基于表面能理论的倒装芯片封装下填充流动研究

为了预测倒装芯片封装中的下填充过程,通常要首先通过繁复的方法来求解平均毛细压.为了避免此问题,从能量的角度分析了倒装芯片封装工艺中的下填充流动过程.认为下填充是较低表面能的界面代替较高表面能的界面的过程,所释放的表面能用于形成流体流动的动能和克服阻力的能量损耗,期间能量守恒.在此分析的基础上建立了下填充流动的新模型.建立了可视化的下填充流动实验装置,并用下填充实验验证了所建立新模型的准确性.该模型避免了计算平均毛细压的复杂过程,并可方便地扩展到焊球排布形式不同的倒装芯片.     

球形焊点三角形排列倒装芯片底部填充的能量法研究

对于具有球形焊点且呈正三角形排列的倒装芯片,由于其待填充的空隙结构复杂,难以通过平均毛细压来建立底部填充的解析模型.因此通过能量变化来分析底部填充过程以避免平均毛细压的计算.首先分析了底部填充过程中表面能的变化、动能的变化和流道壁面对流动的阻力损耗;然后根据能量守恒定律得到了反映底部填充过程的新解析模型;最后用计算流体力学(CFD)软件对底部填充过程进行了三维数值模拟,以此验证了基于能量法的新解析模型.能量法更具有通用性,可用于研究焊点形状和排列方式复杂的倒装芯片底部填充过程.     

倒装芯片封装中下填充流场渗透率的数值分析

倒装芯片封装中的下填充流场可以假设为多孔介质流场,其渗透率的求解对研究下填充流动过程至关重要。根据下填充流场所具有的周期性结构,通过单胞数值模拟的方法得到了下填充流场的渗透率。通过对渗透率数据的分析,发现了渗透率和下填充流场参数之间的关系,并建立了计算渗透率的幂律模型。其中幂律模型的底是下填充流场的孔隙率,系数仅与芯片和基板的间隙有关,指数仅与芯片和基板的间隙相对于焊球直径的比值有关。通过实例分析表明,与其他模型相比,用基于幂律模型的渗透率所计算出的填充时间更符合实验结果。     

倒装芯片下填充流动二维化数值分析方法的应用

下填充流动是确保倒装芯片可靠性的重要封装工艺,其流场和流动过程具有明显的二维特征,通过降维得到的二维化数值分析新方法能高效地模拟下填充流动过程.针对一种焊球非均匀、非满布的典型倒装芯片,用该数值分析方法模拟了单边下填充流动的过程,并用实验对模拟结果进行了检验.实验采用了可视化的下填充流动装置,倒装芯片试样采用硅-玻璃键合(SOG)方法制作.将数值模拟结果与实验结果比较发现,无论是流动速度还是流动前沿的形态,两者均呈现出较高的吻合度.这表明:针对下填充流动的二维化数值分析方法兼具高效性和准确性,具有较高的应用价值.     

焊球分布模式对芯片下填充胶流动的影响

分析了在倒装芯片尺寸、相邻焊球中心之间距离相同的情况下,焊球点满布叉排排列和满布顺排排列对倒装芯片下填充流动的影响。并就焊球点布置密度不同,在顺排和叉排排列两种方式时,用相同的填充时间填充材料流动前端所走过的距离以及其分布情况进行了计算机模拟分析研究。     

喷射下填充--一种新的下填充技术

<正> 1 引言 下填充,就是在倒装焊接装片的芯片下面,或在焊球(或焊柱)组装安装器件的管壳下面填充粘接剂,用以把芯片与封装外壳基板、或封装外壳基板与组装的印制板粘接起来,从而使它们之间由于热膨胀失配产生的集中在芯片与封装外壳、或封装外壳基片与组装印制板间焊料连接点的热应     

用硅压阻应力传感器研究倒装芯片封装应力

电子封装是集成电路产品制造过程中的重要环节,而电子封装所产生的应力则可能会对芯片的性能及可靠性产生影响,因而受到业界的广泛关注。利用半导体压阻效应制造硅压阻应力传感器阵列芯片,将其倒装键合至印刷电路板,填充不同类型的下填料进行固化。通过测量应力传感器芯片上的力敏电阻变化,计算倒装键合和下填料固化等封装工艺引入的应力,并讨论了下填料的性能参数对芯片应力大小的影响。此外,在标定力敏电阻及压阻系数温度效应的基础上,对下填料固化过程的应力变化进行了实时监测,分析了下填料固化工艺引起的应力。     

超级CSP——一种晶圆片级封装

研究了圆片级芯片尺寸封装.使用再分布技术的圆片级封装制作了倒装芯片面阵列.如果用下填充技术,在再分布层里和焊结处的热疲劳应力可以减小,使倒装芯片组装获得大的可靠性.     

焊球植球凸块工艺的可靠性研究

焊球植球是一种最具潜力的低成本倒装芯片凸块制作工艺.采用焊球植球工艺制作的晶圆级芯片尺寸封装芯片的凸块与芯片表面连接的可靠性问题是此类封装技术研究的重点.为此,参考JEDEC关于电子封装相关标准,建立了检验由焊球植球工艺生产的晶圆级芯片尺寸封装芯片凸块与芯片连接及凸块本身是否可靠的可靠性测试方法与判断标准.由焊球植球工艺生产的晶圆级芯片尺寸封装芯片,分别采用高温存储、热循环和多次回流进行试验,然后利用扫描电子显微镜检查芯片上凸块剖面的凸块下金属层分布和测试凸块推力大小来验证凸块的可靠性.试验数据表明焊球植球工艺生产的晶圆级芯片尺寸封装芯片具有高的封装连接可靠性.     

采用MUF的倒装芯片封装技术

业界对信号完整性和电学性能提出了越来越高的要求,因而开始向更薄基板的方向发展,Amkor Technology Inc.开发出一种使用模塑底部填充（MUF）而非毛细底部填充（CUF）的倒装芯片模塑球栅阵列（FCMBGA）封装技术,使得无源器件与倒装芯片的间距更小,同时还提供了更优的薄芯基板变形控制,并可以获得更好的焊料连接可靠性。     

Experimental study of filling behaviors in the underfill encapsulation of a flip-chip

An underfill encapsulant was used to fill the gap between the chip and the substrate around the solder joints to improve the long-term reliability of the flip-chip interconnecting system. The underfill encapsulant was filled by the capillary effect. In this study, experiments were designed to investigate the effects of bump pitch and the edge detour flow on the underfill encapsulation. The bump array was patterned on a glass plate using the lithography technology. This patterned glass plate was used to simulate a flip-chip with solder bumps. The patterned glass was bounded to a substrate to form a simulated flip-chip system. With the lithography technology, it is easy to construct the test samples for underfill flow experiments with different configuration of solder bumps. It was observed that the filling flow was affected by the bump pitch. The edge detour flow depends mainly on the arrangement of the underfill dispensing process.     

An Analytical Model for Predicting the Underfill Flow Characteristics in Flip-Chip Encapsulation

This article describes an analytical model for the prediction of the underfill flow characteristics in a flip-chip package driven by capillary action. In this model, we consider non-Newtonian fluid properties of the encapsulant as opposed to most other studies where Newtonian fluid properties were assumed for the underfill flow. The power-law constitutive equation was applied in our study. The simulation based on this model agreed well with the measurement obtained from the experiments available in literature. It was further shown that this model performs better than the Washburn model traditionally used for the prediction of underfill flow characteristics in the flip-chip packaging. Based on this model, the effects of the solder bump pattern (including bump pitch, solder bump diameter, and gap height) on the process variables (i.e., flow front and filling time) were studied, which facilitated both the package design and the process optimization.     

The effect of solder bump pitch on the underfill flow

An underfill encapsulant was used to fill the gap between the chip and substrate around solder joints to improve the long-term reliability of flip chip interconnect systems. The underfill encapsulant was filled by the capillary effect. In this study, the filling time and pattern of the underfill flow in the process with different bumping pitch, bump diameter, and gap size were investigated. A modified Hele-Shaw flow model, that considered the flow resistance in both the thickness direction and the restrictions between solder bumps, was used. This model estimated the flow resistance induced by the chip and substrate as well as the solder bumps, and provided a reasonable flow front prediction. A modified model that considered the effect of fine pitch solder bumps was also proposed to estimate the capillary force in fine pitch arrangements. It was found that, on a full array solder bump pattern, the filling flow was actually faster for fine pitch bumps in some arrangements. The filling time of the underfill process depends on the parameters of bumping pitch, bump diameter, and gap size. A proposed capillary force parameter can provide information on bump pattern design for facilitating the underfilling process.     

Anisotropic behavior of the capillary action in flip chip underfill

An underfill encapsulant can be used to improve the long-term reliability of flip chip interconnecting system by filling the gap between the chip and substrate around the solder bumps. The underfill encapsulant was filled by a capillary flow. This study was devoted to investigate the anisotropic effects of the capillary action induced by the solder bumps. A modified Hele-Shaw flow model, considering the flow resistance in both the thickness direction and the restrictions between solder bumps, was used. A capillary force model, depending on the direction of filling flow, for full array solder bumps was proposed. The capillary force was formulated based on quadrilateral arrangement of solder bumps. It was found that the capillary action is not the same for different directions. In the 45° direction, enhancement of the capillary flow was noticed for a bump pitch within a critical value. The edge preferential flow during the underfill experiment could be attributed to the anisotropic behavior of the capillary action.     

倒装焊对探测器频响特性影响的理论分析及工艺优化

针对光探测器在倒装焊过程中频响性能恶化的问题,建立等效电路模型分析出其原因,并通过优化倒装焊工艺条件予以有效解决。该电路模型包括探测器芯片、过渡热沉和倒装焊环节三个部分。基于倒装焊后探测器的S11参数和频响曲线提取出倒装焊环节特征参数,确认焊点接触电阻过大是引起探测器频响下降的主要原因。通过优化倒装焊工艺条件,有效减小了焊点接触电阻,基本消除了倒装焊对探测器频响特性的影响。     

Experimental verification of models for underfill flow driven by capillary forces in flip-chip packaging

Underfill process is a very important step in the flip-chip packaging because of its great impact on the reliability of electronic devices. In the control of the underfill dispensing in flip-chip packaging, an analytical model for the underfill flow behavior is required to perform the control action. Traditionally, the Washburn model is used for predicting the viscous flow behavior in the flip-chip underfill process driven by capillary forces. Unfortunately, some studies in the literature have shown that the model does not match the measured results well due to the neglect of the characteristics such as solder bump resistance and non-Newtonian behavior of underfills. Although some underfill flow models have been developed for considering these characteristics, there is no sufficient account for such a mismatch from the literature. In this article, we present an experimental investigation aimed to understand the possible causes responsible for the observed mismatch with the Washburn model. The experimental investigation confirmed that the underfill fluid used in flip-chip packaging shows a complex non-Newtonian behavior and that the Washburn model is, indeed, only applicable to the Newtonian fluid in this setting. Another contribution of the work reported in this article is the provision of measured data on a test bed which was built upon using the off-the-shelf components; as such the data can be used by other researchers to validate their theoretical findings.     

Recent advances in modeling the underfill process in flip-chip packaging

Flip-chip underfill process is a very important step in the flip-chip packaging technology because of its great impact on the reliability of the electronic devices. In this technology, underfill is used to redistribute the thermo-mechanical stress generated from the mismatch of the coefficient of thermal expansion between silicon die and organic substrate for increasing the reliability of flip-chip packaging. In this article, the models which have been used to describe the properties of underfill flow driven by capillary action are discussed. The models included apply to Newtonian and non-Newtonian behavior with and without the solder bump resistance for the purpose of understanding the behavior of underfill flow in flip-chip packaging.     

军用倒装焊器件底部填充胶选型及验证方法讨论

从分析倒装焊器件底部填充的必要性入手,对底部填充胶的选型流程、选型基本方法及重点参数匹配情况进行了分析,优选出4款底部填充材料。通过对4款材料关键参数的理论计算及恒定加速度、热力学耦合仿真计算,优选出一种材料作为样本材料。同时对底部填充材料验证内容进行了梳理,通过试验验证摸索出材料的适用范围及边界条件。该底部填充胶的选型验证方法对于军用混合集成电路其他聚合材料的选型具有一定的指导意义。