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96 I-CONNECT007 MAGAZINE I MARCH 2026 Design Strategy for the 2.5D Interposer A typical 2.5D interposer application may sup- port the interconnect of one or more very-high- terminal-density semiconductor or multiple, related die elements. While the upper surface of the 2.5D interposer accommodates most semiconductor re- distribution and the die-to-die interface, the primary I/O channels and power and ground terminals are located on the bottom surface of the interposer. Limiting the semiconductor package size is a challenge, especially for portable and hand-held electronic applications. Another factor is the quan- tity, size, and pitch of the interface terminals. The base structure (interposer material) selected must also be mechanically stable and physically strong enough to withstand elevated process tempera- tures experienced throughout the entire package assembly process. Base material and process attri- butes for the three preferred interposer variations are outlined in Table 2. Although the overall circuit density potential of the 2.5D interposer is considerably greater than that of mainstream HDI circuit boards, commercial CAD tools are available to accommodate most very-high-density (VHD) interposer development. Package assembly process methodologies can vary a great deal, but several key issues will need to be resolved prior to beginning interposer design: • Selecting of suitable semiconductors for mul- tiple chiplet die packaging • Establishing sources for semiconductor wa- fers or glass-based panels • Specifying the environmental operating con- ditions • Defining package design constraints and process protocols • Stipulating electrical test method and post assembly inspection criteria D2D and D2W (interposer) Joining Methods A goal for a growing segment of the industry is to vertically stack memory die elements. Such stack- ing allows for dramatically higher levels of inte- gration for commercial and consumer electronics applications. The following will outline two joining D ES I G N E R 'S N OT E B O O K TABLE 2: MATERIAL AND PROCESS ATTRIBUTES FOR ORGANIC, SILICON, AND GLASS INTERPOSERS