SMD devices aren't inherently 'smaller' in electronic terms than through hole unless you choose them to be. They are more space efficient since no lead bonding etc.
There can be mechanical issues - generally where a component is mounted away from a pcb support etc so board can flex more. You can get parts with flexible terminations if this is a problem - it's mainly a 'thing' for high reliability where excessive vibratyion may be experienced - automotive / avionics etc.
Have to ask - in what way are they better than film caps (and what type of film) - apart from x10 smaller that is
Agree +1 that COG caps in general are fine - a 'goto' solution.
Last edited:
Have to ask - in what way are they better than film caps (and what type of film) - apart from x10 smaller that is
Agree +1 that COG caps in general are fine - a 'goto' solution.
You can use them for SMD reflow, they're small, and they never have end termination problems that can also cause distortion. Audio Precision used to use some custom film caps for their oscillator, and while most parts were high quality, some had end termination problems that caused the oscillator distortion to increase. They switched to a composite of multiple SMD C0G caps, and this problem disappeared, with lower overall distortion than even the 'good' film caps. Film caps are assembled by mechanically squishing the leads onto the metallization, and this "iffy" contact seems to be the problem. A fired SMD chip has sintered nickel electrodes that are either connected or not, with no possibility for a marginal contact.
I've tested some Murata SMD C0G caps (GRM31C5C2A104JA01L), and compared to some Component Research hermetic foil teflon caps (D51D104KSW), they have lower third harmonic distortion, but the dielectric seems to saturate about 10dB earlier than the CRC teflons, as tested with a varying DC bias along with a high AC drive signal. So, compared to huge, space grade foil teflon caps, the tiny 3216 SMD parts show lower third harmonic levels, but start to show dielectric saturation effects (2nd harmonic) with a smaller AC drive signal and DC bias level. But, back to reality, the signal level that you have to drive these caps to begin to measure distortion is pretty huge, basically around 30 milliamps of signal current before you can see it start to cancel the residual 2nd harmonic distortion level of an APx-555 analyzer, which is around -150dBc. So, for small signal use, a Murata C0G has less 3rd harmonic distortion than a giant, space grade, foil teflon capacitor that probably costs $50 or more, and can still handle very large signal currents with the same 2nd harmonic levels, up to around 10-20mA of signal current.
Last edited:
Thanks for the comprehensive info ' there Monte
Indeed the mechanical advantages - and consequent electronic benefits - of SMD construction shouldn't be overlooked. And, if it's relevant, you don't have to bang as many holes (technical term in your Power / 0V planes.
Good info on the distortion / bias etc - I don't have access to anything that'll let me measure like that !
Indeed the mechanical advantages - and consequent electronic benefits - of SMD construction shouldn't be overlooked. And, if it's relevant, you don't have to bang as many holes (technical term
in your Power / 0V planes.Good info on the distortion / bias etc - I don't have access to anything that'll let me measure like that !
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.