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

Texas Tech University, Nivetha Shivan, May 2012
Figure 4.2: Warpage Measurement Setup [13]
In this diagram, z is the distance between the package and the grated glass plate, p is the
spacing between the grating lines, N is the fringe order which is the number of grating
lines between points A and B, � is the illumination angle and � is the observation
angle. We are interested in measuring the z (warpage), the distance between the grated
plate and the package at the four corners and also at the center. Then, the average of the
distance from the four corners are taken and subtracted from the distance from the
package center.
The sign of the convex warpage is defined as plus (+) while the sign of the concave
warpage is defined as negative (-) as shown in Figure 4.3. This sign convention holds
good for the top surface of the package (die side). There is no distinctive difference
between the moiré patterns produced by the packages with convex warpage and that
produced by the packages with concave warpage.
24