What is PCB engineering?

Overview of PCB Engineering

The field of PCB engineering encompasses several key areas:

  • Circuit design and schematic capture
  • PCB layout and routing
  • Manufacturing and assembly
  • Testing and quality assurance

Skilled PCB engineers are needed to take a product idea from initial concept through to final production. They must have a strong understanding of electronics theory, PCB materials and fabrication processes, design standards, electromagnetic compatibility (EMC), and more.

The Importance of PCB Engineering

PCBs are at the heart of smartphones, computers, appliances, vehicles, medical devices, aerospace systems, and countless other products we rely on every day. The global PCB market is worth over $60 billion annually and growing.

Well-designed, high-quality PCBs are critical for:

  • Product functionality and reliability
  • Miniaturization and integration of electronics
  • Cost reduction and manufacturability
  • Compliance with regulations and standards

Effective PCB engineering helps companies innovate, solve technical challenges, and bring successful products to market quickly and efficiently. It’s an exciting field that combines creativity and analytical skills.

PCB Design Workflow

The pcb design process typically follows these high-level steps:

  1. Concept and Planning

    • Define product requirements and specifications
    • Create block diagram and select key components
    • Consider enclosure size, power, cost targets, etc.
  2. Schematic Design

    • Capture the circuit diagram in EDA software
    • Apply design for manufacturability (DFM) rules
    • Perform simulation and analysis as needed
    • Generate bill of materials (BOM) and net list
  3. PCB Layout

    • Determine board stack-up and dimensions
    • Place components and route traces
    • Optimize signal integrity and EMC
    • Add planes, pours, vias, and mechanical features
  4. Manufacturing Preparation

    • Generate Gerber files and fabrication drawings
    • Create assembly files, e.g. pick-and-place, test points
    • Communicate requirements to manufacturers
    • Order components and PCB fabrication
  5. Verification and Test

    • Inspect first article boards for workmanship issues
    • Perform functional testing and debug
    • Conduct any compliance testing required
    • Release design to volume production

PCB Design Tools

PCB engineers rely on electronic design automation (EDA) software to efficiently develop complex designs. Popular PCB design tools include:

Tool Vendor Key Features
Altium Designer Altium Schematic capture, PCB layout, 3D viewing, simulation
OrCAD Cadence Schematic capture, PCB layout, SPICE simulation, FPGA integration
EAGLE Autodesk Schematic capture, PCB layout, huge parts libraries
KiCad Open source Schematic capture, PCB layout, 3D viewing, free

Advanced PCB tools offer features like:

  • Rules-driven layout and routing automation
  • Signal and power integrity analysis
  • Circuit simulation and optimization
  • 3D mechanical CAD integration
  • Design data management and version control
  • Real-time collaboration for distributed teams

Selecting the right tools depends on the complexity of the designs, engineering team size, budget, and other factors. Many vendors offer free viewer applications to share designs with clients and manufacturers.

PCB Manufacturing Process

After the PCB design is finalized, it’s time for fabrication. The exact manufacturing process varies depending on the PCB type and specifications, but the general flow is:

  1. Material Selection and Preparation

    • Cut copper-clad laminate to panel size
    • Clean and condition surfaces
    • Apply photoresist coating
  2. Imaging and Etching

    • Expose resist with UV light through photo-tool
    • Develop resist to remove exposed areas
    • Etch away unwanted copper in chemical bath
    • Strip remaining resist
  3. Drilling and Plating

    • Drill component holes and vias with CNC
    • Clean and activate hole walls
    • Electroless copper plate to make holes conductive
    • Electrolytic plate to build up copper thickness
  4. Soldermask and Silkscreen

    • Apply soldermask ink over bare copper
    • Expose and develop mask to remove unwanted areas
    • Cure soldermask to harden
    • Print silkscreen legend on top of soldermask
  5. Surface Finish and Cutting

    • Apply surface finish, e.g. HASL, ENIG, OSP
    • Route or punch boards out of panel
    • Electrical test for shorts and opens
    • Visual inspection and packaging

PCB manufacturers can also handle component sourcing, assembly, and final testing as a turnkey service. This allows the PCB designer to focus on the core design tasks.

Common PCB Specifications

PCBs are available in a wide range of materials, thicknesses, copper weights, and more. Here are some of the key PCB specifications that engineers need to consider:

Spec Description Typical Values
Layers Total number of copper layers 1, 2, 4, 6, 8, 10+
Material Laminate material type FR-4, Rogers, Polyimide, Metal Core
Thickness Overall board thickness 0.8mm, 1.0mm, 1.2mm, 1.6mm, 2.0mm
Copper Weight Thickness of copper foil 1/2 oz, 1 oz, 2 oz, 3 oz
Minimum Trace/Space Smallest trace width and separation 3/3 mils, 4/4 mils, 5/5 mils, 8/8 mils
Minimum Drill Smallest finished hole size 8 mils, 10 mils, 12 mils
Surface Finish Final plating on exposed copper HASL, ENIG, OSP, Immersion Silver

The choice of specifications impacts the PCB’s electrical performance, mechanical strength, thermal management, manufacturability, and cost. Designers must balance tradeoffs and follow industry standards like IPC.

Types of PCBs

PCBs can be categorized in different ways based on their construction and use case. Common PCB classifications include:

  • Rigid PCBs – Traditional solid boards made of FR-4 glass-reinforced epoxy laminate. Used for most standard electronics products.

  • Flexible PCBs – Thin, bendable boards made of polyimide or other flexible substrates. Used in compact products like smartphones and wearables.

  • Rigid-Flex PCBs – Combines rigid and flexible sections in one assembly. Allows 3D shaping of the circuit to fit in tight spaces.

  • HDI PCBs – High Density Interconnect boards with fine features and microvias. Enable miniaturization and high signal speeds.

  • rf pcbs – Optimized for high frequency signals, e.g. wireless communications. Use low-loss materials and controlled impedance.

  • Metal Core PCBs – Have a metal base layer for efficient heat transfer. Used for high-power LEDs and automotive applications.

Each type of PCB has its own design guidelines, material options, and manufacturing considerations that PCB engineers must understand.

Signal and Power Integrity

One of the most important aspects of PCB engineering is ensuring good signal integrity (SI) and power integrity (PI). This means the signals and power supplies on the board are clean, stable, and well-controlled.

Signal Integrity Considerations

As digital signals get faster and PCBs get denser, paying attention to SI becomes critical. SI problems that can impact product performance include:

  • Reflections – When signals encounter impedance discontinuities and bounce back, causing noise and timing errors. Minimized by matching trace impedances and terminating signals properly.

  • Crosstalk – When signals couple together through mutual inductance or capacitance, causing interference. Managed by providing adequate spacing, orthogonal routing, and shielding.

  • Skew – When timing differences between related signals, e.g. a bus, cause data corruption. Addressed by length-matching traces and using serpentine delay lines.

  • EMI – When signals radiate or pick up electromagnetic interference, causing product failures or violating emission limits. Contained with proper grounding, filtering, and shielding.

Designers use controlled impedance traces, differential pairs, ground planes, and other techniques to maintain good SI. Specialized tools are used to model and simulate critical signals.

Power Integrity Considerations

Stable and noise-free power delivery is just as important as SI for reliable PCB operation. PI challenges include:

  • DC Drop – When resistive losses cause supply voltages to sag at high current loads. Prevented by using wide traces, copper pours, and multiple supply vias.

  • AC Noise – When transient currents interact with trace inductance and cause supply ripple. Suppressed by adding local decoupling capacitors and optimizing capacitor placement.

  • Ground Bounce – When fast switching currents cause the ground reference to shift, leading to signal degradation. Avoided by separating analog and digital grounds and providing low-impedance return paths.

  • EMI Susceptibility – When noise couples into power planes and causes interference. Reduced by using proper bypassing and filtering near connectors.

PCBs often have split planes for analog and digital power and ground. The PDN (power distribution network) impedance is carefully designed to maintain low noise. PI simulation tools help optimize the bypassing scheme.

Thermal Management

Keeping components cool is another key aspect of PCB engineering. Overheating can cause reliability issues, reduced performance, and even catastrophic failures.

Thermal Design Techniques

Strategies for managing heat on a PCB include:

  • Component Placement – Providing adequate airflow and spacing hot components apart. Keeping temperature-sensitive parts away from heat sources.

  • Heatsinks – Attaching metal fins or blocks to dissipate heat from power devices. May be enhanced with fans or fluid cooling.

  • Metal Core Boards – Using a metal base layer in the PCB stackup to spread heat. Copper or aluminum cores are common.

  • Thermal Vias – Adding vias to transfer heat from component pads to internal or bottom-side planes. Also called thermal relief.

  • Thick Copper – Using 2 oz or greater copper weight for high current traces and planes. Improves current capacity and thermal conductivity.

The PCB designer must calculate power dissipation and temperature rise to ensure the thermal solution is adequate. Thermal simulation software can model heat flow and identify hot spots.

Thermal Regulations and Standards

Depending on the industry and application, there may be specific thermal requirements the PCB needs to meet. Examples include:

  • IPC-2152 – Standard for determining current carrying capacity of PCB traces based on temperature rise.

  • UL 94 – Flammability rating for PCB materials. Required for certain consumer electronics and appliances.

  • MIL-STD-810 – Environmental testing standard for military equipment, including temperature and humidity exposure.

  • ISO 7637-2 – Automotive standard for electrical disturbances from conduction and coupling. Includes tests for transient immunity.

Meeting these standards often requires careful thermal design, material selection, and testing. Working with experienced manufacturing partners is recommended.

PCB Testing and Quality Assurance

Thorough testing and inspection are critical for producing reliable, high-quality PCBs. This includes both in-process checks and final functional testing.

PCB Testing Methods

Common PCB testing techniques include:

  • Automated Optical Inspection (AOI) – Using cameras and image processing to check for defects like missing components, wrong parts, and solder bridging.

  • X-Ray Inspection – Using X-ray imaging to see hidden features like BGA solder joints, vias, and internal traces. Detects voids, cracks, and opens.

  • In-Circuit Test (ICT) – Using a bed-of-nails fixture to make electrical contact with test pads on the board. Checks for shorts, opens, resistance, capacitance, and component values.

  • Flying Probe Test – Using moving test probes to check electrical connectivity and component values. More flexible than ICT but slower.

  • Functional Test – Powering up the board and running test software to exercise its features and performance. May involve boundary scan, JTAG, or other interfaces.

The specific test strategy depends on the PCB complexity, volume, and reliability requirements. Often a combination of methods is used for full coverage.

Quality Standards and Certifications

PCB manufacturers and assemblers often hold quality certifications to demonstrate their processes and controls. Key standards include:

  • ISO 9001 – Quality management system requirements for consistent products and services. Includes documentation, training, and continuous improvement.

  • IPC-A-610 – Acceptability criteria for PCB assemblies. Defines workmanship standards for solder joints, component placement, cleaning, and repair.

  • J-STD-001 – Requirements for soldered electrical and electronic assemblies. Covers materials, methods, and verification for producing high quality solder interconnects.

  • UL Listing – Safety certification for PCBs used in products that must meet UL standards. Involves flammability testing and factory inspections.

Working with properly certified suppliers helps ensure the PCBs will meet the required quality and reliability levels. Regular audits and first article inspections provide additional assurance.

Frequently Asked Questions

What education is needed to become a PCB engineer?

Most PCB engineering roles require at least a bachelor’s degree in electrical engineering, computer engineering, or a related field. Coursework should include circuit analysis, PCB design, EMC, and CAD tools. Hands-on projects and internships are also valuable. Some positions may require a master’s degree for advanced topics like high-speed design or RF engineering.

What skills are important for PCB engineers?

In addition to technical knowledge, important skills for PCB engineers include:

  • Attention to detail and quality focus
  • Problem solving and debugging
  • Communication and teamwork
  • Time management and organization
  • Continuous learning to keep up with new technologies

Proficiency with specific EDA software, like Altium Designer or OrCAD, is often required. Programming skills, like Python or MATLAB, can also be useful for automation and analysis tasks.

How much do PCB engineers earn?

Salaries for PCB engineers vary depending on location, experience level, and industry. According to data from Glassdoor, the national average base pay for a PCB design engineer in the United States is $85,107 per year. Senior-level positions and those in high-cost areas can earn significantly more. Freelance designers may charge hourly rates of $50 to $150 or more.

What are some common PCB design mistakes to avoid?

Some of the most common pitfalls in PCB design include:

  • Incorrect footprints or pinouts for components
  • Failing to consider manufacturability and assembly
  • Neglecting to simulate or test critical signals
  • Improper grounding and power delivery
  • Inadequate documentation and version control

To minimize errors and optimize the design, it’s important to use checklists, follow best practices, and get peer reviews. Involving the manufacturer early can also help identify and resolve potential issues.

What are some emerging trends in PCB engineering?

The PCB industry is constantly evolving to support new technologies and applications. Some key trends include:

  • Smaller, denser PCBs to enable IoT and wearable devices
  • Higher speeds and frequencies for 5G and automotive radar
  • Advanced packaging like 3D-IC and embedded components
  • Flexible and stretchable PCBs for unique form factors
  • Sustainable materials and processes to reduce environmental impact

Staying on top of industry news, attending conferences, and networking with peers can help PCB engineers stay current and adapt to new challenges. With the right skills and mindset, it’s an exciting time to be in the field of PCB engineering.