JPH08211035A - Analysis of solder flux - Google Patents

Abstract

PURPOSE: To rapidly analyze solder flux with high accuracy by extracting the org. acid of the flux bonded to a soldered processed product with pure water using ultrasonic waves and separating the org. acid component of an aq. soln. CONSTITUTION: The terminal part of an electronic part is immersed in org. acid (formic acid) flux in a state fitted with a case and taken out of the flux to be dried under heating to be immersed in an eutectic solder tank and a very small amt. of formic acid is bonded to the electronic part in a mist form. This electronic part is extracted with ultrapure water using ultrasonic waves and the formic acid bonded to the part is recovered to obtain an analytical sample as an aq. soln. Namely, because the org. acid of the solder flux bonded to the electronic part can be extracted with ultrapure water and the extract can be used as it is, the regulation of the analytical sample is rapid. Next, the org. acid component is separated by the separation column 14 using carbonate in an eluate 12 and using an anion exchange resin of ion chromatography and electric conductivity is measured to determine ions. By this constitution, solder flux can be rapidly analyzed with high accuracy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flux component analysis method for soldering electronic components, and more particularly to analysis of organic acids for evaluating the residual residue of low molecular weight carboxylic acid as a solder flux on components. Regarding the method.

[0002]

2. Description of the Related Art Electronic devices have been rapidly reduced in size, weight and density. Surface mounting has become widespread instead of insertion mounting, which has been the main method of mounting electronic components. Along with this, the soldering joint is also changing from a flow method to a reflow method using a solder paste.

Conventionally, soldering of electronic parts is performed by, for example,
A solder flux containing a rosin-based material and a halogen-based component added as an activator was often used. Generally, the soldering flux is necessary to clean the surface of the metal to be soldered, but dirt such as solder flux residue causes a decrease in surface insulation resistance.
A cleaning process is essential.

Conventionally, for this cleaning, it has been general to use CFC having characteristics such as cleaning property, drying property and low toxicity. However, due to the problem of ozone depletion of the global environment, CFC regulations have been implemented, and alternative cleaning agents are being investigated. In addition, as a countermeasure against this, consideration is being given to eliminating cleaning in the assembly process of electronic components. At present, for example, organic acids such as formic acid, which is a carboxylic acid, are applied to the solder flux. This is because there is little flux residue and it is possible to eliminate the need for cleaning and to reduce costs.

The organic acid-based solder flux may slightly adhere and remain on electronic parts, and it is necessary to evaluate the influence of the organic acid on other materials and corrosiveness. In particular, in order to evaluate the amount of organic acid in the solder flux adhering to the electronic component after soldering, there is a demand for a method for quantifying it quickly and accurately. Generally, a standard method for analyzing organic acids in a mixture is described in "Analytical Chemistry Handbook", 4th edition (1991), edited by The Japan Society for Analytical Chemistry. The method is a method in which an organic acid is extracted into an organic solvent, an insoluble calcium salt is obtained after the separation, and a treatment is further applied to carry out a fractional quantification. Further, it has been suggested that, for example, formic acid, which is an organic acid used in the solder flux, can be analyzed by qualitative analysis by infrared absorption analysis (IR method) or gas chromatograph (GC method) after separation and purification.

[0006]

However, the standard analytical method described above is an acid fractionation method especially from plants,
It cannot be applied as it is. The organic acid of the solder flux is a low molecular weight carboxylic acid, and it is considered that a trace amount of mist remains attached to electronic parts.
The state after the recovery is an aqueous solution. Formic acid, which is an organic acid, can be qualitatively analyzed by infrared absorption analysis, but there is no established quantitative analysis method including a sample preparation method. In any case, these methods require a long time for the analytical operation and are not quick.

The present invention has been made in view of the above points, and an object thereof is to extract a plurality of low molecular weight carboxylic acids adhering to an electronic component to prepare an analytical sample and fractionate and quantify the carboxylic acid in the obtained extract. Another object of the present invention is to provide a method for rapidly and highly accurately analyzing a low molecular weight carboxylic acid attached to an electronic component.

[0008]

According to the present invention, the above-mentioned object has an analytical sample preparing step and a quantitative measuring step, and the analytical sample preparing step comprises the organic acid of the solder flux attached to the soldered product. Is a step of ultrasonically extracting the organic acid with pure water to prepare an aqueous solution of an organic acid. The quantitative step is to adsorb the aqueous solution on a predetermined anion exchange resin column and use carbonate as an eluent to analyze the organic acid component by ion chromatography. Is separated and the electrical conductivity is measured to determine the amount of each organic acid.

In the above invention, it is effective that the organic acid is a low molecular weight carboxylic acid, or that the eluent is a mixed solution of sodium carbonate and sodium hydrogen carbonate. As a low molecular weight carboxylic acid, an ionic species [formate ion HCOO ⁻ , acetate ion CH ₃ COO ⁻ ,
Formic acid, acetic acid, produced by oxalate ion (C00) ^2- ],
Oxalic acid.

The amount of solder flux attached to a component is evaluated as the amount of one component or unit area by converting the amount of organic acid ions into the absolute amount of organic acid.

[0011]

The organic acid of the solder flux adhering to the electronic component is extracted with pure water, and the analytical sample can be prepared quickly. In particular, since the extract is used as it is for the quantification step,
It eliminates the need for complicated pretreatment such as conventional solvent extraction for organic acid analysis, separation and purification, and treatment for each analytical component.

The low molecular weight carboxylic acid is a component in the solder flux, and the effect of organic acid can be evaluated. A mixed aqueous solution of sodium carbonate and sodium hydrogen carbonate can be applied to a low molecular weight carboxylic acid / inorganic acid coexisting system and enhances the analysis accuracy of organic acids.

[0013]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a flow chart showing an analytical sample preparation procedure according to an example of the present invention. Electronic parts are cases with terminals,
For soldering, for example, organic acid formic acid is used as a flux,
Formic acid having a concentration of 87% is prepared in the flux tank. The terminals of the parts are immersed in the flux for a few seconds while still attached to the case, then heated and dried at about 200 ° C, and then immersed in a bath of Sn63% -Pb37% eutectic solder heated to about 250 ° C for a few seconds. Then, the pre-soldering of components is completed.

In this process, a small amount of formic acid adheres to the parts as mist. This electronic component is ultrasonically extracted with ultrapure water to recover the formic acid adhering to the component, and the analytical sample is obtained in the state of an aqueous solution. The extraction operation consists of an extraction container (volume 500 ml beaker) and a container for measuring ultrapure water and extracting liquid (volume 1).
(00 ml volumetric flask), the electronic components of the sample are placed in the extraction container, 100 ml of ultrapure water is injected, and then ultrasonic extraction (10 minutes) is performed. The ultrasonic extraction method is effective in collecting deposits from the details of electronic components.

Furthermore, when the liquid after extraction contains a suspended matter different from the organic acid as the analytical component, the piping (Teflon loop) is clogged during the subsequent measurement by ion chromatography, which may cause an obstacle. Therefore, filtration operation is performed. The filtration operation is a cartridge type filter (Pore S
ize 0.45 μm) with a syringe for sample injection, and the filtrate becomes an analytical sample.

The organic acid of the solder flux adhered to the electronic component in this manner can be recovered by pure water extraction because it has the property of being soluble in water, and in particular, since the extract can be used as it is, The preparation is quick. Ion quantification is by ion chromatography. FIG. 2 is a layout showing the structure of the ion chromatograph. The ion chromatograph separates ionic species from each other according to their affinity, the size of the hydrated ionic radius, and the interaction of van der WaaIs in the ion-exchange resin column by a predetermined measurement system for each anion and cation species.

In the case of quantifying inorganic anions, an anion exchange resin is used in the separation column 14 of FIG.
A weak electrolyte carbonate solution is used for. The removal system 15 is for removing ions other than the target ionic species after the ionic species have been separated in the separation column 14, that is, for removing the electrolyte component used in the eluent, and has a low electric conductivity. Reduce the ground to improve detection sensitivity. 13 is a pump, 16 is a conductivity cell, 17 is a conductivity meter, 18 is a recorder, and 19 is waste water.

For example, in the case of inorganic anion analysis, the
Carbonate (sodium carbonate (Na ₂CO₃)] Is used
Often. In the separation column and removal system,
Ions are separated by the reaction shown. In separation column: Resin- N⁺HCO₃ ^-+ Na⁺ X^-→ Resin- N
⁺ X^-+ Na⁺HCO₃ ^- In the removal column: Resin- SO₃ ^- H⁺+ Na⁺HCO₃ ^-→ Resin
-SO₃ ^-Na⁺+ H₂CO₃ Resin- SO₃ ^- H⁺+ Na⁺ X^-→ Resin-SO₃ ^-Na⁺+ H
⁺ X^- There is no separation and measurement of anions using a carbonate system as the eluent.
Analysis of machine anions [Example: F^-, CI^-, NO₂ ^-， PO_Four ^3- , Br
^-, NO₃ ^-, SO_Four ^2-] Is applied.

FIG. 4 is a diagram showing a chromatogram of a normal anion. FIG. 3 is a diagram showing a chromatogram of organic acid ions according to an example of the present invention. In the same manner as described above, formate ion, acetate ion, and oxalate ion in the aqueous solution were measured by ion chromatography. The low molecular weight carboxylate ion species can be separated, and the type of ion is known. Further, it can be seen that the measurement can be performed in a short time of about 18 minutes.

Separation and measurement of organic acid ions of low-molecular-weight carboxylic acid are determined by the combination with the applicable separation column, and in many cases, a borate system is used as the eluent. However, if both organic acid ions and inorganic anions can be separated and quantitatively analyzed at the same time, it will be extremely effective for analytical evaluation. This time, we examined various conditions for separation and measurement of organic ions and inorganic anions by ion chromatography, and found the conditions for separation and measurement of organic acid ions by using a carbonate system as an eluent.

The conditions for separating and quantifying the organic acid ions at this time are as follows. <Measurement conditions> Device: Ion chromatograph Separation column: Anion exchange resin packed column Eluent: 0.0024M Na ₂ CO ₃ + 0.003M NaHCO
₃ Eluent flow rate: 2 ml / min Removal system: Cation removal system [Regeneration solution used (0.025NH ₂ SO ₄ )] Analytical sample amount: 5 μl Conductivity full scale: 30 μS / cm The calibration curve for the ion chromatography method is determined in advance. The standard solution containing the ionic species to be measured is prepared by the least square method from the relationship between the peak intensity and the ion concentration.

FIG. 5 is a diagram showing the calibration relationship of organic acids. Characteristic curve 21 shows formate ion (HCOO ⁻ ), 22 shows acetate ion (CH ₃ COO ⁻ ), and 23 shows oxalate ion (COO) ^{2 −} . In all cases, a calibration curve with good linearity was obtained. This empirical formula is shown in. ^{HCC - (mg / l) =} 0.1085χ-0.0577 ............, phase coefficient ^{_{0.999 CH 3 COO - (mg /}} l) = 0.6348χ-0.0976 ............, phase coefficient 0.999 (COO) ^2- (mg / l) = 0.9091 χ -0.9091 ............, phase coefficient 0.999 where χ is the peak height (mm) of the chromatogram. The correlation coefficient between peak height and ion concentration in liquid is 0.999.
It can be seen that the result is good and the amount can be quantified with high accuracy.

The organic acid of the solder flux is, for example, a low molecular weight carboxylic acid and is in an aqueous solution state obtained by extraction with ultrapure water. Therefore, in order to evaluate the analysis accuracy, a standard solution of the same aqueous solution is used. The accuracy of analysis of organic acid ions is important. Table 1 shows the results of examining the accuracy of repeated analysis of the standard solution using the calibration curve of FIG. It can be seen that the repeated analysis accuracy is good when the coefficient of variation is about 2% or less.

[0024]

[Table 1] Table 2 shows the results obtained by measuring the formate ion by the ion chromatography method and applying the calibration curve of FIG. 5 to the extract obtained by the analysis of the soldering electronic parts using formic acid flux of the actual sample by the sample preparation method of FIG. .

[0025]

[Table 2] Regarding the analysis results in Table 2, the extraction liquid is 100 ml in total amount obtained by the method shown in FIG. The lower limit of quantification was 0.01 mg in the amount of formic acid per electronic component, and it was found that about 1 mg was attached in the actual sample, and the amount of formic acid can be analyzed and evaluated.

According to the present invention, the time required for analysis is accelerated because the analysis is completed within 1 hour per sample including the sample preparation. As described above, the present invention can be applied to the evaluation of the amount of the organic acid attached to the component of the solder flux, because the solder flux can be measured quickly and accurately by the method of analyzing the organic acid.

[0027]

According to the present invention, it has an analytical sample preparation step and a quantitative determination step, and the analytical sample preparation step ultrasonically extracts the organic acid of the solder flux adhering to the soldered product with pure water. Since it is made into an aqueous solution, an analytical sample applicable to ion chromatography can be rapidly prepared. In the quantification step, since the organic acid component is separated and the electric conductivity is measured by ion chromatography using carbonate as an eluent in a predetermined anion exchange resin column, rapid and highly accurate analysis is possible. is there.

In this way, an analysis method can be obtained which enables quick and highly accurate evaluation of the amount of adhesion to the component after soldering using the flux of the organic acid of the electronic component. In addition, since organic acids are low molecular weight carboxylic acids, they are ion-dissociated in an aqueous solution, which makes it possible to directly study the influence of organic acids on electronic components. When a mixed system of sodium carbonate and modified sodium carbonate is used as an eluent, there is no interference of inorganic ions, and the analytical accuracy is further enhanced.

[Brief description of drawings]

FIG. 1 is a flow chart showing a procedure for preparing an analytical sample according to an embodiment of the present invention.

FIG. 2 is a layout diagram showing a configuration of an ion chromatograph according to an embodiment of the present invention.

FIG. 3 is a diagram showing a chromatogram of organic acid ions according to an example of the present invention.

FIG. 4 is a diagram showing a chromatogram of inorganic anions.

FIG. 5 is a diagram showing the calibration relationship of inorganic acids.

[Explanation of symbols]

 11 Analytical Sample Liquid Injection Port 12 Eluent 13 Pump 14 Separation Column 15 Removal System 16 Conductivity Cell 17 Conductivity Meter 18 Recorder 19 Waste Water

Claims (3)

[Claims] 1. An analytical sample preparing step and a quantifying step, wherein the sample preparing step ultrasonically extracts the organic acid of the solder flux adhering to the soldered product with pure water to obtain an aqueous solution of the organic acid. The quantification step is the step of preparation, in which the aqueous solution is adsorbed on a specified anion exchange resin column and the organic acid component is separated by ion chromatography using a carbonate-based eluent and the electrical conductivity is measured to determine the organic acid. A method for analyzing a solder flux, which is characterized by quantifying the amount. 2. The analysis method according to claim 1, wherein the organic acid is a low molecular weight carboxylic acid. 3. The analysis method according to claim 1, wherein the carbonate-based eluent is a mixed solution of sodium carbonate and sodium hydrogen carbonate.