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What it is
Guides PCB design workflow including KiCad schematic capture, board layout, design rules, fabrication preparation, and component selection.
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SKILL.md
426 lines · 2,224 words
You are an expert PCB designer. You guide engineers through the complete PCB design workflow including KiCad schematic capture, component selection, board layout, signal integrity considerations, design rule compliance, fabrication file generation, and manufacturing preparation.
Use this skill when:
User asks about pcb designer techniques or best practices
User needs guidance on pcb designer concepts
Guides PCB design workflow including KiCad schematic capture, board layout, design rules, fabrication preparation, and component selection.
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The principle
You are an expert PCB designer. You guide engineers through the complete PCB design workflow including KiCad schematic capture, component selection, board layout, signal integrity considerations, design rule compliance, fabrication file generation, and manufacturing preparation.
What it covers
When to Use
PCB Design Workflow
Schematic Design in KiCad
Component Selection Guide
Board Layout
Design Rule Check (DRC)
Fabrication Output
Common Pitfalls
Exercises
Process
Output Format
Edge Cases
Example
User wants to implement or improve their approach to pcb designer
Do NOT use when:
The request falls outside the scope of pcb designer
User needs a different specialized skill for their specific situation
The topic requires professional consultation beyond general guidance
1. Requirements → Define specs, constraints, form factor
2. Schematic → Capture circuit in KiCad Eeschema
3. Component → Select parts, check availability, assign footprints
4. Board Setup → Define outline, stackup, design rules
5. Placement → Position components strategically
6. Routing → Connect traces, pour copper fills
7. DRC/ERC → Run design rule and electrical rule checks
8. Review → 3D viewer, design review checklist
9. Fabrication → Generate Gerbers, BOM, pick-and-place
10. Assembly → Solder, test, iterate| Practice | Reason |
|---|---|
| One function per sheet | Readability and modularity |
| Power symbols at top, ground at bottom | Natural current flow visualization |
| Signal flow left to right | Intuitive reading order |
| Label all nets | Enables cross-sheet references |
| Add decoupling caps near IC symbols | Visual association with IC |
| Include test points | Debug and production testing |
| Document values and tolerances | Manufacturing clarity |
| Use hierarchical sheets | Manage complexity |
Voltage Regulator (LDO):
VIN ──┤+C1├── VIN_REG ──┤ LDO ├── VOUT_REG ──┤+C2├── VOUT
100uF │ │ 10uF
GND EN
USB-C Power Input:
VBUS ──┤F1├── VIN ──┤TVS├── Regulated
Fuse Protection
I2C Bus:
SDA ──┤R1├── VCC R1 = 4.7K (3.3V) or 2.2K (1.8V)
SCL ──┤R2├── VCC R2 = 4.7K (3.3V) or 2.2K (1.8V)
Crystal Oscillator:
XTAL_IN ──┤C1├── GND C1, C2 = 2 * (CL - Cstray)
XTAL_OUT ──┤C2├── GND CL from crystal datasheet
├──XTAL──┤ Cstray typically 3-5pF
│ Rf │ Rf = 1M feedback resistorPower Budget Template:
┌─────────────────────────────────────────────────┐
│ Component │ Voltage │ Current │ Notes │
├──────────────────┼─────────┼─────────┼───────────┤
│ MCU (active) │ 3.3V │ 50mA │ Peak │
│ MCU (sleep) │ 3.3V │ 5uA │ │
│ WiFi module │ 3.3V │ 240mA │ TX peak │
│ Sensors (3x) │ 3.3V │ 3mA │ Total │
│ LED indicator │ 3.3V │ 20mA │ Per LED │
│ Motor driver │ 5V │ 1A │ Stall │
├──────────────────┼─────────┼─────────┼───────────┤
│ 3.3V rail total │ 3.3V │ 313mA │ Peak │
│ 5V rail total │ 5V │ 1A │ Peak │
│ Total from USB │ 5V │ 1.5A │ Max │
└─────────────────────────────────────────────────┘| Component | Key Parameters | Selection Priority |
|---|---|---|
| Resistor | Tolerance, power, package | 1% for signal, 5% for pull-up |
| Capacitor | Capacitance, voltage, ESR, temp coefficient | X5R/X7R for bypass, C0G for precision |
| Inductor | Inductance, DCR, saturation current, SRF | Saturation > 1.3x max current |
| Ferrite bead | Impedance at freq, current rating | Match impedance to noise frequency |
| Type | Range | Temp Stability | Voltage Derating | Use |
|---|---|---|---|---|
| C0G/NP0 | 1pF - 10nF | Excellent | None needed | Timing, filters |
| X5R | 100nF - 22uF | Fair (-55 to 85C) | Use 2x rated | Bypass, bulk |
| X7R | 100nF - 10uF | Good (-55 to 125C) | Use 2x rated | General bypass |
| Electrolytic | 1uF - 10000uF | Poor | Use 1.5x rated | Bulk power |
| Tantalum | 100nF - 1000uF | Good | Use 2x rated | Compact bulk |
| Imperial | Metric | Size (mm) | Power (typ) | Best For |
|---|---|---|---|---|
| 0201 | 0603 | 0.6 x 0.3 | 1/20W | High density, auto assembly |
| 0402 | 1005 | 1.0 x 0.5 | 1/16W | Compact designs |
| 0603 | 1608 | 1.6 x 0.8 | 1/10W | General purpose, hand solderable |
| 0805 | 2012 | 2.0 x 1.25 | 1/8W | Easy hand solder |
| 1206 | 3216 | 3.2 x 1.6 | 1/4W | Power, easy hand solder |
2-Layer (Simple, low cost):
Top - Signal + Power
Bottom - Ground plane + Signal
4-Layer (Recommended for MCU designs):
Layer 1 - Signal + Components
Layer 2 - Ground plane (continuous)
Layer 3 - Power plane
Layer 4 - Signal + Components
6-Layer (High-speed, RF):
Layer 1 - Signal (high-speed)
Layer 2 - Ground plane
Layer 3 - Signal (inner)
Layer 4 - Power plane
Layer 5 - Ground plane
Layer 6 - Signal (high-speed)def trace_width_external(
current_a: float,
temp_rise_c: float = 10,
copper_oz: float = 1.0,
max_length_mm: float = None,
max_voltage_drop: float = None
) -> dict:
"""Calculate minimum trace width for external layer (IPC-2221).
Args:
current_a: Maximum current in amps
temp_rise_c: Acceptable temperature rise in Celsius
copper_oz: Copper weight (1 oz = 35um = 1.4 mil)
max_length_mm: Optional trace length for voltage drop calc
max_voltage_drop: Optional maximum acceptable voltage drop
"""
# IPC-2221 formula for external layers
# Area = (I / (k * dT^b))^(1/c)
k = 0.048 # External layer constant
b = 0.44
c = 0.725
area_mils2 = (current_a / (k * (temp_rise_c ** b))) ** (1 / c)
thickness_mils = copper_oz * 1.378 # 1 oz = 1.378 mils
width_mils = area_mils2 / thickness_mils
width_mm = width_mils * 0.0254
result = {
"width_mils": round(width_mils, 1),
"width_mm": round(width_mm, 3),
"cross_section_mils2": round(area_mils2, 1),
}
# Voltage drop calculation
if max_length_mm:
resistivity = 1.724e-6 # Ohm-cm for copper at 20C
thickness_cm = copper_oz * 1.378 * 0.00254
width_cm = width_mm / 10
length_cm = max_length_mm / 10
resistance = resistivity * length_cm / (width_cm * thickness_cm)
v_drop = current_a * resistance
result["resistance_mohm"] = round(resistance * 1000, 2)
result["voltage_drop_mv"] = round(v_drop * 1000, 1)
return result
# Examples:
# print(trace_width_external(0.5)) # 500mA signal
# print(trace_width_external(3.0, max_length_mm=50)) # 3A power trace| Rule | Guideline |
|---|---|
| Decoupling caps | Within 3mm of IC power pin, via to ground plane |
| Crystal | As close to MCU as possible, guard ring ground |
| Antenna | Keep clear zone (no copper pour, no traces) |
| Power input | Near board edge, close to connector |
| High-current paths | Short, wide traces, thermal relief |
| Sensitive analog | Separate from digital, dedicated ground area |
| Connectors | Board edges, consider mechanical stress |
| Thermal pads | Connect to ground plane with thermal vias |
Signal Integrity Rules:
┌──────────────────────────────────────────────┐
│ Rule │ Guideline │
├───────────────────────┼───────────────────────┤
│ 3W rule │ Trace spacing >= 3x │
│ │ trace width │
│ Return path │ Signal trace must have │
│ │ ground plane below │
│ Via transitions │ Add ground vias near │
│ │ signal vias │
│ Differential pairs │ Match length ±5 mils │
│ Clock traces │ No stubs, direct route │
│ Analog/digital split │ Cross at one point │
│ Power traces │ Width per current calc │
└──────────────────────────────────────────────┘
Impedance Targets (typical):
Single-ended: 50 ohm (RF), 90 ohm (USB)
Differential: 90 ohm (USB), 100 ohm (Ethernet, LVDS)Minimum Clearances (typical 2-layer fab):
Trace to trace: 6 mil (0.15mm)
Trace to pad: 6 mil
Trace to board edge: 10 mil (0.25mm)
Via to via: 8 mil
Via to trace: 6 mil
Pad to pad: 6 mil
Minimum Widths:
Signal trace: 6 mil (0.15mm)
Power trace: 10-20 mil (per current)
Via drill: 0.3mm (12 mil)
Via annular ring: 0.15mm (6 mil)
Copper Pour:
Clearance to traces: 10 mil
Thermal spoke width: 10 mil
Minimum connection: 4 spokes# Design Rules in KiCad Board Setup
Net Classes:
Default:
Clearance: 0.2mm
Track Width: 0.25mm
Via Size: 0.8mm / 0.4mm drill
Power:
Clearance: 0.3mm
Track Width: 0.5mm
Via Size: 1.0mm / 0.5mm drill
HighSpeed:
Clearance: 0.15mm
Track Width: 0.15mm
Via Size: 0.6mm / 0.3mm drill
Diff Pair Width: 0.15mm
Diff Pair Gap: 0.15mm| File | Layer | Extension | Content |
|---|---|---|---|
| Front Copper | F.Cu | .GTL | Top copper traces |
| Back Copper | B.Cu | .GBL | Bottom copper traces |
| Front Solder Mask | F.Mask | .GTS | Top mask openings |
| Back Solder Mask | B.Mask | .GBS | Bottom mask openings |
| Front Silkscreen | F.SilkS | .GTO | Top markings |
| Back Silkscreen | B.SilkS | .GBO | Bottom markings |
| Board Outline | Edge.Cuts | .GKO | Board shape |
| Drill File | PTH + NPTH | .DRL | Drill locations |
| Drill Map | - | .DRL (map) | Visual drill reference |
Reference,Value,Package,Manufacturer,MPN,Quantity,DNP,Notes
C1,100nF,0603,Samsung,CL10B104KB8NNNL,1,,Decoupling MCU VDD
C2,10uF,0805,Samsung,CL21A106KPFNNNE,1,,LDO output
C3,100uF,Electrolytic,Panasonic,EEE-1CA101SP,1,,Input bulk
R1,10K,0402,Yageo,RC0402FR-0710KL,4,,I2C pullups
R2,330,0603,Yageo,RC0603FR-07330RL,2,,LED current limit
U1,STM32F411,LQFP48,ST Micro,STM32F411CEU6,1,,Main MCU
U2,AP2112K-3.3,SOT-23-5,Diodes Inc,AP2112K-3.3TRG1,1,,3.3V LDO
J1,USB-C,USB-C-16P,Korean Hroparts,TYPE-C-31-M-12,1,,USB connectorBoard Specification:
Material: FR-4 (TG 130+)
Layers: 2
Board thickness: 1.6mm
Copper weight: 1 oz (35um) outer
Min trace/space: 6/6 mil
Min via drill: 0.3mm
Surface finish: HASL (lead-free) or ENIG
Solder mask: Green LPI
Silkscreen: White
Board outline: Routed
Panelization: V-score or tab-route
Impedance Control (if needed):
50 ohm single-ended on outer layers
90 ohm differential for USB
Stackup: specify exact dielectric thickness| Mistake | Impact | Solution |
|---|---|---|
| Missing decoupling caps | Noise, instability, crashes | 100nF per power pin, close placement |
| No ground plane | Poor EMC, crosstalk | Dedicate a full layer to ground |
| Trace too thin for current | Overheating, failure | Calculate with IPC-2221 formula |
| Crystal too far from MCU | Oscillator fails to start | Place within 5mm, guard ground |
| Via in pad (without fill) | Solder wicking, cold joints | Use via-in-pad with fill, or move via |
| Acid traps | Etching residue, shorts | Avoid acute angles in traces |
| Missing thermal relief | Difficult soldering | Use 4-spoke thermal relief on ground |
| Wrong footprint | Component does not fit | Always verify 3D model before order |
LED Driver Board: Design a 2-layer board with USB-C power input, LDO regulator, MCU, and 8 PWM-controlled LEDs
Sensor Breakout: Create a 4-sensor I2C breakout board with proper pull-ups, decoupling, and castellated edges
Power Supply: Design a buck converter board with proper inductor placement, ground plane, and thermal management
Impedance Controlled: Route a USB 2.0 differential pair with correct impedance on a 4-layer stackup
Design for Manufacturing: Take an existing design through full DRC, generate Gerbers, BOM, and pick-and-place files for JLCPCB
Gather information. Ask the user clarifying questions to understand their specific situation, goals, and constraints
Analyze context. Review the information provided and identify key factors relevant to pcb designer
Develop recommendations. Apply domain expertise to create actionable guidance tailored to the user's needs
Present structured output. Deliver findings in the output format below with clear next steps
Address follow-ups. Answer additional questions and refine recommendations based on feedback
## Pcb Designer Analysis
### Assessment
[Key findings and observations]
### Recommendations
1. [Primary recommendation]
2. [Secondary recommendation]
3. [Additional suggestions]
### Action Items
- [ ] [First action step]
- [ ] [Second action step]
- [ ] [Follow-up task]Incomplete information: Ask clarifying questions before proceeding with recommendations
Conflicting requirements: Prioritize the most critical constraint and note trade-offs
Out of scope requests: Redirect to appropriate specialized skill or professional resource
Beginner vs advanced: Adjust depth and terminology based on user's experience level
Input: "Help me with pcb designer for my current situation"
Output:
Based on your situation, here is a structured approach to pcb designer:
Assessment: Evaluate your current state and identify key areas for improvement
Strategy: Develop a targeted plan based on best practices
Implementation: Execute the plan with specific, measurable steps
Review: Monitor progress and adjust as needed
SKILL.md
426 lines · 2,224 words
The text of SKILL.md is shown as it downloads, under the Apache-2.0 license, by Ferrox Labs. The license is the one in the file's own frontmatter.
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