Directional Vector
The angular direction of the maximum normal strain relative to the reference axis of a strain gauge rosette defines the primary vector of mechanical deformation. Knowing the principal strain angle is necessary to understand how external forces are acting on a circuit board during assembly steps like depaneling or ICT. This value is calculated from the three strain values collected by a rosette using circle-stress mathematics.
Identifying where the stress originates allows engineers to adjust the process to protect fragile components.
Deformation Analysis
When a circuit board undergoes bending, the forces propagate in complex paths dictated by the board geometry and mount locations. The principal strain angle reveals whether the board is experiencing simple bending, twisting, or complex multi-axial distortion. If the angle aligns with the long axis of a ceramic capacitor, the component is at a much higher risk of cracking.
Adjusting the tooling or component placement can reorient the board’s response to external loads.
Process Alignment
Comparing the measured direction of strain with the axis of mechanical clamping fixtures identifies misalignment in the machine setup. This principal strain angle helps isolate the specific clamp or pin that is applying unbalanced force to the board. Correction involves adjusting the fixture to ensure a uniform pressure distribution.
