Thermal management is a hot topic in modern design—especially as electronic components get more powerful and compact. To help our mechanical design team get a solid grasp on the basics, I developed an in-house workshop series on thermal management. This article recaps the first session.
We’ll cover thermal resistance (how hard it is for heat to flow), series vs. parallel heat paths, and the difference between hands-on thermal design vs. purely relying on simulation. Future posts in this series will dive into heat sinks, fans, interface materials, and more.
Thermal Resistance Basics
Think of thermal resistance as the “difficulty” heat has getting through a material. In analogy to Ohm’s law, the heat flow driven by a temperature difference is limited by the thermal resistance. A thick, insulating material has a high thermal resistance (blocks heat), while a thin metal layer has a low thermal resistance (lets heat flow easily).
In practice, we often write heat flow as proportional to the temperature difference divided by the resistance—meaning more resistance means less heat flow for the same temperature rise. By calculating each material’s resistance (which depends on thickness, area, and thermal conductivity), we can predict how much temperature will drop across it.
In our session we drew simple “thermal circuits” on the whiteboard. Like electrical resistors, each layer or interface adds thermal resistance in series. In the simplest case:
R_total = R1 + R2 + …
This means every additional layer (TIM, metal, enclosure wall) adds to the total resistance.
Series vs. Parallel Heat Paths
Heat can also split into multiple paths, which changes how we combine resistances.
- Series: R_total = R1 + R2
- Parallel: 1/R_total = 1/R1 + 1/R2
If heat flows through two layers in series, the resistances add. But if there are parallel paths for heat—for example, a soldered metal stud and an insulating block both conducting heat—the total resistance is reduced. More paths always lower the overall thermal resistance. This is analogous to parallel resistors in electricity.
Conceptually, you can imagine heat choosing the “path of least resistance.” In a wall, more heat flows through the metal studs than through the insulation. In a PCB, more heat flows through copper planes than through FR4. Understanding these paths helps when calculating a system’s effective resistance.
Thermal Design vs. Simulation
One key takeaway from our workshop was that thermal design and thermal simulation are not the same thing.
Good thermal design starts early with simple calculations, rules of thumb, and critical thinking about heat flow. Simulation tools (CFD or thermal models) are just one tool in the toolbox.
Simulation is extremely helpful, but it won’t automatically turn a poor design into a good one. In practice we use simulation to guide iterations, but we always verify with measurements or prototypes. The goal is to design in good cooling—heat sinks, airflow paths, material choices—early in the process, instead of relying solely on late-stage simulations.
Looking Ahead to Future Sessions
This session was just the start of our in-house training. In upcoming posts I’ll cover more specific cooling strategies and components, including:
- Heat sinks and heat pipes
- Fans and airflow design
- Thermal interface materials (TIMs)
- Enclosure and PCB layout
- Practical simulation workflows
- Radiation and solar gain
Each future post will go deeper into these topics. If you’re interested in thermal management, follow along as we explore these concepts in more detail!