Temperature dependency of coefficient of hygroscopic swelling of molding compound

Many polymer based materials, such as molding compound and underfill, 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 absorption induces swelling and deformation in a package and leads to failure in some cases. For example, when polymer materials swell upon absorbing moisture, while the adjacent non-polymeric materials, such as lead frame and silicon chip, do not, this induces hygroscopic mismatch stresses in a package [1]. It has been reported that swelling induced stresses are comparable to thermally induced stresses [2]. In this study, a new faster and accurate CHS (coefficient of hygroscopic swelling) measurement method using DIC (Digital Image Correlation) was proposed to measure CHS of molding compound material at various temperatures (between 25degC to 180degC). With this measurement, temperature dependency of CHS was quantified and reported. In addition to DIC, the results were utilized by the combination of TGA (Thermal Gravitational Analysis)/TMA (Thermal Mechanical Analyzer) method and finite element analysis (FEA).