JP2018532046A - Plating bath composition for electroless plating of gold and method for depositing gold layer - Google Patents

Abstract

An electroless gold plating water bath containing at least one source of gold ions and at least one reducing agent for gold ions, wherein the formula (I) wherein the residues R ¹ and R ² are 2 Selected from the group consisting of branched alkyl, unbranched alkyl, cycloalkyl, or combinations thereof, having ˜12 carbon atoms, wherein each of residues R ¹ and R ² is Electroless gold plating water bath, characterized in that it contains at least one ethylenediamine derivative as a plating accelerator compound, the same or different), and a method for depositing gold. This electroless gold plating water bath is suitable for providing a flexible gold layer useful for wire bonding and soldering applications required for electronic components.

Description

  The present invention relates to an electroless gold plating water bath composition for electroless plating of a gold layer on a substrate, and a method for depositing gold. Plating baths are particularly suitable for the production of printed circuit boards, IC substrates, semiconductor devices, glass interposers and the like.

Background Art Gold layers are of great interest in the manufacture of electronic components and in the semiconductor industry. Gold layers are often used as solderable and / or wirebondable surfaces in the manufacture of printed circuit boards, IC substrates, semiconductor devices, and the like. Generally, the gold layer is used as the final finish before soldering and wire bonding. Conventionally used in the art to provide good strength for wire bonding while providing sufficient electrical connection and durability between copper wire and wire bonded to copper wire There are a collection of various layers. In particular, electroless nickel electroless gold (ENIG), electroless nickel electroless palladium substituted gold (ENEPIG), direct substituted gold (DIG), electroless palladium substituted gold (EPIG) and electroless palladium autocatalytic gold (EPAG) There is. Although these technologies were established a while ago, there are still many open issues. Such problems include corrosion of the nickel layer placed between the gold and copper wires (nickel corrosion), and insufficient stability of the gold plating bath (which is highly undesirable due to the cost of the bath ). It is also highly desirable to deposit the gold layer at a sufficient plating rate and implement the manufacturing process economically. Another desirable property of the gold layer is its optical appearance, which should be lemon yellow and no discoloration of the gold layer is acceptable.

  Today, the size of electrical components is so small that electrolytic processes that require electrical connection to the substrate cannot be used. Therefore, an electroless metal deposition process (electroless plating) is used. In general, electroless plating represents a method that does not use an external power source to reduce metal ions. Usually, a plating process using an external power source is described as an electrolytic plating method or a galvanic plating method. Non-metallic surfaces can be pretreated to make them receptive or catalytic to metal deposition. All or some selected surfaces can be appropriately pretreated. The main components of the electroless metal bath are metal salts, reducing agents, and optional complexing agents, pH adjusting agents and additives such as stabilizers. Complexing agents (also referred to in the art as chelating agents) are used to chelate deposited metals and to prevent metals from precipitating out of solution (ie, as hydroxides, etc.) Is done. The chelating metal provides a metal that can be used as a reducing agent that converts metal ions into metal form.

  A further form of metal deposition is displacement plating. Displacement plating is another metal deposition that uses neither an external power source nor a chemical reducing agent. The mechanism is based on replacing metal from the underlying substrate with metal ions present in the displacement plating solution. This is an obvious drawback of displacement plating. This is because the deposition of thicker layers is usually limited by the porosity of the layer.

  In most cases, electroless gold plating baths use one or both types of electroless plating. Even when a reducing agent is added to the plating bath, substitutional plating can occur, but the rate is significantly reduced.

  In the context of the present invention, electroless plating is understood to be (mainly) an autocatalytic deposition using a chemical reducing agent (referred to herein as a “reducing agent”).

  US 2012/0129005 (US2012 / 0129005 A1) discloses an electroless gold plating bath containing a water-soluble gold compound and an alkylenediamine, dialkylenetriamine or the like. However, such gold plating solutions lack sufficient stability and plating speed and are therefore not applicable in industrial processes (see Example 4).

US Patent Application Publication No. 2008/0138507 (US 2008/0138507 A1) describes aldehyde compounds as reducing agents and N-substituted ethylenediamine derivatives such as N ¹ , N ² -dimethylethylenediamine and N ¹ , N ² -bis (methylol). ) -Electroless gold plating bath using ethylenediamine is reported. Again, however, the plating bath described in this specification lacks plating rate and stability (see Example 4). In general, it is sufficient for the gold plating bath to have a plating rate of 150 nm / h or higher, preferably 200 nm / h or higher or ideally 250 nm / h or higher to meet today's industrial requirements. is there.

The object of the present invention is to provide an electroless gold plating water bath composition capable of depositing a gold layer at a sufficient plating rate, and to provide a method for said purpose. Another object of the present invention is to provide an electroless gold plating water bath that has sufficient stability and can be used for a long time.

  Yet another problem is that the gold layer formed does not show discoloration.

（上記式中、残基Ｒ^１およびＲ^２は、２〜１２個の炭素原子を有し、かつ分枝鎖状のアルキル、非分枝鎖状のアルキル、シクロアルキルまたはこれらの組み合わせから成る群より選択され、ここで残基Ｒ^１およびＲ^２はそれぞれ、同じまたは異なる）
によるめっき促進剤化合物としての少なくとも１種のエチレンジアミン誘導体を含有することを特徴とする。 SUMMARY OF THE INVENTION These problems are solved by the electroless gold plating water bath according to the present invention, which contains at least one gold ion source and at least one reducing agent for gold ions. And formula (I):

(Wherein the residues R ¹ and R ² have 2 to 12 carbon atoms and are composed of branched alkyl, unbranched alkyl, cycloalkyl, or combinations thereof) Wherein residues R ¹ and R ² are each the same or different)
It contains at least one ethylenediamine derivative as a plating accelerator compound.

  Furthermore, these problems are addressed by a method for depositing a gold layer from the above plating bath, and in a gold plating bath containing at least one gold ion source and at least one reducing agent for gold ions. This can be solved by using a plating accelerator compound.

1 shows a test substrate with a number of copper pads to be plated. Ten different spots for measuring the layer thickness are also shown (circles marked with 1 to 10).

Detailed Description of the Invention In this specification, an ethylenediamine derivative according to formula (I) shall refer to a plating accelerator compound.

によるめっき促進剤化合物は、残基Ｒ^１およびＲ^２を有し、この残基Ｒ^１およびＲ^２は、２〜１２個の炭素原子を有し、かつ分枝鎖状のアルキル、非分枝鎖状のアルキル、シクロアルキルまたはこれらの組み合わせから成る群より選択され、ここで残基Ｒ^１およびＲ^２はそれぞれ、同じまたは異なる。 Formula (I)

Plating promoter compound according to have a residue R ¹ and R ^2, the residues R ¹ and R ² have 2 to 12 carbon atoms, and branched alkyl, unbranched Selected from the group consisting of chained alkyl, cycloalkyl or combinations thereof, wherein the residues R ¹ and R ² are each the same or different.

The amine moiety in the plating accelerator compound of formula (I) is a secondary amine moiety. The inventors have discovered that a sufficient plating rate and a sufficiently stable gold plating bath are not possible with each diamine or with a diamine derivative having a methyl residue for R ¹ and R ² (Example 4). reference).

In a preferred embodiment of the present invention, the residues R ¹ and R ² of the plating accelerator compound of formula (I) are 2-8 carbon atoms, more preferably 2-6 carbon atoms, even more preferably It has 2 to 4 carbon atoms.

In another preferred embodiment of the invention, the residues R ¹ and R ² in formula (I) are the same. In yet another preferred embodiment of the invention, the alkyl residues R ¹ and R ² in formula (I) do not have a terminal hydroxy moiety (—OH). The inventors have discovered that the terminal hydroxy moieties attached to the alkyl residues R ¹ and R ² are disadvantageous for the stability of the plating bath (see Example 4). In yet another preferred embodiment of the invention, residues R ¹ and R ² in formula (I) do not have a terminal primary amino moiety. This is because the inventors have found that the terminal amino moiety bonded to the residues R ¹ and R ² is also disadvantageous for the stability of the plating bath (see Example 4). In another more preferred embodiment of the present invention, residues R ¹ and R ² do not have additional amino and / or hydroxy moieties. Even more preferably, the alkyl residue has no substituent and consists only of carbon and hydrogen atoms.

It is particularly preferred that the plating accelerator compound is selected from the group consisting of: N ¹ , N ² -diethylethane-1,2-diamine, N ¹ , N ² -dipropylethane-1,2-diamine. , ^N 1, ^{N 2} - diisopropyl ^{1,2-diamine, N 1,} N ² - ^{Jibuchiruetan-1,2-diamine, N 1,} N ² - diisobutyl ^{1,2-diamine, N} 1, N ² - di -tert- ^{Buchiruetan-1,2-diamine,} N 1, ^{N 2} - ^{dipentyl-1,2-diamine,} N 1, ^{N 2} - di ^{isopentyl-1,2-diamine, N} 1, N ² - di -sec- ^{Penchiruetan-1,2-diamine,} N 1, ^{N 2} - di -tert- ^{Penchiruetan-1,2-diamine,} N 1, ^{N 2} - dineopentyl-1,2-di ^{Min, N 1,} N ² - ^{dihexyl-1,2-diamine, N 1,} N ² - di (1-methylpentyl) ^{ethane-1,2-diamine, N 1,} N ² - di (2-methylpentyl ) ^{ethane-1,2-diamine, N 1,} N ² - di (3-methylpentyl) ^{ethane-1,2-diamine, N 1,} N ² - di (4-methylpentyl) ethane-1,2-diamine , ^N 1, ^{N 2} - di (1,1-dimethylbutyl) ^{ethane-1,2-diamine, N 1,} N ² - di (1,2-dimethylbutyl) ^{ethane-1,2-diamine, N} 1, N ² -di (1,3-dimethylbutyl) ethane-1,2-diamine, N ¹ , N ² -di (2,2-dimethylbutyl) ethane-1,2-diamine, N ¹ , N ² -di (2,3-dimethylbutyl) ethane-1,2-diamine and N , ^{N 2} - di (3,3-dimethylbutyl) ethane-1,2-diamine.

Most preferably, R ¹ and R ² are branched alkyl residues having 3 to 6 carbon atoms. Surprisingly, it has been found that the use of branched alkyl residues having 3-6 carbon atoms for R ¹ and R ² results in higher plating rates with even better bath stability. (See Example 5).

  The concentration of the at least one plating accelerator compound according to formula (I) in the electroless gold plating water bath according to the invention is preferably 0.001-1 mol / L, more preferably 10-100 mmol / L, even more preferably 25. It is in the range of ~ 75 mmol / L. When more than one plating accelerator compound is contained in the electroless gold plating water bath according to the present invention, the concentration is based on the total amount of all plating accelerator compounds.

  The electroless gold plating water bath according to the present invention is synonymously referred to as an aqueous solution. The term “aqueous solution” means that the primary liquid medium (which is the medium in solution) is water. Additional water miscible liquids (eg, alcohols) and other water miscible polar organic liquids can be added. Basically, the aqueous solution contains more than 50% by weight of water.

  The electroless plating bath according to the invention can be prepared by dissolving all components in an aqueous liquid medium, preferably in water.

The electroless gold plating water bath according to the present invention contains at least one gold ion source. Gold ions can be in either Au ⁺ , Au ³⁺ or both oxidation states. The gold ion source can be any water-soluble gold salt having the oxidation state. Preferably, the gold ion source includes gold cyanide, ammonium gold cyanide, gold (I) cyanide alkali metal (gold (I) potassium cyanide, sodium gold (I) cyanide, trisodium gold disulfide, three Potassium gold disulfide and triammonium gold disulfide), gold thiosulfate, gold thiocyanate, gold sulfate, gold chloride and gold bromide. Preferably, the gold ion source is an alkali metal (I) cyanide and can be added to the plating water bath in the form of a solution containing this salt. The concentration of gold ions in the electroless gold plating water bath according to the present invention is preferably in the range of 0.1 to 10 g / L, more preferably 0.3 to 6 g / L.

  The electroless gold plating water bath further contains at least one reducing agent for gold ions. The reducing agent for gold ions is preferably selected from the group consisting of: aliphatic aldehydes such as formaldehyde, acetaldehyde, propionaldehyde, n-butyraldehyde, α-methylvaleraldehyde, β-methylvaleraldehyde Aliphatic dialdehydes such as glyoxal and succindialdehyde; aliphatic unsaturated aldehydes such as crotonaldehyde; aromatic aldehydes such as benzaldehyde, o-nitrobenzaldehyde, m-nitrobenzaldehyde, p -Nitrobenzaldehyde, o-tolualdehyde, m-tolualdehyde, p-tolualdehyde, o-hydroxybenzaldehyde, m-hydroxybenzaldehyde, p-hydroxybenzaldehyde, Such as phenylacetaldehyde; sugars having an aldehyde group (—CHO), such as glucose, galactose, mannose, ribose, maltose, lactose, etc .; and precursors of formaldehyde, such as urotropine, 1,3-bis (hydroxymethyl) -5,5 -Dimethylimidazolidine-2,4-dione (DMDM hydantoin), paraformaldehyde, glyoxylic acid, glyoxylic acid source and glycolic acid. The term “glyoxylic acid source” encompasses glyoxylic acid and any compound that can be converted to glyoxylic acid in aqueous solution. In aqueous solution, the acid-containing aldehyde is in equilibrium with its hydrate. A suitable source of glyoxylic acid is a dihaloacetic acid, such as dichloroacetic acid, which hydrolyzes in aqueous media to the glyoxylic acid hydrate. Alternative sources of glyoxylic acid are bisulfite adducts, hydrolysable esters or other acidic derivatives. The bisulfite adduct can be added to the electroless gold plating water bath according to the present invention or can be formed in situ. Bisulfite adducts can be produced from glyoxylate and either bisulfite, sulfite or metabisulfite. Formaldehyde, glyoxylic acid source and glyoxylic acid are preferred, and formaldehyde is most preferred.

  The concentration of at least one reducing agent for gold ions is preferably 0.0001 to 0.5 mol / L, more preferably 0.001 to 0.3 mol / L, and even more preferably 0.005 to 0.005. It is in the range of 12 mol / L.

  While not being bound by theory, the inventors have made great ingenuity by using specific ethyleneamine derivatives, such as triethylenetetramine, and reducing agents for gold ions, such as formaldehyde (or its oxidation product, formic acid). It has been discovered that this may result in precipitation and reduced plating rates. Common reaction products are, for example, aminal, enamine and amide derivatives. Therefore, the molar ratio of the plating accelerator compound according to formula (I) to the reducing agent for gold ions in the electroless gold plating water bath according to the present invention is 0.5-9, preferably 0.8-3.0, More preferably, it is preferred to limit the formation of undesirable reaction products to the extent possible by selecting from 1.0 to 2.0 (see Example 6). When more than one plating accelerator compound according to formula (I) and / or more than one reducing agent for gold ions are used in the electroless gold plating water bath according to the invention, this ratio is Calculated based on the total mass of all compounds.

  Furthermore, the electroless gold plating water bath according to the present invention optionally contains at least one complexing agent. The at least one optional complexing agent present in the electroless gold plating water bath according to the present invention is preferably selected from the group consisting of carboxylic acids, hydroxycarboxylic acids, aminocarboxylic acids, aminophosphonic acids or salts of the foregoing. Is done. The at least one optional complexing agent functions as a complexing agent for metal ions dissolved from the substrate during plating, such as nickel ions or copper ions, as well as a complexing agent for gold ions. . A preferred carboxylic acid is, for example, oxalic acid or a salt thereof. Preferred hydroxycarboxylic acids are, for example, tartaric acid, citric acid, lactic acid, malic acid, gluconic acid and salts of the foregoing. Preferred aminocarboxylic acids are, for example, glycine, cysteine, methionine and salts of the foregoing. Preferred aminophosphonic acids are nitrilotri (methylphosphonic acid) (usually abbreviated as ATMP), diethylenetriaminepentakis (methylphosphonic acid) (usually abbreviated as DTPMP) and ethylenediaminetetra (methylenephosphonic acid) (usually abbreviated as EDTMP). . In all cases, the sodium, potassium and ammonium salts of the compounds are also suitable. The concentration of at least one optional complexing agent is preferably in the range of 0.1 to 50 g / L, more preferably 0.5 to 30 g / L.

  More preferably, the electroless gold plating water bath according to the present invention contains two different complexing agents and / or salts thereof, such as hydroxycarboxylic acid or salt thereof, and aminocarboxylic acid or salt thereof.

  The electroless gold plating water bath according to the present invention optionally contains a crystal modifier selected from the group consisting of thallium ions, arsenic ions, selenium ions and lead ions. Such a crystal modifier is preferably added to the electroless gold plating water bath according to the present invention in a concentration range of 0.00001 to 0.1 g / L. Useful sources for the ions can be their water-soluble salts, such as nitrates, sulfates and halides.

The electroless gold plating water bath according to the present invention optionally contains at least one stabilizer selected from the group consisting of a source of cyanide ions, hydantoin and its alkyl derivatives such as alkylhydantoins and dialkylhydantoins, In this context, alkyl residues include C ₁ -C ₈ alkyl, preferably methyl, which alkyl residues are cyclic and / or alicyclic, branched or unbranched. Sulfur compounds such as 2-mercaptobenzothiazole, 2-mercaptobenzimidazole, mercaptoacetic acid, 3- (2-benzothiazolylthio) -1-propanesulfonic acid, mercaptosuccinic acid, thiosulfuric acid, thioglycol, thiourea, thioapple Acids, and aromatic nitrogen compounds such as benzotriazole, 1,2, -, and the like aminotriazole. A suitable source of cyanide ions can be any soluble cyanide salt, such as an alkali metal cyanide (including sodium cyanide, potassium cyanide).

  The concentration of any stabilizer can be selected depending on its chemical structure and can be determined by one skilled in the art by routine experimentation. The concentration of the optional stabilizer is preferably in the range of 0.0000001 to 0.2 mol / L, and this concentration is more preferably in the range of 0.000001 to 0.1 mol / L. Such stabilizers are added to the electroless gold plating bath as before to improve its life and prevent plate-out.

  In a preferred embodiment, two or more stabilizers are used. More preferably, the source of cyanide ions is at a concentration of 0.0003-5 mmol / L, the one or more hydantoins and alkyl derivatives thereof are at a concentration of 10-100 mmol / L, and / or the sulfur compound is 0.000001- Selected at a concentration of 0.05 mol / L.

  In another preferred embodiment of the present invention, the electroless gold plating water bath according to the present invention does not contain a second source of deliberately added reducible metal ions (impurities normally present in industrial raw materials). This does not take into account the trace amount of pure gold), allowing a pure gold precipitate to be formed. Pure gold deposits are flexible and malleable and are particularly suitable for wire bonding and soldering. The trace amount of impurities is understood to be less than 1% by weight of compounds present in industrial raw materials.

  The pH of the electroless gold plating water bath according to the present invention is preferably in the range of 5-9, more preferably 6-8, and even more preferably 6.5-7.5. The target pH value is adjusted, for example, by using an acid such as phosphonic acid or a base such as sodium hydroxide or potassium hydroxide. It is advantageous and therefore preferred to continuously control and adjust the pH value during plating since this also improves the life of the plating bath.

（残基Ｒ^１およびＲ^２は、２〜１２個の炭素原子を有し、かつ分枝鎖状のアルキル、非分枝鎖状のアルキル、シクロアルキルまたはこれらの組み合わせから成る群より選択され、ここで残基Ｒ^１およびＲ^２はそれぞれ、同じまたは異なる）
のエチレンジアミン誘導体を金めっき水浴中で使用する。このような金めっき水浴は無電解金めっき浴であってよく、これは、置換型金めっき浴、自己触媒型金めっき浴、および自己触媒型めっきと置換型めっきとの混合物を使用した金めっき浴、ならびに電解めっき浴を含む。 Formula (I) with residues R ¹ and R ² to adjust the plating rate and improve its stability:

(Residues R ¹ and R ² have 2 to 12 carbon atoms and are selected from the group consisting of branched alkyl, unbranched alkyl, cycloalkyl, or combinations thereof; Where residues R ¹ and R ² are the same or different, respectively)
Are used in a gold plating water bath. Such a gold plating bath may be an electroless gold plating bath, which is a gold plating using a displacement gold plating bath, a self-catalytic gold plating bath, and a mixture of self-catalytic and displacement plating. Baths, as well as electroplating baths.

  Preferably, the plating accelerator compound is used in an electroless plating bath, preferably an electroless plating bath containing at least one gold ion source and at least one reducing agent for gold ions.

The method of depositing the gold layer on the substrate is as follows:
(I) preparing a substrate;
(Ii) contacting at least part of the surface of the substrate with the gold plating water bath according to the present invention;
In this order, thereby depositing the gold layer on at least a portion of the surface of the substrate.

  This contact is preferably accomplished by immersing at least a portion of the substrate or the surface of the substrate in a plating bath or by spraying the plating bath onto the substrate or at least a portion of the surface of the substrate.

  At least a part of the surface of the substrate preferably consists of a metal or metal alloy, in which case the gold is nickel, nickel alloy, eg nickel phosphorus alloy, nickel boron alloy, cobalt, cobalt alloy, eg cobalt phosphorus alloy, cobalt molybdenum Phosphorus alloys, cobalt molybdenum boron alloys, cobalt molybdenum boron phosphorus alloys, cobalt tungsten phosphorus alloys, cobalt tungsten boron alloys, cobalt tungsten boron phosphorus alloys, palladium, palladium alloys such as palladium phosphorus alloys, palladium boron alloys, copper and copper alloys, and Deposited on at least a portion of the surface of a substrate made of a metal or metal alloy selected from the group consisting of gold or gold alloys. The electroless gold plating water bath according to the present invention can be used to deposit a gold layer on a gold substrate, and can be used to thicken an existing gold layer obtained from, for example, a displacement type gold plating bath Can do.

  As is known in the art, the substrate can be pretreated prior to plating. Such pre-treatment mainly includes a cleaning step using a solvent and / or a surfactant to remove organic contaminants, an acid to remove the oxide, and optionally etching using an oxidizing agent or a reducing agent. Process, as well as an activation process. By the latter process, the noble metal is deposited on the surface or a part of the surface, and the surface or the part of the surface becomes more receptive for plating. Such a noble metal can be palladium that can be deposited as a salt, which is then reduced on the surface into elemental palladium. Alternatively, it can be deposited in colloidal form and optionally exposed to an accelerating step with an acid, such as hydrochloric acid, to remove any protective colloid, such as a tin colloid. Usually, such an active layer is not an individual layer but an island-shaped palladium aggregate. However, in the context of the present invention, the active layer is considered to be a metal substrate.

  The temperature of the electroless gold plating water bath according to the present invention is preferably in the range of 30-95 ° C., more preferably 70-90 ° C., even more preferably 75-85 ° C., and even more preferably 77-84 ° C. during plating. It is in. The plating time is preferably in the range of 1 to 60 minutes, more preferably in the range of 5 to 30 minutes. However, if thinner or thicker deposits are desired, the plating time can be outside the above range and can be adjusted accordingly.

  It is preferable to replenish the components used during plating continuously or at regular intervals. Such components are, inter alia, a gold ion source, a reducing agent for gold ions, at least one stabilizer and a plating accelerator compound. If necessary, the pH value can likewise be adjusted continuously or at intervals.

  The electroless gold plating water bath according to the present invention can be used by horizontal type, vertical type and spray type plating apparatuses.

  It is an advantage of the present invention that the stability of the electroless gold plating water bath according to the present invention is improved compared to gold plating baths known in the art (see Example 5). As used herein, stability shall be understood as the bath life before the compound from the bath precipitates ("plate out") and the bath cannot be used for plating purposes.

  A further advantage is that the gold plating water bath according to the present invention allows a sufficient plating rate of 250 nm / h or more (the thickness of the plated metal layer deposited over time) (see Examples 1-3 and 5). . Most of the somewhat stable plating baths known in the art do not allow sufficient plating rates.

  Thus, a unique feature of the electroless gold plating water bath according to the present invention is that it provides a very stable gold plating bath at a sufficient plating rate, thus enabling a more economically feasible gold plating process.

  The gold plating water bath according to the present invention forms uniform gold deposits with slight layer thickness differences. The standard deviation of the gold layer thickness is less than 10% or even less than 8%. This slight deviation is advantageously achievable even when plating on various substrates having different sizes.

  The invention is further illustrated by the following non-limiting examples.

Examples Basic Procedures Pallabond (R) CLN, Pallabond (R) ME, PallaBond (R) Pre Dip, PallaBond (R) Aktivator and PallaBond (R) ACT V3 STD are available from Atotech DeutschlandHand It is a product. In all cases, the gold ion source was K [Au (CN) ₂ ].

A printed circuit test board having multiple copper pads of different sizes in the range of 0.25-49 mm ² on both sides was used as the substrate in all tests. These substrates were cleaned and etched prior to activation with palladium. Palladium was then deposited on the copper surface, and then a gold layer was plated thereon. Different pads (where the layer thickness was determined) are shown in FIG. The pads each had the following areas: 1: 0.25 mm ² , 2: 0.52 mm ² , 3: 0.68 mm ² , 4: 0.97 mm ² , 5: 1.33 mm ² , 6: ^{1.35mm 2, 7: 3.3mm 2,} 8: 6.7mm 2, 9: 25mm 2, 10: 49mm 2.

Determination of Metal Deposit Thickness and Plating Rate For ten copper pads, the deposit thickness was measured on each side of the test plate. The selected copper pads have different sizes, and these copper pads are used to determine the layer thickness by XRF on an XRF instrument Fischerscope XDV-SDD (Helmut Fischer GmbH, Germany). By assuming that the structure of the precipitate is layered, the layer thickness can be calculated from such XRF data. The plating rate was calculated by dividing the resulting layer thickness by the time required to obtain the layer thickness.

  The layer thickness uniformity was specified as the standard deviation from the average thickness value.

Example 1 (Invention): N ¹ , N ² -Diisopropylethane-1,2-diamine as Plating Accelerator Compound A gold plating bath containing the following components was prepared by dissolving all components in water:

The substrate was subjected to the following process steps (Table 1) by immersing the substrate in each solution using the given parameters.

After this process sequence, the thickness of each metal layer was measured. The plating rate was calculated as described above.

  The gold layer was lemon yellow. Further, the plating rate was very high, sufficiently exceeding the necessary minimum value of 250 nm / h. The distribution of layer thickness was also very uniform with a deviation of only 5.6%.

Example 2 (Invention): N ¹ , N ² -Dipropylethane-1,2-diamine as Plating Accelerator Compound The process described in Example 1 was repeated, wherein the gold plating bath was 50 mmol / L N ^{1, N 2} - instead of diisopropyl 1,2-diamine, ^N 1, ^{N 2} of 50 mmol / L - contained dipropyl-1,2-diamine. These results are summarized in the following table.

  The gold layer was lemon yellow. The plating rate was very high, exceeding the necessary minimum value of 250 nm / h. The layer thickness distribution was also very uniform with a deviation of only 6.6%.

Example 3 (Invention): N ¹ , N ² -Diethylethane-1,2-diamine as Plating Accelerator Compound The process described in Example 1 is repeated, wherein the gold plating bath is N ¹ , N ^2- instead of diisopropyl ^1,2-diamine, N 1, ^{N 2} - but contained diethyl-1,2-diamine, the concentration was the same. These results are summarized in the following table.

  The gold layer was lemon yellow. The plating rate was very high, clearly exceeding the necessary minimum value of 250 nm / h. The layer thickness distribution was also very uniform, with a deviation of only 6.4%.

Example 4 (Comparative): Repeat the process described in Use Example 1 other amines, in which the gold plating ^bath, N 1, ^{N 2} - instead of diisopropyl 1,2-diamine, listed in Table 5 And other compounds. The results for 20 minutes of gold plating are summarized in this table.

  Various compounds having an amino moiety were tested. If each plating rate was too low to meet the industrial requirement of today's plating rate of 250 nm / h, the stability test was omitted.

Compound A had only a tertiary amine moiety and no alkyl residues R ¹ and R ² . When this compound was used in a gold plating bath instead of the plating accelerator compound, almost no gold plating occurred. The gold layer was very uneven, and the standard deviation of the layer thickness was 58%.

  Compound B was an alkylene diamine derivative having only primary and tertiary amino moieties (having only methyl residues). Gold plating was very slow when this compound was used in a gold plating bath instead of a plating accelerator compound. The gold layer was very uneven, and the standard deviation of the layer thickness was 53%.

  Compounds C and D are alkanolamines having only a tertiary amino moiety or only one secondary amino moiety. Gold plating was slow when these compounds were used in a gold plating bath instead of a plating accelerator compound. In addition, the gold layer was very uneven, and the standard deviation of the layer thickness was 24% for Compound C and 33% for Compound D.

  Compounds E and F did not have a sufficiently long alkyl residue and plating was slow when these compounds were used in a gold plating bath instead of a plating accelerator compound. Compounds E and F are structures similar to plating accelerator compounds according to formula (I), but they have no alkyl residues or short alkyl residues. In the case of Compound E, the gold layer thickness was non-uniform, with a standard deviation of 14.4%, while for Compound F, the deviation was 6.4%.

  Compound G had two terminal hydroxy moieties. When this compound was used in a gold plating bath instead of the plating accelerator compound, the plating rate was high, but the stability of the gold plating bath was insufficient. Within a day, the gold plating bath deteriorated irreversibly and could no longer be used for gold plating. The standard deviation of the gold layer thickness was 6.3%.

  Compound H had two terminal primary amino moieties. When this compound was used in a gold plating bath instead of the plating accelerator compound, the plating rate was sufficiently high, but the stability of the gold plating bath was low. Within 3 hours, the gold plating bath deteriorated irreparably. The standard deviation of the gold layer thickness was 8.5%.

  In summary, comparative compounds A-F did not allow sufficient plating rates for gold baths containing these compounds. The plating rate was always even below 200 nm / h and was therefore not sufficient for today's industrial requirements.

  Comparative compounds G and H as additives provided a sufficient plating rate, but the stability of each gold plating bath was not satisfactory.

Example 5 (Invention): Stability and Life of Gold Plating Bath Gold was deposited on the substrate for a longer time using the gold plating baths of Examples 1-3. The stability of the gold plating bath and the plating rate were monitored over time. When plateout occurred, the solution was filtered and reused. Every day during the experiment, the pH value was measured and adjusted to 7.1 with KOH and / or H ₃ PO _{4 as} needed. A gold ion source, a cyanide ion source and a plating accelerator compound were continuously replenished during plating.

Table 6 provides information regarding the stability of gold plating baths containing different plating accelerator compounds. The plating bath was visually inspected on a daily basis immediately after preparation (day 0) and for a week. Also, during this test period, gold was deposited on the substrate using a gold plating bath every day. These results are summarized in Table 7. The values listed in this table are the deposition thickness (nanometers) obtained after 20 minutes of plating.

In the case of N ¹ , N ² -diethylethane-1,2-diamine and N ¹ , N ² -dipropylethane-1,2-diamine, which are linear plating accelerator compounds, although slight precipitation occurred The plating bath still allowed the gold layer to be deposited without causing a decrease in the plating rate. The branched plating accelerator compound, N ¹ , N ² -diisopropylethane-1,2-diamine, showed no precipitation over 7 days and resulted in a good plating rate over the entire test time. Therefore, it is considered that the stability of the bath is improved by the plating accelerator compound having a branched alkyl residue.

Example 6 (Invention): Ratio of Plating Accelerator Compound to Reducing Agent for Gold Ions A gold plating bath containing the following components was prepared by dissolving all components in water.

The gold plating bath was adjusted to a pH value of 7.1 with KOH / H ₃ PO ₄ . The substrate was subjected to the method described in Table 1, where the electroless gold plating process was carried out for only 10 minutes.

The method was repeated several times using different gold plating baths while increasing the amount of plating accelerator compound, where the amount of reducing agent for gold ions was kept at the same level. These results are shown in Table 8.

  It can be seen that the highest plating rate can be obtained when the molar ratio of the plating accelerator compound to the reducing agent for gold ions is in the range of 1 or 2-1. Furthermore, the plating rate decreased as the amount of the plating accelerator compound was increased.

  Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification or practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with the true scope of the invention being defined only by the following claims.

Claims (15)

In an electroless gold plating water bath containing at least one gold ion source and at least one reducing agent for gold ions, the formula (I):

(Wherein the residues R ¹ and R ² have 2 to 12 carbon atoms and are composed of branched alkyl, unbranched alkyl, cycloalkyl, or combinations thereof) Wherein residues R ¹ and R ² are each the same or different)
The electroless gold plating water bath according to claim 1, which contains at least one ethylenediamine derivative as a plating accelerator compound. Residues R ¹ and R ² in formula (I) is characterized in that it contains 2 to 8 carbon atoms, an electroless gold plating bath of claim 1 wherein. Wherein the residues R ¹ and R ² in formula (I) are the same electroless gold plating bath of claim 1 or 2 wherein. Residues R ¹ and R ² in formula (I), characterized in that it does not also have additional amino moiety and / or hydroxy moiety, electroless gold plating bath of any one of claims 1 to 3 . Residues R ¹ and R ^{2 in} formula (I) are branched alkyl residues having 3 to 6 carbon atoms, any one of claims 1 to 4 The electroless gold plating water bath according to item.   Electroless gold according to any one of claims 1 to 5, characterized in that the concentration of at least one plating accelerator compound according to formula (I) is in the range of 0.001 to 1 mol / L. Plating water bath.   The electroless gold plating water bath according to claim 6, characterized in that the concentration of at least one plating accelerator compound according to formula (I) is in the range of 10 to 100 mmol / L.   At least one reducing agent for gold ions is selected from the group consisting of aliphatic aldehydes, aliphatic dialdehydes, aliphatic unsaturated aldehydes, aromatic aldehydes, sugars with aldehyde groups and precursors of formaldehyde The electroless gold plating water bath according to any one of claims 1 to 7, characterized in that:   Electroless gold plating water bath according to any one of claims 1 to 8, characterized in that the molar ratio of reducing agent to plating accelerator compound according to formula (I) is in the range of 0.8-3. .   The electroless gold plating water bath according to any one of claims 1 to 9, wherein the pH of the electroless gold plating water bath is in the range of 5-9.   The electroless gold plating water bath according to any one of claims 1 to 10, wherein the concentration of gold ions is in the range of 0.1 to 10 g / L.   The electroless gold plating water bath further contains at least one complexing agent selected from the group consisting of carboxylic acids, hydroxycarboxylic acids, aminocarboxylic acids, aminophosphonic acids or salts of the foregoing. The electroless gold plating water bath according to any one of claims 1 to 11. A method of depositing a gold layer on a substrate,
(I) a step of preparing a substrate (ii) a step of contacting at least a part of the surface of the substrate with the electroless gold plating water bath according to any one of claims 1 to 12 in this order, thereby Depositing the gold layer on at least a portion of the surface of the substrate.   14. A method for depositing a gold layer on a substrate according to claim 13, wherein at least a part of the surface is made of a metal or a metal alloy, in which case the gold is nickel, a nickel alloy such as a nickel phosphorus alloy, nickel boron. Alloy, cobalt, cobalt alloy, such as cobalt phosphorus alloy, cobalt molybdenum phosphorus alloy, cobalt molybdenum boron alloy, cobalt molybdenum boron phosphorus alloy, cobalt tungsten phosphorus alloy, cobalt tungsten boron alloy, cobalt tungsten boron phosphorus alloy, palladium, palladium alloy, for example The method being deposited on at least a portion of the surface comprising a metal or metal alloy selected from the group consisting of palladium-phosphorus alloys, palladium boron alloys, copper and copper alloys, and gold or gold alloys. Formula (I) having residues R ¹ and R ² :

(R ¹ and R ² have 2 to 12 carbon atoms and are selected from the group consisting of branched alkyl, unbranched alkyl, cycloalkyl, or combinations thereof, wherein Residues R ¹ and R ² are each the same or different in a gold plating water bath containing at least one source of gold ions and at least one reducing agent for gold ions)
Use of ethylenediamine derivatives as plating accelerator compounds.

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