Fig. 1. Overall structure diagram of linear laser phase-locked thermal imaging system for semiconductor chip detection consisting of excitation, sensing, and control units

Fig. 2. Overview of baseline-free crack visualization algorithm

Fig. 3. Diagrams of thermal wave generation by modulated CW laser beam and corresponding thermal response captured by IR camera. (a) Intensity of modulated CW excitation laser; (b) corresponding thermal response in time domain

Fig. 4. Roberts cross convolution kernels. (a) Compute K_x of gradient edge at +45°; (b) compute K_y of gradient edge at -45°

Fig. 5. Experimental setup of linear laser phase-locked thermal imaging technology for detecting crack of semiconductor chip

Fig. 6. Semiconductor pressed chip specimens

Fig. 7. Microscopic images of semiconductor chip specimens with cracks. (a) Vertical cracks of pressed chip; (b) horizontal cracks of pressed chip

Fig. 8. Typical raw thermal images obtained from pressed chips. (a) Vertical line excitation on intact chip; (b) horizontal line excitation on intact chip; (c) vertical line excitation on vertically cracked chip; (d) horizontal line excitation on horizontally cracked chip

Fig. 9. Raw thermal images obtained from intact chip with vertical line excitation. (a) 0 ms; (b) t (50 ms); (c) T (500 ms)

Fig. 10. Phase-locked amplitude images obtained from raw thermal images in Fig. 8. (a) Vertical line excitation on intact chip; (b) horizontal line excitation on intact chip; (c) vertical line excitation on vertically cracked chip; (d) horizontal line excitation on horizontally cracked chip

Fig. 11. Discontinuous images obtained from chips. (a) Without crack; (b) with vertical crack; (c) with horizontal crack

Fig. 12. Final images obtained after de-noising process. (a) Without crack; (b) with vertical crack; (c) with horizontal crack