KR102402402B1 - Tin electroplating bath and tin plating film - Google Patents

Abstract

A tin electroplating bath is provided for obtaining a tin plating film in which generation of tin whiskers is suppressed upon application of an external stress to the tin plating film. The tin electroplating bath contains at least one compound selected from the group consisting of a flavonoid compound and its glycoside, a compound having a xanthene skeleton and its glycoside, and a compound having an acridine skeleton and a glycoside thereof, do.

Description

TIN ELECTROPLATING BATH AND TIN PLATING FILM

The present invention relates to a tin electroplating bath and a tin plating film. In particular, it relates to a tin plating film in which generation of tin whiskers is suppressed when an external (mechanical) stress is applied to the tin plating film, and a tin electroplating bath used for forming the tin plating film.

BACKGROUND ART Films such as tin plating and tin alloy plating are formed on electronic device components such as connectors, terminals, and IC chips from the viewpoint 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, in Patent Document 1, in a method for surface treatment of a plating material in which tin or a tin-lead alloy is plated on a metal material, a benzotriazole-based compound prescribed as an inhibitor, a prescribed mercaptobenzothiazole-based compound, and a prescribed Electrolysis of the plating material as an anode is shown in a surface treatment solution containing one or two or more selected from the group consisting of triazine-based compounds. It is shown that the tin or tin-lead alloy plating material surface-treated by this method has little deterioration of solderability and has excellent corrosion resistance.

Patent Document 2 proposes a tin and tin/lead alloy plating solution capable of forming bright plating over a wide current density region. As the plating solution, an aqueous solution for electroplating of tin and a tin/lead alloy, an alkanesulfonic acid as an acid, a divalent tin salt or a divalent tin salt and a divalent lead salt of an alkanesulfonic acid as a metal salt, poly as a dispersant A tin and tin/lead alloy plating solution containing one or two or more of oxyethylene alkylphenyl ether or polyoxyethylene naphthyl ether and chlorobenzaldehyde, naphthoaldehyde and picolinic acid as a brightener is disclosed.

Patent Document 3 proposes a plating bath excellent in reflow property, leveling property, and solderability of the electrodeposition film, and excellent in stability over time having a wide gloss range from a low current density area to a high current density area. . Specifically, as the plating bath, in a main plating bath containing alkanesulfonic acid and/or alkanolsulfonic acid and their divalent tin salt and/or divalent lead salt, at least one surfactant, at least one aromatic aldehyde, and at least A plating bath formed by adding one type of N-substituted unsaturated fatty acid amide compound is shown.

In addition, Patent Document 4 discloses an aqueous plating bath containing no fluoride or borofluoride salt, and for providing a glossy film such as tin with a smooth, uniform thickness. An aqueous plating bath comprising (A) a bath-soluble metal salt such as stannous salt, (B) at least one kind of alkanesulfonic acid or alkanolsulfonic acid, and (C) at least one kind of nonionic, cationic or amphoteric a surfactant, (D) at least one primary brightener among aromatic aldehydes, acetophenones, and carbonyl compounds having a specified group, and (E) at least one secondary brightener among lower aliphatic aldehydes and substituted olefins as specified A plating bath containing

By the way, it is known that a whisker will generate|occur|produce in a tin or a tin alloy plating film when an internal stress exists in a film. This whisker causes a problem that the circuit is short-circuited. Since the generation of this whisker is largely suppressed by the addition of lead to the plated film, there was no problem in the era when the tin-lead alloy plated film was mainstream. However, with the lead-free movement due to the enforcement of the RoHS (Restriction of Hazardous Substance) directive, improvement measures were again required. For this reason, various methods of reducing the internal stress of a tin plating film or a tin alloy plating film, such as improving a plating solution, have been proposed. However, even if the internal stress is reduced and the film itself does not easily generate whiskers, when an external stress is applied to the film, there is a problem that whiskers are generated due to the external stress. For example, in a connector, a lead is inserted with respect to the connector pin to which the tin or tin alloy plating film was given, and an external load is applied to the contact point with the lead in the connector pin. That is, an external pressure is applied to the tin or tin alloy plating film formed on the surface of the connector pin (hereinafter, this state may be referred to as "contact pressure"), and it becomes the same as the state in which the said internal stress is occurring. Doing so makes it prone to tin whiskers. Hereinafter, a tin whisker resulting from such an external stress may be referred to as a "contact pressure whisker".

The tin or tin alloy plating forming method disclosed in Patent Documents 1 to 4 was not studied until suppression of the generation of the contact pressure whiskers. Heretofore, as a method for preventing the generation of the contact pressure whisker, a method of forming a tin alloy plating film using a plating solution containing an element effective for preventing the generation of the contact pressure whisker together with tin is exemplified. For example, in Patent Document 5, by forming a silver plating as a bismuth segregation suppressing layer on a base material and making a connector provided with a surface layer made of a tin-bismuth alloy thereon, it is possible to effectively suppress the generation and growth of whiskers. is appearing Patent Document 6 shows that a tin-containing material layer is formed after forming a gold plating as a base layer, followed by heat treatment to form a tin-gold intermetallic compound to suppress whisker.

However, the method of the said patent documents 5 and 6 is expensive, and when 2 or more types of metal elements are essential, management of the alloy ratio of a plating bath and a plating film becomes essential. In particular, when a tin-silver alloy plating bath or a tin-bismuth alloy plating bath is used 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, if the surface of the tin anode plate or the plated object to be plated is left immersed in the plating bath during de-energization, silver or bismuth will be deposited on the tin anode plate or the coated object. Substitution and precipitation on the surface of the forbidden substance may make it unusable. Moreover, as mentioned above, there also exists a problem that cost becomes high compared with tin plating.

As another method for preventing the occurrence of a contact pressure whisker, a reflow treatment method in which the tin film is melted above the melting point is exemplified. In this method, although the contact pressure whisker is suppressed, it cannot be prevented completely, and another problem arises that solder wettability falls.

Moreover, in the case of a narrow connector between connector pins, a gold plating process may be performed. When gold plating is performed, there is naturally no generation of the above-mentioned contact pressure whiskers, but there is a problem in that the cost is significantly increased.

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

The present invention has been made in view of the above circumstances, and its object is to form a tin-plated film in which generation of tin whiskers is suppressed when an external stress is applied to the tin-plated film without incurring an increase in cost. It is to realize an electroplating bath.

The tin electroplating bath of the present invention capable of solving the above problems is one selected from the group consisting of a flavonoid compound and a glycoside thereof, a compound having a xanthene skeleton and a glycoside thereof, and a compound having an acridine skeleton and a glycoside thereof It is characterized in that it contains the above compound (hereinafter referred to as compound X). Hereinafter, the tin electroplating bath of this invention may be called "electroplating bath" or "plating bath".

As the compound X, it is preferable to use at least one compound selected from the group consisting of the above flavonoid compounds and glycosides thereof.

It is preferable to make it contain 0.0001 g/L or more and 5 g/L or less of the said compound X in the ratio which occupies in an electroplating bath.

In the present invention, a tin plating film obtained by using the tin electroplating bath, the tin plating film characterized in that the Vickers hardness at the t/2 position of the cross section in the film thickness (t) direction of the tin plating film is 10 or less also included.

The tin plating film obtained by using the tin electroplating bath of the present invention suppresses the occurrence of whiskers due to the external stress even when an external stress is applied thereto.

BRIEF DESCRIPTION OF THE DRAWINGS It is a photograph which shows an example of the whole image of an indentation in evaluation of the whisker suppression effect of an Example.
FIG. 2 is an enlarged photograph of a part of FIG. 1 , and is a photograph showing an example of whisker length measurement.
Fig. 3 is a view for explaining the measurement positions of the length and diameter of the whisker in the Example.

The present inventors have found that an electroplating method for forming a tin plating film in which generation of tin whisker is suppressed without causing a cost increase when external stress is applied to the tin plating film is used for forming the tin plating film. Paying attention to the electroplating bath, earnest research was repeated. As a result, in the tin electroplating bath, at least one compound selected from the group consisting of a flavonoid compound and its glycoside, a compound having a xanthene skeleton and its glycoside, and a compound having an acridine skeleton and a glycoside thereof (hereinafter referred to as " Compound X") was contained as an essential component, it was found that the intended purpose could be achieved, and the present invention was completed.

Although the mechanism by which a contact pressure whisker is suppressed by adding the said compound X to a plating bath is still not fully elucidated, it thinks as follows. That is, it is thought that the crystal size of Sn which comprises metal plating becomes large when the said compound X exists in a tin electroplating bath, and the fall of the hardness of a plating film arises as a result. And, by decreasing the hardness of the plating film, even when an external stress is added, the stress is dispersed and relieved in the plating film, in other words, since the external stress is not locally accumulated, it is estimated that the generation of contact pressure whiskers is suppressed.

Examples of the flavonoid compound and its glycosides include flavones such as chrysin, luteolin, apigenin and its glycosides apiin; of flavanols; isoflavones such as genistin, daidzein and its glycosides daijin; flavanols such as catechin, epicatechin, epigallocatechin, epicatechin gallate, epigallocatechin gallate, and theaflavin (Catechins); Flavanones such as naringenin and its glycosides naringin and hesperetin and its glycosides hesperidin; Chalcones such as cartiminidin and its glycosides cartamine; Cyanidin and its glycosides cyanine; Anthocyanidins, such as delphinidin and its glycoside delphine, pelargonidin, and its glycoside pelargonine; etc. are mentioned.

Compounds having a xanthene skeleton and glycosides thereof include xanthylium, 3,6-bis(ethylamino)-9-[2-(ethoxycarbonyl)phenyl]-2,7-dimethylxanthylium chloride, 3, 6-diamino-9-(2-carboxyphenyl)xanthylium, 3,6-bis(diethylamino)xanthylium chloride, fluorescein, carcein, uranine, tetraiodofluorescein, fluorescein- 4-isothiinate etc. are mentioned.

Compounds having an acridine skeleton and glycosides thereof include acridine, 3,6-dimethylaminoacridine, acrylflavin, 9(10H)acridone, 9-aminoacridine, acrrinol, 9-phenylacridine, proplavin, and the like.

Among the compounds X, flavonoid compounds and glycosides thereof are particularly preferred. Among them, flavonols and glycosides thereof are more preferable.

In order to sufficiently exhibit the above effects and to suppress burning and seizure at high current density and to produce a plated film satisfactorily, the preferable content of the compound X in the electroplating bath (when contained alone, it is a single amount , when it contains two or more types) is preferably 0.0001 g/L or more, more preferably 0.001 g/L or more, and still more preferably 0.005 g/L or more. On the other hand, when there is too much content of the said compound X, the improvement of the whisker suppression effect is not seen, but the cathode current efficiency falls. Therefore, it is preferable that content of the said compound X shall be 5 g/L or less, More preferably, it is 2 g/L or less, More preferably, it is 1 g/L or less.

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

[Tin salt]

A tin salt is an essential component for the structure of a plating film. The form of the tin salt used for this invention will not be specifically limited if it is normally used in the field|area of an electroplating bath. The stannous salts include stannous salts and stannous salts.

Examples of the stannous salt (tin salt (II)) include tin alkanesulfonic acid (II) such as tin methanesulfonate (II), and tin alkanolsulfonate (II) such as tin isethionate (II). (II); tin sulfate (II), tin borofluoride (II), tin chloride (II), tin bromide (II), tin iodide (II), tin oxide (II), tin phosphate (II), tin pyrroline (II), tin acetate (II), tin citrate (II), tin gluconate (II), tin tartrate (II), tin lactate (II), succinate (II), tin sulfamic acid (II), borofluoride Inorganic tin compounds, such as tin (II), a tin formate (II), and a tin silicate (II); etc. are mentioned. As said stannous salt (tin salt (IV)), sodium tartrate, potassium tartrate, etc. are mentioned.

As said tin salt, organic tin sulfonate (II), such as tin alkanolsulfonic acid (II), such as tin alkanesulfonate (II), such as said tin methanesulfonate (II), and tin isethionate (II), is especially preferable.

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, from 5 to 100 g/L, preferably from 10 to 70 g/L.

When a strong acid plating bath is used as the tin electroplating bath of the present invention, since the tin salt (IV) is insoluble in a strong acid, a complexing agent may be added together. The complexing agent is not specifically limited, For example, sodium sulfite, potassium sulfite, ammonium sulfite, sodium cyanide, potassium cyanide, sodium thiosulfate, potassium thiosulfate, ammonium thiosulfate, phosphoric acid, boric acid, citric acid, gluconic acid, tartaric acid, Lactic acid, malic acid, ethylenediamine, triethanolamine, glycine, alanine, hydroxyethylethylenediaminetriacetic acid (HEDTA), ethylenediaminetetraacetic acid (EDTA), cyclohexanediaminetetraacetic acid, diethylenetriaminepentaacetic acid (DTPA), tri Ethylenetriaminehexaacetic acid (TTHA), hydroxyethyliminodiacetic acid (HIMDA), dihydroxyethyliminoacetic acid (DHEIMA), dihydroxyethylethylenediaminediacetic acid (DHEDDA), glycine, iminoacetic acid, nitrile Rotriacetic acid (NTA), aminotrimethylenephosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, ethylenediaminetetramethylenephosphonic acid, diethylenetriaminepenta(methylenephosphonic acid), etc. can be used. . These complexing agents can be used individually by 1 type or in combination of 2 or more types.

Although content of the said complexing agent is not specifically limited, It is preferable to set it as about 1-500 g/L, and it is more preferable to set it as about 10-300 g/L. When there is too little content of a complexing agent, tin will precipitate in a plating bath, and bath stability will worsen. On the other hand, when there is too much content of a complexing agent, complex formation with Sn ²⁺ advances excessively, a precipitation rate falls, and it becomes impossible to form the plating film of the film thickness made into desired. Moreover, it becomes difficult to dissolve a complexing agent, and it may become uneconomical.

The plating bath of the present invention does not necessarily contain an alloying element as described above. However, the alloying element may be contained within a range that does not adversely affect precipitation of plating, film hardness, manufacturability, and cost. As said alloying element, In etc. which can suppress film hardness low are mentioned, for example. However, bismuth or silver as an alloying element is not preferable because the problem of the potential difference mentioned above arises. Moreover, when copper is used as an alloying element, since film hardness becomes high easily and whisker is easy to generate|occur|produce, it is unpreferable. Moreover, lead is not preferable from a viewpoint of being lead-free as mentioned above.

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

An inorganic acid, an organic acid, and its water-soluble salt act on the stability of a plating bath by adjusting pH etc. It also acts on electrical conductivity (voltage).

The inorganic acid and organic acid used for this invention will not be specifically limited if it is a thing normally used for a plating film. For example, sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, sulfamic acid, etc. are mentioned as said inorganic acid. Examples of the organic acid include organic sulfonic acids (alkanesulfonic acids such as methanesulfonic acid and alkanolsulfonic acids such as isethionic acid), carboxylic acids (aromatic carboxylic acids, aliphatic saturated carboxylic acids, and aminocarboxylic acids). . Considering the stability of the liquid, etc., it is preferably organic sulfonic acid, and more preferably methanesulfonic acid.

These may exist as a free form, and may exist as a water-soluble salt like the water-soluble salt of an inorganic acid and the water-soluble salt of an organic acid. 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 potassium salt, sodium salt, ammonium salt, and magnesium salt.

In this invention, the said inorganic acid and organic acid, and its water-soluble salt may be used independently and may use 2 or more types together. If the preferred content of the above components in the electroplating bath (when contained alone, it is a single amount, when two or more types are contained, it is the total amount) is too small, the stability of the plating bath deteriorates, and deposits etc. tends to be easy. Therefore, it is preferable that the said content sets it as 50 g/L or more, More preferably, it is 100 g/L or more. On the other hand, even if the said component is added excessively, since the addition effect of the said component is saturated and unnecessary, it is preferable that the said content shall be 500 g/L or less, More preferably, it is 300 g/L or less.

[Non-ionic surfactant]

A nonionic surfactant has a role of improving the wettability of the plating bath with respect to a base material.

As said nonionic surfactant, the thing of an alkylene oxide type is used preferably. Specifically, polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, polyoxyethylene alkylamine, polyoxyethylene alkylamide, polyoxyethylene fatty acid ester, polyoxyethylene polyhydric alcohol ether, ethylene oxide propylene oxide block polymerization type; Ethylene oxide propylene oxide random polymerization type, propylene oxide polymerization type, etc. can be used. Among these, polyoxyethylene alkylphenyl ether is particularly preferably used.

In this invention, said nonionic surfactant may be used independently and may use 2 or more types together. When the preferred content of the nonionic surfactant in the electroplating bath (when contained alone, it is a single amount, when two or more types are contained, it is the total amount) is too small, burning or sticking occurs at high current density In some cases, it is preferable to set it as 0.05 g/L or more, and more preferably 1 g/L or more. On the other hand, when the said nonionic surfactant is contained excessively, a plating film may blacken, and the defect that a color nonuniformity generate|occur|produces may be produced. Therefore, it is preferable that the said content shall be 100 g/L or less, More preferably, it is 50 g/L or less.

[Antioxidant]

When using tin salt (II), antioxidant prevents oxidation of the divalent Sn ion in a bath and oxidation of other bath components, and has a role of stabilizing a bath. Moreover, when using tin salt (IV), it contributes to stability of Sn complex. As said antioxidant, catechol, hydroquinone, 4-methoxyphenol (p-methoxyphenol), etc. can be used.

These may be used independently and may combine 2 or more types. When the preferable content of the antioxidant in the electroplating bath (when containing alone, it is a single amount, when containing two or more types, the total amount of these) is too small, sufficient antioxidant effect is not obtained, so 0.1 g/ It is preferable to set it as L or more, More preferably, it is 0.2 g/L or more. On the other hand, when there is too much said content, the fall of electric current efficiency etc. (occurrence|production of seizure), or deterioration of the physical property of the plating bath by the decomposition product (deterioration of viscosity and antifoaming property) may be caused. Therefore, it is preferable that the said content shall be 10 g/L or less, More preferably, it is 5 g/L or less. The concentration of the antioxidant does not change in the case of the tin salt (II) or the tin salt (IV).

[Organic solvent]

The organic solvent is used for the purpose of dissolving the compound X in the plating bath. Moreover, it is used for the purpose of improving stability in a plating bath. As the organic solvent, for example, monohydric alcohols such as methanol and 2-propanol (isopropyl alcohol); dihydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol; thing can be heard

These may be used independently and may use 2 or more types. When the preferable content of the organic solvent occupied in the electroplating bath (when containing alone, it is a single amount, when containing two or more types, the total amount thereof) is too small, sufficient solubility is not obtained and turbidity and precipitation may occur. There is a possibility. Therefore, it is preferable that the said content shall be 5 g/L or more. On the other hand, when there are too many organic solvents, the fall of electric current efficiency etc. (occurrence|production of seizure), or deterioration of the physical property (viscosity and antifoaming property) of the plating bath by a decomposition product may be caused. Therefore, it is preferable that the said content shall be 100 g/L or less, More preferably, it is 70 g/L or less, More preferably, it is 50 g/L or less, More preferably, it is 20 g/L or less.

The pH of the tin electroplating bath is preferably 10 or less. When using tin salt (II) especially, when pH is too high, tetravalent tin will become easy to generate|occur|produce. Therefore, it is preferable to set it as pH 3 or less. On the other hand, when the tin salt (IV) is used, if the pH is too high or too low, complex formation is impossible and the stability of the plating bath is lowered. Therefore, it is preferable to make pH into the range of 3-10. It is preferable to use the same acid as the free acid contained in the used tin salt for the said pH adjustment, for example, in the case of tin methanesulfonic acid, it is preferable to use methanesulfonic acid for pH adjustment.

When performing electroplating using the tin electroplating bath of the present invention, for example, the conditions such as bath temperature, current density, plating bath immersion time, and the like, methods and conditions commonly used in tin electroplating can be adopted. have.

As for the tin plating film obtained by electroplating using the tin electroplating bath prescribed|regulated by this invention, the Vickers hardness of the t/2 position in the film thickness (t) direction cross section is suppressed to 10 or less. The said Vickers hardness becomes like this. Preferably it is less than 9.0, More preferably, it is 8.5 or less. In addition, when the role etc. as a protective film of a tin plating film are considered, the lower limit of Vickers hardness is about 4 in general.

This application claims the benefit of the priority based on Japanese Patent Application No. 2014-120714 for which it applied on June 11, 2014. The entire content of the specification of Japanese Patent Application No. 2014-120714 for which it applied on June 11, 2014 is taken in for reference of this application.

Example

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited by the original examples, and it is also carried out with appropriate changes within a range that can be suitable for the purpose of the preceding and following descriptions. Of course, it is possible, and all of them 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, first, various components (water-soluble tin salt, acid, surfactant, compound X, antioxidant, organic solvent) listed in Tables 1A to 1D below are contained. A tin electroplating bath was prepared. In Table 1A - Table 1D, a blank means that it is not added. In addition, all of the plating baths of Table 1A - Table 1D were pH 1 or less. Using the plating bath, as in the plating process shown below, a tin electroplating film was applied to the surface of a substrate made of a phosphor bronze material. was formed so that it might become a film thickness of 30 micrometers, and the sample in which the tin plating film was formed was obtained.

(Plating process)

Electrolytic degreasing (2 min) → Water washing (30 sec) → Pickling (30 sec) → Water washing (30 sec) → Base nickel plating (film thickness 1.5 µm, the following conditions) → Water washing (30 sec) → Pickling (30 sec) → Washing with water (30 sec) → Tin plating (under the following conditions) → Washing with water (30 sec) → Washing with ion exchange water → Drying

In the base nickel plating in the above step, a nickel sulfamate plating bath (composition, nickel sulfamate: 300 g/L, nickel chloride: 15 g/L, boric acid: 30 g/L) is used as the plating bath, , electroplating was performed under the following conditions.

(Nickel plating conditions)

Cathode current density: 8 A/d㎡

Liquid temperature: 50 degrees Celsius

Plating time: 60 seconds

pH: 4.0

Moreover, in the tin plating in the said process, electroplating was performed under the following conditions.

(Tin plating conditions)

Cathode current density: 20 A/d㎡

Liquid temperature: 50 degrees Celsius

Plating time: For samples for evaluation of whisker suppression effect: 12 seconds

For samples for film hardness measurement: 180 seconds

Using the obtained sample, evaluation of the whisker suppression effect and measurement of film hardness were performed as follows.

[Evaluation of whisker inhibitory effect]

The whisker inhibitory effect was evaluated using the evaluation sample. The evaluation WHEREIN: The load test and whisker measurement were performed based on the whisker test method (JEITA RC-5241) of the connector for electronic devices of the Electronic Information Technology Industry Association standard. Specifically, a load of 200 g was locally applied to the tin-plated film using a zirconia ball indenter with a diameter of 1 mm by the ball indenter method using a load tester and allowed to stand for 120 hours. Then, the load was removed from the tin plating film, and the indentation point of the tin plating film was observed with the magnification of 2,000 times with a scanning electron microscope (SEM). The SEM image was used to measure the whiskers arising from the perimeter of the indentation. An example of the SEM image of the said indentation is shown in FIG. Moreover, in FIG. 2, a part of the SEM image of the said FIG. 1 is enlarged, and the photograph which showed an example of whisker length measurement is shown.

In this Example, the thing with an aspect-ratio (length/diameter) of 2 or more was set as the "whisker" to be measured, and the length and number were measured. The whisker length was measured as in Annex 2 of JEITA ET-7410. The measuring positions of the length and diameter of the column-shaped whiskers are as shown in FIG. 3 , and the measuring positions of the length of the wire-shaped whiskers are as shown in FIG. 2 . When the whisker is bent as shown in FIG. 2, the longest point in the straight line distance was measured.

For whiskers with a length of 1 µm or more that can be seen with the naked eye, the number of whiskers having a length of 1 µm or more and 10 µm or less and whiskers having a length of more than 10 µm were counted. 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 of each number of whiskers having a length of 1 µm or more and 10 µm or less and whiskers having a length of more than 10 µm was obtained as an average value per one indentation. And it evaluated by the following criteria. In the following standards, the cases of A and B were judged as pass, especially the case of A was judged as good, and the case of C was judged as failing.

(Evaluation standard)

A: No whiskers exceeding 10 µm in length were observed, and 5 or less whiskers having a length of 1 µm or more and 10 µm or less were observed.

B: No whiskers exceeding 10 µm in length were observed, and 6 or more whiskers having a length of 1 µm or more and 10 µm or less were observed.

C: One or more whiskers having a length of more than 10 µm were observed.

[Measurement of hardness of tin plating film]

The said evaluation sample was embedded in resin, and the Vickers hardness of the t/2 position in the film thickness (t) direction cross section of a tin plating film was measured. Measurement conditions are as follows. The Vickers hardness is shown in "film hardness [Hv]" of Table 1A - Table 1D.

(Measurement conditions for film hardness)

Measuring instrument: Akashi Co., Ltd. micro hardness tester HM-124

Load: 0.0010 kg (0.0098 N)

Holding time: 15 seconds

Application rate: 10 µm/sec

These results are written together in Table 1A - Table 1D.

[Table 1A]

[Table 1B]

[Table 1C]

[Table 1D]

In Tables 1A to 1D, Examples 1-27 are inventive examples satisfying the requirements of the present invention. In these examples, since the tin plating film is formed using the plating bath containing the prescribed|regulated compound X, even if an external stress is applied to the obtained tin plating film, whisker generation|occurrence|production is suppressed. On the other hand, Comparative Examples 1 to 6 do not contain the prescribed compound X, Comparative Example 1 is 2-mercaptobenzothiazole shown in Patent Document 1, Comparative Example 5 is methacrylic acid shown in Patent Document 3; Comparative Example 6 is an example containing methacrylic acid shown in Patent Document 3 and naphthoaldehyde shown in Patent Documents 2 and 4. In all of these comparative examples, long whiskers were generated.

Moreover, when Examples 1-27 and the film hardness of Comparative Examples 1-6 are compared, the film hardness of Examples 1-27 is falling rather than Comparative Examples 1-6. In Examples 1-27, since the tin-plated film was formed using the compound X as described above, the obtained tin-plated film had reduced film hardness, and as a result, the stress was relieved when an external stress was applied. , it is thought that whisker generation was suppressed.

In particular, as the result of the whisker evaluation of Examples 1 to 4, 6, 7, 10, 12, 13, 15, 17 and 18 is A, when a flavonoid or a glycoside thereof is used as the compound X, whisker generation is It can be seen that it can be sufficiently suppressed. In addition, when flavonoids or glycosides thereof are used, it can be seen that whisker generation can be sufficiently suppressed when the film hardness is less than 9.0.

Claims (7)

At least one compound selected from the group consisting of a flavonoid compound and its glycoside, a compound having a xanthene skeleton and a glycoside thereof, and a compound having an acridine skeleton and a glycoside thereof (hereinafter referred to as compound X), and
At least one organic solvent selected from the group consisting of monohydric alcohols and dihydric alcohols
contains
The content of the organic solvent is a tin electroplating bath, characterized in that 5 g / ℓ ~ 100 g / ℓ. The method of claim 1,
A tin electroplating bath using, as the compound X, at least one compound selected from the group consisting of the flavonoid compound and its glycosides. 3. The method of claim 1 or 2,
A tin electroplating bath containing 0.0001 g/L or more and 5 g/L or less of the compound X in the electroplating bath. A tin plating film obtained by using the tin electroplating bath according to claim 1 or 2, characterized in that the Vickers hardness at the t/2 position of the cross section in the film thickness (t) direction of the tin plating film is 10 or less. tin plating film. A tin plating film obtained using the tin electroplating bath according to claim 3, wherein the tin plating film has a Vickers hardness of 10 or less at the t/2 position of a cross section in the thickness (t) direction of the tin plating film. . 3. The method of claim 1 or 2,
The monohydric alcohol is at least one selected from the group consisting of methanol and 2-propanol,
The tin electroplating bath, wherein the dihydric alcohol is at least one selected from the group consisting of ethylene glycol, diethylene glycol, and triethylene glycol. delete

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