Christophe Prior

Combined effects of humidity and thermal stress on the dielectric properties of epoxy-silica composites

Abstract We report on the effects of hydrothermal ageing on the dielectric properties of epoxy-silica composites used for microelectronic packaging. The study was carried out for samples with various degrees of curing. Epoxy compounds were subjected to moisture exposure (standard JEDEC procedures) and consecutive thermal stress (240°C). Changes in the dielectric constant and in the loss factor were measured in the 100 Hz–100 kHz frequency range. It is found that water absorption increases with curing. After ageing the dielectric constant is decreased and the loss factor increased. Cured materials have a higher resistance against hydrothermal ageing.

Dielectric properties of epoxy/silica composites used for microlectronic packaging, and their dependence on post-curing

We studied the dielectric properties (dielectric constant and loss factor) of epoxy molding compounds used for electronic packaging, as a function of frequency (100 Hz–100 kHz) and temperature (25–100 °C). Studies were performed for samples with different formulations (various silica and carbon black contents). At room temperature a loss peak is found at 50 kHz, whose intensity is enhanced by carbon black addition. Additional loss is detected below 1 kHz when the temperature is increased up to 100 °C. We also studied the influence of post-mold curing time (0–12 h at 165 °C) on the dielectric properties. The dielectric constant monotonically decreases with post-mold cure to level off to a minimum value for long post-cure durations. The loss factor first increases for short post-curing times, and then decreases as post-cure is continued. The origin of loss is discussed with reference to common relaxation processes observed in epoxy polymers.