Understanding Chip on Board (COB)
Chip on Board (COB) technology involves mounting bare silicon dies directly onto a printed circuit board (PCB). In this approach, the pads on each die are connected to the board traces through wire bonding and then covered with a protective encapsulant, commonly recognized as the black “glob top.” Some assemblies include an underfill layer to relieve mechanical stress.
The process generally follows three steps: die attachment, wire bonding, and encapsulation. By eliminating individual chip packages, COB reduces the number of components, saves board space, and can lower production costs.
Certain designs use flip chip technology instead of wire bonding to further shorten interconnect distances and enhance performance. This technique is particularly useful in high-speed, high-integration optical modules, typically 800G and above. COB is also widely used in LED modules, where multiple small dies are positioned closely together. The visible epoxy covering is sometimes referred to as the “black blob,” giving the method its familiar name.
Benefits and Key Applications of COB Technology
Chip on Board offers significant advantages in electronics design and manufacturing. Its ability to reduce size and improve performance makes it a preferred choice for many modern devices.
Advantages of COB Technology
- Compact assemblies: COB reduces overall component size, enabling smaller, more efficient designs.
- Higher component density: Multiple dies can be placed closely together, maximizing functionality in limited space.
- Improved signal quality: Shorter interconnects reduce parasitic effects, enhancing performance.
- Enhanced thermal management: Direct contact with the printed circuit board (PCB) enables more effective heat dissipation.
- Cost efficiency: Eliminating individual chip packaging often lowers the cost per function.
Common Applications
COB technology is widely used across various industries:
- LED lighting: COB is popular in lamps, spotlights, and display modules for consistent brightness and compact form factors.
- Consumer electronics: Affordable gadgets like toys and calculators often conceal dies under epoxy.
- Wearables and sensors: Custom sensor modules and small wearable devices benefit from space-efficient COB assemblies.
- Radio-frequency designs: COB minimizes inductance and capacitance, improving performance in RF circuits.
Considerations and Industry Trends
Despite its advantages, COB has limitations. Reworking assemblies can be challenging, and maintaining cleanliness and protection during manufacturing is critical. Thermal performance depends heavily on PCB design; poorly designed layouts may not deliver better cooling than conventional packaging.
Even so, engineers adopt COB when compact size, heat management, or cost reduction is a priority. Lighting manufacturers and module makers increasingly ship products using COB technology. The COB LED market alone reached $2.64 billion in annual sales in 2021, with a reported growth rate of 11.4% per year.
Comparing COB and Traditional Chip Packaging
Traditional IC Packaging: Enclosed and Ready to Mount
Standard ICs begin as diced silicon wafers, with each die placed inside a protective package. The package serves multiple purposes: it shields the die from moisture and physical damage, provides solderable leads or balls, and helps conduct heat away from the chip. Inside, tiny wires or bumps link the die to these leads. Once packaged, the IC can be handled and mounted on a PCB like any other component. This method has been the standard for decades and is what people typically associate with “chip packaging.”
COB Approach: Direct-to-Board Dies
COB skips the separate package entirely. The bare die is attached straight to the PCB, with its pads connected to the board’s traces via wire bonds or flip-chip bumps. Without the traditional casing, assemblies are more compact, evaluations by TESAT/ESA show space savings of at least 20% compared with conventional packaged parts.
Short interconnects also reduce parasitic inductance and capacitance. For reference, a typical 1 mm wire bond adds around 1 nH, while a flip-chip bump can be as low as 50 pH, dramatically improving high-frequency performance.
Comparing Performance: COB vs Traditional Packaging
| Aspect | Chip on Board (COB) | Traditional Packaging |
| Data speed | Short, direct connections reduce signal delay and enable faster data transfer. | Extra distance through the package leads to delay. |
| Electrical and thermal performance | Heat can dissipate directly into the PCB and encapsulant; short interconnects lower resistance and loss. | Heat exits through the package; longer leads and materials add resistance and inductance. |
| Signal integrity and EMI | Reduced parasitics improve signal quality and minimize electromagnetic interference (EMI), which is unwanted radiation or noise that can affect nearby electronics. | Longer interconnects increase parasitic effects, which can degrade signal quality and generate more EMI. |
| Signal path length | Die connects directly to PCB pads, keeping paths short. | Die connects through package leads, creating longer electrical paths. |
Compact and Efficient COB Designs
Applications include: edge devices, portables, LED displays, and IoT sensors.
By mounting bare dies directly on the PCB, COB allows devices to become smaller and lighter, making it easier to integrate advanced functionality into limited spaces. Short interconnects enhance signal performance by reducing parasitic capacitance and inductance, while heat dissipates more efficiently through the PCB and encapsulant, helping to maintain stable operation.
Supporting Digital, Analog, and Mixed-Signal Designs
COB technology enables the coexistence of digital ICs, analog front ends, and mixed-signal blocks on a single module. Wire bonding provides a reliable connection for various die types, while short interconnects improve signal integrity and reduce losses.
Examples include COB camera modules, where image sensors integrate analog stages with digital control. The same assembly flow can handle logic, RF, and precision analog circuits in one compact design.
FICG’s Expertise in COB Technology
FICG delivers end-to-end optical module solutions by combining advanced component packaging with silicon photonics. Our R&D integrates DSPs, laser diodes, driver ICs, and SiPh into CPO modules targeting 3.2T, while 1.6T OSFP SiPh products are expected to begin pilot runs and shipments in 2024.
As an EMS provider, FICG specializes in advanced optical transceiver manufacturing, collaborating closely with customers on design and development. Our production lines handle 008004 parts (0.25 × 0.125 mm), support ~100 µm die pitch, and cover rigid-flex assemblies, underfill, glob-top, and full wire-bond processes. We ship 100G–800G modules at scale with MES traceability, AOI/SPI/X-ray inspection, and are ramping 1.6T production with strong first-pass yields.
Each generation reduces power consumption, aligning with our ESG commitments on energy use and waste reduction. Our solutions serve data center and telecom applications across QSFP-DD, OSFP, and OSFP-XD form factors.
Advancing Electronics with Chip-on-Board Technology
COB allows edge modules to pack compute, memory, RF, and sensors closely together. Short interconnects minimize parasitic inductance and capacitance, thereby enhancing signal integrity and increasing I/O speed.
Combining system-in-package and multi-chip modules keeps footprints compact while providing the bandwidth and low latency needed for edge computing, resulting in smaller, faster, and more efficient systems.
