- DFA – Design for Assembly
- DFC – Design for Conservation
- DFD – Design for Documentation
- DFM – Design for Manufacturing
- DFP – Design for Production
- DFR – Design for Repair / Recycle
- DFT – Design for Test
- DFS – Design for Safety
How to DFX
- Identify what you are Designing For
- Perhaps list them based on priority
- Make a list of all of the items
- Make a timeline for which DF applies when in the product life
- Create a list of key design criteria
- This will vary based on where the product is in the design cycle
- Schedule specific focused time to have a team review the DF
- Have the main designer present, but it is best to have other perform the DF checks
- Have a sign off and circle back process
- If it passes then have the team sign off and move to the next stage
- If it fails, have a process of fixing and asses if another full DF meeting is needed
- Perhaps just a small DF meeting to address one thing
- At then end of the product design cycle you will have a folder of completed design checks that help validate the release of the product
DFA vs DFM vs DFP
Techniques for making revisions easier
- Put circuits that you know need adjustment where you can reach them with a soldering iron or a probe
- 0 ohm resistors
- Make for very easy configuration changes
- DNI/DNP – lots of people don’t know this is a thing
- Multiple footprints
- Parallel components
- Room for soldering!
- Test points – different from component terminations
- Keep lists of things to remove for production
Special thanks to whixr over at Tymkrs for the intro and outro!
About The Hosts
Parker Dillmann is MacroFab's Co-Founder, and Lead ECE with backgrounds in Embedded System Design, and Digital Signal Processing. He got his start in 2005 by hacking Nintendo consoles into portable gaming units. He also runs the blog, longhornengineer.com, where he posts his personal projects, technical guides, and appnotes about board layout design and components. Parker graduated with a BS in Electrical and Computer Engineering from the University of Texas.
Stephen Kraig began his electronics career by building musical oriented circuits in 2003. Stephen is an avid guitar player and, in his down time, manufactures audio electronics including guitar amplifiers, pedals, and pro audio gear. Stephen graduated with a BS in Electrical Engineering from Texas A&M University.
Host 2 00:10
Hello, and welcome to the Mac fab engineering podcast. We're your hosts, Parker,
Host 1 00:15
Dolman and Steven Craig.
Host 2 00:16
This is episode 295. So, based off some discussion from last week, we kind of have this idea of this podcast.
Host 1 00:28
We're talking about design for everything today.
Host 2 00:31
D F E, which is not a thing. If it is a trademark. Yeah, it's ours. If not, no trademark trademark infringed.
Host 1 00:44
So So Okay, let's talk a little bit about the design force. So what are we talking about when we say designed for x? Well,
Host 2 00:54
This is designed for and pertaining for electronic manufacturing, right? Because this party can mean lots of different things, depending on what industry you're in.
Host 1 01:05
It can be, frankly, it can mean whatever you want. Really. That's true. No one's holding your feet to the fire in terms of design for and I'm doing air quotes. Yeah. Designed
Host 2 01:16
For for anyways, so there's D F, a design for assembly, though I've also heard this called designed for production as well. And but some people, they separate those two out as different things. Then there's design for manufacturing, which is like the common one DFM. You have d f r, which is kind of a new one. And it's designed for repair. This is what that all the right to repair movement and that kind of stuff. Also, I've kind of like, designed for recycle. Because making it so easily comes apart also makes it easier to recycle. Because you can separate all the components out into all the different materials. Another kind of like old standby for the design fours is designed for test DFT. And then it's also designed for safety. Is there anything else in that list?
Host 1 02:15
I mean, probably that
Host 2 02:19
Probably is Yeah. I came up with the idea. This was for the podcast for we had Pecan Street on and it was designed for conservation, kind of like low power and reducing resources and that kind of stuff. We never got to that topic. Hopefully in the future we get to do what I was corny DFC, which is probably will be a more important thing that engineers will have to think about in the future.
Host 1 02:51
But I always have to think of more criteria, right? There's always more stipulations to what more
Host 2 02:56
Stipulations. And then you had an idea that was also called DFR, that we were gonna talk about last week, but just ran out of time. But this that was designed for revisions, though, we already have a DFR, which is designed for repair. So what would you call this? Design for revisions? instead? You can do DFE design for versions?
Host 1 03:19
Yeah. DF Rev. I don't, I'm not I'm not entirely sure. It's not really. Okay. So, when we say D, F, and then you put some letter after it, unofficially, that actually means something. And I say on officially, because like I said, people aren't holding your feet to the fire, it can mean, whatever you really want to, but depending on what hat you're wearing that day, a DF design for thing means that you are approaching a set of criteria, and you're designing to meet those and then you're checking against that. So it's less of like, Oh, I'm keeping my, my criteria. In my, in my head of what I'm doing. It's more of an official like, say sheet of paper that says, Here are the things your your design targets that meet whatever this category is. So if it's designed for assembly, how was your thing assembled? And how is that how does the design meet all of those criteria? So it's a little bit more official, but for the most part, it's, it's inside the doors of whatever your company is.
Host 2 04:30
Exactly. It's, it's, it's basically coming out. So let's say you're you have a design, it's I view these as design fours. You're not even at really the initial is like, these are some things to think about depending on what your product is like the think about when you're first doing your design, but these are more like reviews, right 100% 100 Where you will you will go through a DFM process. To make your design more manufacturable. Now, going through that a couple times you learn some tips and tricks, and then you start to incorporate that more on the front end of your design. Same thing with like, the big one that's like designed for safety, where like, you need to, let's say you're designing, you know, safety critical device, you will probably start designing that safety, critical design stuff at the beginning of your product design lifecycle instead of like at the end with a review process. But the whole idea is, all these D F's are review checks, to make sure that you're hitting the criteria that you should be hitting for your product.
Host 1 05:43
Well, and that's just the thing. So so let's say you're, you're kicking off a brand new product, and the sales team has said, hey, the the, that's that's one design for sales. Oh, gosh, that Yeah. You'll never pass ever. Sorry.
Host 2 05:57
No, no, it's not that design for sales. The first page of the datasheet has to have all the buzzwords Oh, that's how you pass the F set sales.
Host 1 06:06
Yeah, well, there you go. Design for sales. All it is, is writing the first page of your data sheet. That's it. First Page of your data sheet, add the blinking lights, say you're you're kicking off a new product, and you go through the whole set of hey, sales has told us that we need this new gizmo that does all of these things. So you write up the your your project, documentation that shows here are all my big goals that I'm going to hit the all of your D F criteria, effectively will be in that document, but they're not made, there may be not spelled out every single one of them. So your high level criteria, here's how much we expect this product to cause here's the major features that we want this product to do, here's the lifespan of it, here's, you know, manufacturing plan, general things, all of those go in your your project document, that's that's the big slide deck that you showed the VP and things, all of your DF, things are within the engineering team, these are all of the design criteria that are checked against that maybe you know, the sales team is not going to look at or the VP is not going to look at but they're all things that we hold near and dear to our heart as engineers in the engineering team. So I think I think one of the best places to kind of start with all of this is to just identify which DFC apply to you, you know, are you assembling the product? Great. Yeah, then it's probably not a bad idea to have a DFA check and design for assembly check. Are you? Do you have testing involved with your product, great, have a D, F T, check on there. And inside of each one of these D F categories, it's a great idea, I think to create some kind of document. That is a list of the key design criteria of what what are we going for with this test? What are we going for with assembly? And what are the things that we care about in this? And here are a criteria of for our design?
Host 2 08:13
Yeah, and these can be really simple criteria, like for if you're a small OEM, your design for assembly might be reduced tools and make sure it doesn't take longer than x time to build. Right? That can be the two criteria.
Host 1 08:30
Great. Yeah. I mean, I think that's a that's a great example. So just simple, simple criteria that are things that you can ask a question about, and ask, hey, does this design actually meet this criteria?
Host 2 08:43
Does it meet their criteria, and maybe it's something that's can be somewhat measurable. And so you can see if you improved your your product or not, in regards to these processes, right.
Host 1 08:58
So then creating a schedule, that is that is based off of these design for checks, is a really great way to kind of plan out your design cycle for the entire product, say, hey, you know, we have our initial concept phase. And then maybe at that point, we have a design for a check that is based off of that initial phase. And then once you have prototypes in hand, and you're you've gotten a little bit further, maybe you start asking questions about Oh, should we start doing a DFM and asking about how this is actually built. And then maybe you're further down the line, and you know, you can actually get it built? Now we start talking about DFT and designed for testing and things. Is this going to actually meet all of our criteria for testing. Yeah.
Host 2 09:43
And not just not an individual testing device, but what you should be testing on that device. You know, sometimes you don't need to test everything. Sometimes you just need to, you know, test the final output of the device or you want to do a full product sweep. It really depends on the use of To make sure the LED turns on, right, a simple smoke test. But that's part of the DFT.
Host 1 10:05
The DFT will tell you that like, what do we need to know from the test? And how deep do we need this test to be? And if maybe you even have criteria where you say like, we know that due to the cost of this device, we can't the test can't be longer than one minute. So what can we accomplish in one minute, and does our hardware and our software support what we need to find out in that one minute. So I think it's really important to have a sign off and a circle back process with this. So what I mean by that is if say, your prod project, or product manager, that's handling all of these def checks, have a have a system where you know, or you create a document that saying, Hey, this is what we're looking for this is this is the point of this entire design for check, regardless of what it is assembly test, production, repair, whatever it is, you're creating a list of all of the criteria for that, grab a schedule a whole time with a specific team on your design team, and say, Hey, for the next X hours, we're going to be doing a DFT, we're going to be doing a DFM check on this new product and make it specific focus time, I've in the past, I've taken half a week, or even a few days, where it's just like, hey, don't bother me and this other person, were doing a def check on this product. And we spend all day going part by part based on whatever def check, we're doing DFM or do whatever. And we go one by one. And our main goal. And our focus is this def check. And I kind of say that because it's like, if you're if you're just kind of like have this on the side burner, you might not have the right focus to actually really look at that criteria and see if you're hitting your target goals. But in terms of the whole process of going from nothing to something with your product design, I think it's really helpful to have these scheduled checks in there. So if you can have it set up if your team is large enough and capable enough to be able to set apart, you know, a full day or two or three to say, hey, we're looking at design for manufacturing today. I say go for it. And then the circle back process is something where you say if, say we get to design for manufacturing, we go through products, great, but we found XYZ problems with it. Okay, have a circle back process where you go and address all of those problems come back and you have a second mini DFM, or maybe even a third or a fourth or fifth, you keep going until it's done. This isn't a one time thing. It's an iterative process that that goes until you're absolutely complete with it. Or even if you have major problems, schedule a whole nother design for manufacturing check. That is, you know, two, three days or whatever you need in order to accomplish it.
Host 2 13:14
And even if you identify something that you probably won't you, let's say you identified a problem in DFM, but you're like, Well, it kind of has still be built that way, right? Sometimes as it happens, you should still document that you discovered that problem. Because what's going to happen is down the road, another engineer is gonna take a look at this and be like, Well, why is it designed this way? The naked, pull up that note and go, Okay, that's why that's why this wasn't DFM doubt because it has to be this certain way. Making sure knowledge doesn't get lost is probably a big part of the de F umbrella as well. Write everything down.
Host 1 13:56
And these become the big milestones. So you know, as you're as you're going through your product development cycle. And, you know, if you're the project manager, and you're having to give status updates to the engineering manager or someone above them, these become those big hallmarks of saying like, Hey, we've passed this, we've all been we've all approved, we put our signature on it, we've passed design for assembly or whatever it is. And you know, if there's more information needed, you can pull out the documentation in the criteria and said, Hey, we checked for this, this and this, we've all approved that. It's it's correct and good to go. And then the nice thing is at the end of the entire design cycle, once you've actually released your product, you can have a folder of all of your DFR or sorry, your DF X checks. And you have kind of a timeline and an approval checklist effectively of all of the design checks that you've gone through. It's also like Parker was saying it's helpful for remember What's happened are remembering design decisions that, you know, on the surface look odd. But if you if you look back at history, you can say like, oh, right, that's why we did it. But it's also nice to be able to look back. If there is ever a problem in the future. You know, have has this been checked for before? Or has this been reviewed? Well look at all of your DEF checks. And, you know, the problem with this is, there's not like, one size fits all or anything, you know, when you when you go to start a new product, you it's up to you to kind of design these checks, design all of whatever D F's are necessary for the the product launch. So instead of trying to keep all the information in your head, it's nice, it's a lot nicer to kind of chunk it out into these steps, and then build it into the process, or build it into the schedule just makes things a lot more clean and organized.
Host 2 15:56
Well, not there's not but also the whole point of chucking it out so that when you focus on, let's just say designed for manufacturing, you only focus on the stuff that matters for manufacturing. And that actually brings up this topic I just thought of, which is the difference between design for assembly, verse design for manufacturing verse design for production, because when you look up, kind of like a thesaurus, assembly, manufacturing and production, kinda all mean the same thing. But in the DF world, they mean, maybe not drastically different things, but they give you different focal points of what you should address in your products. So like for DFM, it's basically can you even build this device for the price that you want? Or at a time basically, the can you build it for the timeframe that you have your lead time? Whereas designed for production is can you build your device in the volume you want? Right, and then assembly is kind of a combination, I actually take the back from the manufacturing for retirement assemblies, more like the lead time stuff, I guess. But making sure that the system level all works. That's how I would explain it.
Host 1 17:21
I think it's also valid to bring your vendors in, if they're willing to listen to, you know, listen to your rant about this stuff for a while. I think it would be totally reasonable to say like, Hey, here's our design files. It's early on in production. Can you give us some DFA on this, especially if your vendor is going to be the one doing the A part of DFA Yes, right. Yeah. Cuz they might have some really great insight. In fact, DFM when it comes to a contract manufacturer, on the electronic side of things 90% of the DFM part is just making sure there's no like goofy hiccups that will just cause things to grind to a halt.
Host 2 18:04
It most of it is, is that part that you picked going to fit that footprint on the board? That's the majority of DFM.
Host 1 18:13
Right? Or, you know, did, did you somehow or somewhere put a 2000 hole via on a board or something, something that's just going to like, cause delays in process from something kind of dumb, you know?
Host 2 18:29
Yeah. Whereas DFA is, I guess more pertaining to the, it's funny, it's actually more than manufacturing process side, then the DFM actually is, which is like reflow temperatures, making sure all your parts are compliant. Like if you need lead free, and you got a a part that does not, can't survive lead free temperature reflow. That's a DFA problem. Because then you have to manually basically put that part on by hand. Or let's
Host 1 19:02
Say that I'm just pulling something random out here. Let's say that there's some requirement for a part that it must be washed. DFA might be like, Okay, well, now we know that one part must be washed, or all the other parts able to be washed.
Host 2 19:18
So DJ from chat says, I see DFM as using knowledge of the manufacturer assembly process to make your design cheaper, reliable, easier to make stuff like minimizing layer count, knowing where to replace SMT verse plated through hole, etc. That is part of it. Yes.
Host 1 19:35
See, I think there's another layer to it. In fact, there's there's a more basic layer on top of that, or I guess beneath that, all that knowledge that you're talking about DJ is the engineer side of being able to turn knobs and pull levers in order to control cost on a design and less of a pulling those same levers just to make sure that it even function A lot of times with DFM, it's can this board even be made?
Host 2 20:05
That actually you could say DJ, you created a new def design for being counter. We already have a DFC designed for conservation
Host 1 20:15
Designed to be inexpensive,
Host 2 20:18
Host 1 20:21
Yeah, well, you know, and that's just the thing, like, you can create any DF you want,
Host 2 20:28
Right? Like, you know, this is just focusing on a set of criteria
Host 1 20:32
Being well, above and beyond focusing, it's focusing, and then documenting, or at least somehow creating history that you did it and that you approved it, or didn't approve it one way or the other. And so design for cost. If that is a high criteria, then absolutely,
Host 2 20:50
Yeah. And it would be okay, you not tarnish. Okay, my board needs to cut my hardware needs to cost X dollars. So you'd lists all your bill material, you'd list out how much your boards are cost, and you go, okay, am I hitting my target? If not, let's go back and reduce our bomb, may we get away with going to a two layer board or four layer board? Or we can reduce the board size? That's what you do there? Instead of looking at Can I, you know, as my footprints Correct? You're not looking at your footprints or being correct in a design for inexpensive.
Host 1 21:27
Right. Right. Exactly. Unless for whatever reason, your footprints cause a design to be super large versus super small, or you know, but no, that could be part
Host 2 21:37
Of it not I remember ti web bench actually has that functionality where so ti web bench for people who don't know is a a online application at TI has that you basically give it your power supply parameters like your voltage in and then you give it your voltage out and how much current you want. And it will design using all the flavors of TI chips that has a design a switch your power supply, basically. And it actually does I really, everything I've built using that try bench works. And they will give you all the part numbers anyways, one of the criteria you can select is, is the total landing area have all the components that it is that that design requires. So you could read and also there's cost, you can sort by cost you can sort by, basically you give it priorities, you give it priorities. And so if you if you needed to reduce size, you because of board costs, you could you could certainly do that, and pick a different typography for your switcher that, you know, maybe won't require such a big inductor.
Host 1 22:55
So Casey ate a PDF in the chat mentions, matching your board house and assembler capabilities in terms of a design check, perhaps designed for manufacturing? And I think yeah, I think that's great. I think that's that's spot on. And in fact, say you were say you were doing a design for manufacturing, check with your engineering team. And let's just pretend you already have a board done, or you're most of the way done. And you had some really unique characteristics about this board, you know, small holes or extended capabilities or required a really thin traces or something like that. You could in that design for manufacturing check you, you could ask the question, do we really need that? If we really need that is? Sure. Great. Okay, we've all agreed we really need really laser drilled holes or something like that. Okay, well, then, then you can go and match that to your board house or your assembly capabilities and create a list of, hey, here are the people who say they can do this reliably. Or maybe you come to the conclusion that like, Oh, hey, there's really super uber made amazing ice that does everything under the sun. We don't actually need that I see. And that was driving the reason for that we need really small laser holes or something like that. Yeah,
Host 2 24:11
Like you can switch from a BGA package or LGA over to like a QFN package. And then, you know, get rid of having to have laser drills or blind bird vias and that kind of stuff. And
Host 1 24:26
That reduces the cost and it opens up your, which board houses you can get and which manufacturers are happy with you. And so, yeah, I think that's a really good point.
Host 2 24:36
That's one thing about looking at design for assembly and manufacturing is, you know, depending on how small your board has to be, you pick different packages, right? Like you don't like the cheapest chip components out there are the oh six size parts, like I Oh 603 Excuse me. So those are the typically the cheapest chip components out there for like resistors and capacitors. And so if you don't need to go smaller than that, because of layout concerns like, oh, 4202 or one or Oh 105 Don't, don't do it, because then you're just you're in your unnecessarily increasing the complexity and cost of your board, right? kind of went down that design for cost route a little bit more than the rest on this list. So the one I want to talk about a lot is this one that you came up with last week, designed for revision. Because this is kind of important with the current supply chain issues that the entire world is having right now.
Host 1 25:51
100%. So, one of the things about, and I kind of came up with this just it's sort of anecdotal was with a lot of stuff I do at work. Design for revision isn't something that you necessarily have in mind when you're creating a new design, because a lot of times the mentality of hey, I'm creating this new design, like the mentality, first time, perfect, right, right. And I don't know how many times I've heard like, goofy phrases that are like, Oh, you always have time to get it right. The second time, or, you know, like, I don't just just a lot of phrases, or just mentality of like, it is possible to get it right the first time. Of course, it's possible to get it right the first time, it has not been my experience that most people get it right the first time. It's not even my experience that most people get it right the second time, like you need revisions, and I'm talking about prototype provisions, I'm not even talking about revisions, after production has begun on this, I'm talking about, there's a new thing that you are trying to develop, it will go through revision processes, that's just inevitable. So when you're designing a revision, I think it is totally worthwhile to at least have in the back of your mind, this might be revised again. In fact, even if you're designing the last revision for initial production, there is a high likelihood that it will still get revised sometime in the future. So keeping that in mind, will actually alter some of the or can alter some of the design decisions that you make, depending on where you are in the design process. So I just wanted to call out a handful of tricks and tips that I've learned throughout the process, where I've made mistakes, not in not necessarily on the board itself, or the the revision itself, and mistakes I've made in terms of setting things up for being more difficult to find out that I need a new revision. So first of all, if you are developing a circuit that you are perhaps a little unsure of, or a circuit that you know, you're going to need to test, this one might seem simple, but it's amazing how often we make mistakes on this, put circuits that you're unsure of in a location on the board that you can actually access. And what I mean by that is with a with a a probe or a multimeter or your scope, somehow
Host 2 28:32
The big chunky
Host 1 28:33
Relay, or like, if if your system is an assembly of boards that all come together, try not to put the circuits that you need to test in a place where you have to solder wires into them just to get access to the signals you want. Put it on a side of the board that's just easily accessible. I've made that mistake before and it's it's a nightmare when you're doing development on it. Pretty simple, little Jack but I've certainly overlooked that. So the next thing on here is zero ohm resistors, zero ohm resistors are your friend when it comes to making revisions to boards. So don't be afraid to pepper your board with zero ohm resistors or, or pads that that you can configure with zero ohm resistors in order to change aspects of the circuitry. I feel like this might be a little bit more apply more to my style of things just because I do a lot of circuitry that even though I'm confident it will function I'm not confident someone will like it. My end product someone has to actually enjoy whereas like like my criteria is someone needs to be happy with it. Whereas a lot of other engineers criteria is it has to hit these targets and as long as it hits the These targets, it's done with mine. Some, like I said, somebody needs to be happy with it. So it's really helpful to have extra pads to be able to solder in resistors, or capacitors to change the function of the circuit. So I've learned to put zero ohm resistors in places, just in case I need them. Because I can always get rid of that later on. Yeah,
Host 2 30:23
And zero resistors are really good. You have here as make easy configuration changes. I'm using those on the tour, for example, for the sub, the voltage supply side for my 50 volt safety relay. Because the supply chain is so messed up on everything, including like electromechanical devices, like relays. And for my production runs, I can't I can't get a three volt 3.3 volt coil for everything. Well, I can get if I mix 3.3 volt five volt and 12 volt coils, I get my whole production run. And all I do all I did was I put zero jumpers on which coil voltage it's going to pull from. Right, right. So I basically saved saved my production run by making that simple change.
Host 1 31:20
Well and think about it, if you didn't have it set up as a configurable item like that, you'd have to have three individual active order revisions to be well and like what I mean, I mean activated because you could build anyone at any time, right? Yes. And that kind of makes it that's just way more to manage from the from every aspect. So having a configurable is really nice. I like
Host 2 31:47
KC eight some chats. suggestion is zero ohm resistors to allow swapping RX and TX when you make a route error. And your schematic happens all the time. Yeah, there's RX go to RX was RX go to Tx. I don't know that someone who designed the symbol in your EDA tool.
Host 1 32:05
Good point. Yeah, you don't know. Right? You know, I do a lot of comparative and analog logic on it. I'll put zero ohm jumpers to be able to reverse analog logic. In case I got it wrong if if something needs to go high as opposed to going low at a certain time. I'll just put zero jumpers so I can flip it around. And then at the end of the day, like I just mark whichever one is properly working and then put that in the final revision. I that saved my bacon before. But yeah, RX TX. That's That's because who hasn't put those on backwards? Right. Yeah, crickets, right. So okay, here's the next one. And this is for newcomers to engineering. I certainly, it's this is so simple, but I didn't know it until I saw it for the first time. DNI which is do not install. What that means is, it is perfectly acceptable to write a bill of materials. And to call out a part on your board and say don't put apart there. In other words, like, you can have a resistor or a capacitor and say just don't put the resistor capacitor, leave it unpopulated, leave no part in that place. This
Host 2 33:28
The thing about that is make sure you tell your CM, that is your intention to so if you have a component that doesn't like a on your board, that doesn't have a part se, C eight DNI or DNP. Like, make sure your CM knows that because what will happen is they go in, start loading up their their machines and go there's supposed to be a part there, right? I don't know, the customer didn't say anything about
Host 1 33:55
It. It gets confusing, right? You're confusing, you know, the easiest way to do that, at least in my experience is on your bill of materials. If it's a an Excel spreadsheet, and just include a column that says DNI question mark, and you just say yes or no. And that tells the CM really quickly. Yes, they intended a part to be there or No, they did not want a part to be there. Don't Don't let your CM guess on that, because they'll get wrong some of the time.
Host 2 34:23
Yeah, that's actually one of our data, data checks is backfat is, so we'll get a placement list. And then we'll also get the bill material list. And what we do is we take them, we take both of them and then match them together, make sure every placement has a bill of material entry and vice versa. And then
Host 1 34:42
You have even even a do not install, right?
Host 2 34:46
Yeah, so So the bill material should have to do not install list, but in the placement list should have every single placement on the board, right? Regardless if it's a DNI or whatever. And then she matched them up and you always get some entries that on the bottom that are don't have placements and some placements that don't have entries on the bomb. And then you, you have a nice little report to go, Hey, these are your discrepancies in your design. So that's actually a design for assembly step would be for you to basically do that yourself and figure out do you have any mismatches in your data?
Host 1 35:22
Right? So d&i, great, great example. Basically, any op amp I run, if I'm running, if I'm doing some kind of analog something or other, I will always include extra pads for the feedback path on that. So if I have a resistor in the feedback, I will always include an extra set of Oh 603, or something like that pads. In case in prototyping, I find I want to have some capacitance in the feedback path, I have pads for it to just install very simple. And I don't have to do something goofy, like piggyback a capacitor on top of resistor, it just makes development significantly easier. And if I find that I don't need a part on those pads, most of the time, I don't remove the pads. I leave them even for production. And they're just always DNI and that it, it doesn't lead to confusion. It makes things helpful in the future. Let's say something changes and we can't get whatever op amp we were using previously, we can only get this new flavor of op amp. But we find that that new flavor of op amp oscillates with the particular components. And we didn't intend that and it needs an extra 100. Pico farad. Well, I've got pads for that. You're good to go. So good go design for revision.
Host 2 36:46
Yeah. You know, and adding extra footprints. We just came up with a no def. Yeah. Designed for certification testing. Yeah, yeah, yeah, yeah, of having extra pads on, on, especially IO lines that are coming off your board to like cables and stuff for ferrite bead networks and that kind of stuff. And you can have them word, the pads just there. And then you know, the traces just Dart across the pads. And then if you actually in you, oh, I am too high a blob of all frequency, go in there, cut the trace, and saw the part tested again, make sure you pass if you pass, then you just make that layout change for production. That's I've done that before. ferrite beads for sure.
Host 1 37:33
That's another really great example of great places to plate, put zero ohm resistors, you put zero ohm resistors. And you can replace those with an inductor or ferrite bead or something like that, especially if they're in your power rail. Another great example there is if you have zero ohm resistors, right at the end of whatever your power supply is, you can depopulate that zero ohm resistors in salt, solder and wires. And now you have the ability to access your load with whatever meter. Whereas previously, you know, if you didn't have that there good luck and ain't happening right. You know, one other thing to keep in mind is I know there's a tendency when you're doing revisions, like oh, I can make this layout absolutely perfect. And if I use a two, a one or a four or two components, I can get really tight and all of these parts right up next to the parts and you feel really good about like how perfect your layout is. And then you get the board. And you know, and you find out you need to make changes. And it's a giant pain in the ass to D solder components. Keep in mind that if you ever have to D solder components and solder new ones on, it's helpful to think about that while you're laying out the board like, oh, is this a circuit that I know I'm going to potentially need to make some changes to Well, can I even get my soldering iron into this circuit?
Host 2 38:57
Yeah. So when you're doing your prototypes, you should definitely think about designed for prototyping and odf. Whereas can you actually modify your board easier, adding extra pads where you can you know, or test points that you can end up just like when you start moving more into production, where you can shrink all your parts together, you can remove test points, that kind of stuff.
Host 1 39:19
You know, and that brings up a good point. If you if you if you find out that your prototype needs some modifications, and you end up making those modifications, and then it works. worked fine. It if you find out that your prototype works fine, and it'll pass every test that you need it to, it may not even be necessary to redo the layout to make it more tight because you already found it works fine, right? Yeah. All I'm
Host 2 39:45
Saying is just from a, you know, you're prototyping and then you're you don't have to hit your form factor on the first prototype is what I'm getting at
Host 1 39:55
100%. Yeah, and simple, simple examples of getting your soldering iron Going into place like, say you have a T sub component. And next to you have a big inductor, it's not a great idea to put a really tiny component smashed in between those two, because how are you going to get a soldering iron Jaws down into that? Like, it's
Host 2 40:13
Not just that that's also a DFM slash DFA is, during reflow, you're going to create a heat shadow in there. And so that that little SOT 23 might not get reflowed
Host 1 40:28
Or worse and Oh 402 capacitor that's in between those? Yes, yes, yeah. Also, I, you know, I work pretty regularly with components that are pretty sensitive to hot air, they'll, they'll withstand a trip through the reflow oven. But if I need to reflow some components on the board with hot air, there's a good chance I'll melt some other components. That's also worth keeping in mind, if you have a component that's really sensitive to hot air will put it on its own little island, if possible, away from other parts. And that helps with repair ability to, there's certain designs I've made where I've made mistakes in that area. And if I ever have to reflow something near that other component, I know I just have to break is brought to buy and sometimes entities. So having multiple footprints is is really helpful. But also having parallel components helps at the same time. So say if, in fact, kind of that goes back to what we started this section with with right now is if parts are hard to get right now, hard to find. So if you know that you can have parallel footprints or parallel components that could both do the job but have different footprints. If you're, if you're design can handle that, put both footprints on there. And label one is DNI based off of what you need it what you can get. In fact, we have an example of like that, I have work right now where we have a product that it has two different footprints on it, and we can populate one or another codec that will both get the job done, they both function basically exactly the same way. But because things are so hard to get right now we have to pick one and build based off of what's available. One other thing too, that really is helpful, you'd be surprised at how often this will save your bacon is just put test points on your board. And a test point can be as simple as just an exposed pad that's dedicated to a test point, or dedicated to being a test point, that obviously you can put your probe down on an end termination of a resistor or capacitor or whatever. But a lot of times, having dedicated test points makes life a whole hell of a lot easier in terms of validating your revision. And so having dedicated test points, honestly, it'll make things go a little bit faster or good bit faster. And it may actually end up working out that when it comes to design for tests, you keep some of those test points, such that you can tell the operator Hey, put probe on test point one or, or whatever,
Host 2 43:15
Or you make a like a, a fixture that hits those test points. Bingo better nail style tester.
Host 1 43:23
I've certainly had some customers supply documents that are like, you know, put your probe on this side of our five and put this other one on that side of and I don't like that because you either have to memorize it. And then that's something you can forget. Or every single time you go to do that test, you have to have whatever PDF up and you know, shows all these pictures of like probe here and here and here. And that's
Host 2 43:47
Not just that, though is that's highly dependent on what solder paste, you're using to assemble those boards because there's the you're using a washable flux, sure, that should be perfectly fine. But if you're using any flux, that's a no clean that no clean flux is going to have a residue on that solder joint. And yet, they're never going to have a really good connection with a probe, you will have to scrape it off and hit that probe. Funny enough, like because I see this all the time because macro fab we have for our, our prototyping, we have jet printers, instead of stencils for our prototype level stuff. And that paste it's a special paste for those jet printers. And it's no clean flux is like a hard caramel shell when you look under it with a scope. It's actually amazing because it doesn't really leave residue except on the joint itself. It's really weird as we're no clean flux, but it leaves it like a Carmel shell and you can kind of like poke at it and like flake off like Yeah. What do you find if you pro Do afterwards but if you try to hit the probe on it, like without doing that it's
Host 1 45:05
The probe is not a reliable connection. Yeah, it's
Host 2 45:08
Not a reliable connection all.
Host 1 45:09
Also you don't you don't want your operator stabbing at the end terminations of really small components. And, you know, they'll twist it around and dig it in. Damage.
Host 2 45:19
Yeah, micro fracturing, especially ceramics. I would suspect that you could probably damage a, like a thin film resistor that way too.
Host 1 45:29
If you just have an exposed, you know, say one millimeter ring of each egg plated copper, that's really easy to hit. With, uh, with
Host 2 45:40
That. I know, we're, we're going way into this, like, this is almost like designed for it's designed for DEF CFT. Make sure those pads, you remove your solder paste. Yeah, don't put paste. Yeah, that's what Basil is bad. Because then you create the same problem.
Host 1 46:00
Right, right, exactly. But But, so kind of back to at the beginning of this one is saying, you know, when I was saying like, maybe you have a circuit that you're not 100% confident on. And the reason you're putting it on this board is because you're going to test it and find out. Don't be afraid if you have the area, put test points for as many nets as you feel comfortable with even test points for all the nets, right, and
Host 2 46:26
Going back to zero, you can isolate that circuit. And so you can build up so like you can just get your board and just build that one section, and then all and then just leave the zero ohms depopulated. And so you could just like feed that's that that part of the circuit a signal and see if you're getting your expected output before bringing everything else up. I know you like to do that with especially power supplies on like new designs. I've always been like, let it rip on power supply designs, I'm like, I test I trust ti workbench, I'm gonna power this thing up with a little little current limit, but I'm gonna power right up. Well, okay, so with,
Host 1 47:08
With switch mode power supplies, I love the ability to vary the load or determine the load, like I. So if you have a zero ohm that disconnects your power supply from the entire circuit, you now have access to that you can put an active load on it, and you can step your load and you can see the response of the power supply, like doing all of those tests. If you don't have the ability to disconnect a power supply on on your board like that, it makes it that much more difficult, or it just makes it guesswork at that point. So a simple three sent zero ohm resistor can be really helpful in a case. Yeah,
Host 2 47:49
DJ from chat says solid bridges and solid jumpers are a cool alternative to zero ohm resistors, which I don't fully agree especially from the manufacturer side. Because it's really hard to reliably put down let's just say it's just two pads. With no copper in between them, it's actually really hard to make that automatic in terms of like laying down pastes, because the pace will want to ball up and pull away from the solder mask it's in between you can put just a thin trace that you cut, of course in between there, but the only it might be a better way but the only way I can think of like reliably putting out a solder joint is to our solder bridge is to manually do it with solder and iron which might be fine for for prototyping but for relying on that for anything even production because now you're adding a manual step to put the solder joints down just doesn't seem to really work too well. I don't know what your experience is on Etsy
Host 1 48:56
You know actually I kind of have an I have an example of the opposite of of that in a way right now. I've got a product that is dc coupled in a particular portion of the circuit but there may be a situation that we want to AC couple it. So what I did was I put down Oh 805 pads down and then I put a small little connecting trace that kind of goes around the pads but I left enough room I've shorted the pads but I left enough room to put an exacto blade in there in case I want to cut the trace and then sawed our capacitor down I'm now AC coupled it
Host 2 49:30
I'm pretty I'm almost 100% certain we want to leave it dc coupled but I left myself the ability to AC couple E's what I was saying is you can have a little trace you can cut that's basically it Yeah, it's just relying on solder paste and a stencil and then that through reflow to actually like bridge. I actually the funny thing is solder on the solder paste actually really doesn't want to like create shorts that way Like solder resist is a really good name for that material because solder paste does not really stick to it or it's kind of like what's the name? Hydro is a hydro scopic when a material rejects water phobic, hydrophobic, right? It's hydrophilic. So solder resist is solder phobic.
Host 1 50:30
Also, I'm talking a little bit out of my butt here. But it in this situation, it doesn't matter too much, but not too much. But it's worth it is worth considering in case you are putting high current through this solder paste is not the best conductor out there. Copper is way better of a conductor than solder paste. And that's kind of one of the whole point of solder paste is that you're not relying on gobs and gobs of it to do the job for you.
Host 2 51:01
Gotcha. I wonder what the difference between like SAQ 305, and like s and 99? Because a conductivity would be I mentioned that SN nine nine is way better. Connectivity wise. Not sure. No, no, you're shaking your head. And I thought you knew that answer. And you're like, Ah, I thought better you Parker, you know that
Host 1 51:24
Will? Actually so. Gosh, what is it? I think Evie blog has a whole video about I'm pretty sure TV blog. Yeah, have you seen I saw the video where he added solder to like a trace to increase its capacity by reducing its resistance. And it doesn't actually do a great job of it. No, but it does reduce the resistance. It does, but not as much as you would think. Now as much it's like having a thicker, bigger, better design trace is actually better than just adding solder on top of a trace. Because the the conductivity of copper is significantly better than just solder on top.
Host 1 52:10
Yeah, so it's, it's worthwhile, even though like your boss probably would hate it, and the bean counters would hate it, it's worthwhile to consider that what you're designing now is maybe not going to be your last revision, and there will be something in the future. So it's worth considering, like my in my design decisions right now. might impact how much how many more revisions I have to do to get this right. So set yourself up for the best success with the the revision that you're doing. And sometimes that involves just adding a whole bunch of stuff that doesn't at first make sense. Or maybe it involves adding a whole bunch of extra things like Do not install pads or test pads or zero ohm resistors that you might not even end up using. But if you ever have to, you'll thank yourself the first time you put one of those down and need it.
Host 2 53:06
Yep, yep. Yeah. I think that's going to wrap up this podcast.
Host 1 53:11
I love it. Even with one topic we can still bang out 50 something minutes of Yeah.
Host 2 53:16
So next week is pretty sure it's gonna be the idea fab contest. On that contest. podcast. Yeah, I guess it kind of is a contest. It's like, one we're all trying to one up each other. Right? Yeah, it's all about one upping each other. So we're gonna have Scott and Eric. Eric from there not the idea further the idea tank idea tank podcast. Is that correct? I
Host 1 53:44
Think that's right. Yes. Idea tank.
Host 2 53:47
I didn't tank podcast we're gonna have them back on podcast for the third almost it's the third time ever but twice in two years. The gap between the first and second one was like two and a half years old like that. I'm hoping we can do this like an annual thing because it's a lot of fun. Basically, we come up with each of us comes up with an idea like a million dollar or billion dollar idea and we try to it's like Shark Tank except for stupid
Host 1 54:16
People. We market it to each other. Yeah market to each other.
Host 2 54:20
Well at least So Steven like Scott and Eric actually come up with like legit ideas that could be companies and then we come up with though you came up with your go away
Host 1 54:36
AI last year that would I bet you people would pay money for that. I really do. Yeah.
Host 2 54:41
So what we want to do is I'm gonna come up with an idea Stephens gonna come up with a a Scott's gonna come up with the end. Eric is going to come up with idea. We also want our community to come up with some ideas in our Slack channel or on Twitter or in Twitch chat because we're going to livestream it of course And I want to at the end of the podcast is pitch the community ideas to the group and see what we think about it.
Host 1 55:12
So I love it. I love the idea. So if you haven't heard the previous two podcasts, they were episode number 77 and episode 223. So there's a big gap right there. Yeah, like there's a lot of episodes in between there. So go back and listen to those other two. So you get an idea of what this third episode will be like. And then, on Tuesday, the 28th we will get the community's ideas and present them in the podcast. So yeah, if you have an idea, join up on our Slack channel.
Host 2 55:47
Backfat backfat.com/slack, or in there 6pm. central time at twitch.tv/macro. Fab. That's the live stream. Because we'll probably like have a running list of people just like posting ideas. And then we'll read from those at the end. Because it's gonna be a lot of fun. I this is one of my I always like doing collaborative podcasts. Not that you're not great, Steven. All the time, but it's always fun to mix it
Host 1 56:20
Up. Yo, yeah, yeah, it's it's these ones are these ones are fun. Yeah. I've already been coming up with ideas for teaming. Oh, scheming real hard. I've got some I've got some concepts I'm working on right now.
Host 2 56:37
So that was the macro engineering podcast where your host Sparky Dolman
Host 1 56:41
And Steven Craig. Later everyone. Take it easy.
Transcribed by https://otter.ai