Does anyone please know of any clever designs for 4-point bend rigs that can hold the load themselves (without a tensile test machine) and can uniformly distribute the load between all pins, even if small manfacturing misalignments are present? The samples will be reasonably small, about 70 mm long and up to 5 mm thick, and displacement would need to controllable at the 10-100 micrometre level. I'm envisioning some sort of system where the sample loading pins and some other levers and pivots create a mechanical linkage that constrains the rig to bend symmetrically when a bolt is turned. Or, if the rig is not actually constrained to bend symmetrically, it will have its lowest energy configuration when it does deform symmetrically.

Flip-chip plastic ball grid array (FC-PBGA) packages are widely used in high performance components. However, its die back is normally under tensile stress at low temperatures. This paper presents a probabilistic mechanics approach to predict the die failure rate in the FC-PBGA qualification process. The methodology consists of three parts:

1. die strength test using four-point bending (4PB) method;
2. the radius of curvature (ROC) measurement of the assembled FC-PBGA at room temperature;
3. Finite element method (FEM) stress analysis.