Hi. In a previous video, we took a look at a failure of a multi-layer ceramic capacitor inside a power supply module and this is actually the second time this has happened to me. As I pointed out in the previous video where the ceramic capacitors have actually failed short circuit and they've been across a high power source which has been able to deliver a lot of energy into that capacitor and they catch a light and needless to say, that can ruin your day in if you're designing a product like this. So quite a few people have asked and I thought it's quite worthy to do another video on this, actually looking in more detail of exactly what's happening here and more importantly, what you can do to either reduce your chances of this happening or basically eliminated almost entirely any issues in when you're designing a product cuz this is one of those more obscure things that you're not gonna learn in school.

This is like real manufacturing practicality stuff, so it's really fascinating. Let's take a look so you can see in the photo. Here are the before and after. before we had a multi-layer ceramic capacitor in there soldered between two pins and that was the mistake here.

Pins that have big screw terminals on them, so when you screw in those terminals on the other side of the board, you get transfer of mechanical stress onto these ceramic capacitors and ceramic is actually brittle so they tend to crack get micro cracks in them and generally these can fail short-circuit and that's exactly what happened here. The capacitor are shorted, it dumped all the energy into that capacitor, and that caught a light. and well, it ain't there anymore. But there's actually another two ways at least that these capacitors can fail.

The other one is by thermally stressing them. You could have one end on a big ground plane, or both ends on a big ground plane. For example, on one end can matter because when your board goes through the reflow oven, then the copper can retains the heat very well. So if you've got one end of the capacitor, for example, hooked to a large ground plane and the other one not just going off on a tiny trace, that might impart differential thermal differentials, which can also work rocky a ceramic capacitor, so it's not as common.

But thermal stress is one thing mechanical stress, which is what we are going to look at in this video, and the other is just infant mortality. manufacturing. You know issues caused by the component manufacturer. You know, if you buy them from the Shenzhen market, you don't know what sort of quality you're getting, but even though that even the good quality ones, there's just a manufacturing Belko thing.

You will occasionally get some out lawyers that could fail short and do a similar sort of thing. And I Showed this table here of a ceramic capacitor fires from Ni C Components called and it's a nice little summary of the different failure modes at Mechanical Stress. As we got to look at here, thermal stress as I said and those intrinsic defects and how to mitigate them. So that's just a useful table there.

I'll have to link in the web page down below to that one. So what's actually the problem here with mechanical stress? Well, this very handy graphic from the University of Maryland their Center for Advanced Lifecycle Engineering once again, I'll link it in. Down below shows your multi-layer ceramic capacitor and you can see the multi layers. They sometimes they can have dozens and dozens or a hundred layers in there inside, you know, especially your really high capacitance ones.

Like people take for granted the 10 micro farad or higher even hundred micro farad multi-layer out capacitors. They're very modern technology and they rely on very tight manufacturing. Tolleson tolerances. With all these different layers of the plates in, they're separated by the dielectric material and they can be very fragile.

They're encased in a ceramic dielectric material and as I said, it can be quite brittle, so in this case it's exaggerated. But if you've got your PCB and you capacitors mounted on there when it flexes like this and the flexion can be due to as we saw in the power supply that failed when you screw in the screw terminals on the thing that can empower. not huge stress like that, but just enough. You don't need much tiny amount of stress at one end of the capacitor or both ends and crack because ceramic is very brittle and you can actually see the this is a micro cross-sectional photograph 250 microns.

You can see the size there and you can see it's cracked right through the plates there. and that one's probably going to end up as an open capacitor, but they so very often fail as a short-circuit if they fail open. Okay, your product might fail, but it's not going to catch a light and things like that. But if they fail, short-circuit and you've got it across a power supply, input or output that's capable of putting a lot of energy into that, it can catch a light.

So nasty. But yeah, these, this is what actually happens inside there and it's very difficult to actually detect these things. and there's various are techniques to do it. You can, you know, the cross-sectional cut them, you can actually measure.

You can do an impedance analysis test like flying probe test on the board and things like that. so you can get this board flexion from simply installing the board is one of them. You can get a drop, for example, if you're if you've got a mounting post here and here and your product is dropped, you'll get a little bit of flexion like that, especially if you've got heavy components like a transformer on there or something. Your board might do a flex like that and bingo.

You can crack your ceramic capacitors nasty. You could also have our board plug in connectors, for example. You got your mounting posts here. You've got your nice big Phoenix Contact plugs or whatever you plug them in.

After you've installed your board, you can get tiny little flexion on there. You've no doubt seen this on art. You know, computer motherboards and things like that. When you're pressing the RAM into the thing you've got at, you know, squeeze it.

That's putting stress on the board and you can really come a gutter with that. Another way to crack them that you might not think of after you've had them machine assembled. You may not do this yourself. It might just happen at the assembly factory when you penalize boards like this.

I've done a whole separate video on penalized, couple of videos on penalizing boards with routes and slots, and V scores and things like that. If you gots a V score boards and you snap them, snup the boss like outlet, you know you've already assembled them. All your components are assembled on there. Then you guys snap the boards off.

That can ruin your day as well. You can actually impart flexion in your board and crack your ceramic capacitors. So if you've got the slotted our boards like this, trying to push them out with your thumbs, for example, we've got those breakout tabs once again, in part in four. so that's why it's recommended to actually get the side cutters in there and actually cut out the boards from the panel so that you're reducing the stress on the board.

So let's take a look at the PCB layout level and see how you can mitigate these sort of problems. And these things might seem obvious, but it's very simple to overlook these when you're designing boards and designing products. Please excuse the crude if the model didn't have time to build the scale or to paint up. We've got one capacitor on here and a connector and we've got our four mounting posts here.

And obviously if you press the connector on there, that board is going to just flex a tiny little bit and your capacitor is going to do the same because it's mounted in the middle. What can you do about this? Well, there's several things you can do about. this one is to have another mounting hole. For example, OOP There we go.

You know you could have another mounting hole there and it takes the mechanical stress away. So the first thing is just to stop the flexion happening if at all possible. Which means extra mounting posts. And you know things like that.

Put in mechanical connectors, you can move the connector over to here so that it's near some mounting holes. If you didn't want to, you know, have an extra one in here. If you've got the flexibility to do that sort of thing, then that can greatly reduce the stress or eliminate the stress on the capacitor. But let's say that you just had it like this: What's another thing you can do? Or you can simply like if you have a look at the board here, that's the three dimensional so that when you you can see that when you plug the connector in there, the board's going to flex a little bit like that when you plug it in and your capacitor is on the axes like that and that is the most you saw in the stress photo here.

the stress fracture. They happen on the axes like that. so when the capacitor they goes down like that. so what can you do? It's easy.

you can simply to reduce the stress on the capacitor, rotate it like that, so then you're not on that axes where it's where the solder points are like that, and when it flexes like that, if you know what I mean, if you rotate the capacitor like that, you're not gonna get nearly the same sort of longer tune or stress if I'm calling it the correct term on the ceramic substrate. So it's not going to crack like that, you're just sitting. by simply rotating that component, you've already greatly reduced the stress on that. So if there are stress points on your PCB and you can't eliminate them for system design reasons or whatever I'm you can't put in extra mounting posts or whatever it is, then simply rotating your components can make a huge difference and probably eliminate the issue entirely.

So let's take the connector out of the equation here for a second and say that you want to reduce the stress from the mechanical standoffs. You know, when you screw them in and things like that that could be causing an issue. And your capacitor for layout reasons, has to be right close to your mechanical standoff there? Well, what can you do about it? There's a simple trick. one way to do it is to add mechanical stress, relieving slots into your board like this.

So if we have a look at the 3d view, you can see that we've just rounded out a slot in there. Don't worry about the artifact there, a slot around. You're mounting holes like that so that less mechanical stress is transferred through the board to your components surrounding it. but it still provides the mechanical rigidity.

And by the way, multi-layer ceramic capacitors aren't the only electronic components to be susceptible to stress. If you get a really high precision voltage reference, you'll find that they are. It's quite common to find them actually surrounded by an isolation slot like this around the chip. They might come in an SOA package like that.

and if you see a slot and around like that, it means that they're actually trying to isolate any stress any flexion on the board like that into the chip because the mechanical stress can couple into the voltage reference and it can drift. and also it's a really subtle things. It's not going to ruin the chip or anything but it. You know, accurate voltages references like this: Thermal expansion of the board can do this not only isolating mechanical stress, but thermal expansion of the board.

The Fr4 material will have a certain value for its thermal expansion. For example, you can get different piece of B materials with different thermal expansion coefficients and that's a way to isolate our components. but that's got nothing to do with a ceramic cracking and things like that. but you could if you had to isolate your capacitor with a slot like that.

But that's yeah, that's pretty extreme. Generally you want to reduce it using some other technique. so PCB techniques are pretty simple. One is to stop the stress happening at all, not only in the piece of be handled in phase, but also in the product phase.

If you've got connectors and screw terminals and other types of things. I Just avoid that happen. or you can reduce the effect by mounting holes and just being aware of where the stress points are in your board. And third is to add isolation.

Mechanical stress isolation slots where appropriate on your board. And speaking of thermal expansion of the PCB, this can be a real problem. and say if you're designing a LED board for example, LEDs On there you might have an aluminium or other high-power components. A lot of common thing to do these days is to have an aluminium backed board so that it can be used as a heat sink.

Our substrate well aluminium has a thermal expansion constant and you can get thermal expansion issues on a aluminium back board like that. so you've got to be careful with the thermal stresses. They're a much higher coefficient than a fiberglass are if our for PCB that you used to. so just be careful there.

and just some other micro photographs here of some cracking. in this case, an 18-12 multi-layer ceramic capacitor. You can get the cracks running all the way through like that. I Just love these.

They're beautiful how they can get these photos. They can also show up on x-rays as well. You don't have to cut them in half to actually see this, but I think they're pretty horrific stuff inside these brittle ceramic capacitors. The other risk mitigation technique you can do I Mention this in the video is there you can put two capacitors in series.

Yes, you have your capacitance, but this increases your a liability because of one that does fail short then the other one. The other capacitor is there to take up the slack basically. and yes, it'll have capacitance when you put them in series. but then if one fails short in your product will still continue to work as long as it can handle the double capacitance.

Because you're getting rid of one, so you double the capacitance there. So this is actually a very common technique for high reliability products, especially if your product if your capacitors are going directly across a power source, input or output as we've mentioned. But unfortunately this doesn't help you in the case of the capacitors failing open circuit, which they most certainly can. If either of those capacitors fail open circuit, Do you do any of the mechanical or thermal stresses or whatnot, or the intrinsic fire of the capacitor, then that's not going to help you.

Your capacitance is going to vanish, but at least your product is not going to catch on fire. So the way to mitigate that, of course, would be to have two of them and in another two in parallel with that. But that's getting pretty extreme. and another technique is to simply use smaller size capacitors.

The smaller you go, the less flexion overall you're going to get for a given unit length. So you know some people might have a blanket rule. I'm not going to be used bigger than Oh 805 ceramic capacitors, multi-layer ones for example, because if the extra risk the larger the component goes, you go to 12:06 and then bigger ones. You get some of the real monster sized ones, then it doesn't take much reflection at all to actually crack those, so the smaller ones you know they could be a valid reason for going for those.

Oh 402s Now, of course, another obvious technique to eliminate this sort of model a ceramic capacitor shorting problem is to simply not use multi-layer ceramic capacitors. And sometimes that's an option. You might use a film type, you might use a ten or more. you know, there's something else.

But multi-layer ceramic capacitors are very popular. For the reason that they're A, they're incredibly the volumetric capacitance per unit volume is incredibly high. and they're cheap. They're surface mountable.

everything else. Yeah, they got downsides. they're microphonic as I've done videos on and they're susceptible to cracking and stuff like this. But they're used for you know, very legitimate reasons.

but you could in high reliability products like directly across the mains. for example, you might use a film type a capacitor. you know, your X2 rated caps for example. But there is another option.

There are companies that actually manufacture multi-layer ceramic capacitors that are intrinsically safe and certified. Seifer is one example. Here they've got a flexi cap thing there are certified for. You know your X, X & Y capacitors go directly across the mains.

Once again, there are higher mains as of incredibly high energy source. so you want certified capacitors go across there. and they actually offer a range of these certified. You know they're tested by proved by Ul and Tuv and everyone else under the Sun rated for directly across these supplies.

And they are multi layers remote capacitors and they use this using that flexi cap technology and there's other companies that actually AVX Kemet There's a whole range of almost every legitimate capacitor manufacturer on the planet is going to offer specific model A ceramic capacitors that solve is very specific problem. So let's have a look at TDK here there another manufacturer of our components that have you know this flexi type our technology that can help reduce or practically eliminate the issue here. Now if we have a look at this they've got these. They put the multi-layer ceramic capacitors on what's called a mega cap.

they're the lead frames and I showed this in a previous video and the lead frames on there. They can actually take the stress and you can actually see here that compared to a regular capacitor. this is the flex mm in the board here and I'll show you the standard for that in a minute. The Flex amount in millimeters compared to the cracking in the thing and it needs like they start cracking it like four millimeters are flexing and things like that whereas using this technology here with these just these adding these little lead frame things in then you can basically get up to ten millimeters of flex in the board with no cracking whatsoever.

and there's actually a our standard for this at some a AEC our standard it's an Automotive Electronics Council Q 205 is a specific one for flexion of the board here and they like the supports like this. A 45 millimeters out, this is the standard When they talk about flex generally that it can survive. this is what they're talking about here. so you know a little weight comes down on the supports and how much they flex by and that's how much they can actually survive flexing.

So just mounting that alone can practically eliminate all of your issues here. and here you go. That the Mega Cap features eggs, orbs, stress of the board, flexure by its unique metal frames can be mounted on aluminium circuit boards Beauty provided with metal caps that exhaust by mechanical shocks and in a flexure, it's not just shock. Also features improved vibration resistance as well.

They can. So there, that's talking about Micro Phonics there. they might be able to reduce or change the resonant mode of the Mitral Micro Phonics if that's a problem and you can get more capacitance because you can physically stack them with these lead frames and they got lower ESR and ESL etc. But yeah, there you go.

So very common in automotive applications and another type if you don't want to use those lead frame types because that the extra process they might cost money or whatever you make them might not be able to afford the height. Whatever is to use these soft terminations you can see in this particular case all the manufacturers will have their own technology and ways of implementing this, but they actually have a a conductive resin layer inside there so that actually takes the stress. D Couples our stress from the mechanical end caps to the ceramic dielectric, yet it still allows the conduction through so it is really quite deep there and you can see once again they can flex up to ten millimeters. and with these soft termination technology, it's not gonna cause the problem beauty.

And you can actually see here. It doesn't stop these things cracking, but what a does? you can see on the left-hand side here is your traditional multi-layer ceramic capacitor and you can see that there's a big stress crackle right through there. It's horrible. the soft termination ones can still crack, but they don't crack the ceramic dielectric inside.

Yeah, it might peel off a little bit, but you still got that conductive epoxy r-type stuff in there to go through. So there you go. I'm just terrific technology and this is such a serious problem that the manufacturers have had to develop very specific manufacturing component manufacturing techniques to reduce and eliminate this sort of problem. It's a big deal, but in this particular case, for this soft termination TDK technology, you can see that they're the basically the main main disadvantage apart from probably extra cost to manufacture these things is you know, a 12.5 percent decrease in nominal capacitance and volumetric capacitance or whatnot.

But that's a small price to pay for having a reliable product in some markets like the automotive and other high vibration, high stress environments demand this sort of reliability. and this is an interesting graph. Here are using this soft termination technology: the amount of cracks issues per number of times dropped. Look at.

You know the regular multi-layer ceramic caps just go up and up and up the more times you drop them. That mechanical stress can add up to a point where you might start with a little micro crack doesn't damage your product, but then that can get bigger and that can provide a crack point to make it bigger. So every time the product is dropped it can cause an issue. And well, if you get your capacitors from the one humpin II their stall at the Shenzhen market, you know and you need a reliable product.

Well, that can cause a big issue. So, but if you spend money, you can buy the capacitors that are super reliable like this. The other way to do it is you can actually Tek sell these capacitors that are effectively two capacitors in series in the one that case. the way they've arranged the layers in there.

As you can see, it's basically a a arrangement of two serial capacitors in there. So you get the volumetric size. It's probably going to be decreased. The capacitance is going to be decreased, but you don't have to have two physical components which take up more space size when you've got the footprints and everything else associated with them.

But once again, if these things don't have the soft termination technology or the lead frame technology, they're just simply a lower-cost more reliable version that prevent the short in capacitor problem. These things effectively will fail open if they're going to fail. And another way you can guarantee inner from a manufacturing point of view that you can get these to guarantee to fail open is that you can actually extend the length of the materials inside. so this is all part of the menu.

a factoring thing. Once again, the data sheets will probably I don't know if they guarantee it, but they will say you know it's almost guaranteed to fail open The risk of it failing short because the cracks usually happen at the end terminations as we've seen in there. So if you move the plates back from the edges where the cracks typically happen, then you practically eliminate the possibility of a short because it just you know it physically can't happen. You can see down here this crack goes down here.

A regular one can actually short out the plates, but this one can't because they don't overlap until they get further within the chip. So that's pretty neat. So here's a nice little last summary of: T decays For different tentative, you know one technique is not perfect. So I need four different techniques to mitigate the problem of flex causing cracks in issues and shorts in male ceramic caps.

So the mega cap the soft termination. I'll let you read that a bit, you know. Cost: Obviously the higher the open mode ones are the highest cost. Look at that.

I Wouldn't have thought so, but obviously they need larger ceramic material to act I Do that and they're going to be physically larger on the board as well for a given volumetric efficiency and stuff like that. So the obvious: the cost. The smallest one is simply the lead frame because they just take their existing capacitors which are all even manufacturing in the quad billions and they just solder on some little lead frames on the end. the other ones a soft termination and the series design.

I'm surprised the soft termination is actually, you know, isn't right up there in the highest cost. but I guess they've perfected the technology. That's it's not too bad. So I just have a very brief look here at the end of this: TDK Soft Termination Technology: Look at this.

It shows you a very nice little diagram of how they actually do that, the conductive resin layer, and everything else. So I was just wondering how much what's the cost difference here between these and regular ones? Let's take a quick look now if we go on mousey here and actually have a look at a specific TDK part number for a 1 Microfarad Oh 402 multi-layer ceramic capacitor with soft Termination Technology here we go 2.8 cents in a in 10000 quantity. So if we go over here and just find an equivalent, just a generic one. but check this it out.

This is interesting. The Mouser parametric search actually has the termination type a specific soft flexible termination. and of course, if you choose that that only the TDK parts will show up because that's a specific TDK thing. and they've put that into the parametric search.

But that's really quite useful, isn't it? I Like it? But anyway, if we search for all the catalog for one microfarad Oh 402 capacitors, sort by price. We're looking at one point three cents there. so basically half the price. So basically it doubles the price for that in volume 10,000 as a reasonable volume in for that soft termination technology.

So there you go. and if you use some of the other ones, they are more expensive again. But yeah, that's you know W cost. But if you got a lot of caps on your board that can really ruin your Bom cost and and ruin your day.

but something like a you know, an automotive product liability is the number-one thing. So they're not going to skimp on cost, they're gonna specify that specific part number. For example, it must be that no substitutions and that's it right? You know they must buy it and they buy it from the original. You know, a reputable certified source, so make sure they don't get any.

You know those substituted crap quality parts somewhere in the supply chain or something like that. But and they would pay double or even more for these, especially if you got big ones that are, you know, like equivalent to let the film capacitors, the X1, the Y1 kind of ones that go directly across the mains. They could cost a lot more or whatnot if you wanted the volumetric, efficient efficiency of the model A ceramic capacitors, but you're one of that reliability and guaranteed certification. You'll pay for that anyway.

There you go. I've ruffled on long enough about cracks and micro cracks and short in and how to reduce those in multi layers in product design. For multi-layer ceramic capacitors, it really is a big issue that all the major manufacturers out there have solutions to solve this specific problem. So I hope you found that interesting.

If you did, please give it a big thumbs up. And I'm sure I've missed some things. There's other techniques you can do as well. you know it's probably not entirely comprehensive, but anyway, I hope you found it useful and as always discussed down below and there'll be links to various application notes and data sheets down below.

Catch you next time.