On 2/21/19 2:07 AM, steve wrote:> I am seeing some failures of ceramic capacitors in a product I designed. These are 1206 22uf 10V ceramic caps, we do not specify a manufacturer. The caps are on the output of a 3.3V 1amp 2MHz dc to dc converter (5 amp inductor 2.2uH), there are two in parallel. They become resistive, around 200 ohms. The ripple current is around 0.4 amps total, so I cant see that it is excessive ripple current, they are not near mounting holes so I cant see mechanical issues, and they initially pass test but fail in the field. Heating the cap does not have much effect on the resistance. > Any pointers would be appreciated. > Thanks >You say you've got two caps in parallel. What's the correlation between one failing and the other failing on a given unit? Do they tend to both go, or does it tend towards one dead, one live? -- Rob Gaddi, Highland Technology -- www.highlandtechnology.com Email address domain is currently out of order. See above to fix.
Ceramic capacitor failure
Started by ●February 21, 2019
Reply by ●February 21, 20192019-02-21
Reply by ●February 21, 20192019-02-21
On Thursday, February 21, 2019 at 5:07:33 AM UTC-5, steve wrote:> ... we do not specify a manufacturer. ...Are you able to identify the manufacturer?
Reply by ●February 21, 20192019-02-21
On Thu, 21 Feb 2019 02:07:29 -0800 (PST), steve <steve.jones@scannex.co.uk> wrote:>I am seeing some failures of ceramic capacitors in a product I designed. These are 1206 22uf 10V ceramic caps, we do not specify a manufacturer. The caps are on the output of a 3.3V 1amp 2MHz dc to dc converter (5 amp inductor 2.2uH), there are two in parallel. They become resistive, around 200 ohms. The ripple current is around 0.4 amps total, so I cant see that it is excessive ripple current, they are not near mounting holes so I cant see mechanical issues, and they initially pass test but fail in the field. Heating the cap does not have much effect on the resistance. >Any pointers would be appreciated. >ThanksSee if your exceeding the cap voltage during turn on. That can cause a failure rather quickly, even if it does not travel to the rest of the circuit because of some inductance. Cheers
Reply by ●February 22, 20192019-02-22
On 21/02/2019 10:07, steve wrote:> I am seeing some failures of ceramic capacitors in a product I designed. These are 1206 22uf 10V ceramic caps, we do not specify a manufacturer. The caps are on the output of a 3.3V 1amp 2MHz dc to dc converter (5 amp inductor 2.2uH), there are two in parallel. They become resistive, around 200 ohms. The ripple current is around 0.4 amps total, so I cant see that it is excessive ripple current, they are not near mounting holes so I cant see mechanical issues, and they initially pass test but fail in the field. Heating the cap does not have much effect on the resistance. > Any pointers would be appreciated. > Thanks >It's a common failure mode at high temperatures, which probably doesn't apply here. Board flex can also cause this and Flexiterm caps help along with not flexing the board or mounting in a different place/orientation or just using through hole parts. I have also seen this apparent partial short where there was nothing wrong with the capacitor, just some burnt on flux underneath. Worth taking a capacitor off to measure it just in case... Cheers -- Clive
Reply by ●February 22, 20192019-02-22
steve <steve.jones@scannex.co.uk> wrote:> I am seeing some failures of ceramic capacitors in a product I designed. > These are 1206 22uf 10V ceramic caps, we do not specify a manufacturer.Where are you fabbing your product? I have heard manufacturers in certain countries have a tendency to 'optimise' your product by replacing your parts with cheaper ones which can be of dubious quality. I'd start by chatting with the factory and seeing if you can find out what parts they fit. Theo
Reply by ●February 25, 20192019-02-25
On Friday, February 22, 2019 at 11:33:59 PM UTC, Theo wrote:> > I am seeing some failures of ceramic capacitors in a product I designed. > > These are 1206 22uf 10V ceramic caps, we do not specify a manufacturer. > > Where are you fabbing your product? > > I have heard manufacturers in certain countries have a tendency to > 'optimise' your product by replacing your parts with cheaper ones which can > be of dubious quality. > > I'd start by chatting with the factory and seeing if you can find out > what parts they fit. > > TheoThanks, I will try and get further information from give that a try. I think of there was over voltage on the cap, the semiconductors on the board would fail too, the output goes straight to a power plane, and also the external supply is 7.2V which is below the voltage rating of the capacitor, and also once powered the units stay powered.
Reply by ●February 25, 20192019-02-25
On Thursday, February 21, 2019 at 5:47:42 PM UTC, Rob Gaddi wrote:> On 2/21/19 2:07 AM, steve wrote: > > I am seeing some failures of ceramic capacitors in a product I designed. These are 1206 22uf 10V ceramic caps, we do not specify a manufacturer. The caps are on the output of a 3.3V 1amp 2MHz dc to dc converter (5 amp inductor 2.2uH), there are two in parallel. They become resistive, around 200 ohms. The ripple current is around 0.4 amps total, so I cant see that it is excessive ripple current, they are not near mounting holes so I cant see mechanical issues, and they initially pass test but fail in the field. Heating the cap does not have much effect on the resistance. > > Any pointers would be appreciated. > > Thanks > > > > You say you've got two caps in parallel. What's the correlation between > one failing and the other failing on a given unit? Do they tend to both > go, or does it tend towards one dead, one live? > > -- > Rob Gaddi, Highland Technology -- www.highlandtechnology.com > Email address domain is currently out of order. See above to fix.Only one of the two fails, then the output feeds the 3v3 power plane, which also has a lot of capacitance/decoupling caps etc.
Reply by ●February 25, 20192019-02-25
On Friday, February 22, 2019 at 11:33:59 PM UTC, Theo wrote:> steve < > > I am seeing some failures of ceramic capacitors in a product I designed. > > These are 1206 22uf 10V ceramic caps, we do not specify a manufacturer. > > Where are you fabbing your product? > > I have heard manufacturers in certain countries have a tendency to > 'optimise' your product by replacing your parts with cheaper ones which can > be of dubious quality. > > I'd start by chatting with the factory and seeing if you can find out > what parts they fit. > > TheoThe factory its put together in is in the UK.
Reply by ●February 25, 20192019-02-25
On Friday, February 22, 2019 at 11:56:12 AM UTC, Clive Arthur wrote:> On 21/02/2019 10:07, steve wrote: > > I am seeing some failures of ceramic capacitors in a product I designed. These are 1206 22uf 10V ceramic caps, we do not specify a manufacturer. The caps are on the output of a 3.3V 1amp 2MHz dc to dc converter (5 amp inductor 2.2uH), there are two in parallel. They become resistive, around 200 ohms. The ripple current is around 0.4 amps total, so I cant see that it is excessive ripple current, they are not near mounting holes so I cant see mechanical issues, and they initially pass test but fail in the field. Heating the cap does not have much effect on the resistance. > > Any pointers would be appreciated. > > Thanks > > > > It's a common failure mode at high temperatures, which probably doesn't > apply here. Board flex can also cause this and Flexiterm caps help > along with not flexing the board or mounting in a different > place/orientation or just using through hole parts. > > I have also seen this apparent partial short where there was nothing > wrong with the capacitor, just some burnt on flux underneath. Worth > taking a capacitor off to measure it just in case... > > Cheers > -- > CliveI have taken the caps off and the fault is with the cap, I have cleaned the cap of flux residue and tried heating and fault stays. It measures 186 ohms, another cap reads 400 ohms. Only one of the two parallel caps fail (Both same part) and no other caps fail (Different parts and smaller). I have looked for ceramic cracks and cant see any but I am not sure if I would see them even if they were there! I have checked power up and the power supply does not over shoot either, Rises in 10ms to 3.3V as expected
Reply by ●February 25, 20192019-02-25
luni, 25 februarie 2019, 14:58:44 UTC+2, steve a scris:> On Friday, February 22, 2019 at 11:56:12 AM UTC, Clive Arthur wrote: > > On 21/02/2019 10:07, steve wrote: > > > I am seeing some failures of ceramic capacitors in a product I designed. These are 1206 22uf 10V ceramic caps, we do not specify a manufacturer. The caps are on the output of a 3.3V 1amp 2MHz dc to dc converter (5 amp inductor 2.2uH), there are two in parallel. They become resistive, around 200 ohms. The ripple current is around 0.4 amps total, so I cant see that it is excessive ripple current, they are not near mounting holes so I cant see mechanical issues, and they initially pass test but fail in the field. Heating the cap does not have much effect on the resistance. > > > Any pointers would be appreciated. > > > Thanks > > > > > > > It's a common failure mode at high temperatures, which probably doesn't > > apply here. Board flex can also cause this and Flexiterm caps help > > along with not flexing the board or mounting in a different > > place/orientation or just using through hole parts. > > > > I have also seen this apparent partial short where there was nothing > > wrong with the capacitor, just some burnt on flux underneath. Worth > > taking a capacitor off to measure it just in case... > > > > Cheers > > -- > > Clive > > I have taken the caps off and the fault is with the cap, I have cleaned the cap of flux residue and tried heating and fault stays. It measures 186 ohms, another cap reads 400 ohms. Only one of the two parallel caps fail (Both same part) and no other caps fail (Different parts and smaller). I have looked for ceramic cracks and cant see any but I am not sure if I would see them even if they were there! > I have checked power up and the power supply does not over shoot either, Rises in 10ms to 3.3V as expectedJust curious: how do you detect the failure. There are two ceramic caps in parallel, both with very little resistance. The equivalent resistance is half the resistance of a single cap. With the failure, no matter how high is the resistance of that cap, the equivalent resistance is still less than the resistance of the single good cap. Is it not enough? I suppose you use two caps to double the capacitance not lower the resistance. btw, 47uF/10V at 1210 (B size) tantalum is quite common. Is it not enough? Too expensive? In this case I bet you can find poscap capacitors these days with better resistance (in fact VERY low) and probably less expensive than tantalum. Hard to say though if less expensive than two ceramics of this size.
