In-situ Characterization of Moisture Absorption and Desorption in a Thin BT Core Substrate

Bismaleimide-triazine (BT) resin/glass fiber laminates are commonly used as a substrate core material in microelectronic packaging. Their moisture absorption and diffusion behavior have a significant impact on package reliability. The traditional method to determine moisture absorption relies on a weight gain measurement metrology with an analytical balance. This approach is generally not suitable for thin films. In this study, the moisture absorption-desorption behavior of a thin BT core was characterized in-situ using a sorption TGA over a temperature range of 30 to 80degC, in an environment of up to 80% relative humidity. From the experimental results, the moisture diffusivity and the saturated moisture content have been determined. Within the experimental temperature range, the diffusivity can be described by the Arrhenius equation and the activation energy can be computed. The obtained results are compared with literature data. The impact of moisture diffusion in BT core on the reliability of ultra-thin stacked chip scale packages (UT/SCSP) will be discussed.