Soldering from bottom of pcb

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I’m wondering if there’s any difference between soldering from the top or bottom of a pcb? Last time I soldered from the top and created a real mess of flux residue. Also, this pcb is fairly tightly packed with components so cleaning thoroughly afterwards is difficult. I’m picky and want to leave a clean pcb. If I trim the thru hole leads flush cleaning the bottom seems like it would be much easier.
What do you think?
 
You can do it either way. The solder will often wick through the via to the other side anyway.
Most solder the bottom (foil) side of the board, not the top (component) side.

If you are picky, I'd trim each lead so there is around 2-3mm of lead left protruding from the bottom side,
and then solder. Of course the component has to be held in place until all the leads are soldered.
 
@intojazz - I'd strongly advise not trimming the leads flush with the board either before and particularly after soldering. i.e. don't trim the actual solder ever, just trim the lead flush with the top of your solder. No matter which side you solder from, you should have solder on the pads on both sides of the board. I solder whenever possible on the non-component side.

Yes, that leaves "pointy" edges, but a toothbrush and/or a lab brush (with the bristles cut a bit shorter) along with some good flux cleaner or high percentage IPA will have it sparkling. To me, that's easier than cleaning around the actual components if you solder on the component side.

YMMV. Have fun.
 
Also regarding trimming the leads: I used to trim things close to the board. Then I needed to clip test leads on. Between tight component spacing on top, and my super-flush leads on the bottom, this proved hard. Now I always live a bit of a leg poking out just in case.
 
THERE IS a reason PCB drawing software defines:
"Component side"
and
"Solder side"

Think about it.

By the same token, massively used wave soldering machines, the Industry standard, apply solder to the bottom side.

Also for decades now Hobbyists and even Factory hand assemblers have been soldering on the bottom side.

There should be some reason for that,it can´t be only a passing fashion.
 
Oh, the solder blobs look nice 😉

Problem is contracted and disappearing electrolytic plastic sleeves, trimmer pots encapsulated in a single block of solder and DIL packages with all pins joined by solid solder bridges.

Pots, switches and connectors filled with solder also might be a factor 🙂

Factory operators might just grab the board from a corner with a pair of long nose pliers and submerge it in a bucket of molten solder 🙂
 
I soldered up a pcb yesterday and can’t believe I haven’t always done it this way. The component side of the board looks perfect. No flux residue whatsoever. This is my learning curve, but I’m making progress so thanks guys
 
Yes agreed,
Very amazing and looks like quite the production.
I must add, seems like this type of work is one way in which products are so affordable and perhaps not the best quality. I’m always skeptical about electronics I order through ali express and the like