Selective Antipad Backdrilling for High-Speed PCB Signal Integrity
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Solution Overview
Problem
High-speed printed circuit boards (PCBs) face signal integrity disturbances due to unused via stubs, which increase with higher frequency applications, and backdrilling to remove stubs can limit PCB density by requiring significant metal removal.
Innovation Solution
A multilayer PCB design with selectively sized antipads and a 'stair-stepped' routing pattern for signal layers, allowing for controlled backdrilling that minimizes stub length and maintains signal integrity while preserving metal density for power and signal delivery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If backdrilling is performed to remove via stubs, then signal integrity is improved, but metal density is reduced due to large antipad areas
Solution Approach 1:
The patent applies different antipad sizes at different locations: larger antipads are used in lower signal layers where backdrilling is performed, while smaller antipads are used in higher signal layers where metal density is critical. This local differentiation allows effective stub removal where needed while preserving metal resources where signals are already routed.
Solution Approach 2:
The patent segments the antipad structure into multiple layers with different sizes. Lower layers have larger antipads to facilitate backdrilling operations, while upper layers have smaller antipads to maintain metal density. This segmentation allows each layer to be optimized for its specific function in the signal routing hierarchy.
2Manufacturing precision
If larger antipads are used to accommodate backdrilling, then stub removal is effective, but available area for signal lines and power distribution is reduced
Solution Approach 1:
The patent implements location-specific antipad sizing where larger antipads are strategically placed only in layers requiring backdrilling for stub removal, while smaller antipads are used in layers where metal area is more valuable for signal and power routing. This resolves the contradiction by applying the area-consuming feature only where manufacturing precision is critical.
Solution Approach 2:
The patent resolves the area conflict by distributing antipad functions across multiple vertical layers. Instead of requiring large antipad area in a single layer, the structure uses moderate-sized antipads across several layers, with size variation optimized for each layer's specific backdrilling and routing requirements.
3Length of moving object
If signals are routed through lower layers, then stub length is reduced, but metal removal requirements increase
Solution Approach 1:
The patent segments the signal routing across multiple layers with a stair-stepped pattern. Signals transition from lower layers (where stubs are removed) to upper layers (where metal is preserved), effectively segmenting the routing path to balance stub length reduction against metal conservation.
Solution Approach 2:
The patent performs preliminary backdrilling and antipad formation in lower layers before final signal routing is completed. This preliminary removal of stubs in lower layers enables subsequent routing in upper layers without the harmful effects of long stubs, while the upper layer routing preserves metal density.
Data Source
AI summary
A printed circuit board (PCB) may include antipads, used to provide clearance for backdrilling, which may be sized to allow backdrilling in a way that minimizes the presence of stubs. The PCB may include pads to connect a component to the PCB and vertically disposed vias connected to at least some of the pads. The PCB may further include horizontally disposed signal layers, electrically connected by the vias, to route signals from the component, received from the vias, to an edge of the component, in which signals associated with the component closer to an inner portion of the component are routed to the edge of the component on higher ones of the signal layers than signals associated with the component further from the inner portion of the component.