Soldering/Troubleshooting Solder Problems

Soldering Issues

Summary

Excessive solder applied to joints increases the possibility of unwanted solder bridges between adjacent joints.
Too little solder results in low joint strength. Solder should completely fill printed circuit board pads all around the component lead being soldered.
Moving the work before the solder solidifies creates a fractured joint. The solder to metal bond is fractured just before the solder has solidified. These issues may go undetected for years. This joint often appears dull and grainy, especially at the interface.
Too little heat causes a cold solder joint. This joint may adhere, but can be expected to fail in time. This joint likely does not have feathered edges where it interfaces with the pad and lead. Generally, appears as a solder globule rather than a joint with feathered edges. It may be shiny.
Excessive tip temperatures cause oxidation of the tip and solder to rolls off the tip rather than wetting it. A non-wetted/tinned soldering tip requires an extended application time to work. Pads can even delaminate from a circuit board if too much heat is applied.
Soldering a contaminated PCB or one with excessive oxide will produce a non-functioning joint. The solder tends to ball up and roll off the joint rather than bonding.
No flux or too little flux produces an unacceptable solder joint; Solder will often ball up instead of flowing.
Soldering electronic parts with acid core solder, corrosive flux, or conductive flux.

Flux

The first issue is old flux.

With rosin cored solders, you don't need additional flux, right? Over time, the lead in the solder reacts with the flux in its core, reducing effectiveness. Not only does flux core solder have a shelf life, so does flux. Over time they are not as effective. Another issue rarely discussed is poor quality solder. Always buy the best solder you can find. Quality solders are made with pure alloys, for better performance. Lesser quality solders will have other metals in the alloy which alter its characteristics and performance.

Quality Solder
Solder which has not reached its expiry date
1. Fresh flux is the antidote to this issue.
Flux which has not expired
Read the manufacturer's data sheets for their soldering products

Solder Will Not Take or Beads Up on the Surface

Soldering-PCB-bad

Soldering-PCB-good

This is what wetting is. The solder will alloy with the metal and form a bond. If the solder will not wet, the result is solder which can be removed completely using a tool.

On a clean surface the solder will flow. On a dirty surface it will ball up and not stick to it.

Reasons for Poor Wetting

Oxidation on solder surfaces. If a solder tip is left hot without a covering, it may react with oxygen and lead to improper wetting.
Temperature: If the temperature is too low, the solder won’t flow adequately into the joint. Too high temperatures can rapidly burn off solder as a vapour, impeding proper solder wetting.
Over application of the iron. Holding the iron's tip to the components for an extended period can lead to burned flux and damaged.
Insufficient wetting. Oils, grease, dirt, or failing to apply heat to both parts can lead to insufficient wetting and lack of bonding.

A dirty joint will usually cause smoking (i.e. overheated flux), darkening of the joint, and problems with solder flowing through the joint. The remaining flux will have a dark, burnt appearance.

Desolder, clean up the parts, try again.

Material not be suitable for soldering with lead/tin solder (e.g., aluminium).

Aluminum will not solder using lead/tin solder.

Cold Solder Joint

Resulting joint is dull, crystalline or grainy-looking; solder 'beads up' on the surface; solder does not appear to 'wet' the joint. These symptoms are generally classed as a "cold solder joint.

The objects you wish to solder together have moved before being allowed to cool.
Not enough heat applied to allow solder to melt and flow into the joint via capillary action.

Moving a solder joint before it freezes doesn't allow the solder to bond to the pieces being joined.
The joint was inadequately heated due to a low wattage iron, inappropriate tip size or too large a joint.

Sometimes re-heating the joint and adding more solder is sufficient; otherwise, desolder, clean up the parts, then try again. If the problem is due to a too-small iron or too-large parts, obtain a larger iron, soldering gun, or a torch to supply additional heat. Be careful of 'collateral damage;' i.e. melting of the surrounding materials. A soldering iron should be at least 60W, or use a temperature-controlled station and increase the heat/change tips.

When solder changes from liquid to solid, it passes through a plastic state. Moving the joint when it is in this state ruins it. One solution is to a Eutectic solder. It has a slightly different tin/lead ratio (63/37 instead of 60/40). It goes rapidly from liquid to solid and spends almost no time in the plastic state. Therefore, movement of the joint is much less of a problem.

BTW: If you ask for eutectic solder, the store clerk may not know what you're talking about. Just ask for 63/37.

As a general rule, a solder joint can be remelted three times. After that, face the fact that the joint was not properly prepared. Remove all the solder and start over. You can remove solder with a solder sucker or solder wick. If the solder wick isn't working well, apply a little flux first to the wick.

If the joint is shiny, you have a good joint. A dull colour indicates trouble. If you re-melt a joint and the colour goes dull then the solder has probably oxidized.

Solder Forms a Spike

Probable Cause – Overheating the joint and/or the flux.
- Flux can be burned away with excessive heat
Desolder, clean the parts and try again.

Large Blobs of Solder on Joint

Too much solder!
- Using a light gauge solder helps control the amount of solder applied.
Although the main problem with too much solder is an unsightly appearance, excess solder can cause short circuits if it connects things it is not supposed to, or blocks trains from running down the rails!
This is where the "solder sucker" comes into play. Make the solder sucker ready – if it is spring loaded, depress the plunger. If it's a squeeze syringe, squeeze it. Heat the joint until the solder turns shiny (melted).
With careful coordination, press the tip of the solder sucker into the molten solder and let it go! Much of the solder should disappear into the tool. You may have to poke a stiff wire into the business end of a solder sucker to unclog it from time to time. Make sure there is sufficient solder remaining in the joint!

In many applications, such as building hand laid turnouts, only a little solder is needed to make the joint.

Strands of Wire not Embedded in Solder; Parts Loose

Not enough solder used.
Solder should surround all strands of wire; parts should be held firmly by the solder, sometimes re-heating the joint and adding more solder is sufficient; otherwise, desolder and clean up the parts, then try again.

To tin a wire, start in the middle, add a little solder and move the iron toward the insulation, then move toward the end. You should be able to identify strands of wire when properly done. Additional flux will improve the result.

Surrounding Objects Charred, Melted, or Damaged

Probable Cause - "Collateral Damage" due to soldering in too-tight quarters; poor control of business end of the iron, inadequate or excessive heat.

Iron is too hot, or tip is too large. Reduce temperature and/or replace the tip.
Iron isn't hot enough, or tip is too small.
1. If it is not hot enough to make the joint within two seconds, continued application of heat will allow the energy to travel further into the work (heatsink), possibly melting or damaging something. At the joint it doesn't get hot enough to melt solder effectively.

Low wattage irons can be an issue. Their problem is that they cannot recover quickly when the heat energy is transferred to the work. An iron in the 40 to 60W range is usually adequate, a soldering station with the ability to control the temperature is the best option.

The soldering iron is HOT! Plastics will melt, other materials will char.
Be more careful in the future.
Make changes to the tip and temperature used to minimize the time needed to heat and solder the work.

Notice that many of the problems are fixed in the same way – Desolder and clean up the parts, then try again. This does cure a lot of problems; soldering is generally a reversible process, except for a thin coating of solder on the parts (they are now 'tinned').

Helpful Videos

The following videos may be helpful when soldering: