Designing for Adaptation

Created: October 23, 2018
Updated: March 16, 2020
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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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