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Release date:2024-10-10
Designing a qualified PCB board has significant requirements for the quality of PCBA processing. So, what are the commonly used parameters for evaluating the quality of multi-layer PCB boards?
The commonly used parameters for evaluating the quality of PCB boards include glass transition temperature (Tg value), coefficient of thermal expansion (CTE), PCB decomposition temperature (Td), heat resistance, electrical performance, and PCB water absorption rate. Now, let us explain in detail the glass transition temperature and thermal expansion coefficient for you:
1、 Glass transition temperature (Tg value)
At a certain temperature, the substrate of copper-clad laminate is hard and brittle, known as glassy state: above this temperature, the substrate becomes soft and the mechanical strength significantly decreases. The critical temperature that determines material properties is called the glass transition temperature.
Too low Tg temperature can cause PCB deformation and damage components at high temperatures.
2、 Coefficient of thermal expansion (CTE)
CTE quantitatively describes the degree of expansion of a material after heating. CTE refers to the length that a unit length of material elongates for every 1 ℃ increase in ambient temperature. Lead free soldering requires PCB boards to have a lower coefficient of thermal expansion due to the high soldering temperature. Especially for multi-layer PCB circuit boards, the Z-direction CTE has a significant impact on the layer resistance of metalized holes. Especially during multiple welding or repairs, repeated expansion and contraction can cause the fracture of the metalized pore layer.
