Soldering Lead Came

Historically soldering tips were copper, placed in braziers. One tip was used until it became too cool, when it was placed back in the brazier of charcoal and the next tip was used. Later gas irons were used and currently electric soldering irons are most commonly used.

Soldering lead came is different from soldering electronics or copper foil. For electronic soldering less heat is needed, cleanliness is all important, suitable flux is required, and the iron is held differently, among other things.

The lead needs to be clean and bright to enable the solder to stick to it. If it's fairly new lead it may be solderable without further preparation before adding the flux. However, if the lead is dull and oxidized, you should scrape the lead in the area to be soldered with the blade of a lead knife, or glazing nail.

Then the flux can be applied.  Paste flux or tallow works best as neither flows in its cold state.  This means that you can flux the whole panel at one time without the liquid flowing away or drying.  And once the whole panel is fluxed, you do not need to stop during the soldering process.

an example of paste flux

Example of a tallow stick.  It has the appearance of a candle, but without the wick.

Example of the application of tallow to a joint

The iron is held over-handed (as you would a bread knife) in order to get the handle low enough to have the tip flat on the lead. You can allow the weight of the iron to press gently against the joint to transfer the heat into the lead or foil.

Example of a gas powered soldering iron. The flat face of the soldering bolt is held in full contact with the joint.

The solder is fed to the iron tip in one of several ways.  

• One is to place the solder over the joint and melt a small amount off the solder stick and pause to allow the solder to heat the joint and bind the metal together.  Move the solder away as soon as it is melted, so it doesn't become attached. As soon as you see the solder at the joint melt and spread, lift the iron straight up.
• Another method is to apply the solder to the iron before placing the iron on the joint and allow the solder to run to the joint.
• A very fast way of soldering, which runs the risk of melting the lead, is to heat the joint and then apply the solder to the iron.  This ensures the joint is hot so the solder quickly attaches the metal together.

This image represents the principle of soldering any metal, not just computer boards

The most common concern is whether there is enough solder on the joint. Very little solder is required to stick the joints together. Often a securely soldered joint shows the ends of the cames. For cosmetic reasons it is usual to use enough solder to disguise the ends of the cames. It is not a structural requirement.

An electric soldering iron is held over-handed (as you would a bread knife) in order to get the handle low enough to have the tip flat on the lead. This will be a 15 to 20 degree elevation from the horizontal. Allow the weight of the soldering iron to do the work for you. 

Let it rest on the joint after you apply the solder.  Take the solder away from the iron and joint so it doesn't become attached to the joint.  As soon as the solder spreads from under the bit, lift the iron straight up. This process will take only a few seconds, and much less than 5.

Example of smooth flat solder joints.

Avoid "painting" or dragging the iron across the joint. Moving the iron and solder around does two things.  It makes for a weak joint as the solder does not have the chance to become stable and so a "pasty" joint is formed.   Moving the iron around during the soldering of the joint also provides sharp points where the iron was moved quickly off the join. There should be no points sticking up from the solder joint. 

The object is to have a shiny, smooth, slightly rounded solder joint. If a solder joint is not satisfactory you can re-flux and re-heat. Don't apply large amounts of solder - it's easier to add more solder than to remove excess.