Tg value

The glass transition temperature Tg is a critical parameter for materials used in printed circuit board PCB manufacturing. This parameter denotes the temperature at which a material transitions from a glassy state to an elastic state during continuous heating.

PCBs with a high Tg value are especially important for applications exposed to extreme conditions. Let's explore the importance of Tg, the benefits of high-Tg PCBs, and the areas where these boards are useful.

Tg: A Crucial Parameter for Heat Resistance

The glass transition temperature Tg is a key indicator of material heat resistance. The typical Tg value for FR4 PCBs is around 140 degrees Celsius, corresponding to the material's plastic behavior. In the case of high-Tg PCBs, this value is significantly higher, exceeding 170 degrees Celsius, which means the material remains elastic at higher temperatures.

When the operating temperature reaches or exceeds the Tg value, the PCB starts to change from a solid to a liquid state, which can lead to device failure. This is especially relevant for applications exposed to high temperatures, such as industrial processes, automotive electronics, and telecommunications.

Benefits of High-Tg PCBs

High-Tg PCBs offer several advantages: Here is their list.

Stability: High-Tg PCBs have greater stability in terms of heat resistance, chemical resistance, and humidity resistance. This is crucial for devices in demanding environments.

Heat Dissipation: These boards have the ability to efficiently dissipate heat, which is essential for high-power density devices and those generating significant heat, such as high-performance computer processors.

Ideal for Multilayer and HDI PCBs: High-Tg materials are often the choice for multilayer boards and high-density interconnect (HDI) PCBs due to their ability to maintain reliability in complex designs.

Applications of High-Tg PCBs 
High-Tg PCBs find applications in various industries that demand high heat resistance and stability. These include:

• Industrial Control: High-Tg PCBs are essential for programmable logic controllers (PLCs) used in long-term manufacturing processes involving cutting, grinding, welding, and metal melting. These devices generate high temperatures and vibrations, and high-Tg PCBs ensure the reliability of such operations.
   
• Automotive Electronics: In the automotive industry, high-Tg PCBs are crucial for engine control units and other electronic components that must withstand the high temperatures generated during vehicle operation.
   
• Telecommunications: High-Tg PCBs are key for switching gates and communication devices that generate significant heat. These devices need to remain reliable and stable during extended operation.

Materials for High-Tg PCBs

Materials designed for high-temperature Tg PCB production are non-flammable and resistant to temperature extremes. These materials include epoxy resins and polymers with flame-retardant properties, enhancing their durability.

1. FR4: FR4, short for Glass Fiber Reinforced Epoxy Laminate, is an epoxy glass laminate composite known for its flame-retardant properties. FR4 offers high resistance to moisture and temperature fluctuations, important for high-Tg PCBs. It effectively dissipates heat, ensuring conductor and dielectric stability.
    
2. IS410: This laminate and prepreg material achieves a Tg of 180°C. It can withstand repeated temperature fluctuations and is tested for high-temperature soldering, up to 288°C. IS410 is also suitable for lead-free soldering in PCB industrial production.
    
3. IS420: This high-performance epoxy resin material offers excellent thermal performance and has low coefficient of thermal expansion compared to standard FR4 materials. It can block UV radiation, making it useful for automated optical inspections in PCB manufacturing and suitable for applications requiring high stability.
    
4. Venture Isola-G200: A bismaleimide/triazine (BT) and epoxy resin blend that offers superior thermal, mechanical, and electrical properties compared to most BT epoxy materials. It excels in thermal resistance, mechanical strength, and electrical performance, making it a common choice for high-density multilayer PCBs requiring reliability.

Materials with high Tg used in the production of printed circuit boards at Gatema PCB

• The top-tier epoxy laminate and prepreg, ISOLA 370HR, represent the best lead-free compatible product in its class for highly reliable applications across a wide range of markets. 370HR provides excellent thermal performance with a low coefficient of thermal expansion (CTE), mechanical and chemical properties, and moisture resistance that match or exceed the performance of traditional FR-4 materials. Tg = 180°C.
  
   
• The material Ventec VT47 is a high-quality FR-4 material suitable for high-performance applications. Ventec VT47 is a phenolic resin with a Tg value of 180°C.
  
   
• Laminates made from ISOLA Tera® MT40 exhibit exceptional electrical properties that remain highly stable across a broad frequency and temperature range. The Tg value for ISOLA Tera® MT40 is 200°C.
  
   
• DuPont™ Pyralux® AP is a double-sided, copper-clad laminate and polyimide composite with a polyimide film bonded to a copper foil. This material is ideal for multilayer applications like flex and rigid-flex, requiring advanced material properties, thermal resistance, and high reliability. The glass transition temperature of DuPont™ Pyralux® AP is Tg = 220 degrees Celsius.
  
  
   
• ROGERS hydrocarbon ceramic laminate, Rogers RO4003C, is designed to offer excellent high-frequency performance. The material, featuring PTFE resin and ceramics, offers a Tg of >280°C. Similar properties are exhibited by Roger RO4350B, which is also used for pruduction at Gatema PCB.
  
   
• ThinFlex-W22, W-2005RD-C is a double-sided (D/S) copper-clad laminate using ThinFlex TPI film and copper foil laminated on both sides. ThinFlex-W22 material is designed for a wide range of flexible circuit applications requiring advanced material performance and high reliability with a Tg ≧ 350°C.
  
   
• All the mentioned materials used at Gatema PCB are primarily designed for multilayer PCBs with higher Tg requirements. These materials have slightly higher processing demands but find application in the automotive, medical, industrial, and communication and computing technology sectors.

Conclusion

PCBs with a Tg above 170°C are essential for applications facing extreme temperatures, humidity, and chemicals. It holds that the higher the Tg value, the better the heat resistance of the printed circuit board and its resistance to moisture. The ability of PCBs to withstand extreme influences while maintaining stability and reliability is indispensable for many industrial sectors. The development and production of high -Tg PCBs contribute significantly to the stability of electronic devices, which has an undeniable impact on modern technology.