Hi, it's Twitter question time. Let me know. Leave it down in the comments down below. if you want me to do more of these, I do.

of course. um, follow me on Twitter none of that. X rubbish. Follow me on Twitter and uh, you can ask me questions anytime and I'm always answering uh questions there.

but I thought this one might just make an interesting video. this I have covered it in bits and pieces in uh, previous videos, but we'll go into it a little bit more here. It's a simple question abanav sorry I'm butchering that pronunciation I'm uh, sure, but he asked, uh, he's designing a PCB trace for us 70 to 80 amp so a substantial amount of current. how should I design the trace from the connectors to a mosfet uh device for this current rating.

Is it possible to use only one layer and it's a through-hole uh device so we won't get go into like the routing and all that. So is it possible using only one layer? So I presume that is asking that because well, he's got other routing constraints and doesn't want to chew up the bottom or internal uh planes assuming it's even multi-layer board. It might just be a double-sided don't know because it is a through-hole uh device. so it could only be a double-sided board, but you know you don't know.

Anyway, the first thing you want to do is you want to. Um, basically when you pass current through any conductor of course copper is on the PCB is a conductor and of course Ohm's law if you've got resistance yet at a certain current, it's going to drop uh, voltage using Ohm's law so that could be a problem. but we won't go into the design aspects of like the voltage drop and things like that. but that is one of the things that you have to consider in the design.

but also the power dissipation is going to heat up I squared Ah, losses. um I You know the current squared times the resistance of uh, the trace and you can have a big giant plane. It's still going to have resistance on it and you have to sort of like take that into account. One of the things you really need to do with this is like there's a few rule of thumb things and you can have little you know, simple charts and stuff like that which give you a rough uh Trace diameter for a certain current and stuff like that.

but there's much more engineering and science actually behind it so you really need. At a minimum you need a PCB Trace calculator and the one I use here I'll show you it's a Saturn PCB design. you've it's free, you can just download it I'll leave a link uh down below and it's got all sorts of stuff. like it's got tons of stuff.

I Won't go into all the stuff it's got, but one of the things it does is it's got conductor properties here so we can put in the various parameters uh, up here and then it will give us the conductor DC resistance, How much resistance that tracer's got? So I can use Ohm's light. Now we can calculate the voltage. well. no, it already calculates the voltage drop for us.

There it is, and the maximum conductor current that it's capable of. But there's a lot of stuff that goes into this, so let's have a look. There are three major things that dictate how much a maximum current a particular PCB Trace can handle. One, of course, is the diameter of the trace.

Now, obviously, if you've got a little tiny thin, you know, 10th hour Trace it's not going to carry much current at all. all. so you're thicker. The Wider Trace You make it the more current because it's going to lower the resistance.

it's going to have less I squared our losses, it's gonna. It's not going to heat up as much. So that's the first thing. but not all copper is the same.

So the second thing is the thickness of the copper because PCB comes in different copper thicknesses and none of this, uh, metric rubbish. We want Imperial for this because we work in Imperial and when you order your PCB for manufacture, you should be specifying the copper thickness of every layer in your PCB Stack Up and I've done videos on Stack Up In You Know not specifically on that, but you've covered it in previous videos. but basically every piece of copper in your like, you know, if it's an eight layer board, you've got eight layers of copper in there and you can individually specify the thickness of each layer and the copper in your PCB stack up it's called. So if you've got uh A if you want to run a like real heavy current on one particular plane or one particular uh layout of your board, then you can specify okay, I want a much thicker copper on that layer and the manufacturer will do that for you.

And if you don't specify any of this, they'll just give you this standard stack up which might be a one ounce copper is which is 35 Micron uh thickness. You can change it over to Metric. There it is there. Um, one ounce copper is your standard thickness, but if you've got a multi-layer board, they'll often use half ounce thick or maybe even quarter ounce thick copper on those inner layers.

So if you don't specify it, the manufacturer is just potluck what you actually get. You won't get more than one ounce because you know Copper's expensive, right? and they want to keep the cost low. so you stand aboard, you won't get any more thickness than one ounce uh, copper on your on any of the layers on your board. If unless you specifically ask for it, then you might jump up to.

usually you jump up to two ounce for that so it's twice as thick so it's going to be lower resistance. And you know, like once you get to like four or five something like that that's really thick as right, really thick and expensive copper and you do that for like, really exotic. Um, you know, applications if you want really high current board, but it's got to be really dense. For example, when you can't make your Trace really thick because you've got real tight routing in there and stuff like that, you might have to go to four or five ounce copper room.

You could even get an exotic one even thicker than that. And the third parameter, which is not as important, but it matters um, is whether or not the Copper's on the top uh, external layer of the PCB so the top of the bottom, or whether it's in the internal layers of the PCB because they'll have different thermal properties because if your conductor is dissipating heat and it's wedged in the middle of it, sandwiched in the middle of the board like this, fiberglass is a pretty good insulator, right? So the heat can't get out so the temperature will right like it'll that heat will get trapped. it can't escape so it'll get hotter which will increase its resistance. And right? Well, it doesn't run away, but right it's it's going to get higher resistance the hotter it gets, whereas the outer layers, they're going to cool more easily.

and also the solder mask over the tracers can make a difference as well. If you've got solder mask over there, that's an instant insulative layer on your copper, so that can matter as well. But generally you know, unless you're really getting down to the nuts and bolts of it. Yeah, you know there's only two major ones: the thickness of the copper, thickness of the copper, and the width of the copper.

But the layer stack matters too. But it's not like a copper. Trace just suddenly bursts open and catches on fire or breaks. You know, because you can't actually use a piece to be as a fuse.

A PCB Tracer is a fuse and there's a little bit of Art and Science that goes into that. I might have even covered that in a video somewhere I Can't really remember. It doesn't just suddenly magically stop carrying current. it just gets hotter and hotter and it might delaminate from the board.

Like you know, it glows red hot or whatever, right? So it's all about the temperature rise that you're willing to tolerate in your design. Now you can see here: this is one of the parameters: 20 degrees C temperature rise Me personally I Prefer to put a 10 degrees C temperature rise if I'm doing these calculations, but it's entire, There's no reason for that. It's just my own personal rule of thumb for a 10 degree C temperature rise. and then there's ambient temperature as well if you want to get really fancy pantsy.

Okay, so let's actually start using this to do a basic thing. Let's say we've got standard one ounce copper here. Okay, and we've got no plating. Okay, the plating is another thing that matters.

It's not only the solder mask over the top that can impact, but most boards are usually solder mask over bear copper or smobc. So you can just say beer PCB Like that. Okay, and we're going to use external layer. So we've got an external PCB layer here and we've got a bare PCB which will have the solder mask over the top and it doesn't really matter whether have a solder must.

In fact, they don't even have the solder mask in this calculation. but technically it can make a little Teensy bit of difference. So one ounce copper and 10 mL is ridiculous, right? So let's go for a hundred thou, right? hundred thou Trace 100 Mil Trace Not that millimeter rubbish. And the conductor length here? Um, we don't know.

So it depends on your particular layouts, so the total resistance will depend on the conductor length. Uh, of course. and then uh, that will determine the voltage drop, which you're willing to tolerate because that might be part of your electrical design rather than the third. You've got two issues here.

You've got electrical and thermal arm as well, and you might even have high frequency stuff. That's why they've got like skin depth over here and skin skin depth percentage. Anyway, we won't definitely won't go into that. We're talking about like DC current.

so 100 Mil is plain present. No parallel conductors doesn't matter. Uh, for purposes here ambient temperature, we're just going to run that it's an external layer so let's solve that. Okay, there you go.

It's five milliohms there for a hundred mil wide trace and that can do a nominal 3.28 amps. So generally at. So if you try to put 3.3 amps through a hundred mil wide conductor and we can convert that to Metric for you Metric Fanboys 2.54 millimeters. There you go.

it's gonna at 3.3 amps, it's going to rise 10 degrees celsius if it's on the outside of your board. Is that acceptable to you? I know, right? So we're talking 80 amps here. Okay, 80 What was it? 70 to 80. 70 years.

let's take 80 amps Metric right? 25 millimeter wide? Trace right? A one inch Trace Let's actually solve that with one ounce copper is only going to do 12.6 amps. so we're going to have to Let's double it to two ounce copper. Okay, so twice as thick copper. So we go from 12.67 to 20.9 there, it's not quite doubling.

If we go a four again, will it get to 40? No. it gets to 34 right? It starts to limit it so you can see that you got like really thick copper here. for a one inch wide. Trace Okay so this is getting quite an issue.

So he talks about like putting it on a single layer. You're really starting to push it. like four ounce copper. That's pretty specialized.

You're going to some PCB out cheap PCB Houses just won't do that and you won't get this on your regular. You know your five dollar prototype board right? You're not going to get that. They might give you a half ounce copper and then you're only limited to 8 amps. So really, we need double that in a 25 millimeter wide.

Trace like a one inch a wide. Trace You probably don't want to make it any wider than that on your PCB right? That takes up a massive massive around amount of room. so you might want to actually uh, you know, put some solder coat over the top of that right? so you can get a tin plate. uh for example so you know, but unfortunately right, this plating thickness doesn't actually take into account.

um, like the template uh, process. that's really hard to control. So if you go I want? if you go to your PCB manufacturer I want a template on that? um please. then it's yeah.

the the control thicknesses. Yeah, it's I've done a dedicated video on that and how much difference a tin plate actually makes I've done some practical experiments on that I'll link it in, but you can't really control that but you might be able to tell them to Actually, you know Plate at a certain thickness or whatever, right? But once again, this is a big increase in manufacturing cost. piece of being manufacturers will do absolutely anything. Oh, the good ones will.

They'll bend over backwards. They'll do anything you tell them to do, but they'll charge you for it. Okay, so if we did that, you know one ounce, uh, plate in thickness. we're still only at 40 amps, right? We still have to double that.

Even going to like, we're still not there. So let's just go to a random PCB manufacturer here and you'll notice that they go from one ounce up to 13 ounce copper. This is insane, but there's trade-offs there with they actually tell you minimum track, uh, space requirements and all that sort of stuff. But they say they can do 13 ounce and they they can.

but generally they're only going to go up to I Think this manufacturer only says like three ounces. Kind of like our standard process, so you know anything over that. they're gonna like, order the materials special, they may not have it in stock and they're gonna get it's going to cost you an absolute fortune and all that sort of stuff, right? And then you've got the surface finish over here. Okay, and generally you're going to get a, uh, what's called a hassle right? which is a hot air surface level, uh, finish.

So they just put it's basically solder coat. um that's that's basically what it is and then you're familiar with like the gold flash boards the you know, the immersion gold and I show on my boards before that uh they have come with immersion uh silver for example. you can get immersion tin and you can get you know there's all sorts of stuff and you get nickel plated ones and all sorts of stuff right? Playing copper you generally as I said um if you want. Here's an example.

if you want your traces to be coded with solder coat like this one here. okay yeah that can increase uh your current handling capacity but it's not really a Control process they they can't Really Yeah, it might be hot air finished. You might be able to see like you know, like a few Bubbles and stuff in there right? right? It's not. It's not really a controlled that controlled a process.

You can't really guarantee what your resistance is going to be, it's just hot air. It's whatever the process just happens to be, but it can increase your current. Now the way you do that is to remove the solder mask you have to remove the sole older mask over that Trace Otherwise when they do the board you're just going to end up with that uh bare copper because as I said uh the copper under here is just bare copper. It's Smobc solder mask over bare copper.

I'll show you see if I scrape away that uh, solder mask there you can see that is just bare copper underneath this. So the process that they do it happens after they put the solder mask on. So if you want your tracers coated like that in whatever you know, uh, surface finish that you actually, uh, choose here. whatever surface finish you choose, if you want that coated, you have to leave the solder mask off.

So back at one ounce copper here like I'm I'm being tight ass Dave I'm only allowing for a 10 degrees C temperature rise right? So if we go to 20 degree rise like that, okay, you go from 12 to 17 amps there, right? And then if you go up to your four ounce thick copper, you know, Yeah, but you're still not getting a huge amount extra there. Like if I'm willing to make it go 50 degrees above ambient so your PCB Trace will be at 70 degrees right? Remember, this is temperature rise above the ambient temperature. Okay, so we get to our 80 amps. Okay, so if you want to do this single layer and you're willing to Fork out for four ounce copper uh, board material and you could maybe get it, it's going to rise 50 degrees C But once again, these are actually calculations.

There's no. well, there are, there are formulas for this and this is where it gets it from. but it's based on really empirical uh data. and this goes on like it tells you here.

This is uh, based on the IPC standard 2152 with modifiers um and you have to go read the IBC standards. There's actually two IPC standards that cover this. There's the earlier uh, Triple Two uh, one standard here and I just Googled The first thing I got was this Altium article here. Anyway, they linked to some calculators I'm not sure which ones, but yeah, basically.

uh, there's two different standards that'll cover the same thing, the IPC triple Two one and they note here that uh, the triple two one that was based on charts in the linked articles. So someone way back in the early days did some charts like actually old school charts and they've got them in the standards. You can look it up, the hand drawn charts or whatever, or they you know these plotted uh charts and that's where everyone's gotten sort of this data from back in the old days. But there is another standard the IPC 5122 we which is more accurate I don't remember the exact details.

It's been a long time since I've looked at the standards in this regard, but just realize that the formulas are kind of based on yeah, sort of like experimental. Um, you know measured data so it's a bit how you're doing, but it's the best way got now. Interestingly, let's see if internal layer actually makes a difference here. and it it doesn't Right, Internal or external layer actually doesn't make a difference here.

which is interesting because in practice it it kind of sort of does. Although once your board's heated up, you know like it depends on your like your thermal. but the physical uh part of your design matters like if you've got a fan in there and you're blowing over the board. For example, the outer traces.

yeah, they can get better thermal properties than the inner uh Trace is in there, but it's obviously not taken into account in the IPC 22 or 2152 standard and it's going to matter whether or not you actually whether your Trace is adjacent to like a big plane. For example, because you can get conduction between your little trace and the title thin prepreg in there. Um, it's not much different than different distance between thickness between your Uh trace on say an inner layer and the Uh prepreg For example, if you've got it on the outside, it's a bit uh, further apart and this is why they actually have a plain present thing here, right? So if we click yes here then this is our current carry and Trace and you can see it's jumped up. It's it's quite substantial.

It's jumped up from 78 amps here for a once again a one inch wide uh trace for a 50 degree C rise you know and and then it jumps Up to 121 amps. and we're not running the current through that plane. It's not going through this big blue copper plane down here. it's purely the proximity.

This is why they give you yet. Here it is distance to plane right? 10 10 mils here. So metric, you know it's only 0.25 millimeters away. So if we actually go, go from 0.25 millimeters to one millimeter there.

it should like it. It goes up a bit right because this is all thermal conduction through to the plane. even though the current's not running through that plane. Simply Having the plane present, it's it's more better.

Anyway, it gets as you can see like there's a lot of stuff involved in this if you really want to go down. uh, the rabbit hole. But in an answer? Um, to the question here. Um, is it possible to use only one layer and the answer is probably no, not really.

Um, not. unless you use like massive traces and you allowed for, uh, you know, a huge temperature rise and stuff like that. So yeah, you'd be using a you know, at least two uh traces, possibly. Uh, part of your internal uh plane as well.

Um, to get 70 80 amps is quite, uh, substantial. Or you could, uh, as I said, you could like tin plate. You could solder plate the top of those traces and that increases your current handling uh capability. So, but once again, that's not going to be factored into this calculator.

You can't really calculate that because the thickness of of the applied solder you know coating on top is. Yeah, it's not really a controlled uh process. so you go I want it lower resistance? Let's you know I want to carry more current? Ah, I'll just you know, solder code it so you'll see that on all sorts of boards. So let's take it back to a 10 degrees C rise I won a one inch thick a 25 millimeter wide Trace which is you know, quite decent.

You know, probably the biggest one that you want to run on a board. For example, you know, 35 amps? Yeah, nah nah, you've got to look for at least I'd be using double-sided and then you've got to ask yourself, well do I want to Via Stitch uh down between the two layers so you stitch them together. It doesn't really help in the resistance side of things, but it helps with you got extra copper there. It does help a little bit with the thermal dissipation and stuff like that so you might want to uh, you know you might want to Via Stitch along there just as a matter of course, but you don't want to V A Stitch until the crowd cows come home because that just takes away from like your surface area of your copper effectively.

So like yeah, not really. just run two thick traces top and bottom. probably you know, an extra internal R plane to be sure. Yeah, you can get away with this.

uh 70 80 amps. You can get away with this on a double-sided board, but yeah, you're going to have to use a thick um copper. Unfortunately because if you use your standard one ounce stuff you know and like 12 Amps do you double it even use four layers? You're still not going to get enough really. So yeah, you're going to want to be using um specify that thicker Copper from the manufacturer.

and then if you really need like a compact design and you don't like have layout room on your board uh you might consider like a bus bar approach. um I Found one example here. You can see that this board uses these physical bus bars which won't run right across the board like this. and of course you can get you know can make those stickers right and uh but you know you have to get those like custom manufactured and you'd have to go to a company that manufactures uh those.

so you know a specialist manufacturer that uh makes those but yeah, bus bars? um they're you know, quite common on like really dense um you know highly uh populated boards so it's definitely worth uh considering something like that like this one. here's got like three um ones. In this particular case it's carrying uh Power to like all the devices across. Uh the board like this but you know you can get one just one uh specific one that will um you can actually like, you know scroll it down, you can even make it uh yourself.

You know you can get a bit of like alloy rod and then like screw it down into like a uh like a threaded um insert into your board or something like that you know actually in a lot of the tear. Downs I've done uh I think a recent one with the keysight. um High Current Power supply I'll try and include a photo of that here and they use like big bus bars to take the current over and stuff like that. So you know when you start talking you know 70 80 amps something like that so you can do it on your PCB but then um once you get like if you go to four ounce copper here and you only need it for that one trace for example then you get like you're wasting all that copper on the rest of your Board and they'll charge you a lot more because you've got to, they've got to etch all the more copper off and then the thicker copper also limits it increases your art Trace space on your board so you can't do like your fourth hour four thousand or you might not be able to do say your fourth hour fourth hour traces on there you're really thin uh, tracers on your uh board anymore? With that four ounce copy, you might have to put those on another layer which is your one ounce copper or half ounce copper and then dedicate your four ounce layer to all your power.

And for this, um, you know, big current uh traces that you actually need. But yeah, um, but yeah, Bus Bari um things are also a very often used option, but you know it's a custom parts, another the materials part. it's You know it's everything else, but that might be a better trade-off that might actually work out cheaper than the PCB especially if you've got like a large boy you don't want to waste like you know, a big four ounce board like this and you only need one little Trace Like that? you wouldn't do it on the board, you'd you'd design your custom little uh bus bar there. Yeah, no worries.

but there's several ways you can actually do that with thread on metal inserts and you know, just screw down a little aluminum block and then screw it in, tighten it up. and Bob's your uncle and a little trick. If you didn't want to get a custom bus bar manufactured, no worries, you wouldn't be the first person to run just a giant uh wire link across there. Just get a nice thick ass gauge wire and just you cut it to length and solder it on at the production stage and you know, unless you're building a million widgets, Um, then that's a perfectly acceptable solution.

Especially if you've only got like one trace or one or two traces that you need to do. Just get your regular one ounce or a half ounce copper board or whatever, then just put on a big thick as trace and then just bypass your PCB entirely. No worries. And the good part about that is you could have like a this is not a dense layout, but you can have a really dense layout and then you could like snake it around components and you can just you know, squeeze that wire in anywhere.

No worries, and you can carry like 80 amps on that thick as wire. Not a problem and you'll see that. Uh, selecting DC here just removes, uh, your skin effect thing down here. It has no difference to do with the amps down here.

Now, if we actually go up into the program options here, we can actually change the IPC standard so we can use the old standard. okay, obsolete for amperage and so the client a lot of people I swear by that are Triple Two one all the way. another's 2152. Rubbish.

Um, right. So let's just take right a one inch uh Trace with one ounce. uh, copper here. Write the 12.67 amps and let's actually, uh, change that and see how much difference that actually makes the old triple Two one.

It's gone up a lot. Look, it's gone from 12 amps to 25 amps. Okay, just just just between switching between the old and the new standard. Okay, so obviously the new standard much more conservative and then we can do that.

Add little modifiers here, but that's just, you know, tweaking around the edges, right? So, But yeah, there's massive. So if we actually choose the old standard here and we choose our four ounce ounce copper, we practically get to our 70 amps. You know. So maybe right for our 10 degree C temperature rise.

Which one do you actually believe? There's a reason that they you know people thought that the triple Two one wasn't adequate because it was based on the old characteristic curves. And you know, like you know, back from I don't know the 60s or something whenever they measured somebody I don't know um, who measured If you know who, leave it in the comments down below. but dump. yeah, see, it makes it.

It makes a huge difference. Massive difference. so your mileage may vary anyway. If we remove the modifiers here, then we can actually solve for conductor width here.

Okay, so we can actually go in here and we can do our 80 amps like this right? And then it needs. well. three inches. Three inches.

Okay, yeah. good. Like well you can get one half inches on each layer maybe. Or if you use like a full layer board or something, you can use four layers so you can get away with it on the PCB You can get away with it, but that's four ounce copper, right? You use the one ounce copper 12 inches anyone? That's what she said.

And if you're wondering about this, etch Factor here. it basically makes no difference whatsoever. It's just the when you put it in your etch away the copper. The copper just doesn't itch square like that.

it etches, you know, who knows how much etching get over etching and you get breaks in your traces. That's why you can't have a you know you have a minimum Trace width. uh, you know it might be. you know, six thou, four thou, something like that.

or 0.1 millimeters for your metric Fanboys And you can't make traces more than that, because the manufacturer can't guarantee that their etching process is not going to overreach the copper and break the traces. So even though they electrically test the boards, they don't want to over test and like and scrap a whole lot of boards and stuff like that that just cost their money or they'll pass it on to you. Um, so yeah, Edge Factor Um, it makes like when you're talking about really fat traces like this. Yeah, it doesn't matter.

but when we're in the older standard the IPC triple two one, you can see that basically, if you choose the internal and external layer, it makes a heck of a different difference. It's not like as I said, the external layer can carry a lot more current four amps here. So in practice, um, that's why you know the older standard, the triple Two one. You had to sort of like everyone knew that the external layers like they could handle more current, the internal layers due to the insulation and the heating and everything else right? So obviously the more the newer standard is more conservative and as as you saw it make it makes it should make no difference to that and we can actually swap that back right? So let's uh, 21 of 52, swap it back and you'll see that the internal external layout makes no difference to the maximum conductor current.

They've taken that into account with their conservative formula. However, it works out so. um, yeah, meh. So I Hope that's uh, answered the question somewhat and given people at home uh, food for thought and you can, as always you can really go down the rabbit hole on this thing.

And if you go like there's been lots of controversy over the years about the IPC standards for current carrying capacity and based on the old curved characteristic curves and stuff like that and people what you know, there's multiple camps out there of which one's the best one and all sorts of you know, you know, nerds will fight about this sort of stuff. Um, but yeah, it's It's an interesting topic. Current handling? uh, capacity? You know? Basically yeah. The the two rules are how Thick's your copper, how wide your copper, and what sort of temperature rise? Um, you're willing above ambient.

but imagine if it's like a you know Automotive thing in your ambient temperatures gone up to 70 degrees or whatever and your temperature rises above that and you thought, oh yeah, you know 50 degrees C temperature rise? Yeah, no worries. And if you just went, oh, I can do 100 degrees temperature right? Is it a PCB can handle 100 degrees and get a bit worn. Give me get a bit Brown looking after a few years but you know she'll be right. Look at this.

116 amps. Whoa. It's turned red. Why has it turn red? I Think it just yeah.

it literally got too hot there like it's it's 100. It's like 170 degrees. You'd take it down to 20 degrees ambient. and you know, 116 amps? There you go.

Anyway, Yeah, you're gonna. yeah, you're gonna need that. uh, thick ass copper I'm afraid. Anyway, if you enjoyed, uh, that video, if you like me answering these sorts of uh, questions even though I waffled on a bit, um, give it a big thumbs up.

and as always thoughts and comments down below catch you next time. Thank You Foreign.