August_EDFA_Digital

edfas.org ELECTRONIC DEV ICE FA I LURE ANALYSIS | VOLUME 24 NO . 3 34 completed in as little as 3-5 minutes in any part of the package, board, or 300 mm wafer (Fig. 1). This 3D x-ray system architecture uses a modified laminography system called angled CT, which allows the regionof interest (ROI) of a sample tobe held in such away and rotated at 360°, at a very short distance to the x-ray source. This leads to two important advantages. First, it offershigh imaging speedbecause the source-ROI distance is minimized (throughput is inversely proportional to the square of the source to ROI distance due to the inverse square law). Second, anefficient x-raydetectorwitha thick scintillator, such as a flat panel detector, can be used. In contrast to the scintillator-optical-CCD detector in conventional XRM, a flat panel detector with a thick CsI scintil- lator, as used in this 3D x-ray system, is about 10 times more efficient than a scintillator and lens coupled detector. The detection system of this x-ray tool has been carefully optimized for high- resolution, high-throughput operation at voltages up to 160 kVp and power up to 25W. Legacy XRM systems rely on thin scintillators for high-magnification imaging, which are highly inefficient at the high energies needed in semi- conductor package and PCB applica- tions. Featuring 0.5 µm (Fig. 2) spatial resolution anywhere on samples up to 300 mm in diameter, this 3D x-ray system will dramatically improve FA workflows by opening the possibility of imagingwhole intact packages, wafers, and PCBs, mitigating time-consuming and destructive sample preparation protocols. Acquisition times required to scan a larger field of view of the sample at lower resolution is similar to those of a submicron resolution scan. Likewise, the time to scan at submicron resolu- tion does not vary with sample dimen- sion, as shown in Fig. 3. MATERIALS AND METHOD This articledemonstrates thequality of imaging data obtained from intact advanced packages, PCBs, and 300mm wafers using the novel Apex x-ray sys- tem. To benchmark the performance Fig. 4 The package after stress test was scanned at 1.7 µmvoxel with a field of view of 5.0 x 3.9 mm to capture several BGAs. It was followed by rescanning the region of interest at 0.7 µmvoxel with a field of viewof 2.1 x 1.6mmto reveal details of BGA cracks. Each scan was acquired in 30 min. of this tool against conventional XRM, it is also compared with another tool, Sigray model PrismaXRM. The utility of the tool to image difficult-to-image features, for example, RDL in heterogeneous packages; rapid defect characterization of BGAs after a burn-in test of a package module; cracks in traces, voids in organic layer; delamination in the UBM, and non-wet defects is also described. Warpage within a device or PCB which causes local stress and strain resulting in failures can also be detected with this tool. Another application requiring high-resolution imaging with high throughput is construction analysis and reverse Fig. 5 Detecting cracks inRDL interface at progressively increasing resolutiondown to 0.3 µm resolution. Each field of view was set at 2.5-hr exposure time.