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Inspection and Metrology for 2.5/3D Interconnect
Keywords: inspection, metrology, 3D Interconnect
Package-level assembly requires handling 50-100 µm thick die and interposers patterned with microbumps with diameters and pitches as small as 20 µm and 40 µm, respectively. These aggressive die thicknesses, bump diameters, and gap sizes, as well as the use of multi-tier stacks, place new demands on inspection metrology to identify defective bond joints and underfill defects. SAM and 3D x-ray are critical techniques required for outgoing and incoming inspection strategies of 3D interconnect devices. Scanning acoustic microscopy can classify defects using the acoustic signature, while the time-of-flight indicates the depth at which the defect is located. Such tools can detect defects much smaller than their theoretical resolution limits by scanning at a spatial increment that is half the beam diameter. Combined with the application of a small beam diameter and higher frequency, resolution can be significantly improved. Several types of defects were detected in a HyperBGA die assembly including voids and missing bumps, defects at the first interface between the controlled-collapse chip connection (C4) bump and the overlaying die attachment, voids in the underfill volume, and defects at the second interface between the C4 bump and the organic substrate. X-ray inspection and metrology tools can perform geometric magnification imaging, depending on the sample geometry and size of the sample and its proximity to the X-ray source during the full 360° computed tomography (CT) scanning rotation. While 2D X-ray analysis is acceptable for single-layer devices, the complexity of die stacks and the interference of multiple metallization layers reduce the value of information in the images. CT analysis is essential for complex devices as the ability to rotate to any plane increases information content and reduces the effect of interference from multiple metal layers. This presentation will include several examples of 3D inspection and metrology techniques that were applied to die assemblies.
Victor Vartanian, 3D Interconnect Division
Albany, NY

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