Nd对Sn-0.7Cu-0.05Ni焊点组织与力学性能的影响

研究了添加微量稀土元素Nd对Sn-0.7Cu-0.05Ni/Cu无铅焊点再流焊和150 ℃时效条件下焊点界面组织与力学性能的影响. 结果表明,添加适量Nd(质量分数为0.06%)可以优化焊点界面组织,减缓时效过程中Sn-0.7Cu-0.05Ni/Cu界面化合物的生长速率,提高焊点力学性能,增强焊点的可靠性. 时效过程中,添加了0.06%Nd的Sn-0.7Cu-0.05Ni钎料焊点的剪切力始终保持最大,在时效1 440 h后,Sn-0.7Cu-0.05Ni-0.06Nd/Cu焊点的剪切力相比未添加稀土的Sn-0.7Cu-0.05Ni钎料提高了31.9%.     

超低银SnAgCu钎料微焊点力学性能

研究了复合添加Ga/Nd元素对超低银Sn-0.3Ag-0.7Cu钎料微焊点力学性能的影响. 结果表明,复合添加适量Ga/Nd元素可以显著改善微焊点界面组织,抑制微焊点界面附近金属间化合物的生成,从而提高微焊点的力学性能,相比母合金微焊点剪切力提高幅度达到约16%;微焊点的力学性能随着时效时间的增加而降低,降低幅度优于未添加Ga/Nd的微焊点. Sn-0.3Ag-0.7Cu-0.5Ga-0.1Nd钎料微焊点的力学性能在时效处理后仍保持较好的水平,已接近Sn-3.8Ag-0.7Cu钎料微焊点的90%,具有良好的工业应用前景.     

添加0.10%Ce对Sn-0.7Cu-0.5Ni焊料与Cu基板间界面IMC的影响

研究Sn-0.7Cu-0.5Ni-xCe(x=0,0.1)焊料与铜基板间543K钎焊以及453K恒温时效对界面金属间化合物(IMC)的形成与生长行为的影响。结果表明:往Sn-0.7Cu-0.5Ni焊料合金中添加0.10%Ce,能抑制等温时效过程中界面IMC的形成与生长;焊点最初形成的界面IMC为Cu6Sn5,时效10d后,Sn-0.7Cu-0.5Ni和Sn-0.7Cu-0.5Ni-0.10Ce这2种焊料中均有Cu3Sn形成,与Sn-0.7Cu-0.5Ni/Cu焊点相比,Sn-0.7Cu-0.5Ni-0.10Ce/Cu界面IMC层较为平整;该界面IMC的形成与生长均受扩散控制,主要取决于Cu原子的扩散,添加稀土元素Ce能抑制Cu原子的扩散,Sn-0.7Cu-0.5Ni和Sn-0.7Cu-0.5Ni-0.10Ce焊点界面IMC层的生长速率分别为6.15×10-18和5.38×10?18m2/s。     

超低银SAC钎料焊点界面显微组织演化

研究了复合添加Ga/Nd元素的超低银Sn-0.3Ag-0.7Cu钎料在长期时效过程中的微焊点界面组织演化情况. 结果表明,复合添加适量Ga/Nd元素可以显著改善时效后微焊点界面组织,抑制微焊点界面附近大块状金属间化合物以及稀土相的生成. 经720 h时效后,即使在含有过量Nd元素的微焊点界面仍没有发现明显的Ag₃Sn相和稀土相,取而代之的是小块状的新相,结合EDS和XRD分析结果推测该相含有Ga₂Nd与Cu₆Sn₅. 经过长期时效处理后,微焊点抗剪力接近Sn-3.8Ag-0.7Cu焊点抗剪力的90%,具有较好的力学性能.     

Bi对Sn-0.3Ag-0.7Cu-xBi/Ni焊点IMC的影响

无铅钎料和基板间金属间化合物(1MC)的生长对元器件的可靠性有重要影响.使用Sn-0.3Ag-0.7Cu-xBi无铅钎料与Ni盘进行焊接,并对焊点进行了180℃时效试验,时效时间分别为O、24、96、216和384h.采用金相显微镜、扫描电镜和能谱仪观察分析了钎料与Ni界面IMC的生长及形貌变化,并对其焊点IMC层Ni的分布进行了分析,同时对其界面生长速率进行了拟合.结果表明:Sn-0.3Ag-0.7Cu焊料与Ni焊盘之间的IMC是棒状的(CuxNi1-x)6Sn5,Bi的加入并没有起到很好的抑制作用,而是随着Bi含量的增加IMC先增加后减少.Sn-O.3Ag-0.7Cu/Ni焊点IMC中Ni的平均含量(wN)分为15%、5%两区域.由近Ni向钎料基体方向呈下降趋势.但是Sn-O.3Ag-0.7Cu-3.0Bi/Ni焊点IMC中Ni的平均含量在7%左右.时效后IMC层的厚度会随着老化时间的延长而增加,但是Sn-0.3Ag-0.7Cu-xBi/Ni焊点由于Bi的析出IMC增长得缓慢;Sn-0.3Ag-0.7Cu/Ni焊点(CuxNi1-x)6Sn5中15%Ni的含量区域逐渐过渡到5%区域,但是Sn-0.3Ag-0.7Cu-xBi/Ni焊点IMC中Ni的平均含量维持9%较时效前有所增加.通过生长速率计算,Sn-O.3Ag-0.7Cu-xBi/Ni焊点IMC的生长速率随着Bi含量的增加而减少.     

BGA单板结构与板级结构焊点剪切力学行为分析

采用试验方法研究BGA封装结构中焊点的剪切力学行为. 分析并比较了Sn-3Ag-0.5Cu,Sn-0.3Ag-0.7Cu,Sn-0.3Ag-0.7Cu-0.07La和Sn-0.3Ag-0.7Cu-0.07La-0.05Ce四种钎料焊点在单板结构与板级结构中的力学性能. 结果表明, 单板结构中焊点的抗剪强度高于板级结构中焊点的抗剪强度. 在单板结构中,高银焊点的抗剪强度最大,加入稀土元素的低银焊点只是得到了一定程度上的改善,然而对于板级结构,加入稀土元素的低银焊点剪切力学性能基本与高银焊点相当. 在同等拘束条件下,低银焊点的延展性优于高银焊点. 此外,对于同一种钎料而言,单板结构中的焊点断裂在体钎料上,而板级结构则断裂在IMC/体钎料界面处.     

等温时效对SnCuTi/Cu无铅焊点界面反应及力学性能的影响

研究了在125℃时效过程中,Sn-0.7Cu-0.008Ti/Cu焊点界面IMC的生长及抗剪强度的变化。结果表明,Sn-0.7Cu-0.008Ti/Cu焊点界面IMC厚度在时效过程中不断增加,并且与时效时间呈抛物线函数关系;界面IMC形貌由扇贝状转变为波浪状,相组成由单一的Cu6Sn5相转变为Cu6Sn5+Cu3Sn的分层组织。相同时效条件下,钎焊间隙对界面IMC的生长影响不大。焊点的抗剪强度随时效时间的增加而逐渐降低,但微量Ti的加入可明显改善焊点的力学性能。     

剪切载荷下BGA单板结构与板级结构焊点尺寸效应

采用试验方法研究BGA封装结构中焊点的剪切力学行为.分析并比较了Sn-3Ag-0.5Cu,Sn-0.3Ag-0.7Cu,Sn-0.3Ag-0.7Cu-0.07La和Sn-0.3Ag-0.7Cu-0.07La-0.05Ce四种钎料焊点在单板结构与板级结构中的尺寸效应.结果表明,单板结构与板级结构中焊点的抗剪强度均随焊点尺寸的减小而增加,板级结构焊点表现的更加明显.低银焊点与高银焊点的剪切力学性能差距随着焊点尺寸的减小逐渐降低.随着焊点尺寸的减小,单板结构中焊点的剪切应变逐渐增加;板级结构则遵循先增加后减小的变化规律.此外,高银焊点随焊点尺寸的减小断裂模式由韧脆混合型向韧性断裂形式转变,另外三种低银焊点断裂模式不变,仅是断裂位置向体钎料侧偏移.     

Cu/Sn-0.7Cu-0.05x/Cu焊点界面组织形貌及力学性能的研究

研究了Cu/Sn-0.7Cu-0.05Ni/Cu和Cu/Sn-0.7Cu-0.05Fe/Cu焊点的界面组织形貌、钎料铺展性能及焊点力学性能。结果表明:在Sn-0.7Cu钎料中添加Fe和Ni颗粒均可以抑制金属间化合物层生长,使得界面致密平整,同时减小了液态钎料在铜基板上的表面张力,提高了铺展性能,而且使钎料的抗拉强度和塑性性能得到了一定程度的提高。与Fe颗粒相比,Ni颗粒的添加能更好地改善钎焊焊点的性能。     

界面金属间化合物对铜基Sn-3.0Ag-0.5Cu焊点拉伸断裂性能的影响

研究了Cu/Sn-3.0Ag-0.5Cu/Cu焊点在(150±1)℃时效温度下,0～1 000 h不同时间时效后焊点的拉伸断裂性能以及界面金属间化合物(IMC)的组织形态和成分.结果表明随着时效时间的延长,焊点拉伸强度降低,拉伸断裂主要发生于Solder/IMC界面或/和IMC/IMC界面,而且断口形貌逐渐由韧窝状断口为主向解理型脆性断口转变.SEM研究发现,时效过程中界面IMC不断长大、增厚并呈针状或块状从Cu/Solder界面向焊点心部生长,时效1 000 h的焊点中IMC分层明显.半焊点结构为Cu/Cu3Sn/Cu6Sn5/Solder,同时,在靠近铜基体的IMC中有Kirkendall空洞存在.     

Sn-0.3Ag-0.7Cu-xNd钎料显微组织及性能

研究了稀土元素Nd的添加量对超低银无铅钎料Sn-0.3Ag-0.7Cu的润湿性能、显微组织和力学性能的影响.结果表明,微量Nd元素的加入可以显著改善Sn-0.3Ag-0.7Cu超低银无铅钎料的润湿性能和焊点的力学性能,并且能够起到细化基体组织的作用.当钎料中Nd元素的质量分数达到0.1%时,钎料的综合性能最佳,基体组织最为均匀细化.虽然Ag元素含量的降低使钎料的性能有所下降,但是加入适量Nd元素后钎料的润湿性能已接近传统Sn-3.8Ag-0.7Cu钎料.     

时效对Sn-Cu-Ni-xPr/Cu焊点组织与性能的影响

采用Sn-Cu-Ni-xPr无铅钎料对片式电阻进行钎焊试验,并且利用加速老化试验模拟片式电阻中焊点的服役环境,研究了时效过程中Sn-Cu-Ni-xPr焊点界面化合物层的厚度以及焊点抗剪强度的变化.结果表明,随着时效的进行,片式电阻Sn-Cu-Ni-xPr焊点的厚度不断增加,抗剪强度不断下降.与此同时,添加微量稀土元素Pr可有效提高Sn-Cu-Ni-xPr焊点的力学性能,当Pr元素含量为0.05%时,焊点力学性能优良,且在长时间的时效条件下仍然优于其它焊点.     

Improving the shear strength of Sn–Ag–Cu–Ni/Cu–Zn solder joints via modifying the microstructure and phase stability of Cu–Sn intermetallic compounds

This study focuses on the correlation between high-speed impact tests and the interfacial reaction in Sn-3.0Ag-0.5Cu-0.1Ni/Cu (wt%) and Sn-3.0Ag-0.5Cu-0.1Ni/Cu-15Zn solder joints. Adding Ni into the Sn–Ag–Cu solder alters the interfacial morphology from scallop type to layer type and exhibits high shear strength after reflow in both solder joints. However, the shear strength of Sn-3.0Ag-0.5Cu-0.1Ni/Cu solder joints degrades significantly after thermal aging at 150 °C for 500 h. It is notable that Sn-3.0Ag-0.5Cu-0.1Ni/Cu-15Zn solder joints still present higher shear strength after aging at 150 °C. The weakened shear strength in Sn-3.0Ag-0.5Cu-0.1Ni/Cu solder joints is due to stress accumulation in the interfacial (Cu,Ni)₆Sn₅ compound induced by the phase transformation from a high-temperature hexagonal structure (η-Cu₆Sn₅) to a low-temperature monoclinic structure (η'-Cu₆Sn₅). However, doping small amounts of Zn into (Cu,Ni)₆(Sn,Zn)₅ can inhibit the phase transformation during thermal aging and maintain strong shear strength. These experiments demonstrate that Sn-3.0Ag-0.5Cu-0.1Ni/Cu-15Zn solder joints can act as a stable connection in the micro-electronic packaging of most electronic products at their average working temperatures.     

Thermal reliabilities of Sn-0.5Ag-0.7Cu-0.1Al2O3/Cu solder joint

The effects of trace addition of Al₂O₃ nanoparticles (NPs) on thermal reliabilities of Sn-0.5Ag-0.7Cu/Cu solder joints were investigated. Experimental results showed that trace addition of Al₂O₃ 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 Al₂O₃ NPs could slow down the shear force reduction of solder joint during thermal services, which was attributed to the pinning effect of Al₂O₃ 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 cm²/h in IA process, and from 0.92×10^-10 to 0.53×10^-10 cm²/h in TC process. This indicated that trace addition of Al₂O₃ NPs can improve both IA and TC reliabilities of Sn-0.5Ag- 0.7Cu/Cu joint, and a little more obvious in IA reliability.     

Development of high strength Sn-0.7Cu solders with the addition of small amount of Ag and In

Nowadays, a major concern of Sn-Cu based solder alloys is focused on continuously improving the comprehensive properties of solder joints formed between the solders and substrates. In this study, the influence of Ag and/or In doping on the microstructures and tensile properties of eutectic Sn-0.7Cu lead free solder alloy have been investigated. Also, the effects of temperature and strain rate on the mechanical performance of Sn-0.7Cu, Sn-0.7Cu-2Ag, Sn-0.7Cu-2In and Sn-0.7Cu-2Ag-2In solders were investigated. The tensile tests showed that while the ultimate tensile strength (UTS) and yield stress (YS) increased with increasing strain rate, they decreased with increasing temperature, showing strong strain rate and temperature dependence. The results also revealed that with the addition of Ag and In into Sn-0.7Cu, significant improvement in YS (∼255%) and UTS (∼215%) is realized when compared with the other commercially available Sn-0.7 wt. % Cu solder alloys. Furthermore, the Sn-0.7Cu-2Ag-2In solder material developed here also exhibits higher ductility and well-behaved mechanical performance than that of eutectic Sn-0.7Cu commercial solder. Microstructural analysis revealed that the origin of change in mechanical properties is attributed to smaller β-Sn dendrite grain dimensions and formation of new inter-metallic compounds (IMCs) in the ternary and quaternary alloys.     

等温时效中稀土Er对Sn-3.8Ag-0.7Cu无铅钎料显微组织演化的影响

系统研究了等温时效中添加微量稀土Er对Sn-3.8Ag-0.7Cu钎料合金显微组织演化规律的影响.结果表明,Er对Sn-3.8Ag-0.7Cu钎料显微组织及等温时效过程中显微组织的演化产生了重要影响.在钎焊过程中,Er有效地细化了钎料组织,改变了钎料内部Cu-Sn金属间化合物的形态、尺寸及分布情况.在等温时效过程中,钎料内部生成的ErSn3金属间化合物为组织的再结晶过程提供了大量的形核质点,有效避免了再结晶组织的粗化及裂纹的产生和扩展.     

Pb-free solders for flip-chip interconnects

A variety of lead-free solder alloys were studied for use as flip-chip interconnects including Sn-3.5Ag, Sn-0.7Cu, Sn-3.8Ag-0.7Cu, and eutectic Sn-37Pb as a baseline. The reaction behavior and reliability of these solders were determined in a flip-chip configuration using a variety of under-bump metallurgies (TiW/Cu, electrolytic nickel, and electroless Ni-P/Au). The solder micro-structure and intermetallic reaction products and kinetics were determined. The Sn-0.7Cu solder has a large grain structure and the Sn-3.5Ag and Sn-3.8Ag-0.7Cu have a fine lamellar two-phase structure of tin and Ag₃Sn. The intermetallic compounds were similar for all the lead-free alloys. On Ni, Ni₃Sn₄ formed and on copper, Cu₆Sn₅Cu₃Sn formed. During reflow, the intermetallic growth rate was faster for the lead-free alloys, compared to eutectic tin-lead. In solidstate aging, however, the interfacial intermetallic compounds grew faster with the tinlead solder than for the lead-free alloys. The reliability tests performed included shear strength and thermomechanical fatigue. The lower strength Sn-0.7Cu alloy also had the best thermomechanical fatigue behavior. Failures occurred near the solder/intermetallic interface for all the alloys except Sn-0.7Cu, which deformed by grain sliding and failed in the center of the joint. Based on this study, the optimal solder alloy for flip-chip applications is identified as eutectic Sn-0.7Cu. Editor’s Note: A hypertext-enhanced version of this article can be found at www.tms.org/pubs/journals/JOM/0106/Frear-0106.html For more information, contact D.R. Frear, Interconnect Systems Laboratories, Motorola, Tempe, AZ 85284; (480) 413-6655; fax (480) 413-4511; e-mail darrel.frear@motorola.com.