edfas.org ELECTRONIC DEV ICE FA I LURE ANALYSIS | VOLUME 25 NO . 1 40 Li, Intel, indicated that for her lab they would like to use a single tool for the whole delayering process with high milling rates. Automating the process will be beneficial as well. Jim Colvin, FA Instruments, discussed backside thinning and critical issues during preparation. Colvin highlighted the non-planarity issueswhen exposingmultilayer dies. He revealed the successful thinningof theSi substrate of the die in a package by iterative RSTmeasurements and polishing to obtain a planar surface. He also emphasized thermal management during preparation such as having a local bath during the CNC process. Colvin extended the discussion by opening the floor for primer topics that of interest in the sample preparation community. A large number of attendees participated, generating discussions on measuring uniformity of sample preparation techniques, the preparation for SIL lens measurements, and multichip module discussion. Susan Li, Cypress Semiconductor, responded to a participant question regarding themultichipmodule that Sunday’s tutorial discussed, specifically on the through-silicon vias (TSVs). Overall, the sessionprovidedattendees aplatformto share their experiences and inquire about new techniques for their applications. ISTFA 2022 SYSTEM ON PACKAGE USER GROUP Chair/Co-Chairs: Bryan Tracy, Kevin Distelhurst, Lihong Cao, and Wentao Qin btracy@tesla.com, kevin.distelhurst@globalfoundries.com, lihong.cao@aseus.com, wentao.qin@onsemi.com Following the lead of ISTFA’s 2021 keynote speaker, Ravi Mahajan, Intel, entitled “AdvancedPackaging for Heterogeneous Integration,” the Systemon Package (SOP) UsersGroupaddressed the failure analysis demands of this technology by offering two invited speakers. Wentao Qin, ON Semi, reviewed the physics of laser ablation for failure analysis. He showed interesting examples of how the laser can be tuned to remove such diversematerials as polymers and copper ground planes. Opening silicon windows on the back side of flip chip packages for circuit edit was of special interest because this preparation method did not result in die cracking or chipping. A lively discussion ensued, with a focus on the analyst taking extra care to avoid exposure of the laser to the die surface. The consensus was, determine the safe depth of package removal using a sacrificial unit such that the final clearing of the molding compound could be done with a brief exposure to fuming nitric acid. This was deemed a useful and “die-safe” compromise to ensure the failure analysis could proceed to a successful conclusion. The principal concernwith the laser decapping process is that the silica beads in the packaging material can act as focusing lenses, channeling the laser energy into the die before the molding compound is fully removed. The SOPUsers Group is indeed indebted to Yan Li, Intel Corp., who provided, on very short notice, a delightful and thought-provoking surveyof thenumerous failureanalysis challenges for heterogeneous packages. First, Li identified three key packaging trends: die stacking, chiplets, andheterogeneous packaging itself. Themodern SOP is a slightly frightening combinationof package type andboard topography, with at least five types of interconnection. In terms of interconnect trends, Li presented some early results where Cu-Cu connections were used to replace solderbased joints. In terms of electrical fault isolation of SOPs, it is clear that the need for 3D EFA is increasing. Artificial intelligence (AI) continues to expand into failure analysis, with the opportunity to make improvements in defect detection, image noise reduction, and failure mode identification using clustering and pattern recognition. For large databases, it now seems possible to determine root cause by an intelligent querying of failure analysis reports. Instrumental advances such as GHz scanning acoustic microscopy look capable of identifying smaller defects nondestructively. Li concluded her talk by paraphrasing Richard Feynman, by saying “we would like to know the position of every atom and, by the way, its chemi- cal composition.” The session was a resounding success where the scarcity was time, and not a lack of questions or interest. The chairs are quite certain the SOPUsers Groupwill continue to be an annual affair at ISTFA. “...LI IDENTIFIED THREE KEY PACKAGING TRENDS: DIE STACKING, CHIPLETS, AND HETEROGENEOUS PACKAGING ITSELF.”
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