[sdiy] To SMT orNot to SMT.. that is my question

Jay Schwichtenberg jays at aracnet.com
Sat Dec 21 01:54:40 CET 2013


I've no problem with doing SMT. But I've been soldering a very long time and
have decent equipment. If I need better I usually work somewhere where I can
work on it with even better tools. 0.02 pitch pins on ICs aren't that bad if
you use flux, a good iron and a magnifier. One thing I learned last year
from a YouTube video is that when you put solder on the iron it boils off
the flux pretty fast. Putting flux on the board before you solder fine pitch
ICs makes it a lot easier.

One aspect I'd like to address is just the board layout itself. Granted
there are a lot of people here that don't work in electronics and just
layout boards the best way they know how. A lot of thru hole boards aren't
done all that well and I avoid them. (OK, I rant about it, get comments
about it, I'm not calling anyone out, just trying to throw some helpful info
out there.)

Some examples:
* Got the room, use a wide trace. Especially on power supply and high
current (LEDs, 555s) things.
* Don't put tiny pads down just bigger than the lead or pin. Put a big one
down so the pad won't lift when you have to change a part.
* Don't put islands that aren't connected to anything on the board. These
can act as antennas or capacitors especially in high frequency circuits.
* Put your bypass caps between the power supply and the load, not power
supply, load and then bypass.
* VERSION/REVISION numbers on the silk screen or board and change them if
you change ANYTHING on the board.
* Yes boards are priced by the square inch or cm. But think about the guy
who has little or no experience soldering. If you pack the components really
tight can they (oe even you) fix or modify the board?
* A lot of SMT pads are optimized to be optimal for the parts. I've noticed
that between versions of PCB software the pads for 2 lead parts have gotten
smaller. Go in and create your own pads which are bigger. That will make
soldering easier.
And lastly, this is one area that I thing SMT makes thing better.
* Look up the mechanicals for the parts and specify the part if there are
space/lead considerations. Check the common distributors (Mouser, Digikey,
Farnell, ...) to see who has them. Seen a lot of boards where you're fitting
a big part in a small space or lead spacing. SMT the parts a 1206 or 0805
then that's what it is.

Happy holidays, get to work on that synth back log!
Jay S





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