Study of moisture transport in silicone gel for IGBT modules

In this paper, an original study on moisture absorption and desorption inside silicone gel for power modules is presented. Silicone gel from two suppliers has been cured at different conditions and exposed to a defined humid environment for a defined amount of time. The mass of gel, the relative humidity, and the temperature at a certain depth beneath the gel surface have been measured, and the moisture diffusion coefficients inside the specimens have been calculated. For the two materials we observed significantly-different changes in gel mass, but similar humidity levels deep inside the gel. The influence of curing and bake-out conditions as well as the difference in absorption and transport in the materials has also been discussed.