Author: Changsu Kim

Date/Time/Location of Defense: 7/21/2023 at 12:00 pm in EGR-2162


-Professor Bongtae Han (Chair)

-Professor Patrick McCluskey

-Professor Peter Sandborn

-Professor Michael Osterman

-Professor Sung W. Lee (Dean’s Representative)

Title: Measurements of Effective Cure Shrinkage of Epoxy Molding Compound and Induced In-line Warpage during Molding Process

Abstract: Cure shrinkage accumulated only after the gel point is known as effective cure shrinkage (ECS), which produces residual stresses inside molded components.  The ECS of an epoxy-based molding compound (EMC) is measured by an embedded fiber Bragg grating (FBG) sensor.  Under a typical molding condition, a high mold pressure inherently produces large friction between EMC and mold inner surfaces, which hinders EMC from contracting freely during curing.  A two-stage curing process is developed to cope with the problem.  In the first stage, an FBG sensor is embedded in EMC by a molding process, and the FBG-EMC assembly is separated from the mold at room temperature.  The molded specimen is heated to a cure temperature rapidly in the second stage using a constraint-free curing fixture.  The ECS of an EMC with a filler content of 88 wt% is measured by the proposed method, and its value is 0.077%.  The measured ECS can be used to predict the warpage caused by molding processes.  The validity of the prediction can be verified only by measuring the warpage during molding.  A point-based measurement technique utilizing uniquely-generated multiple beams and binarization-based beam tracing method is developed to cope with the challenges associated with the warpage measurement during molding.  The proposed method is implemented successfully to measure the warpage of a bimaterial disk that consists of aluminum and EMC as a function of time during molding process.  Measurements are repeated to establish the measurement accuracy of the proposed method.