PCB Blog - Electric soldering iron welding method in PCBA

There are many places in the design, processing and testing of PCB A that need to use electric soldering iron for manual welding. The difference between manual welding of electric soldering iron and machine welding, such as wave soldering and reflow soldering, is that manual soldering of soldering iron is affected by many human factors. Unlike machine welding, once the process parameters are adjusted, the production is stable. There are also problems of welding temperature and welding time in manual welding. We first introduce the manual lead-free welding process of electric soldering iron, the welding process window, and the principle of heat transfer of electric soldering iron to the pad. We should deeply understand the meaning of welding temperature and welding time. Only through theoretical guidance and diligent practice can we become qualified skilled workers.

PCB A

Make preparations before welding

1. When we first use a new electric soldering iron, we should first have a preliminary understanding of the characteristics of the soldering iron itself, such as working voltage, electric power, heat recovery rate, and the size and variety of the soldering iron head;

2. It is necessary to know whether the type of solder is lead-free solder and the thickness of their melting point tin wire;

3. Understand the type of components, such as plug-in or SMD components and thermal sensitive keys;

4. Have an understanding of the material of the printed board, the plating type of the bonding pad, such as whether tin base, gold plating, osp and parameters. Generally, the temperature of the gold-plated plate should be appropriately higher than that of the tin base plate, and the heat absorption of the multi-layer plate should be greater than that of the double-layer plate and the single-layer plate;

5. Be familiar with the size of welding spot and the speed of heat dissipation of welding surface;

6. The anti-static performance of the electric soldering iron, whether the workbench has anti-static grounding port, usually when the electric soldering iron is connected to the power supply, the anti-static channel should also be connected.

In a word, it is very useful to be familiar with the performance of the tool and the basic parameters of the welding object to adjust the temperature and model of the soldering head. Of course, if conditions permit, the welding process parameters can be further confirmed by testing the temperature of the PCBA and PCBA test welding.

Operation method of electric soldering iron in PCB processing and assembly

Operators who use electric soldering iron for manual welding for the first time should be strict with themselves, develop good operation habits, achieve correct welding posture, and master the basic operation steps of welding and the basic essentials of manual welding.

1. Correct welding posture

In the manual welding of electronic products, sitting welding is generally adopted. The height of the workbench and seat should be appropriate. The relative position between the operator's head and the electric soldering iron should be kept at 30~50cm. Hold the soldering iron in one hand and the tin wire in the other hand, and visually weld the points.

2. Method of holding electric soldering iron by welding operator

Generally, according to the size of the electric soldering iron, there are three different operation methods: reverse grip method, positive grip method and pen grip method. Among them, the reverse grip method is suitable for the operation of welding large solder joints with high-power electric soldering iron larger than 75 watts; The positive grip method is suitable for the operation of medium-power electric soldering iron and electric soldering iron with elbow, while the pen grip method is suitable for the welding of components on printed circuit boards with low-power electric soldering iron, which is mainly used for the manual welding of electronic products.

3. Electric soldering iron contact solder joint direction

When using the pen grip method to weld electronic products, the electric soldering iron should contact the solder joint in a 45 degree direction, which is conducive to operation and observation of the formation of the solder joint.

4. How to handle the tin wire

There are usually two methods for holding the solder wire, one is suitable for continuous welding, and the other is suitable for intermittent welding (the welding point is usually large.. During the actual welding operation, wear gloves when holding the solder wire, especially the lead-containing tin wire, to prevent the skin from contacting with lead frequently.

5. Basic operation of manual welding

The manual welding operation process can be divided into five steps, which are required to be completed within 3~5 seconds. They are:

5.1. Prepare to approach the soldering head and tin wire to the soldering pad;

5.2. For heating, first place the soldering iron head on the pad, which is the first preheating of the pad;

5.3. Lay the tin wire on the contact part between the soldering iron head and the soldering pad to melt it quickly;

5.4. After the solder joint is formed, remove the tin wire first;

5.5. Remove the electric soldering iron and cool the solder joint into shape;

In the case of small welding spot, the three-step method can also be used to complete the PCBA welding, and step bc and step de in the five-step method can be combined into one.