Difference between 1206 and 0603 cap?

[bronson]

Yeah, size, duh.  But, anything else?  I ask because of the attached schematic...  Why do they use 0603 caps for power supply decoupling but 1206s in the signal path?  Why not just use 0603s everywhere?

Hoping someone knows offhand.

This is from a Microchip application note, btw: http://ww1.microchip.com/downloads/en/AppNotes/01426A.pdf  Related, if anyone has an opinion on the MCP3911 ADC, I'm interested.  This device has preposterously good numbers for its price.

[Rerouter]

Less voltage de-rating if you look at the datasheets for just about any ceramic capacitance your pushing your luck past 40% voltage rating on a 0603, but on a 1206 you can generally get up around 70-80% of voltage rating before the capacitance begins to sag dramatically,

[mariush]

1206 could handle more current, depending on resistor, could have lower temperature coefficient (better for current sense), but could also be susceptible to microphonics ( vibrations, board flexing,  noise can affect value)... there's an increase risk of tombstoning when reflowing 1206 resistors.., the voltage derating issue mentioned above... 

[Psi]

There's also creepage distance, because 0603 requires tracks closer together, compared to 1206, there's a limit on the voltage regardless of the components actual rated voltage.

One of my projects recently used a reluctance sensor IC which required 1206 resistors on the inputs purely because the voltage produced by the sensor could theoretically get up to a few hundred volts.

[bronson]

Fudge, I forgot to attch the schematic.  Here it is.

Creepage makes a lot of sense.  Since the signal comes from off-board, it would follow that it requires different components.

But I think I'd rather have that ESD flash over my cap's footprint and into GNDA instead of blasting its way into the ADC's input...  Oh, and the signal path is using 0603 resistors, just the caps are bigger.

Tempco, maybe...  Guess it's time to start downloading smd cap datasheets!  That makes for a fun afternoon.   

[bronson]

After studying the circuit some more, it seems they only need a 6V rating for the rails, but want a 20V rating for the analog inputs.  And that needs a bigger package.

Nice guess Rerouter.  Seems obvious in retrospect!