What is the flux?
The flux is a kind of high temperature resistant coating. In order to prevent bridge and short circuit in the welding process, the welding materials can be protected by the resistance flux on the parts that do not need to be welded, so that the solder can only be carried out on the welding joints that need to be welded.
The use of flux is especially important for high density printed circuit board, which can reduce the repair rate and save solder, so that the thermal shock of the printed circuit board is less, and the surface of the board is not easy to bubble and delaminate. The common green coating on printed circuit boards is flux.
1. Advantages of flux
(1) it can avoid or reduce the defects such as bridging, drawing and welding and connecting rod, so that the solder joint is full, the repair quantity of plate is reduced greatly, the welding quality is improved, and the reliability of products is ensured.
After the use of the flux, except for the pad, the other lines are not tin, can save a lot of solder. In addition, because of less heat, faster cooling and lower temperature of printed circuit board, it plays the role of protecting components and integrated circuits.
The part of the board is covered by flux film, which increases the hardness, and is a good permanent protective film for printed circuit board. It can also prevent the surface of printed circuit board from being damaged by machinery.
2. Classification of flux
There are many kinds of flux, according to whether its film-forming material is cured by heating or light, it can be divided into two kinds: heat curing and light curing.
The film forming materials used in heat curing flux include phenolic resin, epoxy resin amino resin and alkyd resin. They can be used alone or in combination, or they can be modified for use. These film-forming materials need to be heated and solidified at 130 ~ 150C.
Heat curing flux has the advantages of strong adhesion, high temperature resistance of 300C, low price and high bonding strength. The drawback is that it contains solvent and is toxic; the heating temperature is high and the time is long, that is, to bake at 200C high temperature for 2 h, so the printed circuit board is prone to warp deformation, and the excessive heating time also leads to high energy consumption; the continuous production process cannot be realized. As a result, the production cycle is long.
Light curing flux is also called Guang Min flux. The film material it uses is unsaturated polyester resin containing saturated ethylene resin, acrylic epoxy resin and so on. Its advantage is that the curing time is short, under the high pressure mercury lamp irradiation, as long as 23min can solidify, saved a lot of energy.