Development of B-spline X-ray Diffraction Imaging techniques for die warpage and stress monitoring inside fully encapsulated packaged chips

Advanced packaging is a key “More than Moore” (MtM) enabling technology [1]. In all of these advanced packaging processes the semiconductor die are becoming much thinner (e.g. 25-50 μm thick) and many packages include multiply stacked silicon die. This leads to very thin packages where there is a trade-off between the thickness of constituent package layers and their rigidity, thus leading to reliability problems. Currently there are no compelling metrologies that can non-destructively measure the stress and/or warpage of the semiconductor die inside these packaged chips. Furthermore, since the thermal processing of these packages leads to the generation of thermal/mechanical stresses a new metrology, which is capable of real-time, or near real-time, monitoring of the generation or amelioration of these stresses during the thermal processing, would be a major advantage. In this study, we report on recent advances in the development of a new technique, which we describe as B-Spline X-Ray Diffraction Imaging (B-XRDI), which produces a reconstruction of strain field and/or lattice misorientation data from x-ray diffraction data/images of the in situ semiconductor die inside a test wirebonded encapsulated BGA package. High-speed digital x-ray topography images are captured at a synchrotron source (ANKA, Germany and Diamond, UK) in times as short as 8 seconds for a full 8 mm × 8 mm semiconductor die inside the fully encapsulated packages. Using a laboratory-based source (Jordan Valley Bede D1 High Resolution X-Ray Diffractometer) and applying the B-Spline technique, maps are also produced of the entire silicon die, which reveal warpage via measurements of x-ray rocking curve full-widths-at-half-maximum (FWHM) as a function of position across the encapsulated packages. These maps are also correlated with warpage measurements performed by mechanical and interferometric profilometry and finite element modelling (FEM).