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JANUARY 2023 I DESIGN007 MAGAZINE 47 between these layers. Prepreg comes in sev- eral thicknesses to help match the electrical requirements of the design. Note that the copper foil in this step becomes the eighth layer in an eight-layer PCB design. 8. Applying the Layers In this step, each etched and oxidized core is placed on top of the previous core's prepreg until the top layer is reached, where copper foil is applied again. 9. Assembling the Book Finally, the completed layers are assembled into books. Depending on overall panel thick- ness, multiple panels can be contained within a single book. Separator sheets are placed between the panels to keep them from stick- ing together. In addition, shims can be added to evenly distribute pressure and maintain a consistent flatness across panels. ermal lagging material is generally placed between the steel plates on either end of the book and the first panel. is helps control the heat flow at a predictable rate into the manu- facturing panels during lamination. 10. Pressing the Book Finally, using heat and mechanical pres- sure under vacuum, the prepreg is heated up and the epoxy liquefied in order to distribute it evenly. e epoxy then cools and hardens, bonding all the layers into a single panel. e PCB is now ready to have holes drilled into and through it, creating a finished multi- layer PCB. Designing multilayer boards will become increasingly common, and it makes sense for designers of every experience level to become more familiar with best practices. DESIGN007 Matt Stevenson is vice president at Sunstone Circuits. To read past columns, click here. by John Watson After finishing the statue of David, Michelan- gelo—Italian sculptor, painter, architect, and poet of the High Renaissance—was asked how he had created such a beautiful work of art. He said, "The sculpture was already complete within the marble block before I started my work. I merely had to chisel away the superfluous material." After decades of being in the industry and seeing countless designs, it's still amaz- ing to see the excep- tional beauty of a well- done PCB design. For designers, each PCB begins as a blank canvas; not knowing what the final product will look like, we walk a fine line between engineering and artistry, often produc- ing fascinating results. There is a uniqueness to every PCB design. If I gave the same schematic to 10 individuals and asked them to complete the design, I can guaran- tee that each designer would come up with some- thing different. This is a result of blending each person's understanding of engineering require- ments with their own touch of artistry. From the very start of a project, there is a "flow" to the cir- cuit in the schematic. With signals, best practice is to go from left to right, from inputs to outputs. With the powers and grounds, we move from the top down to the bottom. Seeing how different people interpret this process always makes me geek out a little, because in a PCB, we can clearly see evidence of the artistic tendency. There is a stunning beauty to the multi-layered colors and the various details of connections and features, such as length tuning, impedance matching, etc. It indeed can only be described as art. To read the rest of this column, click here. Elementary, Mr. Watson The Art of the PCB

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