DE2040930B2 - Process for electroless copper deposition and bath for carrying out the process - Google Patents

Description

The invention relates to electroless copper deposition on electrically non-conductive objects, especially those made of plastic. The two material components are then used in the finished product separately adhering favorable properties combined, resulting in technical and aesthetic advantages for their use for numerous purposes results.

Thus, the low weight and the slight deformation, which lead to the widespread use of plastics have helped to better exploit them when using mechanical properties and the attractive decorative effects of metal coatings can be combined.

The copper-plating of an electrically non-conductive plastic object initially requires the chemical Deposition of a conductive metal layer on the plastic surface. Then you can if necessary further ivfetallschichten from metal salt solutions electrolytically on the electrolessly deposited layer to be deposited.

When plastics are prepared for chemical copper plating, the plastic becomes one

ίο Sequence of treatments prior to electroless metal deposition subject. The plastic surface becomes microporosity, usually through chemical etching awarded. The plastic prepared in this way is then used for electroless metal deposition in a known manner

z. B. catalyzed with a noble metal.

Also are compositions for chemical copper plating baths known. They consist e.g. B. from a soluble cupric salt, e.g. B. Copper Sulphate; a complexing agent for the Curpiion, z. B. Rochelle Salt; an alkali hydroxide to adjust the pH; a carbonate radical as a buffer and a reducing agent for the Cupriion, e.g. B. formaldehyde. The mechanism by which objects catalysed with Surfaces, e.g. B. a plastic with catalytically active palladium metal on its surface, are automatically copper-plated in such solutions is in the literature, e.g. in US-PS 28 74 072, described.

Baths for the electroless copper deposition of the above However, the type described are inherently unstable and decompose quickly. In part, this is due to that catalytic nature of the copper deposition reaction. Many substances, including copper, Steel, nickel, iron, palladium, gold, silver, and even dust particles, catalyze these solutions. These Particles penetrate the solution, and if they are numerous they can cause a precipitate and Start decomposition.

Up to now it was necessary, for example, to cover plastic-lined containers for electroless plating baths use as metal containers, e.g. B. stainless steel, with the loss of valuable chemicals would be metallized. Even in plastic-lined containers, scratches in the liner set in Decomposition in progress as the scratches form pits in which were generated during the metallization reaction Hydrogen is concentrated.

In order to avoid this premature decomposition of copper plating baths, inhibitors or

so-called catalyst "poisons" added, e.g. B. compounds with a carbonate residue, e.g. B. sodium carbonate, Sodium bicarbonate, cupricarbonate. Although these stabilizers Increase the life of the baths considerably, as they form for the metallization bath themselves poisons and can therefore only be used in very small quantities. But there even these smallest Amounts which are essential for stabilization and which are poisons, slow down the rate of metal deposition. Larger amounts would, though

fau make the baths extremely stable, but the separation bring to a standstill on a surface catalyzed by a noble metal, which is why such stable baths are unusable. In practice one has therefore become accustomed to a compromise between

! •> ^r > to close stability and deposition rate. For similar reasons, higher bath temperatures, while having the advantage of increasing the rate of deposition, have generally not been achieved

used because such temperatures also favor decomposition.

The object of the invention is therefore to create a method for electroless copper plating of objects using a highly stabilized, currentless bath with simultaneous compliance high copper deposition rates.

The invention also includes the bath used.

The method according to the invention is characterized in that an object with a copper deposition catalyzing noble metal on its surface in a first, electroless bath and after Deposition of a thin copper coating immersed in a second, electroless copper plating bath is, this second bath one to prevent the copper deposition on a catalytic the surfaces of the object bearing an effective precious metal have a sufficient concentration of inhibitors, however, they do not deposit copper on the surfaces bearing the first copper coating prevented. This over-stabilized second bath results in a surface catalyzed with noble metal no more metal deposition, but on the first coating, which does not affect the rate of metallization a significantly higher stabilizer concentration allows due to the high stabilizer concentration However, the metallization bath can now last much longer without the risk of decomposition be used.

A two-stage electroless nickel plating is known, with the pre-nickel plating being the main nickel plating is intended to facilitate, without the stability of the baths used playing a role. Rather be the conventional baths used.

It has also been proposed as a catalyst for chemical copper deposition in addition to the known precious metals in the same way as this copper for a subsequent single-stage Use copper plating. The bath used for this contains cyanide in order to obtain a ductility of the To achieve copper plating, which has a stabilizing effect at the same time. The cyanide concentration had to be but to be kept within the usual limits, since the same baths are also used for the copper-plating of with Noble metals catalyzed objects were used, which poisoned at higher cyanide concentration and thus became ineffective.

In the detailed description below, the bath in which the first thin copper plating is deposited, referred to as the "Streif" bath, while the bath, in which additional copper is deposited, is called the "copper plating" bath.

Electroless deposition of Copper. In the grinding bath, the deposition of copper by the catalytically active noble metal takes place the non-conductive surface started; in the copper plating bath the metal deposition is through catalyzes the thin metal film applied in the spray bath.

The concentration of inhibitor in the copper plating bath is such that, if the object with a catalytically active noble metal would be introduced directly on its surface without first having to use the sanding bath pass through, no copper would be deposited on the object. The inhibitor concentration in the The copper plating bath ensures an extremely stable bath because it is used to prevent copper deposition A sufficient inhibitor concentration on a catalyzed surface also causes decomposition as a result of the Prevents the presence of other metallic impurities

The grinding bath has the usual composition for electroless copper deposition; z. B. it contains the following compounds in aqueous solution within the ranges given below:

Components

Molar concentration

Soluble cupris salt
Complexing agent
Reducing agent
pH adjuster

0.02-0.15
0.03-0.75
0.05-1.50

sufficient to adjust a pH value of 12-14

Since only a thin copper film is deposited in the spray bath, the bath volume can be so small that that the solution can be replenished in an economical manner or discarded if decomposition occurs can be. For this reason, the Streifbad can be used without any inhibitor or only with a small amount Inhibitor operated.

As the most effective inhibitors for electroless copper plating the water-soluble cyanides have turned out to be. These include alkali metal cyanides, e.g. B. potassium cyanide and sodium cyanide, complex metal cyanides and water-soluble nitriles, i.e. containing a -CN group organic compounds. Baths for electroless copper deposition falling within the scope of the invention contain compounds within the ranges given below:

Components

Molar concentration

Soluble cupris salt
Complexing agent
Reducing agent
Alkali hydroxide (up to
a pH of
12 to 14)
Cyanide inhibitor
water

0.02-0.15
0.03-0.75
0.05-1.50

0.10-2.00
0.0015-0.24
up to 1 liter

It should be noted that the concentrations of complexing agent and reducing agent in a relationship to the concentration of cupric ions in solution and that the upper limit of the Reducing agent concentration is arbitrary and depends on economic considerations, as even very high concentrations do not adversely affect the performance of the solution.

The method according to the invention also enables the bath to be operated at an elevated temperature, without any noticeable problems of decomposition. In this way one achieves the advantages of a high metallization speed due to operation at high temperatures, without valuable Chemicals are lost and production problems arise.

The method and solutions according to the invention are described below with reference to FIG the electroless copper plating of acrylonitrile / butadiene / styrene plastic, hereinafter referred to as ABS plastic

referred to, described in more detail. The preparation and activation of the plastic does not form as such Part of the invention.

A molding made of ABS plastic is cleaned with an organic chemical solvent if necessary pre-etched and then in a chemical etching bath, e.g. B. a mixture of chromic acid and Sulfuric acid, etched. After cleaning the etched item, including rinsing with a alkaline cleaning agent, the object is sensitized in a stannous chloride-hydrochloric acid bath and then in a bath of a noble metal salt, e.g. B. palladium chloride, activated to on the surface of the Plastic to give a catalytically active noble metal. After rinsing to remove Excess palladium from the surface of the object is dipped into the grit, which forms part of the method according to the invention.

The grinding bath can be a common solution for electroless copper deposition with the following composition:

Components

concentration

Rochelle salt

caustic soda

Copper sulfate

sodium

formaldehyde

water

34 g / liter
12 g / liter

7 g / liter

6 g / liter
25 ecm / liter
up to 1 liter

The grinding bath is typically kept at room temperature. The palladium metal on his Surface-bearing plastic object is about 30 seconds to about 3 minutes in the Streifbad immersed and then removed. This immersion time is sufficient for the deposition of a thin copper film the entire surface of the object. In addition to the preparation of the object, the sandbath is also used for electroless metal deposition in a copper plating bath also as a collector for the Main amount of impurities that would otherwise be introduced directly into the bath.

After being removed from the grit, the plastic object, which has a thin copper deposit, becomes the object brought directly into the bath for electroless copper deposition.

To increase the deposition rate, the bath is, as described above, on a elevated constant temperature, preferably maintained between about 32 and 60 ° C. An example of one The composition of the copper plating bath is as follows:

example 1

Conversion of the sodium bicarbonate in the solution to Sodium carbonate required.

The plastic article is held in the bath for 3 to 6 minutes. So much will happen during this time further copper deposited so that a subsequent electrolytic metal plating is possible. To Removal from the bath, the object is rinsed and watered and, if an ecktroplating is required, fed to the electroplating process.

ABS moldings were prepared and activated as described above and then placed in a copper strip bath maintained at room temperature and having a composition as in the previous example. The objects bearing a thin copper coating were then immersed in a bath having the composition of Example 1. The bath was kept at 40 ° C. The total immersion time in the two baths was about 5 minutes. The adhesive strength of the electrolessly deposited copper coatings was about 10 kg, determined by a conventional peel test. The bath was operated for 2 to 3 months with no noticeable degradation and with a minimum of rejuvenating chemicals.

Since the inhibitor has a certain tendency to reduce the metallization rate with increasing concentration shows, the inhibitor concentration is expediently kept at a value that corresponds to Suppression of copper deposition on surfaces other than those with a thin copper coating provided of the plastic object is sufficient. However, if higher inhibitor concentrations are used to be safe Achieving a stabilized solution is required, the rate of copper deposition can be substantial be kept constant by taking the cupric ion concentration together with the concentrations increased in reducing agents and caustic alkali. The following are examples of balanced amounts of inhibitor-reductant caustic soda in aqueous solutions illustrate the practice of the invention:

Example 2

Components

Molar concentration

Copper sulfate 0.036 Rochelle salt 0.138 Sodium bicarbonate 0.11 formaldehyde 0.11 Free sodium hydroxide 0.125 Potassium cyanide 0.006 water up to 1 liter

Components

Molars
concentration

Copper sulfate Example 3 0.02 Rochelle salt 0.096 50 sodium bicarbonate 0.11 formaldehyde 0.067 Potassium cyanide 0.0C 16 Free sodium hydroxide 0.1 Temperature 38 ° C
55

Components

Molars
concentration

The free sodium hydroxide listed above is that amount which is necessary for the formation of the chelate and for the Copper sulfate

Rociielles salt

Sodium bicarbonate

formaldehyde

Potassium cyanide

Free sodium hydroxide

Temperature 45 ° C

0.084

0.188

0.11

0.40

0.10

0.30

Example 4

Components

Molars
Concentralization

Copper sulfate 0.11 Rochelle salt 0.41 formaldehyde 0, S0 Potassium cyanide 0.24 Free sodium hydroxide 0.625 Temperature 49 ° C

Plastic articles prepared, sensitized and activated as described above were after immersion in a streak bath, immersed in baths with compositions each having the Corresponding to the above examples and were kept at the temperature indicated in each case. the Plastic objects copper-plated in this way all had firmly adhering electroless deposits Copper coatings. If you dipped objects with a catalytically active precious metal on their surfaces into the plating baths of Examples 1-4 without them

To send first through the Streifbad, so it was on your Objects no copper deposited.

The invention thus provides an extremely stable, insensitive composition that is suitable for electroless Copper plating can be used for long periods of time without any noticeable change in composition is. This solution can also be used in containers made of: stainless steel with heaters and filters; stainless steel can be used. As a result of the

ίο stability of the solution will be roughness in the deposited coating is avoided and the bath for electroless metal deposition can be used at elevated temperatures temperatures can be operated with a simultaneous improvement in production speeds.

The method and the baths according to the invention can also be used for objects which, although the Letters after are conductive, but offer conditions or properties that allow the creation of a satisfactory plating by conventional electrolytic plating methods sufficient current prevent density. This applies e.g. B. on steel objects with dimples and depressions. The expression "Non-conductive" is intended to include such conditions or properties.

Claims (7)

Patent claims: 1. Process for electroless copper deposition using a pre-metallization bath the actual metallization, characterized in that an object with a the copper deposition catalyzing noble metal on its surface in a first, electroless working bath and after deposition of a thin copper coating in a second, currentless working copper plating bath is immersed, this second bath one to prevent the Copper deposition on a catalytically active noble metal bearing surfaces of the object Has sufficient inhibitor concentration, which, however, reduces the copper deposition on the first Surfaces bearing crop overlay are not prevented 2. The method according to claim 1, characterized in that a plastic object is used will. 3. The method according to claim 1, characterized in that a water-soluble cyanide is used as the inhibitor is used. 4. The method according to claim 1, characterized in that the second copper plating bath on im is kept substantially constant temperature between 32 and 60 ° C. 5. The method according to claim 3, characterized in that the cyanide concentration between Is 0.0015 and 0.24 moles per liter of solution. 6. The method according to claim 3, characterized in that the second bath is a 0.02 to 0.15 mol soluble cupric salt, 0.03 to 0.75 mol of a complexing agent for cupric ions, at least 0.05 mol Reducing agent, an alkali hydroxide up to the adjustment of a pH value between 12 to 14 and 0.0015 up to 0.24 moles of water-soluble cyanide-containing bath is used. 7. Aqueous bath for electroless copper deposition according to claims 1 to 6, containing Cupric ions, a complexing agent for cupric ions, a reducing agent and a pH adjuster, characterized in that the solution nor contains an inhibitor in such a concentration as that used to prevent copper deposition on surfaces carrying a catalytically active noble metal, but not for prevention copper deposition on a thin copper coating is sufficient.