| With the development of microelectronics industry, the working temperature of electronic components becomes higher and higher. In order to cope with the growing demand for high-temperature electronic components, a new generation semiconductors such as SiC, GaN and packaging materials AlN, Si3N4have been developed, but the key materials high-temperature solder with low-cost and high-performance developed slowly. Currently, only Sn-95Pb, Sn-98Pb,Au-0.28at.%Ge, Zn-6Al and Zn-4Al-3Mg-3.2Ga high temperature solders are available on the market, which can withstand300℃without melting and failures. However, lead harms the environment, gold is a precious metal, and zinc and aluminum have poor wetting ability with base material. Therefore, solders with low-cost, environment-friendly, and higher strength above300℃are urgently needed in microelectronics industry. However, the market currently can not provide such solders.Considering this, this paper concentrates on the development of high temperature solder with low-cost and shear strength at300℃above10MPa. The following are main results.(1) Using VC and NaBH4as reducing reagent, and PVP, Arabic gum, ammonium citrate as dispersant, copper sulfate solution as mother liquor, micron copper was prepared by chemical reduction method. The effects of varied kinds of reducing agent, dispersant and pH value on morphology and particle size were investigated. The results showed the higher the pH value is, the smaller and the more spherical the powder will become and spherical copper powder with0.5～1μn of particle size can be prepared under the condition of the pH8by using VC as reductive agent. The dispersibility of the PVP is well compared with the Arabic gum and ammonium citrate. Besides, the size of the powder is about0.5μm by using NaBH4as reducing reagent and it is more spherical.(2) This paper studied the preparation and performance of Cu-Sn solder paste. The copper powder with the size of1μm by liquid phase reduction and the tin powder with the size of2μm were mixed by Ball-milling. Besides, the aids of the different kinds and quantities were added in the jar to prepare the solder paste to study their performance, respectively, such as F3A, JS-E-31,3A, and JS-E-15X. This paper shows that the aids promote the chemical reaction to aid the formation of Cu6Sn5intermetallic compound and reduce the residual amount of tin-it reduces as the temperature rises and the time of the sintering increases through studying the phase transformation and the changes of microstructure in the sintering process of Cu-Sn solder paste in argon atmosphere at300℃. When the sintering temperature300℃, the sintering time4h, the aids is JS-E-15X, the residual amount of tin is the least and the sintering phase include Cu6Sn5, Cu3Sn, and Sn.(3) The solder paste prepared by mixing0.5μm spherical copper particles,2μm spherical tin particles and JS-E-15X flux was used to perform the red copper soldering experiment. The soldering process, seam microstructure and mechanical property were analyzed. In the soldering process, the soldering temperature is efficiently decreased to230℃-300℃because of the formation of liquid phase of melting tin. Owing to the formation of intermetallic compounds Cu6Sn5and Cu3Sn during the soldering process, the operation temperature of the soldered materials is more than400℃. The seam microstructure is made of sparse Cu6Sn5phase and dense Cu3Sn phase. Increasing the soldering pressure is beneficial to improve the density of the seam structure, thereby improve the high temperature shear strength. The fracture mechanism is brittle fracture. The shear strength of the seam at300℃in air is above10MPa. |
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