典型Sn基焊料凸点互连结构电迁移异同性

研究了Sn37Pb,Sn3.0Ag0.5Cu和Sn0.7Cu三种焊料BGA焊点在电迁移作用下界面的微观组织结构.在60℃,1×103 A/cm2电流密度条件下通电187h后,Sn37 Pb焊点阴极界面已经出现了空洞,同时在阳极有Pb的富集带;Sn3.0Ag0.5Cu焊点的阴极界面Cu基体大量溶解,阳极金属间化合物层明显比阴极厚;对于Sn0.7Cu焊料,仅发现阳极金属间化合物层厚度比阴极厚,阴极Cu基体的溶解不如SnAgCu明显,电迁移破坏明显滞后.     

典型Sn基焊料凸点互连结构电迁移异同性

研究了Sn37Pb,Sn3.0Ag0.5Cu和Sn0.7Cu三种焊料BGA焊点在电迁移作用下界面的微观组织结构.在60℃,1×103 A/cm2电流密度条件下通电187h后,Sn37 Pb焊点阴极界面已经出现了空洞,同时在阳极有Pb的富集带;Sn3.0Ag0.5Cu焊点的阴极界面Cu基体大量溶解,阳极金属间化合物层明显比阴极厚;对于Sn0.7Cu焊料,仅发现阳极金属间化合物层厚度比阴极厚,阴极Cu基体的溶解不如SnAgCu明显,电迁移破坏明显滞后.     

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6.5 A直流电下通电36 h和48 h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36 h使剪切抗力降低约30%,电迁移48 h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...     

SnAgCu无铅焊点原位电迁移IMC演变

在28℃.3.25A直流电下,对Cu/Sn3.0Ag0.5Cu/Cu对接无铅焊点进行原位电迁移实验,观察了通电120,168,384和504 h后焊点横截面的微观组织形貌.结果表明,电迁移初期,Cu<,6>Sn<,5>化合物遍布整个焊点截面,随时间延长,不断从阴极向阳极迁移聚集;当通电504 h后,焊点内已看不到金属间...     

镧对Sn3.5Ag0.5Cu钎料组织性能影响

运用莱卡显微镜、扫描电镜和能谱分析等手段,研究了稀土元素La的添加量对Sn3.5Ag0.5Cu钎料及其与Cu基体焊接后微观组织及性能的影响。结果表明:添加不同含量的稀土La均能使钎料及其与Cu基体焊接后组织与性能得到改善,其中以w(La)达到0.05%时为最优,显微硬度及剪切强度分别提高14%和10.7%。键参数函数计算结果表明La具有"亲Sn"倾向,可细化钎料组织,降低IMC(界面金属间化合物)的长大驱动力。     

La对Sn3.5Ag0.5Cu钎料界面组织和性能的影响

通过SEM和EDAX等,研究了La添加量对Sn3.5Ag0.5Cu钎料与Cu基体焊合界面IMC微观组织及性能的影响。结果表明:添加不同量的La均对Sn3.5Ag0.5Cu与Cu基体焊合后的组织有细化作用并增强其力学性能。其中以w(La)达到0.05%时最优,剪切强度可提高10.7%。材料热力学理论计算结果表明,La具有"亲Sn"倾向,添加少量La到Sn3.5Ag0.5Cu钎料中,可减小Cu6Sn5/Cu界面Sn的活度,降低IMC的长大驱动力。     

SnAgCu焊点电迁移诱发IMC阴极异常堆积

为了研究电迁移过程中焊点与焊盘界面金属问化合物(IMC)的变化,在28℃下,对无铅Sn3.0Ag0.5Cu焊点进行了6.5A直流电下的电迁移实验.结果发现,通电144h后,阳极侧IMC层变厚,平均达到10.12 μm;阴极侧IMC层大部分区域变薄至0.86μm,局部出现Cu焊盘的溶解消失,但在界面边缘处出现Cu3Sn5...     

Sn基无铅钎料与Cu基板间化合物Cu_6Sn_5的研究进展

主要介绍了Sn基无铅钎料和Cu基板在界面处反应生成的金属间化合物Cu6Sn5与焊接点可靠性的关系。综述了近年来Cu6Sn5的研究进展,内容包括:Sn基无铅钎料在Cu基板上形成的Cu6Sn5的生长形态、晶体取向、生长动力学以及纳米颗粒对界面Cu6Sn5尺寸及形貌的影响。     

镍磷锗对SnAgCuCe系钎料性能及组织的影响

为改善Sn3.0Ag0.5CuCe(SAC305Ce)无铅钎料的性能,向其添加了微量Ni、P及Ge并进行了研究。结果表明,同时添加质量分数为0.10%Ni、0.01%P和0.05%Ge,150℃时效168h后,钎料综合性能最佳。钎料合金组织中共晶组织的分布较为密集,IMC厚度有轻微增加,润湿力约0.48mN,剪切强度约62MPa。     

Sn对BiSbCu钎料钎焊工艺性能的影响

在BiSbCu钎料中添加Sn,分析Sn对BiSbCu钎料合金钎焊工艺性能的主要指标——钎料熔点和铺展面积的影响.结果表明:在Bi5Sb2Cu钎料合金中加入Sn可以显著降低钎料的熔点和显著增强钎料合金的铺展性能.当Sn的质量分数为10％时,Bi5Sb2Cu钎料的铺展面积为26.22 mm2,钎焊工艺性能最好.     

电迁移作用下的微焊点振动疲劳行为研究

研究了不同电迁移时间(0～96 h)和电流密度(0～1.52×104A/cm2)对Sn-3.0Ag-0.5Cu微焊点振动疲劳行为的影响.结果显示,在电迁移时间和电流密度均为0时,微焊点的振动疲劳循环次数大于1 170次,疲劳寿命大干234 min;而在125℃服役温度下,当振动频率为0.8 Hz,交变应力为0～20 M...     

无铅焊点在热疲劳和电迁移作用下的组织演变

研究了Cu/Sn-58Bi/Cu焊点接头在室温和55℃下通电过程中阴极和阳极界面处微观组织的演变,电流密度均采用104A/cm2。结果表明,室温条件下通电达到25 d,Bi原子由阴极向阳极发生了扩散迁移,在阳极界面处形成了厚度约22.4μm的均匀Bi层,而阴极出现了Sn的聚集。加载55℃通电2 d后,焊点发生了熔融,阴极界面处形成了厚度为34.3μm的扇贝状IMC,而阳极界面IMC的厚度仅为9.7μm。在IMC层和钎料基体之间形成了厚度约7.5μm的Bi层,它的形成阻碍了Sn原子向阳极界面的扩散迁移,进而阻碍了阳极界面IMC的生长,导致了异常极化效应的出现。     

Effect of surface finish on the failure mechanisms of flip-chip solder joints under electromigration

Two substrate surface finishes, Au/Ni and organic solderable preservative (OSP), were used to study the effect of the surface finish on the reliability of flip-chip solder joints under electromigration at 150°C ambient temperature. The solder used was eutectic PbSn, and the applied current density was 5×10³ A/cm² at the contact window of the chip. The under bump metallurgy (UBM) on the chip was sputtered Cu/Ni. It was found that the mean-time-to-failure (MTTF) of the OSP joints was six times better than that of the Au/Ni joints (3080 h vs. 500 h). Microstructure examinations uncovered that the combined effect of current crowding and the accompanying local Joule heating accelerated the local Ni UBM consumption near the point of electron entrance. Once Ni was depleted at a certain region, this region became nonconductive, and the flow of the electrons was diverted to the neighboring region. This neighboring region then became the place where electrons entered the joint, and the local Ni UBM consumption was accelerated. This process repeated itself, and the Ni-depleted region extended further on, creating an ever-larger nonconductive region. The solder joint eventually, failed when the nonconductive region became too large, making the effective current density very high. Accordingly, the key factor determining the MTTF was the Ni consumption rate. The joints with the OSP surface finish had a longer MTTF because Cu released from the substrate was able to reduce the Ni consumption rate.     

Fatigue-creep crack propagation path in solder joints under thermal cycling

The present study investigates the thermal fatigue crack propagation path in a eutectic solder joint between a 2512 leadless chip resistor and a printed wiring board which had experienced thermal cycling between -55 and 125°C. This was achieved through the microstructural examination of fractured surfaces of the joints. Patches of finely spaced striations were observed in a predominant shear strain field in the joints. These striations were attributed to the tensile strain components in the field and used to add the identification of the fatigue crack propagation direction. It was observed that cracks did not simply propagate across the depth of the joint from the inner end (the heel) to the outer end (the toe) in the longitudinal direction, but from a corner point on the free edge of the heel to the center across the joint depth, making an angle of about 70° with respect to the longitudinal direction.     

Maximum entropy fracture model and its use for predicting cyclic hysteresis in Sn3.8Ag0.7Cu and Sn3.0Ag0.5 solder alloys

Appropriate constitutive, damage accumulation and fracture models are critical to accurate life predictions. In this study, we utilize the maximum entropy fracture model (MEFM) to predict and validate cyclic hysteresis in Sn3.8Ag0.7Cu and Sn3.0Ag0.5 solder alloys through a damage enhanced Anand viscoplasticity model. MEFM is a single-parameter, information theory inspired model that aims to provide the best estimate for accumulated damage at a material point in ductile solids in the absence of detailed microstructural information. Using the developed model, we predict the load drop during cyclic fatigue testing of the two chosen alloys. A custom-built microscale mechanical tester was utilized to carryout isothermal cyclic fatigue tests on specially designed assemblies. The resultant relationship between load drop and accumulated inelastic dissipation was used to extract the geometry and temperature-independent damage accumulation parameter of the maximum entropy fracture model for each alloy. The damage accumulation relationship is input into the Anand viscoplastic constitutive model, allowing prediction of the stress–strain hysteresis and cyclic load drop. The damage accumulation model is validated by comparing predicted and measured load drops after 55 and 85 cycles respectively for Sn3.8Ag0.7Cu and Sn3.0Ag0.5 solder alloys. The predictions agreed to within 10% and 20% of the experimental observations respectively for the two alloys. The damage enhanced Anand model developed in this study will enable the tracking of crack fronts during finite element simulations of fatigue crack initiation and propagation in complex solder joint geometries.     

片式电阻混合焊点热循环负载可靠性研究

对在不同工艺参数下形成的、并且经过不同周数热循环负载的片式电阻混合焊点、有铅焊点和无铅焊点进行了外观检测和剪切测试。结果显示,在不同工艺参数下形成的混合焊点的剪切力,随热循环周数的变化趋势有所不同,但是在保证片式电阻焊端和焊料充分熔融的情况下,部分混合焊点的平均剪切力比有铅焊点高,热循环1 000周后,为9.1～11.1 N。