ISO 9455-3:2019

Overview

ISO 9455-3:2019 is an internationally recognized standard that specifies test methods for determining the acid value of soft soldering fluxes, specifically types 1 and 2 as defined in ISO 9454-1. The standard presents two methods for measuring the acid value:

• Method A: Potentiometric titration method (reference method)
• Method B: Visual end-point titration method (alternative procedure)

Both methods provide accurate and reliable ways to quantify the acid value-a key parameter that impacts flux performance during soldering operations. This standard is essential for manufacturers, quality control laboratories, and researchers working with soft soldering fluxes.

Key Topics

Acid Value Determination

• The acid value indicates the amount of acidic substances present in the soldering flux. It is expressed in milligrams of potassium hydroxide (KOH) per gram of non-volatile matter.
• Measuring acid value is critical for ensuring fluxes meet performance standards and help maintain reliable solder joints.

Method A – Potentiometric Titration

• Involves titrating a prepared flux solution with a standard solution of tetrabutylammonium hydroxide using a glass electrode and pH or millivoltmeter readings.
• The acid value is calculated based on the titration curve’s inflection point, which signals the completion of neutralization.
• Suitable solvents for sample dissolution include propan-2-ol, ethanol, toluene, or an ethanol/toluene mixture depending on solubility.
• Supports both manual and automated titration procedures for laboratory flexibility.

Method B – Visual Titration

• Utilizes an indicator (phenolphthalein) to visually detect the endpoint of titration with potassium hydroxide solution in an alcohol medium.
• Considered an alternative to potentiometric titration, suitable where instrumentation is limited.
• Requires careful solvent selection for flux solubility and accurate endpoint detection.

Sampling and Preparation

• Flux samples must be accurately weighed and dissolved without loss of volatile components.
• Tests are performed in triplicate to ensure reproducibility.

Calculation and Reporting

• Acid values are computed using standardized formulas considering sample weight, titrant volume, and solution normality.
• Results are averaged from replicate tests and include blank determinations to ensure accuracy.

Applications

• Quality Control: Ensures flux acid levels comply with manufacturing specifications, which affects solderability and corrosion resistance.
• Material Certification: Validates flux batches prior to shipment and use in electronics manufacturing.
• Research and Development: Assists in assessing the effect of flux composition on solder joint quality by monitoring acid levels.
• Compliance Testing: Meets regulatory requirements for flux performance and safety in international markets.

Implementing the ISO 9455-3:2019 testing protocols enhances production reliability and maintains consistent soldering quality, minimizing failures in electronic assemblies.

Related Standards

• ISO 9454-1: Defines flux types 1 and 2, providing classification relevant to acid value testing.
• ISO 9455-1 and ISO 9455-2: Provide complementary test methods for determining non-volatile content in soft soldering fluxes, which is foundational for accurate acid value calculations.
• ISO/IEC Directives: Guidelines for the development and harmonization of ISO standards and test procedures.

Adhering to ISO 9455-3:2019 alongside these related ISO standards ensures comprehensive evaluation of soldering flux quality and supports standardization efforts in electronics manufacturing worldwide.