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Comprehensive Quantification of Moisture Sorption Characteristics in Polymer Material of Thin Film Form
Keywords: Moisture Sorption, Thin Film, Diffusion Modeling
Moisture absorbed in polymer material has a significant effect on its reliability. Delamination of the layers in printed circuit board during the manufacturing process (particularly soldering) is a leading cause of product failure. Also, high temperature environment with humidity degrades characteristics of material properties such as electrical conductivity of conducting polymer in flexible touch screen panel. Hence, there is the need for a quick test which can predict failure before production. In this paper, the procedures for measuring moisture sorption properties of thin film form of polymer materials such as solder resist (SR) and polyethylene terephthalate (PET) using thermogravimetry method and vapor transmission rate to characterize the moisture diffusion in polymer is presented. FEA implementation for moisture diffusion modeling is performed, in which temperature dependent material properties are characterized. The thermal-moisture analogy for diffusion modeling is employed for consideration of the temperature dependent material properties so that transient temperature and spatially non-uniform temperature loading problem is suitably incorporated. The measurement of permeability is used for validation of moisture diffusion characteristics. The moisture sorption properties of SR and PET are obtained through permeation measurement. Anisotropic characteristics of test specimen in moisture permeation over water boiling temperature (100 degrees) with 100% relative humidity (RH) condition are experimentally explored for investigation of possible re-crystallization in polymer. Linear permeation modeling based on Fick's law is employed and analytical/numerical solutions are compared for validation of measurement. The effect of aspect ratio of the test specimen for valid dimensional assumption in modeling is presented based on measurement of permeation through edge seal test, in which the conservation of vapors across each material edge side is explored to measure experimentally. Finally, the effects of polymer backbone on permeation in several different type of SR and PET of thin film form are discussed for investigation of the nature of the polymer material. We will explore the moisture induced failure on reliability at the interfacial layer in multi-layered printed circuit board by making correlation between quantification of moisture sorption characteristics through PCB package and the onset of delamination in epoxy molding compound layer.
Heejin Park, Senior Research Engineer
Samsung Electro-Mechanics Co., LTD.
Suwon, Gyeonggi-Do 443-743,

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