Designing for Adaptation

In the world of hardware engineering, board re-spins are costly, time-consuming, and often avoidable with proper planning. Hunter Scott, Director of Hardware Engineering at Reach Labs, shared valuable insights on "Design for Hacking" (DFH) at Altium Live 2018 - strategies that make PCB modifications easier when inevitable design changes arise.

Three Core Principles

Scott organizes his approach around three fundamental techniques:

1. Isolate Subcircuits

Breaking your design into isolated modules creates flexibility and debugging opportunities:

• Use series resistors (precision small values are better than 0-ohm)
• Implement load switches for digital control of isolation
• Add removable jumpers and fuses
• Include connectors between major circuit blocks

This approach allows you to test modifications on specific sections without affecting the entire board and facilitates A/B testing of different implementations.

2. Give Yourself Options

The design phase is the perfect time to build in flexibility:

• Embrace "DNP" (Do Not Populate) components liberally
• Include footprints for filter configurations (pi/T networks)
• Add DNP RF and debug connectors
• Design footprint-in-footprint layouts that accommodate multiple component packages
• Consider castellated modules for easily swappable subcircuits
• Break out spare I/O pins and status/setting pins
• Incorporate spaces for shields that may be needed for EMC compliance

3. Make Changes Easy

When modifications become necessary:

• Use vias in pads strategically (but carefully)
• Place abundant and well-labeled test points throughout your design
• Use potentiometers instead of fixed resistor dividers for tunable settings
• Choose LDOs with high input voltage ranges for power flexibility
• Keep components on the same side when possible
• Leave adequate space for soldering iron access
• Avoid permanent materials (potting, conformal coating) until designs are finalized

Special Considerations for RF

RF circuits often intimidate designers, but several techniques make modifications more approachable:

• Implement RF jumpers for testing and isolation
• Use thin-gauge coaxial cable for modifications
• Include semi-rigid pigtails with proper ground pads
• Design with coplanar waveguides for easier probing
• Select antenna structures that accommodate adjustments

Practical Tips

The presentation emphasized practical design habits:

• Document thoroughly with commented schematics and labeled test points
• Use silkscreen effectively to mark pin numbers and component designators
• Consider using circuit tape for secure wire management during modifications
• Select component packages with external pins rather than difficult-to-modify QFNs
• Avoid ultra-small components (0201, 0402) when possible

By incorporating these defensive design strategies, hardware engineers can create adaptable boards that accommodate changes without requiring complete re-spins - saving time, money, and frustration throughout the product development cycle.

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