Correlated full-field and pointwise temporally resolved measurements of thermomechanical stress inside an operating power transistor

• Full-field temporal speckle interferometry synchronized to pointwise measurements.
• Wire bond bending is measured inside an operating microelectronic power device.
• Temporal unwrapping of discontinuous phase fields having large values.
• Deformation, temperature and electric parameters are measured concomitantly.
• Spatial and temporal derivatives of physical quantities are estimated.

The paper describes a measurement system based on time-resolved speckle interferometry, able to record long series of thermally induced full-field deformation maps of die and wire bonds inside an operating power transistor. The origin of the deformation is the transistor heating during its normal operation. The full-field results consist in completely unwrapped deformation maps for out-of-plane displacements greater than 14 μm, with nanometer resolution, in presence of discontinuities due to structural and material inhomogeneity.These measurements are synchronized with the measurement of heatsink temperature and of base-emitter junction temperature, so as to provide data related to several interacting physical parameters. The temporal histories of the displacement are also accessible for any point. They are correlated with the thermal and electrical time series.Mechanical full-field curvatures may also be estimated, making these measurements useful for inspecting physical origins of thermomechanical stresses and for interacting with numerical models used in reliability-related studies.