High Tg & Ultra-High Tg Epoxy Mold Compounds

The glass transition temperature (Tg) of an Epoxy Mold Compound

As explained in the article on how epoxy mold compounds cure, the glass transition temperature (Tg) of an epoxy molding compound is the temperature above which epoxy properties, specifically the coefficient of thermal expansion (CTE) and the dynamic modulus (E), change.

As you can see in Figure 1, the glass transition temperature, though often presented on technical datassheets as a single value is actually more accurately defined as a range. On the left side of the range, the epoxy mold compounds exhibit a hard or glassy behavior, characterized by a high modulus, high hardness and high stiffness. On the right side of the glass transition temperature the epoxy mold compound has a lower modulus, lower hardness and lower stiffness.

Similarly, the lower line represents the dimension or volume of the EMC. On the left of the glass transition region, the coefficient of thermal expansion (CTE), measured in parts per million per degree Celcius (or ppm/°C) is linear and its rate ofd expansion increases more slowly. On the right side of the Tg region, the CTE increases much more quickly, typically 3 to 4 times as much in the case of epoxy molding compounds.