JPH10204676A - Tin-silver alloy electroplating bath and tin-silver alloy electroplating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tin-silver alloy electroplating bath which makes it possible obtain a uniform tin-silver alloy plating film having good appearance without the preferential deposition of silver and the displacement deposition of the anode and the plating film of silver. SOLUTION: This tin-silver alloy electroplating bath contains (A) tin (II) salt, (B) silver salt, (C) one or >=2 kinds of the acids selected from among sulfuric acid, phosphoric acid, phosphonic acid, hydroxycarboxylic acid, alkane sulfonic acid and alkanol sulfonic acid, (D) thiourea, (E) nonionic surfactant, (F) one or >=2 kinds of the additives selected from among a mercapto group-contg. arom. compd., dioxy arom. compd. and unsatd. carboxylic acid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electroplating bath for forming a tin-silver alloy plating film used as a substitute for a tin-lead alloy solder, and a tin-silver alloy electroplating method.

[0002]

2. Description of the Related Art
When soldering to an electronic component, a printed circuit board, or the like, tin plating or tin-lead alloy plating is mainly performed. However, tin plating has a problem of whisker generation, and tin-lead alloy plating has caused a problem that lead contained therein is a cause of environmental pollution in recent years, and a tin alloy solder material without lead has been required.

[0003] Therefore, recently, in view of the regulation on the use of lead, conventional tin has been used for soldering various components constituting electronic devices such as chip components, hoop materials, lead frames, semiconductor packages, bumps, printed boards, and the like. -It is required to use a tin-silver alloy as a substitute for the lead alloy solder. Therefore, there is a need for the development of an electroplating bath for forming a tin-silver alloy plating film.

Conventionally, as a tin-silver alloy electroplating bath,
A bath in which a nonionic surfactant is added to tin alkanesulfonate, silver alkanesulfonate, and alkanesulfonic acid is known (JP-A-8-13185).

[0005] However, the conventional tin-silver alloy plating bath has a small acicular or dendritic shape of several microns to several millimeters on the edge, edge or entire surface of the object to be plated during the plating operation.
Beard, granular, and powdery deposits, burns, burns, and the like are likely to occur, causing poor plating appearance, poor film thickness and alloy composition, and short-circuit failure between adjacent leads.

Further, this type of simple bath has a problem that silver is more likely to be deposited preferentially than tin, and a silver substitution precipitation reaction is apt to occur on a tin or tin-silver alloy electrode and a deposited plating film. In some cases, difficulties occur in the plating operation, and the adhesion of the plating film is easily hindered.

Further, unlike the above-mentioned strong acid bath, a neutral to weakly alkaline tin-silver alloy electroplating bath composed of silver chloride, silver iodide, potassium iodide, and potassium pyrophosphate has also been disclosed. However, if such a bath is used for plating a printed circuit board, it tends to erode the organic resist film and cause troubles such as floating.

The present invention is an improvement of the above circumstances, and provides a plating film having a good appearance, has no inconvenience such as preferential precipitation of silver and substitutional precipitation, and is preferably used for plating a printed circuit board. -To provide a silver alloy electroplating bath and a plating method.

[0009]

Means for Solving the Problems and Embodiments of the Invention The present inventors have made intensive studies to achieve the above object, and as a result, completed the present invention.
(A) stannous salt, (B) silver salt, (C) one or more acids selected from sulfuric acid, phosphoric acid, phosphonic acid, hydroxycarboxylic acid, alkanesulfonic acid and alkanolsulfonic acid, (D) ) Containing one or more additives selected from thiourea, (E) nonionic surfactant, (F) mercapto group-containing aromatic compound, dioxyaromatic compound and unsaturated carboxylic acid. Characterized by tin
Provided are a silver alloy electroplating bath and a tin-silver alloy electroplating method comprising immersing an object to be plated in the tin-silver alloy electroplating bath and electroplating.

According to the present invention, the obtained tin-silver alloy plating film has needle-like, dendritic, powdery, granular precipitates, burns,
In addition to having a good appearance without kogation and the like, tin 99.9 to 10% by weight and silver 0.1 to 90% by weight are selected by selecting the amount of tin ions and silver ions as the alloy composition of the plating film.
In this case, preferential precipitation of silver, substitutional precipitation of silver on the tin or tin-silver alloy anode and the plating film does not occur, and the alloy composition of the plating film is almost equal to tin ions in the plating bath, This is consistent with the ratio of silver ions. In addition, the cathode current density can be selected in a wide range of 0.1 to 100 A / dm ² , and each plating method of rack, barrel, and rackless (high-speed method such as hoop and jet) can be adopted.

The present invention also relates to a stannous salt, a silver salt and one or more acids selected from sulfuric acid, phosphoric acid, phosphonic acid, hydroxycarboxylic acid, alkanesulfonic acid and alkanolsulfonic acid. When the object to be plated is immersed in an electroplating bath containing tin-silver alloy, and silver is used for electroplating, silver metal is used as an anode, and silver ions are supplied in accordance with the deposition of silver from the plating bath. In addition to performing the electrolytic elution of the metal anode, replenishment of stannous ions in accordance with the deposition of tin from the plating bath is performed by adding and dissolving a stannous salt or stannous oxide to the plating bath. A tin-silver alloy electroplating method is provided. Furthermore, a tin-silver alloy containing a stannous salt, a silver salt, and one or more acids selected from sulfuric acid, phosphoric acid, phosphonic acid, hydroxycarboxylic acid, alkanesulfonic acid and alkanolsulfonic acid. The object to be plated is immersed in the electroplating bath, and when performing electroplating, the object to be plated is immersed in the plating bath while supplying power to the object to be plated, and the plated object is pulled up from the plating bath while supplying power to the object to be plated. Thus, there is provided a tin-silver alloy electroplating method characterized by the above.

Further, a stannous salt, a silver salt and one of acids selected from sulfuric acid, phosphoric acid, phosphonic acid, hydroxycarboxylic acid, alkanesulfonic acid and alkanolsulfonic acid.
The object to be plated is immersed in a tin-silver alloy electroplating bath containing a seed or two or more types, and when performing electroplating, a silver metal is used as an anode, and silver corresponding to the precipitation of silver from the plating bath is used. The replenishment of ions is carried out by electrolytic elution of the silver metal anode, and the replenishment of stannous ions in accordance with the deposition of tin from the plating bath is achieved by adding and dissolving a stannous salt or stannous oxide to the plating bath. Performing tin-silver alloy electroplating, wherein the plating object is immersed in the plating bath while supplying power to the object to be plated, and pulled up from the plating bath while supplying power to the plated object to be plated. Provide a way.

As described above, silver is used as the anode and Sn ²⁺
If the plating bath is supplied, the plating bath becomes (A)-
Even in a simple bath which does not contain all of the component (F) and is mainly composed of the components (A), (B) and (C), there is no silver substitution precipitation on the anode, and the Ag ⁺ concentration in the plating bath varies. In addition, by supplying power when the object to be plated is immersed in the plating bath or pulled up from the plating bath, there is no silver substitution precipitation on the object to be plated or the plating film deposited on the object to be plated, and the plating film This also eliminates poor adhesion, and the above-described method can more reliably prevent difficulty in plating.

Hereinafter, the present invention will be described in more detail.
As described above, the tin-silver alloy plating bath according to the first invention of the present invention comprises (A) stannous salt, (B) silver salt, (C) sulfuric acid, phosphoric acid, phosphonic acid, and hydroxycarboxylic acid. , Alkanesulfonic acid and alkanolsulfonic acid, (D) thiourea, (E) nonionic surfactant, (F) mercapto group-containing aromatic compound, dioxyaromatic compound and Contains one or more additives selected from unsaturated carboxylic acids.

Here, the stannous salt and silver salt may be any as long as they can be dissolved in an acid described later.
As a tin salt, stannous organic sulfonic acid such as stannous methanesulfonate, stannous sulfate, stannous chloride, stannous gluconate,
Stannous citrate, stannous lactate and the like can be used,
As the silver salt, silver alkanesulfonate such as silver methanesulfonate, silver sulfate, silver chloride, silver gluconate, silver citrate, silver lactate and the like can be used.

The content of stannous salt is 1 to 9 as Sn ^2+.
9 g / L, particularly preferably 5 to 36 g / L,
The silver salt content is preferably 1 to 99 g / L, particularly preferably 1 to 20 g / L, as Ag ⁺ . In this case, Sn
The ratio between ²⁺ and Ag ⁺ can be selected as appropriate,
n ²⁺ : Ag ⁺ = 99: 1 to 10:90, preferably 9
9: 1 to 50:50, especially 98: 2 to 60:40 by weight). Ag ⁺ is less silver composition ratio in the plating film to be deposited too small than the proportion, likely disadvantage occurs such as reducing the effect of tin whiskers prevention and solder wettability improvement, Ag ⁺ is from the ratio If the content is too large, the composition ratio of silver in the deposited plating film increases, and the melting temperature of the plating film becomes too high, and the hardness of the plating film becomes too high, and disadvantages such as being unsuitable for soldering are likely to occur.

The acid of the component (C) used in the plating bath of the present invention is one or more selected from sulfuric acid, phosphoric acid, phosphonic acid, hydroxycarboxylic acid, alkanesulfonic acid and alkanolsulfonic acid. Here, examples of the hydroxycarboxylic acid include monocarboxylic acids such as lactic acid, dicarboxylic acids such as gluconic acid, tartaric acid, and malic acid, and tricarboxylic acids such as citric acid. Unsubstituted and substituted alkanesulfonic acids and alkanolsulfonic acids are used. Unsubstituted alkanesulfonic acid is C _n H _{2n + 1} SO ₃ H (where n is 1 to ₃₎ .
5, preferably 1 or 2).

As the unsubstituted alkanolsulfonic acid, those represented by the following formula can be used.

[0019]

Embedded image (However, m is 0 to 2 and k is 1 to 3)

As the substituted alkanesulfonic acid and alkanolsulfonic acid, those in which a part of the hydrogen atoms of the alkyl group has been substituted with a halogen atom, an aryl group, an alkylaryl group, a carboxyl group, a sulfonic acid group or the like can be used.

Specifically, methanesulfonic acid, ethanesulfonic acid, isethionic acid, propanesulfonic acid, 2-propanesulfonic acid, butanesulfonic acid, 2-butanesulfonic acid, pentanesulfonic acid, chloropropanesulfonic acid, Hydroxyethane-1-sulfonic acid, 2-hydroxypropanesulfonic acid, 2-hydroxybutane-1
-Sulfonic acid, 2-hydroxypentanesulfonic acid, 2
-Sulfoacetic acid, 2- or 3-sulfopropionic acid, sulfosuccinic acid and the like are exemplified, and one or more of these can be used in combination.

The content of the acid is 50 to 400 g / L,
In particular, it is preferably 100 to 200 g / L. 50
If the amount is less than g / L, the stability of the plating bath is deteriorated, and a precipitate tends to be easily generated. If the amount is more than 400 g / L, the excess amount tends to be ineffective.

The thiourea (D) used in the plating bath of the present invention functions as a complexing agent for tin and silver.

The content of the thiourea is 10 to 200 g.
/ L, especially 50-100 g / L. If the amount is less than 10 g / L, the effect of the addition may not be sufficiently exerted, and if the amount is more than 200 g / L, the refinement of crystals of the deposited plating film may be hindered.

In the present invention, a nonionic surfactant is used as the component (E). As the nonionic surfactant, a known nonionic surfactant used in a tin-silver alloy electroplating bath can be used. In particular, polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, polyoxyethylene alkyl amino ethers, polyoxyethylene fatty acid esters, polyoxyethylene polyhydric alcohol ethers, ethylene oxide propylene oxide block copolymers, and the like are preferably mentioned. it can.

The content of the component (E) is from 0.01 to 5
0 g / L, particularly preferably 4 to 8 g / L,
If the amount is less than 0.01 g / L, burns and burns may occur at a high current density, and if the amount is more than 50 g / L, the plating film may become blackish or color unevenness may occur.

The plating bath of the present invention further contains one or more additives selected from aromatic compounds containing a mercapto group, dioxyaromatic compounds and unsaturated carboxylic acids as component (F). These additives are added to the plating bath in the form of fine needles, dendrites, of the order of several microns to several millimeters on the edges, edges or the entire surface of the article to be plated.
It has an effect of preventing the generation of mustache, granular, powdery precipitates, burns, burns, and the like. In this case, as the mercapto group-containing aromatic compound, 2-mercaptobenzoic acid,
Examples thereof include mercaptophenol, 2-mercaptobenzoxazole, and 2-mercaptobenzothiazole, and the content is 0.01 to 20 g / L, particularly 0.01 to 5 g / L.
g / L is preferable.

As the dioxy aromatic compound, dioxybenzophenone, 3,4-dioxyphenylalanine,
Examples thereof include resorcin, catechol, hydroquinone, and diparin, and the content is preferably 0.001 to 20 g / L, particularly preferably 0.001 to 4 g / L.

Examples of the unsaturated carboxylic acid include benzoic acid, fumaric acid, phthalic acid, acrylic acid, citraconic acid, methacrylic acid and the like.
L, particularly preferably 0.01 to 2 g / L.

The content of the above-mentioned additive is as described above. If the content is too small, fine needles of the order of several microns to several millimeters are formed on the edges, edges or the whole surface of the article to be plated during the plating operation. Dendritic, whisker-like, granular, powdery precipitates and the like tend to be easily generated. If the amount is too large, the entire plating film tends to be blackened or color unevenness tends to occur.

The plating bath of the present invention includes the above (A) to
In addition to the component (F), gelatin, peptone and the like can be added, if necessary. The plating bath of the present invention is composed of the above-mentioned components, and its pH is usually 1 or less. In some cases, the plating bath may be a weak acid bath or a weak alkali bath having a pH of 1 to 9, especially about 2 to 7.

When a tin-silver alloy is electroplated on an object to be plated using the plating bath of the present invention, the object to be plated is not particularly limited, and any object that can be electroplated can be used. Good, but especially the bath of the present invention is used for chip parts, hoop material, lead free, semiconductor package, bump,
It is suitable for electric / electronic parts such as a printed circuit board that requires soldering.

The plating method may be a rack method or a barrel method, and a high-speed plating method using a hoop, a jet or the like is also effectively employed, and the plating method is not limited.

The cathode current density (D _k ) is appropriately selected in the range of 0.1 to 100 A / dm ² depending on the plating method and the like, but is 0.5 to 5 A / dm ² in the case of the ordinary rack method.
Especially 1 to 3 A / dm ² , 0.1 to 1 A in the case of the barrel method
/ Dm ² , particularly preferably 0.2 to 0.5 A / dm ² .

The plating temperature is usually from 15 to 35 ° C., and generally may be room temperature. Stirring of the plating bath may be non-stirring, but is preferably performed by a method such as cathode rocking, liquid flow by a pump, or stirring by a stirrer.

As the anode, a soluble anode such as tin, silver or a tin-silver alloy can be used, and an insoluble anode such as a platinum-plated titanium plate, a platinum plate, or carbon can also be used. When tin is used for the anode plate, silver salt is used. When silver is used, stannous salt is used. When an insoluble anode is used, stannous salt and silver salt are supplied at appropriate intervals. It is necessary to maintain the ratio of Sn ²⁺ and Ag ^{+ in} the bath at a predetermined ratio.

The tin-silver alloy electroplating bath of the present invention usually has a cathode current efficiency of 70 to 98%.

According to the present invention, Sn ²⁺ and Ag in the plating bath
By appropriately selecting the ratio of ⁺ and plating by the method described above, tin 99.9 to 10% by weight and silver 0.1 to
A tin-silver alloy plating film of 90% by weight was obtained, and the obtained plating film was dense, had a good appearance, and had good solderability.

In the plating operation, preferential silver deposition,
There is no silver substitution on the anode or plating film, and even when plating on a printed circuit board, the organic resist film does not erode and float, so workability is good and plating film adhesion is good. Things.

The second invention of the present invention provides (i) a stannous salt,
An object to be plated in a tin-silver alloy electroplating bath containing a silver salt and one or more acids selected from sulfuric acid, phosphoric acid, phosphonic acid, hydroxycarboxylic acid, alkanesulfonic acid and alkanolsulfonic acid Immersion, when performing electroplating, using silver metal for the anode, replenishing silver ions according to the deposition of silver from the plating bath by electrolytic elution of the silver metal anode, and tin from the plating bath (Ii) a tin-silver alloy electroplating method, wherein replenishment of stannous ions in accordance with precipitation is performed by adding and dissolving a stannous salt or stannous oxide to a plating bath; A tin-silver alloy electrode containing a tin salt, a silver salt, and one or more acids selected from sulfuric acid, phosphoric acid, phosphonic acid, hydroxycarboxylic acid, alkanesulfonic acid and alkanolsulfonic acid. When the object to be plated is immersed in a bath and electroplating is performed, the object to be plated is immersed in the plating bath while supplying power to the object to be plated, and the plated object is lifted from the plating bath while supplying power to the object to be plated. A tin-silver alloy electroplating method, wherein (i)
ii) Tin-silver alloy containing stannous salt, silver salt, and one or more acids selected from sulfuric acid, phosphoric acid, phosphonic acid, hydroxycarboxylic acid, alkanesulfonic acid and alkanolsulfonic acid When the object to be plated is immersed in an electroplating bath and silver plating is performed, silver metal is used for the anode, and silver ions are replenished in accordance with the precipitation of silver from the plating bath by electrolytic elution of the silver metal anode. At the same time, replenishment of stannous ions in accordance with the deposition of tin from the plating bath is performed by adding and dissolving a stannous salt or stannous oxide to the plating bath, and the plating is performed while supplying power to the plating object. A tin-silver alloy electroplating method characterized by dipping in a bath and pulling up the plated object from the plating bath while supplying power to the plated object.

In this case, the method (iii) in which the method (i) and the method (ii) are used in combination is preferable. As the plating bath, a plating bath containing (A) to (F) according to the first invention as an essential component can be effectively used, but the components (A), (B) and (C) are mainly used. Preferably, a bath to which the component (E) is added can be used. In addition,
The plating conditions are the same as those described above.

[0042]

EXAMPLES The present invention will be described below in detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

Example 1 Stannous methanesulfonate 23 g / L (Sn ²⁺ 9 g / L) Silver methanesulfonate 2 g / L (Ag ⁺ 1 g / L) Thiourea 100 g / L Gluconic acid 200 g / L Poly Oxyethylene nonyl phenyl ether 5 g / L (number of moles of added EO 7) 2-mercaptobenzoic acid 1 g / L citraconic acid 0.5 g / L pH <1 Cathode current density 0.5 A / dm ² Bath temperature 25 ° C. Stirring Barrel Anode Tin (99.99 wt% or more) Plating time: 120 minutes Silver supply Silver methanesulfonate was directly supplied to the plating solution in the plating tank. In this case, the replenishment frequency was once every 60 minutes, and the replenishment was 0.1 g / L · silver.

Example 2 Stannous methanesulfonate 36 g / L (Sn ²⁺ 14 g / L) Silver sulfate 9 g / L (Ag ⁺ 6 g / L) Methanesulfonic acid 200 g / L DL-lactic acid 200 g / L Thio Urea 150 g / L polyoxyethylene tallow amino acid 3 g / L (number of moles of EO added 7) 2-mercaptobenzothiazole 2 g / L acrylic acid 0.5 g / L pH <1 Cathode current density 2 A / dm ² Bath temperature 25 ° C. Stirring Cathode locker Anode Tin 70wt%, silver 30wt% Plating time 10 minutes

Example 3 Stannous sulfate 33 g / L (Sn ²⁺ 18 g / L) Silver methanesulfonate 23 g / L (Ag ⁺ 12 g / L) Citric acid 200 g / L Ammonium sulfate 100 g / L Thiourea 150 g / L L Polyoxyethylene lauryl ether 10 g / L (number of moles of EO added 4) 2-mercaptobenzothiazole 3 g / L fumaric acid 0.3 g / L pH 7.0 Cathode current density 3 A / dm ² Bath temperature 25 ° C. Stirring Cathode locker Anode Silver (99.99 wt% or more) Plating time: 10 minutes Tin replenishment Stannous sulfate was directly added to the plating solution in the plating tank, dissolved, and replenished. The frequency of replenishment was once every 10 minutes, and the replenishment of tin was 0.1 g / L.

Example 4 Stannous sulfate 58 g / L (Sn ²⁺ 32 g / L) Silver sulfate 15 g / L (Ag ⁺ 8 g / L) Sulfuric acid 200 g / L Thiourea 200 g / L Gluconic acid 200 g / L Ethylene Oxide Propylene oxide 7g / L Block copolymer (total molecular weight 2500, EO / PO = 60/40) Hydroquinone 2g / L pH <1 Cathode current density 5A / dm ² Bath temperature 25 ° C Stirring Jet Anode Platinum Plating time 5min Tin, silver Replenishment Stannous sulfate and silver sulfate were directly added to the plating solution in the plating tank, dissolved, and supplied. The frequency of replenishment was once every 5 minutes, with 0.8 g / L * of tin and 0.2 g / L * of silver.

Comparative Example 1 Stannous methanesulfonate 18 g / L (Sn ²⁺ 9 g / L) Silver methanesulfonate 2 g / L (Ag ⁺ 1 g / L) Methanesulfonic acid 100 g / L Polyoxyethylene nonylphenyl Ether 5 g / L (number of moles of EO added 7) pH <1 Cathode current density 0.5 A / dm ² Bath temperature 25 ° C. Stirring Barrel Anode Tin (99.99 wt% or more) Plating time 120 minutes Silver supply Silver methanesulfonate It was supplied directly to the plating solution in the plating tank. The frequency of replenishment is once every 60 minutes, and 0.1 times as silver The replenishment was 1 g / L times.

Comparative Example 2 Stannous sulfate 33 g / L (Sn ²⁺ 18 g / L) Silver sulfate 23 g / L (Ag ⁺ 12 g / L) Potassium iodide 200 g / L Potassium pyrophosphate 200 g / L Polyoxy Ethylene lauryl ether 10 g / L (number of moles of added EO 4) pH 9.0 Cathode current density 3 A / dm ² Bath temperature 25 ° C Stirring Cathode rocker Anode Platinum Plating time 10 minutes Replenishment of tin and silver Tin stannous sulfate and silver sulfate It was added directly to the plating solution in the plating bath, dissolved and replenished. The frequency of replenishment was once every 5 minutes, with 0.8 g / L * of tin and 0.2 g / L * of silver.

Using the plating bath, plating was performed under the above conditions. In this case, in Example 1 and Comparative Example 1, plating was performed using a chip component such as a chip resistor, a chip capacitor, or a crystal oscillator as a product to be plated by barrel plating. In Examples 2 to 4 and Comparative Example 2, the rack method was used, and plating was applied to a lead frame, a semiconductor package, a bump, a printed circuit board, and the like as products to be plated.

As a result of examining the appearance of the obtained plating film, Examples 1 to 4 were all uniform, semi-gloss, gray-white plating films having a needle-like, dendritic, whisker-like, granular, powdery, etc. No precipitate was generated, and there were no plating appearance defects such as burns and burns. The silver content in the plating film was 9 wt%, 27 wt%, 37 wt%, and 19 wt%, respectively, and was close to the alloy composition in the plating bath. Also, even if a plating test is performed using the product to be plated as a printed circuit board, a good plating film can be obtained without any change, floating on the organic resist film of the printed circuit board, defects such as peeling do not occur, and penetration of the plating solution does not occur. Not at all.

In Comparative Example 1, the color was gray and slightly uneven, the silver content in the plating film was 35 wt%, and the amount of silver deposited was considerably larger than the alloy composition in the plating bath. Also,
On the tin anode, silver was completely substituted and precipitated.

In Comparative Example 2, there was a slight unevenness in grayish white.
The silver content in the plating film was 36 wt%, which was close to the alloy composition in the plating bath. However, when a plating test was performed using the product to be plated as a printed circuit board, the organic resist film on the printed circuit board floated, peeled off, and the plating solution was removed. It was quite infiltrated.

Example 5 Stannous methanesulfonate 18 g / L (Sn ²⁺ 9 g / L) Silver methanesulfonate 2 g / L (Ag ⁺ 1 g / L) Methanesulfonic acid 100 g / L Polyoxyethylene nonylphenyl Ether 5 g / L (7 moles of EO added) pH <1 Cathode current density 0.3 A / dm ² Bath temperature 25 ° C Stirring Barrel Anode Silver (99.99 wt% or more) Plating time 240 minutes Tin replenishment Tin oxide Dissolved in a separate tank and replenished. The replenishment frequency was tin, which was 0.3 g / L times, every 40 minutes.

By adopting the above plating method, there is almost no change in the amount of tin and silver in the plating solution between the initial plating and after 240 minutes of plating, and the appearance and appearance of the plating film (tin-silver alloy) obtained The amount of silver in the plating film was 8 to 10% by weight, and was almost the same at the initial stage of plating and after 240 minutes, and was stable.

In the above plating method, the silver anode was used, so no silver substitution precipitation occurred. However, when the tin-silver (90/10) alloy was used as the anode and tin was not supplied. During the suspension of the plating operation, the silver in the plating solution was displaced and precipitated on the tin-silver alloy anode, and the silver amount in the plating solution decreased and the tin amount increased accordingly. A tin-silver alloy plating film having a low tin content was obtained.

Example 6 Stannous 2-hydroxypropanesulfonate 63 g / L (Sn ²⁺ 16 g / L) Silver 2-hydroxypropanesulfonate 10 g / L (Ag ⁺ 4 g / L) 2-hydroxypropanesulfone Acid 200 g / L Polyoxyethylene nonylphenyl ether 8 g / L (7 moles of EO added) pH <1 Cathode current density 2 A / dm ² Bath temperature 25 ° C. Stirring Cathode locker Anode Silver (99.99 wt% or more) Plating time 20 minutes Replenishment of tin Stannous oxide was directly added to the plating solution in the plating tank, dissolved and supplied. The replenishment frequency is 0.1 every 10 minutes as tin. The supply was 5 g / L times.

By employing the above plating method, there is almost no change in the amount of tin and silver in the plating solution between the initial plating and 20 minutes after the plating, and the appearance and appearance of the plating film (tin-silver alloy) obtained. The amount of silver in the plating film was 18 to 20 wt%, which was almost the same at the initial stage of plating and after 20 minutes, and was stable.

In the above plating method, the silver anode was used, so that no silver substitution precipitation occurred. However, when the tin-silver (80/20) alloy was used as the anode and the tin was not supplied. During the suspension of the plating operation, the silver in the plating solution was displaced and precipitated on the tin-silver alloy anode, and the silver amount in the plating solution decreased and the tin amount increased accordingly. A tin-silver alloy plating film having a low tin content was obtained.

[Example 7] Under the solution composition and plating conditions of Example 5, when the object to be plated was immersed in the plating solution without supplying power, when the object to be plated was immersed in the plating solution, substitutional precipitation of silver in the plating solution occurred. This results in poor adhesion between the plated product and the plating film, and silver is replaced and deposited on the plating film surface if the power is not supplied when pulling up the plated product after plating, resulting in a blackish powder appearance Was something.

On the other hand, by supplying power when immersing the object to be plated in the plating solution and when pulling it up from the plating solution, there is no silver deposition on the object to be plated or the plating film.
The adhesion between the plated product and the plating film was good, and the appearance of the plating film was good.

[Embodiment 8] Under the solution composition and plating conditions of Example 6, when the product to be plated was immersed in the plating solution without supplying power, the substitutional precipitation of silver in the plating solution occurred in the product to be plated. This results in poor adhesion between the plated product and the plating film, and silver is replaced and deposited on the plating film surface if the power is not supplied when pulling up the plated product after plating, resulting in a blackish powder appearance Was something.

On the other hand, by supplying power when immersing the product to be plated in the plating solution and when pulling it up from the plating solution, there is no silver deposition on the product to be plated or the plating film.
The adhesion between the plated product and the plating film was good, and the appearance of the plating film was good.

[0063]

EFFECT OF THE INVENTION By using the tin-silver alloy electroplating bath of the present invention, a tin-silver alloy plating film having a uniform and good appearance can be obtained without preferential precipitation of silver and substitution precipitation of silver on an anode or a plating film. Obtainable.

Claims (5)

[Claims] 1. An acid selected from the group consisting of (A) stannous salt, (B) silver salt, (C) sulfuric acid, phosphoric acid, phosphonic acid, hydroxycarboxylic acid, alkanesulfonic acid and alkanolsulfonic acid. One or more additives selected from the group consisting of (D) thiourea, (E) a nonionic surfactant, (F) a mercapto group-containing aromatic compound, a dioxy aromatic compound and an unsaturated carboxylic acid. A tin-silver alloy electroplating bath characterized by comprising: 2. A method for electroplating a tin-silver alloy, comprising immersing an object to be plated in the plating bath according to claim 1 for electroplating. 3. Tin containing a stannous salt, a silver salt and one or more acids selected from sulfuric acid, phosphoric acid, phosphonic acid, hydroxycarboxylic acid, alkanesulfonic acid and alkanolsulfonic acid. -An object to be plated is immersed in a silver alloy electroplating bath and silver metal is used for the anode when performing electroplating, and silver ions are supplied in accordance with the deposition of silver from the plating bath. By elution,
Tin-silver alloy electroplating wherein replenishment of stannous ions in accordance with the deposition of tin from a plating bath is performed by adding and dissolving a stannous salt or stannous oxide to the plating bath. Method. 4. Tin containing a stannous salt, a silver salt and one or more acids selected from sulfuric acid, phosphoric acid, phosphonic acid, hydroxycarboxylic acid, alkanesulfonic acid and alkanolsulfonic acid. -Immersing the object to be plated in a silver alloy electroplating bath, and immersing the object in the plating bath while supplying power to the object to be plated, and performing the plating while supplying power to the object to be plated when performing electroplating. A tin-silver alloy electroplating method characterized in that it is raised from a bath. 5. Tin containing a stannous salt, a silver salt and one or more acids selected from sulfuric acid, phosphoric acid, phosphonic acid, hydroxycarboxylic acid, alkanesulfonic acid and alkanolsulfonic acid. -An object to be plated is immersed in a silver alloy electroplating bath and silver metal is used for the anode when performing electroplating, and silver ions are supplied in accordance with the deposition of silver from the plating bath. By elution,
The replenishment of stannous ions in accordance with the precipitation of tin from the plating bath is performed by adding and dissolving a stannous salt or stannous oxide to the plating bath, and supplying the plating object to the plating bath while supplying power. A tin-silver alloy electroplating method, characterized in that it is dipped and pulled up from the plating bath while supplying power to the plated object.