ISO 9455-16:2019

Overview

ISO 9455-16:2019 specifies a standardized flux efficacy test using the wetting balance method to assess how well a liquid soft-soldering flux promotes wetting of a metal surface by molten solder. The method provides a qualitative comparative assessment between a test flux and a standard flux (for example, a reference rosin-based flux). It applies to all liquid flux types classified in ISO 9454-1 and is intended for laboratory evaluation of flux performance under controlled surface and environmental conditions.

Key Topics and Requirements

• Test principle: Measure wetting force vs time using a wetting balance; compare test flux performance to a standard flux.
• Scope: Applicable to liquid fluxes classified in ISO 9454-1; current method is comparative (qualitative) though provisions exist for reproducible surface preparation to move toward quantitative use.
• Apparatus: Wetting balance and instrumentation in accordance with IEC 60068-2-69; solder bath capable of maintaining liquidus + 35 °C.
• Solder alloys and temperatures: Examples provided include Sn60Pb40 at 235 °C ± 3 °C and Sn96.5Ag3.0Cu0.5 at 255 °C ± 3 °C; other combinations possible by agreement.
• Test pieces: Copper strips (typical width 10.0 mm ± 0.1 mm; thickness 0.10 mm or 0.30 mm); clean, burr-free, handled with clean tongs.
• Surface preparation / ageing: Multiple options to simulate realistic or contaminated surfaces:
  • Artificial sulfidation (Annex B)
  • Steam ageing (per IEC 60068-2-20)
  • Damp-heat steady-state ageing (per IEC 60068-2-78)
• Procedure highlights:
  • Clean test pieces (acid clean, rinses, acetone)
  • Apply flux, allow solvent evaporation (typical drying 20 s ± 5 s, adjustable by agreement)
  • Immerse at 20 mm/s ± 5 mm/s to 3 mm ± 0.2 mm or 4 mm ± 0.2 mm depth, hold 5–10 s, withdraw at same speed
  • Record wetting-force trace; perform 10 replicates per flux and complete within 45 minutes of preparation
• Results: Typical trace shows wetting force vs time; analysis compares characteristic wetting times and forces against the standard flux prepared per Annex A.

Applications and Users

• Who uses it: flux manufacturers, solder material suppliers, electronics manufacturing engineers, quality assurance labs, and R&D teams developing or qualifying soft soldering fluxes.
• Practical uses:
  • Comparative evaluation of new flux formulations
  • Incoming inspection and supplier qualification
  • Process development for wave or selective soldering where flux wetting behavior is critical
  • Failure analysis to determine flux-related wetting deficiencies

Related Standards

• ISO 9454-1 - Classification and requirements for soft soldering fluxes
• IEC 60068-2-69 - Wetting balance (force measurement) method
• IEC 60068-2-20 - Steam ageing (solderability tests)
• IEC 60068-2-78 - Damp-heat steady-state ageing
• ISO 9453 - Solder alloy composition references

Keywords: ISO 9455-16:2019, wetting balance method, flux efficacy test, soft soldering fluxes, solderability, ISO 9454-1.