Coplanarity Measurement
Optical surface profiling of substrate flatness is conducted by projecting a reference grating onto a component and observing the interference pattern created by its shadow. High-resolution shadow moiré systems utilize these fringe patterns to measure out-of-plane displacement across the entire surface of an electronic package. This technique enables non-contact, full-field warpage evaluation of printed circuit boards and silicon dies.
Metrological Accuracy
Sourcing reliable warpage data requires a high-precision glass grating with a known line density that is calibrated against primary dimensional standards. In a shadow moiré system, the resolution of the height measurement depends directly on the angle of incidence of the light source and the pitch of the grating. Environmental vibrations and airflow can disturb the fringe patterns, introducing measurement noise that requires digital filtering.
Continuous calibration of the camera and light source maintains measurement accuracy.
Grating Alignment
The distance between the physical grating and the component must be tightly controlled during the test sequence. If this gap is too large, the shadow loses contrast and the fringe pattern becomes too blurry to resolve.
Thermal Sweep
Integrating a thermal chamber allows researchers to observe dynamic warpage as the component undergoes heating and cooling cycles. This measurement is necessary for predicting solder joint defects that occur during assembly reflow. The captured shadow moiré data help engineers optimize substrate material selection by identifying the temperature points where maximum thermal expansion mismatch occurs.
Accurate temperature profiles ensure that the laboratory measurements correspond directly to the conditions found in industrial reflow ovens.
