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Research Papers

A Novel Projection Moiré System for Measuring PWBA Warpage Using Simulated Optimized Convective Reflow Process

[+] Author and Article Information
Reinhard E. Powell

School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332

I. Charles Ume

School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332charles.ume@me.gatech.edu

J. Electron. Packag 131(2), 021006 (Apr 01, 2009) (6 pages) doi:10.1115/1.3103938 History: Received January 13, 2008; Revised November 05, 2008; Published April 01, 2009

The shadow moiré technique is a widely used method of measuring printed wiring board (PWB) warpage. It has a high resolution, high accuracy, and is suitable for use in an online environment. The shortcoming of the shadow moiré technique is that it cannot be used to measure PWBs populated with chip packages. In this paper, a novel warpage measurement system based on the projection moiré technique is presented. The system can be used to measure bare PWBs, as well as PWBs populated with chip packages. In order to use the projection moiré system to accurately determine the warpage of PWBs and chip packages separately, an automated chip package detection algorithm based on active contours is utilized. Unlike the shadow moiré technique, which uses a glass grating, the projection moiré technique uses a virtual grating. The virtual grating sizes can be adjusted, making it versatile for measuring various PWB and chip package sizes. Without the glass grating, which is a substantial heat inertia, the PWB/printed wiring board assembly (PWBA) sample can be heated more evenly during the thermal process. The projection moiré system described in this paper can also be used to measure the warpage of PWBs/PWBAs/chip packages during convective reflow processes. In this paper, the characteristics of the projection moiré warpage measurement system will be described. In addition, the system will be used to measure the warpage of a PWB and plastic ball grid array packages during a Lee optimized convective reflow process (Lee, N.-C., 2002, Reflow Soldering Processes and Troubleshooting SMT, BGA, CSP, and Flip Chip Technologies, Butterworth-Heinemann, MA). It is concluded that this projection moiré warpage measurement system is a powerful tool to study the warpage of populated PWBs during convective reflow processes.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 5

Integrated projection moiré warpage measurement system

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Figure 6

Calibration block used to verify accuracy of projection moiré warpage measurement system

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Figure 7

PWBA test vehicle

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Figure 8

Simulation of optimized convective reflow profile using projection moiré warpage measurement system

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Figure 9

Out-of-plane displacement plot of PWBA at 25°C before heating

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Figure 10

Out-of-plane displacement plot of PWBA at 183°C

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Figure 11

Out-of-plane displacement plot of PWBA at 210°C

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Figure 12

Out-of-plane displacement plot of PWBA at 25°C after cooling

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Figure 13

Example of sample surface with no rigid body motion present

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Figure 14

Examples of sample surface with rigid body motion present

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Figure 1

Schematic of projection moiré setup

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Figure 2

Moiré fringe pattern for bare PWB

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Figure 3

Phase image for bare PWB

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Figure 4

(a) Initial snake constructed around PBGA package; (b) snake converged around PBGA package

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