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46 DESIGN007 MAGAZINE I JANUARY 2023 it down into a series of easy steps by looking at the assembly of an eight-layer PCB. 1. Grouping the Layers e internal layers are grouped into pairs. For an eight-layer build, layers 2 and 3 are paired together, as are layers 4 and 5, and lay- ers 6 and 7. What about layers 1 and 8? As they are on the outside, they'll be added later. 2. Imaging the Layers ese pairs are imaged together onto both sides of a copper-clad laminate core, creating three distinct double-sided inner layer panels. is image is a representation of the copper image defined by the electronic data for each copper layer. 3. Etching the Images Once the layers are all imaged, they'll be etched. Etching removes the unwanted copper cladding, which creates spaces while simulta- neously defining traces and pads. 4. Inspecting the Etched Layers Aer etching is complete, the layers are inspected to ensure that etched images are defect-free. 5. Preparing for Lamination e defect-free etched layers are then pre- pared for the lamination process using a chem- ical process that roughens up the copper to make sure it bonds to the prepreg. ere are several different names for this chemical process, including oxide, black oxide, and alternative oxide, to name a few. 6. Laying Up and Pressing the Layers Once the oxide process is finished, the inner layers of the PCB are ready to be laid up and pressed into a single panel. A multilayer layup starts with preparing the lamination book. is book contains top and bottom plates made from steel, steel pins for alignment, thermal lagging material, stainless steel shims, PTFE release sheets, and, of course, the manufacturing panels. 7. Creating the Manufacturing Panels e manufacturing panel is created by plac- ing copper foil onto the alignment pins followed by prepreg layers. Prepreg is short for "pre- impregnated," which refers to a partially cured glass-reinforced epoxy resin in sheet form. e prepreg has two functions. First, it bonds the external foil to the adjacent cop- per layer and creates the dielectric insulator