Development of a nondestructive inspection method for detecting open failures of micro bump interconnections in three dimensionally stacked LSI chips

We have proposed a new nondestructive evaluation method for detecting delamination between a chip and metallic bumps by measuring local surface deformation of the chip. The magnitude of the local surface deformation was analyzed using a three-dimensional finite element analysis. The local deformation of a silicon chip between adjoining two bumps is a strong function of the magnitude of the mismatch of the thermal expansion coefficient between bump material and underfill material. The amplitude of the local deformation due to the delamination of metallic bumps exceeds 200 nm easily, and it sometimes reaches 600 nm when the underfill material was assumed to be epoxy resin. To confirm that such estimated local deformation of a chip thinner than 100 μm appears in actual stacked structures, we applied a confocal scanning blue laser microscope to measure the local deformation. The measured local deformation was about 200 nm when the thickness of a chip was 100 μm, as was predicted by a finite element analysis. Therefore, it is concluded that a nondestructive inspection method for detecting open failures of bump interconnections in three-dimensional stacked structure has been established.