FR4 Types Based on Tg and Conductive Anodic Filament (CAF) Resistance

Low Tg FR4 (Tg < 130°C): Common in standard applications, this material is cost-effective but has limited thermal resistance and lower CAF resistance. It’s suitable for devices operating under normal temperature conditions.

Medium Tg FR4 (Tg 130°C – 180°C): This type strikes a balance between performance and cost. It offers moderate thermal and CAF resistance, making it ideal for consumer electronics and some industrial applications.

High Tg FR4 (Tg > 180°C): Best suited for high-density or high-power electronics, high Tg FR4 provides superior thermal resistance and excellent CAF resistance. Essential for environments with high operating temperatures, it’s used in automotive, industrial, and high-performance computing applications.

CAF resistance is a critical factor, especially in environments prone to moisture and high electrical biases. CAF formation is a failure mechanism in PCBs where conductive filaments form within the laminate, potentially causing short circuits. High Tg FR4 materials typically offer better resistance to CAF, making them a preferred choice for advanced double-sided PCBs that require higher reliability and longer lifespans in challenging conditions.

When selecting FR4 for advanced double-sided PCBs, several factors must be considered:

Operating Temperature: High Tg FR4 is recommended for environments with elevated temperatures.

CAF Resistance: Materials with higher CAF resistance are essential for applications susceptible to moisture and high voltage stress to prevent board failures.

Mechanical Stress: High Tg FR4 offers better mechanical stability under thermal stress, which is crucial for densely packed double-sided PCBs.

Cost vs. Performance: High Tg FR4 materials provide superior performance but are more expensive. The choice depends on the application’s budget and performance requirements.
In conclusion, selecting FR4 for advanced double-sided PCBs involves carefully assessing the operating environment, thermal and electrical stresses, and cost considerations. High Tg FR4 with enhanced CAF resistance is often preferred for demanding applications where reliability and longevity are paramount.