Glass transition temperature

In amorphous plastics, the glass transition (Tg) separates the brittle, glassy state below the glass transition temperature from the rubbery, soft-elastic state above it. If a printed circuit board base material is heated and the glass transition temperature is exceeded, the expansion of the substrate increases strongly, especially in the Z-direction. At the same time, the deformability of the material increases, i.e. the modulus of elasticity decreases.