ABSTRACT
Synchrotron radiation micro-tomography (SRµT) is a non-destructive three-dimensional (3D) imaging technique that offers high flux for fast data acquisition times with high spatial resolution. In the electronics industry there is serious interest in performing failure analysis on 3D microelectronic packages, many which contain multiple levels of high-density interconnections. Often in tomography there is a trade-off between image resolution and the volume of a sample that can be imaged. This inverse relationship limits the usefulness of conventional computed tomography (CT) systems since a microelectronic package is often large in cross sectional area 100-3,600 mm(2), but has important features on the micron scale. The micro-tomography beamline at the Advanced Light Source (ALS), in Berkeley, CA USA, has a setup which is adaptable and can be tailored to a sample's properties, i.e., density, thickness, etc., with a maximum allowable cross-section of 36 x 36 mm. This setup also has the option of being either monochromatic in the energy range ~7-43 keV or operating with maximum flux in white light mode using a polychromatic beam. Presented here are details of the experimental steps taken to image an entire 16 x 16 mm system within a package, in order to obtain 3D images of the system with a spatial resolution of 8.7 µm all within a scan time of less than 3 min. Also shown are results from packages scanned in different orientations and a sectioned package for higher resolution imaging. In contrast a conventional CT system would take hours to record data with potentially poorer resolution. Indeed, the ratio of field-of-view to throughput time is much higher when using the synchrotron radiation tomography setup. The description below of the experimental setup can be implemented and adapted for use with many other multi-materials.
Subject(s)
Imaging, Three-Dimensional/methods , Synchrotrons , Phantoms, Imaging , Tomography, X-Ray ComputedABSTRACT
Phase transformations that occur in both the heat-affected zone (HAZ) and the fusion zone (FZ) of a carbon-manganese steel spot weld have been investigated using time-resolved X-ray diffraction (TRXRD) with time resolutions down to 50 ms. It is found that in both zones the gamma(f.c.c.) --> alpha(b.c.c.) transformation on cooling is twice as fast as the forward transformation of alpha --> gamma on heating. Profile analysis of the major Bragg reflections recorded in the TRXRD patterns reveals similarities and differences in the microstructural evolution with time in the HAZ and in the FZ. The latter undergoes melting and solidification in addition to solid-state transformations. With increasing temperature, the (110) d-spacing of the alpha phase prior to and during the alpha --> gamma transformation and the (111) d-spacing of the gamma phase just after the same transformation exhibit a decrease. The observed (and unusual) lattice contraction with temperature rise may be attributed to chemical effects, such as carbide precipitation in the alpha matrix, and/or mechanical effects due to stress relief. In the FZ, the gamma-Fe that forms has a preferential (200) texture on solidification of the liquid, whereas, on cooling in the HAZ, the gamma-Fe retains largely a (111) texture that is induced in the alpha --> gamma transformation on heating. On cooling in the HAZ, the width of the gamma(111) reflection increases initially, which is indicative of microstrain developing in the f.c.c. lattice, but decreases as expected, with a reduction of thermal disorder, on further cooling until the completion of the gamma --> alpha transformation. In the FZ, however, the microstrain in the gamma phase increases steadily on solidification and more rapidly for the duration of the gamma --> alpha transformation on further cooling. The final microstructure of the FZ is likely to consist of a single alpha phase dispersed in two morphological entities, whereas in the HAZ the alpha phase persists in one morphological entity in the final microstructure.
