Siemens has published a white paper that examines whether package designers need to adopt IC tools and design styles in the move from organic packages to 2.5DIC packages that use much finer interconnect and silicon substrates.
Based on a paper presented at the IMAPS conference last year, “An organic package designer’s guide to transitioning to FOWLP and 2.5D design” covers the key changes package designers need to make but points that the migration does not require a wholesale change in tooling and methodologies though the novel forms of packaging offer opportunities for codesign and system-level optimizations. As a result, the paper argues, “A tool, such as Xpedition Substrate Integrator (xSI), that can plan, manage, and analyze an entire system early in the design process is clearly advantageous.”
However, even though the change to a silicon substrate may imply the need for packaging designers to learn dedicated place-and-route tools, the authors note that bringing information from a suitable process design kit (PDK) into EDA tools designed for packaging is an effective approach though there are some changes in how the silicon behaves compared to organic substrates.
For example, localized metal density plays a key role in controlling etch rates and the resulting widths of interconnect lines on each metal layer on the silicon die. However, density rules imported into a packaging-oriented tool with sufficient capacity can perform the necessary design-rule checks (DRC). This has the advantage of maintaining an interactive rather than script-controlled user interface as well as support for elements such as differential pairs and filled shapes that do not exist in the same way in IC design tools.
Additional tools such as Calibre3DSTACK implement checks to ensure consistency between package and the constituent ICs: whether bumps placed and oriented correctly, for example.
The paper, available from Siemens’ website, concludes: “In most cases system and packaging teams do not have to abandon their existing tool set to support these designs. In fact, the packaging design tool set can offer additional capabilities with respect to multi-component system design and component stacking better than an IC layout tool.”