DocumentCode :
3490101
Title :
Mechanics of moisture for polymers: Fundamental concepts and model study
Author :
Fan, Xuejun
Author_Institution :
Dept. of Mech. Eng., Lamar Univ., Beaumont, TX
fYear :
2008
fDate :
20-23 April 2008
Firstpage :
1
Lastpage :
14
Abstract :
Reliability issues associated with moisture have become increasingly important as advanced electronic devices demand for new materials, more function integration and further miniaturization. However, the fundamentals of the mechanics of moisture transport and the subsequent failures in polymers have not been investigated extensively. This paper is devoted to some fundamental concepts of moisture absorption, diffusion, and swelling. The mathematical descriptions of moisture phase transition with temperature, and the governing equations for a deforming polymer with moisture effect are presented. The non-Fickian sorption behavior is discussed and a widely-used two-stage theory is introduced. It has been found that water sorption (immersion into liquid water bath) has very different transport mechanism at surface compared to the moisture sorption (moisture in air). The state of moisture within polymers and its interactions with polymer matrix, fillers and additives are discussed. It has been suggested that, in most of cases, the majority of absorbed water molecules neither show significant interaction with other water molecules nor with their environment. Those ´unbound´ moisture stays in free-volumes and does not contribute to hygroscopic swelling. Swelling is caused by water molecules bound to the polymer matrix. Although the free volume fraction is usually in the range of 1% to 5%, the pore size is always below nanometers and not detectable by the conventional measurement techniques such as SEM and mercury intrusion. An approximate estimate of free volume fraction using weight gain data is introduced. A vapor pressure model, which allows the whole-field vapor pressure calculations, is presented. Finally the governing equations for a deforming polymer with the consideration of moisture are developed.
Keywords :
approximation theory; diffusion; estimation theory; moisture; polymers; reliability; sorption; swelling; vapour pressure; advanced electronic devices; approximate estimation; free volume fraction; hygroscopic swelling; mathematical descriptions; moisture absorption; moisture diffusion; moisture swelling; moisture transport mechanics; nonFickian sorption behavior; polymers; reliability issues; vapor pressure model; water molecules; water sorption; Absorption; Equations; Materials reliability; Microelectronics; Moisture; Packaging; Polymers; Temperature; Thermal expansion; Thermal stresses;
fLanguage :
English
Publisher :
ieee
Conference_Titel :
Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Micro-Systems, 2008. EuroSimE 2008. International Conference on
Conference_Location :
Freiburg im Breisgau
Print_ISBN :
978-1-4244-2127-5
Electronic_ISBN :
978-1-4244-2128-2
Type :
conf
DOI :
10.1109/ESIME.2008.4525043
Filename :
4525043
Link To Document :
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