DE2202777B2 - 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 with my content of 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. The case here may arise that with different coefficients of thermal expansion 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 rate, the unevenness of the precipitation, the insufficient use of the materials and other disadvantages that do not occur in the case of a deposition at increased temperature.

U.S. Patent No. 2,430,581 discloses, inter alia. Metallization baths with a vain content of NiekeläCetät, Nätfiumhypophosphit, hydrazine hydrate and methanol or Ethanol described. In these baths, which react alkaline, is likely to a certain extent as a result the equilibrium reaction sodium alcoholate is present. However, this patent does not indicate that alcoholate are added to the bath for the electroless deposition of nickel at room temperature must and how the production of this bath has to be done,

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 uniform at room temperature and with sufficient deposition rate and stable covers 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 thereby is characterized in that a first, hochkonzen trated aqueous hypophosphite solution an alcoholate added and this is combined with a second, weakly concentrated aqueous solution of the remaining ingredients.

Advantageous embodiments of the invention are shown in

laid down 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 _x HyOH. The individual alcoholates have different effects on the life of the bath, the rate of precipitation and the Utilization of the materials. All of the alcoholates mentioned delay the decomposition of the bath Room temperature, d. H. they increase its lifespan.

jo Every alcoholate has an associated nickel deposition rate that ensures a constant The concentration of the hypophosphite ions likewise remains constant during the deposition resulting change in the rate of precipitation

) S speed is therefore essentially due to the changes in the concentrations of the hypophosphite ions and the Attributed to nickel ions.

It was found that with increasing complexity of the alcoholate residue, the precipitation rate The methylate residue (OCH3) causes a higher speed than the ethylate residue (OC ₂ H ₅ ). Is z. B. Sodium methylate (NaOCH ₃ ) is placed in a certain bath, the nickel chloride as a source for the material to be deposited and reducing sodium Contains hypophosphite in a given concentration, the rate of precipitation is 25μπι / η at a certain temperature. If sodium ethylate (NaOCjH ₅ ) is used instead of sodium methylate, the speed is only about 19 to 20μηΊ / Ιι.

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

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

w) Modify way to obtain a specific rate of precipitation. The hypophosphite concentration and the molar ratio of nickel too Hypophosphite ions (Ni + VHjPOj ") seem to be the The speed of precipitation has the greatest influence

b5 send sizes to be.

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 added to the first, highly concentrated solution umi then combining both solutions and not adding the alcoholate to the entire solution in the last case the alcoholate seems to react with the larger amount of water and is broken down into inert components by hydrolysis, while its 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, a further improvement in the precipitation conditions can be achieved without you. This affects the way in which the alcoholate works.

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 — 3

NiCl ₂ · 6 H ₂ O NH ₄ CI

NaH ₂ PO ₂ · H ₂ O Na ₂ QH 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

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 18 ° C-50 ° C

While almost all methods of adding an alcoholate to an electroless plating bath, which contains hypophosphite ions, as beneficial for the Deposition process are to be seen, one obtains the: most favorable properties for the precipitation rate, if this is described in the following «! 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. The egg solution contains the other components of the entire bath; with the exception of the alcoholate (NaOCH,) 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, whereby the amount of the bath should be 5.71, 50 ml of water are sufficient for solution A. In your 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 generating hydride ions that have a strongly 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 more effective than baths where 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

is solution to be given to increase the effectiveness of the Bades, especially the rate of precipitation, to increase even further. The unexpected result here is that the sodium succinate does not in any way affect the mode of action of the alcoholate is affected. It has been found that the Sucdnat an improvement of the desired. Properties of the bath was achieved by about 100%.

The approximate value of the sodium hypophosphite (NaH ₂ PO ₂ - H ^^ concentration in the solution can be can be determined when the exact concentration of nickel ions is known

For the above examples, 30 g NiCl ₂ · 6 H ₂ O per liter and 45 g NaH ₂ 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 and a smaller sodium hypophosphite concentration of also 30 g per liter, the molar ratio of hypophosphite ions to nickel ions is about 23- This molar ratio can be almost be kept constant if appropriate additions to the solution during the deposition process take place. From the nickel ion concentration in g / I and the molar ratio, the concentration of Rate hypophosphite ions calculated in g / l.

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

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 is released either in the form of hydrogen gas, hydrogen ions or hydride ions. Because of the observed high precipitation rates, it can be assumed that hydride ions play an important role as intermediates, because these act as a strong reducing agent are known. Research has shown that the pH of the bath remains nearly constant over the life of the solution, indicating that hydrogen ions, which normally cause an increase in acidity, very little or not at all be generated.

bo The following tables show the rates of deposition of nickel from the examples 1 to 3 solutions described, whereby individual parameters have been changed. The amount of each bath is 5.71 unless otherwise indicated. the end

h ^r > Table 1 shows the rates of precipitation as a function of various alcoholate additives at given concentrations of nickel and hypophosphite salts.

Table 1

Alcoholate

μιη / h

NiCh 6H ₃ O conc. NaII ₃ PO ₃ conc.

T ° [C)

NaOCH ₃ NaOC ₂ H ₅ NaOC ₃ H ₈ Without alcoholate

19-20

15-18

0 (see fab. 7)

30 g / l 30 g / l 30 g / l 30 g / l

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

24
24
24
24

Table 2 shows the dependency of the lower table 3 b Impact speed from the time of precipitation, 15

the molar ratio of the nickel ions to the concentration of hypophosphite ions changing in the manner shown NiCl ₂ -6 H ₂ O. The individual precipitation rates were obtained from measurements on six successively coated samples, which were immersed for increasingly longer time intervals in a bath in which the materials consumed during the six coating processes were not replaced. The total amount of the bath here was 1.91; cds alcoholate, sodium methylate was used 25

Concentration NaH ₂ PO ₂

μιη / 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 / i 30 g / l 30 g / l 30 g / l

21.6 21.6 21.6

22.9 24.1 25.4

Table 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

Precipitation time μιη / h molar ratio
(Ni ⁺² / H ₂ PO ₂ ~) J5 Traticnen exhibited. In the examples
no alcoholate was added. After ₃ of table 7 Table 4 0.5 h 17.0 0.417 1.5 h 16.7 0.410 21.6 g / l 3.0 h IU 0.424 Molar ratio 21.6 g / l μπι / h 5.0 h 7.1 0.436 41) (Ni ⁺² / H ₂ PO ₂ ~) 21.6 g / l 7.5 h 5.1 0.451 21.6 g / l ! 0.5 h 3.3 0.471 0.30 21.6 g / l 30.5 0.38 23.9 45 0.42 19.8 The following table 3a contains the amount of precipitation 0.47 After ₃ 11.2 speeds in a bath with a total 0.49 7.4 of 3.81 with a constant concentration of the nickel salt Table 5 and changing concentration of hypophosphite.
Table 3b shows the rate of precipitation 50 13.5 g / l under the same conditions, but with constant hypo- Molar ratio
(Ni ⁺² m, por) 13.5 g / l μπι / h phosphite concentration and changing nickel salt 13.5 g / l concentration. As an alcoholate was also here 13.5 g / l Methylate chosen 0.30 13.5 g / l 30.5 V) 0.38 13.5 g / l 23.9 0.42 19.8 0, <4 16.3 Table 3a 0.47 After ₃ 11.4 Concentration Concentration μιη / h b0 0.49 6.6 of NaH ₂ PO ₂ of NiCl ₂ · 6 H ₂ O Table 6 2.7 g / l 5 g / l 30 g / l 3.8 Molar ratio 2.7 g / l μπι / h 10 g / l 30 g / l 8.9 bi (Ni ⁺² / H ₅ POf) 2.7 g / l 15 g / l 30 g / l 16.5 2.7 g / l 20 g / l 30 g / l 21.6 0.30 2.7 g / l 31.7 30 g / l 30 g / l 25.4 0.38 24.1 40 g / l 30 g / l 27.9 0.43 20.3 50 g / l 30 g / l 30.5 0.47 11.4 0.50 8.9

Table 7 Table 10

Molar ratio NaOCH ₃ μΐη / η (Ni ⁺² ZH ₂ PO ₇ ")

Molar ratio
(Ni ⁺ VH ₂ PO ₂ ")

Sodium succinate μηι / h

(Na ₂ C ₄ II ₄ O ₄ -OH ₂ O)

0.30
0.38
0.42
0.47
0.4 «

0 g / l 2.3 0.30

0 g / l 1.0 0.38

0 g / l 0.0 (some precipitation) 0.43

Og / I 0.0 (some precipitation) _l0 0.48

Og / I 0.0 (some precipitation) 0.51

20.0 g / l
20.0 g / l
20.0 g / l
20.0 g / l
20.0 g / l

22.9-28.5 19.1-23.1 17.0-19.1 12.9-14.5 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 hypophosphite ions. This ratio should be between the values 035 and 0.29. The lower the molar ratio, the greater the rate of precipitation However, as the precipitation progresses, this ratio becomes larger, so that the Precipitation rate decreases. The reason for the increase in the molar ratio is that the consumption of the hypophosphite ions is about three times that of the nickel ions.

It is therefore very important to have hypophosphite ions and nickel ions during the precipitation of the solution to be added to the extent that these have been consumed. It just need these two materials in the form of Nickel chloride and sodium hypophosphite are supplements. Subsequent additions of alcoholates are not required during the life of the bath. This also applies to ammonium chloride, as chloride ions be supplied by nickel chloride and ammonium ions by 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 the hypophosphite and the alcoholate and a weaker one concentrated aqueous solution of the other ingredients was prepared a The results of Tables 8 up to 10 were achieved with baths (5.7 l bath amount) in which the alcoholate becomes a finished solution all components of the bath was added.

Table 8

Molar ratio
(Ni "VH ₂ PO?)

Well.,

in / h

U.3U
0 ^ 8
0.43
0.48
0.51

Table 9

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

17.8 16.8 14.5 10.2 6.9

Molar ratio
(NrVH ₂ PO ₂ ")

NaOCH;

Ltn / b

0.30
0.37
0.44
0.47
0.50

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

17.8 16.5 14.5 10.0

7.4 Table 9 shows that an increase in the sodium methylate concentration the value contained in Table 8 has little influence on the rate of precipitation Table 8 shows significantly lower precipitation rates than the table 4 on. From this it can be concluded that the reaction of the methylate with the reducing agent, which favors the precipitation process at room temperature, weakened in a dilute system or even prevented.

The comparison of Table 10 with Table 8 shows the amplification effect created by adding sodium succinate to a bath created by the feed of sodium methylate to the final dilute solution is obtained. From the following VaDeIIe ti is the increase in the rate of precipitation can be seen when the sodium succinate is placed in a bath, which is more advantageous Way by combining a concentrated solution of methylate and sodium hypophosphite and a dilute solution of the further ingredients is prepared. It should be noted that the Precipitation rates in Table 11 those in Table 4 by a considerable amount Exceed value. From this it can be concluded that at the same time as the alcoholates there are also other, the Precipitation-promoting substances such as succinates can be added to the bath, with both Agents promote the reduction and deposition of nickel.

Tabel

Molar ratio
(NrVH ₂ PO ₂ ")

Sodium succinate jxm / h

(Na ₂ C ₄ H ₄ O ₄ 6 H ₃ O)

0.29 0.37 0.43 0.48 55 0.50 20.0 g / l
20.0 g / l
20.0 g / l
20.0 g / l
20.0 g / l

36.8-40.6 30.5-33.3 26.7-29.2 15.2-17.8 11.9-13.2

Tables 12 to 15 contain the precipitation rates for nickel with an addition of sodium propylate as well as sodium ethylate, lithium ethylate and Bariumäthytet 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.

9 22nd 02 777 10 Table 15 Barium ethylate Table 12 (Ni ⁺² / H ₂ PO ₂ ~) Ba (OC ₂ Hs) ₂ μm / h Sodium propylate Na (OC ₃ H ₈ ) 0.30 11.3 g / l 20.6 1 (Ni ⁺² / H ₂ PO ₂ ~) 4.15 g / l μπι / h 5 0.37 11.3 g / l 20.0 I. 0.30 4.15 g / l 17.8 0.44 11.3 g / l 18.0 f 0.31 4.15 g / l 17.0 0.47 11.3 g / l 10.2 § 0.45 4.15 g / l 15.2 0.50 11.3 g / l 6.8 I. 0.47 4.15 g / l 10.4 10 0.30 0.0 g / l 2.5 0.50 0.0 g / l 5.6 Research suggests that alcoholates are the 0.30 Na (OC ₃ II ₈ ) 2.5 Separation of metals similar to nickel, (Ni ^{+ 2} / H ₂ PO ₂ ) (in / h ΙΊ z. B. iron and cobalt, not at room temperature 33.2 g / l favor. When using nickel alloys, 0.30 33.2 g / l 17.5 in which the proportion of nickel ice predominates, was 0.37 33.2 g / i 16.5 However, it was found that here too the alcoholate in ö, 44 33.2 g / l i5, ö -ΊΙ desired way on the precipitation process 0.48 33.2 g / l 10.6 acts. Examples of this are shown in the following tables 0.50 5.1 16 and 17. Table 13 2Ί Table 16 Sodium ethylate Na (OC ₂ H ₅ ) Ni ^{f +} + Co ⁺ VH ₂ PO ₂ NaOCH ₃ μm / h (Ni ^{+ 2} ZM ₂ PO ₂ ) at / h i (> 0.625 2.7 g / l 16.5 3.4 g / l 0.700 2.7 g / L 10.2 0.30 3.4 g / l 20.6 0.800 2.7 g / L 5.8 0.37 3.4 g / l 19.5 0.44 3.4 g / l 18.3 0.47 3.4 g / l 10.2 ) ") Table 17 0.50 0.0 g / l 6.8 0.30 2.5 Ni ^{+ +} + Fe ^{+ +} / H ₂ PO ₂ NaOCH ₁ μΐη / h Na (OC ₂ H ₅ ) 40 0.625 2.7 g / 1 17.3 (Ni ⁺ -VlI ₂ PO ₂ ) at / h 0.700 2.7 g / l 8.1 27.0 g / l 0.800 2.7 g / L 5.1 0.30 27.0 g / l 20.3 0.37 27.0 g / l 19.3 4 ^r > Preparing the pad for deposition 0.44 27.0 g / l 17.8 depends on what is used as a base 0.47 27.0 g / l 9.9 Material. With many materials, ζ. Β. Glass, epoxy or 0.50 6.3 50 Paper, the surface should be clean and covered with a Table 14 known sensitizers have been pretreated. Lithium ethylate In terms of electrical properties, | Li (OC ₂ H ₅ ) found that all layers corresponding to | (Ni ⁺² / H ₂ PO ₂ ~) μπι / h prepared documents through the described | 55 electroless deposition obtained, conductive 1 2.6 g / l were, at least to the extent that the k 0.30 2.6 g / l 20.3 Application of further coatings on electrolytic 0.37 2.6 g / l 19.5 Ways was possible. ■; ' 0.44 2.6 g / l 18.3 0.47 2.6 g / l 10.2 60 0.50 0.0 g / l 6.8 0.30 2.3

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 agent and ammonium hydroxide, characterized in that an alcoholate is added to a first highly concentrated aqueous hypophosphite solution added and this is combined with a second, weakly concentrated aqueous solution of the remaining ingredients. 2. The method according to claim 1, characterized in that an alcoholate from the first solution the group of sodium methylate, ethylate or Propylate is added. 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 while keeping the molar ratio of the nickel to hypophosphite ions constant the deposition to a value in particular between 0.35 and 0.29.