Learn PCB Design: From Idea to Printed Circuit Board

What Is a Printed Circuit Board (PCB)?

A Printed Circuit Board is the physical foundation of every electronic device. In industrial environments, you find these boards everywhere: from sensor reading modules to motor control boards and I/O units.

A PCB consists of an insulating substrate (typically FR-4) covered with one or more copper layers. The copper is etched to form electrical pathways that connect electronic components together. Instead of messy wiring, a PCB provides reliable and repeatable connections suitable for mass production.

In factories, reliability is not optional but essential. A well-designed board operates for years without failure, while a poorly designed one can bring an entire production line to a halt. The cost of fixing a design error after manufacturing is tens of times higher than catching it early.

FR-4 is the most widely used substrate material, composed of glass fiber reinforced epoxy. It withstands temperatures up to 130 degrees Celsius, which is sufficient for most industrial applications. For extremely high-temperature environments, alternative materials like Polyimide can handle up to 260 degrees.

Board Layers: From Single-Sided to Multilayer

Boards are classified by the number of copper layers:

• Single-sided: One copper layer. Suitable for simple circuits like LED driver boards or basic relay modules. The cheapest to manufacture but limited in circuit complexity.
• Double-sided: Two copper layers. The most common choice for industrial applications. Sufficient for most control and sensor units. Uses vias to connect both sides.
• Multilayer: Four or more layers. Used for complex circuits such as high-speed microcontroller boards or network communication modules.

In industrial design, a 4-layer board is the optimal choice when you need a dedicated Ground Plane to reduce electromagnetic interference. The inner layers are typically used for ground and power, while the outer layers carry signals and components.

Typical 4-layer stack-up:

• Layer 1 (front): Signals and components
• Layer 2 (inner): Complete ground plane (Ground Plane)
• Layer 3 (inner): Power plane (Power Plane)
• Layer 4 (back): Additional signals and components

Layer cost: A 4-layer board costs roughly twice as much as a double-sided board. However, in many cases the improved electrical performance justifies the price difference, especially in applications requiring high accuracy in sensor readings or high-speed communication.

Core Components: Traces, Pads, and Vias

Three elements form the basic structure of any PCB:

Traces: Copper lines that carry signals and power between components. The trace width determines how much current it can handle. A 0.25mm trace is sufficient for digital signals, but power lines may need 1mm or more. In industrial applications, it is always better to use wider traces than the theoretical minimum to ensure an adequate safety margin.

Pads: Copper areas where component leads are soldered. They come in various shapes: circular for through-hole components and rectangular for SMD components. Pad size affects soldering ease and the strength of the mechanical connection.

Vias: Copper-plated holes that connect layers together. They allow signals to pass from the top side to the bottom side and vice versa. Several types are available:

• Through-hole Via: Penetrates the entire board. The most common and cheapest.
• Blind Via: Connects an outer layer to an inner layer only.
• Buried Via: Connects two inner layers without appearing on the surface.

In standard industrial design, through-hole vias are sufficient for most needs. The common size is 0.3mm for the hole and 0.6mm for the surrounding copper annular ring.

Clearance: The minimum distance between any two copper elements. The typical value is 0.2mm for normal signals. In high-voltage circuits, much larger clearances may be needed to prevent electrical arcing.

PCB Design Stages: From Idea to Board

The PCB design process follows a sequential workflow:

1. Requirements definition: What is the board's function? What voltage and current are needed? What size constraints exist? What is the operating environment (temperature, humidity, vibration)?
2. Schematic capture: Drawing the electrical circuit using standard symbols. This is the most important stage because it defines the circuit's function.
3. Component selection: Choosing actual parts with their footprints. Verifying availability and ensuring prices are suitable.
4. Board layout: Placing components and routing traces on the physical board. This stage determines electrical and thermal performance.
5. Design review (DRC): Running automated checks for errors before manufacturing. Includes spacing, connectivity, and electrical rule checks.
6. Manufacturing file export: Generating Gerber files and bills of materials.
7. Fabrication and assembly: Sending files to the manufacturer and receiving the finished boards.
8. Testing and verification: Testing the manufactured board and confirming it meets specifications.

Each stage builds on the previous one, and an error in the early stages compounds in later stages. The golden rule: spend more time on the schematic and review, and less time fixing manufactured boards.

Typical time allocation for each stage (medium-complexity board):

• Requirements and schematic: 40% of project time
• Board layout: 30%
• Review and verification: 20%
• Manufacturing and testing: 10%

Component Types: SMD vs Through-Hole

Surface Mount Devices (SMD): Soldered directly onto the board surface. Smaller in size and allow higher component density. Resistors in 0603 or 0805 packages are the most commonly used in industrial design. SMD components reduce parasitic inductance, improving performance in high-frequency circuits.

Common SMD package sizes:

• 0201: Very small, requires precision assembly machines
• 0402: Small, possible to hand-solder but difficult
• 0603: A practical size for hand soldering with some practice
• 0805: The most common industrial size, easy to hand-solder
• 1206: Relatively large, very comfortable for hand soldering

Through-Hole Components: Their leads pass through holes in the board. Easier to solder by hand and more mechanically robust. Preferred for connectors and power relays in industrial applications where components are subject to pull and push forces.

In practice, most industrial boards use a mix of both types: SMD for small components like resistors, capacitors, and integrated circuits, and through-hole for terminal connectors and components subject to mechanical stress such as relays and fuses.

Practical Example: A Simple Temperature Sensor Board

Consider designing a small board for reading temperature in a factory environment:

Requirements:

• DS18B20 temperature sensor (digital, 1-Wire protocol)
• ATtiny85 microcontroller to read the sensor
• 5V supply derived from a 24V industrial power source
• Terminal block connector for wiring
• Temperature range: -10 to +85 degrees Celsius
• Vibration resistance for factory environments

Key Components:

• 7805 linear voltage regulator (24V to 5V)
• Filter capacitors: 100uF electrolytic at input and 100nF ceramic at output
• 4.7k ohm pull-up resistor for the data line
• Green status LED with 1k ohm resistor to indicate power-on state
• 4-pin terminal block (24V, GND, Data, Shield)

Board Size: 40mm by 30mm, double-sided, suitable for DIN rail mounting inside a plastic enclosure. M3 mounting holes in all four corners.

Component Placement:

• Voltage regulator and capacitors on the left side (power section)
• Microcontroller in the center
• Sensor connector on the right side
• Power connector at the top

This simple example shows how all concepts come together: signal traces, wider power traces, vias to connect both sides, and a mix of SMD and through-hole components. Even in the simplest boards, you need to apply good design principles.

Summary

The printed circuit board is the backbone of every industrial electronic system. Understanding the basics of layers, traces, and component types is the first step toward designing reliable boards.

Key takeaways from this lesson:

• A PCB consists of copper layers on an insulating FR-4 substrate.
• A double-sided board is sufficient for most industrial applications, and 4 layers for advanced projects.
• Traces, pads, and vias are the fundamental building blocks.
• A mix of SMD and through-hole is the standard in industrial boards.
• The design process starts with requirements and ends with testing.

The concepts we learned in this lesson will be the foundation for everything that follows. In the upcoming lessons, we will dive deeper into each stage of the design process, starting with schematic capture.