Effects of different air gaps of underfill encapsulant on multi-stack printed circuit board

IF 1.6 4区工程技术 Q3 ENGINEERING, ELECTRICAL & ELECTRONIC

Microelectronics Reliability Pub Date : 2024-11-02 DOI:10.1016/j.microrel.2024.115533

Mohamad Aizat bin Abas , Muhamed Abdul Fatah bin Muhamed Mukhtar

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Abstract

This paper studies the effect of different air gaps on multi-stack printed circuit board (PCB) using finite volume method (FVM). Air gaps of 150 mm² and 450 mm² were introduced to investigate their influence on flow parameters such as filling time, pressure distribution, and void formation during the capillary underfill encapsulation process. It was found that increasing the air gap size improved the filling time by 10 %, though it also doubled the pressure, which helps reduce void formation but requires careful control to prevent encapsulant overflow. Throughout the study, an L-type dispensing method was applied on a perimeter type multi-stack BGA with wall type barrier added on the sides of the multi-stack PCB to prevent encapsulant. This new wall type barrier henceforth requires comprehensive study on the size of the air gaps to ensure crucial flow parameters such as void formation, filling time, pressure distribution and flow front pattern are optimized. Two air gap sizes given as 150 mm² and 450 mm² are used in this study. Moreover, the fluid flow patterns from both studies are investigated to determine the problem of racing effect and void formation. Based on the findings, it was found that 10 % improvement in the filling time can be made by using a bigger air gap of 450 mm². However, with bigger air gap, the pressure increases two-fold which can be good in reducing the void formation though the trade-off can be on the risk of excessive overflow of encapsulant.

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不同气隙的底部填充封装剂对多堆栈印刷电路板的影响

本文采用有限体积法（FVM）研究了不同气隙对多层印刷电路板（PCB）的影响。引入了 150 mm2 和 450 mm2 的气隙，以研究它们对毛细管底部填充封装过程中填充时间、压力分布和空隙形成等流动参数的影响。研究发现，增加气隙尺寸可将填充时间缩短 10%，但同时也会使压力增加一倍，这有助于减少空隙的形成，但需要小心控制以防止封装剂溢出。在整个研究过程中，在周长型多层 BGA 上采用了 L 型点胶方法，并在多层印刷电路板的两侧添加了壁式阻隔层，以防止封装剂。因此，需要对这种新型壁式阻隔层的气隙大小进行全面研究，以确保空隙形成、填充时间、压力分布和流前模式等关键流动参数得到优化。本研究采用了 150 mm2 和 450 mm2 两种气隙尺寸。此外，还对这两项研究的流体流动模式进行了调查，以确定赛车效应和空隙形成问题。研究结果表明，使用 450 mm2 的较大气隙可将填充时间缩短 10%。不过，气隙增大后，压力增加了两倍，这有利于减少空隙的形成，但同时也会带来封装剂过度溢出的风险。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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来源期刊

Microelectronics Reliability 工程技术-工程：电子与电气

CiteScore

3.30

自引率

12.50%

发文量

342

审稿时长

68 days

期刊介绍： Microelectronics Reliability, is dedicated to disseminating the latest research results and related information on the reliability of microelectronic devices, circuits and systems, from materials, process and manufacturing, to design, testing and operation. The coverage of the journal includes the following topics: measurement, understanding and analysis; evaluation and prediction; modelling and simulation; methodologies and mitigation. Papers which combine reliability with other important areas of microelectronics engineering, such as design, fabrication, integration, testing, and field operation will also be welcome, and practical papers reporting case studies in the field and specific application domains are particularly encouraged. Most accepted papers will be published as Research Papers, describing significant advances and completed work. Papers reviewing important developing topics of general interest may be accepted for publication as Review Papers. Urgent communications of a more preliminary nature and short reports on completed practical work of current interest may be considered for publication as Research Notes. All contributions are subject to peer review by leading experts in the field.