Fig. 1. A structural model and meshing of a single welding spot

Fig. 2. (a) Laser energy time distribution function; (b) Laser energy space distribution function

Fig. 3. Displacement field at 0.16 μs

Fig. 4. (a) Displacement of points on the upper surface; (b) Displacement of points on the lower surface

Fig. 5. Multi-solder joint model

Fig. 6. Transmitted waves of solder and missing solder

Fig. 7. Schematic diagram of the laser ultrasonic test platform

Fig. 8. BGA package circuit board prototype

Fig. 9. Result of C-scan test

Fig. 10. (a) Results of A-scans at normal area and solder area; (b) Denoised results of Fig.10(a)

Fig. 11. B-scan results of I and II marked in Fig 9 (a) B-scan at line I; (b) B-scan at line II