Ceramic capacitor class II dielectrics.

Go To Last Post
22 posts / 0 new
Author
Message
#1
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Hello,

Does anyone know how to test capacitors for different dielectric types?

I am seeing a massive drop in capacitance of one particular component in a circuit board. The previous boards worked fine but a new batch are problematic.

The capacitor in question takes about half an hour to drop by 50%, which is making me think of a temperature related type problem, hence dielectric. That is a partially loaded scenario using an LCR meter with a dc bias enabled.

Can anyone advice me how to determine the dielectric?

Thanks,
Murdo.

This topic has a solution.

There are already a million monkeys in front of a million keyboards, and the internet is nothing like Shakespeare!

Last Edited: Thu. Apr 18, 2019 - 08:52 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

The first thing that comes to mind is to test some known parts of different dielectric and see how they work in your test setup. Then compare the unknown.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Not related to any temperature changes, but you mention you have bias on them when you measure them.

 

What size are the capacitors?  We had a big surprise here with 100nF 0201s.  Nominal capacitance at 0 Volts about 70% of marked and they can drop down to 7-10nF at say 10Volts.

Last Edited: Thu. Apr 18, 2019 - 01:13 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

You should be able to find out from the supplier what the dielectric type is. Example is Y5V. Some are VERY voltage sensitive and some are very temperature sensitive. Higher voltage rating for a given physical size tend to be worse It tends to be far worse for high-K dielectrics and these are exactly the dielectrics that have to be used in small size, high-capacitance, higher voltage parts. You can get reasonable dielectrics to 10uF 9V in 0805 package. It tends to go down pretty rapidly as the capacitance per unit volume per volt rating increases beyond that.

 

It is possible that the supplier substituted a higher voltage rated part (which would seem to be OK), resulting in a more voltage sensitive dielectric.

 

Jim

 

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I'm suspecting the board house put what they could find on the pcb and now Murdo's having problems. Due to the current supply problems with passives, this assumption would not be too left of field. I gather the challenge is to figure out what was actually put on the board.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

 big surprise here with 100nF 0201s

100,000 pF?  Hard to believe you could get that many pF in something that small.  If I hadn't heard it, I'd guess maybe 5 or 20 pF tops.  Guess those have some tricked out dielectrics.    

Next up will be the the 2 watt resistor in a flea-sized pkg.

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Yes, there is a very significant shortage of ceramic caps. I would not be surprised if the assembler did not substitute something else, thinking it would be "OK".

 

Jim

 

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

avrcandies wrote:

 big surprise here with 100nF 0201s

100,000 pF?  Hard to believe you could get that many pF in something that small.  If I hadn't heard it, I'd guess maybe 5 or 20 pF tops.  Guess those have some tricked out dielectrics.    

Next up will be the the 2 watt resistor in a flea-sized pkg.

They are common standard now. As they are used in masses in smartphones. 10uF 0402 also seems to be getting popular as its prices seem to be dropping rapidly.

 

If they decided to put an Y5V capacitor on the board you are in some trouble. they have a +80% -20% tollerance, but as a side effect can do -80% to +20% on voltage.

We used them long time back as they were extremely cheap and easy to get, and then all of the sudden a design started to act up.

A colleague dug into it and though the normal spec is stated as being +80% -20% there is a notice in the datasheet that it on top of that has a capacitance change of -80% +20% over temperature and voltage.

No need to say we then abandoned them even our head of production quickly agreed on that one ( he is the one that has to tell the higher level management that the price of our product had gone up so was not happy to say it polite)

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Thanks guys for responding overnight.
I’ll let you all know what I find today in the lab.
Murdo..

There are already a million monkeys in front of a million keyboards, and the internet is nothing like Shakespeare!

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

You might find this interresting:  https://www.niccomp.com/resource...

 

Jim

 

Click Link: Get Free Stock: Retire early! PM for strategy

share.robinhood.com/jamesc3274

 

 

 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

NIC is in the electrolytic business, so they are going to emphasize attributes where electrolytic caps are "better" than ceramics. None the less, those graphs are illuminating. One needs to be a bit careful, however, because not all ceramic dielectrics are created equal.

 

West Coast Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

This reply has been marked as the solution. 
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 2

Well I got there in the end. Although, frankly, I wish I hadn’t!

I had specified a 22uF, x7r, 10V, 10%, 1206 ceramic capacitor. Due to breathtaking datasheet-itis one of the biggest manufacturers in the world claims its parts meet that definition even though they can be more than 50% below rated value. Technically they are also correct, although there is some amazing camouflage going on.

It is down to the Vdc derating, the disconnect with the ceramic cap dielectric definitions, and a strange time constant.

My experience (never a good thing to rely on) was that ceramics lose 20% or so at half voltage and that’s where you aim them. Obviously similar rules of thumb apply eg the well known effects in aluminium electrolytics.

Well one (or more) manufacturer says in the datasheet its caps (calls it an example) lose 20% at half max voltage, but in the detail of the simulation section of the component page on their website you can dig up a graph of what to actually expect - guess what -48%. Now this is where it gets hinky. Because the dielectric specifications (eg x7r, y5v, etc) relate to changes of value limits with temperature, if the Vdc loss stays within the 15% range then they can claim its x7r compliant. Note - this excludes the 10% tolerance and any thermal derating.

The next interesting thing is the time constant - I assumed there was a thermal affect when it took 1/2 an hour to start to fail. No, it turns out the Vdc derating change in value is an extremely slow effect. So even though I used an expensive thermal camera the component never got above 30’c.

Put it all together and my 22uF actually gives me circa 10uF! The filter it is part of then stops working, the noise creeps between the circuits and voila, my product stops after thirty minutes due to the noise contaminating all the rf signals. Some other manufacturers are going the same way, but not all, so I now have to work out how to fix the filter knowing that the capacitors that get used could vary between -10% and -55% in value. Don’t even ask about the esr...

The irony is that the part on the board is already being replaced by the manufacturer. The recommended replacement is EVEN WORSE on the Vdc! Combined with the current supply problems meaning you will never be able to buy the same part code twice.

Interesting four days, lots of experimentation, and some learning I hope I never need again! Beware the ceramic capacitor!

Thank you all (here and other websites) for supplying ideas - they all coalesced into the solution today.

Murdo.

There are already a million monkeys in front of a million keyboards, and the internet is nothing like Shakespeare!

Last Edited: Thu. Apr 18, 2019 - 08:51 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

 

 

22uF, x7r, 10V, 10%, 1206 ceramic capacito

Interesting four days, lots of experimentation, and some learning I hope I never need again! Beware the ceramic capacitor!

Well, that's what you'd expect when you try to pack an immense amount of capacitance into something that small.  Anything much above, 0.47uF , I've always used electrolytics, or possibly a film type (below about 2.2uF).   If you don't need accuracy, then maybe theses miniaturized caps might be fine.

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Some LDOs require significant output capacitance for stability. Sometimes as much as several microfarads. Early on, there were cautions about NOT using ceramic caps because of the low ESR, which could lead to more instability. Newer LDO designs can usuually tolerate ceramic but you HAVE to pay attention to the spec sheet. Even the newer ones have cautions about certain dielectric types with high temperature coefficients, warning that you need to insure that the minimum C requirement is met over the full temperature range of the product. 

 

As a result, the LDO manufacturers often recommend larger physical size to accommode lower K dielectric. Often, these LDOs will NOT work with standard aluminum electrolytics because the ESR is too HIGH. If you are going to use electrolytic for these applications, then tantalum is often recommended but there are some newer types that will also meet the requirements. Even these, however typically have a volume (and footprint area) that is several times that of ceramic.

 

In the end, there is NOTHING wrong with ceramic caps, so long as you pay attention to the specs. Ceramics will often be half the price of an equivalent tantalum of the same value and voltage rating.

 

Jim

 

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Hi Jim,
Yes I agree - ceramic caps are good, like any component, in their place. In this case it is in a filter between two parts of a circuit.
I do think that manufacturers implying certain things, then hiding the real data, all while making components which are much lower spec than traditionally has been the case is verging on crooked. I know there is a supply crisis at present in the industry, but churning out rubbish components and hiding the facts, is no solution.
What is the Latin phrase for this - caveat emptor I think. Well no one died so I guess it’s just life.
Murdo.

There are already a million monkeys in front of a million keyboards, and the internet is nothing like Shakespeare!

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

MurdoMcLeod wrote:

Beware the ceramic capacitor!

 

Not all ceramic capacitors are the same, they use different cermaic's with different properties.

Deviations of capacitance as soon as you try to use them is a well known limitation of ceramic capacitors, and different ceramics behave in different ways.

Hopefully somebody will find a ceramic that increases the capacitance if the capacitor is charged with a negative voltage.

 

Doing magic with a USD 7 Logic Analyser: https://www.avrfreaks.net/comment/2421756#comment-2421756

Bunch of old projects with AVR's: http://www.hoevendesign.com

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Hopefully somebody will find a ceramic that increases the capacitance if the capacitor is charged with a negative voltage

How about one that holds extremely steady!!   Materials keep getting better.

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

NPO / COG ceramic dielectric is very stable though they are rated as "temperature compensating", the spec'd temperature coefficient is +/-30ppm/C and the voltage coefficient is small enough to be contained within the component tolerance. 

 

For many of us, the big problem with NPO is that 1nf, or so, is about the largest value you can get in 0805 package. 

 

Just checked AVX. 22nf 16V can be had in 0805 that is 1.52mm high. Standard for 0805 16V is 1.8nf (0.94mm high). You pay a substantial premium for the higher values. Basically, the same limits to 50V.

 

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

It’s been a salutary lesson in researching capacitors before you use them.

The first problem I have found in trying to get a part (which is also in stock somewhere) similar to the ones we’ve used for the last few years, is that most manufacturers don’t release the Vdc data curve at all, and the rest make you dig in their websites for it (many of them punt their simulators but the coverage is nowhere near half).

The second problem is how to design a filter for example when components of the same (alleged) spec of capacitor can vary their capacitance due to Vdc, temp, etc between -10% and -73% (based on my research in the last 48 hours)?

I did notice what Jim has found; that AVX parts do seem to be better than everybody else’s parts - lower change with Vdc, wider operating range, more available data - not sure if you pay for it but I will definitely keep them in mind.

Right, enough of work everyone. Have a great Easter holiday and don’t eat too much chocolate.

Murdo.

There are already a million monkeys in front of a million keyboards, and the internet is nothing like Shakespeare!

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Wow. I'll eye my chip capacitors more suspiciously!

The largest known prime number: 282589933-1

In my humble opinion, I'm always right. 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Is this a problem just for tiny

surface mount ceramic capacitors

or also for through-hole parts?

--Mike

 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Not sure which "problem" you refer to.

 

If it is the vagaries of various dielectrics, then SMT and through-hole share. The big difference is that through-hole are not forced into the small dielectric volume situation like SMT is. So, there is not the push into the unusually high K materials for through-hole. 

 

If it is the supply problem, then, yes, both, but bigger for SMT. SMT ceramic cap demand has been growing faster than manufacturing capability. I suspect that though-hole demand growth is probably much slower (maybe even negative for some types). You can generally get though-hole. And, for small quantity, you can usually get SMT. It is the larger purchases (whole reel or multiple reel) that is tough.

 

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net