IEC 61249-3-3:1999

Overview

IEC 61249-3-3:1999 defines requirements for adhesive coated flexible polyester film (PETP) used in the manufacture of flexible printed wiring and flexible printed boards. It covers one-sided (coverlay/covercoat) and two-sided (bonding film) adhesive-coated polyester films, specifying material construction, thickness ranges, adhesive types, required properties after curing, and packaging/marking rules. The standard is intended for material suppliers, PCB fabricators and testing labs involved in flexible printed circuit (FPC) production.

Key Topics and Technical Requirements

• Material composition: Flexible polyester (PETP) film coated with B‑staged adhesives of polyester, acrylic or epoxide type.
• Film thickness (without adhesive): Preferred nominal values and maximum permitted tolerances-examples include 25 µm (±20%), 50 µm (±15%), 75–125 µm (±10%).
• Adhesive thickness: Defined as the difference between coated and uncoated thickness; typical adhesive thickness range 12.5 µm to 75 µm with ±20% tolerance. Preferred adhesive thicknesses: 20, 25, 38, 50, 75 µm.
• Designation: Standardized code format (example) - PET-IEC-61249-3-3-A-25-50-0-FV1, indicating film type, adhesive type (A/E/P), adhesive and film thicknesses and flammability rating.
• Electrical properties after curing (selected values from IEC 61189-2 tests):
  • Surface resistance: ≥ 2×10^12 Ω (min) in humidity chamber (optional)
  • Volume resistivity: ≥ 2×10^4 Ω·m (min)
  • Relative permittivity (after damp heat): ≤ 4.5
  • Dielectric dissipation factor: ≤ 0.05
  • Electrical strength: ≥ 60 kV/mm
• Copper foil bond & mechanical:
  • Peel strength: ≥ 0.7 N/mm as received; ≥ 0.6 N/mm after 10 s thermal shock
  • No blistering or delamination after thermal shock
• Dimensional stability (coverlays): Limits on shrinkage due to peeling or heating (e.g., ≤ 2.5 µm/mm for peeling).
• Packaging/marking: Rolls only (standard lengths 50/75/100 m), core ID ≥ 75 mm, limited splices, and mandatory roll labeling (manufacturer, material ID, thicknesses, batch, date, etc.).
• Normative references: IEC 60249-1 (test methods), IEC 61189-2 (test methods for interconnection materials).

Applications and Who Uses It

• Flexible printed circuit (FPC) manufacturers selecting coverlays or bonding films for multilayer flex and rigid-flex PCBs.
• Material suppliers specifying PETP film product data sheets and compliance claims.
• PCB fabricators applying lamination and bonding processes, ensuring adhesive flow and bond strength.
• Test laboratories and QA teams verifying electrical, mechanical and dimensional properties per IEC 61189-2 referenced methods.
• Sectors: consumer electronics, automotive electronics, medical devices and other industries using flexible interconnects.

Related Standards

• IEC 60249-1 - Base materials test methods
• IEC 61189-2 - Test methods for materials for interconnection structures

Keywords: IEC 61249-3-3, adhesive coated polyester film, PETP, coverlay, bonding film, flexible printed boards, peel strength, electrical strength, lamination, flexible PCB materials.