Hi I thought I'd do a video answering a Twitter question even though I've already answered it on Twitter I Thought it might be of interest to others and I wanted to test out my new rig here. it's not fully finished yet but I thought I'd do a video trying it I've got my pen tablet here hooked up to my Blackmagic atem and I'm doing this all sitting with this backdrop. Let me know what you think instead of over at my uh, regular desktop. leave comments down below what you think of this form factor.

It's not polished yet, but yeah, we'll get around to it anyway. let's see what we've got here. Um, this question comes from um Ian Hanson Uh, follow me on Twitter By the way, ask me questions on there all day, every day. that's all I do answering questions on Twitter Um and then he's posted this and I thought this was really interesting.

Uh, it says every once in a while I see a board like this I Figure maybe it's for some kind of noise or decoupling purpose or something, but perhaps someone could tell me. uh, if this has a name and more about it. Well, I don't know about a name for it, but he's talking about what he's talking about. Here is the our bypass caps here and how they're all like a because there's a lot of them and they're all neatly surrounding the chips as you can see here and um, and all the passage.

just the sheer number of passives and now they've laid out in sort of a grid. Arrangement So let's take a look here. So I'll go over to my drawboard uh PDF program. For those who don't know, it's an Aussie program and uh I can just draw on this.

So let's take a look at what's actually going on here. Okay, well first of all, what is this board? Uh, it dates from. You can see it down here having it figured out how to pan with this thing yet. Um, it's from 2004 so this would have been designed early 2000 so we're talking at least 20 years ago.

It's a bit younger than I expected I Thought this was like a late 80s or something. but anyway, what this is is, it's a VGA card apparently with us some video capture as well. So presumably this is your VGA output here and these are video video capture I don't know what kind of video inputs if you know, leave it in the comments down below. I'll put a link down to a page which has info on this and it's a super Savage Ixc and uh, it's an 86c 584 as you can see.

manufactured 26 week. um O2 here. So it's a VGA chipset and obviously the the Altera Cyclone up here is probably doing like the video. Well no, this is probably the video capture.

Uh yeah, it's a Phillips I can see the Philips symbol I can't make out the symbol so this is probably the this is this would be the capture uh memory for the video input. Anyway, this is. um. anyway.

let's not worry about the details of the card. Why does the layout look like this? Why are all these by look? Look at all these bypass caps. Why are there all surrounding the chip like this? And why are? And why is everything like in rows and columns like this? It's all beautifully neatly laid out. Why is this case? Well, oh, there's uh.

several reasons for this. The first of all, uh, is this. this appears to be a single-sided low. There are load.

There are a couple of components on the back, but they're not populated. Uh, he didn't post a photo but I Found another photo online and they're not populated. So you've got to think of the mindset of the designer of this board. not only the PCB designer, but also the actual designer of the circuitry, right? Typically, there's multiple Engineers on a design like this, especially in one of this, uh, complexity.

And there'll be, you know, software and firmware people. and they'll be, you know, uh, production people. Uh, probably not people. but you know, at least a production person involved.

And there'll be a PCB designer usually. And then there'll be the designer of the actual circuit. We'll be doing the schematic and you know, and everything else. So multiple Engineers.

So you've got to put yourself in the mindset. now. when they're manufacturing this, they probably wanted to lower the cost, so they went for a single sided load. So all the components are on one side.

and the problem is when you got a BGA package like this and you've only got components on one side, you've got all your little individual pins in there. Okay, please excuse the crew. Dear, the model didn't have time to build scale or to paint it. You can see how my tablet is actually uh, touch sensitive.

so get different size pins. bloody BGA chips anyway, right? So you've got all your pins under your BGA chip like that now. of course, the chip of this complexity will have multiple power pins and multiple ground pins. And the multiple power pins they could be for different voltage cores.

Uh Insider though this one I haven't looked at the data sheet, can't seem to find the data sheet readily for it, but let's just assume it's just a single uh rail. Okay, it's not that complex, but you've got multiple power pins and ideally you would have a bypass or the recommendation for the manufacturer will be a bypass capacitor per pin. Or even if it's not recommended in the data sheet, that will often be the mindset of uh designers. it's just sort of like the done thing.

It's the de facto standard. Oh yeah, if you have a Power Pin you have a bypass pin with it, you don't always need it. It's kind of like one of those belt and braces things. You're just like nobody ever got fired for putting a bypass cap on a pin unless you're pinching pennies and you're doing months in.

I have to link up my video uh, months in and reducing capacitors in the circuit until they stop working. It's very interesting stuff. The designer of this thing probably just went well. I Like however many uh bypass caps are here, probably is how many power pins have actually had.

Some of them aren't uh, bypass caps, but all of them are. They're probably all like 100n. They don't look any. and remember, we're talking a long time ago.

Sometimes there's you know, 10 microfarad bypass ceramic. uh, capacitor rubbish. right back then you know One mic was like big um, so yeah, so there's no huge value. Uh, so if they want to bulk a capacitance, that's why they're using these uh, tantalums around here.

So that's the first reason what's happened here is that that the designer has simply used one bypass capacitor per pin. and then they threw the schematic over the cubicle War to the PCB designer and the PCB design has got their schematic. They import it and uh, and then you know they've got all their parts and they're laying and they're starting to lay out the board and they go well. I've got to put all the bypass caps.

and well, somebody told me from production that we can only afford a single-sided load. so I can't put the bypass capacitors where they should be which would actually be like on the bottom here. So you would actually have like, you know, a bypass cap right next to the pin and then you'd have the Via typically not uh, via in Pad but you know it'll be very close to it and this is why. Flip over any modern board and if you see a bunch of bypass caps there, you almost certainly on the back of an Fpga or a you know, a BGA micro My Pen's diet.

Oh goodness. So yeah. Usually you add bypass caps on the bottom of uh, the pins. that's as close the pin as possible.

You minimize the trace, inductance and everything else. So in this particular case they there was no option, right? The bypass pins caps had to go around outside the chip like this. and of course you've got some like excess space in here, but this is probably once again, this could be a production uh requirement in that the pick and place machines that they're using at a particular assembly house for example might have had requirements that, um, you know, hey, we don't want caps close to, uh, the chip or we don't want. This is why the footprints are actually quite large as well.

If you have a look at the size of the footprints, right? this is. geez, You can drive a truck through there, right? So there. Once again, this could come from an in-house requirement. for example, where they have an approved footprint and this is a thing in big companies, you will have a certain you know if you've got an 0603 or an 0805 cap, for example, you will have an approved footprint for a specific uh contract manufacturer for your board.

for example, it'll be all set up and done and then they might have you know they just uh went well. I've got to use that and I've got to have uh, the space in requirement as well. so that could have been driven by the manufacturer. although this looks quite large and spaced out, so I would say that probably you know In good bet is that the PCB designer just? well, they had room and they like to lay it, you know? and they didn't want the silk screens overlapping and stuff like that.

you know, because that's sort of like ugly. They don't want them overlapping and so they spaced them out nicely around the chip like this and could have put them a bit closer. But as I said, there might have been requirements for that. so you simply place them all your bypass caps around the outside and you want to have them all in line because you're You know, you take pride in your PCB layout so you want to have them you know in nice vertical and horizontal arrangements and then if we zoom in there You can actually see they've got the Vias there and there.

like either side there. uh, like, well, that one. Oh yeah, that one's there. I Don't know why they didn't put it there.

Oh geez, you know they went to all this effort to make make it aesthetically pleasing and they put the put the Via there. I Would have been disappointed in myself if I did that. You know symmetry. Come on.

Um, Anyway, so these these uh caps are obviously being via stitched directly down to the ground and power layers. probably just one power layer on here. it's probably all just five volt uh, logic or something like that back then. um, or it could.

there could be an extra 3.3 volt layer in there, but who knows. right? Anyway, so the other reason for, uh, the amount of the sheer amount of bypass caps like all in here like this, like you know, there's just tons of them. Like this is because there was, uh, no pushback from the PCB design and the PCB designer. If they knew you know designer layout, which a PCB designer often does, although not always I've worked with um, top-notch PCB designers who come from a drafting background.

They've got no electronics knowledge at all. but you pick up. Um, you know you do pick up stuff over the years. This is back when you know things weren't as advanced as they are now and you know you've got to understand stands, signal integrity, and all sorts of stuff, right? It's not that an engineer can't do a PCB layout, it's just it helps if you have.

So there was probably no pushback from the PCB designer going. hey, look, come on, you're making me do a single sided load. We don't need 20 bypass caps. You don't need a power supply bypass cap per pin.

It's just going to be sufficient to rely on some bulk decoupling. You know, like you might put one bulk decoupling cap here. just you know, like surround it because you see there's one just big Power plane. like you're not optimizing your inductance you know, and getting close to the power pins anyway.

So you know you could have said oh, you know, just a couple here. a couple here, and a couple here just to you know, make it nice and dandy, right? And you don't need a cap per pin. So there was probably no pushback from the PCB designer there. Or but this should have been picked up by the actual designer.

they should have. You know they should know, right? If you're designing this, you should have a, uh, like a thought in mind of you know layout, you should be thinking about layout when you're actually designing this thing. If they knew it was a single-sided load or that was their intention of it, clearly they wanted this to be single-sided load. or definitely, you know you would have put the bypass caps on the bottom of the chip down here.

There's no absolutely no doubt about that you would have done that. So obviously they'll constrain with that. So you would have sort of like gone back to the drawing board a bit. And you know, rethought your bypassing strategy and the same things happened over here.

On like these: these chips over here, right? Some of these, like, there's a whole row of bypass caps there, right? There's a whole bunch of them. Not all of them might be, uh, bypass, uh, cast, but a good lot of them will be. And yeah, it's And there's another one there, that one's got two. Vias Actually, instead of one, they're trying to lower their inductance there by using the two Vias But and yeah, once again, they probably had like a bypass cap per pin.

But because this is a quad flat pack like this, you can actually actually be near the pins like this. so you know there's a reason to do that. But we've got another BGA chip up here and probably you know. Look, they've got some larger ones.

here. Are these like 1206s or something? Actually, they look to be output from there. There's a regulator there. Yes, that 3.3 I.

Don't know, we can't see that. But yeah, you're going to have a similar sort of problem around that. BGA And you know these bypass caps here are probably from the Altera uh Cyclone They've got a couple of more caps over here, but once again, that is a quad uh, flat pack. But why have them in all these nice grid? Arrangements Like this? Well, this could be done by an old-time PCB designer who was, you know, old school from you know, 70s, 80s who's used to laying stuff out in grids.

That's if, just look at any old school board. In fact, I probably got one. Just so happened to have an old school board here and this is how it was done back in the day. You know what all the chips would be in like row Arrangements Like this and they're all all the correct orientation so that the auto routing of these boards or even if your manual are routed, it all of the traces on the top for example would go in One Direction and all the traces on the bottom would go in the other direction.

I Don't know. No, you might not be able to see through this solder mask, but I've shown this in uh, previous videos where yeah, all the traces will go horizontal here and all the tracers will go vertical here and that just makes laying out the board easier. And I'd say that uh, somebody has you know gone in with a similar mentality here. Just everything needs to be in nice rows and also PCB designers they love Symmetry and they love just the Aesthetics of boards.

and I reckon the piece I I would have been quite proud of this board, right? It didn't like apart from like just from us. an aesthetic uh, point of view having all the caps in nice rows and columns and rows like this, it's just it's beautiful. So yeah, there's quite a few reasons there. One, this is a single-sided load so that would have determined various things.

B There was no pushback from the PCB designer to go. Hey, look, come on. this is a bit silly. We don't need one bypass cap per pen.

We can get away with a lot less, right? This is just getting nutso. Uh, three. they might have had uh requirements uh for spacing requirements and things like that from the assembly house and then they might have had standard Footprints company foot approved Footprints to work from company approved space ends and DRC requirements for the board. and you know, all sorts of like older School requirements that might have been carried on from like a decade earlier, but they still use them today and they might have the piece of their designer, might have still been working around those uh DRC constraints and stuff like that and then, well, if you're told I've got to lay out this board and here's all these caps.

Yeah, why not. just you know, make them in nice neat rows and columns like this and it just that's why it looks like this. So yeah, there are like, you know, half a dozen so of reasons that go into something like this. good or bad.

Um, as I said like you, really, you don't need this many bypass caps, You don't In this particular case, having a bypass cap per pin just because you're defined it so on the schematic and that was you know, like the done thing, it's just no, no. Somebody should have you know, stopped and thought about, uh, this board and gone. Yeah, yeah, no. Um, we can get away with a lot less bypass caps than all these.

and look, they didn't even have room for the still screen designators either. You'll you'll notice like like they put U17 here, right? There's a little fiducial. Um, actually, they've done that fiducial. That fiducial's done on this silk screen layer.

You don't do fiducials on your silk screen layer because you can get offsets on your uh on your silk screen compared to your copper layers. And really, the alignment of a a fiducial um Mark is at a fiducial mark as a reference. Mark Used by the camera for the pick and place um machine so that it knows where to accurately. Place Uh, the components.

And you don't put that on your silk screen layer. That's a golden rule. You put it on your copper layer. Um, so that, uh yeah, it's more accurate.

So then any offset errors on your silk screen and your copper don't matter. Oh yeah, there we go. I Totally missed that. 3.3 volt uh rail there.

So yeah. And then there's another adjustable rail there so that you know there's probably some like, um, internal, you know, know, sort of like ground, uh, in there, probably just for that one chip. and the bypass caps do that and you just don't need all those. It's just it's it.

It's just silly stuff. Um, just a couple of bulk decoupling caps would have been fine for something like this. and this is not. you know, really huge, modern, like.

you know, high performance like you used to, uh, these days and really the only way you can actually get better performance is as I said, put them on the bottom of the chip under there, right near the pin and then have a via going uh, straight up or V is going straight up to uh, the balls. Um, and then you know you're actually bypassing individual uh pins and then you know you at least get some benefit there. Otherwise, from an inductive point of view, you're talking about like one big solid. You know, 3.3 volt rail and ground will go over the whole Board of course.

I Don't think you'd have split, uh, planes on something like maybe up here. Like if you've got like, if this is like as is an analog uh section or something like we can something like that if that's your analog section with your video video ends or whatnot, you know you might have separate split grounds up there or something like that. But yeah, but Julie um speaking Yeah like pass caps would have been fine on something like that. you know, just a you know, one one over on the far side, here, one here, just a bulk.

uh, you can get away with bolt because there's a lot of uh, debate. and if you go and actually use the uh simulation tools to actually try and simulate bypassing which is really Advanced really expensive software tools, you can actually do it. but the specialized um, signal analysis uh tools to do this. And yeah, you can often find that well, just one bulk decoupling cap is going to work something like that.

Unless you're talking about real like modern, complex Fpgas with multiple things and they have like you know, 50 page documents of just how to power up and bypass and sequence the power rails on a modern Fpga air modern processor, or something like that. It's really strict, but yeah, maybe this uh VGA chip I don't you know it's it's kind of like Old School uh compared to Modern stuff and you could have just got away with a couple of bypass caps. But anyway, there's some possible reasons why this thing looks the way it does. So I thought that was an interesting question.

If you got other uh, you know, theories why it looks the way it does leave them in the comments down below and let me know please in the comments how you like this new setup. It's not polished yet, but it's good enough for Australia Catch you next time.