Impact of thermal ageing on cohesive and adhesive strengths of overmould materials: Characterisation methods and implementation in FEM

This paper reports the impact of ageing on the cohesive and adhesive strength of overmould materials used in electronic packages. For so-called harsh environment applications, the overmoulded package operates in an ambient at a continuous temperature of 175°C, or sometimes even 200°C. At these high temperatures, it can be expected that the overmould material and its interfaces degrade. In order to select the right overmould materials, ageing tests have been performed on different commercially available materials. Static bending experiments are used to measure the elastic modulus, the ultimate strength and the interface strength. The impact of the materials properties changed by thermal ageing, are implemented in Finite Element Models. For a particular package, the study shows after how many hours of ageing, the stresses can lead to overmould cracking.