EMI/EMC vs component size

[chitransh92]

Hello Folks.

I am trying to understand the EMI/EMC phenomenon and its relation with the component size.

In my design I have used almost 800 component with 0603 package and now I am planning to change this package to 0402.
Out of these 800 there are almost 300 caps and out of other 500 almost 10% ferrites and 90% Resistor.

My question is, if I plan to change the 300 caps, how will the change in EMI/EMC performance be? will it be improved or degraded?
(of course retesting would clear things easily but for a discussion sake, if I do not retest then...)

Thank you.

[mairomaster]

I would be surpriced if the change from 0603 to 0402 has a noticeable effect. If you have EMC problems the reason is probably something else.

[chitransh92]

mairomaster , i have not changed them yet.
I need to understand how should I gauge the affects of changing the size.

[robertferanec]

In some design guides they recommend to use smaller capacitors e.g. 0201 and they are saying, it is for better performance. So, size of capacitors really may influence your design and smaller size decoupling capacitors may do better. I believe the reason is, that the pads are closer, so for example the current loops will be smaller. This may help for example with noise on power and that could also help with EMC. But I do not have any practical results on this topic - also I am not sure how big the difference would be.

[nihial]

Smaller capacitors usually mean less inductance, it improves decoupling and thus reduces the noise. If you use caps for EMI filters, as they have lower inductance they'll also work better than big caps.