Proper Soldering Technique

Proper Soldering Technique


Figure 1 above shows proper soldering technique. The diagram shows the tip of the soldering iron being inserted into the joint such that it touches both the lead being soldered and the surface of the PC board.

Then, solder is applied into the joint, not to the iron directly. This way, the solder is melted by the joint, and both metal surfaces of the joint (the lead and the PC pad) are heated to the necessary temperature to bond chemically with the solder.


Figure 2 shows the typical result of a bad solder joint. This figure shows what happens if the solder is “painted” onto the joint after being applied to the iron directly. The solder has “balled up,” refusing to bond with the pad (which did not receive enough heat from the iron).

With this technique in mind, please read the following list of pointers about electronic assembly. All of these items are important and will help develop good skills in assembly:
1. Keep the soldering iron tips away from everything except the point to be soldered. The iron is hot and can easily damage parts, cause burns, or even start a fire. Keep the soldering iron in its holder when it is not being held.

2. Make sure that there is a damp sponge available used for cleaning off and tinning the tip. Soldering is basically a chemical process and even a small amount of contaminants can prevent a good joint from being made.

If you feed the solder into the soldering iron rather than the joint, the solder will ball up, refusing to bond with the improperly heated PC board pad.
3. Always make sure that the tip is tinned when the iron is on. Tinning protects the tip and improves heat transfer.
To tin the iron, clean the tip and wipe it on a damp sponge and then immediately melt some fresh solder onto the tip. The tip should be shiny and coated with solder. If the iron has been idle for a while, always clean and then re-tin the tip before continuing.

4. The tips of the irons are nickel-plated, so do not file them or the protective plating on the tips will be removed.

5. A cold solder joint is a joint where an air bubble or other impurity has entered the joint during cooling. Cold solder joints can be identified by their dull and mottled finish. The solder does not ow and wrap around the terminal like it should.
Cold joints are brittle and make poor electrical connection. To fix such a joint, apply the tip at the joint until the solder re-melts and flows into the terminal.
If a cold solder joint reappears, remove solder with desoldering pump, and re-solder the joint.

6. Do not hold the iron against the joint for an extended period of time (more than 10 seconds), since many electronic components or the printed circuit board itself can be damaged by prolonged, excessive heat. Too much heat can cause the traces on the printed circuit board to burn off.

Some components that are particularly sensitive to heat damage are: diodes, ICs, and transistors