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We have successfully demonstrated the application of fiber Bragg grating sensors to detect the solder interconnect debounding between flip chip ball grid array and printed circuit board in four-point bend tests. Four sensors, due to their small size, are surface-mounted on the four-corners of the ball grid array substrate, about 1 mm from the solder balls that allow more sensitive strain measurement under board flexure. The measured strain data are compared with the data from strain gauge, daisy chain resistance, and dye and pry test. The preliminary results show that the fiber sensors are capable of detecting the onset of solder joint fracture, strain relaxation, and extent of the failure.