DD159268A3 - PROCESS FOR THE GALVANIC DEPOSITION OF COPPER LAYERS ON PCB - Google Patents

Abstract

The invention relates to a method with which the deposition of smooth, ductile layers is to be achieved by new electrolyte additives. The aim and object of the invention is the development of a method which avoids the discarding of the electrolyte and rejects, ensures an increase in throughput and a higher deposition rate and realizes the deposition of smooth, uniform and ductile copper layers in a wide current density range. The process according to the invention for the electrodeposition of copper layers from sulfuric acid copper electrolytes containing dialkyldisulfide disulfonic acids and water-soluble polyethers as brightening agents is characterized in that at cathodic current densities of 2 to 6A / dm high 2 and temperatures of 20 to 32 degrees C polymeric N, N Dimethyl-3,4-dimethylenpyrrolidiniumverbindungen of the general formula I, in which n numbers from 10 to 300 and x high - anions mean in amounts of 0.3 to 5 mg / l are added. The application of the invention extends to the manufacture of printed circuit boards.

Description

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a) Title of the invention

Process for the electrodeposition of copper layers on printed circuit boards

b) Field of application of the invention

The invention relates to a method for the electrodeposition of copper layers. Circuit boards, with which the addition of new electrolyte additives is intended to achieve the deposition of smooth, ductile layers with higher bath performance.

^ c) Characteristic of the known technical solutions

The galvanic deposition of copper layers from cyanide electrolytes has been known for a long time. The copper layers are matt, the applicable current density range is small and existing roughness of the base material are reinforced by this type of copper coating, so that electrolysis process with cyanide copper electrolytes can be used today only for pre-coppering with very low layer thicknesses.

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Instead of cyanide electrolytes later pyrophosphate copper electrolytes have been introduced, but which are no longer sufficient because of their low load capacity today's performance requirements.

Sulfuric acid copper electrolytes with organic additives have been known for more than two decades, so that high deposition rates are possible. These sulfuric acid copper electrolytes contain organic brighteners and leveling agents and are used for the deposition of well-adhering, nonporous and glossy layers, for example for the production of the intermediate copper layer in decorative corrosion protection in the production of printing rolls and for galvanic processes.

Of many proposed organic additives, a combination of mercaptoalkanesulfonic acids or their oxidation products, the dialkyl disulfide disulfonic acids, has been well established in practice with water-soluble aliphatic polyethers and forms the state of the art. By combining with other additives, for example by the addition of heterocyclic compounds, the current density-gloss range (SDG) of such acidic electrolytes could be improved.

Purely the production of copper layers on printed circuit boards sulfuric acid high performance electrolytes with additives of the aforementioned type are not applicable, since the high leveling ability for this purpose is not desirable. The achievable with these electrolytes ductility of copper is not enough for the PCB manufacturing by far. Process for the production of plated-through printed circuit boards should primarily fulfill the following conditions:

- Deposition of ductile copper, in order to avoid the tearing of the copper layer during the soldering process,

- uniform structure of smooth layers,

large current density-gloss range,

- highest possible deposition rate.

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The copper-plating process developed for decorative corrosion protection does not meet these requirements, as there are insufficient performances, especially at very low current densities. The simultaneous achievement of gloss and leveling in acidic high-performance electrolytes requires the use of organic brighteners in such a concentration range which does not permit excellent ductility of the deposited copper layers. The brighteners or their electrochemical degradation products are incorporated into the copper layer, which results in a reduction in ductility. an increase in hardness and an increase in the internal stresses of the layer result.

However, in the first place, the demand for particularly good ductility must be placed on a galvanic copper plating process for printed circuit boards.

It has therefore also been proposed to destroy the brighteners known electrolyte additives by oxidation with hydrogen peroxide partially oxidative (DD-PS 118 444) to improve the ductility of the copper layers.

For this reason, other process proposals want to galvanize at all without additives (German Pat. No. 2,630,688) in order to obtain the good ductility of the matt copper from sulfuric acid electrolytes. Although the ductility is improved by these process proposals, at the same time a matt, partially rough copper is deposited, which does not meet the quality requirements for plated-through printed circuit boards.

Purely the electrodeposition of copper within the holes of plated-through printed circuit boards requires electrolytes that provide suitable layers over a wide current density range. Specifically, they must provide uniform, smooth and ductile copper plating, especially at low current densities.

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By combining dialkyl disulfide sulfonic acids and water-soluble polyethers with polymeric bases, for example hydroxyalkyl derivatives of polyimines (DD-PS 82 858), an extension of the appropriate current density range could be achieved. · Later proposals, such polyamines subsequently with benzyl chloride (DE-OS 2,105,472) or epoxides ( DE-OS 2 818 725) and to use the obtained, partially quaternized polyimines as electrolyte additives, brought about a further improvement of the suitable current density range, so that such combinations could be used in methods of printed circuit board copper plating.

However, these electrolyte additives have the disadvantage that the polyamines used have a varying and incomplete Quaternierungsgrad, even when working with excess alkylane. Copper electrolytes of this type, which partly contain quaternary imines in combination with dialkyldisulfide disulfonic acids and a polyether, have the further disadvantage that in them the electrochemical degradation and the consumption of the additional components can be uneven and, for example, an accumulation of reducing substances (indicated by an increased bromine content). Titer), which may require control, possibly premature regeneration or discarding of the electrolyte.

d) Aim of the invention;

It is the object of the invention to develop a method for the electrodeposition of copper layers on printed circuit boards, which does not have the disadvantages of the known technical solutions, also excludes the discarding of the electrolyte and avoids rejects and ensures an increase in throughput.

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e) Presentation of the essence of the invention

- The technical task

The invention has for its object to provide a method for the electrodeposition of copper layers on printed circuit boards, which smooth, uniform and extremely ductile copper layers can be deposited in a wide current density range, so that both within the holes in the field of lowest current densities, as well A perfect layer formation takes place on the surfaces »At the same time, a higher deposition rate is to be achieved ·

Features of the invention

The technical object is achieved in that the, suitable current density range of acidic copper electrolyte e, which contain as a brightener a combination of Dialkyldisulfiddisulfonsäure with an aliphatic polyether, by polymeric H, N-Dimethy1-3,4-dirnethylen-pyrrolidinium compounds of the general formula I

/ - CH ₂ - CH - CH - CH ₂ - · \

^l 2

H ₂ C

nx

CH

CHO

is significantly extended, wherein in the general formula I η numbers from 10 to 300 and x " anions, such as

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Chloride, bromide or equivalents sulfate or peroxodisulfate.

By processes employing electrolytes with the aforementioned additives in combination with a compound of general formula I, smooth, uniform, highly ductile copper layers are deposited both in the bores and on the surfaces.

Suitable polymeric pyrrolidinium salts of the formula I are readily preparable by free-radical polymerization of dimethy1-diallylammonium salts (DD-PS 141 028, DD-PS 141 029 and DD-WP C07C / 210 852). The degree of quaternization of these polymers is always 100%. Compounds of the formula I cause addition of the extension of the applicable Stramdichtebereich.es. also an increase in the effectiveness of the gloss-forming additives, so that galvanizing can be carried out with very low concentrations of organic bath additives. «

As a result, the incorporation of electrochemical decomposition products in the copper layers is reduced, whereby the ductility is increased so that the thermal shock occurring during the soldering process does not lead to cracking.

According to the invention, the copper electrolytes used in addition to the polymers of formula I at the same time conventional combinations for gloss formation from dialkyl disulfide according to the following examples according to Table 1 in conjunction with Table A der.DD-PS 82 858, wherein the acids are preferably used in the form of their alkali metal salts » Table 1 1. HO ₃ S - (CH ₂ ) ₄ - S ₂ - (CH ₂ ) ₄ - SO ₃ H 2o HO ₃ S - (CH ₂ ) ₃ - S ₂ - (CH ₂ ) ₃ - SO ₃ H

3 c HO "S - CH₀ - CHOH - CH₀ - p₀ - CH₀ - CHOH - CH₀ - SO "H 3 2d d. d dρ

4. HO ₃ S - CH ₂ - CHCH ₃ - S ₂ - CHCH ₃ - CH ₂ - SO ₃ II

5. HO ₇ S - (CH ₂ ) ₃ - S ₂ - (CH ₂ ) ₂ - SO ₃ H

6. HO ₃ S - CH ₂ CH ₂ -S ₂ - CH ₂ CH ₂ - SO ₃ H.

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and polyethers according to the following examples according to Table 2 in conjunction with Table C of DD-PS 82 858 Table 2 1 · HO - GH ₂ CH ₂ - (O-CH ₂ CH ₂ ) _n -O-CH ₂ CH ₂ -OH

η = 75 - 250 ·

2. HO - CH ₂ - CHCH ₃ - (0-CH ₂ -CHCH _{3) Q} - 0 - CH ₂ CHCH ₃ - OH

η = 8-20

3. HO - CH ₂ - CHCH ₃ - O - CH ₂ - CHCH ₃ - (0-CH ₂ -CH _{2) Q} -

O - CH ₂ --CH ₂ --OH

ⁿ = 5 ° - ¹⁰ °

4. HO - CH ₂ CH ₂ - O - (CH ₂ CH ₂ - O) _n - CH ₂ CH ₂ - OSO ₃ H

η - 75 - 250

The used, preferably sulfuric acid electrolytes should have the following composition:

CuSO ₄ . 5 H ₂ O 60 - 150 g / liter

H ₂ SO ₄ - 225-150 g / liter

HCl 0.02-0.1 g / liter

The preferred cathodic current density is 2-6 A / dm, the preferred electrolyte temperature 20 - 32 ⁰ C and the anodic current density should be lower than the cathode current density.

The electrolyte movement is preferably carried out in the usual way by air. The anode material used is phosphorus-alloyed copper. With sufficient dosage, the combination of a substance of Table 1 with a polyether of Table 2 as an additive in a sulfuric acid electrolyte in a narrow current density range leads to the formation of shiny but not leveled and insufficiently ductile copper layers.

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The strontium gloss range is different for different combinations of individual substances. Thus one is able to influence the scope of the current density gloss range by selecting suitable combinations.

Basically, Bs is therefore recommended to combine several representatives of Table 1 with several substances of Table 2.

In admixture with such gloss-forming multicomponent mixtures, the additives of the general formula I according to the invention lead to excellent results.

The test shows that smooth, shiny copper layers can be obtained in the range of 0.1-10 A / dm 2. In addition, it has been found that in electrolytes containing polyethers in mixtures of which one component is a representative of the group Table 2 - Type '2 , an accumulation of reducing degradation products (indicated by the increase in the bromate titer) does not occur, causing a defect previously known method is avoided.

The additives are preferably used in the following concentration ranges:

Poly-N, N-dimethyl-3,4-methylene-pyrrolidinium salts, general formula I 0.0003 - 0.005 g / liter

Electrolyte disulfide disulfonic acid, Table 1 0.003-0.03 g / liter

Electrolyte polyether, Table 2 0.005 - 0.03 g / liter

electrolyte

The dosage is carried out either individually or in admixture as a combined ready-added electrolyte. Compared with previously used electrolytes, the deposition rate can be increased by using higher cathodic current densities (> 3 A / dm ² ), if the copper sulfate content to about 120 g, the sulfuric acid content to about 180 g / liter and the working temperature to 27 to 32 ⁰ G. increase.

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Thus, the application of the method according to the invention leads to an increase in the plating power at a constant electrolyte volume.

f) embodiment

The invention will be explained in more detail below with reference to exemplary embodiments.

Example 1:

a) A polished brass sheet was degreased, de-capped and galvanized in the copper sulfate electrolyte of the following composition for 15 min at 2 A / dm ² , air movement and 22 ⁰ C electrolyte temperature: 70 g / l CuSO ₄ ♦ 5 H ₂ O.

175 g / l H ₂ ^ SO ₄

50 mg / 1 Cl "

7.5 mg / 1 HO ₃ S - CH ₂ -.CHCH ₃ - S ₂ - CHCH ₃ - CH ₂ - SO ₃ H

12 mg / 1 polyethylene glycol MG 4000 The deposit is dull and rough.

b) A further polished brass sheet was degreased, decanted and galvanized in the copper electrolyte of the composition mentioned under a) after addition of 1.3 mg / l of the additive of general formula I. The deposit is mirror-polished, smooth and even.

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Example 2:

A polished brass sheet was degreased, dekapiert and in the copper electrolyte of the following composition for 15 min.

galvanized at 5 A / drn ² and 30 ⁰ C electrolyte temperature:

125 g / l CuSO ₄ .5H ₂ O

185 g / l H ₂ SO ₄ .

70 mg / 1 Cl "

20 mg / 1 polyethylene glycol MW 6000 20 mg / 1 H ₂ O ₃ S-CH ₂ -CHOH-CH ₂ -S ₂ -GH ₂ -CHOh-CH ₂ -SO ₃ H 5 mg / 1 addition of the general formula I

The deposition is mirror-like and even.

Example 3:

A polished brass sheet was degreased, dekapiert and in the copper electrolyte of the following composition for 15 min. galvanized at 3 A / dm and 22 ⁰ C electrolyte temperature:

70 g / l CuSO ₄ .5H ₂ O 175 g / l H ₂ SO ₄ 50 mg / 1 Cl.

7 mg / 1 polyethylene glycol MW 20000

7 mg / 1 polypropylene glycol IvRY 700

5 mg / 1 H ₂ O ₃ C-CH ₂ -CHOH-CH ₂ -S ₂ -CH ₂ -CHOh-CH ₂ -SO ₃ H

5 mg / l HO ₃ C- (CH ₂ ) ₃ -S ₂ - (CH ₂ ) ₃ -SO ₃ H 2.55 mg / l Addition of the general formula I The precipitate is smooth, mirror-like and uniform.

Example 4:

a) A polished stainless steel sheet is degreased, passivated and in the following copper electrolyte for 30 min. galvanized at 3 A / dm ² , air movement and 22 ⁰ C electrolyte temperature

70 g / l CuSO 4 .5H ₂ O 175 g / l H ₂ SO ₄

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50 mg / 1 GI ""

8 mg / 1 Polyethylene glycol 4000 8 mg / 1 of polypropylene glycol 700 \ 5 mg / 1 HO ₃ S-CH _2-OH -OHOH ₂ -S ₂ -CH ₂ -CHOH-CH ₂ -SO ₃ H

^ 5 mg / 1 HO ₃ S-CH ₂ CH ₂ CH ₂ -S ₂ -CH ₂ CH ₂ CH ₂ -SO ₃ H

The deposited copper layer is hard and less ductile,

b) A further deposition was carried out after addition of 5 mg / 1 addition of the general formula I. The copper layer is mirror-polished, smooth, uniform and has a very good ductility.

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Claims (3)

Invention claims: 1. A process for the electrodeposition of copper layers on printed circuit boards of sulfuric acid Glanzkupferelek- 'trolytes, which contain as GlanzmittelDialkyldisulfiddisulfon acids and water-soluble polyethers, characterized in that at cathodic current densities of 2-6 A / dm and temperatures of 20 to 32 ⁰ C polymers N, H-dimethyl-3,4-dimethylene-pyrrolidinium compounds of the general formula I. U - OH - OH - CH ₀ \ \ - CHo - CH - CH - CHn - \ H ₉ O CH ² X ₊ / CH j CH ₃ in which η denotes numbers of 10 to 300 and x.sup. anions, such as chloride, bromide or equivalents of sulphate or peroxodisulphate, in amounts of 0.3 to 5 mg / l. 2. The method according to item 1, characterized in that two or more Dialkylsulfiddisulfonsäuren be combined with two or more aliphatic polyethers to a brightener and added. 3. The method of item 1, and 2, characterized in that when using mixtures of polyethers one component is a polypropylene glycol having an average molecular weight of 500 - 900.