Today's printed circuit assemblies comprise of several layers with components populated on both sides of the PCBs. This presents challenges to conventional 2D nondestructive X-ray techniques due to shadowing and absorption of the x-ray energy. Tilting of the samples while imaging helps to get around this problem, however, often it might not always be adequate. This article proposes a non-destructive method for detecting solder defects at the second level interconnect using 3D X-ray tomography. A total of 6084 solder joints of 0.8mm and 0.5mm pitch BGAs were analyzed. Correlation between dye stain and package pull analysis and 3D-uCT X-ray revealed a 100% correlation. Virtual cross sections obtained using 3D x-ray tomography methods showed that it is possible to evaluate non-destructively the solder joint failure mode "H" known as "head-pillow or snowman" at the second level interconnect.

Printed Circuit Board (PCB) assemblies are moving toward lead-free (LF) alloys and away from the traditional Sn-Pb alloy [1]. This change is creating new and unique failure modes as the process adapts to accommodate the higher temperatures of the new process [2]. In addition, mis-processed lots are more likely due to the complexity of assembling a mix of Sn-Pb and leadfree solders, components, PCBs, solder pastes, and fluxes. This case study helps to highlight the challenge and provides an example of what can happen, how to detect it, and how the defects can cause reliability failures.