Cadence PCB Best Practices

Learn more at Cadence Online Support https://support.cadence.com © 2024 Cadence Design Systems, Inc. All rights reserved worldwide. Page 7 Working with Backdrilling in Allegro PCB Designer: Best Practices Apply BACKDRILL_OVERRIDE property to symbols, pins or vias for explicit backdrill from each backdrill side to a specific layer in stack-up. (used on test coupons) Minim ize layer pairs Backdrill Cross Section Chart – Enable "Backdrill span" option. Each backdrill pass represented showing backdrill depth and tapered end Must Not Cut Layer surface Backdrill Flow in the Allegro PCB Designer Net Identification Assign BACKDRILL_MAX_PTH_STUB property to nets targeted for backdrilling Exclusion, Overrides & Restrictions Apply BACKDRILL_MIN_PIN_PTH property to symbol or pins to ensure backdrill depth does not violate m in plating depth rules Apply BACKDRILL_PRESSFIT_CONNECTOR property to a symbol which prevents the backdrilling of the critical pin contact area for press fit compliant pins (manufacturer requirement) Apply BACKDRILL_EXCLUDE property to symbol, pins or vias to exclude these elements from backdrill processing. Initial Layer Pair Creation Manual layer pair initialization based on deepest backdrill layer from each backdrill side Enter Manufacturing stub length under the Drill Parameters tab of Backdrill and Analysis form . Fabrication vendor remaining stub without comprising the Must Not Cut Layer (Op tional) Layer Pair Creation based on Analysis (Layer Pair Initialization – Analysis) Minim ize electrical stub length Verify Padstack Backdrill data Verify that padstacks in the design contain backdrill data which is used at backdrill locations Select Details button under Padstack Parameters tab for a report of padstack missing backdrill data Provide report to librarian so backdrill data in library padstacks can be updated and refresh padstacks in design (recommend ed) Under Padstack Parameters tab verify undersize and oversize values. These values used during backdrill to update padstacks Analysis, Reporting and Backdrill Run Analyze to generate Backdrill Plunge counts – manual layer pair initialization only Evaluate layer pairs and number backdrill plunges per layer pair. Adjust layer pairs, routing, max stub length as required to yield the best backdrill solution. Review log file for violations, exclusions, overrides and general backdrill statistics Once satisfied with setup and analysis results, run Backdrill to commit backdrill to design. NOTE: Resolve any possible DRCs caused by the increased clearance at backdrill locations Supporting Documentation NC Drill & Legends – Enable "Include backdrill" option. Each backdrill pass represented as unique legend or file . Actual Backdrill size – no oversizing.

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