Soldering SMD components

ElectricXII · August 2022

I'm going to have a bash at fixing my EHX B9 pedal. I've built pedal kits and fixed simple stuff like wah pedals, but those were all through hole PCBs. SMD boards are miniscule in comparison and quite daunting.

Are there any electronics gurus out there with some tips for soldering SMD components? E.g, how do you hold tiny capacitors and resistors in place when soldering?

Danny1969 · August 2022

Well sometimes you use solder paste and then a hot air gun to melt the paste and the component sinks in it. Other times it's a case of removing the old comonent, tinning the pads with leaded solder. then hold the component on the pad with tweezers and solder tack one end .... then move to other end, make sure straight and solder properly, then back to the other end and solder properly.
Caps, resistors etc aren't really a challenge as they only have 2 joints. Opamps and larger chips are harder to remove without using too much heat. There's a product called chipquick that is very low melting point that will help you change I'Cs without risk of damage to the board.

Before you attack anything though, take apart something that's broke and just practice removing and desoldering the components.

jasonbone75 · August 2022

To add to Danny's post:

Angled pointy tweezers - your hand and forearm end up roughly parallel with the board and it stabilises everything nicely. You have more control of the orientation and can keep them in line much easier than with straight tweezers.

I normally use a solder wick to remove chips but you must be confident and quick to avoid the heat as mentioned above. If you are not re-using the chip then wick away both sides then snip the legs with sharp cutters. That way you can remove the individual pins with the tiniest amount of heat and ensure that the board remains pristine. Most times they will cling to the tip and can be wiped off in your tip cleaner.

I differ in that I use clean pads not tinned for all components - but they must be clean and preferably fluxed. For me the major advantage is that you ensure the component is sitting flush in contact with the board before tacking one end down. This works for replacing components as well if you wick the pads after removal, clean with a solvent and brush then flux.

Possible gotchas:
1. Pointy tweezers are sharp and it is easy to damage resistors and caps with them if careless.
2. Ensure the solder has cooled adequately before moving to the other end - if it is still soft you will pivot the component as the solder flows on the other end.
3. If you reheat resistors/caps too often or apply too much heat in one application the pads will break away from the end. Chuck them, clean up and start with a fresh one.

ElectricXII · August 2022

@Danny1969 @jasonbone75 Thanks guys for the tips. Very timely as I'm having a go today. The trickiest thing for me, other than squinting through the magnifying glass of my third hand, is actually holding the component in place while I solder. Perhaps if I tin the component, then hold it in place on the PCB with the tweezers in one hand, and use the soldering iron with the other I might get it to fix?

Danny1969 · August 2022

@ElectricXII ;
What component is it ?

ElectricXII · August 2022

@Danny1969 I'm trying this mod:

https://www.thegearpage.net/board/index.php?threads/ehx-mel-9-boot-issue-fix-no-output.2200164/

jasonbone75 · August 2022

Clunky! I would just use a dab of superglue to fix down the transistor with it's pin just touching the header pin. Once that is fixed everything else would be simple.

ElectricXII · August 2022

@jasonbone75 ;Getting the wire to solder to the pin of the transistor where it meets the resistor is a nightmare. I've already fried a transistor and a resistor. I've only got one more transistor!

jasonbone75 · August 2022

Flux is your friend. Any type will help. Flux the existing joint, tin the wire (critical step this, strip the wire tin it with fresh solder and trim it down to length with sharp cutters), hold it on top, add fresh solder to the iron and tap it down on the wire. Remove iron quickly, hold wire steady. The flux burns away chemically cleaning the existing solder, the wire will drop straight into the "puddle".

I would offer to do it for you but you aren't going to want to make the trip from Scotland to Cambridge!

Danny1969 · August 2022

ElectricXII said:

@Danny1969 I'm trying this mod:
https://www.thegearpage.net/board/index.php?threads/ehx-mel-9-boot-issue-fix-no-output.2200164/

You can use a 1/4 watt normal resistor rather than the SM version ... That trip point chip can first be soldered on s small break out board too to make things easier.
The way they have done the mod in that link looks a bit of a bodge to me

ElectricXII · August 2022

jasonbone75 said:

Flux is your friend. Any type will help. Flux the existing joint, tin the wire (critical step this, strip the wire tin it with fresh solder and trim it down to length with sharp cutters), hold it on top, add fresh solder to the iron and tap it down on the wire. Remove iron quickly, hold wire steady. The flux burns away chemically cleaning the existing solder, the wire will drop straight into the "puddle".

I would offer to do it for you but you aren't going to want to make the trip from Scotland to Cambridge!

Danny1969 said:

ElectricXII said:

@Danny1969 I'm trying this mod:
https://www.thegearpage.net/board/index.php?threads/ehx-mel-9-boot-issue-fix-no-output.2200164/

You can use a 1/4 watt normal resistor rather than the SM version ... That trip point chip can first be soldered on s small break out board too to make things easier.
The way they have done the mod in that link looks a bit of a bodge to me

Thanks for the additional advice guys. I did manage to get it all soldered together but it didn't work. There was maybe a bad joint somewhere, but I'd lost the will to live. I've removed the mod components and I'm going to flog it as for spares or repair.

It's a shame, as it's a great pedal when it's working, and it was really useful for three or four songs in our set. I'm not sure if I want to risk buying another as they are pretty notorious for unreliability.

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Soldering SMD components

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