Double-sided SMT soldering

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tassie tiger
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Double-sided SMT soldering

Post by tassie tiger » Tue Jan 12, 2021 8:30 pm

Hi all,
Have checked the DIY Learning Materials and a few other places, but still looking for advice/guidance on SMT soldering as a noob to this type.
I don't have a reflow oven at the moment, so I can either hand-solder or hot-air-rework-gun solder.

For ref. I'm doing some Korb DLFO's https://github.com/Korb-Modular/04_DLFO ... ter/02_PCB.

For double-sided PCB's with surface mount passives and IC's, is it best to:-
  • Hot-air-gun passives on side 1
  • Hot-air-gun passives on side 2, and hope there's no dislodging of passives on side 1 via heat transfer thru the PCB
  • Hot-air-gun IC's on side 1
  • Hot-air-gun IC's on side 2, and hope there's no dislodging of everything on side 1
or some other order / technique?

Many thanks,
J

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Re: Double-sided SMT soldering

Post by guest » Tue Jan 12, 2021 8:43 pm

depends upon what you prefer doing. if you find hot air gun to be the easiest, you can hot air gun all the parts on one side, and then hand solder the other side. you can also hot air gun the second side, but its a little tough to control the heat profile with a gun, so some parts might fall off. doing a small section at a time and letting the board cool down would help here. but, there are few enough parts on this board that just hand soldering shouldnt take too long.
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col
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Re: Double-sided SMT soldering

Post by col » Tue Jan 12, 2021 8:46 pm

Hot-plate, pick and place the side with most components then hand-solder the side with least components. Hot air is only good for rework, it's crap for fully populating a board.

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tassie tiger
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Re: Double-sided SMT soldering

Post by tassie tiger » Tue Jan 12, 2021 10:45 pm

Thanks folks.
Haven't got a hot-plate either, yet. Probably need to get something cheap via Gumtree Aus to start experimenting with.
In the meantime I will probably use hot-air for most of side 1 and then hand-solder side 2 as suggested.

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col
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Re: Double-sided SMT soldering

Post by col » Tue Jan 12, 2021 10:49 pm

Can pick hot-plates up real cheap secondhand, I even found one in hard rubbish on the street, I have two now. Way better than hot air.

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Bartimaeus
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Re: Double-sided SMT soldering

Post by Bartimaeus » Tue Jan 12, 2021 11:00 pm

hot plate only helps for one side though. for the other, you'll still need hot air or hand soldering.

still, a $30 one from target can make that first side a lot easier: https://www.sparkfun.com/tutorials/59

but if this is a one-off board, and you don't plan to do this often, use hot air for one side and hand solder the other. hot air gets the job done fine in a pinch.

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executiveBlaster
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Re: Double-sided SMT soldering

Post by executiveBlaster » Thu Jan 14, 2021 6:45 pm

I have never had parts to fall off of the other side using a heat gun.

I mix a little flux in with some solder paste, dab it on to all the pads, place the components, and hit it with the hot air gun, then do the other side. I've been doing this for years, tried stencils and hot plates but this method has always worked the best for me, albeit a little goofy. I now make sure to solder as little as possible hehe

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Re: Double-sided SMT soldering

Post by OIP » Thu Jan 14, 2021 11:09 pm

looking at the board, if those passive pads are big enough to press an iron tip against with the part on them, if it was me i would just hand solder the whole thing using a chisel tip. it's low parts and good spacing, won't take long at all. and tinning one pad per part will be less effort than putting paste on.

the electrolytics can be a bit of a pain as the little tab is tucked against plastic and the pads are underneath, maybe reflow that side and hand do the other side.

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tassie tiger
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Re: Double-sided SMT soldering

Post by tassie tiger » Fri Jan 15, 2021 6:54 am

I figured 'what the heck' and tried hot-air-gun on side #2 after completing side #1, spurred on by executiveBlaster's opinion.
Nothing seems to have fall off, and I have inspected all the solder joints with my trusty Belomo 10x loupe; all looks OK so far.
I must admit to accelerating the recommended reflow curve though.
Proof of the pudding, so to speak, will come after I've done the THT components and plugged it in. Fingers crossed.

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executiveBlaster
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Re: Double-sided SMT soldering

Post by executiveBlaster » Sat Jan 16, 2021 12:26 am

I always way overshoot the recommended reflow curve, I set the hot air to 420c and go to town. I've toasted some components very rarely, but it's something to consider if soldering SMD LEDs, for instance.

if you haven't tried JLCPCB.com, I do highly recommend checking them out. the process takes a little bit of getting used to, but they will solder your surface mount components for what bare PCBs cost 10 years ago. I just ordered 20 each of two large 4 layers designs covered in components for ~$300. I've gotten 10 boards of synth projects for around $60 there. if you're just getting resistors and caps put on for you, it's a close to free service, really. this is how I avoid most soldering :) they don't do any through hole, but if I never soldered at all I'd eventually get bad at it ¯\_(ツ)_/¯

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