CH646200A5 - METHOD FOR DEFLECTIVE METAL DEPOSITION AT INCREASED DEPOSITION SPEED. - Google Patents

Description

The aim of the present invention is to enable a method for increasing the deposition rate of electroless metal deposition baths.

Another object of the invention is to describe processes and bath compositions which have a higher deposition rate and which simultaneously produce firmly adhering metal deposits.

Yet another object of the invention is to describe methods and bath compositions for electroless copper deposition that operate at speeds that were previously thought to be unreachable.

According to the present inventions, it was found that firmly adhering copper layers can be produced from baths which operate without current at a high deposition rate if these baths have a pH of more than 10 and contain a compound which brings about a depolarization of the anodic or the cathodic or both partial reactions, and if these baths work with a pH value which is above the pH value at which the greatest deposition rate is achieved without the depolarizing additive mentioned, so that a copper layer can be electrolessly deposited faster at the same pH value and temperature than it would be possible without this additive at the same pH and temperature.

In general, the depolarizing agent should achieve at least 20% and up to 100% depolarization, or between 35% and 90% of the polarization of the anodic or cathodic or both reactions. In other words, the depolarizer should cause an acceleration of at least 20% up to 100% or between 35% and 90% of the cathodic or anodic reaction or both.

The increase in the rate of deposition of firmly adhering copper deposits from de-energized copper baths varies over a wide range and is largely dependent on the bath composition and the desired quality of the metal deposit. In general and surprisingly, the increase is

Deposition rate according to the present invention is at least 300% and depends on the other bath components. However, deposition rates have also been observed which are 1000% or even 5000% higher than previously known. Such deposition rates were completely unexpected and surprising.

Similarly, the deposition rate also varies when using the method and bath compositions according to the invention, if these baths are used in continuous operation and to achieve firmly adhering metal deposits. The baths according to the invention have a deposition rate at room temperature of more than 7 x 10-3 mm and generally more than 9 x 10 -3 mm, or even that between 9 and 25 x 10 "3 mm per hour, and even higher At higher temperatures, the deposition rate even increases to 70 x 10-3 mm per hour and above, and the achievement of such deposition rates was completely unexpected and surprising, especially since such deposition rates were also achieved in continuous operation, for example over 8 hours kept constant by adding the used components, these baths can be used successfully for several weeks in continuous operation It must be noted that the high deposition rates of these baths means that continuous operation is usually not necessary.

Electroless copper deposition according to the method according to the invention has a number of advantages, including in particular shorter deposition times and thus increased production capacity. In addition, the baths according to the invention cause significantly lower costs in terms of equipment, investment and energy in comparison to previously conventional baths. In contrast to most other production processes, the process according to the invention is very suitable, in particular for automatic operation, with short dwell times.

The copper bath liquid according to the invention contains, as usual, copper ions, a complexing agent for copper ions, a reducing agent and an agent for adjusting the pH and is characterized in that the copper bath liquid contains at least one additive in addition to other constituents which relates to the cathodic half reaction or the anodic half-reaction, or both, has a depolarizing effect and that the pH of the bath liquid is adjusted to exceed that which corresponds to the maximum deposition rate of the bath liquid without this additive, which causes the build-up of the adherent copper layer with a deposition rate that is higher is that which occurs when using the liquid without this additive at the same pH and temperature.

The process according to the invention is preferably carried out as follows:

A. Use the copper bath solution with at least one of the depolarizing additives and

B. the pH of the solution according to A is set to a value which is above the maximum of the deposition rate of the same solution without addition of dopolarization, so that a higher deposition rate is achieved at the same pH value and the same temperature. The depolarizing agent, which also acts as an accelerator, is generally selected from an organic compound with a delocalized rc bond, such as a) heterocyclic aromatic nitrogen and sulfur compounds;

5

10th

15

20th

25th

30th

35

40

45

50

55

60

o5

646 200

4th

b) non-aromatic nitrogen compounds with at least one delocalized 7t bond;

c) aromatic amines and

. d) mixtures of the compounds mentioned.

The terms “depolarizing agent” and “accelerator” are interchangeable in the description of the present invention.

The most suitable depolarizing agents according to the invention have a lone pair of electrons on the nitrogen atom adjacent to a% bond.

Examples to be mentioned here are heterocyclic nitrogen compounds according to A (a) from the group of the pyridines, for example pyridine, cyanopyridine, chloropyridine, vinylpyridine, aminopyridine, 2-pyrazolo- (4,3-c) -pyridine, 3-v-triazolo- ( 4,5-b) pyridine, 2,2'-dipyridyl, picolines and the like; Pyradizine; Pyrimidines, e.g. m-diazine, 2-hydroxypyrimidine, 2-oxy-6-aminopyrimidine (cytosine) and the like; Pyrazine; Triazine; Tetrazine; Indoles, e.g. indole, tryptamine, tryptophan, 2,3-indolinedione, indoline, and the like; Purines, for example 6-aminopurine (adenine); Phenanthrolines, e.g. o-phenanthroline; Quinolines, e.g. B. 8-hydroxyquinoline; Azoles, e.g. Pyrrole, dibenzopyrrole, pyrroline and the like; Diazoles, e.g. 1,2-pyrazole, 1,3-imi-dazole and the like; Triazoles, e.g. Pyrrodiazole, benzotriazole, diphenyltriazole, isotriazole and the like; Tetrazoles and benzodiazoles, e.g. Indazole, benzimidazole and the like. Also useful in the context of the present invention are mercapto derivatives and thio derivatives of the aforementioned compounds, such as, for example, mercaptopyridines, mercaptopyrimidines, thiazoles, thiazoline, thiazolidine, mercaptothiazoles, imidazole ethiols, mercaptoimidazole, mercapturines, mercaptoquinazolinones, thiodiazoles, tothiodiazole, mercaptotriazole, mercaptoquinoline and the like.

An example of group A b) are urea derivatives and guanidines and guanidine derivatives.

For group A c), for example, p-nitro-benzylamine, anilines, phenylenediamines and mixtures of these may be mentioned.

The depolarizers or accelerators mentioned are generally used in very low concentrations, which are between 0.0001. and 2.5 g / 1, usually between 0.0005 and 1.5 g / 1, and preferably in the range from 0.001 to 0.5 g / 1. The actual concentration of the accelerator depends on the compounds selected as depolarizing agents and the bath composition within the specified limits.

In a further embodiment of the invention, other metal ions can also be present in the bath in addition to the copper ions, preferably metals or group VIII; Of these, cobalt and / or nickel are particularly suitable. These metals can be added in the form of their salts, such as sulfates or halides, and the addition of a complexer for these metal ions may be desirable. A tartrate is particularly suitable for this. As a general rule, the concentration of these metal ions should be from 0.005 to 30% of the copper ion concentration.

The copper ions are usually added to the bath in the form of their soluble salt. The choice of salt is essentially determined by economic considerations. Preferably copper sulfate is usually used, but also copper halides, e.g. Copper chloride or copper bromide, copper nitrate and acetate, and other organic and inorganic copper salts are also useful. Although water-soluble copper salts are generally preferred, copper oxide or hydroxide can also be used; these are then dissolved in the bath solution by the complexing agent (s) located therein.

Possible complexing agents for copper ions are those generally used in electroless plating baths, including but not limited to. Rochelle salt, the mono-, di-, tri- and tetrasodium salts of ethylenediaminetetraacetic acid, hereinafter referred to as “EDTA” for short, diethylenediaminepentaacetic acid, nitrile-acetic acid and their alkali salts, gluconic acid, gluconates, tri-ethanolamine, diethylaminoethanol and gluconone as well as modified ethylenediamine acetates, e.g. N-hydroxyethyl ethylenediamine triacetate, phosphonates, e.g. Ethylene diamine tetrate (methylene phosphoric acid) and hexamethylene diamine tetra (methylene phosphoric acid).

Alkanolamines are preferably used as complexing agents, for example N, N, N ', N'-tetrakis (2-hydroxypropyl) ethylenediamine (also referred to in the description as “quadrol”), triethanolamine, ethylenenitrilotetraethanol, nitrilotri-2-propanol , Tetrahydroxyethylenediamine and N-hydroxyethyl-N, N ', N' - (trihydroxypropyl) ethylenediamine.

All of these compounds are commercially available or can be prepared as described in the literature.

The reducing agent is selected, for example, from the following: formaldehyde and formaldehyde derivatives, for example paraformaldehyde, trioxane, dimethylhydantoin, glyoxal; Borane; Borohydride; Hydroxylamines; Hydrazine and hypophosphite.

A water-soluble alkali or alkaline earth metal hydroxide is preferably used to adjust the pH, for example magnesium hydroxide, calcium hydroxide, potassium or sodium hydroxide or a similar substance. Sodium hydroxide is generally preferred for economic reasons. The pH value is always monitored during bath operation and adjusted to the desired value by appropriate additions.

As a further constituent, a small amount of a wetting agent, preferably less than 5 g / l, can optionally be added to the bath. “Pluronic” P85 from BASF Wyandotte Corp., a non-ionic block polymer made from ethylene oxide and propylene oxide, or “Gafac” RE610 from GAF Corp., an anionic phosphate ester, have proven to be suitable wetting agents.

The concentrations of the various constituents, as can be used for the baths according to the invention, can vary widely within the limits specified below:

Copper salt 0.002-1.20 mol

Reducing agent 0.03-3.00 mol

Copper ion complexes 0.5 to 20 times that

Copper concentration of alkali metal hydroxide sufficient to set a pH of 10 to 14, preferably 11 to 14, measured at room temperature. Make up to 1 liter with water

For non-aqueous baths, for example, organic solvents such as dimethylformamide, dimethyl sulfoxide and acetylacetate have proven their worth.

A bath suitable for the invention is preferably composed as follows:

Soluble copper salt,

preferably copper sulfate 0.002-0.4 mol of alkali metal hydroxide, sufficient to adjust preferably NaOH to a pH of between 11.2 to

13.7 (at room temperature)

5

10th

15

20th

25th

30th

35

40

45

50

55

60

d5

5

646 200

Formaldehyde 0.06-0.5 mol (reducing agent)

Copper ion complexer 0.002-2.0 mol

Fill up to 1 liter of water

Appropriate concentrates can be produced for production, which are then diluted before use.

With the specified bath composition it must be taken into account that certain components such as copper ions, reducing agents, copper ion complexes and the depolarizing agent are consumed in the bath operation; these bathroom components are supplemented in the bathroom as required.

The concentration of the depolarizing agent and the pH value are constantly monitored. The depolarizing agent is added to the bath in a concentration of at least 0.0001, usually at least 0.0005 and up to 2.5 g / l. After adding the depolarizing agent, the pH value is adjusted so that a higher deposition rate is achieved than in the bath solution without depolarizing agent at the same pH value.

The surface to be metallized should be free of grease and free of poisonous substances.

If non-metallic surfaces are to be copper-plated, they must be pretreated as is known for electroless metal deposition. Metallic surfaces must be free of grease and oxides.

With inert metal surfaces, e.g. stainless steel, pretreatment with a hydrochloric acid palladium chloride solution is advantageous.

After the pretreatment and / or sensitization, the surface is added to the electroless copper plating bath, which is done either by immersion in or by spraying the solution. The residence time corresponds to the desired metal layer thickness. In practice, the procedure is usually that the surfaces to be metallized are firmly mounted and the metallization solution is moved. Of course, the opposite can also be done.

The metallization solutions are usually prepared in such a way that the complexing agent for copper ions is added to the copper salt solution and thus forms a water-soluble copper complex or chelate. The complexing agent can be added in the form of a base, a salt or a water-soluble derivative. The other constituents are then added to the copper solution in any order.

The inventive method can be carried out in a wide temperature range, for example between 15 ° C and the boiling point, 100 ° C, preferably 20 and 80 ° C. It must be mentioned that shiny copper deposits can be achieved at temperatures of 25 ° C.

Areas of application for the present invention include rapid metallization of non-conductors to avoid charging or insulated cables for the production of coaxial cables or for glass mirroring.

The metal deposition rates obtained from electroless baths using the method according to the invention are of the same order of magnitude as those normally achieved with electroplating.

The method according to the present invention is particularly suitable for the production of printed circuits and the metallization of plastic articles. The copper layer can be built up to the desired thickness by electroless or galvanic metal deposition of copper, or copper, nickel and chrome.

If formaldehyde is used as the reducing agent, the two partial reactions can be expressed by the following equations:

Anodic (A) CH2O + 2 OH - HCOO- +! / 2m + H2O + le ~ Cathodic (C) Cu + + + 2e ~ -> - Cu °

The terms "cathodic" and "anodic" were taken from the electroplating here. Without being bound by any theory, this is intended to express that both reactions take place during the deposition process, but on the same macroscopic surface, but in different microscopic areas. If the surface on which metal is deposited becomes anodic, the speed of the anodic reaction increases with increasing current density, and the surface becomes more and more positive. If an accelerator according to the invention is added to the bath solution, the polarization at a specific current density is lower than the potential, or the polarization caused by the deposition is lower than without a depolarizer. The potential difference between a bath with and without a Depola riser additive, measured at the same current density, is a measure of the acceleration achieved in the anodic reaction.

The measurement of the polarization can be carried out according to the usual, galvanostatic, electrochemical methods, according to which a certain current passes through the solution from the anode to the cathode. If the anode is the electrode to be examined, the current will polarize it. The difference in the voltage between the polarized anode and a reference electrode, for example a calomel electrode, and the voltage measured between the two electrodes at rest indicates the polarization.

In FIG. 1, the depolarization D measures the decrease in the polarization P at the current i, as is caused by the presence of one of the polarizing agents according to the invention, expressed in percent. If D is zero, the acceleration of the deposition is also zero; if D is greater than zero, this corresponds to accelerations that are greater than zero.

It is similar with regard to cathodic polarization. If the surface to be metallized is the negative electrode of an electrical cell, the cathodic reaction can be measured. The measured depolarization at the cathode is also a measure of the acceleration of the cathodic reaction.

It was found that the acceleration effect of the depolarizing agents largely depends on the complexer for copper ions. Using the bath composition below, the effectiveness of a number of different depolarization additives was measured.

Bath compositions for Tables I and II:

Tartrate ligand bath

Rochelle salt

54.3 g / 1

Formaldehyde (37% solution)

10 ml / 1

CuS04-5H20

18 g / 1

Rochelle salt: copper (molar ratio)

5: 1

PH value

12.8

temperature

25 ° C ±

the atmosphere

accelerator

0.001 g / 1

5

10th

15

20th

25th

30th

35

40

45

50

55

60

o5

646 200

Quadrol ligand bath

N, N, N ', N'-tetrakis (2-hydroxypropyl)

ethylenediamine 34 g / 1

Formaldehyde (37% solution) 10 m / 1

CuS04 ■ 5H20 18 g / 1

Quadrai: copper (molar ratio) 1.6: 1

pH 12.8

Temperature 25 ° C ± 1 ° C atmosphere

Accelerator 0.001 g / 1

EDTA ligand bath

EDTA (Na2) 43.3 g / 1

Formaldehyde (37% solution) 10 ml / 1

CuS04-5H20 18 g / 1

Na2EDTA: copper (molar ratio) 1.6: 1

pH 12.8

Temperature 25 ° C ± 1 ° C atmosphere accelerator

A constant direct current was used to measure the depolarization in percent and the polarization was recorded. The results are summarized in Table I.

The results in Table I show that the various compounds according to the invention which can be used as accelerators have different effects on the cathodic and the anodic reaction.

Table I

Anodic and cathodic depolarization (in%)

Ligand

accelerator

Depolarization (%)

Anodic

Cathodic

N, N, N'N'-tetra-

Cytosine

79

28

kis- (2-hydroxy-

Adenine

82

31

propyl) ethylene

Benzitriazole

72

27th

diamine

Sodium 2-mer-captobenzo-

thiazole

79

37

Pyridine

70

20th

Guanidine

0

49

EDTA

Cytosine

78

56

Guanidine

0

52

Tartrate

Cytosine

0

35

Guanidine

0

35

The effects of the 25 cathodic and anodic depolarizations caused by a depolarizing agent can add up, as can be seen in Table II. The gravimetric acceleration factor A is defined as the ratio between the deposition rate with and without the addition of depolarization. The measurement results were obtained under the same conditions as in Table I.

0.001 g / 1

Table II

Gravimetric acceleration factor A and depolarization

Deposition rate gravimetric

(currentless) gravimetric acceleration

(xl0 ~ 3mm / h factorA

Ligand Accelerator Without With Depolarization (%)

Accelerator Accelerator Anod. Cathod. Total

Tartrate cytosine 0.5 0.9 1.8 0 35 35

N, N, N ', N'-tetrakis

(2-hydroxypropyl

ethylenediamine) cytosine 2.8 6.4 2.3 79 28 107

EDTA cytosine 1.0 2.5 2.5 78 56 134

Table II shows an increase in the deposition rate of 180 to 250% when using cytosine and the optimum pH value, depending on the ligand present in the electroless copper plating bath. Such a result was surprising and unpredictable.

In addition to the depolarizing agents mentioned here by name, there are of course a large number of further depolarizing agents which can be used in connection with the present invention.

The process according to the invention is further described by the following examples.

In the examples, the deposition rates are determined either «gravimetrically» or by the so-called «blow-through method».

According to the «gravimetric method», a sheet of stainless steel, 3x5 cm, after cleaning, sensitization and a rinsing process is exposed to a bath of the specified composition for 15 minutes, rinsed, dried at 100 ° C. for 20 minutes, and then weighed . Then the foil is freed of the deposited copper by immersion in nitric acid, rinsed, dried and weighed again. Then the thickness of the deposited metal deposit can easily be determined from the surface and 50 weight.

For the so-called “burn-through test”, an epoxy glass plate 0.175 cm thick with a copper cladding on both sides and a large number of non-copper-plated holes 0.1 cm in diameter is used. The plate is cleaned with a 55 alkaline detergent at 50 ° C and rinsed in water. The copper surface is then treated with a 10% sodium sulfate solution, rinsed and then brought into contact with 10% sulfuric acid and 30% hydrochloric acid. The hole walls are then treated with a conventional palladium chloride / tin chloride sensitizer for electroless metal deposition. After the subsequent rinsing, the excess tin salt is removed from the plate by treatment with 5% fluoroboric acid, which contains 4 g / 1 N- (2-hydroxyethyl) -ethylenediamine tri-acetic acid, and rinsed again with water. The substrate is then immersed in a copper plating bath for 15 to 30 minutes as described later. During this period, 2 to 4 x 10 ~ 3 mm copper are deposited. More accurate

7

646200

The substrate is said to be immersed in bath A for 15 minutes and in bath B or C for 30 minutes. After the metal deposition, a rinsing process and subsequent drying, the maximum current capacity of the perforated wall metallization is determined according to the so-called “burn-through test” 5. For this purpose, a current is applied to one or more of the copper-plated perforated walls and increased evenly by 3 amps per second until the maximum capacity of the copper layer on the perforated wall is reached. At this point, the copper layer from the hole wall is destroyed and the current passage is consequently interrupted; this point is registered. The relationship between the copper layer thickness and the maximum current capacity is given by the following equation:

"" Burn through "layer thickness

Copper layer thickness = 0.2 x; —r ~: -:

Hole diameter

The deposition rate is measured in 10 ~ 3 mm per hour. Deposition rates determined in this way are identified by “BO”; all other deposition rates were determined by gravimetric means.

Example 1 25

This example shows the use of pyridine, a heterocyclic aromatic nitrogen compound, as an accelerator or depolarizer for copper deposition from a bath of the following composition:

30th

Bad A

N, N, N ', N'-tetrakis

(2-hydroxypropyl) ethylenediamine

CUS04-5H20

Formaldehyde (37% solution) wetting agent ("Pluronic" P85) sodium hydroxide

0.1 g / l pyridine are added to bath A. The effect of pyridine at different pH values is shown in Fig. 2; the measurements were carried out at a bath temperature of 25 ° C. The comparison curve shows the course of the deposition rate as a function of the pH values without the pyridine addition according to the invention. The comparison values were compiled in the following table:

45

Bathroom A *

Bad A + pyridine pH

Deposition pH

Abscheidungsge

speed

dizziness

(10_3mm / h)

(10 ~ 3 mm / h)

12.4

9 5 **

12.4

10.7 (BO)

13.1

6.3

13.1

14.2 **

* Comparative test

** highest deposition rate example 2

The procedure according to Example 1 is repeated, with the difference that the copper sulfate is replaced by the equivalent amount of copper acetate and 2-mercaptopyridine, a heterocyclic aromatic nitrogen compound, is added as a depolarizing additive. The measurement results are summarized in the following table:

Bathroom A *

Bad A + 2 mercaptopyridine

PH

Separation pH

Abscheidungsge

dizziness

dizziness

(10_3mm / h)

(10 ~ 3mm / h)

12.4

9.5 ** (BO)

12.4

12.5 (BO)

12.8

6.7

12.8

14.0 **

34 g / 1 18 g / 1 35

20 ml / 1 0.001 g / 1 to set the desired pH 40

* Comparative test

** highest deposition speed

Example 3

This example shows the effect of two of the depolarization additives according to the invention which are used together, namely the sodium salt of 2-mercapto-benzothiazole and 2-hydroxypyridine, which are heterocyclic aromatic nitrogen compounds. The procedure of Example 1 using bath A is repeated with these two additives; the results are summarized in the following table:

2-mercapto-benzothiazole (sodium salt) g / 1

2-hydroxypyridine g / 1 pH

Separation speed (10_3mm / h)

0 * 0.002 ** 0 ** 0 **

0 0 13.3 13.3

0.001 0.005 13.0 13.0

0.002 0.002

0.001 0.005 13.3 13.3

5.8 11.7 (BO) 7.9 11.5 12.3 13.3

* Comparative experiment without a depolarizing additive ** Comparative experiment with one of the two depolarizing additives

The combination of 2-hydroxypyridine and 2-mercaptobenzothiazole causes a greater increase in the deposition rate than just one of the two substances and a bright and shiny copper deposit. If only 2-mercaptobenzothiazole is added, the bath stability increases compared to the comparison bath without any addition, but the copper deposit does not have the desired appearance. If only 2-hydroxypyridine is added, the copper deposit is bright and shiny.

50

Example 4

The procedure of Example 1 is repeated with p-nitrobenzylamine hydrochloride as a depolarizing agent, an aromatic amine. The substance A is added to bath A in an amount of 0.1 g / l.

60

Bathroom A *

Bad A +

2-nitrobenzylamine hydrochloride pH

Separation pH

Abscheidungsge

dizziness

dizziness

(10 ~ 3mm / h)

(10 ~ 3 mm / h)

12.4

9.5 ** (BO)

12.4

10.5 (BO)

12.9

6.3

12.9

11.8 (BO) **

* Comparative test

** highest deposition speed

646 200

8th

Example 5

The process according to Example 1 is carried out with a depolarizing additive to bath A in the form of 0.005 g / 12,2-dipyridil. The results are summarized below: 5

Bathroom A *

Bad A + 2,2'-dipyridile

PH

Separation pH

Abscheidungsge

dizziness

dizziness

(10-3 mm / h)

(10_3mm / h)

12.4

9.5 ** (BO)

12.4

10.3 (BO)

12.7

7.0

12.7

11.0 ** (BO)

It was found that the copper has lower internal stresses at higher temperatures. At 70 ° C the formaldehyde content of the bath was reduced to 12 ml / 1. It has to be mentioned that a deposition rate of 65 x 10-3 mm per hour, as was achieved at 70 ° C, is quite extraordinary; The deposition rate of 19.3 x 10 ~ 3 mm per hour, which was achieved at a bath temperature of 38 ° C, is also quite extraordinary.

10th

* Comparison test ** highest deposition rate

Example 6

This example shows the influence of elevated temperatures on the deposition rate of baths with the additives according to the invention.

The procedure of Example 1 is now repeated with the addition of 0.002 g / 12-mercaptobenzothiazole to bath A at a temperature of 26.38 and 70 ° C. The results are summarized below:

2-mercaptobenzo-thiaozole

(Sodium salt) g / 1 pH (measured at room temperature) bath temperature (° C) deposition rate (10 ~ 3mm / h)

0.002

13.2 26

0.002

13.2 38

13.0 (BO) 19.3

0.002

13.2 70

65

Example 7

This example serves to illustrate the influence of other metal ions besides copper; Metals from Group VIII of the Periodic Table were used. The procedure according to Example 1 is repeated with the electroless metal-depositing baths according to Table III. The results of this table show that additions of metal ions from group VIII have a favorable effect on the deposition rate. The bath work in the presence of the additives used according to the invention shows a very significant increase in the deposition rate compared to control baths which do not contain such an additive. In addition, it must be noted that the additives as used in Examples 1 25 to 7 give copper deposits of good adhesive strength, in which the copper is usually not braced, while the control baths without additives do not or only poorly adhering deposits of lower quality surrender.

30th

Table III

N, N, N ', N'-tetrakis

(2-hydroxypropyl)

ethylenediamine

CuS04 • 5H2O

Formaldehyde (37%)

Wetting agent ("Pluronic" P-85)

NaOH

2- Merkaptob enzothiazole

(Sodium salt)

NiS04-6H20

CoCl-2H20

PdCh

Potassium sodium tartrate pH

Deposition speed (10 ~ 3mm / h)

34 g / 1

34 g / 1

34 g / 1

34 g / 1

34 g / 1

34 g / 1

18 g / 1

18 g / 1

18 g / 1

18 g / 1

18 g / 1

18 g / 1

20 ml / 1

20 ml / 1

20 ml / 1

20 ml / 1

20 ml / 1

20 ml / 1

0.001 g / 1

0.001 g / 1

0.001 g / 1

0.001 g / 1

0.001 g / 1

0.001 g / 1

to pH

to pH

to pH

to pH

to pH

to pH

0.002 * g / 1

0.002 g / 1

0.002 * g / 1

0.002 g / 1

0.0015 * g / 1

0.0015 g / 1

0g / l lg / 1

0g / l

0g / l

0g / l

0g / l

0g / l

0g / l

0g / l

4.5 g / 1

0g / l

0g / l

0g / l

0g / l

0g / l

0g / l

0g / l

0g / l

0g / l

1.6 g / 1

0g / l

4.5 g / 1

0g / l

0g / l

13.4

13.4

13.2

13.2

13.2

13.2

10.4

19th

12.8

15

9

12

: Comparative test without additional Group VIII metal

Example 8

This example shows the influence of cytosine, also an accelerator according to the invention, in a deposition bath of the following composition:

Bad B

Tetrasodium ethylenediaminetetraacetate

dihydrate 138 g / 1

CuS04-5H20 14.7 g / 1

Formaldehyde (37% solution) 30 ml / 1

NaOH to adjust the pH

When using the above-described gravimetric method for determining the deposited copper-60 layer thickness, a foil made of stainless steel, 3x5 cm, was used. The film was sensitized for the metal deposition from electroless baths and then immersed in bath B, to which 0.004 g / l cytosine had previously been added. The bath temperature was 25 ° C.

od The effect of the cytosine at different pH on the deposition rate is illustrated in FIG. 3 and can also be seen from the following measurement results:

9

646 200

Bathroom B *

Bad B + cytosine pH

Separation pH

Abscheidungsge

dizziness

dizziness

(10-3mm / h)

(10 ~ 3mm / h)

12.4

5.3 **

12.4

9.3

12.75

4.5

12.75

10.4 **

* Comparative test

** highest deposition rate example 9

The procedure of Example 8 is repeated with 0.005 g / 12-mer-kaptobenzothiazole as a depolarizing additive instead of cytosine. The results are summarized below:

Bathroom B *

Bad B + 2-mercaptobenzothiazole pH

Separation pH

Abscheidungsge

dizziness

dizziness

(10-3 mm / h

(10 ~ 3 mm / h)

12.4

5.3

12.4

11.0 **

13.1

3.5

13.1

7.3

* Comparison test ** highest deposition rate

Example 10

The method according to Example 8 is carried out with 0.003 g / 12-mer-kaptopyrimidine as a depolarizing additive; the results are summarized below and can be seen in FIG. 4.

Bathroom B *

Bad + 2-mercaptopyrimidine pH

Abscheidungsge

PH

Abscheidungsge

dizziness

dizziness

(10_3mm / h)

(10_3mm / h)

12.4

5.3 **

12.4

5.3

13.0

3.5

13.0

8.8 **

* Comparative test

** highest deposition rate example 11

The process according to Example 8 is carried out with 0.005 g / 1 guanine dinhydrochloride, a non-aromatic nitrogen compound, as a depolarizing agent. The results are illustrated in Figure 5 and summarized in the table below:

Bathroom B *

Bad B + guanidine HCl pH

Separation pH

Deposition

dizziness

speed

(10_3mm / h)

(10-3 mm / h)

12.4

5.3 **

12.4

8.0

12.72

4.4

12.72

10.5 **

* Comparative test

** highest deposition speed

Examples 8 to 11 show a clear increase in the deposition rate in the baths with the depolarizing additives according to the invention compared to the baths without these additives.

Example 12

This example gives a bathroom assembly according to the invention.

approach with which a particularly high deposition speed is achieved:

Copper sulfate

18 g / 1

"Quadrol"

36 g / 1

"Pluronic" P85 (wetting agent)

1 mg / 1

2-mercaptobenzothiazole

1.5 mg / 1

NÌS04-6H20

0.61 g / 1

Rochelle salt

1.0 g / 1

formaldehyde

12.0 ml / 1

NaOH

37.0 g / 1

4-hydroxypyridine

40.0 mg / 1

pH

13.15

(at 25 ° C)

temperature

70 ° C

The deposition rate with this bath was 32 x 10-3 mm per hour, the ductility of the deposited copper was good (two bends of 90 ° each), the stability of the bath was very good. The high ductility of the copper deposit at such a high deposition rate from an electroless bath is particularly remarkable.

Example 13

This example also shows the high deposition rate that is achieved with the baths according to the invention.

Copper sulfate 18 g / 1

"Quadrol" 34 g / 1

Formaldehyde 15 ml / 1

"Pluronic" P85 (wetting agent) 1 mg / 1

2-mercaptobenzothiazole 1.5 mg / 1

pH 13.2

Polyox coagulant 1.0 mg / 1

Deposition speed 72 x 10_3mm / h

Temperature 70 ° C

Example 14

This example shows the application of the method according to the invention with particularly concentrated baths. Such baths make it unnecessary to fill up the individual bath components either by continuous additions or by portions.

Bad C

N, N, N ', N'-tetrakis (2-hydroxy-

propyl) ethylenediamine 65.4 g / 1

CuSÛ4-5H20 50.0 g / 1

Formaldehyde (37% solution) 20.0 ml / 1

"Pluronic" wetting agent P85 0.001 g / 1

Sodium hydroxide 3.9 g / 1

pH 13.2

Temperature 25 ° C

In this example, the deposited copper layer thickness was determined by gravimetric determination, as described above. In the present case, however, a copper plate was used instead of a stainless steel plate. The diluted bath A according to Example 1 was used for comparison. The measurement results are summarized in the table below:

5

10th

15

20th

25th

30th

35

40

45

50

55

60

or

646 200

bath

Cytosine (mg / 1)

Deposition speed (10_3mm / h)

A

0

3.6

C.

0

4.0

C.

5

7.9

C.

10th

9.8

c

15

10.5

c

20th

11.3

c

40

9.1

The deposition rates achieved with the addition of cytosine were completely unexpected. The accelerations achieved here prove the effectiveness of the depolarizing additives according to the invention in highly concentrated baths. So far only diluted baths have been examined. In this context, diluted baths are baths that contain a copper content of less than 0.1 mol / 1 and usually 0.6 mol / 1. According to the method according to the invention, electroless plating baths with a copper content higher than 0.1 mol / l can be used to achieve deposition rates of more than 7 x 10-3 mm per hour. A comparison of baths A and C also shows that in the baths without the addition of cytosine, an increase in the copper ion concentration (18 g / 1 CuS04-5H20 in bath A compared to 50 g / 1 in bath C) does not significantly increase the deposition rate . Rather, it is the presence of cytosine, with appropriate adjustment of the pH, that achieves higher deposition rates.

In addition to the examples described above, it should also be noted that when the process according to the invention is used with two depolarizing additives, such as 2-mercaptobenzothiazole in combination with imidazole or 4-hydroxypyridine, glossier copper deposits are achieved than without any addition or when using 2 -Merkaptobenzothiazole alone. When using a combination of pyridine with 2-mercaptobenzothiazole, both greater bath stability and a shinier copper deposit are achieved than when using 2-mercaptobenzothiazole alone.

The following compounds are very particularly effective accelerators: 2-mercaptobenzothiazole, 4-hydroxypyri-

10th

din, 2-mercaptopyridine, aminopyrazine, pyrido (2,3, b) pyrazine, cytosine, guanidine hydrochloride, pyridine, 2-hydroxypyridine, paranitrobenzylamine, hydrochloride, imidazole and mixtures thereof.

As a result of the high deposition rate from the baths according to the invention, frequent additions of the individual bath components are required in the case of dilute solutions. As shown in Example 14, it is possible to use concentrated baths that make frequent replenishment of the used bath components unnecessary.

In general, any compound can be used as a depolarizing additive which enables 20%, preferably 30%, depolarization of the anodic, cathodic or both partial reactions.

The following can be used to demonstrate the invention in the production of printed circuits:

A copper-clad, glass fiber-reinforced epoxy material serves as the starting material and is provided with a number of holes. Surface and holes are cleaned with an alkaline cleaning agent at 50 ° C and then rinsed with water. The copper surface is then cleaned with a 10% aqueous sodium persulfate solution, rinsed again and then brought into contact with 10% sulfuric acid and 30% hydrochloric acid. 25 After the pretreatment, the hole walls are sensitized to the electroless metal deposition; One of the usual palladium chloride / tin chloride solutions is used as a sensitizing agent. Then it is briefly rinsed in water and treated with 5% fluoroboric acid to remove excess tin salt and rinsed again with water. The material which is now ready for the copper plating process according to the invention is immersed in one of the copper deposition baths described above, and 2 to 4 × 10 -3 mm copper are deposited.

35 Then part of the surface is covered with a mask and the exposed areas are copper-coated using conventional methods. A tin-lead alloy is then applied using electroplating. The mask layer is removed with a weakly alkaline solution and the original copper layer is etched away with an ammoniacal CuCh solution. The end product is a printed circuit with copper conductors on the surface, copper-plated holes and coated with a tin-lead layer.

G

5 sheets of drawings

Claims (16)

646 200 2nd PATENT CLAIMS 1. Method for electroless metal deposition with increased deposition speed of firmly adhering copper layers on metallic and non-metallic surfaces or parts from metallization baths, the pH value of which exceeds 10, characterized in that the copper plating bath liquid contains at least one additive in addition to other constituents which relates to the cathodic half reaction or the anodic half reaction, or both, has a depolarizing effect, and that the pH of the bath liquid is adjusted to exceed that which corresponds to the maximum deposition rate of the bath liquid without this additive, whereby the build-up of the adherent copper layer causes a deposition rate which is higher than that which occurs when using the liquid without this additive at the same pH value and the same temperature. 2. The method according to claim 1, characterized in that the addition brings about an at least 20% depolarization of the anodic half-reaction. 3. The method according to claim 1, characterized in that the addition brings about an at least 20% depolarization of the cathodic half reaction. 4. The method according to claim 1, characterized in that the addition causes at least a 20% depolarization of both the anodic and the cathodic half-reaction of the deposition process. 5. The method according to claim 1, characterized in that the bath liquid contains copper ions, a complexing agent for copper ions, a reducing agent and an agent for adjusting the pH, and their deposition rate initially increases with the pH, reaches a peak value and then with increasing pH decreases again, and that the bath liquid contains at least one compound as a depolarizing additive which has delocalized 7t bonds. 6. The method according to claim 5, characterized in that the depolarizing additive is selected from the group of heterocyclic aromatic nitrogen and sulfur compounds, non-aromatic nitrogen compounds which have at least one delocalized 7i bond, aromatic amines and mixtures thereof. 7. The method according to any one of claims 1 to 6, characterized in that the depolarizing additive from the series of 2-mercaptobenzothiazole, 4-hydroxypyri-din, 2-mercaptopyridine, aminopyrazine, pyrido- (2,3-b) -pyra- zin, cytosine, guanidine hydrochloride, pyridine, 2-hydroxypyridine, para-nitrobenzylamine hydrochloride, imidazole and mixtures thereof. 8. The method according to any one of claims 1 to 7, characterized in that the bath liquid contains the depolarizing additive in an amount of at least 0.001 g / liter. 9. The method according to claim 8, characterized in that the concentration of the additive does not exceed 2.5 g / liter. 10. The method according to any one of claims 5 to 9, characterized in that the depolarizing addition of the bath liquid contains a lone pair of electrons on the nitrogen atom adjacent to the 7t bond. 11. The method according to any one of claims 1 to 10, characterized in that the bath liquid additionally contains ions of at least one metal from Group VIII of the Periodic Table of the Elements. 12. The method according to claim 11, characterized in that the copper plating is carried out in the presence of a concentration of the metal ions of 0.005 to 30 percent by weight, based on the weight of the copper salt. 13. The method according to any one of claims 1 to 12, characterized in that the reducing agent used is selected from formaldehyde and its derivatives, boranes, borohydrides, hydroxylamine, hydrazine and hypophosphite. 14. A copper bath liquid containing a depolarization additive for carrying out the method according to one of the claims 1 to 11, characterized in that it has a deposition rate at a pH value which is greater than 11 which corresponds to that of the same bath composition without addition same pH and temperature, and at least Is 7 x 10 ~ 3 mm per hour. 15. Bath solution according to claim 14, characterized in that its deposition rate at room temperature is at least 9 x 10 ~ 3 mm per hour. 16. Bath solution according to claim 14, characterized in that it has a copper layer of at least Separates 30 x 10 ~ 3 mm per hour and that it contains the copper salt in a concentration of at least 0.1 mol / liter. Electroless plating baths for metallizing metallic and / or non-metallic supports have long been known and widely used. These baths are characterized by the fact that they deposit metal deposits of any thickness on any substrate without external power supply, which distinguishes them from galvanic baths. However, they also differ from metallization processes such as mirroring or those that form a metal deposit due to an exchange deposition in that the achievable layer thickness is only a few millionths of a centimeter. A disadvantage of the older methods for electroless metal deposition was that the electroless metal plating baths were either unstable from the beginning or at least became so after a short period of use, which made them unusable. Such baths also tend to provide dark or off-color precipitates that have no firm bond with the substrate to be metallized and easily detach from it. As a remedy for the instability, a number of stabilizers such as 2-mercaptobenzothiazole, 2,5-dimerkapto-l, 3,4-thio-diazole and 8-mercaptopurine or o-phenanthroline, 1-phenyl 5-mercaptotetrazole, 2,2 ' -Dipyridyl and 2- (2-pyridyl) -benzimi-dazol and the like are proposed. Later, further stabilizers were proposed: thiazoles, isothiazoles and thiozines, benzotriazole, diazole, imidazole, pyrimidine and guanidine and others, as well as 2,2'-biquinoline, 2,9-dimethyIphenanthroIin and 4,7-diphenyI-1,10- phenanthroline. However, it had to be determined that such stabilizers significantly reduce the deposition rate [cf. Schoenberg, The Journal of the Electrochemical Society, 118, p. 1571 (1971)]. U.S. Patent 3,708,329 describes that three ring heterocyclic aromatic nitrogen compounds, one of which carries a hydroxyl group, also serve as accelerators and do not cause a reduction in metal deposition rate. In the same patent, Schoenberg even describes an increase in the deposition rate in the presence of the compounds mentioned; the highest separation rate he achieved for a bath working at room temperature is 3.1 x 10-3 mm per hour. This deposition rate is greater than all of the up to 5 10th 15 20th 25th 30th 35 40 45 50 55 60 o5 3rd 646 200 at that time in the literature, deposition rates for metal deposition baths stable over longer periods. The "fastest" deposition baths currently available on the market are manufactured by Dyna-chem (DC-920) and MacDermid (9027) and achieve deposition speeds of 5 x 10-3 mm per hour. US Pat. No. 3,377,174 describes a short-term bath for electroless metal deposition which deposits a 0.5 x 10-3 mm thick metal layer within 5 minutes. So far, there has been a general belief that metal deposits of sufficient quality, i.e. Precipitation of uniform structure and firmly adhering to the base, can only be achieved with deposition rates of less than 6 x 10-3 mm. Furthermore, experience had shown that at higher deposition rates the metal deposit was of poor quality and tended to flake off; the adhesion to the surface to be metallized was also insufficient. When we speak of "adherent" metal layers in the following, this means a metal deposit which not only has good adhesion to the base, but which can be peeled off from the base as a complete film and has a uniform metal foil in shape and structure , regardless of the document. If we speak of “non-adhesive” metal layers in the following, this means a metal deposit that tends to peel off.