Purpose

This paper aims to present new analytical model for the filling times prediction in flip-chip underfill encapsulation process that is based on the surface energetic for post-bump flow.

Design/methodology/approach

The current model was formulated based on the modified regional segregation approach that consists of bump and post-bump regions. Both the expansion flow and the subsequent bumpless flow as integrated in the post-bump region were modelled considering the surface energy–work balance.

Findings

Upon validated with the past underfill experiment, the current model has the lowest root mean square deviation of 4.94 s and maximum individual deviation of 26.07%, upon compared to the six other past analytical models. Additionally, the current analytically predicted flow isolines at post-bump region are in line with the experimental observation. Furthermore, the current analytical filling times in post-bump region are in better consensus with the experimental times as compared to the previous model. Therefore, this model is regarded as an improvised version of the past filling time models.

Practical implications

The proposed analytical model enables the filling time determination for flip-chip underfill process at higher accuracy, while providing more precise and realistic post-bump flow visualization. This model could benefit the future underfill process enhancement and package design optimization works, to resolve the productivity issue of prolonged filling process.

Originality/value

The analytical underfill studies are scarce, with only seven independent analytical filling time models being developed to date. In particular, the expansion flow of detachment jump was being considered in only two previous works. Nonetheless, to the best of the authors’ knowledge, there is no analytical model that considered the surface energies during the underfill flow or based on its energy–work balance. Instead, the previous modelling on post-bump flow was based on either kinematic or geometrical that is coupled with major assumptions.

中文翻译：

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基于表面能量的倒装芯片底部填充工艺分析填充时间模型

目的

本文旨在为倒装芯片底部填充封装工艺中的填充时间预测提供新的分析模型，该模型基于凸点后流动的表面能量。

设计/方法/方法

当前模型是基于改进的区域隔离方法制定的，该方法由碰撞和碰撞后区域组成。考虑到表面能 - 功平衡，对膨胀流和随后的无扰流集成在后碰撞区域进行建模。

发现

与过去的底部填充实验验证后，与过去的其他六个分析模型相比，当前模型的均方根偏差最低为 4.94 秒，个体偏差最大为 26.07%。此外，当前分析预测的后碰撞区域的流动等值线与实验观察一致。此外，与之前的模型相比，当前在凸点后区域的分析填充时间与实验时间更加一致。因此，该模型被视为过去填充时间模型的即兴版本。

实际影响

所提出的分析模型能够以更高的精度确定倒装芯片底部填充工艺的填充时间，同时提供更精确和逼真的凸点后流动可视化。该模型有利于未来的底部填充工艺改进和封装设计优化工作，以解决长时间填充工艺的生产力问题。

原创性/价值

分析底部填充研究很少，迄今为止仅开发了七个独立的分析填充时间模型。特别是，在之前的两个作品中只考虑了脱离跳跃的扩展流。尽管如此，据作者所知，没有考虑底部填充流动过程中的表面能或基于其能量-功平衡的分析模型。相反，之前对碰撞后流动的建模基于运动学或几何学，并结合了主要假设。