Issue link: https://iconnect007.uberflip.com/i/1524755
AUGUST 2024 I SMT007 MAGAZINE 59 Figure 8 shows an overall cross-section image of the same location presented by CT scan. It presents one failed CTBGA228, which showed signs of failure initiation at 2,188 cycles. Failed CTBGA assembly separated and submitted for cross-section and dye-and-pry analysis. Cross- section along the edge of the device did not show major anomalies in the interconnect any- where along the outer row. Dye-and-pry analy- sis revealed significant solder ball disconnects, specifically in the middle and inner rows of the BGA. Following the results of dye-and-pry, a second cross-section plane was performed on the second row of the CTBGA228. Most of the solder balls on the second plane cross-section exhibited near-complete cracking through the solder ball. A failed CABGA208 SnPb assembly was evaluated by micro-sectioning for further failure verification, which failure was estab- lished by continuous daisy-chain resistance monitoring. Figure 9 shows a typical shear fail- ure for an "As Received" condition that showed a fine, straight crack path at the package side. Crack initiated at the balls under the corner die edges that are shown to be the most suscepti- ble to cracking due to the highest CTE mis- matches. Figure 7: CT image of area of interest for failed CTBGA228. Figure 8: Cross-section and dye-and-pry images for CTBGA228 assembly at 3,000 biased cold TCs, which failed at 2188. Failures were in solder and at the package side.