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RESEARCH PAPERS

Experimental and Numerical Investigation of the Reliability of Double-Sided Area Array Assemblies

[+] Author and Article Information
S. Chaparala

Department of Mechanical Engineering,  State University of New York, Binghamton, Binghamton, NY, 13902schapara@binghamton.edu

J. M. Pitarresi, S. Mandepudi

Department of Mechanical Engineering,  State University of New York, Binghamton, Binghamton, NY, 13902

S. Parupalli1

Department of Mechanical Engineering,  State University of New York, Binghamton, Binghamton, NY, 13902

M. Meilunas

 Universal Instruments Corporation, Binghamton, NY, 13905

1

Currently with Intel Corporation, Hillsboro, OR.

J. Electron. Packag 128(4), 441-448 (Feb 23, 2006) (8 pages) doi:10.1115/1.2353280 History: Received October 05, 2005; Revised February 23, 2006

One of the primary advantages of surface mount technology (SMT) over through-hole technology is that SMT allows the assembly of components on both sides of the printed circuit board (PCB). Currently, area array components such as ball grid array (BGA) and chip-scale package (CSP) assemblies are being used in double-sided configurations for network and memory device applications as they reduce the routing space and improve electrical performance (Shiah, A. C., and Zhou, X., 2002, “A Low Cost Reliability Assessment for Double-Sided Mirror-Imaged Flip Chip BGA Assemblies,” Proceedings of the Seventh Annual Pan Pacific Microelectronics Symposium, Maui, Hawaii, pp. 7–15, and Xie, D., and Yi, S., 2001, “Reliability Design and Experimental work for Mirror Image CSP Assembly”, Proceedings of the International Symposium on Microelectronics, Baltimore, October, pp. 417–422). These assemblies typically use a “mirror image” configuration wherein the components are placed on either side of the PCB directly over each other; however, other configurations are possible. Double-sided assemblies pose challenges for thermal dissipation, inspection, rework, and thermal cycling reliability. The scope of this paper is the study of the reliability of double-sided assemblies both experimentally and through numerical simulation. The assemblies studied include single-sided, mirror-imaged, 50% offset CSP assemblies, CSPs with capacitors on the backside, single-sided, mirror-imaged plastic ball grid arrays (PBGAs), quad flat pack (QFP)/BGA mixed assemblies. The effect of assembly stiffness on thermal cycling reliability was investigated. To assess the assembly flexural stiffness and its effect on the thermal cycling reliability, a three-point bending measurement was performed. Accelerated thermal cycling cycles to failure were documented for all assemblies and the data were used to calculate the characteristic life. In general, a 2X to 3X decrease in reliability was observed for mirror-image assemblies when compared to single-sided assemblies for both BGAs and CSPs on 62mil test boards. The reliability of mirror-image assemblies when one component was an area array device and the other was a QFP was comparable to the reliability of the single-sided area array assemblies alone, that is, the QFP had almost no influence on the double-sided reliability when used with an area array component. Moiré interferometry was used to study the displacement distribution in the solder joints at specific locations in the packages. Data from the reliability and moiré measurements were correlated with predictions generated from three-dimensional finite element models of the assemblies. The models incorporated nonlinear and time-temperature dependent solder material properties and they were used to estimate the fatigue life of the solder joints and to obtain an estimate of the overall package reliability using Darveaux’s crack propagation method.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

Double-sided assemblies

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Figure 2

Cross-sectional details of BGA and CSP assemblies

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Figure 3

Side view of 50% offset CSP assembly

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Figure 4

Typical backside chip capacitor array

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Figure 5

Test fixture for measuring coupon stiffness

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Figure 6

Octant symmetry finite element model of the single-sided BGA assembly

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Figure 7

50% offset CSP model

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Figure 8

Mixed assembly (BGA/QFP) model

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Figure 9

Decrease in assembly reliability versus increase in assembly stiffness for the CSP test coupons

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Figure 10

Typical measured cooling curve of an assembly

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Figure 11

Moiré horizontal displacement fringe pattern of single-sided BGA assembly (right side shown)

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Figure 12

Horizontal displacement Moiré fringe pattern of double-sided BGA assembly (right side shown)

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