DE2202777C3 - Process for producing a bath for the electroless deposition of nickel and nickel alloys and its use - Google Patents

Description

The invention relates to a method for producing a bath for the electroless deposition of nickel and nickel alloys containing nickel ions, alcoholate, hypophosphite, buffering agents and Ammonium hydroxide, as well as its uses.

Baths containing hypophosphite ions have been made more uniform for electroless deposition, Nickel coatings strengthened by phosphorus are used. In the previously known baths come in handy Usable precipitation rates, however, only at elevated temperatures, e.g. above 65 ° C. In this case, the case may arise that at different thei mix expansion coefficients of the base and the coating of this is removed from the base during the cooling that takes place after the application solves. A deposition at room temperature has so far hardly been carried out because of the low precipitation speed, the unevenness of the precipitation, insufficient utilization of the materials as well as other disadvantages that do not occur in the case of a deposition at elevated temperatures appear.

U.S. Patent No. 2,430,581 discloses, inter alia. Metallizing baths with a content of nickel acetate, sodium hypophosphite, Hydrazine hydrate and methanol or ethanol are described. In these baths that are alkaline react, sodium alcoholate is likely to be present to a certain extent as a result of the equilibrium reaction. However, this patent does not indicate that the bath for the electroless deposition of nickel alcoholate must be added at room temperature and how this bath is to be made Has

The object of the present invention is therefore to provide a method for producing a bath for electroless To indicate deposition of nickel and nickel alloys, with which at room temperature and with sufficient Deposition rate uniform and stable coatings can be produced. In addition, the bathroom should have a long service life

ίο have, and a good utilization of the used Materials should be guaranteed.

The object of the invention is achieved by a method of the type mentioned at the beginning, which is characterized in that an alcoholate is added to a first, highly concentrated aqueous hypophosphite solution and this is combined with a second, weakly concentrated aqueous solution of the other components.
Advantageous refinements of the invention are set out in the subclaims

According to the invention, alcoholates are used which are obtained by reacting one of the metals sodium, potassium, lithium or barium with an alcohol of the formula C ₁ HjOH. The individual alcoholates have different effects on the lifespan of the bath, the rate of precipitation and the utilization of the materials. All of the alcoholates mentioned delay the decomposition of the bath at room temperature, ie they increase its lifespan.

Each alcoholate has an associated nickel deposition rate, which also remains constant for a constant concentration of the hypophosphite ions. Which during the deposition resulting change in the rate of precipitation

J5 speed is therefore essentially due to the changes in the Concentrations of hypophosphite ions and nickel ions.

It was found that with increasing complexity of the alcoholate residue, the rate of precipitation decreases. The methylate residue (OCHs) causes a higher speed than the ethylate residue (OC2H5). Is z. B. Sodium methylate (NaOCHs) in a certain Bath given the nickel chloride as a source for the material to be deposited and reducing sodium hypophosphite contains in a predetermined concentration, at a certain temperature the Precipitation rate 25 μm / h. If sodium ethylate (NaOC2Hs) is used instead of sodium methylate, so the speed is only around 19 to 20μητ / π.

Without the addition of an alcoholate, the bath decomposes at room temperature after about 24 to 36 hours Hours. By adding an alcoholate this time span could be reduced to at least 8 weeks at the same time Temperature conditions are extended.

The concentration of the added alcoholate hardly seems to change during the deposition process to change. At least it is not necessary to maintain that concentration or in any

bo way to change to get a specific precipitation rate. The hypophosphite concentration and the molar ratio of nickel to hypophosphite ^{ions (Ni + 2} / H2PO2 ~) appear to be the variables that have the greatest influence on the rate of precipitation.

The bath used for the deposition is preferably made up of two separate solutions. the first solution contains a source for the hypophosphite

ions and the least possible, for their solution required amount of water. The second solution contains the other components dissolved in water With the exception of the alcoholate in a much weaker concentration. It was found that the bathroom has significantly more favorable properties with regard to the deposition process if the alcoholate is used the first, highly concentrated solution is added and then both solutions are combined and the alcoholate do not first add to the entire solution. In the latter case, the alcoholate appears with the larger amount of water to react and is broken down into inert components by hydrolysis, while at his Adding to the first, highly concentrated solution, a nucleophilic reaction between the alcoholate and the Hypophosphite seems to take place by adding succinate ions to the second, less concentrated Solution .can further improve precipitation conditions can be achieved without affecting the mode of action of the alcoholate will.

The invention is explained in more detail below with reference to several exemplary embodiments The list shows the composition of three different baths used for nickel deposition reproduced.

Example

NiCl ₂ · _{6H 2} O
NH ₄ Cl

NaH ₂ PO ₂ .H ₂ O
Na ₂ C ₄ H ₄ O ₄ · 6 H ₂ O
NaOCH ₃ (example 1)
NaOC ₂ H ₅ (example 2)
NaOC ₃ H ₈ (example 3)
NH ₄ OH

temperature

-3

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
l «° C-50 ° 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, one obtains the most favorable properties for the rate of precipitation if the one described below Process for making 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 just enough to dissolve the hypophosphite. Solution B contains the other components of the entire bath with the exception of the alcoholate (NaOC * Hj) in a larger amount of distilled water than is necessary to set the desired concentration of the bath. At a concentration of 30 to 50 g hypophosphite per liter of the bath, the amount of the bath being 5.7 liters, 50 ml of water are sufficient for solution A. According to the preferred method, the alcoholate is added to solution A, and then both solutions A and B are combined to form the finished bath. If the alcoholate (e.g. methylate) is added to the highly concentrated solution A, only a very small amount of hydrolysis takes place. Instead, there appears to be a strong nucleophilic reaction between the alcoholate and the hypophosphite, presumably producing hydride ions that have a strong reducing effect.

If the hydrolysis can take place to a greater extent, then the number of hydride ions (H ~) 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 in a concentrated solution should be combined and only then the less concentrated solution of the other components of the Bath is added. Baths that way

ίο have a substantial (e.g. 4- to 5 times higher effectiveness than baths, in which the alcoholate in the finished, weakly concentrated Solution is given.

Sodium succinate (Na ₂ C ₄ H ₄ O ₄ · 6 H ₂ O) can be added to the solution to further increase the effectiveness of the bath, especially the rate of deposition. The unexpected result is that the sodium succinate in no way adversely affects the action of the alcoholate. It was found that the succinate improved the desired properties of the bath by about 100%.

The approximate value of the sodium hypophosphite (NaH ₂ PO ^ · H ₂ O) concentration in the solution can be determined if the exact concentration of nickel ions is known.

For the above examples give 30 g of NiCl ₂ .6H ₂ O per liter and 45 g of NaH ₂ PO ₂ ■ H ₂ O per liter of a molar ratio of hypophosphite ions to nickel ions of about 3.25. With the same nickel chloride concentration and a smaller sodium hypophosphite concentration of also 30 g per liter, the molar ratio of hypophosphite ions to nickel ions is about 2.3. This molar ratio can be close to

J5 can be held constant when during the deposition process appropriate additions are made to the solution. From the nickel ion concentration in g / l and the concentration of the hypophosphite ions in g / l can be calculated from the molar ratio.

The chemical reaction between the bath and the coating substrate is caused by the following

Relationship reproduced:

Ni ⁺² + 2e-Ni ° [-0.23V]

It is also believed that because the alcoholate residue is highly nucleophilic, the alcoholate is also present the hypophosphite reacts nucleophilically and hydrogen either in the form of hydrogen gas, hydrogen ions or hydride ions are released. Because of the

Thus determined high precipitation rates can be assumed that hydride ions are intermediate play an essential role because these are known to be a powerful reducing agent. Investigations have shown that the pH of the bath is almost constant over the life of the solution remains, indicating that hydrogen ions, which normally cause an increase in acidity, generated only to a very small extent or not at all.

The following tables show the deposition rates of nickel from the examples 1 to 3 solutions described, whereby individual parameters have been changed. The amount of each bath is 5.7 1, unless otherwise indicated. Table 1 shows the precipitation rates in Dependence on different alcoholate additives at given concentrations of nickel and hypophosphite salts evident.

Table 1

Alcoholate

μΐτι / h NiCI ₂ - 6 H ₂ O conc. NaH ₂ PO ₂ conc. T ° [C]

After ₃ 25th 30 g / l NaOC ₂ H ₅ 19-20 30 g / l NaOC ₃ H ₈ 15-18 30 g / l Without alcoholate 0 (see tab. 7) 30 g / l

g / l
g / l
g / l
g / l

24 24 24 24

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

Table 3 b

concentration
NiCl ₂ -OH ₂ O

concentration
NaH ₂ PO ₂

μΐη / h

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

21.6 21.6 21.6 22.9 24.1 25.4

Table 2

30th

Precipitation time μΓπ / h

Molar ratio (Ni ⁺² ZH ₂ PO ₂ ") Tables 4 to 7 show the dependence of the rate of precipitation on the molar ratio of the nickel ions to the hypophosphite ions, the individual baths having different sodium methylate concentrations. In the examples in the table, no alcoholate was added.

Tabel

0.5 h
1.5 h
3.0 h
5.0 h
7.5 h
10.5 h

17.0

16.7

11.5

7.1

5.1

3.3

0.417 0.410 0.424 0.436 0.451 0.471

35 molar ratio
(Ni ⁺ VH ₂ PO ₂ ")

40

0.30 0.38 0.42 0.47 0.49 molar ratio
(Ni ^{+ 2} / H ₂ PO ₂ ~)

The following table 3a contains the precipitation rates in a bath with a total amount of 3.8 1 with a constant concentration of the nickel salt and changing concentration of hypophosphite. Table 3b shows the rate of precipitation under the same conditions, but constant hypophosphite concentration and changing nickel salt concentration Here, too, 0.30 methylate was chosen as the alcoholate. 0.38

0.42 0.44 55 0.47 0.49

Table 3a

concentration
of NaH ₂ PO ₂

Concentration of NiCl ₂ -6H ₂ O

μΐτι / h

Table 6

5 g / l 30 g / l 3.8 AROUND 10 g / l 30 g / l 8.9 15 g / l 30 g / l 16.5 0.30 20 g / l 30 g / l 21.6 65 0.38 30 g / l 30 g / l 25.4 0.43 40 g / l 30 g / l 27.9 0.47 50 g / l 30 g / l 30.5 0.50

After ₃

21.6 g / l
21.6 g / l
21.6 g / l
21.6 g / l
21.6 g / l

After ₃

13.5 g / l
13.5 g / l
13.5 g / l
13.5 g / l
13.5 g / l
13.5 g / l

Molar ratio NaOCH ₃
^{+ 2} / H ₂ PO ₂ ")

2.7 g / l
2.7 g / l
2.7 g / l
2.7 g / l
2.7 g / l

μΐη / h

30.5 23.9 19.8 11.2 7.4

μπι / h

30.5 23.9 19.8 16.3 11.4 6.6

μηι / 1ι

31.7 24.1 20.3 11.4 8.9

Table 7 Table 10

Molar ratio NaOCH ₃ μιτι / h
(Ni ⁺ VH ₂ PO ₂ I.

Molar ratio
(Ni ⁺ VH ₂ PO ₂ ")

Sodium succinate μηι / Ιι

(Na ₂ C ₄ H ₄ O ₄ -OH ₂ O)

0.30
0.38
0.42
0.47
0.49

Og / 1
Og / 1
Og / 1
Og / 1
Og / 1

2.3 0.30 20.0 g / l 22.9-28.5 1.0 0.38 20.0 g / l 19.1-23.1 0.0 (some precipitation) 0.43 20.0 g / l 17.0-19.1 0.0 (some precipitation) IO ° '48 20.0 g / l 12.9-14.5 0.0 (some precipitation) 0.51 20.0 g / l 9.4-11.2

The precipitation rates obtained and also the stability of the bath are reversed proportional to the molar ratio of nickel to den Hypophosphite ions. This ratio should be between the values 0.35 and 0.29. The lower the molar Ratio, the greater the rate of precipitation As precipitation progresses however, this ratio becomes larger, so that the precipitation speed decreases. The reason for the increase in the molar ratio is that the consumption of hypophosphite ions is about three times as high is as large as that of the nickel ions.

It is therefore very important during the precipitation to supply hypophosphite ions and nickel ions to the solution as these have been consumed. Only these two materials need to be supplemented in the form of nickel chloride and sodium hypophosphite. Subsequent additions of alcoholates are not required during the life of the bath. This is also true for ammonium chloride, since chloride ions from nickel chloride and ammonium ions from Ammonium hydroxide.

Tables 8 to 10 serve for comparison with Tables 4 to 6. The results in Tables 4 to 6 were achieved with the help of baths, according to the invention from a concentrated solution of hypophosphite and the alcoholate and a less concentrated aqueous solution of the other ingredients were manufactured. The results of Tables 8 to 10 were obtained with baths (5.7 1 bath amount) to which the alcoholate was added to a finished solution of all the components of the bath.

Table 9 shows that an increase in the sodium metiiviSt-ivonzcntrauon UL / Cr ucn m ucr ι SuCuC υ contained value 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, is weakened or even prevented in a dilute system.
Comparison of Table 10 with Table 8 shows the enhancement effect obtained by adding sodium succinate to a bath made by adding sodium methylate to the final diluted solution. The following Table 11 shows the increase in the precipitation rate when the sodium succinate is placed in a bath which is advantageously prepared by combining a concentrated solution of the methylate and sodium hypophosphite and a dilute solution of the other ingredients. It is to be noted that the precipitation rates in Table 11 exceed those in Table 4 by a considerable amount. From this it can be concluded that, at the same time as the alcoholates, other substances that favor the precipitation process, such as succinates, can also be added to the bath, both agents promoting the reduction and deposition of nickel.

"5 Table 11

Table 8

Molar ratio
(Ni'Vh ₂ PO ₂ )

After ₁

'ira / h

Molar ratio
(Ni * VH ₂ PO:)

Sodium succinate
(Na ₂ C ₄ H ₄ O ₄ -OH ₂ O)

am / h

2.7 g / l 17.8 0.29 20.0 g / l 36.8-40.6 0.30 2.7 g / l 16.8 0.37 20.0 g / l 30.5-33.3 0.38 2.7 g / l 14.5 0.43 20.0 g / l 26.7-29.2 0.43 2.7 g / l 10.2 0.48 20.0 g / l 15.2-17.8 0.48 2.7 g / l 6.9 55 0.50 20.0 g / l 11.9-13.2 0.51

Table 9

Molar ratio
(Ni * ² / H ₂ PO ₂ ")

Well,

0.30 21.6 g / l 17.8 0.37 21.6 g / l 16.5 0.44 21.6 g / l 14.5 0.47 21.6 g / l 10.0 0.50 21.6 g / l 7.4

Tables 12 to 15 contain the precipitation rates for nickel with an addition of sodium propylate as well as sodium ethylate, lithium ethylate and barium ethylate The baths used were advantageously made up of two solutions different strength concentration produced The results of these tables compared to those of Table 7 support the fact that all alcoholates electroless deposition deposition of nickel at room temperature.

Table sodium propylate

(Ni ⁺ VH ₂ PO ₂ -)

0.30 0.31 0.45 0.47 0.50 0.30

Na (OC ₃ II ₈ )

4.15 g / l 4.15 g / l 4.15 g / l 4.15 g / l 4.15 g / l 0.0 g / l

| xm / h

17.8

17.0

15.2

10.4

5.6

2.5

Table 15
Barium ethylate

(Ni ⁺ VII ₂ PO ₂ ")

0.30
0.37
0.44
ίο 0.47
0.50
0.30

Ba (OC ₂ Hs) ₂

11.3 g / l
11.3 g / l
11.3 g / l
11.3 g / l
11.3 g / l
0.0 g / l

μπι / Ιι

20.6

20.0

18.0

10.2

6.8

2.5

VIl ₂ PO ₂ ")

0.30 0.37 0.44 0.48 0.50

Table sodium ethylate

VII ₂ PO ₂ -)

0.30 0.37 0.44 0.47 0.50 0.30

Na (OC ₃ II ₈ )

33.2 g / l 33.2 g / l 33.2 g / l 33.2 g / l 33.2 g / l

Na (OC ₂ II ₅ )

3.4 g / l 3.4 g / l 3.4 g / l 3.4 g / l 3.4 g / l 0.0 g / l

μηι / Ιι

17.5 16.5 15.0 10.6

5.1

[xm / h

20.6

19.5

18.3

10.2

6.8

2.5

Research suggests that alcoholates are the Deposition of metals similar to nickel, e.g. B. Lisen and cobalt, not at room temperature favor. When using nickel alloys, in which the proportion of nickel predominates, was however, found that here too the alcoholate has a desired effect on the precipitation process acts. Examples of this are shown in Tables 16 and 17 below.

Table 16

Ni ** + Co ^{+ +} / I ₂ PO ₂ 'NaOCH ₃

0.625
0.700
0.800

2.7 g / l
2.7 g / l
2.7 g / l

μΐτι / h

16.5

10.2

5.8

(Ni ⁺ VH ₂ PO ₂ ")

0.30 0.37 0.44 0.47 0.50

Na (OC ₂ H ₅ )

27.0 g / l 27.0 g / l 27.0 g / l 27.0 g / l 27.0 g / l

μΐη / h

20.3

19.3

17.8

9.9

6.3

Table 17

^{4 (1} Ni ⁺ * + Fe ⁺ -VH ₂ PO ₂ NaOCH ₃

0.625

0.700

0.800

2.7 g / l
2.7 g / l
2.7 g / l

μΐη / η

17.3 8.1 5.1

Table lithium ethylate

INi ⁺ VH ₂ PO ₂ ")

0.30 0.37 0.44 0.47 0.50 0.30

Li (OC ₂ H ₅ )

2.6 g / l 2.6 g / l 2.6 g / l 2.6 g / l 2.6 g / l 0.0 g / l

μπι / π

20.3

19.5

18.3

10.2

6.8

2.3

The preparation of the base for the deposition depends on the base used Material. With many materials, e.g. B. Glass, epoxy or paper, the surface should be clean and covered with a known sensitizers.

With regard to the electrical properties, it was found that all layers applied accordingly prepared documents were obtained by the described electroless deposition, conductive were, at least to the extent that the application of further coatings on electrolytic

bo ways was possible.

Claims (5)

Patent claims: 1. Process for producing a bath for the electroless deposition of nickel and nickel alloys With a content of nickel ions, alcoholate, hypophosphite, buffering agents and Ammonium hydroxide, characterized in that that to a first highly concentrated aqueous hypophosphite solution an alcoholate added and this with a second, weakly concentrated aqueous solution of the remaining ingredients is united. 2. The method according to claim 1, characterized in that an alcoholate from the group of sodium methylate, ethylate or propylate is added to the first solution. 3. The method according to claim 1, characterized in that the second solution for setting the pH of the bath to a value in the range of 7 to 9 a buffering agent and ammonium hydroxide can be added. 4. The method according to claims 1 and 3, characterized in that the second solution Additionally succinate ions can be added. 5. Use of a bath prepared according to claims 1 to 4 for the electroless deposition of Nickel and nickel alloys at room temperature and keeping the molar ratio constant the nickel to hypophosphite ions during the deposition to one value in particular between 0.35 and 0.29.