Residual stress measurement through the thickness of ball grid array microelectronics packages using incremental hole drilling

Abstract

Microelectronic packages typically consist of several layers of polymer, silicon, and composite materials, which are bonded together under heat and pressure. The mismatch in thermo-mechanical properties between different layers can induce significant residual stresses in the fabrication process that may lead to delamination at the interface between the bonded layers. Therefore, it is important to develop a reliable method to determine residual stresses. In this study, incremental hole drilling method was used to determine fabrication-induced residual stresses in a ball grid array (BGA) microelectronics package. First, a small hole was drilled in several steps at the center of a strain gauge rosette bonded to the surface of the BGA package. This released residual stresses trapped at each depth increment and deformed the component. The corresponding surface strains were measured in three directions using rosette gauges. Then, the residual stress was calculated based on the integral method, in which the measured strains are converted to the residual stresses using a calibration matrix whose elements are obtained from a finite element model. The three in-plane components of the residual stress through the thickness of different layers of a BGA package, including molding compound, silicon chip, die attach, and the composite substrate, were reported based on the incremental hole drilling method. These findings show that the incremental hole drilling method can be used as a reliable method to estimate the residual stresses over the entire thickness of microelectronic packages, and evaluate their effect on the reliability under service conditions.