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46 DESIGN007 MAGAZINE I JULY 2025 • IT and IS: Immersion tin and immersion silver • ENIG: Electroless nickel/immersion gold • ENEPIG: Electroless nickel/electroless palla- dium/immersion gold • OSP: Organic solderability preservative Developing the HDI or UHDI circuit board is not a trivial endeavor. Materials and process complex- ities play a significant role in terms of manufac- turability and the direct cost of fabricating multi- layer circuit boards. The challenge here is to select the most suitable base materials for the applica- tion while meeting the end-product's electrical and operating environment requirements. The best advice for the circuit board designer is to establish a dialogue with the circuit board fabrication specialist early on for each new design. In regard to fabrication process efficiency and meeting the cost target for the circuit board, fabricators encourage the designer to evaluate the overall physical aspects of the circuit in order to simplify the design. For example, reducing conductor width and spacing will significantly contribute to reducing layer count. As far as implementing SBU technol- ogy, the most expensive stackup configuration requires multiple sequential laminations. So, reduc- ing the circuit layer stackup on each side of the board will have a very positive impact on unit cost. Resources • Rush Inc., a U.S.-based PCB manufacturing service company based in Silicon Valley • Design Guidelines for Surface Mount and Microelectronics, by Vern Solberg Vern Solberg is an independent technical consultant, specializing in SMT and microelectronics design and manufacturing technology. To read past columns, click here. D ES I G N E RS N OT E B O O K Metal halide perovskite solar cells (PSCs) are among the most promising terawatt-scale photovol- taic technologies, combining high power conversion efficiency with the advantages of low-cost solution processing. For rapid commercialization of PSCs, en- suring high reproducibility in device fabrication is es- sential—particularly in the surface treatment steps. However, the surface condition of perovskite films often fluctuates between fabrication batch- es, operators, and laboratory environments, owing to uncontrollable variations in processing history and local atmosphere. Even minor changes in tem- perature, stoichiometry, humidity, and solvent evap- oration dynamics can significantly alter the surface state. These instabilities undermine the reliability of passivation: Concentrations of passivating agents that are empirically optimized for one condition may fail—or even backfire—under another. In this study, we introduce a saturated passivation (SP) strategy that universally addresses surface- state variability and significantly improves the repro- ducibility of high-performance PSC fabrication. The term "saturated" refers to a state in which surface defects are fully passivated, with only a trace amount of low-dimensional perovskite remaining—sufficiently thin so as not to impede interfacial charge transport. Conventional passivation strategies rely on iden- tifying an optimal concentration C to balance defect passivation and charge transport. However, this bal- ance is easily disrupted by surface fluctuations in- duced by process instability, making it difficult to consistently achieve C. The SP strategy consistently improves perfor- mance across diverse perovskite compositions, film fabrication processes, device architectures, and scales, offering a generalizable pathway toward more robust and scalable perovskite photovoltaics. (Source: Westlake University) Researchers Solve Key Manufacturing Hurdle for Perovskite Solar Cells