IEC 61249-3-4:1999

Overview

IEC 61249-3-4:1999 is an international sectional specification from IEC for adhesive coated flexible polyimide film used in flexible printed boards and other interconnecting structures. It defines material construction, adhesive types (acrylic or epoxide), dimensional limits, performance requirements and packaging/marking rules for films coated on one side (coverlay/covercoat) or both sides (bonding films). The standard references IEC 61189-2 test methods for electrical and mechanical verification.

Key topics and technical requirements

• Material & construction
  • Flexible polyimide base film coated on one or both sides with B-staged acrylic or epoxy adhesives.
  • Film thickness preferred values: 12.5, 25, 50, 75, 125 μm with specified maximum tolerances (e.g., 12.5 μm ±30%, 25 μm ±20%, 50 μm ±15%, 75 μm ±10%, 125 μm ±10%).
  • Adhesive thickness range: 12.5 μm to 75 μm; preferred thicknesses: 20, 25, 38, 50, 75 μm (±20% tolerance).
• Electrical properties after curing (measured per IEC 61189-2)
  • Surface and volume resistivity minimums (after damp heat): ≥ 10^10 Ω·m (volume) and ≥ 10^10 Ω (surface) where applicable.
  • Dielectric strength: ≥ 60 kV/mm.
  • Relative permittivity ≤ 4.5, dissipation factor ≤ 0.05 (after damp heat/recovery where specified).
• Mechanical / bond properties
  • Copper peel strength: ≥ 0.7 N/mm as received; ≥ 0.6 N/mm after 10 s thermal shock; ≥ 0.35 N/mm after dry heat at 125 °C (optional).
  • No blistering or delamination after thermal shock.
  • Dimensional stability for coverlays: peeling-induced change ≤ 1.5 μm/mm; heating at 150 °C change ≤ 3.0 μm/mm.
• Packaging, marking and roll tolerances
  • Rolls on cores ≥ 75 mm ID; standard lengths 50, 75 or 100 m; slit-width tolerance ±1 mm (±5 mm if not slit).
  • Marking must include manufacturer, material ID, film/adhesive thickness, coating sides, flammability grade, batch/roll number, length/width, manufacturing date.
• Testing & acceptance
  • Test methods: normative reference IEC 61189-2; sampling and acceptance to be agreed between purchaser and supplier.

Applications and users

• Typical uses: coverlay/covercoat for flexible printed wiring, bonding films for lamination in flexible/rigid-flex PCBs, local mechanical/environmental reinforcement.
• Primary users:
  • PCB designers and manufacturers (flex and rigid-flex fabrication)
  • Materials suppliers and laminators
  • Quality assurance and test laboratories
  • Procurement/specification engineers for electronics and aerospace/automotive electronics where flex circuits are used

Related standards

• Normative test methods: IEC 61189-2 (test methods for materials for interconnection structures)
• Related materials standards in the IEC 61249 series (e.g., base material flammability in IEC 61249-3-2)

Keywords: IEC 61249-3-4, adhesive coated flexible polyimide film, flexible printed circuit, coverlay, bonding film, polyimide film, peel strength, dielectric strength, IEC 61189-2.