Calculation and Validation of Thermomechanical Stresses in Flip Chip BGA Using211 the ATC4.2 Test Vehicle

摘要

We report the first in situ measurements of thermomechanical stresses in a 1000211u001eI/O 250 (micro)m pitch piezoresistive flip chip test chip assembled to a 755 I/O 211u001e1.0 mm pitch 35 mm Ball Grid Array (BGA). The BGA substrates employed build-up 211u001edielectric layers containing micro-vias over conventional fiberglass laminate 211u001ecores. Experimental data, which include in situ stress and die bending 211u001emeasurements, were correlated to closed form and Finite Element Method (FEM) 211u001ecalculations. Cracking and delamination were observed in some of the experimental 211u001egroups undergoing temperature cycling. Through use of bounding conditions in the 211u001eFEM simulations, these failures were associated with debonding of the underfill 211u001efillet from the die edge that caused stresses to shift to weaker areas of the 211u001epackage.