Soldering/Troubleshooting Solder Problems

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Soldering Issues

The first problem is old flux.

With rosin cored solders, you don't need additional flux, right?

Maybe. Over time, the lead in the solder reacts with the flux, reducing its effectiveness. Not only does solder have a shelf life, so does flux. Over time they are not effective.

Another issue rarely discussed is poor quality solder. Always try to buy the best solder you can find. Quality solders are made with pure alloys, which means better performance. Lesser quality solders will have other metals in the alloy which alter its characteristics and performance.

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

Solder will not "Take;" 'Beading 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.

Oil, grease or dirt present
A dirty joint will usually cause smoking (i.e. overheated flux), darkening of the joint, and problems with solder flowing through the joint.
Desolder, clean up the parts, try again.
Material not be suitable for soldering with lead/tin solder (e.g. aluminium).
Aluminum won't solder with lead/tin solder

Joint is crystalline or grainy-looking; solder 'beading up' on the surface; solder does not appear to have 'wet' the joint.

These symptoms are generally classed as a "cold" solder joint.
Probable Cause 1 - The objects you wish to solder together have been moved before being allowed to cool
Probable Cause 2 - Not enough heat applied to allow solder to melt and flow into the joint via capillary action
Explanation 1 - Moving a solder joint before it freezes doesn't allow the solder to bond to the pieces being joined
Explanation 2 - The joint was not heated adequately 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 and 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 soldering 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. That's when moving the joint ruins it. One solution is to use 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, moving 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 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.

Generally, as long as 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 become oxidized.

Solder Forms a "Spike"

Probable Cause - Overheating the joint and/or the flux.
Flux can be burned away if heated too high
Desolder and clean the parts, then try again.

Large Blobs of Solder on Joint

Too much solder!
Although the main problem with too much solder is unsightly appearance, excess solder can cause short circuits if it connects things it's 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, make it ready. 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!

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.
  1. Iron is too hot, or tip is too large. Reduce temperature and/or replace the tip.
  2. 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.
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: