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
Component Footprint Sizes
The numbers in the Imperial and Metric columns refer to the dimensions of the component package in thousandths of an inch (Imperial) and tenths of a millimeter (Metric), respectively. For example: 0402 (Imperial) / 1005 (Metric): This package size is 0.04 inches (1.0 mm) long and 0.02 inches (0.5 mm) wide. This should give a sense of physical size when assigning footprints to a schematic.
Footprint (Imperial)
Footprint (Metric)
Acceptable for BREADS
Comment
0402
1005
No
Very small; difficult to solder manually; not recommended for DIY projects.
0603
1608
Sometimes
Small; acceptable for some advanced DIY but not ideal for ease of assembly.
0805
2012
Yes
Preferred minimum size for BREADS; better than 0603 but still small for DIY soldering.
1206
3216
Yes
Very easy to handle and solder manually.
1210
3225
Yes
Slightly larger than 1206; still easy to solder, provides better thermal dissipation.
1812
4532
Yes
Larger footprint; good for power components or higher current requirements.
2220
5650
Yes
Very large; suitable for high power, larger components.
Silkscreen Color Chart
Category
Color
Use
Rationale
Examples
Prototype
Blue
2-layer prototype boards
Distinctive color used to differentiate prototype versions.
DCMT, RLHT
Red
4-layer prototype boards
High contrast with white silkscreen enables easier debugging and inspection.
SOLR, FPSG
Yellow
Carrier/adapter boards
Unique appearance for quick visual identification in a mixed batch of prototypes.
Atlas Sci. pH/DO/ORP/EC, can-nano-shield
Production
Green
2-layer production boards
Standard choice for production due to reliability, low cost, and ease of inspection.
DCMT, RLHT
Black
4-layer production boards
Offers a professional and aesthetic look, indicating complexity for consumer electronics.
SOLR, FPSG
Purple
Carrier/adapter boards for production (special editions)
Differentiates special editions or unique branding from standard production runs.
Atlas Sci. pH/DO/ORP/EC, can-nano-shield
Special Use
White
Boards requiring high light reflection or exposed boards
Chosen for aesthetics and applications needing enhanced light reflection properties.