How to Select Tg of PCB ？
6 min
- What is the Tg of PCB?
- PCB Tg Class
- How to Select TG of PCB ?
What is the Tg of PCB?
In PCB manufacturing, abbreviation "Tg" stands for "Glass transition temperature", which is the temperature at which a material transits from a solid state to a rubbery elastic state during heating. As we all know, the PCB must be flame-resistant. It cannot burn at a specific temperature; instead, it can only become soft.
When the temperature exceeds Tg, the PCB substrate material FR-4 undergoes a transition from a brittle and hard state to a soft state. This transition can lead to dimensional changes and distortion of the PCB, ultimately affecting its mechanical and electrical properties. Therefore, when selecting PCB materials, you need to consider the required operating temperature range to ensure that the Tg value of the selected material can meet the design requirements.
PCB substrates with high Tg values can ensure that electronic devices can function properly under various environmental conditions, whether it is during hot summers or cold winters. In PCB design and manufacturing, selecting a substrate with an appropriate glass transition (Tg) value is a crucial factor in ensuring the quality and performance of the product.
PCB Tg Class
In PCB manufacturing, engineers select the appropriate FR-4 substrate based on the application's requirements. Standard base material is an epoxy resin system, and Tg value is the most common indicator used to classify FR-4 base material grades.
According to temperature, it is generally divided into three levels, namely the general Tg, medium Tg, and high Tg.
General Tg:
The Glass transition temperature (Tg) of low FR4 sheets is typically around 130-140℃. However, due to its excellent physical properties, well-established production technology, and affordability, it remains the preferred material for the majority of circuit board manufacturers. For example, when it comes to general 3C digital consumer electronics products, the temperature requirements are not high, and it is sufficient to choose a standard Tg value. That's it.
Generally, the processing technology of Tg plate is mature and simple, the production cost is low, and it has good economic efficiency.
Medium Tg
The medium Tg value is around 150°C. Compared to ordinary FR4 sheets, Tg150 sheets offer improved heat resistance, moisture resistance, and chemical resistance. They can operate reliably for extended periods in high-temperature, high-humidity, and corrosive environments. Therefore, Tg150 boards are suitable for use in fields with higher requirements, such as high-speed digital circuits, microwave frequency circuits, and high-frequency circuits. However, processing Tg150 plates is more challenging than processing ordinary Tg plates, and the cost of these plates is high.
High Tg
If the glass transition (Tg) value of the substrate is above 170°C it indicates that the PCB will have high heat resistance, moisture resistance, chemical resistance, constant resistance and other important characteristics. This is crucial in the lead-free tin spray process, where a high Tg value is essential.
If there are time constraints during PCB processing, multiple PCB layers, high welding temperature (≥230℃), high working temperature (above 100℃), or significant welding thermal stress (such as wave soldering), it is advisable to select a high Tg plate.
High Tg sheets are primarily used in high multi-layer printed circuit boards (10 layers), automotive industry, packaging materials, embedded substrates, precision instruments for industrial control, routers, and other industries. fields.However, it should be noted that the higher the Tg value, the higher the cost of the PCB circuit board.In general, a higher Tg value indicates better temperature resistance for the board, resulting in less board deformation and improved resistance to warpage.
However, due to the high glass transition (Tg) point, it indicates that the temperature requirements of the board are also high during processing and pressing. As a result, the particle board will be relatively hard and brittle, which will affect the quality of subsequent mechanical drilling and the electrical characteristics of it’s use to some extent. The cost should be based on your needs, taking into account the same time.
Electrical, mechanical, chemical, and thermal properties need to be considered when choosing the appropriate laminate. In general scenarios, medium and low Tg FR-4 can completely satisfy.
For multi-layer PCBs, JLCPCB currently provides high TG FR-4 options. For example, " High Precision PCB " service can manufacture PCBs up to 20 layers, which is very useful for projects that require complex layouts and large-scale integration. This high TG FR-4 material can maintain stability in high temperature environments and provide good performance.
How to Select TG of PCB ?
Choosing the maximum operating temperature (Tg) of a PCB is an important decision that determines the reliability and performance of the PCB in high-temperature environments. Here are some suggestions for choosing a PCB Tg:
1. Understand the application environment: First, determine the maximum temperature that may occur in your application environment. Consider the temperature conditions under which your PCB will operate, including ambient temperature, expected heat generation, and dissipation, etc. This will help you determine the desired PCB Tg (glass transition) range.
2. Consider the maximum operating temperature of the components: Check the maximum operating temperature of the components you plan to use on the PCB. Make sure that the Tg of the selected PCB is at least able to meet the maximum operating temperature requirements of all components. Generally, the Tg of the PCB should be higher than the maximum operating temperature of the component to ensure the normal operation and lifespan of the component.
3. Choose the appropriate PCB material: Select a PCB material with a high Tg. Tg represents the ability of the PCB substrate to maintain its structural strength and electrical properties under continuous high-temperature conditions.
4. Consider the PCB manufacturing process: Different PCB manufacturing processes may have an impact on the glass transition temperature (Tg) of the PCB. Certain manufacturing processes may reduce the Tg of a PCB. When selecting a PCB manufacturer, it is important to have a clear understanding of their manufacturing processes and their ability to control the glass transition temperature (Tg) in order to ensure that they can meet your Tg requirements.
In short, selecting the maximum operating temperature (Tg) for a PCB requires considering factors such as the application environment, the maximum operating temperature of components, PCB materials, and manufacturing processes. Make sure the selected PCB has a high enough Tg to ensure the reliability and performance of the PCB in high-temperature environments.
Keep Learning
Your Ultimate Guide to PCB Rulers
In the world of PCB design and manufacturing, having the right tools is crucial for achieving accuracy and precision. One such tool that has gained popularity among professionals and hobbyists is the PCB ruler. This specialized measuring tool is designed to provide accurate measurements, reference information, and component footprints, assisting designers, engineers, technicians, and assemblers in various stages of PCB development. In this guide, we'll explore what a PCB ruler is, the features and mea......
How Laser Drilling Delivers Precision and Density in Advanced PCB Manufacturing
Key Takeaways Laser Drilling has become the cornerstone technology for precision and high-density PCB manufacturing, enabling microvias as small as 25-75μm — far beyond the 150μm limit of mechanical drilling. By delivering superior accuracy, contactless processing, excellent signal integrity, and reliable blind/stacked vias, it empowers advanced HDI board designs essential for modern electronics. From optimal stackup selection to professional plating and DFM practices, mastering laser drilling is key ......
Reducing CTE Mismatch Stress: Practical Ways to Build More Reliable PCBs
Key Takeaways CTE mismatch (FR4’s high Z‑axis CTE vs. copper) creates thermal stress that causes PCB warpage, via cracks, delamination, and solder fatigue—worse under lead‑free reflow and thermal cycling. Mitigate it with symmetric stackups and balanced copper, higher‑Tg/low‑CTE materials, and tight process control (lamination, cooling, moisture, and consistent via plating). Are you aware that the coefficient of thermal expansion of standard FR4 in the Z-axis can be up to 70 ppm/C, whereas copper has ......
Why UL94 V0 Matters for Safe and Reliable PCB Manufacturing
Key Takeaways UL94 V0 is the highest flame rating for PCB materials, requiring self-extinguishing within 10 seconds with no flaming drips. It greatly reduces fire risk and has become the de facto standard for safe, reliable PCBs in consumer, industrial, automotive, and medical applications. JLCPCB offers UL94 V0 compliant FR4 and high-Tg materials by default, ensuring regulatory compliance (UL, CE, CCC) and long-term reliability without compromising performance or budget. Never sacrifice V0 rating for......
How to Choose the Right UL94 Rating for Safe and Reliable PCBs
Key Takeaways This article explains how to choose the right UL94 rating to ensure PCB fire safety and compliance: V-0 is the common baseline for most electronics, V-1/HB are typically for lower-risk or non-regulated uses. It also stresses that rating performance depends on material selection, thickness, and process control, so use UL-certified laminates and a traceable, UL-capable manufacturer. Have you heard that just one PCB that catches fire can produce poisonous fumes, annihilate an entire product......
Why Sequential Lamination Delivers Superior HDI PCBs
Did you ever ask yourself how smartphone manufacturers can crust a thousand connections into a credit card-sized board? The process is referred to as sequential lamination, which is a multi-cycle process that is used to fabricate PCBs on a layer-by-layer basis, releasing microvia structures and routing densities that cannot be accessed by a single-press process. Without it, the slick, high-performance electronics that we all use on a daily basis would not appear the way that they do now. With data rat......