Quantifying Strain Gradients in Dense Circuit Board Assemblies
Quantifying dynamic strain gradients and rate-dependent tensile limits around dense BGA corners prevents latent dielectric pad cratering during assembly.
Stacked Strain Gage
Multiaxial Transducer
Sensor configurations consisting of two or more independent measuring grids bonded atop one another allow for the determination of strain in multiple directions at a single point. The stacked strain gage occupies a smaller surface area than a planar arrangement. It is used when space on the circuit board is limited by high component density.
Data Collection
Each layer of the stacked strain gage measures the deformation along a specific axis without the need for lateral spacing between the sensors. In pcb testing, the stacked strain gage captures the complex stress state near a bga component during lead free reflow or mechanical shock. This arrangement minimizes the errors caused by strain gradients across the board surface.
The vertical offset between the grids is accounted for during the data analysis to ensure the accuracy of the principal stress calculation.
Precision Loading
Careful installation is required to ensure that the adhesive layer between the grids does not introduce excessive thickness or damping. A stacked strain gage provides the resolution required for validating finite element models in small form factor devices. The sensor remains the preferred tool for high density assembly validation where surface real estate is at a premium.