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by PumpkinSpice
957 days ago
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Are you looking at the same thing? There clearly are decoupling caps not far from the chip. There's no rule to say you need to use 10 x 100 nF capacitors in 0603. They are more cost-efficient, but they're more work to solder by hand. The DC-DC module also seems like a sensible choice for hand assembly. These things cost about a buck or two these days. This board is clearly meant to display the electronic components in plain view and be easy to solder at home. |
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The Microchip documentation for the SAMS70 literally recommends 15x 100nF capacitors, as well as a 4.7uF capacitor for the buck converter, and a second 4.7uF bulk decoupling capacitor.
That's 17x capacitors if you're just following the manufacturer's recommendation.
https://onlinedocs.microchip.com/oxy/GUID-174CB4CE-C435-49E8...
The board as shown in that blog has ZERO of them. Madness. Each 100nF capacitor "should" be directly adjacent to the power-pin its decoupling, fractions of a mm away. And to make sure there's enough room for everything to go on (fractions of a mm is very small), you want to use 0603, or 0402, or smaller parts just for convenience.
But 0603 is already troublesome for hand-placing IMO. (though the even smaller 0402 is still possible in my experience). So as I said, it starts to get masochistic with these sizes IMO. But still, I'd personally try to get at least a decoupling capacitor on each power-pin as the documents recommend (even if its a larger 0805 or bigger).
In any case, the ~4 capacitors that he places is very much on the low-end compared to the ~17 recommended.
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> They are more cost-efficient, but they're more work to solder by hand.
These are all surface mount parts, which means you're soldering using frying-pan and/or toaster-oven at this point.
Or at least, you _SHOULD_ be doing that (or maybe get a real hotplate, lol. But my pancake electric griddle works perfect). Its way more convenient.
You apply the solder paste. Then you drop the capacitor into place with tweezers, and the solder-paste is sticky enough to "grab" the capacitor. You then place all other components. Easy-peasy.
Heat the entire board to 330F (assuming low-melt lead-free solder) using the frying pan for 10-seconds and done. Some people like adding a 1/4" aluminum plate to make the heat more consistently applied.
Components are designed for 500F for 10 seconds btw (aka: standard lead-free solder). So you have a lot of leeway with regards to the frying pan method in practice. But you should keep a strict timer as some parts are really sensitive to that "for 10 seconds" requirement. A proper reflow oven and/or hotplate obviously does the job better with automatic controls, but this is all slow enough that you can do it by hand by just turning the dial up/down with a stopwatch in your hands.