While most of us in advanced packaging is familiar with CEA-Leti, CEA-List ( Laboratoire d’Intégration de Systèmes et des technologies) is one of three specialized technological research institutes of CEA  specializing in digital systems.

Denis Dutoit, of CEA-List, presentation on “Chiplet Partitioning Can Balance Among Performance, Flexibility and Scalability” at the recent Chiplet Summit. He discussed chiplet partitioning as the new IC design paradigm. I especially liked the slides shown in Figures 1 and 2 for their simplicity in explaining the overall chiplet concept of disaggregation and reaggregation.

chiplet partitioning
Figure 1: System disaggregation and reaggregation for chiplet partitioning (Source: CEA-List)

Dutoit explains that system disaggregation consists of both functional and structural partitioning as shown in Figure 2.

chiplet partitioning
Figure 2: Functional and structural partitioning system disaggregation. (Source: CEA-List)

Reintegration (reaggregation) requires both advanced packaging technologies and die-to-die interfaces and protocols.

chiplet partitioning
Figure 3: Advanced packaging schemes for chiplet partitioning (Source: CEA-List)

Chiplet Partitioning Needs Heterogeneous Integration

Keith Felton of Siemens EDA discussed “Chiplet-Based Heterogeneous Advanced Packaging” and showed the project flow in Figure 4. He discussed the need to pivot from design-level to system-level optimization. He noted that using chiplets with advanced package brings multiple benefits including:

  • Lower wafer costs
  • Simpler die/chiplet designs
  • Lower power
  • IP reuse
  • Faster time-to-market
  • Better overall system performance
Figure 4: Chiplet-based HI project flow. (Source: Siemens EDA)

Siemens EDA and CEA-Leti Collaborate on Chiplet Warpage

A joint collaboration between Siemens EDA and Leti shared their thoughts on the impacts of warpage on chiplet-based modules.

Stresses can have both electrical impact (stress impact on the band structure of Si) and mechanical impact (Interconnect fracture – cracking of ULK/ ELK dielectrics, delamination; bump fatigue, and cracking). Stress is unavoidable due to the mismatch of materials’ thermo-mechanical properties. Local stress sources include solder balls and Cu pillars, TSVs, edges of neighbor die, etc.

Figure 5: Examples of warpage on chiplet-based modules.
  • Combining FEA simulations with layout analysis capabilities allows obtaining chip-package interconnect (CPI) stresses with any desired resolution, by applying a multi-scale simulation technique.
  • EDA methodology for assessment of CPI stress impact on circuits performance has been developed by linking stress analysis with SPICE simulations
  • For the purpose of mechanical failure analysis in the early stage of a package design, the warpage measurements can be used for the tool’s calibration.
  • Analysis of the CPI stress distribution in chip metallization is performed for the estimation of interconnect fracture probability; linked thermal-mechanical simulations – for operational stresses.

DFT for Chiplet-based HI and SiP

Figure 6: 3D Stacked IC test challenges.

Rajesh Pendurkar, from Capgemini (a French consulting company) discussed “DFT (design for test) for Chiplet-based Heterogeneous ICs and SiPs”. He noted the following 3D stacked IC test challenges:

  • DFT architectures need to be carefully planned from the bottom up
  • Test standards have typically focused on board-level testability (IEEE 1149.1)
    • Scan vectors using automatic test pattern generation
    • Built-in self-test (BIST) for memory and logic structures
    • The importance of known-good die (KGD)
  • Package level DFT
    • Integration of KGD implementing varying DFT techniques, ie: memory die interfacing with logic die.
    • Pre- and post-package test for large and dense arrays of inter die interconnects vertical interconnections using through silicon vias (TSVs)
    • Test pattern re-use from constituent chiplets
    • IO bandwidth costly repair
  • System level DFT

He then told us we should be using the four IEEE test standards 1149.1, 1500, 1687, and 1838 and that system DFT with chiplets requires top-down architecture and bottom-up implementation.

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Phil Garrou

Dr. Philip Garrou is a subject matter expert for DARPA and runs his consulting company…

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