有限元方法对SCSP粘结剂溢出问题的研究

利用有限元分析方法对SCSP器件内部粘结剂的溢出问题进行了研究.对粘结剂不同溢出高度的模型进行有限元建模分析,模拟结果能很好地和实验结果相吻合.为了有效减少由热应力引发产生的分层,模拟得到了粘结剂溢出高度的最佳控制范围.     

粘结剂形态及尺寸对QFN器件热应力的影响

使用有限元软件MSC.Marc分析了芯片粘结剂的形态、厚度和宽度对典型微电子封装QFN(四方扁平无引脚封装)器件热应力的影响。结果表明:在有限元网格密度相同的条件下,粘结剂形态的不同会对QFN器件的热应力产生较大影响,粘结剂无溢出形态的最大热应力为85.87MPa,而粘结剂有溢出形态的最大热应力为77.84MPa,并且最大热应力出现的位置也不同;粘结剂的厚度和宽度对热应力的影响不明显;由于粘结剂形态的不同界面热应力的分布会有较大差别。     

采用叠层焊点的PBGA组件温度场模拟分析

运用有限元软件ANSYS建立了采用叠层焊点的塑料球栅阵列(Plastic Ball Grid Array,PBGA)结构有限元分析模型,基于该模型对PBGA结构在典型工作环境下的稳态温度场分布进行了模拟,对比传统单层焊点与叠层焊点对PBGA结构温度场的影响,并分析了焊点高度和PBGA结构各部分材料导热系数对内部温度的影响。结果表明:焊点结构形式(单层和叠层)和焊点高度对PBGA组件温度场影响不大;PCB的导热系数对PBGA组件温度场影响最大,其次是塑封和基板,粘结剂对PBGA组件温度场影响很小。     

功率型倒装结构LED系统热模拟及热阻分析

为了了解功率型倒装结构LED系统各部分热阻,找出LED系统散热关键,对功率型倒装结构LED系统进行了有限元热模拟,同时结合传热学基本原理分析了各部分的热阻.结果表明,LED系统中凸点,Si-submount管壳和散热体的自身热阻较小,而芯片、粘结剂、散热体-环境的热阻较大,占系统热阻主要部分.因此优化设计芯片与散热体,选取导热率高的粘结剂,可以有效降低LED系统的热阻,成为LED系统散热设计的关键.     

功率型倒装结构LED系统热模拟及热阻分析

为了了解功率型倒装结构LED系统各部分热阻,找出LED系统散热关键,对功率型倒装结构LED系统进行了有限元热模拟,同时结合传热学基本原理分析了各部分的热阻.结果表明,LED系统中凸点,Si-submount管壳和散热体的自身热阻较小,而芯片、粘结剂、散热体-环境的热阻较大,占系统热阻主要部分.因此优化设计芯片与散热体,选取导热率高的粘结剂,可以有效降低LED系统的热阻,成为LED系统散热设计的关键.     

叠层CSP芯片封装热应力分析与优化

对四层叠层CSP（SCSP）芯片封装器件,采用正交试验设计与有限元分析相结合的方法研究了芯片和粘结剂——8个封装组件的厚度变化在热循环测试中对芯片上最大热应力的影响．利用极差分析找出主要影响因子并对封装结构进行优化。根据有限元模拟所得结果．确定了一组优选封装结构,其Von Mises应力值明显比其它组低,提高封装器件的可靠性。     

MEMS热风速计流固耦合模拟

通过设置流-固耦合面和固-固耦合面,采用ANSYS软件对MEMS热风速计进行了有限元模拟,基本解决了热风速计有限元模拟中遇到的多物理场耦合问题.通过对不同风速,不同风向情况下的风速计芯片的热分布进行了模拟和分析,得到了一些有助于芯片设计的结论.最后,为了验证模型的正确性,进行了实验测量.实验数据与模拟结果基本相符,误差在8%以内.     

热压印中聚合物填充过程的仿真分析

基于有限元方法并借助ANSYS软件对热压印过程中二维的聚合物填充过程进行模拟.聚合物加热温度高于剥离转化温度时,采用Mooney-Rivlin模型表示聚合物的机械性能.详细分析了深宽比、凹槽宽度、占空比、摩擦系数对聚合物变形的影响.数值计算结果表明,深宽比对聚合物高度影响显著;凹槽宽度对聚合物形成单、双峰结构影响较大;占空比影响残留比率;摩擦系数对聚合物高度的影响较小.在制作高质量的热压印图形中,该数值分析结果有助于优化过程参数.     

基于分离式共节点模型的建筑物定向倾倒切口数值模拟研究

利用有限元Ansys/ls-dyna对建筑结构爆破拆除的定向倒塌进行模拟,利用分离式共节点模型对抚顺大酒店的爆破拆除进行数值模拟,通过对单根柱子的数值模拟进行研究,然后初步分析分离式共节点模型存在的问题,在大量数值模拟实验的基础上,找出钢筋失效应变的修正系数范围,就这种现象提出了三种可能。同时,基于重心失稳理论和经验公式理论,选取了多个切口高度进行定向倾倒研究,通过选取不同的切口高度进行大量的数值模拟实验,在数值计算结果分析的基础上,得出"楼坚强"形成的主要原因是切口高度不够的结论。     

W波段回旋行波管电子枪热分析

利用有限元软件ANSYS对W波段回旋行波管电子枪进行了热应力分析.在给定热子功率下对阴极组件的温度场分布和热形变分布进行了模拟,并通过实验进行验证.测试的温度分布基本与模拟结果基本一致.最后,利用EGUN软件对电子枪形变前后进行了模拟.     

胶层厚度对多点支撑光窗面形的影响

以某型战斗机光雷保护罩采用的多点支撑光窗为研究对象,建立胶层连接的多点边缘支撑结构模型,通过仿真分析胶层厚度对多点边缘支撑光窗面型的影响。建立“压块-胶层-光窗”有限元分析模型,在结构航向过载、航向随机振动、高低温冲击情况下,对不同胶层厚度仿真结果数据处理,分析胶层厚度对光窗面形变形的影响。结果可知:胶层在0.1~0.5 mm范围内,光窗表面PV值与RMS值,在过载冲击与随机振动仿真试验中,随着胶层厚度的增加呈现先减小后增加的趋势;在温度冲击仿真中,呈现逐渐减小的趋势。     

Effect of Size of Lid-Substrate Adhesive on Reliability of Solder Balls in Thermally Enhanced Flip Chip PBGA Packages

Six design cases of lid-substrate adhesive with various combinations of widths and heights were analyzed to investigate how the size of the adhesive affects the reliability of the solder balls of thermally enhanced flip chip plastic ball grid array (FC-PBGA) packages in thermal cycling tests. Analysis results were compared with data on the reliability of conventional FC-PBGA packages. Thermal-mechanical behavior was simulated by the finite element (FE) method and the eutectic solder was assumed to exhibit elastic-viscoplastic behavior. The temperature-dependent nonlinear stress/strain relationship of the adhesive was experimentally determined and used in the FE analysis. Darveaux's model was employed to obtain the predicted fatigue life of the solder ball. Simulation results reveal that the fatigue life of the solder balls in thermally enhanced FC-PBGA packages is much shorter than that in conventional FC-PBGA packages, and the life of solder balls increases with both the width and the height of the adhesive. However, the effect of the width of the adhesive on the reliability of the solder ball is stronger than that of the height. Moreover, increasing either the width or the height reduces the plastic strain in the adhesive at critical locations, indicating that the reliability of the adhesive can be improved by its size. The predicted results of the life of solder balls for some selected studied packages are also compared with experimental data from thermal cycling tests in the paper     

加固液晶显示器高温环境下热应力探究

为了探究加固液晶屏高温下热应力影响,建立了基于ANSYS的液晶屏复合结构的有限元分析模型,模拟分析了二维模型等效应力和液晶层上边界Y方向应力的分布情况。仿真结果表明,当环境温度上升到70℃,胶层中气泡和裂纹附近会发生应力集中,液晶盒上边界也会发生相应位置Y方向应力集中。将三种光学胶实际测试的力学数据代入模型分析发现,光学胶的弹性模量和热膨胀系数越大,引起的应力集中也越明显。基于模拟分析,胶层中含有裂纹时液晶屏所受应力最大,因此加工中应避免胶层出现裂纹。在对液晶屏粘贴ITO玻璃时,应该选用弹性模量和线膨胀系数较小的光学胶。     

多界面脱粘红外无损检测中热激励方法的研究

红外热波检测中热激励方法的选择直接影响缺陷的可检出性和实际检测效果。本文对薄粘接层的界面脱粘检测中的热激励方法进行了分析比较。通过构建多界面脱粘缺陷模型,用有限元分析软件COMSOL对不同热激励下脱粘的红外无损检测做仿真计算,研究热激励方法与检测灵敏度之间的关系,为制定准确的红外检测实验方案提供数值依据。     

基于半功率带宽法的行波超声电机谐响应分析

该文以本单位研制的中空行波超声电机定子为对象,进行了有限元建模及谐响应仿真,发现定子阻尼比的设置对仿真结果的准确性影响较大。通过多普勒激光测振系统测得定子模态参数,利用半功率带宽法求出定子模态阻尼比,代入模型后仿真跟实测结果基本吻合,工作模态B_(011)频率仿真误差为1.66%,振幅仿真误差为4.61%。将定子齿特征参数化,分析了齿距和齿高对定子模态的影响。根据低转速、大扭矩的电机设计目标选取了合适的齿参数,加工出新定子实物。基于同样阻尼比再次进行有限元仿真并对新定子进行激光测振,对比得到工作模态B_(011)频率仿真误差为0.62%,振幅仿真误差为1.94%,验证了有限元谐响应仿真的准确性。此外,对原定子和新定子组装的电机进行性能测试,后者最高空载转速降低了30%,堵转扭矩提升了20%,符合预期设计。准确的参数化有限元模型有助于促进超声电机的快速化设计,提高了对符合电机目标功能的设计参数的选择效率。     

Finite element simulation of thermal fatigue in multilayer structures: thermal and mechanical approach

The large difference in thermal expansion between dissimilar materials present in any electronic package is the source of a major problem to be solved in order to achieve improved reliability. In this paper, simplified thermal and mechanical finite element models are presented for the analysis of thermal stress derived problems. The problems investigated here include, thermal stresses in adhesive backbonds in surface mounted structures and effects of thermal fatigue in soft solder interfaces in conventional power modules such as insulated gate bipolar transistors modules. Full multi-dimensional mechanical and thermal analysis is made by using the commercial engineering computer package . Validation of the thermal simulation is achieved by comparison between simulation and experimental test results, whereas a simple analytical model based upon the lap joint theory is used to verify the structural simulation.     

红外探测器杜瓦冷头的低温可靠性研究

红外探测器杜瓦冷头结构受温度冲击时容易损伤,甚至会导致探测器组件失效。这是红外探测器组件产品研制中不可避免的可靠性问题之一。针对红外探测器杜瓦冷头的低温可靠性问题展开了相关研究。结合粘接失效原理和有限元仿真,讨论了粘接胶厚度、溢胶等情况对杜瓦冷头低温应力、冷头-冷指粘接面积与探测器温度关系的影响。结果表明,胶层状态是影响杜瓦冷头低温损伤和温度传导的重要原因。产品研制过程中可通过控制粘接胶层来降低大面阵探测器粘接结构的低温应力,从而提高冷头结构的低温可靠性。     

Process-dependent contact characteristics of NCA assemblies

The physical contact characteristics of a nonconductive adhesive (NCA) type of flip-chip-on-glass (FCOG) assemblies during manufacturing process and temperature variation is explored by using three-dimensional (3D), nonlinear finite element analysis together with the so-called "death-birth" simulation technique. The contact mechanics of two typical types of micro-bump bonding technologies, i.e., the metal (i.e. Au alloy) and composite bumps, are extensively addressed, and substantially compared. The validity of the modeled contact characteristics is further verified by an electrical contact resistance measurement that adopts a four-point probe method and an equivalent circuit approach. Finally, through the parametric study, the dependence of the contact stress at the bumps and the peeling stress at the UV resin on a number of geometry and material design parameters is effectively identified. Both the modeling and experimental results show that the bump height uniformity is a key factor in the overall contact performance of the assembly, and should not be neglected from the analysis. In addition, it is identified that the composite-bump bonding technology outperforms the metal-bump assembly as a whole in terms of the contact consistency and stability due to its better bump uniformity and compliance. Furthermore, it is surprising to find that there is a full disagreement in the parametric results of the bump height and Al thickness between the shorter bump and the taller among those nonuniform bumps, and more importantly, an increase of the bump height or a reduction of the Al overcoat thickness would enhance the overall contact performance of the assembly.     

贴片焊层厚度对功率器件热可靠性影响的研究

贴片工艺是用粘接剂将芯片贴装到金属引线框架(一般是由铜制成)上的过程.富铅的Pb/Sn/Ag软焊料在功率器件封装贴片工艺中作为粘接剂应用十分广泛.从功率器件整体来看,贴片焊层毫无疑问是影响器件可靠性最重要的因素之一,其不仅具有良好的导电导热性能,而且该焊层能够吸收由于芯片和引线框架之间的热失配而产生的应力应变,保护芯片免于受到机械应力的损伤.基于Darveaux的热疲劳寿命分析模型,利用功率循环加速实验以及有限元方法具体分析了贴片焊层厚度BLT对于功率器件热可靠性的影响.并通过实验与仿真的结果,提出提高功率器件热可靠性的设计原则.