I'm designing an hot plate made of an aluminum PCB capable to heat up to ~50°C.
Having the area I want to heat up and thus the trace length to cover most of it, to determine the track width that I need I used a couple of common online tools (1, 2), which gave me different results.
Then I noticed that one was using IPC2221 (older) and the other was using IPC2152 (newer) as the standard to calculate the result. Reading about it online I found out that IPC2221 was based on 50-years old measurement, and so it would make sense to use the newer IPC2152, but what troubles me is that the Trace Width for external layers (which is what I'm gonna be using) is 1.29 mm for IPC2221 and 3.36 mm for IPC2152: a difference of more than 2x!
How is it possible that they differ by so much?
Have people been making inaccurate PCB's the whole time because of IPC2221?
Should I use IPC2152 results?
Thanks
Best Answer
The temperature rise is for the copper trace itself sitting on piece of (fairly thermally insulating) FR4. That's why the numbers are different for internal and external layer.
I don't think you can directly apply it in your application. I suggest determining the required power experimentally (find a piece of aluminum of the same thickness and overall dimensions, mount it similarly, and heat it with one or more power resistors bolted to it).
Then you can use the tools to calculate the required trace width for the required resistance at the operating temperature (copper has a positive tempco so you'll need a bit lower resistance at room temperature). There's also a correction for the corners that you may need to apply since current crowds in corners.
Incidentally, 50 year old measurements may well be done better than more current ones. I've often had to look up much older papers to find work done to high standards (for example for magnetic shielding).