1532 PCB Design and Fabrication

1532.1 Learning Objectives

By the end of this chapter, you will be able to:

Understand the PCB design workflow from schematic to fabrication
Select appropriate PCB design tools for different skill levels
Apply best practices for component placement and trace routing
Choose between PCB manufacturing services based on requirements
Perform proper PCB assembly and testing

1532.2 PCB Design Process

1532.2.1 Schematic Capture

Creating circuit diagrams showing component connections is the first step in PCB design.

Popular Tools:

Tool	Cost	Best For
KiCad	Free, open-source	Professional-grade, all skill levels
Eagle	Free (limited)	Hobbyists, Autodesk ecosystem
EasyEDA	Free	Beginners, integrated with JLCPCB
Altium Designer	$2000+	Professional, complex designs
Fritzing	Free	Beginners, visual approach

1532.2.2 Component Selection

Choose components available in manufacturer’s libraries
Verify footprints match physical components
Consider availability and cost (check DigiKey, Mouser stock)
Plan for production: prefer common, multi-sourced parts

1532.3 PCB Layout Best Practices

1532.3.1 Component Placement

Start with connectors - define board edge locations
Place critical components - MCU, antenna, power
Group related components - sensors near MCU, power near input
Maintain antenna keep-out zones - no traces/copper under RF sections

1532.3.2 Trace Routing

Rule	Recommendation
Power traces	20+ mils for 1A, calculate for higher
Signal traces	8-12 mils typical
Spacing	Follow manufacturer minimums (6-8 mils)
Vias	Minimize; keep away from pads

1532.3.3 Power and Ground

Use solid ground plane - reduces EMI, improves signal integrity
Star grounding for analog/digital separation if needed
Decoupling capacitors - place within 5-10mm of IC power pins
Bulk capacitors - at power input for transient handling

1532.3.4 Knowledge Check

Show code

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  const container = document.getElementById('kc-proto-8');
  if (container && typeof InlineKnowledgeCheck !== 'undefined') {
    container.innerHTML = '';
    container.appendChild(InlineKnowledgeCheck.create({
      question: "You're designing a 2-layer PCB for an ESP32 IoT sensor. The design includes Wi-Fi antenna, I2C sensors, and a switching power supply. During layout, which consideration is MOST critical for reliable operation?",
      options: [
        {text: "Routing all traces on the top layer to simplify manufacturing", correct: false, feedback: "Single-layer routing forces longer traces and prevents ground planes. This increases EMI, degrades signal integrity, and is actually harder to route for complex designs."},
        {text: "Maintaining antenna keep-out zone and solid ground plane under RF section", correct: true, feedback: "Correct! ESP32 antenna performance depends critically on the ground plane beneath it and clear keep-out zones. Routing traces near the antenna or removing ground copper degrades Wi-Fi range dramatically (50m to 5m)."},
        {text: "Using the thinnest possible traces to save board space", correct: false, feedback: "Thin traces increase resistance and limit current capacity. Power traces need adequate width (20+ mils for 1A), and thin signal traces are harder to manufacture reliably."},
        {text: "Placing all components on one side for easier hand soldering", correct: false, feedback: "While single-sided placement simplifies assembly, it increases board size and may force poor component placement. The antenna and ground plane considerations are more critical for functionality."}
      ],
      difficulty: "hard",
      topic: "prototyping"
    }));
  }
}

1532.4 2-Layer vs 4-Layer PCBs

Factor	2-Layer	4-Layer
Cost	$2-5 for 5 boards	$15-25 for 5 boards
Routing	More challenging	Easier, dedicated layers
Signal integrity	Adequate for low-speed	Better for high-speed
Ground plane	Shared with routing	Dedicated internal layer

Use 4-layer when: - High-speed signals (>10 MHz SPI, USB, etc.) - Dense component placement - RF designs (Wi-Fi, BLE) needing solid ground - Precision analog circuits

Use 2-layer when: - Simple sensor boards - Low-speed I2C/UART communication - Cost is the primary constraint - Beginner projects

1532.5 PCB Manufacturing

1532.5.1 Service Comparison

Service	Cost (10 boards)	Turnaround	Strengths
JLCPCB	$2-5	1-2 weeks	Cheapest, assembly service
PCBWay	$5-10	1-2 weeks	Good quality, flex PCBs
OSH Park	$15-25	2-3 weeks	US-based, purple boards
Seeed Fusion	$5-10	1-2 weeks	Good SMT assembly

1532.5.2 Design Rules

Check manufacturer specifications for: - Minimum trace width (typically 6-8 mils) - Minimum spacing (typically 6-8 mils) - Minimum drill size (typically 0.3mm) - Via specifications (through-hole, blind, buried)

1532.5.3 Quality Checklist

Before ordering: - [ ] Run Design Rule Check (DRC) - [ ] Verify Gerber files visually - [ ] Check silkscreen for readability - [ ] Confirm component footprints match datasheets - [ ] Order 2-3 extra boards for testing

1532.6 Assembly Techniques

1532.6.1 Through-Hole Assembly

Start with low-profile components (resistors, diodes)
Progress to taller components (capacitors, ICs)
Finish with connectors and tall parts
Trim leads after soldering
Inspect joints visually

1532.6.2 Surface Mount (SMD) Assembly

Component Sizes (difficulty increases as size decreases): - 1206 (3.2 x 1.6 mm) - Easy to hand solder - 0805 (2.0 x 1.25 mm) - Common, manageable - 0603 (1.6 x 0.8 mm) - Requires steady hands - 0402 (1.0 x 0.5 mm) - Requires magnification

Hand Soldering Process: 1. Apply solder paste (stencil or syringe) 2. Place components with tweezers 3. Reflow with hot air or reflow oven 4. Inspect under magnification

1532.6.3 Testing Procedure

Visual inspection - solder bridges, cold joints
Continuity testing - check power and ground
Power on with current limiting - catch shorts
Functional test - verify each subsystem

1532.7 Common PCB Issues and Solutions

Issue	Cause	Solution
Wi-Fi weak/no connection	Ground plane under antenna	Create keep-out zone
Random resets	Power supply noise	Add decoupling capacitors
I2C communication fails	Missing pull-ups	Add 4.7k pull-up resistors
Component overheating	Trace too narrow	Increase trace width
Manufacturing rejects	Violates design rules	Run DRC before ordering

1532.8 Quiz: PCB Design

Question: A breadboard prototype works perfectly, but the same circuit on PCB fails. What is the MOST likely cause?

Breadboards have significant parasitic capacitance between holes that inadvertently acts as decoupling, stabilizing circuits. PCBs lack this - without explicit decoupling caps near ICs, circuits can oscillate or fail. This is a classic breadboard-to-PCB trap that catches beginners.

Question: Reading PCB trace width tables, 10mil (0.254mm) trace carries 0.5A with 10C temp rise. Your 2A power trace should be what width?

Current capacity scales with trace cross-sectional area, and temperature rise is non-linear due to thermal dissipation. For 4x current (0.5A to 2A), need approximately 4x width to maintain same temperature rise (10mil to 40mil). Using online calculators or IPC-2221 tables confirms this.

1532.9 What’s Next

Continue to Best Practices and Debugging to learn design principles, power management strategies, and systematic debugging techniques for hardware prototypes.