SDG #088 Ceramic Capacitors will Blow Up your PCB

Multilayer ceramic capacitors are usually treated as the most boring part on a board, but they have a failure mode that can turn a working PCB into a scorched one. This video looks at why MLCCs crack, what happens electrically when they do, and why the damage is often far worse than the loss of a few nanofarads of capacitance.

The core problem is mechanical. The ceramic dielectric body is brittle and the terminations are soldered rigidly to the board, so anything that flexes the PCB puts the capacitor in tension. Depanelising, connector insertion, screw-down mounting points, board handling and even test fixture probing can all seed a microcrack between the internal electrode layers. Thermal shock during soldering, especially manual rework with an iron directly on a large case size, does the same thing from the inside. Cracks frequently do not fail open; they create a low resistance path across the plates that draws current from whatever rail the capacitor sits on. On a supply with a stiff source and no current limit, that becomes localised heating, charred FR4 and sometimes flame.

The practical takeaways are worth applying to any design. Keep ceramics away from board edges, mounting holes and connector stress zones, orient them so flex acts across the shorter dimension, prefer smaller case sizes or flexible termination parts on high stress rails, and use reflow or hot air rather than dwelling with a soldering iron. On safety critical or mains adjacent rails, series resistance, fusing or film capacitors are the safer choice. It is a useful reminder that a passive component can be a fire risk if the failure mode is not designed around.