Thanks to the relatively recent rise of affordable printed circuit board manufacturing services, many of those reading Hackaday are just now learning the ropes of PCB design. For those still producing the FR4 equivalent of “Hello World”, it’s an achievement enough that all the tracks go where they’re supposed to go. But eventually your designs will become more ambitious, and of course with this added complexity will come new design considerations. For example, how do you prevent a PCB from boiling itself in high-current applications?
It’s exactly this question that Mike Jouppi hoped to answer when he hosted last week’s Hack Chat. It’s a topic he takes very seriously, enough that he actually started a company called Thermal Management LLC dedicated to helping engineers deal with PCB thermal design issues. He also chaired the development of IPC-2152, a standard for correctly sizing board tracks based on how much power they should carry. It is not the first standard to address the issue, but it is certainly the most modern and comprehensive.
It is common for many designers, who may refer to data that in some cases date back to the 1950s, to simply oversize their tracks out of prudence. Often this is based on concepts that Mike says his research has proven inaccurate, such as the assumption that the inner traces of a PCB tend to get hotter than those on the outside. The new standard is designed to help designers avoid these potential pitfalls, though he notes it’s still an imperfect analog to the real world; additional data, such as mounting configuration, should be considered to get a better idea of a board’s thermal properties.
Even with such a complex subject, there are some tips that are broadly applicable enough to keep in mind. Mike says the thermal properties of the substrate will always be poor compared to copper, so using internal copper faces can help conduct heat through the board. For SMD parts that produce a lot of heat, large copper-plated vias can be used to create a parallel thermal path.
Towards the end of the chat, Thomas Shaddack comes up with an interesting idea: Since a trace’s resistance will increase as it gets hotter, could this be used to determine the temperature of internal PCB traces that would otherwise be difficult to measure? Mike says the concept is good, but if you want to get an accurate reading you need to know the nominal resistance of the track to calibrate against. Definitely something to keep in mind for the future, especially if you don’t have a thermal camera that allows you to see inside the inner layers of a PCB.
A rig used to test the thermal properties of various track configurations.
While the Hack Chats tend to be rather informal, this time around we noticed some pretty focused questions. It was clear that there were people with very specific problems who needed help. It can be difficult to address all the nuances of a complex issue in a public chat, so in a few cases we know Mike has contacted the attendees directly so he can talk them through the issues one-on-one.
While we can’t always promise you’ll get that kind of personalized service, we think it’s testament to the unique networking opportunities available to those who participate in the Hack Chat, and thank Mike for going the extra mile to make sure ensuring that everyone’s questions were answered to the best of their ability.
The Hack Chat is a weekly online chat hosted by leading experts from all corners of the hardware hacking universe. It’s a great way for hackers to connect in a fun and casual way, but if you can’t attend live, these summary messages and the transcripts posted on Hackaday.io will make sure you don’t miss a thing.
This post PCB Thermal Design Hack Gets Hot And Heavy
was original published at “https://hackaday.com/2022/04/08/pcb-thermal-design-hack-gets-hot-and-heavy/”
