I. UL Certification Standards for Copper Clad Laminates (CCL)

As the base material of PCBs, the UL certification for Copper Clad Laminates (CCL) mainly relies on sub-standards within the UL 746 series, with the core applicable standard being:

• UL 746E《Standard for Industrial  Laminates, Printed Circuit Base Materials, and Reinforced Base Materials  for Flexible Printed Wiring》
       This standard is specifically formulated for industrial laminates,    printed circuit base materials (including CCLs), and reinforced base      materials for flexible printed wiring. It focuses on evaluating the material's:

• Electrical performance (e.g., insulation resistance, dielectric strength);

• Mechanical performance (e.g., tensile strength, flexural strength);

• Thermal stability (e.g., heat distortion temperature, flame resistance);

• Environmental durability (e.g., moisture resistance, chemical resistance), etc.
        After a CCL passes UL 746E certification, it can be used as a qualified base material in PCB production. Its performance data (such as Relative       Temperature Index, RTI) will be included in UL's material database, providing a foundation for downstream PCB certification.

II. UL Certification Standards for Printed Circuit Boards (PCB)

As end products, the core standard for UL certification of Printed Circuit Boards (PCBs) is:

• UL 976《Standard for Printed Wiring      Boards》
       This standard is specifically developed for the safety and performance of printed wiring boards, focusing on evaluating PCBs in      practical applications in terms of:

• Heat resistance (e.g., heat resistance during soldering, stability at long-term operating temperatures);

• Mechanical integrity (e.g., conductor adhesion,vibration/impact resistance);

• Electrical safety (e.g., insulation spacing, voltage withstand capability);

• Flame resistance (e.g., compliance with UL 94 flammability ratings), etc.
        In addition, PCB UL certification may also involve sub-standards such as UL 746F (for testing flexible PCB interconnect       structures), depending on the PCB type (rigid, flexible, rigid-flex, etc.).

·        Summary