Experimental Validation and Finite Element Simulation of a 64 Lead TQFP and a 68 Lead PLCC

Finite element analysis (FEA) of electronic packaging has expanded in the last few years. Analyses have increased in number and model complexity. There continues to be, however, a lack of acceptance of the analytical results. The uncertainty is due to unknowns about the real condition of the model regarding separation at materials interfaces, cracks, and material behavior at critical temperatures. Acceptance is gained when FEA results are supported by experimental validation. Two experimental techniques, piezoresistive stress chip and laser moiré interferometry, are used to quantify the stress and deformation fields in electronic packaging. The Sandia Mechanical Stress Test Chip, a piezoresistive device, was molded into a 68 lead PLCC to measure the effects of the die attachment process and encapsulation process on the die surface stress distribution. Stresses in the chip produce resistance changes in the array of sensors on the chip surface revealing the stress distribution on the chip. Laser moiré interferometry was used to measure deformation of a 64 lead thin quad flat pack (TQFP) and a 68 lead plastic leaded chip carrier (PLCC). Laser moiré interferometry is an optical technique providing whole field in-plane displacement contour maps. These measurements are compared with die surface stress and package distortion calculated using FEA.