JP3878959B2 - Tin plating solution, tin plating method using the tin plating solution, and tin plating solution adjustment method - Google Patents

Abstract

Provided is a tin plating solution which is less susceptible to forming a sludge even after the storage for a long time and has a markedly long life as a plating solution. A tin plating solution for carrying out an electrolytic tin plating, characterized in that it contains a tin salt as a supply source of a tin ion in an amount of 5 to 30 g/L in terms of tin, a chelating agent for chelating and stabilizing the tin ion and a pH adjusting agent; and a method for preparing the tin plating solution, characterized in that it comprises adding tin methanesulfonate into a solution being neutral to alkaline, to thereby form a tin chelate complex.

Description

The present invention relates to a tin plating solution, a plating method using the tin plating solution, and a tin plating solution adjusting method. In particular, the present invention relates to a tin plating solution that does not generate sludge as found in conventional tin plating solutions.

  Conventionally, tin plating solutions have been widely used as terminal plating and oxidation corrosion prevention plating in the field of electronic component materials. In recent years, due to the demand for lead-free solder, it is also used as a substitute for solder.

  Among the technical fields that use tin plating solutions, in the field of multilayer ceramic capacitors that are chip parts, it is common to form a tin plating layer on the surface of the external electrode of the multilayer ceramic capacitor. The tin plating layer of the external electrode of the multilayer ceramic capacitor has excellent solder wettability, and functions as a useful one when surface-mounted on a printed wiring board through a surface mounting process such as solder reflow.

  However, as a well-known fact among those skilled in the art, the tin plating solution has conventionally suffered from the precipitation of tin oxide (hereinafter simply referred to as “sludge”), which lacks long-term stability. . Therefore, it was necessary to use the tin plating solution immediately after the bathing. Moreover, the tin plating solution that lacks long-term storage stability causes the composition to change every time during the plating operation, and the properties of the plating solution change, thus stabilizing the quality of the resulting plating film. It was difficult to guarantee the quality of the plating solution. In the shortest-life tin plating solution, sludge was observed immediately after the bathing, and the tin plating solution became cloudy.

  Conventionally, there is a tin plating solution having a composition as disclosed in Patent Document 1. However, the solution life as a plating solution is short, bath management is difficult, and management costs increase. There is also a tin plating solution as used in Patent Document 2. And the tin plating solution experimentally adjusted based on the manufacturing method disclosed in these patent documents shows that sludge is almost certainly generated after an average of 24 hours in an environment at room temperature.

JP-A-10-245694 JP-A-2-170996 JP 2001-110666 A

  However, a tin plating layer formed using a tin plating solution in which sludge is generated generally has a solder dewetting phenomenon due to poor solder wettability with respect to the tin plating layer. Moreover, when the tin plating solution in the state where sludge is generated is used, it becomes difficult to form a uniform coating of the tin plating layer. Furthermore, if the tin plating solution in which sludge is generated is continuously used in the plating apparatus, clogging of various pipes occurs, and the maintenance of the apparatus becomes complicated.

  Conventionally, various methods have been studied by those skilled in the art in order to eliminate the generation of sludge in the tin plating solution. As a result, other than the method using the ammonia component in a large amount as disclosed in the above-mentioned Patent Document 3, an effective solution method cannot be found, and it is recognized as a characteristic of the tin plating solution, and even a problem that has been praised halfway. there were.

  And the drawback of tin plating solution using a large amount of ammonia component is that the odor caused by the ammonia is a problem, and at the same time, the working environment is directly deteriorated, and at the same time, the corrosion of copper products and copper parts in the vicinity of the plating tank is promoted. However, active use is difficult due to the need for capital investment to strengthen the mist ventilation of the plating tank.

  From these facts, if the solution life after building bath is long, excellent long-term storage stability, and tin plating solution that does not change its quality during long-term plating operation can be supplied to the market, the technical benefits to society can be measured. It will not be.

  Therefore, the present inventors have come up with the following tin plating solution as a result of intensive studies.

Tin plating solution: The tin plating solution according to the present invention is a tin plating solution for performing tin plating by an electrolytic method, and is a premixed mixture of water, a pH adjuster, and a chelating agent and having a pH value of 6-12. In this solution, a tin chelate complex is formed by adding a tin salt to the preconditioning solution so that the tin content is 5 g / L to 30 g / L and stirring sufficiently, and 10 ° C. to It is stored at 40 ° C., and sludge does not occur for more than 7 days .

  And it is preferable that the said tin salt used for the tin plating solution which concerns on this invention uses 1 type, or 2 or more types chosen from the 1st tin salt soluble with water.

  In the tin plating solution according to the present invention, the chelating agent may be one or more selected from gluconic acid, gluconate, citric acid, citrate, pyrophosphoric acid, pyrophosphate, 30 g / L to 300 g / It is preferable to contain it so that it may become L concentration.

  In the tin plating solution according to the present invention, the pH adjuster is an alkaline pH adjuster, and one or more selected from sodium hydroxide, potassium hydroxide, and aqueous ammonia are used in an amount of 5 g / L to 140 g / L. It is preferable to make it contain so that it may become a density | concentration.

  In the tin plating solution according to the present invention, the pH adjuster is an acidic pH adjuster, and one or more selected from methanesulfonic acid, ethanesulfonic acid, sulfuric acid, and isethionic acid is 10 g / L to 300 g. / L is preferably included.

  In the tin plating solution concerning this invention, it is preferable to contain antioxidant so that it may become a 0.1g / L-30g / L density | concentration.

  It is a pH adjuster for finely adjusting the pH of the tin plating solution according to the present invention to the acidic side, and if necessary, one or two of methanesulfonic acid and sulfuric acid are added, and the pH ranges from 4 to 10 It is preferable to do.

  It is a pH adjuster for finely adjusting the pH of the tin plating solution according to the present invention to the alkaline side, and one or two kinds of sodium hydroxide, potassium hydroxide, and ammonia water are added as necessary, and pH 4 It is preferable to be in the range of ~ pH10.

  In the tin plating solution according to the present invention, when it is necessary to add a conductive salt, it is preferable to include one or more selected from sodium sulfate and ammonium sulfate so as to have a concentration of 1 g / L to 150 g / L. .

  In the tin plating solution according to the present invention, one or more selected from a nonionic surfactant, a cationic surfactant, and an amphoteric surfactant as a brightening agent are included so as to have a concentration of 0.1 g / L to 30 g / L. Preferably.

Tin plating method: As a tin plating method using the tin plating solution according to the present invention, it is preferable to perform electrolysis under conditions of a bath temperature of 10 ° C to 40 ° C.

Method for adjusting tin plating solution: It is a method for adjusting a tin plating solution according to the present invention, and it is preferable to adopt a tin plating solution adjusting method characterized by being adjusted by the following procedures A) and B). .

A) Water, a pH adjuster, and a chelating agent are mixed to prepare a premixed solution (preliminary adjuster) having a pH value of 6 to 12.
B) A tin salt is added to the preconditioning solution, and the tin content is added so as to have a concentration of 5 g / L to 30 g / L and stirred sufficiently to form a tin chelate complex to obtain a tin plating solution.

  In the method for preparing a tin plating solution according to the present invention, it is preferable to add a step of adding an antioxidant to the tin plating solution prepared by the above method.

  In the tin plating solution adjusting method according to the present invention, a tin plating solution adjusting method in which a step of further adding a conductive salt is added to the tin plating solution adjusted by the above method.

  A method for adjusting a tin plating solution according to the present invention, the method comprising adding a step of adding a brightener to the tin plating solution adjusted by the above method.

  The tin plating solution according to the present invention described above is suitable for forming a tin plating layer of a chip part such as a multilayer ceramic capacitor that is frequently used for tin plating among electronic parts.

  Even if the tin plating solution according to the present invention does not contain a large amount of an ammonia component, precipitation of tin oxide hardly occurs, the solution life after the bathing is prolonged, and management as a plating solution is facilitated. Moreover, since this tin plating solution can be used as a neutral region, it does not damage ceramics, electrodes, etc. in electronic components.

  And the tin plating using the tin plating solution according to the present invention can be used at a bath temperature exceeding 30 ° C., and since there is appropriate liquid evaporation, it does not cause a significant increase in the amount of waste liquid. The processing load can be reduced.

  Further, the tin plating solution adjustment method according to the present invention does not require a special apparatus and method, but a pH adjuster and a chelating agent are mixed, and methanesulfonic acid as a conductive salt is added thereto. Mixing and stirring, preparing a neutral to alkaline premixed solution in advance, and adding tin methanesulfonate to form a tin chelate complex efficiently in the neutral to alkaline region. It is possible to obtain a tin plating solution having a long solution life that does not occur.

  Furthermore, by using the tin plating solution and the tin plating method according to the present invention, tin having excellent film thickness uniformity and stable quality on the surface of chip parts such as multilayer ceramic capacitors in a long-time plating operation. A plating layer can be formed.

  Hereinafter, the embodiment according to the present invention will be described in the order of a tin plating solution, a tin plating method, a tin plating solution adjustment method, and a chip component.

Embodiment of Tin Plating Solution: A tin plating solution according to the present invention is prepared by mixing water, a pH adjuster, and a chelating agent into a premixed solution having a pH value of 6 to 12, and the tin content in the preconditioned solution is 5 g. A tin chelate complex is formed by adding a tin salt to a concentration of / L to 30 g / L and stirring sufficiently, and the sludge is stored for 7 days or more under conditions of 10 ° C. to 40 ° C. It does not occur . Except for the tin plating solution that uses a large amount of ammonia among the tin plating solutions supplied to the conventional market, sludge is generated within 5 days after the bathing, and the properties of the tin plating bath are changed to generate sludge. If tin plating is continued in this state, quality deterioration as a tin plating layer is caused. Therefore, renewal work of the tin plating solution in a short period is required, which is a big problem from the viewpoint of cost increase and stable operation of tin plating. On the other hand, the tin plating solution according to the present invention will be described in detail in the following tin plating solution adjustment method, but by including a chelating agent and a pH adjusting agent that chelate and stabilize tin ions, a neutral region ~ By performing chelation in the alkaline region (pH 6 to pH 12), most of the tin ions are contained as a tin chelate complex . Therefore, since tin is stable as a tin chelate complex in a tin plating solution, a temperature of 10 ° C. to 40 ° C. that could not be achieved with a conventional tin plating solution, even if any combination of the components described below was performed. Even in the area, sludge does not occur for more than 7 days. In the examples described later, a tin plating solution that is most excellent in solution stability and does not generate sludge even after 365 days at a temperature of 40 ° C. is disclosed.

  The tin salt that is a tin ion supply source of the tin plating solution used here is a stannous salt that is soluble in water (hereinafter simply referred to as “tin salt”). Among the tin salts, it is preferable to use one or more selected from tin methanesulfonate, tin sulfate, tin sulfamate, and tin pyrophosphate. And it is preferable to make content of the tin salt in the tin plating solution concerning this invention contain 5g / L-30g / L in conversion of tin. When the tin salt content is less than 5 g / L in terms of tin, the current efficiency is lowered and the plating rate does not satisfy the industrially required productivity, and at the same time the smoothness and film thickness uniformity of the tin plating layer Damaged. On the other hand, when the content of the tin salt exceeds 30 g / L in terms of tin, the amount of tin in the plating solution increases, and the electrodeposition rate of tin is too fast, making it difficult to control the thickness of the plating layer. Therefore, it becomes impossible to avoid the precipitation of tin oxide. The tin salt content in the tin plating solution according to the present invention is more preferably 10 g / L to 20 g / L in terms of tin. In terms of industrial production, there is usually a certain level of fluctuations in the plating conditions when tin plating is performed. Considering the inevitable fluctuations in the plating conditions that cannot be managed, more stable quality tin This is because a plating layer can be formed.

  Next, the chelating agent stabilizes tin ions supplied from a tin salt as a chelate complex in a tin plating solution. The chelating agent referred to in the present invention includes one or more selected from gluconic acid, gluconate, citric acid, citrate, pyrophosphate, pyrophosphate so as to have a concentration of 30 g / L to 300 g / L. Preferably. This is because the chelating agent described here efficiently forms a chelate complex with tin ions ionized into a solution from a tin salt that is a tin ion supply source. Among these, by using sodium gluconate or citric acid, the most stable tin chelate complex can be formed, and the tin plating solution having the longest solution life can be obtained with the most remarkable effect of preventing precipitation of tin oxide. Here, the concentration of the chelating agent in the tin plating solution is originally determined according to the type of the chelating agent and the amount of tin in the plating solution. However, even if any of the above-mentioned chelate complexes is used, the chelating agent concentration has an appropriate amount in the range of 100 g / L to 200 g / L. And when using together 2 or more types of chelating agents, the total density | concentration of 2 or more types of chelating agents should just become the range of 100 g / L-200 g / L density | concentration. When the chelating agent concentration is less than 100 g / L, it is difficult to form a chelate complex with all of the tin ions in the plating solution on the premise of the amount of tin in the plating solution, and there is free tin ions. Precipitation cannot be prevented. On the other hand, even if the concentration of the chelating agent exceeds 200 g / L, it becomes an excessive amount for the formation of a chelate complex with tin ions in the plating solution, resulting in wasted resources.

The pH adjuster is a neutral to alkaline region so that the tin ion supplied from the tin salt in the tin plating solution reacts with the chelating agent to form a tin chelate complex. In order to stabilize the tin chelate complex once generated, the tin plating solution according to the present invention is finally used to obtain a pH suitable for performing tin plating . The pH adjusting agent includes an alkaline pH adjusting agent and an acidic pH adjusting agent.

  As the alkaline pH adjuster referred to in the present invention, one or more selected from sodium hydroxide, potassium hydroxide, and aqueous ammonia are used. The reason why these were selected as alkaline pH adjusting agents is that a good tin plating layer can be formed without affecting the properties of the plating solution when performing tin plating. These alkaline pH adjusters promote ring-opening of the chelating agent so that chelation between the chelating agent and tin ions is facilitated. More specifically, the alkaline pH adjusting agent is added in an amount of 5 g / L to 140 g / The L concentration is included. When the alkaline pH adjuster is less than 5 g / L, ring opening of the chelating agent cannot be promoted. On the other hand, even if the alkaline pH adjuster is added in an amount exceeding 140 g / L, the ring-opening efficiency of the chelating agent is not improved, and excessive addition is considered in consideration of the range of the tin salt amount. More preferably, an alkaline pH adjuster is contained so as to have a concentration of 30 g / L to 70 g / L. Within this range, stable chelation of tin ions with a tin salt added afterwards is possible, and pH adjustment with an acidic pH adjuster described below is facilitated.

  And the acidic pH adjuster used together with an alkaline pH adjuster includes 10 g / L to 300 g / L of one or more selected from methanesulfonic acid, ethanesulfonic acid, sulfuric acid, and isethionic acid. The reason why these were selected as acidic pH adjusting agents is that a good tin plating layer can be formed without affecting the properties of the plating solution when performing tin plating. And this acidic pH adjuster produces | generates tin chelate from a neutral area | region to a weak alkali area | region by making the pH value of the plating solution in the middle of the adjustment once made into the alkaline area with the alkaline pH adjuster in the range of 6-12, and is stable It is used to make it. When 300 g / L or more of an acidic pH adjuster is added and the pH of the plating solution being adjusted is less than pH 6, tin ion chelate cannot be stabilized, and sludge generation is recognized early in the final tin plating solution. On the other hand, when the acidic pH adjuster is added in an amount of less than 10 g / L, it becomes a strong alkali region of pH 12 or higher of the plating solution in the middle of adjustment, and subsequent fine adjustment of the tin plating solution is difficult, and erosion with the ceramic is easy. The tin plating solution.

Next, the pH adjuster for fine adjustment is a pH adjuster for finely adjusting the pH of the tin plating solution according to the present invention to the acidic side (hereinafter referred to as “acid pH adjuster for fine adjustment”). There is a pH adjusting agent (hereinafter referred to as “alkaline pH adjusting agent for fine adjustment”) for finely adjusting the pH of the tin plating solution according to the present invention to the alkaline side. These pH adjusting agents for fine adjustment are added as necessary, and are used for final pH adjustment as a tin plating solution. Therefore, the timing of addition, generate a Suzuki rate is to use at any stage after stabilization.

  And as an acidic pH adjuster for fine adjustment, 1 type or 2 types of methanesulfonic acid and a sulfuric acid are added, and the plating solution pH value is the range of 4-10, More preferably, the pH value is the range of 6-8. It is preferable to do. Further, as an alkaline pH adjuster for fine adjustment, one or two kinds of sodium hydroxide, potassium hydroxide, and ammonia water are added, and the plating solution pH value is in the range of 4 to 10, more preferably pH value of 6 to 6. A range of 8 is preferable. When the pH value of the tin plating solution is in a strongly acidic region of less than 4, there is a high possibility that the ceramic portion used in the chip component such as a multilayer ceramic capacitor to be subjected to tin plating is eroded. When the pH value of the tin plating solution is in a strongly alkaline region exceeding 10, the ceramic portion may also be eroded. In addition, the stability of the tin chelate complex produced at the same time is impaired, tin cannot be fixed and becomes tin ions, and precipitation of tin oxide occurs, so that the solution life as a tin plating solution is shortened. Therefore, the range specified as more preferable is close to the neutral region in order to reliably prevent the ceramic erosion by the tin plating solution and to ensure the long life of the tin plating solution.

  And it is preferable to include an antioxidant in the tin plating solution according to the present invention from the viewpoint of extending the life of the tin plating solution. This is to prevent spontaneous oxidation due to contact between the atmosphere and the plating solution, and to efficiently prevent the precipitation of tin oxide. Here, it is preferable to contain an antioxidant so as to have a concentration of 0.1 g / L to 30 g / L. Of the antioxidants, it is preferable to use one or more selected from catechol, hydroquinone, ascorbic acid, ascorbate, and phenylenediamine. When the antioxidant concentration is less than 0.1 g / L, a sufficient antioxidant effect cannot be obtained. And even if it adds antioxidant concentration exceeding 30 g / L, the antioxidant effect cannot be acquired more than it and the lifetime improvement of tin plating liquid cannot be expected. In addition, it is not preferable to add an antioxidant in an excessive amount because a quality change as a tin plating solution occurs. Therefore, more preferably, the concentration of the antioxidant is used in the range of 1 g / L to 10 g / L. This is because a reliable antioxidant effect can be obtained, and quality changes as a tin plating solution due to excessive addition of an antioxidant can be reliably prevented.

  In the tin plating solution according to the present invention, even the composition described above can be electrolyzed without particularly adding a conductive salt. However, when it is necessary to further stabilize the energized state at the time of electrolyzing the tin plating solution, increase the current efficiency of tin deposition, and increase the productivity, it is preferable to add a conductive salt. When addition of a conductive salt is required, it is preferable to include one or more selected from sodium sulfate and ammonium sulfate so as to have a concentration of 1 g / L to 150 g / L. Here, the reason why sodium sulfate and ammonium sulfate were used as the conductive salt is that they have the smallest change in the quality of the tin plating solution and there is no impurity remaining in the tin plating layer. When the addition amount of this conductive salt is less than 1 g / L, the effect of improving the current-carrying stability when electrolysis is performed cannot be obtained. And even if the addition amount of this conductive salt exceeds 150 g / L, the current-carrying stability at the time of electrolysis does not improve any more, resulting in wasted resources.

  Further, in the tin plating solution according to the present invention, the concentration of one or more selected from nonionic surfactants, cationic surfactants, and amphoteric surfactants as brighteners is 0.1 g / L to 30 g / L. It is also preferable to include them. This brightener smoothes the tin plating layer obtained by electrolyzing the tin plating solution, and contributes to the improvement of film thickness uniformity.

  More specifically, the brightener referred to here is a nonionic (nonionic) surfactant that has a hydrophilic group that does not ionize in water, and is therefore affected by the hardness of the water and the electrolyte. It is difficult to use in combination with all other surfactants. Nonionic surfactants are classified into ester type, ether type, ester / ether type and others according to their structure. The tin plating solution according to the present invention includes higher alcohols, alkylphenols, fatty acids, amines, alkylenediamines, fatty acids. It is preferable to use one or more of amide, sulfonamide, polyhydric alcohol, and polyoxyalkylene adduct of glucooxide.

  A cationic (cationic) surfactant is a surfactant that has a property of ionizing a portion with a hydrophobic group in water into a cation. Therefore, it is strongly adsorbed on a negatively charged solid surface. It has the property to do. Specific examples of the cationic (cationic) surfactant that can be used in the tin plating solution according to the present invention include lauryl trimethyl ammonium salt, cetyl trimethyl ammonium salt, stearyl trimethyl ammonium salt, lauryl dimethyl ethyl ammonium salt, octade Cenyldimethyl-ethylammonium salt, lauryldimethylammonium betaine, stearyldimethylammonium betaine, dimethyl-benzyllaurylammonium salt, cetyldimethylbenzylammonium salt, octadecyldimethylbenzylammonium salt, trimethylbenzylammonium salt, triethylbenzylammonium salt, hexadecylbililine Dinium salt, lauryl biridinium salt, dodecyl picolinium salt, lauryl imidazolinium salt, olei Imidazolinium salts, stearylamine acetate, laurylamine acetate, it is preferable to use one or two or more one of octadecylamine acetate.

  Furthermore, an amphoteric surfactant is a surfactant that exhibits properties of an anionic surfactant in an alkaline region and properties of a cationic surfactant in an acidic region when dissolved in water. Specifically, the amphoteric surfactant that can be used in the tin plating solution according to the present invention may be one or more selected from alkylcarboxybetaine type, alkylaminocarboxylic acid type, and alkylimidazoline type. preferable.

  Among the surfactants as the brightener, it is most preferable to use either lauryldimethylaminoacetic acid betaine or polyoxyethylene lauryl ether. This is because these surfactants are excellent in stability in a tin plating solution, have a high effect of improving the solution life as a tin plating solution, and also have a high effect of obtaining film thickness uniformity of the formed plating film.

  And when the concentration in the case where the surfactant is included as a brightener in the tin plating solution is less than 0.1 g / L, the effect of smoothing the tin plating layer and improving the film thickness uniformity can be obtained. I can't. On the other hand, even if the brightener concentration exceeds 30 g / L, neither the smoothing effect of the tin plating layer nor the effect of improving the film thickness uniformity is improved further.

Embodiment of Tin Plating Method: The tin plating method using the tin plating solution according to the present invention is preferably electrolyzed under a bath temperature condition of 10 ° C to 40 ° C. What is characteristic of this plating method is that the plating operation can be performed in a bath temperature range of 10 ° C to 40 ° C. When the bath temperature is less than 10 ° C., the built-in strain is high and coarse tin plating crystals are precipitated, making it difficult to obtain a tin plating layer that is smooth and excellent in film thickness uniformity. On the other hand, when the bath temperature is higher than 40 ° C., the evaporation of the plating solution becomes noticeable, the composition variation of the tin plating solution is severe, and the solution life is shortened.

  The conventional tin plating solution lacks solution stability as a plating solution and has a short solution life. Therefore, the plating operation has to be performed at a bath temperature of about room temperature. In contrast, by using the tin plating solution according to the present invention, a tin plating operation in a high temperature range where the bath temperature exceeds 30 ° C. becomes possible. By performing the plating operation at a bath temperature of 30 ° C to 40 ° C, moderate evaporation of the plating solution moisture occurs and the amount of plating waste solution is reduced within a range that does not degrade the quality of the tin plating solution. This makes it possible to reduce the wastewater treatment load.

The current density at this ^time, it is preferable to employ a range of ^{0.05A / dm 2 ~0.5A / dm 2} . When the current density is less than 0.05 A / dm ² , the deposition rate of tin is naturally slow, and industrial productivity is not satisfied. On the other hand, when the current density exceeding 0.5 A / dm ² is employed, the smoothness of the tin plating film is impaired.

Embodiment of Method for Adjusting Tin Plating Solution: The method for adjusting a tin plating solution according to the present invention is characterized by being adjusted by the following procedures A and B. This tin plating solution preparation method is characterized in that a tin salt is added to a neutral to alkaline aqueous solution containing a chelating agent to form a tin chelate complex.

In the step A), water, a pH adjuster, and a chelating agent are mixed to obtain a premixed solution having a pH value of 6-12. Since the types and contents of the “pH adjusting agent” and “chelating agent” mentioned here have been described above, the description here is omitted to avoid redundant description. Therefore, the adjustment procedure will be mainly described.

  That is, a pH adjusting agent and a chelating agent are added to a predetermined amount of water having a purity such as ion-exchanged water or pure water, and sufficiently stirred and mixed. There is no strict restriction on the order of adding the pH adjusting agent and the chelating agent at this time. However, when using sodium hydroxide particles, it is common to first dissolve sodium hydroxide particles that take a certain amount of time to dissolve, and then add a chelating agent. Examples of the pH adjuster here include an alkaline pH adjuster and an acidic pH adjuster as described above. Therefore, although there is no restriction | limiting in particular regarding these addition orders, etc., it is preferable to add in order of an alkaline pH adjuster and an acidic pH adjuster. The alkaline pH adjuster promotes ring opening of the chelating agent so that chelation between the chelating agent and tin ions is facilitated. Therefore, after the ring opening of the chelating agent, tin chelate is generated from the neutral region to the weak alkaline region, with the pH value of the plating solution in the middle of adjustment once adjusted to the alkaline region with the acidic pH adjuster in the range of 6-12 This is because it is preferably stabilized.

  In the step B), a tin salt is added to the preconditioning solution, and the tin content is added to a concentration of 5 g / L to 30 g / L and stirred sufficiently to form a tin chelate complex and a tin plating solution. To do. At this time, tin plating according to the present invention having a basic configuration is performed by adding a tin salt to the preliminary mixed solution so that the concentration is 10 g / L to 30 g / L in terms of tin, and sufficiently stirring and mixing. Liquid adjustment is complete. The adjustment process of the tin plating solution described above is premised on being performed at room temperature. Thereafter, it is also desirable to additionally provide the following steps.

  It is also preferable to add a step of adding an antioxidant to the tin plating solution prepared as described above. The antioxidant is as described above, and is added so that the concentration of the antioxidant in the tin plating solution is 0.1 g / L to 30 g / L. There is no particular limitation on the method of addition.

  Moreover, when the pH value of the tin plating solution obtained by the above-mentioned process deviates from an appropriate range, using the above-described acidic pH adjuster for fine adjustment, the plating solution pH value is in the range of 4 to 10, More preferably, a pH fine adjustment step in which the pH value is in the range of 6 to 8 is preferably provided. The acidic pH adjuster for fine adjustment mentioned here includes the above-described alkaline pH adjuster for fine adjustment and the acidic pH adjuster for fine adjustment.

  In the tin plating solution according to the present invention, if it is necessary to further stabilize the energized state when electrolyzing the tin plating solution, to increase the current efficiency of tin deposition, and to increase the productivity, a conductive salt is subsequently added. It is preferable to provide a step of additionally adding. In this case, the conductive salt preferably contains one or more selected from the above-mentioned sodium sulfate and ammonium sulfate so as to have a concentration of 1 g / L to 150 g / L.

  Furthermore, in the tin plating solution according to the present invention, it is also preferable to provide a subsequent brightener addition step in order to smooth the tin plating layer obtained by electrolyzing the tin plating solution and improve the film thickness uniformity. . The brightener referred to herein may contain one or more selected from the above-mentioned nonionic surfactants, cationic surfactants, and amphoteric surfactants so as to have a concentration of 0.1 g / L to 30 g / L. preferable.

Embodiments of Chip Parts: The above-described tin plating solution according to the present invention includes chip-type multilayer ceramic capacitors, chip-type ceramic coils, chip-type ceramic thermistors, inductors, varistors, resistors that are frequently used among electronic parts. It is suitable for forming a tin plating layer of a chip part such as a vessel.

  In this example, a tin plating solution was prepared through the following steps I to V.

Step I: Sodium gluconate as a chelating agent was added to ion-exchanged water to dissolve granular sodium hydroxide as an alkaline pH adjuster. Further, 70 wt% methanesulfonic acid was added as an acidic pH adjuster to obtain a pH 12 premixed solution.

Step II: Tin methanesulfonate was added to the premixed solution to perform a chelation reaction to form a tin chelate complex, thereby obtaining a tin plating solution having a basic composition.

Step III: In this step, sodium hydroxide was added as a fine-tuning alkaline pH adjusting agent among the fine-tuning pH adjusting agents so that the final tin plating solution pH was 4.0.

Step IV: Ascorbic acid as an antioxidant was added to the tin plating solution and mixed and stirred.

Step V: Subsequently, lauryldimethylaminoacetic acid betaine was added as a brightener and mixed and stirred. As a result, a tin plating solution having the following composition was obtained.

(Tin plating solution composition)
Tin methanesulfonate (tin conversion): 14g / L
Sodium hydroxide: 42 g / L
Sodium gluconate: 120 g / L
Methanesulfonic acid: 135 g / L
Ascorbic acid: 3 g / L
Lauryldimethylaminoacetic acid betaine: 1 g / L
pH: 4.0

(Evaluation of long-term storage stability of tin plating solution)
The tin plating solution was stored at room temperature in an air atmosphere. As a result, sludge was not generated even after 365 days. The tin plating solution did not generate sludge even after 365 days, even when sodium hydroxide was added to adjust the pH value to 10. Even when the liquid temperature was 40 ° C., sludge was not generated under the same conditions.

(Observation of tin plating layer)
Using the tin plating solution, a nickel layer having a thickness of 2 μm is provided on the surface of a copper external electrode in a 2012 size (2 mm × 1.2 mm) multilayer ceramic capacitor, and a current density of 0.1 A / min is provided on the surface of the nickel layer. Electrolysis was performed under the conditions of dm ² and a bath temperature of 30 ° C. to form a tin plating layer having a thickness of 5 μm, which was used as a test sample. And the surface of this tin plating layer was observed with SEM (scanning electron microscope), and the observation image was shown in FIG. As is clear from comparison with the comparative example, no abnormal precipitation was observed, and a uniform surface coating was achieved.

(Solder wettability evaluation)
In the case of a tin plating layer formed on the surface of an external electrode or the like of a multilayer ceramic capacitor, solder wettability is very important when considering that these chip components are surface-mounted on a printed wiring board or the like. Here, a 20% rosin-isopropanol solution is applied as a flux to the test sample, and a solder paste equilibrium method using SWET-2100 (solder bath temperature 215 ° C., 6/4 solder) manufactured by Tarchin Kester Co., Ltd. The test was performed in (rapid heating mode). Here, a pressure cooker test (2 atm, 105 ° C., 100% RH, 4 hours) was performed on the test sample, and the characteristics were evaluated before and after that. Showed wetting.

  The above Example 1 is compared with Comparative Example 1 described later. Therefore, Table 1 summarizes the tin plating solution adjustment procedure of Comparative Example 1 and Example 1 and the presence / absence of sludge generation and solder wettability.

  In this example, through steps I to V similar to those in Example 1, ion-exchanged water was mixed with sodium gluconate as a chelating agent, sodium hydroxide as an alkaline pH adjusting agent, and methanesulfone as an acidic pH adjusting agent. Mixing in order of acid to make a pH 12 premixed solution, where there is a tin salt, tin methanesulfonate, an alkaline pH adjuster for fine adjustment, sodium hydroxide, an antioxidant, ascorbic acid, a brightener, lauryl Dimethylaminoacetic acid betaine was added in this order to prepare a tin plating solution having the following composition.

(Tin plating solution composition)
Tin methanesulfonate (tin conversion): 20g / L
Sodium hydroxide: 31 g / L
Sodium gluconate: 150 g / L
Methanesulfonic acid: 68 g / L
Ascorbic acid: 3 g / L
Lauryldimethylaminoacetic acid betaine: 1 g / L
pH: 6.0

(Evaluation of long-term storage stability of tin plating solution)
The tin plating solution was stored at room temperature in an air atmosphere. As a result, sludge was not generated even after 365 days. In the tin plating solution, even when sulfuric acid or sodium hydroxide was added to change the pH value in the range of 4 to 10, no sludge was generated even after 365 days. Even when the liquid temperature was 40 ° C., sludge was not generated under the same conditions.

(Observation of tin plating layer)
The surface state was observed using SEM in the same manner as in Example 1, but it had a very good uniform surface. Since this observation image is the same as in Example 1, the description is omitted.

(Solder wettability evaluation)
The characteristics were evaluated before and after the pressure cooker test in the same manner as in Example 1, and all showed good solder wetting with a zero cross time of 2 seconds or less.

  The above Example 2 is compared with Comparative Example 2 described later. Therefore, Table 2 summarizes the tin plating solution adjustment procedures of Comparative Example 2 and Example 2 and the presence / absence of sludge generation and solder wettability.

  In this example, through steps I to V similar to those in Example 1, ion-exchanged water was mixed with sodium gluconate as a chelating agent, sodium hydroxide as an alkaline pH adjusting agent, and methanesulfone as an acidic pH adjusting agent. Mixing in the order of acids to make a premixed solution of pH 12, where there are tin methane sulfonate, tin salt, sodium hydroxide, alkaline pH adjuster for fine adjustment, ascorbic acid, antioxidant, brightener By adding lauryldimethylaminoacetic acid betaine in this order, a tin plating solution having the following composition was prepared.

(Tin plating solution composition)
Tin methanesulfonate (tin conversion): 20g / L
Sodium hydroxide: 35 g / L
Sodium gluconate: 150 g / L
Methanesulfonic acid: 68 g / L
Ascorbic acid: 3 g / L
Lauryldimethylaminoacetic acid betaine: 1 g / L
pH: 8.0

(Evaluation of long-term storage stability of tin plating solution)
The tin plating solution was stored at room temperature in an air atmosphere. As a result, sludge was not generated even after 365 days. Even when the liquid temperature was 40 ° C., sludge was not generated under the same conditions.

(Observation of tin plating layer)
The surface state was observed using SEM in the same manner as in Example 1, but it had a very good uniform surface. Since this observation image is the same as in Example 1, the description is omitted.

(Solder wettability evaluation)
The characteristics were evaluated before and after the pressure cooker test in the same manner as in Example 1, and all showed good solder wetting with a zero cross time of 2 seconds or less.

  The above Example 3 is contrasted with Comparative Example 3 described later. Therefore, Table 3 summarizes the tin plating solution adjustment procedure of Comparative Example 3 and Example 3 and the presence / absence of sludge generation, solder wettability, and the like.

  In this example, a tin plating solution having the following composition was prepared through steps I to V similar to those in example 1. The difference was that citric acid was used instead of sodium gluconate as a chelating agent. That is, the ion-exchanged water is mixed with citric acid, which is a chelating agent, sodium hydroxide, which is an alkaline pH adjuster, and methanesulfonic acid, which is an acidic pH adjuster, in this order to obtain a premixed solution having a pH of 6.0. A tin plating solution was prepared by adding tin methanesulfonate, a tin salt, sodium hydroxide as an alkaline pH adjuster for fine adjustment, ascorbic acid, an antioxidant, and betaine, lauryldimethylaminoacetate, a brightener. .

(Tin plating solution composition)
Tin methanesulfonate (tin conversion): 20g / L
Sodium hydroxide: 31 g / L
Citric acid: 150 g / L
Methanesulfonic acid: 68 g / L
Ascorbic acid: 3 g / L
Lauryldimethylaminoacetic acid betaine: 1 g / L
pH: 6.0

(Evaluation of long-term storage stability of tin plating solution)
The tin plating solution was stored at room temperature in an air atmosphere. As a result, sludge was not generated even after 365 days. Even when the liquid temperature was 40 ° C., sludge was not generated under the same conditions.

(Appearance of tin plating layer)
In the same manner as in Example 1, the surface state was observed using SEM. And the surface of this tin plating layer was observed with SEM (scanning electron microscope), and the observation image was shown in FIG. As is clear from comparison with the comparative example, no abnormal precipitation was observed, and a uniform surface coating was achieved.

(Solder wettability evaluation)
The characteristics were evaluated before and after the pressure cooker test in the same manner as in Example 1, and all showed good solder wetting at zero cross time seconds or less.

  The above Example 4 is contrasted with Comparative Example 4 described later. Therefore, Table 4 summarizes the tin plating solution adjustment procedure of Comparative Example 4 and Example 4 and the presence / absence of sludge generation, solder wettability, and the like.

  In this example, a tin plating solution having the following composition was prepared through steps I to V similar to those in example 1. The difference was that polyoxyethylene lauryl ether was used in place of the brightener lauryldimethylaminoacetic acid betaine. That is, ion-exchanged water is mixed with sodium gluconate, which is a chelating agent, sodium hydroxide, which is an alkaline pH adjuster, and methanesulfonic acid, which is an acidic pH adjuster, in this order to prepare a premixed solution of pH 12, where A tin plating solution was prepared by adding tin methanesulfonate, a salt, sodium hydroxide, an alkaline pH adjuster for fine adjustment, ascorbic acid, an antioxidant, and polyoxyethylene lauryl ether, a brightener, in that order. .

(Tin plating solution composition)
Tin methanesulfonate (tin conversion): 14g / L
Sodium hydroxide: 42 g / L
Sodium gluconate: 120 g / L
Methanesulfonic acid: 135 g / L
Ascorbic acid: 3 g / L
Polyoxyethylene lauryl ether: 1 g / L
pH: 4.0

(Evaluation of long-term storage stability of tin plating solution)
The tin plating solution was stored at room temperature in an air atmosphere. As a result, sludge was not generated even after 365 days. Even when the liquid temperature was 40 ° C., sludge was not generated under the same conditions.

(Observation of tin plating layer)
The surface state was observed using SEM in the same manner as in Example 1, but it had a very good uniform surface. Since this observation image is the same as in Example 1, the description is omitted.

(Solder wettability evaluation)
The characteristics were evaluated before and after the pressure cooker test in the same manner as in Example 1, and all showed good solder wetting with a zero cross time of 2 seconds or less.

  The above Example 5 is compared with Comparative Example 5 described later. Therefore, Table 5 summarizes the tin plating solution adjustment procedure of Comparative Example 5 and Example 5 and the presence / absence of sludge generation, solder wettability, and the like.

  In this example, a tin plating solution having the following composition was prepared through steps I to V similar to those in example 1. The difference was that tin sulfate was used in place of the tin salt tin methanesulfonate, and polyoxyethylene lauryl ether was used in place of the brightener lauryldimethylaminoacetic acid betaine. That is, ion-exchanged water is mixed with sodium gluconate, which is a chelating agent, sodium hydroxide, which is an alkaline pH adjuster, and methanesulfonic acid, which is an acidic pH adjuster, in this order to prepare a premixed solution of pH 12, where A tin plating solution was prepared by adding tin sulfate as a salt, sodium hydroxide as an alkaline pH adjuster for fine adjustment, ascorbic acid as an antioxidant, and polyoxyethylene lauryl ether as a brightener in this order.

(Tin plating solution composition)
Tin sulfate (tin conversion): 14g / L
Sodium hydroxide: 42 g / L
Sodium gluconate: 120 g / L
Methanesulfonic acid: 135 g / L
Ascorbic acid: 3 g / L
Polyoxyethylene lauryl ether: 1 g / L
pH: 4.0

(Evaluation of long-term storage stability of tin plating solution)
The tin plating solution was stored at room temperature in an air atmosphere. As a result, sludge was not generated even after 365 days. Even when the liquid temperature was 40 ° C., sludge was not generated under the same conditions.

(Appearance of tin plating layer)
In the same manner as in Example 1, the surface state was observed using SEM. And the surface of this tin plating layer was observed with SEM (scanning electron microscope), and the observation image was shown in FIG. As is clear from comparison with the comparative example, no abnormal precipitation was observed, and a uniform surface coating was achieved.

(Solder wettability evaluation)
The characteristics were evaluated before and after the pressure cooker test in the same manner as in Example 1, and all showed good solder wetting with a zero cross time of 2 seconds or less.

  The above Example 6 is compared with Comparative Example 6 described later. Accordingly, Table 6 summarizes the tin plating solution adjustment procedure of Comparative Example 6 and Example 6 and the presence / absence of sludge generation and solder wettability.

In this example, a tin plating solution having the following composition was prepared through steps I to V similar to those in example 1. The difference was that catechol was used in place of the antioxidant ascorbic acid, and polyoxyethylene lauryl ether was used in place of the brightener lauryldimethylaminoacetic acid betaine. That is, ion-exchanged water is mixed with sodium gluconate, which is a chelating agent, sodium hydroxide, which is an alkaline pH adjuster, and methanesulfonic acid, which is an acidic pH adjuster, in this order to prepare a premixed solution of pH 12, where A tin plating solution was prepared by adding tin methanesulfonate as a salt, sodium hydroxide as an alkaline pH adjuster for fine adjustment, catechol as an antioxidant, and polyoxyethylene lauryl ether as a brightener in this order.

(Tin plating solution composition)
Tin methanesulfonate (tin conversion): 14g / L
Sodium hydroxide: 42 g / L
Sodium gluconate: 120 g / L
Methanesulfonic acid: 135 g / L
Catechol: 3g / L
Polyoxyethylene lauryl ether: 1 g / L
pH: 4.0

(Evaluation of long-term storage stability of tin plating solution)
The tin plating solution was stored at room temperature in an air atmosphere. As a result, sludge was not generated even after 365 days. Even when the liquid temperature was 40 ° C., sludge was not generated under the same conditions.

(Observation of tin plating layer)
The surface state was observed using SEM in the same manner as in Example 1, but it had a very good uniform surface. Since this observation image is the same as in Example 1, the description is omitted.

(Solder wettability evaluation)
The characteristics were evaluated before and after the pressure cooker test in the same manner as in Example 1, and all showed good solder wetting with a zero cross time of 2 seconds or less.

  The above Example 7 is compared with Comparative Example 7 described later. Therefore, Table 7 summarizes the tin plating solution adjustment procedure of Comparative Example 7 and Example 7 and the presence / absence of sludge generation and solder wettability.

  In this example, a tin plating solution having the following composition was prepared through steps I to V similar to those in example 1. The difference is that ascorbic acid, which is an antioxidant, is added, and at the same time, sodium sulfate, which is a conductive salt, is added. That is, ion-exchanged water is mixed with sodium gluconate, which is a chelating agent, sodium hydroxide, which is an alkaline pH adjuster, and methanesulfonic acid, which is an acidic pH adjuster, in this order to prepare a premixed solution of pH 12, where Add sodium methanesulfonate, which is a salt, sodium hydroxide, which is an alkaline pH adjuster for fine adjustment, ascorbic acid, which is an antioxidant, sodium sulfate, which is a conductive salt, and lauryldimethylaminoacetic acid betaine, which is a brightener. The tin plating solution was adjusted.

(Tin plating solution composition)
Tin methanesulfonate (tin conversion): 20g / L
Sodium hydroxide: 31 g / L
Sodium gluconate: 150 g / L
Methanesulfonic acid: 68 g / L
Ascorbic acid: 3 g / L
Sodium sulfate: 70 g / L
Lauryldimethylaminoacetic acid betaine: 1 g / L
pH: 6.0

(Evaluation of long-term storage stability of tin plating solution)
The tin plating solution was stored at room temperature in an air atmosphere. As a result, sludge was not generated even after 365 days. Even when the liquid temperature was 40 ° C., sludge was not generated under the same conditions.

(Observation of tin plating layer)
The surface state was observed using SEM in the same manner as in Example 1, but it had a very good uniform surface. Since this observation image is the same as in Example 1, the description is omitted.

(Solder wettability evaluation)
The characteristics were evaluated before and after the pressure cooker test in the same manner as in Example 1, and all showed good solder wetting with a zero cross time of 2 seconds or less.

  The above Example 8 is compared with Comparative Example 8 described later. Therefore, Table 8 summarizes the tin plating solution adjustment procedure of Comparative Example 8 and Example 8 and the presence / absence of sludge generation and solder wettability.

Comparative example

[Comparative Example 1]
This comparative example 1 changed the tin plating solution adjustment order of Example 1, and adjusted the tin plating solution through the following i) process-process v).

i) Step: Sodium gluconate as a chelating agent was added to ion-exchanged water and mixed in the order of 70 wt% methanesulfonic acid as an acidic pH adjuster to prepare a strongly acidic premixed solution having a pH of 1 or less.

Step ii): Tin methanesulfonate was added to the premixed solution and mixed well.

Step iii): Granular sodium hydroxide as an alkaline pH adjuster was dissolved in a premixed solution to which tin methanesulfonate was added to obtain a tin plating solution having a basic structure.

Step iv): Ascorbic acid as an antioxidant was added to the tin plating solution and mixed and stirred.

v) Step: Subsequently, lauryldimethylaminoacetic acid betaine was added as a brightener and mixed and stirred. As a result, a tin plating solution having the following composition was obtained.

(Tin plating solution composition)
Tin methanesulfonate (tin conversion): 14g / L
Sodium hydroxide: 42 g / L
Sodium gluconate: 120 g / L
Methanesulfonic acid: 135 g / L
Ascorbic acid: 3 g / L
Lauryldimethylaminoacetic acid betaine: 1 g / L
pH: 4.0

(Evaluation of long-term storage stability of tin plating solution)
The tin plating solution was stored at room temperature in an air atmosphere. As a result, generation of sludge was observed after 2 days from bathing.

(Appearance of tin plating layer)
In the same manner as in Example 1, the surface state was observed using SEM. And the surface of this tin plating layer was observed with SEM (scanning electron microscope), and the observation image was shown in FIG. As apparent from comparison with Example 1, it can be seen that abnormal precipitation was observed on the surface of the tin plating, and a uniform surface coating could not be formed. The tin plating layer observed here was formed using a tin plating solution in which sludge was generated.

(Solder wettability evaluation)
The characteristics were evaluated before and after the pressure cooker test in the same manner as in Example 1. However, in order to show good solder wettability, a zero cross time of 3 seconds or more was required.

  In order to compare the above Comparative Example 1 with Example 1, they were simultaneously shown in Table 1 so that the tin plating solution adjustment procedure, the presence / absence of sludge generation, and the solder wettability can be easily compared.

[Comparative Example 2]
In Comparative Example 2, the same steps i to v as in Comparative Example 1 were followed, and the ion-exchanged water was mixed in the order of sodium gluconate, which is a chelating agent, and methanesulfonic acid, which is an acidic pH adjuster, to a pH of 1 or less. A strongly acidic premixed solution is added in this order: tin methanesulfonate tin, alkaline pH adjuster sodium hydroxide, antioxidant ascorbic acid, brightener lauryldimethylaminoacetic acid betaine Then, a tin plating solution having the following composition was prepared.

(Tin plating solution composition)
Tin methanesulfonate (tin conversion): 20g / L
Sodium hydroxide: 46 g / L
Sodium gluconate: 150 g / L
Methanesulfonic acid: 135 g / L
Ascorbic acid: 3 g / L
Lauryldimethylaminoacetic acid betaine: 1 g / L
pH: 6.0

(Evaluation of long-term storage stability of tin plating solution)
The tin plating solution was stored at room temperature in an air atmosphere. As a result, generation of sludge was observed after 1 day from the bathing.

(Observation of tin plating layer)
The surface state was observed using SEM in the same manner as in Example 1. However, as in Comparative Example 1, abnormal precipitation was observed on the tin plating surface, and a uniform surface coating could not be formed. I understood. Since this observation image is the same as that of Comparative Example 1, the description is omitted. The tin plating layer observed here was formed using a tin plating solution in which sludge was generated.

(Solder wettability evaluation)
The characteristics were evaluated before and after the pressure cooker test in the same manner as in Example 1. However, in order to show good solder wettability, a zero cross time of 3 seconds or more was required.

  In order to compare the above Comparative Example 2 and Example 2, they were simultaneously shown in Table 2 so that the tin plating solution adjustment procedure, the presence or absence of sludge generation, and the solder wettability can be easily compared.

[Comparative Example 3]
This comparative example 3 is mixed with ion-exchanged water in the order of sodium gluconate, which is a chelating agent, and methanesulfonic acid, which is an acidic pH adjuster, in the order of steps i to v similar to those of comparative example 1. A strongly acidic premixed solution is added in this order: tin methanesulfonate tin, alkaline pH adjuster sodium hydroxide, antioxidant ascorbic acid, brightener lauryldimethylaminoacetic acid betaine Then, a tin plating solution having the following composition was prepared.

(Tin plating solution composition)
Tin methanesulfonate (tin conversion): 20g / L
Sodium hydroxide: 50 g / L
Sodium gluconate: 150 g / L
Methanesulfonic acid: 135 g / L
Ascorbic acid: 3 g / L
Lauryldimethylaminoacetic acid betaine: 1 g / L
pH: 8.0

(Evaluation of long-term storage stability of tin plating solution)
The tin plating solution was stored at room temperature in an air atmosphere. As a result, the generation of sludge was already seen during bathing.

(Observation of tin plating layer)
The surface state was observed using SEM in the same manner as in Example 1. However, as in Comparative Example 1, abnormal precipitation was observed on the tin plating surface, and a uniform surface coating could not be formed. I understood. Since this observation image is the same as that of Comparative Example 1, the description is omitted. The tin plating layer observed here was formed using a tin plating solution in which sludge was generated.

(Solder wettability evaluation)
The characteristics were evaluated before and after the pressure cooker test in the same manner as in Example 1. However, in order to show good solder wettability, a zero cross time of 3 seconds or more was required.

  In order to compare the above Comparative Example 3 with Example 3, they were simultaneously listed in Table 3 so that each tin plating solution adjustment procedure, the presence or absence of sludge generation, and the solder wettability can be easily compared.

[Comparative Example 4]
This comparative example 4 prepared the tin plating solution of the following compositions through the i process-v process similar to the comparative example 1. FIG. The difference was that citric acid was used instead of sodium gluconate as a chelating agent. That is, citric acid, which is a chelating agent, and methanesulfonic acid, which is an acidic pH adjusting agent, are mixed with ion-exchanged water in this order to form a strongly acidic premixed liquid having a pH of 1 or less. Then, sodium hydroxide as an alkaline pH adjuster, ascorbic acid as an antioxidant, and betaine lauryldimethylaminoacetate as a brightener were added in this order to prepare a tin plating solution having the following composition.

(Tin plating solution composition)
Tin methanesulfonate (tin conversion): 20g / L
Sodium hydroxide: 46 g / L
Citric acid: 150 g / L
Methanesulfonic acid: 135 g / L
Ascorbic acid: 3 g / L
Lauryldimethylaminoacetic acid betaine: 1 g / L
pH: 6.0

(Evaluation of long-term storage stability of tin plating solution)
The tin plating solution was stored at room temperature in an air atmosphere. As a result, the generation of sludge was already seen during bathing.

(Appearance of tin plating layer)
In the same manner as in Example 1, the surface state was observed using SEM. And the surface of this tin plating layer was observed with SEM (scanning electron microscope), and the observation image was shown in FIG. As apparent from comparison with Example 4, it can be seen that abnormal precipitation was observed on the surface of the tin plating, and a uniform surface coating could not be formed. The tin plating layer observed here was formed using a tin plating solution in which sludge was generated.

(Solder wettability evaluation)
The characteristics were evaluated before and after the pressure cooker test in the same manner as in Example 1. However, in order to show good solder wettability, a zero cross time of 3 seconds or more was required.

  In order to compare the above Comparative Example 4 and Example 4, they are listed in Table 4 so that each tin plating solution adjustment procedure, sludge generation, and solder wettability can be easily compared.

[Comparative Example 5]
This comparative example 5 prepared the tin plating solution of the following compositions through the i process-v process similar to the comparative example 1. FIG. The difference was that polyoxyethylene lauryl ether was used in place of the brightener lauryldimethylaminoacetic acid betaine. That is, citric acid, which is a chelating agent, and methanesulfonic acid, which is an acidic pH adjusting agent, are mixed with ion-exchanged water in this order to form a strongly acidic premixed liquid having a pH of 1 or less. Then, sodium hydroxide as an alkaline pH adjuster, ascorbic acid as an antioxidant, and polyoxyethylene lauryl ether as a brightener were added in this order to prepare a tin plating solution having the following composition.

(Tin plating solution composition)
Tin methanesulfonate (tin conversion): 14g / L
Sodium hydroxide: 42 g / L
Sodium gluconate: 120 g / L
Methanesulfonic acid: 135 g / L
Ascorbic acid: 3 g / L
Polyoxyethylene lauryl ether: 1 g / L
pH: 4.0

(Evaluation of long-term storage stability of tin plating solution)
The tin plating solution was stored at room temperature in an air atmosphere. As a result, generation of sludge was observed after 2 days from bathing.

(Observation of tin plating layer)
The surface state was observed using SEM in the same manner as in Example 1. However, as in Comparative Example 1, abnormal precipitation was observed on the tin plating surface, and a uniform surface coating could not be formed. I understood. Since this observation image is the same as that of Comparative Example 1, the description is omitted. The tin plating layer observed here was formed using a tin plating solution in which sludge was generated.

(Solder wettability evaluation)
The characteristics were evaluated before and after the pressure cooker test in the same manner as in Example 1. However, in order to show good solder wettability, a zero cross time of 3 seconds or more was required.

  In order to compare the above Comparative Example 5 with Example 5, they are listed in Table 5 at the same time so that each tin plating solution adjustment procedure, the presence or absence of sludge generation, and the solder wettability can be easily compared.

[Comparative Example 6]
This comparative example 6 prepared the tin plating solution of the following compositions through the i process-v process similar to the comparative example 1. FIG. The difference was that tin sulfate was used in place of the tin salt tin methanesulfonate, and polyoxyethylene lauryl ether was used in place of the brightener lauryldimethylaminoacetic acid betaine. That is, in ion-exchanged water, sodium gluconate, which is a chelating agent, and methanesulfonic acid, which is an acidic pH adjuster, are mixed in this order to form a strongly acidic premixed solution having a pH of 1 or less. Sodium hydroxide as an alkaline pH adjuster, ascorbic acid as an antioxidant, and polyoxyethylene lauryl ether as a brightener were added in this order to prepare a tin plating solution having the following composition.

(Tin plating solution composition)
Tin sulfate (tin conversion): 14g / L
Sodium hydroxide: 42 g / L
Sodium gluconate: 120 g / L
Methanesulfonic acid: 135 g / L
Ascorbic acid: 3 g / L
Polyoxyethylene lauryl ether: 1 g / L
pH: 4.0

(Evaluation of long-term storage stability of tin plating solution)
The tin plating solution was stored at room temperature in an air atmosphere. As a result, generation of sludge was observed after 2 days from bathing.

(Appearance of tin plating layer)
In the same manner as in Example 1, the surface state was observed using SEM. And the surface of this tin plating layer was observed with SEM (scanning electron microscope), and the observation image was shown in FIG. As apparent from comparison with Example 6, it can be seen that abnormal precipitation was observed on the surface of the tin plating, and a uniform surface coating could not be formed. The tin plating layer observed here was formed using a tin plating solution in which sludge was generated.

(Solder wettability evaluation)
The characteristics were evaluated before and after the pressure cooker test in the same manner as in Example 1. However, in order to show good solder wettability, a zero cross time of 3 seconds or more was required.

  In order to compare the above Comparative Example 6 with Example 6, they were simultaneously shown in Table 6 so that each tin plating solution adjustment procedure, the presence or absence of sludge generation, and the solder wettability can be easily compared.

[Comparative Example 7]
This comparative example 7 prepared the tin plating solution of the following compositions through the i process-v process similar to the comparative example 1. FIG. The difference was that catechol was used in place of the antioxidant ascorbic acid, and polyoxyethylene lauryl ether was used in place of the brightener lauryldimethylaminoacetic acid betaine. That is, ion-exchanged water is mixed with sodium gluconate, which is a chelating agent, and methanesulfonic acid, which is an acidic pH adjuster, in this order to form a strongly acidic premixed liquid having a pH of 1 or less. Tin, sodium hydroxide as an alkaline pH adjuster, catechol as an antioxidant, and polyoxyethylene lauryl ether as a brightener were added in this order to prepare a tin plating solution having the following composition.

(Tin plating solution composition)
Tin methanesulfonate (tin conversion): 14g / L
Sodium hydroxide: 42 g / L
Sodium gluconate: 120 g / L
Methanesulfonic acid: 135 g / L
Catechol: 3g / L
Polyoxyethylene lauryl ether: 1 g / L
pH: 4.0

(Evaluation of long-term storage stability of tin plating solution)
The tin plating solution was stored at room temperature in an air atmosphere. As a result, generation of sludge was observed after 2 days from bathing.

(Observation of tin plating layer)
The surface state was observed using SEM in the same manner as in Example 1. However, as in Comparative Example 1, abnormal precipitation was observed on the tin plating surface, and a uniform surface coating could not be formed. I understood. Since this observation image is the same as that of Comparative Example 1, the description is omitted. The tin plating layer observed here was formed using a tin plating solution in which sludge was generated.

(Solder wettability evaluation)
The characteristics were evaluated before and after the pressure cooker test in the same manner as in Example 1. However, in order to show good solder wettability, a zero cross time of 3 seconds or more was required.

  In order to compare the comparative example 7 and the example 7, the tin plating solution adjustment procedure, the presence / absence of sludge generation, and the solder wettability are shown in Table 7 at the same time.

[Comparative Example 8]
This comparative example 8 prepared the tin plating solution of the following compositions through the i process-v process similar to the comparative example 1. FIG. The difference is that ascorbic acid, which is an antioxidant, is added, and at the same time, sodium sulfate, which is a conductive salt, is added. That is, ion-exchanged water is mixed with sodium gluconate, which is a chelating agent, and methanesulfonic acid, which is an acidic pH adjuster, in this order to form a strongly acidic premixed liquid having a pH of 1 or less. Add tin, alkaline hydroxide pH adjuster, ascorbic acid antioxidant, sodium sulfate conductive salt, brightener lauryldimethylaminoacetate betaine in this order, It was adjusted.

(Tin plating solution composition)
Tin methanesulfonate (tin conversion): 20g / L
Sodium hydroxide: 46 g / L
Sodium gluconate: 150 g / L
Methanesulfonic acid: 135 g / L
Ascorbic acid: 3 g / L
Sodium sulfate: 70 g / L
Lauryldimethylaminoacetic acid betaine: 1 g / L
pH: 6.0

(Evaluation of long-term storage stability of tin plating solution)
The tin plating solution was stored at room temperature in an air atmosphere. As a result, generation of sludge was observed after 2 days from bathing.

(Observation of tin plating layer)
The surface state was observed using SEM in the same manner as in Example 1. However, as in Comparative Example 1, abnormal precipitation was observed on the tin plating surface, and a uniform surface coating could not be formed. I understood. Since this observation image is the same as that of Comparative Example 1, the description is omitted. The tin plating layer observed here was formed using a tin plating solution in which sludge was generated.

(Solder wettability evaluation)
The characteristics were evaluated before and after the pressure cooker test in the same manner as in Example 1. However, in order to show good solder wettability, a zero cross time of 3 seconds or more was required.

  In order to compare the above Comparative Example 8 and Example 8, they are simultaneously shown in Table 8 so that each tin plating solution adjustment procedure, sludge generation, and solder wettability can be easily compared.

[Comparative Example 9]
This comparative example 9 is the following composition completely different from the above-described comparative examples 1 to 8, and a tin plating solution having a conceivable composition was prepared. Here, the mixing order of the following components was not particularly problematic, and each component was dissolved in water as a solvent so as to have a predetermined concentration, and the pH was adjusted with ammonia water.

(Basic composition of tin plating solution)
Stannous sulfate (in tin equivalent): 25 g / L
Diammonium hydrogen citrate: 95 g / L
Alkylamine type surfactant: 0.1 g / L
Ammonium sulfate: 13 g / L
pH (adjusted with aqueous ammonia): 7.0

(Evaluation of long-term storage stability of tin plating solution)
The tin plating solution was stored at room temperature in an air atmosphere. As a result, generation of sludge was observed after 1 day from the bathing.

[Comparative Example 10]
This comparative example 10 is the following composition completely different from the above-described comparative examples 1 to 8, and a tin plating solution having a conceivable composition was prepared. Here, the mixing order of the following components was not particularly problematic, and each component was dissolved in water as a solvent so as to have a predetermined concentration, and the pH was adjusted with sodium hydroxide.

(Basic composition of tin plating solution)
Stannous sulfamate (in terms of tin): 50 g / L
Malic acid: 450 g / L
Alkylamine type surfactant: 0.1 g / L
pH (adjusted with sodium hydroxide): 6.0

(Evaluation of long-term storage stability of tin plating solution)
The tin plating solution was stored at room temperature in an air atmosphere. As a result, generation of sludge was observed after 5 hours from the bathing.

<Contrast between Example and Comparative Example>
Comparison between Example 1 and Comparative Example 1 As is clear from Table 1, the tin plating solutions of Example 1 and Comparative Example 1 are identical when viewed simply from the composition and pH. What is different is the mixing procedure of the components. That is, in Example 1, sodium gluconate, which is a chelating agent, sodium hydroxide, which is an alkaline pH adjusting agent, and methanesulfonic acid, which is an acidic pH adjusting agent, are added in this order to ion-exchanged water, and the solution pH is set to 12, In addition, tin methanesulfonate tin, which is a tin salt, is added to ensure the production of a tin chelate complex. Then, sodium hydroxide, which is an alkaline pH adjusting agent for fine adjustment, ascorbic acid, which is an antioxidant, and lauryldimethylaminoacetic acid betaine, which is a brightener, are added in this order.

  On the other hand, Comparative Example 1 added ion-exchanged water in the order of sodium gluconate, which is a chelating agent, and methanesulfonic acid, which is an acidic pH adjuster, as a strongly acidic solution having a pH of 1 or less. Some tin methanesulfonate is added. As a conventional method for producing a tin plating solution, a method of adding a tin salt in the acidic region has been adopted. After that, in order to bring the pH of the tin plating solution closer to the neutral range, sodium hydroxide as an alkaline pH adjuster, ascorbic acid as an antioxidant, and lauryldimethylaminoacetic acid betaine as a brightener are added in this order. .

  Thus, Example 1 and Comparative Example 1 differ only in the mixing order of the constituent components, but their solution properties are completely different. Therefore, it can be said that even if the amounts of the constituent components are the same, the manner in which the tin component contained in the tin plating solution exists is completely different. This is supported by the following contents. In the case of Example 1, even when stored in an air atmosphere at room temperature to 40 ° C., no sludge is observed even after 365 days. On the other hand, in the case of Comparative Example 1, generation of sludge was confirmed after only 2 days. Further, in the case of Example 1, even when the pH of the solution is increased to 10 using sodium hydroxide or stored in an air atmosphere at room temperature to 40 ° C., generation of sludge is observed even after 365 days. Absent.

  And in the case of the tin plating solution of Example 1, even after 365 days had passed, even if the tin plating layer of the test sample subjected to the plating test was observed with an SEM, the deposited particles seemed to be spread flatly. The surface is very good and a very good surface is obtained (in the above and the following, this is simply referred to as “uniform surface”). On the other hand, in the case of the tin plating solution of Comparative Example 1, when the generation of sludge is recognized, the surface of the tin plating layer has deposited particles such that the deposited particles are spread flatly and further deposited thereon. This is recognized and cannot be said to be a uniform surface (in the above and the following, such a state is referred to as “abnormal precipitation”).

  Furthermore, regarding the solder wettability, in the case of the tin plating solution of Example 1, it is possible to form a tin plating layer having good solder wettability even after 365 days have elapsed. On the other hand, in the case of the tin plating solution of Comparative Example 1, when the generation of sludge is recognized, the solder wettability deteriorates.

Comparison between Example 2 and Comparative Example 2: The relationship between Example 2 and Comparative Example 2 is basically the same as the relationship between Example 1 and Comparative Example 1. Fundamentally, the mixing procedure of the components is different. However, since the addition amount of methanesulfonic acid which is an acidic pH adjusting agent contained in Example 2 and Comparative Example 2 are different, the final tin plating solution has a pH of 6.0. Thus, the addition amount of the alkaline pH adjuster is also changed.

  That is, the components of the tin plating solution of Example 2 are the same as those of Example 1, and the mixing order is also the same. And the structural component of the tin plating solution of the comparative example 2 is the same as that of the comparative example 1, and the mixing order is also the same. However, Example 2 and Example 1, and Comparative Example 2 and Comparative Example 1 are different from each other in the amount of components as shown in Table 2.

  Thus, Example 2 and Comparative Example 2 differ only in the mixing order of the constituent components, but their solution properties are completely different. Therefore, as in the case of Example 1, it can be said that even though the constituent components are the same, the manner in which the tin component contained in the tin plating solution exists is completely different. This is supported by the following contents. In the case of Example 2, even when stored in an air atmosphere at room temperature to 40 ° C., no sludge is observed even after 365 days. On the other hand, in the case of Comparative Example 2, generation of sludge was confirmed after only 1 day. In the case of Example 2, even when sodium hydroxide is used, the solution pH is arbitrarily changed between 4 and 10, stored in an air atmosphere at room temperature to 40 ° C., after 365 days have elapsed. There is no generation of sludge.

  In the case of the tin plating solution of Example 2, even after 365 days, even if the tin plating layer of the test sample subjected to the plating test was observed with an SEM, a very good uniform surface was obtained. . On the other hand, in the case of the tin plating solution of Comparative Example 2, when the generation of sludge was observed, abnormal precipitation was observed on the surface of the tin plating layer, and it was confirmed that the defective state was apparent.

  Further, regarding the solder wettability, in the case of the tin plating solution of Example 2, it is possible to form a tin plating layer having good solder wettability even after 365 days. On the other hand, in the case of the tin plating solution of Comparative Example 2, when the generation of sludge is recognized, the solder wettability deteriorates.

Comparison between Example 3 and Comparative Example 3 The relationship between Example 3 and Comparative Example 3 is basically the same as the relationship between Example 1 and Comparative Example 1. Fundamentally, the mixing procedure of the components is different. However, in Example 3 and Comparative Example 3, since the addition amount of methanesulfonic acid, which is an acidic pH adjuster contained therein, is different, the final tin plating solution has a pH of 8.0. Thus, the addition amount of the alkaline pH adjuster is also changed.

  That is, the components of the tin plating solution of Example 3 are the same as in Example 1 and the mixing order is also the same. And the structural component of the tin plating solution of the comparative example 3 is the same as that of the comparative example 1, and the mixing order is also the same. However, Example 3 and Example 1, and Comparative Example 3 and Comparative Example 1 are different in the amount of components as shown in Table 3, respectively.

  Thus, Example 3 and Comparative Example 3 differ only in the mixing order of the constituent components, but their solution properties are completely different. Therefore, as in the case of Example 1, it can be said that even if the constituent components are the same, the manner of the presence of the tin component contained therein as the tin plating solution is completely different. This is supported by the following contents. In the case of Example 3, even when stored in an air atmosphere at room temperature to 40 ° C., no sludge is observed even after 365 days. On the other hand, in the case of Comparative Example 3, generation of sludge was already confirmed at the time of bathing.

  In the case of the tin plating solution of Example 3, even after 365 days had passed, a very good uniform surface was obtained even when the tin plating layer of the test sample subjected to the plating test was observed with an SEM. . On the other hand, in the case of the tin plating solution of Comparative Example 3, when the generation of sludge was observed, abnormal precipitation was observed on the surface of the tin plating layer, and it was confirmed that an obvious defective state was obtained.

  Furthermore, regarding the solder wettability, in the case of the tin plating solution of Example 3, it is possible to form a tin plating layer having good solder wettability even after 365 days have elapsed. On the other hand, in the case of the tin plating solution of Comparative Example 3, when the generation of sludge is recognized, the solder wettability deteriorates.

Comparison between Example 4 and Comparative Example 4 In Example 4, citric acid was used in place of sodium gluconate as the chelating agent of Example 1. That is, in Example 4, citric acid as a chelating agent, sodium hydroxide as an alkaline pH adjusting agent, and methanesulfonic acid as an acidic pH adjusting agent were added in this order to ion-exchanged water, and the solution pH was adjusted to 6.0. In addition, tin methanesulfonate, which is a tin salt, is added to ensure the production of a tin chelate complex. Then, sodium hydroxide, which is an alkaline pH adjuster for fine adjustment, ascorbic acid, which is an antioxidant, and betaine lauryldimethylaminoacetate, which is a brightener, are added in this order, and the final tin plating solution has a pH of 6. 0.

  On the other hand, in Comparative Example 4, a citric acid that is a chelating agent and methanesulfonic acid that is an acidic pH adjuster are added to ion-exchanged water in this order to form a strongly acidic solution having a pH of 1 or less, which is a tin salt. Adds tin methanesulfonate. As a conventional method for producing a tin plating solution, a method of adding a tin salt in the acidic region has been adopted. And then, in order to bring the pH of the tin plating solution closer to the neutral range, sodium hydroxide as an alkaline pH adjuster, ascorbic acid as an antioxidant, betaine lauryl dimethylaminoacetate as a brightener are added in this order. The pH of a typical tin plating solution was 6.0. However, in Example 4 and Comparative Example 4, since the addition amount of methanesulfonic acid, which is an acidic pH adjusting agent contained therein, is different, the final tin plating solution has a pH of 6.0. Thus, the addition amount of the alkaline pH adjuster is also changed.

  In Example 4 and Comparative Example 4, the mixing order of the constituent components is merely different, but the solution properties are completely different. Therefore, as in the case of Example 1, it can be said that even if the constituent components are the same, the manner of the presence of the tin component contained therein as the tin plating solution is completely different. This is supported by the following contents. In the case of Example 4, even when stored in an air atmosphere at room temperature to 40 ° C., no sludge is observed even after 365 days. On the other hand, in the case of Comparative Example 4, generation of sludge was already confirmed at the time of bathing.

  In the case of the tin plating solution of Example 4, even after 365 days, even if the tin plating layer of the test sample subjected to the plating test was observed with an SEM, a very good uniform surface was obtained. . On the other hand, in the case of the tin plating solution of Comparative Example 4, when generation of sludge was observed, abnormal precipitation was observed on the surface of the tin plating layer, and it was confirmed that an apparently defective state was obtained.

  Furthermore, regarding the solder wettability, in the case of the tin plating solution of Example 4, it is possible to form a tin plating layer having good solder wettability even after 365 days. On the other hand, in the case of the tin plating solution of Comparative Example 4, when the generation of sludge is recognized, the solder wettability deteriorates.

Comparison of Example 5 and Comparative Example 5 In Example 5, polyoxyethylene lauryl ether was used in place of the lauryl dimethylaminoacetic acid betaine which is the brightener of Example 1. That is, in Example 5, sodium gluconate, which is a chelating agent, sodium hydroxide, which is an alkaline pH adjuster, and methanesulfonic acid, which is an acidic pH adjuster, are added in this order to ion-exchanged water, and the solution pH is set to 12, In addition, tin methanesulfonate tin, which is a tin salt, is added to ensure the production of a tin chelate complex. And then, ascorbic acid as an antioxidant and polyoxyethylene lauryl ether as a brightener were added in this order, and the pH of the final tin plating solution was adjusted to 4.0.

  On the other hand, Comparative Example 5 added ion-exchanged water in the order of sodium gluconate, which is a chelating agent, and methanesulfonic acid, which is an acidic pH adjuster, as a strongly acidic solution having a pH of 1 or less. Some tin methanesulfonate is added. After that, in order to bring the pH of the tin plating solution closer to the neutral region, sodium hydroxide as an alkaline pH adjuster, ascorbic acid as an antioxidant, and polyoxyethylene lauryl ether as a brightener are added in this order. The pH of a typical tin plating solution was 4.0.

  In Example 5 and Comparative Example 5, only the mixing order of the constituent components is different, but the solution properties are completely different. Therefore, as in the case of Example 1, it can be said that even if the constituent components are the same, the manner of the presence of the tin component contained therein as the tin plating solution is completely different. This is supported by the following contents. In the case of Example 5, even when stored in an air atmosphere at room temperature to 40 ° C., no sludge is observed even after 365 days. On the other hand, in the case of the comparative example 5, generation | occurrence | production of sludge was confirmed after only 2 days progress from a bath.

  In the case of the tin plating solution of Example 5, even after 365 days had passed, a very good uniform surface was obtained even when the tin plating layer of the test sample subjected to the plating test was observed by SEM. . On the other hand, in the case of the tin plating solution of Comparative Example 5, when the generation of sludge was recognized, abnormal precipitation was observed on the surface of the tin plating layer, and it was confirmed that an apparent defective state was obtained.

  Furthermore, regarding the solder wettability, in the case of the tin plating solution of Example 5, it is possible to form a tin plating layer having good solder wettability even after 365 days. On the other hand, in the case of the tin plating solution of Comparative Example 5, when the generation of sludge is recognized, the solder wettability deteriorates.

Comparison of Example 6 and Comparative Example 6 In this Example 6, instead of tin methanesulfonate, which is the tin salt of Example 1, tin sulfate was used, and instead of brightener lauryldimethylaminoacetic acid betaine, Polyoxyethylene lauryl ether was used. That is, in Example 6, sodium gluconate, which is a chelating agent, sodium hydroxide, which is an alkaline pH adjusting agent, and methanesulfonic acid, which is an acidic pH adjusting agent, are added to ion-exchanged water in this order, and the solution pH is set to 12, In addition, tin sulfate, which is a tin salt, is added to ensure the production of a tin chelate complex. And then, ascorbic acid as an antioxidant and polyoxyethylene lauryl ether as a brightener were added in this order, and the pH of the final tin plating solution was adjusted to 4.0.

  On the other hand, Comparative Example 6 added ion-exchanged water in the order of sodium gluconate, which is a chelating agent, and methanesulfonic acid, which is an acidic pH adjuster, as a strongly acidic solution having a pH of 1 or less. Some tin sulfate is added. After that, in order to bring the pH of the tin plating solution closer to the neutral region, sodium hydroxide as an alkaline pH adjuster, ascorbic acid as an antioxidant, and polyoxyethylene lauryl ether as a brightener are added in this order. The pH of a typical tin plating solution was 4.0.

  Also in Example 6 and Comparative Example 6, the mixing order of the constituent components is merely different, but the solution properties are completely different. Therefore, as in the case of Example 1, it can be said that even if the constituent components are the same, the manner of the presence of the tin component contained therein as the tin plating solution is completely different. This is supported by the following contents. In the case of Example 6, even when stored in an air atmosphere at room temperature to 40 ° C., no sludge is observed even after 365 days. On the other hand, in the case of the comparative example 6, generation | occurrence | production of the sludge was confirmed after only 2 days passed since a bath.

  In the case of the tin plating solution of Example 6, even after 365 days, even if the tin plating layer of the test sample subjected to the plating test was observed with an SEM, a very good uniform surface was obtained. . On the other hand, in the case of the tin plating solution of Comparative Example 6, when the generation of sludge was observed, abnormal precipitation was observed on the surface of the tin plating layer, and it was confirmed that an apparent defective state was obtained.

  Furthermore, regarding the solder wettability, in the case of the tin plating solution of Example 6, a tin plating layer having good solder wettability can be formed even after 365 days have elapsed. On the other hand, in the case of the tin plating solution of Comparative Example 6, when the generation of sludge is recognized, the solder wettability deteriorates.

Comparison of Example 7 and Comparative Example 7 In this Example 7, catechol was used instead of ascorbic acid which is the antioxidant of Example 1, and polyoxy was used instead of brightener lauryldimethylaminoacetic acid betaine. Ethylene lauryl ether was used. That is, Example 7 was prepared by adding sodium gluconate, which is a chelating agent, sodium hydroxide, which is an alkaline pH adjuster, and methanesulfonic acid, which is an acidic pH adjuster, in this order to ion-exchanged water, and setting the solution pH to 12, In addition, tin methanesulfonate tin, which is a tin salt, is added to ensure the production of a tin chelate complex. After that, catechol which is an antioxidant and polyoxyethylene lauryl ether which is a brightener are added in this order, and the final tin plating solution has a pH of 4.0.

  On the other hand, Comparative Example 7 added ion-exchanged water in the order of sodium gluconate, which is a chelating agent, and methanesulfonic acid, which is an acidic pH adjuster, as a strongly acidic solution having a pH of 1 or less. Some tin methanesulfonate is added. Then, in order to bring the pH of the tin plating solution close to the neutral region, sodium hydroxide as an alkaline pH adjuster, catechol as an antioxidant, and polyoxyethylene lauryl ether as a brightener are added in this order. The pH of the tin plating solution was 4.0.

  In Example 7 and Comparative Example 7, the mixing order of the constituent components is merely different, but the solution properties are completely different. Therefore, as in the case of Example 1, it can be said that even if the constituent components are the same, the manner of the presence of the tin component contained therein as the tin plating solution is completely different. This is supported by the following contents. In the case of Example 7, even when stored in an air atmosphere at room temperature to 40 ° C., no sludge is observed even after 365 days. On the other hand, in the case of the comparative example 7, generation | occurrence | production of sludge was confirmed after only 2 days passed since a bath.

  In the case of the tin plating solution of Example 7, even after 365 days, even if the tin plating layer of the test sample subjected to the plating test was observed with an SEM, a very good uniform surface was obtained. . On the other hand, in the case of the tin plating solution of Comparative Example 7, when the generation of sludge was observed, abnormal precipitation was observed on the surface of the tin plating layer, and it was confirmed that an apparent defective state was obtained.

  Furthermore, regarding the solder wettability, in the case of the tin plating solution of Example 7, it is possible to form a tin plating layer having good solder wettability even after 365 days. On the other hand, in the case of the tin plating solution of Comparative Example 7, when the generation of sludge is recognized, the solder wettability deteriorates.

Comparison between Example 8 and Comparative Example 8: In Example 8, ion-exchanged water, sodium gluconate as a chelating agent, sodium hydroxide as an alkaline pH adjusting agent, and methanesulfonic acid as an acidic pH adjusting agent in this order. In addition, the solution pH is set to 12, and tin methanesulfonate tin, which is a tin salt, is added thereto, and a method of reliably producing a tin chelate complex is adopted. Then, ascorbic acid as an antioxidant and sodium sulfate as a conductive salt are added at the same time, and lauryldimethylaminoacetic acid betaine as a brightener is added in this order, and the final tin plating solution has a pH of 6.0. did.

  In contrast, Comparative Example 8 was prepared by adding sodium gluconate, which is a chelating agent, and methanesulfonic acid, which is an acidic pH adjuster, to ion-exchanged water in this order as a strongly acidic solution having a pH of 1 or less. Some tin methanesulfonate is added. As a conventional method for producing a tin plating solution, a method of adding a tin salt in the acidic region has been adopted. And then, in order to bring the pH of the tin plating solution close to the neutral region, sodium hydroxide as an alkaline pH adjuster, ascorbic acid as an antioxidant and sodium sulfate as a conductive salt are simultaneously added to be a brightener. Lauryldimethylaminoacetic acid betaine was added in this order to adjust the final tin plating solution pH to 6.0. However, in Example 8 and Comparative Example 8, since the addition amount of methanesulfonic acid, which is an acidic pH adjuster contained therein, is different, the final tin plating solution has a pH of 6.0. Thus, the addition amount of the alkaline pH adjuster is also changed.

  In Example 8 and Comparative Example 8, only the mixing order of the constituent components is different, but the solution properties are completely different. Therefore, as in the case of Example 1, it can be said that even if the constituent components are the same, the manner of the presence of the tin component contained therein as the tin plating solution is completely different. This is supported by the following contents. In the case of Example 8, even when stored in an air atmosphere at room temperature to 40 ° C., no sludge is observed even after 365 days. On the other hand, in the case of the comparative example 8, generation | occurrence | production of sludge was confirmed after only 2 days passed since a bath.

  In the case of the tin plating solution of Example 8, even after 365 days, a very good uniform surface was obtained even when the tin plating layer of the test sample subjected to the plating test was observed with an SEM. . On the other hand, in the case of the tin plating solution of Comparative Example 8, when the generation of sludge was observed, abnormal precipitation was observed on the surface of the tin plating layer, and it was confirmed that an obvious defective state was obtained.

  Furthermore, regarding the solder wettability, in the case of the tin plating solution of Example 8, a tin plating layer having good solder wettability can be formed even after 365 days have elapsed. On the other hand, in the case of the tin plating solution of Comparative Example 8, when the generation of sludge is recognized, the solder wettability deteriorates.

  And the observation regarding the comparative example 9 and the comparative example 10 is described. Although Comparative Example 9 and Comparative Example 10 do not have examples to be directly compared, they are listed as possible tin plating solution compositions, and are for comparing the solution life until sludge generation with each of the above examples. It is. In the tin plating solution of Comparative Example 9, generation of sludge is observed after 1 day has elapsed since the bathing as described above. Moreover, generation | occurrence | production of sludge is seen in the tin plating solution of the comparative example 10 after 5 hours have passed since the bathing. Furthermore, it was also confirmed that a uniform tin plating film could not be formed with the tin plating solutions of Comparative Example 9 and Comparative Example 10 after confirming the generation of sludge. That is, when compared with the tin plating solution according to the present invention described above, it can be easily understood that the solution life of the tin plating solutions of Comparative Example 9 and Comparative Example 10 is extremely short.

  The tin plating solution according to the present invention does not generate sludge even after a period of one year, and has a significantly longer solution life after bathing compared to conventional tin plating solutions, and is easy to manage the plating solution. It is excellent in economic efficiency. The tin plating solution according to the present invention can be plated in the range of 10 ° C. to 40 ° C., and has an appropriate liquid evaporation. This can reduce the total cost.

  In addition, the method for adjusting the tin plating solution according to the present invention does not require a special apparatus and technique, but can utilize existing facilities effectively, simply by adopting a certain adjustment procedure. .

It is a SEM observation image of the tin plating layer formed using the tin plating solution which concerns on this invention after the elapse of 365 days from a foundation bath. It is a SEM observation image of the tin plating layer formed using the tin plating solution which concerns on this invention after the elapse of 365 days from a foundation bath. It is a SEM observation image of the tin plating layer formed using the tin plating solution which concerns on this invention after the elapse of 365 days from a foundation bath. It is a SEM observation image of the tin plating layer formed using the tin plating solution which sludge generate | occur | produced two days after the bathing. It is a SEM observation image of the tin plating layer formed using the tin plating solution which sludge generate | occur | produced in the stage at the time of a bath. It is a SEM observation image of the tin plating layer formed using the tin plating solution which sludge generate | occur | produced two days after the bathing.

Claims (16)

A tin plating solution for performing tin plating by an electrolytic method,
Water, a pH adjuster, and a chelating agent are mixed to prepare a premixed solution having a pH value of 6 to 12, and a tin salt is sufficiently added to the preconditioned solution so that the tin content is 5 g / L to 30 g / L. And a tin chelate complex formed by stirring, and stored at 10 ° C. to 40 ° C. so that sludge does not occur for more than 7 days. The said tin salt is a tin plating solution of Claim 1 using 1 type, or 2 or more types chosen from the 1st tin salt soluble with water. The chelating agent includes one or more selected from gluconic acid, gluconate, citric acid, citrate, pyrophosphate, and pyrophosphate so as to have a concentration of 30 g / L to 300 g / L. Or the tin plating solution of Claim 2. The said pH adjuster is an alkaline pH adjuster, Comprising: The 1 type (s) or 2 or more types chosen from sodium hydroxide, potassium hydroxide, and ammonia water were included so that it might become a 5g / L-140g / L density | concentration. The tin plating solution according to any one of claims 1 to 3. The pH adjuster is an acidic pH adjuster, and includes 10 g / L to 300 g / L of one or more selected from methanesulfonic acid, ethanesulfonic acid, sulfuric acid, and isethionic acid. The tin plating solution according to claim 4. The tin plating solution according to any one of claims 1 to 5, comprising an antioxidant in a concentration of 0.1 g / L to 30 g / L. A pH adjuster for finely adjusting the pH to the acidic side, wherein one or two of methanesulfonic acid and sulfuric acid are added to adjust the pH to the range of pH4 to pH10. The tin plating solution as described. A pH adjuster for finely adjusting the pH to the alkali side, wherein one or two kinds of sodium hydroxide, potassium hydroxide, and ammonia water are added to make the pH range from 4 to 10. The tin plating solution according to any one of 7 above. The tin plating solution according to any one of claims 1 to 8, which is a conductive salt and contains one or more selected from sodium sulfate and ammonium sulfate so as to have a concentration of 1 g / L to 150 g / L. Any one of Claim 1-Claim 9 which contains 1 type, or 2 or more types chosen from a nonionic surfactant, a cationic surfactant, and an amphoteric surfactant as a brightener so that it may become a 0.1g / L-30g / L density | concentration. A tin plating solution according to claim 1. It is a tin plating method using the tin plating solution in any one of Claims 1-10, Comprising: The tin plating method characterized by electrolyzing on conditions with a bath temperature of 10 to 40 degreeC. It is a tin plating solution adjustment method in any one of Claims 1-10, Comprising: It adjusts by the procedure of the following A) and B), The tin plating solution adjustment method characterized by the above-mentioned.
A) Water, a pH adjuster, and a chelating agent are mixed to obtain a preliminary adjustment solution having a pH value of 6-12.
B) A tin salt is added to the preconditioning solution, and the tin content is added to a concentration of 5 g / L to 30 g / L and stirred sufficiently to form a tin chelate complex to obtain a tin plating solution. The tin plating solution adjusting method according to claim 12, wherein a step of adding an antioxidant to the tin plating solution is added. The tin plating solution adjusting method according to claim 12, wherein a step of finely adjusting a pH value is added to the tin plating solution. The tin plating solution adjusting method according to claim 12, wherein a step of adding a conductive salt to the tin plating solution is added. The tin plating solution adjusting method according to claim 12, wherein a step of adding a brightener to the tin plating solution is added.