Glass Transition Temperature (Tg) is the critical temperature point at which a resin substrate (such as epoxy resin) transforms from a hard "glassy state" to a soft and elastic "rubber-like state." Below this temperature, the material maintains dimensional stability and mechanical strength. Above this temperature, the material begins to soften and its mechanical and electrical properties decline sharply.
High Tg PCB: Generally, PCB substrates with a Tg value of ≥ 150°C are defined as high Tg materials. The Tg of a conventional FR-4 is generally around 130–140°C.
🔥 Super Heat Resistance
It can withstand the high temperature of lead-free welding (usually over 260°C), and the underlayment structure remains stable in high-temperature environments without problems such as delamination or deformation. For instance, in the soldering process, ordinary PCBs may soften and fail due to high temperatures, while high Tg PCBs can pass the 288°C tin furnace test without any issues such as board explosion or copper foil peeling.
📐 Stable Mechanical & Dimensional Properties
The coefficient of thermal expansion (CTE) is lower than that of conventional plates, which can reduce warping caused by temperature changes and prevent the copper layer at the through holes from cracking. This feature is particularly crucial in multi-layer boards of 8 layers or more, ensuring the reliability of the connection of the plated through holes.
⚡ Outstanding Electrical & Chemical Properties
Most high Tg plates have a low dielectric constant (such as 3.5±0.05@1GHz for some high-end models) and low dielectric loss (as low as 0.002), which can reduce high-frequency signal attenuation and crosstalk, and are suitable for high-speed signal transmission. At the same time, it has strong chemical resistance — its performance remains intact even after wet treatment and immersion in chemical solutions, and it can withstand humid environments suitable for complex working conditions.
The boards of high Tg PCBs are mostly high-performance resin substrates. The Tg values of different materials vary greatly, adapting to the requirements of different scenarios. The common types are as follows:
| Material | Tg Value |
|---|---|
| Rogers RO4350B | 280°C |
| Rogers RO4003C | 280°C |
| Alon 85N | 250°C |
| Isola FR408HR | 180°C |
| Weichuang6 | 185°C |
The BMS system of new energy vehicles, the ECU in the engine compartment, etc., tend to generate a large amount of heat during operation. High Tg PCBs can operate stably in this high-temperature environment, ensuring driving safety.
5G base station antennas, optical modules, servers, and switches have extremely high requirements for high-frequency signal transmission. The low-loss characteristic of high Tg boards ensures signal integrity and improves data transmission efficiency.
Satellite communication boards and polar environment radar control boards need to withstand extreme temperature differences ranging from -40°C to 125°C. PCBs using substrates like TG180 can enhance thermal cycling tolerance and reduce failure rates.
Ultrasound imaging devices and high-temperature disinfected medical equipment rely on the stability of high Tg PCBs under high-temperature and long-term operation to avoid the impact of equipment failure on diagnosis and treatment.