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36 PCB007 MAGAZINE I JUNE 2025 wear out. Wear and tear on the bits leads to increased drill smear and rougher hole walls, not to mention additional heat generation. One must understand that in this scenario, the drill hit count must be reduced. Summary It has been suggested that producing high- quality, high-reliability printed circuit boards requires strict adherence to processing guide- lines and vigilance in understanding and exe- cuting the principles of troubleshooting. A thorough understanding of each process step is critical in minimizing or eliminating non- The Printed Circuit Designer's Guide to... DFM Essentials, Chapter 5: Via Structures conforming defects—the ones that cost the fabricator money and can lead to lost cus- tomers. Each process must be deeply under- stood on its own merits. Mechanical drilling is one such process. Yes, it is possible to be perfect. PCB007 Michael Carano brings over 40 years of electronics industry experience with special exper- tise in manufacturing, perfor- mance chemicals, metals, semi- conductors, medical devices, and advanced packaging. To read past columns, click here. Microvias Buried and blind vias have been used in the indus- try for quite some time, but were limited by via size, officially defined in IPC-2226. One of the most important tech- nological advance- ments that made HDI viable was the de- velopment of the mi- crovia: a very small hole (typically 0.006" [0.152 mm] or small- er) that only connects certain layers either as "blind" or "buried" via holes. This rep- resents a totally new way of making electri- cal connections between layers on a PCB. Traditional PCB technology has utilized through- holes generated by mechanical drills. This limits the minimum size of via that can be fabricated. Mechani- cally drilled vias are typically drilled through the en- tire PCB, connecting the two outside layers with all of the internal layers. However, by also incorporat- ing sequential lamination and controlled depth drill- ing, mechanically drilled vias can connect the same layers as microvias, only using a larger via size. The ability to strategically connect only certain pads on certain layers greatly reduces the real estate need- ed for a PCB design and allows a much greater den- sity in a smaller footprint. Types of Vias • Through via (through-hole): This is the tradi- tional via connecting the top layer all the way to the bottom layer • Blind via: Used to connect one surface layer with at least one internal layer • Buried via: Used to create connections of inter- nal layers with no contact to the surface layers • Via-in-pad: A type of blind via in which the via hole is drilled in a surface mount pad, elim- inating the need to run a trace and via pad from each SMT pad. Typically done with mi- crovias, but can be done with traditional blind vias as well • Filled vias: Completely filling the via with ei- ther a non-conductive or conductive paste. Conductive fill is typically used for heat dissi- pation; non-conductive fill is used to closely match the thermal expansion of the substrate Continue reading... by Anaya Vardya, American Standard Circuits / ASC Sunstone Circuits BOOK EXCERPT