Fundamentals of Electronic Engineering: Introduction to Electric Soldering Technology

In electronic production, the joints of components need to be welded. The quality of welding has a great impact on the quality of production. Therefore, to learn electronic production technology, you must master welding technology and practice basic welding skills.

1. Welding tools

1. Electric soldering iron

Electric soldering iron is the most commonly used soldering tool. We use a 20W internal heating electric soldering iron. See Figure 1.

Figure 1

Before using a new soldering iron, use fine sandpaper to polish the tip, heat it up, dip it in rosin, and touch the soldering wire with the tip blade to evenly coat the tip with a layer of tin. This will make soldering easier and prevent oxidation on the tip surface. If an old soldering iron tip is severely oxidized and blackened, use a steel file to remove the surface oxide to expose the metallic luster, then re-tin it before use.

The soldering iron should use 220V AC power supply . Pay special attention to safety when using it. The following points should be carefully followed:

It is best to use a three-pole plug for the soldering iron. Make sure the shell is properly grounded.

Before use, carefully check whether the power plug and power cord are damaged and whether the soldering iron tip is loose.

When using the soldering iron, do not hit it hard. Prevent it from falling. If there is too much solder on the soldering iron tip, wipe it off with a cloth. Do not swing it around to avoid scalding others.

During soldering, the soldering iron should not be placed randomly. When not soldering, it should be placed on the soldering iron stand. Be careful not to place the power cord on the soldering iron tip to prevent the insulation layer from being burned and causing an accident.

After use, you should cut off the power supply in time and unplug the power plug. After cooling, put the soldering iron back into the tool box.

2. Solder and flux

When soldering, solder and flux are also required.

(1) Solder: Soldering electronic components generally uses solder wire with a rosin core. This type of solder wire has a low melting point and contains rosin flux, making it extremely easy to use.

(2) Soldering flux: Commonly used soldering flux is rosin or rosin water (rosin dissolved in alcohol). Using soldering flux can help remove oxides on the metal surface, facilitate soldering, and protect the soldering iron tip. When soldering larger components or wires, solder paste can also be used. However, it is corrosive to a certain extent, and the residue should be removed promptly after soldering.

3. Auxiliary tools

In order to facilitate welding operations, needle-nosed pliers, side-cutting pliers, tweezers and knives are often used as auxiliary tools. You should learn to use these tools correctly.

Needle Nose Pliers Side Cutting Pliers Tweezers Pocket Knife

Figure 2 Auxiliary tools

2. Pre-welding treatment

Before soldering, the component pins or the soldering parts of the circuit board should be treated before soldering (see Figure 3).

1. Remove the oxide layer at the welding site

You can use the broken saw blade to make a knife to scrape off the oxide layer on the surface of the metal lead to expose the metallic luster of the lead.

The printed circuit board can be polished with fine gauze paper and then coated with a layer of rosin alcohol solution.

2. Tin plating of components

Tin the scraped lead wire. You can dip the lead wire in rosin alcohol solution, press the hot soldering iron tip with tin on the lead wire, and rotate the lead wire. This will make the lead wire evenly coated with a very thin layer of tin. Before welding the wire, the insulation sheath should be stripped off, and then the above two treatments can be performed before formal welding. If it is a multi-strand wire, it should be twisted together after polishing, and then tinned.

Scrape off the oxide layer and evenly plate a layer of tin

Figure 3 Pre-welding treatment

3. Welding Technology

After completing the pre-welding treatment, welding can be officially carried out.

1. Welding method (see Figure 4).

Welding Check Shortening

Figure 4 Welding

(1) Hold the soldering iron in your right hand. Use needle-nosed pliers or tweezers in your left hand to hold the component or wire. Before soldering, the soldering iron should be fully preheated. The blade of the soldering iron tip should be tinned, that is, it should be covered with a certain amount of solder.

(2) Place the tip of the soldering iron close to the soldering point. The soldering iron should be at an angle of about 60° to the horizontal plane. This will allow the molten tin to flow from the tip to the soldering point. The time the tip stays at the soldering point should be controlled to be 2 to 3 seconds.

(3) Lift the soldering iron tip. Keep holding the component with your left hand. Wait until the solder at the soldering point cools and solidifies before releasing your left hand.

(4) Use tweezers to turn the lead wire to make sure it is not loose, then use side cutting pliers to cut off the excess lead wire.

2. Welding quality

When welding, make sure that each solder joint is firmly welded and in good contact. Ensure the welding quality. A good solder joint is shown in Figure 5

Figure 5

(A) The solder point should be bright, smooth and without burrs, with a moderate amount of solder. The solder and the object to be soldered should be firmly integrated. There should be no false solder joints or false solder joints.

Cold soldering means that only a small amount of tin is soldered at the solder joint, resulting in poor contact and intermittent connection. False soldering means that the soldering seems to be done on the surface, but it is not actually done. Sometimes the lead wire can be pulled out of the solder joint by hand. These two situations will bring great difficulties to the debugging and maintenance of electronic production. Only through a lot of careful soldering practice can these two situations be avoided.

When soldering a circuit board, be sure to control the time. If it is too long, the circuit board will be burned or the copper foil will fall off. When removing components from the circuit board, you can stick the soldering iron tip on the solder joint, and after the tin on the solder joint melts, pull out the component.