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The PCB board with qualified design has great requirements for the quality of PCBA processing. What are the commonly used parameters related to PCB quality evaluation?

The commonly used parameters for evaluating PCB board quality include glass transition temperature (Tg value), coefficient of thermal expansion (CTE), PCB decomposition temperature (Td), heat resistance, electrical performance, and PCB water absorption. Now, let's explain the glass transition temperature and thermal expansion coefficient for you in detail:

1、 Glass transition temperature (Tg value)

The base material of CCL is hard and brittle under a certain temperature, which is called glass state. Above this temperature, the base material becomes soft and the mechanical strength becomes significantly lower. This critical temperature that determines the properties of materials is called the glass transition temperature.

If the Tg temperature is too low, PCB will be deformed and components will be damaged under high temperature.

2、 Coefficient of thermal expansion (CTE)

CTE quantitatively describes the degree of expansion of materials after heating. CTE refers to the elongation of material per unit length when the ambient temperature increases by 1 ℃. Lead free soldering requires PCB board to have lower thermal expansion coefficient due to high soldering temperature. Especially for multilayer PCB, the CTE in Z direction has a great influence on the layer resistance of metallized holes. Especially when welding or repairing for many times, after many times of expansion and contraction, the metallized hole layer will be broken.