HDI Printed Circuit Boards – A revolution in miniaturization and electronic performance
HDI Printed Circuit Boards represent the current standard for advanced electronic applications.
In the electronics industry, the trend is clear: devices are becoming smaller, more powerful, and faster.
High-Density Interconnect (HDI) printed circuit boards play a key role. These boards allow for much higher circuit density than traditional PCBs and are essential for modern technologies—from smartphones and IoT devices to medical equipment and automotive electronics.
What are HDI PCBs and how do they differ?
HDI Printed Circuit Boards are designed to achieve extremely high routing and component density. This means:
- Finer trace widths and spacings – typically 50–100 µm (some ultra-thin HDI PCBs reach 25 µm).
- Microvias – diameters of 75–150 µm.
- Blind and buried vias, connecting only selected layers.
- Board layers – HDI PCBs often have 4 to 12 layers, and up to 20 layers for advanced applications.
- Surface finishes – ENIG (Electroless Nickel Immersion Gold) or HASL (Hot Air Solder Leveling) for better solderability and durability.
Advantages of HDI interconnects
Miniaturization and Integration
Smaller vias and tighter spacing allow the board to be up to 50% smaller without losing functionality.
Improved Electrical Performance
- Impedance: 20–100 Ω ±10% for high-speed signals
- Signal integrity: Reduced crosstalk and EMI due to shorter paths
- High-frequency capability: up to hundreds of MHz or even GHz
Higher Reliability
- Microvias reduce mechanical stress
- Vibration and thermal shock resistance: typically −40 °C to +125 °C
Flexible Design
- Combination of rigid-flex HDI Printed Circuit Boards are designed to achieve extremely high routing and component density. for hybrid applications
- Support for complex packages: SiP, MCP, BGA
What are SiP, MCP, and BGA?
SiP – System in Package
Definition: An integrated system combining multiple chips and passive components (resistors, capacitors) into a single package.
Purpose: Enables small, compact modules functioning as a complete subsystem (e.g., Wi-Fi or Bluetooth modules).
Advantages: Reduces device size, simplifies integration, and improves electrical connections between chips inside the package.
Applications: Mobile phones, IoT devices, sensors.
MCP – Multi-Chip Package
Definition: Similar to SiP, but refers to a package containing multiple chips of the same or different types combined within one casing.
Purpose: Saves space and reduces board complexity by integrating multiple chips into a single package.
Advantages: Smaller PCB footprint and faster communication between chips.
Applications: Memory modules, CPU + memory combinations in mobile devices.
BGA – Ball Grid Array
Definition: A type of integrated circuit package with spherical contacts (balls) on the underside instead of traditional pins.
Purpose: Allows high-density connections and reliable soldering in a small form factor.
Advantages: Better heat dissipation, high soldering reliability, suitable for high-speed signals.
Applications: Processors, graphics chips, memory chips.
Simply put:
SiP and MCP are packages that combine multiple chips into one small module. BGA is a specialized method of connecting a chip to a board with high interconnect density.
How HDI PCBs are made – Technical overview
- Material selection: FR-4, polyimide, PTFE (for high-frequency applications)
- Inner layer fabrication: Etching photoresist patterns with ±10 µm tolerance
- Inner layer inspection: Automated optical inspection (AOI)
- Layer lamination: Pressure 4–10 MPa, temperature 180–220 °C
- Microvia drilling: Laser (UV or CO₂) or mechanical, diameter 75–150 µm
- Hole metallization: Copper plating, thickness 2–10 µm
- Outer traces: Trace width 50–100 µm, spacing 50–100 µm
- Surface finish: ENIG 3–5 µm Au, HASL ±25 µm
- Final inspection: Electrical testing (Flying Probe Test), visual AOI check.
AOI is a method of inspecting PCBs
AOI is a method of inspecting PCBs using cameras and visual analysis without physical contact. “Visual” means the system examines the board with a camera, detects defects, and compares them to the digital board design. X-ray inspection for BGA and microvias is also part of the final quality check.
Applications of HDI Printed Circuit Boards
Thanks to their miniaturization, high performance, and reliability, HDI Printed Circuit Boards are used in:
- Smartphones and tablets
- Wearables and IoT devices
- 5G systems and high-speed communication
- Automotive electronics
- Medical devices
Conclusion
HDI Printed Circuit Boards are the current standard for advanced electronic applications: they enable miniaturization, high reliability, and electrical performance that traditional PCBs cannot achieve.
With precise manufacturing, microvias, and complex layer structures, modern electronic devices can meet the growing demands for performance and compact size. With the rise of 5G, AI, and advanced IoT technologies, the importance of HDI Printed Circuit Boards are designed to achieve extremely high routing and component density. will only continue to grow.