The VIC-3D Stereo Microscope Measurement System

Non-Contact Full-Field Microscopic Strain Measurement System

Exclusive distortion correction module for exceptional accuracy.

VIC-3D™ Microscope System Overview

The VIC-3D Micro system from Correlated Solutions is a highly accurate optical system for measuring surface shape, deformation, and strain on micro-scale specimens subject to an applied load. The high-magnification measurements are obtained by utilizing a stereo microscope combined with high-resolution digital cameras, a custom designed beam splitter, and a precision 3-axis motorized stage.  This turn-key solution is ideal for measuring everything from composite fibers to solder joints.

Technology Background

Traditionally, three-dimensional DIC measurements have been difficult to obtain on specimens where high magnification is required. This is due to the lack of optics with sufficient depth-of-field to acquire two high magnification images from different viewing angles. Stereo microscopes overcome the depth-of-field limitation, however, their internal construction prevents proper image distortion correction using traditional calibration methods. These uncorrected images will result in severely biased shape and strain measurement data. In fact, it is not uncommon to observe bias levels of several thousand microstrain.

To overcome this problem, Correlated Solutions has developed and an easy-to-use calibration method that corrects for the complex, non-radial, optical distortions present in stereo microscopes. The VIC-3D Micro calibration method computes and corrects for the non-parametric distortion fields of the stereo microscope, and has been shown to completely eliminate shape and strain bias from the measurements. Below is an example of the type of measurements achieved with the VIC-3D Micro system.


Application Example

Understanding the behavior of solder joints in IC Packaging components is essential to design a robust product. Using traditional measurement methods, such as extensometers or strain gauges, measuring the strength of solder joints is not a trivial task due to the size limitation of such devices. 3D Digital Image Correlation is an ideal tool for measuring the localized strain distribution, however, standard lenses only allow for 1:1 magnification, which makes the smallest field-of-view possible approximately 9mm. Furthermore, using standard lenses on two cameras positioned in stereo to optimize image overlap and achieve an acceptable depth-of-field adds to the complexity of the setup, which also increases the challenge to obtain reliable measurements. The VIC-3D Mirco System addresses both of these challenges by measuring full-field strain and deformation on fields of view from 0.7mm – 7mm. This innovative system simplifies the entire procedure for obtaining micro-scale measurements on the individual solder joints. The data from a tensile test with a soldered joint is shown below.

To prepare the digital image correlation system for testing, two 5.0 MP monochrome cameras were mounted to Correlated Solutions’ specially designed beam splitter. The beam splitter mounts to a zoom  body and provides rigid mounting for the stereo-rig as well as easy adjustment capability so that independent image overlap, focus, and stereo angle can be achieved. Attached to the zoom body is an objective lens with a fitted ring light. The stereo microscope system mounts to a 3-axis motorized or manual precision translation stage for exact position control.

The copper dogbone specimen was soldered together at the center of the gauge area. The solder region was 82 microns in thickness. The dogbone width was 3.0 mm, but here, a 1.0 mm region on the edge was analyzed so strain distribution through the solder could be investigated. This region is indicated in Figure 1. The sample was loaded in tension until failure and images were taken about every 2lbs of applied load. During the test, 23 image pairs were analyzed so that strain development could be observed and analyzed. Figures 3 and 5 show the y-axis (strain in the tensile loading direction) at the last image taken before failure.

Data extraction tools in Vic-3D enable the user to investigate global or user-defined local areas. Any of the variables may be extracted into plots and tabular data. In Figure 3, a line is drawn throughout the solder interface in the high strain region. Figure 4 displays the average y-axis strain within the user defined solder region. The red line in Figure 4 displays the strain for the last image taken before failure and the gray lines demonstrate how that strain developed throughout the test.

Load data was recorded through an analog signal and plotted against variables for global and user-defined local regions. Figure 6 displays the load vs. strain graph for the average global strain.

System Features

  • Field of view (zoom range): 0.8mm-7mm
  • Full-field measurements of 3D coordinates, displacements, velocities, and complete strain tensors
  • Automatic calibration
  • Image pairs can be automatically overlapped with a simple adjustment
  • Powerful tools for visualizing data
    • Contour displays which can be overlaid onto images of the test specimen
    • Data extraction from 3D plots based on user defined lines and circles
    • Post-processing tools for statistical analysis, stress-strain curves, and more
  • Convenient exporting of data with the FLEXPortTM data tool
    • Data can be exported in Tecplot/plain ASCII, Matlab, and STL formats
    • Node data can be easily extracted for FEA validation
  • One year of technical support and software upgrades
    • Live technical support is available Mon-Fri 9am-5pm EST
    • On-site support and consulting are also available
  • One-year replacement warranty for defects in materials and/or workmanship on all parts

More Information

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