Title:
METHOD AND COMPOSITION FOR DIRECT METALLIZATION OF NON-CONDUCTIVE SUBSTRATES
Kind Code:
A1


Abstract:
The present invention relates to a method for the metallization of an electrically non-conductive substrate using a thiosulfate conductor which employs a thiosulfate-containing conductor solution further comprising an alkali metal ion selected from the group consisting of lithium, potassium, rubidium, caesium, and combinations thereof.



Inventors:
Konigshofen, Andreas (Leverkusen, DE)
Kesseler, Corinna (Oberhausen, DE)
Application Number:
11/672670
Publication Date:
05/22/2008
Filing Date:
02/08/2007
Assignee:
Enthone Inc. (West Haven, CT, US)
Primary Class:
Other Classes:
106/1.18
International Classes:
C25D5/54; C23C30/00
View Patent Images:
Related US Applications:



Primary Examiner:
WONG, EDNA
Attorney, Agent or Firm:
STINSON LLP (ST LOUIS, MO, US)
Claims:
What is claimed is:

1. A method for metallizing an electrically non-conductive substrate comprising the steps: (a) contacting the electrically non-conductive substrate with a metal containing activator solution to yield an activated substrate; (b) contacting the activated substrate with a conductor solution comprising (i) a source of thiosulfate and (ii) a source of alkali metal ion selected from the group consisting of lithium, potassium, rubidium, caesium, and combinations thereof, to yield an electrically conductive substrate; (c) contacting the electrically conductive substrate with an electrolytic plating solution comprising a source of deposition metal ions; and (d) applying an external source of electrons to reduce the deposition metal ions and deposit a metal or metal alloy layer on the electrically conductive substrate.

2. The method of claim 1 wherein the alkali metal ion source is added to the conductor solution as a salt comprising an anion selected from the group consisting of fluoride, chloride, bromide, nitrate, sulfate, and combinations thereof.

3. The method of claim 1 wherein the source of thiosulfate is selected from the group consisting of sodium thiosulfate, sodium thiosulfate pentahydrate, silver thiosulfate, ammonium thiosulfate, barium thiosulfate, magnesium thiosulfate hexahydrate, potassium thiosulfate, potassium thiosulfate hydrate, palladium(II) potassium thiosulfate monohydrate, and 2-benzyl-2-imidazoline thiosulfate, and combinations thereof.

4. The method of claim 1 wherein the source of thiosulfate is selected from the group consisting of sodium thiosulfate, silver thiosulfate, and a combination thereof.

5. The method of claim 1 wherein the conductor solution further comprises a completing agent selected from the group consisting of tartaric acid, salts of tartaric acid, ethylenediamine tetraacetic acid (EDTA), salts of ethylenediamine tetraacetic acid, citric acid, salts of citric acid, and combinations thereof.

6. The method of claim 1 wherein the deposition metal ions are copper ions or nickel ions.

7. The method of claim 1 wherein the alkali metal ion is selected from the group consisting of lithium, potassium, and combinations thereof.

8. The method of claim 7 wherein: the metal ions are selected from the group consisting of Ni and Cu; the conductor solution has a pH between about 11.5 and about 13.5 and comprises the source of thiosulfate in a concentration between about 0.001 mol/L and about 0.5 mol/L, and the source of alkali metal ion selected from the group consisting of lithium, potassium, and combinations thereof in a concentration between about 0.01 mol/L and about 5 mol/L.

9. The method of claim 8 wherein the conductor solution comprises the source of thiosulfate in a concentration between about 0.01 mol/L and about 0.02 mol/L, and the source of alkali metal ion is selected from the group consisting of lithium, potassium, and combinations thereof in a concentration between about 0.2 mol/L and about 1 mol/L.

10. The method of claim 9 wherein the conductor solutions comprises: about 0.013 mol/L sodium thiosulfate as the source of thiosulfate; about 0.6 mol/L lithium chloride as the source of alkali metal ion; and a complexing agent in a concentration between about 0.01 and about 5 mol/L.

11. A method for metallizing an electrically non-conductive substrate comprising the steps: (a) contacting the electrically non-conductive substrate with a metal-containing activator solution comprising between about 100 and about 300 mg/L Pd, between about 5 and about 20 g/L Sn, and between about 100 and about 350 ml/L concentrated HCl to yield an activated substrate; (b) contacting the activated substrate with a conductor solution having a pH between about 11.5 and about 13.5 and comprising (i) a source of thiosulfate in a concentration between about 0.001 mol/L and about 0.5 mol/L, and (ii) a source of lithium ion in a concentration between about 0.01 mol/L and about 5 mol/L, to yield an electrically conductive substrate; (c) contacting the electrically conductive substrate with an electrolytic plating solution comprising a source of deposition metal ions selected from the group consisting of Cu and Ni; and (d) applying an external source of electrons to reduce the deposition metal ions and deposit a metal or metal alloy layer on the electrically conductive substrate.

12. A conductor solution for rendering the surface of an electrically non-conductive substrate electrically conductive for the galvanic deposition of a metal layer, a metal alloy layer, or a metal compound layer on the electrically non-conductive substrate, the conductor solution comprising: (a) a source of thiosulfate ion; and (b) an alkali metal ion selected from the group consisting of lithium, potassium, rubidium, caesium, and combinations thereof.

13. The conductor solution of claim 12 wherein the alkali metal ion is added to the conductor solution as a salt comprising an anion selected from the group consisting of fluoride, chloride, bromide, nitrate, sulfate, and combinations thereof.

14. The conductor solution of claim 12 wherein the alkali metal ion is added at a concentration between about 0.01 mol/L and about 5 mol/L.

15. The conductor solution of claim 12 wherein the source of thiosulfate is selected from the group consisting of sodium thiosulfate, sodium thiosulfate pentahydrate, silver thiosulfate, ammonium thiosulfate, barium thiosulfate, magnesium thiosulfate hexahydrate, potassium thiosulfate, potassium thiosulfate hydrate, palladium(II) potassium thiosulfate monohydrate, and 2-benzyl-2-imidazoline thiosulfate, and combinations thereof.

16. The conductor solution of claim 12 wherein the source of thiosulfate is selected from the group consisting of sodium thiosulfate, silver thiosulfate, and a combination thereof.

17. The conductor solution of claim 12 wherein the source of thiosulfate is added at a concentration between about 0.001 mol/L and about 0.5 mol/L.

18. The conductor solution of claim 12 further comprising a complexing agent selected from the group consisting of tartaric acid, salts of tartaric acid, ethylenediamine tetraacetic acid (EDTA), salts of ethylenediamine tetraacetic acid, citric acid, salts of citric acid, and combinations thereof.

19. The conductor solution of claim 12 comprising the source of thiosulfate in a concentration between about 0.01 mol/L and about 0.02 mol/L, and the source of alkali metal ion is selected from the group consisting of lithium, potassium, and combinations thereof in a concentration between about 0.2 mol/L and about 1 mol/L.

20. The conductor solution of claim 12 comprising: about 0.013 mol/L sodium thiosulfate as the source of thiosulfate; about 0.6 mol/L lithium chloride as the source of alkali metal ion; and a complexing agent selected from the group consisting of tartaric acid, salts of tartaric acid, ethylenediamine tetraacetic acid (EDTA), salts of ethylenediamine tetraacetic acid, citric acid, salts of citric acid, and combinations thereof in a concentration between about 0.01 and about 5 mol/L.

Description:

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from DE patent application number 10 2006 005 684.1 filed Feb. 8, 2006.

FIELD OF THE INVENTION

The present invention relates to a method for the direct metallization of electrically non-conductive substrates. Furthermore, the invention relates to a treatment solution for generating a first conductive layer on electrically non-conductive substrates for the deposition of a metal or alloy layer.

BACKGROUND OF THE INVENTION

Different methods are known for the direct metallization of electrically non-conductive substrates, such as printed circuit boards or structural parts made of plastic.

For example, German Patent DE3323476 discloses a method for the galvanic metallization of articles having at least one non-metallic surface to be at least partially metallized. Herein, in a first treatment step, metallic seeds or particles are applied to the surface to be metallized. In a subsequent process step, the pre-treated substrates are introduced into an electrolytic plating bath that contains additional components selected from among methylene blue, methyl violet, alkylphenoxypolyethoxyethanols, non-ionic fluorocarbons, polyoxyethylene compounds, block copolymers of polyoxyethylene and polyoxypropylene, allylthiocarbamides, tetramethylthiuramide sulfide, 2,4,6-(2-pyridyl)-s-triazine, a nitrogen comprising heterocyclic compound, triphenylmethane colors, thiocarbamides or thiourea derivatives, saccharine, and o-benzaldehydesulphonic acid derivatives.

Furthermore, European Patent Application EP0538006 discloses a method of metallizing electrically non-conductive substrates in which, in a first treatment step, the substrates to be metallized are contacted with a palladium-tin activator, wherein palladium seeds settle on the surface of the substrate. After activation, a post-activation occurs in a metal salt solution that comprises a metal that can be reduced by a metal of the activator solution, a complexing agent as well, and an alkali metal ion. The thus prepared substrates can afterwards be acidically metallized.

U.S. Pat. No. 5,238,550 discloses a method for the metallization of electrically non-conductive substrates in which a precious metal colloid that is adsorbed on the surface of the substrate is converted into corresponding chemically stable metal sulphides which serve as base for a direct metallization. Herein, in a first treatment step, the substrates are covered with precious metal colloids, preferably palladium tin colloids. In a subsequent treatment step, the precious metal colloids present on the surface of the non-conductive substrate are converted into corresponding metal sulphides by means of a basic thiosulphate solution.

U.S. Pat. No. 4,895,739 discloses a comparable method in which the precious metal colloids that have been deposited on the surface in a first treatment step are also converted into suitable metal chalcogenes.

In all of the above-described methods, the substrates to be metallized are conditioned in a suitable manner before metallization. Usually, such a conditioning is carried out by means of suitable etching baths, such as for example dichromate-sulfuric acid etch. Depending on the nature of the related metallization method, the chosen etching conditions have a clear influence on the final metallization result.

The treatment conditions during the activation or post-activation of the non-conductive substrates, such as, for example, the chosen temperature or eventual movements of the substrate in the treatment solution during the contacting further influence the metallization result.

Therefore, the metallization methods known from the state of the art can often only be used in limited application fields, either because of the chosen process parameters, the selected etching bath, or the plastic to be metallized.

SUMMARY OF THE INVENTION

It is thus the object of the present invention to provide a method for the metallization of an electrically non-conductive substrate that has a wide application range and can be employed with a wide variety of etching solutions.

BRIEF DESCRIPTION OF THE FIGURE

FIG. 1 is a photograph of the test specimens depicted in Table 4.

Briefly, therefore, the present invention is directed to a method for metallizing an electrically non-conductive substrate comprising contacting the electrically non-conductive substrate with a metal containing activator solution to yield an activated substrate; contacting the activated substrate with a conductor solution comprising (i) a source of thiosulfate and (ii) a source of alkali metal ion selected from the group consisting of lithium, potassium, rubidium, caesium, and combinations thereof, to yield an electrically conductive substrate; contacting the electrically conductive substrate with an electrolytic plating solution comprising a source of deposition metal ions; and applying an external source of electrons to reduce the deposition metal ions and deposit a metal or metal alloy layer on the electrically conductive substrate.

In another aspect the invention is directed to a method for metallizing an electrically non-conductive substrate comprising contacting the electrically non-conductive substrate with a metal-containing activator solution comprising between about 100 and about 300 mg/L Pd, between about 5 and about 20 g/L Sn, and between about 100 and about 350 ml/L concentrated HCl to yield an activated substrate; contacting the activated substrate with a conductor solution having a pH between about 11.5 and about 13.5 and comprising (i) a source of thiosulfate in a concentration between about 0.001 mol/L and about 0.5 mol/L, and (ii) a source of lithium ion in a concentration between about 0.01 mol/L and about 5 mol/L, to yield an electrically conductive substrate; contacting the electrically conductive substrate with an electrolytic plating solution comprising a source of deposition metal ions selected from the group consisting of Cu and Ni; and applying an external source of electrons to reduce the deposition metal ions and deposit a metal or metal alloy layer on the electrically conductive substrate.

The invention is also directed to a conductor solution for rendering the surface of an electrically non-conductive substrate electrically conductive for the galvanic deposition of a metal layer, a metal alloy layer, or a metal compound layer on the electrically non-conductive substrate, the conductor solution comprising a source of thiosulfate ion; and an alkali metal ion selected from the group consisting of lithium, potassium, rubidium, caesium, and combinations thereof.

Other objects and features will be in part apparent and in part pointed out hereinafter.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

This invention claims priority from German application DE 10 2006 005 681.1 filed Feb. 8, 2006, the entire disclosure of which is incorporated by reference.

The present invention is directed to a method for the metallization of an electrically non-conductive substrate. The metallization method comprises the following process steps:

(a) contacting the electrically non-conductive substrate with a metal-containing activator solution to thereby yield an activated substrate;

(b) contacting the activated substrate with a treatment solution comprising a thiosulfate to thereby yield an electrically conductive substrate; and

(c) contacting the electrically conductive substrate with an electrolytic plating solution comprising a source of deposition metal ions; and

(d) applying an external source of electrons to thereby reduce the deposition metal ions and deposit a metal or metal alloy layer on the electrically conductive substrate.

The treatment solution, more particularly called a conductor solution, comprising a thiosulfate further comprises an alkali metal ion selected from the group consisting of lithium, potassium, rubidium, caesium, and combinations thereof. Surprisingly it has been found in tests carried out by the applicant that the addition of an alkali metal ion selected from the group consisting of lithium, potassium, rubidium, caesium, and combinations thereof to the thiosulfate containing conductor solution leads to clearly better metallization results.

For example, it has been found that the addition of the above mentioned alkali metal ions to the thiosulfate containing conductor solution leads to good metallization results, even in case of unfavorable pre-treatment conditions, such as for instance different etching baths for the conditioning of the plastic surface to be metallized. Furthermore, the deposition results are also good within wide temperature ranges if the thiosulfate containing conductor solution according to the invention is used. The thiosulfate containing conductor solution of the present invention may be used for both copper and nickel metallization of electrically non-conductive substrates.

Furthermore, it has been found as very advantageous that the use of the thiosulfate containing conductor solution leads to a high independence of the metallization methods with respect to mechanical influences, such as for example the flow of the electrolytic solutions against the substrate in the metallization bath or during activation.

Advantageously, the alkali metal ion selected from the group consisting of lithium, potassium, rubidium, caesium, and combinations thereof may be added to the thiosulfate containing conductor solutions as a salt comprising an anion selected from the group consisting of fluoride, chloride, bromide, nitrate, sulfate, and combinations thereof. Adding the alkali metal ion added as one of these salts minimally changes, if at all, solution pH.

The thiosulfate ion may be added to the thiosulfate containing conductor solutions from a wide variety of thiosulfate sources. Exemplary sources of thiosulfate ion include sodium thiosulfate, sodium thiosulfate pentahydrate, silver thiosulfate, ammonium thiosulfate, barium thiosulfate, magnesium thiosulfate hexahydrate, potassium thiosulfate, potassium thiosulfate hydrate, palladium(II) potassium thiosulfate monohydrate, and 2-benzyl-2-imidazoline thiosulfate. Additionally, compounds such as for example polythionic acids which release thiosulfate under alkaline conditions can serve as thiosulfate source. Preferred thiosulfate ion sources are sodium thiosulfate and silver thiosulfate.

The source of thiosulfate ion may be added to the thiosulfate-containing conductor solution at a concentration between about 0.001 mol/L and about 0.5 mol/L, preferably between about 0.01 mol/L and about 0.02 mol/L. In one embodiment, sodium thiosulfate may be added at a concentration of about 0.013 mol/L (about 2.0 g/L sodium thiosulfate or about 3.2 g/L sodium thiosulfate pentahydrate).

The thiosulfate-containing conductor solution is preferably adjusted to an alkaline pH, such as a pH greater than about 9.0, preferably between about 11.5 and about 13.5. Alkali metal hydroxides or alkaline earth metal hydroxides can be used for basic pH adjustment. Preferably, an alkali metal hydroxide, such as sodium hydroxide or potassium hydroxide, is used as the pH adjuster.

The thiosulfate-containing conductor solution may additionally comprise a complexing agent. Suitable complexing agents are tartaric acid, salts of tartaric acid, ethylenediamine tetraacetic acid (EDTA), salts of ethylenediamine tetraacetic acid, citric acid, salts of citric acid, combinations thereof, or other suitable complexing agents for the colloid metal that is introduced in the activation step. Preferably, the complexing agent is a tartaric acid salt, such as for example potassium sodium tartrate.

The complexing agent may be added to the thiosulfate containing conductor solution at a concentration between about 0.01 mol/L and about 5 mol/L, preferably between about 0.1 mol/L and about 0.5 mol/L. In one embodiment, the complexing agent is potassium sodium tartrate added at a concentration of about 0.25 mol/L (about 52.5 g/L potassium sodium tartrate or about 70.5 g/L potassium sodium tartrate tetrahydrate).

As stated above, the thiosulfate-containing solution additionally comprises an alkali metal ion selected from the group consisting of lithium, potassium, rubidium, caesium, and combinations thereof. Preferably, the alkali metal salt is lithium or potassium. The sources of these ions are typically a salt comprising an anion selected from the group consisting of fluoride, chloride, bromide, nitrate, sulfate, and combinations thereof. The source of the alkali metal ion may be added at a concentration between about 0.01 mol/L and about 5 mol/L, preferably between about 0.2 mol/L and about 1.0 mol/L. In one embodiment, the source of alkali metal ion is lithium chloride added at a concentration of about 0.6 mol/L (about 25 g/L).

The process for metallizing an electrically non-conductive substrate employing the thiosulfate containing conductor solution of the present invention comprises the following steps in one preferred embodiment:

Etch;

Rinse;

Palladium/Tin metal activation;

Rinse;

Treatment with thiosulfate containing solution;

Rinse; and

Electrolytic Metallization.

In the above method, rinsing may be accomplished by immersing or spraying distilled and/or deionized water.

Substrates that may be used in the process of the present invention may comprise any electrically non-conductive material, such as a plastic material. Exemplary plastic materials includes acrylonitrile butadiene styrene (ABS), a blend of ABS and polycarbonate (ABS/PC), polypropylene (PP), polyetheretherketones (PEEK), polyamide (PA), acrylonitrile styrene acrylate (ASA), and styrene acrylonitrile (SAN). Preferred plastics for metallization are acrylonitrile butadiene styrene (ABS) and a blend of ABS and polycarbonate (ABS/PC).

In the first etching step, the plastic surface, such as the ABS surface, is conditioned with an etching solution. The etching solution may comprise a combination of etchants. Exemplary etchants include chromium(III) ion at a concentration between about 0.1 g/L to about 20.0 g/L, sulfuric acid at a concentration between about 300 g/L and about 500 g/L, and chromic acid at a concentration between about 300 g/L and about 500 g/L. Preferably, the etching solution further comprises between about 100 mg/L and about 300 mg/L palladium ions. In one embodiment, the etching solution is a dichromate-sulfuric acid etching solution comprising chromium trioxide at a concentration of about 350 g/L, sulfuric acid at a concentration of about 400 g/L, chromium(III) ion at a concentration of about 5 g/L, and palladium ion at a concentration of about 20 mg/L. In one embodiment, the etching solution is chromic acid etch solution comprising chromium trioxide at a concentration between about 1000 g/L and about 1100 g/L, chromium(III) ion at a concentration between about 50 g/L and about 60 g/L, and palladium ion at a concentration of about 20 mg/L. The plastic substrate may be etched by exposing the substrate to the etching solution, typically by immersing, between 1 and 20 minutes, such as between 5 and 20 minutes, at a temperature between about 50° C. and about 80° C.

The etched plastic surfaces may be rinsed and then activated by a standard palladium tin activator solution. The palladium tin activator solution may comprise palladium at a concentration between about 100 mg/L and about 300 mg/L, tin(II) ion at a concentration between about 5 g/L and about 20 g/L, and hydrochloric acid (concentrated) at a concentration between about 100 mL/L and about 350 mL/L. In one embodiment, the palladium tin activator solution comprises 300 mL/L HCl (37%), 15 g/L Sn(II) ion, and 250 mg/L palladium. The palladium tin activator solution typically comprises colloids comprising a palladium core and a tin(II) chloride shell. The etched plastic substrate may be activated by exposing the etched plastic substrate to the palladium tin activator solution for between 2 and 5 minutes at a temperature between about 30° C. and about 50° C. with agitation at a speed between about 300 revolutions/minute and about 700 revolutions/minute.

After activation and further rinsing, the activated plastic substrates may be treated with the thiosulfate containing conductor solution comprising a source of thiosulfate, an alkali metal ion, a complexing agent, and a pH adjuster. Without being bound by a particular theory, it is thought that the thiosulfate ion in the conductor solution reduces surface resistance of the treated plastic substrate by reacting with the palladium-tin(II) chloride colloids that adsorbed onto the surface of the activated substrate. The thiosulfate is thought to react with tin(II) ions to form conductive tin(II) sulfide. Moreover, it is thought that the thiosulfate ion removes tin(II) chloride from the surface of the palladium-tin(II) chloride colloids, thereby exposing conductive palladium metal. The conductor solution further comprises alkali metal ions, which have been shown to further increase the conductivity of the treated plastic surface.

The activated plastic substrate may be treated in the conductor solution by exposing the substrate to the solution for between about 2 and about 10 minutes at a temperature between about 40° C. and about 70° C. Exposure is typically by immersing the substrate in the conductor solution. Treatment of the activated substrate with the conductive solution in this manner yields an electrically conductive substrate.

The plastic surfaces prepared according to the above-described method are then metallized in either a standard acid copper electrolyte or in a standard nickel electrolyte. Exemplary copper metallization chemistries include CUPROSTAR® 1541, CUPROSTAR® 1525, CUPROSTAR® 1526, CUPROSTAR® 1560, and CUPROSTAR® LP-1, all available from Enthone Inc. (West Haven, Conn.). Exemplary nickel metallization chemistries include ELPELYT® MONOLITH POP, ELPELYT® ELOX, and LECTRO-NIC, all available from Enthone Inc. (West Haven, Conn.).

The electrically conductive plastic substrate may be metallized by immersion in any of the above-described electrolytic plating solutions. Metallization occurs by an electrolytic plating process in which an external source of electrons is applied to the electrically conductive substrate to reduce copper ions or nickel ions to copper metal or nickel metal on the surface of the substrate. Electrolytic plating of copper may occur for three minutes at 3 Ampere. Electrolytic plating of nickel for one minute at 2 Volts and for two minutes at 3 Volts. Under these conditions, the treated plastic surfaces may be completely plated with metal after three minutes.

Having described the invention in detail, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims.

EXAMPLES

The following non-limiting examples are provided to further illustrate the present invention.

Example 1

Three ABS workpieces were etched for 10 minutes at 66° C. in a dichromate-sulfuric acid etching solution comprising chromium trioxide (350 g/L), sulfuric acid (400 g/L), chromium(III) ion (15 g/L), and palladium ion (20 g/L). The workpieces were rinsed and activated for 4 minutes at 40° C. in a Pd/Sn activator comprising concentrated hydrochloric acid (300 mL/L), tin (II) ion (15 g/L), and palladium (250 mg/L). The workpieces were rinsed again.

Three different conductor solutions were prepared. The compositions of the three conductor solutions are shown in the first column of Table 1. Each workpiece was post-treated for 4 minutes at 55° C. in a conductor solution. The ABS workpieces were thoroughly rinsed with demineralised water and dried. The surface resistance of each workpiece was measured. The resistances of each workpiece after this initial treatment are shown in the second column of Table 1.

After the initial resistance measurement, sodium thiosulfate (0.013 mol/L) was added to the conductor solutions. The workpieces were exposed to the conductor solutions containing sodium thiosulfate and dried. The surface resistance of each workpiece was again measured. The resistances of each workpiece after this initial treatment are shown in the third column of Table 1.

Finally, lithium chloride (0.6 mol/L) was added to all three conductor solutions and the above-described tests were repeated. The surface resistances (fourth column of Table 1) were reduced by more than 50% in all three workpieces by adding lithium chloride to the conductor solution.

TABLE 1
Surface Resistance on ABS Workpieces
After adding Na
ConductorInitialthiosulfateAfter adding
SolutionResistance(0.13 mol/L)LiCl (0.6 mol/L)
NaOH (1 mol/L)95 kΩ2.5 kΩ1.2 kΩ
Tartaric acid
(0.25 mol/L)
NaOH (1 mol/L)77 kΩ1.8 kΩ0.7 kΩ
K—Na-tartrate
(0.25 mol/L)
NaOH (1 mol/L)69 kΩ2.2 kΩ0.9 kΩ
K—Na-tartrate
(0.25 mol/L)
[Pd(NH3)4]Cl2
(0.2 mmol/L)

Example 2

In a DOE (design of experiment), conductor compositions of varying compositions were tested to determine which composition has the widest field of application. For this, several ABS workpieces were slipped on identical holders, etched, activated, treated in the various conductor solutions, and metallized. Four different conductor solutions were prepared, the composition of which are shown in Table 2. Moreover, two different etching baths were tested, two different motional intensities in the activator solution were tested, and two different metallization electrolytic plating solutions were tested. The conditions of these variables are shown in Table 3 and respectively called A or B.

TABLE 2
Composition of the Conductor Solutions
Treatment Parameters: 4 minutes at 55° C.
Solution 1Solution 2Solution 3Solution 4
NaOH   1 mol/L1mol/L   1 mol/L   1 mol/L
K—Na-tartrate 0.25 mol/L0.25mol/L 0.25 mol/L 0.25 mol/L
LiCl 0.6 mol/L0.6mol/L 0.6 mol/L 0.6 mol/L
CuSO4 5H2O0.016 mol/L
K iodide0.012 mol/L
Na thiosulfate0.013mol/L0.013 mol/L
[Pd(NH3)4]Cl20.2mmol/L

TABLE 3
Description of the DOE variables
DOE variables
AB
Metallization5 liters commercial5 liters commercial
blasted nickelblasted copper
sulfamate electrolyteelectrolyte
(ELPELYT ® Monolith)(CUPROSTAR ® 1525) at
at 45° C. with 225° C. with 2 anodes:
anodes:metallization 3
metallization 1minutes at 3 Ampere
minute at 2 Volt,
then 2 minutes at 3
Volt
Etching bathChromic acid etchDichromate sulphuric
comprising CrO3 (1100 g/L),acid etch comprising
Cr3+ (55 g/L),CrO3 (350 g/L), H2SO4
and palladium 20 mg/L):(400 g/L), Cr3+ (15 g/L),
16 minutes atand palladium
67° C.(20 mg/L): 8 minutes
at 67° C.
ActivatorHCl (37%, 300 mL/L),HCl (37%, 300 mL/L),
solutionSn(II) (15 g/L),Sn(II) (15 g/L),
palladium (250 mg/L):palladium (250 mg/L):
4 minutes at 40° C. and4 minutes at 40° C. and
agitation speed ofagitation speed of
700300
revolutions/minuterevolutions/minute

According to DOE, 8 experiments were carried out in all 4 conductor solutions, wherein the order was randomly chosen. The substrates were metallized by electrolytic plating for 3 minutes. The results are shown in Table 4. In Table 4, the first letter indicates the type of metallization bath, the second letter indicates the type of etching bath, and the third letter indicates the agitation speed of the activator. For example, combination ABA means: nickel-plated, etched in chromic sulphuric acid, activated at 700 r/min.

TABLE 4
% covering (front and rear face) after 3 minutes metallization
AAAAABABAABBBAABABBBABBB
Solution 16060985080100100100
Solution 28090100907530100100
Solution 31009710065100100100100
Solution 45085100201005100100

From Table 4, it is apparent that conductor solution 3 (containing both thiosulfate and lithium ion) gave the best metallization result for nearly all combinations. Solution 3 was bested by solution 2 (also containing both thiosulfate and lithium ion) only with respect to combination ABB. FIG. 1 is a photograph of the test specimens depicted in Table 4, with the specimens in the same arrangement as in the table.

When introducing elements of the present invention or the preferred embodiments(s) thereof, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes could be made in the above compositions and processes without departing from the scope of the invention, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.