With the rapid development of the electronics industry and the continuous improvement of product quality, the excellent soldering process plays an increasingly important role in the electronics industry. Therefore, we systematically study the soldering theory and have considerable problems in solving the welding defects and improving the quality. help.

Below, we will focus on the basic principles of soldering, flux, solder, automatic soldering machine, SMT wave soldering technology, bad causes and countermeasures after automatic soldering, zero defect management of soldering engineering, etc. according to the company's actual situation. .

A, the principle of soldering

Before studying the materials and equipment used in welding engineering, we must first understand the basic principles of soldering. Otherwise, we cannot visually verify the solder joints formed by soldering and the effects of different parts on the project.

1 wetting

Wetting is the protagonist in the welding behavior, and the joining is the effect of bonding the liquid solder to the substrate to achieve the bonding. When the solder is wetted on the substrate, the two are chemically bonded to each other to form a continuous joint. Under actual conditions, the substrate is often eroded by air and the surrounding environment, and an oxide layer is formed. It blocks solder and does not achieve good wetting.

Soldering machine manufacturer

1, welding and gluing

When the two materials are glued together, the surfaces of the two materials are adhered to each other by a mechanical bond between them. Soldering is the formation of an intermolecular bond between the solder and the metal. The molecules of the solder penetrate into the molecular structure of the base metal to form a strong, fully metallic structure. When the solder dissolves, it is also impossible to wipe it off completely from the metal surface because it has become part of the base metal.

2, wetting and no wetting

The greased metal sheet is immersed in water without wetting. For example, the metal sheet is washed in a hot cleaning solvent and carefully dried, and then immersed in water, the liquid will completely diffuse to the surface of the metal sheet. A thin, uniform film layer is formed after it wets the metal sheet.

3, clean

When the solder surface and the metal surface are very clean, the solder will wet the metal surface. If the cleaning is not enough, a very thin layer of contamination is formed between the solder and the metal. Almost all of the metal will oxidize immediately when exposed to air. This extremely thin oxide layer will wet the solder on the surface of the anti-condensation metal. effect.

By the same token, in the manufacturing process of our company's cordless phones, many PCB solder PADs are exposed to the air for a long time without any cleaning measures, and the oxide layer formed will seriously affect the quality of the soldering behind ( This will also help us to study the INT phenomenon of the surface contact charging chip. 4. The function of the capillary is to combine the two clean metal surfaces and immerse them in the molten solder, which will wet the two metals. The surface climbs upwards, which fills the gap between the adjacent surfaces, which is capillary action. The dirty metal surface has no wetting action and the solder does not fill this point.

In the automatic soldering process, when a printed circuit board of a plated through hole passes through a wave soldering furnace, the force of capillary action fills the hole with tin and forms a solder strip on the printed circuit board instead of wave. The pressure pushes the solder into the hole, and understanding this problem serves as a guide for us to solve the short circuit of the printed circuit board through the hole in the soldering process.

5, surface tension

Cleaning the metal surface with a solvent reduces the surface tension (in the soldering process, we introduce the flux “FLUX”, which removes oxides between the metal and the solder, allowing the tin to wet the wet metal surface).

Contaminants in the solder increase the surface tension, and the solder temperature also affects the surface tension. The higher the temperature, the smaller the surface tension, but this effect is lower than the oxidation produced by it.

WETTING ANGLE q, the angle between the solder surface and the copper plate, is the basis for all solder joint inspections. The smaller the q, the better the wetting.