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Stop using 0603 or bigger resistors and capacitors?

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The passives are usually the smaller problem, as there are often alternative manufacturers, at least for the normal parts. When you need somerhing special, like 1 kV capacitor, 1ppm/K resistors the size is anyway not the main factor to consider and they may come in larger case only.

There was the shortage of MLCCs, but now we have a shortage with chips and this quite some chips first going to storage and thus a tendency to see less need for the common passives. So I don't expect a new shortage of those small parts.
With the resistors one can usually choose an alternative part, often even a different package on the same pads if really needed.  Changing the PCB to also take smaller size is usually not a big deal.  Going up can be more tricky.

It is much worse with the semiconductors. Many have no easy pin compatible direct replacement. Even some relatively common parts get short on supply - at least with a chance to find higher price substitutes, though these also can run out fast. Special/unique parts are effected too.

IC shortages suck right now, I've never seen anything like this before.  My current PCB has ~1400 components with around 160 unique components.
Its normal for a board with this many unique components to have to re-spec 1-3 of the chip capacitors or resistors when PCB's are done (as Digikey may no longer have that particular part available).
This last time I had to respec over 20 of the components, most of which were IC's.  I made it a point to order the components before the boards this time, and I'm glad I did, as several IC's were unavailable in the preferred package and I had to rework the board for the package that was in stock.  This is an automotive board prototype, and I even had to stick non-automotive IC's on this one, as the AEC qualified variants are currently unobtainium.  At least it allows the software people to start working with the board.  I'm still a bit worried as the uP I'm using (NXP S32K144) is out of stock EVERYWHERE in N.A. and everyone is stating December 2022 for restock.

If you're thinking about playing 3-shell monty with resistor/capacitor package sizes, I recommend just laying out your board for 0805 everywhere, as it is the biggest package (but DON'T route a trace between the pads).  You can then go back and move to smaller footprints without having to knock other components around due to lack of space, you just have to fix pad entries.  It goes without saying, but double check your capacitor voltage ratings, and resistor power ratings, when moving to the smaller footprints.

Personally, while I prefer 0603s or higher, I made sure that my generic, 2-terminal components like resistors and capacitors, can take 0402s and 0603s so I'm not limited to one or the other.


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