Three SMT welding methods and tips for using solder wire

The Circuit board manufacturer and circuit board designer will explain the three SMT welding methods and tips for using solder wire

SMT welding method

Welding is the core technology of electronic assembly. Welding quality directly affects the performance and servICe life of electronic products. Welding methods can be divided into fusion welding, pressure welding and brazing.

1、 Welding method

1. Fusion welding is to heat the connection part of two weldments to the melting state without pressure, so that it can be cooLED and solidified into a whole to complete welding. Fusion welding is divided into arc welding, electroslag welding, plaSMA arc welding and gas welding;

2. Pressure welding refers to the welding process in which pressure must be applied to the weldment while heating (or not) to complete the welding. Pressure welding is divided into forging welding, resistance welding, friction welding and cold pressure welding;

3. Brazing is a method that uses metal materials with a melting point lower than that of the weldment (the metal to be welded, or the base metal) as filler metal, heats the weldment and filler metal to a temperature higher than the melting point of the filler metal and lower than the melting temperature of the base metal, wets the base metal with liquid filler metal, fills the joint gap and diffuses with the base metal to connect the weldment. Brazing is divided into soft soldering and brazing. The welding with melting point lower than 450 ℃ is called soft soldering, and the welding with melting point higher than 450 ℃ is called brazing. Whether manual welding, DIP welding, wave soldering or reflow soldering, all belong to brazing.

The quality objective of SMT processing is to improve the pass through rate. It is different from fusion welding and pressure welding. Fusion welding is to use external heat source (such as electric arc) to locally heat and melt the connected components, that is, the area near the base metal interface, and then cool to form a joint, which is characterized by melting the base metal; Pressure welding is to apply pressure to make the atomic distance of the welded surface close to the lattice distance. At the same time, in resistance welding, the base metal will melt. Brazing realizes the connection of brazed parts through molten metal (brazing), in which the base metal is not melted and the filler metal is melted.

Tips for using solder wire in SMT

1、 Use tips

1. Do not wrap the solder wire around your fingers during use. Tightly clenched on your fingers will hurt your skin and make it difficult to move the solder wire. The solder wire should be held at the side of your thumb, index finger and middle finger. The length of the tin wire should be 4CM to 8CM. If it is too long, it is easy to shake, so that the welding is not in place, and if it is too short, it is easy to burn your fingers.

2. Solder wire shall be wetted with solder frequently when heating and wiped off before use. The oxide on the soldering iron head shall not be filed or knocked. When the affinity is reduced by oxidation, the soldering iron head shall be cleaned with soldering tin. As the soldering tin contains flux, the oxide can be removed. If this is not possible, it can be wiped with decontamination powder.

3. The electric soldering iron is used for soldering. How to hold the soldering iron: When holding the soldering iron, keep your fingers away from the metal part of the soldering iron. The preheated electric soldering iron (the preheating time is 3 minutes to 5 minutes) cannot be waved at people to avoid scalding yourself and the people around. When welding, the electric soldering iron less than or equal to 60W should be held like a pen, and the electric soldering iron greater than or equal to 80W should be generally held in the palm of your hand for welding. There is a layer of zinc oxide alloy on the surface of the tip of the new soldering iron. Before use, put a layer of tin on the tip to clean it. On and off duty, the soldering head shall be cleaned with solder wire and coated with solder to prevent oxidation; During the use of the soldering iron, the soldering iron head shall be cleaned frequently with a sponge to keep it clean.

The above are the three SMT welding methods and tips for using solder wire explained by the circuit board manufacturer.