Dave, that's been a very instructive video!
In automotive applications, there were several design rules on MLCCs, for safety reasons, that the whole xx k$ car does no burn.
These rules were violated in this application:
- Don't place MLCCs at the edge of a PCB (biggest mechanical stress during PCB assembly / further manufacturing bending situations)
- Never place single MLCCs directly on the battery input (automotive clamps 15 & 30)
- Use relaxed PCN layout and handling on MLCCs, like enough space to connectors, not too much solder mass, smaller case size, (1206 gives higher mechanical stress, due to mismatch PCB vs. MLCC ceramic), no manual soldering, etc.
- Use enough headroom in voltage rating, for sufficient voltage compliance and ESD resistance, especially on capacitors, which have direct access to connectors to the outside of the application.
- use 100V types when the board supply system (or the application itself) might introduce inductive spikes on the supply line
If MLCCs are used at the battery input, there were several safety measures to be implemented:
- use two MLCCS in series, each from different supplier. If one fails fatally (shorting), the other will avoid complete short
- use safety types, with 'soft' or 'flexible' termination. These fail open, but do no short
- Use small case sizes (1206 not preferred), and avoid "on-the-edge" values, that's the highest capacitance / voltage type of a case size.
- Don't use too small case size, as these are more susceptible to ESD damage... 0603 and 0805 preferred.
- Generally, use MLCCs of known-good suppliers only (which also have a QA system). These also implement additional surge testing in their production line, for example.
Frank
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