冷却速率对Sn-3.5Ag焊料中Ag_3Sn金属间化合物的形貌及分布的影响

Morphology and Distribution of Ag_3Sn Intermetallic Compounds of Sn-3. 5Ag Solder under Different Cooling Rates

SnAg焊料合金中Ag3Sn金属间化合物(IMCs)的形态和分布对焊点的可靠性能有着显著的影响。采用X射线衍射(XRD),能量色散谱(EDS)和扫描电镜(SEM)等手段来表征Sn-3.5Ag(Sn-3.5%(质量分数)Ag)共晶焊料的铸态组织显微结构,研究不同冷却速率对Ag3Sn金属间化合物的形貌及分布的影响。实验采用预热石墨模(炉冷)、室温石墨模(空冷)、水冷铜模(水冷)及单辊甩带法(急冷)获得了冷却速率分别为1,10,1×103和1×106K·s-1的Sn-3.5Ag合金样品。研究表明,随着冷却速率增加,晶粒生长时间变短,导致共晶组织细小。Ag3Sn金属间化合物的形貌随着冷却速率增加,表现出了由片状→有片状尾巴的针状→针状→球状的趋势发展。脆性的球状Ag3Sn相在焊料中起到了弥散强化的作用,增强了焊料合金的力学强度,而片状Ag3Sn相则对力学性能有害。本研究得出了Sn-3.5Ag焊料维氏硬度与基体中金属间化合物Ag3Sn晶粒尺寸的关系:HV=9.51+0.11d(1/2),得到该合金的相关常数:Hv,o=9.51和K=0.1。

The morphology and distribution of Ag3 Sn intermetallic compounds （IMCs）of Sn-Ag solder alloys had a significant influence on the mechanical strength of solder joints. The aim of the current study was to analyze the characterization of the microstructure of the asast Sn-3.5Ag （Sn-3.5% Ag） eutectic solder alloy and the effect of different cooling rates on the Ag3Sn intermetallic compounds morphology and distribution by X-ray diffraction （XRD）, energy dispersive spectroscopy （EDS） and scanning electron microscopy （SEM）. With controlled cooling rates of 1, 10, 1 × 103 and 1 × 106 K·s^-1 , Sn-3.5Ag alloy samples were obtained by cooling specimens in different ways ： preheated graphite mold （furnace-cooled）, room temperature graphite mold （air-cooled）, water-cooled copper mold（water-cooled） and single roll method（ rush cold）. The results showed that with cooling rate increasing, the growth time of grain got shorter, resulting in fine eutectic. Specifically, the AgaSn intermetallic compounds exhibited a plate-like→needle-like with plate-like tails→needle-like→spherical-like evolution as the cooling rate increased. Brittle spherical-like Ag3Sn phase played a dispersion-strengthened role in the solder and enhanced the mechanical strength of solder alloy, while the plate-like Ag3 Sn phase was harmful to the mechanical properties. The relation between Vickers hardness of Sn-3.5Ag solder and Ag3 Sn crystal grain size was HV = 9.51 ＋ 0.1 1/√d the alloy-related constants were Hv, o = 9.51 and K = 0.1, respectively.