硅胶粘弹性对大功率LED可靠性的影响

基于动态单悬臂梁DMA实验测定了多频条件下LED封装用硅胶的粘弹性特性参数,用数据处理软件拟合得到松弛时间、剪切松弛系数、体积松弛系数等参数。通过有限元软件ANSYS分别模拟了硅胶线弹性和粘弹性两种不同性质下,LED器件在–55~+125℃热循环条件下的总体变形、等效应力及应力最大点的剪切应力变化趋势。结果表明,基于硅胶的粘弹性特性的LED的可靠性模拟结果更接近实际情况。     

PCB粘弹性对QFN焊点可靠性的影响

基于动态拉伸DMA实验所获得的FR—4PCB的蠕变柔量曲线,用广义Maxwell模型表征了PCB的粘弹性蠕变松弛特性。通过有限元软件MSC Marc分别模拟了基于PCB弹性和粘弹性两种不同性质下,QFN器件在–55～+125℃热循环条件下的应力应变,并利用修正后的Coffin-Masson方程分别计算了它们的热疲劳寿命。结果表明,基于粘弹性条件下QFN焊点可靠性模拟结果更接近实际情况。     

PBGA中环氧模塑封装材料的热力学应力分析

本文采用有限元模拟的方法,对塑封焊球栅阵列PBGA的再回流焊接过程及其后的热循环进行了仿真,其中环氧模塑封装材料EMC采用了粘弹性和线弹性两种材料模式。仿真中主要对EMC再回流焊接过程产生的残余应力和热循环载荷下的热应力／应变进行了分析;也讨论了EMC材料模式对应力值的影响。结果表明:线弹性模式的EMC的应力值明显高于粘弹性模式的;在热循环载荷下EMC中应力水平并不高,但开裂应变却非常高,因此在EMC中很可能引发疲劳裂纹。     

硅胶粘弹性对大功率LED可靠性的影响

基于动态单悬臂梁DMA实验测定了多频条件下LED封装用硅胶的粘弹性特性参数,用数据处理软件拟合得到松弛时间、剪切松弛系数、体积松弛系数等参数.通过有限元软件ANSYS分别模拟了硅胶线弹性和粘弹性两种不同性质下,LED器件在-55～+125℃热循环条件下的总体变形、等效应力及应力最大点的剪切应力变化趋势.结果表明,基于硅胶的粘弹性特性的LED的可靠性模拟结果更接近实际情况.     

EMC材料特性对MEMS加速度计封装可靠性的影响

采用有限元法分析了EMC(环氧模塑封材料)材料特性对MEMS(微电子机械系统)加速度计封装可靠性的影响.使用有限元软件ANSYS分别模拟了加速度计的输出电压、悬臂梁的挠度以及加速度计芯片的等效应力在温度循环载荷下的变化情况.结果发现,EMC的材料模式不同,MEMS加速度计的性能有明显差异.在使用EMC温度相关弹性模式和...     

D2-FBGA热循环载荷下的结构参数优化

利用动态机械分析仪(DMA),测定环氧模塑封材料(EMC)的粘弹性数据;经过数据拟合处理,得到有限元仿真所需的相关参数.将D2-FBGA中芯片厚度、粘结剂厚度、部分EMC厚度及基板厚度作为优化参数,选用正交实验设计,建立了这四个参数的正交表;并用MSC、 Marc,计算了D2-FBGA在热循环载荷下的热应力分布.通过统计软件stata,建立了最大等效应力与上述参数的关系的回归方程;分析了各个结构参数对器件最大等效应力的影响程度;使用单纯形法,得出一组最优结构参数及对应的最大等效应力值.结果表明:通过优化,器件的最大等效应力从(90.58 MPa)下降到66.84 MPa,优化效果明显.     

锂氧电池复合电解质电化学性能研究

将LiPF_6溶入EC/EMC/DMC作为锂氧电池电解质主体,并分别加入[Emim]BF_4和[DEME]TFSI离子液体制成复合电解质材料,组装成锂氧电池。通过循环伏安、交流阻抗、恒流充放电等方式研究复合电解质的电化学性能。结果表明,LiPF_6溶入EC/EMC/DMC-[Emim]BF_4体系复合电解质表现出较优的电化学性能,在0.025×10~(–3)A·cm~(–2)电流密度下电池首次放电比容量为2 672×10~(–3)Ah·g~(–1),能量密度达6.468×10~(–3) Wh·cm~(–2)。     

模塑封器件模塑化合物与铜的界面裂纹扩展

针对环氧模塑化合物(EMC)与铜的界面沿特定路径的准静态界面裂纹扩展问题,利用ANSYS建模仿真了单个位移及循环位移载荷条件下界面裂纹扩展;以界面裂纹扩展的J积分为分析目标,分别在铜材料为线弹性和弹塑性的两种工况下,分析了循环位移载荷对界面裂纹扩展的影响规律。结果表明,在弹性条件下,循环载荷卸载过程裂纹尖端张开角为0,界面闭合;弹塑性条件下,卸载过程裂纹张开角不为0,界面不闭合,且屈服应力越小,两种材料的界面间隙越大,J积分数值越小。     

基于扇出型封装塑封材料性能的表征研究

扇出型封装在塑封过程中会出现芯片偏移及翘曲等缺陷,详细了解环氧塑封材料(EMC)的特性能够准确预测封装材料、结构、塑封工艺对塑封效果的影响。针对用于扇出型封装的EMC材料采用动态机械分析仪、差示扫描量热仪、流变仪测试其动态力学性能、固化动力学性能、流变学性能和热容,并建立可用于有限元分析的材料特性数学模型。结果表明,EMC在150℃等温固化60 min后具有最少残余固化;100℃环境下黏度随温度增加速率最快;时温等效原理可预测实验频率以外的力学行为。模型曲线与实验数据的拟合优度均大于0.982,材料表征模型满足准确性与适用性的要求。     

DFN封装翘曲和应力分析与优化

回流焊过程中,双边扁平无引脚(DFN)封装会因为巨大的温度变化产生翘曲和应力,影响超高频射频识别(RFID)芯片的性能和可靠性.选取DFN3封装为例从理论方面分析结构和材料参数对封装翘曲和应力的影响,发现减小环氧塑封料(EMC)热膨胀系数(CTE)、增大其杨氏模量均能减小封装翘曲;通过有限元仿真分析得出的结论与理论分析相一致.为了减小封装翘曲和应力,选定具有更小CTE的9240HF10AK-B3(Type R)作为新型EMC.通过有限元仿真结果对比发现,在25℃时,采用新型EMC的封装翘曲增大了 16.8％,应力减小了 4.1％;260℃时,其封装翘曲减小了 45.7％,应力减小了 9.2％.同时,新型EMC的RFID芯片标签回波损耗较之前优化了 6.59％.     

An improved methodology for determining temperature dependentmoduli of underfill encapsulants

Finite element analyses (FEAs) have been widely used to preventively predict the reliability issues of flip-chip (FC) packages. The validity of the simulation results strongly depends on the inputs of the involved material properties. For FC packages Young's modulus-temperature relationship is a critical material property in predicting of the package reliability during -55°C to 125°C thermal cycling. Traditional tensile tests can obtain the modulus at selected temperatures, but are tedious, expensive, and unable to accurately predict the Young's modulus-temperature relationship within a wide temperature range. Thus, this paper is targeted to provide a simple but relatively accurate methodology to obtain the Young's modulus-temperature relationship. In this paper, three commercial silica filled underfill materials were studied. A simple specimen (based on ASTM D638M) preparation method was established using a Teflon mold. A dynamic-mechanical analyzer (DMA) was used to obtain the stress-strain relationship under controlled force mode, storage and loss modulus under multi-frequency mode, and stress relaxation under stress relaxation mode. A simple viscoelastic model was used and an empirical methodology for obtaining Young's modulus-temperature relationship was established     

以均匀设计法对SCSP器件工艺参数的优化

利用有限元法研究了堆叠芯片封装(SCSP)器件在封装工艺过程中的热应力分布。将工艺过程中的固化温度、升温速率等工艺参数作为优化变量,采用均匀设计方法对其进行了优化组合,并为后续的回归分析产生样本点。通过回归分析得出工艺参数与最大等效应力之间的回归方程,并将回归方程作为优化算法近似的数学模型。结果表明:最大等效应力出现在EMC固化工艺中,所以在固化阶段SCSP器件容易产生可靠性问题。通过优化,最大等效应力由222.4MPa下降到了169.0MPa。     

Viscoelastic Effect of FR-4 Material on Packaging Stress Development

In the microelectronics device, FR-4 material is one of the key component materials in the packaging structure. The structure of FR-4 is featured as a typical orthotropic polymer composite material reinforced with glass fiber. Although the material may exhibit viscoelastic behavior, the material is commonly regarded as temperature-dependent elastic one in the microelectronics reliability analysis. The purpose of this study is to investigate the material property modeling effect of FR-4 on the reliability prediction. To obtain the FR-4 material properties, a series of stress relaxation test was performed. Based on the data, the behavior of the FR-4 was modeled as orthotropic temperature-dependent elastic and viscoelastic. An analytical method was employed to calculate the engineering constants required for the calculations. The elastic calculation was performed by ANSYS, and the viscoelastic calculation by a FORTRAN program, respectively. The FORTRAN program was written separately, and capable of calculating the viscoealstic calculations when the material is orthotropic. Board on chip (BOC) packaging structure, a new type of the first level packaging for memory chip, was considered for the stress development analysis. The results were compared to examine the difference based on the FR-4 material property modeling.     

SCSP中芯片黏结层在焊接时的可靠性

提出了一个细观力学模型,该模型同时考虑了热膨胀和蒸汽膨胀对叠层芯片尺寸封装(SCSP)中芯片黏结层变形的影响.当初始温度确定时,由该模型可求得给定温度下芯片黏结层内部的蒸汽压力和孔隙率,从而判断芯片黏结层在焊接回流时的可靠性.当温度从100℃升高到250℃时,芯片黏结层的饱和蒸汽压、等效弹性模量及孔隙率分别从0.10 ...     

Time-domain viscoelastic constitutive model based on concurrent fitting of frequency-domain characteristics

A numerical procedure for constructing the multiaxial viscoelastic model for polymeric packaging material over a wide range of temperature is presented. By using the proposed best-fitting procedure, experimentally measured frequency-domain Young's and shear storage moduli are used to calculate the time-domain bulk and shear relaxation moduli which describe the three-dimensional constitutive behavior of a viscoelastic solid. The numerical procedure incorporates restrictions that ensure that the derived time-domain material function is physics compatible. The proposed procedure was applied to construct the viscoelastic constitutive models of epoxy molding compounds (EMCs), and compared to results obtained by using approximate-formula based direct conversion procedure. It was shown that, without using the proposed procedure, the directly calculated time-dependent Poisson's ratio oscillates significantly in the rubbery regime and is physically inadmissible. To validate the constitutive model constructed by using the proposed procedure, a numerical finite element model that incorporates the viscoelastic constitutive model of the EMC was applied to simulate warpage of an overmolded package under the solder reflow process and compared to experimental shadow Moiré measurements.     

复合陶瓷颗粒/环氧模塑料的制备与性能

选用SiO_2、Al_2O_3、Si_3N_4三种陶瓷颗粒的复合填充环氧模塑料(EMC),研究了不同填料种类、含量对EMC导热系数、热膨胀系数(CTE)、介电常数等性能的影响随着填料百分含量的增加,EMC的热导率、介电常数也随之增加,而其热膨胀系数显著下降相同体积百分含量下,Al_2O_3、Si_3N_4复合体系EMC热导率和介电常数高于SiO_2、Si_3N_4复合体系,而其热膨胀系数比后者低。百分含量为60%时,前者热导率达到2．254 W(m·K)~(-1)、后者达到2．04w(m·K)~(-1)。百分含量为65%时,其CTE分别为1．493×10~(-5)K~(-1)、1．643×10~(-5)K~(-1),同时两体系复合材料的介电常数可以维持在较低水平