DE2202777A1 - Process for depositing nickel - Google Patents

Description

Boeblingen, January 17, 1972 bm-fr

Applicant: International Business Machines Corporation, Armonk, N.Y. 10504 Official File number: New registration File number of the applicant: Docket PO 970 048 Process for depositing nickel

The invention relates to a method for the electroless deposition of nickel or nickel alloys with a hypophosphite as Aqueous bath containing reducing agent.

Baths with a hypophosphite reduction are used to produce uniform, phosphorus-strengthened nickel coatings by electroless deposition. In the known baths but practically usable rainfall rates occur only at an elevated temperature, eg, about 65 ⁰ C on. In this case, the case may arise that, given different coefficients of thermal expansion of the base and the coating, it will detach from the base when it cools down after application. However, deposition at room temperature has so far hardly been carried out due to the low rate of deposition, the non-uniformity of the deposition, the inadequate utilization of the materials and other disadvantages compared to deposition at elevated temperature.

It is therefore the object of the present invention to provide a method for the electroless deposition of nickel or nickel alloys which, even at room temperature, provides uniform and stable coatings and with a sufficient rate of deposition, a relatively long service life, both as well as good utilization of the materials used

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will. This object is achieved according to the invention in the method mentioned at the beginning in that an alcoholate is added to the bath. Preferably, the bath is also a source for Succinate ions added. The bath is advantageously formed from an aqueous solution of sodium hypophosphite, an alcoholate, a source of nickel ions, a source of succinate ions, a buffering agent, and sufficient ammonium hydroxide to keep the Bring the pH of the solution in the range of 7-9. For making the aqueous bath, it is preferable to use a strong concentrated solution of the hypophosphite and the alcoholate and a relatively weakly concentrated solution of the other components of the bath formed and then both solutions combined. Alcoholates are used, which are produced by reacting with one of the metals sodium, potassium, lithium or barium an alcohol of the form OC H can be obtained. The single ones

χ y

Alcoholates have various effects on the lifespan of the bath, the rate of precipitation and the utilization of the materials. All of the alcoholates considered delay the decomposition of the bath at room temperature, ie they increase its service life. Each of them causes an associated nickel deposition rate, which also remains constant for a constant concentration of hypophosphite ions. The change in the rate of deposition which occurs during the deposition is therefore essentially due to the changes in the concentrations of the hypophosphite ions and the ions of the nickel. _N

It has been found that the greater the complexity of the alcoholate radical, the lower the rate of precipitation. The radical of the simple methylate (OCH ₃ ) causes a higher rate than the radical of the ethylate (OC ₂ H ₅ ). If, for example, sodium methylate (NaOCH ₃ ) is placed in a specific bath containing nickel chloride as a source for the material to be deposited and a given concentration of reducing sodium hypophosphite, the rate of precipitation at a certain temperature is 25 µm / h. Used instead of the

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Sodium methylate sodium ethylate (NaOC ₂ H ₅ ) is used, the speed is only about 19 to 20 μm / h.

Without the addition of an alcoholate, the bath decomposes at room temperature after about 24 to 36 hours. By adding an alcoholate, this tent span could last at least 8 weeks the same temperature conditions can be extended.

The concentration of the added alcoholate seems to hardly change during the deposition process. At least it isn't necessary to maintain this concentration, or in any way Way to change to get a specific precipitation rate. The hypophosphite concentration and the molar

+2 - ratio of nickel to hypophosphite ions (Ni / H ₂ PO ₂ ) seem

to be the variables that have the greatest influence on this speed.

The bath used for the deposition is preferably made up of two separate solutions. The first solution contains the source material for the hypophosphite ions and the smallest possible amount of water required to dissolve them. The second Solution has the other components, with the exception of the alcoholate, dissolved in water in a much weaker concentration. It has been found that the bath has significantly more favorable properties in terms of the deposition process if you do that Add alcoholate to the first, highly concentrated solution and then combine both solutions and not the entire solution first Solution adds. In the latter case, the alcoholate appears to react with the larger amount of water and, due to hydrolysis, becomes inert Constituents get broken down, while when it is added to the first, highly concentrated solution, a nucleophile Reaction between the alcoholate and the hypophosphite appears to be taking place.

By adding succinate ions to the second, less concentrated Solution can further improve the precipitation

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conditions can be achieved without affecting the mode of action of the alcoholate. The invention is explained in more detail below with the aid of several exemplary embodiments. In The following list shows the composition of three different baths used for nickel deposition.

Examples 1-3 6H ₂ O 1) NiCl ₂ . 2) NH ₄ Cl 2 · ^Η 2 ^Ο 3) NaH ₂ PO ₄ O ₄ .6H ₂ O Na ₂ C ₄ H (Example After _{3 5} (example NaOC ₂ H ₈ (example NaOC ₃ H NH ₄ OH

25.0-30 / 0 g / l 45.0-55.0 g / l 30.0-50.0 g / l 16.0-20.0 g / l 2.7-21.6 g / l 2.7-21.6 g / l 2.7-21.6 g / l

to adjust the pH value to the range 7-9

Temperature - 18 ⁰ C - 50 ⁰ C

While almost all methods of adding an alcoholate to a bath for electroless deposition, which contains hypophosphite ions, are to be regarded as advantageous for the deposition process, the most favorable properties for the rate of precipitation are obtained if the method described below is used for Preparation of the bath is carried out.

Two solutions A and B are prepared. Solution A contains sodium hypophosphite (NaH ₂ PO ₂ ) in a small amount of distilled water that is just sufficient to dissolve the hypophosphite. Solution B contains the other components of the entire bath with the exception of the alcoholate source (NaOC K) in a larger one

χ j

Amount of distilled water that is required to make a

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to achieve the desired concentration of the bath. At a concentration of 30 to 50 g of hypophosphorus per liter of the bath, whereby the amount of the bath should be 5.7 1, are for solution A 50 ml of haters is enough. In the preferred method, the source materials for the alcoholate are added to solution A. and then both solutions A and B are combined to form the finished bath. If the alcoholate (e.g. a methylate) is too the highly concentrated solution A is added, hydrolysis takes place only to a very small extent. Instead one appears strong nucleophilic reaction to occur between the alcoholate and the hypophosphite, presumably producing hydride ions which are a strongly reducing agent.

If hydrolysis can take place on a large scale, then will the number of hydride ions (H) will be less than in the example described above, and the effectiveness of the bath will be reduced. It follows that the alcoholate and the hypophosphite are first combined in a concentrated solution and only then should the less concentrated solution of the other components of the bath be added. Baths, which are prepared in this way have a much higher (e.g. 4-5 times) effectiveness than baths in which the alcoholate is added to the finished, weakly concentrated solution will.

Sodium succinate (Na ₂ C ₄ H ₄ O ₄ ^ H ₂ O) can also be added to the solution in order to increase the effectiveness of the bath, in particular the rate of precipitation. The unexpected result is that the sodium succinate in no way adversely affects the functioning of the alcoholate. It was found that the succinate improved the desired properties of the bath by about 100%.

The approximate values of the sodium hypophosphite (NaH ₂ FO ₂ .ü-0) concentration in the solution can be determined if the exact concentration of the nickel ions is known

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For the above examples, 30 g NiCl ₂ .6H ₃ O per liter and 45 g NaH ₃ PO ₂ .H ₂ O per liter result in a molar ratio of hypophosphite ions to nickel ions of about 3.25. With the same nickel chloride concentration of 30 g per liter and the smaller sodium hypophosphite concentration of likewise 30 g per liter, the molar ratio of hypophosphite ions to nickel ions is about 2.3.

This molar ratio can be kept almost constant if appropriate additions are made during the deposition process * the solution.

The chemical reaction between the bath and the one to be coated Document is represented by the following relationship:

Ni ⁺² + 2e —► Ni ⁰ C-0.23 V]

It is also believed that since the alcoholate radical is a strong nucleophilic agent, the alcoholate radical and the Hypophosphite react, releasing hydrogen atoms in the form of either hydrogen gas, hydrogen ions, hydride ions will. Because of the high rates of precipitation that have been found, it can be assumed that hydride ions have a significant influence here, since they act as a strong reducing agent Means are known. Studies have shown that the pH of the bath is almost constant during the life of the solution remains, which indicates that hydrogen ions, which normally cause an increase in the acid content, are generated only to a very small extent or not at all.

The following tables show the precipitation rates of nickel from the solutions described in the preceding Examples 1 to 3, individual parameters having been changed. The amount of each bath is 5.7 l, unless otherwise indicated. Table 1 shows the precipitation rates as a function of the different alcoholate additions

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rates at the given concentrations of the nickel and hypophosphorous salts represent.

Table 1

Alcoholate pm / h NiCl ₂ -OH ₂ O conc. NaH ₂ PO ₂ conc.

After ₃ 25th 30th g / i NaOC ₃ H ₅ 19-20 30th g / i NaOC ₃ H ₈ 15-18 30th g / i without
Alcoholate 0 (see
Tab. 7) 30th g / i

30th g / i 24 30th g / i 24 30th g / i 24 30th g / i 24

Table 2 shows the dependence of the rate of precipitation of the time of precipitation, the molar ratio of the nickel ions to the hypophosphite ions being shown in the Way changed. The individual precipitation rates were obtained from measurements on six successively coated samples taken for increasingly longer time intervals in a Bath in which the materials consumed during the six coating operations were not replaced. The total amount the bath here was 1.9 1; sodium methylate was used as alcoholate.

Table 2

Precipitation time pm / h molar ratio (Ni ⁺² / H ₂ PO ₂ ~)

0.5 h 17.0 0.417

1.5 h 16.7 0.410

3.0 h 11.5 0.424

5.0 h 7.1 0.436

7.5 h 5.1 0.451

10.5 h 3.3 0.471

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The following table 3a contains the precipitation rates in a bath with a total amount of 3.8 l at constant Concentration of the nickel salt and changing concentration of the hypophosphite. Table 3b shows the rate of precipitation under the same conditions, but with constant hypophosphite concentration and changing nickel concentration. For the alcoholate, a methylate was also chosen here.

Table 3

Concentration of

concentration
of NiCI ₂ .6H ₂ O

at / h

5 g / l IO g / l 15 g / l 20 g / l 30 g / l 40 g / l 50 g / l

b) Concentration NiCl ₂ .6H ₂ O

30 g / l 3.8 30 g / l 8.9 30 g / l 16.5 30 g / l 21.6 30 g / l 25.4 30 g / l 27.9 30 g / l 30.5 concentration pa / h NaH ₂ PO ₂ 30 g / l 21.6 30 g / l 21.6 30 g / l 21.6 30 g / l 22.9 30 g / l 24.1 30 g / l 25.4

5 g / l 10 g / l 15 g / l 20 g / l 25 g / l 30 g / l

Tables 4 to 7 show the dependence of the rate of precipitation on the molar ratio of the nickel ions to the hypophosphite ions, with the individual baths having different sodium methylate concentrations exhibited. In the examples according to Table 7, no alcoholate was added.

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Table 4

molar ratio (Ni ⁺² / H ₂ PO ₂ ~) NaOCH ₃ p / h

0.30 21.6 g / L 30.5

0.38 21.6 g / l 23.9

0.42 21.6 g / L 19.8

0.47 21.6 g / l 11.2

0.49 21.6 g / L 7.4

Table 5

molar ratio (Ni ⁺² / H ₂ PO ₂ ~) NaOCH ₃ p / h

0.30 13.5 g / l 30.5

0.38 13.5 g / l 23.9

0.42 13.5 g / l 19.8

0.44 13.5 g / l 16.3

0.47 13.5 g / l 11.4

0.49 13.5 g / l 6.6

Table 6

molar ratio (Ni ⁺² / H ₂ PO ₂ ") NaOCH ₃ p / h

0.30 2.7 g / L 31.7

0.38 2.7 g / l 24.1

0.43 2.7 g / l 20.3

0.47 2.7 g / L 11.4

0.50 2.7 g / l 8.9

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Table 7

molar ratio (Ni ⁺² / H ₂ PO ₂ ~) NaOCH ₃ µm / h

0.30 O g / L 2.3

0.38 O g / L 1.0

0.42 O g / l 0.0 (something never

The punch)

0.47 O g / l 0.0 (something never

The punch)

0.49 O g / 1 0.0 (something never

The punch)

The precipitation rates obtained and also the stability of the bath are inversely proportional to the molar ratio of the nickel to the hypophosphite ions. This ratio should lie between the values 0.35 and 0.29. The lower the molar ratio, the greater the rate of precipitation. However, as the precipitation progresses, this ratio increases, so that the precipitation rate decreases. The reason to increase the molar ratio is that the consumption of hypophosphite ions is about three times as great as that of nickel ions.

It is therefore very important that the Solution to supply hypophosphite ions and nickel ions as these have been consumed. All you need are these two materials in the form of nickel chloride and sodium hypophosphite supplements to become. Subsequent additions of alcoholates are not required during the life of the bath. This also applies to Ammonium chloride, since chlorine ions are supplied by the nickel chloride and ammonium ions by the ammonium hydroxide.

Tables 8 to 10 serve for comparison with Tables 4 to 6. The results in Tables 4 to 6 were obtained with the aid of baths which, in the preferred manner, consist of a concentrated solution of the hyposphophite and the alcoholate and a black

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rather concentrated aqueous solution of the other ingredients were manufactured. The results of Tables 8 to 10 were achieved with baths in which the alcoholate was in a finished solution all components of the bath was given.

Table 8 at / h , 5 molar ratio (Ni ⁺² / H ₂ PO ₂ ~) NaOCH ₃ 17.8 ,1 0.30 2.7 g / l 16.8 ,1 0.38 2.7 g / l 14.5 , 5 0.43 2.7 g / l 10.2 , 2 0.48 2.7 g / l 6.9 0.51 2.7 g / l Table 9 at / h molar ratio (Ni ⁺² / H ₂ PO ₂ ~) NaOCH ₃ 17.8 0.30 21.6 g / l 16.5 0.37 21.6 g / l 14.5 0.44 21.6 g / l 10.0 0.47 21.6 g / l 7.4 0.50 21.6 g / l Table 10 at / h molar ratio Sodium succinate (Ni ⁺² / H ₂ PO ₂ ~) (Na ₂ C ₄ H ₄ O ₄ .6H ₂ O) 22.9-28 0.30 20.0 g / l 19.1-23 0.38 20.0 g / l 17.0-19 0.43 20.0 g / l 12.9-14 0.48 20.0 g / l 9.4-11 0.51 2O.O g / l

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The table shows that an increase in the sodium methylate concentration above the value contained in Table 8 has little effect on the rate of precipitation. Table 8 shows significantly lower precipitation rates than Table 4. From this it can be concluded that the reaction of the Methylate with the reducing agent, which promotes the precipitation process at room temperature, in a diluted System is weakened or even prevented.

The comparison of Table 10 with Table 8 shows the reinforcing effect, which is caused by the addition of sodium succinate a bath made by adding sodium methylate to the final, dilute solution. From the following table 11 the increase in the precipitation rate can be seen when the sodium succinate in a Bath is given, which is prepared in an advantageous manner by combining a concentrated solution of the methylate and sodium hypophosphite and a dilute solution of the other ingredients. Note that the precipitation rates in Table 11 are those in Table exceed by a considerable amount. From this it can be concluded that at the same time as the alcoholates there are also other, Substances that favor the precipitation process, such as succinates in can be given to the bath, both agents promoting the reduction and deposition of nickel.

Table 11

molar ratio of sodium succinate pm / h

(Ni ⁺² / H ₂ PO ₂ ~) (Na ₂ C ₄ H ₄ O ₄ .6H ₂ O)

0.29 20.0 g / l 36.8-40.6

0.37 20.0 g / l 30.5-33.3

0.43 20.0 g / l 26.7-29.2

0.48 20.0 g / l 15.2-17.8

0.50 20.0 g / l 11.9-13.2

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Tables 12 to 15 contain the precipitation rates for nickel with an addition of sodium propylate and of Sodium ethylate, lithium ethylate and barium ethylate. The used Baths were advantageously made up of two solutions with different made with strong concentration. The results of these tables in comparison with those of Table 7 support the Belief that all alcoholates a considerable advantage of the precipitation process in the electroless deposition of Effect nickel at room temperature.

Table 12 - Sodium Propylate

(Ni ⁺² / H ₂ PO ₂ ~) Na (OC ₃ H ₈ ) | am / h

0.30 4.15 g / L 17.8

0.31 4.15 g / l 17.0

0.45 4.15 g / L 15.2

0.47 4.15 g / L 10.4

0.50 4.15 g / l 5.6

0.30. 0.0 g / l 2.5

(Ni ^{+ 2} / H ₂ PO ₂ ~) Na (OC ₃ H ₈ ) jom / h

0.30 33.2 g / L 17.5

0.37 33.2 g / l 16.5

0.44 33.2 g / L 15.0

0.48 33.2 g / l 10.6

0.50 33.2 g / l 5.1

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Table 13 - Sodium Ethylate

(Ni ^{+ 2} / H ₂ PO ₂ ") Na (OC ₂ H ₅ ) p / h

0.30 3.4 g / L 20.6

0.37 3.4 g / l 19.5

0.44 3.4 g / L 18.3

0.47 3.4 g / L 10.2

0.50 3.4 g / l 6.8

0.30 0.0 g / l 2.5

(Ni ⁺² / H ₂ PO ₂ ~) Na (OC ₂ H ₅ ) pm / h

0.30 27.0 g / L 20.3

0.37 27.0 g / l 19.3

0.44 27.0 g / L 17.8

0.47 27.0 g / l 9.9

0.50 27.0 g / l 6.3

Table 14 - Lithium ethylate

(Ni ^{+ 2} / H ₂ PO ₂ ") Li (OC ₂ H ₅ ) pm / h

0.30 2.6 g / L 20.3

0.37 2.6 g / l 19.5

0.44 2.6 g / L 18.3

0.47 2.6 g / L 10.2

0.50 2.6 g / L 6.8

0.30 0.0 g / l 2.3

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Table 15 - Bariura ethylate

(Ni ⁺² / H ₂ PO ₂ ~) Ba (OC ₂ H ₅ ) ₂ pm / h

0.30 11.3 g / L 20.6

0.37 11.3 g / l 20.0

0.44 11.3 g / l 18.0

0.47 11.3 g / L 10.2

0.50 11.3 g / l 6.8

0.30 0.0 g / l 2.5

Investigations suggest that alcoholates promote the deposition of metals that are similar to nickel, e.g. iron and cobalt, do not favor at room temperature. When using nickel alloys, in which the proportion of nickel predominates, was however, it was found that the alcoholate also has a desired effect on the precipitation process. Examples show the following tables 16 and 17.

Table 16 at / h Ni ⁺⁺ + CO ⁺⁺ / H ₂ PO ₂ " After ₃ 16.5
10.2
5.8 0.625
0.700
0.800 2.7 g / l
2.7 g / l
2.7 g / l
Table 17 at / h Ni ⁺⁺ + Fe ⁺⁺ / H ₂ PO ₂ " After ₃ 17.3
8.1
5.1 0.625
0.700
0.800 2.7 g / l
2.7 g / l
2.7 g / l

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The preparation of the substrate for the deposition is directed according to the material used for the base. With many materials, e.g. glass, epoxy or paper, the surface should be clean and pretreated with a known agent. In terms of electrical properties, it was found that all Precipitation that occurs on appropriately prepared documents the electroless deposition described were obtained, were conductive, at least to the extent required, for the application to enable further coatings by electrolytic means.

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Claims (8)

"~ 17" * PATENT CLAIMS Process for the electroless deposition of nickel or nickel alloys with an aqueous bath containing a hypophosphite as reducing agent, characterized in that that an alcoholate is added to the bath. 2. The method according to claim 1, characterized in that a source of succinate ions is additionally added to the bath will. 3. The method according to claim 1 and 2, characterized in that the bath consists of an aqueous solution of sodium hypophosphorus (NaU ₂ PO ₂ ), an alcoholate, a source of nickel ions, a source of succinate ions, a buffering agent and sufficient ammonium hydroxide to Bringing the pH of the solution in the range of 7-9 is formed. 4. The method according to any one of claims 1 to 3, characterized in that that for the preparation of the aqueous bath a highly concentrated solution of the hypophosphite and the alcoholate and a relatively weakly concentrated solution of the other components of the bath are formed and that the both solutions are then added together. 5. The method according to any one of claims 1 to 4, characterized in that that an alcoholate is used which is produced by the reaction of one of the metals sodium, potassium, lithium or barium is obtained with an alcohol of the form OC H. χ y 6. The method according to claim 5, characterized in that sodium methylate is used as alcoholate. 7. The method according to claim 5, characterized in that sodium ethylate is used as alcoholate. Docket po 970 048 209840/0964 8. The method according to claim 5, characterized in that as Alcoholate sodium propylate is used. Docket PO 970 048 209840/0964