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36 The PCB Magazine • October 2017 but these tools are much too slow to provide useful data on the thousands of high-speed nets on a single board, not to mention a line pro- ducing hundreds of boards a day. But a new X- ray technology has entered the market that pro- vides both the speed and resolution. And by in- tegrating advanced image analysis and machine learning software with this new high-speed X- ray solution, the era of high-speed X-ray is upon us. A tool with these capabilities is currently un- der development with commercial release an- ticipated in the first quarter of 2018. What does this mean for PCB manufacturers? 1. Stub compliance. No more shipping boards with only coupon test data. 100% of the high-speed net via stubs can be quickly and ac- curately measured prior to shipment. 2. No more slivers from back-drill misalign- ment. Slivers are a killer and can occur random- ly across a board. As layer counts increase, back- drill alignment becomes tougher. At the same time, denser designs limit the drill size that can be used for back-drilling, taking away even more design margin. 3. 56 Gbps and higher speed boards are no longer stub length limited. State-of-the-art for stub length is about seven mils maximum to- day. It is crucially important that the PCB in- dustry move to shorter stub length technology. This can only be achieved by contour mapping of signal layers as laminated. High-speed X-ray metrology is the only method available to map the signal layer position in a board stack and feed this information into the drill recipe to in- dividually target the drill depth for each indi- vidual net. What about their customers? 1. Time to market. High-speed X-ray is the only means of confirming that the dimensions on the finished board match those in the de- sign. New product introductions (NPI) can quickly identify the causes of any performance issues on a single cycle. 2. More design margin available. Instead of using design margin to accommodate poorly manufactured boards, designers can instead op- timize for cost and performance. 3. Credibility in the field. When a manu- facturer sells a router or switch that is field up- gradable, they need to know that the backplane can perform at higher speeds than as originally shipped. Line card swaps that turn into forklift box exchanges are a terrible outcome for every - one that can be avoided by tightening PCB manu- facture process control and ensuring compliance. Conclusion The electronics industry is characterized by continuous improvements in size and perfor- mance. As the industry moves forward, inflec- tion points arise where doing things the same way can no longer achieve acceptable results. We are at that point in high-speed networking applications now and the quantity of boards that need to meet these tighter specifications is only going to grow. High-speed X-ray metrol- ogy allows contour mapping of as-built signal layers for tighter targeting and compliance test- ing of stubs and other features for conformance to design. PCB Scott Jewler is co-founder of SVXR, an X-ray metrology company bring- ing new and innovative technology to the printed circuit board industry. To contact Jewler, click here. PCB SIGNAL INTEGRITY OPTIMIZATION USING X-RAY METROLOGY Figure 2: X-ray of multilayer PCB with wide dynamic enabling detection of individual signal layers.