Thermal stability requirements for high-frequency PCBs

High-frequency PCBs (Printed Circuit Boards), often used in RF, microwave, and high-speed digital applications, require excellent thermal stability to maintain signal integrity, reliability, and performance under demanding conditions. The thermal stability requirements typically include:

1. Low Coefficient of Thermal Expansion (CTE)

Why it matters: Minimizes dimensional changes during temperature fluctuations, critical for multi-layer alignment and via reliability.

Requirement: CTE values close to copper (~17 ppm/°C in-plane) are ideal.

2. High Glass Transition Temperature (Tg)

Why it matters: Ensures the material remains dimensionally stable and mechanically robust at high operating temperatures.

Requirement: Tg ≥ 170°C is preferred for high-frequency/high-power applications.

3. High Decomposition Temperature (Td)

Why it matters: Indicates the temperature at which the material begins to chemically degrade.

Requirement: Td > 300°C is recommended for reliable thermal performance during soldering or long-term use.

4. Stable Dielectric Properties Over Temperature

Why it matters: Dielectric constant (Dk) and loss tangent (Df) must remain stable with temperature to ensure signal consistency.

Requirement: Minimal variation in Dk/Df from -40°C to +125°C or higher.

5. Good Thermal Conductivity

Why it matters: Helps dissipate heat generated by high-speed signals or RF power.

Requirement: Thermal conductivity > 0.5 W/m·K is beneficial for thermal management.

6. Resistance to Thermal Cycling

Why it matters: Prevents delamination, microcracks, and material fatigue under repeated heating and cooling.

Requirement: Proven reliability over hundreds to thousands of thermal cycles from -55°C to +125°C or beyond.

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