基板稀土微合金化对Sn3Ag0.5Cu/Cu钎焊界面反应的影响

研究了在Cu基板中加入质量分数1%的稀土元素Ce、Er后,与Sn3Ag0.5Cu(SAC305)无铅钎料进行钎焊并时效处理后的界面反应及其化合物(IMC)生长行为。结果表明:钎焊完成后,在SAC305/Cu钎焊界面只观察到Cu_6Sn_5,而SAC305/Cu-1Ce及SAC305/Cu-1Er界面还有Cu_3Sn形成;在时效处理过程中,纯Cu基板上的金属间化合物生长速率最快,Cu-1Ce基板次之,Cu-1Er基板最慢,且形成的IMC厚度也是依次递减;加入质量分数1%的Ce、Er元素对IMC生长均有抑制作用,且Er的抑制作用较Ce强。     

Sn-9Zn/Cu 焊点界面反应及其化合物生长行为

通过扫描电镜(SEM)等手段研究了Sn-9Zn/Cu在不同浸焊时间与时效时间等条件下的界面反应及其金属间化合物(IMC)生长行为。结果表明:在浸焊后,Sn-9Zn/Cu钎焊接头界面形成了扇贝状的界面化合物Cu5Zn8,IMC层厚度随着浸焊时间与时效处理时间的增加而增加,未时效处理的焊点界面IMC与铜基板接触的一面较为平直,而与钎料接触的一侧呈现出锯齿状,随着时效时间的增加,界面变得越来越不平整;另外在IMC层与焊料之间产生裂缝现象,分析认为是由于钎料与IMC之间的热膨胀系数差异导致热应力形成裂缝。浸焊600 s后的试样在时效15 d后IMC层与Cu基板接触侧产生了与初始金属间化合物Cu5Zn8不同的三元化合物Cu6(Sn,Zn)5。     

Sn-58Bi-0.5Ce/Cu界面金属间化合物的性能研究

研究了Sn-58Bi-0.5Ce/Cu钎焊接头在120℃时效过程中界面组织形貌及金属间化合物层(IMC)的厚度变化。结果表明:在Sn-58Bi-0.5Ce/Cu钎焊接头界面处形成了较为平坦的双层金属间化合物,靠近钎料的上层为Cu6Sn5相,邻近Cu基板的下层为Cu3Sn相。等温时效处理后,IMC层逐渐凸起,且随着时效时间的增加,IMC层不断增厚。通过对实验数据进行拟合,得到钎焊接头界面IMC层的生长速度常数为5.77×10–17m2/s。     

无铅钎料焊点界面与剪切行为的研究

研究了三种不同合金钎料回流时间和老化时间对焊点界面行为和剪切性能的影响。结果表明:回流时间和老化对金属间化合物的生长和剪切力有相似的影响;焊后界面处和焊料中均有明显的金属间化合物;随着回流时间和老化时间的延长,金属间化合物生长明显。层厚不断增大;界面形貌从长针状转变成扇贝状,并且齿高减小;合金成分对剪切力影响不明显。在中速应变率下,剪切力减小。Sn-3.5Ag显现出较好的剪切性能,剪切力为77~82 N。     

电子封装与组装焊点界面反应及微观组织研究进展

软钎焊焊点界面反应是连接金属的最古老的冶金工艺过程。随着倒装芯片(FC)、球栅阵列(BGA)和芯片级封装(CSP)等面封装技术的兴起,近年来Sn基钎料被广泛应用于微电子制造,包括芯片和基板之间的封装互连以及基板与印制电路板之间的组装互连。这就需要系统地研究Sn基钎料焊点界面反应及微观组织。从形态学、热力学和动力学的角度回顾总结了SnPb共晶钎料、高Pb钎料和无Pb钎料与Cu、Ni、Au/Ni/Cu、PdAg焊盘之间的界面反应。     

SnBiEr/Cu界面反应及时效过程中IMC的研究

采用SEM观察等手段研究了Sn58BixEr(x=0,0.1,0.5;表示添加质量分数0.01%,0.5%的Er)/Cu钎焊接头界面反应以及在120℃时效过程中金属间化合物(IMC)的生长行为。实验结果表明:Sn58BixEr/Cu钎焊接头IMC层厚度随着钎焊温度的升高而增厚,添加微量的Er能够有效抑制界面IMC的生长。在时效过程中,界面IMC层的厚度随着时效时间的增加而逐渐增厚。通过对实验数据进行拟合,得出120℃时效温度下Sn58Bi0.1Er/Cu和Sn58Bi0.5Er/Cu的IMC层的生长速率常数分别为3.42×10–16 m2/s和2.84×10–16 m2/s。     

Sn3．5Ag0．75Cu钎料与Au／Ni／Cu焊盘接头老化过程中IMC组织的演变

通过SEM（Scanning Electron Microscope）背散射照片和EDX（Energy Dispersive X-Ray Spectroscopy）成分分析研究了无铅钎料Sn3．5Ag0．75Cu与Au／Ni／Cu焊盘接头在老化过程中其界面金属间化合物（IMC）的生长演变过程；在175℃温度条件下老化72h后发现Cu可以穿过Ni层参与形成界面金属间化合物（Au，Ni，Cu）Sn4和（Au，Ni，Cu）6Sn5；基于金属间化合物生长动力学理论计自得该焊点结构中AuSn4生长的活化能为53．78KJ／mol。[第一段]     

Ti对Sn0.7Cu无铅钎料润湿性和界面的影响

研究了Ti的加入对Sn0.7Cu无铅钎料润湿性能以及钎料/Cu界面微观组织的影响.结果表明:在Sn0.7Cu中添加微量Ti,提高了钎料的润湿性能,可使铺展面积提高5％左右,当钎焊时间为3s时,界面金属间化合物(IMC)形貌由原来的扇贝状变为锯齿状;随着钎焊时间延长,Sn0.7Cu/Cu和Sn0.7Cu0.008Ti/C...     

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。     

电子封装中Cu/Cu_3Sn/Cu焊点的制备工艺及组织演变

采用电镀的方法在Cu基板沉积4μm厚Sn层作为钎料,在不同参数下对双钎料Cu/Sn+Sn/Cu三明治结构进行钎焊连接,得到可形成全Cu_3Sn焊点的最优工艺参数组合为:Ar气保护下300℃,3 h,1 N。然后研究了全Cu3Sn焊点形成过程中不同金属间化合物(Cu_6Sn_5和Cu_3Sn)的生长形貌和界面反应机理。结果表明,钎焊10 min后在Cu-Sn界面形成了扇贝状的Cu_6Sn_5,并且在Cu基板与Cu_6Sn_5之间有一层很薄的Cu_3Sn出现,Cu/Cu_3Sn和Cu3Sn/Cu_6Sn_5界面较为平整。随着时间延长,上下两层Cu6Sn5相互接触并融为一体,直至液态Sn完全被消耗,而Cu_3Sn通过消耗Cu_6Sn_5而快速增长,直到界面区全部形成Cu_3Sn。     

Thermodynamic prediction of interface phases at Cu/solder joints

A thermodynamic method to predict the intermetallic compound which forms first at the substrate/solder interface during the soldering process has been suggested through calculations of metastable phase equilibria between the substrate and the liquid solder and by comparison of the driving forces of formation of individual intermetallic compound phases. It has been applied to the interfacial reaction between Cu substrate and Sn-Ag, Sn-Zn eutectic solders. The prediction from thermodynamic calculations was in good agreement with observed experimental results. The solid-state growth behavior of compound phases formed at the interface of Cu/Sn-Zn and Cu/Sn-Ag eutectic solder joints was explained and a schematic diffusion path suggested through calculated ternary phase diagrams.     

Interfacial reaction between Sn-0.7Cu (-Ni) solder and Cu substrate

The interfacial reaction between Sn-0.7mass%Cu-(Ni) solders and a Cu substrate was investigated to reveal the effect of the addition of Ni to Sn-Cu solder on the formation of intermetallic compounds (IMCs). Sn-0.7Cu-xNi solders (x=0, 0.05, 0.1, 0.2 mass%) were prepared. For the reflow process, specimens were heated in a radiation furnace at 523 K for 60 sec, 300 sec, and 720 sec to estimate the interfacial reaction between the molten solder and Cu substrate. Then, for the aging process, some specimens were heat-treated in an oil bath at 423 K for 168 h and 504 h. The cross sections of soldered specimens were observed to measure the dissolution thickness of the Cu substrate and the thickness of the IMC and to investigate the microstructures of IMC. The results showed that, just after the reflow process, the dissolution thickness of the Cu substrate increased with the increase of Ni content in the Sn-0.7Cu-xNi solder and the thickness of the IMC between the solder and Cu substrate was the minimum in the Sn-0.7Cu-0.05Ni solder. After the aging process, the IMC grew with the increase of aging time. In the case of 0.05% Ni, the IMC thickness was the thinnest regardless of aging time. It is clear that 0.05% Ni addition to Sn-0.7Cu solder very effectively inhibits the formation and growth of the IMC between solder and Cu substrate. Electron probe microanalysis of the IMC showed that the IMC layer in the Sn-0.7Cu-Ni solder contained Ni, and the IMC was expressed as (Cu_1−y ,Ni _y )₆Sn₅.     

Morphology and growth kinetics of intermetallic compounds in solid-state interfacial reaction of electroless Ni-P with Sn-based lead-free solders

A comparative study of solid/solid interfacial reactions of electroless Ni-P (15 at.% P) with lead-free solders, Sn-0.7Cu, Sn-3.5Ag, Sn-3.8Ag-0.7Cu, and pure Sn, was carried out by performing thermal aging at 150°C up to 1000 h. For pure Sn and Sn-3.5Ag solder, three distinctive layers, Ni₃Sn₄, SnNiP, and Ni₃P, were observed in between the solder and electroless Ni-P; while for Sn-0.7Cu and Sn-3.8Ag-0.7Cu solders, two distinctive layers, (CuNi)₆Sn₅ and Ni₃P, were observed. The differences in morphology and growth kinetics of the intermetallic compounds (IMCs) at the interfaces between electroless Ni-P and lead-free solders were investigated, as well as the growth kinetics of the P-enriched layers underneath the interfacial IMC layers. With increasing aging time, the coarsening of interfacial Ni₃Sn₄ IMC grains for pure Sn and Sn-3.5Ag solder was significantly greater than that of the interfacial (CuNi)₆Sn₅ IMC grains for Sn-0.7Cu and Sn-3.8Ag-0.7Cu solders. Furthermore, the Ni content in interfacial (CuNi)₆Sn₅ phase slightly increased during aging. A small addition of Cu (0.7 wt.%) resulted in differences in the type, morphology, and growth kinetics of interfacial IMCs. By comparing the metallurgical aspects and growth kinetics of the interfacial IMCs and the underneath P-enriched layers, the role of initial Cu and Ag in lead-free solders is better understood.     

回流次数对Sn3.8Ag0.7Cu-xNi/Ni焊点的影响

研究了复合无铅焊料Sn3.8Ag0.7Cu-xNi(x=0.5,1.0,2.0)与Au/Ni/Cu焊盘在不同回流次数下形成的焊点的性能.结果表明,Ni颗粒增强的复合焊料具有良好的润湿性能,熔点小于222℃;X为0.5的焊料界面IMC由针状(CuNi)6Sn5演化为双层IMC,即多面体状化合物(CuNi)6Sn5和回飞棒...     

Growth of Sn and intermetallic compounds in Sn-Ag-Cu solder

The microstructure of the Sn-Ag-Cu solder is examined by optical microscopy and scanning electron microscopy (SEM) for various compositions near the ternary eutectic for different cooling rates from the solder melt. Focus is on the size and orientation of Sn grains as indicated by cross-polarized, light optical microscopy, and pole figures from x-ray diffraction. We find that both composition and cooling rate have strong influences on Sn grain size, with Sn grain size increasing an order of magnitude as Cu concentration increases from 0% to 1.1%. Cyclic growth twinning, with twinning angles near 60°, is observed in Sn-Ag-Cu alloys near the composition Sn-3.9Ag-0.6Cu.     

Morphology of intermetallic compounds formed between lead-free Sn-Zn based solders and Cu substrates

The morphologies of intermetallic compounds formed between Sn-Zn based solders and Cu substrates were investigated in this study. The investigated solders were Sn-9Zn, Sn-8.55Zn-0.45Al, and Sn-8.55Zn-0.45Al-0.5Ag. The experimental results indicated that the Sn-9Zn solder formed Cu₅Zn₈ and CuZn₅ compounds on the Cu substrate, while the Al-containing solders formed the Al_4.2Cu_3.2Zn_0.7 compound. The addition of Ag to the Sn-8.55Zn-0.45Al solder resulted in the formation of the AgZn₃ compound at the interface between the Al_4.2Cu_3.2Zn_0.7 compound and the solder. Furthermore, it was found that the cooling rate of the specimen after soldering had an effect on the quantity of AgZn₃ compound formed at the interface. The AgZn₃ compound formed with an air-cooling condition exhibited a rougher surface and larger size than with a water-quenched condition. It was believed that the formation of the AgZn₃ compound at the interface occurs through heterogenous nucleation during solidification.     

A study on the reaction between Cu and Sn3.5Ag solder doped with small amounts of Ni

The reaction between Cu and the Sn-Ag solders doped with different amounts of Ni is studied. Four different solders with the Ag concentration fixed at 3.5 wt.% and Ni concentrations varied between 0.0 wt.% and 1.0 wt.% are used. In contrast to the reaction between Ni and the Sn-Ag solders doped with different amounts of Cu, the type of intermetallic compound formed does not depend on the Ni concentration. The compound Cu₆Sn₅ forms for all the Ni concentrations used. For the Ni-doped solders, the Cu₆Sn₅ phase contains a small amount of Ni. The compound Cu₃Sn appears subsequently between Cu₆Sn₅ and Cu as the reaction time increases. The addition of Ni has the effect of substantially increasing the amount of intermetallic compound at the interface. The addition of Ni also produces two distinct Cu₆Sn₅ regions at the interface. The outer region contains more Ni, and the inner region contains less Ni. This study also finds that, during solid-state aging, the growth of Cu₃Sn becomes slower when Ni is added to the solder. The findings of this study are rationalized using the Cu-Ni-Sn isotherm.     

Electromigration effect on intermetallic growth and Young’s modulus in SAC solder joint

Solid-state intermetallic compound (IMC) growth behavior plays and important role in solder joint reliability of electronic packaging assemblies. The directional impact of electromigration (EM) on the growth of interfacial IMCs in Ni/SAC/Ni, Cu/SAC/Ni single BGA ball solder joint, and fine pitch ball-grid-array (FPBGA) at the anode and cathode sides is reported in this study. When the solder joint was subjected to a current density of 5,000 A/cm² at 125°C or 150°C, IMC layer growth on the anode interface was faster than that on the cathode interface, and both were faster than isothermal aging due to the Joule heating effect. The EM affects the IMC growth rate, as well as the composition and mechanical properties. The Young’s modulus and hardness were measured by the nanoindentation continuous stiffness measurement (CSM) from planar IMC surfaces after EM exposure. Different values were observed at the anode and cathode. The energy-dispersive x-ray (EDX) line scan analysis was conducted at the interface from the cathode to anode to study the presence of species; Ni was found in the anode IMC at SAC/Cu in the Ni/SAC/Cu joint, but not detected when the current was reverse. Electron-probe microanalysis (EPMA) measurement on the Ni/SAC/Ni specimen also confirmed the polarized Ni and Cu distributions in cathode and anode IMCs, which were (Ni_0.57Cu_0.43)₃Sn₄ and (Cu_0.73Ni_0.27)₆Sn₅, respectively. Thus, the Young’s moduli of the IMC are 141 and 175 GPa, respectively.     

纳米压痕法分析无铅焊点内界面金属化合物的力学性能

根据实际工艺流程和服役工况制备了微电子封装中3种无铅焊点(Sn3.0Ag0.5Cu、Sn0.7Cu和Sn3.5Ag)内界面金属化合物(IMC)的试样;利用扫描电镜(SEM)和能量色散X射线荧光光谱仪(EDX)对所制IMC的形貌和化学成分进行了分析;另外,借助纳米压痕仪,采用连续刚度测量(CSM)技术在不同的加载速率下对所制IMC的弹性模量和硬度进行了测量。结果表明,3种无铅焊点内的IMC均为Cu6Sn5,其弹性模量分别为98.93±3.37,113.55±4.58和(102.16±3.11)GPa,硬度分别为5.18±0.14,5.78±0.11和(5.55±0.19)GPa。