IEC 61249-4-5:2005

Overview

IEC 61249-4-5:2005 is an international sectional specification for polyimide, modified or unmodified, woven E‑glass prepreg of defined flammability used as unclad bonding sheets in multilayer printed boards. The standard defines material construction, appearance and cured properties, flammability classification (vertical burning test), delivery forms (rolls, sheets, cut panels), quality assurance and ordering information. The published text specifies a minimum glass transition temperature (Tg) for fully cured material of 170 °C and uses brominated flame retardants incorporated in the polymeric structure to achieve the defined flammability rating.

Key topics and requirements

• Materials and construction
  • Reinforcement: woven E‑glass fabric (per IEC 61249-6-3)
  • Resin system: polyimide (modified or unmodified) impregnated and B‑staged
• Thermal and electrical properties
  • Glass transition temperature (Tg): 170 °C minimum (after curing per supplier instructions)
  • Electric strength after cure: minimum 25 V/µm (measured on bonded plies)
• Flammability
  • Defined by a vertical burning test on cured specimens; flame resistance provided by brominated retardants integral to the resin
• B‑stage and process parameters (examples and tolerances)
  • Resin content: typical tolerance ±3%
  • Treated weight: typical tolerance ±3%
  • Resin flow: typical tolerance ±5%
  • Melt viscosity and gel time are specified by agreement between user and supplier (example tolerances provided in the document)
  • Volatile content ≤ 2% (maximum)
• Appearance and mechanical limits
  • Dewetted areas (“fish eyes”) > 10 mm not permitted; ≤10 mm limited to 10 per 300 × 300 mm
  • Distortion/non‑perpendicular yarn orientation ≤ 10% over 300 mm
  • Creases exposing glass yarns are not permitted; edge resin loss due to cutting ≤ 2 mm
• Quality and supply
  • Requirements for quality systems, qualification and conformance inspection, certificate of conformance, SDS, packaging, shelf life and ordering data

Applications and users

• Primary use: bonding sheets for laminating multilayer PCBs (in conjunction with laminates per IEC 61249-2-11 and multilayer board spec IEC 62326-4)
• Also used to bond other laminate types where a high‑temperature, flame‑retardant polyimide prepreg is required
• Typical users: PCB manufacturers, laminate and prepreg suppliers, materials engineers, process/quality engineers, procurement and compliance teams in electronics assembly and aerospace/industrial sectors

Related standards

• IEC 61189-2 (test methods for materials)
• IEC 61249-2-11 (polyimide laminated sheet)
• IEC 61249-6-3 (woven E‑glass reinforcement)
• IEC 62326-4 (rigid multilayer printed boards)
• ISO 9000, ISO 14001, ISO 11014-1 (quality, environment, safety data sheets)

Keywords: IEC 61249-4-5, polyimide prepreg, woven E‑glass, flame retardant prepreg, prepreg materials, multilayer PCB bonding sheet, glass transition temperature, vertical burning test.