Thermal Resistance and Heat Transfer in PCB Design

[@fairuzahmadnaufal4196]

thanks a lot Zach, you help me to solve my assignment on that topic. Well, I've watched tons of your videos on the Altium Academy.

[@Sam-dc9bg]

Thanks for the lesson. Well explained. Knowing about this is one of the big things that separates a professional from the hobbyist or student. The professional checks if a component can overheat across the entire performance range before the assembly of the prototype.

[@manjunathr.m262]

Great information, love from india

[@AltiumAcademy]

Thanks for watching!

[@shakurhajibagheri38]

thank you very much , very good info, God bless you

[@AltiumAcademy]

Glad it was helpful!

[@manaspulikathra7509]

@Altium Academy Hello Zach.. How do we calculate the Effective Rth if there is an exposed pad (like a FET Drain) on the bottom side of the component. Do we consider RthJA in this case too? and how the multi layer pcb and via numbers can help in such scenarios if we need to avoid heatsinks

[@Zachariah-Peterson]

If the component is well-documented then it will typically have a some thermal resistance measurement or calculation that includes the bottom-side pad on the component. Not all components will have this level of documentation unfortunately. I'll have to do some digging to see how to calculate this and maybe we can do it for an upcoming video. Once you include the PCB it gets very complex and you might need a simulator. For the vias, placing multiples in parallel essentially means the resistances add in parallel.

[@himanshushukla7587]

how can we calculate copper area on pcb for heat transfer.. or this video shows heat sink for heat transfer if we can use copper pad (open masking) then how to calculate PAD size ..

[@liamsnow03]

Love this content!

[@AltiumAcademy]

thanks!

[@hvstechnology8048]

How can we calculate power dissipation of track width or copper area..

[@Zachariah-Peterson]

The power dissipation (the portion of power converted to heat) is determined using the current sourced into the trace and its resistance. The DC resistance is simple to calculate using a simple definition, you can find the formula and the electrical conductivity of copper on wikipedia.

[@danterp3]

I appreciate all the great technical videos Zach, thank you. I would be glad to see example calculations for a LED driver or mosfet, pulling info from datasheet to calculate conduction and switching losses and then estimating temperature change. Practical, easy to understand guidance on switching losses is hard to come by. After looking through a few text books, online articles and videos I still am not totally clear how to calculate switching loss using the values from a real life datasheet. For example PMN30UN rise and fall times list specific conditions (Vds=15V Id=3.7A Vgs=4.5V) which are not my conditions (Vds=30V Id=1.8A Vgs=3.3V). Is there some way I need to utilize Qgs and Qgd to calculate the rise and fall times for my application? Otherwise what is the point of these values and the gate charge waveform (figure 15) shown in every mosfet datasheet?

[@Zachariah-Peterson]

This is a great question and I'm sorry it's taken so long to notice this! I'll have to go through and do this calculation for a video.

[@mjunaediqbal]

My question is that how to design a heat sink for power MOSFETs in SOIC packages for example SI4401bdy. It is noticed that the heat dissipation don't give in the datasheets.

[@Zachariah-Peterson]

Hi Junaid, There are some vendors that sell heatsinks for standard MOSFET packages. I know there are some available for TO and SOT packages, I'm not sure about SOIC packages. Hope this helps!

[@arlindbanushi]

Hi, how about setting the PCB sealed under vacuum? Or it has benefits mostly on high power PCB.

[@Zachariah-Peterson]

This is a bad thing to do if you want to dissipate heat. In vacuum, the only mechanism for a component to dissipate heat is through radiation. For a PCB in air, you want to be at high pressure as air will have higher thermal conductivity.

[@maks886]

How to interpret a thermal impedance graph?

[@eldorado3523]

it's how easy it is for a bulk material to conduct heat as a function of its temperature. The higher the thermal conductivity, the easier it transfers heat between and to its surroundings.

[@maks886]

@@eldorado3523 That's thermal resistance - thermal impedance has something to do with temperature change in time, but I don't fully understand it yet

[@ivelinivanov8845]

Great job! Thanks a lot for all the info you have provided with all your videos! Heat sinks are one approach of cooling down our PCB. Could you also show how we could do this with Thermal Via? Thanks a lot in advance! :D

[@Zachariah-Peterson]

I think the better way to think about thermal vias is redistributing the heat so that you move it away from a hot component and into other parts of the PCB. So for example if connected to an internal plane, that plane can help transfer heat away from the component.