IEC 61249-4-1:2008

Overview

IEC 61249-4-1:2008 specifies requirements for epoxide woven E-glass prepreg of defined flammability used mainly as bonding sheets for the manufacture of multilayer printed boards. The prepreg is a B‑stage, epoxy‑impregnated woven E‑glass fabric formulated to meet a vertical burning (defined flammability) rating - achieved using brominated fire retardants integrated in the polymer matrix. After lamination per supplier instructions, the cured material is specified to have a glass transition temperature (Tg) ≥ 120 °C. This sectional specification aligns with multilayer board manufacture practices in IEC 62326-4 and bonding to laminates per IEC 61249-2-7.

Key topics and technical requirements

• Material composition
  • Woven E‑glass reinforcement impregnated with majority di‑functional epoxide resin.
  • Flame retardancy provided by brominated additives in the resin.
• Flammability
  • Defined by a vertical burning test (see Table 1 in the standard).
• Thermal
  • Post‑lamination Tg ≥ 120 °C (when cured according to supplier instructions).
• Appearance & handling criteria
  • Dewetted areas (fish eyes): >5 mm not permitted; ≤5 mm allowed up to 10 per 300×300 mm.
  • Broken filaments: acceptance agreed between supplier and user.
  • Distortion of fill yarns: ≤10% over any 300 mm.
  • Creases and edge conditions: limits on resin loss (edge resin loss ≤2 mm for cut panels).
• B‑stage (prepreg) properties
  • Typical controlled parameters: resin content, treated weight, resin flow, scaled flow thickness, melt viscosity, cured thickness.
  • Example tolerances: resin content ±3% (e.g., 45 ± 3 %); resin flow ±5% (e.g., 25 ± 5 %); treated weight ±3% (e.g., 16.8 ± 0.5 g).
  • Optional checks: volatile content, gel time.
• Post‑cure properties
  • Electric strength, relative permittivity and dissipation factor, cured thickness and flammability.
• Quality & delivery
  • Inspection, qualification and conformance testing per IEC test methods (e.g., IEC 61189 series).
  • Delivery forms: rolls, sheets, cut panels. Requirements for packaging, marking, shelf life, certificates and safety data sheets are included.

Applications and users

• Primary users: PCB manufacturers producing rigid multilayer boards, laminate and prepreg suppliers, fab engineers and procurement teams.
• Secondary users: test laboratories, compliance and quality managers, and design engineers specifying stackups needing flame‑retardant bonding layers with Tg ≥ 120 °C.
• Typical applications: bonding layers in multilayer printed circuit boards, joining different laminate types where defined flammability and thermal performance are required.

Related standards

• IEC 61249-2-7 (epoxide E‑glass base materials)
• IEC 62326-4 (rigid multilayer PCB sectional specification)
• IEC 61189-2 / IEC 61189-3 (test methods for materials and visual inspection)
• ISO 9000, ISO 11014-1, ISO 14001 (quality, SDS and environmental management)

Keywords: IEC 61249-4-1, epoxide woven E‑glass prepreg, prepreg materials, multilayer boards, defined flammability, vertical burning test, glass transition temperature, resin content, resin flow, PCB materials standard.