I am using Microchip's SAMA5D27C-D1G-CU. In the reference design all the decoupling capacitor packages are 0201.
I have the same capacitor with all the specifications suggested by Microchip, except package.
The package I have is 0603. May I know if there is any problem using 0603 package for decoupling?
The wonderful black art of decoupling...
The imporant thing with decoupling is you are trying to reduce the inductive loop between the chip's power and ground. This is simple in theory: put a capacitor between the two pins as close as possible. This reduces the inductive loop, which gives a better power reponse to the high frequency demands the IC puts on the power rails.
Looking at it as reducing the size of the loop highlights a few things, the main one being position of the capacitors to the pins matter, gound and power connections are both important (check vias for the full path, not just power or just ground) and the size of componets matter.
Clearly a 0402 capacitor has better high frequency response than 0805, but not as good as 01005. But the important question is, are you worried about those high frequencies? That is something which depends on your application and the switching involved. As the datasheet specifies a package size, that is what I would attempt to do. 0201 package is pretty common, so you can get hold of the devices, but they are very small so if you're soldering by hand they may be too much. I have done 0201s, that is possible, 0402s are OK, 0603s are my choice if I'm doing it by hand. (NOTE: I'm talking about the imperial package size)
The usual rule I follow is "largest capacitor in smallest package", as the smallest package has the lowest inductance, and therefore will absorb high frequencies easily. Higher capacitor value, will handle higher amplitude noise. But I also follow the datasheet advice.
As this is a processor, you have lots of high frequency things to worry about. I would aim to follow the datasheet where possible, and personally I would go for 0201s, as you can fit a lot of them in a small space and so can keep the capacitors closer to the pins. But if you are only using the processor in limited ways, and can cope with a bit of a hit on reliability, I think you'd get away with 0402s, maybe you 0603s.
To answer your question in one word: possibly. But how hard is it to get the right size capacitors? How hard would it be to follow the datasheet advice fully the first time compared to building it, have a problem and have to re-spin the board to rule out it being a decoupling issue?
The key property that has to be satisfied for any decoupling scheme is the power supply impedance for the load.
It is fine, make sure to fill the area of your decoupling caps with the same number of via pairs and with the same capacitance per board area.
When you use 0603 instead of 0402, you generally have space for fewer capacitors. To offset this, it is prudent to use more capacitance per component, so the capacitance per board space is the same or higher. Otherwise the low frequency impedance could be too high.
ESR is usually not a major roadblock for MLCC, so even if you have slightly fewer components, the impedance in the peak (given by ESR) should be well below the supply impedance requirements.
Which brings us to the ESL limited frequency range (>100 MHz). Using larger capacitor packages can be worse for ESL. But the largest impact on ESL is the via pattern. You should space vias as close as possible, ideally between the capacitor pads for a 0603, or within the pads if that is allowed in manufacturing. If you place the vias as close as possible within your manufacturing constraints, there will be essentially no difference in ESL for a single component between 0603 and 0402. Still, because you would use more of the smaller capacitors, you would also have more via pairs. You can compensate for this by adding more via pairs to your 0603 capacitors.
