(copied from a youtube email)

Hey, great tutorial you wrote over soldering.
But i need to solder on a non-through hole pcb (a line).
I have seen other vids and they recommend to solder like this:

First they pre-tin both parts (for example, a wire and pcb trace), then they place the wire above the pre-tinned trace and quickly uses the iron’s heat to heat up the parts and make a joint. (P.S. I have also included a video, so you can see how they do it)

Is this the correct way to solder?
(I will attach a picture, so you can see what i need to do)
http://www.acidmods.com/tutorials/images/joysolderpoints.jpg

Thanks

youtube soldering video

That will probably work. A few comments, though:

There might be “solder mask” covering the PCB trace, which is there to keep solder from sticking to it. If so, you can try removing it with steel wool or a razor knife by gently scraping it away. Also, something called a “conformal coating” may be covering the circuit. This is basically a layer of epoxy that “conforms” to the surface to protect it from dust and moisture. You can try steel wool on this or something called a “Conformal Coating Remover Pen.” We don’t sell those yet, but you should be able to google it.

The way I’d recommend going about this:

• get some 30 gauge wire, preferably solid.
• cut the wire to length, strip both ends and bend the wire to shape so you’re not trying to tug on the wire after one side is soldered. Here are some wire strippers that will work for this gauge.
• tin it—hold the wire with magic hands or some other clamp, put the soldering iron tip on one side of the wire, melt solder on the other side.
• add some liquid flux to the trace (assuming there isn’t a solder mask or conformal coating)
• Press the the tinned wire down on the fluxed trace with the iron tip. The solder on the wire should wick out to the trace. The main thing is that the solder should look like it’s clinging to the trace, not just sitting on top.
• If you don’t have flux, try pressing the tinned wire down on the trace with the iron, and then touching the wire with solder. The goal is to have active flux available when the connection is made. If you follow the video’s advice, pre-tin both the wire and pad, and then heat them together, there’s some chance no active flux will be around for the final joining. All that being said, any of the above methods will probably work for you (including the video), but you wanted the “right” way :)

Experiment around a bit, do what works, and if you want to know how professional PCB repair shops use jumper wires, check out this jumper repair guide

A couple more comments on the video: You don’t need to rub everything with steel wool before soldering—only if it’s old and corroded. You also shouldn’t be applying lots of pressure on joints with the tip. Keep a clean tip and tin it so there will be a solder heat bridge between the tip and joint.

So if you use liquid flux, the only thing you will have to do, is to apply some flux to the trace (clear of soldermask or coating), pressing the pre-tinned wire with the soldering iron down on the trace and the solder on the wire should ‘wick’ out and then there is a joint, right?

But is liquid flux necessary? Do you also have to clean the joint?
Are there any other things you will have to keep in mind?

Yeah, that should work. There may not be enough solder on the tinned wire, in which case you’d have to add more by either pre-tinning the trace, add a bit more “tinning” solder to your iron first, or melt solder directly on the wire. I haven’t done a lot of this, so I recommend trying some things and seeing what you can get away with. This goes especially for the flux—if you can get a good joint without it, then great. The only worry is that, without it, you could end up with a ball of solder just sitting on top of the trace or wire, and not bonding to it. This is almost certainly due to a lack of fresh flux during the soldering operation. Unless the trace or wire is heavily oxidized, or coated with something (solder mask, conformal coating, lacquer coating on the wire, etc.).

Lemme know how this turns out for you, ie, what you found actually necessary.

the only other thing I haven’t mentioned already is that the industrial specs require strain relief in all jumpers so any tug on the wire will be absorbed by a small bend / slack in the wire, and not directly pull on the joint.

At the end of the day, if the solder looks like it’s not just sitting on top, and you can give a light tug without the joint breaking, you’re probably good to go :) I wouldn’t lose too much sleep over the right way to do it unless you’re manufacturing hundreds and don’t want a single one to break after 5 years of service. Hope this helps.

Can you use soldering paste instead of liquid flux?
Because i’m having a hard time to find liquid flux while soldering paste is almost everywhere.

I’d still recommend just tinning the wire and pressing it against the trace with your iron. Or holding it down with the iron and melting solder on top. You should be able to do it without liquid flux… have you had problems?

Solder paste is a completely different animal. Check out our experimentation with solder paste and a toaster oven

Solder paste requires the use of a hot air, a toaster oven or some other way to “reflow” it. It’s used for surface mount soldering and is a mixture of a gel-like flux and many tiny solder balls.

We sell liquid flux , but unfortuantely, it’s classified as a hazardous good, and we don’t have authorization to ship it yet. That’s in progress, though, and we should be able to accept orders sometime next week.

Is cleaning flux residues necessary? If so, do you have to use brush with alcohol or can you also use a tissue?

Check out the flux section of our soldering guide for lots more info.

I’ve spent a lot of time and research trying to decide whether to recommend cleaning for hobbyist / prototype projects, and at this point I feel comfortable saying that you probably don’t need to clean off residues unless you use a water-soluble type flux or flux-cored solder, which I don’t recommend in the first place. Most rosin-based flux residues are non-conductive and non-corrosive, but this depends on both the activity level of the flux and and the manufacturer.

If you buy the solder we sell, the manufacturer claims its residues do not require cleaning in most cases despite the fact it’s a relatively active flux.

From their spec sheet:

“Kester 44 possesses excellent fluxing ability, the flux residue is non-corrosive and non-conductive under normal conditions of use. When exposed to an elevated temperature and humidity environment (38°C, 94% RH) for 72 hours, there is no evidence of corrosion caused by the flux residue. Throughout its many years of wide usage, 44 Rosin Flux has produced many billions of soldered connections. In all these billions of solder joints, involving the most delicate and critical of electrical and electronic components, there has never been an authentic instance of corrosion by the flux residue under normal conditions.”

To add to the confusion (I wouldn’t trust anyone that portrays this question to be black and white), almost all manufacturers would clean residues from this type of flux, and a large percentage of them even clean off residues from “no-clean” fluxes. Manufacturers have different goals, though. They’re trying to make thousands of products that last for many years with zero failures.

cleaning flux residues:

If you’re feeling paranoid, don’t trust the manufacturer of your solder (does anyone know what’s really inside RadioShack® solder?), or are using water-soluble flux:

• For rosin-based flux, be sure to clean off the residues quickly because they harden soon after soldering. A brush and alcohol are nice, but lint-free wipes with alcohol could also work. Our ChipQuik SMD removal kit comes with some individual alcohol wipe packages (link provided for the picture at the bottom). I don’t recommend using a tissue or paper towel because they can leave bits of lint and cloth all over the circuit.
• For water-soluble residues (which must be cleaned off), use warm water and possibly brush action.

Hello , it’s me again. Waited a long time for parts to arrive, but finally today i got all parts and started soldering. Since i now (finally) have liquid flux pen, i thought i use that. Here is the part i needed to solder: Part
I needed to solder the wire on the copper pad. So i fluxed the pad with the wire, then i put a little tin on the soldering iron. I then put the tinned tip on the wire and pad… and nothing happens! I assumed it would ‘wick’ out and bond like you said, but nothing happens. I tried it again, this time flux was boiling, but the solder did not bond to the connection. What am i doing wrong?

Thanks

First, sorry for the delay on getting everything. We got hit by hackaday and makezine at the same time, and fell behind on some orders.

My first impression of your joint is that the copper looks it might be corroded. The flux we sell is very mild, which makes it safe without cleaning for most circuits, but can’t do much for severe oxidation. Try rubbing the copper with steel wool or sand paper first. I’ve heard that a pink eraser works great, also.

Secondly, you shouldn’t need extra flux for that circuit. Just hold a tinned tip against the wire and pad at the same time, and then apply wire-solder to the opposite side. The flux contained in the solder wire should be sufficient.

Hope that works for you.

Reading through this thread again and seeing your circuit, I think I may have unintentionally talked you into buying a bottle of liquid flux you really didn’t need. The method I initially talked about involving flux is good for really small traces, but you have an extremely large trace to solder to—I wouldn’t even call that a trace, just a pad. If you don’t think you’ll need the flux in the future and feel like you’ve wasted your money, email us (support_at_CuriousInventor_com) off list and we’ll work something out.

Nah, i don’t think i wasted my money, because i still need to do the very small traces, just thought maybe it would also work with the pad.
Anyway thanks for your help!

Hey, just finished soldering and have to say: it wasn’t so hard as i thought.
But using the liquid flux method, it does work. But i used the old method: putting the iron tip against the end of the wire and melting solder on the other side, close to the insulation, if you know what i mean. So my prefered method is the old way. =)

glad to hear it. It’d be interesting to hear what others have experienced… there are a lot of variables: solder type / size, trace size, wire size and age (old = more oxidized and harder to solder…

If you ever get into soldering surface mount components, you’ll definitely get some use out of the flux.

any bad effect to components (SMD IC, connectors & etc) if using alcohol based cleaning solvant? currently i’m using a cleaning solvant call Kester 5252. is that a good solvant?

I’m pretty sure you’re OK with alcohol and would be very surprised if there were any risks (to the PCB or components) with Kester 5252 spec

Maybe someone else has some actual testing data, I’m just basing on the fact that I’ve heard of many people in industry that use alcohol for cleaning.