热载荷下金属间化合物厚度对焊点可靠性的影响

研究了在热循环载荷条件下,不同厚度的金属间化合物IMC(Intermetallic Compound)层对焊点可靠性的影响。采用Anand本构模型描述无铅焊点在热载荷条件下的粘塑性力学行为,运用有限元模拟电子封装器件在热载荷循环下的应力应变的变化规律,确定关键焊点的位置,得到关键焊点的关键点的应力、应变与时间关系的曲线,分析IMC层厚度与寿命关系曲线,并确定其函数关系。研究表明:在热载荷条件下IMC层厚度越大,其焊点的可靠性越低,寿命越短。在IMC层厚度为8.5μm时,IMC厚度对焊点寿命的影响率出现明显的变化,影响率由–32.8突然增加到–404,当IMC厚度为14.5μm时,焊点的寿命值出现了跳跃。     

波峰焊及再流焊无铅焊点组织演变规律的研究

以电子封装线上的波峰焊无铅焊点Sn-0.7Cu/Cu、回流焊无铅焊点Sn-3Ag-0.5Cu/Cu为对象,研究了150 ℃时效过程中无铅焊点处金属间化合物(IMC)、焊料合金组织的演化规律及界面处金属间化合物生长的动力学.试验结果表明:两种无铅焊点处IMC层的厚度随着时效时间的延长而增加,IMC层的生长基本上符合抛物线规律,因此IMC层的长大受元素扩散控制;且两种无铅焊点处IMC层的生长速率常数相近,但Sn-0.7Cu焊料中Sn的晶粒尺寸较Sn-3Ag-0.5Cu中的大;长期时效后,在试样的IMC层内发现有孔洞产生.     

表面贴装锡基焊点长期贮存可靠性及寿命预测研究

互连焊点的室温贮存寿命预测对于电子产品的可靠应用具有重要的工程意义。采用高温加速贮存试验,对有铅钎料（62Sn36Pb2Ag）表面贴装的电容焊点以及有铅钎料（63Sn37Pb）和无铅钎料（SAC305）混合组装的BGA焊点进行了长期贮存寿命预测。利用扫描电子显微镜对在3种温度（367.15 K、393.15 K和423.15 K）下贮存不同时间（1天、4天、9天、16天、25天、36天、49天）的界面金属间化合物（IMC）微观形貌进行了表征,对其生长动力学进行研究并建立了生长模型。选取IMC的厚度作为关键性能退化参数,依据初始IMC厚度分布为失效密度函数,获得了两种类型焊点的可靠度函数,进而确定两种焊点的特征寿命及中位寿命。     

等温时效对SnSb4.5CuNi/Cu焊接接头力学性能的影响

SnSb4.5CuNi/Cu焊点在175℃进行等温时效,分析了不同时效时间的SnSb4.5CuNi/Cu焊点中金属间化合物(IMC)组织形貌演变,通过纳米压痕法测量SnSb4.5CuNi/Cu焊点界面IMC的硬度和弹性模量,对焊接接头进行拉伸强度和低周疲劳测试。结果表明,时效48 h的焊缝中Cu6Sn5呈曲率半径均匀的半圆扇贝状特征,IMC的弹性模量与铜基板很接近,在恒幅对称应变条件下焊点的抗低周疲劳的性能最佳,焊点的抗拉强度高;当时效时间大于48 h,焊接接口的抗疲劳性能和抗拉伸强度逐渐变差。     

Sn-3Ag-0.5Cu/Ni微焊点多次回流焊后IMC厚度及组织分析

采用Sn-Ag-Cu焊球(直径200,300,400和500μm),镀Ni盘,研究1,3,5次回流焊条件下焊点的IMC厚度及显微组织与焊球尺寸间的关系。结果表明:对于同一尺寸的焊球,随着回流焊次数的增加,IMC的厚度增大,形状由平直状逐渐过渡为体钎料一侧凹凸不平;在同一回流焊次数下,随着焊球尺寸的增大,IMC厚度减小,形貌相对没有明显差别。IMC的组成成分随着Ni向体钎料方向的不断扩散而从Sn、Ag、Cu合金变成Sn、Ag、Cu、Ni合金,其主要组成部分为(Cu,Ni)6Sn5。     

热老化条件下SAC305焊点的界面反应

研究对比了BGA/SAC305/Cu双界面焊点和SAC305/Cu单界面焊点在150℃条件下经过不同时间的等温时效后界面化合物的形态,并对BGA/SAC305/Cu和SAC305/Cu焊点内部组织进行了观察。试验结果表明：随着时效时间的增加,焊点界面化合物的厚度逐渐增加,表面趋于平坦,且SAC305/Cu单界面焊点出现...     

Sn58Bi-xW复合钎料焊点微观组织及性能的研究

采用SEM、EDX等手段,研究了Sn58Bi-x W钎料润湿性能、组织形貌及焊点接头力学性能。结果表明:适量W颗粒可以提高Sn58Bi润湿性,随着W颗粒含量的增加,钎料的润湿性呈现先上升后下降的趋势,W质量分数为0.05%时润湿性最好,其铺展面积为132.73 mm~2。W颗粒可以有效细化Sn58Bi钎料合金的微观组织,减小焊点界面IMC厚度,当W添加量为质量分数0.1%,Sn-58B钎料的微观组织最为细小,界面IMC的厚度为0.71μm,焊点的抗拉强度最高,达101.6 MPa。     

磁场对Sn-0.3Ag-0.7Cu焊点显微组织及性能影响研究

以Sn-0.3Ag-0.7Cu(SAC0307)低银无铅钎料焊点为研究对象,在焊点凝固过程中施加2.3T匀强磁场,通过观察低银无铅焊点显微组织变化,揭示磁场对焊点凝固及固态扩散行为影响;利用Fe、Ni增强元素对比得出SAC0307在不同环境下的凝固和固态扩散行为。将焊点置于电流密度为3×10~3 A/cm~3的磁电耦合环境下,观察了磁电耦合条件下焊点的显微组织演变过程,并总结了磁场对焊点电迁移行为的影响。结果表明:静磁场条件下,焊点界面处IMC形态由扇贝状向针状转变;IMC倾向于向钎料内部快速生长;Fe、Ni的加入进一步促进IMC生长。     

IMC生长对无铅焊球可靠性的影响

通过模拟及实验研究了IMC层及其生长对无铅焊点可靠性的影响.采用回流焊将无铅焊球(Sn3.5Ag0.7Cu)焊接到PCB板的铜焊盘上,通过-55～125℃的热循环实验,获得了IMC厚度经不同热循环次数后的生长规律.采用有限元法模拟了热循环过程中IMC厚度生长对无铅BGA焊点中应力变化的影响,并由能量疲劳模型预测了无铅焊点寿命.计算结果显示,考虑IMC层生长所预测的焊点热疲劳寿命比不考虑IMC层生长时缩短约30%.     

Sn0.7Cu-xEr/Cu焊点界面反应及其化合物层生长行为研究

通过回流焊工艺制备了Sn0.7Cu-x Er/Cu(x=0,0.1,0.5)钎焊接头,研究钎焊温度及等温时效时间对接头的界面金属间化合物(IMC)的形成与生长行为的影响。结果表明:Sn0.7Cu钎料中微量稀土Er元素的添加,能有效抑制钎焊及时效过程中界面IMC的形成与生长。在等温时效处理过程中,随着时效时间的延长,界面反应IMC层不断增厚,在相同时效处理条件下,Sn0.7Cu0.5Er/Cu焊点界面IMC层的厚度略小于Sn0.7Cu0.1Er/Cu焊点界面的厚度。通过线性拟合方法,得到Sn0.7Cu0.1Er/Cu和Sn0.7Cu0.5Er/Cu焊点界面IMC层的生长速率常数分别为3.03×10–17 m2/s和2.67×10–17 m2/s。     

The effect of soldering process variables on the microstructure and mechanical properties of eutectic Sn-Ag/Cu solder joints

Fundamental understanding of the relationship among process, microstructure, and mechanical properties is essential to solder alloy design, soldering process development, and joint reliability prediction and optimization. This research focused on the process-structure-property relationship in eutectic Sn-Ag/Cu solder joints. As a Pb-free alternative, eutectic Sn-Ag solder offers enhanced mechanical properties, good wettability on Cu and Cu alloys, and the potential for a broader range of application compared to eutectic Sn-Pb solder. The relationship between soldering process parameters (soldering temperature, reflow time, and cooling rate) and joint microstructure was studied systemati-cally. Microhardness, tensile shear strength, and shear creep strength were measured and the relationship between the joint microstructures and mechani-cal properties was determined. Based on these results, low soldering tempera-tures, fast cooling rates, and short reflow times are suggested for producing joints with the best shear strength, ductility, and creep resistance.     

回流焊对SnAgCu焊点IMC及剪切强度的影响

研究了回流焊次数对Sn-0.3Ag-0.7Cu-xNi/Cu(x=0,0.05)焊点的界面反应及其剪切强度的影响。结果表明:随着回流焊次数的增加,界面金属间化合物(IMC)Cu6Sn5和(Cu1-xNix)6Sn5的厚度均增加。在钎料中添加w(Ni)为0.05%,可有效抑制IMC的生长,与回流焊次数无关。回流焊次数对Sn-0.3Ag-0.7Cu/Cu和Sn-0.3Ag-0.7Cu-0.05Ni/Cu的剪切强度影响都不大,五次回流焊后剪切强度略有下降,剪切强度分别为21MPa和25MPa。发现断裂面部分在钎料中,部分在钎料和IMC之间。     

Sn-Ag-Cu焊料中金属间化合物对焊接性能的影响

讨论了Sn-Ag-Cu焊料与Cu焊盘间在回流焊过程中形成的金属间化合物(IMC)的种类、形态,Ag含量和Cu含量对IMC的影响,IMC在老化过程中的生长演变及其对焊接性能的影响。结果表明:Sn-Ag-Cu焊料与Cu焊盘之间的金属间化合物主要是Cu6Sn5和长针状的Ag3Sn,Ag和Cu的添加对组织有明显细化作用,但过量添加会影响IMC的性能。IMC的演变主要是与老化温度、老化时间有关,较厚的IMC不利于焊接性能的提高。     

冷却速率对无铅再流焊焊点质量的影响（续完）

无铅再流焊中冷却速率影响焊点力学性能及可靠性。快速冷却可以细化组织,间接控制金属间化合物厚度和形态,影响焊点断裂模式,提高焊点综合性能。但是由于元件与PCB等材料的热不匹配性而造成的较大应力,易造成元件或焊点失效等。通过对文献中研究结果的总结,设计了炉冷、空冷和水冷等几种再流焊冷却方式,并对焊点进行了强度测试和组织成分分析,建议工业用最佳冷却斜率控制在3℃/s～6℃/s。     

冷却速率对无铅再流焊焊点质量的影响(待续)

无铅再流焊中冷却速率影响焊点力学性能及可靠性。快速冷却可以细化组织,间接控制金属间化合物厚度和形态,影响焊点断裂模式,提高焊点综合性能。但是由于元件与PCB等材料的热不匹配性而造成的较大应力,易造成元件或焊点失效等。通过对文献中研究结果的总结,设计了炉冷、空冷和水冷等几种再流焊冷却方式,并对焊点进行了强度测试和组织成分分析,建议工业用最佳冷却斜率控制在3℃/s～6℃/s。     

Characteristics of the Sn-Pb eutectic solder bump formed via fluxless laser reflow soldering

In an attempt to develop a fluxless reflow solder bumping process, the effects of processing variables, which include energy input rate and time, and the shape of solder disk on the microstructure of the solder/Cu pad interface and the shear strength of the joints were investigated. It was demonstrated that a proper combination of the variables could lead to the formation of a spherical solder bump with shear strength comparable to that formed via the conventional reflow soldering process. In addition, the kinetics of Cu pad dissolution into the solder during laser heating was modeled numerically to elucidate intermetallic formation mechanism at the solder/Cu pad interface. Jointly appointed by CAAM at POSTECH     

Effect of substrate metallization on interfacial reactions and reliability of Sn-Zn-Bi solder joints

The scope of this paper covers a comprehensive study of the lead-free Sn-Zn-Bi solder system, on Cu, electrolytic Ni/Au and electroless Ni(P)/Au surface finishes. This includes a study of the shear properties, intermetallic compounds at the substrate-ball interface and dissolution of the under bump metallization. The Sn-8Zn-3Bi (wt.%) solder/Cu system exhibited a low shear load with thick IMCs formation at the interface. The dissolution of the Cu layer in the Sn-Zn-3Bi solder is higher than that of the other two Ni metallizations. It was found that the formation of a thick Ni-Zn intermetallic compound (IMC) layer at the solder interface of the electrolytic Ni bond pad reduced the mechanical strength of the joints during high temperature long time liquid state annealing. The solder ball shear-load for the Ni(P) system during extended reflow increased with an increase of reflow time. No spalling was noticed at the interface of the Sn-Zn-3Bi solder/Ni(P) system. Sn-8Zn-3Bi solder with electroless Ni(P) metallization appeared as a good combination in soldering technology.     

Microstructure of eutectic 80Au/20Sn solder joint in laser diode package

Laser diodes (LD) are usually bonded onto heat sinks for the purposes of heat dissipation, mechanical support and electrical interconnect. In this study, energy dispersive X-ray analysis (EDX) and electron backscatter diffraction (EBSD) are employed to investigate the microstructure evolution of 80Au/20Sn solder joint in LD package. During reflow, Pt-Sn and (Au, Ni)Sn IMCs were formed at the respective LD/solder and solder/heatsink interfaces, while δ, β and ζ′ phases of Au/Sn intermetallics were found in the solder joint. The Au-rich β and ζ′ phases in the solder joint limit the growth of interfacial IMCs. Chip shear testing showed that the failure occurred within the LD, with partial brittle fracture at the GaAs substrate and partial interfacial delamination at the GaAs/SiN interface. The strong solder bond can be attributed to the high mechanical strength of 80Au/20Sn solder, which provides improved stability for high temperature applications.     

回流焊对SnAgCuBi/Cu焊点IMC及剪切强度的影响

利用金相显微镜和扫描电镜对多次回流焊后的Sn-0.3Ag-0.7Cu-xBi/Cu焊点IMC和剪切断口形貌进行了观察和分析。结果表明:Bi的加入提高了接头剪切强度,且随着Bi含量的增加而增加,当w(Bi)为4.5%时达最大值45.07MPa,同时Bi的加入有效抑制了焊点IMC的增长。经过5次回流焊后,未加入Bi的焊点剪切强度由24.55MPa下降到20.82MPa,而加入w(Bi)为3.0%的焊点剪切强度由35.95MPa下降到32.46MPa。