EP1423557B1 - Electrolytic solution for electrochemical deposition of gold and its alloys - Google Patents

Abstract

An aqueous electrolytic solution for electrochemical deposition of gold or its alloys includes at least a soluble gold compound designed for electrolytic deposition and, optionally at least a secondary metal compound designed for co-deposition in the form of a gold alloy. The solution includes 0.3 to 3 moles per mole of gold contained in the electrolytic solution of an organic compound having one or two aldehyde functions, this organic compound being or an organic compound having 3 to 20 carbon atoms and one or two aldehyde functions in the form of a saturated or unsaturated, linear or branched aliphatic group, or a group containing at least a saturated, unsaturated or aromatic cycle. The organic compound may further include at least a heteroelement selected among oxygen, nitrogen, sulfur and phosphorus or be in the form of a salt, in particular a sulphonate. The presence of the organic compound enables increasing the speed of electrodeposition and/or decreasing contact resistance.

Description

The present invention relates to an electrolytic bath intended for the electrochemical deposition of gold or its alloys.

Electrolytic gilding was born in the wake of the invention of the battery by Alisandro Volta. It is indeed Luigi Brugnatelli, pupil and collaborator of Volta, professor of chemistry at the University of Pavia, who discovered in 1805 the way to gild silver medals using the battery. The process he used is described in particular in a letter addressed to Van Mons, from Brussels. Brugnatelli used a solution of gold chloride in ammonia, in which the object to be browned was immersed, and made the latter communicate by a silver or steel wire with the negative pole of a battery. . The process had no echo at the time probably because of the impossibility of obtaining with the Volta battery a constant current, therefore a satisfactory deposit, or else because of the state of war which persisted until 'in 1815 which made this invention of was not mentioned by distinguished scientists commissioned by Napoleon to communicate scientific progress after the French Revolution. We had to wait for the results of Antoine Becquerel's research on the causes of current irregularity and on the general means of overcoming it and the invention of Daniell's constant current battery. This current source then makes it possible to obtain homogeneous and ductile metallic deposits. It was Auguste de la Rive, a physicist from Geneva, who first actually applied the pile to the gilding. He obtained, in 1840, a deposit of electrolytic gold on brass, copper and silver by using a solution of gold chloride under a very weak current. The deposit still had a lack of adhesion. Indeed the acid electrolyte constantly attacked the surface of the substrate. Several people brought their contribution to improving the process on the Shore such as Elsner, Boettger, Perrot and Smée. It was at the end of 1840 that the precursor of modern gold baths appeared with the work of the English brothers Henry and George Elkington and the Frenchman Henry de Ruolz who developed the use of alkaline solutions of gold cyanide in cyanide. potassium.

These are the types of electrolytes that have been used for almost eighty years without any modification being made to carry out the electrolytic gilding. The applications of these baths were jewelry, gilding of bronzes and zincs of art, used especially for the making of pendulums, candelabras, cups, chandeliers, and the manufacture of golden threads for trimmings.

It was the development of the electronics industry in the early 1940s that sparked renewed interest in gold baths. Users of electroplating were looking for shiny, hard deposits, good conductors and with thickness control, among others. The research carried out to obtain these results led to the development of acid and neutral gold baths, intended for shiny deposits in the 1950s. The sixties saw the development of acid baths of alloyed gold leading to deposits having specific physical properties like ductility, resistance to corrosion, purity of deposit etc. It is also at this time that the electrolytes of non-cyanide gold reappeared with always the objective of obtaining shiny and hard gold deposits. In the seventies, the ever increasing sophistication of electronics but especially the strong growth in the price of gold led users of gold baths to develop selective plating methods and to minimize the quantity of gold. in deposits by developing baths of gold alloys rather than pure gold. The increase in the consumption of electronic products has also been a determining factor in research of electrolytes allowing the deposition rate to be increased with a high leveling power and good penetration, that is to say while obtaining a good distribution of the deposit. Since the 1980s and the advent of acid baths of hard gold combined with nickel, cobalt, iron, indium or other metals, research has focused on improving them by addition of organic additives allowing these electrolytes to be used under high current densities (brighteners, surfactants), to increase the resistance to friction (teflon, carbon chains) or to increase the cathodic yield (formates). Growing concerns about ecotoxicological problems allow us to see the appearance of new gold baths without cyanide or sulfite but unfortunately with much lower performance than those obtained with cyanide acid gold baths.

The most demanding applications in terms of plating speed are undoubtedly those of connectors. In fact, since the 1940s, the connector industry has grown steadily, implying an increasingly massive production of parts coated with precious metal.

With a view to optimizing production costs, the speed of deposition of metals in surface treatment is the parameter that it has been and which is still most often asked to optimize (AM Weisberg in Gold Plating Technology, FH Reid and W. Goldie, Electrochemical Publications Limited, Ayr, 1974).

The gold baths most efficient in terms of electrodeposition speed, retaining on deposit its excellent properties of gloss, ductility, porosity, hardness, resistance to corrosion and friction, low contact resistance are the baths called "Acid Hard Gold" which are intended for deposits of gold hardened by alloying a very small amount of a common metal, most often cobalt or nickel, derived from an acid electrolyte based on the citric acid / citrate system.

Improving the speed of plating is also a demand in the jewelry industry with types of baths ranging from citrate-based electrolytes to phosphate-based electrolytes.

Until now, the methods of improving the electrodeposition speed were based either on the addition of a gold reducer making it possible not to affect the cathodic yield by the reduction of gold (III) originating from l oxidation of the gold salt (I) constituting the anode bath (US4238300, US4670107, US4795534), either on the addition of an organic or metallic brightener allowing the use of higher current densities to the detriment of the cathodic yield (US4767507, US4591415).

At the present time, despite the drawbacks exposed above, cyanide baths for electrolytic deposition of gold remain widely used because of their performance. However, one of the well-known drawbacks of such baths is that the presence of cyanides in the bath is responsible for the formation of polymers during electrolytic deposition. These polymers pollute the deposits and consequently affect the quality of the electrolytic deposit.

Furthermore, it is conventional to resort to the use of secondary metals, in particular cobalt and nickel as hardener and / or brightener of the electrolytic deposits of gold.

It is in particular frequent to prepare so-called “hard gold” gold deposits from aurocyanide solutions buffered by the citric acid-potassium citrate system at pH between 4 and 5, and containing cobalt as hardening metal for the deposit. . These deposits are accompanied by a co-deposition of carbon and nitrogen. There is therefore a contaminant formed during the electrodeposition of gold from such baths. The presence of this contaminant seems responsible for the relatively strong contact resistance of the deposit in two different ways. The polymers increase the contact resistance of the deposit, not only by forming a film on the surface of the deposit but also by being present within this deposit. The formation of polymers is dependent on the availability of free cyanides in the electrolyte. The amount of polymer included in the deposit is also largely dependent on the level of cobalt included.

In addition, the presence of cobalt oxides on the surface of the deposit is also responsible for the contact resistance of the gold-cobalt deposits, in particular, by the formation of a complex with the free cyanides.

Thus, the problems associated with the use of cyanide gold baths are further increased in the case of alloys and especially in the case of gold-cobalt alloys widely used when seeking hard gold deposits.

The publication entitled "Notes on the electrodeposition of thick gold deposits", Charles L. BAUER, Plating (1952), 39, 1335-6, describes tests carried out to improve the properties of a thick deposit of gold intended to thermoforming applications. In the bath used according to this document, vanillin is used at a concentration of 0.3 g / L for a gold concentration of 18 g / L and it is specified in this document that, among 30 auxiliary agents tested, only the vanillin and potassium sulfite have improved the quality of the deposits and that vanillin allows to obtain much finer grains, which means that vanillin is used in this bath as a brightener.

Czech patent CS 107 253 1 describes a process intended to deposit two successive layers of bright and hard gold using an electrolytic bath containing vanillin as a brightening agent at a concentration of 0.5 g / L, for an auropotassium cyanide concentration of 8 g / L, which corresponds to a vanillin concentration of the order of 0.1 mole per mole of gold to be deposited.

M.Dettke et al. have described in patent US3878066 a process using a combination of formaldehyde, acetaldehyde or one of their bisulfitic compound with arsenic and an aliphatic amino compound for obtaining a deposit of very bright gold and having excellent adhesion.

The property of aldehydes to cyanylate in the presence of cyanide is well known. It is in particular implemented in US Pat. No. 5,380,562, which relates to a process for the chemical deposition of gold using a bath comprising a cyanoaurate or an alkali cyanide, a reducing agent, an alkali hydroxide, an agent for controlling the formation of crystals and a stabilizing agent, and in which an aldehyde or a ketone is added at the same time as the gold salt, so as to avoid the accumulation of free cyanides in the bath.

It has now been demonstrated that the use of well-defined aldehydes in baths intended for the electrolytic deposition of gold or gold alloys makes it possible to considerably increase the speed of the deposition of metal or of the alloy. reducing contact resistance and minimizing environmental problems, especially when using cyanide baths.

The present invention makes it possible, in particular, to improve the speed of gold plating by allowing the use of gold electrolytes with high current densities, up to 120 A / dm ² , without affecting the yield. cathode.

Thus, the invention relates according to a first aspect to an electrolytic bath intended for the deposition of gold or gold alloys, this bath containing a well-defined auxiliary agent making it possible to considerably improve the speed of electrodeposition of gold or of its alloys, while reducing the contact resistance and allowing the use of high current densities.

According to a second aspect, the invention relates to a process for the electrolytic deposition of gold or gold alloys on a substrate, using the bath of the invention as an electrolytic bath.

According to a third aspect, the invention relates to a new use of a well-defined family of organic compounds having at least one aldehyde function as an auxiliary intended to improve the performance of an electrolytic deposition process for gold or alloys thereof. gold on a substrate.

The invention applies to all known methods using a step of electrodeposition of gold or gold alloys, in the field of decoration as well as in electronics and connectors.

It is of particular interest in the case of the processes for the electrolytic deposition of gold from a cyanide bath, in particular from an electrolytic bath containing gold in the form of aurocyanide or auricyanide and , very particularly, in the case of gold deposits hardened by a secondary metal, in particular by cobalt, iron or nickel.

• ■ d'un groupe aliphatique, linéaire, ramifié, saturé ou insaturé, ou
• ■ d'un groupement contenant au moins un cycle saturé, insaturé ou aromatique,

ledit composé organique pouvant comprendre en outre au moins un hétéroélément choisi parmi l'oxygène, l'azote, le soufre et le phosphore ou être sous la forme d'un sel, en particulier d'un sulfonate.According to one of its essential characteristics, the invention relates to an aqueous electrolytic bath for the electrochemical deposition of gold or its alloys comprising at least one soluble compound of gold intended to be deposited electrolytically and, optionally at at least one secondary metal compound intended to be codeposited in the form of an alloy with gold, characterized in that it additionally comprises from 0.3 to 3 moles per mole of gold contained in the electrolytic bath of a compound organic comprising one or two aldehyde functions, said organic compound being an organic compound comprising from 3 to 20 carbon atoms and one or two aldehyde functions in the form:

• ■ an aliphatic group, linear, branched, saturated or unsaturated, or
• A group containing at least one saturated, unsaturated or aromatic cycle,

said organic compound possibly further comprising at least one heteroelement chosen from oxygen, nitrogen, sulfur and phosphorus or being in the form of a salt, in particular a sulfonate.

Thus, the invention according to this first aspect relates to an aqueous electrolytic bath intended for the electrochemical deposition of gold or its alloys. A person skilled in the art knows perfectly well that a bath intended for the electrolytic deposition of a metal is distinguished from a bath known as a "chemical bath" for depositing the same metal not only by its operating conditions (current flow and presence electrodes in the case of the electrochemical bath) but also by the nature of its constituents.

Thus, for example, in the case where gold is deposited via a soluble salt such as an aurocyanide, a chemical bath will comprise a large quantity of reducing agents and will be characterized by the presence of a high concentration in free cyanides, while in an electrochemical bath we will seek to eliminate, as much as possible, the presence of free cyanides. Furthermore, the orders of magnitude of the deposition rates from a chemical bath and from an electrochemical bath have nothing to do with, which precludes a priori the use of chemical baths to produce continuous deposits on substrates. .

What essentially characterizes the first aspect of the invention is that the electrolytic bath can be constituted by any bath conventionally used for the electrodeposition of gold or gold alloys, from the moment when it also contains a compound organic comprising one or two aldehyde functions as defined above.

The electrolytic baths of the invention advantageously contain from 1.5 to 2.5 moles of said organic compound comprising one or two aldehyde functions per mole of gold, preferably of the order of 2 moles of said organic compound per mole of gold .

It will be readily understood that the amount of organic compound with an aldehyde function will depend both on the concentration of soluble gold salts in the bath and on the molar mass of this aldehyde.

The electrolytic baths of the invention advantageously contain gold contents which can vary widely but in general are between 1 and 100 g / L (the contents of soluble salts are related to the metal content).

Thus, the content of compounds carrying one or two aldehyde functions can vary within very large proportions. In general, the baths of the invention contain, depending on the molar base of the aldehyde, from 0.1 to 50 g / L of at least one organic compound comprising one or two aldehyde functions as defined previously.

The family of organic compounds which can be used according to the invention as an auxiliary agent in an electrochemical deposition bath for gold or gold alloys is an organic compound comprising from 3 to 20 carbon atoms and at least one aldehyde function .

They can be aliphatic compounds but also compounds containing one or more rings, these compounds possibly also containing at least one heteroelement such as oxygen, nitrogen, sulfur and phosphorus.

The family of products which can be used according to the invention also includes the salts of the above products and in particular the sulfonates which also have the advantage of having surfactant properties if they are sufficiently long.

In general, advantageously one will choose among the above products those which are soluble in the medium or at least those which are soluble therein by adding, if necessary, a surfactant or any other product making it possible to make soluble in the bath. the organic compound with aldehyde function.

According to a variant, the organic compounds used according to the invention will be chosen from aldehydes of formula R-CHO in which R is a linear or branched, saturated or unsaturated aliphatic group comprising from 3 to 12 carbon atoms.

The alkyl chains comprising from 3 to 9 carbon atoms will preferably be chosen.

According to another variant, the organic compound comprises from 4 to 20 carbon atoms and comprises at least one saturated, unsaturated or aromatic ring or is in the form of a salt, in particular a sulfonate, of one of these compounds .

When resorting to organic compounds containing a ring, in particular when this ring is aromatic, for obvious reasons of solubility of this compound, a compound is preferably chosen in which the ring, in particular the aromatic ring, carries at most two substituent groups.

According to yet another variant, the organic compound comprises 4 to 20 carbon atoms and contains at least one saturated, unsaturated or aromatic heterocycle or is in the form of a salt, in particular a sulfonate, of one of these compounds.

Advantageously, the organic compound used according to the invention will be chosen from the group consisting of propionaldehyde, butyraldehyde, isovaleraldehyde, valeraldehyde, capronalddehyde, hexaldehyde, heptaldehyde, caprylic aldehyde, pelargonaldehyde, decanal, undecanal, laurylaldehyde, acrolein, crotonal, benzaldehyde, phenylacetaldehyde, cuminic aldehyde, cinnamaldehyde, anisaldehyde, phthalic aldehyde.

As explained above, the electrolytic bath intended for depositing gold or its alloys will moreover comprise all the additives commonly used in such baths.

• a) différents métaux agissant comme brillanteurs minéraux ou comme durcisseurs,
• b) des métaux dits "métaux secondaires" ou "métaux d'alliages" généralement choisis dans les périodes 4, 5 et 6 de la classification périodique des éléments selon Mendeleïev, à une concentration comprise généralement entre 0,01 et 60 g/L.
  Ces métaux d'alliages sont d'une façon générale choisis parmi le cobalt, le nickel, le fer, l'indium, le cadmium, l'arsenic, le manganèse, l'étain, le plomb et le cuivre.
  Les métaux préférés seront le cobalt, le nickel et le fer.
  Toutefois, c'est avec le cobalt que l'effet de diminution de la résistance de contact dû à la présence du composé à fonction ald éhyde sera le plus net.
  D'une façon générale, le métal secondaire est introduit dans le bain sous forme de sulfate, de carbonate, d'hydroxyde, d'oxyde, d'acétylacétonate, de citrate, de gluconate, de sulfamate ou d'un mélange de ces composés.
• c) des agents brillanteurs :
  Ces agents brillanteurs sont tous ceux classiquement utilisés dans le domaine du dépôt électrolytique de l'or.
  On choisira avantageusement comme agent brillanteur l'acide 3-(3-pyridyl) acrylique ou l'acide 3-(3-quinolyl) acrylique ou un de leurs sels à des teneurs comprises entre 0,01 et 10 g/L.
• d) des sels conducteurs :
  Ces sels contribuent au bon fonctionnement du système électrolytique. D'une façon générale, le bain contient au moins 10 g/L d'un sel conducteur, de préférence choisi dans le groupe constitué des sels de citrate, de phosphate, de borate ou de sulfate et de leurs mélanges.
• e) des agents de type tampon destinés à stabiliser le pH, ledit tampon étant de préférence de type acétique, citrique, borique, phosphorique ou phtalique.
• f) des agents mouillants :
  A titre d'agents mouillants, on choisira de préférence le tolyletriazol ou le benzotriazol.

It may therefore include in particular:

• a) different metals acting as mineral brighteners or as hardeners,
• b) metals called "secondary metals" or "alloy metals" generally chosen in periods 4, 5 and 6 of the periodic classification of the elements according to Mendeleev, at a concentration generally between 0.01 and 60 g / L.
  These alloy metals are generally chosen from cobalt, nickel, iron, indium, cadmium, arsenic, manganese, tin, lead and copper.
  The preferred metals will be cobalt, nickel and iron.
  However, it is with cobalt that the effect of reducing the contact resistance due to the presence of the aldehyde-functional compound will be most marked.
  Generally, the secondary metal is introduced into the bath in the form of sulfate, carbonate, hydroxide, oxide, acetylacetonate, citrate, gluconate, sulfamate or a mixture of these compounds .
• c) brightening agents:
  These brighteners are all those conventionally used in the field of electrolytic deposition of gold.
  Advantageously, the 3- (3-pyridyl) acrylic acid or the 3- (3-quinolyl) acrylic acid or a salt thereof at a content of between 0.01 and 10 g / L will be chosen as the brightening agent.
• d) conductive salts:
  These salts contribute to the proper functioning of the electrolytic system. Generally, the bath contains at least 10 g / L of a conductive salt, preferably chosen from the group consisting of citrate, phosphate, borate or sulfate salts and their mixtures.
• e) agents of the buffer type intended to stabilize the pH, said buffer preferably being of the acetic, citric, boric, phosphoric or phthalic type.
• f) wetting agents:
  As wetting agents, tolyletriazol or benzotriazol will preferably be chosen.

Finally, even if the invention is not limited to electrolytic baths in which the gold is in the form of aurocyanide or of auricyanide, the invention applies very particularly to this type of bath, well known for having as disadvantage in the prior art of causing pollution of the electrolytic deposit by formation of polymers.

Thus, the organic compound with aldehyde function according to the invention is found to be introduced in a particularly advantageous manner in the baths in which the gold is in the form of auri- or aurocyanide but it can also be used in other baths with the effect of improving the performance of electroplating. We can, in particular, introduce it into baths where gold is in the form of aurosulfite, aurothiosulfate or gold chloride.

According to a second aspect, the invention relates to a method of electroplating gold or a gold alloy, according to which the electrolysis of an electrolytic bath as defined above is carried out.

As previously explained, the presence of an aldehyde-functional organic compound as defined above considerably improves the performance of all electrolytic baths of deposits of gold or gold alloys and in particular cyanide baths containing gold under form of aurocyanide or auricyanide.

The main advantages of the introduction of the organic compound with aldehyde function are to improve the speed of electroplating, to decrease the contact resistance and to allow the use of particularly high current densities.

The improvement of the invention is applicable to all types of electrolytic gold deposition processes and for all types of application, whether in decoration, for the preparation of electronic components and in connectors.

The current densities used in the methods of the invention can vary over wide ranges, generally between 0.5 and 120 A / dm ² .

Of course, current densities of less than 10 A / dm ² will generally be used for applications in the decoration field, whereas for so-called "high speed" applications, current densities of the order of 10 will be used. at 120 A / dm ² , this type of high-speed process is generally reserved for the electronics and connector industry.

The method of the invention, insofar as it allows the use of particularly high current densities of up to 120 A / dm ² finds a particularly advantageous application in electronic applications where it is sought to work with a maximum deposition rate and where the desired deposits must be, among other things, shiny, ductile and non-porous. To obtain high productivity, the baths used in this field must operate at the highest possible current densities, which allows in particular the use of the auxiliaries used according to the invention.

However, the baths of the invention can also be used at lower speeds and current densities and, in particular in decoration applications.

As previously stated, the improvement of the invention is applicable to all the processes conventionally used for the deposition of gold or gold alloys.

In particular, all the types of conventionally used anodes, soluble or insoluble, can be used in the process of the invention.

However, use will preferably be made of insoluble anodes and preferably of platinum titanium, of platinum coated with iridium oxide or of precious metal such as platinum and a metallized substrate will be placed as a cathode.

Finally, as already explained and as is apparent from the examples which follow, the invention relates according to a third aspect to the use of an organic compound as defined above in an electrolytic bath intended for the electrolytic deposition of gold or of a of its alloys, as an auxiliary agent improving the speed of electrodeposition of gold or its alloys and / or decreasing the contact resistance.

• Or   1 à 100 g/L
• Métal d'alliage tel que Co, Ni, Fe, Cd   0 à 50 g/L
• Brillanteur, de préférence acide 3-(3- pyridyl) acrylique   0,01 à 10 g/L
• Acide citrique et/ou citrate de potassium   10 à 300 g/L
• Aldéhyde   0,01 à 100 g/L

Les conditions opératoires sont avantageusement les suivantes :

• pH   3,5 à 12 (en fonction de la nature du complexe d'or)
• Température   10 à 75°C
• Agitation   Modérée, à très vigoureuse
• Densité de courant   0,1 à 80 A/dm²
• Anode   Toutes celles classiquement utilisées, en particulier titane platiné, platine recouvert d'oxyde d'iridium ou métal précieux tel que le platine

The preferred bath formulations according to the present invention can be non-restrictively described by the following general composition in which the concentrations of metallic derivatives (gold and optionally alloy metals) are related to the metal:

• Gold 1 to 100 g / L
• Alloy metal such as Co, Ni, Fe, Cd 0 to 50 g / L
• Gloss, preferably 3- (3- pyridyl) acrylic acid 0.01 to 10 g / L
• Citric acid and / or potassium citrate 10 to 300 g / L
• Aldehyde 0.01 to 100 g / L

The operating conditions are advantageously as follows:

• pH 3.5 to 12 (depending on the nature of the gold complex)
• Temperature 10 to 75 ° C
• Moderate to very vigorous agitation
• Current density 0.1 to 80 A / dm ²
• Anode All those conventionally used, in particular platinum titanium, platinum coated with iridium oxide or precious metal such as platinum

EXAMPLES

In the examples, the concentrations of gold and alloy metals are referred to the metal.

• a) Dans tous ces exemples, le substrat à métalliser, est préparé par une procédure convenable, selon la nature du métal. Par exemple, les substrats cuivreux ou en nickel, sont préalablement dégraissés électrolytiquement, après un rinçage à l'eau, le substrat est dépassivé dans de l'acide sulfurique dilué à 5-20% en volume, le substrat est rincé à l'eau désionnisée avant d'être introduit dans un des électrolytes de l'invention.

The following examples illustrate the good performance of the invention.

• a) In all of these examples, the substrate to be metallized is prepared by a suitable procedure, depending on the nature of the metal. For example, copper or nickel substrates are pre-degreased electrolytically, after rinsing with water, the substrate is passivated in sulfuric acid diluted to 5-20% by volume, the substrate is rinsed with water deionized before being introduced into one of the electrolytes of the invention.

• Comme sel conducteur, on peut utiliser le sulfate de sodium, mais aussi le sulfate de potassium ou le sulfate d'ammonium ou un de leur mélange.
• Un tampon acétique, citrique, borique, orthophosphorique, ou tout autre système tampon efficace dans la gamme de pH concernée peuvent être utilisés pour stabiliser le pH du bain.
• Un agent mouillant peut être ajouté pour éviter l'adsorption d'hydrogène formé à la cathode lors de l'électrolyse et par conséquent éviter son inclusion dans le dépôt. Un agent mouillant cationique, anionique ou non ionique peut convenir, on pourra par exemple utiliser le benzotriazol en faible quantité.

Optionally, some additives can be added. So :

• As conductive salt, it is possible to use sodium sulphate, but also potassium sulphate or ammonium sulphate or one of their mixture.
• An acetic, citric, boric, orthophosphoric buffer, or any other effective buffer system in the pH range concerned can be used to stabilize the pH of the bath.
• A wetting agent can be added to prevent the adsorption of hydrogen formed at the cathode during electrolysis and therefore avoid its inclusion in the deposit. A cationic, anionic or nonionic wetting agent may be suitable, for example, benzotriazol may be used in small quantities.

EXAMPLE 1 Decorative gold bath (comparative example)

• Gold (introduced as potassium aurocyanide) 2 to 10 g / L
• Ammonium citrate 90 to 130 g / L
• Trans 3- (3-pyridyl) acrylic acid 0.5 to 1.5 g / L
• pH (Citric acid / potassium hydroxide) 3.5 to 5
• Temperature 40 to 60 ° C
• Moderate to vigorous agitation
• Current density 1 to 20 A / dm ²
• Platinum Titanium Anode

This bath deposits more than 99.9% gold, the deposit is shiny, ductile, with a contact resistance of 12 mOhm, low porosity and excellent resistance to corrosion. Its electrodeposition speed is 0.05 to 0.5 µm / min. it is ideally used in the so-called "fastening" or "dipping" processes.

EXAMPLE 2 Decorative gold bath

• Gold (introduced as potassium aurocyanide) 2 to 10 g / L
• Ammonium citrate 90 to 130 g / L
• Trans 3- (3-pyridyl) acrylic acid 0.5 to 1.5 g / L
• Pelargonaldehyde 0.5 to 4 g / L
• pH (Citric acid / potassium hydroxide) 3.5 to 5
• Temperature 40 to 60 ° C
• Moderate to vigorous agitation
• Current density 1 to 20 A / dm ²
• Platinum Titanium Anode

This bath deposits more than 99.9% gold, the deposit is shiny, ductile, with a contact resistance of 5 mOhm, low porosity and excellent resistance to corrosion. Its electrodeposition speed is 0.1 to 0.7 µm / min. It is ideally used in so-called "fastening" or "dipping" processes.

EXAMPLE 3 Decorative gold bath

• Gold (introduced as ammonium aurosulfite) 2 to 10 g / L
• Potassium bisulphite 2 to 15 g / L
• Arsenic (as oxide) 2 to 50 mg / L
• Isovaleraldehyde 0.5 to 4 g / L
• pH (Boric acid / potassium hydroxide) 8 to 12
• Temperature 40 to 60 ° C
• Moderate to vigorous agitation
• Current density 1 to 10 A / dm ²
• Platinum Titanium Anode

This bath deposits more than 99.9% gold, the deposit is shiny, ductile, has low porosity and excellent corrosion resistance, with a contact resistance of 7 mOhm. It is deposited at a speed of 0.1 to 0.7 µm / min. It is ideally used in the so-called "fastening" or "dipping" processes.

EXAMPLE 4 High-speed gold-cobalt bath

• Gold (introduced as potassium aurocyanide) 5 to 20 g / L
• Cobalt (as sulfate) 0.5 to 1.5 g / L
• Potassium citrate 50 to 180 g / L
• Trans 3- (3-pyridyl) acrylic acid 0.5 to 1.5 g / L
• Butyraldehyde 0.5 to 10 g / L
• pH (Citric acid / potassium hydroxide) 3.5 to 5
• Temperature 40 to 60 ° C
• Vigorous to very vigorous agitation
• Current density 10 to 80 A / dm ²
• Platinum Titanium Anode

This bath deposits gold at almost 99.5%, the deposit is shiny, ductile, with low contact resistance, low porosity and excellent resistance to corrosion. Cobalt acts here not only as a metallic brightener but also as a hardening alloy metal. It allows the deposit to present a good resistance to friction and to pass positively the test known as "British Telecom". It is ideally used in the so-called "continuous" "selective deposition with masking" or "selective jet deposition" processes.

The contact resistance is 5 mOhm after thermal aging for 1 hour at 250 ° C. As an indication, it is under the same conditions of 14 mOhm, when the bath does not contain aldehyde. (Measurement according to standard ASTM B667-97).

The deposition rate is 0.5 to 11 µm / min with aldehyde, 0.4 to 8.5 µm / min without aldehyde using as a deposition means a rotary cathode rotating at a speed of 1.5 m / s or jet deposit material.

EXAMPLE 5 High speed gold-nickel bath

• Gold (introduced as potassium aurocyanide) 5 to 20 g / L
• Nickel (as sulfate) 0.5 to 1.5 g / L
• Potassium citrate 50 to 180 g / L
• Trans 3- (3-pyridyl) acrylic acid 0.5 to 1.5 g / L
• Butyraldehyde 0.5 to 10 g / L
• pH (Citric acid potassium hydroxide) 3.5 to 5
• Temperature 40 to 60 ° C
• Vigorous to very vigorous agitation
• Current density 10 to 80 A / dm ²
• Platinum Titanium Anode

This bath deposits gold at almost 99.5%, the deposit is shiny, ductile, with a contact resistance of 7 mOhm, low porosity and excellent resistance to corrosion, and leads to a speed of 0, 5 to 11 µm / min. Nickel acts as a metallic brightener and as a hardening alloy metal. It allows the deposit to present a good resistance to friction and to pass positively the test called "British Telecom". It is ideally used in the so-called "continuous", "selective deposition with masking" or "selective jet deposition" processes.

EXAMPLE 6 High speed gold-cobalt bath

• Gold (introduced as potassium aurocyanide) 5 to 20 g / L
• Cobalt (as acetylacetonate) 0.5 to 1.5 g / L
• Potassium citrate 50 to 180 g / L
• Formic acid 30 to 60 g / L
• Trans 3- (3-pyridyl) acrylic acid 0.5 to 1.5 g / L
• Heptaldehyde 0.5 to 10 g / L
• pH (Citric acid / potassium hydroxide) 4.5 to 6
• Temperature 40 to 60 ° C
• Vigorous to very vigorous agitation
• Current density 10 to 80 A / dm ²
• Platinum Titanium Anode

This bath deposits gold at almost 99.5%, the deposit is shiny, ductile, with a contact resistance of 7 mOhm, low porosity and excellent resistance to corrosion, and leads to a deposition rate of 0.5 to 11 µm / min. Cobalt acts as a metallic brightener and as a hardening alloy metal. It allows the deposit to present a good resistance to friction and to pass positively the test known as "British Telecom". ". It is ideally used in the so-called "continuous", "selective deposition with masking" or "selective jet deposition" processes.

EXAMPLE 7 High Speed Gold-Cobalt Bath

• Gold (introduced as potassium aurocyanide) 5 to 20 g / L
• Cobalt (as gluconate) 0.5 to 1.5 g / L
• Potassium citrate 10 to 50 g / L
• Trans 3- (3-pyridyl) acrylic acid 0.5 to 1.5 g / L
• Hexaldehyde 0.5 to 10 g / L
• pH (Citric acid / potassium hydroxide) 4.5 to 6
• Temperature 40 to 60 ° C
• Current density 10 to 80 A / dm ²
• Platinum Titanium Anode

This bath deposits gold at almost 99.5%, the deposit is shiny, ductile, with a contact resistance of 7 mOhm, low porosity and excellent resistance to corrosion. It leads to a deposition rate of 0.5 to 11 µm / min. Cobalt acts as a metallic brightener and as a hardening alloy metal. It allows the deposit to present a good resistance to friction and to pass positively the test known as "British Telecom". ". It is ideally used in the so-called "continuous", "selective deposition with masking" or "selective jet deposition" processes.

Claims (21)

1. An aqueous electrolytic bath for electrochemically depositing gold or its alloys comprising at least one soluble gold compound intended to be deposited electrolytically and, optionally, at least one secondary metal compound intended to be co-deposited in the form of an alloy with gold, characterised in that it further comprises 0.3 to 3 moles, per mole of gold contained in the electrolytic bath, of an organic compound comprising one or two aldehyde functions, said organic compound being an organic compound having 3 to 20 carbon atoms and one or two aldehyde functions in the form :

   ■ of a linear, branched, saturated or unsaturated aliphatic group, or

   ■ of a group containing at least one saturated, unsaturated or aromatic ring,

   it being possible for said organic compound to further comprise at least one heteroelement selected from oxygen, nitrogen, sulphur, and phosphorus, or to be in the form of a salt, particularly in the form of a sulphonate.
2. The electrolytic bath according to claim 1, characterised in that it contains 1.5 to 2.5 moles of said organic compound comprising one or two aldehyde functions per mole of gold, preferably of the order of 2 moles of said organic compound per mole of gold.
3. The electrolytic bath according to one of claims 1 or 2, characterised in that said organic compound is an aldehyde of formula R-CHO in which R is a linear or branched, saturated or unsaturated aliphatic group having 3 to 12 carbon atoms.
4. The electrolytic bath according to one of claims 1 or 2, characterised in that said organic compound has 4 to 20 carbon atoms and comprises at least one saturated, unsaturated or aromatic ring, or is in the form of a salt, particularly in the form of a sulphonate, of one of these compounds.
5. The electrolytic bath according to one of claims 1 or 2, characterised in that said organic compound has 4 to 20 carbon atoms and contains at least one saturated, unsaturated or aromatic heterocycle, or is in the form of a salt, particularly in the form of a sulphonate, of one of these compounds.
6. The electrolytic bath according to one of claims 1 to 3, characterised in that said organic compound is selected from the group consisting of propionaldehyde, butyraldehyde, isovaleraldehyde, valeraldehyde, capronaldehyde, hexaldehyde, heptaldehyde, caprylic aldehyde, pelargonaldehyde, decanal, undecanal, laurylaldehyde, acrolein, crotonal, benzaldehyde, phenylacetaldehyde, cuminic aldehyde, cinnamaldehyde, anisic aldehyde, phthalic aldehyde.
7. The electrolytic bath according to one of claims 1 to 6, characterised in that it contains 1 to 100 g/L of gold.
8. The electrolytic bath according to one of claims 1 to 7, characterised in that it contains at least one metal acting as inorganic brightener or as hardener.
9. The electrolytic bath according to one of claims 1 to 8, characterised in that it contains at least one secondary metal selected from periods 4, 5 and 6 of Mendeleev's periodic classification of the elements, at a concentration of between 0.01 and 60 g/L.
10. The electrolytic bath according to claim 9, characterised in that said secondary metal is cobalt, nickel or iron, preferably cobalt.
11. The electrolytic bath according to claim 9, characterised in that said secondary metal is introduced into said bath in the form of sulphate, carbonate, hydroxide, oxide, acetylacetonate, citrate, gluconate, sulphamate, or of a mixture of these compounds.
12. The electrolytic bath according to one of claims 1 to 11, characterised in that it contains an organic brightening agent.
13. The electrolytic bath according to claim 12, characterised in that it contains 0.01 to 10 g/L 3-(3-pyridyl)acrylic acid or 3-(3-quinolyl)acrylic acid or one of their salts.
14. The electrolytic bath according to one of claims 1 to 13, characterised in that it contains at least 10 g/L of a conducting salt, preferably selected from the group consisting of citrate, phosphate, borate or sulphate salts, and their mixtures.
15. The electrolytic bath according to one of claims 1 to 14, characterised in that it contains a buffer intended for stabilising the pH, said buffer preferably being of acetic, citric, boric, phosphoric, or phthalic type.
16. The electrolytic bath according to one of claims 1 to 15, characterised in that it contains at least one wetting agent, preferably tolyltriazole or benzotriazole.
17. The electrolytic bath according to one of claims 1 to 16, characterised in that the gold is introduced in the form of cyanoaurate (I) or cyanoaurate (III).
18. A method of electrodepositing gold or an alloy of gold, characterised in that it comprises electrolysing an electrolytic bath as defined in one of claims 1 to 17 in implementing current densities of between 0.5 and 120 A/dm².
19. The method according to claim 18, characterised in that said electrolysis is carried out using insoluble anodes, preferably of platinum-containing titanium, of iridium oxide-covered platinum or of precious metal such as platinum and a metallised substrate placed as cathode.
20. Use, in an electrolytic bath intended for electrolytically depositing gold or one of its alloys, of an organic compound as defined in claim 1 or one of claims 3 to 6, as auxiliary agent which improves the speed of electrodeposition of gold or of its alloys and/or which reduces the contact resistance.
21. Use according to claim 20, characterised in that said agent is used at a concentration of 0.3 to 3 mole per mole of gold contained in the bath, preferably at a concentration of 1.5 to 2.5 moles, per mole of gold contained in the bath, more preferably at a concentration of the order of 2 moles per mole of gold contained in the bath.