Moisture diffusion and vapour pressure modeling of IC packaging

A new physical quantity-wetness fraction-has been introduced to overcome the concentration discontinuity in the application of Fick's diffusion equation to multi-material systems such as in plastic IC packaging. This enables the use of commercial thermal diffusion software to model the transient moisture diffusion phenomenon in IC packaging. More significantly, the wetness fraction provides a simple means of computing the vapour pressure in a delaminated region within an IC package when it is heated up to 230/spl deg/C during reflow solder. The approach was bench marked against published works and found to corroborate remarkbly well despite its simplicity.