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Design007-Aug2022

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46 DESIGN007 MAGAZINE I AUGUST 2022 does the PCB still meets the customer's desired quality outcome? Also, consider this: Are you introducing problems into the design that may not show up way down the road? How- ever, that is another subject for another day. 4. Manage the risk. Lastly, manage your risk; don't let risk man- age you. We all are too young to get ulcers. I don't need that stress. Stay in complete control of your design process and know the impact of your decisions. Honestly, this may happen by trial and error, and that's okay. It is a learning process but be informed by asking questions of your team—designers, engineers, fabricators, assemblers, etc.—about how you can improve that process. Finally, let us all take a collective deep breath; come on, everyone join in, including you in the back, and know that our present situation will pass. We will come out the other side stronger and better designers because of it. It's during the rough times that we find who we are but, more importantly, what we are made of on the inside. We are PCB designers. DESIGN007 John Watson, CID, is a customer success manager at Altium. To read past columns, click here. Chapter 1: High Emissivity Regarding basic principles of thermal dissipation there are three ways of dissipating energy: • Conduction • Convection • Radiation Integrated metal substrate (IMS) printed circuit boards rely predominantly on heat conduction all the way through the different layers of the sub- strates from a hot point (the base of the component) to a cold point (the furthest surface of the metal base) and, usually, thereafter, through a dissipator. Ideally, the thermal engineering of the package, soldered connection(s) to the substrate, dielectric layer, IMS metal base, and dissipator should con- duct heat as effectively as possible away from the die and into the ambient temperature. That is, they should have the highest possible thermal conductivity (or low thermal resistance, the one being the inverse of the other). However, various other properties are needed, and the entire system cannot be designed solely around thermal perfor- mance. The different elements of the "stackup" (noting that inside the package there is typi- cally some combination of metallic parts such as bond wires and/or lead- frame, ceramics or plas- tics, FR-4 or similar sub- strate in the case of a sys- tem-in-package device or high-performance MPU, and adhesives) can be mod- elled as a series of dissimilar thermal resistances. Ultimately, thermal energy conducted into the metal base is transferred into the ambient by radia- tion. The effectiveness of this transfer is influenced by factors such as the emissivity of the surface and the radiating area in contact with the surrounding air. The emissivity is dependent on the material as well as the surface finish (basic physics tells us that a matte black surface radiates heat more effec- tively than a shiny surface–and also absorbs heat radiated from nearby sources more effectively than a polished surface). Download this title today! BOOK EXCERPT The Printed Circuit Designer's Guide to... Thermal Management with Insulated Metal Substrates, Volume 2

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