A nondestructive evaluation system for detecting open failures of micro bump interconnections in 3D-stacked structures

A nondestructive evaluation system for detecting delamination between a chip and micro bumps in 3D-stacked structures is indispensable for highly reliable and low-cost manufacturing. In stacked structures, it is hard to inspect the adhesion condition of metallic bumps that connect a lower chip with an upper chip because most of the bumps are invisible. We have, therefore, proposed a new nondestructive evaluation method for detecting delamination between a chip and metallic bumps by measuring the local surface deformation of the chip. We have already validated that the local deformation of thinned chips significantly increases when the defects such as a lack and delamination of bumps occur. In this research, the theoretical limit of the minimum detectable gap of the delamination was analyzed using a finite element method. It was found that 1 μm-thick delamination can be detected. In addition, to improve the accuracy of this evaluation method, noise factors that affect the amplitude of the local surface deformation of a chip were discussed and the noise reduction algorithm was proposed based on the analytical results. For example, the effect of the fluctuation of bump height can be eliminated by analyzing the difference of local deformation between before and after underfill filling. In order to validate the effectiveness of this inspection method for detecting open failures in 3D-stacked structures, we made test area-arrayed 3D-stacked chips and measured the local deformation at a surface of the test chips. It was confirmed that the defects of the bump interconnections could be detected precisely by measuring the change of the amplitude in 3D-stacked structures. Therefore, we concluded that a nondestructive evaluation system for micro bump interconnections in 3D-stacked structures has been established successfully.