Tin alloy plating solution

Abstract

To provide a tin alloy plating solution, in which: a SnO2 sludge is prevented from forming in the plating solution even during long-term storage; a decline of concentration of Ag ions or Cu ions in the plating solution is suppressed; and the concentration of Ag ions or Cu ions can be stabilized.SOLUTION: A tin alloy plating solution of the present invention includes: (A) a soluble salt including at least a stannous salt; (B) a soluble salt of a nobler metal than tin; (C) a complexing agent of tin composed of a sugar alcohol in which the number of carbon atoms is from 4 to 6, inclusive; (D) a free acid; (E) and an antioxidant. The content of the complexing agent of tin is from 0.1 g / L to 5 g / L, inclusive. The concentration of divalent tin ions (Sn2+) is 30 g / L or more.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a tin alloy plating solution for manufacturing bumps that become protrusion electrodes of a tin alloy on a substrate when mounting a semiconductor integrated circuit chip on the circuit substrate.

Background Art

[0002] Conventionally, a non-cyanide Au-Sn alloy plating solution containing a non-cyanide soluble gold salt, a Sn compound composed of tetravalent Sn, and thiomonicarboxylic acid which is a thiocarboxylic acid-based compound has been disclosed (for example, Patent Document 1 (see Claims 1 to 3, Paragraphs

[0017] and

[0024] )). In this non-cyanide Au-Sn alloy plating solution, sugar alcohols are further contained, and these sugar alcohols are D-(-) sorbitol or xylitol. Also, regarding the concentrations of the soluble gold salt and the Sn compound composed of tetravalent Sn, they are set according to the ratio of the target Au-Sn alloy, etc., but preferably 1 to 10 g / L as the metal of Au and 1 to 20 g / L as the metal of Sn. If the metal concentration is too low, there are problems such as insufficient deposition efficiency, and if the concentration is too high, problems such as poor solution stability are likely to occur.

[0003] Patent Document 1 states that in the non-cyanide Au-Sn alloy plating solution configured as described above, the impact on the environment can be reduced, and a decrease in solution stability such as precipitation due to oxidation of the Sn compound does not occur, so that efficient Au-Sn alloy plating can be performed on plating objects such as semiconductor wafers.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the non-cyanide Au-Sn alloy plating solution disclosed in Patent Document 1 above, even when the concentration of Sn as a metal is in the range of 1 to 20 g / L, at the upper limit value of this range, Sn 4+ has a still high concentration, so when stored for a long time, SnO 2 sludge is generated in the plating solution, and precious metal ions (Au ions, Ag ions, and Cu ions) more precious than Sn ions are precipitated by substitution on the sludge, resulting in a problem that the concentrations of Au ions, Ag ions, and Cu ions in the plating solution decrease.

[0006] An object of the present invention is to provide a tin alloy plating solution that hardly generates SnO 2 sludge in the plating solution even when stored for a long time, suppresses a decrease in the concentration of Ag ions or Cu ions in the plating solution, and can stabilize the concentration of Ag ions or Cu ions.

Means for Solving the Problems

[0007] A first aspect of the present invention includes (A) a soluble salt containing at least a primary tin salt, (B) a soluble salt of a metal more precious than tin, (C) a tin complexing agent composed of a sugar alcohol having 4 to 6 carbon atoms, (D) a free acid, and (E) an antioxidant, and the content of the tin complexing agent is 1 g / L or more 5 g / L or less, The content of the soluble salt of a metal nobler than the tin is 0.1 g / L or more and 2 g / L or less, and the concentration of divalent tin ions (Sn 2+ ) is 30 g / L or more, which is a tin alloy plating solution.

[0008] A second aspect of the present invention is an invention based on the first aspect, characterized in that the pH is further 3 or less.

[0009] A third aspect of the present invention is an invention based on the first aspect, characterized in that the metal more precious than tin is further silver or copper.

[0010] A fourth aspect of the present invention is an invention based on the first aspect, and further shieldIt is characterized in that the concentration of tetravalent tin ions (Sn4+) is 5 g / L or less after storage at 40 °C for 6 months under light container sealing conditions.

Advantages of the Invention

[0011] In the tin alloy plating solution of the first aspect of the present invention, it contains (A) a soluble salt containing at least a primary tin salt, (B) a soluble salt of a metal nobler than tin, (C) a tin complexing agent composed of a sugar alcohol having 4 to 6 carbon atoms, (D) a free acid, and (E) an antioxidant. The content of the tin complexing agent is 0.1 g / L or more and 5 g / L or less, and the concentration of divalent tin ions (Sn 2+ ) is 30 g / L or more. Therefore, in the presence of a free acid, a sugar alcohol having 4 to 6 carbon atoms acts together with the antioxidant to strongly stabilize divalent tin ions (Sn 2+ ). As a result, even after long-term storage, sludge of SnO 2 is less likely to occur in the plating solution, and a decrease in the concentration of Ag ions or Cu ions in the plating solution can be suppressed to stabilize the concentration of Ag ions or Cu ions.

[0012] In the tin alloy plating solution of the second aspect of the present invention, since the pH of this tin alloy plating solution is 3 or less, the plating speed can be increased by setting the current density to 2 ASD or more. In the non-cyanide Au-Sn alloy plating solution shown in Patent Document 1, since the pH is in the neutral range, it can only be used at a low plating speed in the low current density range of 1 ASD or less, and there is a problem of poor productivity.

[0013] In the tin alloy plating solution of the third aspect of the present invention, since the metal nobler than tin is silver or copper, it has effects such as excellent solder wetting properties, mounting strength, bendability, and reflowability, and is less likely to generate whiskers. When mounting a semiconductor integrated circuit chip on a circuit board, bumps serving as tin-silver or tin-copper protruding electrodes can be efficiently manufactured on the substrate.

[0014] In the tin alloy plating solution according to the fourth aspect of the present invention, immediately after bath formation or after storage at 40 ° C for 6 months under the condition of sealing a light-shielding container, the concentration of tetravalent tin ions (Sn 4+ ) is 5 g / L or less. Therefore, the concentration of tetravalent tin ions (Sn 4+ ) is low, and even after long-term storage, it is difficult for sludge of SnO 2 to be generated in the plating solution. As a result, precious metal ions (Ag ions and Cu ions) more precious than Sn ions in the plating solution are not deposited by substitution on the sludge of SnO 2 , and the concentrations of Ag ions and Cu ions in the plating solution do not decrease.

Embodiments for Carrying Out the Invention

[0015] Next, embodiments for carrying out the present invention will be described. The tin alloy plating solution of the present invention contains (A) a soluble salt containing at least a first tin salt, (B) a soluble salt of a metal more precious than tin, (C) a tin complexing agent composed of a sugar alcohol having 4 to 6 carbon atoms, (D) a free acid, and (E) an antioxidant.

[0016] 〔Tin Alloy〕 The tin alloy produced by the tin alloy plating solution of the present embodiment is an alloy of tin (Sn) and a predetermined metal selected from silver (Ag), copper (Cu), gold (Au), and bismuth (Bi). Examples include binary alloys such as SnAg alloy, SnCu alloy, SnAu alloy, and SnBi alloy, and ternary alloys such as SnCuAg alloy.

[0017] 〔Soluble Salt (A) Containing at Least a First Tin Salt〕 The soluble salt (A) containing at least a first tin salt used in the tin alloy plating solution of the present embodiment dissolves in water to form divalent tin ions (Sn 2+) is a salt that generates. Examples of soluble salts include halides, sulfates, oxides, alkanesulfonates, arylsulfonates, and alkanolsulfonates. Specific examples of alkanesulfonates include methanesulfonate and ethanesulfonate. Specific examples of arylsulfonates include benzenesulfonate, phenolsulfonate, cresolsulfonate, and toluenesulfonate. A specific example of alkanolsulfonate is isethionate. Also, the divalent tin ion (Sn 2+ ) concentration in the tin alloy plating solution of this embodiment is 30 g / L or more, preferably 40 g / L or more. Further, immediately after the initial bath formation of this embodiment, or after storage at 40 °C for 6 months under the condition of sealing the light-shielding container, the concentration of the tetravalent tin ion (Sn 4+ ) in the tin alloy plating solution is preferably 5 g / L or less, more preferably 2 g / L or less. Here, the reason for limiting the divalent tin ion (Sn 2+ ) concentration to 30 g / L or more is that when it is less than 30 g / L, there is a problem that the uniform electrodeposition property deteriorates during high-speed plating at a current density of 2 ASD or more. Also, the reason for limiting the tetravalent tin ion (Sn 4+ ) concentration to 5 g / L or less is that when it exceeds 5 g / L, sludge of SnO 2 is likely to occur in the plating solution during long-term storage, and precious metal ions (Ag ions and Cu ions) more valuable than Sn ions in the plating solution are deposited by substitution on the sludge of SnO 2 , resulting in a decrease in the concentrations of Ag ions and Cu ions in the plating solution.

[0018] The soluble salt (A) containing at least a first tin salt (hereinafter referred to as soluble tin salt (A)) may be used alone or in combination of two or more. The content of the soluble tin salt (A) in the tin alloy plating solution of the present embodiment, in terms of the amount of tin, is preferably in the range of 5 g / L or more and 200 g / L or less, more preferably in the range of 20 g / L or more and 100 g / L or less. When the content of the soluble tin salt (A) is excessively low, tin deposition is generally unlikely to occur normally in the range of a current density of 1 ASD or more and 20 ASD or less (ASD: ampere per square decimeter) used for bump plating, and good bump formation may not be achieved. On the other hand, when the content of the soluble tin salt (A) is excessively high, it becomes difficult to form bumps due to an increase in the viscosity of the plating solution, and in addition, since it contains more tin than necessary, the cost of the plating bath may increase.

[0019] [Soluble salt (B) of a metal nobler than tin] The soluble salt (B) of a metal nobler than tin used in the tin alloy plating solution of the present embodiment is a salt soluble in water. Examples of the metal nobler than tin include at least one or two or more metals selected from silver, copper, gold, and bismuth. Examples of the soluble salt (B) of these metals nobler than tin are the same as those of the soluble tin salt (A). Among these metals, it is preferable to contain silver or copper. This has effects such as excellent solder wettability, mounting strength, bendability, and reflowability, and is less likely to generate whiskers. Also, when mounting a semiconductor integrated circuit chip on a circuit board, bumps serving as tin-silver or tin-copper protruding electrodes can be efficiently manufactured on the board. The alloy of tin and silver (SnAg alloy) has a low melting point of 221°C at the eutectic composition (Sn-3.5 mass% Ag), and the alloy of tin and copper (SnCu alloy) has a low melting point of 227°C at the eutectic composition (Sn-1.7 mass% Cu). Both have advantages such as excellent solder wettability, mounting strength, bendability, and reflowability, and are less likely to generate whiskers. The soluble salt (B) of a metal nobler than tin may be used alone or in combination of two or more. The content of the soluble salt (B) of a metal nobler than tin in the plating solution of the present embodiment, in terms of the amount of the metal, is preferably in the range of 0.01 g / L or more and 10 g / L or less, more preferably in the range of 0.1 g / L or more and 2 g / L or less. When the content of the soluble salt (B) of a metal nobler than tin is excessively small or excessively large, the composition of the deposited solder alloy cannot be made the eutectic composition, and the characteristics as a solder alloy cannot be obtained.

[0020] [Complexing agent for tin] Examples of the complexing agent for tin composed of a sugar alcohol having 4 carbon atoms include L-threitol, meso-erythritol, etc. Examples of the complexing agent for tin composed of a sugar alcohol having 5 carbon atoms include L-(-)-arabinitol, D-(+)-arabinitol, DL-arabinitol, ribitol, xylitol, etc. Further, examples of the complexing agent for tin composed of a sugar alcohol having 6 carbon atoms include D-iditol, L-iditol, L-sorbitol, D-sorbitol, L-mannitol, D-mannitol, galactitol, etc.

[0021] In the tin alloy plating solution of the present embodiment, the content of the tin complexing agent composed of sugar alcohol having 4 to 6 carbon atoms is 0.1 g / L or more and 5 g / L or less, preferably 1 g / L or more and 2.5 g / L or less. Here, when the carbon number of the sugar alcohol is less than 4, no interaction with the antioxidant occurs in the presence of free acid, and the complex-forming ability with respect to Sn 2+ ions is insufficient, so the generation of sludge of SnO 2 cannot be suppressed, noble metals more precious than tin are deposited by a substitution reaction, and the concentration of noble metals more precious than tin in the plating solution decreases. When the carbon number of the sugar alcohol exceeds 6, no interaction with the antioxidant occurs in the presence of free acid, and the complex-forming ability with respect to Sn 2+ ions is insufficient, so the generation of sludge of SnO 2 cannot be suppressed, noble metals more precious than tin are deposited by a substitution reaction, the concentration of noble metals more precious than tin in the plating solution decreases, the effect of the additive (brightening agent) is further reduced, and appearance defects occur in the film after plating. Further, the content of the above tin complexing agent is limited within the range of 0.1 g / L or more and 5 g / L or less because when it is less than 0.1 g / L, the generation of sludge of SnO 2 cannot be suppressed, noble metals more precious than tin are deposited by a substitution reaction, and the concentration of noble metals more precious than tin in the plating solution decreases, and when it exceeds 5 g / L, the effect of the additive (brightening agent) is reduced, and appearance defects occur in the film after plating.

[0022] In addition, as a tin complexing agent other than the tin complexing agent composed of the sugar alcohol having 4 to 6 carbon atoms, oxycarboxylic acids, polycarboxylic acids, and monocarboxylic acids can be used. Specific examples include gluconic acid, citric acid, glucoheptonic acid, gluconolactone, acetic acid, propionic acid, butyric acid, ascorbic acid, oxalic acid, malonic acid, succinic acid, glycolic acid, malic acid, tartaric acid, or salts thereof. Preferably, gluconic acid, citric acid, glucoheptonic acid, gluconolactone, glucoheptalactone, or salts thereof. In addition, ethylenediamine, 3,6-dithia-1,8-octanediol, ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), nitrilotriacetic acid (NTA), iminodiacetic acid (IDA), iminodipropionic acid (IDP), hydroxyethylethylenediaminetriacetic acid (HEDTA), triethylenetetraminehexaacetic acid (TTHA), ethylenedioxybis(ethylamine)-N,N,N',N'-tetraacetic acid, mercaptotriazoles, mercaptotetrazoles, glycines, nitrilotrimethylphosphonic acid, 1-hydroxyethane-1,1-diphosphonic acid, or salts thereof, such as polyamines and aminocarboxylic acids, are also effective as tin complexing agents.

[0023] The tin complexing agent other than the tin complexing agent composed of the sugar alcohol may be used alone or in combination of two or more. In the tin alloy plating solution of the present embodiment, the content of the complexing agent for tin other than the tin complexing agent composed of the sugar alcohol is generally preferably in the range of 0.1 g / L or more and 10 g / L or less, more preferably in the range of 0.5 g / L or more and 5 g / L or less.

[0024] <pH of the tin alloy plating solution> The tin alloy plating solution of this embodiment can be applied to a tin alloy plating bath in an acidic pH range. In the field of bump formation using an Sn alloy plating solution, a plating rate of 2 ASD or more is desired from the viewpoint of productivity. In order to ensure a plating rate of 2 ASD or more, the pH of the plating solution is preferably 3 or less, and more preferably less than 1. In order to adjust the pH of the tin alloy plating solution as described above, a pH adjuster can be included. Examples of the pH adjuster include various acids such as hydrochloric acid and sulfuric acid.

[0025] 〔Free acid (D)〕 Examples of the free acid (D) include hydrogen chloride, hydrogen bromide, sulfuric acid, alkanesulfonic acid, arylsulfonic acid, or alkanol sulfonic acid. Specific examples of the alkanesulfonic acid include methanesulfonic acid and ethanesulfonic acid. Specific examples of the arylsulfonic acid include benzenesulfonic acid, phenolsulfonic acid, cresolsulfonic acid, or toluenesulfonic acid. A specific example of the alkanol sulfonic acid is isethionic acid. The free acid (D) has the effect of increasing the conductivity of the tin alloy plating solution. Also, the free acid (D) may be used alone or in combination of two or more. The content of the free acid in the tin alloy plating solution of this embodiment is preferably in the range of 5 g / L or more and 500 g / L or less, and more preferably in the range of 30 g / L or more and 300 g / L or less.

[0026] 〔Antioxidant (E)〕 The tin alloy plating solution of this embodiment contains an antioxidant. Examples of the antioxidant include ascorbic acid or its salts, pyrogallol, hydroquinone, phloroglucinol, trihydroxybenzene, catechol, cresol sulfonic acid or its salts, catechol sulfonic acid or its salts, hydroquinone sulfonic acid or its salts, and the like. For example, in an acidic bath, hydroquinone sulfonic acid or its salts are preferred, and in a neutral bath, ascorbic acid or its salts are preferred. Further, the antioxidant may be used alone or in combination of two or more. The content of the antioxidant in the tin alloy plating solution of this embodiment is preferably in the range of 0.01 g / L or more and 20 g / L or less, more preferably in the range of 0.1 g / L or more and 10 g / L or less, and still more preferably in the range of 0.1 g / L or more and 5 g / L or less.

[0027] 〔Additive〕 The tin alloy plating solution of this embodiment may further contain additives such as a surfactant and a brightening agent.

[0028] 〔Surfactant〕 The surfactant has the effects of enhancing the affinity between the tin alloy plating solution and the object to be plated, adsorbing on the surface of the plating film during the formation of the tin alloy plating film, suppressing the crystal growth of the tin alloy in the plating film, and refining the crystals, thereby improving the appearance of the plating film, improving the adhesion to the object to be plated, and equalizing the film thickness. As the surfactant, various surfactants such as anionic surfactants, cationic surfactants, nonionic surfactants, and amphoteric surfactants can be used.

[0029] Specific examples of anionic surfactants include alkyl sulfates, polyoxyethylene alkyl ether sulfates, polyoxyethylene alkyl phenyl ether sulfates, alkyl benzene sulfonates, alkyl naphthalene sulfonates, and the like. Specific examples of cationic surfactants include monoalkylamine salts, dialkylamine salts, trialkylamine salts, dimethyldialkylammonium salts, trimethylalkylammonium salts, and the like. Specific examples of nonionic surfactants include alkanols, phenols, naphthols, bisphenols, alkylphenols having 1 to 25 carbon atoms, arylalkylphenols, alkylnaphthols having 1 to 25 carbon atoms, alkoxyl phosphates (salts) having 1 to 25 carbon atoms, sorbitan esters, polyalkylene glycols, aliphatic amides having 1 to 22 carbon atoms, etc., to which 2 to 300 moles of ethylene oxide (EO) and / or propylene oxide (PO) are added and condensed. Specific examples of amphoteric surfactants include carboxybetaine, imidazoline betaine, aminocarboxylic acid, and the like.

[0030] The surfactant may be used alone or in combination of two or more. The content of the surfactant in the tin alloy plating solution of this embodiment is generally preferably in the range of 0.01 g / L or more and 50 g / L or less, more preferably in the range of 0.1 g / L or more and 20 g / L or less, and still more preferably in the range of 1 g / L or more and 10 g / L or less.

[0031] 〔Brightening agent〕 The brightening agent is added to form a plating film uniformly and densely and to smooth the plating film. The brightening agent consists of a first brightening agent and a second brightening agent, and contains at least one of them. In addition, in order to enhance via filling properties and suppress the generation of voids, it is preferable to use two types of the first brightening agent and the second brightening agent. Examples of the first brightening agent include one or more selected from the group consisting of aromatic carbonyl compounds, aliphatic aldehydes, aromatic aldehydes, aliphatic ketones, and aromatic ketones. Examples of the second brightening agent include α,β-unsaturated carboxylic acids or their amides, or salts thereof.

[0032] The first brightening agent is a carbonyl compound containing an aldehyde or a ketone, and does not contain α,β-unsaturated carboxylic acid of the second brightening agent. As the first brightening agent, it is preferable to use an aromatic carbonyl compound. The aromatic carbonyl compound has the effect of refining the crystal grains of the tin alloy in the tin alloy plating film. The aromatic carbonyl compound is a compound in which a carbonyl group (-CO-X: where X represents a hydrogen atom, a hydroxy group, an alkyl group having 1 to 6 carbon atoms or an alkoxy group having 1 to 6 carbon atoms) is bonded to a carbon atom of an aromatic hydrocarbon. The aromatic hydrocarbon includes a benzene ring, a naphthalene ring and an anthracene ring. The aromatic hydrocarbon may have a substituent. Examples of the substituent include a halogen atom, a hydroxy group, an alkyl group having 1 to 6 carbon atoms and an alkoxy group having 1 to 6 carbon atoms. The carbonyl group may be directly bonded to the aromatic hydrocarbon or may be bonded via an alkylene group having 1 to 6 carbon atoms. Specific examples of the aromatic carbonyl compound include benzalacetone, cinnamic acid, cinnamaldehyde, and benzaldehyde. In addition, the following are exemplified as the first brightening agent. Examples of the aliphatic aldehyde include formaldehyde, acetaldehyde, and allyl aldehyde. Examples of the aromatic aldehyde include 2-chlorobenzaldehyde, 3-chlorobenzaldehyde, 4-chlorobenzaldehyde, 2,4-dichlorobenzaldehyde, 2,6-dichlorobenzaldehyde, 2,4,6-trichlorobenzaldehyde, 1-naphthaldehyde, 2-naphthaldehyde, 2-hydroxybenzaldehyde, 3-hydroxybenzaldehyde, 4-hydroxybenzaldehyde, 2-methylbenzaldehyde, 3-methylbenzaldehyde, 4-methylbenzaldehyde, m-anisaldehyde, o-anisaldehyde, p-anisaldehyde, and the like. Examples of the aliphatic ketone include acetylacetone. Further, examples of the aromatic ketone include 2-chloroacetophenone, 3-chloroacetophenone, 4-chloroacetophenone, 2,4-dichloroacetophenone, 2,4,6-trichloroacetophenone, and the like.These may be used alone or in combination of two or more. The content of the first brightening agent in the tin alloy plating solution of the present embodiment (the amount alone when included alone, and the total amount of these when two or more are included) is preferably in the range of 0.01 mg / L or more and 500 mg / L or less, more preferably in the range of 0.1 mg / L or more and 100 mg / L or less, and still more preferably in the range of 1 mg / L or more and 50 mg / L or less. If the content of the above components is too small, the addition effect may not occur. On the other hand, if the content of the above components is too large, it may inhibit the smoothing of the plating film.

[0033] Examples of the second brightening agent include acrylic acid, methacrylic acid, picolinic acid, crotonic acid, 3-chloroacrylic acid, 3,3-dimethylacrylic acid, 2,3-dimethylacrylic acid, methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 2-dimethylaminoethyl methacrylate, methacrylic anhydride, methyl methacrylate, etc. The second brightening agent also includes amides of α,β-unsaturated carboxylic acids (such as acrylamide, etc.) and salts of α,β-unsaturated carboxylic acids (such as salts of potassium, sodium, ammonium, etc.). The content of the second brightening agent in the tin alloy plating solution of the present embodiment (the amount alone when included alone, and the total amount of these when two or more are included) is preferably 0.01 g / L or more and 50 g / L or less, and more preferably 0.05 g / L or more and 10 g / L or less. If the content of the above components is too small, the addition effect may not occur. On the other hand, if the content of the above components is too large, it may inhibit the smoothing of the plating film.

[0034] The tin alloy plating solution of this embodiment contains (A) a soluble salt containing at least a primary tin salt, (B) a soluble salt of a metal nobler than tin, (C) a tin complexing agent composed of a sugar alcohol having 4 to 6 carbon atoms, and (D) a free acid. The content of the tin complexing agent is 0.1 g / L or more and 5 g / L or less, and the concentration of divalent tin ions (Sn 2+ ) is 30 g / L or more. Since the sugar alcohol having 4 to 6 carbon atoms acts together with the antioxidant in the presence of the free acid, the divalent tin ions (Sn 2+ ) can be strongly stabilized. As a result, even after long-term storage, sludge of SnO 2 is less likely to occur in the plating solution, and a decrease in the concentration of Ag ions or Cu ions in the plating solution can be suppressed to stabilize the concentration of Ag ions or Cu ions.

[0035] As a method for forming a plating film using the plating solution of this embodiment, electroplating is used as described above. The current density during plating film formation by electroplating is preferably in the range of 0.1 ASD or more and 100 ASD or less, more preferably in the range of 0.5 ASD or more and 20 ASD or less. The solution temperature is preferably in the range of 10°C or more and 50°C or less, more preferably in the range of 20°C or more and 40°C or less.

Example

[0036] Next, examples of the present invention will be described in detail together with comparative examples.

[0037] <Example 1> To an aqueous solution of tin methanesulfonate, methanesulfonic acid as a free acid, 3,6-dithia-1,8-octanediol and mercaptotetrazole as silver complexing agents, meso-erythritol as a sugar alcohol (tin complexing agent), and polyoxyethylene polyoxypropylene alkylamine (obtained by adding 25 moles of ethylene oxide (EO) and 30 moles of propylene oxide (PO) to alkylamine and condensing them) as a surfactant, and benzalacetone as a brightening agent were mixed and dissolved, and then a silver methanesulfonate solution was added and mixed. Finally, ion-exchanged water was added to prepare a SnAg plating solution (tin alloy plating solution) having the following composition. The aqueous solution of tin methanesulfonate was prepared by electrolyzing a metallic tin plate in an aqueous methanesulfonic acid solution, and the aqueous solution of silver methanesulfonate was prepared by electrolyzing a metallic silver plate in an aqueous methanesulfonic acid solution. Table 1 below shows the types of metals nobler than tin, the types of sugar alcohols, the number of carbon atoms in the molecule, the content ratio, the types of antioxidants, and the content ratio, respectively.

[0038] (Composition of SnAg plating solution (tin alloy plating solution)) Tin methanesulfonate (Sn 2+ as): 50 g / L Silver methanesulfonate (Ag + as): 0.5 g / L Methanesulfonic acid (as free acid): 100 g / L 3,6-Dithia-1,8-octanediol (as silver complexing agent): 2 g / L meso-Erythritol (as tin complexing agent (sugar alcohol)): 2 g / L Mercaptotetrazole (as tin complexing agent): 1 g / L Hydroquinone (as antioxidant): 1 g / L Polyoxyethylene polyoxypropylene alkylamine (surfactant): 5 g / L Benzalacetone (as brightening agent): 5 mg / L Ion-exchanged water: remainder pH: less than 1

[0039]

Table 1

[0040] <Examples 2 to 12 and Comparative Examples 1 to 6> As shown in Table 1, an SnAg plating solution (tin alloy plating solution) was prepared in the same manner as in Example 1, except that the type, the number of carbon atoms in the molecule, and the content ratio of the sugar alcohol were changed from those in Example 1.

[0041] <Example 13> Stannous methanesulfonate (Sn 2+ As) concentration was changed to 30 g / L, and an SnAg plating solution (tin alloy plating solution) was prepared in the same manner as in Example 8.

[0042] <Example 14> As shown in Table 1, an SnAg plating solution (tin alloy plating solution) was prepared in the same manner as in Example 5, except that the antioxidant was changed to hydroquinone sulfonic acid.

[0043] <Example 15> As shown in Table 1, an SnCu plating solution (tin alloy plating solution) was prepared in the same manner as in Example 11, except that the noble metal more precious than tin was changed to copper.

[0044] <Comparative Example 7> As shown in Table 1, an SnAg plating solution (tin alloy plating solution) was prepared in the same manner as in Example 1, except that no sugar alcohol was used, the type of antioxidant was the same as that in Example 1, and only its concentration was changed.

[0045] <Comparative Example 8> As shown in Table 1, an SnAg plating solution (tin alloy plating solution) was prepared in the same manner as in Example 1, except that no sugar alcohol was used and the type and concentration of the antioxidant were changed.

[0046] <Comparative Test> The following tests (a), (b), and (c) were conducted using the SnAg plating solutions (tin alloy plating solutions) or SnCu plating solutions (tin alloy plating solutions) of Examples 1 to 15 and Comparative Examples 1 to 8. (a) Residual rate of Ag in SnAg plating solution or Cu in SnCu plating solution When the SnAg plating solutions (tin alloy plating solutions) or SnCu plating solutions (tin alloy plating solutions) of Examples 1 to 15 and Comparative Examples 1 to 8 were stored for a predetermined period, the residual rate of Ag or Cu in the plating solutions was determined as follows. First, the Ag concentration (g / L) or Cu concentration (g / L) in the plating solution at the initial stage (immediately after bath formation) was measured using ICP-OES (inductively coupled plasma optical emission spectrometry). This Ag concentration or Cu concentration was defined as the 'initial concentration'. Next, 1 L of the above SnAg plating solution or SnCu plating solution was placed in a washed polyethylene light-shielding container and sealed, and after being left standing and stored in a Panasonic incubator set at 40°C for 6 months, the Ag concentration (g / L) or Cu concentration (g / L) in the SnAg plating solution was measured using ICP-OES. This Ag concentration or Cu concentration was defined as the 'concentration after storage'. Furthermore, the residual rate (%) of Ag in the SnAg plating solution or Cu in the SnCu plating solution was calculated by the following formula (1). Residual rate of Ag or Cu (%) =(Concentration of Ag or Cu after storage / Initial concentration of Ag or Cu) × 100 (1) The results are shown in Table 2 below. In Table 2, the plating solutions with a residual rate of Ag or Cu in the plating solution of 80% or more were judged as 'good', and the plating solutions with a residual rate of less than 80% were judged as 'bad'.

[0047] (b) Sn in SnAg plating solution or SnCu plating solution 4+ Concentration The Sn concentration in the SnAg plating solutions (tin alloy plating solutions) or SnCu plating solutions (tin alloy plating solutions) of Examples 1 to 15 and Comparative Examples 1 to 8 was determined as follows. First, the total Sn concentration in the plating solution was measured using ICP-OES (inductively coupled plasma optical emission spectrometry). This Sn concentration was defined as the 'total Sn concentration'. Next, for the above SnAg plating solution or SnCu plating solution, the Sn concentration was measured by redox titration using iodine. This Sn concentration was defined as the 'Sn concentration'. Furthermore, the Sn in the SnAg plating solution or SnCu plating solution 4+ Concentration 2+ Concentration 2+ Concentration 4+The concentration (g / L) was calculated by the following formula (2). Sn 4+ Concentration (g / L) = Total Sn concentration - Sn 2+ Concentration (2)

[0048] (c) Plating performance using SnAg plating solution or SnCu plating solution The SnAg plating solutions or SnCu plating solutions of Examples 1 to 15 and Comparative Examples 1 to 8 were separately placed in a Hull cell manufactured by Yamamoto Plating Tester Co., Ltd. A copper Hull cell plate was placed as a cathode in the solution, and a platinum plate was placed as an anode. A Hull cell test was conducted to evaluate the plating performance of the plating solution. As the plating conditions, the solution temperature was 30°C, the current density was 4 ASD, and the plating treatment time was 10 minutes. During the plating process, the plating solution was stirred with a cathode rocker. The results are shown in Table 1. The plating performance tests were carried out both initially (immediately after bath formation) and after storage (static storage at 40°C for 6 months). In Table 1, the appearance of the plating film was visually observed. A plating film with no abnormal deposition such as nodules and with gloss was judged as 'good'. On the other hand, a plating film with the occurrence of abnormal deposition such as nodules or with loss of gloss was judged as 'bad'.

[0049]

Table 2

[0050] <Evaluation> As is clear from Tables 1 and 2, in the plating solution of Comparative Example 1, since the number of carbon atoms in the molecule of the sugar alcohol was less than C3, which was less than the appropriate number of carbon atoms in the molecule (C4 or more and C6 or less), the Ag residual rate after static storage at 40°C for 6 months was as low as 20%, and the stability of Ag was poor (bad). The appearance of the plating film deteriorated after the above storage period, and the judgment was bad.

[0051] In the plating solution of Comparative Example 2, since the number of carbon atoms in the molecule of the sugar alcohol was more than the appropriate number of carbon atoms in the molecule (C4 or more and C6 or less), which was C7, the Ag residual rate after standing storage at 40 °C for 6 months was as low as 64%, and the stability of Ag was poor (defective). At the same time, the action of the additive (brightening agent) was also hindered, and the appearance of the plating film was defective both initially (immediately after bath formation) and after storage, and the judgment was defective.

[0052] In the plating solution of Comparative Example 3, although the number of carbon atoms in the molecule of the sugar alcohol was within the range of the appropriate number of carbon atoms (C4 or more and C6 or less), which was C6, its content was less than the appropriate amount (0.1 g / L or more and 5 g / L or less), which was 0.01 g / L. Therefore, although there was no problem with the appearance of the plating film initially (immediately after bath formation), after 40 °C and 6 months of standing storage, the concentration of Ag decreased, and the judgment was defective.

[0053] In the plating solution of Comparative Example 4, although the number of carbon atoms in the molecule of the sugar alcohol was within the range of the appropriate number of carbon atoms (C4 or more and C6 or less), which was C6, its content was more than the appropriate amount (0.1 g / L or more and 5 g / L or less), which was 10 g / L. Therefore, the Ag residual rate after standing storage at 40 °C for 6 months was as high as 92%, and there was no problem with the stability of Ag (good). However, the action of the additive (brightening agent) was hindered, and the appearance of the plating film was defective in the initial state (immediately after bath formation), and the judgment was defective.

[0054] In the plating solution of Comparative Example 5, since gluconic acid, which is not a sugar alcohol, was used, the Ag residual rate after standing storage at 40 °C for 6 months was as low as 54%, and there was a problem with the stability of Ag (defective). The appearance of the plating film deteriorated after the above storage period, and the judgment was defective.

[0055] In the plating solutions of Comparative Examples 6 to 8, since no sugar alcohol was added, regardless of the type and content ratio of the antioxidant, the Ag residual rate after standing storage at 40 °C for 6 months was all as low as 10%, and there was a problem with the stability of Ag (defective). The appearance of the plating film deteriorated after the above storage period, and the judgment was defective.

[0056] In contrast, in the plating solutions of Examples 1 to 15, the number of carbon atoms in the molecule of the sugar alcohol was within an appropriate range of C4 or more and C6 or less, and its content was within an appropriate amount range of 0.1 g / L or more and 5 g / L or less. Therefore, the residual rate of Ag or Cu after standing storage at 40 °C for 6 months was as high as 80% or more and 96% or less, and there was no problem with the stability of Ag or Cu (good). The appearance of the plating film had no abnormal precipitation such as nodules from the initial stage (immediately after bath formation) to after the elapse of the above storage period, had luster, and the judgment was good.

Industrial Applicability

[0057] The tin alloy plating solution of the present invention can be used to form a part of electronic components such as semiconductor wafers and bump electrodes of printed circuit boards.

Claims

1. (A) a soluble salt containing at least a first tin salt, (B) a soluble salt of a metal nobler than tin, (C) a tin complexing agent composed of a sugar alcohol having 4 to 6 carbon atoms, (D) a free acid, (E) an antioxidant, and the content of the tin complexing agent is 1 g / L or more and 5 g / L or less, the content of the soluble salt of the metal nobler than tin is 0.1 g / L or more and 2 g / L or less, A tin alloy plating solution in which the concentration of divalent tin ions (Sn ２＋ ) is 30 g / L or more.

2. The tin alloy plating solution according to Claim 1, having a pH of 3 or less.

3. The tin alloy plating solution according to Claim 1, wherein the metal nobler than tin is silver or copper.

4. The tin alloy plating solution according to claim 1, wherein the concentration of tetravalent tin ions (Sn ４＋ ) is 5 g / L or less after storage at 40°C for 6 months under the condition of sealing the light-shielding container.

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