mTest-a new approach to measure material properties from microscopic specimens

Thermo-mechanical reliability analysis for advanced electronic packaging requires additional material testing approaches. A new approach based on image correlation algorithms has been tested and established as the mTest method. It allows one to measure strains on microscopic images picked up from test specimens. These average strains over microscopically small areas can be used to determine different kinds of material properties, where strain values are required as essential input data. The method has been introduced by an automated measurement system for the determination of CTE values and Poisson ratios. The authors present measurement results for CTE values on composite materials like flip chip underfills as well as on thermoplastics with anisotropic CTE behavior. The mTest equipment and the achievable measurement capability are demonstrated. A discussion of typical CTE measurement errors illustrates how to provide adequate measurement data for real material behavior. The advantage of mTest measurements over classical TMA is shown for the CTE determination on flip chip underfill materials.