DE2439075A1 - CHEMICAL PLATING PROCESS - Google Patents

Description

The present invention relates to chemical reducing Plating or electroless plating with nickel or cobalt, particularly of surfaces of materials which normally are non-catalytic to the plating bath. Examples for such base materials are copper, chromium-containing corrosion-resistant steels, the iron alloy Kovar (with a Content of nickel and cobalt), silver, electrically conductive molybdenum manganese and tin oxide-antimony oxide compositions as well other materials.

The chemical deposition of nickel or cobalt on surfaces of the aforementioned type can be carried out in that one Bringing the surface into contact with an active metal (such as steel or aluminum) imposes a weak cathode potential on it or they are pretreated in an acidic palladium chloride solution. However, these methods have drawbacks, in particular

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when the metal surfaces are in the form of separate isolated areas, as is the case with printed circuit boards the case is.

With the help of steel shot, which is rolled over the surface or thrown in a drum, isolated surface areas can be activated / grounded. However, if the number of surface areas per sheet increases and the individual surfaces become smaller, larger quantities of shot are required and the proportion of effective coverage is reduced. It is not uncommon for 186 dm (20 ft) of shot to be used to ^{plate 1.86 dm 2} (0.2 ft ² ) of circuit patterns in 100 percent yield. Furthermore, with the help of steel racks or racks on a sheet metal track (eg a sheet copper track), the local catalytic activity necessary for this can be generated so that the plating can start on the track. Of course, the rake would normally not touch all of the surface areas to be plated on a control panel, which is why this method would not be effective for such a plating.

The aforementioned Surfaces also activated. However, this method requires a special design and application technology Care to ensure 100 percent activation and difficult to identify with disjointed patterns such as the ladders on switchboards. A palladium treatment generally activates the aforementioned surfaces, however, it also activates the ceramic or plastic surfaces on which metal is deposited; this degrades the quality while shortening the distance between the conductor paths.

Electroless or chemical reducing plating with nickel and cobalt is known and described in numerous patents as well described in other literature. The relevant patent literature includes the following patents, which are referred to here express reference is made to:

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U.S. Patent 3,096,182 describes the use of Alkali borohydrides as reducing agents in chemical plating baths. U.S. Patent 3,338,726 relates to the use of amine boranes as reducing agents. U.S. Patent No. 3,738,819 relates to the use of alkali cyanoborohydrides electroless plating. All of these patents are the property of the assignee of the present invention. Also the USA patent 3,295,999 discloses further details regarding these materials. In these patents, boron compounds used as a reducing agent, which leads to the incorporation of boron into the nickel or cobalt coating; see the United States patents 3,045,334 and 3,674,447 (coating also contains thallium); both of the aforementioned patents are the property rights of the applicant of the present invention.

The use of hypophosphite reducing agents is also known. A discussion of this technology can be found in "Modern Electroplating", ed.F.A. Lowenheim, pages 699 Ms 708, Published by John Wiley & Sons, Inc. (1968).

Dimethylamine borane and sodium hypophosphite solutions were added used aluminum surfaces after appropriate treatments and before chemical plating with nickel or cobalt in to keep the groomed condition; See U.S. Patent 3,667,991, however, aluminum is typically opposed to chemical Plating baths catalytically, and the aforementioned solutions are used to prevent the formation of oxides as possible and the To ensure the formation of a more even and more firmly adhering coating. As for this use purpose, dimethylamine borane and sodium hypophosphite considered equivalent; Aluminum can be treated with the aforementioned without treatment Electroless plating of solutions with nickel or cobalt.

According to one of its embodiments, the present invention provides a method for plating nickel or. cobalt by chemical reduction of a plating bath to the surface of an electrically conductive material, which is normally is non-catalytic to the plating bath except when it is treated according to the invention; this procedure exists

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in that prior to plating the surface with a pretreatment solution a reducing agent in the form of an alkali metal borohydride, alkali metal cyanoborohydride or amine borane in contact brings and then brings the surface into contact with the plating bath to the chemical reduction of nickel or to achieve its deposition on the surface.

When plating nickel on copper, especially in the form of Conductor patterns on control panels made of polymers or plastics or on ceramic bases, is the preferred way of working in that the surface is slightly etched by pretreatment with an oxidizing ammonium persulfate solution and then with an aqueous solution containing at least about 0.5 g / liter (preferably 1 to 20 g / liter) of dimethylamine borane a temperature of 25 to 65 ° C and a -p ^ value of 3.5 to 11.0 pretreated. The workpiece treated in this way becomes then electroless plating by conventional methods without any thorough wash down of the reducing agent from the workpiece. On the plastic control panel or there is no electroless plating on the ceramic base. Diethylamine borane is a viable alternative for dimethylamine borane.

Examples of electrically conductive materials which are non-catalytic generally opposite the plating baths, however, can be used in the invention are copper and its alloys with a copper content of at least 50 $, iron alloys having an iron content of at least about 50 io and a chromium content of 12 ^, an iron alloy containing about 29 io nickel, 17 $ cobalt and the remainder essentially iron, silver, sintered, fritted compositions of oxide powders and at least one metal from the group gold, silver, platinum and alloys with a content of at least 50 io of one or more of these metals, tin oxide with a small but effective amount of Antimonoxidzusammensetzungen to increase the electrical conductivity, and a layer consisting essentially of molybdenum and manganese oxide sintered powder composition. Some compositions of gold

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powder in frits, especially frits containing bismuth oxide, are non-catalytic compared to the plating baths. These as well as similar compositions of precious metals, such as platinum and silver alloys, are among the plating bases to which the invention is applicable. Palladium behaves towards the plating baths normally catalytically. The percentages here relate to the weight, unless it is is stated otherwise.

The preferred embodiments of the present invention are explained below.

The following description describes the plating according to the invention of test specimens made of different metals. Two types of nickel-boron plating systems are used.

A plating bath is used for the amine-borane plating system the following ingredients (in distilled water):

Nickel acetate 50 g / liter

Lactic acid 25 g / liter

Sodium citrate 25 g / liter

Thiodiglycolic acid 0.1 g / liter

Dimethylamine borane 2.5 g / liter

Wetting agent 0.1 g / liter

The bath works at a p "value set using ammonia of 6.5 and a temperature ranging from 55 to 65 ° C below Stir. Although various wetting agents can be used, an anionic surface active agent is used here, namely linear sodium dodecylbenzenesulfonate (marketed by Monsanto Chemical Co. as "Santomers S"). More suitable Amine boranes are described in the aforementioned U.S. Patents 3,338,726 and 3,295,999. Dimethylamine borane and diethylamine borane are both particularly useful.

A plating bath is used for the sodium borohydride plating systems

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from the following ingredients (in distilled water):

Nickel chloride hexahydrate 30 g / liter

Ethylenediamine βθ g / liter

Sodium hydroxide kO g / liter

Sodium borohydride 0.3 g / liter

Thallium sulfate 50 mg / liter

The bath works at a ρ value of 14 and a temperature

rl

of 92 C with stirring.

Metals plated include copper, type 3l6 corrosion resistant steel (17 % Cr, 12 JSNi, 2.5 % Mo), Kovar alloy (29 % Ni, 17 £ Co, 0.3 % Mn, balance Fe), silver in a glass frit in the form of an electrically conductive metallization, chemically deposited tin oxide with a content of 2 % antimony oxide (an effective proportion to make the former electrically conductive), and molybdenum-manganese oxide metallizations. The last three compositions are on a ceramic substrate. The other materials are either in the form of sheet metal strips or as a conductive pattern on a plastic switchboard. The molybdenum-manganese-oxide metallizations are produced by heating a frit of molybdenum and manganese powder in wet hydrogen. The manganese is oxidized and forms effective compounds (such as spinels) on ceramic substrates, e.g. B. alumina or beryllium oxide. This technology is known and is described in "Ceramic to Metal Bonding", Helgesson, Boston Technical Publishers, Inc. (1968). Silver can serve as a conductor on electrical panels in various forms. In an advantageous form, it is in the form of a powder in a glass frit. Such types of applications are described in U.S. Patents 2,819,170, 2,822,279 and 2,385,580. All of these patents are the property of the assignee of the present invention; they are expressly referred to here.

It has been found that upon brief immersion, the aforesaid

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Materials in dilute aqueous dimethylamine borane solutions and then rapid immersion in electroless nickel or Cobalt baths that use plating within a minute, while without the amine-borane treatment, no coating is formed he follows. The concentration of the amine borane in water can be range from as little as 1 g / liter to 20 g / liter. You can go with Immersion times of only 15 seconds work. The solution temperature is preferably 25 to 65 ° C. The p "value of the solution should be in the range from 3.5 to 11.0. Under certain circumstances, such as in the presence of lactic acid, a ρ ,, range is from 7 to 11 is preferable. Any material remaining on the surface after immersion in the dimethylamine borane should not be washed down by this.

The mechanism on which the invention is based has not been clarified; the invention is not intended to be limited by any particular theoretical explanation of the process. However, it is possible that the process according to the invention leads to weak adsorption of the amine borane in proportions effective for initiating the plating process, it can act on the creation of more active ones Place and prevention of their reoxidation based on or it may be based on other mechanisms.

The condition of the metal prior to treatment with the amine borane can affect the extent of initiation. The surface must be are in a state opposite to amine-borane adsorption is receptive. In the case of copper, prior etching with ammonium persulfate is beneficial.

Conductors plated in the manner described above show no activation of ceramic or plastic surfaces and almost no broadening of the conductive paths while having good adhesion and complete coverage.

It should be noted that other commonly used reducing agents, such as hydrazine, sodium hypophosphite and formaldehyde

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show no effect promoting the copper coating if one it uses instead of amine boranes. Treatment in an amine borane causes a certain amount of amine borane to be added to the de-energized bath transferred. This leads to a reduction in the need for refilling, which can be beneficial.

example 1

A glass epoxy board with a copper circuit pattern will last 30 seconds treated in 20 percent ammonium persulfate solution at room temperature. The copper is etched evenly and has a uniform pink color. The board is rinsed thoroughly so that no ammonium persulfate gets into the amine-borane solution is abducted. The panel is then treated for 2 minutes in a 0.2 percent dimethylamine borane solution at room temperature. The panel is then immersed in the amine-borane plating bath without rinsing. Nickel separates within 10 seconds

on the copper, and a complete coverage of about a hundred individual conductor paths is found. The panel is plated for H5 minutes to apply a 0.005 mm (0.2 mils) thick nickel-boron coating. Plating of the plastic or widening of the conductor paths do not occur. The adhesion of the coating is acceptable.

If other panels are processed in an analogous manner, but omitting the ammonium persulfate treatment step, no activation takes place; even treatment with HCl or HpSO ₂ does not result in a useful substitute. Plating does not occur if the amine-borane treatment step is omitted or if the panel is thoroughly rinsed after this step.

Example 2

Several copper sheets (2.5 * 1 χ 5.08 cm) are cleaned in trichlorethylene _{vapors, then for about 30 seconds in 20g e} weight percent ammonium persulphate in the cold (room temperature) or

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about 24 ° C), rinsed in distilled water for about 30 seconds, then immersed in a dimethylamineborane solution (1 g / liter; ρ value different) in the cold for about 2 minutes and finally in a fresh amine-borane plating bath without rinsing or delay immersed at 65 ^{° C.} The test results are compiled in the table below.

Tabel

p. value of

Dimethylamine borane solution

Results

5 6

7 8

10 11

no plating

complete coverage 15 seconds

complete coverage 15 seconds

complete coverage 15 seconds

complete coverage 15 seconds

complete coverage 15 seconds

complete coverage 15 seconds

complete coverage 15 seconds

complete coverage 15 seconds

within within within within

within within within within within within

The coatings are left to plating for about 5 minutes take place. The adhesion of the nickel-boron coating to the copper sheets is satisfactory in all cases.

A comparative sheet is made in the manner described above machined except that one involves immersion in a dimethylamine borane solution omits. There is no plating of the sheet

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in the amine-borane plating bath, although this even during the aforementioned successful attempts are left in the bathroom. Another comparative sheet is also given at the end of the aforementioned Edited attempts. It is not pretreated in dimethylamine borane solution and does not receive a cladding layer either.

This example shows that the activation of the copper is due to the dimethylamine borane pretreatment step. At the If this step is omitted, no coating will form on the nickel. It turns out that the activation level within a wide range ρ range (including acidic, neutral and alkaline conditions) can be carried out effectively.

Example 3

A glass epoxy switchboard (2.5 ² ^ x 10.2 cm) with copper conductor patterns is treated according to Example 1 with a dimethylamine borane solution (1 g / liter; ρ value 9). When immersed in the amine-borane plating bath, plating occurs within 30 seconds. It is found that the approximately 100 insulated copper conductor paths are coated within 15 minutes, while no coating takes place on the plastic. If the dimethylamine borane treatment step is dispensed with, there is no nickel plating on the copper.

This example shows that the copper can be activated by dimethylamine borane, even if it is in the form of numerous isolated ones Individual areas is available.

example H

Several copper sheets are processed by using a cleaning, Carries out the etching and activation stage and then immersing the panels in a fresh amine-borane plating bath at 60 ° C for 10 minutes. In the tables below, "APS" means ammonium persulfate, "DMAB" dimethylamine borane and "NHP" sodium hypophosphite.

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Tabel

Cleaning level

Äfczstufe Activation level Comments

acetone

Methanol

Methanol

H methanol

Methanol

MO percent HCl, cold, 2 min

20 percent APS, cold, 15 sec

20 percent APS, cold, 15 sec

20 percent APS, cold, 15 sec DMAB, 1 g / liter,
min rinsed,
cold

DMAB, 1 g / liter
2.5 min, cold
P _H = 8.8

no coating; 0.2 mg weight loss of the sheet

no coating; 0.2 mg weight loss of the sheet

no coating; 0.1 mg weight loss of the sheet

no coating; 0.2 mg weight loss of the sheet

coating formation; 31.9 mg weight gain of the sheet

This example again illustrates the importance of dimethylamine borane for activation and shows that minor procedural deviations, such as a thorough rinse after the Dlmethylaminboran treatment stage, can have the consequence that no activation takes place.

Example 5

In these tests, the duration of immersion in the dimethylamine borane solution varies.

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Tabel

Cleaning level

Methanol

Methanol

Methanol

Methanol

Methanol

Etching stage

20 percent APS, cold, 15 sec

20 percent APS ₃ cold, 15 sec

20 percent APS, cold, 15 sec

20 percent APS, cold, 15 sec

20 percent APS, cold, 15 sec

Activation level

DMAB (ig / liter), cold, 1.5 min

DMAB (1 g / liter), cold, 30 sec

DMAB (1 g / liter), cold, * J0 sec

DMAB (1 g / liter), cold, 15 sec

DMAB (1 g / liter), cold, 5 sec

Remarks

coating formation; 5 ^, 7 mg weight gain of the sheet

coating formation; 60.9 mg increase in weight of the sheet

coating formation; 67.3 mg weight gain of the sheet

Coating formation

Coating formation

This example shows that there is only a very short residence time in the dimethylamine borane activator solution for the activation of the copper is required.

Example 6

In these tests, the concentration of the dimethylamine borane in the activator solution until it is no longer sufficient to activate the copper.

Tabel

Cleaning level

Etching stage

Activation level

Remarks

Methanol

Methanol

20 percent APS, cold, 15 sec

20 percent APS, cold, 15 sec

DMAB (35 g / liter), cold, 1 min

DMAB (17.5 g / liter), cold, 1 min

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Plating within <5sec

Plating within <5 see

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Ports, the table

Cleaning etching level

Activation level

Remarks

Methanol
k methanol

Methanol

Methanol

Methanol

Methanol

Methanol

20 percent APS, cold, 15 seconds

20 percent AP5, cold, 15 seconds

20 percent APS, cold, 15 seconds

2 Op ro ζ ent i ge s APS, cold, 15 sea

20 percent APS, cold, 15 seconds

20 percent APS, cold, 15 seconds

20 percent APS, cold, 15 see DMAB (8.8 g / liter), cold, 1 min

DMAB (4, * J g / Liter), cold, 1 min

DMAB (2.2 g / liter), cold, 1 min

DMAB (I,! G / liter), cold, 1 min

DMAB (0.5 g / liter), cold, 1 min

DMAB (0.25 g / liter), cold, 1 min

DMAB (0.125 g / liter), cold, 1 min

Pla-ting within <5 see

Plating within <5 see

Plating within <5 see

Plating within <5 see

Plating within <5 see

one board is plated, another is not

no plating on two panels

This example shows that even dilute dimethylamine borane solutions can cause activation; the lower limit of the dimethylamine borane concentration is in the range from 0.25 to 0.5 g / liter.

Example 7

In this example, various conductive, but non-catalytic surfaces are degreased with trichlorethylene vapor and then 2 minutes in a 0.1 percent dimethylamine borane -Activator solution (1 g / liter) in the cold with a p ^ value of

ri

8.5 and then immersed in the amine-borane plating bath:

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a) Kovar seals

b) molybdenum-manganese thick film metallization
Alumina ceramic

c) Silver thick film metallization on glass

d) electrically conductive tin oxide on glass

e) corrosion-resistant steel of the type

In all cases, the nickel-boron plating of these objects in the bath takes place within 15 seconds. Without the dimethylamine borane activation step, no plating occurs on any of these items, even after 15 minutes in the bath. this
illustrates the wide range of applications of the dimethylamineborane activation stage.

Example 8

In this example, sodium borohydride is used as an experimental activator used for the sodium borohydride bath. Copper sheets are used as test substrates.

Cleaning etching level
step

Tabel

Activation level

1 methanol 2O percent
APS, cold, 1 min

2 methanol 20 percent NBH, 25.6 g / liter,

APS, cold, 1 min cold, 2 min

3 methanol 20 percent NBH, 12.3 g / liter,

APS, cold, 1 min cold, 2 min

4 methanol 20 percent NBH, 6.2 g / liter

APS, cold, 1 min cold, 2 min '

5 methanol 20% NBH, 3.1 g / liter,

APS, cold, 1 min cold, 2 min

-Ik-

Remarks

no plating within 10 minutes in a fresh sodium borohydride bath at 920c

Plating within 15 seconds

Plating within 15 seconds

Plating within 15 seconds

no plating within 10 min

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Forts, the table

Cleaning etching level

6 methanol 20 percent APS, cold, 1 min

Activation level

NBH, 5 min in the bathroom

Remarks

no plating within 10 min

This example shows that the pretreatment with sodium borohydride activation of the nickel-boron coating of copper surfaces can be achieved.

example

In this example, dimethylamine borane is used to activate the copper plating process in an acidic nickel-phosphorus plating bath. The nickel-phosphorus bath contains 30 g of nickel chloride per liter. 6 HpO, 50 g of sodium hydroxyacetate and 10 g of sodium hypophosphite. The p _H ~ value of the bath is 5, the temperature 90 ° C.

Tabel

Cleaning etching level

Activation level

Remarks

1 methanol 20 percent APS, cold, 1 min

2 methanol 20 percent NHP (10 g / liter)

APS, cold, 1 min

3 methanol 20 percent DMAB (1 g / liter)

APS, cold, 1 min

no plating within 60 minutes in the Ni / P bath

no plating

Plating within 5 seconds

This example shows that the nickel-phosphorus plating on copper by prior immersion in dimethylamine borane solutions can be activated.

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Comparison test

This test involves additional trials with sodium hypophosphite and hydrazine hydrate as a reducing agent instead of dimethylamine borane carried out in the activation stage.

Tabel

Cleaning Etching stage Activation level Remarks Plattie step 1 methanol 20 percent NHP (10 g / liter), no total APS, cold, 2 min, tion Plattie cold, 1 min P _H ⁴ »5 2 methanol 20 percent NHP (10 g / liter), no total APS, cold, 2 min, tion Plattie cold, 1 min Ph ^k > ⁵ 3 methanol 20 percent NHP (10 g / liter), no total APS, cold, 2 min, tion Plattie cold, 1 min Ph ⁷ - ° k methanol ' 20 percent NHP (10 g / liter), no total APS, cold, 2 min, tion Plattie cold, 1 min P _n 9.0 5 methanol 20 percent Hydrazine hydrate no total APS, (50 ml / liter), tion cold, 1 min cold, 2 min, Plattie P _H 10.8 6 methanol 20 percent Hydrazine hydrate no total APS, (50 ml / liter), tion cold, 1 min cold, 2 min, Plattie P _H 7.0 7 methanol 20 percent Hydrazine hydrate no total APS, (50 ml / liter), tion cold, 1 min cold, 2 min,
FTT ~ 3 ~

This test highlights the ineffectiveness of the others mentioned above Reducing agent within a reasonable p ^ range and despite a high concentration of solution.

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Comparison test 2

In this test, formaldehyde is used in the activation stage used by dirnethylamine borane as a reducing agent. As test surfaces copper sheets are used.

Tabel

Cleaning etching level

Activation level Comments

Methanol

Methanol

Methanol

20 percent APS, cold, 1 min

20 percent APS, cold, 1 min

20 percent APS, cold, 1 min

Formaldehyde, 50 ml / liter, cold, p _u 4.3 * 2 min ^M

Formaldehyde, 50 ml / liter, cold, p _TT 8.5, 2 min. ⁿ

Formaldehyde, 50 ml / liter, cold, p "10.5 2 mm

no Platbierung within minutes in fresh bath at 65 Sylek® 201 ⁰ C.

no plating

no plating

This test illustrates the ineffectiveness of formaldehyde as a reducing agent within a reasonable p ^ range and despite a high concentration of solution.

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Claims (10)

P 2k 39 075. 8 **** October 31, 1974 E.I. du Pont de Nemours -änd Corünany IC-6131 2439075 P a t e η t a η s ρ r 1. Method of plating nickel or cobalt by chemical Reduction of a plating bath to the surface of a electrically conductive material, which is normally non-catalytic to the plating bath, thereby gekennzei cn net that the surface before the Plating with a pretreatment solution of a reducing agent from the group of the alkali metal borohydrides, alkali metal cyanoborohydrides and amine boranes and then contacting the surface with the plating bath brings to achieve the chemical reduction of nickel or cobalt or their deposition on the surface. 2. The method according to claim 1, characterized in that the reducing agent Dimethylamineborane at a concentration of is at least about 0.5 g / liter. 3. A method for plating nickel according to claim 1, characterized characterized in that the plating bath includes water, a soluble nickel salt and a reducing agent containing boron. H. A method according to claim 1, characterized in that the plating bath contains water, a soluble nickel salt and a reducing agent containing phosphorus. 5. The method according to claim 2, characterized in that the dimethylamine borane in the pretreatment solution in one concentration is in the range of about 1 to 20 g / liter. 6. The method according to claim 1, characterized in that the electrically conductive material which is normally non-catalytic to the plating bath, the following Belongs to a group of substances (percentages relate to weight): - New page 18 - 509810/0995 IC-6131 Copper and its alloys with a copper content of at least 50 %; ■ Iron alloys with an iron content of at least 50 % and a chromium content of 12 % ·> an iron alloy, which contains about 29 % nickel, 17 % cobalt and the remainder essentially iron, Silver; a sintered, fritted composition of oxide powders and at least one metal from the group consisting of gold, silver, platinum and alloys with a content of at least 50 % of one or more of these metals; Tin oxide with a small amount of but effective for increasing the electrical conductivity of Antimony oxide compositions; and a sintered powder composition consisting essentially of molybdenum and manganese oxide. 7. The method according to claim 6, characterized in that the selected The material is copper and that this is brought into contact with a solution of an oxidizing agent before it is brought into contact with the pretreatment solution. 8. The method according to claim 7, characterized in that the oxidizing agent is ammonium persulfate. 9. The method according to claim 6, characterized in that the selected material is in the form of an electrically conductive Pattern is present on an electrically non-conductive substrate, with planar areas of the substrate between and adjacent to areas of the pattern are exposed to the surface and wherein contact with the pretreatment solution results in a plating of the selected metal with nickel in the plating bath, while the electrically non-conductive substrate, which is also in contact with the pretreatment solution - 19 - 50981 0/0995 IC-6131 is not plated with nickel in the plating bath. 10. Method of plating nickel by chemical reduction a plating bath on the surface of a copper pattern on an electrically non-conductive substrate, wherein the Pattern and the underground form a workpiece and with planar areas of the underground between and adjacent to surfaces of the copper pattern exposed on the surface through the following successive stages: 1) Immersing the workpiece in an aqueous solution of ammonium persulfate to oxidize the copper components the surface and subsequent rinsing; 2) immersing the workpiece in an aqueous solution of dimethylamine borane at a concentration of at least about 0.5 g / liter for treating the copper components on the surface to make them catalytically to make compared to the subsequently used plating bath, and 3) Immersing the workpiece in a plating bath containing nickel acetate and dimethylamine borane aqueous solution to deposit a nickel coating on the copper portions of the surface, the electrically non-conductive surface areas of the substrate remain unplated. - 20 - 509810/0995