Factors to Determine PCB Laminate Quality
The main factors to determine PCB laminate quality are glass transition temperature Tg, coefficient of thermal expansion (CTE), PCB decomposition temperature Td, heat resistance, electricity conduction and PCB water absorption.
Tg temperature is lower, high temperature will make PCB distorted and components damaged. So to select PCB laminate, we have to make sure that Tg is higher than circuit work temperature and more than 170 degree centigrade for lead free process. SMT requires low CTE. For lead free soldering, PCB laminate CET should be much lower. CTE of direction Z does big impacts on soldering of metal hole. What’s more, SMT requires PCB not distorted even for second reflow soldering. Regarding electricity conduction, there are some special values for dielectric constant<2.5, dielectric loss<0.02, dielectric strength (breakdown voltage > 40kV for 0.5mm thickness PCB), insulation resistance>10^4 M OHM, volume resistance>10^3 M OHM* cm, Anti-arc erosion performance>60s, water absorption<0.8%.