Overview
EN ISO 9455-3:2020 - Soft soldering fluxes - Test methods - Part 3: Determination of acid value, potentiometric and visual titration methods (ISO 9455-3:2019) is a CEN-adopted ISO standard describing two validated laboratory methods for measuring the acid value of soft soldering fluxes of types 1 and 2 (as defined in ISO 9454‑1). The document specifies a potentiometric titration (Method A) as the reference method and an alternative visual end‑point titration (Method B), including reagents, apparatus, procedures (manual and automated), calculation and reporting requirements.
Key topics and technical requirements
- Scope: Applies only to flux types 1 and 2 (ISO 9454‑1).
- Methods:
- Method A - Potentiometric titration (reference): dissolve a weighed sample (≈0.5 g solid or 2.0 g liquid) in a suitable solvent (propan-2-ol, anhydrous ethanol, toluene or ethanol/toluene mix), titrate with 0.1 M tetrabutyl ammonium hydroxide, record pH or mV, plot titration curve and determine the end-point from the inflection (derivative) of the curve.
- Method B - Visual titration: alternative titration using a visual indicator to identify the end-point.
- Reagents: analytical grade solvents and a standardized tetrabutyl ammonium hydroxide solution (0.1 mol/l) are specified; solvents should be neutralized as indicated.
- Apparatus: pH/millivolt meter, glass electrode, saturated calomel or Ag/AgCl reference electrode, stirrer, burette, and optionally an automated titration system with processor unit.
- Procedure controls: carry out determinations in triplicate, use blank determinations, select solvent based on solubility, and document automated system settings per manufacturer manual.
- Reporting: calculation method and required test report content are defined; precision information is included in the standard.
Applications and users
This standard is practical for:
- Flux manufacturers performing quality control of soft soldering flux acidity.
- Independent testing laboratories and QC departments verifying conformity of flux batches.
- Electronics assemblers, soldering engineers and procurement teams needing objective acid value data for process control and material selection.
- Standards committees and compliance officers referencing harmonized European/ISO methods.
Practical benefits include standardized, reproducible acid-value measurement for process optimization, material comparison, and traceable QC records.
Related standards
- ISO 9454‑1 - Classification of soft soldering fluxes (flux types 1 and 2).
- ISO 9455‑1 / ISO 9455‑2 - Related test procedures referenced for non-volatile matter and sample handling.
- EN ISO 9455 series - other parts covering additional flux test methods.
Keywords: EN ISO 9455-3:2020, acid value, soft soldering fluxes, potentiometric titration, visual titration, tetrabutyl ammonium hydroxide, flux testing, ISO 9454-1, soldering flux QC.
