Design Contraints

This is for classic two layer boards BREADS has originally been constrained to.

General PCB Constraints

Parameter	Constraint
PCB Dimensions	100 mm x 70 mm
Mounting Hole Size	M3 bolts, 5 mm inset at each corner
Minimum Trace Size	0.5 mm
Minimum Feature Spacing	0.2 mm
Pad Copper Width	Greater than 0.5 mm
Recommended Component Package Size	1206 or greater *

Component Placement and Sizing Constraints

Parameter	Constraint
Standard Component Placement	Components should have clearance for easy soldering and heat dissipation
Through-hole Components	Should remain on the top layer
Surface-mount Components	Should be flipped to the bottom layer
Component Sizing Constraints	Components should be grouped by sub-circuit, with large components on the top layer and clearance for heat dissipation
Standard Components	Arduino Nano, interface connector, power filtering capacitors

Routing and Layer Constraints

Parameter	Constraint
Routing for Single-layer Boards	All routing on the bottom layer
Vias for Two-layer Boards	Aim to keep traces on bottom later; use large enough vias (1 mm) with pads to allow for wire bridges if necessary
Power Planes for Two-layer Boards	Ground plane on top, dominant supply voltage on the bottom layer
Plane Usage	Minimize use of planes due to redundant milling issues with CAM software

Labeling and Configuration Constraints

Parameter	Constraint
Jumper Configuration	Clearly labeled, with a recommended configuration table
Labeling Requirements	All device designators should be in the same orientation, clear labeling for all connectors and test points
Loaf Interface Connector	Standard 10-pin female header centered on the left side of the PCB
External Connector Pitch	2.54 mm (0.1”)

Manufacturing and Compatibility Constraints

Parameter	Constraint
Digital Manufacturing Compatibility	Boards should be manufacturable on commonly available circuit milling machines
Mechanical Definition - Slice Casing	3D printed, solid infill, layer height under 0.5 mm
Emergency Stop Interlock Chain	Must be wired such that “open state” indicates the device should be in an E-Stop State
Component Selection	Prefer through-hole, socket-able chips for easy soldering and replacement