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Research Papers

Hygro-Thermo-Mechanical Reliability Assessment of a Thermal Interface Material for a Ball Grid Array Package Assembly

[+] Author and Article Information
Xi Liu

Computer Aided Simulation for Packaging Reliability (CASPaR) Laboratory, George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0405xi.liu@gatech.edu

Jiantao Zheng

 IBM Server and Technology Group, Hopewell Junction, NY 12533jzheng@us.ibm.com

Suresh K. Sitaraman

Computer Aided Simulation for Packaging Reliability (CASPaR) Laboratory, George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0405suresh.sitaraman@me.gatech.edu

J. Electron. Packag 132(2), 021004 (Jun 11, 2010) (8 pages) doi:10.1115/1.4001746 History: Received January 21, 2010; Revised May 06, 2010; Published June 11, 2010; Online June 11, 2010

The thermal efficacy of thermal interface material (TIM) is highly dependent on its ability to adhere to the surfaces of interest. Any delamination of the TIM from the die or the lid will increase the local thermal resistance and, thus, will reduce the overall effectiveness of the TIM. Although significant amount of work has been done on understanding the thermal and moisture effects of various polymer materials used in microelectronic package assemblies, very limited work has been done to study the effect of temperature and moisture on TIM delamination. In this paper, a sequential hygro-thermal-mechanical finite-element model has been developed to mimic the loadsteps associated with package assembly as well as moisture soaking under 85°C/85RH over 500 h. The predictions from the models have been validated with a wide range of experimental data including laser Moiré data for thermomechanical loading and digital image correlation data for hygro-thermo-mechanical loading. Weight gain and coordinate-measurement machine have been used to characterize moisture diffusivity and moisture expansion coefficient of various polymer materials in the package assembly. The developed models show the evolution of normal strain in TIM during various loadsteps and provide important insight into the potential for TIM delamination under package assembly process and moisture soaking. Thus, the models can be used for developing various designs and process steps for reducing the chances for TIM delamination.

Copyright © 2010 by American Society of Mechanical Engineers
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References

Figures

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Figure 6

(a) Ux displacement fringe comparison (overall) and (b) Ux displacement fringe comparison (chip edge)

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Figure 7

(a) Uy displacement fringe comparison (overall) and (b) Uy displacement fringe comparison (chip corner)

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Figure 8

Deck-level warpage (after underfilling, loadstep 1)

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Figure 9

Module-level moisture weight gain

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Figure 10

Card-level moisture weight gain

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Figure 11

Module-level, laminate bottom warpage (sample 1)

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Figure 12

Card-level, board bottom warpage (sample 1)

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Figure 13

Laminate bottom warpage (module-level)

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Figure 14

Board bottom warpage (card-level)

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Figure 15

(a) Stress σy in the TIM after lid attach and cool down to room temperature (loadstep 3) and (b) strain εy in the TIM after lid attach and cool down to room temperature (loadstep 3)

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Figure 16

Strain εy in the TIM at the reflow temperature (loadstep 4)

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Figure 17

Strain εy In the TIM at room temperature after reflow (loadstep 5)

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Figure 18

TIM strain history during the whole process (loadstep 1 to 8)

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Figure 19

(a) Thermal-mechanical strain εy in the TIM after 500 h 85°C/85RH soaking (loadstep 7), (b) hygromechanical strain εy in the TIM after 500 h 85°C/85RH soaking (loadstep 7), and (c) hygro-thermal-mechanical strain εy in the TIM after 500 h 85°C/85RH soaking (loadstep 7)

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Figure 1

Wetness and temperature analogy

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Figure 2

Weight gain of laminates under 85°C/85RH

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Figure 3

Flow chart of coupled hygro-thermal-mechanical analysis

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Figure 4

FE model for hygro-thermal-mechanical analysis

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