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.

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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.