What is a high-Tg PCB?
What is Glass Transition Temperature (Tg)?
Glass transition temperature, called Tg, is one of the most important properties of plastics and epoxy materials. Tg also shows the quality of the glass fiber cloth used in PCBs. Compared with HDT (Heat Deflection Temperature), Tg is not always more important, but it still matters. Tg is the temperature when the long chains in a plastic gain larger segmental motion.
When the use temperature is below Tg, the motion of polymer chain segments is mostly frozen. The material shows more ordered, lattice-like structure. The plastic is hard, stiff, and brittle. We call this the glassy state.
When the use temperature is above Tg, the polymer chain segments have more freedom to move. The plastic becomes softer and more flexible. We call this the rubbery state.
So Tg is the temperature where the material shifts from glassy to rubbery. Tg is the highest temperature at which a substrate keeps its rigidity. In other words, ordinary PCB substrate materials will soften, deform, or even melt at high temperature. At the same time, their mechanical and electrical properties fall fast.
Tg and Board Behavior
Tg marks a clear change in material behavior. Below Tg, the board keeps its shape and mechanical strength. Above Tg, the board may bend and lose stiffness. This change also affects electrical properties. Dielectric loss and insulation behavior can change as temperature moves across Tg. For PCB design and assembly, knowing the Tg helps choose proper materials and processes.
Categories of PCB Tg Values
Manufacturers divide board materials by Tg ranges. Typical groups are:
- Normal Tg boards: 130 °C to 150 °C. Examples: KB-6164F (140 °C), S1141 (140 °C).
- Medium Tg boards: 150 °C to 170 °C. Examples: KB-6165F (150 °C), S1141-150 (150 °C).
- High Tg boards (higher cost): 170 °C and above. Examples: KB-6167F (170 °C), S1170 (170 °C).
Note: For some consumer and network products, S1141 was common. In QC reports it sometimes shows Tg = 130 °C and sometimes Tg = 135 °C. This shows that testing and grade naming can vary.
Advantages of High-Tg Materials
- Higher stability: If you raise the Tg of the PCB substrate, you also raise heat resistance, chemical resistance, moisture resistance, and device stability.
- Better for high power density designs: If a device has high power density and large heat generation, high-Tg PCBs help manage heat.
- Design flexibility: With better thermal properties, you can change board size or layout and still meet power and thermal needs. You can use bigger PCBs or different stackups when heat is better managed.
- Ideal for multilayer and HDI PCBs: Multilayer and HDI boards are dense. They create higher heat levels. High-Tg boards help keep manufacturing and product reliability.
- Improved resistance: When Tg rises, the board’s resistance to heat, moisture, and chemicals improves. Stability in service also improves.
- Better for lead-free soldering: Lead-free reflow uses higher temperatures. Boards with higher Tg handle these temperatures better.
- Lower warpage in SMT: High-Tg materials deform less during SMT and reflow. They give higher reliability. Risks like high-temperature cracking and copper blistering are lower than with low-Tg boards. In normal handling, high-Tg material can feel more brittle, but at high temperature its strength and dimensional stability (CTE behavior) are better than low-Tg materials.
Performance of High-Tg PCBs
With fast growth in electronics, high-Tg materials are widely used in computers, communication devices, precision instruments, and test equipment. To reach higher functions and more layers, PCB substrates need higher heat resistance as a basic requirement. Also, with high-density assembly like SMT and chip mounting technologies, and with trends to thinner boards, smaller holes, and finer routing, substrate heat resistance becomes critical.
The difference between typical FR-4 and high-Tg FR-4 shows in many ways. Mechanical strength, adhesion, water absorption, dimensional stability, and thermal behavior after moisture uptake all vary. Under thermal stress and thermal expansion, high-Tg boards keep shape and function better. For this reason, demand for high-Tg boards has risen. Their price is higher than standard boards.
High-Tg materials are popular in LED lighting. LED packages dissipate more heat than ordinary parts. An FR-4 board with the right structure can be much cheaper than a metal core board and still meet thermal needs in some designs.
Why Use FR-4 to Make High-Tg PCBs?
Some applications need PCBs that work at 200 °C or higher. To run reliably at such temperatures, we must use materials made for high temperature. One common choice is FR-4. High-Tg FR-4 boards can handle much higher glass transition temperatures and still give useful properties:
- Improved impedance control.
- Better thermal management.
- Lower moisture uptake.
- Stable performance in service.
FR-4 is a flame-retardant, glass-fiber-reinforced epoxy. It has many benefits that suit high-Tg PCB needs:
- It resists many lamination cycles and fits complex PCB processes.
- It supports lead-free assembly.
- FR-4 types are many. There are PTFE types, ceramic-filled PTFE, and thermoset hydrocarbon bases. You choose by need.
FR-4 Special Properties
FR-4 offers key strengths for high demand uses:
- Good electrical performance: This keeps signal quality in high frequency and high temperature.
- It can handle special drilling and plated through-hole (PTH) processes for complex boards.
- PTH reliability is good: This lowers the risk of connection failure at high temperature.
- The cost is lower than many high-end materials while performance is good.
- Stable dissipation factor (Df) compared with some other materials. This reduces signal loss.
- Good chemical resistance to resist process chemicals and field exposure.
- Shock and vibration resistance, plus flame retardancy: Make boards safer in rough use.
- It fits PCB designs that need tight impedance control for high speed signals.
FR-4 High-Tg PCB Application Areas
Because FR-4 high-Tg boards handle heat well, they serve many industries that need stable thermal behavior. Typical areas include:
- Computing, storage, and peripherals.
- Consumer electronics.
- Networking and telecom systems.
- Aerospace and defense.
- Medical devices.
- Industrial control and instruments.
- Automotive and transport.
How to Choose the Right FR-4 Material
There are many FR-4 variants. Choosing the right one is key because material choice sets the final PCB stability and best performance. Before selecting a substrate, check these factors:
- Dielectric constant: It affects signal speed and impedance.
- Loss tangent or dissipation factor: It affects signal loss.
- Thermal conductivity: It affects heat removal.
- Glass transition temperature (Tg): This is the core indicator that sets the upper heat limit.
- Coefficient of thermal expansion (CTE): It affects dimensional stability at high temperature.
- Electrical properties like insulation resistance and breakdown voltage.
When Do You Need a High-Tg PCB?
If your board must withstand heat loads that reach about Tg + 25 °C, then you need high-Tg material. If a product runs at 130 °C or higher, high-Tg boards add safety and reliability. A main driver is lead-free soldering. Lead-free processes use higher peak temperatures. For this reason many PCB makers now use high-Tg materials.
Typical Uses of High-Tg PCBs
If a product has higher power density and heat will affect the heatsink or other parts, high-Tg boards are a good choice. As high-Tg boards grow in popularity, you will see them where electronics run at higher temperatures. PHILIFAST offers high-heat PCBs to meet many industry needs and to meet customer specs with short lead times. Example applications include:
- Gateways and routers.
- RFID readers and tags.
- Power inverters.
- Antenna and RF boards.
- Wireless repeaters and boosters.
- Contract manufacturing services (PCBA for clients).
- Low-cost PLC and control units.
- Embedded system development boards.
- Embedded computer systems.
- AC power and power supply modules.
PHILIFAST High-Tg Materials
PHILIFAST stocks and uses several high-Tg and related materials. Below are common names and types used in the industry. These names are trade names and grade codes from resin and laminate suppliers.
| Material Category | Specific Models/Trade Names |
|---|---|
| High-Tg FR-4 (halogen-free) | Shengyi S1165, Kingboard HF-170 |
| Normal Tg FR-4 (halogen-free) | Shengyi S1155, KB-6165G |
| High CTI types | Shengyi S1600L, KB-6165GC, KB-6169GT |
| Other high-Tg FR-4 grades and trade names | FR408, FR408HR, IS410, FR406, GETEK, PCL-370HR; S1000-2, IT180A, IT-150DA; N4000-13, N4000-13EP, N4000-13SI, N4000-13EP SI; Megtron4, Megtron6 (Panasonic); EM-827 (Taiguang); GA-170 (Hongren); NP-180 (Nanya); TU-752, TU-662 (Taiaoyao); TU-872; MCL-BE-67G(H); MCL-E-679(W); MCL-E-679F(J) (Hitachi) and related grades such as IT180A, GETEK, PCL-370HR, N4000-13 series, S1000-2 and S1000-2M |
These lists cover many commercial laminates and prepregs used for high-Tg and high-performance boards. You can pick a grade by test data and by your process needs.
Key Processing and Reliability Notes
- High-Tg materials resist reflow and multiple lamination cycles. This helps complex multilayer builds.
- Higher Tg reduces the chance of delamination during thermal cycles, but you must still control process variables like pressure, temperature profile, and resin fill.
- Moisture absorption matters. Even high-Tg materials can take on moisture. Drying and storage procedures still matter for reliable assembly.
- CTE match is important. The board CTE should match component and laminate behavior to reduce solder joint stress, especially for BGAs and large chips.
- For HDI and fine pitch work, choose materials with stable dielectric and low loss for signal integrity.
Summary
Tg is the temperature where plastic changes from hard and glassy to soft and rubbery. High-Tg PCB materials keep structure and function at higher temperatures. They help with lead-free soldering, high power density, and tight design needs like multilayer and HDI. FR-4 remains a common and cost-effective choice for high-Tg boards. You must pick the material grade that fits your electrical, thermal, and mechanical needs. PHILIFAST provides many high-Tg options to meet different industry requirements.