Chip-on-Board Assembly Explained: A Guide to High-Density Electronic Packaging
As electronic devices continue to shrink while performance expectations rise, manufacturers are increasingly turning to advanced packaging techniques to achieve higher functionality in smaller footprints. One such technique is Chip-on-Board (CoB) assembly—a proven and versatile method used across semiconductor, medical, aerospace, photonics, and research-driven applications.
This article explains what chip-on-board assembly is, how it works, its advantages, and where it is most commonly used, particularly in R&D, prototyping, and low-volume production environments.
What Is Chip-on-Board Assembly?
Chip-on-board (CoB) assembly is an electronic packaging process in which bare semiconductor die are mounted directly onto a substrate, such as a printed circuit board (PCB), ceramic carrier, or hybrid substrate. Instead of first packaging the chip into a conventional IC package, the die is bonded directly to the board and then electrically connected using fine wire bonds.
Once interconnection is complete, the exposed die and wire bonds are typically protected with a glob-top epoxy or encapsulation material, providing mechanical support and environmental protection.
CoB is often considered a subset of die bonding and wire bonding technologies, combining both processes into a compact, high-density assembly solution.
How Chip-on-Board Assembly Works
Chip-on-board assembly is a multi-step process requiring careful control, precision handling, and clean working conditions:
- Substrate Preparation – Cleaning, plasma treatment, or surface conditioning to ensure optimal adhesion and electrical reliability.
- Die Attach (Die Bonding) – The bare semiconductor die is placed directly onto the substrate using a conductive or non-conductive adhesive, depending on thermal and electrical requirements.
- Wire Bonding – Fine aluminium or gold wires are ultrasonically bonded between the die pads and the substrate bond pads to establish electrical connections.
- Encapsulation – A glob-top epoxy or encapsulant is applied to protect the delicate die and wire bonds from mechanical damage, moisture, and contaminants.
- Inspection and Testing – High-magnification optical inspection and electrical testing verify bond integrity, alignment accuracy, and overall assembly quality.
Key Advantages of Chip-on-Board Assembly
- Miniaturisation and High Density – Eliminates conventional IC packaging to significantly reduce size and weight.
- Improved Electrical Performance – Shorter interconnect lengths reduce parasitic inductance and resistance, improving signal integrity.
- Thermal Management – Direct mounting of the die onto the substrate can improve heat dissipation.
- Design Flexibility – Enables customised layouts, materials, and interconnect strategies.
- Cost Efficiency for Low Volumes – Avoids high tooling costs and minimum order quantities for prototypes and small batch builds.
Typical Applications of Chip-on-Board Assembly
- Medical electronics – implantable devices, diagnostic sensors, and portable monitoring equipment
- Photonics and optoelectronics – laser drivers, detectors, and optical modules
- MEMS sensors – accelerometers, pressure sensors, and microfluidic devices
- Aerospace and defence – lightweight, high-reliability electronic modules
- Research and university projects – experimental devices and custom test platforms
- Start-up prototyping – early-stage product development without committing to high volumes
Chip-on-Board vs Traditional IC Packaging
- Size: Ultra-compact vs larger footprint
- Performance: Excellent signal integrity vs moderate
- Flexibility: High vs limited
- Volume suitability: Low to medium vs medium to high
- Customisation: Extensive vs minimal
Why Precision Matters in Chip-on-Board Assembly
Successful chip-on-board assembly depends on micron-level accuracy, controlled processes, and experienced operators. Misalignment, contamination, or poor bond quality can compromise performance or long-term reliability.
Precision engineering providers with integrated die bonding, wire bonding, micro assembly, and inspection capabilities are best placed to deliver consistent, high-quality CoB assemblies.
Chip-on-Board Assembly at ICT
With over 30 years of experience in micro precision manufacturing, ICT supports chip-on-board assembly for universities, research organisations, start-ups, and specialist OEMs. By combining manual die bonding, ultrasonic wire bonding, controlled surface preparation, and detailed inspection, ICT enables customers to develop and validate advanced electronic devices without the constraints of mass production.
Conclusion
Chip-on-board assembly remains a powerful and relevant packaging solution for modern electronics, offering compact design, excellent performance, and unmatched flexibility.
As device architectures continue to evolve, chip-on-board assembly will remain a cornerstone technology for engineers pushing the boundaries of miniaturisation and functionality.
Sources
- Microelectronics Packaging Handbook – Rao Tummala
- IEEE Electronics Packaging Society – Chip-on-Board Technology Overview
- Semiconductor Industry Association – Advanced Packaging Technologies
- ASM Assembly Materials – Die Attach and Wire Bonding Fundamentals
