Objective Ball Grid Array (BGA) is a widely used modern integrated circuit packaging method, which plays an important role in aerospace, vehicle manufacturing, electronic communications and other fields due to its large number of I/O pins, small size, and good heat dissipation performance. Because of technical and environmental influences, BGA solder joints are prone to have various defects. In order to ensure the reliability of electronic packaging, it is necessary to inspect them with a high-precision, high-reliability non-destructive testing technology. Laser ultrasonic detection technology has the advantages of high precision, fast response, no damage, etc. Optical microphone is a new type of ultrasonic receiving device, which has low cost, wide bandwidth range, high sensitivity and a broad development stage. Therefore, a ultrasonic detection of BGA solders based on optical microphone is studied in this paper.

Methods In this paper, the process of ultrasonic wave excitation by pulsed laser on the surface of the material is theoretically analyzed, and the thermal-mechanical coupling numerical simulation model of BGA solder joint is established by using the finite element simulation software COMSOL to simulate the propagation law of ultrasonic waves inside the solder joint and the influence of internal defects on ultrasonic propagation. Finally, the laser ultrasonic testing system based on optical microphone was used to perform laser ultrasonic scanning tests on the prepared BGA package circuit board samples with simulated defects, and the results were processed by Lanczos denoising algorithm.

Results and Discussions The results show that the laser with a wavelength of 532 nm and a single pulse energy of 2.66 mJ can detect solder joints with defects with diameters of 7 mm and 5.5 mm. The position and size of the solder joints and simulated defects in the C-scan results are consistent with the actual situation (Fig.9). The A-scan results (Fig.10) are consistent with the simulation results (Fig.6). In the B-scan results (Fig.11), there is a significant difference between the normal solder joint area and the simulated defect area.

Conclusions Through the theoretical analysis, finite element simulation and experimental detection of the process of laser exciting ultrasonic on BGA samples, it is proved that the all-optical laser ultrasonic detection can effectively detect the solder joint defects in BGA packaging. Laser ultrasonic testing has unique advantages in locating and dimensioning BGA solder joint defects, and has broad development prospects in the field of real-time quality inspection in the process of integrated circuit manufacturing and usage.