Through Hole Manufacturing

Hello, and welcome to the Mac fab engineering podcast. We're your hosts, Parker, Dolman.

And Steven Craig,

this is episode 281.

So we've gone through 281 episodes, and I realized now 280 Okay, well, you're right, you're right. And so by the time you've listened to this, that we will have gone through 281 episodes. So we've gone this far. And in that amount of time, we've talked about through hole manufacturing for PCBs, probably a handful of times, but I don't think we've ever like dedicated talking about it. So I felt like, let's just have an episode where we where we take a chunk of time, and we talked about through hole manufacturing, and all the nuance behind it and, and kind of what Parker and I know about it, what we know to look out for and some of the things to do to make you successful. So when it comes to through hole manufacturing, will actually let me back up, when it comes to surface mount manufacturing. Surface mount has been around for quite a while, and it's sort of the de facto standard for PCB, right. But no matter how much you kind of walk through the differences between surface mount through hole manufacturing, you really can't get away from through hole, you're pretty much always going to have some kind of through hole manufacturing, it's very difficult to make a board that has just surface mount, right. So it's worth, it's worth understanding the processes that go behind through hole manufacturing. And it's worth understanding what you need to know, as a designer to make sure that you're successful things. So when it comes to the processes, Barker, what are the what are the general processes that you'll see at a contract manufacturer for the whole process?

So most? So the process we're talking about, like the manufacturing processes, right, like actually the putting the parts on the board and performing a process, say

I've gotta say, I've got a through hole part, and I've got a board with a footprint, and I want to make those two forever.

Okay, so you get some bubble gum chewed up, stick underneath the park, stick the park now. So you got a couple different ways of soldering this component onto the board. The hand soldering is the first one most low volume manufacturing that's to roll guess what people are soldered in those parts on. That's it's actually very interesting that that's probably was the first way soldering was ever done on boards was by hand, which makes sense. But we still do it today.

It's unavoidable. Like, oh, yeah, hand soldering will

always exist. Yeah, will always exist unless we have soldering robots. So I actually haven't seen these in a long time, but they do exist and have seen them in some CSMs. But soldering robots are basically a mechanical version of a hand solder is it actually has an iron that's on a robot arm, and then it has a a wire feed, that feeds solder, and then it goes around and puts the tip down onto the where you want the joint to be made. And then it feeds a little bit of solder into it, and then it backs off, goes to the next one. That's kind of been replaced. I don't know, when those were introduced or something like are were Mainstays, because I don't see a lot CMS with those anymore. But what's kind of replaced those is selective soldering. But before we get to selective soldering, we're going to talk about wave soldering. So wave soldering is kind of like the mass production way of doing through hole. And so what that is, is basically there is a, a pool of liquid tin, or lead if you're doing leaded solder, and most most CMOs are gonna be lead free. So you have a pool of liquid of liquid tin, and then there's a pump that's pumping liquid metal around into a wave, that's like a, an actual wave and actual wave above the surface and then your, your PCB assembly is pre populated with all the components and then that board dips down and rides the wave through the through the to the 10 liquid 10 Basically, now there's other steps in there. You have to apply flux to the board. You have to preheat the board, preheat the board, and we're gonna get more into this later but you also your leads have to be formed and trimmed correctly, because if your leads are too long, your your parts go into like basically it's called the blade that's in that it's forming the wave, it will kit the wave and then your board will flip over and then spill all the parts plus the board into the vat of liquid tin.

And then you contaminate everything.

It's that's wave soldering is always just baffles my brain, because you're like, because you're sitting at room temperature, and you're looking at like this like two foot by one foot block of basically just molten metal. That's just a fountain of it to the wave. And then, so what replaced solder and robots, which is basically an iron that moves around on a gantry and gets soldered, is selective soldering. So think of like a localized wave solder.

It's a chocolate fountain on a CNC bed.

Yeah, felt that's a it's a tin fondue machine. And so yeah, it's a little fountain or a little wave, and actually call it a wave. It's a standing wave, basically. But it's a little tiny point. And there's different nozzle sizes for it. But it's so instead of moving the board onto a giant, like horizontally wide wave, it's actually a little wave and you drive the wave around under the board. Now, some some actually drive the PCB around machines, but most of them drive the vat of tin around to solder the boards. And the thing, the trick with all these different processes is different design criteria for them. hand soldering, as long as you can get an iron into where you need to stick the solder at, you're good to go. But if you want to do quote, cheap, unquote, you know, p th assembly, you have to have some, you have to go to wave or selective soldering. So there's definitely different design criteria for those.

So yeah, let's Okay, so let's, let's go back real quick and just recap that for different processes that you can generally expect that your your contract manufacturer will have at least one of these four, if not multiple of the foreigners hand soldering, their soldering robot, which there's probably a better name for that. But that's what we've always called it. hand soldering, soldering, robot, wave solder and selective solder. And those are your four major processes that you'll find that a contract manufacturer, so if your board contains any through hole, or if it's predominantly through hole, a, we'll go through one of those processes. Now, let's rank those real quick in terms of general cost of of what you're going to see. And then let's talk about the design criteria behind them.

So you say cost, there's also those cost per unit. And then there's an R ri cost. Yep. So separate those two out. So on the most expensive per unit, the lowest NRA cost, hand soldering, for sure. I actually don't know what it is for soldering robot, because I've actually never designed anything or pushed or got anything quoted using one. Well, I guess it's going to be NRAS when we hire than hand soldering because you have to program it. And it does take time. It's only a little bit faster than hand soldering. So the price per unit is probably a little bit cheaper in the hand soldering, but not too much.

I used to work with a contract manufacturer out in San Antonio and they had a solder robot. And and you have it you have it exactly right. The one thing Okay, so hand soldering takes is generally the most costly because it's just almost 100% labor, just human labor doing your work. Soldering robot still requires a good bit of labor because in my experience, it requires an operator sit there and watch it do the work because it has to it has to be inspected and and it's prone to failure. So you have a trained technician who's out there making the programs for it that are not the easiest things to do because there's a lot of input variables as to like what angle are you approaching things do you have like, like what kind of tip are you using on the side of robot and things like that? So it takes a train the operator to do it and then they have to monitor it so it's fairly expensive. And it's not fast?

Yeah. And then on. So if we were going up on the NRA costs and then down on the per unit costs, the next thing would be way would be selective soldering. So selective soldering, you're only you're only NRA costs are the is the program of the machine itself as well. But those take more to it. It takes less time than hand soldering, but not as much time as the next thing which is wave soldering. So where soldering is the quickest because you are, you're literally dunking the bottom side or the side of the board that you're soldering into just liquid solder, and then pulling it back out. But you have more energy costs, mainly in most, most boards nowadays are double sided assemblies with surface mount parts. Well, if you have surface mount parts in contact with liquid solder, it's just going to rip the parts right off the board. And because they will just D solder, and your your contract manufacturer won't get be too happy with you because that water gets stuck in the impeller and the machine. So what So what, so what they do is they design a wave solder palette that basically masks off the parts of the board that you don't want dunked in the solder, and right through that way.

So, yeah, DJ Oh 27x in the Twitch stream asked, if you're going to wave solder, you have to have a human place the through hole components, right. And in my experience, you will depending on the board, you'll have, you know, one to many humans on a conveyor in front of the wave solder. And each one is responsible for however many X amount of through hole parts, and they place their parts and it goes down the line. So yeah, you do you do pay for, you know, human labor to insert parts wave solder out of out of this entire group is is your high, high volume manufacturing option here. You can easily pay for a handful of people that stuff parts 24/7 If you're cranking out boards, 24/7. And so so if you're talking about high volume manufacturing, wave soldering, certainly the way to go.

Yeah. And on the inserting components, the part has to get into the board somehow. Now, back in the day, when through hole components was the mainstay, you actually had machines that could auto lead form and auto we're going to get to the lead form in a bit but auto lead form and auto trim and auto insert components like resistors and two boards. Those machines don't really exist anymore. I've never seen one in a factory. They probably do exist still

they do. Yeah, but but they're rare.

Yeah, the dinosaur machines to probably I bet you not a lot of manufacturers still make those machines.

You know, a lot of a lot of cheapo power supplies and things and Single Side power supplies, they go into appliances and stuff are still through hole. So there are still machines that that service those but they're not there's there's a high likelihood that your your contract manufacturer is not going to have that correct.

Actually, the last appliance that I took apart, that was it was a much newer plants. It was a single sided PCB, but it was service mouth.

So just how to clean side? Yep. So when it comes to wave soldering, the one thing to keep in mind is that your board is going to enter into the the machine in one direction, it's going to exit the machine in one direction. So you have a direction through which the board actually makes contact with the wave of molten solder. And depending on which direction that is that can have an impact on how your your parts get soldered. So I'll be honest, I don't know all the details on that there's a lot of information, because because I honestly haven't had to design around that. But that's something to keep in mind. The way you orient your board the way it goes through and the way you orient your connectors, you can actually prevent solder shorts and other problems based off of which direction it's going through. And if you see these large volume manufacture boards that are designed for wave solder, a lot of times you'll see like big arrows in silkscreen on the board that that indicate Hey, go this direction through the wave solder because there was a lot of attention paid to that. So if you're perpendicular or parallel to the wave, you can get different. Well, you can experience different issues with the wave. So one thing with a wave solder machine is that it's usually blanketed in an inert cast like nitrogen or something like that to make sure that the machine that the wave doesn't produce a ton of dross because you have this huge wave of molten metal there and if it makes contact with oxygen, it can grow oxide skin over the wave. And that just makes for awful solder.

It's like metal putting skin right right. Well, okay, so

if that ever goes wrong in the machine, then whatever boards getting soldered, there is just virtually garbage at that point.

So go Back to your orientation components. I haven't really seen that too big of a deal for connectors. But it's mainly for what I've seen it for is there is a process of soldering SMT parts through a wave solder. Oh, if you if you apply glue to them. Yeah, so how that works is, instead of applying solder paste to your board, putting the parts on and then reflow on it, what they do is they dispense a.of glue in the center of each part, they put the parts down, run that through the reflow. And that bakes that glue. I think some of them are air cooled, but I think pretty sure most of them are thermal cured. And then they run that whole puppy through the roof, the the the wave solder, after all the through hole parts have been put on it, of course, and that will soldered. Now SMT parts were never really designed for that and they have closely leads together. And so depending on the orientation, you will get bridging, you will definitely get bridging if they are not put in the right way. I would definitely not recommend designing your product for s&t reflow, through a wave solder. But if you're building a billion of something that might be a consideration, you shave off one process, right?

I've seen that in in high volume products like TVs and things like that. If you ever if you ever pull out a board from like a computer monitor or TV or something like that, and you see their surface mount passive, like resistors, and caps. And you see this little blob of red crap that's around the those parts, those have been glued down. And there's, there's a handful of different reasons why somebody might design that into it. But like Parker was saying this is kind of one of the main ones is such that it can survive going through a wave machine. Yeah,

it's for that. And the whole reason to do it is to because getting rid of one process makes your product just that much more cheaper to manufacture. See, I wouldn't worry too much about especially in low volume connector orientation. Even for wave soldering, the main thing is actually is keeping, if you have bottom side parts, first of all, try to not have bottom side parts. Yes, single sided load will always be cheaper. Yeah, that will always be cheaper. You still might need a pallet. Because if you have large open vias, the solder will actually flow up through the via, and spill out over on top of the board.

But or if you're panelized, and have cutouts in your in Yeah, that's it.

But besides that, the other thing is, is trying to keep your you have to talk to your client, your manufacturer of what they're DRC is for that, but keeping your components your s&t parts away from the the through hole, and so that there's enough space for the fixturing to basically seal up against

it. Exactly. And so that's that's the the pallets of what you're talking about. So these pallets create like a a protective heat shield against the wave since the wave can flow onto your through hole parts, and it doesn't make contact with your SMD parts. So if you're designing a board, and you know that there's going to be through hole parts on the top side and SMD on the bottom side, you're going to want to make sure that you know what your proper clearances are for your pallet to be around. And in fact, what's what's really convenient if you have the ability to create a new layer in your EDA tool or even a silkscreen layer of an outline of where the palette will rest against your board that helps your manufacturer ensure that everything is connected properly.

But even more, I guess, important is that and that spacing is for selective soldering. So if you're in that middle ground of you're still not doing enough to make a full palette worthwhile. But you want to be you know, cheaper than hand soldering is that selective soldering range and selective soldering has really taken off, especially here in the United States. For contract manufacturers. It used to be no one had them, but over like the last 10 years, like almost every cm has one now. Because they you don't have to have an RFP for a pallet. But on the other end of that, though, is you have to have more space between your solder lead location and your SMT component on the bottom side, because you're driving a nozzle around that's, you know, 10 millimeters wide, and that comes anywhere near a surface mount part. It's just going to D solder that component. I think at macro fab are I have to ask our operations but I'm pretty sure the DRC is just, I think 10 millimeters

And when you're laying out a small board, 10 millimeters is massive. Yeah. And so something to keep in mind that clearance, if, if possible, that clearance is the edge of your through hole pad to the edge of the next component. So that 10 millimeters will add up really quickly. So at WMD, we use a, I believe it's a six millimeter nozzle, and we can get away with three millimeter clearance. Now that's like sniping things with it. That means we're not taking the nozzle up and moving it across. That means we're just going up and then down and to the next component an up and down. Oh,

so y'all doing point the point? Well,

I mean, we don't prefer to. But if we have to, we can, the best situation is to take the nozzle up. Like say, if you have like a header like a header of 10 pins and header, we'd like to hit the edge and then drive across it. That does the best solder job. But if we're in a really tight space, we can, you know, bounce up and down and snipe pins, but that that's the most difficult and the least reliable form of selective soldering. The best way is if you can drive the pot upwards, start on one pin and then go across a line of pins or maybe circular or however it works. That's the best situation. So keeping that in mind as a designer like yeah, it might make sense to electrically to put a component right next to a pin because okay, you know, it's the most ideal situation electric Yeah, but from a manufacturing side, that's usually garbage.

And it would be even hard to make a palettes that that would work for that too. Like if you're going to wave soldering. So I have to ask Chris Kolbert at Netfabb what uh, what the minimum on that machine is

that you know, okay, so if you're getting a you have you have your, your, your electrical design done, and you're looking to get prototypes on your on your next world's best widget and you want to get three of them made. hand soldering is probably the situation that's going to happen for you. Because people are not going to go through the trouble of creating palettes or creating programs for you think they'll just hands out of your components. And that's good enough. But say you've gone all the way through your manufacturing plan, you've done manufacturing, ramp ups and things like that, you're ready to make a million of your widgets, well, it's probably going to go through wave soldering. So this is sort of like a tiered process and depending on your quantity will put you in a bucket of one of these four processes.

So what's also really important with that deals with these processes is also lead forming. And it's something that I find that a lot of designers and companies kind of forget about because SMT there's no lead for me you pick the board you pick the part out of the reel or off the tray, put it on the board

it's done that's it

with lead forming with hand soldering, you don't really besides like if you have to do a fancy like bending a leg a certain way you don't have to worry about lead forming for the hand soldering you put the part in solder trim it I guess that's the your lead for me is trimming. Because actually when you talk about wave soldering or selective soldering, you have to lead form everything in form of your trimming Well not everything but most most components they have long legs you have to trim it to the right length so that when they go through the machine correctly and not catch the the nozzle of either the wave solder or the selective solder oh man this the nightmares of of on the remember that old selector solder we had at Mac fab.

What was it the the old

rhythm rhythm rhythm the really old one we have we actually have we have a new rhythm now that's like amazing. Yeah, but so we bought this rhythm RPS rhythm used. And it was already on its last legs. But we rebuilt it Stephen I rebuilt that machine. And we had we had that thing cooking. Like it was awesome. But one time we had an operator left one of the leads about had been like only like 100 mil, like a couple million, maybe a millimeter was too long on the bottom. And so it caught the nozzle and it just tipped the nozzle off the machine off the top of the machine. And so then you have instead of a like a six millimeter nozzle of solder coming out. It's now it turned into like two inches in diameter of just molten metal spraying. Yeah. And that nozzle that is a is a choke down. And so it actually hampers the flow. And so when we Got a pump like max out because that pump was so worn out. Without that restriction it just spewed a I think it like half emptied that that tin pot all inside that machine before the operator was like, Oh, that's not good. Oh, I should stop. I just stopped this machine. Oh, good solder the hell on board though. Yeah.

One solid sheet of solder on the bottom. Oh man. So yeah, like, okay, it's going to be dependent upon every machine because every every manufacturer machine is going to have different requirements. But if you're looking at a cross section of the board the distance that a leg protrudes from the bottom of the board, there is a specification on that. So most manufacturers will handle that for you. But you're gonna get charged based on how you're gonna charge for it, how much time they have to take in trimming all of those legs.

Yeah, so picking apart that might be already preformed already that fits your footprint, or picking apart that doesn't have that has right shaped legs already. But we'll also go into actually like lead forming like if you have to bend legs a certain way. I've seen some like MOSFETs, that had to had the legs bent for voltage considerations actually. Because like if you dealt with, with the legs on the component or for they're far enough away for the voltage isolation, but you can't make the pads on the board far enough away. So you have to lead form where the legs out. I've seen that before. But so those try to find lead forming parts like tools that already exist and not want to get custom made, especially right now. Like I'm trying to get some custom tooling for this for a customer made right now. Then it's like it's like 22 weeks right now. Leave? Yeah, to get some jobs basically machined.

Yeah. And also like, that's okay,

some jobs for pair of pliers. So you can don't necessarily,

maybe a rule of thumb here is not your contract manufacturer is the expert in this realm, or you should, you should consider them the expert in this realm, but they're not necessarily, you shouldn't necessarily rely on them to design a thing for you. So if you need if you need some kind of lead forming work with your contract manufacturer, knowing what kind of tools they have, like, for example, we have a pneumatic lead forming tool at my job. You know, if you were to become a client with us, and you needed some kind of unique lead forming something rather, I could share with you what machine we have, we could both get in contact with the manufacturer of the machine and look at their catalog of dyes that are available. And then maybe one of those would work for you. But But maybe like I what I'm getting here is don't if you were to work with me, you shouldn't necessarily rely on me to design your lead forming tool custom. And you shouldn't necessarily design your lead forming tool custom and then expect me to use it.

Correct? Yeah. Yeah, non trimming and trimming leads to like, what we have is a we have a machine that you can just put pretty much any pitch part into it. And then you hit a little foot pedal at shears on the bottom of the parts off right off the leads, which is a really convenient way to turn those parts correctly

with the machine I have for lead forming. It does both you basically replace the head. And one head is basically a guillotine that just cuts them to the right length or the other one does fancy stuff and bends at the right way. Yeah. The you know, the other option is a lot of through hole components come with pre bent leads, you can you can purchase a flavor of a component that has pre bent leads. And that's almost always the most ideal situation. So like it's up to 92 transistors a lot of times will come with pre bent legs that fit in nicely and stand up well. So go with those if you can.

And one thing that's not in here but should be for lead forming, well, I guess it's not really lead forming, but it's it comes after this after lead forming. It's offsets component offsets. So for s&p parts, they just go onto the board and you solder it there's no there's no height besides the height of the components. With through hole, you can put it flush to the board you can have an offset because there's there's variability in the height of the component. So if you need the height to be set, to a certain like so you're attaching to a heat sink, or or you have LEDs that need to reach up to light Get your enclosure height do front panel, you need to call that out in your assembly documentation. And a way to do that process and you should talk to your contact manufacturer on on that, like at macro fab, we actually 3d print all that stuff, we 3d print, like if you need a component that has a five millimeter offset will print and a fixture that does that offset for us. You know,

I remember we started doing that when when I was back at the Fed way back in the old building, we would make little spacers that just slid in and yeah,

so you basically you, you put the spacer on the board, slide the part in solder it and then you can slide the spacer back out. There's also a lot of components that are like that, that are designed to be soldered in place or put into place like sleeves that go around LEDs, and then you drop that whole thing on the board, some have snap ins, those are mainly used also for support. Whereas if you remove the spacers, nothing to support it. That's also a thing to keep in consideration is like, if there's a certain specific offset that you part needs to have, call that out. Make sure that your contract manufacturer knows about it and so that they can get the right tooling spun up for it.

I would say the one of the biggest offenders of that is LEDs. So like let's say you have a PCB and then somewhere up above that PCB you have the user panel, I've seen so many times people say Insert led such that it's in flush with panel or it goes into some hole in the panel. Well, that wording right there tells me that I have to push the led up to into that hole in the panel and then solder it in place. That's not a machinable operation that immediately means hand soldering. So that's, that's one way of designing but you're guaranteed to be designing a lot of costs into your product at that.

At that point, you're basically making custom custom fitted boards

well and like I said, LEDs are sort of the main offender in that in that situation. So many LEDs have or so many manufacturers make readily available LED standoffs that that are just a tube of plastic with holes in them that an LED just slides in it takes a second longer for the operator to slide the led into that and then push it on to the board and then it is machinable and even though you're spending more money on a standoff you save way more money in the in the long run with labor.

Well, not just labor but also like in and waste. So let's say you custom fit that led to be the right length. So like you put it in the hole in the enclosure and put your board on solder you put it all together and doesn't work. Well that PCB or like the enclosure is bad, like the silkscreen strong on it or get scuffed or something. Well, there's no interchangeable parts there anymore because that board is fitted to that that patch solder out panel now. Yes, yeah, solder. Solder in place assemblies. Yeah, that's a whole different topic,

ya know, like, avoid them if possible. Yeah. So then yeah, so lead forming with a dye or a hand tool. Those are those are completely acceptable. But that's, that's a conversation to have with a contract manufacturer. And as we always say, like the earlier you can get in contact with your contract manufacturer, the better as opposed to like, calling one of us up and being like, hey, we have this whole project ready to go, here's all these tools you'll need to buy in order to do my thing, and figure it all out. And the documentation is garbage, like not a good way of handling that. So if you know you need something lead form, like let's say, it's example I'm aware of is, you know, some resistors have a like a power rating. But that power rating is only true if they're elevated off the board such that they have airflow underneath them. Well, sometimes they have unique lead forming such that they the leads themselves, hold them up in the air. Okay, that's a situation where maybe we could purchase a dye and and specifically cut and bend those leads for that situation. Now keep in mind that if that's something that we have to purchase and install, I mean, you're going to end up getting charged for that dye. That's not something that will float for you.

Most OEMs just hide that into the their price he

gets rolled into it. It gets rolled in Yeah. I have seen some cool machines before I've never actually got the chance to use them but it Okay, so it's it I call it a pizza cutter. Basically think of a huge like think of a deli slicer where the where the blade is horizontal. You've put all your through hole components in doesn't matter the length of the leg. You just insert them all the way and then you do Slide them across this giant pizza cutter, and it cuts all the leads to the right length on it, which is pretty neat. It's really, really fast for for doing it. The one problem with it is none of the components are supported. So they're all just to go out. Yeah, well, yeah, the problem is you have to design the board properly to for that machine. So not only do you have to have design criteria for the whatever process of soldering, you'd have to have design criteria for the cutting machine. So those machines are really great for high volume stuff where you can afford to look at every single component under a microscope like that, but I don't like most of the time. Like what Parker and I were talking about the little foot pedal, pneumatic, a chunk, a chunk, choppers, and up getting the job done.

And before we go on to PCB design for through hole manufacturing, since was still kind of talking about process and lead forming and stuff is there was I had the author post the video game, but there's an old RCA radio company. video out there has made in about the 50s when transistors were started to be like, you get a train a single transistor radio.

Oh, this was this video was well before OSHA was a thing.

Yeah, so they're, they don't have a wave solder machine. But they have a wheel. It's a it's a it's a solder pinwheel or Ferris Wheel. Ferris Wheel. It's a Ferris wheel for boards. And so a so they have like little trays that are that it's like a what do you call those a basket on a Ferris Wheel? Basket your basket. So it's a basket. So think about the baskets that go around on a Ferris wheel. And but the hanger the part that hooked up to it, that pivot come off. And so the boards go get into those hangers or baskets. And then they dip it into the resin flux. So like, like it's like stamping it, but there's like a basically a a warm bath of resin. Yeah, for the flux. Because they just dip the complaint, or the ear wax. Yeah. But well, it's liquid. So because they can so they can dip it and not push the parts out. So just dip the whole thing in it. And then they put it in the Ferris Wheel. And it goes around that set rates and just dunks the board the bottom of the board into molten lead.

But but not like it's molten lead, but it's like it's like a pot that's like 12 inches by like eight inches of just molten like, and it's open to the environment. Like if you just stuck your hand in it, like that'd be on you. I guess that's the way they guess. And the amount of fumes this thing explode because it's completely covered in flux. And then it hits a molten bath of of metal. And then there's just this operator who's standing next to it, and it's just lalalalalala

OPERS also smoking problems.

It's a really cool

cigarette super filter.

This solder fumes tastes great.

Okay, let's move on to PCB design. Yep, throw.

Okay. So when I was I was kind of thinking about this earlier, when when you look up a datasheet. For any surface mount part, I shouldn't say any but a large portion of surface mount devices, they give you a complete footprint. They give you a footprint that shows you know here's the extents of the components, here's all the pads, here's your openings for your mask. And like they give you everything you need to know. But when it comes to through hole components, most of the time, you're lucky if you get 50% of it. So

most time, it's just like, here's where you should drill holes. And here's the diameter of the holes.

Yeah, here's a recommended diameter of a recommended diameter, but they rarely give you the size of the pad or the ring. They never do. I've never seen that. Right? Yeah. So at best through whole data sheets are half 50% done,

let's say and this is something that I don't know about because what I do through hole parts that are like this, I so the next thing is is like annular ring size. I just go that looks big enough. So I am not up to snuff on on this. We're about to go through

right now. Well, okay, so here's the thing, there is actually like a proper way to do it. So, but yeah, but before we do that, let's just talk about the holes real quick. So So when it comes down to a hole for a through hole component, it's 99% of the time it's going to be circular, right? Doesn't necessarily have to be and it used to be if it wasn't circular you pay a lot of money because they had to do X processing on it. But, and more modern PCBs, they can plate non circular holes, so slots and things like that. But 99% of the time, you just punching a circular hole in it, and then you're plating the barrel of that hole. Right? Okay. So there's some rules of thumb when it comes to how you size those. But most of the time your datasheet is, if it is a specifically through hole solderable component, they will give a recommended hole size and in general, I would recommend using that hole size. If you don't have a recommended hole size on there, my rule of thumb is if it's circular go 10 Thau larger than that

10th Owl, the dye angle of of the pen because most pens are square

and profile well most like header pins, but like resistor legs and capacitor legs are going to be circular.

Oh, they're round. But yes, but most

don't make that don't make that mistake, you'll be what the square root of two under if you if you go off of the wrong side.

Yes. So make sure that you're the diameter you're picking or the the diameter of your hole will actually fit your your pins. Brown pins are easy, because it's round pin round hole. But sometimes you have square pegs that go out to go into a round hole, and you run a loss to be bigger than the diagonal of that square

will same thing with a rectangle, if it's a rectangle go off of the diagonal of a rectangle and make it larger than that. So

10 mils larger is a good rule of thumb, then I guess you can also look at your contract manufacturer and what PC manufacturers are using, and seeing what their tolerance on the drill hits are. So that's a way you would actually calculate that, well, here's

the here's how I arrived at 10th out I've actually never once had a problem with 10,000. I've had problems with doing other things before. So most contract manufacturers when they come to drill size and drill location, it's three Thau tolerance is what they what they suggest. And then most component manufacturers that I've run into with like resistor leg size, it's three Tao tolerance. So if your three Thau off on your your drill size, your three Thau off on your drill location and your three Thau off on your component legs, size tolerance, you're still nine Thau off, it'll still work. And there's tons of given played through hole. So 10,000 will pretty much always get you there. If if I was making it something like a kit for somebody to solder as like my first soldering thing, I'd make it 15 or 20,000. Just make that make it really big. So there's like no problems whatsoever. But for general manufacturing, I found 10th out works fairly well. Now, there are more specifications for this. So that's a rule of thumb from Steve Craig 10th out, but I've just never really run into an issue with that. If I was doing something for automatic insertion, I would 100% go off of what my contract manufacturer says. Because the 10th thou tolerance on leg leg bend position for a machine to push into a hole. Like that's really, really tight, I would think they would want more than that. And then, yeah, so noncircular through whole legs are acceptable. It's still something worth checking with your contract manufacturer. I mean, if you're going to start making something really weird, or really small, or really big, then you have to you have to start asking questions. I'm like, Is this acceptable? Or is this going to start costing me a lot of money because they're not having to plate you know, a huge amount of area with gold, or I'm asking for a 4000s slot and a boy that I want pleaded like those two things are ridiculous, right? But But say you have like, great example, a lot of potentiometers and boards. They have mounting tabs that are rectangular, you could put a giant circle on there to account for the for the rectangular mounting legs on there, but you're gonna waste a ton of solder because you're just filling up a huge circle on there. It's not

just that either you also are you start introducing a placement positional errors. So like if you're if that most on that potentiometer is going to a panel that has a machine hole that, you know gets melted up to, well, if you got a lot of slop in the PCB footprint. Well, that part's not going to be in the right position.

Right, right. So if you're trying to fit a rectangle into a circle, you're gonna have I'm sorry, a, a yeah rectangle into a circular hole. Your circular hole is going to have to be enormous to fit the rectangle. So if you can get away with a slot, then you can get a lot closer and hit your target a lot faster. Are a lot easier. Okay, so yeah, let's talk about annular rings real quick. And it seems like annular rings confuse a lot of people. So an annular ring is the amount of copper that exists outside of the hole and to the edge of the through hole pad. So when you're looking at a through hole pad, the pad itself is basically the annular ring. It's from the hole to the edge of the of the pad on there. So the annular ring is up to the designer 99% of the time, most data sheets don't call out what size annular ring, because take, let's let's take pin headers as an example. Point one inch pin headers, you know, the spacing between the pins, but they don't give you the annular ring. And a lot of reasons why is because you can change what that annular ring is, let's say you have high voltage on it, you might want to go with smaller annular rings, such as your creepage in between each pin is different. Or if you want it to be really easy to solder because you know you're doing hand soldering, you might go with larger annular rings if you're Voldemort, oblong ones, or oblong? Yeah, actually, I had I had a client that was very, very particular about having a very specific oblong pad because they liked soldering that so I had to design a custom pad for them for that exact situation. So annular rings are kind of up to the designer. However, there are some standards that that dictate how to calculate annular ring. So we have a we have a link here that will post up in the show notes, Mac fab.com. What slash podcast is how you get to the blog post. So this website gives a basic way to calculate IPC standard for annular rings. So IPC has a bunch of documents when it comes to PCB footprint land pattern designs. So there's actually four different IPC standards that apply to general PCB footprint design, but but they include through holes, so there's IPC, 222122222223, and 7351. So that's generic standards on printed circuit boards, sectional design standard for rigid organic printed boards, sectional design standards for rigid, Rigid Flex printed boards. And then Generic Requirements for surface mount design and land pattern standards. That last one being 7351. And so IPC 7351, is the document that's going to give these calculations on how to actually say, Here's my hole, here's a handful of other characteristics about it, how big should my annular ring be? Now, the funny thing is, that calculation still has wiggle room in it, because it still has, the designer still gets to choose characteristics about it.

Yeah. And and also, one thing to take into consideration of design, your annual hearing is also the DRC, and your ports being made correct. And you make your annual everything too big, you're gonna violate the DRC of your board. And Correct, yeah, and you'll have to do also going the other way, too.

So the general rule of thumb goes, the bigger your component gets, the bigger your annular ring gets. And the reason for that is, like mechanical stability, say, if you have a little fourth watt resistor, you can usually get away with a much smaller annular ring on your pads, because it's it doesn't have as much mass flapping around in the wind. But if you have a giant like one farad capacitor on your board, it's gonna have a big annular ring, because it wants you need more solder to create a mechanical bond to the board. So that's just the very loose rule on annular rings. So IPC 7351, has three different classifications within it. Now now, I'll pause for a second, I really wish that there was some kind of portal that we could go read these things. These are not, you can't just go to Google and type in IPC 7351 and just read the PDF. I mean, you sort of can, but it's, I guess, it's a little bit of Yoho in a way, but

like to have the official up to date document, you usually have to purchase these, these documents. Most not a lot of contract manufacturers will have these available. They might not have the most recent up up to date, but they might have them so it's what's worth having a conversation with them. They might also have an engineer who just knows the information in his head.

So how much how much does it cost to get a copy? Well, because if you're let's say you're a metal machinist, usually you buy the metal machine is handbook. which has all the Anssi standards for, like how to cut threads of different sizes and all those tolerances has all that stuff in it. This is that equivalent for electrical engineers for layout designers, I guess. How much is what's the price difference? There?

Depends. Each one has its own price. And I'm not 100% certain, but I believe there's also a service that you can, like rent them in a way. So

as a machinist handbook is about 30 bucks.

That's yeah, these are much more than that. I've seen some of these standards go up to like 800. But I think that that was a group of standards, not just a single one. Actually, I pulled up a really cool image, I found online, two images, actually, so So Parker, if you go to the bottom of our show notes, I've got these images if you want to share them in the Twitch stream, and we'll have them in our show notes. These are super awesome. It's a cartoon image of a PCB manufacturing floor, the first image, and it shows every machine that you would generally find on a contract manufacturer. And as you look through the image, it shows which standard applies to each one of those machines. Oh, I've never seen this squeeze integrate. It's so great. So like, all the way down to like document handling. So on the very top left of the image, you have digital data, you have somebody who's handling like Gerber's coming in IBC. 2581 refers to how your contract manufacturer should handle your gerber files and handle, you know, passing things in between all the way down to in the in the top right of the image you have cleaning, here's the IPC standards on how to clean a PCB. So if you're interested in like a very particular portion of the manufacturing process, you can look at this image and see that if you're just more of a words, and in numbers guy, there's another image down below. That's a flowchart that just shows here's how a board is made, and which standard applies to it. So if you scroll down Parker's that's down there. So these are all the IPC standards that apply to that, which, if you look at the very bottom of this list, its data transfer and electronic product documentation. That's all the IPC standards that apply to it. The very next thing in line is the design and land patterns. And these are the IPC standards that applied to that. So um, okay, so yeah, so So back to the classifications in IPC 7351, there's three separate classifications that that will determine your calculation of your your annular ring, you see, this is why surface mount is so much easier, like somebody's done all this for you,

right? Well, it's in the datasheet already done most time. And you

there's, there's a little bit of knob turning and like, adjustment, you can do a very small amount and surface surface map, there's a lot more in through hole. So okay, so the three things you have control over you have your performance classification, you have your productivity levels, and then you have the land pattern determination. So, your performance classification is the classification to which they, the contract manufacturer will inspect your board to. So class one, two or three. Oh, IPC class 123. Is it a McDonald's toy? Is it a washing machine? Or is it a space shuttle? Basically,

like, I like how there's no difference between a washing machine that special though, like there's no in between there? Right? Like, you just hop that level, right? Yep.

You know, I've heard it been said before, if you're trying to kill somebody or save somebody's life, it's class three. So military or medical, right? So okay, the productivity levels are not numbered, they're the productivity levels are A, B, and C. And those refer, kind of boil it down those referred to how hard it is to make your, your your product. And that's a really simple way of putting it. So let's say let's say your board is really sparsely populated, and you have the ability to make big landing pads, and everything's really easy to solder well, then your productivity level is a lot easier. But let's say you, things are a lot more constrained and you have small annular Rings and Things is a lot more difficult to make. So those are levels A, B, and C. And then the last thing is your land pattern determination. So perhaps, perhaps your board is so densely populated that your annual earnings have to be small. Your land pattern determination is basically a density level on your board. So A, B and C. Refer to that So all the details of that are in 7351. And before this podcast, I Googled, you can find PDFs of 7351, they might be slightly old, but the bulk of the material is generally the same. So, all said and done, if you're really looking to fine tune your product, and let's say you're you're making a bazillion of whatever these are, these are all things that you're going to want to discuss with your contract manufacturer, and you're gonna want to pay attention to each one of these. In general, if you're if you're making a, you know, a moderate amount of your product, what I've found as a, as a simple rule of thumb with annular ring, if you take your whole size and you multiply it by two, you'll get an okay annular ring. So the two rules is better than my rule. Oh, yeah, just look at it looks good enough, right? I just don't do a lot through. So the two rules of thumb, take your lead size, add 10 1000s to it, take that whole size, multiply it by two, and you have your whole size and your annular ring. And that generally works. Now it's the Craig rule of thumb, that's the correct rule of thumb. And like if you you know, I hold no responsibility for broken or non working products or anything like that, you know, obviously, you wouldn't have to test anything, it's just using those general rules, I've never really had much of a problem with

them. And if you don't want to, if you want some more explanation behind Craig's rule, thumbs, IPC 7351.

Oh, it's gonna give you an IPC. 7351 is like hundreds of pages of just, just nerd text. Like, they're great. I really wish I had a hard copy of it, because I would leave through it and I would actually read this stuff. I just don't have a few 100 bucks lying around to buy all of these standards. Yep. All right. Cool. Yeah, I think that kind of gives a general overview of through hole manufacturing, as we always say, if if you know your board is going to have these kinds of processes on it, get in contact with the contract manufacturer, ask what machines they have, and start designing around those processes. Your contract manufacturer will be able to give you more concrete numbers as opposed to like, oh, just take your whole and multiply by two. They'll be able to give

you they might actually tell you they might be listeners of this podcast

that's true. They might say us that might say that. No, yeah, Craig's rule

so that was the Mac fab engineering podcast.

We're your hosts Parker, Dolman and Steven Greg. Let everyone take it easy

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