TWI715991B - Aqueous composition for depositing a tin silver alloy and method for electrolytically depositing such an alloy - Google Patents

Abstract

The present invention refers to aqueous composition for depositing a tin silver alloy, the composition comprising (a) tin ions, (b) silver ions, (c) at least one first compound independently selected from the group consisting of unsubstituted bis(aminophenyl)disulfides, substituted bis(aminophenyl)disulfides, unsubstituted dipyridyldisulfides, and substituted dipyridyldisulfides, and (d) at least one second compound of formula (II)

, and salts thereof, wherein independently X denotes a C1 to C10 alkyl moiety comprising one or more than one sulfhydryl group, R¹ denotes hydrogen, methyl, ethyl, linear C3 to C5 alkyl, branched C3 to C5 alkyl, unsubstituted phenyl, substituted phenyl, unsubstituted benzyl, or substituted benzyl, and R² denotes methyl, ethyl, linear C3 to C5 alkyl, branched C3 to C5 alkyl, unsubstituted phenyl, substituted phenyl, unsubstituted benzyl, or substituted benzyl.

Description

Aqueous composition for depositing tin-silver alloy and method for electrodepositing the alloy

The present invention relates to an aqueous composition for depositing tin-silver alloys; a method for electrolytically depositing the alloy on a substrate; and a use of the composition to deposit tin-silver alloy solder bumps or tin The silver alloy welding cover is electrolytically deposited on the pillar.

In modern packaging technology, an obvious trend of size reduction is observed to realize the increase in the performance of electronic devices and the improvement of their functions. Solder caps on copper pillars have been found to be an interesting and promising alternative to conventional solder ball applications, especially for flip-chip applications in microelectronic devices.

The welding cap on the copper pillar is usually composed of two elements: (i) a structural element made of copper forming a pillar, such as a cylinder, and (ii) the welding cap on the top of the pillar. A large number of such capped copper pillars are usually arranged on the die, which is a part of the wafer. Compared with conventional solder ball applications, the solder cap on the copper pillar provides improved thermal and electrical properties due to the substantial amount of copper in the capping pillar, which provides excellent electrical connection and increased conductivity. The solder cap provides electrical and mechanical connections between the individual pillars and corresponding features (such as the pillars of another die).

The additional advantage of the solder cap on the copper pillar is that the shape of the pillar is slender compared to the spherical conventional solder ball application. This allows the distance (also called pitch) between two adjacent pillars to be reduced, which is a key factor in advanced packaging.

The solder cap usually contains tin and in many cases is a tin-silver alloy; usually it does not contain lead. This alloy generally provides excellent solderability and is a suitable replacement for the leaded solder caps and solder balls previously used.

Depositing these tin-silver alloys is known in the art. For example, JP 2006-265573 A discloses a cyanide-free tin-silver alloy electroplating bath, which improves the solderability and appearance of electrodeposited films obtained from the tin-silver bath.

EP 0 854 206 B1 relates to an acidic tin-silver alloy electroplating bath that is substantially free of cyanide and a method for electroplating tin-silver alloy on a substrate.

US 2014/0251818 A1 mentions a cyanide-free tin alloy electroplating solution, which has excellent continuous stability, and a method for electroplating tin alloy on conductive objects using a tin alloy electroplating solution. The tin alloy electroplating solution contains tin ions, one or more additional metal ions of silver, copper, bismuth, indium, palladium, lead, zinc or nickel, and peptides with cysteine residues.

WO 03/046260 A2 relates to an electrolytic bath used for electrodeposition of silver-tin alloys. In addition to water serving as a solvent with a pH value of less than 1.5, it contains water-soluble silver compounds, water-soluble tin compounds and organic complexing agents. In order to obtain a stable electrolytic bath capable of uniformly depositing dense tin-silver alloys with any type of composition, aliphatic complexing agents with sulfur groups and amine groups are used as complexing agents, whereby these functional groups are bonded to different carbon atoms.

EP 1 553 211 B1 relates to a tin-silver-copper electroplating solution containing 30-90% by weight of water, sulfonic acid, tin ions, copper ions and silver ions. The concentration of silver ions is 0.01 to 0.1 mol/L. The ion concentration is 0.21 to 2 mol/L, the copper ion concentration is 0.002 to 0.02 mol/L, and the molar ratio of silver ion to copper ion is in the range of 4.5 to 5.58.

US 6,607,653 B1 relates to a tin-copper alloy electroplating bath, tin-copper-bismuth alloy electroplating bath or tin-copper-silver alloy electroplating bath containing soluble metal compounds and specific sulfur-containing compounds.

EP 2 221 396 A1 relates to a composition comprising one or more sources of tin ions, one or more sources of alloy metal ions, and these metal ions are selected from the group consisting of silver ions, copper ions and bismuth ions, one Or more flavonoids and one or more compounds with the following formula: HOR(R'')SR'SR(R'')OH, where R, R'and R'' are the same or different, and have 1 to An alkylene group of 20 carbon atoms.

Although there are known methods, the deposition of tin-silver alloys (usually by electrolytic deposition) requires highly complex and precise deposition methods to obtain welding caps with high uniformity measurements. Only then can the appearance of dendrites on the pillars be effectively reduced or even completely avoided. Such dendrites are irregular and uneven welding caps, and may even bridge two adjacent pillars. In this situation, the entire die carrying a large number of pillars with solder caps may become useless and need to be thrown away. There is still a lack of suitable methods and compositions for separately obtaining copper pillars with substantially dendritic-free solder caps, and they are extremely needed to reduce the number of defective products.

Objective of the present invention The objective of the present invention is to provide an aqueous composition for depositing tin-silver alloys, which overcomes the above-mentioned problems. In detail, the purpose is especially to obtain a tin-silver alloy with high uniformity, for example to obtain extremely uniform welding caps on the pillars and substantially avoid dendrites (as defined above); especially at 20 A/dm ² to 30 At a very high current density in the A/dm ² range. In addition, the purpose is that the tin-silver alloy can also be used to form solder bumps with the advantages mentioned above.

Another object of the present invention is to also provide a corresponding method for electrolytic deposition of the tin-silver alloy, which is especially used for electrolytically depositing tin-silver alloy solder bumps and tin-silver alloy solder caps on pillars, thereby suppressing solder caps and solder The appearance of dendrites of both bumps.

(II)及其鹽， 其中獨立地 X表示包含一或多個氫硫基之C1至C10烷基部分， R¹ 表示氫、甲基、乙基、直鏈C3至C5烷基、分支鏈C3至C5烷基、未經取代之苯基、經取代之苯基、未經取代之苯甲基或經取代之苯甲基，且 R² 表示甲基、乙基、直鏈C3至C5烷基、分支鏈C3至C5烷基、未經取代之苯基、經取代之苯基、未經取代之苯甲基或經取代之苯甲基。 SUMMARY OF THE INVENTION These objects are solved by an aqueous composition for depositing tin-silver alloys, the composition comprising (a) tin ions, (b) silver ions, (c) at least one first compound, which are independently selected Free from the group consisting of: unsubstituted bis(aminophenyl) disulfide, substituted bis(aminophenyl) disulfide, unsubstituted dipyridyl disulfide and substituted two Pyridyl disulfide, and (d) at least one second compound of formula (II)

(II) and salts thereof, wherein independently X represents a C1 to C10 alkyl moiety containing one or more sulfhydryl groups, R ¹ represents hydrogen, methyl, ethyl, linear C3 to C5 alkyl, branched C3 To C5 alkyl, unsubstituted phenyl, substituted phenyl, unsubstituted benzyl or substituted benzyl, and R ² represents methyl, ethyl, linear C3 to C5 alkyl , Branched C3 to C5 alkyl, unsubstituted phenyl, substituted phenyl, unsubstituted benzyl or substituted benzyl.

In addition, another object is solved by a method for electrolytically depositing a tin-silver alloy on a substrate. The method includes the following steps: (A) Provide the substrate, (B) Provide an aqueous composition according to the present invention, preferably as described throughout this article, (C) contacting the substrate with the aqueous composition and supplying electric current, so that the tin-silver alloy is electrolytically deposited on the substrate.

In addition, these objects are solved by using the aqueous composition according to the present invention, preferably as described throughout the text, the aqueous composition is used to electrolyze tin-silver alloy solder bumps or tin-silver alloy solder caps Deposited on metal pillars, preferably used to electrolytically deposit tin-silver alloy solder caps on copper pillars.

Our experiments show that the water-based composition, method and use as defined above produce excellent uniform tin-silver solder caps. These covers are excellent for metal pillars, especially copper pillars (see examples below). In addition, the formation of dendrites is reduced or even completely prevented.

In the context of the present invention, the term "at least one" means (and can be exchanged with) "one, two, three or more than three".

The term "independently" means that, for example, in at least one second compound of formula (II), X, R ¹ and R ² in the first compound of formula (II) are independently selected from the aqueous composition of the present invention X, R ¹ and R ^{2 in} the second compound of formula (II) and other compounds. In addition, for example, at least one first compound is independently selected from a plurality of compound groups. This means that if, for example, two first compounds are selected, each compound can be selected from a different group of compounds. Sulfide. In other words, the first compound selection of the two first compounds is independent of the second first compound selection of the two first compounds.

The composition of the present invention is an aqueous composition, which means that water is the main component. Therefore, based on the total weight of the aqueous composition, the aqueous composition exceeds 50% by weight, preferably at least 60% by weight, even more preferably at least 70% by weight, and most preferably 80% by weight or more is water. Preferably, the aqueous composition contains substantially no organic solvent; more preferably, it contains no organic solvent at all. In addition, the aqueous composition is preferably an aqueous solution, that is, homogeneous and therefore preferably does not contain any particles.

In the context of the present invention, the term "at least" in combination with a specific value means (and can be exchanged with) this value or greater than this value. For example, "at least 70% by weight" means (and can be exchanged for) "70% by weight or greater than 70% by weight".

In the context of the present invention, the term "substantially free of" an object (for example, a compound, material, etc.) independently means that the object does not exist at all or exists only in a minimal and non-interfering amount (in the range) without affecting The intended purpose of the present invention. For example, the object may be added or used unintentionally, for example as an inevitable impurity. "Substantially free" preferably means 0 (zero) ppm to 50 ppm based on the total weight of the aqueous composition of the present invention (when defined for the aqueous composition), or based on the total weight of the tin-silver alloy (for When the alloy is defined); preferably 0 ppm to 25 ppm, more preferably 0 ppm to 10 ppm, even more preferably 0 ppm to 5 ppm, most preferably 0 ppm to 1 ppm. Zero ppm means that the corresponding object is not included at all.

It is preferably the aqueous composition of the present invention, wherein the composition is acidic, preferably the composition has a range of -2 to +4, more preferably a range of -1 to +2, and most preferably -0.5 To a pH in the range of +1.2. In general, acidic compositions (especially having a pH range as defined above) generally do not contain cyanide, which is desirable for environmental reasons. Therefore, the composition of the present invention is also preferably free of cyanide. In addition, the pH range mentioned above results in improved quality of deposited tin-silver alloys compared to compositions with a pH significantly higher than 4 or even alkaline. In addition, if the pH is within the pH range defined above, the stability is improved. Especially if the pH is significantly higher than 4 or even alkaline, improper precipitation is observed. In order to prevent precipitation in compositions whose pH is significantly higher than 4 or even alkaline, very powerful complexing agents such as cyanide which are harmful to the environment are usually used. However, this can be successfully avoided in the composition and method of the present invention. Therefore, wastewater treatment is simplified and environmental problems are prevented. In the context of the present invention, reference is made to pH at a temperature of 20°C.

The aqueous composition of the present invention is used to deposit tin-silver alloys, preferably tin-silver alloys that are substantially free of sulfur.

The aqueous composition of the present invention contains (a) tin ions and (b) silver ions to deposit tin-silver alloys. In the aqueous composition, the tin ion is preferably tin(II) ion and the silver ion is preferably silver(I) ion.

Preferably it is the aqueous composition of the present invention, wherein in the aqueous composition, based on the total volume of the aqueous composition, tin ions are in the range of 20 g/L to 200 g/L, preferably 25 g/L to In the range of 150 g/L, more preferably in the range of 30 g/L to 120 g/L, even more preferably in the range of 35 g/L to 100 g/L, most preferably in the range of 40 g/L to 90 g/L The total concentration within the range exists. Concentrations significantly below 20 g/L usually result in unduly low deposition rates. If the concentration significantly exceeds 200 g/L, solubility problems are often observed. The ideal balance of deposition rate and solubility is obtained within the preferred concentration range defined above. The best results have been obtained with concentrations ranging from 35 g/L to 100 g/L and 40 g/L to 90 g/L.

The tin ion system comes from a tin ion source. The tin ion source of the tin ions is preferably at least one tin salt, more preferably at least one inorganic tin salt and/or at least one organic tin salt. The preferred inorganic tin salt is selected from the group consisting of tin oxide, tin sulfate and tin sulfide. The preferred organotin salts are selected from the group consisting of tin acetate, tin citrate, tin oxalate and tin alkyl sulfonate. More preferably, it is the aqueous composition of the present invention, wherein the tin ion is derived from at least one organotin salt, preferably from at least one tin alkyl sulfonate. In the aqueous composition of the present invention, tin methanesulfonate is most preferred. Preferably, in each tin ion source, tin is present in the form of tin (II).

Preferably it is the aqueous composition of the present invention, wherein in the aqueous composition, based on the total volume of the aqueous composition, the silver ion is in the range of 0.1 g/L to 10 g/L, preferably 0.2 g/L to In the range of 8 g/L, more preferably in the range of 0.3 g/L to 6 g/L, even more preferably in the range of 0.4 g/L to 4 g/L, most preferably in the range of 0.5 g/L to 2 g/L The total concentration within the range exists. Concentrations significantly lower than 0.1 g/L usually result in insufficient amounts of silver in the tin-silver alloy, resulting in improper mechanical and electrical properties in the corresponding solder caps and solder bumps. If the concentration significantly exceeds 10 g/L, the composition is not stable enough and precipitation is sometimes observed. In addition, usually too much silver is incorporated into the tin-silver alloy, which significantly increases the melting point of the corresponding solder cap, which is improper in the subsequent reflow process. The ideal melting point obtained is within the preferred concentration range defined above, the best being within the range of 0.4 g/L to 4 g/L and 0.5 g/L to 2 g/L, respectively.

The silver ions come from a source of silver ions. The silver ion source of the silver ions is preferably at least one silver salt, more preferably at least one inorganic silver salt and/or at least one organic silver salt. The preferred inorganic silver salt is selected from the group consisting of silver oxide, silver sulfate and silver nitrate. The preferred organic silver salt is selected from the group consisting of silver acetate, silver citrate, silver oxalate and silver alkyl sulfonate. More preferably, it is the aqueous composition of the present invention, wherein the silver ion is derived from at least one organic silver salt, preferably from at least one silver alkyl sulfonate. In the aqueous composition of the present invention, silver methanesulfonate is most preferred. Preferably, in each silver ion source, silver exists in the form of silver (I).

Most preferably, the silver ion source and the tin ion source comprise alkyl sulfonate, more preferably alkyl sulfonate. This is especially preferred if the pH in the aqueous composition of the present invention is (re)adjusted by means of alkyl sulfonic acid. In this case, only one type of organic acid anion is present in the composition of the present invention.

Preferably it is the aqueous composition of the present invention, wherein the molar ratio of tin ion to silver ion is in the range of 200:1 to 5:1, preferably in the range of 150:1 to 10:1, more preferably in the range of 125:1 It is in the range of 12:1, preferably in the range of 100:1 to 15:1. If the molar ratio significantly exceeds 200:1, the silver will generally not be fully incorporated into the tin-silver alloy. If the molar ratio is significantly lower than 5:1, in some cases, the tin-silver alloy contains too much silver. However, if the mole is as defined above, especially in the range of 125:1 to 12:1 and 100:1 to 15:1, respectively, an excellent uniform tin-silver alloy is obtained and dendritic in the pillars of the solder cap Crystallization is largely suppressed.

It is very preferably the composition of the present invention, wherein the composition is substantially free of halide ions, and most preferably, chloride ions. First, silver chloride is extremely insoluble in aqueous environments. Secondly, in some cases, it has been observed that, in particular, the presence of chloride ions in low amounts does not necessarily cause the immediate precipitation of insoluble chlorides, which can lead to deposition defects in tin-silver alloys. Therefore, it is better not to use the tin ion source and the silver ion source containing halide anions, optimal chloride ion.

In some cases, the aqueous composition of the present invention is preferred, wherein the composition additionally contains copper (II) ions, and the total concentration is preferably 0.06 g/L to 5 g/L based on the total volume of the aqueous composition. L, the total concentration is more preferably 0.3 g/L to 4 g/L, and the total concentration is even more preferably 0.8 g/L to 3 g/L. This composition is used to substantially deposit tin-silver-copper alloys.

In some such cases, the aqueous composition of the present invention is preferred, wherein the total concentration of the composition is 0.06 g/L to 0.6 g/L, preferably 0.2 g/L based on the total volume of the aqueous composition To 0.5 g/L, more preferably 0.3 g/L to 0.4 g/L of copper (II) ion. In such cases, copper is only incorporated into the tin-silver alloy to a very limited extent.

In an alternative case, the aqueous composition of the present invention is preferred, wherein the composition contains a total concentration of 0.7 g/L to 5 g/L, preferably 1 g/L to 4.2 based on the total volume of the aqueous composition g/L, more preferably 1.3 g/L to 3.6 g/L, even more preferably 2.1 g/L to 3.1 g/L of copper (II) ion. In such cases, copper is incorporated into the tin-silver alloy to a significant degree.

However, in most cases, it is particularly desirable that the aqueous composition of the present invention does not include copper ions, so that the obtained tin-silver alloy is substantially free of copper, and preferably does not contain copper. Therefore, in such cases, the aqueous composition of the present invention is preferred, wherein the composition does not substantially contain copper ions, preferably does not contain copper ions, and preferably does not substantially contain copper ions and bismuth ions. It does not contain copper ions and bismuth ions.

Preferably, the aqueous composition of the present invention does not substantially contain nickel ion, zinc ion, iron ion, lead ion and aluminum ion, and preferably does not contain nickel ion, zinc ion, iron ion, lead ion and aluminum ion.

Preferably, the tin ions and the silver ions are the only depositable metal ions in the aqueous composition. This means that these metal ions are the only metal ions deposited in the tin-silver alloy. It is preferably the aqueous composition of the present invention, wherein in the aqueous composition, based on the total weight of all metal cations from Groups 3 to 15 in the aqueous composition, the total weight of the tin ions and the silver ions accounts for 80% to 100% by weight of all Group 3 to Group 15 metal cations in the aqueous composition, preferably at least 90% by weight, more preferably at least 95% by weight, even more preferably at least 98% by weight, most preferably at least 99% by weight %. Groups 3 to 15 refer to the 18 groups in the periodic table.

In addition to (a) tin ions and (b) silver ions, the aqueous composition of the present invention comprises (c) at least one (preferably one) first compound (as described throughout this article) and in addition (d) at least one (more Preferably one) the second compound of formula (II).

The at least one first compound is independently selected from the group consisting of: unsubstituted bis(aminophenyl) disulfide, substituted bis(aminophenyl) disulfide, unsubstituted dipyridine Disulfides and substituted dipyridyl disulfides are preferably independently selected from the group consisting of unsubstituted bis(aminophenyl) disulfides, substituted bis(aminophenyl) ) Disulfide and unsubstituted dipyridyl disulfide, more preferably independently selected from the group consisting of: unsubstituted bis(aminophenyl) disulfide and substituted bis(aminobenzene) The disulfides are preferably independently selected from the group consisting of unsubstituted bis(aminophenyl) disulfides. In the context of the present invention, unsubstituted means that no additional substituents (that is, functional groups) are included, and substituted means that there are additional substituents (that is, functional groups).

In the unsubstituted bis(aminophenyl) disulfide, each phenyl moiety preferably contains a single amino group. Preferably, the unsubstituted bis(aminophenyl) disulfide is selected from the group consisting of 4,4'-diaminodiphenyl disulfide (also known as 4,4'-disulfide) Thiodiphenylamine) and 2,2'-diaminodiphenyl disulfide (also known as 2,2'-dithiodiphenylamine). More preferably, it is the aqueous composition of the present invention, wherein at least one of the first compounds is 2,2'-diaminodiphenyl disulfide. The most preferred is the aqueous composition of the present invention, in which 2,2'-diaminodiphenyl disulfide is the only first compound.

The unsubstituted dipyridyl disulfide is preferably selected from the group consisting of 4,4'-dipyridyl disulfide and 2,2'-dipyridyl disulfide.

Preferably, it is the aqueous composition of the present invention, wherein the substituted bis(aminophenyl) disulfide and the substituted dipyridyl disulfide have at least one substituent, which is independently selected from the group consisting of: C1 to C4 alkyl, C1 to C4 alkoxy, hydroxyl, sulfhydryl, carboxyl, amine, nitro and halide.

In the case of substituted bis(aminophenyl) disulfides, the amino substituent represents the second amino group in at least one of the two phenyl moieties.

Particularly preferred is the aqueous composition of the present invention, wherein the substituted bis(aminophenyl) disulfide has at least one substituent, which is independently selected from the group consisting of: C1 to C4 alkyl, C1 to C4 Alkoxy, hydroxyl, sulfhydryl, carboxyl, amine, nitro and halide are preferably selected from the group consisting of C1 to C3 alkyl, C1 to C4 alkoxy, hydroxyl and sulfhydryl, more It is preferably selected from the group consisting of C1 to C3 alkyl, C1 to C3 alkoxy and hydroxyl.

Especially preferred is the aqueous composition of the present invention, wherein the substituted dipyridyl disulfide has at least one substituent, which is independently selected from the group consisting of C1 to C4 alkyl, C1 to C4 alkoxy, Hydroxy, sulfhydryl, carboxyl, amine, nitro, and halide are preferably selected from the group consisting of C1 to C3 alkyl, C1 to C4 alkoxy, hydroxyl, sulfhydryl and amino, more preferably It is selected from the group consisting of C1 to C3 alkyl, C1 to C3 alkoxy, hydroxyl and amino.

Even better is the aqueous composition of the present invention, wherein the substituted dipyridyl disulfide has at least one substituent, which is independently selected from the group consisting of methoxy, ethoxy, methyl, and ethyl , Hydroxyl and amino groups.

Most preferably, the substituted dipyridyl disulfide has at least one amine substituent.

Preferably it is the aqueous composition of the present invention, wherein the total concentration of all the first compounds is 1 mmol/L to 100 mmol/L, preferably 5 mmol/L to 80 mmol/L, based on the total volume of the aqueous composition, It is more preferably 10 mmol/L to 60 mmol/L, even more preferably 15 mmol/L to 50 mmol/L, and most preferably 20 mmol/L to 40 mmol/L. Preferably, the total concentration as defined above is formed by only one first compound, most preferably by 2,2'-diaminodiphenyl disulfide (2,2'-dithiodiphenylamine). If the total concentration is significantly lower than 1 mmol/L or significantly higher than 100 mmol/L, undue changes in tin-silver alloys are often observed. In addition, in many cases, problems with the stability of the bath are observed.

(II)及其鹽， 殘基X中包含一或多個，較佳一個氫硫基(SH基)。At least one second compound of formula (II)

(II) and its salts, the residue X contains one or more, preferably one sulfhydryl group (SH group).

In the compound of formula (II), X represents a C1 to C10 alkyl moiety containing the one or more, preferably a sulfhydryl group, preferably a C1 to C8 alkyl moiety, more preferably a C1 to C6 moiety, or even more Preferably the C1 to C5 alkyl moiety, most preferably the C1 to C4 alkyl moiety, each contains one or more, preferably one sulfhydryl group. For example, if X is a C1 alkyl moiety containing one sulfhydryl group, then X represents -CH ₂ -SH.

Among the C1 to C10 alkyl moieties, the alkyl moiety having three or more carbon atoms is linear or branched, preferably linear. The linear alkyl moiety is preferably covalently linked to the nitrogen atom in formula (II) via a terminal carbon atom in the linear alkyl moiety. Therefore, the linear alkyl moiety is preferably a normal alkyl moiety.

In the compound of formula (II), R ¹ represents hydrogen, methyl, ethyl, linear C3 to C5 alkyl, branched C3 to C5 alkyl, unsubstituted phenyl, substituted phenyl, unsubstituted Substituted benzyl or substituted benzyl, preferably R ¹ represents hydrogen, methyl, ethyl, linear C3 to C5 alkyl or branched C3 to C5 alkyl, more preferably R ¹ represents hydrogen, Methyl, ethyl or straight-chain C3 to C5 alkyl, most preferably R ¹ represents methyl or ethyl. In the context of the present invention, branched C3 alkyl means its isomeric form.

In the compound of formula (II), R ² represents methyl, ethyl, linear C3 to C5 alkyl, branched C3 to C5 alkyl, unsubstituted phenyl, substituted phenyl, unsubstituted Benzyl or substituted benzyl, preferably R ² represents methyl, ethyl, linear C3 to C5 alkyl or branched C3 to C5 alkyl, more preferably R ² represents methyl, ethyl or Straight chain C3 to C5 alkyl group, most preferably R ² represents methyl or ethyl.

Preferred substituents in the substituted phenyl and substituted benzyl groups are independently selected from the group consisting of hydroxyl, C1 to C3 alkyl, C1 to C3 alkoxy, amine, nitro and carboxyl .

At least one second compound of formula (II) acts as a complexing agent in the aqueous composition of the present invention. Preferably, it is the aqueous composition of the present invention, wherein the compound of formula (II) is the only complexing agent in the composition. Especially preferably, the aqueous composition of the present invention does not substantially contain glycine, cysteine and glutathione, preferably does not contain glycine, cysteine and glutathione, and more preferably The above does not contain amino acids with at least one sulfhydryl group and peptides with at least one sulfhydryl group, preferably without amino acids with at least one sulfhydryl group and peptides with at least one sulfhydryl group, the most substantial It does not contain amino acids and peptides, and preferably does not contain amino acids and peptides at all. Our experiments indicate that amino acids and peptides have a negative impact on the shelf life of the aqueous composition of the present invention, and ultimately cause stability problems. In some cases, it has been observed that the storage period does not exceed six months, which is inappropriate. In contrast, it is desirable to obtain a storage period of more than six months, and the compound of formula (II) will not have a negative impact on the storage period, preferably a storage period of more than six months.

In the aqueous composition of the present invention, the compound of formula (II) unexpectedly provides a second advantage. Generally, during the use of the aqueous composition of the present invention, at least one compound of the first compound is reduced, resulting in its monomerization. This singulation basically meets the needs. Generally, due to the aromatic ring with a hydrogen sulfide group, this produces an extremely unpleasant odor. However, in the context of the present invention, it has been observed that the compound of formula (II) only reduces the compound of at least one first compound to a degree that prevents unpleasant odors to a large extent. Instead, a gradual and self-adjusting reduction is obtained so that the total amount of monomeric first compounds remains extremely low but high enough to ensure the operational ability of the aqueous composition. This is beneficial to people who work in close contact with the corresponding composition.

Therefore, the combination of at least one first compound of formula (II) and at least one second compound of formula (II) produces a number of unexpected advantages.

(IIa)及其鹽， 其中獨立地 R¹ 表示氫、甲基、乙基、直鏈C3至C5烷基、分支鏈C3至C5烷基、未經取代之苯基、經取代之苯基、未經取代之苯甲基或經取代之苯甲基，較佳R¹ 表示氫、甲基、乙基、直鏈C3至C5烷基或分支鏈C3至C5烷基，更佳R¹ 表示氫、甲基、乙基或直鏈C3至C5烷基，最佳R¹ 表示甲基或乙基， R² 表示甲基、乙基、直鏈C3至C5烷基、分支鏈C3至C5烷基、未經取代之苯基、經取代之苯基、未經取代之苯甲基或經取代之苯甲基，較佳R² 表示甲基、乙基、直鏈C3至C5烷基或分支鏈C3至C5烷基，更佳R² 表示甲基、乙基或直鏈C3至C5烷基，最佳R² 表示甲基或乙基，且 n表示1、2、3或4，較佳n表示1、2或3。Preferably it is the aqueous composition of the present invention, wherein at least one second compound of formula (II) is a compound of formula (IIa)

(IIa) and salts thereof, wherein independently R ¹ represents hydrogen, methyl, ethyl, linear C3 to C5 alkyl, branched C3 to C5 alkyl, unsubstituted phenyl, substituted phenyl, Unsubstituted benzyl or substituted benzyl, preferably R ¹ represents hydrogen, methyl, ethyl, linear C3 to C5 alkyl or branched C3 to C5 alkyl, more preferably R ¹ represents hydrogen , Methyl, ethyl, or linear C3 to C5 alkyl, most preferably R ¹ represents methyl or ethyl, R ² represents methyl, ethyl, linear C3 to C5 alkyl, branched C3 to C5 alkyl , Unsubstituted phenyl, substituted phenyl, unsubstituted benzyl or substituted benzyl, preferably R ² represents methyl, ethyl, linear C3 to C5 alkyl or branched C3 to C5 alkyl, more preferably R ² represents methyl, ethyl or linear C3 to C5 alkyl, most preferably R ² represents methyl or ethyl, and n represents 1, 2, 3 or 4, preferably n Represents 1, 2 or 3.

In the context of the present invention, linear C3 to C5 alkyl groups and branched C3 to C5 alkyl groups preferably and specifically include n-propyl, isopropyl, n-butyl, isobutyl, second butyl, and first Tributyl, n-pentyl, 2-methylbutan-2-yl, 2,2-dimethylpropyl, 3-methylbutyl, pentane-2-yl, pentane-3-yl, 3-methylbutan-2-yl and 2-methylbutyl.

The most preferred is the composition of the present invention, wherein at least one second compound of formula (II) is 2-(dimethylamino)ethanethiol.

In the aqueous composition of the present invention, the compound of formula (II) preferably has a positive charge at the nitrogen atom due to the preferred highly acidic pH (for pH, see the details above).

Preferably it is the aqueous composition of the present invention, wherein the total concentration of all the second compounds of the formula (II) is 5 mmol/L to 100 mmol/L, preferably 8 mmol/L based on the total volume of the aqueous composition To 80 mmol/L, more preferably 10 mmol/L to 60 mmol/L, even more preferably 15 mmol/L to 50 mmol/L, most preferably 20 mmol/L to 40 mmol/L. Preferably, the total concentration as defined above is formed by only one second compound, and most preferably only by 2-(dimethylamino)ethanethiol. If the total concentration is significantly lower than 5 mmol/L, the silver ions are not sufficiently complexed and improper precipitation is usually observed.

It is preferably the aqueous composition of the present invention, wherein the molar ratio of all the first compounds to all the second compounds is in the range of 10:1 to 1:10, preferably in the range of 7:1 to 1:7, more preferably In the range of 5:1 to 1:5, even better in the range of 4:1 to 1:4, most preferably in the range of 3:1 to 1:3, even best in the range of 2:1 to 1:2 Inside. If the molar ratio is significantly higher than 10:1 or significantly lower than 1:10, the stability of the aqueous composition is negatively affected in some cases. In addition, in some cases, the total amount of silver in the tin-silver alloy is negatively affected, resulting in a tin-silver alloy containing too high or too little silver.

The aqueous composition of the present invention preferably contains other compounds.

It is preferably the aqueous composition of the present invention, which further comprises (e) At least one organic acid anion, preferably alkylsulfonic acid anion, most methanesulfonic acid anion.

The at least one organic acid anion is preferably obtained from a tin ion source and/or a silver ion source.

Also preferably, the at least one organic acid anion is obtained from organic acids, preferably at least one alkyl sulfonic acid, and most preferably from methanesulfonic acid.

Preferably, the at least one organic acid anion is obtained from a tin ion source, a silver ion source and an organic acid. In this case, the aqueous composition of the present invention preferably contains only one type of organic acid anion, which is excellent. Therefore, it is most preferable to be the aqueous composition of the present invention, wherein in the composition, alkylsulfonate, preferably methanesulfonate is the only organic acid anion. This provides several advantages because the solubility of metal ions is generally higher in the presence of alkyl sulfonic acid. In addition, the improper oxidation of tin (II) ions to tin (IV) ions is significantly reduced. In addition, it has been observed that the corrosive effect of alkyl sulfonic acids is reduced compared to strong mineral acids.

Alkyl sulfonic acid is the preferred acid because it acts as an optimal pH adjuster and generally produces a very strong acidic pH. If other organic acid anions are used, preferably acetate, oxalate and citrate as organic acids or used in tin ion sources and/or silver ion sources, additional strong acids are usually required to obtain a better strong acid pH, such as strong inorganic Acid, which includes additional inorganic anions. This is preferable for the reasons stated above, for example. Therefore, it is preferably the aqueous composition of the present invention, wherein the composition contains substantially no inorganic acid, preferably no inorganic acid. Instead, strong organic acids are preferred in the composition of the present invention.

Preferably it is the aqueous composition of the present invention, wherein in the aqueous composition, the total concentration of all organic acid anions is 0.5 mol/L to 4.0 mol/L, preferably 0.6 mol/L to the total volume of the aqueous composition 2.5 mol/L, more preferably 0.7 mol/L to 2 mol/L, even more preferably 0.8 mol/L to 1.5 mol/L, and most preferably 0.9 mol/L to 1.3 mol/L. Preferably, the total concentration as defined above is formed by only one type of organic acid anion, more preferably only by alkyl sulfonate, and most preferably only by methanesulfonate. If the total concentration significantly exceeds 4.0 mol/L, the composition is no longer sufficiently stable. In addition, an excessively high total concentration causes serious problems or even damage on the substrate. If the total concentration is significantly lower than 0.5 mol/L, the conductivity of the aqueous composition is usually insufficient.

In order to improve the wettability, the aqueous composition of the present invention preferably contains at least one surfactant. The type of surfactant is not particularly limited. Therefore, it is preferably the aqueous composition of the present invention, which further comprises (f) At least one surfactant, preferably selected from the group consisting of nonionic surfactants, amphoteric surfactants, cationic surfactants and anionic surfactants, preferably nonionic surfactants and cationic surfactants Better alkoxylated cationic surfactants and polyether nonionic surfactants, even better alkylene oxide copolymers and alkoxylated amines, best ethylene oxide/propylene oxide copolymers and ethylene oxide Oxylated amines.

It is preferably the aqueous composition of the present invention, wherein the total concentration of all surfactants is 0.1 g/L to 20 g/L, preferably 0.4 g/L to 10 g/L, based on the total volume of the aqueous composition. Best 0.6 g/L to 8 g/L, best 1 g/L to 5 g/L. If the total concentration is significantly lower than 0.1 g/L, the wettability is insufficient in many cases. If the total concentration significantly exceeds 20 g/L, improper foam formation is usually observed.

In order to avoid or at least suppress foaming, the aqueous composition of the present invention further preferably contains at least one defoamer, at least in many cases.

The aqueous composition of the present invention preferably contains tin (II) ions. However, tin (II) ions are easily oxidized, which generates tin (IV) ions. This oxidation is inappropriate because it promotes the precipitation of tin (IV) species such as tin (IV) oxide. To avoid oxidation, it is better to use antioxidants. Therefore, it is preferably the aqueous composition of the present invention, which further comprises (g) At least one antioxidant, which is preferably selected from the group consisting of compounds containing hydroxylated ring moieties, most preferably selected from the group consisting of catechol, hydroquinone, resorcinol, phenolsulfonic acid, ascorbic acid And naphthalene sulfonic acid.

Preferably the hydroxylated ring part is a hydroxylated aromatic compound, more preferably benzenediol, even more preferably selected from the group consisting of catechol, hydroquinone and resorcinol, most preferably selected from resorcinol and The group consisting of hydroquinone. The most preferred is the aqueous composition of the present invention, in which at least one antioxidant is resorcinol, and more preferably, resorcinol is the only antioxidant in the aqueous composition of the present invention. The antioxidant as defined above is strong enough to avoid oxidation of tin (II) ions to tin (IV) ions without reducing tin (II) ions to metallic tin.

The aqueous composition of the present invention is preferably used for electrolytic deposition of tin-silver alloys and is preferably not used for electroless deposition.

Preferably it is the aqueous composition of the present invention, wherein the total concentration of all antioxidants is 1.0 mmol/L to 100 mmol/L, preferably 2.0 mmol/L to 70 mmol/L, more preferably based on the total volume of the aqueous composition 4.0 mmol/L to 40 mmol/L, even better 5.0 mmol/L to 20 mmol/L, most preferably 6.0 mmol/L to 15 mmol/L. Preferably, the total concentration as defined above is formed by only one type of antioxidant, more preferably formed only by benzenediol, and most preferably formed only by resorcinol. If the total concentration as defined above significantly exceeds 100 mmol/L, insufficient plating efficiency is observed in many cases. If the total concentration is significantly lower than 1.0 mmol/L, oxidation of tin (II) ions into insoluble tin (IV) species cannot be sufficiently prevented and improper precipitation may be observed in some cases.

If it is known that at least one antioxidant is a typical antioxidant, it is preferable to count the amount of this compound in the total concentration of all the antioxidants mentioned above. In particular, if at least one antioxidant is an organic acid and contains a hydroxylated ring moiety, the amount of the compound is counted among the total concentrations of all the antioxidants mentioned above.

As mentioned above, the present invention also relates to a method for electrolytically depositing a tin-silver alloy on a substrate. The method includes the following steps: (A) Provide the substrate, (B) Provide an aqueous composition according to the present invention, preferably as described above, (C) contacting the substrate with the aqueous composition and supplying electric current, so that the tin-silver alloy is electrolytically deposited on the substrate.

The above mentioned about the aqueous composition of the present invention also applies to the method of the present invention.

In step (A) of the method of the present invention, a substrate is provided, preferably a conductive substrate. In some cases, it is preferable to use the method of the present invention, wherein the substrate is a semiconductor base substrate, and preferably includes a conductive layer or a semiconductive layer on it. This conductive or semi-conductive layer is also often referred to as a seed layer. The type of seed layer is not particularly limited. The best seed layer is a copper seed layer.

The substrate is preferably or includes at least one metalloid and/or gallium, more preferably or includes at least one element selected from the group consisting of silicon, germanium and gallium, and most preferably or includes silicon. If the substrate itself has insufficient conductivity, it preferably includes the conductive layer or semi-conductive layer mentioned above.

The method of the present invention is most preferred, wherein the substrate is a wafer, preferably a wafer containing a conductive layer or a semi-conductive layer thereon, and most preferably a copper seed layer.

In other cases, the method of the present invention is preferred, wherein the substrate is a non-conductive substrate, preferably a glass or plastic substrate or a substrate containing glass or plastic. In this case, the substrate preferably already at least partially contains a conductive seed layer, or a conductive seed layer deposited in a subsequent processing step.

Preferably, the method of the present invention, wherein the substrate (as previously defined) includes a plurality of individual structural components. Preferably the method of the present invention, wherein the substrate includes a plurality of metal features, preferably a plurality of metal pillars and/or a region with at least one metal layer, more preferably a plurality of copper pillars and/or a region with at least one copper layer.

Preferably, the aspect ratio of the metal feature is in the range of 1:40 to 15:1 (height:width), preferably in the range of 1:30 to 10:1, more preferably in the range of 1:20 to 7. :1 within the range. The preferred aspect ratios of the metal pillars and the copper pillars are in the range of 1:1 to 10:1, and more preferably in the range of 1:1 to 7:1. The preferred aspect ratios of the metal bumps and the copper bumps are in the range of 1:40 to 1:1, and preferably in the range of 1:30 to 1:10. In the context of the present invention, individual structural features and metal features include individual geometrical forms, such as pillars, points, and regions, respectively, which can be achieved by the method of the present invention for the deposition of tin-silver alloys.

Preferably, it is the method of the present invention, wherein the metal pillars and the copper pillars each have a cylindrical shape. Preferably, the metal pillars and copper pillars respectively have a range of 3 µm to 100 µm, preferably a range of 5 µm to 90 µm, more preferably a range of 9 µm to 80 µm, even more preferably 15 µm to 70 µm The best height is within the range of 20 µm to 70 µm. Preferably, the metal pillars and copper pillars have a width in the range of 5 µm to 100 µm, preferably in the range of 10 µm to 80 µm, and more preferably in the range of 10 µm to 30 µm.

In the method of the present invention, the metal bumps and the copper bumps can have any shape; preferably, they are cylindrical, polygonal, and/or rectangular.

Preferably, the metal bumps and the copper bumps have a thickness of 0.5 µm to 50 µm, preferably 1 µm to 30 µm, more preferably 2 µm to 25 µm, even more preferably 3 µm to 20 µm, most preferably 4 µm to 15 µm. Height within µm. Preferably, the bump has a width of at least 50 µm, preferably at least 80 µm, and more preferably at least 100 µm.

In step (B), the aqueous composition of the present invention, which is preferably as described in the entire text, is provided, usually in a tank for electrolytic metal deposition.

In step (C) of the method of the present invention, a tin-silver alloy is electrolytically deposited on the substrate. Step (C) requires that the substrate is sufficiently conductive to electrolytically deposit a tin-silver alloy. The substrate provided in step (A) is already sufficiently conductive, or the substrate provided in step (A) is processed in a subsequent step to make it sufficiently conductive before step (C). Therefore, the substrate in step (C) preferably includes at least one conductive layer or semi-conductive layer so that a tin-silver alloy is electrolytically deposited thereon. Preferably, at least one conductive layer or semi-conductive layer is a conductive metal layer, a conductive semi-metal layer or a conductive non-metal layer. Most preferably, it is a conductive metal layer, preferably a metal copper layer, usually a copper seed layer.

The method of the present invention is preferred, wherein in step (C), the tin-silver alloy is deposited as solder caps and/or solder bumps on the pillars.

In the method of the present invention, the substrate is operated as a cathode to deposit a tin-silver alloy in step (C).

It is preferably the method of the present invention, wherein the current is direct current, preferably having a cathode current density in the range of 1 A/dm ² to 100 A/dm ² , more preferably having a cathode current density in the range of 3 A/dm ² to 70 A/dm ² The cathode current density within the range is preferably within the range of 5 A/dm ² to 50 A/dm ² . In some cases, the direct current in the preferred step (C) is not supplemented by current pulses. This means that preferably in step (C), direct current is the only current.

Our experiments show that the method of the present invention produces excellent results, especially at relatively high current densities. This means that an excellent and uniform tin-silver alloy is deposited under such current density, and in addition, the number of dendrites is very low. This is especially true when compared to compositions containing amino acids with at least one sulfhydryl group, such as cysteine (see the examples below). Therefore, the method of the present invention is particularly preferred, wherein the current includes a cathode current density in the range of 10 A/dm ² to 40 A/dm ² , more preferably in the range of 12 A/dm ² to 35 A/dm ² The direct current.

The method of the present invention is preferred, wherein in step (C), the contact and current application lasts for 3 seconds to 400 minutes, preferably 5 seconds to 200 minutes, most preferably 6 seconds to 100 minutes. If the contact is significantly less than 3 seconds, usually an incomplete tin-silver alloy is deposited and the uniformity of the welding cap is insufficient.

In step (C) of the method of the present invention, it is preferable to deposit a tin-silver alloy layer, the thickness of the layer is preferably in the range of 1 µm to 150 µm, more preferably in the range of 4 µm to 100 µm, even more preferably in the range of 7 µm Within the range of 90 µm, preferably within the range of 10 µm to 80 µm.

Preferably, it is the method of the present invention, wherein the silver content in the electrolytically deposited tin-silver alloy is in the range of 0.1% to 10% by weight, preferably 0.5% to 10% by weight, based on the total weight of the electrolytically deposited tin-silver alloy In the range of 5% by weight, preferably in the range of 1.5% to 3.5% by weight. Optimally, the remainder of the tin-silver alloy is tin. Therefore, the main metal in the tin-silver alloy is tin. Therefore, the method of the present invention is preferable, wherein the tin content in the electrolytically deposited tin-silver alloy is at least 60% by weight, preferably at least 70% by weight, more preferably based on the total weight of the electrolytically deposited tin-silver alloy At least 80% by weight, even more preferably at least 90% by weight or at least 95% by weight, most preferably at least 96.5% by weight, and even best at least 98.5% by weight or at least 99.5% by weight. It is highly desirable to obtain the tin-silver alloy as described above and because of its excellent solderability, it is very suitable for use as a solder cap on a pillar and as a solder bump.

The method of the present invention is preferred only in some cases where the tin-silver alloy contains copper.

In most cases, the tin-silver alloy obtained by the method of the present invention is not a ternary alloy, and more preferably is not a tin-silver-copper alloy. Preferably, the tin-silver alloy does not substantially contain, preferably does not contain one, more than one or all elements in the group consisting of zinc, nickel, iron, copper, bismuth, aluminum and lead. In particular, the tin-silver alloy obtained by the method of the present invention is substantially free of lead, and preferably does not contain lead.

It is preferably the method of the present invention, wherein in step (C), the aqueous composition has a temperature in the range of 5°C to 90°C, preferably in the range of 15°C to 60°C, more preferably in the range of 20°C to 50°C , The best temperature in the range of 22℃ to 40℃. If the temperature is significantly lower than 5°C, a sufficient deposition rate is not obtained. If the temperature is significantly higher than 90°C, improper evaporation occurs and the bath is unstable.

The present invention also relates to the use of the aqueous composition of the present invention, which is used to electrolytically deposit tin-silver alloy solder bumps or tin-silver alloy solder caps on metal posts, preferably for electrolytic deposition of tin-silver alloy solder caps On the copper pillar. The foregoing contents regarding the aqueous composition of the present invention and the method of the present invention are equally applicable to the foregoing uses, respectively. The present invention is described in more detail by the following non-limiting examples.

Example 1. Aqueous composition for depositing tin-silver alloy: In the first step, different aqueous compositions were prepared as follows: 1.1 Aqueous composition E-1 (according to the invention): Aqueous composition E-1 according to the invention Contains the following as surfactants: 45 g/L tin (II) ion, 1 g/L silver (I) ion, about 1 mol/L methanesulfonic acid, about 10 mmol/L resorcinol, 20 mmol/L To 40 mmol/L 2,2'-dithiodiphenylamine, 20 mmol/L to 40 mmol/L 2-(dimethylamino)ethanethiol and ethylene oxide/propylene oxide copolymer and ethoxy Gylated amine. The pH is approximately zero.

1.2 Comparison of aqueous composition C-1 (not according to the invention): For comparison purposes, the comparative aqueous composition C-1 contains 40 g/L tin (II) ion, 1 g/L silver (I) ion, about 1 mol/L methanesulfonic acid, about 5 mmol/L hydroquinone, 10 mmol/L to 20 mmol/L 2,2'-dithiodiphenylamine, about 20 mmol/L cysteine and surfactant. The pH is approximately zero. Comparative aqueous composition C-1 represents the prior art JP 2006-265573 A.

2. Method for electrolytic deposition of tin-silver alloy on the substrate (deposition experiment): In the second step, deposition was performed and a tin-silver alloy was deposited in each deposition experiment.

A silicon-based wafer test piece is provided as a substrate, which exhibits conductivity with the aid of a copper seed layer of approximately 500 nm, each containing nine crystal grains with a plurality of cylindrical copper pillars (height: 10 µm). A copper pillar is formed in the corresponding photoresist. Without removing the photoresist, a tin-silver alloy is deposited on the top of the copper pillar to form a corresponding solder cap. Thus, a copper pillar with a tin-silver solder cap was obtained.

To this end, 1000 ml of the corresponding aqueous composition prepared in the first step is provided.

* 支柱內不均勻性 ** 晶粒內不均勻性(評估來自各晶粒之九個支柱)Subsequently, the corresponding substrate is immersed into the corresponding composition for different contact times according to the supplied current density, so that about 15 µm tin-silver solder caps are deposited in each case (depending on the applied current density, immersion for 60 seconds to 120 seconds) second). The temperature of each composition was 25°C and the stirring was set to 300 rpm. After each deposition experiment, the number and average area of dendrites and the uniformity of the weld cap were determined. The parameters and corresponding results of each deposition experiment are summarized in Table 1. Table 1. Parameters and results of deposition experiment

* Inhomogeneity within the pillars ** Inhomogeneity within the die (Evaluation comes from nine pillars of each die)

Table 1 shows that in the deposition experiment using the aqueous composition E-1, the number of dendrites was not significant, even at a relatively high current density such as 30 A/dm ² . This was also observed for the average area of dendrites, and the average area of dendrites was significantly higher in the comparative aqueous composition C-1.

An optical microscope (Olympus LEXT OLS4000) was used to measure the number of dendrites and the average area of dendrites using the software "Olympus Stream Enterprise Desktop 2.2".

The benefits of the aqueous composition of the present invention are further shown in Figures 1 and 2, where Figure 1 shows the result of using the aqueous composition E-1 and Figure 2 shows the result of the comparative aqueous composition C-1, both of which are at 30 Under A/dm ² . In Figure 1 there are almost no dendrites, of which significantly more dendrites can be seen in Figure 2.

In addition, compared with the corresponding capped copper pillars obtained with the comparative water-based composition C-1, the copper pillars with welded caps obtained with the aqueous composition E-1 showed higher uniformity, at a level of 30 A/dm ² This is especially true at current density. This can be seen in the parameters WIP and WID, which are well known in this technical field.

The same improvement has been observed in the case of copper bumps instead of copper pillars (data not shown).

3. Determining the complex characteristics by titration experiment: In order to evaluate the complex properties of various compounds for silver ions, several titrations were performed. The results are summarized in Figure 3.

These titrations are performed as follows: In the first step, a stock aqueous solution (concentration of complex compound: 50 g/L) containing the corresponding compound for silver ions is prepared.

In the second step, the portion from the stock solution is gradually added to the titration solution containing silver methanesulfonate (concentration corresponding to 1 g/L Ag (I) ion) and silver rotating disk electrode (RDE) (1000 rpm) in. The reference electrode was used to measure the overpotential change after adding a portion from the stock solution. The temperature of the titrated solution is 25°C.

Figure 3 shows that the complex properties are significantly different in the test compounds.

Compound A alone (2,2'-dithiodiphenylamine) does not provide any significant complex properties. The overpotential remains almost zero in the range of 0 g/L to 6 g/L of compound A. Compound B alone (2-(dimethylamino)ethanethiol) exhibited significant complex properties for silver ions. According to Figure 3, a maximum overpotential of approximately -250 mV is obtained at approximately 3 g/L of compound B.

Similar to compound B, compound D (glutathione) alone exhibited significant mismatch characteristics and a similar maximum overpotential of about -250 mV. However, compared to compound B, compound D has a weaker ability to form corresponding complexes. This can be found in higher concentrations of compound D, which is necessary to obtain an overpotential, especially in the range of -50 mV to -200 mV. This means that Compound D is not as effective as Compound B at lower concentrations. In addition, glutathione as an organic compound has the following disadvantages in some cases: it is not stable enough over time in the corresponding aqueous composition (storage period).

Compound C (L-cysteine) alone also exhibits significant complexing properties for silver ions, and is a typical complex compound in known compositions (compare JP 2006-265573 A). Figure 3 shows that compound C is a very powerful complex compound. The maximum value of approximately -250 mV has been obtained at a relatively low concentration of less than 2 g/L. Generally speaking, if complex formation occurs at an already extremely low concentration, the working concentration in the corresponding aqueous composition is usually also low. In this case, maintaining such a low working concentration is challenging and requires extremely sensitive analytical tools, which is usually undesirable.

Compound E also exhibits a maximum overpotential of about -250 mV, and therefore is very similar to compound B, compound C, and compound D in this respect. In contrast, compound E forms strong complexes very quickly. This can be found in the fact that the maximum overpotential is almost obtained at 1 g/L. Although compound D is extremely capable of forming complexes, the working concentration is usually too low and it is very demanding to maintain this working concentration in the corresponding aqueous composition.

The combination of A and B and A and C is the only way to obtain extremely strong complexes. In each case, a maximum overpotential of approximately -400 mV is obtained. This strong complex formation is required to avoid undue silver precipitation. Generally, if the silver ions are not sufficiently complexed to cause the precipitation of insoluble silver species in the aqueous composition or the silver is deposited on the corresponding substrate too quickly even in the absence of current, precipitation will occur. However, only the combination of A and B additionally shows the required working concentration range to obtain an overpotential in the range of -250 mV to -400 mV. In addition, the combination of A and C has the following disadvantages: the corresponding solder caps are more likely to form dendrites (compare item 2 above). In the stock solutions of the combination of A and B and the combination of A and C, respectively, compared with 50 g/L of compound B and C, respectively, compound A was present in approximately equal molar amounts. The total concentration of compound A in the stock solution is the same as the concentration of compound A for the combination of A and B and the combination of A and C, respectively.

A‧‧‧A letter emphasizing the dendritic crystal formed on the top of the cylindrical copper pillar

Fig. 1 is a top view of a section of crystal grains containing a plurality of copper pillars obtained according to the present invention, the plurality of copper pillars having tin-silver solder caps (shown as black dots). For other details, see the examples below. The silicon-based wafer test piece containing the die is displayed in light gray.

2 is a top view of a section of crystal grains containing a plurality of copper pillars obtained according to the prior art (JP 2006-265573 A, see the examples below), the plurality of copper pillars having tin-silver solder caps (shown as black dots). Again, the silicon-based wafer test piece containing the die is displayed in light gray. In the upper right corner, the letter "A" emphasizes the dendrites formed on the top of the cylindrical copper pillar. Figure 3 is a graph showing the complex properties of various compounds of silver ions. On the x-axis, the concentration of the corresponding compound in g/L is given, and on the y-axis, the overpotential depending on the compound concentration is given. In the figure, the letters have the following meanings: A: 2,2'-dithiodiphenylamine, B: 2-(dimethylamino)ethanethiol, C: L-cysteine, D: glutathione Peptides and E: Cysteamine.

Claims (15)

An aqueous composition for depositing tin-silver alloys, the composition comprising (a) tin ions, (b) silver ions, (c) at least one first compound, which is independently selected from the group consisting of: unsubstituted Bis(aminophenyl) disulfide, substituted bis(aminophenyl) disulfide, unsubstituted dipyridyl disulfide and substituted dipyridyl disulfide, and (d ) At least one second compound of formula (II)

(II) and salts thereof, wherein independently X represents a C1 to C10 alkyl moiety containing one or more sulfhydryl groups, and R ¹ represents hydrogen, methyl, ethyl, linear C3 to C5 alkyl, branched C3 To C5 alkyl, unsubstituted phenyl, substituted phenyl, unsubstituted benzyl or substituted benzyl, and R ² represents methyl, ethyl, linear C3 to C5 alkyl , Branched C3 to C5 alkyl, unsubstituted phenyl, substituted phenyl, unsubstituted benzyl or substituted benzyl. The composition of claim 1, wherein the at least one second compound of formula (II) is a compound of formula (IIa)

(IIa) and salts thereof, wherein independently R ¹ represents hydrogen, methyl, ethyl, linear C3 to C5 alkyl, branched C3 to C5 alkyl, unsubstituted phenyl, substituted phenyl, Unsubstituted benzyl or substituted benzyl, R ² represents methyl, ethyl, linear C3 to C5 alkyl, branched C3 to C5 alkyl, unsubstituted phenyl, substituted Phenyl, unsubstituted benzyl or substituted benzyl, and n represents 1, 2, 3, or 4. The composition of claim 1 or 2, wherein the substituted bis(aminophenyl) disulfide and the substituted dipyridyl disulfide have at least one substituent, which is independently selected from the group consisting of : C1 to C4 alkyl, C1 to C4 alkoxy, hydroxyl, hydrogen sulfide, carboxyl, amine, nitro and halide. The composition of claim 1 or 2, wherein the composition is acidic and has a pH in the range of -2 to +4. The composition of claim 1 or 2, wherein the molar ratio of all the first compounds to all the second compounds is in the range of 10:1 to 1:10. Such as the composition of claim 1 or 2, wherein the molar ratio of the tin ions to the silver ions is in the range of 200:1 to 5:1. The composition of claim 1 or 2, which further comprises (e) at least one organic acid anion. The composition of claim 1 or 2, further comprising (f) at least one surfactant, which is selected from the group consisting of nonionic surfactants, amphoteric surfactants, cationic surfactants and anionic surfactants Agent. The composition of claim 1 or 2, further comprising (g) at least one antioxidant, which is selected from the group consisting of compounds containing hydroxylated ring moieties. The composition of claim 1 or 2, wherein the composition does not contain copper ions. The composition of claim 1 or 2, wherein in the aqueous composition, based on the total weight of all Group 3 to Group 15 metal cations in the aqueous composition, the tin ion and the silver ion The weight altogether accounts for 80% to 100% by weight of all Group 3 to Group 15 metal cations in the aqueous composition. A method for electrolytically depositing tin-silver alloy on a substrate, the method comprising the following steps: (A) Provide the substrate, (B) Provide the aqueous composition according to any one of claims 1 to 11, (C) contact the substrate with the aqueous composition and supply electric current, so that the tin-silver alloy is electrolytically deposited on On the substrate. The method of claim 12, wherein the silver content in the electrolytically deposited tin-silver alloy is in the range of 0.1% by weight to 10% by weight based on the total weight of the electrolytically deposited tin-silver alloy. The method of claim 12 or 13, wherein the substrate includes a plurality of metal features. A use of the aqueous composition according to any one of claims 1 to 11, which is used for electrolytic deposition of tin-silver alloy solder bumps or tin-silver alloy solder caps on metal pillars.

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