Practical
At the end of the 1990s when many build-up printed circuit board solutions were proposed, build-up printed circuit boards were also officially put into practical use in large quantities until now. It is important to develop a robust test strategy for large, high-density printed circuit board assemblies (PCBA, printed circuit board assembly) to ensure compliance and functionality with design. In addition to building and testing these complex assemblies, the money invested in the electronics alone can be high, possibly reaching $25,000 for a unit when it is finally tested. Because of such high costs, finding and repairing assembly problems is an even more important step now than it was in the past. Today’s more complex assemblies are approximately 18 inches square and 18 layers; have more than 2,900 components on the top and bottom sides; contain 6,000 circuit nodes; and have more than 20,000 solder points to test.
new project
New developments require more complex, larger PCBAs and tighter packaging. These requirements challenge our ability to build and test these units. Moving forward, larger boards with smaller components and higher node counts will likely continue. For example, one design currently being drawn for a circuit board has approximately 116,000 nodes, over 5,100 components, and over 37,800 solder joints requiring testing or validation. This unit also has BGAs on the top and bottom, the BGAs are next to each other. Testing a board of this size and complexity using a traditional bed of needles, ICT one way is not possible.
Increasing PCBA complexity and density in manufacturing processes, especially in testing, is not a new problem. Realizing that increasing the number of test pins in an ICT test fixture was not the way to go, we started to look at alternative circuit verification methods. Looking at the number of probe misses per million, we see that at 5000 nodes, many of the found errors (fewer than 31) are likely due to probe contact issues rather than actual manufacturing defects (Table 1). So we set out to bring the number of test pins down, not up. Nevertheless, the quality of our manufacturing process is evaluated to the entire PCBA. We decided that using traditional ICT combined with X-ray tomography was a viable solution.
Post time: Mar-03-2023