Why solder will not stick

How can I get it to stick? A classic reason solder won't stick to something is because you're not getting it hot enough. My interns come to me with this problem all the time. Make sure the tip of the iron is nice and shiny. Touch some solder on it, and it should melt almost instantly. Initially the solder won't be too keen, but when the metal reaches the right temperature, the solder will suddenly be attracted to it, and you'll see it move slightly.

Now that the pad has reached temperature, you can touch the solder anywhere on the pad and it should melt almost instantly. I often add solder this way so I know I'm adding it to a nice hot pad. What you're worried about is oxidation. Solder bonds to metal, but not metal oxides. Gold doesn't oxidize readily, but other compounds found on circuit boards, like copper and nickel, do so readily. A flux pen should be a part of every soldering tool set.

The ProtoShield product uses a gold-based plating system, and claims features like "The PCB surface is gold-plated for maximum durability" and "Gold plated PCB: solders easily and very resistant to corrosion. Gold is great because it doesn't oxidize readily, but it has the problem that it dissolves in solder, and then reacts to form compounds mainly AuSn4, which weaken the solder joint.

Joint weakness is a problem primarily for processes which put the gold on in thick layers - "Immersion gold" - because there's more gold to dissolve and form those intermetallics which weaken the joint.

This would be a concern if you were using surface mount connectors, or something which did not go through the board, but the sheer bulk of your solder joint should make this less problematic. If you're reworking the joint, make sure you have it quite clean, as the residue is damaging to your joint. The dissolving property is a problem for plating processes which put the gold in a very, very thin layer - "ENIG", or electroless nickel immersion gold - which means that all of the gold dissolves in less than one second, and you're really soldering to the thicker nickel plating below, and using the gold to protect the nickel, like galvanized steel.

This is gaining popularity in big production systems, which rarely need to do rework, and the reduced need for flux from plating with gold makes the process easier. The gold will be gone if you try to do rework, so you'll need to use flux with your solder on the nickel surface which isn't that big a deal.

I'm guessing that this is your problem. There has already been some great advice given so I'll provide some extra info about the surface finish on the ProtoShields and all the other PCBs that Freetronics has done so far and the reasoning behind the decision.

Unfortunately there's no one "best" PCB surface finish and all finishes have both good and bad points, so it's a matter of making a decision based on trade-offs that are most appropriate for the intended use. That's "Electroless Nickel Immersion Gold", and consists of an underlying layer of nickel with a thin layer of gold over the top. The gold layer is very thin and not intended to provide the main structure of the track, it just acts as a protective coating for the nickel to prevent it tarnishing before it's soldered.

One downside is that it takes a bit more solder to complete a joint because the surface hasn't yet been pre-tinned, and because there isn't an existing layer of solder to melt against the iron and increase the initial contact area hence increasing the rate of heat transfer it can take an extra second or so to get the joint hot.

HASL boards are dipped in molten solder and then the excess is cleaned off using hot-air knives to leave behind the thinnest possible layer of solder. The solder itself then protects the underlying track from corrosion while making it extremely easy to solder, because the whole pad is pre-tinned. It's generally the cheapest finish available and a great choice for general-purpose boards.

One downside to HASL is that even after the hot-air knife has cleaned off as much excess as possible, the meniscus of the solder will still cause the edges of pads to be slightly rounded.

That makes surface-mount parts not sit down quite as flat as they would on an ENIG board. So you'd expect that for a board like a prototyping shield the obvious solution would be to go for HASL. But there's a catch.

Scrape any wire to be soldered with the back of a knife or any flat piece of metal Fig. If the wire is extremely dirty, dip it into a flux. Do not touch the wire with your hands after it has been cleaned. Natural oils in the skin may cause the solder not to stick.

Although the core of solder contains flux, additional flux may be required on extremely difficult soldering jobs. Liquid flux can be brushed on the metal if required. You will need flux if you are soldering with bar solder, which does not contain a core of flux. If solder remains on the tip of the pencil, gun or iron for any period of time, the flux boils out and must be replaced. If you find it difficult to get solder to stick on galvanized metal or any other hard-to-solder surface, add some flux Fig.

This will normally improve the sticking capacity of the solder. If you are attempting to solder any coated surface, such as enamelware, you must chip away the coated area before applying the solder Fig.

Solder will not stick to coated surfaces. When soldering electrical wire, separate the wires to be soldered and scrape them clean Fig. Each section of the wire should then be "tinned" or coated with a thin layer of solder. Apply this thin coating of solder by holding the wire on the hot tip of the soldering tool and feeding the rosin-core solder from the top Fig.

You will need a small bench vise or some other holding device to provide a "third hand" for soldering jobs of this type. After the wires have been thoroughly tinned, twist them together Fig.

After the wires have been twisted together, apply a small amount of flux to the exposed wire to remove any oil that might have been left on the wiring during the twisting process. A small paper cup makes an excellent holding device for soldering small pieces of wire Fig.

Make a slot in each side of the cup to hold the wire in a firm position. Also, fill the bottom of the cup with water. This will make the cup more stable and reduce the chances of a flame-up. Note in Fig. This eliminates the danger of electrical shorts and lessens the amount of buildup when the soldered spots are taped for insulation. When the wires have been twisted together and fluxed, they are ready for soldering Fig.

Hold the hot soldering tool under the joint to be soldered and feed the solder from the top. Let the solder melt and run down until the joint is thoroughly covered.

Allow the soldered joint to cool completely before applying any pressure. After the solder cools and becomes hard, test it to make sure the soldered joint is secure. Always use a rosin-core solder for soldering electrical wiring. NEVER use an acid-flux solder for soldering electrical wire. Joints soldered properly should look somewhat like those illustrated in Fig.

A joint that is properly twisted and soldered is as strong as any uncut section of the wire. Basically the solder separates from the circuit board. What am I doing wrong? PottedMeat Lifer. Apr 17, 12, You need to make sure the points you are soldering together are clean. If the connector is already in there and you can't get it out try using a tiny piece of scouring pad or sandpaper to make the contact shiny and try soldering again.

Flux in the solder you use will also help to clean the area. The solder should flow easily like mercury when hot and be shiny when cool. QuixoticOne Golden Member. Nov 4, 1, 0 0. Toshiba made a few million of them like that. To warranty repair it they soldered it back on and epoxied the jack to the board. Visual inspection should go a long way toward identifying the problem.

Like 0. Don't use a plumbing iron or a general purpose torch either. Once well soldered, consider finding a way to use non-conductive epoxy to secure the jack, though that would reduce the future repairability of it, so do it carefully after you've verified that it works.. Mar 4, 27, Solder is not effective unless there is a decent mechanical connection beneath the solder.