Regardless of the laminated structure, the final product is copper foil laminated with the medium.The materials that affect the circuit performance and process performance are mainly dielectric materials. Therefore, the choice of PCB plates is mainly dielectric materials, including semi-cured sheets and core plates.
The choice of materials mainly considers the following factors.
1) Glass transition temperature (Tg)
Tg is a polymer-specific property, a critical temperature that determines material properties, and a key parameter in selecting substrate materials. When the temperature of the PCB exceeds Tg, the coefficient of thermal expansion becomes large.
According to the Tg temperature, PCB boards are generally classified into low Tg, medium Tg and high Tg sheets. In the industry, the Tg plate of about 135 ° C is usually classified as a low Tg plate; the Tg plate of about 150 ° C is classified as a medium Tg plate; and the Tg plate of about 170 ° C is classified as a high Tg plate.
If the PCB is processed more times (more than 1 time), or the PCB layer is more than 14 layers, or the soldering temperature is high (>230 °C), or the operating temperature is high (more than 100 °C), or the welding thermal stress is large. (such as wave soldering), should choose high Tg sheet.
2) Thermal expansion coefficient (CTE)
The coefficient of thermal expansion is related to the reliability of welding and use. The principle of selection is to match the expansion coefficient of Cu as much as possible to reduce the thermal deformation (dynamic deformation) during welding.
3) Heat resistance
The heat resistance mainly considers the ability to withstand welding temperature and the number of times of welding. The actual welding test is usually carried out using slightly more stringent process conditions than normal welding.
It can also be selected according to performance indexes such as Td (temperature of 5% weight loss during heating), T260, T288 (thermal cracking time).
4) Thermal conductivity
5) Dielectric constant (Dk)
6) Body resistance, surface resistance
7) Moisture absorption
Moisture absorption affects the storage period and assembly processability of the PCB. Generally, the sheet is easily delaminated when welded after moisture absorption.
The above is all about how the PCB board should be selected. If you have more PCB boards and doubts about PCBA processing, please contact Jingbang through the official website homepage. We will use more than ten years of industry experience for your detailed analysis.