Research Papers

Damage Initiation and Propagation in Voided Joints: Modeling and Experiment

[+] Author and Article Information
Leila Jannesari Ladani

Department of Mechanical and Aerospace Engineering, Utah State University, Logan, UT 84341ladani@engineering.usu.edu

Abhijit Dasgupta

Department of Mechanical Engineering, University of Maryland, College Park, MD 20742

J. Electron. Packag 130(1), 011008 (Feb 04, 2008) (11 pages) doi:10.1115/1.2837562 History: Received February 01, 2007; Revised August 29, 2007; Published February 04, 2008

This study examines damage initiation and propagation in solder joints with voids, under thermomechanical cyclic loading. An accelerated thermal cycling test is conducted on printed wiring assemblies (PWAs) containing 256 input/output (I/O) plastic ball grid arrays (PBGAs) with voided solder joints. Destructive and nondestructive failure analyses of the solder balls are used to detect the presence of voids and to relate the extent of damage propagation to the number of thermal cycles. Particular cases of voided and damaged joints are selected from these tests, to guide the development of a strategy for modeling damage propagation, using a three dimensional global-local finite element analysis (FEA). The displacement results of the global FEA at the top and bottom of the selected solder balls are used as the boundary conditions in a local FEA model, which focuses on the details of damage initiation and propagation in the individual solder ball. The local model is error seeded with voids based on cases selected in experiment. The damage propagation rate is monitored for all the cases. The technique used to quantify cyclic creep-fatigue damage is a continuum model based on energy partitioning. A method of successive initiation is used to model the growth and propagation of damage in the selected case studies. The modeling approach is qualitatively verified using the results of the accelerated thermal cycling test. The verified modeling technique described above is then used for parametric study of the durability of voided solder balls in a ChipArray Thin Core BGA with 132 I/O (CTBGA132) assemblies, under thermal cycling. The critical solder ball in the package is selected and is error seeded with voids with different sizes and various distances from damage initiation site. The results show that voids in general are not detrimental to thermal cycling durability of the CTBGA132 assembly, except when a large portion of the damage propagation path is covered with voids. Small voids can arrest the damage propagation, but generally do not provide a significant increase in durability because the damage zone deflects around the void and also continues to propagate from other critical regions in the solder ball.

Copyright © 2008 by American Society of Mechanical Engineers
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Figure 1

Damage propagation algorithm using method of “successive initiation”

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Figure 2

Example of damage contour plots for local model of solder ball undergone thermo-mechanical cycling through Steps 1–10 of SI

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Figure 3

Global FEA model for one-quarter of PBGA256 assembly, with applied boundary conditions

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Figure 4

Average damage calculated using FEA for 64 balls in the quarter package of BGA with 256 I/O and illustration of the cases selected for local modeling

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Figure 5

Mesh convergence conducted for the critical solder ball

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Figure 6

(a) 3D local model: (b) contour plot of damage based on EP model

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Figure 7

SI comparison between Cases 1 and 5; solder ball with big void in the middle and solder ball without void

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Figure 8

Damage propagation length normalized with respect to total path length

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Figure 9

Damage growth in solder joint with small void at initiation site

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Figure 10

Qualitative comparison between crack length developed in experiment and predicted by FEA

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Figure 11

Cross-sectioning planes parallel to the edge of the package

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Figure 12

(a) Die and pry of a damaged joint showing circumferential development of damage; (b) FEA analysis showing the circumferential development of damage

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Figure 13

Global-local modeling for parametric study of voids

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Figure 14

(a) Cases studied for influence of size; (b) void distance varied with respect to initiation site; (c) location of void from top side view

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Figure 15

Damage contours sites predicted by EP method, showing damage initiation site in (a) unvoided joint and (b) joint with small void at the initiation site

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Figure 16

Damage initiation, propagation, and total life, normalized with respect to results for a void-free joint

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Figure 17

Normalized life with respect to unvoided joint for small void placed in different locations on damage propagation path




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