Refined Micro Moire System and its Applications to Chip Scale and Flip-Chip Packages

Abstract

Abstract The chip scale package (CSP) and flip-chip (FC) technologies are currently developed by electronic industry for high performance, high density and miniaturized assembly applications. The reliability of these packages continues to be a major concern due to the increase of die size, circuit density, and operating temperature. Moiré interferometry is a full field optical method, which can be used for the thermal mechanical deformation measurement of electronic packages and packaging materials. By using ordinary moiré interferometry, fringes represent displacement contour of 417 nm. In most cases, in a solder bump of CSP and FC packages, the thermal mechanical deformation is usually only 2 or 3 fringes (with relative displacement of about 1.2 μm), but the local strain of the bump is high because of the small size of the bump. It is difficult to resolve the local strain value for ordinary moiré interferometry, which can only resolve strain values averaged over a relative larger area. Based on high magnification and phase shifting method, refined micro moiré interferometer is expected to have a localized sensitivity and resolution for localized strain measurements. By using high precision close-loop controller for phase shifting in the refined moiré system, excellent results were obtained in the thermal mechanical deformation study of CSP samples and in the study of the solder bump mis-registration effect of FC samples. The results also showed that refined micro moiré method is effective in resolving deformation within a small area like a corner of a C4 bump.