Gold-tin alloy electroplating solution, electroplating method and products

Abstract

This invention relates to the field of gold-tin alloy electroplating, and discloses a gold-tin alloy electroplating solution, an electroplating method, and a product. The electroplating solution includes a stabilizer, wherein the stabilizer content is 0.01-50 g / L; the stabilizer includes a first stabilizer and a second stabilizer; the mass ratio of the first stabilizer to the second stabilizer is 1-10:1; the first stabilizer includes at least one selected from ethylenediamine alkyl-substituted derivatives, ethylenediamine phenyl-substituted derivatives, and ethylenediamine alkylhydroxy-substituted derivatives; the second stabilizer includes at least one selected from antipyrine, diantipyrine, ascorbic acid, pyrogallol, hydroquinone, resorcinol, trihydroxybenzene, catechol, cresolsulfonic acid, catecholsulfonic acid, and hydroquinonesulfonic acid. This electroplating solution can form a stable alloy composition for the electroplated layer over a wide current density range.

Description

Technical Field

[0001] This invention relates to the field of gold-tin alloy electroplating, specifically to a gold-tin alloy electroplating solution, an electroplating method, and a product. Background Technology

[0002] Gold-tin eutectic alloy refers to a gold-tin alloy with a mass percentage of 80wt% and 20wt% (atomic percentages of 70at% and 30at%) of Au and Sn, respectively. Its melting point is 278℃. During welding, it forms a eutectic structure consisting of a mixture of ζ(Au5Sn) and δ(AuSn) phases. Due to its moderate welding temperature, high yield strength, lack of flux, good wettability, low viscosity, high corrosion resistance, high creep resistance, and good thermal and electrical conductivity, it is widely used in the high-reliability packaging of optoelectronic devices in fields such as communications, satellites, remote sensing, radar, automobiles, and aerospace.

[0003] As shown in the Au-Sn alloy phase diagram, the melting point of gold-tin alloys is highly sensitive to alloy composition near the eutectic point. Even slight deviations in composition cause a sharp increase in melting point. Therefore, precise control of the alloy composition of gold-tin eutectic solder is crucial, posing a significant challenge to the preparation of gold-tin eutectic solder via co-deposition alloy electroplating. This is partly due to the large difference in equilibrium potentials between gold and tin ions, specifically E0... (Au + / Au)=1.73V, E (Au 3+ / Au)=1.50V, E (Sn 2+ / Sn)=-0.14V、E (Sn 4+ Since the voltage ( / Sn) is -1.87V, co-deposition is difficult to achieve in simple electroplating solutions. It is necessary to add a suitable complexing agent to the electroplating solution to change the equilibrium potential of the metal ions and increase cathode polarization, so that the deposition potentials of gold and tin ions are close to each other, thus achieving co-deposition. Furthermore, even if co-deposition of gold and tin ions is achieved, the composition of the plating alloy is dependent on the electroplating current density; that is, the composition of the plating alloy fluctuates with changes in the electroplating current density and cannot remain relatively stable over a wide range of current densities. This is extremely detrimental to accurately controlling the composition of the plating alloy, especially when electroplating on large-size semiconductor substrates of 4 inches or larger. The distribution of current density on the substrate varies greatly, leading to fluctuations in the plating alloy composition in local areas and resulting in fluctuations in the melting point, which may cause soldering problems.

[0004] CN102011158A discloses a cyanide-free gold-tin alloy electroplating solution and uses a positive amplitude pulse electroplating method, but only at a peak current density of approximately 12 mA / cm². 2A gold-tin eutectic alloy was obtained, but the alloy composition of the plating layer around Sn 30 at% was highly sensitive to changes in current density, resulting in a narrow usable current density range. US20050252783A1 discloses a gold-tin alloy electroplating solution containing an ethoxylated compound with phosphate functional groups as an alloy stabilizer, achieving stable deposition of the eutectic gold-tin alloy across the entire current density range. The gold content of the plating layer is between 75% and 85% by weight, while the tin content is between 15% and 25% by weight. However, the specific current density range is not disclosed, and the 10% range needs further reduction. JP2001192886A discloses a gold-tin alloy electroplating solution containing a nitrogen-containing heterocyclic compound as an alloy stabilizer, achieving a compositional range of less than 5 wt% for gold-tin alloys on 4-inch substrates. However, the specific current density range is not disclosed, and the range needs further reduction. JP2001200388A discloses a gold-tin alloy electroplating solution containing an organophosphate compound as an alloy stabilizer, which suppresses the compositional variation of the gold-tin alloy on a 4-inch substrate to below 5 wt%. However, it does not disclose the specific current density range, and the variation needs to be further reduced. Although the gold-tin alloy electroplating solution of the aforementioned patent invention reduces the current density dependence of the plating alloy composition, this dependence is not sufficiently reduced, and the compositional variation of the gold-tin alloy needs to be further reduced. Especially when electroplating large-size semiconductor substrates or complex patterns, the uneven distribution of local current density increases the instability of the plating alloy composition, resulting in melting point differences and easily causing soldering reliability problems. Summary of the Invention

[0005] The purpose of this invention is to overcome the problem of unstable alloy composition of electroplated layers in existing electroplating solutions over a wide current density range, and to provide a gold-tin alloy electroplating solution, electroplating method, and product, wherein the electroplating solution can form a stable alloy composition of the electroplated layer over a wide current density range.

[0006] To achieve the above objectives, the first aspect of the present invention provides a gold-tin alloy electroplating solution, wherein the electroplating solution includes a stabilizer, and the content of the stabilizer is 0.01-50 g / L;

[0007] The stabilizer includes a first stabilizer and a second stabilizer; the mass ratio of the first stabilizer and the second stabilizer is 1-10:1;

[0008] The first stabilizer includes at least one of ethylenediamine alkyl-substituted derivatives, ethylenediamine phenyl-substituted derivatives, and ethylenediamine alkylhydroxy-substituted derivatives;

[0009] The second stabilizer includes at least one of antipyrine, diantipyrine, ascorbic acid, pyrogallol, hydroquinone, phlorogallol, trihydroxybenzene, catechol, cresol sulfonic acid, catechol sulfonic acid, and hydroquinone sulfonic acid.

[0010] A second aspect of the present invention provides an electroplating method, comprising: electroplating using the above-mentioned gold-tin alloy electroplating solution, wherein the electroplating operating conditions include: temperature 25-60℃; current density range 0.1-1ASD.

[0011] A third aspect of the present invention provides an article comprising a substrate and a gold-tin alloy layer disposed on the substrate, wherein the gold-tin alloy layer is obtained by electroplating with the gold-tin alloy electroplating solution described in the first aspect or by electroplating with the electroplating method described in the second aspect.

[0012] The gold-tin alloy layer is suitable for chip soldering or wafer bumping.

[0013] Through the above technical solution, the gold-tin alloy electroplating solution of the present invention not only makes the precipitation potentials of gold and tin metal ions close to each other to achieve co-deposition, but also greatly reduces the dependence of the coating composition on the current density. It can form a stable alloy composition of the electroplating layer in a wide current density range from low to high current density, with the range controlled below 2wt%. The alloy composition of the electroplating layer is accurate, uniform and consistent, with small differences in alloy melting points and excellent eutectic welding performance. Attached Figure Description

[0014] Figure 1 This is a microscope image of the gold-tin eutectic bump after electroplating in Example 1;

[0015] Figure 2 This is a SEM image of the gold-tin eutectic bump after electroplating in Example 1;

[0016] Figure 3 This is a microscope image of the gold-tin eutectic bump after reflow in Example 1;

[0017] Figure 4 This is a SEM image of the gold-tin eutectic bumps after reflow in Example 1;

[0018] Figure 5 This is a microscopic image of the defective gold-tin eutectic bumps after reflow in Comparative Example 1.

[0019] Figure 6 This is a microscopic image of the defects in the gold-tin eutectic bumps after reflow, as shown in Comparative Example 2. Detailed Implementation

[0020] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0021] In this invention, the stabilizer, buffer, conductive salt, chelating agent, and surfactant can be the compounds themselves described below, or chemically acceptable salts thereof, i.e., salts that can dissociate to provide the core functional groups of the aforementioned compounds.

[0022] In this invention, unless otherwise specified, "first" and "second" do not indicate a sequence or limit the specific materials or steps; they are merely used to distinguish that these are not the same material or step. For example, in "first stabilizer" and "second stabilizer," "first" and "second" are used only to indicate that these are not the same stabilizer.

[0023] The first aspect of the present invention provides a gold-tin alloy electroplating solution, wherein the electroplating solution includes a stabilizer, wherein the content of the stabilizer is 0.01-50 g / L;

[0024] The stabilizer includes a first stabilizer and a second stabilizer; the mass ratio of the first stabilizer and the second stabilizer is 1-10:1;

[0025] The first stabilizer includes at least one of ethylenediamine alkyl-substituted derivatives, ethylenediamine phenyl-substituted derivatives, and ethylenediamine alkylhydroxy-substituted derivatives;

[0026] The second stabilizer includes at least one of antipyrine, diantipyrine, ascorbic acid, pyrogallol, hydroquinone, phlorogallol, trihydroxybenzene, catechol, cresol sulfonic acid, catechol sulfonic acid, and hydroquinone sulfonic acid.

[0027] The gold-tin alloy electroplating solution provided by this invention includes a first stabilizer and a second stabilizer in a specific ratio, and the stabilizers have a specific content. Using the gold-tin alloy electroplating solution provided by this invention not only makes the deposition potentials of gold and tin metal ions close to each other to achieve co-deposition, but also reduces the dependence on current density to stabilize the alloy composition of the coating. It can form a stable alloy composition of the electroplating layer in a wide current density range from low current density to high current density, and the range is controlled below 2wt%.

[0028] According to the present invention, preferably, the content of the stabilizer is 0.1-25 g / L, for example, it can be 0.1 g / L, 0.5 g / L, 1.0 g / L, 1.5 g / L, 2.0 g / L, 2.5 g / L, 3.0 g / L, 3.5 g / L, 4.0 g / L, 4.5 g / L, 5.0 g / L, 5.5 g / L, 6.0 g / L, 6.5 g / L, 7.0 g / L, 7.5 g / L, 8.0 g / L, 8.5 g / L, 9.0 g / L, 9.5 g / L, 10.0 g / L, 10.5 g / L, 11.0 g / L, 11.5 g / L, 12.0 g / L, 12.5 g / L, 13.0 g / L. The concentrations are 1-10 g / L, 13.5 g / L, 14.0 g / L, 14.5 g / L, 15.0 g / L, 15.5 g / L, 16.0 g / L, 16.5 g / L, 17.0 g / L, 17.5 g / L, 18.0 g / L, 18.5 g / L, 19.0 g / L, 19.5 g / L, 20.0 g / L, 20.5 g / L, 21.0 g / L, 21.5 g / L, 22.0 g / L, 22.5 g / L, 23.0 g / L, 23.5 g / L, 24.0 g / L, 24.5 g / L, 25.0 g / L, and any value within the range of any two values.

[0029] In this invention, if the content of the stabilizer is too low, it cannot effectively reduce the dependence on current density to stabilize the alloy composition of the coating; if the content of the stabilizer is too high, the coating in the high current density area will become rough or burnt.

[0030] According to the present invention, preferably, the mass ratio of the first stabilizer and the second stabilizer is 2-8:1, for example, it can be 2:1, 2.2:1, 2.4:1, 2.6:1, 2.8:1, 3:1, 3.2:1, 3.4:1, 3.6:1, 3.8:1, 4:1, 4.2:1, 4.4:1, 4.6:1, 4.8:1, 5:1, 5.2:1, 5.4:1, 5.6:1, 5.8:1, etc. The ratios 6:1, 6.2:1, 6.4:1, 6.6:1, 6.8:1, 7:1, 7.2:1, 7.4:1, 7.6:1, 7.8:1, 8:1, and any value within the range of any two values ​​are more conducive to reducing the dependence of the coating composition on the current density. The alloy composition that can form a stable electroplated layer can be achieved in a wide current density range from low to high current density, and the range is controlled below 2wt%.

[0031] According to the present invention, preferably, the second stabilizer is antipyrine and / or diantipyrine.

[0032] In the prior art, antipyrine and diantipyrine are used as antioxidants for divalent tin. However, in this invention, antipyrine and diantipyrine are combined with ethylenediamine derivatives as alloy stabilizers. This not only brings the deposition potentials of gold and tin ions closer together to achieve co-deposition, but also reduces the dependence on current density to stabilize the alloy composition of the coating. Furthermore, it can form a stable alloy composition of the electroplated layer within a wide current density range from low to high current density, with the range controlled below 2 wt%.

[0033] According to the present invention, preferably, the alkyl-substituted ethylenediamine is selected from at least one of N-methylethylenediamine, N,N-dimethylethylenediamine, N,N'-dimethylethylenediamine, N,N,N'-trimethylethylenediamine, N,N,N',N'-tetramethylethylenediamine, N,N-diethyl-N'-methylethylenediamine, N,N'-diethyl-N,N'-dimethylethylenediamine, N,N,N',N'-tetraethylethylenediamine, and N-isopropyl-N-methylethylenediamine, and more preferably N,N'-dimethylethylenediamine and / or N,N,N',N'-tetramethylethylenediamine.

[0034] According to the present invention, preferably, the phenyl-substituted ethylenediamine is selected from at least one of N-phenylethylenediamine, N-methyl-N'-phenyl-1,2-ethylenediamine, N-benzylethylenediamine, N-benzyl-N-methyl-1,2-diaminoethane, N'-benzyl-N,N-dimethylethylenediamine, 1,2-diphenylethylenediamine, N,N'-diphenylethylenediamine, N,N-dibenzylethylenediamine, N,N-dimethyldiphenylethylenediamine, 1,2-bis(2-hydroxyphenyl)ethylenediamine, N,N-bis(2-hydroxyphenyl)ethylenediamine-N,N'-diacetic acid, and N,N'-bis(1-naphthylmethyl)-1,2-diphenyl-1,2-ethylenediamine, and more preferably at least one of N,N'-diphenylethylenediamine, N,N-dibenzylethylenediamine, and 1,2-bis(2-hydroxyphenyl)ethylenediamine.

[0035] According to the present invention, preferably, the alkyl hydroxyl-substituted ethylenediamine is selected from at least one of 2-hydroxyethyl ethylenediamine, N-(2-hydroxyethyl)ethylenediamine, N,N'-bis(2-hydroxyethyl)ethylenediamine, N,N-bis(2-hydroxyethyl)ethylenediamine, N,N,N',N'-tetra(2-hydroxyethyl)ethylenediamine, N-(2-hydroxypropyl)ethylenediamine, N-(3-hydroxypropyl)ethylenediamine, N,N,N',N'-tetra(2-hydroxypropyl)ethylenediamine, and N,N,N',N'-tetrahydroxypropyl ethylenediamine, and is more preferably N,N'-bis(2-hydroxyethyl)ethylenediamine and / or N,N,N',N'-tetra(2-hydroxypropyl)ethylenediamine.

[0036] In this invention, the use of ethylenediamine alkyl substitutes, ethylenediamine phenyl substitutes, and ethylenediamine alkyl hydroxy substitutes within the above-mentioned preferred range can reduce the dependence on current density to stabilize the alloy composition of the coating, and further enable the formation of a stable alloy composition of the electroplated layer within a wide current density range from low to high current density.

[0037] According to the present invention, preferably, the electroplating solution further includes gold cyanide salt and divalent tin salt.

[0038] The gold-tin alloy electroplating solution of this invention is a cyanide-based system, which has a much higher stability than cyanide-free systems. It will not produce turbidity or precipitation (gold deposition) even after long-term use. At the same time, it has a wide current density operating window and uses DC electroplating instead of pulse electroplating, making operation and control easy and suitable for actual production.

[0039] According to the present invention, preferably, the content of gold cyanide salt, calculated by metal element, is 1-50 g / L, for example, it can be 1 g / L, 2 g / L, 3 g / L, 4 g / L, 5 g / L, 6 g / L, 7 g / L, 8 g / L, 9 g / L, 10 g / L, 11 g / L, 12 g / L, 13 g / L, 14 g / L, 15 g / L, 16 g / L, 17 g / L, 18 g / L, 19 g / L, 20 g / L, 21 g / L, 22 g / L, 23 g / L, 24 g / L, 25 g / L, 26 g / L. The values ​​are 27 g / L, 28 g / L, 29 g / L, 30 g / L, 31 g / L, 32 g / L, 33 g / L, 34 g / L, 35 g / L, 36 g / L, 37 g / L, 38 g / L, 39 g / L, 40 g / L, 41 g / L, 42 g / L, 43 g / L, 44 g / L, 45 g / L, 46 g / L, 47 g / L, 48 g / L, 49 g / L, 50 g / L, and any value within any range of any two values, preferably 3-30 g / L, more preferably 5-15 g / L.

[0040] In this invention, when the content of gold cyanide salt meets the above-mentioned preferred range, it is more beneficial to reduce the dependence of the coating alloy composition on the current density. This is likely because, based on metal element content, the higher the content of gold cyanide salt in the plating solution, the higher the plating current density. When the gold content is too low, the obtained coating often has coarse crystals and is easily contaminated by impurities. Higher gold content means that the plating solution containing a large amount of gold adhering to the plated material will be carried away after plating, resulting in gold waste.

[0041] This invention allows for a wide range of choices of gold cyanide salts. Preferably, the gold cyanide salt is selected from at least one of sodium gold cyanide, potassium gold cyanide, ammonium gold cyanide, sodium gold cyanide, potassium gold cyanide, and ammonium gold cyanide, more preferably at least one of sodium gold cyanide, potassium gold cyanide, and ammonium gold cyanide, and more preferably potassium gold cyanide. The cyanide ion, acting as a ligand for gold, significantly shifts the gold deposition potential negatively and possesses the highest complexation stability constant, resulting in better stability of the electroplating solution compared to non-cyanide ion ligands.

[0042] According to the present invention, preferably, the gold cyanide salt is potassium gold cyanide, and the pH of the electroplating solution is 3-7, preferably 3.5-4.5.

[0043] Alternatively, the gold cyanide salt is potassium gold cyanide, and the pH of the electroplating solution is 1-3, preferably 1.5-2.5.

[0044] In this invention, different pH values ​​are selected for different gold cyanide salts, which is beneficial for the dissolution of gold cyanide salts and for maintaining their stability.

[0045] The pH of the electroplating solution can be adjusted by adding a pH adjuster. This invention does not have any particular limitation on the pH adjuster, as long as it can make the electroplating solution meet the above pH. For example, at least one of potassium hydroxide, sodium hydroxide, ammonia, and hydroxycarboxylic acid can be selected.

[0046] In this invention, hydroxycarboxylic acid refers to a class of organic carboxylic acid compounds whose molecular structure contains both hydroxyl (-OH) and carboxyl (-COOH) functional groups. For example, it can be citric acid and / or tartaric acid.

[0047] According to the present invention, preferably, the content of divalent tin salt, calculated as a metal element, is 1-50 g / L, for example, it can be 1 g / L, 2 g / L, 3 g / L, 4 g / L, 5 g / L, 6 g / L, 7 g / L, 8 g / L, 9 g / L, 10 g / L, 11 g / L, 12 g / L, 13 g / L, 14 g / L, 15 g / L, 16 g / L, 17 g / L, 18 g / L, 19 g / L, 20 g / L, 21 g / L, 22 g / L, 23 g / L, 24 g / L, 25 g / L, 26 g / L. The values ​​are 27 g / L, 28 g / L, 29 g / L, 30 g / L, 31 g / L, 32 g / L, 33 g / L, 34 g / L, 35 g / L, 36 g / L, 37 g / L, 38 g / L, 39 g / L, 40 g / L, 41 g / L, 42 g / L, 43 g / L, 44 g / L, 45 g / L, 46 g / L, 47 g / L, 48 g / L, 49 g / L, 50 g / L, and any value within any range of any two values, preferably 3-30 g / L, more preferably 5-18 g / L.

[0048] According to the present invention, preferably, the divalent tin salt is selected from at least one of stannous chloride, stannous sulfate, stannous methanesulfonate, stannous pyrophosphate and stannous oxide, and is more preferably stannous chloride and / or stannous sulfate.

[0049] According to the present invention, preferably, the mass ratio of gold cyanide salt to divalent tin salt, based on metal elements, is 0.7-1.2:1. For example, it can be 0.7:1, 0.75:1, 0.8:1, 0.85:1, 0.9:1, 0.95:1, 1:1, 1.05:1, 1.1:1, 1.15:1, 1.2:1, or any value within the range of any two values. Preferably, it is 0.8-1:1, which is beneficial for further obtaining a eutectic or near-eutectic gold-tin alloy.

[0050] According to the present invention, preferably, the electroplating solution further includes a complexing agent, the content of which is 5-500 g / L, preferably 30-300 g / L, and more preferably 50-150 g / L.

[0051] In this invention, if the complexing agent content is too low, divalent tin may precipitate as white precipitate; if the content is too high, the specific gravity of the gold-tin alloy electroplating solution will be too large, affecting the performance and service life of the plating solution.

[0052] According to the present invention, preferably, the complexing agent is selected from at least one of oxalic acid, malonic acid, succinic acid, citric acid, gluconic acid, glucoheponic acid, tartaric acid, malic acid, lactic acid, glyceric acid, glycolic acid, glycine, alanine, glutamic acid, ornithine, and cysteine, and more preferably from at least one of oxalic acid, gluconic acid, glycine, and citric acid. The gold-tin alloy electroplating solution of the present invention uses the above-mentioned complexing agent to promote and maintain the solubility of divalent tin ions at the given pH value.

[0053] In this invention, the complexing agent can be the compound itself as described above, or a chemically acceptable salt thereof, i.e., a salt that can dissociate to provide the core functional group of the above-mentioned compound.

[0054] Furthermore, the gold-tin alloy electroplating system of the present invention employs the aforementioned complexing agent, compounded with at least one of ethylenediamine alkyl-substituted derivatives, ethylenediamine phenyl-substituted derivatives, and ethylenediamine alkylhydroxy-substituted derivatives, and supplemented with antipyrine and / or diantipyrine to form a synergistic coordination system. This system can significantly reduce the dependence of the coating alloy composition on current density, achieve precise and stable control of the alloy composition, and ensure the uniformity of coating performance.

[0055] According to the present invention, preferably, the gold-tin alloy electroplating solution further includes a buffer and / or a conductive salt.

[0056] The present invention allows for a wide range of choices of buffers, as long as they can provide a buffering effect. Preferably, the buffer is selected from inorganic acids and / or organic hydroxy acids, and is preferably at least one of boric acid, phosphoric acid, citric acid, tartaric acid, and malic acid.

[0057] More preferably, the buffering agent of the present invention is a compound that can act as both a buffering agent and a complexing agent.

[0058] In this invention, the organic hydroxy acid refers to an organic carboxylic acid compound whose organic molecular skeleton is simultaneously connected with a carboxyl group (-COOH) and a hydroxyl group (-OH).

[0059] According to the present invention, preferably, the content of buffer in the gold-tin alloy electroplating solution is 1-500 g / L, more preferably 10-100 g / L.

[0060] According to the present invention, preferably, the conductive salt includes at least one selected from the following: inorganic potassium salt, inorganic sodium salt, inorganic ammonium salt, organic potassium salt, organic sodium salt, and organic ammonium salt.

[0061] Preferably, the inorganic acid is selected from at least one of sulfuric acid, nitric acid, and phosphoric acid.

[0062] Preferably, the organic acid is selected from at least one of oxalic acid, succinic acid, glutaric acid, malonic acid, citric acid, tartaric acid, and malic acid.

[0063] More preferably, the conductive salt of the present invention is a compound that can act as both a conductive salt and a complexing agent.

[0064] The present invention allows for a wide range of conductive salt content selection, as long as it can achieve the conductive effect. Preferably, the conductive salt content in the gold-tin alloy electroplating solution is 1-500 g / L, and more preferably 10-100 g / L.

[0065] According to the present invention, preferably, the gold-tin alloy electroplating solution further includes a chelating agent.

[0066] According to the present invention, preferably, the chelating agent is an aminocarboxylic acid compound and / or a phosphonic acid compound.

[0067] According to the present invention, preferably, the aminocarboxylic acid compound is selected from at least one of iminodiacetic acid, aminotriacetic acid, and ethylenediaminetetraacetic acid.

[0068] According to the present invention, preferably, the phosphonic acid compound is selected from at least one of hydroxyethylidene diphosphonic acid, aminotrimethylenephosphonic acid, and ethylenediaminetetramethylenephosphonic acid.

[0069] According to the present invention, preferably, the content of chelating agent in the electroplating solution is 0.1-100 g / L, more preferably 0.5-50 g / L.

[0070] In this invention, the use of the above-mentioned chelating agent and dosage is beneficial for further removing impurity metals from the electroplating solution.

[0071] According to the present invention, preferably, the gold-tin alloy electroplating solution also includes a surfactant.

[0072] According to the present invention, preferably, the surfactant is selected from at least one of nonionic surfactants, anionic surfactants, amphoteric surfactants, and cationic surfactants.

[0073] In this invention, the nonionic surfactant is selected from the condensation products of ethylene oxide and / or propylene oxide with at least one of aryl ethers, alkyl ethers, quinoline, phenanthroline, alkylquinoline, alkylphenanthroline, phenol, styrene-modified phenol, alkylphenol, naphthol, and alkylnaphthol, for example, the condensation product of ethylene oxide and alkylphenol OP-10 (octylphenol polyoxyethylene ether).

[0074] In this invention, the anionic surfactant is selected from at least one of alkyl sulfates, polyoxyethylene alkyl ether sulfates, polyoxyethylene alkylphenyl ether sulfates, alkylbenzene sulfonates, and alkylnaphthalene sulfonates.

[0075] In this invention, the amphoteric surfactant is selected from at least one of carboxybetaine, sulfobetaine, imidazoline betaine, and aminocarboxylic acid.

[0076] In this invention, the cationic surfactant is selected from at least one of trialkylamine salt, dimethyl dialkylammonium salt, and trimethyl alkylammonium salt.

[0077] According to the present invention, preferably, the content of surfactant in the electroplating solution is 0.01-20 g / L.

[0078] A second aspect of the present invention provides an electroplating method, comprising: electroplating using the above-mentioned gold-tin alloy electroplating solution, wherein the electroplating operating conditions include: temperature 25-60℃; current density range 0.1-1ASD.

[0079] Compared with PVD preparation technology (evaporation or sputtering), the gold-tin alloy electroplating solution and electroplating method of this invention for preparing gold-tin eutectic solder have comparable accuracy and uniformity in the composition of the coating alloy, but are more efficient and have lower costs.

[0080] According to the present invention, preferably, the electroplating operating conditions include a temperature of 35-45°C. If the plating bath temperature is too high, it may affect the stability of the plating bath; if the plating bath temperature is too low, the upper limit of the usable current density will decrease.

[0081] According to the present invention, preferably, the electroplating operating conditions include a current density range of 0.1-1 ASD, more preferably 0.5-1 ASD. If the current density is too high, the plating layer will be rough or scorched; if the current density is too low, the electroplating rate will be slow and the efficiency will be low.

[0082] According to the present invention, preferably, the anode of the electroplating is an insoluble anode, preferably at least one of platinum plate, platinum titanium mesh, and iridium oxide.

[0083] In this invention, the electroplating method using the gold-tin alloy electroplating solution of this invention can be implemented using currently known electroplating methods. Electroplating can also be performed using selective electroplating.

[0084] In this invention, the selective electroplating method includes: coating a substrate with a photoresist material, exposing and developing the area to be electroplated, then contacting the treated substrate with the gold-tin alloy electroplating solution of this invention, and using a DC power supply under the above-mentioned preset electroplating process parameters to deposit a gold-tin eutectic alloy in the area to be electroplated.

[0085] The electroplating solution of this invention will not corrode the photoresist material on the substrate surface during the entire electroplating process.

[0086] According to the present invention, preferably, the photoresist material can be at least one of dry film photoresist, wet film photoresist, or photoresist.

[0087] A third aspect of the present invention provides an article comprising a substrate and a gold-tin alloy layer disposed on the substrate, wherein the gold-tin alloy layer is obtained by electroplating with the gold-tin alloy electroplating solution described in the first aspect or by electroplating with the electroplating method described in the second aspect.

[0088] The gold-tin alloy layer is suitable for chip soldering or wafer bumping.

[0089] Unless otherwise specified, all examples and comparative examples below are conventional methods; the reagents, materials and instruments used are commercially available and / or prepared using methods known in the art, unless otherwise specified.

[0090] Example 1

[0091] A plating solution with a pH of approximately 4 was prepared using 10 g / L potassium gold cyanide (based on gold content), 11 g / L stannous chloride (based on tin content), 50 g / L potassium citrate, 50 g / L citric acid, 5 g / L N,N'-dimethylethylenediamine, 1 g / L antipyrine, 0.5 g / L nitric acid, and 0.5 g / L OP-10. Electroplating with this solution was tested at 40°C in a Hastelloy bath for 5 minutes at a current of 0.2 amps. The composition of the coatings at current densities of 0.1–1 ASD was analyzed using scanning electron microscopy (SEM / EDX) via energy-dispersive X-ray diffraction. The results are listed in Table 1.

[0092] Comparative Example 1

[0093] The method of Example 1 was followed, except that the N,N'-dimethylethylenediamine and antipyrine composition was replaced with 10 g / L of the nitrogen-containing heterocyclic compound nicotinic acid, and the results are listed in Table 1.

[0094] Comparative Example 2

[0095] The method of Example 1 was followed, except that 20 g / L of the organophosphate compound 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP) was used instead of the N,N'-dimethylethylenediamine and antipyrine composition. The results are listed in Table 1.

[0096] Comparative Example 3

[0097] The method of Example 1 was followed, except that the N,N'-dimethylethylenediamine and antipyrine composition were not added. The results are listed in Table 1.

[0098] Example 2

[0099] A plating solution with a pH of approximately 4.5 was prepared using 15 g / L potassium gold cyanide (based on gold content), 18 g / L stannous chloride (based on tin content), 75 g / L potassium gluconate, 75 g / L gluconic acid, 8 g / L N,N'-diphenylethylenediamine, and 1 g / L antipyrine. Electroplating with this solution was tested at 40 °C in a Hastelloy bath for 5 minutes at a current of 0.2 A. The composition of the coatings at current densities of 0.1–1 ASD was analyzed using scanning electron microscopy (SEM / EDX) via energy-dispersive X-ray diffraction. The results are listed in Table 1.

[0100] Example 3

[0101] A plating solution with a pH of approximately 3.5 was prepared using 5 g / L potassium gold cyanide (based on gold content), 5 g / L stannous sulfate (based on tin content), 25 g / L potassium oxalate, 25 g / L oxalic acid, 1 g / L N,N,N',N'-tetra(2-hydroxypropyl)ethylenediamine, and 0.5 g / L antipyrine. Electroplating with this solution was tested at 40 °C and a current of 0.2 A in a Hastelloy bath for 5 minutes. The composition of the coatings at current densities of 0.1–1 ASD was analyzed using scanning electron microscopy (SEM / EDX) via energy-dispersive X-ray diffraction. The results are listed in Table 1.

[0102] Example 4

[0103] The method of Example 1 was followed, except that the second stabilizer, antipyrine, was 0.5 g / L and the mass ratio was changed from 5:1 in Example 1 to 10:1. The results are listed in Table 1.

[0104] Example 5

[0105] The method of Example 1 was followed, except that N,N'-dimethylethylenediamine was replaced by N-methylethylenediamine by mass, and the results are listed in Table 1.

[0106] Example 6

[0107] Following the method of Example 1, except that antipyrine and other substances were replaced with catechol, the results are listed in Table 1.

[0108] Example 7

[0109] The method of Example 1 was followed, except that potassium citrate was replaced by sodium lactate and citric acid was replaced by lactic acid. The results are listed in Table 1.

[0110] Example 8

[0111] A plating solution with a pH of approximately 2.0 was prepared using 10 g / L potassium gold cyanide (based on gold element), 11 g / L tin sulfate (based on tin element), 100 g / L glycine, 20 g / L N,N,N',N'-tetramethylethylenediamine, and 4 g / L antipyrine. Electroplating with this solution was performed in a Hastelloy bath at 40 °C for 5 minutes at a current of 0.2 A. The composition of the coatings at current densities of 0.1–1 ASD was analyzed using scanning electron microscopy (SEM / EDX) via energy-dispersive X-ray diffraction. The results are listed in Table 1.

[0112] Example 9

[0113] The method of Example 1 was followed, except that 11 g / L stannous chloride was replaced with 16 g / L stannous chloride, and the mass ratio of gold to tin was changed from 0.9:1 in Example 1 to 0.6:1. The results are listed in Table 1.

[0114] Comparative Example 4

[0115] The method of Example 1 was followed, except that the contents of the first stabilizer and the second stabilizer were changed to 50 g / L N,N'-dimethylethylenediamine and 10 g / L antipyrine, respectively, while the mass ratio remained unchanged at 5:1. The results are listed in Table 1.

[0116] Comparative Example 5

[0117] The method of Example 1 was followed, except that antipyrine was not added and the content of N,N'-dimethylethylenediamine was 6 g / L. The results are listed in Table 1.

[0118] Comparative Example 6

[0119] Following the method of Example 1, except that antipyrine was replaced by ethylenediaminetetraacetic acid, the results are listed in Table 1.

[0120] Test case

[0121] Gold-tin eutectic bumps were fabricated using a 4-inch semiconductor substrate and subjected to reflow melting testing. The fabrication process for the gold-tin eutectic bumps is as follows: sputtering a seed layer of TiW / Au, photolithography, development, electroplating the gold-tin eutectic bumps, removing the photoresist, and etching the seed layer. Using the plating solutions prepared in the examples and comparative examples, the semiconductor substrate was electroplated at 40°C with an average current density of 0.7 ASD, and then reflow tested in a reflow oven at 310°C for 3 seconds.

[0122] Microscopic image of gold-tin eutectic bumps after electroplating in Example 1 is shown below. Figure 1 and Figure 2 As shown in the figure, the gold-tin bumps on the entire substrate have a good appearance after electroplating. A microscopic image of the gold-tin eutectic bumps after reflow in Example 1 is shown below. Figure 3 As shown in the figure, the gold-tin bumps after reflow are smooth, full, and have good solderability. The SEM image of the gold-tin eutectic bumps after reflow in Example 1 is shown below. Figure 4 As shown in the figure, a eutectic structure of ζ phase (light color) and δ phase (dark color) is generated after reflow.

[0123] Microscopic image of the defective gold-tin eutectic bumps after reflow in Comparative Example 1 is shown below. Figure 5 As shown in the figure, the gold-tin bumps on the substrate after reflow were not completely melted, resulting in poor solderability.

[0124] Microscopic image of the defective gold-tin eutectic bumps after reflow in Comparative Example 2 is shown below. Figure 6 As shown in the figure, the gold-tin bumps on the upper part of the substrate after reflow hardly melt, resulting in poor solderability.

[0125] Plating solution stability test: The plating solution was visually observed through a 50℃ constant temperature water bath, and the evaluation results are listed in Table 1.

[0126] ◎No problems occurred after the plating solution was placed in the Hastelloy bath for 3 months following the test.

[0127] ○ Slight turbidity or sedimentation occurred after the plating solution was left in the Hastelloy bath for 1 month following the test.

[0128] Slight turbidity or sedimentation occurred after the X plating solution was tested in the Hastelloy bath and left for 1 week.

[0129] The XX plating solution produced turbidity or sedimentation after being tested in the Hastelloy bath.

[0130] Table 1

[0131]

[0132] As shown in Table 1, within a wide current density range of 0.1-1 ASD, the plating solutions of Examples 1-8 of the present invention readily yield a eutectic alloy composition with a gold content of approximately 80 wt%, with a gold content range within 2 wt%, and the plating solution exhibits good stability. The plating solution of Example 9 yields a hypoeutectic alloy composition with a gold content of 75 wt%, with a gold content range within 2 wt%. On the other hand, the plating solutions of Comparative Examples 1-6, which do not contain the alloy stabilizer of the present invention, are less likely to yield a eutectic alloy composition with a gold content of approximately 80 wt%. The gold content fluctuates greatly with changes in current density, and even abnormal scorching of the plating layer occurs. Furthermore, the plating solution exhibits poor stability.

[0133] The results show that, compared with the comparative example, the electroplating solution provided by this invention can easily obtain a eutectic alloy composition with a gold content of about 80 wt% within a wide current density range of 0.1-1 ASD, with the gold content range within 2 wt%. At the same time, the plating solution has good stability. In contrast, the comparative example is difficult to obtain a eutectic alloy composition with a gold content of about 80 wt%, the gold content fluctuates greatly with the change of current density, and the plating solution has poor stability. This invention solves the problem of unstable alloy composition of the electroplated layer in the existing technology within a wide current density range.

[0134] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A gold-tin alloy electroplating solution, characterized in that, The electroplating solution includes gold cyanide, divalent tin salt, complexing agent, and stabilizer, wherein, based on metal elements, the content of gold cyanide is 1-50 g / L; the content of divalent tin salt is 1-50 g / L; the content of complexing agent is 5-500 g / L; and the content of stabilizer is 0.01-50 g / L. The mass ratio of gold cyanide salt to divalent tin salt, calculated by metallic element, is 0.7-1.2:

1. The complexing agent is selected from at least one of oxalic acid, malonic acid, succinic acid, citric acid, gluconic acid, glucoheponic acid, tartaric acid, malic acid, lactic acid, glyceric acid, glycolic acid, glycine, alanine, glutamic acid, ornithine, and cysteine. The stabilizer includes a first stabilizer and a second stabilizer; the mass ratio of the first stabilizer and the second stabilizer is 1-10:1; The first stabilizer is selected from at least one of ethylenediamine alkyl-substituted derivatives, ethylenediamine phenyl-substituted derivatives, and ethylenediamine alkylhydroxy-substituted derivatives; The alkyl-substituted ethylenediamine is selected from at least one of N-methylethylenediamine, N,N-dimethylethylenediamine, N,N'-dimethylethylenediamine, N,N,N'-trimethylethylenediamine, N,N,N',N'-tetramethylethylenediamine, N,N-diethyl-N'-methylethylenediamine, N,N'-diethyl-N,N'-dimethylethylenediamine, N,N,N',N'-tetraethylethylenediamine, and N-isopropyl-N-methylethylenediamine. The phenyl-substituted ethylenediamine is selected from at least one of N-phenylethylenediamine, N-methyl-N'-phenyl-1,2-ethylenediamine, N-benzylethylenediamine, N-benzyl-N-methyl-1,2-diaminoethane, N'-benzyl-N,N-dimethylethylenediamine, N,N'-diphenylethylenediamine, N,N-dibenzylethylenediamine, and N,N-dimethyldiphenylethylenediamine. The alkylhydroxy-substituted ethylenediamine is selected from at least one of N-(2-hydroxyethyl)ethylenediamine, N,N'-bis(2-hydroxyethyl)ethylenediamine, N,N-bis(2-hydroxyethyl)ethylenediamine, N,N,N',N'-tetra(2-hydroxyethyl)ethylenediamine, N-(2-hydroxypropyl)ethylenediamine, N-(3-hydroxypropyl)ethylenediamine, N,N,N',N'-tetra(2-hydroxypropyl)ethylenediamine, and N,N,N',N'-tetrahydroxypropylethylenediamine. The second stabilizer is selected from at least one of antipyrine, pyrogallol, hydroquinone, phlorogallol, and catechol.

2. The gold-tin alloy electroplating solution according to claim 1, characterized in that, The stabilizer content is 0.1-25 g / L; And / or, the mass ratio of the first stabilizer to the second stabilizer is 2-8:

1.

3. The gold-tin alloy electroplating solution according to claim 1, characterized in that, The gold-tin alloy electroplating solution also includes a buffer and / or a conductive salt; The buffer is an inorganic acid and / or an organic hydroxy acid, and the content of the buffer is 1-500 g / L; The conductive salt includes at least one of the following: inorganic potassium salt, inorganic sodium salt, inorganic ammonium salt, organic potassium salt, organic sodium salt, and organic ammonium salt, and the content of the conductive salt is 1-500 g / L.

4. The gold-tin alloy electroplating solution according to claim 1, characterized in that, The gold-tin alloy electroplating solution also includes a chelating agent, the content of which is 0.1-100 g / L; The chelating agent is an aminocarboxylic acid compound and / or a phosphonic acid compound.

5. The gold-tin alloy electroplating solution according to any one of claims 1-4, characterized in that, The gold-tin alloy electroplating solution also includes a surfactant; the surfactant is selected from at least one of nonionic surfactants, anionic surfactants, amphoteric surfactants, and cationic surfactants, and the surfactant content is 0.01-20 g / L.

6. An electroplating method, characterized in that, include: Electroplating is performed using the gold-tin alloy electroplating solution according to any one of claims 1-5, wherein the electroplating operating conditions include a temperature of 25-60°C. Current density range: 0.1-1 ASD.

7. An article characterized in that, The article comprises a substrate and a gold-tin alloy layer disposed on the substrate, wherein the gold-tin alloy layer is obtained by electroplating with the gold-tin alloy electroplating solution according to any one of claims 1-5 or by electroplating with the electroplating method according to claim 6. The gold-tin alloy layer is suitable for chip soldering or wafer bumping.

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