Qualification of the Assembly Process of Flip-Chip BGA Packages ...

Texas Tech University, Nivetha Shivan, May 2012
angle. The moiré patterns are formed only when the package is curved or bent. If the
package is not curved, then moiré fringes will not be produced.
The moiré pattern is formed as a result of superimposing two images that have similar
spatial frequencies. It contains bright and dark fringes. The bright fringes are produced
when the etched lines on the glass plate fall directly on their shadows, similar to
constructive interference. The dark fringes are produced when the etched lines on the
glass are out of phase with their own shadows, similar to destructive interference. Figure
4.1 is an image of how a typical moiré fringe of a BGA package will look like. Figure 4.2
explains the setup for the warpage measurement.
Figure 4.1: Moiré Pattern of a BGA Package [12]
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