Electronic devices can face the threat of high temperatures during their operation. This high-temperature threat can arise from the external ambient temperature or the heat generated by the device itself while in operation. Regardless of the source of the threat, these unexpected high temperatures can potentially impact various aspects of electronic devices, including their performance, dimensions, operating conditions, precision, and reliability. Due to the extensive differences among electronic devices, it is essential to ensure that each device can meet its intended performance specifications while minimizing adverse effects.
One method to ensure that a printed circuit board meets its design specifications is by using high Tg PCB substrate material. This PCB substrate is made from durable materials and is suitable for electronic devices that need to operate under extreme conditions, providing reliability and performance in high-temperature environments.
What is High Tg PCB?
Tg stands for Glass Transition Temperature. When a substrate material faces high temperatures, it transitions from a glassy state to a rubbery state. High Tg PCB refers to circuit board that can withstand higher temperatures without deformation or turning rubbery. A common misconception among beginners is assuming that any material capable of withstanding higher temperatures qualifies as a high Tg PCB. In the PCB field, different substrate materials can be chosen depending on the application, such as:
- FR-4: Composed of woven glass fibers impregnated with resin, providing good electrical insulation and high mechanical strength.
- FR-2: Structurally similar to FR-4 but made with phenolic resin and paper-based substrate.
- Polyimide: A flexible and high-temperature-resistant material widely used in flexible PCB, especially in medical and aerospace applications.
- Rogers: An expensive, low-loss substrate material primarily found in high-frequency applications.
- Aluminum-based: Uses aluminum as the substrate material and is ideal for applications that require good heat dissipation, such as LED.
- PTFE: The preferred material for low dielectric constant applications, often using polytetrafluoroethylene as the substrate.
- Ceramic-based: Combines high thermal conductivity and electrical insulation properties, suitable for high-power and high-temperature applications.
Among the seven materials listed above, only FR-4 falls under the category of High Glass Transition Temperature PCB. Although aluminum PCB and ceramic PCB exhibit higher heat resistance, they do not belong to the traditional category of glass fiber substrates. Some common glass fiber substrates include FR-4, FR-2, CEM-1, and CEM-3. Typically, we classify materials with a glass transition temperature above 170°C as high Tg PCB, above 150°C as mid-range Tg PCB, and above 130°C as low Tg PCB.
Why High Tg PCB
To achieve high Tg, manufacturers need to put in more effort, such as using high Tg resins, increasing the glass fiber content, and enforcing stricter manufacturing process controls. Undoubtedly, these factors significantly increase the manufacturing cost of PCB. So, why do we still use high Tg PCB?
One clear advantage is the improved heat resistance of PCB. Traditional PCB typically have a Tg value between 130°C and 140°C. This means that under ideal conditions, PCB can operate below 140°C. However, in real-world applications, we also need to consider the coefficient of thermal expansion, which refers to the issue of substrate expansion due to temperature changes. Traditional PCB typically have a coefficient of thermal expansion ranging from 12 ppm/°C to 18 ppm/°C, meaning the actual working temperature may be lower than 100°C.
In contrast, high Tg PCB have Tg values exceeding 170°C and coefficient of thermal expansion between 5 ppm/°C and 8 ppm/°C. This implies that high Tg PCB can operate at higher temperatures and are less affected by heat. This advantage makes high Tg PCB highly favorable in high-power density applications where there is a higher chance of heating. In standard PCB solutions, increasing the board’s size is the approach to improve heat dissipation and enhance thermal performance, but with high Tg PCB board, you can achieve the same performance without increasing the size. This caters to the trend of miniaturization in the electronics industry. Additionally, high Tg PCB can be used to enhance heat resistance in more compact and densely packed circuitry, such as multilayer PCB and HDI PCB.
When Do You Need High Tg PCB
Using high Tg PCB materials is the best choice when your project demands printed circuit boards that can withstand harsh high-temperature environments. It ensures stable signal transmission and helps prevent costly failures. So, in which applications is the use of high Tg circuit board recommended?
For prominent electronics manufacturers looking to build their brand, high Tg PCB can indirectly boost user satisfaction. With environmental regulations driving increased awareness about the harmful effects of toxic substances in electronics on human health and the environment, lead-free processing has become crucial. However, lead-free soldering demands higher temperatures that standard PCB may not endure. High Tg PCB ensures your circuit boards remain reliable during the soldering process, avoiding defects in the final product.
High-power devices in applications such as base stations, fiber optic equipment, and power circuits often operate in high-power density and high-frequency environments. Over time, continuous high-voltage supply and component heating can cause internal temperatures to rise, potentially leading to device damage. The best choice for dealing with high-temperature environments would be metal core PCB. However, due to the difficulty of processing metal baseboards, they might not meet the circuit performance requirements. High temperature printed circuit board material provide a solution. You can use FR4 as the substrate material, an easily processed material that allows for multi-layer circuit layouts to meet electrical performance requirements. Its high glass transition temperature enables it to function in high-temperature environments.
High Tg PCB are equally beneficial in industrial, automotive, military, and aerospace applications. These sectors demand higher device reliability, and the devices need to withstand extreme conditions, including high temperatures, moisture, mechanical vibrations, chemical corrosion, and more. Increasing the glass fiber content with high Tg PCB enhances their reliability in resisting these challenges, ensuring critical systems operate optimally and reducing the probability of failures. This, in turn, lowers maintenance and repair costs.
Here’s a table listing some common high Tg PCB materials, their manufacturers, and their respective Tg temperature values in degrees Celsius:
Glass transition temperature
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