倒装焊中复合SnPb焊点形态模拟

本文给出了倒装焊(flip-chip)焊点形态的能量控制方程,采用Surface Evolver软件模拟了倒装焊复合SnPb焊点(高Pb焊料凸点,共晶SnPb焊料焊点)的三维形态.利用焊点形态模拟的数据,分析了芯片和基板之间SnPb焊点的高度与焊点设计和焊接工艺参数的关系.研究表明:共晶SnPb焊料量存在临界值,当共晶SnPb焊料量小于临界值时,焊点的高度等于芯片上高Pb焊料凸点的半径值;当共晶SnPb焊料量大于临界值时,焊点的高度随共晶SnPb焊料量的增加而增加.另外,采用无量纲的形式给出了焊点高度与共晶焊料量、焊盘尺寸、芯片凸点的尺寸,芯片重量之间的关系模型,研究结果对倒装焊焊点形态的控制、工艺参数的优化和提高焊点可靠性具有指导意义.     

倒装焊SnPb焊点热循环失效和底充胶的影响

采用实验方法 ,确定了倒装焊 Sn Pb焊点的热循环寿命 .采用粘塑性和粘弹性材料模式描述了 Sn Pb焊料和底充胶的力学行为 ,用有限元方法模拟了 Sn Pb焊点在热循环条件下的应力应变过程 .基于计算的塑性应变范围和实验的热循环寿命 ,确定了倒装焊 Sn Pb焊点热循环失效 Coffin- Manson经验方程的材料参数 .研究表明 ,有底充胶倒装焊 Sn Pb焊点的塑性应变范围比无底充胶时明显减小 ,热循环寿命可提高约 2 0倍 ,充胶后的焊点高度对可靠性的影响变得不明显     

倒装焊SnPb焊点热循环失效和底充胶的影响

采用实验方法,确定了倒装焊SnPb焊点的热循环寿命．采用粘塑性和粘弹性材料模式描述了SnPb焊料和底充胶的力学行为,用有限元方法模拟了SnPb焊点在热循环条件下的应力应变过程．基于计算的塑性应变范围和实验的热循环寿命,确定了倒装焊SnPb焊点热循环失效Coffin-Manson经验方程的材料参数．研究表明,有底充胶倒装焊SnPb焊点的塑性应变范围比无底充胶时明显减小,热循环寿命可提高约20倍,充胶后的焊点高度对可靠性的影响变得不明显．     

引线框架材料对铜合金与锡铅焊料界面组织的影响

采用老化试验、金相分析、扫描电镜(SEM)及能谱分析(EDX)等手段对引线框架铜合金与SnPb共晶焊料界面组织进行了分析研究。结果表明,引线框架材料对铜合金与SnPb共晶焊料界面组织有很大的影响,焊点在160℃高温老化300 h后,CuCrZr系合金和CuNiSi合金与SnPb的界面金属间化合物为Cu6Sn5,其厚度在5~10 mm; 而C194合金与SnPb的界面金属间化合物为分布有Pb颗粒的Cu6Sn5,厚度已高达60~70 mm,同时还发现有微小空洞存在,影响焊点的可靠性。与C194合金相比,CuCrZr系合金和CuNiSi合金具有更好的焊接可靠性。     

不同基板的CBGA焊点在热循环下的力学特性研究

采用粘塑性本构Anand方程描述SnPb钎料的变形行为,用有限元方法对CBGA组件焊点结构进行二维模型分析;同时,选用不同的基板材料(Al2O3、AlN、SiC),考察焊点在热循环加载过程中的应力应变等力学行为.研究结果表明,最外侧焊点受到的应力应变最大,所以裂纹最有可能从最外侧焊点处萌生,并沿着基板一侧扩展;焊点的高应力发生在热循环的低温阶段,升降温过程中的蠕变和非弹性应变的累积显著,应力应变迟滞环在热循环的最初几个周期内就能很快稳定.模拟结果得出,采用BeO基板材料时焊点的应力应变最小,其可靠性最高.     

热循环条件下无铅焊点可靠性的有限元分析

通过有限元数值模拟对Sn3.5Ag0.75Cu无铅焊料焊点的可靠性问题进行了分析。采用统一粘塑性Anand本构方程对焊料焊点结构进行有限元分析,研究焊点在热循环加载过程中的应力应变等力学行为。研究结果表明,在焊点内部焊点与基板结合处的应力较大,而焊点中央的应力较小;焊点在低温阶段的应力最大,在高温阶段应变最大;在升降温阶段的应力应变变化较大,而在保温阶段的应力应变变化较小。     

BGA焊点的失效分析及热应力模拟

焊点可靠性问题是发展球栅阵列（Ball Grid Array，BGA）技术需解决的关键问题。本论文采用立体显微镜检查、x-ray检查、金相切片分析、SEM、EDX等方法详细分析了失效BGA焊点的微结构、裂纹情况、金属间化合物、及空洞对可靠性的影响，得出引起焊点失效的主要原因。在此基础上，采用ANSYS有限元软件，模拟分析了热载荷作用下CBGA焊点的三维应力应变行为。研究了影响焊点（鼓形、柱形）热应力应变分布的几个因素（半径、高度、间距），为在实际焊接过程中，对从焊点形态的角度控制焊点质量提供了理论依据。同时还研究了两种典型无铅焊球（Sn95．5／Ag3．8／Cu0．7，Sn96．5／Ag3．5）与含铅焊料（Sn／37Pb）的热应力应变分布，并对结果作了分析比较。得出Sn95．5/Ag3．8／Cu0．7焊点的von mises等效应力应变最大值小于Sn96．5／Ag3．5焊点与Sn／37Pb焊点，为电子焊料无铅化材料体系的选择提供了理论依据。     

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.     

QFP焊点可靠性研究

随着人们对健康和环境的要求越来越高,无铅焊料的研究倍受封装业的重视。塑性应变是影响电子封装焊点可靠性的主要因素,文章采用在多次温度循环条件下进行有限元数值模拟的方法,针对由不同元素(Sn,Pb,Ag,Cu)及配比构成的焊料,计算QFP焊点的塑性应变,定量评估其可靠性。给出焊料各参数对焊点可靠性的影响程度,仿真表明焊料激活能与气体常数的比值的变化对焊点可靠性影响最大,相应的焊点Y向塑性应变均值仅为优化前的11%。所得的结果可为今后QFP封装时的焊料选择提供新的理论依据。     

Constitutive modeling on creep deformation for a SnPb-based composite solder reinforced with microsized Cu particles

In the present work, the creep strain of solder joints is measured using a stepped load creep test on a single specimen. Based on the creep strain tests, the constitutive modeling on the steady-state creep rate is determined for the Cu particle-reinforced Sn37Pb-based composite solder joint and the Sn37Pb solder joint, respectively. It is indicated that the activation energy of the Cu particle-reinforced Sn37Pb-based composite solder joint is higher than that of Sn37Pb solder joint. In addition, the stress exponent of the Cu particle-reinforced Sn37Pb-based composite solder joint is higher than that of the Sn37Pb solder joint. It is expected that the creep resistance of the Cu particle-reinforced Sn37Pb-based composite solder joint is superior to that of the Sn37Pb solder. Finally, the creep deformation mechanisms of the solder joint are discussed.     

In-situ observation of material migration in flip-chip solder joints under current stressing

This investigation studies how electron flow distribution and the vacancy concentration gradient affect the diffusion of solder atoms in a flip-chip solder joint under current stress. The migration of materials was traced by monitoring the positions of 21 Pb grains of the eutectic PbSn solder joint. Experimental results indicate that the displacements of the Pb grains were not uniform along the electron flow direction. Additionally, certain Pb grains exhibited lateral displacements. The nonuniform material migration is attributable to the combined effect of electromigration and the vacancy concentration gradient, which was caused by electromigration. By measuring the displacements of the Pb grains, we estimated that the DZ* value of Sn in eutectic SnPb solder was 5×10⁻¹⁰ cm²/s.     

Characterization of 63Sn37Pb and 80Au2OSn solder sealed opticalfiber feedthroughs subjected to repetitive thermal cycling

A highly accurate prediction of hermeticity lifetime is made for eutectic 63Sn37Pb and 80Au20Sn alloy solder sealed optical fiber-Kovar ^TM nosetube feedthroughs subjected to repetitive thermal cycling. Thermal fatigue fracture of the Sn-Pb solder/Kovar^TM interface develops when cracks, initially generated from creep deformation of the solder, propagate gradually through the junction in the axial direction. A nonlinear axisymmetric finite element analysis of the 63Sn37Pb fiber feedthrough seal is performed using a thermo-elastic creep constitutive equation, and solder joint fatigue based on accumulated strain energy associated with solder creep imposed by temperature cycling is analyzed. Additionally, thermal effective stress and plastic strain is studied for alternative 80Au20Sn solder by the finite element method with results indicating significant increase in useful life as compared to 63Sn37Pb. SEM/EDX metallurgical analysis of the solder/Ni-Au plated Kovar^TM nosetube interface indicates that AuSn₄ intermetallic formed during soldering with 63Sn37Pb also contributes to joint weakening, whereas no brittle intermetallic is observed for 80Au20Sn. Hermetic carbon coated optical fibers metallized with Ni,P-Ni underplate and electrolytic Au overplating exhibit correspondingly similar metallurgy at the solder/fiber interface. Combined hermeticity testing and metallurgical analysis carried out on 63Sn37Pb and 80Au20Sn alloy solder sealed optical fiber feedthroughs after repetitive temperature cycling between -65 and +150°C, and -40 and +125°C validated the analytical approach     

陶瓷封装倒装焊器件Sn-Pb微焊点的电迁移行为

高密度陶瓷封装倒装焊器件的焊点尺寸已降低至100μm以下,焊点电流密度达到10~4 A/cm~2以上,由此引发的电迁移失效成为不可忽视的问题。以陶瓷封装菊花链倒装焊器件为研究对象,开展了Sn10Pb90、Sn63Pb37焊点热电环境可靠性评估试验,通过电连接检测及扫描电子显微镜(SEM)等方法对焊点互连情况进行分析。结果表明,Sn63Pb37焊点阴极侧金属间化合物(IMC)增长明显,表现出明显的极化现象,IMC厚度的平方与通电时间呈线性关系。通电时间达到576 h后Sn63Pb37焊点阴极侧产生微裂纹,而Sn10Pb90焊点在通电576 h后仍未出现异常,表现出优异的电迁移可靠性。研究结果对于直径100μm微焊点的陶瓷封装倒装焊器件的应用具有重要的意义。     

Failure Morphology After Drop Impact Test of Ball Grid Array (BGA) Package With Lead-Free Sn–3.8Ag–0.7Cu and Eutectic SnPb Solders

High strain-rate drop impact tests were performed on ball grid array (BGA) packages with solder compositions of (in wt%) Sn-3.8Ag-0.7Cu (SnAgCu) and eutectic Sn-37Pb (SnPb). Solder balls were joined to the metallizations of plated Ni on the device side and plated Cu on the board side. The BGA packages were tested at 1500 g within 0.5 ms, resulting in an imposed bending strain of 0.2-0.3%. Both SnAgCu and SnPb joints failed at the interface at the device side but the detailed failure morphology differed significantly. The crack location for the eutectic SnPb was primarily through the solder and seldom extended through an entire bump. The SnPb joints also exhibited bulk solder deformation. The SnAgCu joints showed extremely brittle behavior with an interfacial failure at the (Ni,Cu)₃Sn₄ intermetallics/Ni under bump metallization (UBM) interface. The strain rate sensitivity of bulk solder defines the drop test performance and the eutectic SnPb solder showed better drop impact performance due to a less strain rate sensitivity     

In-Situ Observation of Electromigration in Eutectic SnPb Solder Lines: Atomic Migration and Hillock Formation

The real-time microstructural evolution during electromigration of eutectic SnPb solder lines with an edge drift structure was examined using an in-situ scanning electron microscope (SEM) technique. The test temperature and the current density were either 100°C or 50°C and 6 × 10⁴ A/cm² or 8 × 10⁴ A/cm², respectively. In-situ microstructural observation of the depleted phases and quantitative analysis of the number of hillock phases made it clear that the dominant migrating element and dominant hillock phase were Sn and Pb at room temperature, respectively, while both dominant migrating element and dominant hillock phase were Pb at 100°C. Such temperature dependence of the dominant hillock phase in the eutectic SnPb solder can be understood by considering the atomic size factors of the metallic solid solutions. We suggest that at high temperature, it is easier for Pb atoms to be injected into the Pb phase (Pb-phase hillocks); while at low temperature, Pb-phase hillocks were squeezed by Sn, which penetrated the Pb phase.