1Scope This test method specifies two methods for the determination of the acid value of a flux of type L,M or H.
Method A is a potentiometric titration method and is to be considered the reference method.
Method B is an alternative,visual end-point,titration method. 2Applicable Documents
ISO9455Soft Soldering Fluxes,Test Methods
IPC-TM-650Test Methods Manual
2.3.34Solids Content,Flux
IPC J-STD-004Requirements for Soldering Fluxes
3Test Specimen A minimum of2.0grams of liquid flux,10 grams of solder paste,150grams of cored wire or10grams of solder preforms.
4Apparatus and Reagents
4.1General
4.1.1Use only reagents of recognized analytical quality and only deionized water.
4.1.2Ordinary laboratory apparatus.
4.2For Potentiometric Titration Method(Method A)
4.2.1Tetrabutyl ammonium hydroxide,0.1M(0.1mole/L). Use a commercially available standard solution or one pre-pared from a commercially available concentrated standard solution by dilution with2-propanol(4.2.2).Alternatively,pre-pare a0.1M tetrabutyl ammonium hydroxide solution by dilut-ing a commercial concentrated solution with2-propanol and standardize this solution against an accurately weighed amount of benzoic acid(about0.5g)dissolved in dimethylfor-mamide,previously neutralized to thymol blue.
4.2.22-Propanol.Neutralized with tetrabutyl ammonium hydroxide solution(4.2.1)to a faint pink color using phenol-phthalein as an indicator.4.2.3Ethanol,anhydrous.Neutralized with tetrabutyl ammo-nium hydroxide solution(4.2.1)to a faint pink color using phe-nolphthalein as an indicator.
4.2.4Toluene.Neutralized with tetrabutyl ammonium hydroxide solution(4.2.1)to a faint pink color using phenol-phthalein as an indicator.
4.2.5Ethanol/toluene mixture.Mix equal volumes of the neutralized anhydrous ethanol(4.2.3)and neutralized toluene (4.2.4).
4.2.6Phenolphthalein Indicator.
4.2.7Millivoltmeter or pH meter.
4.2.8Glass electrode.
4.2.9Saturated calomel,or silver chloride/silver,electrode.
4.2.10Magnetic or mechanical stirrer with variable speed drive.
4.2.11Burette capable of delivering aliquots of0.1ml to1.0 ml.
4.3For Titration with Visual End-Point(Method B)
4.3.1Ethanol,anhydrous.Neutralized with potassium hydroxide,0.1M in alcohol(4.3.5),to a faint pink color using phenolphthalein as an indicator.
4.3.2Toluene.Neutralized with potassium hydroxide,0.1M in alcohol(4.3.5),to a faint pink color using p
henolphthalein as an indicator.
4.3.3Ethanol/toluene mixture.Mix equal volumes of the neutralized anhydrous ethanol(4.3.1)and neutralized toluene (4.3.2).
4.3.42-Propanol.Neutralized with potassium hydroxide,0.1 M in alcohol(4.3.5),to a faint pink color using phenolphthalein as an indicator.
Material in this Test Methods Manual was voluntarily established by Technical Committees of IPC.This material is advisory only
and its use or adaptation is entirely voluntary.IPC disclaims all liability of any kind as to the use,application,or adaptation of this
material.Users are also wholly responsible for protecting themselves against all claims or liabilities for patent infringement.
Equipment referenced is for the convenience of the user and does not imply endorsement by IPC.
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4.3.5Potassium hydroxide solution,0.1M in alcohol.Use a commercially available standard solution or one prepared from a commercially available concentrated standard solution by dilution with ethanol(4.3.1).Alternatively,prepare an approxi-mate0.1M potassium hydroxide solution by dissolving3±0.1g potassium hydroxide(KOH)in500ml of ethanol(4.3.1), and standardize this solution against an accurately weighed amount of benzoic acid(about0.5g)dissolved in ethanol (4.3.1).
4.3.6Phenolphthalein indicator solution.Add1g of phenol-phthalein to approximately50ml methanol and mix.When dissolved,dilute to100ml with methanol and mix.
5Procedures
5.1Potentiometric Titration(Method A)
faint
5.1.1By preliminary experiments,determine whether the sample is soluble in2-propanol,anhydrous ethanol,toluene or the ethanol/toluene mixture.If the sample is not completely soluble in any of these solvents,select the one in which the sample appears to be the most soluble.If the sample is equally soluble in all four solvents,then use neutralized 2-propanol(4.2.2).
5.1.2Carry out the following procedure,in triplicate,on the flux sample.
5.1.2.1Weigh,to the nearest0.001g,2to5g of the liquid flux sample,taking steps to prevent loss of volatile matter during the weighing.The larger size(≈5g)sample is required for very low solids fluxes.Transfer the weighed sample to a 250ml low form beaker.
5.1.2.2Dilute the sample to100ml with2-propanol(4.2.2), or the selected solvent(4.2.3to4.2.5),according to the solu-bility characteristics of the flux.Cover with a watch glass and dissolve the flux by gentle agitation.
5.1.2.3Place the beaker on the stand of the titration assem-bly with the electrodes,stirrer and burette in position.Adjust the speed of the stirrer to give vigorous stirring without splash-ing.Titrate with the0.1M tetrabutyl ammonium hydroxide solution(4.2.1),adding1.0ml portions and recording the pH or mV meter reading after each addition.As the end-point is approached,reduce the additions of titran
t to0.1ml and con-tinue titrating past the end-point.5.1.2.4Plot the pH or potential values against the volume of titrant added to obtain the titration curve.The point of inflec-tion of the curve corresponds to the end-point of the titration.
Note:The point of inflection of the curve may conveniently be determined by using the derivative curve.
5.1.2.5Carry out a blank determination,using reagents only,for comparison purposes.
5.2Visual Titration(Method B)
5.2.1By preliminary experiments,determine whether the sample is soluble in2-propanol,anhydrous ethanol,toluene or the ethanol/toluene mixture.If the sample is not completely soluble in any of these solvents,select the one in which the sample appears to be the most soluble.If the sample is equally soluble in all four solvents,then use neutralized etha-nol(4.3.1)as the selected solvent.
5.2.2Carry out the following procedure,in triplicate,on the flux sample.
5.2.2.1Weigh,to the nearest0.001g,sufficient flux sample to correspond to approximately1g of nonvolatile matter(see IPC-TM-650,Test Method2.3.34),taking steps in the case of liquid flux sample
s to prevent loss of volatile matter during the weighing.
5.2.2.2Transfer the weighed sample to a suitable flask or beaker and add100ml of the selected solvent.Stir until the sample has dissolved as completely as possible.Do not heat.
5.2.2.3Add three drops of phenolphthalein indicator solu-tion(4.3.6)and titrate with the0.1M potassium hydroxide solution(4.3.5)until a faint pink color persists throughout the titrated solution for15seconds.
5.2.2.4Carry out a blank determination,using reagents only,for comparison purposes.
5.3Calculation of Results The acid value is expressed in milligrams of potassium hydroxide per gram of nonvolatile matter,regardless of the alkali used to perform the titration.
5.3.1The acid value(expressed in milligrams of potassium hydroxide per gram of nonvolatile matter)is given by:
56.11VM
mS
Revision
A
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Revision
A
Where:
V is the volume,in ml,of alkali used(tetrabutyl ammonium
hydroxide for Method A,potassium hydroxide for Method B).
M is the molarity of the alkali used.
m is the mass,in grams,of the sample taken.
S is the percentage nonvolatile matter,expressed as a frac-
tion,determined as described in IPC-TM-650,Test Method
2.3.34.
5.3.2The acid value of the flux under test is calculated as
the mean of the results obtained on each of the three test
samples.
6Notes
6.1Safety Observe all appropriate precautions on MSDS
for chemicals involved in this test method.
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