银含量对快速热冲击下Sn−xAg−0.5Cu焊点显微组织和力学性能的影响

使用高频感应加热设备研究Ag含量对快速热冲击下Sn−xAg−0.5Cu焊点的显微组织和剪切强度的影响。结果表明,Ag含量的增加使焊点表面更致密光滑,减少焊点内部长条状Cu6Sn5金属间化合物(IMC)的产生,从而提高焊点的抗氧化性。Ag能够加快焊点界面IMC层的生长速度,Cu6Sn5层的生长速度由体扩散和晶界扩散共同决定,Cu3Sn层的生长速度由体扩散和界面反应共同决定。在快速热冲击环境下,焊点的断裂模式从韧性断裂转变为脆性断裂,而高Ag含量使得焊点的断裂模式转变时间更短,降低焊点的抗热疲劳性能。

Drop failure modes of Sn-3.0Ag-0.5Cu solder joints in wafer level chip scale package

To reveal the drop failure modes of the wafer level chip scale packages （WLCSPs） with Sn-3.0Ag-0.5Cu solder joints, board level drop tests were performed according to the JEDEC standard. Six failure modes were identified, i.e., short FR-4 cracks and complete FR-4 cracks at the printing circuit board （PCB） side, split between redistribution layer （RDL） and Cu under bump metallization （UBM）, RDL fracture, bulk cracks and partial bulk and intermetallic compound （IMC） cracks at the chip side. For the outmost solder joints, complete FR-4 cracks tended to occur, due to large deformation of PCB and low strength of FR-4 dielectric layer. The formation of complete FR-4 cracks largely absorbed the impact energy, resulting in the absence of other failure modes. For the inner solder joints, the absorption of impact energy by the short FR-4 cracks was limited, resulting in other failure modes at the chip side.

新型水基高分子焊锡球表面处理剂及其性能研究

为解决焊锡球在长期存放与运输过程中易被氧化的问题,以Sn3.0Ag0.5Cu焊锡球为研究对象,研制出一种新型水基高分子焊锡球表面处理剂,此种表面处理剂是由苯并三氮唑和聚乙烯醇4000作为成膜剂,使用抗坏血酸作为抗氧化剂,并添加少量碱性配位剂与表面活性剂制成。表面处理剂处理后对焊锡球进行抗氧化性测试、剪切强度测试、空洞测试以及包覆情况测试与Raman光谱表征,结果表明:经此种表面处理剂处理后的焊锡球焊点剪切强度提高48%;焊锡球焊点空洞率低于4%,符合业内要求(低于15%)。上述结果说明此种表面处理剂处理过后的焊锡球会在表面形成一层致密的抗氧化薄膜,能提高焊球的抗氧化性能。

微量稀土元素对Sn3.0Ag0.5Cu无铅焊料合金组织与性能的影响

研究稀土元素对Sn3Ag0.5Cu无铅焊料合金显微组织及性能的影响。结果表明：当稀土含量（wRE）为0.05%~0.25%时,对该无铅焊料合金的导电性和腐蚀性影响不大,但使其熔化区间温度降低;可以提高焊料的铺展面积,细化组织,提高其力学性能。比较Ce、Er、Y、Sc四种稀土元素对焊料合金的影响,发现Ce元素可以更好地提高焊料合金的综合性能,Er次之。

电迁移对Sn3.0Ag0.5Cu无铅焊点剪切强度的影响

通过热风回流焊制备了Cu/Sn3.0Ag0.5Cu/Cu对接互连焊点,测试了未通电及6.5A直流电下通电36h和48h后焊点的剪切强度。结果表明,电迁移显著地降低了焊点的剪切强度,电迁移36h使剪切抗力降低约30%,电迁移48h降低约50%。SEM观察断口和界面形貌表明,界面金属间化合物增厚使断裂由韧性向脆性转变。

Ag-GNSs/Sn-Ag-Cu复合钎料焊点的润湿性能及界面生长特征研究

采用Ag涂覆石墨烯纳米片(Ag-GNSs)作为增强体,制备Sn-3.0Ag-0.5Cu-(Ag-GNSs)新型复合无铅钎料,然后在Cu基板上制备了钎料焊点,并进行了150℃不同时长的等温时效处理,研究了不同含量的Ag-GNSs对无铅钎料Sn-3.0Ag-0.5Cu的润湿性、Cu基板/钎料界面金属间化合物(IMC)生长特性的影响。结果表明,适量的Ag-GNSs可以显著地改善钎料的润湿性,当Ag-GNSs含量达到0.05wt%时润湿性最佳,与Sn-3.0Ag-0.5Cu钎料相比润湿角降低了54.43%。随着等温时效时间的延长,IMC层厚度增大,其生长行为由扩散控制。Ag-GNSs的添加可以抑制IMC层的生长,当Ag-GNSs的含量为0.05wt%时扩散系数达到最小值2.356×10^(-18)m^(2)/s。在0~0.2wt%范围内,Ag-GNSs的最佳添加量为0.05wt%。

Influence of bismuth on microstructure,thermal properties,mechanical performance,and interfacial behavior of SAC305−xBiCu solder joints

This research sought to improve the properties of SAC305 solder joints by the addition of 1 and 2 wt.%Bi.The effects of bismuth doping on the microstructure,thermal properties,and mechanical performance of the SAC305−xBiCu solder joints were investigated.Bi-doping modified the microstructure of the solder joints by refining the primaryβ-Sn and eutectic phases.Bi-doping below 2 wt.%dissolved in theβ-Sn matrix and formed a solid solution,whereas Bi additions equal to or greater than 2 wt.%formed Bi precipitates in theβ-Sn matrix.Solid solution strengthening and precipitation strengthening mechanisms in theβ-Sn matrix increased the ultimate tensile strength and microhardness of the alloy from 35.7 MPa and 12.6 HV to 55.3 MPa and 20.8 HV,respectively,but elongation decreased from 24.6%to 16.1%.The fracture surface of a solder joint containing 2 wt.%Bi was typical of a brittle failure rather than a ductile failure.The interfacial layer of all solder joints comprised two parallel IMC layers:a layer of Cu6Sn5 and a layer of Cu3Sn.The interfacial layer was thinner and the shear strength was greater in SAC305−xBiCu joints than in SAC305Cu solder joints.Therefore,small addition of Bi refined microstructure,reduced melting temperature and improved the mechanical performance of SAC305Cu solder joints.

Effects of bismuth on growth of intermetallic compounds in Sn-Ag-Cu Pb-free solder joints

The effects of Bi addition on the growth of intermetallic compound (IMC) formation in Sn-3.8Ag-0.7Cu solder joints were investigated. The test samples were prepared by conventional surface mounting technology. To investigate the element diffusion and the growth kinetics of intermetallics formation in solder joint, isothermal aging test was performed at temperatures of 100, 150, and 190℃, respectively. The optical microscope (OM) and scanning electron microscope (SEM) were used to observe microstructure evolution of solder joint and to estimate the thickness and the grain size of the intermetallic layers. The IMC phases were identified by energy dispersive X-ray (EDX) and X-ray diffractometer (XRD). The results clearly show that adding about 1.0% Bi in Sn-Ag-Cu solder alloy system can refine the grain size of the IMC and inhibit the excessive IMC growth in solder joints, and therefore improve the reliability of the Pb-free solder joints. Through observation of the microstructural evolution of the solder joints, the mechanism of inhibition of IMC growth due to Bi addition was proposed.

Effect of diode-laser parameters on shear force of micro-joints soldered with Sn-Ag-Cu lead-free solder on Au/Ni/Cu pad

Soldering experiments with Sn-3.5Ag-0.5Cu lead-free solder on Au/Ni/Cu pad were carried out by means of diode-laser and IR reflow soldering methods respectively.The influence of different heating methods as well as output power of diode-laser on shear force of micro-joints was studied and the relationship between the shear force and microstructures of micro-joints was analyzed.The results indicate that the formation of intermetallic compound Ag3Sn is the key factor to affect the shear force and the fine eutectic network structures of micro-joints as well as the dispersion morphology of fine compound Ag3Sn,in which eutectic network band is responsible for the improvement of the shear force of micro-joints soldered with Sn-Ag-Cu lead-free solder.With the increases of output power of diode-laser,the shear force and the microstructures change obviously.The eutectic network structures of micro-joints soldered with diode-laser soldering method are more homogeneous and the grains of Ag3Sn compounds are finer in the range of near optimal output power than those soldered with IR reflow soldering method,so the shear force is also higher than that using IR reflow soldering method.When the output power value of diode-laser is about 41.0 W,the shear force exhibits the highest value that is 70% higher than that using IR reflow soldering method.

Effect of cerium on microstructure and mechanical properties of Sn-Ag-Cu system lead-free solder alloys

The melting point, spreading property, mechanical properties and microstructures of Sn-3.0Ag-2.8Cu solder alloys added with micro-variable-Ce were studied by means of optical microscopy, scanning electron microscopy(SEM) and energy dispersive X-ray(EDX). The results indicate that the melting point of Sn-3.0Ag-2.8Cu solder is enhanced by Ce addition; a small amount of Ce will remarkably prolong the creep-rupture life of Sn-3.0Ag-2.8Cu solder joint at room temperature, especially when the content of Ce is 0.1%, the creep-rupture life will be 9 times or more than that of the solder joint without Ce addition; the elongation of Sn-3.0Ag-2.8Cu solder is also obviously improved even up to 15.7%. In sum, the optimum content of Ce is within 0.05%-0.1 %.

Direct active soldering of Al_(0.3)CrFe _(1.5)MnNi_(0.5) high entropy alloy to 6061-Al using Sn-Ag-Ti active solder

Al0.3CrFe1.5MnNi0.5 high entropy alloys(HEA)have special properties.The microstructures and shear strengths of HEA/HEA and HEA/6061-Al joints were determined after direct active soldering(DAS)in air with Sn3.5Ag4Ti active filler at 250°C for 60 s.The results showed that the diffusion of all alloying elements of the HEA alloy was sluggish in the joint area.The joint strengths of HEA/HEA and HEA/6061-Al samples,as analyzed by shear testing,were(14.20±1.63)and(15.70±1.35)MPa,respectively.Observation of the fracture section showed that the HEA/6061-Al soldered joints presented obvious semi-brittle fracture characteristics.

Combined effects of Bi and Sb elements on microstructure,thermal and mechanical properties of Sn−0.7Ag−0.5Cu solder alloys

This research investigated the combined effects of addition of Bi and Sb elements on the microstructure,thermal properties,ultimate tensile strength,ductility,and hardness of Sn−0.7Ag−0.5Cu(SAC0705)solder alloys.The results indicated that the addition of Bi and Sb significantly reduced the undercooling of solders,refined theβ-Sn phase and extended the eutectic areas of the solders.Moreover,the formation of SbSn and Bi phases in the solder matrix affected the mechanical properties of the solder.With the addition of 3 wt.%Bi and 3 wt.%Sb,the ultimate tensile strength and hardness of the SAC0705 base alloy increased from 31.26 MPa and 15.07 HV to 63.15 MPa and 23.68 HV,respectively.Ductility decreased due to grain boundary strengthening,solid solution strengthening,and precipitation strengthening effects,and the change in the fracture mechanism of the solder alloys.

Effect of adding Ce on interfacial reactions between Sn-3.0Ag-0.5Cu solder and Cu substrate

The formation and the growth of Cu-Sn intermetallic compound (IMC) layer at the interface between Sn-3.0Ag-0.5Cu-xCe solder and Cu substrate during soldering and aging were studied. The results show that Cu6Sn5 IMC is observed at the interface between solder and Cu substrate in all conditions. After aging for 120 h,the Cu3Sn IMC is then obtained. With increasing aging time,the scalloped Cu6Sn5 structure changes to a plate structure. The Cu3Sn film always forms with a relatively planar interface. By adding a small amount of the rare earth element Ce (only 0.1%,mass fraction) into the Sn-3.0Ag-0.5Cu solder alloy,the growth rate of the Cu-Sn IMC at the interface of solder alloy system is decreased. When the time exponent is approximately 0.5,the growth of the IMC layer is mainly controlled by a diffusion over the studied time range.

Effects of rare earth element Ce on solderabilities of micron-powdered Sn-Ag-Cu solder

Several important properties of the micron-powdered Sn-Ag-Cu-Ce solder, including the spreadability, spreading ratio, wetting time, and melting point, were investigated for verifying the effects of rare earth element Ce on solderabilities of micron-powdered Sn-Ag-Cu solder. The solidus and the liquidus of the micron-powdered Sn-Ag-Cu-Ce solder are 193.6℃ and 218.4℃, respectively, about 28℃ and 3℃ lower than the melting point of the block Sn-Ag-Cu solder, which reminds the existence of the surface effect of the micron-powdered solder. By adding Ce into Sn-Ag-Cu alloy, its wetting time on pure copper can be obviously decreased. For the Sn-Ag-Cu-0.03%Ce, the soldering temperature is 250℃, and the wetting time on pure copper is close to 1s, with the soldering temperature approaching to 260℃, the wetting time is dropped to 0.8s, which is close to the wetting time, 0.68s, of Sn-Pb solder at 235℃.

Thermal reliabilities of Sn−0.5Ag−0.7Cu−0.1Al_(2)O_(3)/Cu solder joint

The effects of trace addition of Al_(2)O_(3) nanoparticles(NPs)on thermal reliabilities of Sn−0.5Ag−0.7Cu/Cu solder joints were investigated.Experimental results showed that trace addition of Al_(2)O_(3) NPs could increase the isotheraml aging(IA)and thermal cyclic(TC)lifetimes of Sn−0.5Ag−0.7Cu/Cu joint from 662 to 787 h,and from 1597 to 1824 cycles,respectively.Also,trace addition of Al_(2)O_(3) NPs could slow down the shear force reduction of solder joint during thermal services,which was attributed to the pinning effect of Al_(2)O_(3) NPs on hindering the growth of grains and interfacial intermetallic compounds(IMCs).Theoretically,the growth coefficients of interfacial IMCs in IA process were calculated to be decreased from 1.61×10^(−10 )to 0.79×10^(−10) cm^(2)/h in IA process,and from 0.92×10^(−10) to 0.53×10^(−10) cm^(2)/h in TC process.This indicated that trace addition of Al_(2)O_(3) NPs can improve both IA and TC reliabilities of Sn−0.5Ag−0.7Cu/Cu joint,and a little more obvious in IA reliability.

Microstructures and properties of Sn-Ag-Cu lead-free solder alloys containing La

Trace amounts of La were utilized to improve the melting behaviors,microstructures,tensile properties and microhardness of Sn-3.0Ag-0.5Cu lead-free solder alloy. La has little effect on the melting behavior of Sn-3.0Ag-0.5Cu alloy according to the differential thermal analysis(DTA) tests. The X-ray diffraction(XRD) patterns show that β-Sn,Ag3Sn and Cu6Sn5 coexist in the as-cast solder alloys and LaSn3 phases emerge when adding 0.4% La. The microstructures modified by La are more uniform and much finer than that of baseline alloy,and the coarse LaSn3 particles with complex dendrites are observed by optical microscopy(OM) and scanning electron microscopy(SEM) when the addition of La is up to 0.4%. The composition of the LaSn3 phases is identified by energy-dispersive spectroscopy(EDS). There are considerable improvements in mechanical properties with 0.05% and 0.1% addition,but degenerations by adding 0.4%La. The Vickers microhardness of β-Sn and eutectic area are both enhanced with the addition of La and the microhardness of LaSn3 is much larger than those of β-Sn and eutectic area.

Influence of Thermal Cycling on the Microstructure and Shear Strength of Sn3.5Ag0.75Cu and Sn63Pb37 Solder Joints on Au/Ni Metallization

The influence of thermal cycling on the microstructure and joint strength of Sn3.5Ag0.75Cu （SAC） and Sn63Pb37 （SnPb） solder joints was investigated. SAC and SnPb solder balls were soldered on 0.1 and 0.9 μm Au finished metallization, respectively. After 1000 thermal cycles between -40℃ and 125℃, a very thin intermetallic compound （IMC） layer containing Au, Sn, Ni, and Cu formed at the interface between SAC solder joints and underneath metallization with 0.1 μm Au finish, and （Au, Ni, Cu）Sn4 and a very thin AuSn-Ni-Cu IMC layer formed between SAC solder joints and underneath metallization with 0.9 μm Au finish. For SnPb solder joints with 0.1 μm Au finish, a thin （Ni, Cu, Au）3Sn4 IMC layer and a Pb-rich layer formed below and above the （Au, Ni）Sn4 IMC, respectively. Cu diffused through Ni layer and was involved into the IMC formation process. Similar interfacial microstructure was also found for SnPb solder joints with 0.9μm Au finish. The results of shear test show that the shear strength of SAC solder joints is consistently higher than that of SnPb eutectic solder joints during thermal cycling.

Sn-Ag-Cu钎料的制备与显微组织性能研究

Sn-Ag-Cu系低银钎料凭借其优良的工艺和力学性能被普遍认为是最有前途的含铅钎料替代品。为了研究低银钎料的制备及其显微组织特性,制备银的质量分数分别为0、0.3%、0.5%、1.0%的四组低银钎料。比较分析熔化温度与银的质量分数对低银钎料的熔化特性、显微组织、抗拉强度及润湿特性的影响。结果表明,添加少量的银可以降低锡铜钎料的熔化温度,使锡铜钎料的晶粒变得细小,晶粒排列得更加紧密。当钎料中银的质量分数为1.0%时,钎料的抗拉强度达到47.4 MPa,在紫铜基体上的铺展面积为39.9 mm2,润湿角为5.01°。

用于功率器件封装的新型Cu@Sn@Ag焊片性能

提出了一种用于焊接半导体芯片的新型焊接材料Cu@Sn@Ag焊片。对比分析了Cu@Sn@Ag焊片和商用PbSn5Ag2.5焊片焊层的孔隙率和力学性能,采用这两种焊片封装了110 A商用Si器件并对其进行了电学、热学性能和功率循环可靠性对比。结果表明:优化后的Cu@Sn@Ag焊片孔隙率小于4%,焊层剪切强度平均值约为35 MPa;相应器件的最小热阻为0.18 K/W,且经过150000次的有源功率循环(温差为60℃)后正向压降增长率基本小于2%,Cu@Sn@Ag焊片的性能和器件功率循环可靠性高于商用PbSn5Ag2.5焊片。基于瞬态液相扩散焊接(TLPS)的Cu@Sn@Ag焊片可以实现高铅焊片的无铅化替代,是一种具有良好应用前景的耐高温芯片焊接材料。

不同剪切速率下锡银铜系/镍金焊点的断裂行为研究

对锡银铜系高可靠性焊料合金的研究虽然已经较为广泛,但是缺乏对其焊点在不同应变速率下的剪切强度和断裂模式的研究。本文将牌号为SAC305和Innolot不同成分的锡银铜系焊料合金锡膏印刷在镍金镀层(Ni(P)/Au)上回流成BGA焊点,采用DAGE4000HS焊接强度测试仪进行不同剪切速率下的剪切性能测试,并对其剪切曲线、剪切强度及断裂能进行计算和分析,再采用金相显微镜和扫描电子显微镜(SEM)对焊点界面微观结构及断口进行表征分析。结果表明:合金本身成分的差异导致焊点界面金属间化合物层(IMC层)厚度和分布存在差异,随着剪切速率的增加,SAC305和Innolot合金焊点的强度总体上都随之增加,且焊点的断裂模式由焊点基体内部的韧性断裂向界面金属间化合物脆性断裂发生转变,Innolot合金由于其他金属元素添加导致的强化作用使得其剪切强度得到较大提升而塑性损伤。