Issue link: https://iconnect007.uberflip.com/i/1520213
74 SMT007 MAGAZINE I MAY 2024 sample. Figure 4 shows a conceptual image of the behavior of light in SM, and Figure 5 shows a contour pattern created by SM on one of the samples under test. Controls e following parameters were kept as con- trols during all phases of each test: • SM grating pitch: 200 lines per inch • Sample coating: White high temperature paint (for increased resolution) • Temperature profile: See Figure 3 • Sample support: Dark red high tempera- ture glass • Sample region of interest: Sample edges tracked during heating via automatic edge recognition technology, with an inset to the center of the outer solder ball row • Working distance from grating: 1.25 mm during acquisition, 3.75 mm during heat- ing and cooling • Temperature uniformity: Top and bottom heating and multi-zone oven used to mini- mize temperature variation from sample to sample and within individual samples. Variables Independent variables: • Moisture exposure • Sample type dependent variables: • Coplanarity gauge (highest point to lowest point) • 3S warpage gauge (coplanarity + sign des- ignation to indicate direction of curvature, including a "transition" category between positive and negative curvature) • Shape name gauge (samples placed into 1 of 9 defined shape categories) 3S warpage and shape names are further defined in the white paper, "Surface Mount Figure 4: Shadow moiré visual concept. Figure 5: Shadow moiré pattern.