Moisture induced swelling in epoxy moulding compounds

Microelectronic components are introduced to an increasing number of applications as part of a controlling or monitoring device, as sensors or as means to tracking. Depending on the application, extreme loading profiles may need to be endured such as high temperatures, random vibrations or humid and even wet environments. Absorbed moisture has a plasticizing effect on the physical properties of polymers. Furthermore, moisture leads to corrosion of metallic parts of the devices and therefore molding compounds are used to protect sensible electronics. However, the epoxy matrix of the molding compounds tends to absorb water molecules and subsequently exhibits a swelling behavior which is unique to the chemistry of the epoxy. Since most other materials involved do not swell when exposed to moisture, a stress between the materials is induced which is similar in origin (dimensional change in materials) and magnitude as the thermal mismatch induced stresses or chemical shrinkage. It is important to know both absorption and desorption properties of used epoxy systems. This paper represented results of moisture diffusion in different high filled epoxy molding compounds using two parallels analysis methods - Thermo Gravimetric Analyzer (TGA) and Thermal Mechanical Analyzer (TMA) at different loading conditions. TGA as a commonly measurement method for analysis of in-situ weight changing due to moisture absorption and desorption. Thermal Mechanical Analyzer was coupled with a conventional humidity generator to be able to in-situ measure the swelling strain of the sample. The enhanced TMA-technique can be used for measuring the dimensional changes of specimens as a function of variable temperature and humidity. The results can be used for integrated finite element analysis methodology, which couples the transient moisture diffusion and the hygroscopic swelling with temperature range.