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RESEARCH PAPERS

Reliability Investigation for Encapsulated Isotropic Conductive Adhesives Flip Chip Interconnection

[+] Author and Article Information
Liu Caroline Chen

Swedish Microsystem Integration Technology (SMIT) Center & Electronics Production, Department of Microtechnology and Nanoscience, Chalmers University of Technology, Kemivagen 9, 412 96 Gothenburg, Swedencaroline.chen@mc2.chalmers.se

Zonghe Lai, Zhaonian Cheng, Johan Liu

Swedish Microsystem Integration Technology (SMIT) Center & Electronics Production, Department of Microtechnology and Nanoscience, Chalmers University of Technology, Kemivagen 9, 412 96 Gothenburg, Sweden

J. Electron. Packag 128(3), 177-183 (Aug 07, 2005) (7 pages) doi:10.1115/1.2227057 History: Received March 03, 2004; Revised August 07, 2005

Isotropic conductive adhesives (ICA) are gaining more and more application interests in electronic manufacturing, however, their failure mechanism is not been fully understood. In this paper we present reliability investigations on an encapsulated ICA flip chip interconnection. Experimental work included product lifetime measurement, cross section observation, and whole module warpage scanning. Results revealed that the chip-size effect on the ICA lifetime was obvious. A theoretical analysis was conducted with Finite Element Method (FEM) simulation. Viscoelastic models for adhesives and underfill materials were employed, and the comparison with an elastic model was made. Calculated equivalent stresses Seqv and shear stress σxy fitted well with the experimental lifetime measurement, thus a lifetime relationship similar to the Coffin-Manson formula was established to predict the thermal fatigue life of an encapsulated ICA flip chip. Furthermore, the influences of underfill properties on the ICA reliability were discussed.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

ICA printed substrate with good quality (a) and some defects (b)

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Figure 2

Profiles of the top surface of an assembled chip (a) in the X direction; (b) in the Z direction

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Figure 3

Accumulative failure functions for four chip sizes

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Figure 4

SEM pictures for ICA joints after 1000cycles. (a) A change in contact resistance from 37to160mΩ, and (b) without changes in contact resistance (17mΩ)

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Figure 5

Crack initiation and growth along Ag flaks in ICA

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Figure 6

A 2D geometry model for FEM, showing the mesh for the whole and the local structure

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Figure 7

(a) Equivalent stress Seqv; (b) shear stress σxy distribution in ICA joints at temperature—45°C (unit: MPa)

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Figure 8

Calculated warpage on the top of chip surfaces

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Figure 9

Calculated stresses in ICA versus chip size for both the elastic (TD) and visoelastic model

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Figure 10

Log relationship between lifetime and calculated stress, and fitted linear equations as LogS=KLogN50%+M

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Figure 11

Relationship between Young’s Modulus of underfill and the lifetime of ICA joints

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Figure 12

Relationship between CTE of underfill and the lifetime of ICA joints

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