophosphite ion concentration. Referring to FIGURE 3, there is shown a plot of plating rate per unit time in arbitrary units versus increasing hypophosphite ion concentration in a mixed cobalt-nickel bath as described above. As can be seen, the plating rate increased on a linear scale with increasing concentration of hypophosphite ion. However, previous investigators have found that when the concentration limit of hypophosphite ion reaches approximately 30 gm./1., these baths spontaneously decompose within a very few minutes. When oxygen is bubbled through a bath at the rate of to bubbles per second per liter of solution, it has been found that hypophosphite ion can be increased to as high as 96 gm./ 1. Of course, as can be seen from the chart of FIGURE 3, the plating rate is no longer increased at concentrations above approximately 48 gm./l. However, the permissible increase concentration of hypophosphite ion above 48 gm./l. can still prove to be useful in view of the fact that this ion will not have to be replenished in the bath as frequently as has been required heretofore.
While the mixed cobalt-nickel plating bath shows peak plating rate occurring at about 48 gm./l., hypophosphite, a plain electroless nickel bath of the type previously described, showed the following rate.
H PO Weight of deposit, mg. gm./l. gm./l. 5 gm./l. 5.75
Plating was done on nickel metal strips having a surface of 0.25 in. for a period of 30 minutes with oxygen passing through at 15 to 20 bubbles per second per liter of solution.
As is well known in the art, certain metals are catalytic to the electroless nickel, nickel-cobalt and cobalt type systems. Likewise, methods are known for making noncatalytic surfaces catalytic. As these matters are well known and as they are not part of the present invention, they will not be discussed further herein.
In addition to the advantage of producing thicker plating per unit time, my invention provides still further advantages. The magnetic switching properties of electroless deposited nickel-cobalt is improved with increasing plating rate. I have found that properties heretofore unobtainable with conventional electroless plating tech niques may be realized through the use of the present invention. For example, in a plating bath of the cobaltnickel type codeposit described above and with oxygen passing therethrough at a rate of 10 to 15 bubbles per minute per liter of solution, deposits were obtained which possessed coercivity of 1:5 to 2.5 oersteds. Due to the low coercivity, the film possesses highly desirable properties for magnetic memory and logic units. In order to obtain useful magnetic properties, the bath must additionally contain about 0.33 mg./l. thiourea. Also in order to obtain an oriented deposit, an AC. or DC. field in excess of the H the coercivity of the deposit, is applied across the surface in the direction of desired orientation. In FIG- URE 2 there is schematically illustrated a body to be plated 24 interposed between the poles of a strong magnet 25 to provide the orienting magnetic field.
As an example of the improved megnetic results obtainable through the use of my invention, the following tests were run. Samples of nonmagnetic base materials were plated in accordance with the composite nickel-cobalt bath described above and in a bath identical to the above with the exception that the hypophosphite ion concentration was 50 gm./l. rather than the 83.3 gm./l. indicated in the above example. The properties of the deposit obtained through the two different baths having varying concentration of hypophosphite ion were as follows:
Rate of Deposition, gm. /sq. in
Hypophosphite Ion Concentration S u w( u) Where Tfiswitchin g time H applied field H threshold field S switching coefiicient As can be seen, the switching coeflicient S decreases with increasing plating rate. It is apparent from the above equation that switching time T is directly proportional to S The desirability of the rapid switching time at low drive is, of course, obvious to those using magnetic memory and logic units.
As has already been noted, thiourea and. other related materials have been known to possess utility in class II type stabilization of electroless plating baths. I have found that these materials may be used in conjunction with the present invention to produce both added stability and also to serve in a further useful way. For example, in a bath of the mixed nickel-cobalt type described above using oxygen as a class I stabilizer and a small quantity of thiourea as a class II stabilizer (from -500 lg/l.) the ratio of nickel to cobalt may be controlled by varying the thiourea content. By variation of the ratio of nickel to cobalt, the coercivity of the deposits may be tailored to the desired figures.
The following experiments will serve to illustrate the effect of oxygen and thiourea as controls for ultimate deposit composition in a mixed nickel-cobalt bath of the type previously described.
If one prepares a plating bath of cobalt-nickel and hypophosphite ion as illustrated above and inserts two electr0desone of nickel which is catalytic and one of lead which is noncatalytic-and measures the potential therebet'ween, the following is seen. (Of course, the bath is at constant plating temperature of 200 F.) Plating immediately commences upon the nickel electrode and an of 174 mv. is observed between the electrodes. If oxygen is now coupled into the bath, a fairly rapid change in is observed to about 194 mv. This lower will be maintained as long as oxygen is bubbled through the solution. If the bubbling of oxygen is stopped, the will gradually return to 174 mv. over a period of about 5 minutes.
If nitrogen is bubbled through a solution as in the previously described experiment prior to the bubbling of oxygen, the E.M.'F. Will remain essentially unchanged and may even rise slightly to about mv.
If a bath which has had oxygen bubbling therethrough and which has a potential of about 194 mv. between the electrodes now has nitrogen bubbled through, it will be found that the potential will decay back to the 174 mv. within about 30 seconds. This experiment clearly shows that the oxygen has an effect more than mere agitation.
If thiourea is added to a bath prior to the bubbling of oxygen therethrough, the potential of the bath will rise above l74 mv.
The significance of the above experiments is now believed obvious. By regulation of the quantities of oxygen and of thiourea, one may obtain results in accordance with the following observations.
(1) Cobalt content of the deposit decreases when oxygen is passed through the plating solution.
(2) Cobalt concentration of the deposit increases when thiourea is added to the plating solution.
Thus by means of combining class I and class II stabilizers, one may vary the ratio of cobalt to nickel in the deposit and thereby tailor the coercivity, within limits, to desired values.
Having thus described my invention, I claim:
1. The process of chemically plating a body of which at least surface portions are catalytic with at least one metal of the class consisting of nickel and cobalt, which comprises providing a hot aqueous plating bath including cations of at least one metal of the group consisting of cobalt and nickel and including anions of hypophosphite, maintaining the oxygen content of said bath at near saturation level, contacting said body with said hot plating bath, and allowing said body to remain in contact with said bath until the desired thickness of metal is deposited thereon.
2. The process of chemically plating a body of which at least surface portions are catalytic with nickel which comprises providing a hot plating bath including nickel ions and hypophosphite ions, maintaining the oxygen content of said bath at near saturation level, contacting said body with said hot plating bath, and allow-ing said body to remain in contact with said bath until the desired thickness of metal is deposited thereon.
3. The process of claim 2 wherein the hypophosphite ion concentration is from about 17 gm./l. up to about 96 gm./l. 4. The process of chemically plating a body of which at least surface portions are catalytic with a codeposit of nickel and cobalt which comprises providing a hot aqueous bath including cations of nickel and cobalt and hypophosphite ion, maintaining the oxygen content of said bath at near saturation level, contacting said body with said hot bath and allowing said body to remain in contact with said bath until the desired thickness of metal is deposited thereon.
5. The process of chemically plating a body of which at least surface portions are catalytic with at least one metal of the class consisting of nickel and cobalt, which comprises providing a hot aqueous bath including cations of at least one metal of the group consisting of cobalt and nickel and including anions of hypophosphite in concentration from about 17 up to 96 grams per liter, maintaining the oxygen content of said bath at near saturation level, contacting said body with said hot plating bath, and allowing said body to remain in contact with said bath until the desired thickness of metal is deposited thereon.
6. The process of claim 5 wherein the cations are both nickel and cobalt and the concentration of hypophosphite is about 4 8 gm./l.
7. The process of chemically plating a non-magnetic 8 body of which at least surface portions are catalytic with a nickel-cobalt alloy possessing magnetic properties useful for memory units which comprises providing a hot aqueous plating bath including nickel ions, cobalt ions, hypophosphite ions, and from -500 ,ug./1. of thiourea, maintaining the oxygen content of said bath at near saturation level, placing said body in said plating bath, applying a magnetic field across the surface of said body greater than H the coercivity of the deposit, and allowing said body to remain in said bath until the desired thickness of metal is deposited thereon.
8. The process of chemically plating a non-magnetic body of which at least,the surface portions are catalytic with a metallic coating having improved magnetic switching properties which comprises preparing a solution of about'0.25 M cobalt ion, about 0.23 M nickel ion, 06 M ammonium ion, about 0.78 M hypophosphite ion, 0.34 M citrate ion, 0.33 mg./l. thiourea and a pH of about 7.5, maintaining said solution essentially saturated with oxygen, heating said bath to about 200 F., immersing said body in said =bath, applying a magnetic field in excess of 2.5 oersteds across the surface of said body, and allowing said body to remain in said bath until the desired thickness of metal is deposited thereon.
References Cited by the Examiner UNITED STATES PATENTS 2,819,188 1/1958 Metheny et a1. 2,929,742 3/1960 Minjer et al. 2,938,805 5/1960 Agens 117-130 X MURRAY KATZ, Primary Examiner.
RALPH S. KENDALL, Examiner.
Claims (1)
1. THE PROCESS OF CHEMICALLY PLATING A BODY OF WHICH AT LEAST SURFACE PORTIONS ARE CATALYTIC WITH AT LAST ONE METAL OF THE CLASS CONSISTING OF NICKEL AND COBALT, WHICH COMPRISES PROVIDING A HOT AQUEOUS PLATING BATH INCLUDING CATIONS OF AT LEAST ONE METAL OF THE GROUP CONSISTING OF COBALT AND KICKEL AND INCLUDING ANIONS OF HYPOPHOSPHITE, MAINTAINING THE OXYGEN CONTENT OF SAID BATH AT NEAR SATURATION LEVEL, CONTACTING SAID BODY WITH SAID HOT PLATING BATH, AND ALLOWING SAID BODY TO REMAIN IN CONTACT WITH SAID BATH UNTIL THE DESIRED THICKNESS OF METAL IS DEPOSITED THEREON.
Priority Applications (3)
Application Number | Priority Date | Filing Date | Title |
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US245234A US3261711A (en) | 1962-12-17 | 1962-12-17 | Electroless plating |
DE19631521367 DE1521367A1 (en) | 1962-12-17 | 1963-12-17 | Process for chemical plating of objects |
GB4981463A GB1073351A (en) | 1962-12-17 | 1963-12-17 | Improvements relating to the chemical deposition from plating baths of nickel and cobalt |
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US245234A US3261711A (en) | 1962-12-17 | 1962-12-17 | Electroless plating |
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US245234A Expired - Lifetime US3261711A (en) | 1962-12-17 | 1962-12-17 | Electroless plating |
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Cited By (9)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3382079A (en) * | 1964-12-16 | 1968-05-07 | Ibm | Electroless ni-fe deposition process |
US3489661A (en) * | 1965-04-02 | 1970-01-13 | Ind Bull General Electric Sa S | Electrolytic processes for the production of thin ferromagnetic film |
US3940533A (en) * | 1972-04-24 | 1976-02-24 | Rhone-Poulenc-Textile | Method of attaching metal compounds to polymer articles |
US3992300A (en) * | 1972-09-27 | 1976-11-16 | Trw Inc. | Apparatus for controlling iron content of a zinc phosphating bath |
US4086374A (en) * | 1975-04-25 | 1978-04-25 | Fuji Photo Film Co., Ltd. | Production of magnetic recording material |
US4229492A (en) * | 1977-12-30 | 1980-10-21 | Amchem Products, Inc. | Control of autodeposition baths |
US4357372A (en) * | 1977-12-30 | 1982-11-02 | Amchem Products, Inc. | Control of autodeposition baths |
US4550036A (en) * | 1984-10-18 | 1985-10-29 | Hughes Aircraft Company | Electroless silver plating process and system |
US20110135824A1 (en) * | 2005-09-30 | 2011-06-09 | Ron Rulkens | Electroless Deposition System |
Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US2819188A (en) * | 1954-05-18 | 1958-01-07 | Gen Am Transport | Processes of chemical nickel plating |
US2929742A (en) * | 1957-03-05 | 1960-03-22 | Minjer Clara Hinderina De | Electroless deposition of nickel |
US2938805A (en) * | 1958-03-31 | 1960-05-31 | Gen Electric | Process of stabilizing autocatalytic copper plating solutions |
-
1962
- 1962-12-17 US US245234A patent/US3261711A/en not_active Expired - Lifetime
Patent Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US2819188A (en) * | 1954-05-18 | 1958-01-07 | Gen Am Transport | Processes of chemical nickel plating |
US2929742A (en) * | 1957-03-05 | 1960-03-22 | Minjer Clara Hinderina De | Electroless deposition of nickel |
US2938805A (en) * | 1958-03-31 | 1960-05-31 | Gen Electric | Process of stabilizing autocatalytic copper plating solutions |
Cited By (9)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3382079A (en) * | 1964-12-16 | 1968-05-07 | Ibm | Electroless ni-fe deposition process |
US3489661A (en) * | 1965-04-02 | 1970-01-13 | Ind Bull General Electric Sa S | Electrolytic processes for the production of thin ferromagnetic film |
US3940533A (en) * | 1972-04-24 | 1976-02-24 | Rhone-Poulenc-Textile | Method of attaching metal compounds to polymer articles |
US3992300A (en) * | 1972-09-27 | 1976-11-16 | Trw Inc. | Apparatus for controlling iron content of a zinc phosphating bath |
US4086374A (en) * | 1975-04-25 | 1978-04-25 | Fuji Photo Film Co., Ltd. | Production of magnetic recording material |
US4229492A (en) * | 1977-12-30 | 1980-10-21 | Amchem Products, Inc. | Control of autodeposition baths |
US4357372A (en) * | 1977-12-30 | 1982-11-02 | Amchem Products, Inc. | Control of autodeposition baths |
US4550036A (en) * | 1984-10-18 | 1985-10-29 | Hughes Aircraft Company | Electroless silver plating process and system |
US20110135824A1 (en) * | 2005-09-30 | 2011-06-09 | Ron Rulkens | Electroless Deposition System |
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