CB FI 434

Circuit Break Podcast #434

The Other VCC

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June 7, 2024, Episode #434

In this episode, Parker and Stephen dive into the intricacies of capacitor selection, discussing various types of capacitors, their properties, and how different factors affect their performance. They also touch on the new custom bare PCB service offered by MacroFab. The episode is rich with technical details, tips for selecting capacitors, and practical advice for engineers.

Key Discussion Points

  • Introduction to the new custom bare PCB service by MacroFab
  • Detailed explanation of capacitor types: Class 1 and Class 2
  • Importance of voltage coefficient of capacitance (VCC)
  • Challenges in selecting capacitors for different applications
  • Comparison between different capacitor sizes and their effects
  • Tips for avoiding edge cases in capacitor selection
  • Explanation of how barium titanate affects capacitor performance
  • Murata's Sim Surfing tool for capacitor data
  • Impact of capacitor choice on manufacturing and performance
  • Best practices for selecting capacitors in design projects

Relevant Links

Community Questions

  • What are your thoughts on the voltage coefficient of capacitance (VCC) and its impact on capacitor selection?
  • How do you handle the challenges of selecting capacitors for your projects?
  • Have you used Murata's Sim Surfing tool for capacitor data? If so, how has it helped you?

MacroFab

This show is brought to you by [MacroFab](https://macrofab.com/], which provides a platform for electronics manufacturing services (EMS), hardware development, designing and prototyping for individuals, startups, and businesses. Key MacroFab services include PCB (Printed Circuit Board) fabrication, assembly, and testing. Customers can use MacroFab's platform to upload their PCB designs, select components, and specify manufacturing requirements.

We Want to Hear From You!

Subscribe to Circuit Break wherever you get your podcasts! And join our online discussion hub at forum.macrofab.com to keep the conversation going with electrical engineering experts and experimenters! You can also email us at podcast@macrofab.com.

Capacitor Comparison - Voltage Coefficient

Capacitor Comparison - Voltage Coefficient

About the Hosts

Parker Dillmann
  Parker Dillmann

Parker is an Electrical Engineer with backgrounds in Embedded System Design and Digital Signal Processing. He got his start in 2005 by hacking Nintendo consoles into portable gaming units. The following year he designed and produced an Atari 2600 video mod to allow the Atari to display a crisp, RF fuzz free picture on newer TVs. Over a thousand Atari video mods where produced by Parker from 2006 to 2011 and the mod is still made by other enthusiasts in the Atari community.

In 2006, Parker enrolled at The University of Texas at Austin as a Petroleum Engineer. After realizing electronics was his passion he switched majors in 2007 to Electrical and Computer Engineering. Following his previous background in making the Atari 2600 video mod, Parker decided to take more board layout classes and circuit design classes. Other areas of study include robotics, microcontroller theory and design, FPGA development with VHDL and Verilog, and image and signal processing with DSPs. In 2010, Parker won a Ti sponsored Launchpad programming and design contest that was held by the IEEE CS chapter at the University. Parker graduated with a BS in Electrical and Computer Engineering in the Spring of 2012.

In the Summer of 2012, Parker was hired on as an Electrical Engineer at Dynamic Perception to design and prototype new electronic products. Here, Parker learned about full product development cycles and honed his board layout skills. Seeing the difficulties in managing operations and FCC/CE compliance testing, Parker thought there had to be a better way for small electronic companies to get their product out in customer's hands.

Parker also runs the blog, longhornengineer.com, where he posts his personal projects, technical guides, and appnotes about board layout design and components.

Stephen Kraig
  Stephen Kraig

Stephen Kraig is a component engineer working in the aerospace industry. He has applied his electrical engineering knowledge in a variety of contexts previously, including oil and gas, contract manufacturing, audio electronic repair, and synthesizer design. A graduate of Texas A&M, Stephen has lived his adult life in the Houston, TX, and Denver, CO, areas.

Stephen has never said no to a project. From building guitar amps (starting when he was 17) to designing and building his own CNC table to fine-tuning the mineral composition of the water he uses to brew beer, he thrives on testing, experimentation, and problem-solving. Tune into the podcast to learn more about the wacky stuff Stephen gets up to.

Transcript

Parker Dillmann
Welcome to circuit break from MacroFab, a weekly podcast about all things engineering, DIY projects, manufacturing, industry news, and choosing capacitors. We're your hosts, electrical engineers, Parker Dillmann.

Stephen Kraig
And Stephen Kraig.

Parker Dillmann
This is episode 434. And before we jump into the podcast, we have a macro fab announcement or an update so to speak. We now offer bare slash unpopulated PCBs. So forever we've always done PCB assembly and we've kind of shied away from just supplying bare boards to customers but we've had enough customers essentially request for them to able to buy bare PCBs and so to explain more about that I have Kyle from product to talk about that.

Kyle McLeod
We're really excited to offer bare PCBs to our customers. This is something our customers have been asking for. And we found that we have a really, good position to offer, high quality boards, boards with a lot of custom specs, engineering support on getting your boards manufactured and really, our goal is to give you the opportunity to, you know, order a board that you are confident in when you're doing your prototyping, that the board you get is gonna be, is gonna work, is gonna be usable when you go to add your components to it and then you're not gonna have to start over or spend a lot of time questioning and did you make a a mistake or is there something wrong with the board that the manufacturer didn't capture. So we think we have really good, high quality boards. We have lots of custom specs.

Kyle McLeod
And really, I think the most exciting thing is is that when you go to scale to production or if you're in production and you wanna iterate on your design, we have made it really easy in the platform to switch between a bare PCB and your PCB with components. So, if you've uploaded your PCB and you've added your bill of materials, you don't have to go and create a different PCB to order the bare boards. You can just turn off the components for your order and we'll let you order that bare board. When you want to view the components again, you turn them back on and all your bill bill of materials, all your placement data is still there. And so you can work, on your on your designs, keep keep your designs intact without having to maintain a separate bare PCB file and a, assembled PCB file.

Kyle McLeod
And we think that's gonna make it really easy for our customers. Another thing, by having all of the same offerings from our specs and from our manufacturers. We allow our customers to easy transition easily transition from prototype to production because you don't have to upload new files, you don't have to wonder, you know, if if you were to do a prototype with 1 shop and then shift to somebody else, you know, they're gonna have different requirements. And so, by doing everything with Macrofab, you can keep all of your your data, with the same person. We make it really easy to add those components on and order your assemble boards, once you're ready for production.

Kyle McLeod
So, yeah. Bare PCBs is something we're we've been very excited about. We think it's a really nice, smooth feature for prototyping and for for iterating on your your production products as well.

Parker Dillmann
So, yeah. Check out our new custom PCB service on our website atmacrofab.com/customhyphen PCBs and take your projects to the next level. Whether you're prototyping or ready for production, MacReb has you covered. Okay. Let's jump into this capacitor selection topic, Steven.

Parker Dillmann
What what is this about?

Stephen Kraig
You know, it's at work. We've been talking about this recently. Just the idea of how do you pick a capacitor. Like you go to digi key, you go to mouser, you go anywhere And as a designer, you know you need a particular value. You know some of the other parameters you need.

Stephen Kraig
But how do you go about actually selecting a an appropriate capacitor? And it ends up being quite a bigger thing than you think. There's every decision you make flows downstream to all the people that have to deal with your decision. And I like framing it that way because, you know, we as electrical engineers, a lot of times can get pigeonholed in our thinking of I found this perfect thing that works for me, and this is it. That's it.

Stephen Kraig
It's done. I as long as I just put it on my bill of materials, put on my schematic, my work is done, wash my hands. But there's so much more to it, you know, when it comes to purchasing, when it comes to actually getting it, when it comes to putting it on the board, when it comes to validating it. There's so much more to that. So I wanted to touch on a handful of topics with that and maybe bring up some stuff that that we haven't really spoken about before.

Stephen Kraig
Way back when I don't actually, I don't remember the date, but but on episode 141, so many episodes ago, we had James Lewis, otherwise known as the Bald Engineer, come on. The episode was called It Depends, an in-depth look at MLCCs with James Lewis, where we were talking about some similar concepts of what we're mentioning today with selecting capacitors. James Lewis has some experience working with KEMET in the past, and and he really brought some really cool information about how capacitors are made and a lot of other good information, and I wanna kinda jump off that today since we haven't talked about this in a while. So first of all, capacitors kind of come in in fact, let let me stop by saying capacitors come in a ton of different varieties. Today, I just wanna talk about MLCCs, multilayer ceramic capacitors.

Stephen Kraig
And that's your, like, bog standard tan looking capacitor that you see on a bazillion different boards. There are so many other variants of how capacitors are made that we're not going to be covering today. Really wanna just look at MLCCs. Now MLCCs come in 2 different classes, class 1 and class 2. Class 1 is your COGNPO dielectric capacitor.

Stephen Kraig
So that should be TEMCO that they, that is part of the material that they're made of, which is calcium zirconium oxide. The pros of class 1 capacitors is that they have really good temperature stability. They have really good aging effects, and they basically are very stable capacitors. The cons to these is that they typically have a limited capacitance range. You're not really gonna get high capacitance values in a class one capacitor, and they tend to also be in the smaller size range.

Stephen Kraig
So, you know, if you're looking for a 100 microfarad 1210 capacitor, just pretty much forget class 1 and forget the benefits you get from having, a good dielectric and a stable capacitor. You you're pretty much relegated to class 2. Class 2 caps are made

Parker Dillmann
of They are also more expensive typically.

Stephen Kraig
Typically. Correct. Typically. Class 2 capacitors are made of barium titanate, and that's the bulk of your capacitors. The x seven r, the y five v's, the just the generic capacitor that you find everywhere is almost guaranteed to be a class 2 capacitor.

Stephen Kraig
So the one the main topic that I actually wanted to kind of break into today was something that was mentioned back in episode 141 but not really expanded upon, and that is the voltage coefficient of capacitance. So it may not it's interesting because this topic is something that isn't called out on datasheets and it doesn't even have a standard way of determining it. But class 2 MLCC capacitors have a voltage dependence to their capacitance, which I find somewhat interesting that it's that this characteristic of capacitors are is not on data sheets. It's not called out. It's not defined.

Stephen Kraig
But if you know it exists, you know it exists. This this kind of stuff that actually gets to me when it comes to new people getting into electronics because I remember when I was first learning electronics, capacitors, like, after I finally got a grip on what a resistor actually is, I'm like, okay. Let's look at this next category. And it was capacitors, and it's like, oh my god. Like, you you 10 x the parameters that I have to care about now, and I have no idea what any of them are.

Stephen Kraig
And without even being told, like, the data sheet doesn't even mention it, the actual parameter that you care the most about, the capacitance, is a function of the voltage that you apply across them, which is mind boggling, but it's something that you have to keep in mind. So in in research for this, I actually was not aware of this, but there is a body called the Electronics Industries Alliance, the EIA. And this is one of the bodies that sets the names of the parameters of everything that goes into a datasheet. I shouldn't say everything, but, a a good chunk of them. So when you say, like, capacitance or whatnot, it's defined, like, this is one of the bodies that says, here's what capacitance is and capacitor should or a capacitor datasheet should include that.

Stephen Kraig
And it's interesting because this voltage coefficient of capacitance just is not part of the EIA whatsoever. So this can really catch newcomers. And in fact, I I think there's plenty of people who are well past being a newcomer who probably are not aware of this just because you don't know about it unless you know about it.

Parker Dillmann
Yeah. And the thing that this would affect the most is, like, on feedback circuits.

Stephen Kraig
This is yes. This this can affect virtually everything.

Parker Dillmann
It affects everything that you

Stephen Kraig
Timing circuits. If you are trying to couple an AC signal from one part of your circuit to another part of the circuit, this can add distortion. There's so many different things that you know, this one if you weren't aware of this and your circuit started acting strange, it could take you forever to figure out what this is. So Mhmm. Let's let's let's sort of define it.

Stephen Kraig
So voltage coefficient of capacitance. Basically, if you apply a DC bias to a capacitor, its capacitance value actually changes. And changes as in decreases, not always. There are some situations where it actually increases, but for the most part, it is a decrease, and it can be a significant decrease. We're not talking about, you know, 1, 2%.

Stephen Kraig
In some cases, it can be 85%, 90% across the voltage range of a capacitor. So that lovely little 1 microfarad you got and you that you think is 1 microfarad in your circuit, if you apply, you know, a particular voltage across it, it could be acting like something significantly less if you're not aware of this. It has different effects at DC and AC as well. And so even if you have combination of DC and AC, it has different effects. For the most part, though, any data you find will show, what happens across, with a DC bias on there.

Stephen Kraig
Something that's also interesting to note is when you look up a data sheet for a capacitor, the you will be provided with a capacitance value. You should also be provided that datasheet should include the test conditions at which they determined that capacitance. So because if you are trying to replicate that or if you are trying to test a capacitor yourself, if you test at different parameters, like a like testing at a different frequency or testing with a different DC bias with whatever LCR meter you're using, you very likely will get a different value. So that's important to keep in mind if you ever do need to test capacitors. If you're comparing what you're monitoring or measuring, you or if if you're looking at it to validate something on a datasheet, make sure you're using the exact same test conditions exactly because of this voltage coefficient of capacitance.

Parker Dillmann
Yeah. My experience with those testers is they use a low voltage, and that might be because or maybe not because of this, but it helps them more accurately represent the capacitance that because of the the that that it's almost like a negative coefficient, basically.

Stephen Kraig
Yeah. Effectively, it is. If you zoom in on the the charts at DC values that are really close to 0, it can actually increase in capacitance. And it's important to note that, you know, we were talking about class 1 and class 2 capacitors earlier. This voltage coefficient of capacitance only applies to class 2 capacitors.

Stephen Kraig
So your x seven r's, your x five r's, all of those type of capacitors. It only applies to those. It does not apply to class one caps. And here's the thing, it applies to them because this is a material process. This or not a material.

Stephen Kraig
This is due to the material that that they're made of. So, I mentioned earlier that class 2 capacitors are made of barium tight, titanate. In my research, I found some really cool stuff about this. So, when capacitors are made, I think James Lewis even went through this. In fact, yeah.

Stephen Kraig
He he did back in episode 141, because he was asking us questions about how long does it take to make a capacitor, which if I remember right, it was 2 weeks.

Parker Dillmann
Something like that.

Stephen Kraig
I think it was 14 days, something like that. Regardless, there's a kilming operation where they have to heat and cool the capacitors, where they're basically drying out the ceramic material and solidifying it.

Parker Dillmann
Yeah. They're making capacitor brownies.

Stephen Kraig
Exactly. So when the capacitors are hot, the crystal and structure of the barium titanate forms what's called a cubic crystal. So basically, like a diamond shape. And barium titanate has barium, oxygen, and titanium in it. Above the curie temperature of the material the the titanium atom actually sits at the dead center of that diamond lattice shape.

Stephen Kraig
And because of that actually, let me let me let me move on to the what happens when it when the temperature goes below the curie temperature. The crystal and structure actually morphs slightly. So as the capacitor cools, the crystal forms a different shape which is actually called a tetragonal crystal. So, think of taking that diamond shape and stretching it out a little bit. And the interesting thing about it is during that process when it's going from the cubic crystal to a tetragonal crystal, that titanium atom that's at the center of the diamond displaces and moves ever so slightly.

Stephen Kraig
And that actually causes the crystal lattice in the capacitor to become unbalanced, and it forms an electric field within the the crystal and structure. Now as it's cooling and annealing effectively, you get a bunch of grain boundaries and and areas with that all cancel each other out. So, yes, you have individual e fields, but they all cancel each other out. But perhaps you can see where I'm going with this. That all occurs or happens when the capacitor is effectively at 0 volts.

Stephen Kraig
But now you have all of these dipoles created inside of this crystalline lattice. So once you start applying an external e field, which it's not external because we're talking about the actual you're applying a voltage to the plates, you're adding an e field inside the crystal and lattice. Now the individual dipoles of every crystal within there start fighting against the DC bias that you're applying to it, and that actually reduces the capacitance, because now your electric field is being modified by every single dipole within there. So it's fascinating that just the slight movement of a titanium atom as the crystal cools is what is the cause of this voltage coefficient of capacitance. Because you're literally setting up a whole bunch of tiny e fields that resist when you're applying an e field.

Parker Dillmann
Didn't a couple podcast episodes ago, we talked about barium titanite.

Stephen Kraig
I I would not be surprised if that's used in the production of many other components.

Parker Dillmann
Well, it was with capacitors. It was when was this?

Stephen Kraig
Oh, was this that

Parker Dillmann
It's like the new capacitors That

Stephen Kraig
was that that battery. Right?

Parker Dillmann
Yeah. It's it's a new capacitor to help offload charging cycles off batteries. Mhmm. Yeah. And that was they were using barium basically, it's the same stuff, but I think they fixed they were able to, like, fix something with the structure.

Parker Dillmann
I wonder if that's what it was.

Stephen Kraig
Okay. So I have done a bit of research on it seems like most people or most manufacturers of MLCCs use barium titanate as the the the fundamental ceramic. But everyone has their own 11 herbs and spices that they that they dope it with basically in order to adjust the parameters based off of your capacitor, whatever you're looking for. And so maybe there's a slightly different formula that they used for whatever that charging capacitor was.

Parker Dillmann
Yeah. They're saying that it's they're basically modifying the 3 d structure of it, and then they're sandwiching it between 2 others materials, which might be your the 11 herbs and spices

Stephen Kraig
Exactly. And And maybe those extra little dopants reduce this effect or change it in whatever way.

Parker Dillmann
But that now it makes more sense when we're about that article. That was episode 431, so it was Oh,

Stephen Kraig
that was just a few weeks ago. Yeah.

Parker Dillmann
It was a month ago at this point. That's why I was, like, I remember titanate because I couldn't pronounce it. Yeah. And so, yeah, that that's so I was wondering why because I saw a bit of titanate. I'm like, oh, that was I know this is in capacitors.

Parker Dillmann
We talked about this a month ago. And so they must have those researchers must have been able to fix that problem, or they're using it in a different way.

Stephen Kraig
Here's the here's the thing. Because because capacitors are so inexpensive and they're so prolific, they're everywhere, that just makes me think that barium titanate is probably not that expensive. Because for the most part with manufacturing, everyone's going to standardize on the cheap thing that just works. Right? Mhmm.

Stephen Kraig
So so I wouldn't be surprised if there are methods to fix or or correct or or maybe modify this voltage coefficient of capacitance, but it may be expensive. The additive that you add in there may, you know, blow the blow the lid off of how expensive capacitors are. I don't know. We'll we'll see. Because because if that's the case, then start throwing this into everything and now your class 2 capacitors all become class ones and Mhmm.

Stephen Kraig
I mean, not necessarily. Regardless. So so yeah. To kinda get back to where, you know, we're we're talking about selecting capacitors and now we've gone off under this voltage coefficient of capacitance thing. The whole point of bringing this up is that this is something that doesn't necessarily isn't necessarily in your head when you go to Digi Key and click point 1 capacitor 50 volt 0 805.

Stephen Kraig
Right? And you're like, oh, cool. I I get it.

Parker Dillmann
Sort by cheapest. Right.

Stephen Kraig
If it if it's COVID, sort by most available. Right?

Parker Dillmann
Yeah. Yeah.

Stephen Kraig
2018 was dark times. It was rough. It was real rough.

Parker Dillmann
That was the capacitor shortage era. Yeah. That COVID was the active components shortage. Yeah.

Stephen Kraig
So I wanna bring up I wanna bring up something from Murata that is pretty cool. If somebody hasn't seen this before, it's called sim surfing, s I m surfing. Murata has a database of all of their components or all of I guess, all of their components. I've I've mostly only looked at capacitors. But in this database, it provides you with much more information than what you get out of just the data sheets.

Stephen Kraig
So on sim surfing, you can actually get the curves that show this voltage coefficient of capacitance. And so I I had some fun earlier today. I went and grabbed 2 Murata capacitors. 2 with all exactly the same parameters except one was an 0805 size and one was an 0402 size. And so if you're just an engineer going out to pick a cap and just you you you select all the parameters the same, What's what's the difference between an 0805 and an 0402 other than the fact that one's bigger than the other.

Stephen Kraig
Right?

Parker Dillmann
Yeah. One's twice as big.

Stephen Kraig
So, you know, obviously, this is a podcast. Our listeners won't be able to see this, but I actually in in our show notes, I posted 2 graphs that show the voltage coefficient of capacitance for both this 0805 and this 0402. And across 0 to 50 volts, the 0805 has a reduction in in capacitance of about 40%. And in comparison, across a voltage of 0 to 50 volts on the 0402, it has a change of capacitance close to 90%. So all parameters, exactly the same, dielectric.

Stephen Kraig
They're even made of the same material, just different size capacitor has a huge impact on the voltage coefficient of capacitance. And that's not something like, I keep saying this. You're not gonna find that in the datasheet. You just have to know it, it, or you have to listen to circuit break and you'll you'll learn.

Parker Dillmann
Right? Yeah. You have to be a breaker.

Stephen Kraig
You have to be a breaker. That's so so and a lot of this is what's got me thinking more recently about talking with my team at work about how do you pick a capacitor? How do you pick how do you know when to say 0 805 versus 0402 versus 0603? Because right now, I could go to Digi Key, and I could find capacitors with the exact same parameters in 10 different sizes. Which one do I pick?

Stephen Kraig
You know, I've been designing boards for over a decade now. I like 0 4 0 twos. They tend to work with the ICs that I play with. They're small enough that they fit the pitches of a lot of the ICs I I go with. But size isn't just everything.

Stephen Kraig
Right? And this is one really great example of that where, yeah, you could be picking a pass a capacitor and you could be completely screwing yourself over by doing that.

Parker Dillmann
Yeah. It's I don't know if you're gonna get to this, but, well, I I typically do too because I use, you know, 0 42s for bypass capacitors a lot.

Stephen Kraig
Mhmm.

Parker Dillmann
0.1 microfarad bypass capacitors. What I'll do is I'll pick a much higher voltage so my, like, my rail will be 3.3 volts and I won't pick a 6 volt capacitor. I'll pick, like, a 16 volts because I know that that curve, I'm gonna be in the better part of the coefficient curve, so to speak.

Stephen Kraig
That's that's that's a good way of handling it. Yeah.

Parker Dillmann
And I I actually I learned that on the episode with James Lewis, episode of 41, 141. So that sounds like,

Stephen Kraig
oh, you you basically prederate your design.

Parker Dillmann
Yes. You have to prederate just because of the voltage ratings on these capacitors or if you can swing the price and like, 0.1 microfarads is a very small value, and so you can probably get a class 1 that's in an 042 that fits that.

Stephen Kraig
Yeah. Maybe. Maybe. Class class ones, they they I bet you could. It's been a while since I've looked for a class 1.1 microfarad, but that's starting to get to the point the upper limit of what class 1 caps can handle.

Stephen Kraig
So this voltage coefficient of capacitance, it is obviously material dependent. Right? It's barium titanate, but it is also dependent on your capacitive plate spacing. So let's take a second and just think about what's inside of a capacitor. Yeah.

Stephen Kraig
I mean, it is a it's a brick of ceramic, right, with a bunch of plates inside. In fact, if you see, like, a cross section of a capacitor, it's surprisingly similar to the drawings you had in your textbooks. Right? It's literally just plates next to each other with ceramic dielectric in between them. Nothing particularly special.

Stephen Kraig
So let's think about the knobs that you can turn to adjust parameters on a capacitor. Let's just play with an 0402 in our mind real quick. Let's say I'm a capacitor manufacturer and I've got an 0402 that I wanna design and it's a, let's say, it's a point 1 microfarad. And so I design it up and blah blah blah. And then marketing comes down and was like, oh, no.

Stephen Kraig
That was supposed to be a 1 microfarad capacitor. What are the knobs that I have to turn in order to make my design go from 1 to sorry, 0.1 to 1 farad, I can add more plates into the capacitor. Right? Or I can get the plates closer to each other.

Parker Dillmann
I'm gonna derail you a little bit. Yeah. But you are right. So I'm why am I why am I on Digi Key what's dotbe Belgium? I don't know.

Parker Dillmann
Why am I on Digi Key's Belgium? Yeah. It is Belgium. Why am I on Digi Key Anyways, I'm on the Belgium Digi website.

Stephen Kraig
Yeah. Finding a class 1.1.

Parker Dillmann
A class 1.1 microfarad, the smallest size is apparently o seven 4, which I've never heard of that, but 1206.

Stephen Kraig
Yeah. Right. So if you want What's o

Parker Dillmann
seven zero four?

Stephen Kraig
Isn't that like a military designation? I think it might be.

Parker Dillmann
I'm looking. I've never heard of it before.

Stephen Kraig
Yeah.

Parker Dillmann
Like, keep going. Sorry.

Stephen Kraig
But but yeah. So that's a good point. A quick tangent real quick. Class 1 capacitors with NPO, COG, dielectric, or tempco is you you're limited to the high picofarad range. You're you're not gonna get much past the nanofarads range without getting, you know, a 1206.

Stephen Kraig
And then at that point, you know, if if your circuit can handle it, great.

Parker Dillmann
But They're expensive too.

Stephen Kraig
They're they're expensive. Class 1 is usually your low value stuff.

Parker Dillmann
Yeah. When I'm building a board or designing a circuit, I'll use a class one for, like, my loading capacitors on my oscillators, like, my crystal oscillators.

Stephen Kraig
Oh, yeah.

Parker Dillmann
Because those are also they're, like, 0.0047 picofarad or something like that. I can't remember on top of my head.

Stephen Kraig
Well and and what's funny is at a certain point, it's actually hard to not get a class 1 capacitor. Yes. Like, at a certain point, they just all are class 1. So Yeah. I shouldn't say all, but

Parker Dillmann
it's 27 picofarads or something like that. Right. Depends on the capacitor in the circuit, of course. But

Stephen Kraig
Yeah. Okay. So so so back to the back to that little game we're playing. If I if I'm making an 0402, if I want to up the capacitance, so I say I'm the designer of the actual capacitor, I can add more plates to a capacitor, or I can get the plates closer to each other. I really can't change the size of the plates too much because I'm fixed to my 0402 size.

Stephen Kraig
Right? If you think about it, those actions that I'm talking about, adding more plates or getting them closer together end up being the same or having the same result. And if my voltage coefficient of capacitance is highly dependent upon your capacitor spacing, then just by upping that capacitance via those options that I've given, I've actually made my voltage coefficient of capacitance even worse. So something to keep in mind when selecting a capacitor, if you have a given package size, say, 0402, if you're looking at capacitances on the high end so, basically, take your little you the slider on Digi Key or the filter slider. Look at the far extreme side where it has the highest values.

Stephen Kraig
Those are gonna have your worst voltage coefficient of capacitance. And then you have to weigh, do I pick an 0402 or do I pick whatever size that has a terrible VCC or do I just bump up in size? Because if you think about it, like, the next knob, in terms of me being a manufacturer of the next knob I would have would be making my plates bigger. If I make my plates bigger on my capacitor, then I don't have to get them closer together. I can get a better VCC by just upping the size of my capacitor.

Stephen Kraig
So just like those charts I showed where I have an 0402 and 0805, it's proof of this showing that the 0805 has a much lower VCC than the 0402. Because on in the 0402 to get the same capacitance density, they have to shove more plates closer together, which leads to a worse VCC.

Parker Dillmann
I gonna bet you that's because with the plates being closer together and more of those plates probably, you have more the effect of that titanium atom shifting around.

Stephen Kraig
I think so,

Parker Dillmann
like, those interactions between the charge and those atoms are closer together.

Stephen Kraig
You also have a higher density of the e field in a more localized area. So the effect that each individual e field from the crystalline lattice gets compounded. Mhmm. So if you want a lower VCC, pick a larger capacitor for the a larger sized capacitor for the same capacitance value. What's interesting is kind of rule of thumb here actually applies to almost all the parameters on a capacitor.

Stephen Kraig
If you think about it, getting the plates closer together will actually reduce your voltage rating on the capacitor because now you have less of an of a jump for things to arc across or for, the dielectric to break down. So capacitors with a higher capacitance value in a smaller package will inherently have a lower maximum voltage range unless those 11 herbs and spices help out. There's always exceptions to all of these rules that, manufacturers have come up with. But in we're talking about, like, generic capacitors here.

Parker Dillmann
Yeah. I'm looking at this this chart between this 0 805. So the worst case for that 0805 is negative 40%. If you basically applied like let's say negative 40% was like the worst you could suffer that actually makes that 042 capacitor actually only really be a 16 volt capacitor instead of 50 volt.

Stephen Kraig
Right. Right. Yeah. And in fact, the 0 805 at at 10 volt DC applied is almost still the same value. Yeah.

Stephen Kraig
Maybe there is some kind of rule of thumb where it's like if you apply 1 fifth of the voltage, then you're within some reason. I don't know. I don't I'm not sure about that, but it is kind of interesting that that sim surfing website that's the the it's made by Murata. It's it's sort you only find Murata parts on it, but you can get all of this data and you can see all of this data and you can get, printouts of every single capacitor you have. So if you really want to fine tune your circuit and know every little thing about it, they have all of their charts on there.

Parker Dillmann
Yeah. My rule of thumb is I just I I guess I've never really used ceramics and high voltage high voltage. I'm doing quotes, like, over 24 volts. I always pick, like, a 16 volt capacitor and whatever size is working on my board for, like, a 3.3 or 5 volt rail. That way I know I'm in the better part of these curves.

Stephen Kraig
Yeah. Yeah. You're in the the closer to 0 part. Yeah. Yeah.

Stephen Kraig
So

Parker Dillmann
50 volts seems like a lot for, like, a point 1 microfarad part.

Stephen Kraig
It is. It is. But I just picked

Parker Dillmann
a voltage fan.

Stephen Kraig
Yeah. But but yeah. I mean, you could run this exercise with basically anything.

Parker Dillmann
Mhmm.

Stephen Kraig
Now this this brings up another point that we hammered home in episode 141, but I wanna I wanna talk about it again. And it was do not pick the extremes or avoid the extremes. So, say, you you're going to find an 0603 extremes. So, say, you you're going to find an 0603 cap, and you have voltages from 6.3 volts all the way up to 500. Don't pick 6.3 and don't pick 500.

Stephen Kraig
What I mean by that is you have the extremes that the manufacturers say they can manufacture all the way across. If you pick something that's on the edge of them, first of all, it becomes more difficult to manufacture those parts typically at the edges of the parameters. And if that part ever goes obsolete, the chance that you would find a substitute for that becomes that much more difficult. That actually kind of plays into what I was saying earlier, like, the decisions you make flow downstream to everyone else. So your purchasing department or your contract manufacturer is gonna get kinda grumpy if you pick an 0201 1000 volt capacitor and they have to match those parameters.

Stephen Kraig
I don't even think that exists, but you get where I'm going with that.

Parker Dillmann
Right? Yeah. I I wonder the these those edge case capacitors. I would love to see the VCC curve on, like, you said the 6.3 volt capacitor because it might just be, like, flat. Right?

Parker Dillmann
It could be really

Stephen Kraig
good. Yeah.

Parker Dillmann
Yeah. It could just be they bend up that part can be, you know, really good, and we just don't know about it because we have to go in a sim surfer

Stephen Kraig
and check it out. I'm actually on it right now.

Parker Dillmann
But I actually only pick parts that I can get that curve from. Oh. Well, I just like I reward the manufacturer that's putting forth the effort

Stephen Kraig
I Like that that's a good way of putting it So

Parker Dillmann
because I think it's a very important value that you know, this is also something that should be taught in school too because this was not taught to me in school at all.

Stephen Kraig
Well, no. I mean, the thing that was taught to me in school was capacitance value. That's it.

Parker Dillmann
Yeah. That's it. And then we had voltage as well, but that was it.

Stephen Kraig
Yeah. I don't even remember if I had voltage. Okay. I'm looking at okay. So this is somewhat of a ridiculous capacitor.

Stephen Kraig
I'm looking at a 6.3 volt. It's a 1206, so it's a pretty big one, but the the cap value is 220 microfarads. So it is a gigantic cap. And across 6.3 volts, it drops 80% capacitance. Oh.

Stephen Kraig
Yeah. But

Parker Dillmann
So you could use that

Stephen Kraig
at, like, 1 volt? Yeah. Or just be okay with the fact that you're gonna have a serious

Parker Dillmann
But I'll put this way is, you know, you're getting what? You're at a 220 microfarads, you're getting 44 usable microfarads out of that capacitor. So if you've calculated your feedback loop on your op amp, right, to and you're like oh, yeah, I need 220 microfarads, and oh, let me go pick this capacitor. It's actually gonna be 44 microfarads. And so you're whatever you're doing with your feedback loop is gonna be way out of whack.

Stephen Kraig
So I I found another cap. This is an 0 6031 microfarad, and it is a 6.3 volt. And across 6 volts, it only drops slightly less than 20%. So it it has so much to do with capacitance density. You know?

Stephen Kraig
If you're shoving to get 220 microfarads into a 1206, that thing is jam packed on the inside, and I guarantee you those plates are really close together.

Parker Dillmann
Yeah. I I'd love to everyone out there that's listening, all you breakers. What would you a capacitor like that for? A 6.3 volts 220 microfarad capacitor no, ceramic that loses near its top end 80% of its capacitance. I'd love to know what the application is for that part.

Stephen Kraig
You know what what what comes to mind is maybe some kind of, like, voltage reference filtering if that voltage reference was, like, 1.2 volts or something like that.

Parker Dillmann
Yeah. That could be it.

Stephen Kraig
I could see something like that.

Parker Dillmann
Yeah. A very low voltage filtering. Yeah. But let's I'll let them know if someone out there has used these parts. I'd love to know what the actual application was.

Stephen Kraig
And they're like, oh, that's why my circuit wasn't performing like I thought.

Parker Dillmann
I could be.

Stephen Kraig
So so yeah. So stay away from the extremes. Don't pick the lowest voltage and don't pick the highest voltage of capacitors with when it comes to values, do the same. Don't pick the highest value capacitor in the smallest package you can. There's a lot of reasons behind that.

Stephen Kraig
I mean, we just went through all the VCC problems, but there's also a lot of difficulty in manufacturing with those. And what's interesting, this is there's difficulty in qualification of those parts. So a lot of parts have to go through life, qualification testing, a lot of temperature testing, and a lot of extra stuff in order to meet whatever extra ratings they have, like automotive and things like that. And if what's funny is if you go to Digi Key and you just select aecdashq200. So the this this passives automotive rating, it automatically eliminates a whole bunch of capacitors that would have been available.

Stephen Kraig
In fact, it takes about 2 thirds of your capacitors out of Digi Key, and that's not necessarily saying that those parts are are bad in any way. But what it does is it kinda gets rid of the extreme cases that would not pass the qualifying test for being automotive. So it sort of gets rid of the extremes and the edge cases for you by just selecting that. But James Lewis had a really interesting point when we talked to him last about this, about how capacitors start out without a capacitance value, and then they kiln them and they kind of level out to a capacitance value after they've dried out in the in the ovens. And that's a fully chemical process.

Stephen Kraig
It's not like something that you can just turn the knob and, like, move a thing in there. It's done. Right? It's a chemical process, and so they're trying to hit hit a target and if you're trying to hit a target that's on the edges, that has that's the hardest for the manufacturer to actually hit. So it makes way more sense to try to pick a value for both for not both, for capacitance, for your voltage, and for your tempco that fits more within the center of the bell curve for any capacitance size.

Stephen Kraig
So in other words, like, a in a 402, if you're trying to pick a 10 microfarad or 402, that is by far an edge case. So that's not going to be something very easy for the manufacturer to create. And so hitting all of their targets with that, all the parameters with it is very difficult. That would be a really good indicator to not select that size of capacitor. Now if we're talking about a 100 picofarads in an 0402, now we're talking.

Stephen Kraig
Now that's something that's right in the center of what makes sense for that size of capacitor. Now, at the same time, if you have, say, find it, like, a 1210, a big cap, and it's a 1 picofarad cap in there, you have the exact opposite thing even though the results are the same. Like, how do you make 1 picofarad in a big capacitor? You're gonna have 2 plates inside. I'm just I I don't know exactly the amount, but you're gonna have, you know, a lot fewer plates and they're gonna be spaced differently.

Stephen Kraig
It's that something like that is also hard for the manufacturer to hit on the low side of things. So that would be a great example of just like the 10 microfiber 4 2, the opposite picking a really low value capacitor in a big package is hard for them to hit. So it all comes down to get a gut feel for what the bell curve of every part looks like in terms of their spread and try to stick near the center of that. And don't be afraid of bumping up to the next value or the next size. Yes.

Stephen Kraig
It is nice to have small components. They fit into your layout and, you know sure. I agree. I've I've been there. But in terms of being able to get parts that consistently work, and if they go obsolete, you can easily find substitutes for them and you don't get bit in the butt by problems with VCC, try to stick to the center of the bell curve.

Stephen Kraig
That's sort of the big main takeaway here.

Parker Dillmann
Larger components also enable you to route between pads.

Stephen Kraig
That's true. That's true.

Parker Dillmann
I think we we used to call those the sneaky traces on this podcast a long time ago.

Stephen Kraig
I remember that. I remember being asked, are you doing sneaky tracing?

Parker Dillmann
Yeah. Because at o four zero two level, you it's I don't think you can fit a trace in there. I need to try, actually. I wonder if

Stephen Kraig
there is With standard manufacturing, yeah, I don't think

Parker Dillmann
you can. With 3 mil, 3 mil, I wonder if you can sneak 1 in. Maybe not. That's, 9 mils total.

Stephen Kraig
I don't think you can. Unless you compromise on your footprint a lot.

Parker Dillmann
Yeah. And then then you get more tombstoning, which is not really a compromise.

Stephen Kraig
No. I you lose way worse.

Parker Dillmann
Yeah. That's way worse. Yeah. I do like designing with one size in mind, but capacitors are always a different game. Usually, I'll try to pick I do usually do, like, 042.

Parker Dillmann
Sometimes I'll bump up the size because of the like, let's say a point 1 microfarad or whatever because it makes sense for, like, the trace it's near. Like, let's say it's on my output of a LDO or whatever, and so I'll have, like, a 10 microfarad cap, which is like a, you know, 1206 size. But then next to it, you know, I need to have, like, a smaller value, like, a 0.1 microfarad or 1 microfarad. And I'll actually pick probably the same size if I can just for thermal loading when it reflows. So that little part doesn't just get overcooked.

Parker Dillmann
Right?

Stephen Kraig
Yeah. Yeah. Yeah. That makes sense. So that's There's also heat shadow.

Stephen Kraig
Right? Yeah. So it might not get cooked enough if it's next to a big component.

Parker Dillmann
Yeah. That that's weird stuff. You just have to learn by just designing lots of boards. Yep.

Stephen Kraig
So Yeah.

Parker Dillmann
I got nothing else to add to this.

Stephen Kraig
Yeah. I think I think I've vomited enough information out.

Parker Dillmann
Let us know. I really wanna know people who use those edge case components, especially that, like, 6.3 volt 220 microfarad that loses 80% over over that 6 volt range.

Stephen Kraig
Also, did you know that it's losing 80%?

Parker Dillmann
Yeah. Yeah. Let us know. What did you use that in the design for? So so thank you for listening to circuit break for macro fab.

Parker Dillmann
We were your hosts Parker Dolan.

Stephen Kraig
And Steve and Craig.

Parker Dillmann
Later everyone.

Stephen Kraig
Take it easy.

Parker Dillmann
Thank you. Yes. You breaker for downloading our podcast Tell your friends and co workers about circuit break the podcast from macro fab leave us a review, too If you have a cool idea project or topic you want us to discuss, let Steven and I in the community of breakers know. Our community where you can find personal projects, discussions about the podcast, and engineering topics and news is located atform.macfabdot com.

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