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Optical waveguiding as a method for characterizing the effect of extended cure and moisture on polyimide films
Author(s) -
Noe Susan C.,
Pan Jeffrey Y.,
Senturia Stephen D.
Publication year - 1992
Publication title -
polymer engineering and science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.503
H-Index - 111
eISSN - 1548-2634
pISSN - 0032-3888
DOI - 10.1002/pen.760321506
Subject(s) - polyimide , materials science , refractive index , birefringence , composite material , moisture , residual stress , curing (chemistry) , swelling , diamine , optics , polymer chemistry , optoelectronics , physics , layer (electronics)
Integrated optics techniques (i.e., guiding light through a thin film) have been used to study the effects of extended cure and moisture exposure on polyimide films as manifested in changes in the TE (in‐plane) and TM (out‐of‐plane) refractive indices and in their difference (birefringence). Mechanical testing of these films has been done using the load‐deflection technique. Du Pont polyimide Pyralin 2555 and 2556 (benzophenone tetracarboxylic dianhydride‐oxydianiline/metaphenylene diamine), cured repeatedly at 400°C and 375°C respectively, show an increase in refractive index as a function of cure (possibly due to densification), as well as an increase in birefringence (due to increased residual stress). Upon exposure to moisture, the TM and TE refractive indices both increase (absorption of the polar water molecule), but the TE index does not increase as much. Mechanical testing has shown that the residual stress in the polyimide film increases with extended cure and decreases with moisture exposure due to moisture‐induced swelling of the film. A model is proposed which relates the optical results to the mechanical measurements. Based on our data, a preliminary stress‐optic coefficient is reported.