In the late 1990s, when numerous schemes for adding layers of printed circuit boards were proposed, they were also officially and extensively applied until now. It is important to develop a robust testing strategy for large, high-density printed circuit board assemblies (PCBA) to ensure compliance with design and functionality. In addition to the establishment and testing of these complex assemblies, the money invested in electronic components alone may be high, reaching $25000 when a unit is finally tested. Due to such high costs, finding and repairing assembly problems is now even more important than in the past. Today's more complex assembly is approximately 18 square inches, with 18 layers; There are over 2900 components on the top and bottom surfaces; Contains 6000 circuit nodes; There are over 20000 welding points that need to be tested.

The new development project requires more complex, larger PCBA, and tighter packaging. These requirements challenge our ability to build and test these units. Furthermore, larger circuit boards with smaller components and higher node counts may continue. For example, a design that is currently drawing a circuit board diagram has approximately 116000 nodes, over 5100 components, and over 37800 solder joints that require testing or confirmation. This unit also has BGA on the top and bottom surfaces, followed by BGA. Using traditional needle beds to test this size and complexity of the board, ICT alone is not possible.

The increasing complexity and density of PCBA in manufacturing processes, especially in testing, is not a new issue. Realizing that increasing the number of test pins in the ICT testing fixture is not the direction to go, we began to observe alternative circuit confirmation methods. Looking at the number of probes not in contact per million, we found that at 5000 nodes, many errors (less than 31) discovered may be due to probe contact issues rather than actual manufacturing defects (Table 1). Therefore, we are working to reduce the number of test needles, rather than increasing them. Nevertheless, the quality of our manufacturing process is still evaluated throughout PCBA. We have decided to combine traditional ICT with X-ray layering method as a feasible solution.