EP0071512B1 - Process for the preparation of an additive for an acid bath for the electrodeposition of copper and use thereof - Google Patents

Abstract

Additive composition for an acid copper electroplating bath, which bath being well adapted for the copper plating of printed circuits, is comprised of (1) the sodium salt of omega -sulfo-n-propyl N,N-diethyldithiocarbamate, (2) polyethylene glycol having an average molecular weight ranging from about 6,000 to 20,000, (3) crystal violet, and (4) sulfuric acid.

Description

The present invention relates to an additive for acid electrolytic copper plating bath, its preparation process and its application to copper plating of printed circuits.

Various compositions of acidic copper plating baths are known for coating by electrolysis.

Thus, French Patent No. 1,255,271 describes acid copper plating baths comprising one or more basic dyes which may in particular contain an ethenyl chromophore, amino compounds devoid of carbonyl groups, an organic sulfonic acid or a water-soluble salt of this acid and which contains, in its molecule at least one azido group, as additional brightening agent an organic compound which has at least one carbon atom linked exclusively to a heteroatom, and which carries a hydrocarbon radical, linked via a sulfur and / or nitrogen atom and one hydrogen of which is replaced by a sulfonic acid group, a thioamide or isothioamide which carries a sulfonic acid group linked to the nitrogen atom of the thioamide or isothioamide group via d 'a hydrocarbon radical, a thiourea derivative in which at least one nitrogen atom is replaced by an alkyl or anyle radical carrying an ether, hydroxyl or carboxyl group.

Furthermore, according to Belgian patent No. 572186, acid copper plating baths containing a content of organic sulfonic acids or their water-soluble salts containing at least one azido group in the molecule, an additional content of alkylated esters are known. -sulfonic of N-mono- or disubstituted dithiocarbonic acids or of their water-soluble salts, an additional content of 1,3,5-triazine-2,4,6-tris- (mercaptoalkane-sulfonic acid) or in their water-soluble salts, an additional content of agents improving the ductility of coatings.

The particular additives described in these patents are however not satisfactory, in particular because they degrade relatively quickly during their use, their stability at temperatures above 25 ° C is low.

• (A) des colorants contenant des groupes triphénylméthane, par exemple le cristal violet et
• (B) les sulfoalcoylsulfures contenant le groupement S-alcoyl-S0₃M.

There are known from US-A-4036 710 copper plating baths containing at least one compound chosen from

• (A) dyes containing triphenylmethane groups, for example violet crystal and
• (B) sulfoalkyl sulfides containing the group S-alcoyl-S0 ₃ M.

• a) les pyridines substituées de formule générale :
  
  où R est un alcoyle inférieur, un alcényle inférieur, un alcoylène-amine, un mercapto, un cyano, un alcoylène 4-pyridyle, un groupe --C(S)NH₂ ou -CH = NOH, ou un groupe de formule -C(O)R' où R' est un groupe alcoyle ou aryle inférieur ou -N(Et)₂,
• b) les pyridines substituées de formule générale :
  
  où R₂ est un groupe amino, chloro, ou β-acide acrylique,
• c) la 2-vinyl-pyridine,
• d) la 2-méthyl-5-vinyl-pyridine,
• e) la quinoléine ou la 3-amino-quinoléine,
• f) l'isoquinoléine, ou
• g) le benzimidazole.

From patent US Pat. No. 4,038,161, processes are known for obtaining regular copper coatings of the type according to which copper is electrolytically deposited from an aqueous acid electrolytic coating bath containing one or more salts of copper soluble in the bath and a free acid, characterized in that a sufficient amount is added to the bath to cause an electrolytic deposition of regular copper, of at least one leveling compound of organic level soluble in the bath and obtained by reacting one or more epihalohydrins with one or more nitrogenous compounds chosen from the group consisting of:

• a) the substituted pyridines of general formula:
  
  where R is a lower alkyl, a lower alkenyl, an alkylene amine, a mercapto, a cyano, a 4-pyridyl alkylene, a group --C (S) NH ₂ or -CH = NOH, or a group of formula - C (O) R 'where R' is a lower alkyl or aryl group or -N (Et) ₂ ,
• b) substituted pyridines of general formula:
  
  where R ₂ is an amino, chloro, or β-acrylic acid group,
• c) 2-vinyl-pyridine,
• d) 2-methyl-5-vinyl-pyridine,
• e) quinoline or 3-amino-quinoline,
• f) isoquinoline, or
• g) benzimidazole.

We know from the article CA vol. 82, n ° 26, June 30, 1975, pages 415-416, the role of dyes containing triphenylmethane groups in electrolytic copper plating baths.

• - une faible dégradabilité dans le bain en fonctionnement, conduisant à une augmentation importante de la durée d'utilisation d'un bain et à une faible consommation de produit,
• - une excellente stabilité à des températures supérieures à 25 °C, conduisant à des consommations en additif à ces températures deux à trois fois plus faibles que celles nécessaires avec les additifs connus,
• - l'additif permet d'utiliser une plage de densité de courant très étendue, par exemple de 1 à 10 A/dm²,
• - on peut utiliser une plage de concentration en additif très étendue sans diminution de la qualité du dépôt électrolytique.

The Applicant has developed an additive and a process for acid electrolytic copper plating bath which overcomes the aforementioned drawbacks and which in particular has the following advantages:

• - poor degradability in the bath in operation, leading to a significant increase in the duration of use of a bath and low consumption of product,
• - excellent stability at temperatures above 25 ° C, leading to additive consumption at these temperatures two to three times lower than that required with known additives,
• the additive makes it possible to use a very wide range of current density, for example from 1 to 10 A / dm ² ,
• - a very wide range of additive concentration can be used without reducing the quality of the electrolytic deposit.

• a) on mélange le N,N diéthyldithiocarbamate de n propyle ω sulfonate de sodium, un polyéthylène glycol de poids moléculaire moyen compris entre 6000 et 20 000, le cristal violet, de l'acide sulfurique,
• b) on opère le mûrissement du mélange ainsi obtenu à une température comprise entre environ 58 et 70 °C et de préférence 60 et 62 °C pendant un temps compris entre 60 et 200 heures et de préférence 75 et 100 heures.

The present invention indeed relates to a process for the preparation of an additive for an acid electrolytic copper plating bath, characterized in that it comprises the following steps:

• a) mixing N, N n-propyl diethyldithiocarbamate de sodium sulfonate, a polyethylene glycol with an average molecular weight of between 6000 and 20,000, violet crystal, sulfuric acid,
• b) the mixture thus obtained is ripened at a temperature between about 58 and 70 ° C and preferably 60 and 62 ° C for a time between 60 and 200 hours and preferably 75 and 100 hours.

The N, N diethyldithiocarbamate of n propyl w sodium sulfonate has the formula:

The violet crystal is constituted by a mixture of variable composition of the hydrochlorides of hexamethyl-, of pentamethyl-, of tetramethylpararosanilines.

According to the invention, use is preferably made of the violet crystal consisting of hexanethylparasoaniline hydrochloride, of formula:

The proportions of the constituents in the additive can vary within wide limits, a concentration of between 0.5 and 10 g / l and preferably between 1 and 3 g / I for N, N sodium propyl sulfonate diethyldithiocarbamate is suitable ; a concentration of between 10 and 100 g / l and preferably 15 and 20 g / l for polyethylene glycol is suitable; a concentration between 0.1 and 1 g / I and preferably 0.2 and 0.5 g / I for the violet crystal is suitable and a concentration between 0.1 and 0.2 N for sulfuric acid is suitable.

• a) on mélange les quatre constituants composant l'additif,
• b) on opère le mûrissement du mélange ainsi obtenu à une température comprise entre environ 58 et 70°C et de préférence entre 60 et 62 °C pendant un temps compris entre environ 60 et 200 heures et de préférence de 75 à 100 heures.

The present invention also relates to the process for preparing the additive. The method is characterized in that it comprises the following steps:

• a) the four constituents making up the additive are mixed,
• b) the mixture thus obtained is ripened at a temperature between about 58 and 70 ° C and preferably between 60 and 62 ° C for a time between about 60 and 200 hours and preferably from 75 to 100 hours.

The components constituting the additive are mixed in the proportions which have been given above.

The additive thus prepared can be used in the acidic copper-plating bath. The concentration of the additive in the bath can vary between approximately 2 and 100 ml / l and preferably 3 and 50 ml / l.

In general, metallization is carried out at temperatures below 60 ° and with current densities varying from 0.5 to 10 A / dm ² . The amperage zone giving the best gloss effects varies according to the proportions of the constituents of the additive. By using the additive according to the invention, it is possible to widen the amperage zone giving the maximum brilliant effect and to increase the certainty of success in practice. As metallic supports, all kinds of metals usually used for this purpose can be used, such as iron, copper, steel, zinc and other base metals or alloys.

The acid copper baths in which the additives according to the invention can be used mainly comprise copper sulphate, the concentration of which can vary between 50 and 250 g / l and sulfuric acid, the concentration of which can vary between 60 and 250 g / I.

The additive according to the invention has excellent chemical stability in acid baths, so that they remain able to function even if one operates at temperatures. relatively high bath.

The additive of the invention can be used in copper plating operations.

The additive according to the present invention is particularly effective for operating the electrolytic copper plating of printed circuits and electroformed parts.

This additive can also be used in combination with other known agents, such as conductive salts, wetting agents or anti-porous agents.

Thus the additive according to the invention makes it possible to obtain copper deposits which are shiny, ductile, leveling and resistant to thermal shock. It also allows, because of its low degradability in the bath during operation, to lead to a significant increase in the duration of use of the bath. In addition, its excellent stability at temperatures above 25 ° C leads to an additive consumption at these temperatures three times lower than with the additives used until now. It also allows use in a very wide current density range as well as a concentration in the copper bath also very wide.

The thickness of the copper deposits obtained with the additive can vary within wide limits; one can, for example, make deposits having a thickness of between a few microns and 5 mm.

The example below illustrates the invention without limiting its scope.

Example Additive preparation

• - 186 litres d'eau distillée, 522 millilitres d'H₂SO₄ présentant une concentration de 36 N,
• - 65 g de cristal violet,
• - 3095 g de polyéthylène glycol présentant un poids moléculaire moyen de 12 000,
• - 186 g de N,N diéthyldithiocarbamate de n propyle ω sulfonate de sodium.

In a 200 liter glass steel reactor, successively introduced

• - 186 liters of distilled water, 522 milliliters of H ₂ SO ₄ with a concentration of 36 N,
• - 65 g of purple crystal,
• 3095 g of polyethylene glycol having an average molecular weight of 12,000,
• - 186 g of N, N n-propyl diethyldithiocarbamate de sodium sulfonate.

The mixture is stirred for approximately two hours, then the temperature is raised to 60 ° C in two hours; the mixture is matured at this temperature for 100 hours and then cooled to room temperature: about 187 liters of additive are thus obtained.

Application

• - Sulfate de cuivre (CuSO₄, 5H₂O) 75 g/I
• - Acide sulfurique 180 g/I
• - Chlorure 50 mg/l

In a tank of 1000 liters of metallization of printed circuits, a bath having the following composition is mounted:

• - Copper sulphate (CuSO ₄ , 5H ₂ O) 75 g / I
• - Sulfuric acid 180 g / I
• - Chloride 50 mg / l

After carrying out an electrolysis of 10 hours at 1 Ampere / dm ² to remove the metallic impurities, 5 liters of additive prepared according to the example are added: the deposits obtained after this addition are shiny, ductile and without internal tension ―the structure of the copper deposited is fine-grained and no breakage appears in the deposit after the thermal shock test (immersion 10 seconds in the solder at 290 ° C then dipped in water).

The range of usable current density extends from 1 to 10 Aldm ² if it is desired to obtain only a glossy deposit resistant to thermal shock, and from 1 to 8 A / dm ² if in addition to these qualities, wishes to obtain a fine grain structure of copper.

• - Intensité : 2 Ampères
• - Durée : 5 minutes
• - Température : 22-24 °C
• - Agitation : oui
• - Volume d'électrolyte : 250 cm³

Monitoring the concentration of the additive bath can be easily carried out using the Hull cell test (Electroplating-Mc Graw-Hill Book Company 1978 pages 148-150) under the following conditions:

• - Intensity: 2 Amps
• - Duration: 5 minutes
• - Temperature: 22-24 ° C
• - Agitation: yes
• - Electrolyte volume: 250 cm ³

In the case of the 1000 liter tank, additions of 1 liter additive will be made each time the width of the burnt area on the Hull cell plate reaches 10 mm. Under these conditions, for a temperature below 26 ° C, the additive consumption will be between 1 and 2 liters for 10,000 amperes / hour and the life of the bath before regeneration on activated carbon will be more than 1.5 million amperes. x hour.

Claims (3)

1. Process for the preparation of an additive for an acidic electrolytic coppering bath, characterised in that it comprises the following stages :

a) ω-(sodium sulphonate)-n-propyl N,N-diethyldithiocarbamate, a polyethylene glycol of mean molecular weight between 6,000 and 20,000, crystal violet and sulphuric acid are mixed, and

b) the mixture thus obtained is ripened at a temperature of between 58 and 70 °C for a period of between 60 and 200 hours.

2. Process according to Claim 1, characterised in that the concentration of w-(sodium sulphonate)-n-propyl N,N-diethyldithiocarbamate is between 0.5 and 10 g/l, the concentration of polyethylene glycol is between 10 and 100 g/l, the concentration of crystal violet is between 0,1 and 1 g/I and the concentration of sulphuric acid is between 0.1 and 0.5 N.

3. Electrolytic coppering process, characterised in that the additive prepared according to Claims 1 or 2 is employed in a coppering bath which principally contains copper sulphate of concentration between 50 and 250 g/I and sulphuric acid of concentration between 60 and 250 g/l, the concentration of the additive in the bath being between 2 and 100 ml/I, the bath temperature being less than 60 °C and the current density being between 0.5 and 10 A/dm².