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Research stacked chip fracture of layered plastic device

Author: LiuYu
Tutor: Wang
School: Fudan University
Course: Materials Physics and Chemistry
Keywords: Interfacial Fracture Stacked die package Bi-material Interface Mixed-mode Fracture Testing Energy Release Rate Mode Mixity
CLC: TN605
Type: Master's thesis
Year: 2011
Downloads: 103
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Abstract

In recent years, as the increasing of I/O numbers and miniaturization of size in semiconductor components,2-D packaging is hard to meet the requirements of applications. With higher density, powerful function, good performance and lower costs,3-D high density packaging, in which stacked-die packaging is most widely used, is becoming the major trend of packaging technology. Stacked-die packaging improves efficiency, electrical performance and reliability while reduces costs. It is widely used in data storage field.3-D high density packaging technologies have improved device performance significantly but also introduced many reliability problems. On one hand,3-D packaging introduced complex multilayer structures. The integrity of the interfaces between different materials becomes challenge when the device is subjected to thermal and mechanical loadings. On the other hand, the small defects, which were introduced during fabrication process, may propagate under mechanical and thermal loadings. Interfacial fracture is usually responsible for the failure of high density plastic packaging devices.In this study, two-die stacked and five-die stacked packaging devices were selected and subjected to highly-accelerated temperature and humidity stress test respectively. By using SAM and SEM technology, the interfacial delaminations in the devices were detected after the stress test. Different delamination modes were observed and analyzed. Three delamination fracture modes were summarized and the failure mechanisms were also analyzed. In order to study the interfacial mixed-mode fractures between different materials, a bi-material sample and a new apparatus to characterize the bi-material interfacial fracture were designed. The sample can be loaded in tension in different angles using the new apparatus. For the Epoxy/Cu and Epoxy/PCB interface of high density plastic packaging devices, fracture experiments were carrried out and the critical loading forces were measured when interfacial fracture occurred. The energy release rate of interfacial fracture and mode mixity were obtained based on the experimental results by the elastic fracture analysis. By analyzing interfaciai fracture morphology of Epoxy/Cu and Epoxy/PCB samples, the fracture modes were summarized.According to the hydrothermal stress test of two-die stacked die packaging devices, three interfacial delamination modes were observed. The delaminations exhibit mixed-mode case which includes opening mode (mode-Ⅰ) fracture with normal stress and sliding mode (mode-Ⅱ) fracture with shear stress According to the stress test of five-die stacked die packaging devices, voids were observed in die attached film layer among the bottom three die. Interfacial delaminations fracture between the bottom face of die and die attached film were also observed and analyzed. For the mixed-mode fracture in actual devices’failure analysis, we designed a bi-material sample and a new apparatus to characterize the mixed-mode fracture of the bi-material interface. According to the fracture experiments of Epoxy/Cu and Epoxy/PCB interface, the relationship between critical energy release rate and mode mixity were obtained. The fracture modes of different mode mixity can be divided into three modes according to the samples’fracture modes analysis. The sample can be loaded in tension in different angles. For the method can provide flexible loading angle, it is possible to cover large range of mode mixity cases. The method suggested in this study can be applied for fracture characterization of other interfaces in electronic packaging.

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