Designing 2.5D Systems
By: Brian Bailey
Connecting dies using an interposer requires new and modified processes, as well as organizational changes.
As more designs hit the reticle limit, or suffer from decreasing yield, migrating to 2.5D designs may provide a path forward. But this kind of advanced packaging also comes with some additional challenges.
How you adapt and change your design team may be determined by where your focus has been in the past, or what you are trying to achieve. There are business, organizational, and technical challenges.
Functional verification traditionally has followed the V diagram, where after a partitioning phase, each piece is independently implemented and verified and then an integration with verification phase takes place to bring the pieces back together. “2.5D integration results in more complex verification strategies and practices, and a greater number of connectivity issues that need to be identified and solved,” says Vladislav Palfy, director of application engineering for OneSpin Solutions. “Verification must be tackled earlier in the process at the block level. Doing this will minimize the risk of bug escapes later that become more critical and harder to detect. It’s important to note that verifying expected behavior is not enough. For a design to be fully verified, making sure the absence of particular behaviors is required. To that end, it should also be pointed out that as these blocks get verified, the understanding of verification coverage also becomes essential. Precise metrics are needed to understand if the design from the block-level to the full SoC has been completely verified. Formal is the only method for ensuring the sanctity of connectivity, the possibility of proving absence of scenarios, as well as making sure coverage goals are met.”