Post by Siemens EDA (Siemens Digital Industries Software)

Heat used to be something you checked at the end. In 3D IC design, that approach doesn’t work anymore. As chips move into stacked architectures, heat doesn’t just spread across the surface, it gets constrained vertically, builds up across layers, and starts interacting between dies in ways that are much harder to predict. Teams are seeing cases where a small change in stack order or material can shift hotspot locations or push temperatures up by double digits, often later in the cycle when there’s very little room to fix it. What’s changing is where thermal shows up in the workflow. Instead of being a late-stage validation step, it’s starting to move earlier into architecture and floorplanning. Decisions like where to place high-activity blocks, how to structure the stack, or how interfaces are defined aren’t just physical design choices anymore, they directly shape thermal behavior across the system. And once those decisions are locked in, your options get limited fast. There’s also a bigger shift happening here. Thermal isn’t just a packaging problem or a cooling problem. It’s tied to everything, performance, reliability, even long-term yield. Relying on stronger cooling later might lower average temperatures, but it doesn’t always fix localized hotspots or internal resistance in the stack. That’s why more teams are focusing on getting the structure right first, before trying to compensate downstream. Because in 3D IC design, thermal isn’t something you solve at the end. It’s something you design for from the beginning.