Hand soldering with an electric soldering iron is not difficult to master, but there are some technical essentials. Those who have long worked in SMT electronic product production have identified four key elements of soldering (also known as 4M): materials, tools, methods, and operators. Among these, human skills are the most critical. Without substantial practice and a deep understanding, one cannot master the technical essentials of soldering; even an experienced worker cannot guarantee the highest quality of every SMT solder joint. Only by fully grasping the principles of soldering and practicing carefully can one acquire basic skills in a relatively short time. The specific methods and tips provided below are shortcuts for beginners to rapidly develop soldering skills.
Beginners should practice diligently and continuously enhance their skills, and should not leave soldering quality issues to be resolved during overall circuit debugging.
1. Correct posture for soldering operation
Mastering the correct posture helps ensure the physical and mental health of the operator and minimizes labor injuries. To reduce harm from chemical substances released when flux is heated and to decrease the inhalation of harmful gases, the distance from the soldering iron to the nose should generally be no less than 20cm, ideally 30cm.
2 Basic Steps of SMT Soldering Operation
To achieve a good solder joint, it’s crucial to master the temperature and soldering time of the soldering iron and to choose the proper contact position between the soldering iron tip and the solder joint. The correct soldering operation process can be divided into five steps:
2.1 Preparation for Soldering: Hold the soldering iron in your right hand and prepare for soldering. Ensure the soldering iron tip is clean, free of slag and other oxides, and has a layer of solder plated on its surface.
2.2 Heating the Weldment: Position the soldering iron tip on the joint of the two weldments to heat the entire weldment for approximately 1-2 seconds. When soldering components on a printed circuit board, ensure the soldering iron tip contacts both the pad and the component lead simultaneously.
2.3 Feeding the Solder Wire: Once the welding surface of the weldment reaches the appropriate temperature, introduce the solder wire to the weldment from the opposite side of the soldering iron. Avoid feeding the solder wire directly onto the tip of the soldering iron.
2.4 Removing the Solder Wire: Once the solder wire has melted sufficiently, promptly move the solder wire to the upper left at a 45° angle.
3 Welding Temperature and Heating Time
Proper temperature is essential for forming good solder joints. To master this temperature, relevant data can help identify the optimal temperature required for different weldment materials and provide the necessary curve. However, during the general soldering process, it is impractical to use thermometers and other instruments for continuous measurement. Instead, an intuitive understanding of the weldment’s temperature is more useful.
Experience shows that the duration the soldering iron tip remains on the weldment is directly proportional to the temperature increase of the weldment. For the same soldering iron, heating different-sized weldments can achieve the same welding temperature by controlling the heating time. However, in practice, heating time cannot be determined solely by this relationship. For larger pieces, a small to medium-power soldering iron may not heat the soldering piece adequately due to its heating capacity being insufficient to compensate for heat loss in the air. Additionally, to prevent internal damage from overheating, some components should not be heated for extended periods. Insufficient heating time can lead to incomplete solder infiltration, resulting in rosin inclusions and cold solder joints.
4 Specific Methods of Soldering
To ensure high quality, specific soldering techniques can vary, but beginners should not overlook the following established methods:
(1) Keep the Soldering Iron Tip Clean: During SMT soldering, the soldering iron tip remains at high temperatures for extended periods and is exposed to flux, which can cause oxidation and black impurities to form. These impurities create an insulating layer that impedes heat transfer between the soldering iron tip and the weldment. Regularly clean the soldering iron tip by wiping it with a damp cloth or sponge. For significant contamination, use a file to remove the oxide layer from ordinary soldering iron tips. Avoid using this method on long-life soldering iron tips.
(2) Increase Heat Transfer by Expanding Contact Area: Ensure that all parts of the weldment needing solder infiltration are evenly heated. Avoid using the soldering iron to apply excessive pressure to the weldment to prevent damage or unnoticed solder bridges. Beginners should not try to speed up soldering by pressing the soldering iron tip onto the soldering surface. Instead, use different soldering iron tips based on the weldment’s shape, or trim the tip to ensure surface contact with the weldment rather than point or line contact, which improves efficiency.
(3) Utilize SMT Solder Bridges for Heating: In non-pipeline operations, solder joint shapes vary, making it impractical to frequently change soldering iron tips. To enhance heating efficiency, use a solder bridge to transfer heat. A solder bridge is created when solder remains on the soldering iron tip, transferring heat between the tip and the solder. Since molten metal has much higher thermal conductivity than air, it heats the solder joints quickly. However, avoid using excessive solder for the bridge to prevent potential misconnections.
Beginners should practice diligently and continuously enhance their skills, and should not leave soldering quality issues to be resolved during overall circuit debugging.
1. Correct posture for soldering operation
Mastering the correct posture helps ensure the physical and mental health of the operator and minimizes labor injuries. To reduce harm from chemical substances released when flux is heated and to decrease the inhalation of harmful gases, the distance from the soldering iron to the nose should generally be no less than 20cm, ideally 30cm.
2 Basic Steps of SMT Soldering Operation
To achieve a good solder joint, it’s crucial to master the temperature and soldering time of the soldering iron and to choose the proper contact position between the soldering iron tip and the solder joint. The correct soldering operation process can be divided into five steps:
2.1 Preparation for Soldering: Hold the soldering iron in your right hand and prepare for soldering. Ensure the soldering iron tip is clean, free of slag and other oxides, and has a layer of solder plated on its surface.
2.2 Heating the Weldment: Position the soldering iron tip on the joint of the two weldments to heat the entire weldment for approximately 1-2 seconds. When soldering components on a printed circuit board, ensure the soldering iron tip contacts both the pad and the component lead simultaneously.
2.3 Feeding the Solder Wire: Once the welding surface of the weldment reaches the appropriate temperature, introduce the solder wire to the weldment from the opposite side of the soldering iron. Avoid feeding the solder wire directly onto the tip of the soldering iron.
2.4 Removing the Solder Wire: Once the solder wire has melted sufficiently, promptly move the solder wire to the upper left at a 45° angle.
3 Welding Temperature and Heating Time
Proper temperature is essential for forming good solder joints. To master this temperature, relevant data can help identify the optimal temperature required for different weldment materials and provide the necessary curve. However, during the general soldering process, it is impractical to use thermometers and other instruments for continuous measurement. Instead, an intuitive understanding of the weldment’s temperature is more useful.
Experience shows that the duration the soldering iron tip remains on the weldment is directly proportional to the temperature increase of the weldment. For the same soldering iron, heating different-sized weldments can achieve the same welding temperature by controlling the heating time. However, in practice, heating time cannot be determined solely by this relationship. For larger pieces, a small to medium-power soldering iron may not heat the soldering piece adequately due to its heating capacity being insufficient to compensate for heat loss in the air. Additionally, to prevent internal damage from overheating, some components should not be heated for extended periods. Insufficient heating time can lead to incomplete solder infiltration, resulting in rosin inclusions and cold solder joints.
4 Specific Methods of Soldering
To ensure high quality, specific soldering techniques can vary, but beginners should not overlook the following established methods:
(1) Keep the Soldering Iron Tip Clean: During SMT soldering, the soldering iron tip remains at high temperatures for extended periods and is exposed to flux, which can cause oxidation and black impurities to form. These impurities create an insulating layer that impedes heat transfer between the soldering iron tip and the weldment. Regularly clean the soldering iron tip by wiping it with a damp cloth or sponge. For significant contamination, use a file to remove the oxide layer from ordinary soldering iron tips. Avoid using this method on long-life soldering iron tips.
(2) Increase Heat Transfer by Expanding Contact Area: Ensure that all parts of the weldment needing solder infiltration are evenly heated. Avoid using the soldering iron to apply excessive pressure to the weldment to prevent damage or unnoticed solder bridges. Beginners should not try to speed up soldering by pressing the soldering iron tip onto the soldering surface. Instead, use different soldering iron tips based on the weldment’s shape, or trim the tip to ensure surface contact with the weldment rather than point or line contact, which improves efficiency.
(3) Utilize SMT Solder Bridges for Heating: In non-pipeline operations, solder joint shapes vary, making it impractical to frequently change soldering iron tips. To enhance heating efficiency, use a solder bridge to transfer heat. A solder bridge is created when solder remains on the soldering iron tip, transferring heat between the tip and the solder. Since molten metal has much higher thermal conductivity than air, it heats the solder joints quickly. However, avoid using excessive solder for the bridge to prevent potential misconnections.
