3D IC Clock Tree Synthesis for Low Cost Pre-Bond Testing
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Solution Overview
Problem
Pre-bond testing of 3D integrated circuits faces challenges due to the need for complete 2D clock trees across multiple tiers, leading to long wirelength and high clock power consumption, as well as complex testing requirements with multiple probe pads, which increase design-for-testing costs.
Innovation Solution
A fully connected 2D clock tree on a backbone die and multiple isolated 2D clock trees on non-backbone dies, connected using a Detachable tree (D-tree) with multiple through-silicon-vias, allowing for pre-bond testing with a single clock probe pad and subsequent removal of the D-tree for post-bond operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a complete 2D clock tree is built on each individual die with a single TSV connection, then pre-bond testing can be enabled, but wirelength increases and clock power consumption increases due to additional buffers
Solution Approach 1:
The clock tree on non-backbone dies is segmented into multiple isolated 2D clock trees that are disconnected after pre-bond testing. During pre-bond testing, these segmented trees are connected via D-tree to enable single-probe testing. After testing, the connections are severed, eliminating the need for buffers and reducing clock power consumption in the final product.
Solution Approach 2:
The D-tree connections and transmission gates are preliminarily configured to enable pre-bond testing before the actual bonding process. The transmission gates are initially enabled to connect the segmented clock trees, allowing test access. After pre-bond testing completes successfully, the transmission gates are disabled to remove the D-tree from the clock distribution network, optimizing post-bond performance.
2Device complexity
If multiple TSVs and an R-tree are used to connect non-backbone dies, then a single clock probe pad can be used for pre-bond testing, but DFT cost increases due to transmission gates requiring global connections
Solution Approach 1:
The clock tree is segmented into multiple isolated 2D clock trees on non-backbone dies, connected during pre-bond testing via a segmented D-tree structure using multiple TSVs. After pre-bond testing, these segments are disconnected, eliminating the need for expensive transmission gates and global control connections required by traditional R-tree approaches.
Solution Approach 2:
The D-tree connection structure is extracted and removed from the clock distribution network after pre-bond testing by disabling transmission gates and burning fuses. This extraction eliminates the DFT overhead of maintaining permanent R-tree connections with transmission gates, reducing DFT cost while preserving the benefit of single-probe pre-bond testing capability.
3Device complexity
If a single TSV connects 2D clock trees on adjacent dies, then the structure is simple, but wirelength increases and more buffers are needed
Solution Approach 1:
The solution transitions from a 2D single-TSV connection approach to a 3D multi-TSV architecture. Multiple TSVs are used to connect corresponding clock trees across adjacent dies in the vertical dimension, reducing the wirelength on each die and eliminating the need for extensive buffer chains while maintaining structural simplicity through standardized vertical interconnects.
Data Source
AI summary
To enable low cost pre-bond testing for a three-dimensional (3D) integrated circuit, a backbone die may have a fully connected two-dimensional (2D) clock tree and one or more non-backbone die may have multiple isolated 2D clock trees. In various embodiments, clock sinks on the backbone die and the non-backbone die can be connected using multiple through-silicon-vias and the isolated 2D clock trees in the non-backbone die can be further connected via a Detachable tree (D-tree), which may comprise a rectilinear minimum spanning tree representing a shortest interconnect among the sinks associated with the 2D clock trees in the non-backbone die. Accordingly, the backbone die and the non-backbone die can be separated and individually tested prior to bonding using one clock probe pad, and the D-tree may be easily removed from the non-backbone die subsequent to the pre-bond testing by burning fuses at the sinks associated with the 2D clock trees.