Welding flux for SnAgCu alloy solder powder and preparation method thereof

Abstract

The invention relates to a soldering flux for Sn-Ag-Cu alloy solder powder, which is characterized by comprising the following compositions in proportion by weight: 25 to 40 percent of organic solvent, 5 to 10 percent of activating agent, 30 to 55 percent of rosin, 5 to 10 percent of thixotropic agent, and 5 to 10 percent of plasticizing agent. The invention also provides a preparation method for the soldering flux. In the invention, the plasticizing agent strengthens the liquidity of residues, so that soldering paste prepared from the soldering flux and the Sn-Ag-Cu alloy solder powder has few residues after welding and can be well spread around welding spots; the residues are transparent so as to ensure good brightness of the welding spots; the corrosion of the residues to the welding spots and components and parts is greatly reduced at the same time; and the proper amount of thixotropic agent makes the soldering paste prepared from the soldering flux and the Sn-Ag-Cu alloy solder powder have high stability and good thixotropic property, and the soldering paste has good sagging resistance in printing and welding, and reduces solder balls generated around the welding spots in reflow soldering.

Description

technical field [0001] The invention relates to a flux, in particular to a flux used for SnAgCu alloy solder powder and a preparation method thereof. Background technique [0002] The traditional solder paste is mainly composed of lead-containing solder powder (such as lead-tin alloy solder powder). As a packaging material for electronic products, it has excellent welding and electrical conductivity for circuit boards that need to be welded, and the solder joints are bright. , full, but in the process of disposing of discarded electronic products (mostly using landfill treatment at present), the lead in solder powder encounters acid rain or acidic groundwater, it will seep into the ground, dissolve in groundwater, pollute the water source, people Drinking lead-contaminated water for a long time can lead to lead poisoning and cause serious harm to health. [0003] In view of the serious harm caused by lead solder powder, lead-free electronic packaging has become a trend arou...

AI Technical Summary

Problems solved by technology

However, since lead-free solder paste contains more active agents and rosin resin, the chemical properties of rosin mainly depend on resin acid. The structural formula of resin acid contains two types of chemical substances, double bond and carboxylic acid. The resin acid in rosin The double bond has a strong chemical reactivity. Under the condition of high temperature and oxygen-containing welding, at the same time, when metal ions are used as a catalyst, the solder powder and oxygen undergo an oxidation reaction, and the resin acids polymerize with each other under the action of the catalyst. Reaction, the produced oxides and polymers have relatively long molecular chains and extremely poor fluidity. In this way, during the second half of reflow soldering, most of the residues composed of these oxides and polymers will remain on the soldering surface. The spot surface has poor fluidity, so there will be more residues covering the surface of the solder joints. Because of the large amount of residues, the thickness of the residues will be thicker, and the brightness of the solder joints will also be affected to a certain extent. , the residue still contains a small amount of active substances, and the residue adheres to the surface of the solder joint for a long time, which will corrode the circuit board and components, and shorten the service life of electronic products to a certain extent

[0005] In addition, although most of the solder pastes containing SnAgCu alloy solder powder (such as the environmentally friendly solder paste disclosed in the Chinese invention patent application publication specification CN101152686A) have good strength, resistance Fatigue characteristics, plasticity, solubility and persistence, but in the three processes of printing, patching and welding, it is easier to produce solder bead defects, mainly manifested in cold collapse during printing and patching (drying after printing) The appearance deformation of the solder paste during the process is called cold collapse), and thermal collapse occurs during the preheating and heat preservation stages of the soldering process (solder paste deformation during heating is called thermal collapse); when the solder paste collapses (collapse is Refers to the change in the appearance of the solder paste during the drying or heating process after printing and patching (including cold collapse and heat collapse) After the phenomenon, the solder paste will produce solder beads in the final reflow soldering stage, and the soldering defect rate is relatively high high