PWB warpage is one of the major SMP(surface mount package) failures together with fatigue failure of bonding wire and solder joint in electronic packages.
In this study, PWB warpage before and after thermal cycling is measured by shadow moir$\'{e}$ method whose limited sensitivity is enhanced by a phase shifting technique. PWB specimens tested are made of FR-4 without Cu foil, FR-4 with one-side Cu foil, and FR-4 with two-side Cu foil, respectively. Experimental measurements show that i) PWB before thermal cycling has some warpage, ii) crosswise directional warpage is larger than lengthwise directional warpage, and iii) PWB of asymmetric structure experiences more serious warpage than that of symmetric structure after thermal cycling as the temperature condition goes higher.
