JP2007057463A - Preparing method of solder sample, solder sample, and analysis method of solder sample - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem, wherein quantitative analysis of a solder material cannot be performed by an X-ray fluorescence analysis device because a solder sample used as a quantitative reference does not exist and sufficient analysis accuracy is not acquired by a surface analyzing apparatus because a component contained in a molten solder segregates during cooling and solidification. <P>SOLUTION: A solder sample of which the contained component hardly segregates can be prepared by a process of cooling and solidifying a molten solder material to produce a solder sample, a process of folding and stacking the cooled and solidified solder sample, and a process of rolling the solder sample. A simple and accurate analysis can be performed by quantitatively analyzing the solder sample with the surface analyzing apparatus. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a solder sample made of a solder material used for joining electronic components and the like, a solder sample, and a method for analyzing a solder sample.

  One of the processes adopted in the mounting technology for producing an electronic circuit board used for various electric products and / or electronic devices is a flow soldering process.

  Hereinafter, a general flow soldering process will be described. In this process, prior to soldering, first, a lead wire of an electronic component is inserted into a through hole to prepare a printed board on which the electronic component is arranged on the upper surface side. At this time, land made of copper foil or the like is formed on the wall surface of the through hole and the region surrounding the through hole on the upper surface side and the lower surface side of the printed circuit board, and this land is connected to the circuit pattern of the printed circuit board. Yes.

  Next, a large number of such printed circuit boards are conveyed at a substantially constant speed by the conveying means in the flow soldering apparatus, and passed over the solder tank. In the solder tank, the solder material is melted in advance, and the melted solder material forms a solder jet by pump means or the like provided in the solder tank. In this process, a much larger amount of solder material is put in the solder tank in a molten state than the amount that can enter the through hole of the substrate. In order to maintain the solder material in a molten state, the solder bath is set to a temperature higher by about 10 to 50 ° C. than the melting point of the solder material to be used. Accordingly, since the solder material exists in a molten state in the solder tank, it exhibits a liquid behavior. Therefore, the solder jet in the solder tank is sprinkled on and contacted with the lower surface of the printed circuit board passing through the solder tank described above.

  The liquid solder material applied to the lower surface of the printed circuit board passes through the annular space between the lead wire of the electronic component and the inner wall of the through hole while getting wet by capillary action from the lower surface of the printed circuit board. After that, it is solidified by lowering the temperature to form a joint made of a solder material. In this way, the lead wire of the electronic component and the land of the printed board are electrically joined by the solder material, and the electronic circuit board is manufactured.

  On the other hand, most of the solder material supplied as described above falls into the solder tank in a molten state by gravity without entering the through hole, and becomes a part of the molten solder material again and circulates. Used. In this circulation process, the molten solder material in contact with the lower surface side of the substrate is actually not only the substrate, but also the wiring pattern formed on the substrate surface, and the plating portion of the lead wire portion of the electronic component and It can also contact the base material. By contact with the molten solder material at a high temperature, the components of the material used in the wiring pattern and the plated portion of the lead part of the electronic component and the base material are eluted into the solder material, and impurities in the molten solder material It becomes.

  In recent years, with increasing interest in protecting the global environment, laws and regulations concerning the disposal of industrial waste such as electronic circuit boards are also progressing, and lead is also becoming the subject of legal regulations worldwide. Corresponding to such laws and regulations, the solder material used for electronic component mounting is shifted from lead solder (Pb-Sn solder) material to lead-free solder material, so-called lead-free solder material. It's getting on.

  When lead-free solder material is used as the solder material, in the above-described flow soldering process, from the electronic component that contacts the molten material at a high temperature, particularly from the plating portion of the lead wire portion of the electronic component The lead component used therein elutes into the molten solder material, and the solder material returns to the solder bath, so that the lead component can become an impurity component in the solder material. The allowable value of the lead component that can be contained in the lead-free solder material is, for example, a very low value of 1000 ppm according to the RoHS (Restriction of Hazardous Substances) directive in the EU, so the solder tank used in the flow soldering process is controlled. Therefore, it is necessary to monitor the composition of the solder material in the tank.

  As methods that can be used to monitor the composition of the solder material, several methods such as atomic absorption spectrometry, ICP (radio frequency inductively coupled plasma) emission spectroscopy, and fluorescent X-ray analysis are known. These methods are used according to the purpose and application. However, if the importance is placed on the relatively short time interval (time span) from sampling until the result is obtained, fluorescence can be used. X-ray analysis is suitable.

About the sample used for X-ray fluorescence analysis, it is preferable that it is solid rather than the form which has fluidity | liquidity like a liquid or powder, and it is preferable that the one side of the solid sample is a smooth surface, In addition, it is known from Patent Document 1 and the like that it is necessary to have a thickness of about 1 mm. When the main component of such a sample is a metal material, the depth at which the irradiated X-ray enters the sample differs depending on the intensity of the irradiated X-ray and the composition of the sample. In the case of materials, information from the surface to a depth of several hundreds of nanometers is generally obtained.
JP 07-128262 A

  Although the operation of the fluorescent X-ray analysis method is simple, in order to obtain sufficient quantitative analysis accuracy, it is necessary to prepare a sample serving as a quantitative reference and correct the apparatus in advance. Currently, there are good commercial products for quantitative reference samples of resin-based materials and general metal materials, but there are no good commercial products for solder materials. The reason is considered to be that segregation is likely to occur when the molten solder material is cooled and solidified.

  When segregation occurs in the solidified sample of the solder material, the composition differs between the surface of the sample or a portion close to the surface and the inside thereof, and thus in the thickness direction. In particular, when quantitatively analyzing the lead component in the solder material, the segregation of the lead component causes the lead component content to differ between the sample surface and the sample interior, and generally the sample surface is greater than the sample interior. The part tends to show a higher content of lead component. Even if such a sample is subjected to fluorescent X-ray analysis, only information about the surface of the sample or a portion close to the surface can be obtained, and an accurate analysis result cannot be obtained. Therefore, until now, it has been difficult to easily perform analysis with sufficient accuracy.

  The present invention solves the above-described conventional problems, and provides a solder sample preparation method, a solder sample, and a solder sample analysis method.

  In order to achieve the above object, a method for producing a solder sample according to the present invention includes a step of cooling and solidifying a molten solder material to form a solder sample, a step of folding and superimposing the cooled and solidified solder sample, and the solder It has the process of rolling a sample. With such a configuration, in the process of cooling and solidifying the molten solder material to obtain a solder sample, even if segregation of the components contained in the solder material occurs, the cooled and solidified solder sample is folded and overlapped. Homogenization is possible by the process and the process of rolling the solder sample, and a solder sample that serves as a quantitative reference for the surface analyzer can be produced.

  The solder sample of the present invention has a multilayer structure, and a single layer has a thickness of 990 nm or less. In addition, each single layer in the multilayer structure has the same composition. With such a configuration, it is possible to quantitatively analyze the solder sample by surface analysis, and by clarifying the composition of the solder sample in advance, it can be used as a quantitative reference sample for the surface analyzer.

  The solder sample analysis method of the present invention is characterized in that the solder sample produced by the solder sample production method is quantitatively analyzed by a surface analyzer. By using a solder sample having a homogenized composition, the solder sample can be easily and accurately analyzed with a surface analyzer.

  As described above, according to the method for producing a solder sample of the present invention, the components contained in the solder sample can be homogenized, and a solder sample serving as a quantitative reference for the surface analyzer can be obtained.

  In addition, since the solder sample of the present invention can be quantitatively analyzed by surface analysis, it can be used as a quantitative reference for a surface analyzer by clarifying the composition of the solder sample in advance.

  Further, according to the solder sample analysis method of the present invention, by using a solder sample whose composition is homogenized, a simple and highly accurate analysis of a solder material composition by surface analysis can be realized.

  Embodiments of the present invention will be described below.

  The method for producing a solder sample of the present invention includes a step of cooling and solidifying a molten solder material to form a solder sample, a step of folding and superimposing the cooled and solidified solder material, and a step of rolling the solder sample. It is characterized by.

  When analyzing a solder sample with a fluorescent X-ray analyzer, information from the surface to a depth of several hundred nm is generally obtained. Therefore, if the film is formed to a thickness of several hundred nm or less by rolling, there is no problem with segregation in the thickness direction of the solder sample in the quantitative analysis using the fluorescent X-ray analyzer.

  Moreover, segregation in the surface direction can also be reduced by repeating the folding and overlapping step and the rolling step.

  Since the solder material sheet having a thickness of several hundreds of nm has low rigidity, there are problems in handling such as wrinkles and tearing. However, by setting the pressure to an appropriate value and repeating the folding and overlapping process and the rolling process, it is possible to make a multilayered solder sample with thin layers, and sufficient rigidity can be secured. It can be handled easily.

  In the present invention, first, a molten solder material is taken out from a solder tank or the like, and cooled and solidified. The solder bath includes Sn-Ag, Sn-Bi, Sn-Zn, Sn-Cu, Sn-Au, Sn-Sb, Sn-Ag-Cu, Sn-Ag-Bi, and Any lead-free solder material selected from the Sn—Ag—Bi—Cu system is stored. The amount of the solder material taken out is not particularly limited, and a part or all of the taken out solder material may be cooled and solidified. The cooling method is not limited to natural cooling or forced cooling using a cooling jig. In the process of folding and stacking the solder sample, tools or a press machine can be used. If the solder sample has high strength and cannot be folded, after the solder sample is thinned with a press machine, etc. You may fold it. Next, the folded solder sample is rolled using a roller mill, a flat plate mill, etc., and the pressure is set so that the solder sample is not broken and can be rolled efficiently. Is preferred. The number of repetitions of the folding and superimposing step and the rolling step can provide a homogenizing effect from the first time. Preferably, the thickness of each layer of the solder sample having a layered structure is 990 nm or less, more preferably 120 nm or less. Set to be. FIG. 1 is a cross-sectional view of a solder sample 1 of the present invention.

  In addition, the repetition of the folding and overlapping process and the rolling process is not limited to alternately performing folding and rolling once, and the frequency of folding and rolling may be arbitrarily set.

  Furthermore, in order to utilize the produced solder sample 1 as a quantitative standard for the surface analyzer, it is necessary to quantify the composition of the solder sample 1. A plurality of solder samples 1 are manufactured under the same conditions in the method of manufacturing the solder sample 1 of the present invention, and a part of the plurality of solder samples 1 is quantitatively measured by an analysis method such as JISZ3910, so that the same conditions are satisfied. The composition of the manufactured solder sample 1 can be quantitatively expressed.

  The quantitative analysis method of the solder material composition of the present invention is characterized in that quantitative analysis is performed using the solder sample 1 produced by the method for producing the solder sample 1 described above.

  The step of cooling and solidifying the molten solder in the present invention, the step of folding the cooled and solidified solder material, and the step of rolling the folded solder material are the steps in the method for producing the solder sample 1 which is a quantitative reference of the surface analyzer. The same is good. The solder sample 1 produced through the process of cooling and solidifying the molten solder material and folding the cooled and solidified solder material and the process of rolling the folded solder material is in a homogeneous state as a sample for surface analysis, Quantitative analysis can be performed with a surface analyzer such as fluorescent X-ray analysis or emission spectroscopic analysis.

  In particular, the fluorescent X-ray analysis can be performed easily and with high accuracy if the solder sample 1 is simple and homogeneous.

  FIG. 2 shows a process flowchart of a simple and highly accurate quantitative analysis method of the solder material composition of the present invention.

(Embodiment 1)
Hereinafter, a method for producing the solder sample 1 serving as a quantitative reference for the surface analyzer according to Embodiment 1 of the present invention will be described in detail.

  Using a handle made of SUS from a solder tank in which a ternary lead-free solder material consisting mainly of tin, silver and copper and containing 96.5% tin, 3% silver and 0.5% copper is melted. Then, about 2 g of the lead-free solder material was taken out and naturally cooled in the handle cage made of SUS to solidify the lead-free solder material. Next, the solidified lead-free solder material was rolled for 1 minute using a hydraulic flat plate mill at a pressure of 2000 kg per square centimeter. As a result of measuring the thickness of the solidified lead-free solder material with a micrometer after the rolling treatment, it was about 1 mm. Next, the rolled lead-free solder material was folded in half at the center using pliers. Next, the folded lead-free solder material was rolled under the same conditions as the rolling, and the thickness was measured. As a result, it was about 1 mm. Further, the folding and the rolling were repeated, and the thickness of the solidified lead-free solder material was measured each time the rolling was performed. As a result, the thickness of the lead-free solder material was about 1 mm each time the rolling was performed.

  When the folding and rolling are performed once, the solidified lead-free solder material has a two-layer structure, and when it is performed twice, a four-layer structure is formed. Thus, each time the folding and rolling are performed once, the number of layers of the solidified lead-free solder material doubles. Further, as described above, even if the folding and the rolling are repeated, the total thickness of the solidified lead-free solder material is substantially constant. For this reason, when the folding and the rolling are performed once, the thickness of the single layer in the multilayer structure of the solidified lead-free solder material is considered to be about ½.

  Next, a cross-sectional observation of the solidified lead-free solder material was performed using an electron microscope, the thickness of the single layer in the multilayer structure was arbitrarily measured at 20 points, and an average value was calculated.

  Table 1 shows the relationship between the folding, the number of repetitions of the rolling, and the thickness of the single layer in the multilayer structure.

  From Table 1, it was confirmed that when the folding and the rolling were performed once, the thickness of the single layer in the multilayer structure was about ½.

  Next, the state of segregation of lead in the solidified lead-free solder material was measured using a fluorescent X-ray analyzer. The segregation situation of lead was evaluated by comparing specific X-ray intensities of lead obtained from each part of the solidified lead-free solder material. The in-plane lead segregation situation was calculated from the variation of the specific X-ray intensities of the lead in a total of five sites including one central portion and four outer peripheral portions in the surface of the solidified lead-free solder material.

  The segregation situation of lead in the thickness direction was calculated from the variation in specific X-ray intensity of lead in five portions in the thickness direction by repeatedly performing fluorescent X-ray analysis and polishing in the thickness direction. First, fluorescent X-ray analysis was performed on the center portions of the front and back surfaces. Next, after polishing about 0.5 g from the surface, the central portion of the polished surface was subjected to fluorescent X-ray analysis. The polishing process and the fluorescent X-ray analysis of the central portion of the polished surface were repeated three times, and together with the analysis results of the front and back surfaces, specific X-ray intensity data of lead at five sites in the thickness direction was obtained.

  X-ray fluorescence analysis was performed using SEA2210A manufactured by SII Nano Technology under the conditions of tube current 1 mA, excitation voltage 31 kv, and measurement time 30 minutes. Table 2 shows the results of repeatedly measuring the specific X-ray intensity of lead in the same part of the same solder sample 1 under the above conditions.

  As shown in Table 2, under the above conditions, the coefficient of variation in repeated measurement was 1.320 (variation coefficient = σ / average value × 100).

  Since the same part is repeatedly measured under the same measurement conditions, the coefficient of variation 1.320 is considered to be a value indicating measurement variation.

  Table 3 shows the measurement result of the characteristic X-ray intensity and the calculation result of the coefficient of variation of the lead at five sites in the surface.

  The coefficient of variation in Table 3 is considered to be the sum of the measurement variation and the in-plane variation of the amount of lead contained in the solder sample 1. In the solder sample not subjected to the folding and rolling, the lead concentration tends to be high at the outer periphery, and the coefficient of variation is 4.472, which is much larger than the coefficient of variation showing the variation at the time of repeated measurement in Table 2. It is increasing. By repeating the folding and rolling, the lead concentration difference between the central portion and the outer peripheral portion is reduced, and when it is repeated 10 times, the coefficient of variation is 1.343, and when it is repeated 13 times, the coefficient of variation is 1.336, and segregation is alleviated. It was confirmed that

  Table 4 shows the measurement result of the characteristic X-ray intensity and the calculation result of variation of the lead in the five parts in the thickness direction.

  In the solder sample not subjected to the folding and the rolling, the lead concentration tends to be high in the surface layer portion, and it was confirmed that the entire solder sample cannot be quantitatively analyzed by the surface analysis.

  Table 5 shows the characteristic X-rays of the lead on the surface of the solder sample 1 by the folding and the rolling by repeating the folding and the rolling for the same solder sample 1 and performing the fluorescent X-ray analysis at each rolling. It is the result of measuring the transition of strength.

  It was found that the lead concentration on the surface of the solder sample 1 was lowered by repeatedly performing the folding and the rolling. This is a phenomenon caused by the fact that lead segregated in the surface layer portion is dispersed by the folding and rolling, the solder sample 1 is homogenized, and the thickness of the single layer in the multilayer structure is reduced. .

  When the number of repetitions of the folding and the rolling is 10 times or more, the decrease in the lead concentration in the surface layer becomes remarkable with the increase in the number of repetitions. In addition, when the number of repetitions was increased at 13 times or more, there was almost no change in the lead concentration, and the value was almost constant.

  When the number of times of folding and rolling is 10 times or more, the single layer thickness in the multilayer structure is 990 nm or less. Generally, when analyzing the solder sample 1 with a fluorescent X-ray analyzer, information from the surface to a depth of several hundred nanometers is obtained. Therefore, when the thickness of the single layer in the multilayer structure becomes 990 nm or less, the influence of the thickness becomes remarkable. It is thought to appear.

  Further, when the folding and rolling are repeated 13 times or more, the single layer thickness in the multilayer structure is 120 nm or less. In the fluorescent X-ray analysis, information from the surface to a depth of several hundred nm is obtained. Therefore, when the thickness of the single layer in the multilayer structure is 120 nm or less, it is considered that the influence of thickness and segregation is greatly reduced.

  Next, ten solder samples 1 were produced by a method of repeating the folding and rolling 13 times. The center part of the front and back surfaces of the ten solder samples 1 produced was subjected to fluorescent X-ray analysis, and the characteristic X-ray intensity of lead was measured. Next, five of the ten solder samples 1 produced were analyzed by atomic absorption using the method of JISZ3910, and the lead content was quantitatively analyzed. Table 6 shows the results of fluorescent X-ray analysis and atomic absorption analysis.

  From the X-ray fluorescence analysis, there was no difference between the front and back in the sample of the solder sample 1 and the variation between the samples of the solder sample 1. Moreover, the variation between the samples of the solder sample 1 was not recognized also from the atomic absorption analysis.

  Using the relationship between the characteristic X-ray intensity of lead measured by the fluorescent X-ray analysis and the lead content measured by the atomic absorption analysis as quantitative reference data of the fluorescent X-ray apparatus, the 10 solder samples 1 produced as described above Among them, five solder samples 1 that were not subjected to the atomic absorption analysis were used as solder samples 1 that serve as a quantitative reference for the fluorescent X-ray analyzer.

(Embodiment 2)
Hereinafter, the quantitative analysis method of the solder material composition of the present invention in Embodiment 2 of the present invention will be described in detail.

  Quantitative analysis of lead content in a solder bath in which ternary lead-free solder material consisting mainly of tin, silver and copper and containing 96.5% tin, 3% silver and 0.5% copper is melted Went.

  Since the step of cooling and solidifying the molten solder material, the step of folding the solder material, and the step of rolling the folded solder material are the same as those in the first embodiment, description thereof will be omitted.

  A solder sample 1 was produced by repeating the step of folding the solder material and the step of rolling the folded solder material 13 times. Next, after quantitatively analyzing the lead content of the solder sample 1 with a fluorescent X-ray analyzer, the lead content was quantitatively analyzed by atomic absorption analysis of JISZ3910 for confirmation. As a result, the quantitative value in the fluorescent X-ray analysis was 705 ppm and the quantitative value in the atomic absorption analysis was 711 ppm, and it was confirmed that simple and highly accurate quantitative analysis was possible.

  According to the method for producing a solder sample of the present invention, it is possible to homogenize the components contained in the solder sample, to obtain a solder sample as a quantitative reference for a surface analyzer, and to obtain a solder material used for joining electronic components and the like. Applicable to composition analysis.

Sectional view of the solder sample of the present invention Process flow chart of quantitative analysis method of solder material composition of the present invention

Explanation of symbols

  1 Solder sample

Claims (8)

A step of cooling and solidifying the molten solder material to form a solder sample;
Folding and stacking the cooled and solidified solder sample;
A method for producing a solder sample, comprising a step of rolling the solder sample folded and overlapped. A step of cooling and solidifying the molten solder material to form a solder sample;
Rolling the cooled and solidified solder sample;
A method for producing a solder sample, comprising the step of folding and overlapping the rolled solder sample. The folding and overlapping step and the rolling step are:
The method for producing a solder sample according to claim 1, wherein the solder sample is repeatedly performed until the thickness of the single layer of the solder sample becomes a thickness in a predetermined range. The target solder material is a lead-free solder material, Sn—Ag, Sn—Bi, Sn—Zn, Sn—Cu, Sn—Au, Sn—Sb, Sn—Ag—Cu. The method for producing a solder sample according to any one of claims 1 to 3, wherein the material is any material selected from a Sn-Ag-Bi system and a Sn-Ag-Bi-Cu system. A solder sample having a multilayer structure, wherein a single layer has a thickness of 990 nm or less. The solder sample according to claim 5, wherein each single layer in the multilayer structure has the same composition. A method for analyzing a solder sample, characterized in that a solder sample produced by the method for producing a solder sample according to claim 1 is quantitatively analyzed by a surface analyzer. 8. The method for analyzing a solder sample according to claim 7, wherein the surface analyzer is an X-ray fluorescence analyzer.

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