KR20170016843A - Tin electroplating bath and tin plating film - Google Patents

Abstract

There is provided a tin electroplating bath for obtaining a tin plating film in which occurrence of tin whisker is suppressed when external stress is applied to the tin plating film. The tin electroplating bath is characterized by containing a flavonoid compound and at least one compound selected from the group consisting of a glycoside, a compound having a xanthene skeleton and a glycoside thereof, a compound having an acridine skeleton and a glycoside thereof do.

Description

TIN ELECTROPLATING BATH AND TIN PLATING FILM [0001]

The present invention relates to a tin electroplating bath and a tin plating film. More particularly, the present invention relates to a tin plating film in which the occurrence of tin whisker is suppressed when external (mechanical) stress is applied to the tin plating film, and a tin electroplating bath used for forming the tin plating film.

A film of tin plating, tin alloy plating, or the like is formed on a component for an electronic device such as a connector, a terminal, and an IC chip from the viewpoints of soldering and corrosion prevention. As a method of forming the tin plating or tin alloy plating, various methods have been proposed so far. For example, Patent Document 1 discloses a method for surface treatment of a plating material in which a metal material is plated with tin or a tin-lead alloy, wherein a benzotriazole-based compound specified as an inhibitor, a specified mercaptobenzothiazole- And triazine-based compounds, the plating material is electrolyzed as a positive electrode. The tin or tin-lead alloy plating material surface-treated by the method shows less deterioration in solderability and has excellent corrosion resistance.

Patent Document 2 proposes a tin and tin / lead alloy plating solution capable of forming a glossy plating over a wide current density range. As the electrolytic solution for electroplating of tin and a tin / lead alloy, there can be used, as the plating solution, alkane sulfonic acid as acid, divalent tin salt of alkane sulfonic acid or divalent tin salt and divalent tin salt as metal salt, Tin and tin / lead alloy plating solutions containing chlorobenzaldehyde, naphthaldehyde and picolinic acid as polishes, and at least one of oxyethylene alkylphenyl ether or polyoxyethylene naphthyl ether.

Patent Document 3 proposes a plating bath which is excellent in reflow property, leveling property and solderability of a plating film, has a wide gloss range from a low current density portion to a high current density portion, and has excellent time-lapse stability . Specifically, as the plating bath, at least one surfactant, at least one aromatic aldehyde and at least one aluminosulfonic acid and / or an alkanol sulfonic acid and / or a divalent tin salt and / Substituted unsaturated fatty acid amide compound is added to the plating bath.

Patent Document 4 also discloses a water-based plating bath for smoothing a uniform film of tin or the like with a uniform thickness without containing any fluoride or boron fluoride salt. (A) a bath soluble metal salt such as a stannous salt, (B) at least one alkane sulfonic acid or alkanol sulfonic acid, (C) at least one nonionic, cationic or amphoteric (D) at least one primary brightener selected from the group consisting of aromatic aldehydes, acetophenones and carbonyl compounds having the specified groups, (E) at least one secondary brightener among the lower aliphatic aldehydes and the prescribed substituted olefins In the plating bath.

It is known that whiskers are generated in the tin or tin alloy plating film when the film has an internal stress. The circuit is short-circuited by the whisker. Since generation of whiskers is largely suppressed by addition of lead to the plating film, there is no problem in the age when the plating film of tin-lead alloy is the mainstream. However, along with the movement of lead-free by the implementation of the Restriction of Hazardous Substance (RoHS) directive, it became necessary to make improvements. For this reason, various methods for reducing the internal stress of the tin-plated coating film or the tin alloy plating film, such as the improvement of the plating solution, have been proposed. However, even if the internal stress is reduced and the coating itself does not generate whiskers well, there is a problem that when external stress is applied to the coating, whiskers are generated due to this external stress. For example, in a connector, a lead is inserted into a connector pin to which a tin or tin alloy plating film is applied, and an external load is applied to a contact point of the connector pin with the lead. That is, external pressure is applied to the tin or tin alloy plating film formed on the surface of the connector pin (hereinafter, this state is sometimes referred to as " contact pressure "), and the internal stress is generated. This will make tin whiskers more likely to occur. Hereinafter, tin whiskers caused by such external stress may be referred to as " contact pressure whiskers ".

The methods of forming the tin or tin alloy plating disclosed in the above Patent Documents 1 to 4 do not consider suppression of the occurrence of the contact pressure whisker. Up to now, as a method for preventing the occurrence of the contact pressure whisker, there is a method of forming a tin alloy plating film by using a plating solution containing tin and an element effective for preventing occurrence of the contact pressure whisker. For example, Patent Document 5 discloses that a silver plating is formed as a bismuth-segregation suppressing layer on a substrate, and a surface layer made of a tin-bismuth alloy is provided thereon, thereby effectively suppressing occurrence and growth of whiskers Is shown. Patent Document 6 discloses that tin-gold intermetallic compounds are formed by forming a gold plating layer as a base layer and then forming a tin-containing layer thereon, followed by heat treatment, thereby suppressing whiskers.

However, the methods of Patent Documents 5 and 6 are expensive, and when two or more kinds of metal elements are essential, it is necessary to manage the alloy ratio of the plating bath and the plating film. Particularly, in the case of using a tin-silver alloy plating bath or a tin-bismuth alloy plating bath as in Patent Document 5, the following problems may occur. That is, since the potential difference between the two metal elements in the plating bath is large, when the surface of the tin positive electrode plate or the plated object to be plated is immersed in the plating bath during the non-electric discharge, silver or bismuth is formed on the tin positive electrode plate It may be displaced on the surface of the molten metal to be unusable. In addition, as described above, there is also a problem that the cost is higher than that of tin plating.

As another method of preventing generation of the contact pressure whisker, there is a method of melting the tin coating film at a melting point or higher, that is, a reflow treatment method. In this method, although the contact pressure whisker is suppressed, it can not be completely prevented, and another problem that the solder wettability is lowered occurs.

In the case of a narrow connector between the connector pins, a gold plating process may be performed. When the gold plating is performed, the contact pressure whiskers do not occur, but there is a problem that the cost is greatly increased.

Japanese Patent Application Laid-Open No. 07-173676 Japanese Patent Application Laid-Open No. 10-036994 Japanese Patent Publication No. 2856857 Japanese Patent Application Laid-Open No. 61-223193 Japanese Laid-Open Patent Publication No. 2011-001630 Japanese Patent Publication No. 5215305

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a tin plating film capable of forming a tin plating film in which the occurrence of tin whisker is suppressed at the time of application of external stress to the tin plating film, Thereby realizing an electroplating bath.

The tin electroplating bath of the present invention capable of solving the above problems is characterized in that the tin electroplating bath of the present invention comprises a flavonoid compound and a glycoside thereof, a compound having a xanthene skeleton and a glycoside thereof, a compound having an acridine skeleton and a glycoside thereof (Hereinafter referred to as " compound X "). Hereinafter, the tin electroplating bath of the present invention may be referred to as an " electroplating bath " or a " plating bath ".

As the compound X, it is preferable to use at least one compound selected from the group consisting of the flavonoid compound and its glycoside.

It is preferable that the compound X is contained in an amount of 0.0001 g / L or more and 5 g / L or less in a proportion occupying in the electroplating bath.

A tin-plated film obtained by using the tin electroplating bath described above, wherein the tin-plated film has a Vickers hardness of 10 or less at a t / 2 position in the cross-section in the film thickness (t) direction of the tin- .

The tin plating film obtained by using the tin electroplating bath of the present invention can suppress the occurrence of whiskers caused by external stress even when external stress is applied.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a photograph showing an example of the entire indentation in the evaluation of the whisker inhibiting effect of the embodiment. Fig.
Fig. 2 is an enlarged view of a portion of Fig. 1, showing a photograph of an example of whisker length measurement.
Fig. 3 is a view for explaining measurement positions of the length and diameter of whiskers in the examples. Fig.

The present inventors have found that an electroplating method for forming a tin plating film in which the occurrence of tin whisker is suppressed when external stress is applied to the tin plating film without causing an increase in cost is used as a tin plating film for forming tin plating film We have focused on electroplating baths and have made intensive studies. As a result, in the tin electroplating bath, one or more compounds selected from the group consisting of a flavonoid compound and a glycoside thereof, a compound having a xanthene skeleton and a glycoside thereof, a compound having an acridine skeleton and a glycoside thereof Quot; compound X ") as an essential component, the present inventors have found that the desired object can be achieved, and thus the present invention has been completed.

The mechanism by which the contact pressure whisker is suppressed by adding the compound X to the plating bath is still not fully understood, but is considered as follows. That is, it is considered that the presence of the compound X in the tin electroplating bath increases the crystal size of the Sn constituting the plating, resulting in a decrease in the hardness of the plating film. It is presumed that the occurrence of contact pressure whiskers is suppressed because the hardness of the plated film is lowered so that even when external stress is applied, the stress is dispersed in the plating film and relaxed, in other words, external stress is not locally accumulated.

Examples of the flavonoid compound and its glycoside include flavones such as chrysin, rhetheorin, apigenin and apigenin which are glycosides thereof, galantine, ken phenol, myrcetin, morin, quercetin and its glycosides, Flavanols such as catechin, epicatechin, epigallocatechin, epicatechin gallate, epigallocatechin gallate, teaplavin, and the like; (Catechins), naringenin and its glycosides, naringin, hesperetin and its glycoside hesperidin, etc .; carnimidins and their glycosides, carthamides such as carthamine, cyanidin and its glycosides cyanine, Delphinidins and their glycosides delphin, pelargonidine and anthocyanidins such as pelargonin, its glycoside; and the like.

Examples of compounds having a xanthene skeleton and glycosides thereof include xanthylium, 3,6-bis (ethylamino) -9- [2- (ethoxycarbonyl) phenyl] -2,7-dimethylxanthylum chloride, (Diethylamino) xanthyl chloride, fluorene, carine, uranine, tetraiodofluorene, fluorene-1, 2-diamino- 4-isothianate, and the like.

Examples of compounds having an acridine skeleton and glycosides thereof include acridine, 3,6-dimethylaminoacridine, acrylic flavin, 9 (10H) acridone, 9-aminoacridine, 9-phenyl acridine, and proplavin.

Of the compounds X, particularly flavonoid compounds and their glycosides are preferred. Among them, flavovanols and their glycosides are more preferable.

In order to sufficiently exhibit the above effect and to suppress the burning at the high current density or the pressing of the plating film to obtain a satisfactory plating film, the preferable content of the compound X in the electroplating bath (when contained alone, , And when they contain two or more kinds, they are the total amount thereof) is preferably 0.0001 g / L or more, more preferably 0.001 g / L or more, still more preferably 0.005 g / L or more. On the other hand, if the content of the compound X is too large, the whisker inhibiting effect is not improved and the cathode current efficiency is lowered. Therefore, the content of the compound X is preferably 5 g / liter or less, more preferably 2 g / liter or less, and still more preferably 1 g / liter or less.

The present invention is characterized in that the compound X is used as the tin electroplating bath, and as the other components of the tin electroplating bath, the following components which are usually used for forming the tin electroplating film can be contained.

[Tin salt]

Tin salts are essential components in the construction of the plated film. The form of the tin salt used in the present invention is not particularly limited as long as it is usually used in the field of the electroplating bath. As the tin salts, there are a first tin salt and a second tin salt.

Examples of the first tin salt (tin salt (II)) include organic sulfonic acid tin (II) such as alkane sulfonic acid tin (II) such as alkane sulfonic acid tin (II) such as methane sulfonic acid tin (II), tin (II) phosphate, tin (II) chloride, tin (II) chloride, tin (II) (II), tin acetate (II), tin citrate (II), tin gluconate (II), tin tartrate (II), tin lactate (II), tin succinate (II) And inorganic tin compounds such as tin (II), tin (II) formate, and tin (II) tetrachloride. Examples of the second tin salt (tin salt (IV)) include sodium tartrate, potassium tartrate, and the like.

As the tin salts, tin (II) is particularly preferable, such as tin (II) alkanesulfonate such as tin methanesulfonate (II), and tin (II) alkanolsulfonate such as tin (II) isethionate.

The concentration of tin (Sn ²⁺ ion or Sn ⁴⁺ ion) occupied in the electroplating bath of the present invention is not particularly limited as long as it is controlled so that desired tin plating is performed. The concentration of the tin may be, for example, in the range of 5 to 100 g / l, preferably 10 to 70 g / l.

When a strongly acidic plating bath is used as the tin electroplating bath of the present invention, the tin salt (IV) is insoluble under a strong acid, and therefore a complexing agent may be added together. The complexing agent is not particularly limited and includes, for example, sodium sulfite, potassium sulfite, ammonium sulfite, sodium cyanide, potassium cyanide, sodium thiosulfate, potassium thiosulfate, ammonium thiosulfate, phosphoric acid, boric acid, citric acid, (EDTA), cyclohexanediamine tetraacetic acid, diethylenetriamine 5-acetic acid (DTPA), triethylenediamine tetraacetic acid (DTPA), triethylenediamine tetraacetic acid (DHEA), dihydroxyethylethylenediamine diacetic acid (DHEDDA), glycine, imino acetic acid, nitrile, and the like. (NTA), aminotrimethylenephosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, ethylenediamine tetramethylenephosphonic acid, diethyl Tree or the like may be used amine-penta (methylenephosphonic acid). These complexing agents may be used singly or in combination of two or more.

The content of the complexing agent is not particularly limited, but is preferably about 1 to 500 g / L, and more preferably about 10 to 300 g / L. If the content of the complexing agent is too small, tin is precipitated in the plating bath to deteriorate the bath stability. On the other hand, if the content of the complexing agent is excessively large, the complex formation with Sn ²⁺ proceeds excessively, the deposition rate is lowered, and a plating film having a desired film thickness can not be formed. In addition, it becomes difficult to dissolve the complexing agent and it becomes not economical.

The plating bath of the present invention does not necessarily comprise an alloy element as described above. However, alloying elements may be contained within a range that does not adversely affect plating precipitation, film hardness, manufacture, and cost. As the alloying element, for example, In and the like which can suppress the film hardness to a low level can be cited. However, bismuth and silver as alloying elements are not preferable because the potential difference described above occurs. When copper is used as the alloying element, the film hardness tends to be high, and whiskers tend to be generated, which is not preferable. Further, lead is not preferable from the viewpoint of lead-freeization as described above.

[Inorganic and organic acids and their water-soluble salts]

The inorganic and organic acids and their water-soluble salts act on the stability of the plating bath by adjusting the pH and the like. It also acts on electrical conductivity (voltage).

The inorganic acid and organic acid used in the present invention are not particularly limited as long as they are commonly used for the plating film. Examples of the inorganic acid include sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid and sulfamic acid. Examples of the organic acid include organic sulfonic acids (alkanesulfonic acids such as methanesulfonic acid and alkanesulfonic acids such as isethionic acid), and carboxylic acids (aromatic carboxylic acids, aliphatic saturated carboxylic acids and aminocarboxylic acids) . In consideration of the stability of the liquid and the like, it is preferably an organic sulfonic acid, more preferably methanesulfonic acid.

They may be in the free form or may be present as water-soluble salts such as water-soluble salts of inorganic acids and water-soluble salts of organic acids. The type of the salt is not particularly limited as long as it takes the form of a water-soluble salt, and examples thereof include a potassium salt, a sodium salt, an ammonium salt, and a magnesium salt.

In the present invention, the inorganic acid and the organic acid and the water-soluble salt thereof may be used alone or in combination of two or more. If the preferred content of the above components in the electroplating bath is too small (the amount is solely in the case of being contained alone and the total amount thereof when containing two or more kinds), the stability of the plating bath becomes poor, It tends to be easy. Therefore, the content is preferably 50 g / L or more, and more preferably 100 g / L or more. On the other hand, even if the above components are added in excess, the addition effect of the above components becomes saturated, and therefore, it is unnecessary. Therefore, the content is preferably 500 g / L or less, more preferably 300 g / L or less.

[Nonionic surfactant]

The nonionic surfactant has a role of improving the wettability of the plating bath to the substrate.

As the nonionic surfactant, an alkylene oxide-based surfactant is preferably used. Specific examples include polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene alkylamine, polyoxyethylene alkylamide, polyoxyethylene fatty acid ester, polyoxyethylene polyhydric alcohol ether, ethylene oxide propylene oxide block copolymer type, Ethylene oxide-propylene random copolymerization type, and propylene oxide polymerization type. Of these, polyoxyethylene alkylphenyl ether is particularly preferably used.

In the present invention, the above-mentioned nonionic surfactants may be used singly or in combination of two or more. The preferable content of the nonionic surfactant in the electroplating bath (the amount of the nonionic surfactant when it is contained singly and the total amount of the nonionic surfactant when the two or more kinds are contained) is too small to cause burning or sticking at a high current density It is preferably 0.05 g / l or more, and more preferably 1 g / l or more. On the other hand, if the above nonionic surfactant is contained in excess, the plated film may become black to cause defective color irregularities. Therefore, the content is preferably 100 g / L or less, and more preferably 50 g / L or less.

[Antioxidant]

When the tin salt (II) is used, the antioxidant has a role of preventing oxidation of divalent Sn ions in the bath and oxidation of other bath components and stabilizing the bath. When tin salt (IV) is used, it contributes to the stability of the Sn complex. As the antioxidant, catechol, hydroquinone, 4-methoxyphenol (p-methoxyphenol) and the like can be used.

These may be used alone or in combination of two or more kinds. If the content of the antioxidant in the electroplating bath is too small (a sufficient amount of the antioxidant when contained singly, and a total amount of the antioxidant when containing two or more kinds), a sufficient antioxidant effect can not be obtained. l or more, more preferably 0.2 g / l or more. On the other hand, when the content is excessively large, deterioration (occurrence of sticking) of the current efficiency and deterioration of physical properties (deterioration of the viscosity and defoaming property) of the plating bath due to decomposed products may occur. Therefore, the content is preferably 10 g / L or less, and more preferably 5 g / L or less. The concentration of the antioxidant does not change in the case of tin salts (II) and tin salts (IV).

[Organic solvents]

The organic solvent is used for the purpose of dissolving the compound X in the plating bath. It is also used for the purpose of improving the stability in the plating bath. Examples of the organic solvent include monohydric alcohols such as methanol and 2-propanol (isopropyl alcohol), and divalent alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, etc. ≪ / RTI >

These may be used alone, or two or more kinds may be used. If the content of the organic solvent in the electroplating bath is too small, the solubility becomes insufficient and becomes cloudy, and precipitation may occur. There is a possibility. Therefore, the content is preferably 5 g / liter or more. On the other hand, if the amount of the organic solvent is too large, there is a possibility that the deterioration of the current efficiency or the like (occurrence of sticking) or deterioration of physical properties (viscosity or defoaming property) of the plating bath due to decomposition products may occur. Therefore, the content is preferably 100 g / L or less, more preferably 70 g / L or less, still more preferably 50 g / L or less, still more preferably 20 g / L or less.

The pH of the tin electroplating bath is preferably 10 or less. Particularly when tin salt (II) is used, if pH is excessively high, tetravalent tin is easily generated. Therefore, the pH is preferably 3 or less. On the other hand, when the tin salt (IV) is used, if the pH is excessively high or too low, complex formation is impossible and the stability of the plating bath is deteriorated. Therefore, the pH is preferably in the range of 3 to 10. For adjustment of the pH, it is preferable to use the same acid as the free acid contained in the used tin salt. For example, in the case of tin methanesulfonate, methanesulfonic acid is preferably used for pH adjustment.

The conditions such as the bath temperature, the current density, the plating bath immersion time and the like when the electroplating is carried out by using the tin electroplating bath of the present invention can employ a method or condition usually employed in tin electroplating have.

The tin plating film obtained by using the tin electroplating bath defined in the present invention and subjected to electroplating has a Vickers hardness of 10 or less at the t / 2 position on the cross section in the film thickness (t) direction. The Vickers hardness is preferably less than 9.0, more preferably less than 8.5. Considering the role of the tin-plated film as a protective film, etc., the lower limit of the Vickers hardness is generally about 4.

This application claims the benefit of priority based on Japanese Patent Application No. 2014-120714 filed on June 11, 2014. The entire contents of the specification of Japanese Patent Application No. 2014-120714 filed on June 11, 2014 are incorporated herein by reference.

Example

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the present invention is not limited to the following Examples, but may be carried out by appropriately modifying them in a range suitable for the purpose Of course, all of which are included in the technical scope of the present invention.

In order to investigate the usefulness of the compound X defined in the present invention, it is preferable that the compound X containing the various components (water-soluble tin salt, acid, surfactant, compound X, antioxidant, organic solvent) described in Tables 1A to 1D Tin electroplating bath was prepared. In Table 1A to Table 1D, blank means not added. The plating baths shown in Tables 1A to 1D were all pH 1 or less. A tin electroplating film was formed on the surface of a substrate made of a phosphor bronze material and a sample for evaluation of the whisker suppressing effect was formed to a thickness of 2 占 퐉 and a sample for measuring the following hardness Was formed so as to have a film thickness of 30 占 퐉 to obtain a sample on which a tin plating film was formed.

(Plating processing step)

Electrolytic degreasing (2 minutes), water washing (30 seconds), pickling (30 seconds), water washing (30 seconds), ground nickel plating (film thickness 1.5 μm, (30 seconds) → tin plating (the following conditions) → water (30 seconds) → ion exchange water washing → drying

In the above base nickel plating, the nickel plating bath (composition: nickel sulfate: 300 g / l, nickel chloride: 15 g / l, boric acid: 30 g / l) , And electroplating was performed under the following conditions.

(Nickel plating condition)

Cathode current density: 8 A / dm 2

Solution temperature: 50 ° C

Plating time: 60 seconds

pH: 4.0

In the tin plating in the above step, electroplating was performed under the following conditions.

(Tin plating conditions)

Cathode current density: 20 A / dm < 2 >

Solution temperature: 50 ° C

Plating time: 12 seconds for samples for evaluation of whisker inhibition effect

For sample of film hardness measurement: 180 seconds

Evaluation of the whisker inhibiting effect and measurement of the film hardness were carried out as follows using the obtained samples.

[Evaluation of whisker inhibition effect]

The evaluation sample was used to evaluate the whisker inhibiting effect. In the evaluation, the load test and the whisker measurement were carried out based on the whisker test method (JEITA RC-5241) of the connector for electronic devices of the Electronics and Information Technology Industry Association Standard. Specifically, 200 g of a load was locally added to the tin plating film using a zirconia ball indenter having a diameter of 1 mm by a spherical indenter method using a load tester, and left for 120 hours. Thereafter, the load was removed from the tin-plated film, and the indentation points of the tin-plated film were observed with a scanning electron microscope (SEM) at a magnification of 2,000 times. The SEM image was used to measure the whiskers from the indentation area. An example of the SEM image of the indentation is shown in Fig. Fig. 2 is a photograph showing an example of the whisker length measurement by enlarging a part of the SEM image of Fig. 1. Fig.

In the present embodiment, the length and the number of the whiskers to be measured were measured with an aspect ratio (length / diameter) of 2 or more. The whisker length was measured in accordance with Annex 2 of JEITA ET-7410. The measurement positions of the length and diameter of the whiskers on the column are as shown in Fig. 3, and the measurement positions of the length of the whiskers on the wire are as shown in Fig. When the whiskers were bent as shown in FIG. 2, the longest point in the straight line distance was measured.

The number of whiskers having a length of 1 占 퐉 or more and 10 占 퐉 or less and the number of whiskers having a length of more than 10 占 퐉 were counted as viscous whiskers each having a length of 1 占 퐉 or more. This measurement was performed with one indentation for one sample or a plurality of indentations for one sample. When the plurality of indentations were formed, the average value per indentation was determined for each number of whiskers having a length of 1 占 퐉 or more and 10 占 퐉 or less and whiskers having a length of 10 占 퐉 or more. And evaluated according to the following criteria. In the following criterion, it was judged that the cases of A and B were acceptable, especially the case of A was judged to be good, and the case of C was judged to be rejection.

(Evaluation standard)

A: no whisker having a length of more than 10 μm was observed, and no more than 5 whiskers having a length of 1 μm or more and 10 μm or less were observed.

B: no whisker having a length of more than 10 mu m was observed, and more than 6 whiskers having a length of 1 mu m or more and 10 mu m or less were observed.

C: At least one whisker having a length of more than 10 mu m was observed.

[Measurement of hardness of tin-plated film]

The evaluation sample was embedded in a resin and the Vickers hardness at the t / 2 position on the cross section in the film thickness (t) direction of the tin plating film was measured. The measurement conditions are as follows. The Vickers hardness is shown in " Film hardness [Hv] " in Tables 1A to 1D.

(Measurement conditions of film hardness)

Measuring instrument: Micro hardness tester manufactured by Akashi Co., Ltd. HM-124

Load: 0.0010 kg (0.0098 N)

Duration: 15 seconds

Applied rate: 10 탆 / sec

These results are shown in Tables 1A to 1D.

[Table 1A]

[Table 1B]

[Table 1C]

[Table 1D]

In Tables 1A to 1D, Examples 1 to 27 are inventive examples satisfying the requirements of the present invention. In these examples, since the tin plating film is formed by using the plating bath containing the prescribed compound X, whisker generation is suppressed even when external stress is applied to the tin plating film obtained. In Comparative Examples 1 to 6, 2-mercaptobenzothiazole shown in Patent Document 1 was used in Comparative Example 1, and methacrylic acid, 2-mercaptobenzothiazole in Comparative Example 5, Comparative Example 6 is an example of containing methacrylic acid shown in Patent Document 3 and naphthaldehyde shown in Patent Documents 2 and 4. In these comparative examples, all the whiskers were generated.

In contrast to the film hardnesses of Examples 1 to 27 and Comparative Examples 1 to 6, the film hardness of Examples 1 to 27 was lower than that of Comparative Examples 1 to 6. In Examples 1 to 27, since the tin-plated film was formed using the compound X as described above, the tin-plated film obtained had a reduced film hardness, and as a result, the stress was relaxed when external stress was applied , It is considered that whisker occurrence is suppressed.

In particular, when the flavonoid or the glycoside thereof is used as the compound X, as in the case where the whisker evaluation results of Examples 1 to 4, 6, 7, 10, 12, 13, 15, 17 and 18 are A, Can be sufficiently suppressed. When the flavonoid or its glycoside is used, it can be seen that occurrence of whisker can be sufficiently suppressed when the film hardness is less than 9.0.

Claims (5)

(Hereinafter referred to as " compound X ") selected from the group consisting of a flavonoid compound and a glycoside thereof, a compound having a xanthene skeleton and a glycoside thereof, a compound having an acridine skeleton and a glycoside thereof Tin electroplating bath. The method according to claim 1,
Wherein the compound X is at least one compound selected from the group consisting of the flavonoid compound and its glycoside. 3. The method according to claim 1 or 2,
Wherein the compound X contains 0.0001 g / L or more and 5 g / L or less in a proportion occupying in the electroplating bath. A tin-plated film obtained by using the tin electroplating bath according to any one of claims 1 to 3, characterized in that the Vickers hardness at the t / 2 position in the cross section in the film thickness (t) direction of the tin plated film is 10 or less Lt; / RTI > A tin-plated film obtained by using the tin electroplating bath according to claim 3, wherein the tin-plated film has a Vickers hardness of 10 or less at a t / 2 position in a cross section in the film thickness (t) direction of the tin- .

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