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64 The PCB Magazine • November 2016 UNIQUE IMPLEMENTATION OF A RIGID-FLEX CIRCUIT Figures 16 and 17 show CAF coupon failures. Failure analysis of the original coupons verified electromigrated copper as the defect mode. The orthogonal view in Figure 18 shows voiding and electromigrated copper between and along individual glass fibers. Cross-section of parts and coupons with ro- tated prepreg confirmed the rotation was suc- cessful in the manufacturing environments as shown in Figure 19. Figure 20 shows the rota- tion effect on pre-preg panelization. A second build of coupons was built with and without pre-preg rotation. As seen in Figure Figure 16: CAF coupon fail site. Figure 18: Orthogonal microsection of CAF coupon fail site. Figure 17: Microsection of CAF coupon fail site. Figure 19: Confirmation of prepreg rotation. Figure 20: Prepreg panel utilization with rotation.