For most industrial products that work under complex or harsh application environments, it is very important to make the right decision on circuit design and PCB material selection. Making a balance between cost, specifications, and performance during FR4 Tg PCB material selection is crucial to the final designation. The difference in Tg value means not only different temperature characteristics but also different costs, electrical performance, and warpage.

Tg stands for glass transition temperature. The Tg value refers to the temperature at which the amorphous polymer (including the amorphous part in the crystalline polymer) transforms from the glass state to the high elastic state (rubber state), which can also be said to be an amorphous polymer. The minimum temperature at which the macromolecular segments move freely.

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In terms of PCB: The Tg value is the temperature at which the PCB substrate melts from a solid state to an elastic fluid. The temperature of the mutual transformation between the glass state and the rubber state. When the temperature of the adhesive epoxy resin of the FR-4 substrate is lower than Tg, the material is in a rigid “glass state .”When the temperature is higher than Tg, the material will exhibit properties similar to rubber with softness.

The higher the Tg value of the PCB board, the better the temperature resistance of the board. Usually, in the process of lead-free tin spraying, there are more applications of high Tg PCBF.

Generally, the Tg of the PCB is above 130 degrees, and the FR4 Tg130 material is the most used material for common electronic products; the medium Tg is about 150 degrees or more, and the high TG is generally greater than 170 degrees. The performance of Tg150 and Tg170 is better than Tg130. But with the need for product differentiation, some common consumer products, although their application environment is not as harsh as industrial products, such as home computers and tablets, are upgraded to use FR4 Tg150 material, and high Tg boards are mostly used in high-density and multilayer application. Automobiles, substrates, precision instruments, meters for industrial control, etc. The Tg of the board is increased, and the heat resistance, moisture resistance, chemical resistance, stability, and other characteristics of the printed board will be correspondingly improved and improved, that is, the higher the reliability. Of course, the cost will also increase.

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Although high Tg products have better temperature resistance performance, the substrate with a high Tg value is more rigid and brittle than the substrate with a low Tg value, which will affect the processing efficiency and yield of PCB, especially in the drilling process.

If the PCB board is designed very densely, and the spacing between vias and vias is also small, we recommended using a medium or high Tg value board because the common Tg 130 via spacing design cannot be less than 12mil. The medium Tg 150 can be at least 10mil. The high Tg value is due to the excellent hardness of the plate, and the addition of the new drill tip can effectively improve the strain on the plate glass cloth when drilling and prevent the wick effect.

Therefore, in general, the higher the Tg value, the better the temperature resistance of the board, the better the warpage, and the less likely the PCB is to deform. However, due to the high Tg point, the board needs a higher process temperature during lamination. The resulting PCB will also be relatively hard and brittle, affecting the quality and efficiency of drilling and will also impact reliability. Designers often must prioritize and balance temperature requirements, hole spacing design, and product cost based on the application.