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...     

热循环条件下Sn基钎料接头电迁移行为研究

通过电迁移和热疲劳循环实验,研究了热循环和高电流密度耦合作用下Sn58Bi和Sn3.0Ag0.5Cu钎料焊接接头的失效形式。实验结果表明,在通电和高低温冲击的耦合作用下,两种钎料接头的失效都发生在升温阶段。热循环导致接头内部裂纹的萌生和扩展,导致局部电流密度持续增大,加速了电迁移的发生,最终导致焊点失效。在热电耦合作用下,Sn58Bi钎料接头的使用寿命要长于Sn3.0Ag0.5Cu钎料接头的使用寿命。     

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...     

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...     

电迁移对Ni/Sn63Pb37/Cu焊点界面反应的影响

研究了在125℃,1×103 A/cm2条件下电迁移对Ni/Sn63Pb37/Cu BGA焊点界面反应的影响.回流后,在焊料/Ni界面处形成Ni3Sn4、在焊料/Cu界面处形成Cu6Sn5的金属间化合物.随着电迁移时间增加,芯片侧金属间化合物转变为(Cu,Ni)6Sn5类型化合物,印制板侧Cu6Sn5金属间化合物类型保...     

Sn3.8Ag0.7Cu和Sn37Pb焊点界面显微结构研究

利用扫描电子显微镜（SEM）和透射电子显微镜（TEM）研究了Sn3.8Ag0.7Cu（Sn37Pb）/Cu焊点在时效过程中的界面金属间化合物（IMC）形貌和成份。结果表明：150℃高温时效50、100、200、500h后,Sn3.8Ag0.7Cu（Sn37Pb）/Cu焊点界面IMC尺寸和厚度增加明显,IMC颗粒间的沟槽越来越小。50h时效后界面出现双层IMC结构,靠近焊料的上层为Cu6Sn5,邻近基板的下层为Cu3Sn。之后利用透射电镜观察了Sn37Pb/Ni和Sn3.8Ag0.7Cu/Ni样品焊点界面,结果显示,焊点界面清晰,IMC晶粒明显。     

Sn0.7Cu无铅焊点的电迁移失效模拟及优化分析

基于ANSYS有限元软件,综合考虑电子风力、温度梯度、应力梯度和原子密度梯度四种电迁移驱动机制,采用原子密度积分法(ADI)对倒装芯片球栅阵列封装(FCBGA)的Sn0.7Cu无铅焊点进行电迁移失效模拟。针对焊点直径、焊点高度、焊点下金属层(UBM)厚度三个关键参数进行电迁移失效的正交试验优化,探究焊点尺寸对电迁移失效的影响。研究表明:焊点直径和高度的增加会缩短焊点的电迁移失效寿命(TTF),而UBM层厚度对焊点失效寿命的影响相对较小;焊点局部拉应力对焊点的失效寿命影响较大,通常会加剧焊点的空洞失效。     

SnAgCu凸点互连的电迁移

研究了无铅Sn96Ag3 sCuo s凸点与镀Ni焊盘互连界面的电迁移现象.在180℃条件下,凸点及互连界面在电迁移过程中出现了金属间化合物沿电子流运动方向的迁移,其演化过程呈现出显著的极性效应:阴极互连界面发生了金属间化合物的熟化、剥落和迁移;阳极互连界面则出现了金属间化合物的大量聚集.金属间化合物的演化和迁移造成了阴极处的物质减少,从而诱发空洞的形成和聚集,导致互连面积减小,整体电阻增大,可靠性降低.     

倒装芯片互连凸点电迁移的研究进展

电子产品向便携化、小型化、高性能方向发展,促使集成电路的集成度不断提高,体积不断缩小,采用倒装芯片互连的凸点直径和间距进一步减小和凸点中电流密度的进一步提高,由此出现电迁移失效引起的可靠性问题.本文回顾了倒装芯片互连凸点电迁移失效的研究进展,论述了电流聚集和焊料合金成分对凸点电迁移失效的影响,指出了倒装芯片互连凸点电迁移研究亟待解决的问题.     

Novel Bumping Process for Solder on Pad Technology

A novel bumping process using solder bump maker is developed for the maskless low‐volume solder on pad (SoP) technology of fine‐pitch flip chip bonding. The process includes two main steps: one is the aggregation of powdered solder on the metal pads on a substrate via an increase in temperature, and the other is the reflow of the deposited powder to form a low‐volume SoP. Since the surface tension that exists when the solder is below its melting point is the major driving force of the solder deposit, only a small quantity of powdered solder adjacent to the pads can join the aggregation process to obtain a uniform, low‐volume SoP array on the substrate, regardless of the pad configurations. Through this process, an SoP array on an organic substrate with a pitch of 130 μm is successfully formed.     

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.     

Fine‐Pitch Solder on Pad Process for Microbump Interconnection

A cost‐effective and simple solder on pad (SoP) process is proposed for a fine‐pitch microbump interconnection. A novel solder bump maker (SBM) material is applied to form a 60‐μm pitch SoP. SBM, which is composed of ternary Sn3.0Ag0.5Cu (SAC305) solder powder and a polymer resin, is a paste material used to perform a fine‐pitch SoP through a screen printing method. By optimizing the volumetric ratio of the resin, deoxidizing agent, and SAC305 solder powder, the oxide layers on the solder powder and Cu pads are successfully removed during the bumping process without additional treatment or equipment. Test vehicles with a daisy chain pattern are fabricated to develop the fine‐pitch SoP process and evaluate the fine‐pitch interconnection. The fabricated Si chip has 6,724 bumps with a 45‐μm diameter and 60‐μm pitch. The chip is flip chip bonded with a Si substrate using an underfill material with fluxing features. Using the fluxing underfill material is advantageous since it eliminates the flux cleaning process and capillary flow process of the underfill. The optimized bonding process is validated through an electrical characterization of the daisy chain pattern. This work is the first report on a successful operation of a fine‐pitch SoP and microbump interconnection using a screen printing process.