Inspection Method
Analytical technique used to measure the resistance of a small, localized area of a material to plastic deformation by a diamond indenter. Microhardness testing applies a precisely controlled low load, usually less than two kilograms, to the surface of a sample. The resulting indentation is measured under a microscope to determine the hardness value on scales such as Vickers or Knoop.
This method is particularly suitable for evaluating the properties of thin films, individual grains or small electronic components.
Hardness Calculation
Depth and area of the permanent impression left by the indenter serve as the basis for the final measurement. Because the loads are so small, microhardness testing can distinguish between the different phases within a solder joint, such as the soft tin matrix and the hard intermetallic compounds. The spacing between indentations must be sufficient to avoid the work-hardened zones created by previous tests.
Accurate results require a polished and flat surface to ensure the indenter strikes perpendicular to the sample.
Component Verification
Quality assurance teams use this method to check the tempering of copper leads or the hardness of nickel plating on circuit boards. Excessively hard plating can lead to brittleness and cracking, while overly soft plating may result in poor wear resistance for connector pins. Microhardness testing also identifies the extent of thermal softening that occurs during repeated reflow cycles.
If the hardness values fall outside the specified range, it suggests a problem with the material composition or the heat treatment. Localized material properties determine the overall performance of the assembly.
