Measurement of Effective Chemical Shrinkage of Polymeric Materials Using Fiber Bragg Grating Sensor

Summary form only given. Mechanical and thermal characterization of polymeric materials is critical to "predictive modeling" required for reliability assessment and design optimization at the conceptual stage of a new product development. One of the most critical polymer properties required for predictive stress modeling is "chemical shrinkage" developed during the polymerization process. Residual stresses induced by the chemical shrinkage can largely influence the performance and reliability of package. The issue of "chemical shrinkage" is not new. Numerous testing methods have been developed for many decades and some of them are practiced routinely to measure the intrinsic (or total) chemical shrinkage of polymers. It is important to note, however, that not all of the intrinsic chemical shrinkage contributes to the residual stresses simply because some of chemical shrinkage occurs before polymer builds up any mechanical strength. This study proposes an innovative integrated measurement method to measure the effective chemical shrinkage that contributes to the residual stresses. The method is based on a fiber Bragg grating (FBG) sensor. A polymer of interest is cured around a glass FBG and the Bragg wavelength shift is measured and documented while polymerization progresses at the curing temperature. The method is simple but measures the effective shrinkage accurately regardless of the modulus and coefficient of thermal expansion of the polymer