What Is Chip on Board (COB)?

COB Technology

This method mounts bare silicon dies directly onto a PCB. In the typical approach, pads on the die are wire-bonded to board traces, then protected with an encapsulant—often the black “glob top.” Some builds add underfill for stress relief. The process flow is straightforward: die attach, wire bonding, and encapsulation. Skipping individual chip packages reduces parts count, saves board space, and can lower costs. Shorter interconnects also cut parasitics, while heat can dissipate more easily into the board. In some designs, flip chip is used instead of wire bonding to further shorten interconnect distance and improve performance. In optical module PCBAs, flip chip is particularly suitable for higher-speed, high-integration modules, typically 800G and above. This approach is common in LED modules, where many small dies are placed close together. Engineers often call the visible epoxy bump the “black blob,” and the overall method is known as chip-on-board.

Advantages and Applications

The gains are clear. 

• Smaller assemblies. 
• Higher density. 
• Shorter interconnects that help signal quality. 
• A direct thermal path that helps with cooling. 
• Lower packaging cost per function in many cases. 
  
  

Typical uses include:

• LED lighting engines for lamps, spots, and displays. 
• Cheap gadgets like toys and calculators that hide a die under epoxy. 
• Custom sensor modules and tight wearables. 
• Radio-frequency designs that benefit from low inductance and capacitance.
  
  

There are trade-offs. Rework is difficult, and cleanliness and protection are critical. While COB provides a direct thermal path, actual performance depends heavily on PCB design. Poor layouts may not achieve better cooling than traditional packaging. Even so, engineers pick COB when size, heat, or cost are tight. Many lighting vendors and module makers now ship parts built with COB technology, and COB LEDs are a growing segment—$2.64 billion in annual sales in 2021, with an 11.4% CAGR reported in one study.

How COB Differs From Traditional Packaging

Traditional: Chips Enclosed in Protective Packages before Mounting

Traditional ICs are diced from the wafer. Then each die goes into a package. The case shields and protects the die. It also gives you pins or balls to solder. Inside, thin wires or bumps link the die to the package leads. The package helps heat flow and blocks moisture. The finished part is then mounted to the PCB as a component. This is the flow most people mean by “IC packaging.” 

COB: Eliminates Separate Chip Packaging, Chips Placed Directly on PCB

In COB packaging, the bare die goes straight on the PCB. Pads on the board ring the die. Wires or bumps connect the die pads to those pads. A glob top epoxy seals the area. There is no separate plastic or ceramic case. Eliminating the discrete package can decrease assembly space by at least 20% compared with packaged parts, per a TESAT/ESA evaluation of CoB assemblies.

Interconnects are very short. That cuts parasitics and can improve heat flow into the board. A 1 mm wire bond contributes about ~1 nH of inductance. On the other hand, a flip-chip bump can be around ~50 pH—approximately twenty times lower—which helps high-frequency performance. You still test and protect the assembly, but the package step is gone.

Key Differences

Aspect	Traditional Packaging	COB
Signal travel distance	Die connects through package leads and traces. Paths are longer.	Die connects right to the PCB. Paths are short.
Signal integrity and electromagnetic interference	Longer interconnects add parasitic L/C. That hurts SI and can radiate more.	Shorter links cut parasitics. That helps SI and lowers EMI.
Data transmission	Extra distance and interfaces add delay.	Shorter paths reduce delay. Links can run faster.
Electrical performance and thermal management	Package materials and length add resistance and inductance. Heat leaves via the package.	Short interconnects trim loss. Heat can sink into the PCB and encapsulant.

Use Cases and Flexibility

Use cases: LED Displays, IoT Sensors, Edge Devices, and Portables

As mentioned, chip-on-board mounts bare dies right on the PCB, so products can be smaller and lighter. That helps tight spaces in wearables and handhelds. It also fits edge boxes that need short paths and good heat flow. For LED walls and signage, COB panels allow very small pixel pitch, so viewers can stand close without seeing dots. E.g., a 0.75 mm pixel-pitch wall has a visual acuity distance of 2.6 m, and a 1.5 mm pitch is 5.2 m. That is handy for control rooms and retail. The LED die cluster also cuts parts count and helps heat spread. Camera modules commonly use COB to place image sensors straight on the board, which suits compact IoT sensor nodes.

Flexibility across Digital, Analog, and Mixed-Signal Work

COB technology supports plain digital ICs, analog front ends, and true mixed-signal blocks on the same module. That covers microcontrollers, ADC/DAC paths, radios, and sensor chains. Wire bonding is a standard, reliable interconnect here, so many die types can be attached without exotic steps. Short interconnects help signal integrity and can lower losses. Real products show this combo: image sensors with analog stages and digital control may ship as COB camera modules. So the same assembly flow can serve logic, RF, and precision analog in one build.

FICG’s Unique Strengths with COB Technology

We build optical modules end-to-end, combining advanced component packaging with silicon photonics. Our R&D integrates DSPs, LDs, driver ICs, and SiPh in CPO modules targeting 3.2T, while our 1.6T OSFP SiPh products started pilot run and shipment in 2024. We apply flip-chip, BGA/LGA, and COB technologies to shorten interconnects, improve heat dissipation, and increase density.

As an EMS provider, FICG focuses on advanced optical transceiver manufacturing in close collaboration with customers on design. Our lines place 008004 parts (0.25 × 0.125 mm), support ~100 µm die pitch, and cover rigid-flex, underfill, glob-top, and full wire-bond processes. We ship 100G–800G at scale with MES traceability plus AOI/SPI/X-ray, and 1.6T is entering manufacturing with strong first-pass yields. Each generation achieves lower power, aligned with our group’s ESG goals on energy use and waste. We also build for data center and telecom applications across QSFP-DD, OSFP, and OSFP-XD form factors.

The Role of COB in Future Electronics

COB enables dense edge modules while placing compute, memory, RF, and sensors close together. Short interconnects cut parasitic L and C, so eyes stay cleaner and I/O runs faster. Heat leaves the die through copper planes, thermal vias, and metal-core bases, which lowers junction temperature when layouts follow proven LED rules. System-in-package and multi-chip module co-assembly keep footprints small and deliver the bandwidth and latency edge compute needs. That density suits IoT nodes that must process data locally with tight power budgets. The net result is that a chip on board helps make systems compact, fast, and efficient.

Contact FICG today to learn how our EMS expertise in COB packaging and optical transceiver manufacturing can support your designs with ultra-high density, reliable thermal management, and energy-efficient builds. From data centers and high-speed transceivers to IoT and edge computing, we work alongside customers to bring innovations to market with scalable, production-ready solutions.