Materials characterization of model epoxy-functionalized silsesquioxanes as potential underfill encapsulants

Preliminary data from cured epoxy functionalized silsesquioxane cubes, a novel inorganic/organic hybrid material system, have been presented to explore their potential as a possible advanced material to improve the underfill encapsulant process. The important underfill material properties considered here include the potential flow properties, T_g, and CTE. The single phase nature of these materials has the advantage of reducing the intensive effort needed in filler particle optimization while retaining the ability to include up to 65% by mass silica content. Even for the model system here, using very flexible curing agents, substantial increases in T_g are observed. Unfortunately, the measured CTE values are comparable to unfilled epoxy resins, although T_g is observed to be greater than 200°C. A large performance gap remains between this simple model system and current highly engineered underfill encapsulants, but these preliminary results show promise. Since the chemistry involved allows for the chemical tailoring of the cube functionality, sophisticated epoxy chemistries already developed for current underfill materials can be used as analogous components on these silica cube materials. Mixtures of different functional silsesquioxane cube materials may allow materials developers a larger range of components to tailor specific physical properties