What is High Tg PCB
When the temperature rises to a certain area, the substrate will change from "glass state" to "rubber state", and the temperature at this time is called the glass transition temperature (Tg) of the plate. That is, Tg is the highest temperature (°C) at which the substrate remains rigid. That is to say, the ordinary PCB substrate material not only softens, deforms, melts, etc. at high temperatures, but also exhibits a sharp drop in mechanical and electrical properties.
The general Tg of the PCB is 130 degrees or more, the high Tg is generally greater than 170 degrees, and the medium Tg is greater than about 150 degrees.
A PCB board with a typical Tg ≥ 170 ℃ is called a high Tg board.
The higher the Tg value, the more resistant the sheet is to deformation and the better its dimensional stability. The substrate material of IPC-4101B (2006) standard epoxy/E type fiberglass cloth is divided into three grades according to the height of Tg (commonly known as low, medium and high Tg). It is an important property in the resin of the sheet. It refers to the gradual change of the physical properties of the resin due to the gradual increase of the temperature. It is converted into a viscous state by the amorphous or partially crystalline hard and brittle nature at room temperature, such as glass. The critical temperature is very high and soft in another state like rubber.
Features of High Tg PCB
The Tg of the substrate is improved, and the heat resistance, moisture resistance, chemical resistance, and stability resistance of the circuit board are improved. The higher the TG value, the better the temperature resistance of the sheet, especially in the lead-free process, the High Tg PCB application is more.
With the rapid development of the electronics industry, especially the electronic products represented by computers, the development of high functionality and high multi-layer requires the higher heat resistance of PCB substrate materials as an important guarantee. The emergence and development of high-density mounting technology represented by SMT and CMT makes PCBs more and more inseparable from the high heat resistance of substrates in terms of small aperture, fine wiring and thinning. Therefore, the difference between general FR-4 and high Tg FR-4 is that in the hot state, especially under heat absorption after moisture absorption, the mechanical strength, dimensional stability, adhesion, water absorption, thermal decomposition, There are differences in various conditions such as thermal expansion, and High Tg PCB is significantly better than ordinary PCB substrate materials. In recent years, customers who demand the production of High Tg PCB have increased year by year.
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