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52 DESIGN007 MAGAZINE I OCTOBER 2019 Semiconductor developers continue to offer greater functionality and performance within very small, high-I/O, silicon-based die elements. To meet user demands, these same developers will rely on a growing number of innovative so - lutions for IC packaging and interconnect. Ad- ditionally, to enable even greater system-level functionality, companies are successfully inte- grating two or more already-proven functional elements within a single-package outline (Fig- ure 1). This capability has been motivated by the need for maximizing package miniaturiza- tion, enhancing product performance and to ac- commodate the rapid deployment of new prod- ucts where time to market can be the difference between leading and following. A primary challenge to the PCB design pro- fessional is how best to interconnect these new generations of very fine-pitch, high-I/O semi- conductors. Current examples include a semi- conductor die with a terminal pitch range of 40–60 µm (~0.0016–0.0024") and a terminal geometry as small as 20–30 µm (~0.0008– 0.0012"). Although the individual die elements may be furnished with a uniform array termi- nal format, the terminal size and pitch are of- ten far too small for conventional PCB fabrica- tion capability. Recognizing this issue, companies develop- ing the more advanced computing products are relying more on adopting CTE-matching di- electric materials for the high-density interpos- ers required for redistributing the semiconduc- tor's narrow terminal pattern to a wider termi- nal format. The interposer (commonly referred to as 2.5D) enables the expansion of the IC's terminal pattern to a pitch that is more com- pliant with the technical limitations for man- ufacturing commercial epoxy-glass laminate- based circuit structures. Further, for the sys- tem-in-package (SiP) applications where it is necessary to mount and interconnect two or Design Challenges for Developing High-density 2.5D Interposers, Part 1 Designers Notebook by Vern Solberg, CONSULTANT Figure 1: Multiple die system-level package application utilizing proven elements from varied supplier sources.