Electronic – How to fit RF, power, analog components all together tightly on PCB

pcbpcb-design

Whenever I go through datasheets of boost ICs, MCUs, RF power amplifiers, filters, they have recommended designs for best performance.

For example, where decoupling capacitors should be placed or how X track should be as far as possible from Y domain components.

But when I see teardowns of big tech company products, I see tightly packed passive components right next to each other holding hands.

How is that possible? What am I missing? What do those engineers do to put components so close to each other as shown in image below Galaxy watch teardown and still get the best performance out of them?
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EDIT: What are these dashed lines marked by red arrow? seems like separation of analog and digital domain. But how are they achieved in inner layers?

Best Answer

Hm, couple of things:

  • "reference design" == "best performance" isn't usually what you need. You need adequate performance, and that might be achievable using smaller layouts.
    • Also, you might have been looking simply at different ICs for other markets than highly integrated designs. I find that nowadays, IC manufacturers put a lot of emphasize on things like "smallest 4A step-up converter design in the world!!!11eleven!", and the reference layouts and layout hints have gone in that direction, too.
    • knowing what you need instead of assuming you want "best" is probably really the key here. That requires a lot of experience and planning. That's why experienced designers tend to be expensive...
  • If you're selling a couple millions of something, you can afford multiple generations of prototypes during design. So, you build a "relaxed" PCB first, then shrink the sections, continuously proving everything still works, until you've reached your desired density.
  • A lot of the rules how much spacing you need is based on "there might be interactions if you're closer than that": There might be. Run an EM simulation of your board, and you'll know.
    • Understanding what your crosstalk does, and where exactly it happens: I don't see an obvious problem with the density of the devices in your photo: sure, all these capacitors are close by. But the majority of these are decoupling caps, and cross-coupling into these isn't as terrible. They're literally meant to absorb variations! Also, the currents there flow mostly between the surface of the board and the underside of the capacitor contacts – not a very large area where you can interfere with your neighbor.
  • More layers. Seriously. Layers do wonders. Dedicated power layers with a protective ground/low speed power layer can effectively isolate power and signal.
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