August_EDFA_Digital

edfas.org 33 ELECTRONIC DEV ICE FA I LURE ANALYSIS | VOLUME 24 NO . 3 resolution of most existing 2D or 3D x-ray tools. Because conventional, high resolution 3D x-ray tools are designed to inspect small packages, as sample size increases, the time to detect small defects in large packages or PCBs may increase to several hours or even days, rendering this application impractical. There is a growing awareness among governments, military, and defense contractors that electronic compo- nents may be manufactured in countries or by entities which could potentially insert additional surveillance circuitry (hardware Trojans) within the modules or boards. For national security, it is necessary to identify these circuits. More sowhen thesemodules or boards are used in critical infrastructure, communication devices, or military hardware. The logical choice is to use a nonde- structive technique such as a 3D x-ray imaging tool. X-ray microscopy (XRM) has been used with some success in reverse engineering to derive the CAD file in small PCBs. [5] However, there are several technical and practical issues in x-ray tomography that need to be overcome. One of the known problems of applying existing 3D x-ray imaging tools on large samples such as a flat package and PCB, is that of beam hardening artifacts. [6] These artifacts manifest themselves as streak lines or bands which obscure visualization of smaller defects in FA. For applications involving construction analysis and reverse engineering, these beam hardening artifacts also make image segmentation very tedious and perhaps impracti- cal. Image segmentation is the necessary first step in the workflow to convert a 3D image into a CAD file. [5,7,8] Other categories of defects which are notoriously dif- ficult to discern in x-ray imaging today include defects within the thin redistribution layers (RDL) in advanced packages and defects within low Z materials, including: delamination between Si die and underfill; bulk cracks in the underfill; Si die cracks; and voids within the underfill and in the epoxy. Most of these cat- egories of defects cannot be detected nondestructively by other existing tools either, such as optical metrology or scanning acoustic microscopes. This article describes the develop- ment of a novel laboratory-based 3D x-ray system that has been designed to surmount the existing hurdles in the FA and reverse engineering community. The tool acquires rapid high resolution 3D images of defects at 0.5 µm resolu- tion in intact, large semiconductor and electronic samples. Each scan can be done in as little as a few minutes, regardless of sample size. BREAKTHROUGH IN RAPID HIGH-RESOLUTION IMAGING FOR PACKAGES, PCBs, AND WAFERS A novel 3D x-ray system, the Sigray model Apex XCT 150, uses a combina- tion of many innovations to revamp the traditional approach in imaging semiconductor packages, PCB, and wafers down to submicron resolution. It uses a unique patent pending architec- ture, a high-flux source, high-efficiency detector and software algorithm, where 0.5 µm voxel acquisition time can be Fig. 2 Resolution target showing 0.5 µm spatial resolution in Apex XCT. Fig. 3 High-resolution scan is rapid and is not affected by sample size.