电子封装元件的高阶层离散均匀化分析

将均匀化理论应用于具有非完全(单层内)周期性微结构的倒装焊底充胶电子封装元件，建立了高阶逐层离散层板模型，用解析法分析热载荷下结构的温度应力. 计算结果与有限元解的比较表明，该分析模型和方法是有效的，而且比较简便. 算例分析结果显示，胶层厚度、焊点密度、胶与焊点材料的模量比和体积比，对于焊点温度应力有明显影响.     

Reexamination of the solder ball shear test for evaluation of the mechanical joint strength

Ball shear tests were investigated in terms of the effects of test parameters, i.e., shear height and shear speed, with an experimental and non-linear finite element analysis for evaluating the solder joint integrity of area array packages. Two representative Pb-free solders were examined in this work: Sn–3.5Ag and Sn–3.5Ag–0.75Cu. The substrate was a common solder mask defined (SMD) type with solder bond pad openings of 460 μm in diameter. The microstructural investigations were carried out using scanning electron microscopy (SEM), and the intermetallic compounds (IMCs) were identified with energy dispersive spectrometry (EDS). Shear tests were conducted with the two varying test parameters. It was observed that increasing shear height at a fixed shear speed has the effect of decreasing shear force for both Sn–3.5Ag and Sn–3.5Ag–0.75Cu solder joints, while the shear force increased with increasing shear speed at fixed shear height. Shear heights that were too high had some negative effects on the test results such as unexpectedly high standard deviation values or shear tip sliding from the solder ball. Low shear height conditions were favorable for screening the type of brittle interfacial fractures or the degraded layers in the interfaces.     

低成本基板倒装焊底充胶分层裂缝扩展研究

采用MIL-STD-883C热循环疲劳加载标准，通过电学检测方法测定了B型和D型两种倒装焊封装焊点寿命。并使用无损声学C-SAM高频超声显微镜技术观测这两种倒装焊封装在焊点有无断裂两种情况时芯片／底充胶界面的分层和扩展，计算得到分层裂缝扩展速率。在有限元模拟中采用粘塑性和时间相关模量描述了SnPb焊点和底充胶的力学行为。使用裂缝尖端附近小矩形路径J积分方法作为断裂力学参量得到不同情况下的界面分层裂缝顶端附近的能量释放率。然后由实验裂缝扩展速率和有限元模拟给出的能量释放率得到可作为倒装焊封装可靠性设计依据的Par—is半经验方程。     

涂层/基体材料界面结合强度测量方法的现状与展望

界面结合强度是涂层/基体材料体系中的一项重要力学性能指标.而表征与评价涂层/基体材料的界面结合强度又得依靠实验 方法的测定.由于涂层/基体材料体系的多样性与复杂性, 至今还没有形成适合于测量这类材料的界面结合强度的标准方法. 目前, 常用来测量涂层/基体材料的界面结合强度的方法有：拉伸法、剪切法、弯曲法、划痕法、压入法等.本文就目前表征 与评价涂层/基体材料界面结合强度的测量方法做了综述, 讨论了它们的适用范围, 比较了它们的优势与不足.     

高密度封装倒装焊的新简化模型及疲劳寿命分析

高密度封装结构中存在大量焊球,在进行有限元建模时,考虑到焊球数量多且尺寸小的特点,需简化焊球层模型．本文针对高密度封装结构中倒装焊及底填胶,提出了一种新的简化模型,采用非重点部位简化和材料均匀化相结合的方法,将内部焊球层和底填胶简化为均匀层,只保留外圈几层焊球．通过建立代表性体积单元,计算得到均匀化层的材料参数．讨论了外层焊球圈数对焊球层危险点应力的影响,发现保留外圈两层焊球就能得到非常精确的结果．利用新简化模型计算了高密度封装结构的疲劳寿命,所获得的结果与未均匀化模型结果误差在0.3%以内．     

COHESIVE ZONE MODELING OF INTERGRANULAR CRACKING OF INTERMETALLIC COMPOUNDS IN SOLDER JOINTS

为研究焊锡接点金属间化合物微结构对其微观-宏观力学行为的影响,采用Voronoi图算法构造了金属间化合物的晶粒尺度几何模型,通过在晶粒界面配置内聚力界面单元,提出了模拟金属间化合物晶粒界面裂纹起裂、扩展与连通的有限元数值模拟方法。基于该方法,研究了晶粒形状和晶粒界面缺陷对晶界微开裂模式和整体响应的影响,研究了金属间化合物微结构对焊锡接点强度和破坏模式的影响。结果表明,晶粒形状对整体强度影响不大,但对微裂纹开裂模式有影响。当考虑晶界随机缺陷时,强度较低的晶粒界面对整体强度影响较大。金属间化合物层的厚度对焊锡接点强度和破坏模式均有影响,而金属间化合物与焊料界面的粗糙度主要影响焊锡接点的破坏模式。     

固化温度对碳纤维/环氧基体界面行为影响的分析

对界面粘结性能及热残余应力影响下的单纤维复合材料的界面行为进行了分析。采用界面的弹性-软化内聚力模型,用解析法对单纤维复合材料由固化引起的热残余应力、以及单纤维碎断过程纤维的轴向应力分布进行了模拟,得到了碳纤维/环氧树脂在常温和高温固化两种情况的界面粘结性能。结果表明：与常温固化相比,高温固化后,界面的剪切强度增幅不大,界面的断裂韧性显著增加;高温固化后形成的界面,使界面的软化提前、界面的脱粘延迟;高温固化产生的纤维轴向和界面径向热残余应力对界面的软化均有延迟作用;界面径向热残余应力还对界面的脱粘有延迟作用。     

Study of thermal interfacial resistance between TC11/glass lubrication/K403 joint

The heat transfer between the workpiece/glass lubricant/tool has an effect on the accuracy of the workpiece and tool-life during forging process. Consequently, accurate thermal interfacial resistance (TIR) data are needed for a heat management of the forging system. A test facility and relevant procedure are developed to measure the thermal interfacial resistance across the interface, employing a steady-state method. The effects of the average interfacial temperature, contact pressure and the thickness of the glass lubricant are evaluated. Some experimental results on the temperature dependence of the thermal conductivity of glass lubricant are presented.     

Isothermal low-cycle fatigue testing of microscale solder interconnections

A series of isothermal low-cycle fatigue studies of small to extremely small-volume solder joints has been conducted. These solder microjoints were designed and fabricated using processing which duplicates the microelectronics interconnection structures that might be used in high density, highly integrated flip-chip packaging and all fatigue tests were conducted in fully reversed simple shear both with and without dwells at maximum strain. Results of low-cycle fatigue tests of both single and double-bump 95/5 Pb/Sn solder microjoints in the form of Manson-Coffin (plastic strain amplitude versus fatigue life) plots and post-test failure mode analysis (FMA) carried out using scanning electron microscope (SEM) fractography are presented and evaluated. Paper was presented at the 1991 SEM Spring Conference on Experimental Mechanics held in Milwaukee, WI on June 9–12.     

Effects of interfacial properties on the ductility of polymer-supported metal films for flexible electronics

Polymer-supported metal films as interconnects for flexible, large area electronics may rupture when they are stretched, and the rupture strain is strongly dependent upon the film/substrate interfacial properties. This paper investigates the influence of interfacial properties on the ductility of polymer-supported metal films by modeling the microstructure of the metal film as well as the film/substrate interface using the method of finite elements and the cohesive zone model (CZM). The influence of various system parameters including substrate thickness, Young’s modulus of substrate material, film/substrate interfacial stiffness, strength and interfacial fracture energy on the ductility of polymer-supported metal films is systematically studied. Obtained results demonstrate that the ductility of polymer-supported metal films increases as the interfacial strength increases, but the increasing trend is affected distinctly by the interfacial stiffness.     

Evaluation of the Effect of Thermal Oxidation and Moisture on the Interfacial Shear Strength of Unidirectional IM7/BMI Composite by Fiber Push-in Nanoindentation

Fiber push-in nanoindentation is conducted on a unidirectional carbon fiber reinforced bismaleimide resin composite (IM7/BMI) after thermal oxidation to determine the interfacial shear strength. A unidirectional IM7/BMI laminated plate is isothermally oxidized under various conditions: in air for 2 months at 195 °C and 245 °C, and immersed in water for 2 years at room temperature to reach a moisture-saturated state. The water-immersed specimens are subsequently placed in a preheated environment at 260 °C to receive sudden heating, or are gradually heated at a rate of approximately 6 °C/min. A flat punch tip of 3 μm in diameter is used to push the fiber into the matrix while the resulting load-displacement data is recorded. From the load-displacement data, the interfacial shear strength is determined using a shear-lag model, which is verified by finite element method simulations. It is found that thermal oxidation at 245 °C in air leads to a significant reduction in interfacial shear strength of the IM7/BMI unidirectional composite, while thermal oxidation at 195 °C and moisture concentration have a negligible effect on the interfacial shear strength. For moisture-saturated specimens under a slow heating rate, there is no detectable reduction in the interfacial shear strength. In contrast, the moisture-saturated specimens under sudden heating show a significant reduction in interfacial shear strength. Scanning electron micrographs of IM7/BMI composite reveal that both thermal oxidation at 245 °C in air and sudden heating induced microcracks and debonding along the fiber/matrix interface, thereby weakening the interface, which is the origin of failure mechanism.     

基于微纳米压入法提取无铅焊料合金弹塑性力学参数的研究

本文通过微纳米压入法结合数值模拟研究了无铅焊料合金SnAg3.5 的弹塑性力学性能，分别采用圆柱形压头及两种不同锥角压头对无铅焊料合金进行压入测试：基于圆柱形压头测试过程中接触面积恒定的特点得到了无铅焊料的弹性模量，进一步采用塑性应变梯度理论对两种锥角压头的测试结果予以修正并通过数值模拟反分析得到相应的特征应力值，同时基于压入特征塑性应变与压头锥角的关系式得到两种不同锥角压头下的特征应变值，在此基础上经求解方程组得到焊料合金的初始屈服应力与应变强化因子，进而得到了焊料合金的幂强化弹塑性本构关系．该方法剔除了压入尺度效应的影响并保证了所得本构关系的唯一性，给出了一种通过原位压入测试表征金属材料弹塑性力学性能的有效方法．     

微纳米尺度膜/基结构界面性能的实验研究

为了研究铜膜/有机玻璃结构的界面性能,首先对沉积在有机玻璃基底上300nm厚的铜膜进行了单轴压缩实验,部分区域的薄膜因屈曲而脱离基底。选择在膜/基粘接良好区域、膜/基脱粘区域分别进行等位移纳米压痕实验。利用膜/基粘接良好区域处硬度/弹性模量与压痕位移的关系来确定膜/基结构的临界脱粘位移。基于宏观力学中表征界面性能的能量法,利用两个区域等位移的塑性功差值来确定界面能量释放率。研究结果表明:当压痕位移约450nm时,膜/基结构开始出现界面脱粘,实验测得铜膜/有机玻璃结构的界面能量释放率值在6.81~10.32J/m2之间。     

Stress near apex of dissimilar material with bilinear behavior

This study presents an analytical solution for the asymptotic stress field near the apex of a wedge composed of dissimilar materials exhibiting elastic and/or plastic deformation that can be described by a bilinear material model. Under the same assumptions, previous investigations resulted in eigenvalue differential equations that were not amenable to analytical integration. The present formulation avoids the numerical integration of such equations. After establishing its validity, the corner of the junction formed between a solder ball and a substrate was considered in order the study the effect of the hardening parameter on the strength of the singular stress field. Also, this formulation provides the exact form of the displacement field, which permits the construction of a global element to capture the correct strength of the singular stress field in regions with material and geometric discontinuities.     

石墨烯与柔性基底界面载荷传递的拉曼光谱实验

本文研究了CVD制备的大尺寸石墨烯与柔性PET基底在拉伸变形过程中切向界面载荷传递的问题,采用原位拉曼光谱实验给出了加载过程中石墨烯的正应变、正应力以及界面切应力的分布曲线。分析表明,石墨烯与PET基底间的载荷传递存在四个阶段,分别是初始阶段、粘附阶段、滑移阶段和界面脱粘破坏阶段。在此基础上,本文对50μm、140μm、270μm和600μm四种尺寸石墨烯试件的界面力学性能进行测量,得到了不同尺寸石墨烯试件的界面力学性能参数,并初步给出了基底变形引起的石墨烯切向界面粘接能的变化,同时分析了试件尺寸对石墨烯界面力学性能的影响。实验结果表明,石墨烯材料和柔性基底最大切应力与临界脱粘切向界面粘接能等界面强度指标受到尺寸的显著影响,尺寸越小切向界面强度越高,反之,尺寸越大则越低。     

QFP结构中引脚焊缝界面端的奇异性热应力问题研究

由于引脚、印制电路板和焊接剂的热-机材料属性不同,在受到热载荷或机械载荷时,引脚焊接界面端会产生奇异性应力,有可能产生界面开裂.为了基于界面端奇异场来评价QFP结构引脚界面端力学行为,本文拟采用数值方法求解引脚焊缝任意角度尖劈界面端的应力强度系数.具体步骤为:首先,基于高次内插有限元特征分析法确定两相任意角度尖劈界面端的奇异性指数和应力角分布函数,并引入常数热应力项,获得热-机耦合奇异性应力场表达式;采用有限元分析技术和最小二乘拟合法来获得应力强度系数的数值解.文中考察了热-机材料属性对热载荷下焊接剂/印制电路板界面端应力强度系数的影响,并给出改善界面端热应力状态的建议.     

Tensile and mixed-mode strength of a thin film-substrate interface under laser induced pulse loading

Laser induced stress waves are used to characterize intrinsic interfacial strength of thin films under both tensile and mixed-mode conditions. A short-duration compressive pulse induced by pulsed-laser ablation of a sacrificial layer on one side of a substrate is allowed to impinge upon a thin test film on the opposite surface. Laser-interferometric measurements of test film displacement enable calculation of the stresses generated at the interface. The tensile stress at the onset of failure is taken to be the intrinsic tensile strength of the interface. Fused-silica substrates, with their negative nonlinear elasticity, cause the compressive stress wave generated by the pulse laser to evolve a decompression shock, critical for generation of the fast fall times needed for significant loading of surface film interfaces. By allowing the stress pulse to mode convert as it reflects from an oblique surface, a high amplitude shear wave with rapid fall time is generated and used to realize mixed-mode loading of thin film interfaces. We report intrinsic strengths of an aluminum/fused silica interface under both tensile and mixed-mode conditions. The failure mechanism under mixed-mode loading differs significantly from that observed under pure tensile loading, resulting in a higher interfacial strength for the mixed-mode case. Inferred strengths are found to be independent, as they should be, of experimental parameters.     

Pure-shear Failure of Thin Films by Laser-induced Shear Waves

The measurement of mode-dependent thin film interfacial properties is important in evaluating the quality of the interfaces between thin films and substrates. Previous work has proved that tensile and mixed-mode strength of a thin film/substrate interface can be evaluated using a laser-induced thin film spallation technique. To further examine the application regime of this technique and identify the individual roles of the tensile and shear stress in the resulting interfacial failure, a special sample design is adopted in the current work to realize pure-shear loading at the thin film/substrate interface. Our result demonstrates that for sufficiently high stress amplitude, interfacial failure can be induced solely by the in-plane shear stress and the stress can be quantitatively determined from optical interferometric measurements. Together with the previous tensile and mixed-mode studies, a complete picture of the mode-dependent thin film interfacial strength can now be reliably determined using the laser-induced thin film spallation techniques.     

EXPERIMENTAL INVESTIGATIONS OF STRENGTH,TOUGHNESS AND FAILURE MECHANISM OF THE METAL/EPOXY/METAL ADHESIVE SYSTEM

本文系统地开展了金属/环氧/金属胶结体系的强韧机理及失效行为实验研究,针对铝合金圆棒与铝合金圆棒通过环氧树脂胶层的各种斜截面方向粘结,实验观测了该体系的拉伸变形和失效行为,测量了界面失效载荷对胶层厚度和粘结界面倾斜角的依赖关系;通过引入胶结界面平均正应力、平均剪应力、平均正应变、平均剪应变等概念,可对界面失效强度进行测量,获得界面强度与界面粘结角度以及胶层厚度的关系,进而获得了铝合金/环氧胶层/铝合金体系的强度失效面以及胶结界面的断裂能和胶结体系的能量释放率.上述研究结果为深入认识金属胶结体系的强韧性能和失效机制提供了科学依据,对金属胶结体系的优化设计和性能评判具有重要指导意义.研究结果表明,铝合金/环氧胶层/铝合金体系的拉伸失效总体呈弹脆性破坏特征,失效表现为胶层粘结界面的断裂,失效强度和界面断裂能在胶层厚度为百微米量级时表现出强烈的尺度效应：界面粘结强度随着胶层厚度的减小而显著增大,临界状态的平均正应力和平均剪应力在强度破坏面上近似位于同一圆上,界面断裂能随着胶层厚度的减小而显著减小;与此同时,界面失效强度和界面断裂能也密切依赖于界面粘结角度.     

DETERMINATION OF INTERFACIAL MECHANICAL PARAMETERS FOR AN Al/EPOXY/Al2O3 SYSTEM BY USING PEEL TEST SIMULATIONS

Peel test measurements and simulations of the interfacial mechanical parameters for the Al/Epoxy/Al2O3 system are performed in the present investigation. A series of Al film thicknesses between 20 and 250 microns and three peel angles of 90, 135 and 180 degrees are considered. Two types of epoxy adhesives are adopted to obtain both strong and weak interface adhesions. A finite element model with cohesive zone elements is used to identify the interfacial parameters and simulate the peel test process. By simulating and recording normal stress near the crack tip, the separation strength is obtained, Furthermore, the cohesive energy is identified by comparing the simulated steady-state peel force and the experimental result. It is found from the research that both the cohesive energy and the separation strength can be taken as the intrinsic interfacial parameters which are dependent on the thickness of the adhesive layer and independent of the film thickness and peel angle.