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Research Papers

Detection of Solder Bump Defects in Electronic Packages Using Local Temporal Coherence Analysis of Laser Ultrasonic Signals

[+] Author and Article Information
Jin Yang

George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0405

I. Charles Ume

George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0405charles.ume@me.gatech.edu

J. Electron. Packag 131(1), 011013 (Feb 18, 2009) (11 pages) doi:10.1115/1.3068301 History: Received October 01, 2007; Revised May 05, 2008; Published February 18, 2009

Microelectronics packaging technology has evolved from through-hole and bulk configurations to surface-mount and small-profile configurations. Surface mount devices, such as flip chip packages, chip scale packages, and ball grid arrays, use solder bump interconnections between them and substrates/printed wiring boards. Solder bumps, which are hidden between the device and the substrate/board, are difficult to inspect. A solder bump inspection system was developed using laser ultrasound and interferometric techniques. This system has been successfully applied to detect solder joint/bump defects, including missing, misaligned, open, and cracked solder joints/bumps in flip chips, chip scale packages, and multilayer ceramic capacitors. This system uses a pulsed Nd:YAG laser to induce ultrasound in the electronic packages in the thermoelastic regime; it then measures the transient out-of-plane displacement response on the package surface using the interferometric technique. This paper presents a local temporal coherence (LTC) analysis of laser ultrasound signals and compares it to previous signal-processing methods, including error ratio and correlation coefficient methods. The results showed that LTC analysis increased measurement accuracy and sensitivity for inspecting solder bump defects in electronic packages. Laser ultrasound inspection results are also compared with X-ray and C-mode scanning acoustic microscopy results. In particular, this paper discusses defect detection for 6.35×6.35×0.6mm3 flip chips and flip chips (“SiMAF;” Siemens AG) with lead-free solder bumps.

Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Rectangular windowing function

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Figure 2

Diagram of laser ultrasound-interferometric inspection system

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Figure 3

Board layouts: (a) test vehicle Ι and (b) test vehicle II

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Figure 4

Schematic of open bump locations

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Figure 5

Excitation and detection patterns: (a) test vehicle Ι and (b) test vehicle II

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Figure 6

Time-domain responses of Sn–Pb flip chips at different intervals: (a) 0–164 μs, (b) 0–20 μs, and (c) 100–164 μs

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Figure 7

Local temporal coherence contours of (a) good chip, (b) chip with one open bump, (c) chip with two open bumps, (d) chip with three open bumps, and (e) chip with four open bumps

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Figure 8

Mean of local temporal coherence for Sn–Pb flip chips with open bumps (window width=20.48 μs and time increment=5.12 μs)

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Figure 9

Mean of local temporal coherence for Sn–Pb flip chips with open bumps: (a) (window width=10.24 μs and time increment=5.12 μs) and (b) (window width=20.48 μs and time increment=10.24 μs)

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Figure 10

LTC value at point No. 36 for Sn–Pb flip chips with open bumps

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Figure 11

(a) Mean values of MLTC and (b) value of MLTC at point No. 36 for Sn–Pb flip chips with open bumps

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Figure 12

One-way analysis of MLTC values of eight Sn–Pb test vehicles at two different times: (a) analysis of MLTC values at start time (time=0 μs) and (b) analysis of MLTC values at end time (time=164 μs)

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Figure 13

Top-down X-ray images of Sn–Pb flip chips: (a) good chip, (b) chip with one open bump, (c) chip with two open bumps, (d) chip with three open bumps, and ((e) and (d)) chip with four open bumps

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Figure 14

Ultrasonic signal and CSAM image of Sn–Pb flip chip at die-bump interface

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Figure 15

CSAM images of Sn–Pb flip chips at two adjacent layers: ((a) and (a′)) good chip, ((b) and (b′)) chip with one open bump, ((c) and (c′)) chip with two open bumps, ((d) and (d′)) chip with three open bumps, and ((e) and (e′)) chip with four open bumps

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Figure 16

Dye/pull images of Sn–Pb flip chips with open bumps: (a) pull result and (b) red dye penetration

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Figure 17

Cross section of Sn–Pb flip chip observed in microscopy

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Figure 18

Time-domain signals and power spectra of lead-free flip chip No. 1 (good chip) and chip No. 5 (defective chip)

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Figure 19

Mean values of MLTC for lead-free flip chips

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Figure 20

Top-down X-ray images of lead-free flip chips: (a) good chip and (b) chip with manufacturing defects

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