Pd and pd-ni electrolyte baths

[0001] The invention relates to an electrolyte for the galvanic deposition of palladium or palladium alloys on metallic or conductive substrates. Especially it concerns Pd electrolyte containing possibly further metals and organic oligoamine as a complexing substance with which alloy coatings with e.g. 80% Pd can be deposited for technical and decorative applications. However, the invention relates to a suitable electroplating process using these electrolytes and the special palladium salt preferably used in this method.

[0002] Electroplating deposition of palladium or palladium alloys on metallic substrates has a variety of decorative and technical fields of application. Galvanically settling pure palladium as well as nickel-palladium coatings, possibly with Goldflash, are recognized materials, e.g. for low-current contacts or plug contacts (e.g. for conductor plates) and can be seen as a substitute for hard gold [Galvanotechnik 5 (2002 ), 1210ff, Simon and Yasumura: "Galvanische

Palladiumschichten fur technische Anwendungen in der Elektronik "]. Palladium deposits with very small layer thicknesses on so-called Lead-Frames in semiconductors can also replace the silver used in the connection [Galvanotechnik 6 (2002), 1473ff, Simon and Yasumura:" Galvanische Palladiumschichten fur technische Anwendungen in der Elektronik "].

[0003] Normal palladium-nickel electrolytes contain ammonia and chloride and therefore pose a potential health risk to operating personnel and are harmful from the perspective of corrosion of equipment materials. Ammonia tends to evaporate at ambient temperature. Many sold electrolytes operate at 40 ° C to 60 ° C and therefore cause strong emissions, which are not only irritating to the respiratory tract, but also lead to a lowering of the pH value by volatile ammonia. The electrolyte must therefore be kept at a constant pH by the continuous supply of ammonia.

[0004] To date, several processes without ammonium and / or chloride are known. For example, one type contains organic amines, which, however, form very quickly under previously alkaline operating conditions (up to 65 ° C, pH 9 to 12) and lead to precipitation. In addition, with such electrolytes, inadequate adhesion to nickel-plated substrates must be leveled by processes prior to palladium plating, thereby generating additional costs (Plating & Surface Finishing, (2002) 8, pp. 57-58, JA Abys "Palladium Plating") .

[0005] A recently published article describes a chloride-free palladium-nickel electrolyte based on sulfate (Galvanotechnik, 99 (2008) 3 "pp. 552-557; Kurtz, O .;

- 2 Barhtelmes, J .; Riither, R., "Die Abscheidung von Palladium-Nickel-Legierungen aus chloridfreien Elektrolyten"). The coatings obtained from there show beneficial properties, however, they are ammoniacal, slightly alkaline electrolytes with known disadvantages.

[0006] Another method with organic amines is known from US 4278514 and works at pH values ​​from 3 to 7. Such baths contain imide compounds (e.g. succinimide) as a glossing additive. They are primarily suitable for decorative purposes, because they apply to pure palladium baths. The current densities used are a maximum of 4 A / dm². The described baths work to adjust the pH value with phosphor buffers. However, the incorporation of phosphorus in the deposition layer can negatively affect the quality of the deposition.

[0007] Patent DE4428966 (US5415685) describes a palladium bath in which, in addition to a palladium compound (namely palladium diaminodiazotine) and various ammonium salts (sulfate, citrate and phosphate), a combination of brightening additives is also mentioned. The described ammoniacal process works in the pH range between 5 and 12. A combination of sulfonic acid and an aromatic N-heterocycle is disclosed with the claimed brighteners. Namely, mention is made of oformylbenzolesulfonic acid and 1- (3-sulfopropyl) -2-vinylpyridinebetaine, among others. Further pyridine derivatives mentioned in detail are 1- (3-sulfopropylpyridine betaine and 1- (2-hydroxy-3-sulfopropylpyridine betaine). Both of these substances, according to the authors, have a negative effect on the gloss of the coatings obtained.

[0008] Already in 1986, galvanic deposition of palladium-nickel coatings from electrolyte based on ethylenediamine by Raub and Walz was described (Metalloberflache, 40 (1986) 5, pp. 199-203, D. Walz und Ch. J. Raub, Carl Hanser Verlag, Munich, "Die galvanische Palladium-Nickel-Abscheidung aus ammoniakfreien Grundelektrolyten mit Ethylendiamin als Komplexbildner"). It is explained here that the substance forming the ethylenediamine complexes is able to shift the deposition potentials of both metals so far that it is possible to deposit the alloy.

[0009] The process of US6743346 also uses ethylenediamine as a complexing substance and feeds palladium as a solid compound from palladium sulfate and ethylenediamine. The salt contains 31 to 41% palladium (molar ratios [SO4]: [Pd] between 0.9 and 1.15 and [ethylenediamine]: [Pd] between 0.8 and 1.2). It is not soluble in water, but it dissolves in electrolytes with an excess of ethylenediamine (Plating & Surface Finishing, (2007) 4, pp. 26-35, St. Burling "Precious Metal Plating and the Environment"). The salt allows the use of palladium with less ethylenediamine than usual, but this leads to enrichment of sulfate in the electrolyte salinity and thus to shortening the bath life. The substances 3- (3-pyridyl) acrylic acid or 3- (3-quinolyl) acrylic acid and their salts. It has been mentioned that sulfonate-based brighteners are not able, in particular at current densities from 15 to 150 A / dm2, to guarantee the desired glow in galvanic electrolytes.

[0010] WO 9800652 discloses palladium hydroxocomplexes with respect to them

- 3 applications in electrolytic coating baths. These compounds may possess oligoamines as further complexing reagents. There are no indications in the publication that polishing systems based on neutral salts can be used.

[0011] US 5,178,745 relates to acid palladium electrolytes which as compound complexing agents are selected from the group having organic diamines. It is required that the electrolyte contains an adequate proportion of chloride ions.

[0012] From US 4406755, an electrolytic coating solution is also known which contains palladium in the form of its soluble complexes, among others. with organic polyamines. The bath may show neutral salts, but usually works at acidic pH.

[0013] US 20030047460 refers to new complex salts of palladium sulfate and ethylenediamine. These three components should be contained in an appropriate relationship to each other in the bath. This electrolyte bath also works at an acid pH value.

[0014] The object of the invention was to provide, against the background of the prior art, a further electrolyte and a method operating with this electrolyte, which help to overcome the above-mentioned disadvantages. Specified electrolyte composition or the right way should especially help, also at high current densities and fast electrolysis processes, to produce shiny surfaces, which would be particularly beneficial from an economic and ecological point of view.

[0015] These and further tasks not mentioned here, however, arising from the state of the art are approximately solved by the use of an electrolyte according to the present claim 1. Preferred embodiments of the electrolytes according to the invention are set out in the following claims 2-11 dependent on claim 1. Claim 12 and dependent on claim 11, the following claims 12-15 relate to the method according to the invention with its preferred implementation possibilities. Claim 16 relates to an electrolyte component according to the invention preferred for use according to the invention.

[0016] Due to the use of an aqueous electrolyte for the galvanic deposition of palladium or a palladium alloy on a metallic substrate or conductive, which possesses metal ions complexed with organic oligoamines in the form of their salts with an oxide of hydroxide, hydroxide, bicarbonate and / or carbonate as counterions and polishes based on an inert salt from a quaternary ammonium group and sulfonic acid, it is surprisingly simple to solve with successful task. By means of the electrolytes according to the invention or by the methods used according to the invention, it is now possible, both at low as well as at high current densities, to produce the desired shiny surfaces with excellent quality results. The electrolyte composition according to the invention is in no way approximate from the state of the art.

[0017] The electrolyte according to the invention allows the palladium to be deposited alone or in the form of an alloy bound to other metals. As further metals, those known to the skilled person may be used for this purpose. With regard to these, it may be, for example, nickel, cobalt, iron, indium, gold, silver or tin and mixtures thereof. Preferably, the depositing metal ions are selected from the group consisting of nickel, cobalt, iron and mixtures thereof. The electrolyte contains these metals in the form of their soluble salts. As salts, especially those selected from the group of phosphates, carbonates, bicarbonates, hydroxides, oxides, sulfates, sulfamates, alkanesulfonates, pyrophosphates, phosphonates, nitrates, salts of carbonic acid and mixtures thereof are taken into account.

[0018] The skilled person selects the concentrations used for the metal electrolytes on the basis of his general specialist knowledge. It has been shown that favorable results can be achieved when palladium is used in concentrations of 1-100 g / l, preferably 2-70 g / l, and most preferably 4-50 g / l and particularly very preferably 5-25 g / l in for electrolyte.

[0019] Further deposition of metal ions may be included in concentrations of <50g / l relative to electrolyte. Preferably the concentration of these ions in the electrolyte is <40 g / l, further preferably <30 g / l with respect to the electrolyte. As noted above, the uniform deposition of metal ions occurs under the conditions of the invention, inter alia, preferably when they are complexed. Organic oligoamines have proved to be suitable ligands for these complexes. The use of multi-coordinating ligands, especially those based on di, tri or tetraamines, is preferred. Particularly preferred are those with 2 to 11 C atoms. Particularly preferred is the use of ligands selected from the group consisting of ethylenediamine, trimethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, 1,2-propylene diamine, trimethylene tetraamine, hexamethylene tetramine. In addition, ethylenediamine (EDA) is preferred in this context.

[0020] The skilled person has discretion as to the amount of oligoamine used. When estimating the quantity, he will be guided by the fact that a sufficient amount must be provided to obtain as even a palladium or deposition as possible. palladium alloy. On the other hand, at least economic considerations limit the use of large amounts of oligoamines. An amount of 0.1-5 mol / L oligoamines in the electrolyte is preferred. Further, the concentration is preferably in the range between 0.3 - 3 mol / l. The concentration of oligoamines is particularly preferably 0.5 to 2 mol / l electrolyte.

[0021] Also, the pH of the electrolytes according to the invention can be adjusted according to the skilled person for each application in the acid to neutral range. A setting between pH 3 and pH 7 appears to be advantageous. Furthermore, a range from pH 3.5 to pH 6.5, particularly preferably from pH 4 to pH 6 and particularly preferably around pH 5 to pH 5.5 is preferred. .

[0022] The electrolyte according to the invention exhibits polishing agents based on an inert salt from the quaternary ammonium or acid group. Preferably, the quaternary ammonium compound is those in which the positively charged nitrogen is part

- 5 aromatic ring systems. Such molecules are considered by those skilled in the art to possess mono- or polyatomic aromatic systems, e.g. pyridine, pyrimidine, pyrazine, pyrroline, imidazoline, thiazoline, indoline, carbazoline or such substituted systems. Pyridine or alkyl or alkenyl substituted pyridine derivatives. In addition, it is preferable to choose a polishing agent that has as a component of the molecule a quaternary ammonium compound based on a pyridine derivative.

[0023] As a further component of the molecule, the polishing agent contains an acid group such that it propagates predominantly in the polishing agent to a neutral salt or betaine. Acid group is primarily a group which, under the given conditions, is present in the electrolyte predominantly in deprotonated form. The acid group can be derived from those selected from the group consisting of phosphoric acid, phosphonic acid, sulfuric acid, sulfonic acid, and carbonic acid. Sulfonic acid is particularly preferred as a polishing component.

[0024] The acid group and the quaternary ammonium portion of the brightener may be bonded via (C1-C8) -alkylene, (C1-C8) -alkenylene, (C6-C18) -arylene, which may be present as substituted. The most preferred compounds in this context have been found to be those selected from the group consisting of 1- (3-sulfopropyl) -2-vinylpyridine betaine), 1- (3-sulfopropylpyridine betaine and 1- (2-hydroxy-3-sulfopropylpyridine betaine).

[0025] The brightener may be used in the electrolyte in amounts obvious to those skilled in the art. The upper limit is created by the amount of rinse aid at which the expenditure of costs through its use is no longer justified by the effect achieved. It is therefore preferable to use polishes in quantities of 1 to 10,000 mg / l electrolyte. Particularly preferably the brightener is used in a concentration of 5 - 5000 mg / l electrolyte, most preferably in an amount of 10 -1000 mg / l electrolyte.

[0026] The electrolyte of the invention may contain further components that have a positive effect in terms of bath stability, metal deposition behavior, material quality and electrolysis conditions. As such, in particular, agents that reduce the internal tension of the coating, crosslinking agents, conductive salts, further brightening agents and / or buffering substances, etc. are taken into account by the specialist.

[0027] Cross-linking agents selected from the following groups consisting of anionic cross-linking agents such as sodium lauryl sulfate, sodium dodecylbenzene sulfonate, sodium dioctyl sulfosuccinate, non-ionic cross-linking agents such as polyethylene glycol fatty acid esters can be used as electrolyte surface tension reducing additives. or cationic crosslinkers such as cetyltrimethylammonium bromide.

[0028] Preferably conductive salts selected from the group may be used to improve the conductivity and the ability to evenly distribute the electrolyte.

- 6 consisting of potassium sulphate or sodium, phosphate, nitrate, alkanesulfonate, sulfamate and mixtures thereof.

As buffering substances, preferably, those selected from the group consisting of boric acid or phosphates or carbonic acid and / or their salts can be used, e.g. acetic acid, citric acid, tartaric acid, oxalic acid, succinic acid, malic acid, lactic acid, phthalic acid.

[0030] As further brightening additives, preferably those selected from the group consisting of N, N-diethyl-2-propino-1-amine, 1,1-dimethyl-2-propinyl-1-amine may be used,

2-butene-1,4-diol, 2-butene-1,4-dioletroxylate, 2-butene-1,4-diolpropoxylate, 3-hexine-2,5-diol and sulfopropylated 2-butene-1,4-diol or their salt. Further brighteners may be allylsulfonic acid and / or vinylsulfonic acid and / or propargylsulfonic acid or their alkali salts in quantities of 0.01 to 10 g / l of electrolyte.

[0031] As compounds reducing the internal tension of the coating, preferably those selected from the group consisting of imin disuccinic acid and / or sulfamic acid and / or sodium saccharinate can be used.

[0032] It is preferred whenever no further depositing metal salts with inorganic anions are added to the electrolyte except sulfate or nitrate, bicarbonate or carbonate or oxide, hydroxide or mixtures thereof. This helps to avoid excessive enrichment of various ions in the system, because the depositing metal salts must be supplemented with the addition of the electrolysis process. This procedure, in turn, has a positive effect on the life of the electrolyte. Particularly preferred is the embodiment in which only those depositing metal salts are used whose anions consist of bicarbonate or carbonate ions or oxide, hydroxide or mixtures thereof.

The invention also relates to a method for galvanic deposition of palladium or palladium alloys on metallic or conductive substrate, the electrolyte of the invention being used.

[0034] The palladium or palladium alloy may be electrolytically deposited on a substrate convenient for this purpose. Preferably metallic or Electrically conductive substrates are selected from the group consisting of nickel, nickel alloys, gold, silver, copper and copper alloys, iron and iron alloys. Particularly preferably nickel or copper or according to the invention, the copper alloy is coated with palladium or a layer containing palladium. But also conductive plastics can be subjected to this method according to the invention.

[0035] The electrolytic deposition temperature can be chosen by the skilled person. Preferably a temperature is set at which adequate deposition can take place. This occurs at temperatures between 20 ° C and 80 ° C. Preferably the temperature is set from 30 ° C to 70 ° C and most preferably from 40 ° C to 60 ° C.

[0036] The current density to be set during the electrolysis according to the invention can also be chosen by the specialist according to the underlying electrolysis system. The current densities are preferably between 0.1 and 150 A / dm². 0.1-10.0 A / dm are particularly preferred² for drum and hanger applications and 5.0 - 100 A / dm²for high speed applications. They are most preferably set for high speed applications of 5.0-70 A / dm²and on the contrary in drum and hanger applications most preferably 0.2 - 5 A / dm².

[0037] The process according to the invention is preferably carried out such that the deposition occurs using insoluble anodes. The use of undissolved anodes from platinum titanium or anodes from oxide mixtures is particularly preferred. These are particularly preferred for the undissolved anodes of platinum titanium or iridium / ruthenium / oxide mixtures of titanium or niobium or tantalum-coated tantalum. Graphite or high-grade stainless steel anodes are also possible.

[0038] The subject of the invention is also a special, preferably usable in the method according to the invention, and matched palladium salt. These are palladium complex compounds consisting of a divalent palladium cation, one or more di-, tri- or tetra-coordinated amine ligands and carbonate anions, or two bicarbonate or hydroxide anions or mixtures thereof. The use of multi-coordinating ligands based on di-, tri- or tetraamines is preferred. Particularly preferred are those having 2 to 11 C atoms. Particularly very preferred is the use of ligands selected from the group consisting of ethylenediamine, trimethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, 1,2-propylenediamine, trimethylene tetraamine, hexamethylene tetramine. In addition, ethylenediamine (EDA) is preferred in this context.

[0039] The preparation of new compounds palladium-ethylenediamine can be effected by reacting tetraaminopalladium (II) bicarbonate [Alfa Aesar cat. No. 45082] with ethylenediamine in a molar ratio [Pd]: [ethylenediamine] = 1: 1.0 to 3.0, preferably 1: 1.5 to 2.5, particularly preferably 1: 2.0 to 2.1 according to the following equation. The reaction temperature is preferably between 20 and 95 ° C, particularly preferably between 40 and 90 ° C, particularly very preferably between 60 and 80 ° C.

[{NH₃)₄Pd] (HCO₃)₂ + 2 EDA -> [(EDA)₂Pd] (HCO₃)₂ + 4 NH₃ [0040] The ammonia ligands are exchanged for ethylenediamine. The released ammonia is partly volatilized directly from the solution or it is finally removed by injecting air or an inert gas, e.g. nitrogen. To speed up the process, an additional vacuum can be applied. Other complexes of the invention can be prepared in the same way.

[0041] In the electrolyte of the invention described here, for example, 20 g / l palladium as bis (ethylenediamine) palladium (II) bicarbonate, 16 g / l of nickel as nickel (II) sulfate and 50 g / l of ethylenediamine, brighteners 1- ( 3-sulfopropylpyridine-betaine or 1- (2-hydroxy-3-sulfopropylpyridine-betaine allow high-gloss coatings to be deposited in quantities of 50 to 500 mg / l in the lower current density ranges, in addition to the use of 1- (3-sulfopropylpyridine-betaine or 1- (2-hydroxy-3-sulfopropylpyridine betaine in higher concentrations up to 2 g / l of electrolyte, the current density range is extended. Therefore, it is possible to use the electrolytes in the described electrolytes for the deposition of high speed current density of up to 100 A / dm².

[0042] A further indication for the beneficial effect of, for example, bis (ethylenediamine) palladium (II) bicarbonate in the electrolyte described is shown by the addition of 1- (3sulfopropyl) -2-vinylpyridine-betaine in the smallest amounts. Already 10 ppm allow deposition of smooth as a mirror, poorer in voltage and therefore highly conductive coatings - although also without the additional use of sulfonic acid, as described in US5415685.

[0043] Furthermore, by using about 100-200 ppm 1- (3-sulfopropyl) -2-vinylpyridine betaine it is possible to deposit very thick palladium or palladium alloy coatings. Coatings up to 30 μm thick are highly shiny, free from scratches and very (well) conductive.

[0044] Ammonia and chloride are likewise avoided with the help of the new palladium-nickel electrolyte based on ethylenediamine, whereby the exposure potential and the human odor load and the corrosion of the device are clearly reduced. The disadvantages of previous ammonium and chloride-free processes based on ethylenediamine are avoided. The use of carbonate or bicarbonate as counter-ions for palladium and nickel allows, in particular, to extend the life span. The anions used are not stable in the pH range used, for example between 3 and 5.5, and disintegrate immediately when metal salts are added to carbon dioxide and hydroxide. Easily volatilizing CO2 escapes from the electrolyte and does not lead to an increase in bath density. During electrolysis, the pH value in the electrolyte decreases slightly, whereby the alkaline effect of hydroxide ion formed during the decomposition of carbonic acid is compensated. The pH value during operation remains surprisingly automatically constant by the addition of further palladium salts according to the invention. In contrast here, especially in the case of sulfate when replenishing the metal content during the operation of the bath, the density of the bath increases gradually, until finally the maximum value is reached and the electrolyte is no longer stable.

[0045] This has not been disclosed in the prior art cited.

Examples:

Exemplary Electrolytes [0046] In a 5L beaker, the specified electrolyte components were dissolved in 4L of deionized water.

- 9 Finally, palladium or palladium alloys settle on the copper plate under the given electrolysis conditions.

1. Example - electrolyte Composition:

[0047] Electrolyte for depositing PdNi layers with 80 wt. palladium may have, for example, the following composition:

High speed electrolyte:

[0048]

<td>20 g / l South</td><td>as bis (ethylenediamine) palladium (II) bicarbonate</td>

<td>16 g / l Ni</td><td>as nickel (II) sulfate</td>

<td>50 g / l EDA</td><td>ethylenediamine</td>

<td>500 mg / l</td><td>1- (3-sulfopropyl) pirydynobetainy</td>

<td>Embedding parameters:</td><td></td>

<td> [0049]</td><td></td>

<td>Temperature:</td><td>60 ° C.</td>

<td>pH value:</td><td> 5,0</td>

<td>Current density:</td><td>5 to 70 A / dm²</td>

<td>Deposition rate:</td><td>26 mg / Amin</td>

<td>substrate:</td><td>Copper or copper alloy, possibly nickel-plated</td>

<td>anodes:</td><td>Pt / Ti</td>

<td colspan="2">[0050] The coatings obtained (2 μm) are uniformly shiny, bright, conductive, devoid of cracks in the current density range and have a relatively constant Pd content of 80 up to 83%.</td>

<td>2. Example - electrolyte</td><td></td>

<td colspan="2">Electrolyte for use on the hanger:</td>

<td> [0051]</td><td></td>

<td>10 g / l</td><td>Pd as bis (ethylenediamine) palladium (II) bicarbonate</td>

<td>8 g / l</td><td>Ni as nickel (II) sulfate</td>

- 10 30 g / l 100 mg / l

Embedding parameters.

[0052]

Temperature: pH value: Current density:

ethylenediamine

1- (3-sulfopropyl)

60 ° C.

5,0

0.5 to 5 A / dm²

Deposition rate mg / Amin

Substrate: copper or copper alloy, possibly nickel-plated

Anodes: Pt / Ti [0053] The coatings obtained (2 μm) are uniformly highly shiny, very bright, very conductive, devoid of cracks in the current density ranges and have a relatively constant Pd content of 80 to 83%.

3. Example - Reaction of tetraaminopalladium (II) bicarbonate with ethylenediamine by complexation with ethylenediamine (EDA)

Equipment:

[0054] Three-necked flask, stirrer, heater, thermometer, countercurrent cooler, pH electrode,

reagents:

[0055]

<td>components</td><td>Weight [g]</td><td>Quantity substances [moth]</td><td>Mass molar [G / mol]</td><td>Density [G / cm3]</td><td>Volume [ml]</td>

<td>palladium</td><td> 100*</td><td> 0,940</td><td> 106,4</td><td> -</td><td> -</td>

<td>ethylenediamine (EDA)</td><td> 117</td><td> 1,947</td><td> 60,1</td><td> 0,898</td><td> 130</td>

<td colspan="6">* 277 g Tetraaminopalladium (II) bicarbonate TAPHC (36% Pd)</td>

[0056] Pd: EDA molar ratio = 1: 2.07

- 11 Quality of reagents used:

[0057] Tetraaminopalladium (II) bicarbonate (product number 45082) from Alfa Aesar ethylenediamine 99% for synthesis (e.g. Merck No. 800947) [0058] The mixture per liter of final volume contains 100 g of Pd:

1. Administration of 500 ml deionized water.

2. Add ethylenediamine to water (pH 11.5 to 12).

3. Add tetraaminopalladium (II) bicarbonate in portions, the temperature rises to over 50 ° C. A golden yellow solution is formed. After adding all the palladium salts, the pH is approx.

10,5.

4. Heat to 80 ° C and allow to react 1h. When heated, the color of the solution suddenly changes from golden yellow to green yellow. There is a slight turbidity due to black particles.

5. Let the mixture cool to 50 ° C.

6. Filtration through a glass fiber filter 6: less black residue on the filter, a light yellow solution that smells strongly of ammonia.

7. Turning on air pressure for ammonia depletion.

8. Set the final volume with deionized water.

Mirosława Ważyńska

Patent Attorney