JP5463774B2 - Method for removing Sn oxide film formed on Sn-based plating material surface - Google Patents

Description

  The present invention relates to a method for removing a Sn oxide film formed on the surface of a Sn-based plating material provided with a plating layer containing Sn.

  In general, for electrical / electronic parts such as terminals, connectors, contacts, etc., a Sn-based plating material in which a plating layer containing Sn, specifically, a Sn or Sn alloy plating layer is provided on the surface of copper or a copper alloy Is widely used. In recent years, with the reduction in size, weight, and performance of electric / electronic components, the area of the soldering portion has also decreased, and Sn can be reliably and firmly soldered even with a small soldering area. It is strongly desired to improve the solder wettability of the plating system.

  However, in the case of a Sn-based plated material, a Sn oxide film is formed on the surface of the Sn-based plated material by heat melting treatment during reflow processing for the Sn-based plated material, aging during storage, heating during soldering, and the like.

  Since the melting point of this Sn oxide film is higher than that of Sn or Sn alloy, the melting point of the Sn-based plating material surface is higher than that before the Sn oxide film is formed, and wettability during soldering (hereinafter referred to as “solder wettability”). ”).

  Therefore, it is important to remove the Sn oxide film formed on the surface of the Sn-based plating material due to the heat-melting process during the reflow processing for the Sn-based plating material, the change over time during storage, or the like. And the method of removing a Sn oxide film is disclosed by the following patent documents, for example.

  That is, Patent Document 1 discloses that a Sn-based plating material is immersed in a 5 to 10 wt% ammonium fluoride aqueous solution for 20 seconds or less to remove Sn oxide film and improve solder wettability. Yes. This method shows that eutectic solder at 245 ° C. can ensure solder wettability without flux.

  Next, Patent Document 2 includes (A) an organic acid amine salt, (B) at least one selected from monohydric alcohols, glycols and polar aprotic solvents, and (C) a nonionic surfactant. Using the contained water-soluble solder wettability improving treatment agent, not only the oxidation of electronic component terminals to which nickel plating or Sn alloy plating has been applied is prevented, but also the already formed nickel or Sn oxide film is removed. Therefore, it is disclosed that solder wettability is improved.

  Next, Patent Documents 3 and 4 describe that a reducing gas that is negatively charged by supplying energy to the electrode assembly to generate electrons in the target region and attaching a part of the electrons to a part of the reducing gas. It is disclosed that it is generated and brought into contact with the plated surface of the Sn-based plated material to reduce and remove the Sn oxide formed on the plated surface. It has been shown that fluxless reflow soldering can be realized by reducing the Sn oxide film at a lower temperature than in the prior art.

JP-A-9-78265 JP 2004-176179 A JP 2004-323977 A Japanese Patent Laid-Open No. 2005-2468

  However, in the method disclosed in Patent Document 1, since an ammonium fluoride aqueous solution is used, not only the Sn oxide film but also Sn in the plating layer may be dissolved and removed. For this reason, when only the Sn oxide film is to be removed, it is necessary to precisely control and manage the concentration of the aqueous ammonium fluoride solution and the immersion time of the Sn-based plating material. And providing such management equipment raises cost. In addition, since the aqueous ammonium fluoride solution is toxic, a facility for treating the aqueous ammonium fluoride solution after use is required, which also increases the cost.

  This method is intended to improve solder wettability for soldering using Sn-Pb-based eutectic solder, and is consistent with current soldering that is becoming lead-free. It's hard to say how.

  Next, in the method disclosed in Patent Document 2, it is necessary to separately provide equipment for producing a water-soluble solder wettability improving treatment agent, which increases costs.

  Next, in the methods disclosed in Patent Documents 3 and 4, since a reducing gas having combustibility and toxicity such as hydrogen and halogen compounds is used, it is necessary to ensure safety during and after processing. Requires equipment and increases costs.

  In view of the above problems, the present invention does not require precise control and does not increase the cost when removing the Sn oxide film formed on the surface of the Sn-based plating material to improve the solder wettability. It is an object of the present invention to provide a method for removing an Sn oxide film that can reliably remove only the Sn oxide film without affecting the Sn plating layer by a simple method.

  As a result of intensive studies, the present inventor has found that the above problems can be solved by the invention shown below, and has completed the present invention.

The invention described in claim 1
A method for removing a Sn oxide film formed on the surface of a Sn-based plating material provided with a plating layer containing Sn,
The Sn-based plating material having the Sn oxide film formed on the surface thereof is a mixed solution of ammonia water and ammonium chloride having an ammonium ion (NH ₄ ⁺ ) concentration of 0.1 to 1 M, or a solution of ammonia water and ammonium sulfate. After immersing in the mixed solution , the Sn oxide film is electrolytically reduced by applying a voltage of -1.3 to -1.5 V with respect to the Sn-based plating material being immersed, based on the Ag / AgCl reference electrode. And removing the Sn oxide film.

  As a result of various experiments, the present inventor has developed a Sn oxide film without damaging the plating layer by applying a voltage after immersing the Sn-based plating material having the Sn oxide film formed on the surface thereof in an ammonia buffer solution. It was found that only can be removed reliably.

  As described above, according to the present invention, only the Sn oxide film can be surely removed without damaging the plating layer, so that the solder wettability of the Sn-based plating material is improved and the soldering area is reliably reduced. Soldering is possible.

  And since it is an extremely simple means, it is not necessary to finely control the removal of the Sn oxide film. For this reason, the cost is not increased.

  Moreover, the invention of this claim can also be applied to the current soldering in which lead-free development is progressing.

  In addition, since an ammonia buffer solution is used, the pH hardly changes even when used multiple times and can be used repeatedly many times. In addition, even when a part of Sn elutes as unstable Sn (IV) ions during the treatment process, it is suppressed that the eluted Sn (IV) ions are precipitated again as Sn (IV) compounds in the ammonia buffer solution. Is done. Further, in the case of ammonia water alone, the surface of the treated product cannot be easily cleaned only by washing with water after the treatment because of strong alkali, but in the case of ammonia buffer solution, it can be cleaned only by washing with water.

  In the invention of this claim, the “Sn-based plating material provided with a Sn-containing plating layer” refers to a plating material provided with a Sn or Sn alloy plating layer.

Specific examples of the ammonia buffer include a mixed solution of ammonia water (NH ₄ OH) and ammonium chloride (NH ₄ Cl) having a concentration of ammonium ions (NH ₄ ⁺ ) of 0.1 to 1 M, and ammonia water ( A mixed solution of NH ₄ OH) and ammonium sulfate ((NH ₄ ) ₂ SO ₄ ) is preferably used.

  The voltage applied between the immersed Sn-based plating material and the Ag / AgCl electrode can be set as appropriate. In general, if the potential of the Sn-based plating material is increased to the negative side, a large current flows, so that the processing time can be shortened. However, since the hydrogen generation reaction occurs preferentially, the current efficiency deteriorates. On the other hand, when the potential swing width is reduced, the processing time becomes longer. For this reason, it is preferably set to −1.3 to −1.5 V (potential based on the Ag / AgCl reference electrode. − Indicates that the Sn plating material is a negative electrode). Since the hydrogen generation reaction occurs simultaneously with the end of the reduction of the Sn oxide and gas (hydrogen gas) starts to be generated from the surface of the Sn plating material, the process may be ended when the generation of gas is confirmed.

  ADVANTAGE OF THE INVENTION According to this invention, the removal method of the Sn oxide film which can remove only Sn oxide film reliably without attacking Sn plating layer by the simple method which does not raise cost can be provided. . As a result, the solder wettability of the Sn-based plated material can be improved, and reliable soldering can be performed with a small soldering area.

It is a figure which shows the procedure of the electrolytic reduction process of the sample which gave Sn plating, and the structure of the cell for electrolytic reduction processes. It is a voltammogram which shows the measurement result by the voltammetry method of the sample before an electrolytic reduction process and after an electrolytic reduction process. It is a figure which shows the test result of the solder wettability using the meniscograph testing machine.

  Hereinafter, the present invention will be described based on embodiments. Note that the present invention is not limited to the following embodiments. Various modifications can be made to the following embodiments within the same and equivalent scope as the present invention.

  In this example, the Sn-plated material subjected to the reflow treatment was heated, and the sample in which the Sn oxide film was formed on the surface was subjected to an electrolytic reduction treatment using an ammonia buffer solution as an electrolyte solution to remove the Sn oxide film. It is.

1. Procedure of electrolytic reduction treatment and configuration of electrolytic reduction treatment cell First, the procedure of electrolytic reduction treatment and the configuration of electrolytic reduction treatment cell will be described with reference to FIG. In addition, FIG. 1 is a figure which shows the procedure of the electrolytic reduction process of the sample which gave Sn plating, and the structure of the cell for electrolytic reduction processes.

  In FIG. 1, 10 is a sample on which Sn reflow plating has been applied, and shows a state in which a Sn oxide film is formed on the surface. 11 is a sample from which the Sn oxide film has been slightly removed by electrolytic reduction treatment, 12 is a sample from which the Sn oxide film has been removed, 20 is a Pt electrode used as a counter electrode, and 21 is used as a reference electrode. It is an Ag / AgCl electrode, 30 is a potentiostat / galvanostat, 41 is an open switch, 42 is a closed switch, 50 is a container, and 60 is an electrolyte.

(1) Preparation of test sample An Sn plating material obtained by applying 1 to 1.5 μm of Ni base plating to the surface of a copper substrate and applying 2 to 3 μm of Sn plating to the surface and performing reflow treatment at 150 ° C. for 360 hours. Heated. The sample after heating lost its metallic luster due to oxidation of the surface and turned grayish. This Sn plated plate was cut into a size for meniscograph test (vertical 2.5 cm, horizontal 1 cm) to prepare a test sample.

(2) Removal of Sn oxide film by electrolytic reduction treatment Electrolytic Solution As the electrolytic solution 60, an ammonia buffer solution containing 1M of NH ₄ OH and NH ₄ Cl was used.

B. Electrolytic reduction The potential of the sample was reciprocally swept between −500 mV and −1600 mV at a rate of 10 mV / sec with respect to the reference electrode 21 by the potentiostat 30. As a result, among the Sn oxides formed on the surface of the sample, black SnO is first reduced to be somewhat whitish, and then white SnO ₂ is reduced to the white color indicated by the original Sn (reference numeral 10 → 11 → 12) and it was visually confirmed that the metallic luster was recovered.

2. Test Results (1) Method for Analyzing Sn Oxide The sample after electrolytic reduction was measured by a voltammetric method using the ammonia buffer as an electrolytic solution, and the surface Sn oxide was analyzed. For comparison, measurement was also performed on a sample before electrolytic reduction treatment.

(2) Analysis results The analysis results are shown in FIG. 2A is a measurement result of the sample before the electrolytic reduction treatment (a voltammogram, and FIG. 2B is a measurement result of the sample after the electrolytic reduction treatment. In FIG. 2, the horizontal axis indicates the potential E (mV) ( (Ag / AgCl electrode reference), the vertical axis is current I (mA), and the measurement temperature is room temperature.

As shown in FIG. 2A, the sample before the electrolytic reduction treatment (comparative example) has peaks due to SnO and SnO _{2 at} −1200 mV and −1450 mV, respectively. As shown in FIG. In the sample (Example) after the reduction treatment, no peak is confirmed, and it can be seen that the Sn oxide film is reliably removed. Note that the oxidation peak in the vicinity of −800 mV and the reduction peak in the vicinity of −900 mV in FIG. 2B appear along with the electrochemical oxidation-reduction reaction, and are not related to the reduction reaction of the Sn oxide. .

3. Test of solder wettability (1) Test method Next, the solder wettability of the sample after electrolytic reduction treatment and before electrolytic reduction treatment was examined using a meniscograph tester. The test conditions were as follows and tested according to JIS Z3198-4.

Meniscograph testing machine: SAT-5100 manufactured by Reska
Immersion speed: 5mm / sec
Immersion depth: 2mm
Immersion time: 10 sec
Test temperature: 260 ° C
Solder used: M705 manufactured by Senju Metal Industry Co., Ltd.
Flux used: (1) JS-900-2FA manufactured by Hiroki Co., Ltd. (2) IPA 25% manufactured by Senju Metal Industry Co., Ltd.
The sample was immersed in the length direction.

(2) Test results The test results are shown in FIG. FIG. 3 is a diagram showing a test result of solder wettability using a meniscograph tester. The two diagrams on the left are for the case where the flux (1) is used, and the two diagrams on the right are for the case where the flux (2) is used. The upper two figures are before electrolytic reduction treatment, the lower two figures are after electrolytic reduction treatment, and in these figures, the horizontal axis is time (sec, second), and the vertical axis Is the wetting force (mN).

  From FIG. 3, the zero cross time after electrolytic reduction treatment when fluxes (1) and (2) are used (the time from when dipping to when the wetting force reverses from negative to positive) is 0.68 sec, 1 It can be seen that the zero crossing time is significantly shortened compared to 10 seconds or longer when fluxes (1) and (2) are used without electrolytic reduction treatment. By performing electrolytic reduction treatment in this way, very good solder wettability is exhibited when any flux is used. Of the fluxes (1) and (2) evaluated this time, it was found that particularly excellent solder wettability was obtained when the flux (1) was used.

10 Sample with Sn oxide film adhered 11 Sample with some Sn oxide film removed 12 Sample with Sn oxide film removed 20 Pt electrode 21 Ag / AgCl electrode 30 Potentiostat / galvanostat 41 Open switch 42 Closed State switch 50 container 60 electrolyte

Claims (1)

A method for removing a Sn oxide film formed on the surface of a Sn-based plating material provided with a plating layer containing Sn,
The Sn-based plating material having the Sn oxide film formed on the surface thereof is a mixed solution of ammonia water and ammonium chloride having an ammonium ion (NH ₄ ⁺ ) concentration of 0.1 to 1 M, or a solution of ammonia water and ammonium sulfate. After immersing in the mixed solution , the Sn oxide film is electrolytically reduced by applying a voltage of -1.3 to -1.5 V with respect to the Sn-based plating material being immersed, based on the Ag / AgCl reference electrode. And removing the Sn oxide film.

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