JP2011033377A - METHOD OF QUANTITATING Sn OXIDE AND METHOD OF EVALUATING FLUX - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of quantitating an Sn oxide, capable of accurately quantitating the composition and amount of an oxide film formed on the surface of an Sn-based plating material, as well as, to provide a method of evaluating flux capable of accurately evaluating the active force of flux for soldering. <P>SOLUTION: By the method of quantitating an Sn oxide, an Sn-based plating material formed on the surface of an Sn oxide is dipped into a prescribed ammoniac buffer solution, electrolytic reduction treatment of the Sn oxide is performed by a chronopotentiometry method or a voltammetry method, and the Sn oxide is quantitated from reduction potential and the amount of electricity required for reduction. The method of evaluating flux includes a first quantitative process for quantitating the Sn oxide in the plating material; a heating process for coating the plating material with flux for heating to soldering temperature; and a second quantitative process for quantitating the Sn oxide in the plating material after heating; and by the method of evaluating flux, the active force of flux is evaluated by the reduction ratio obtained from the amount of Sn oxide acquired in the first and second quantitative processes. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a Sn oxide quantification method and a flux evaluation method. Specifically, the Sn oxide quantification method formed on the surface of a Sn-based plating material provided with a Sn-containing plating layer and the quantification method are used. The present invention relates to a method for evaluating a soldering flux.

  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.

  However, a Sn oxide film (hereinafter referred to as “oxide film”) is formed on the surface of the Sn-based plating material by contacting air or chemicals or receiving a thermal history. There are many cases.

  If such an oxide film is formed at a place where soldering is performed, the melting point of this oxide film is higher than that of Sn or Sn alloy, so that the solder wettability on the surface of the Sn-based plating material is lowered and sufficient strength is obtained. Can not be soldered.

  For this reason, when performing soldering, it is necessary to remove the oxide film formed on the surface of the Sn-based plating material to expose and activate the surface of Sn or Sn alloy to ensure sufficient solder wettability. There is. In general, flux is used as a material having such a function.

  However, depending on the type of flux, the removal ability of the oxide film (hereinafter also referred to as “flux activation power”) is different, and the characteristics with respect to solder wettability are also different. It is necessary to grasp in advance the composition and amount of the oxide film formed on the surface, and based on this, it is necessary to employ an appropriate flux that can sufficiently remove the oxide film and improve solder wettability.

  For this purpose, it is necessary to accurately quantify the oxide film formed on the surface of the Sn-based plating material and to evaluate the activity of the flux in advance for various fluxes based on the accurate quantification. .

  By adopting an appropriate flux from the flux whose activity is evaluated in advance, it is possible to improve the efficiency of the soldering operation and optimize the process after soldering.

  Regarding the above-described quantitative determination of the oxide film and evaluation of the activity of the flux, the following techniques are disclosed.

  In Patent Document 1, as a method for evaluating the activity of a flux, a metal plate at 20 ° C. (room temperature) and 400 ° C. is immersed in the flux to be evaluated for 20 minutes, and the amount of the eluted metal is analyzed by atomic absorption analysis or ICP ( Inductively coupled plasma (Inductively Coupled Plasma) is a technique that is measured by an emission analysis method and determines that the higher the amount of eluted metal, the better the solder wettability when using the flux.

  However, this method evaluates under two temperature conditions of normal temperature and 400 ° C., and the soldering temperature (250 to 300 ° C.) of the soldering flux that is made to exhibit the effect at the mounting temperature. It is hard to say that it is sufficient as an evaluation of the activity in

In addition, since the metal concentration determined by this method is very dilute on the order of 10 ⁻² ppm, it is difficult to perform quantitative measurement with high accuracy.

Next, in Patent Document 2, Sn is obtained by a chronopotentiometry method (CP method) using a borate buffer solution (0.1 MH ₃ BO ₃ +0.025 M Na ₂ B ₄ O ₇ ). A method for quantifying oxides (SnO and SnO ₂ ) and evaluating solder wettability is disclosed.

This method reduces the oxide film by applying a constant negative current to the sample and monitors the potential with respect to time, and utilizes the fact that the potential changes little (plateau) while the oxide is reduced. is doing. That is, when the measurement result is represented in a graph by the relationship between potential and time, a flat portion (plateau portion) appears in the process of reducing specific oxides (SnO and SnO ₂ ). Then, the weight of the Sn oxide can be obtained on the basis of the product of the given negative current and the length (time) of the flat portion, that is, the amount of electricity, assuming that Faraday's law is established.

In this measurement process, it is considered that SnO is reduced first and SnO ₂ is subsequently reduced, and it is said that SnO ₂ has a greater adverse effect on solder wettability than SnO (non-patent) Reference 1).

  In the above method, the Sn oxide state is evaluated and the relationship with the solder wettability is examined. The state of the metal surface such as XPS (X-ray photoelectron spectroscopy) or XRD (X-ray diffraction) is used. In the surface instrumental analysis method that is widely used as another analysis, it is difficult to evaluate Sn oxide according to the state, and therefore the electrochemical CP method is used.

However, when a borate buffer solution is used in this CP method, the measured value varies greatly depending on the measurement conditions, and it is difficult to correctly confirm the separation of the two plateau portions of SnO and SnO ₂ described above. There are many cases.

JP 63-104776 A US Pat. No. 5,262,222

S. Cho et al., “Oxidation study of pure tin and it's alloys via electrical chemical analysis”, J. Am. Electronic Mater. 34 (2005) P635

  As described above, when the conventional method is used, it is difficult to accurately quantify the oxide film formed on the surface of the Sn-based plating material. For this reason, it is possible to reliably evaluate the activity of the flux. It was difficult.

  In view of the above problems, the present invention provides a Sn oxide quantification method capable of accurately quantifying the composition and amount of an oxide film formed on the surface of a Sn-based plated material, and the activity of a soldering flux. It is an object of the present invention to provide a flux evaluation method capable of accurately evaluating force.

  As a result of intensive studies, the present inventor has found that the above-mentioned problems can be solved by the invention of each claim shown in the following claims, and has completed the present invention. The invention of each claim will be described below.

The invention described in claim 1
An Sn-based plating material with Sn oxide formed on the surface is immersed in a predetermined ammonia-based buffer solution, and electrolytic reduction treatment of Sn oxide is performed using the chronopotentiometry method or voltammetry method to reduce the reduction potential and reduction. This is a Sn oxide quantification method characterized in that Sn oxide is quantified from the amount of electricity required.

  The present inventor conducted various experiments on a method capable of accurately quantifying Sn oxide regardless of measurement conditions, and used an chronopotentiometry method or a voltammetry method, and an ammonia-based buffer as an electrolyte. It was found that the Sn oxide can be quantified accurately and stably by adopting.

Specifically, by adopting an ammonia-based buffer solution as an electrolytic solution in these methods and performing electrolytic reduction treatment, two types of Sn oxides (SnO and SnO ₂ ) formed on the surface of the Sn-based plating material are obtained. Each can be confirmed accurately, and based on this, each Sn oxide can be accurately quantified.

That is, in the chronopotentiometry method in which the potential is measured while applying a constant negative current to the measurement sample, the respective plateau portions of SnO and SnO ₂ are correctly confirmed by adopting an ammonia-based buffer as the electrolyte. be able to. The amount of each Sn oxide can be accurately quantified based on the product of the applied negative current and the length (time) of the flat portion (plateau portion), that is, the amount of electricity.

Further, in the voltammetry method in which the current is measured while changing the potential, the reduction peaks of SnO and SnO ₂ can be clearly confirmed by employing an ammonia-based buffer as the electrolyte. Then, by obtaining the peak area, the amount of each Sn oxide can be accurately quantified.

As described above, according to the present invention, the amount of Sn oxide can be accurately quantified by any of the chronopotentiometric method and the voltammetric method by adopting an ammonia-based buffer as the electrolytic solution. Can do. In the voltammetry method, SnO and SnO ₂ are confirmed by the reduction peak, so that the measurement result can be easily grasped visually, which is preferable to the chronopotentiometry method.

Examples of the ammonia-based buffer include a mixed solution of ammonia water (NH ₄ OH) and ammonium chloride (NH ₄ Cl) having a total molar concentration of 0.1 to 1.5 M as ammonium ions (NH ₄ ⁺ ). A mixed solution of ammonia water (NH ₄ OH) and ammonium sulfate ((NH ₄ ) ₂ SO ₄ ) or the like is preferably used.

As the concentration of the ammonia-based buffer solution, particularly in the voltammetry method, an ammonia buffer solution in which the two kinds of reagents in the above mixed solution are about 0.5 M each is preferable. When the concentration is low, the SnO ₂ reduction peak tends to be unclear, which is not preferable. On the other hand, when the concentration is high, the SnO ₂ reduction peak is sharp and increases in intensity, but the SnO ₂ reduction peak appears on the lower potential side and is affected by hydrogen generation, making it difficult to estimate the peak area. Thus, accurate quantification becomes difficult.

  In the present invention, the “Sn-based plating material” refers to a plating material in which a plating layer containing Sn, such as Sn or Sn alloy, is provided on the surface of a base material.

The invention described in claim 2
The Sn oxide quantification method according to claim 1 is repeated twice, difference data is created from the first quantification result and the second quantification result, and the reduction of the Sn oxide based on the difference data This is a method for quantifying Sn oxide, characterized in that the amount is determined.

In the voltammetry method, the SnO ₂ reduction peak appears on the low potential side, but it is easily affected by the hydrogen generation reaction, making it difficult to estimate the peak area and perform quantification.

  In the invention of this claim, the quantification is repeated twice, and the difference data is created from the first quantification result and the second quantification result, thereby reducing the influence of the hydrogen generation described above. For this reason, more accurate quantification can be performed.

The invention according to claim 3
A first quantification step of quantifying Sn oxide in the Sn-based plating material having Sn oxide formed on the surface;
A heating step of heating to a soldering temperature after applying flux to the plating material;
A second quantification step for quantifying Sn oxide in the plated material after heating;
And an evaluation step of evaluating the activity of the flux by determining a decrease rate of the Sn oxide amount obtained in the second quantification step with respect to the Sn oxide amount obtained in the first quantification step. ,
3. The flux evaluation method according to claim 1, wherein the first quantification step and the second quantification step are quantification by the Sn oxide quantification method according to claim 1 or 2.

  In the invention of this claim, using the Sn oxide quantification method according to claim 1 or 2, the amount of oxide before flux application is accurately quantified in the first quantification step, and the second Since the amount of oxide after oxide reduction and removal by flux is accurately quantified in the determination step, the rate of decrease in the amount of Sn oxide can be accurately determined, and the activity of the flux can be accurately evaluated.

  And in a 2nd fixed_quantity | assay process, since the flux is heated to soldering temperature, it can be said that an evaluation result is evaluation along mounting temperature.

  In general, the same measurement method is used in the first quantitative process and the second quantitative process. That is, when the chronopotentiometry method is used in the first quantification step, the chronopotentiometry method is also used in the second quantification step, and when the voltammetry method is used in the first quantification step. The voltammetry method is also used in the second quantitative step.

  The present invention provides a Sn oxide quantification method capable of accurately quantifying the composition and amount of an oxide film formed on the surface of a Sn-based plating material, and accurately evaluates the activity of a soldering flux. It is possible to provide a flux evaluation method that can be used.

It is a figure which shows typically the structure of the electrochemical measurement cell used for embodiment of this invention. It is a linear sweep voltammogram in various ammonia system buffer solutions from which the density about the Sn board in which an oxide film was formed differs. It is a linear sweep voltammogram about six types of Sn board from which an oxide film formation processing time differs. A linear sweep voltammogram is a diagram for explaining a procedure for quantifying the SnO and SnO _2. It is a figure which shows the measurement result of the chronopotentiometry (CP) method using the boric-acid type buffer solution and ammonia type buffer solution about Sn board in which the oxide film was formed. A linear sweep voltammogram of the solution of NH 4 _Cl and 0.5M ammonia-based buffer solution 1M of Sn plate oxide film is formed. At 180 ° C. is a linear sweep voltammogram of the solution of NH 4 _Cl in 1M for Sn-plated copper plate was oxide film formation process. It is a linear sweep voltammogram in a 0.5M ammonia buffer solution about Sn plating copper plate heat-processed at 180 degreeC. It is a linear sweep voltammogram in a boric acid system buffer solution and an ammonia system buffer solution about Sn board in which an oxide film was formed. It is a cyclic voltammogram in the ammonia type buffer solution about Sn board before flux application. It is a figure which shows the relationship between an oxide film removal rate and solder wettability (zero cross time).

  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.

A. Method for Quantifying Sn Oxide First, examples relating to a method for quantifying Sn oxide will be described.

1. Embodiment [1] Embodiment 1
In this example, Sn oxide on the surface of Sn is quantified by a voltammetric method using an ammonia-based buffer solution containing NH ₄ OH and NH ₄ Cl at a molar ratio of 1: 1 as an electrolytic solution.

1-1. Selection of Ammonia Buffer Solution Concentration First, the appropriate concentration of the ammonia buffer solution was examined.

(1) Measuring method a. Configuration of Electrochemical Measurement Cell First, the electrochemical measurement cell used in this example will be described. FIG. 1 is a diagram schematically showing the configuration of an electrochemical measurement cell used in this example. (1) of FIG. 1 is a figure which shows the surface of the sample which the acid-added film adhered, (2) It is a figure which shows the state which has stopped the electrolytic reduction once in the middle of electrolytic reduction. (3) is a diagram showing a state immediately before the end of electrolytic reduction.

  In FIG. 1, 10 is a sample to which an oxide film is attached after heat treatment, and 11 is a sample in the middle of a linear potential sweep, and a sample (test electrode: negative electrode) from which some oxide film has been removed by electrolytic reduction. , 12 is a sample from which the oxide film has been removed, 20 is a counter electrode (positive electrode) made of Pt, 21 is an Ag / AgCl electrode (reference electrode), 30 is a potentiostat / galvanostat, and 41 is The switch is in an open state, 42 is a switch in a closed state, 50 is an electrolytic solution container, and 60 is an ammonia buffer solution (electrolytic solution).

B. Concentration of ammonia-based buffer solution used in concentration selection test Six concentrations of NH ₄ OH and NH ₄ Cl were 0.1M, 0.3M, 0.5M, 1.0M, 2.0M and 4.0M, respectively. A concentration ammonia-based buffer solution was used.
C. Test sample (test electrode)
The Sn plate was heated at 180 ° C. for 4 hours (hours), and then heated at 85 ° C. and a relative humidity of 85% for 24 hours (hereinafter, this heat treatment condition is also referred to as “standard heating condition”). An oxide was formed.

D. Measurement by voltammetry The linear potential sweep method was used as the voltammetry method. Specifically, the sample is immersed in each of the six concentrations of the ammonia-based buffer solution, and the potential of the test electrode is 10 mV / sec from the immersion potential (potential when the sample is immersed in the electrolyte). The current was measured by sweeping to a hydrogen evolution potential at a rate.

(2) Measurement results The measurement results are shown in FIG. As shown in FIG. 2, in the case of using an ammonia buffer solution having a concentration of 0.5 M or more, reduction peaks were observed in the vicinity of −1200 mV and −1450 mV. The reduction peak around −1200 mV is a reduction peak corresponding to the reduction reaction of SnO. In addition, it has been confirmed by X-ray diffraction evaluation that this peak indicates a reduction reaction of SnO. Further, the reduction peak near -1450mV is reduction peak corresponding to the reduction reaction of SnO _2.

Thus, when an ammonia buffer solution having a concentration of 0.5 M or more is used, a reduction peak corresponding to the reduction reaction of SnO and SnO ₂ can be reliably observed. Then, it was found that the amount of electricity required for the reduction reaction was obtained from the area of each reduction peak, and SnO and SnO ₂ could be quantified based on the obtained amount of electricity.

On the other hand, at a molar concentration of 0.3 M or less, the shape of the SnO ₂ reduction peak is unclear, indicating that it is not suitable for analysis according to the oxidation state of Sn in which SnO and SnO ₂ exist. Further, from FIG. 2, when the concentration of ammonia-based buffer solution greater than 0.5M, the influence of hydrogen generation is increased (the hydrogen at the same time as the reduction reaction of SnO ₂ is generated, the reduction current corresponding to the reduction of SnO ₂ Therefore, it is difficult to obtain the peak area, that is, the amount of electricity. For this reason, it was found that a concentration of about 0.5M was appropriate for the measurement.

1-2. Experiment Using Samples with Different Surface Oxidation States Next, measurement was performed by the above-described linear potential sweep method using a 0.5M ammonia buffer solution as the electrolyte and samples having different surface oxidation states. Hereinafter, this experiment will be described.

I. Preparation of samples Five types of samples in which a Sn plate was heated at 180 ° C. for 4 hours and then heated at 85 ° C. and 85% relative humidity for 2 hours, 4 hours, 6 hours, 8 hours, and 16 hours to form a film-like oxide on the surface. Was made.

B. Measurement Method The concentration of the ammonia-based buffer solution was fixed at 0.5 M, and the measurement was performed by the same measurement method as described in 1-1.

C. Measurement result
FIG. 3 shows the measurement results of the above five types of samples. Moreover, the measurement result of the sample heat-processed on above-mentioned standard heating conditions is also shown collectively. As shown in FIG. 3, in this experiment, a reduction peak was observed in the vicinity of -1200 mV for all the samples, and a reduction peak was also observed in the vicinity of -1450 mV for the samples other than 2h and 4h.

The peak near -1200 mV is almost the same for the sample heated at 85 ° C. and 85% relative humidity for 4 hours or more, whereas the peak near −1450 mV increases as the heating time increases. From this, it can be seen that SnO ₂ selectively increases in a high humidity state. Thus, according to this Embodiment, it was confirmed that the measurement result reflecting the oxidation state of the surface of each sample is obtained. In the case of the voltammetry method, the measurement result is expressed as a reduction peak, so that it is easier to understand visually than the CP method described later.

1-3. Procedure for obtaining the peak area of the reduction peak As described above, it is difficult to accurately obtain the peak area of the reduction peak of SnO ₂ directly from the measurement results shown in FIGS. In the present embodiment, the peak area of the reduction peak of SnO ₂ is obtained with high accuracy by removing the influence of the hydrogen generation reaction by the following procedure. Hereinafter, the contents will be described with reference to FIG.

I. Step 1
FIG. 4 is a diagram illustrating a procedure for quantifying SnO and SnO ₂ from a linear sweep voltammogram. First, the first measurement is performed under the measurement conditions described above. That is, the potential of the sample is swept from the immersion potential to the hydrogen generation potential at a rate of 10 mV / sec, and the current is measured. In the first measurement, the total value of the reduction current corresponding to the Sn oxide reduction reaction and the reduction current corresponding to the hydrogen generation reaction is measured. The measurement results are shown in the upper part of FIG.

B. Step 2
The potential of the sample after the first measurement (the sample from which SnO and SnO _{2 on the} surface have been reduced and removed by the first measurement) is returned to the immersion potential of the first measurement, and again the hydrogen generation potential as in the first measurement. Sweep until measured. In the second measurement, only the reduction current corresponding to the hydrogen generation reaction is measured. The measurement results are shown in the middle diagram of FIG.

C. Step 3
Subtract the second measurement result from the first measurement result. The results are shown in the lower part. The lower part is a diagram showing the difference (data) from which the measurement error due to the influence of the hydrogen generation reaction is removed. As shown in the lower part, the base line of the SnO ₂ reduction peak portion approaches flat, and thus it can be seen that the peak area is easily obtained. The Sn oxide can be accurately quantified by the above procedure.

[2] Example 2
This example relates to a Sn oxide quantification method in which a 0.5 M ammonia buffer solution is used as an electrolytic solution and Sn oxide on the surface of the Sn plate is quantified by the CP method.

(1) Sample and measurement method a. Sample An Sn plate heat-treated under the standard heating conditions in Example 1 was used as a sample.
B. Measurement method The temporal change in potential was measured when electrolytic reduction was performed at a constant current by the CP method. Specifically, electrolytic reduction was performed at a constant current at a current density of 1 mA / cm ² , and the potential during that time was measured.

(2) Measurement results FIG. 5 is a diagram showing measurement results by the CP method using a boric acid buffer solution and an ammonia buffer solution of an Sn plate heat-treated under standard heating conditions. The results are shown in the lower part of FIG. When an ammonia-based buffer solution was used as the electrolyte, a flat portion corresponding to the reduction reaction of SnO and SnO ₂ was observed as shown in the lower part of FIG. As described above, even when electrolytic reduction is performed using the CP method, two kinds of Sn oxides of SnO and SnO ₂ can be accurately quantified by using an ammonia-based buffer solution as in the case of using the voltammetry method. I understood.

2. Comparative Example For comparison, a test was also conducted on a method for determining Sn oxide by electrolytic reduction of Sn oxide using an NH ₄ Cl solution and a boric acid buffer solution as an electrolytic solution. Hereinafter, each test method and test result will be described.

[1] Comparative Example 1
Comparative Example 1 is an example in which an NH ₄ Cl solution was used as the electrolytic solution and measurement was performed by a voltammetry method.

I. Measuring method a. Samples Samples that were heat-treated under the standard heating conditions in the above examples and samples that were heat-treated at 180 ° C. for 2 h, 4 h, 6 h, and 8 h were used.
b. Electrolyte 1M NH ₄ Cl solution (pH 4.9) was used.
c. Measurement method Measurement was performed by the linear sweep voltammetry method. Specifically, the potential of the sample (test electrode) was swept from the immersion potential (0 V) to the hydrogen generation potential at a rate of 10 mV / sec in the same manner as in the example, and the current was measured.

B. Measurement results a. FIG. 6 is a linear sweep voltammogram in a 1M NH ₄ Cl solution and a 0.5M ammonia-based buffer solution of a Sn plate heat-treated under the standard heating conditions. The measurement result when using a 1M NH ₄ Cl solution is shown in the upper part of FIG. In addition, the measurement results of the present invention using a 0.5 M ammonia buffer solution (pH 9.4) are shown in the lower part of FIG. 6 for comparison.

From the top of FIG. 6, even in a 1M NH ₄ Cl solution, a reduction peak corresponding to the reduction reaction of SnO and SnO ₂ appears, and if there is a concentration of about 1M as NH ₄ ⁺ ions, SnO and SnO ₂ are separated. It can be seen that measurement is possible. However, it can be seen that the 1M NH ₄ Cl solution is more susceptible to hydrogen generation than the ammonia-based buffer solution of the present invention shown in the lower part.

b. Measurement Result of Sample Heat Treated Sn Plated Cu Plate at 180 ° C. The measurement result is shown in FIG. Further, for comparison, FIG. 8 shows the measurement results when the ammonia-based buffer solution of the present invention is used for the same thermal history Cu plate, that is, the same sample as that used in the measurement of FIG.

As shown in FIG. 7, even when a 1M NH ₄ Cl solution is used, a reduction peak corresponding to the SnO reduction reaction is observed. In addition, two peaks that are thought to correspond to the reduction reaction of the Cu—Sn alloy composite oxide are observed on the right side of the SnO reduction peak, but a difference is observed in the behavior of the reduction peaks in FIGS. That is, in the case of FIG. 7, it can be seen that the peak intensity is smaller than the two reduction peaks shown in FIG. 8 except for the reduction peak adjacent to the SnO reduction peak of the sample heated for 2 hours. This is presumably because the complex oxide of the Cu—Sn alloy dissolved in the slightly acidic 1M NH ₄ Cl solution before the measurement. Thus, when an ammonia-based buffer solution is used, measurement can be performed more accurately. Note that the samples used for the measurements in FIGS. 7 and 8 are heat-treated under the condition that SnO ₂ is not generated, and therefore no reduction peak of SnO ₂ is observed.

From the above, if it is limited to the evaluation of SnO and SnO ₂ , it is possible to use a 1M NH ₄ Cl solution, but there is a drawback that it is more susceptible to the hydrogen generation reaction than the ammonia-based buffer solution. Moreover, when making Sn plating Cu board | plate into a measuring object, it turned out that required information may not be fully obtained.

[2] Comparative Example 2
Comparative Example 2 is an example in which a boric acid buffer solution was used as an electrolytic solution, and Sn oxide was quantified by a voltammetric method and a CP method.

I. Measuring method a. Sample A sample heated under standard heating conditions was used.
b. Electrolytic Solution A boric acid buffer solution, specifically, a 0.1 MH ₃ BO ₃ +0.025 M Na ₂ B ₄ O ₇ solution was used.
c. Measurement method c-1. Voltammetry The measurement was performed under the same measurement conditions as in Example 1 by the linear potential sweep method.
c-2. CP Method The CP method was measured under the same measurement conditions as in Example 2.

B. Measurement results a. Measurement result by voltammetry method The measurement result by the voltammetry method is shown in the upper part of FIG. Moreover, the measurement result at the time of using the 0.5M ammonia buffer solution of this invention is combined with the lower stage of FIG. 9 for a comparison. When a boric acid buffer solution was used, no clear reduction peak corresponding to these reduction reactions was observed for both SnO and SnO ₂ as shown in the upper part of FIG. On the other hand, in the case of using the ammonia-based buffer solution, SnO, SnO ₂ together clear reduction peak was observed.

b. Measurement Result by CP Method The upper part of FIG. 5 used in Example 2 shows the measurement result by the CP method of this comparative example. Further, the lower part of FIG. 5 shows the measurement results when the 0.5M ammonia buffer solution was used as described above. As shown in the upper part of FIG. 5, in the case of the CP method, SnO and SnO ₂ cannot be separated. In particular, it can be seen that the behavior of SnO ₂ is difficult to understand and measurement is difficult. In the CP method, a current density of 20 μA / cm ² is recommended, but at such a low current density, depending on the amount of oxide film, it takes several hours to measure, and removal of dissolved oxygen with an inert gas is essential. Therefore, it is not preferable. From the above, it was confirmed that it is difficult to quantify Sn oxide by the CP method using a boric acid buffer solution.

B. Flux Evaluation Method Next, a flux evaluation test using a voltammetry method to which an ammonia-based buffer solution is applied will be described. In this example, after four kinds of fluxes are applied to two kinds of samples, the ability to remove Sn oxide by the flux when heated to the same temperature as soldering is measured, and the samples after heating by the meniscograph method This is an example of evaluating the solder wettability.

(1) Method for quantifying Sn oxide on sample surface a. Measurement of sample before flux application a. Preparation of Test Samples First, three test samples were prepared by cutting two types of samples, Sample A and Sample B, into a width of 10 mm and a length of 25 mm.

b. Quantification of Sn oxide on sample surface by voltammetry method Next, the initial oxide amount of each of the prepared sample A and sample B for each of the three sample surfaces was 0.5 M with good measurement results obtained in Example 1 above. It was measured by a voltammetric method using an ammonia-based buffer solution. In addition, the measurement measured the 1st measurement of the procedure mentioned above and the 2nd measurement continuously using the cyclic voltammetry method, and obtained the measurement result which removed the measurement error by the influence of hydrogen generation reaction. The measurement results are shown in FIG. (A) of FIG. 10 is a figure which shows the measurement result of the sample A, (b) is a figure which shows the measurement result of the sample B. For sample A, two reduction peaks are observed around 1450 mV and 1200 mV for all three samples as shown in (a), and for sample B, three reduction peaks are shown as shown in (b). One reduction peak was observed around 1450 mV in all of the samples. The total amount of Sn oxide was determined from the amount of electricity determined based on the peak area for each of Sample A and Sample B.

B. Measurement of sample after flux application / heating Next, a predetermined amount of four kinds of fluxes to be evaluated, fluxes 1 to 4, are attached to the surfaces of separately prepared samples A and B, and the soldering temperature is up to 260 ° C. After heating, the flux was removed by washing, and in this state, the amount of oxide adhering to the sample for evaluation test was measured by the cyclic voltammetry method in the same manner as described above to determine the total amount of Sn oxide. .

(2) Quantitative Results of Sn Oxide Tables 1 and 2 show the quantitative results of Sn oxides of Sample A and Sample B before flux application and after flux application / heating, respectively. In the table, mC is a unit of millicoulomb of electricity.

  As a result of the test, the oxide removal ability of each of the samples A and B for each of the flux 1 to the flux 4 was quantitatively evaluated as the oxide removal rates shown in Tables 1 and 2.

(3) Solder wettability test a. Test Method The solder wettability of Sample A and Sample B, which were coated and heated with Flux 1 to Flux 4, was tested in accordance with JIS Z3198-4 using a meniscograph tester.

In addition, immersion of the sample A and the sample B was made into the height direction.
The test conditions are as follows.
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.

  A meniscograph test was performed under the above conditions, and wettability was evaluated using zero cross time.

B. Test results The test results are shown in FIG. FIG. 11 is a graph showing the relationship between the solder wettability measured using a meniscograph tester and the oxide removal rate measured by the voltammetry method. The horizontal axis of FIG. 11 is the oxide removal rate by each flux shown in Tables 1 and 2, and the vertical axis is the zero cross time (time from immersion until reaction force becomes zero) (s). Also, ◆ is sample A, and □ is sample B. From FIG. 11, the larger the oxide removal rate, the smaller the zero crossing time and the better the solder wettability. The relationship between the oxide removal rate and the solder wettability corresponds well with the theory, and the evaluation of the flux is You can see that it is done correctly. As a result, it can be seen that the flux can be evaluated by measuring the oxide removal rate using a voltammetric method to which an ammonia-based buffer solution is applied or a Sn oxide quantitative method by the CP method.

  As described above, it was confirmed that the oxide quantification method by the voltammetry method using the ammonia-based buffer solution of this example is an effective method for evaluating the flux. The CP method using an ammonia-based buffer solution is also an effective method. When evaluating the superiority or inferiority of several types of flux, apply each flux to be evaluated to a sample with the same oxide film formation state based on actual soldering, heat, and then wipe off the flux. Each sample is completely reduced by a voltammetric method or an CP method using an ammonia-based buffer solution, and the Sn oxide removal rate of each flux is obtained.

10 Sample with oxide film 11 Sample with some oxide film removed 12 Sample with oxide film removed 20 Pt electrode 21 Ag / AgCl electrode 30 Potentiostat / galvanostat 41 Closed switch 42 Open switch 50 Electrolyte container 60 Ammonia buffer solution

Claims (3)

  An Sn-based plating material with Sn oxide formed on the surface is immersed in a predetermined ammonia-based buffer solution, and electrolytic reduction treatment of Sn oxide is performed using the chronopotentiometry method or voltammetry method to reduce the reduction potential and reduction. A method for quantifying Sn oxide, comprising quantifying Sn oxide from the amount of electricity required.   The Sn oxide quantification method according to claim 1 is repeated twice, difference data is created from the first quantification result and the second quantification result, and the reduction of the Sn oxide based on the difference data A method for quantifying Sn oxide, characterized in that the amount is determined. A first quantification step of quantifying Sn oxide in the Sn-based plating material having Sn oxide formed on the surface;
A heating step of heating to a soldering temperature after applying flux to the plating material;
A second quantification step for quantifying Sn oxide in the plated material after heating;
And an evaluation step of evaluating the activity of the flux by determining a decrease rate of the Sn oxide amount obtained in the second quantification step with respect to the Sn oxide amount obtained in the first quantification step. ,
The flux evaluation method, wherein the first quantification step and the second quantification step are quantification by the Sn oxide quantification method according to claim 1 or 2.

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