| Many polymer based materials are commonly used in plastic encapsulated packages. In spite of many advantages, most of them, however, are hydrophilic and absorb moisture when exposed to a humid environment. Moisture plays an important role in the integrity and reliability of plastic electronic packages. Recent researches have revealed that the level of hygroscopic stresses is comparable to that of thermo-mechanical stresses and ignoring it may cause a serious consequence in reliability assessment. Moisture will also degrade interfacial adhesion strength so that the interface should become more susceptible to delamination or cracking. Hygro-thermo-mechanical stress and adhesion strength degradation synergistically lead to delamination of interfaces, which eventually results in interconnection failures. Moisture resistance sensitivity tests were introduced as one of the major reliability tests for package qualification. Despite the pivotal role of moisture, research activities in moisture induced failure remain relatively low, compared to the thermally induced failure. This is partly due to the lack of material data and aggravated by the lack of material characterization techniques and procedures, and the near absence of such properties from material vendors.;In this study, the moisture diffusion through material is introduced first. Then, the measurement techniques on the diffusivity and solubility as function of temperatures are described. An innovative measurement method based on Digital Image Correlation (DIC) technique is proposed to measure the coefficient of hygroscopic swelling (CHS) of polymeric materials. The modeling and characterization of hygroscopic swelling are introduced and incorporated into the proposed method. Finally, hygro-thermo-mechanical model for stress-strain analysis is developed and applied to a MEMS package to study the hygro-thermal conjugate effect. |
