| High-temperature brazing and low-temperature soldering, as one of the advanced manufacturing processing technology, are of significant importance to modern industrial development. Brazing and soldering, wetting and spreading dynamics of the filler metal over the substrate surface is of decisive significance for joint quality.It is generally accepted that brazing or soldering process requires a liquid metal wets the heterogeneous base material to be joined in prescriptive brazing time.Consequently, in order to control and improve the quality of joint during brazing process, the quantitative moldering and prediction of wetting and spreading of filler metal should be conducted. On the other hand, with the increase of the environmental awareness, the lead-free process of electronic packaging in worldwide is required to further promote. The key problem in the large-scale industrial production should be overcome on account of poverty of processing properities of lead-free solder and the instability of joint reliability. Therefore, this topic aim at exploring the wetting mechanism of a typical brazing or soldering system (AgCu/TC4 in high-temperature brazing system and SnAgZn/Cu in low-temperature soldering) and the growth and coarsening behaviors of intermetallic compounds (IMCs) after alloying Cu substrate.In this dissertation, the weting and spreading of AgCu filler metal over TC4 substrates using a sessile drop technique in a high-purity argon atmosphere were investigated. The wetting and spreading process of molten metal and the triple-line movement were digital record in real time. The results reveal that the substrate surface roughness had a limited impact on the wetting and spreading process, while the temperature dictated the spreading process and mechanisms. At 860 ℃, the entire spreading process involved four stages. On the other hand, at 940 ℃, owing to the more drastic chemical reaction, the entire sprading process exhibited only three stages.At 860 ℃, the wetting kinetics of the rapid spreading stage was determined by the chemical reaction rate, where the interdiffuion between Ti and Cu was the dominant rate-limiting factor during the limited spreading stage. However, at 940 ℃, the wetting kinetics was dominated by the mixed effects of the chemical reactions,dissolution and diffusion into the solid.Further, the microstructure, thermal properties and wetting kinetics of Sn-3Ag-xZn solders(x = 0.4, 0.6, 0.8, 1, 2 and 4 wt.%) were systematically investigated. The results indicate that a small amount of Zn (Zn wt.% ≤ 1 wt.%) had a rather moderate effect on the microstructure morphology of the Sn-3Ag-xZn solders.The microstructures were composed of a β-Sn phase and the mixture of Ag3Sn andζ-AgZn particles. However, the p-Sn phase resuced its volume fraction in the entire microstructure and the intermetallic compounds population increased with the increasing of Zn content. The microstructure was dramatically changed with a further increased in the Zn content. The γ-AgZn phase was formed in a Sn-3Ag-2Zn solder.The ε-AgZn phase was formed in a Sn-3Ag-4Zn solder. The melting temperature and undercooling of the Sn-3Ag-xZn solder alloys decreased with the increase in Zn content, reached to a minimum value when the content of Zn was 1 wt.%, and then increased with further increase in Zn content. The Sn-3Ag-1Zn demonstrated the minimum value of 228.13 ℃ in the melting temperature and 13.87 ℃ in undercooling.The wetting kinetics of the main spreading stage featured the power law of Rn～t (n ＝1), which was controlled by chemical reactions at the triple line.At last, four types of wetting layers (Cu, Cu-8 wt.% Zn, Cu-15 wt.% Zn and Cu-30 wt.% Zn ) reaction with Sn-3.0Ag-0.5Cu (SAC305) solder were fabricated.The effects of alloying Cu substrate on the growth behavior and coarsening behavior of Cu6Sn5 grains of soldered joints were investigated. The results show that the scallop-shaped Cu6Sn5 formed at the interface of SAC305/Cu after reflowing. With the increase of the aging time, a bi-layer structure of Cu6Sn5 and Cu3Sn formed at the interface of SAC305/Cu and some Ag3Sn grains decorated in Cu6Sn5, and Kirkendall voids were observed inside the Cu3Sn layer. However, Cu6Sn5 was the predominant reaction product and Cu3Sn and Kirkendall voids were not observed at the interface of SAC305/Cu-Zn irrespective of aging time. The thickness of IMCs layer increased with increasing aging time. Compared to SAC305/Cu, the additions of Zn can effectively suppress the growth of IMCs. During the aging process, the growth rate constants of IMCs layers of SAC305/Cu, SAC305/Cu-8Zn, SAC305/Cu-15Zn and SAC305/Cu-30Zn were 7.78×10-17, 5.42×10-17, 2.51×10-17 and 1.46×10-17 m2s-1,respectively. The mean diameter of Cu6Sn5 grains increased with the increasing aging time. The relationships of the mean diameter of Cu6Sn5 grains of SAC305/Cu,SAC305/Cu-8Zn, SAC305/Cu-15Zn and SAC305/Cu-30Zn interface joints and aging time were given, i.e., d=1.49t0.237, d=1.46t0.204, d =1.43t0.203 and d=1.71t0.197, respectively. |
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