Development Standards

From concept to purchasing the boards, a number of standards were kept to maintain a certain level of excellence, uniformity and quality from board to board.

Schematic

To retain a smaller bill of materials, increased uniformity with PCB’s and higher quality of components for the PCB’s, standards are defined to optimize performance of the PCB’s. All components will be bought through Digikey.com.

NOTE: The first few boards were developed in Autodesk Eagle but then moved to Kicad very early on in the project.

Resistors:

• Category: Thin Film Resistor
• Mounting Type: Surface Mount
• Package: 0603
• Tolerance: <= 5%
• Power: TBD

Capacitors:

• Category: Ceramic Capacitors
• Mounting Type: Surface Mount
• Package: 0603
• Tolerance: <= 5%
• Voltage Rating: > 30V

Diodes:

• Category: Standard
• Mounting Type: Surface Mount
• Package: SOD-123
• DC Reverse Voltage Vr,max: 30-200V

LEDs:

• Mounting Type: Through Hole
• Pin Pitch: 0.1”

MOSFETs:

• Voltage - Collector Emitter Breakdown (Max): > 40V
• Mounting Type: Surface Mount
• Package: SOT-23-3

Integrated Circuits:

• Mounting Type: Through Hole

Screw Terminals:

• Color: Black
• Mounting Type: Through Hole
• Pin Pitch: 3.5mm
• Manufacturer: On Shore Technology or TE Connectivity

Header Pins:

• Pin Pitch: 0.1”

Along with these criteria, a standard-issue list of parts were selected for basic components (transistors, resistor families, connector families, etc.), but will remain undisclosed for this project.

Before moving to layout, schematics arere iterated through several times to check specific features of the boards - similar to that of a checklist.

PCB schematic Checklist📚

📌 Initial schematic - Building out initial circuitry.

📌 Simplify circuitry - Attempts to simplify any circuitry built in Initial schematic.

📌 Check math - Verifying voltage drops, current and power ratings, and other values are accurate.

📌 Check all IC pinouts - Verifying all IC's are wired correctly.

📌 Add protection circuitry - Add overvoltage, overcurrent, overtemperature, reverse polarity circuitry or 0ohm jumpers to protect important parts of the board.

📌 Add test points - Add test points for future probing important parts of the board.

📌 Add LED’s - Add LED's to visually denote states of certain signal or power lines.

📌 Pass ERC - All schematics MUST pass the ERC with ZERO errors. No exceptions.

Layout

Layout standards were kept very minimal to allow room for boards to be diverse enough to accomplish their respective tasks to the degree necessary to do sos efficiently.

• Traces:
  • Power Lines:
    • 20V: 50 mils
    • 12V: 20 mils
    • 6V, 3V: 10 mils
  • Signal Lines:
    • Longer traces were enlarged per the trace width calculator on Advanced Circuits' website
• Text Font: Futura

Similarly to the schematic phrases, before closing out a board layout, boards were iterated through several times to check specific features of the boards.

PCB Layout Checklist🗺

📌 Initial layout - Initial pass-through of routing traces and placements

📌 Check trace widths - Verifying power and long trace widths are adequate per Advanced Circuits' calculators and standards listed above.

📌 Add silkscreen notes - Adds boxes around components that make up a specific circuit and label the box, adds labels to breakout pin and labels to large signal connectors and standalone power connectors.

📌 Pass DRC - All layouts MUST pass the DRC with ZERO errors. No exceptions.

Production

A number of settings were also maintained between boards to keep boards uniform. All boards were purchased through PCBWay.com.

PCB settings:

• Material: FR-4
• FR4-TG: TG 150-160
• Thickness: 1.6
• Min Track/spacing: 6/6mil
• Min Hole Size: 0.3mm
• Solder Mask: Black
• Silkscreen: White
• Surface Finish: HASL with Lead
• Via Process: Tenting Vias
• Finished Copper: 1oz. Copper (2oz. Copper for any boards that have 20V power)

Assembly

For wiring boards together, a standard color code was established to navigate and differentiate between different types of wires more easily.

Wire Color Codes:

• White: Signal line
• Yellow: Monitoring line
• Green: Reserved for use not defined by other colors
• Black: Ground line
• Red: Power line
• Blue: Revision/Whitewire line