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42 SMT007 MAGAZINE I MARCH 2026 technology, where many small electromo- tors need control and space is limited, and he listed key components and potential suppliers. There are many areas requiring specialist PCBs in the controller, perception, and sensing planes: main control- ler, coprocessor, vision processing unit, visual module, audio process- ing unit, inertial measurement unit, force/torque sensing unit, tactile sensor unit, and LiDAR control unit. In closing, he said, "Innovation happens with a speed as never seen before, and tomorrow this presentation might already need additions!" Refreshed after a reasonably early night and a restful sleep, delegates dutifully re-assembled for Day 2 and Session 4 of EIPC's Winter Conference. Session moderator Martyn Gaudion became a presenter with a thought-provoking presentation on the accuracy of field solvers at UHDI dimensions. Gaudion has a talent for holding the audience's attention while addressing a technically challeng- ing subject, keeping it informative and entertaining. What are UHDI dimensions? Ultra-high density interconnect represents the next generation in density and miniaturisation of PCB design geome- try. It is not simply "smaller HDI," because it gener- ally involves fundamentally different manufacturing processes. Lines and spaces are typically less than 65 microns, sometimes much less. Gaudion's opening slide put a perspective on dimensions. It is a set of engineers' feeler gauges, 0.05 mm being the thinnest—50 microns! He followed with cross-sections of a human hair, 50 to 70 microns, down to 2 microns for a spider's web. His example of a UHDI trace was 25 microns wide and 10 microns thick. To illustrate time-domain reflec- tometry (TDR) measurements, he showed a couple of typical distrib- uted-resistance discontinuities and their reflections dating back to 1970, and compared them with a contemporary 50 ohm plot from one of Polar's test systems, followed by the results of a series of tests on a 75 ohm line. Using a dimensioned schematic cross-section of an offset differen- tial stripline, he demonstrated how the measured differential imped- ance compared with the originally calculated value, and qualified the results by correlation with careful microsectioning. "Is what you made what you designed?" he asked, displaying a microsection showing conductors of 32 microns and 33 microns with a 97-micron space between them. Gaudion commented on the influence of foil roughness, and stressed the importance of compensating for the effect of DC resistance on TDR impedance measurement to avoid the TDR reading being higher than predicted. He further advised to "ensure you made what you think you made," "Turn on the imbalance check on your TDR," and "If in doubt, microsection!" The final technical presentation came from sustain- ability-driven innovator Victor Verlinden, founder and CEO of Virenti in Belgium. He was spread- ing awareness of a breakthrough technology that has advanced into a viable PCB application and is now moving toward scale-up and market entry. His presentation, "Towards sustainable PCB substrates: system-level considerations for bio-based lami- nates," was meant to secure a green future for elec- tronics by replacing fossil-based circuit boards with European bio-based alternatives. Reviewing the current situation, Verlinden noted several areas of concern regarding the sustainabil- ity of traditional laminates, including environ- mental concerns about certain aromatic brominated flame retardants, short- ages of raw materials, particularly glass fabric, increasing geopolitical tension and strain, and, not least, the erosion of local European lami- nate production. Although the system-level frame- work was shifting, the core concept of laminates has not. He mentioned IPC-4101 and showed a chart of its slash M a r t y n G a u d i o n V i cto r Ve rl i n d e n