Using White Light Interferometry for Mesoscale Part Inspection

Measurement of LIGA parts is critical for characterization and understanding of process variables. Traditionally, measurement using coordinate metrology consists of collecting data points from all of the surfaces of a part (e.g., three dimensional data) and comparing these points with target geometry as defined in a CAD file. Systems such as coordinate measurement machines and laser scanners are often used to collect the data. Unfortunately, three dimensional data collection has proven to be quite difficult for mesoscale parts, such as those created using the LIGA process. The inspection techniques used for larger parts cannot be used for parts of this scale because of physical limitations or poor resolution. This paper targets the use of white light interferometry for the analysis of micro-components produced using the LIGA and stereolithography processes. Both of these processes often create parts that are designed to have a constant cross section with planar top and bottom surfaces. Assuming this geometric relationship holds true, the analysis of just the top or bottom surface of the part can provide useful information pertaining to process capability and part geometry. White light interferometry is well-suited to the measurement of these planar surfaces. This paper will discuss techniques used to analyze two dimensional part parameters using white light interferometry in combination with image processing techniques. Several case studies are included to show the abilities of the measurement and processing methods.