Method for producing superfine lead-free solder powder

Abstract

The invention provides a method for producing superfine lead-free solder powder. The method is implemented in a reaction system composed of a high-temperature evaporator, a grain controller, a spraying tank, a collector and the like which are all communicated in sequence. Tin alloy is placed in the high-temperature evaporator to be heated and melted, the temperature is maintained for 1 to 3 hours to acquire even alloy liquid, the power of a plasma gun is then increased rapidly, the flow of nitrogen is adjusted, metal steam is conveyed to the grain controller so as to be gradually cooled, collide with one another and grow, and alloy drops are generated; the alloy drops enter the spraying tank through air flow and rapidly cooled through liquid nitrogen to form solder powder, the solder powder is conveyed to the collector along with the nitrogen, attached to the outer wall of a gas-solid separator in the collector and then collected to a collecting hopper at the bottom of the collector, and therefore the superfine solder powder is acquired, wherein the nitrogen is cyclically used. The superfine lead-free solder powder produced through the method is hemispherical, the average grain diameter ranges from 2 micrometers to 7 micrometers, the powder is distributed narrowly, the oxygen content is low, the purity is high, and alloy components are even.

Description

technical field [0001] The invention relates to the field of surface packaging materials, in particular to a production method of ultrafine (average particle size can be controlled at 2-7 μm) lead-free solder powder. Background technique [0002] In recent years, lead-free has become one of the main topics of academic conferences and environmental protection related to electronic materials, microelectronics manufacturing, electronic packaging, and SMT. Lead is a toxic substance that not only causes serious environmental pollution, but also leads to lead poisoning if absorbed by the human body too much. Ingestion of low doses may affect human intelligence, nervous system and reproductive system. Lead-free means that the lead content in electronic products shall not exceed 0.1% (by weight). This lead-free standard is derived from the "Directive on Restricting the Use of Certain Hazardous Components in Electrical and Electronic Equipment" promulgated by the European Union on F...

AI Technical Summary

Problems solved by technology

Especially at this stage, the ultra-fine solder powder sold on the market is obtained by spraying method, which has low powder yield, small output, high oxygen content, large average particle size and wide distribution, rough surface, and obvious shortcomings. The solder paste made of solder powder produced by this method cannot form fine circuits and effectively fill small pinholes, and cannot meet the requirements of refinement and miniaturization of electronic products.

In addition, the patent No. 201210389898.7 "Submicron Solder Alloy Powder and Its Preparation Method" also reported the preparation method of solder alloy powder. system, the raw materials are Sn metal, Cu metal and Ag metal or Sn metal, Bi metal and Ag metal, there are two main disadvantages: First, the melting point of solder powder is much lower than that of Ni powder and Cu powder, and there is a big problem in its gas cooling , the cooling is seriously insufficient, resulting in the agglomeration and sintering of solder powder, and the alloy composition is uneven; second, the raw material is made of simple metal, and the difference in vaporization and actual content is caused by the difference in saturated vapor pressure, resulting in uneven alloy composition. For metals with very little content in tin alloys, such as Sn96.5Ag3Cu0.5 alloy, the Cu content is very small, and the mass ratio is 0.5%. Calculated according to the output of 10kg / h, the mass of Cu added per hour is 50g. If a single metal Added to high temperature evaporator, the addition of Cu metal is almost impossible to complete

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