Issue link: https://iconnect007.uberflip.com/i/1541840
20 DESIGN007 MAGAZINE I DECEMBER 2025 stackup, like a healthy lifestyle, avoids extremes. A PCB is essentially a lami- nated lasagna of dissimilar ingredients, including epox- ies, woven glass, copper, poly- imides, adhesives, and coat- ings. During fabrication, these layers are heated, pressed, vacuum-sealed, and convinced to behave as a single unified structure. But when the panel cools, each material contracts at its own rate, tugging and pull- ing with its unique coefficient of thermal expansion. The tension is trapped, locked inside the stack like the stiff neck you get from too many hours in front of the laptop. How flat that PCB remains throughout the entire process depends heavily on how well the designer balanced (or didn't balance) the laminates in the stackup. It gets ugly when designers specify rock-solid IPC-6012 manufacturing flatness requirements, occasionally, even redundantly reinforced with bold, all-caps proclamations something like: "PCB SHALL BE FLAT. BOW AND TWIST SHALL NOT EXCEED 0.75%." Then, on the very same drawing, they provide a layers and materials stackup detail so chaotically stratified it could make a geology major reconsider their field of study. Effects of PCB Imbalance Just as an overloaded schedule can warp a design- er's peace of mind, an unbalanced PCB stackup can warp an entire electronics project in both the short and long term. TA RG E T C O N D I T I O N Figure 1: A balanced stackup: symmetry. Figure 2: A severely imbalanced stackup. At the fabrication stage, the first line of defense is often the CAM engineer, who sends an engineering query back to the designer via purchasing, asking to deviate from the specified stackup. But some- times the designer or engineer won't budge. This happens more often than we'd like to admit. What now? Fabricate the order? Imagine a PCB supplier staring at a half-million dollars' worth of warped panels. Can a PCB panel that fails IPC-A- 600 flatness limits be flattened into conformance? Technically, yes, but ethically? There's nothing in most process specs preventing a fabricator from adding a "creative" extra step, for example, rolling the warped PCB panel across the corner of a table to counteract the warp. Theoreti- cally, a supplier could use this method to "flatten" panels back into spec. I'm absolutely not suggesting any reputable fabri- cator actually does this. But if such a technique were applied, what happens downstream?