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COB (Chip on Board) and BOX (Airtight Package) are two types of primary packaging technology in fibre optic transceivers, one solution can be advantageous over the other dependant on use case and form factor.
What is COB technology?
COB (Chip on board) is a form of packaging that directly bonds the chip on the PCB. The circuit is connected by wire bonding and sealed with epoxy resin adhesive or silicone resin top drip. A transceiver with chip-on-board technology connects the laser and receiver to the PCB directly.
There are 3 key components to the COB process:
- Die bonding – bonding a chip to the PCB to form an electrical path.
- Wire bonding – an electrical circuit is created between the chip and the PCB by the welding and bonding of thin metal wires.
- Coupling – ensures the vertical light emitted by the VCSEL is emitted in parallel and enters the optical fibre for transmission.
Because the chip does not need to be individually packaged, but is mounted directly on the PCB, manufacturing costs are lower than BOX packaging. Manufacturing processes such as die bonding, wire bonding and coupling/alignment can be easily automated to support mass production of products.
COB technology enables the integration of multiple optical components and semiconductor chips on a single PCB. The integration of optical components and chips on a single PCB reduces the number of interfaces between the components, leading to higher efficiency and reduced power consumption in the right operating environment.
Where is COB technology used?
COB is mature technology and widely used. In the optical transceiver industry, COB is mainly deployed in form factors designed for short reach applications in controlled, stable environments with constant commercial grade temperatures (0-70 °C) and humidity such as datacentres.
These would typically be commercial operating temperature transceivers with a reach of up to around 100m.
COB would not be recommended for unstable, extended, or industrial temperature environments or long reach applications.
What is BOX packaging?
In BOX packaging, also known as airtight package, the optical chip is encapsulated in a metal box filled with inert gas to protect the optical components from the external environment and improve heat dissipation. The optical path is isolated from the outside world by an optical window.
Where is BOX packaging used?
BOX packaging technology tends to have a more stable optical and electrical performance with improved heat dissipation. In the optical transceiver industry, BOX is traditionally used in long-reach transceivers and environments with uncontrolled environments with fluctuating or non-commercial temperatures and humidity.
Advantages of BOX packaging
Ease of Integration: BOX packaging allows for the integration of laser components into a standardised housing, making it easier to assemble and integrate into transceiver modules or systems.
Enhanced Protection: BOX packaging provides a protective enclosure for the laser components, shielding them from external elements such as dust, moisture, and mechanical stress. This helps to improve the reliability and longevity of the laser components.
Customisation and Flexibility: BOX packaging offers more flexibility for customisation and modification of the transceiver's electrical and mechanical characteristics. Different connector types, power options, and interface configurations can be easily implemented to meet specific application requirements.
Testing and Maintenance: BOX packaging enables easier testing, repair, and replacement of individual laser components. Since the components are not directly mounted on the PCB, they can be accessed and serviced more conveniently, simplifying troubleshooting and maintenance tasks.
Thermal Management: The BOX packaging design often includes features for effective thermal management, such as heat sinks or thermal pads. This helps to dissipate heat generated by the laser components and maintain optimal operating temperatures, ensuring a reliable and stable performance.
Scalability and Future Upgrades: BOX packaged laser components provide scalability options, allowing for future upgrades or replacements without significant modifications to the overall transceiver design. This flexibility is advantageous in evolving network environments.
How do COB and BOX compare?
COB packaging transceiver has good electrical and thermal performance and is suitable for short reach stable, controlled environments. COB is also a more cost-effective solution. The BOX packaging transceiver has a more stable optical and electrical performance suited to long reach and uncontrolled environments.
It is also important to note that BOX packaging transceivers can be used to replace COB packaging transceivers, however it is not advisable to replace BOX optics with COB especially for long reach telecom applications.
From the end user point of view, the main difference between COB and BOX Packaging transceiver optics is the difference in performance, different use scenarios, and cost, COB being a cheaper option than BOX.
The specific application may need to be considered when you wish to make a choice between COB or BOX packaging.
Overall however, BOX packaged laser components in transceivers offer improved protection, customisation options, ease of maintenance, and compatibility, making them a preferred choice for many optical transceiver applications.
ATGBICS and COB / BOX technology
ATGBICS fibre optic transceivers are manufactured using the optimal technology and manufacturing processes for the form factor, reach and use case.
Our default manufacturing option is BOX but where the specific application requires it, we will manufacture using the COB solution.
When building a prototype for clients, we will always consider the use case when deciding on the packaging type.
