Binghamton University

 

Shadow Moire'

Optical Measuring Technique

Shadow Moire'

Shadow-Moire Interferometry is a well established experimental technique that measures out-of-plane displacements (warpage). The sample is placed on a pedestal, and covered with a glass grating of a set frequency. A collimated light source is directed onto the sample from an angle of 45 degrees. A moire pattern is created from the interference of the grating and the shadow of the grating projected onto the sample.

The following are the characteristics of Shadow-Moire

  • Applied to surfaces as opposed to edges
  • Can be used as a function of temperature if sample and grating are placed in an oven. This allows for the simulation of reflow cycles.
  • Resolution is dependent on grating frequency. 1000 lines per inch (lpi) yields 1 mil per fringe order.
  • Post processing techniques allow for the use of Phase Stepping, which further enhances the resolution.
  • Resolution is still limited due to a "washing out" effect of higher frequency gratings.

 
  Examples:
 

 

(1)

Fringe Pattern seen in one of the package using Shadow Moire