Moisture diffusion study in electronic packaging using molecular dynamic simulation

56th Electronic Components and Technology Conference 2006 Pub Date : 2006-07-05 DOI:10.1109/ECTC.2006.1645843

H. Fan, E. Chan, C. Wong, M. Yuen

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引用次数: 20

Abstract

Moisture induced reliability concerns have been extensively studied in package design. Popcorning in plastic-encapsulated IC packages is a defect frequently occurring in solder reflow due to moisture penetration into the packages. Moisture diffusion has a detrimental effect on the epoxy/copper interfacial adhesion and drastically reduces the reliability of the encapsulated package. The present study is focused on the moisture diffusion in both the epoxy molding compound (EMC) and the EMC/Cu interface. In order to evaluate which is the dominating moisture transport mechanism at the interface, molecular dynamic (MD) models were built using the 'Materials studio' software. Based on the conditions of 85degC/85%RH in qualifying tests in humidity chamber, the amount of water molecules are assigned to the packing cells in the MD models. All the MD simulations were performed at a temperature of 85degC using the constant-pressure and temperature ensemble (NPT). Non-bond interactions cut-off distance of 1.5 nm with a smooth switching function was used in all simulations. The simulation in each case study was performed with an interval of 1 femto second (fs) in each MD simulation step. The mean squared displacements of all water molecules were evaluated in each time-step to track the motion of the molecules. Constants of moisture diffusion in both bulk EMC material and EMC/Cu interface can be derived from the mean squared displacements. The MD results show that the value of the moisture diffusion coefficient at the EMC/Cu interface is higher than that in the bulk EMC material. It revealed that moisture can easily penetrate along the EMC/Cu interface. The MD simulation study has demonstrated that the seepage along the interface is the dominant mechanism for moisture diffusion into the EMC/Cu interface in plastic packages. This widely studied mechanism of moisture diffusion via the bulk EMC is an apparent a secondary moisture penetration path to the interface

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用分子动力学模拟研究电子封装中的水分扩散

湿气诱发的可靠性问题在封装设计中得到了广泛的研究。塑料封装IC封装中的起泡是由于湿气渗透到封装中而导致的焊料回流中经常发生的缺陷。水分扩散对环氧树脂/铜界面的粘附有不利影响，并大大降低了封装封装的可靠性。本文主要研究了环氧成型复合材料(EMC)和EMC/Cu界面中的水分扩散。为了评估哪一种是在界面处占主导地位的水分传输机制，使用“Materials studio”软件建立了分子动力学(MD)模型。根据湿室合格试验85℃/85%RH的条件，确定了MD模型中填料单元的水分子量。所有的MD模拟都是在85℃的温度下使用恒压恒温系综(NPT)进行的。在所有模拟中，非键相互作用的截止距离为1.5 nm，具有光滑的开关函数。每个案例研究中的模拟在每个MD模拟步骤中以1飞秒(fs)的间隔进行。在每个时间步中评估所有水分子的均方位移，以跟踪分子的运动。从均方位移可以推导出电磁兼容材料和电磁兼容/铜界面中的水分扩散常数。MD结果表明，电磁兼容/Cu界面处的水分扩散系数高于块体电磁兼容材料。结果表明，水分可以很容易地沿EMC/Cu界面渗透。MD模拟研究表明，沿界面的渗流是塑料封装中水分向EMC/Cu界面扩散的主要机制。这种被广泛研究的湿气扩散机理是一种明显的二次湿气渗透途径

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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56th Electronic Components and Technology Conference 2006

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