无铅焊膏用助焊剂的制备与研究

无铅焊膏用助焊剂需要一定的黏性,选择有机酸和有机胺混合作为活性物质,配合一定量的松香配制出一种助焊剂。通过控制助焊剂中松香的含量,降低不挥发物的含量,减少残留物对元器件的腐蚀。依据标准对所配制的助焊剂进行了性能测试,并与一种松香含量较高的助焊剂比较。结果表明:助焊剂的松香含量降低约10%,在260℃焊接后不挥发物含量降低了近6%,黏度较好,无卤化物,无毒,环保,符合焊膏用助焊剂的要求。     

Ni颗粒增强无铅复合钎料中IMC形态之演变

通过改变钎焊工艺曲线来控制热输入量。研究了Ni颗粒周围金属间化合物(IMC)以及钎料/基板界面处IMC的形态演变。结果表明,随着热输入量由低变高,Ni颗粒周围IMC形态从向日葵状向多边形状发展,最终成为遍布整个钎料层的细碎的IMC形态;而钎料/基板界面层,因Ni颗粒的加入,出现大量的三维孔洞状IMC。从而形成了Cu元素扩散的通道,使得界面层厚度增加且呈线性增长趋势。     

Ag-Au-Ge钎料润湿性的研究

通过对Ag-Au-Ge系三元相图的分析研究, 初步研制了熔化温度在490 ℃的Ag-Au-Ge钎料合金, 并对其润湿性进行了测试。润湿性测试结果表明: 温度在熔点以上60 ℃范围内时, Ag-Au-Ge钎料合金与Ni板润湿性良好。     

纯Sn焊料表面高温氧化膜的腐蚀演化行为（英文）

对150℃高温时效条件下纯锡焊料表面氧化膜形貌、组成、厚度及耐蚀性的演化行为进行研究。结果表明,高温时效加速焊料表面原有自然氧化膜层中的Sn(OH)₄向SnO₂转变,同时加速新鲜Sn基体的氧化,从而使纯Sn焊料表面氧化膜厚度和粗糙度随时效时间的延长逐渐增加。然而,表面氧化膜层的耐蚀性随时效时间的延长呈先增强而后减弱的趋势。此外,还对纯Sn焊料表面氧化膜层的成膜机制及膜层演化机制进行讨论。     

Effective diffusivity of lead free solder alloys

A Monte Carlo simulation based algorithm is developed to compute the effective diffusivity of lead free solder alloys. Simulations are performed to determine the vacancy diffusivity for 95.5Sn–4.0Ag–0.5Cu (SAC405) solder alloy for different paths. Temperature and micro-structural influence on diffusivity are studied. A map of diffusivity versus temperature and average grain size is developed. Significant differences between diffusivity values reported in the literature for the same solder alloy is also discussed.     

Effects of particle size on the mechanical properties of particle-reinforced Sn-Ag composite solder joint

Particulate size has significant influenced on the mechanical properties of particle-reinforced composite solder joints. In this current research, Cu or Ni reinforcement particles were mechanically added to the Sn-3.5Ag eutectic solder, and the effects of the particle size on the mechanical properties of particle-reinforced composite solder joint were systematically studied. This investigation touched on how mechanical properties of the solder joints are affected by particles size. A quantitative formula was set up to correlate the mechanical property of the solder joint with particle size in different processing conditions. Besides, the fracture mechanism of the composite solder joint was analyzed.     

Interface between Sn-Sb-Cu solder and copper substrate

Influence of antimony and copper in Sn-Sb-Cu solder on the melting and solidification temperatures and on the microstructure of the interface between the solder and copper substrate after wetting the substrate at 623 K for 1800 s were studied. Microstructure of the interface between the solder and copper substrates in Cu-solder-Cu joints prepared at the same temperature for 1800 s was observed and shear strength of the joints was measured. Influence of the atmosphere - air with the flux and deoxidising N₂ + 10H₂ gas - was taken into account. Thermal stability and microstructure were studied by differential scanning calorimetry (DSC), light microscopy, scanning electron microscopy (SEM) with energy-dispersive spectrometry (EDS) and X-ray diffraction (XRD). Melting and solidification temperatures of the solders were determined. An interfacial transition zone was formed by diffusion reaction between solid copper and liquid solder. At the interface Cu₃Sn and Cu₆Sn₅ phases arise. Cu₃Sn is adjacent to the Cu substrate and its thickness decreases with increasing the amount of copper in solder. Scallop Cu₆Sn₅ phase is formed also inside the solder drop. The solid solution Sn(Sb) and SbSn phase compose the interior of the solder drop. Shear strength of the joints measured by push-off method decreases with increasing Sb concentration. Copper in the solder shows even bigger negative effect on the strength.     

Fracture Mechanics of Solder Bumps During Ball Shear Testing: Effect of Bump Size

This paper examines the mechanics of ball shear testing with the objective of understanding the mechanism by which the maximum shear force and the rate of crack growth is dependent on the solder bump size. For this, Pb-Sn solder bumps with diameters between 460 μm and 760 μm are soldered to 400 μm-diameter Cu pads and subjected to ball shear testing. In spite of the constant interface area, the bump size significantly impacts the measured shear fracture force and the crack growth rate. Both the fracture force and the crack growth rate increase with bump size, and in the case of the fracture force, the increase is almost linear. Our analysis finds that the linear increase in the fracture force is a result of the bump deformation force, which increases with bump size. A simple model that accounts for the deformation force component is developed and used to extract the true interface fracture force. The estimated true interface fracture force is found to vary little with bump size, tightly converging to the 40 MPa to 48 MPa range. On the other hand, the dependence of crack growth rate on bump size is found to result from the higher degree of rotational moment associated with larger bumps.     

Cu-Ni-Sn: A Key System for Lead-Free Soldering

Being the most complex constituent of the quaternary system Ag-Cu-Ni-Sn, the ternary system Cu-Ni-Sn is the key system for the investigation of the interactions of Ag-Cu-Sn solder alloys with Ni as a contact material. Although this system has been thoroughly studied in the literature, there are still many uncertainties left. In the present work, a study of the phase equilibria in four isothermal sections at 220, 400, 500, and 700°C of the Cu-Ni-Sn system was carried out following a comprehensive literature study. The methods employed were x-ray diffraction (XRD), metallography, and scanning electron microscopy including electron probe microanalysis. The ternary solubilities of the Ni₃Sn₂-Cu₆Sn₅ and Ni₃Sn-Cu₃Sn fields were characterized in detail. So far no continuous solubility between the respective phases has been found. At 25 at.% Sn the existence of two ternary compounds formed from the BiF₃-type (Cu,Ni)₃Sn phase and reported in literature could be confirmed. On the other hand, our results differ significantly from the very recent literature related to lead-free soldering.     

Oxidation Behavior of Rare-Earth-Containing Pb-Free Solders

We have previously shown that small additions of the rare-earth (RE) element La to Sn-Ag-Cu alloys significantly increases their ductility, without significant loss in the overall strength. However, due to the high reactivity of La with oxygen, oxidation of the La-containing phases can affect the mechanical performance of the solder. In this work, we have investigated the effect of the addition of 2 wt.% Ce, La and Y on the oxidation behavior of Sn-3.9Ag-0.7Cu. Oxidation kinetics were established by heating samples in ambient air to 60°C, 95°C or 130°C for up to 250 h. Microstructural characterization of the samples, before and after oxidation, was conducted in order to determine the influence of RE-containing phases on the oxidation kinetics. The oxidation mechanism, including the phenomenon of Sn whiskering during oxidation, is also discussed.