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
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.