Author Topic: SMD design advice  (Read 628 times)

somnif

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SMD design advice
« on: March 10, 2018, 05:43:28 PM »
As I continue my adventures in Eagle, I have taken to making SMD versions of layouts along side through-hole. I want to practice more with surface mount stuff, and its kinda fun playing the puzzle game two different ways. (as a note I haven't been thrilled with any of my layouts yet, but that's another story)

But I run into one continuing issue. How do you folks handle power filtering in SMD layouts? Several expensive MLCC caps in parallel? Stupidly expensive big tantalum caps? Surface mount electrolytics that are bigger than through-hole options?

So far my solution has just been: "Screw it, I'll just have one through hole part on the board" but if there is a cleaner option I would be thrilled to know. I just don't like the thought of paying 2$+ for a single SMD part when I can use a 15 cent low profile cap just as well.

alanp

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Re: SMD design advice
« Reply #1 on: March 10, 2018, 05:56:45 PM »
Panasonic_C and Panasonic_D footprint electro caps seem to be the ticket.

It's easier to just say screw it and use thru-hole electro caps, though. This applies for diodes, too.
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gtr2

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Re: SMD design advice
« Reply #2 on: March 10, 2018, 06:31:10 PM »
Not really sure what your definition of low profile is, but most SMDs electros 100uF and under are less than 7mm Z height.  For lower value electros the diameter can be had in 4mm packages.  Kinda a dime a dozen and quantity is your friend.  They do take up more space than TH even in the 4mm diameter packages when you take into account the bottom footprint.  If you're doing SMD by hand just pick your poison :)  There is no reason to use SMD tant caps which are low ESR unless you have something like a charge pump, to avoid voltage losses.  They are big and expensive.

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gtr2

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Re: SMD design advice
« Reply #3 on: March 10, 2018, 06:34:27 PM »
Also, be aware of MLCCs and voltage derating.  Something to just familiarize yourself with in the SMD world.
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pickdropper

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Re: SMD design advice
« Reply #4 on: March 10, 2018, 06:39:48 PM »
I usually use Tantalum.
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