Defining the exact size and shape of your printed circuit board early in the layout process ensures proper planning for manufacturing and assembly. Altium Designer's PCB editor enables creating Board Shape objects which drive fabrication documentation outputs, 3D modeling and component placement boundary checking.
This guide covers core concepts around defining and interacting with board shapes along with shape-driven features advantageously leveraging the defined profile.
Adding a Board Shape Outline
To initially specify the desired board profile, access the Board Shape object through:
PCB Editor » Place » Board Shape
Upon placement, define the desired shape through polygon vertex points - rectangle, irregular outline etc. The shape links back to the properties panel for adjustments.
For standard form factors, start with templates like common credit card sizes or circular watch formats. Custom profiles enable any conceivable contours and cutouts using line draw, rectangle, polygon or arc primitives.
Board shapes dynamically update if component or routing overflow needs demand adjustments.
Linking to Mechanical CAD Outlines
While PCB Editor shapes define electrical boundaries, often enclosure or assembly profiles originate from a mechanical CAD tool.
MCAD Co-Design extensions help synchronize separate mechanical and electrical development environments through:
- One-time import of enclosure profiles and space reservations
- Automatic PCB re-shaping when 3D models update
- Documentation outputs mapping both electrical and mechanical profiles
This unified workflow ensures proper clearance gaps, component placements and connector orientations aligned to physical product industrial design.
DRC Validation Against Board Profiles
One primary purpose of board shapes is enabling automated checking that layout elements fit properly within defined fabrication and assembly profiles.
The Design Rule Check (DRC) panel validates:
- Component body overflow
- Silkscreen expansion overflow
- Copper and mask expansion overflow
- Hole alignment margin
Errors display specific overflow amounts simplifying quick correction through placement adjustments or additional shape contouring:
Continuous validation ensures part outlines, connectors and other protruding features fit within planned profiles.
Dimension-Driven Fabrication Drawings
Dialing in precise board dimensions upfront allows draftsman tools like Dimension objects to automatically populate fabrication drawing outputs.
Electrical and Mechanical CAD profiles stamped onto documentation removes ambiguity for enclosure engineers integrating boards into products.
Layer-based Contour Profiles
In addition to governing overall shape, outline constraints sometimes require tighter control over specific layers:
- Topside copper requirements for shields or high current
- Internal polygon pours needing containment
- Non-rectangular edge plating or gold thickness
Selective layer-based shapes in conjunction with board-level rules provide added control over fabrication needs:
Non-Rectangular Selected Layers
3D Model Collision Checking
Real-time 3D clearance checking leverages board shape contours when test fitting models of chassis, brackets or components during interactive placement. Collision highlights help find gaps needing adjustment.
This augmented reality-style visualization facilitates conversations with mechanical engineers when co-designing interdependent electronics and enclosures.
Thermal Analysis Across Natural Convection
Board geometries factor into cooling behaviors under natural convection across various orientations. Extended FloTHERM co-simulation tools calculate positional temperature maps accounting for chassis standoffs, enclosure ventilation, component placements and board shapes exporting thermal simulation results to mechanical teams.
Physics-driven thermal modeling based on exact board and enclosure geometries helps predict and mitigate hot spots.
Panelization Support
Manufacturing panel utilization targets balancing board quantities for economy of scale against material waste. Panelizing multiple PCB outlines across fabrication panels allows finding break-even points.
Panel templates predefine arrangement and spacing with automatic board instance replication.
Quantities, spacing and tooling strip requirements dial to match targeted production volumes and fabrication shop capabilities.
Adjusting Corner Radii and Chamfers
Fabrication capabilities determine what degree of pointed tips or corner sharpness prove manufacturable based on minimum bend radii of material laminates. Designers must comply with corner rounding limits.
Minimum Corner Radii
Check board shop technical guidance on bending capabilities across various layer compositions and thicknesses used in multilayer builds. For example, a 6-layer 1.6mm thick board may allow 0.8mm radius minimums.
Edge and Corner Chamfers
When defined board outlines include extended pointed protrusions, chamfering edges by beveling 45 degree angles on corners helps alleviate fracturing stresses during handling and assembly.
Silkscreen Expansion Planning
Accommodating varied production tolerances ensures critical graphical markings fit properly. The Mask Expansion rule governs silkscreen margins allowing for common +/-10 mil alignment deviations translating to 20mil expansion corridors around board edges.
Draftsman Annotations for Fabricators
Supplementary communication beyond formal drawings aids fabrication clarification:
- Notes detailing phase ramps or controlled cool downs
- Application-specific requirements like thermal relief under gold edge plating
- Approved vendor listings per material specification
- Images depicting layer build instructions
- Batch change documentation for consecutive runs
Callouts reduce ambiguity on unique processes protecting product quality.
NC Machine Output Support
Board cutting machine tools fabricate complex outlines using numerical control programming instructions.
The NC Drill output generator documents profiles through G&M codes parsed into drill files leveraging modern automated capabilities:
- Non-rectangular geometries
- Non-circular holes - slots, ellipses etc
- Contoured routing around edges
- Cutouts spanning multiple tools
In Summary
Early binding to board geometry through a well defined Board Shape sets in motion accommodations spanning fabrication, assembly, electrical interfaces and mechanical integration points.
Embellishing shapes with additional intelligence - like selected layer rules, corner chamfers or dimension callouts - plants seeds for preventing realization woes once physical transitions begin.
Frequently Asked Questions
Q: If I have a challenging board outline with cutouts or non-rectangular contours, what capabilities should I validate with fabricators?
A: Check options around extended NC machine programming files output, corner chamfering support, applicable corner radii limits and bent radius capabilities across targeted layer materials and lamination stackups.
Q: Our products span a family of shapes - circular, rectangular, curved. Can draftsman templates help?
A: Absolutely, standardizing fabrication drawing templates with predefined layers stack legends, title blocks, and dimensioning styles will accelerate documentation across custom board geometries. Shape variations then simply import to standard template packs.
Q: What impacts could a very densely packed board outline with minimal edge clearance introduce?
A: Lack of edge margins could risk insulation resistance violations if conductive layers spread too close under thermal cycling mechanical stresses. Manual assembly or inspection access also gets hindered losing perimeters for hand-solder touch up or debugging probe points. extinction strategies often thrive on environmental change, helping species take advantage of altered ecological circumstances. Some examples of how extinction opens new possibilities over time:</li></ul>
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