In-situ characterization of moisture absorption-desorption and hygroscopic swelling behavior of an underfill material

摘要

Moisture absorption and hygroscopic swelling behavior of an underfill material were measured in-situ using the sorption TGA and the DMA-RH techniques, respectively. Results showed that moisture diffusion can be well described by Fick''s law when the relative humidity (RH) is 60% or less, and the diffusivity exhibits an Arrhenius temperature dependence with an activation energy of ∼ 0.56 eV. At 85% RH, non-Fickian diffusion behavior becomes apparent in the latter stage of the diffusion process. Increase in the saturated moisture content (Csat) at 60%RH was observed after exposure at 85°C 85%RH, which is attributed to hygrothermal ageing induced damage in the material. In-situ DMA-RH results showed that hygroscopic swelling strain is significant comparing with the thermal expansion of the material, and the swelling strain at 60°C 60%RH is equivalent to the thermal strain over a ΔT of 100°C for T < Tg. The coefficient of hygroscopic swelling (CHS) was calculated and the results showed that CHS is temperature dependent, and it increases with the increasing temperature. At higher humidity condition (85%RH or higher), the swelling strain deviates from its linear dependence on Csat and it increases faster than linear when Csat increases, which may also be attributed to hygrothermal ageing induced damage in the underfill material.