Reflow disaster and accidental project.

I think that most (?) factory-build SMD boards use a small drop of adhesive (red) before the components are placed which is probably keeping them still during soldering.

Stephen Eyles

https://soldersandfluxes.co.uk/p1213/Lead-Free-Pure-Tin-Solder-Paint.html £17.98 for 125g would last for a long time.

Mike Hughes

I used to use solder paint, when I worked for H.A West (x-ray) ltd in Edinburgh in the early 80's, and you can apply tiny amounts with a very fine artists brush. It is better than than paste for fine work. You only need a minute amount, and stops the smd's floating away. Here is a link to some : https://www.solderconnection.com/p1213/Fryolux-T1333-Pure-Tin-Solder-Paint.html

Mike Hughes

Regardless of the outcome, I've now discovered a use for all my surplus green flashing LED's. Thanks Clive!

Andrew Donaldson

Why not coat the traces next to the resistors with some clear nail polish or something similar thats more heat resistant?

Cool light! I had the urge to shout "Don't walk into the light!"

Nani Isobel

Pop it on the radiator to warm for a few minutes, that helps viscosity!

I've been looking at those pneumatic dispensing systems. The heat plate I use is a generic Chinese one from Amazon. Blue box, thick aluminium top and three buttons to set temperature on LED display.

Big Clive

I've just tested the old paste mixed with fresh flux and it was a good result. Easy to apply and seemed to flow well.

Big Clive

If solder paste is hard to dispense, its gone bad. The flux has dried or separated, or both. Most common paste has a shelf life of a year refrigerated. Slightly more expensive and stable pastes don't require refrigeration and will be good for at least a year or two. You can try to remix old paste if the flux has only separated. To get the air bubbles out of a refilled syringe, I've used a tiny vacuum pump and a pneumatic dependencer end cap to mostly degas the paste and force it towards the bottom of the syringe. Made the solder pads just slightly larger than the device leads, and the traces coming away the pads axial to 2 pin components, they will self align during reflow. "Tombstoning" is when they lift up, oversized pads and too much paste can cause that.

Kadah

That sounds a good tip. I've just been experimenting with solder paste diluted in flux and applied with a blunt probe. The results have been pretty good.

Big Clive

Hey Clive, preheat your PCB to around 35-40 C, and the solder paste will stick to it. If your PCB is cold, the paste won't want anything to do with it.

ANY solder mask (resist) would help this situation.

Mike Cowen

Would using some uv solder mask to block the trace either side of the resistor help to stop them wondering about?

Jono Harley

That is unless you forget to refrigerate your solder paste.. then you’re going to have a bad time. :)

Lostngone

I have a tube of paste, didn't read that it had to be refrigerated either. Can't remember why I bought it now, it flowed OK before but it doesn't want to come out now. Whoops.

Matt Tester

Another cracking video Clive! Yes, I too did this first time around, "school of hard knocks" I guess. Once solder paste is opened I have found it goes off/hard very quickly, and boy, do you have to push hard. So, I purchased a YI.DE.LONG YDL 2000 Semi-automatic dispenser for SMT solder paste. Amazingly powerful. It cost me around £60 (but I got stung on import duty from a seller in China) they sell on Amazon 4x that. I'm really pleased with it. I use a hobbyists compressor, it amazing how easily it controls the solder paste, its fully adjustable and has a foot-switch or another one which clamps to the dispense tube, I prefer that one. The thing I like about a solder resist is when the solder paste flows, the surface tension pulls the component beautifully into alignment. What heat plate/system do you use?

"There are no mistakes, just happy accidents..." -Bob Ross

Michael Thompson

Reflow plates are how commercial manufacturers do the SMD soldering. The reason you see YTubers use hot air is because they bought a "rework" station which is used when a part fails a Quality Assurance check. Someone then debugs the problem and will rework the part removing the faulty part(s) and replacing them with good ones. The ones who use a soldering iron are hard-ass men you don't want to cross, especially if they're female! :-)

Mike Bird

I would suggest using a screen print processes to apply the solder paste. Making a screen should be fairly simple if you do a printout of just the pad placements to make the stencil. You could also do your own solder masking first.

Geoffrey Runyon

Because you don't have solder resist, and the heat is coming from the bottom, ie the reflow plate, the thermal efficiency of copper is so much better than your resistor, it will drag your solder along those traces. A good reflow requires perfect solder resist, even more so than the amount of solder. Great video Clive, these Clive's DIY pcb videos are the best mate.

Mike Wynne

from what little i've seen of reflow soldering - having the solder resist, correct size pads and the minimal amount of solder paste needed is going to get the best results - as surface tension is what pulls the comonents into position. you may need to nudge 1 or 2 parts even with that result but that may be a way to go next?

Russell Peake

While I'm far from being any good at SMD placing, most YT tutorials either use paste and hot air or flux and iron. I'm sure the reflow plate is quicker, but I've rarely seen it used. and most of the people (including yourself) using the other methods of SMD mounting attain really good results. The reflow plate scares me now !

Looks really nice. Thumbs up!