JP5337760B2 - Metal surface treatment aqueous solution and method for preventing discoloration of metal surface - Google Patents

Description

  The present invention relates to a surface treatment solution for a metal, particularly a tin plating film, and a surface treatment method for a tin plating film. Specifically, the present invention relates to a method of applying a surface treatment liquid to the surface of a tin plating film and a treatment liquid thereof before reflow treatment in forming a tin film by a tin plating method.

  Tin or tin alloy plating is superior in its bondability, low cost, electrical characteristics and solderability, so that it requires components such as chip components, crystal oscillators, connector pins, lead frames, and printed circuit boards. And as an etching resist in the manufacturing process of semiconductor devices and printed circuit boards.

  As it is, this tin or tin alloy film forms whisker-like metal deposits called whiskers on the surface as time passes. When whiskers are generated on the surface of a tin or tin alloy film formed on the surface of a substrate such as an electronic component, an electrical short circuit may occur. For the purpose of preventing the generation of the whisker and forming the surface gloss of the tin or tin alloy film by melting, it is known to perform a high temperature treatment, that is, a reflow treatment after the formation of the tin or tin alloy film. However, although the reflow treatment has an effect of preventing whisker generation, there is a problem that the surface of the film after heating is likely to be discolored or oxidized. The discoloration of the surface of the plating film is considered to be one of the causes of the oxidation of the film surface layer. As the oxide film becomes thicker, the discoloration of the film progresses, and the oxidation of the plating film causes the solder wettability to deteriorate. Conventionally, tin-lead alloy plating has been used to cope with such a problem of a tin film which is a metal that is easily oxidized. Lead served to suppress tin oxidation and whisker growth. However, in recent years, attention has been focused on the toxicity of lead, and the use of lead in electronic parts has been restricted. For this reason, lead-free tin or tin alloy plating is required, and oxidation of the plating film and countermeasures against whiskers are also required.

  On the other hand, it is known that a tin plating film is likely to generate a twist on the surface of the film by reflow treatment as compared with a tin-lead alloy plating film. Here, “twist” refers to a wavy convex portion appearing on the tin film, and in some cases, a grain-like pattern may be formed. The twist generated on the surface of the film means non-uniformity of the tin film thickness. In some cases, the base metal (for example, nickel) may be exposed, making it difficult to ensure solderability. Since there is a problem, it is required to prevent twisting from occurring on the plating film.

As surface treatment methods for tin-plated steel sheets, various surface treatment liquids and treatment methods for tin coating have been used. For example, Japanese Patent Publication No. 52-53739 discloses a tin-plated steel sheet using an aqueous solution to which 5 to 50 g / L of phosphoric acid or a combination of phosphoric acid and phosphorous acid or hypophosphorous acid is added as a free acid. Disclosed is a surface treatment. In addition, this publication describes that the treatment bath is adjusted to pH 4 or lower. This publication does not disclose the use of the compound and surface treatment liquid used in the present invention before the reflow treatment.
In Japanese Patent Publication No. 58-1085, an electrotin-plated steel strip is coated with an aqueous solution of an organic acid or a salt thereof having a melting point of 170 to 300 ° C. and decomposing during reflow before the reflow treatment. A method for preventing the occurrence of a grain pattern on a tinned surface is disclosed. This publication describes sodium gluconate, monosodium glutamate, sodium ethylenediaminetetraacetate (EDTA) and the like as the organic acid or a salt thereof. In addition, this publication describes that sodium phosphate does not erase the grain pattern on the tin-plated surface, and this compound is inappropriate. This publication does not disclose the excellent effects of the compounds used in the present invention and their application to electronic components.
Japanese Patent Publication No. 7-286285 discloses a metal surface chemical conversion treatment aqueous solution containing a phosphate ion, an organic phosphonic acid compound and a tin ion and having a pH of 5.0 or less, which is used on the surface of a tin-plated steel sheet. This publication discloses a chemical conversion aqueous solution containing an organic phosphonic acid compound as an essential component, and does not disclose the compound of the present invention and its advantageous effects.

JP 52-53739 A JP 58-1085 A JP-A-7-286285

  In the present invention, even after a reflow treatment is applied to a tin or tin alloy plating film used for an electronic component, the plating film is not twisted, and at the same time, discoloration is suppressed, and good solder wetting is achieved. It aims at providing the plating film which has property, and its formation method.

  In order to achieve the above-mentioned problems, the present inventors have intensively studied a tin plating film surface treatment aqueous solution used before reflow treatment of the plating film. As a result, the present invention has been achieved by finding that it has selective potential compared with an aqueous solution containing another compound having a structure. The surface treatment aqueous solution of the present invention can prevent the plating film from being discolored even after heating in the reflow treatment, prevent the plating film from being twisted, and provide good solder wettability to the plating film.

The invention of the present application includes, as a first aspect, a tin plating film surface treatment aqueous solution for treating the surface of a tin plating film, which contains an ammonium salt of phosphoric acid and has a pH of 3 to 5; a salt of polyphosphoric acid, A tin plating film surface treatment aqueous solution for treating the surface of the tin plating film having a pH of 2 to 10; a surface of the tin plating film containing a salt of maleic acid and having a pH of 4.5 to 8.5 A tin plating film surface treatment aqueous solution for treatment; a tin plating film surface treatment aqueous solution for treating the surface of a tin plating film containing L-arginine and having a pH of 7 to 12; containing glycine and a pH of 4 to 4 A tin plating film surface treatment aqueous solution for treating the surface of the tin plating film; or a mixture of ammonium phosphate and polyphosphoric acid, a mixture of ammonium phosphate and glycine, Provides a tin plating film surface treatment aqueous solution for processing comprises a mixture of a salt of polyphosphoric acid and glycine, the surface of the tin plating film.
Moreover, the surface treatment method of the tin plating film which treats the base | substrate which has a tin film on the surface with the said tin plating film surface treatment aqueous solution as a 2nd aspect is provided.
As a third aspect, there is provided a method for treating a surface of a tin plating film, wherein the surface of the tin film is treated with the tin plating film surface treatment aqueous solution after tin plating is performed on the surface of the substrate.
As a fourth aspect, there is provided a method of forming a tin plating film on a metal, the step of preparing a substrate having a metal on the surface, the step of activating the substrate with an acid, and the activating substrate being tin A method comprising the steps of plating, treating the tin plating film with a surface treatment aqueous solution, and reflowing the tin film, wherein the surface treatment aqueous solution is the tin plating film surface treatment aqueous solution. I will provide a.
According to a fifth aspect of the present invention, there is provided a method for producing an electronic component having a tin film, wherein the tin plating film surface treatment aqueous solution is used between a step of tin plating on a substrate and a step of reflowing the substrate having a tin film. The method includes the step of treating the surface of the tin plating film.

Abbreviations used throughout this specification have the following meanings unless otherwise indicated.
g = gram; mg = milligram; ° C = degrees Celsius; V = volt; A = ampere; m = meter; cm = centimeter; μm = micrometer; L = liter; mL = milliliter; dm ² = square decimeter. All numerical ranges include boundary values and can be combined in any order.
Throughout this specification, the terms “plating solution” and “plating bath” have the same meaning and are used interchangeably.

The tin plating film surface treatment aqueous solution of the present invention comprises one or more compounds selected from the group consisting of an ammonium salt of phosphoric acid, a salt of polyphosphoric acid, a salt of glycine, L-arginine and maleic acid, water, Is included.
In the present invention, the salt of polyphosphoric acid or the salt of maleic acid includes, but is not limited to, alkali metal salts such as sodium salt and potassium salt, ammonium salt and the like.

  One or more compounds selected from the group consisting of ammonium phosphate, polyphosphoric acid salt, glycine, L-arginine and maleic acid salt are 5 to 100 g / L as a compound in the surface treatment aqueous solution. The range is preferably 10 to 80 g / L, and more preferably 30 to 60 g / L.

  The tin plating film surface treatment aqueous solution of the present invention has a predetermined optimum pH range depending on the components contained. For example, when an ammonium salt of phosphoric acid is included, the pH ranges from 3 to 5, preferably from 4 to 4.5; when L-arginine is used, the pH ranges from 7 to 12; In the case of maleic acid salts, the pH is in the range of 6-9; in the case of salts of polyphosphoric acid, the pH is in the range of 2-10, preferably in the range of 6-10; or in the case of glycine, the pH Is in the range of 4-7. When a mixture of an ammonium salt of phosphoric acid and a salt of polyphosphoric acid is included, the pH of the aqueous solution is preferably 4 to 7, more preferably 5 to 6; a mixture of an ammonium salt of phosphoric acid and glycine Preferably, the pH of the aqueous solution is 4-6, more preferably 4-5; or when it contains a mixture of polyphosphate salt and glycine, the pH of the aqueous solution is preferably 7-9. More preferably, it is 7-8. For adjusting the pH value, a known pH adjusting agent can be used. For example, phosphoric acid or acetic acid is used to lower the pH, and aqueous ammonia, sodium hydroxide, or potassium hydroxide is used to increase the pH. . In a preferred embodiment, the pH of the aqueous solution is adjusted with an acid or an alkali constituting the contained component. For example, in the case of an ammonium salt of phosphoric acid, it is preferable to adjust the pH of the aqueous solution with phosphoric acid or ammonia. In the case of a salt of polyphosphoric acid, it is preferable to adjust the pH of the aqueous solution with an alkali component constituting the polyphosphoric acid or the salt. Furthermore, in the case of a salt of maleic acid, it is preferable to adjust the pH of the aqueous solution with an alkali component or maleic acid constituting the salt.

  The surface treatment aqueous solution of the present invention is generally used in a bath temperature range of 10 to 100 ° C, preferably in a range of room temperature (25 ° C) to 70 ° C, more preferably in a range of 40 to 70 ° C.

  In the present invention, known additives such as surfactants, antibacterial agents or solvents can be added as necessary, but these are not essentially required.

  The tin plating film surface treating agent of the present invention can be applied to a substrate by a known method such as dipping treatment or spray treatment. In general, the surface of the tin film is washed with water, and then the tin plating film surface treatment solution of the present invention is applied by an immersion method or a spray method. The processing time is generally from 5 seconds to 120 seconds, preferably from 10 seconds to 60 seconds. Thereafter, the treatment is generally performed in the order of washing with water, washing with pure water, and drying.

  The treatment liquid of the present invention is suitable for treating a tin plating film of an electronic component, for example. Examples of such electronic components include chip components such as chip resistors and chip capacitors, and electronic components such as connector pins, bumps, printed wiring boards, and lead frames.

  As will be understood from the examples given below, the compounds used in the present invention, specifically the ammonium salts of phosphoric acid, the salts of polyphosphoric acid, the salts of glycine, L-arginine and maleic acid, Shows significant effect compared to compounds. That is, when the tin plating film before the reflow treatment is performed with the surface treatment liquid of the present invention, discoloration and twisting of the film surface can be suppressed even after the reflow treatment, and good solder wettability. It is possible to form a tin plating film having

Next, the present invention will be specifically described with reference to examples and comparative examples.
Appearance, discoloration, and twist in the following examples and comparative examples were evaluated as follows.

(1) Appearance After the tin plating film treated with the surface treatment solution was reflowed and dried, the gloss of the surface of the tin plating film and the uniformity of the plating appearance (confirmation of uneven appearance) were observed with the naked eye. evaluated.
1: Glossy / uniform: Glossy and uniform film 2: Glossy / non-uniform: Glossy but non-uniform film 3: Matte / uniform: Non-glossy uniform film 4: Matte / non-uniform: No gloss And non-uniform coating

(2) Discoloration After the tin plating film treated with the surface treatment solution was reflowed and dried, the discoloration of the tin plating film surface was observed with the naked eye and evaluated in four stages.
Excellent: No discoloration Good: Almost no discoloration (gloss is dull)
Possible: Slight discoloration such as white, gray, yellow, etc. Impossible: Brown or purple discoloration

(3) Twist After the tin plating film treated with the surface treatment liquid was subjected to reflow treatment and dried, the tin plating film surface was observed with the naked eye and evaluated in four stages.
Excellent: No twist Good: Almost no twist Yes: There is a slight twist No: There is a twist

Examples 1-4 and Comparative Examples 0-38
A copper lead frame was subjected to cathode electrolytic degreasing at a voltage of 4 V × 1 minute in an alkaline electrolytic degreasing agent (cleaner 160: chemical manufactured by Meltex) at a bath temperature of 60 ° C., washed with water, and a persulfate system at room temperature. Chemical polishing is performed by immersing in a chemical abrasive solution (Actronal 550) for 30 seconds, washing with water, pickling in 10% sulfuric acid solution, washing with water, and an additive watt bath at a bath temperature of 55 ° C. and a current density of 3A / Dm ² × 2 minutes nickel plating to form a nickel film with a thickness of 1 μm, washed with water, and a tin plating film with a thickness of 3 μm using a well-known tin methanesulfonate plating bath (Solderon TMBT-280 tin plating) After being formed and washed with water, it was immersed in an aqueous solution having the composition and pH shown in Table 1 at 25 ° C. for 30 seconds, washed with water, and dried. In addition, as "sodium polyphosphate", sodium polyphosphate manufactured by Kanto Chemical Co., Ltd. was used. After drying, a reflow process was performed at 260 ° C. for 1 minute in a reflow apparatus (RF-330 manufactured by Nippon Pulse Technology Laboratory Co., Ltd.), and the appearance, discoloration, and twist of the tin film were evaluated for each part. The evaluation results are shown in Table 1.

  It was confirmed that the surface treatment aqueous solution prepared with the compounds used in the examples had less discoloration and twisting than the treatment with the aqueous solution of the comparative example for the reflow-treated tin plating film.

Surface treatment aqueous solutions prepared using the compounds of Examples 1 to 4 or maleic acid salts were evaluated in the same manner as in Example 1 under the treatment conditions shown in Table 2. However, for each surface treatment aqueous solution, 50 g / L of the compounds of Examples 1 to 4 or maleic acid was added to water, phosphoric acid or ammonia for monoammonium phosphate aqueous solution, phosphoric acid or sodium polyphosphate aqueous solution for For the aqueous solution of sodium hydroxide, maleic acid or L-arginine, the optimum pH was examined by adjusting each pH value with acetic acid or sodium hydroxide and for the aqueous solution of glycine with acetic acid or ammonia. At the same time, the effect of temperature was examined by changing the bath temperature to 25 ° C. to 60 ° C., which is considered to correspond to the normal operating temperature range.
The evaluation results are shown in Table 2.

For the ammonium salt of phosphoric acid, good results were not obtained for “Yori” at pH 2 and 6 (Comparative Examples 39 and 40), but as shown in Examples 1 and 5-7, pH 4. In 21-4.3, the favorable result was recognized in any of an external appearance, discoloration, and twist. Moreover, this good result was recognized in the temperature range of 25 degreeC-60 degreeC.
Moreover, as for sodium polyphosphate, as shown in Example 2 and 8 to 13, good results were observed in any of appearance, discoloration, and twist at pH 2 to 10. Moreover, this good result was recognized in the temperature range of 25 degreeC-60 degreeC.
As for glycine, as shown in Examples 4 and 14 to 17, good results were observed in any of appearance, discoloration and twist at pH 4 to 9. Moreover, this good result was recognized in the temperature range of 25 degreeC-60 degreeC.
As for L-arginine, as shown in Examples 3, 18 and 19, good results were observed in any of appearance, discoloration and twist at pH 4-9.
For maleic acid, as shown in Comparative Examples 41 and 42, “twist” was not good at pH 4 and 9, but as shown in Example 20, both properties were good at pH 6. It was.

  The tin film surface treatment liquid of the present invention was prepared as shown in Table 3 using two kinds of compounds, and the same evaluation as in Example 1 was performed. However, the bath temperature of the surface treatment aqueous solution was 40 ° C.

Solder wettability test examples 27 and 28
A lead frame was prepared that was subjected to a tin film surface treatment under the same conditions as in Examples 1 and 5 except that the treatment temperature of the surface treatment aqueous solution of Examples 1 and 5 was 60 ° C. The obtained lead frame was subjected to a moisture resistance test treatment (PCT (105 ° C. 100% Rh 4 or 8 hours)) at 105 ° C., 100%, 4 and 8 hours, and the solder wettability of the plating film after the moisture resistance test was determined. The zero cross time was measured and evaluated by the meniscograph method using -5000 (manufactured by RHESCACo., LTD). The measurement conditions are as follows.

Zero cross time measurement conditions Solder bath: Sn / Pb = 63/37
Bath temperature: 235 ° C
Immersion depth: 1mm
Immersion speed: 10 mm / second Immersion time: 5 seconds Flux: Rosin-based inert type Table 4 shows the results obtained from the above measurement test.

The tin plating time was adjusted at each current density so that the plating film thickness was constant.
The surface treatment aqueous solutions of Examples 1 and 5 provided good solder wettability.

  According to the tin plating film surface treatment liquid of the present invention, a film excellent in corrosion resistance and twist resistance can be formed. That is, by using the surface treatment liquid of the present invention before the reflow treatment of the tin plating film, it is possible to reduce the discoloration of the tin film after heating and to form a tin film having good solderability.

Claims (5)

a) plating a tin film on the surface of the substrate;
b) a step of treating the tin film on the substrate surface with an aqueous solution containing a salt of polyphosphoric acid and glycine and having a pH of 7 to 9 before the reflow treatment; and c) a step of reflowing the tin film. A method for surface treatment of a tin plating film comprising   The method of claim 1, further comprising activating the substrate with an acid prior to plating the tin coating onto the substrate. The total amount of salts of polyphosphoric acid and glycine in an aqueous solution is 5 to 100 g / L, The method of claim 1. The total amount of salts of polyphosphoric acid and glycine in an aqueous solution is 10 to 80 g / L, The method of claim 3.   The method of claim 1, wherein the substrate is an electronic component.