How To Improve Your PCB Designs (Common Mistakes)

in this video i'd like to show you some of the most common pcb design mistakes i oftentimes see in shared pcb designs of course i'd like to show you how to improve on these how to improve things such as signal integrity emi and so forth we're going to cover some main topics such as the correct trace widths via sizes and placement clearances between traces what you should pay attention to when you're doing copper fills and copper pulls and things smaller things such as silk screen and so forth as usual this video is sponsored by jlc pcb so thank you very much to them if you would like to order any pcbs or want to use any of my reference designs you can find them under github.com pms67 and i have things such as the little brain sensor board which is an stm32f4 and stm32f1 breakout boards and so forth so all the gerber files and assembly files are there and then you can follow my other videos to see how you can actually use glc pcb to order with assembly the board you're seeing this video is actually part of my pcb design course which i'll be releasing the next month or two if you haven't filled on the server yet and you'd like to put your name on the list for when to be notified when it comes out please do so and i'll leave the link in the description so far we've gotten over a thousand responses which has been great and yeah i'm really looking forward to sharing the course with you a tool i often use when designing pcbs is this one here called the saturn pcb design toolkit and this is really useful and it's free because it has so many things you can calculate for example what conductor impedances you might need for controlled impedance traces it tells you things about crosstalk uh differential pairs and so on so i really recommend you download this from saturnpcb.com and have a little play around the first point i'd like to talk about is trace widths and as you can see in this pcb i have a variety of different choice widths i'm using for example thicker traces here very thick traces in the power section and some thinner traces down here now what i like to do in general for signal traces is always root them as 50 ohm controlled impedance traces of course if it requires something else if you require 60 ohm or 45 ohm trace impedance then of course router does that but in general i always set up a track width for example in keycap up here which will be a 50 ohm trace and i'll generally start off with that for my signal traces the second point is thick and thin traces so for example power you anytime you have higher currents you want to make your traces thick or wider rather and again you can use the pcb design calculator and click on conductor properties and you can find out for given conductor width and a given copper thickness you can find out how much current that can carry for a certain temperature rise so as you can see here in the power section i've done copper poles or rather wide traces and for something like signal traces which are which have virtually no current consumption at all i will do much thinner traces a further point is that regardless with which pcb manufacturer you go with they will always have some some form of capabilities section so if we scroll down we can actually see they have something on minimum trace width and minimum spacing and my recommendation is to always try and stay away from the minimum trace width right so even though they can do 3.5 mils or 0.09 millimeter trace width you don't want to stress these manufacturing capabilities the next point or common mistake i'd like to bring up is that of clearance in particular trace to trace clearance so for example the distance between one trace to the other often times you'll see pcb designs where there's virtually no space between these different traces and that's this can be really problematic for signal integrity reasons and so forth predominantly because you'll get a lot of crosstalk and you can actually calculate the amount of crosstalk using again the saturn pcb design toolkit and the crosstalk calculator and you can see depending on how your conductor spacing is between different traces you can see how what the voltage is that's actually coupled between them and this can actually be really significant and cause problems in digital and analog systems a typical rule is to space traces at least three times the width of the trace away from each other so if this has a certain width i'll go three steps to the left or three steps to the right and then put my next trace there and this makes sure you will have a much smaller or reduced crosstalk than you would if you had the traces running right next to each other for example when i'm coming out for this i squared c line up here one is going straight up but as soon as i get out of the pad i'm going left to give myself more space between these two traces i could have of course just routed it straight up and left but that means i would have all these parallel sections running next to each other whereas if i just go straight up and left i immediately create space between these two traces now clearance of course doesn't just apply to traces it also applies to components so this board is actually a mixed signal pcb so i have an analog section and a digital section and you can see i've tried to keep the digital section and the power section as far as far away as i can from this analog section it's pretty much all about the space right you want as much space as you can between traces and between different sections for example analog and digital so as long as you can maintain a large enough distance you will minimize your crosstalk and that's generally the goal if you have the space use it so the next item on the list is vias and via placement and as you can see here i've got quite a number of vias uh this in particular is either four or six layer board so i have internal ground and 3.3 volt planes which i can essentially just dig down into and connect to my capacitors or whatever needs power or ground so for example i have these bypass or decoupling capacitors close to my main signal processing chip or mcu and you can see how i've placed them first of all the via is very close to the pad it's not in the pad but it's as close as i can get it without it being in the pad once you have that really close and then you have a very thick or rather wide trace going into the pad and this makes sure you're you're minimizing your inductance vias typically always come in pairs so you always have a for example a signal via and then you'll have a ground viewer same with power so have a power over here or 3.3 volt via and a ground via and what you want to do to actually minimize the inductance is not just connect them with thick traces and have them close to the pads but you always want these via pairs close to each other so you want ground and 3.3 volts for example really close to each other to minimize the inductance and you can see with all these bypass and decoupling capacitors this is exactly what i have here here and here i would really recommend you uh to check out this video it's how to achieve proper grounding with a pcb design guru rick hartley and he gave a presentation uh to one of altium's um events and you can see that on autumn's youtube channel and this is possibly the best uh video on pcb design ever watched and honestly the two hours and 20 minutes are well worth your time and you'll know a lot more about how to design pcbs and how they work so i really really recommend you check this out so let's briefly talk about copper fills and copper pores so generally in a multi-layer pcb you will fill internal layers depending on your stack up of course with ground or vcc and so forth here this board as i said before is a mixed signal pcb so i have an analog section and a digital section and what will you notice here i've just highlighted one of the internal layers my main ground plane it is a solid continuous ground plane i am not splitting it and in pretty much 99.9 percent of all cases you shouldn't split your ground plane even with a mixed signal pcb with analog digital domains as i said before the most important thing is that you keep space between analog and digital sections and that will reduce your crosstalk there is no point in putting in a split ground plane in most scenarios there are exceptions of course but most scenarios you want a solid ground plane on the other hand here is one of my internal layers which is the power plane or power planes rather and you can see i have split and sectioned this into different areas depending on the voltages so here i might have 3.3 volts for my digital i have for example 9 volts for my analog and i have the analog 3.3 volts now this is okay to split if but only if you don't run any signals which are directly adjacent on the next layer across these splits so as you can see here the next layer will be my signal layer and i'm not running any signals across these splits in the planes finally let's talk about silk screen and this might be a very small and minor detail but i think it's important that you get your boards produced correctly one thing i see a lot is that people put silk screen so for example these designators here on pants and that won't work in the manufacturing process so they won't be printed and your silk room will be cut off so don't put silkscreen on pads and secondly try not to put silk screen on holes or vias so you can get vias tinted which means they're covered with solder mask and then you can um usually put um silkscreen on vias but it won't look as nice so as you can see here i've tried to move the silk screen so it's just barely on a via and that'll then come out better than if it were directly on the hull but never sacrifice component placement for silk screen placement right the silk screen is there as a guide but it's not as important of course as the component placement

Channel: Phil’s Lab

Views: 38,680

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Id: IclJ9nbtYgI

Length: 9min 26sec (566 seconds)

Published: Mon Jan 18 2021

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[u/Zorgen_Borgen]

This guy's channel is a goldmine.