While historically solid glass filler has been utiUzed in electronic potting compounds, recent studies have shown that hollow glass microspheres may be used as a lightweight alternative. Such hollow glass fillers are readily available at low cost and are termed microspheres, hollow glass beads, hollow glass spheres, or microballoons.
These microspheres, through variations in glass wall thickness and particle diameter, have low densities in the range of 0.1-1.0 g/cm3. Hollow glass microspheres have been widely employed as particulate filler in polymeric systems for over three decades. Hollow glass microspheres have essentially the same CTE as their soUd counterparts, but have a much lower density.
Hollow glass microspheres were originally designed to decrease evaporation of oil and petroleum in large containers and as a means to increase buoyancy in ships and submarines. Hollow glass microspheres have more recently been exploited in the aeronautical, aerospace, automotive, civil and industrial engineering, and electronics industries as syntactic foams.
Incorporation of hollow glass microspheres as filler in polymeric matrixes to produce syntactic foams results in unique composite properties including good shear stiffness and strength, fatigue and impact resistance, low density, and high strength to weight ratio, which have largely facilitated their widespread application.
To obtain the low CTE and pc required, hollow glass filler may be substituted for the standard solid glass filler. However, one possible disadvantage of a hollow microsphere filled epoxy composite is a relatively low modulus and compressive strength when compared to traditional solid glass filler.