Lead-free halogen-free tin paste and production process thereof

Abstract

The invention relates to the technical field of electronic welding, in particular to lead-free halogen-free tin paste which comprises, in weight percent, 88%-90% of tin powder and 10%-12% of paste flux. The tin powder is made of alloys including 88-94.5% of Sn, 0.2-1.2% of Ag, 0.3-0.8% of Cu and 5-10% of Bi. The paste flux comprises rosin, solvents, corrosion inhibitors, activators, thixotropic agents and thickening agents, wherein the activators comprise organic acid and organic amine. The paste flux is prepared by an emulsion dispersion high-speed shearing process. A preparation method of the tin paste includes the steps: placing the tin powder and the paste flux into a sealed stirrer for stirring according to the proportion; pumping vacuum; releasing the vacuum; finishing preparation of the tin paste. The lead-free halogen-free tin paste is low in melting point, fine in weldability, full in welding spot and fine in reliability, achieves fine welding effects and meets environmental protection requirements, and the service life of the tin paste is prolonged.

Description

【Technical field】 [0001] The invention relates to the technical field of electronic soldering, in particular to a lead-free and halogen-free solder paste and a production process thereof. 【Background technique】 [0002] With the rapid development of electronic technology, the integration of electronics is becoming more and more prominent. Therefore, the requirements for the electronic solder used are also getting higher and higher. In recent years, with the enhancement of people's environmental protection, lead-free has also followed. Lead-free solder paste alloys are mainly tin-silver-copper tin powder and halogenated solder paste. The melting point of this type of lead-free solder paste is 217°C-219°C, which is nearly 30% higher than the melting point of the replaced tin-lead solder paste at 183°C. ℃, this lead-free process leads to a higher soldering temperature than before, so the heat-resistant temperature of components and substrates during soldering will also increase...

AI Technical Summary

Problems solved by technology

[0002] With the rapid development of electronic technology, the integration of electronics is becoming more and more prominent. Therefore, the requirements for the electronic solder used are also getting higher and higher. In recent years, with the enhancement of people's environmental protection, lead-free has also followed. Lead-free solder paste alloys are mainly tin-silver-copper tin powder and halogenated solder paste. The melting point of this type of lead-free solder paste is 217°C-219°C, which is nearly 30% higher than the melting point of the replaced tin-lead solder paste at 183°C. ℃, this lead-free process leads to a higher soldering temperature than before, so the heat-resistant temperature of components and substrates during soldering will also increase, but based on the requirements of many components and substrates themselves, the soldering heat-resistant temperature There is no way to improve it. At the same time, a lead-free solder paste of Sn42Bi58 alloy came into being. The solder paste has a melting point of 138°C, and the soldering temperature is greatly reduced, which meets the requirements, but has the defect that the Bi content of the alloy itself is too high, and the solder joints are brittle , easy to crack, and poor reliability; in addition, since the alloy SnPb is replaced, the activity of the solder paste composed of solder paste is required to be greatly increased, so now it is commonly used to add a halogen-containing activator to increase the activity of the solder paste to meet the soldering requirements, but the addition of halogen is for soldering Afterwards, corrosion will occur, which will affect the reliability of solder joints, and halogens (fluorine, chlorine, bromine) are also listed as non-environmentally friendly substances. The existing halogen-free products are usually combined with organic acids as activators. The failure during long-term printing and use is mainly due to the reaction between the organic acid added in the solder paste and the tin powder, which leads to accelerated oxidation of the tin powder, and finally leads to soldering failure

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