Hi way back in episode number 744 linkedin up, the top down below at the end. If you haven't seen it, and I highly recommend you do, Because it's all about surface mount thermal design. How to get power out of Smd thermal components out through your case of your product? And yes, I've actually this might be familiar. I've redrawn this entire thing.

So why am I going over previous material like this? Aha, it's because there's a new part or new parts on the market. That actually. well, they don't revolutionize this, but they provide another really nice option for getting heat out of Smd thermal parts. So I thought we'd take a look at them.

but we really have to go back to this original diagram to explain what we're talking about here. Now obviously I'm not going to go over everything again, but we will recap it. Everything's in that video. I highly recommend you watch it.

I go into much more detail now. of course. it's very easy to get heat out of through hole parts like a To220 package. They've got a big bolt hole in them.

You bolt them into your the sideir case. Bob's your uncle gets the heat out, no worries. How do you do it for an Smd part though? Well, once you've decided that your design is going to be surface mount, you want as much of your design to be a surface mount as possible because then it can all go into the pick and place machine and then it all just magically comes out. You don't want extra bolts and washers and and heat bars and heat sinks that you have to bolt in and screw on and things like that? they're all extra production operation steps, extra cost, everything else.

And yes, you can actually get our surface mount heatsinks suitable for pick and place machines. They're usually quite small because the pick and place machines with their little suction heads don't have you know, a huge amount of suction forceps on your board and then reflow it. Of course, because they're a heat sink. they suck all the heat out of your joint when you try and reflow them, but you know you can get.

Here's an example of some small Smd heat sinks that you can actually get to put on your design and they're okay. But your traditional solution for this is uh in orange here is solder it onto a large copper pad like this and then there you have uh, firm thermal vias like this going through the green pcb here and then in this case through to a thermal transfer block or a thermal transfer bar which then transfers it to the case and you can get rid of the heat from the case. Beauty. And this is where you start talking about your electrical thermal equivalent circuits.

and basically the idea is that current is equal to power from your power source, which is your device. Then it flows through all of the thermal resistances instead of electrical resistances. they're thermal resistors and they've got R Theta there. So Jc, you'll see this in data sheets.

that's junction to case, so inside the little transistor, that from the junction in there, how much thermal resistance to get it to the case. And then you've got thermal resistance of the Via here. thermal resistance of your insulating seal pad, thermal resistance of your heat uh, transfer, block your thermal resistance of your case, and then you've got the ambient temperature and Uh. voltage in this equivalent circuit is equivalent to temperature.

And then you've got essentially what you might call a thermal ground I guess. And then you've got your ambient temperature. So every part through the step, the voltage will increase. If you've got current thrown through here, the voltage at each point will increase and therefore in the thermal equivalent circuit, uh, your temperature will increase.

So your junction up here, the junction temperature up there. it can't exceed the maximum data sheet recommended junction temperature. So the art of thermal design is trying to keep your in worst case conditions, worst case ambient because if ambient rises, everything else rises as well is trying to stay under within your data sheet, temperature limits and temperature of other parts inside which might be affected like electrolytic capacitors for example. if you have them close, they might you know the electrolyte inside heats up, you shorten their life, etc etc.

Now here's where we get into the detail of we're going to talk about these thermal jumpers here. These new components out, that might change the game for a lot of design, so let's take a look at them right? Your traditional uh way of getting your heat out of your part is to have a large amount of copper like this okay, which you dedicate to that particular component or the tab of that component and then you get the heat out and you want that not only because it's a large surface area, but then you have all these vias in here, which via stitch and this is roughly there's a limit. Thermal resistance of a Via is about roughly 50 degrees C per watt for a one millimeter hole for example. and depending on the number of holes you got, then the lower the overall thermal resistance of your via here.

So if you've only got one via trying to get all the power through one via, it's very high high thermal resistance. So it turns out the optimum value is about 10 because beyond that, it starts to like this. You get the effects of the heat spreading across the pad and all sorts of you know, intricate thermal stuff you really need like really expensive thermal modeling software to actually do that properly. but you know, 10 vias or something like that might be optimal.

Anyway, let's actually forget all about uh, getting the heat out to your external metal case, through your thermal transfer block and your sill pad and everything else because that was the previous video. Go watch it. What we're going to focus on today is using these new thermal jumper parts to actually utilize the internal ground plane in your Pcb as a heatsink instead of actually, uh, like you know, using a little Smd heatsink on top, or using thermal, or just using one large pad. you don't have to use thermal vias.

They're only if you want to transfer the heat down to the bottom layer. For some reason because you might have more routing room down there like you might. this might be the top layer, but then you might happen to have like this much space on the bottom layer. for example, you know, because you didn't need the routing room, you might have that room for a large, um, an extra heatsink plain on the bottom side as well as a small one on top.

So you might use thermo vias to get down to the bottom layer and then spread the heat across there and how that heat gets out to the external case. we're not going to worry about in this video, so we're going to assume that the device you're trying to get the heat out of cannot be electrically connected to ground or power plane because you've got your 4-layer Pcb right these days. Four layer Pcbs the cheapest chips, and if you're doing any sort of advanced design, you're probably going to be doing a Four layer board anyway. So you've got this a huge ground and power and likely power plane inside your product.

Why can't you use that as a heat sink? And it's like those Smd heat sinks that we showed before. Yeah, you could use one of those, but they're actually fairly expensive in their own right. and they take up physically height, you know, extra room inside your case. But if you've got a really compact design really low form factor, it might be advantageous.

Greatly advantageous. It might be game changing for you to use your internal ground plane, which is all the way through like this all the way through your product. Why not use that as a heatsink? And of course, uh, you might want to change your layer stack on your Pcb if you do this. Like, usually when you do a full layer board, the ground and power plane is going to be in the middle of your Pcb and the signals are top and tracers are top and bottom layers.

But if thermal is a major consideration in your design, you may actually want to flip that You may want to have power and ground on the outside or at least ground on the outside layer so that either top or bottom so that then you can use it as a heatsink as we'll see using these thermal jumpers because they're absolutely fantastic and game changing. and then of course because the copper is on the outside of the Pcb, it's actually, uh, more readily available to transfer. It doesn't have the insulative properties of the fiberglass wedged in the middle of the Pcb, so having your copper on your top or bottom layer your big ground plane is much more effective. But then you've got to take signal integrity and look out and all that sort of stuff.

But let's assume that thermal is one of your major priorities and you want and you want to or need to just use your ground plane. Well, if you've got your traditional method like this, you can't because this Uh device that you're using can't be electrically connected to ground or power plane, because it'll short out because the Uh tab on the device is electrically. It's the V Out pin or it's the uh, you know, Vn pin or some other electrical pin that's not ground. so you can't just via stitch to ground.

If you're lucky enough to have a device where your thermal tab is either isolated or is grounded, then great. just thermal via stitch down to your ground plane, either internal or external. But where the thermal jumpers come in is, if most parts like this need to be electrically isolated, that's why cell pads exist. That's why you use insulation on the majority of thermal devices because they can't be electrically connected to ground.

So in this case, you have two choices: You can devote a whole lot of your Pcb routing area to just the heat sink. the isolated, electrically isolated heatsink for that particular device. But then you've you've ruined like you're wasting all of that space. If you've got a really dense design, then you can't put any traces on there at all.

It's a real problem. But if you use your ground plane aha, that changes your entire routing. uh, dynamics, and your routing, density, and everything else. So how do you do it with these thermal jumpers? Okay, so let's assume that you've got your Smd part that you want to get the heat out of.

It needs to be electrically isolated, but you want to use your big ground plane as a heat sink. and why wouldn't you? Now of course, you're going to have your copper pad to solder your apart down onto, of course, your Smd part. But then how do we get the heat out to the ground plane? Well, we can get our thermal jumper like this. It looks something like this.

Let's just. I'll just draw it like this: They come in different shapes and sizes. And by the way, when it comes to thermal jumpers, is width better or length better? No, I'm telling you, width is better. You want a short, fat stubby one than a big long one.

Trust me, you're going to get much better thermal transfer from a big fatty. So these thermal jumpers. Here's a photo of them. They just look like, you know, regular Smd resistors available in long, thin, narrow ones, big fat, wide ones.

Or you know, they just look like regular resistors. But they're electrically isolated. There's no resistance in them, and but they're thermally conductive. so you just use, uh, just your regular pads like this for any for that regular package size like that.

and then you simply put a big fat trace in there like that that connects through to this thermal jumper. and then of course, this one here. You would just then put your thermal vias like that to stitch it down to your ground. So now you've got your heat.

It flows from your device. It flows through your copper like this. It's pretty efficient at this point. Then it flows through your thermal jumper like this.

They don't have a zero thermal resistance, but you know they're reasonably low. We'll take a look at the data sheet in a minute, and then it flows into your vias like this. and then it flows down your vias into your big power plane. Big ground plane all over like this.

so you can use your entire board as a heatsink, but taking up very little space. You know, I've drawn it quite large here, but these things can actually take up a small amount of space. and if you want to, you can actually use multiple ones. You can have one here, one here, one on this side.

You can put them all around your device. If you, you know, do your thermal calculations. You're backing your envelope calculations. At the design stages go.

Yeah, I think I'll probably need three of them or something like that. now. These things aren't particularly cheap. They start from like, you know, a thousand of quantities start from about 30 cents a pop.

But hey, they're the little Smd heat sinks are that we looked at before. They're not cheap either. Um, and they take up vertical height. but this way everything's low profile so and enables your design to be a really small size.

But it could be much more efficient because you're using your entire ground plane which could be on the outside of your layer of your board as I said. and then you take the solder mask off. Of course, using the ground plane as a heatsink. then you wouldn't cover it with solder masks.

Generally, that's just less efficient. So that's the beauty of these thermal jumpers and it really is game-changing As far as I'm aware, they've only been out for like the last year or two and they might be expensive, but it could radically change your thermal design for your product. It could really enable it, whereas before you know you had to have this big isolator pad. Now in every design, you can use your ground plane as a heat sink.

Beautiful. All right. We'll just take a quick look at the data sheet here, because well, there's nothing to it and these are fairly new parts you can see down here. Uh, first revision January 2019.

So they're available from two manufacturers that I'm aware of. One is Vachae and the other is, uh, this company. I've never heard of the engineers choice there. They are, uh, American technical ceramics as they call them thermal conductors.

Vichai call them thermal jumpers basically. um, look, it looks very much like a resistor except it's non-conductive They've just got an aluminium nitride uh, substrate inside and that's what is makes it thermally conductive and then just got the regular end caps with the nickel and solder. uh. termination.

You get different finishes and things like that. You can get little Led available yes, lead or lead free. They're saying it's greater than a gig, but they're basically yeah, they're as good as open. I'm A for power supplies, Rf amplifier, synthesizer, switch mode, power supplies.

that would be a biggie and here's a very nice look at: they've got a thermal camera. I I could maybe do some tests, but um, buy these and set up custom Pcb in different configurations. That would be nice. Let me know in the comments down below if you want me to go to that sort of effort, but I don't expect any results.

Uh, different to this, but it'd be nice. Maybe I can check thermal vias and things like that show the difference between pads and ground planes. And I'm you know. so they've just got a resistor here.

I don't know what is that like. looks like the 1206 something like that and they just put in a current through it, heating up the resistor and with nothing right? So with just the extra size pad here, so they have not installed the thermal jumper like they had here. Okay, this is a 1206 size thermal jumper. So this is without the thermal jumper, the resistor gets up to 150 degrees celsius.

But if you whack in the thermal jumper like this and it's got like a large trace in there just connecting the two pads. So this is one pad for the thermal jumper. This is the other pad here. Well, it's got this large pad over here.

There's no looks like there's no via stitching or anything like that. They're just using the thermal jumper, going to just a larger pad here acting as a heatsink. and look, it's dropped down to 95 degrees. Wow, that makes it.

That makes a huge difference. and that's not when connecting it through to the great eye, presumably not connecting it through to the ground plane. So I reckon if you put little thermal vias in there going down to a ground plane, you'll get a substantial improvement over that. 95 degrees.

What you get, I don't know. You can do some back of the envelope calculations. Um, and but then of course it's going through to a much larger heatsink which is your ground plane and how much thermal resistance we're talking about. Well, we've got the data here.

Look at this. So thermal resistance in degrees C per what? not That milli watts per degree C. Thermal conductance? Rubbish. It's one over no bugger that.

Um, we're talking for like an O603. Okay, 14 degrees C per watt, so it's not that great. But as I said, if you go for the short fat one like this is Oc. and what O603 means is that it's uh, half as wide as it is long.

So, but this one, the O612 is twice as wide as it is long and it drops from 14 degrees C per watt to 4 degrees C per watt. So 4 degrees C per watt is you know, on par with like 10 thermal vias or you know, something like that. So it's it's. pretty decent performance and once again, you get a nice big fat one over here.

The 12 25? that'd be that jobby there. Look at that. Just short and fat because you want it fat and wide so that all the thermals can get through. and dielectric uh, with standing voltage 1.5 kilovolts and capacitance is a big thing as well.

because if you've got, if you're using these on switching power transistors, especially Rf applications and things like that, that can be a big deal. So you want them to have ultra low capacitance is 0.07 puff. That's like half a bee's dick. And that does, of course increase for your, uh, wider ones.

Your short fatties like that, so it's a trap, but it's still like it's you know, point two puff. It's nothing. These other parts from my cue bridge, I won't go through them. You can look.

I'll link the data sheets in down below. They're exactly the same. the thermal resistance slightly better. These can get down to look three degrees C per watt, but these ones are available if they're available in aluminium, nitride or beryllium oxide as well.

and the beryllium oxide just a smidge lower thermal resistance. So you know, if you've got some, you know, whiz bang military application and you don't care about cost and just yeah, it's better, More better. It's actually, uh, substantially different for some of these others. Look at this 13 compared to 20 for an 0.603 so there's advantages there.

and the for shay ones. they're available on digikey here. I'm not sure the other website not sure where the others are available from, but look, uh, these are a thousand of, uh, quantities. We're talking like, you know, like 38, uh, cents here and stuff like that, but they can actually go up like 50 a dollar.

Now you're talking a dollar. 26 for the big fatties down here? Wow. Worth every cent. So I think these things are really quite game-changing and they seem to be fairly new parts.

Please leave it down below if these are being available for Donkey's years, but this is the first I've heard of them. So thank you very much for the viewer who, uh, pointed these out to me. These are great. Um, yeah, it could radically enable uh designs, uh, small form factor designs that you just couldn't do before.

So yeah, it could be game changing. Check them out. So there you go. I hope you enjoyed that video.

If you did, please give it a big a thumbs up. And as always, leave comments down below or over on the Eev blog forum link down below. Every video has its own forum thread that's where people can discuss stuff if you don't want to discuss it on the Youtubes and all of my alternative platforms. Youtube went down today, um, famously.

But the good thing is all my videos are available on like half a dozen alternative platforms, so check it out! Catch you next time you.