IEC 61249-2-35:2008

Overview

IEC 61249-2-35:2008 is an international standard published by the International Electrotechnical Commission (IEC) that specifies requirements for reinforced base materials used in printed boards and other interconnecting structures. This part of IEC 61249 focuses on modified brominated epoxide woven E-glass laminate sheets, both clad and unclad, with copper cladding optimized for lead-free assembly processes. The laminate sheets covered have thicknesses ranging from 0.05 mm to 3.2 mm and exhibit defined flammability characteristics validated through vertical burning tests. Key thermal properties, such as a glass transition temperature between 150 °C to 200 °C, are also specified to ensure performance under operational thermal stress.

Key Topics

• Material Composition: The standard defines the use of modified brominated epoxide resins combined with woven E-glass reinforcement, tailored for enhanced flame resistance and thermal stability.
• Copper Cladding for Lead-Free Assembly: Laminates are copper-clad to support modern lead-free soldering techniques used in environmentally conscious electronic manufacturing.
• Flammability Defined by Vertical Burning Test: Strict criteria for flame spread and burning behavior are set to ensure safe usage in electronic equipment, complying with global flammability safety requirements.
• Mechanical and Electrical Properties: Detailed specifications cover flexural strength, dimensional stability, peel and pull-off strength of copper foil, and electrical insulation properties.
• Non-Electrical Characteristics: Surface quality aspects such as indentations, scratches, surface waviness, bow, and twist are addressed to ensure the laminates meet high-quality production standards.
• Thermal Performance: The standard includes measurements for glass transition temperature, thermal decomposition temperature, and thermal resistance, ensuring laminates can endure the heating cycles typical of electronic assembly.
• Quality Assurance and Packaging: Guidance on quality control processes, testing, certificates of conformance, and proper packaging methods to maintain laminate integrity during transport and storage.
• Compliance and Safety Documentation: Requirements for safety data sheets and normative references to foster regulatory compliance and safe handling.

Applications

IEC 61249-2-35:2008 materials are critical for the manufacture of printed circuit boards (PCBs) and other electronic interconnecting structures that require:

• Lead-free assembly processes-supporting environmentally friendly manufacturing with reliable thermal and mechanical endurance.
• High-performance electronic devices-including telecommunications, computing, and consumer electronics where flame resistance and mechanical stability are vital.
• Safety-critical equipment-where adherence to flammability standards reduces fire risks and ensures user safety.
• High-temperature operational environments-thanks to materials with a glass transition temperature of 150 °C to 200 °C that maintain structural and electrical integrity.

These laminates form the foundational substrate in multilayer PCBs, flexible interconnects, and other advanced electronic assemblies.

Related Standards

• IEC 61249 Series: Other parts of the IEC 61249 series address a broad range of materials for printed boards and interconnect structures, focusing on different resin systems, reinforcements, and flammability classes.
• IEC 60335: Safety standards for household and similar electrical appliances, referencing flammability tests applicable to PCB materials.
• IPC Standards: Industry standards such as IPC-4101 also specify laminate materials and performance, providing complementary guidelines for manufacturers.
• ISO/IEC Directives – Part 2: Governs the preparation of IEC publications, ensuring consistency and conformity in the development of international standards.

Keywords: IEC 61249-2-35, printed boards materials, reinforced base materials, modified epoxide laminate, E-glass laminate sheets, copper-clad laminate, flammability standard, vertical burning test, lead-free assembly, glass transition temperature, PCB materials, electronic interconnect structures, thermal stability PCB, flame resistance laminate, electronic industry standards.