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A 1608/0603 multilayer ceramic chip capacitor was functioning as a bypass capacitor for the 3.3V supply of a InvenSense MPU-6050 6 axis (gyro + accelerometer) MEMS sensor. It somehow exploded forming an open circuit, without damaging the sensor IC or any other component on the board, and without affecting its operation.

macro photo of blown component

Illustration of a typical circuit from the InvenSense datasheet:

illustrative typical usage of MPU-6050 from the datasheet

Some parts of the ceramic material are still attached to the PCB and bits of the wreckage are scattered all around. The cap was reflow soldered with lead free solder by the manufacturer and the PCB has not been reworked. I am pretty sure that the component was intact when I first got the board.

I am curious about what failure mode this was, and how to prevent such failures in boards of my own design. Is this a common ocurrence in mass production? I thought these were fairly reliable components.

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  • \$\begingroup\$ What exactly is this PCB used for? A sensor like an MPU-6050 could be found in a phone, but a more likely usage (for a circuit someone would be asking questions about) is an RC quadcopter or a self balancing unicycle or "hoverboard" - ie, things with high powered motor drives that may be spreading unpleasant pulse loads around a poorly designed board. \$\endgroup\$ – Chris Stratton Feb 1 '16 at 0:24
  • \$\begingroup\$ Is this the only unit that failed? It could have been a cracked cap and partially failed with high ESR and failed completely on load. You will need to investigate to eliminate other failure sources like inductive spikes and significant supply noise . If the capacitor is at fault common causes are flexure (bending), bad component stock, and process defects like too much force on the picknplace or debris on pcb during placement \$\endgroup\$ – crasic Feb 1 '16 at 0:31
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    \$\begingroup\$ On the subject of mechanical stress, is that a PCB support right next to the failed capacitor, on the right of the picture? \$\endgroup\$ – user1582568 Feb 1 '16 at 0:35
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    \$\begingroup\$ A 4v-rated cap at 3.3v? That sounds like a design oversight. Typically, caps are chosen to have twice the voltage rating for both some margin of safety, and increased performance. \$\endgroup\$ – rdtsc Feb 1 '16 at 0:52
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    \$\begingroup\$ It's worth pointing out that at 3.3V DC, a 4V rated capacitor may actually lose 50% or more of its rated capacitance. Here's a neat little document. \$\endgroup\$ – uint128_t Feb 1 '16 at 2:06
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Could be high ripple currents (or poor cooling and moderate ripple currents) causing overheating. Or it could be one or several of the mechanical stress/defect sort mentioned in the comments, or a combination of such factors. Without knowing if the capacitor is prone to blowing up on more than one copy of the board it's hard to say for sure. Post-mortem analysis of a single failure without extensive supporting data is not definitive.

Linked below is a TDK app note hosted at Digi-Key which pretty much explains that while MLCCs are often not exactly ripple-current rated, ripple currents do affect them - but it's more of a temperature thing than a specific current. They also mention that when ripple currents are measured on MLCCs it's typically at room temperature - so it's quite possible that some lazy designer found a number, ignored the "25°C" associated, and said whoo-hoo, here's my ripple current - let her rip - at 65°C.

http://www.digikey.com/en/pdf/t/tdk/ripple-current-mlccs

The "4V capacitor on 3.3V supply" (also mentioned in comments after I wrote the above) is likewise a poor design choice that may well contribute, but it's unclear if the spec is what the actual capacitor is, since you indicate a source that is evidently not the manufacturer of the board (chipmaker? in which case they are nuts to spec that) for the spec.

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Most likely the part cracked and that will usually cause it to short. Being on a rail, smoke will be involved.

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