What is Chip on Carrier?

COC is an abbreviation for Chip on Carrier, meaning that the chip is mounted on a carrier.

COC (Chip-on-Chip) technology is a packaging technology that directly mounts a chip onto a carrier, also known as a packaging substrate or packaging plate. This carrier can be a ceramic material or a special plastic. It serves as a bridge between the bare chip and external circuitry and is a crucial component of optoelectronic ICs. Taking the COC form of a semiconductor optical amplifier (SOA) as an example, see Figure 1 below.

The central part of the diagram shows the SOA chip (bare chip), fixed to a ceramic substrate (carrier) using special adhesive or eutectic bonding. See the gray area in the diagram. A thin metal film is deposited on the remaining space on the carrier, as shown by the gold-colored areas at the four corners. Gold wires are then laid between the electrodes of the chip and the metal film, making the metal film a relay island for circuit connections. This creates a COC-type SOA. COC-type SOAs are small, lightweight, and easy to package. They can also be supplied to other optical device manufacturers to combine with other miniature active and passive optoelectronic devices to create new photonic integrated circuits according to their applications and design concepts. This significantly reduces the packaging difficulty and cost for optical device manufacturers, shortens the development cycle of new products, and effectively improves the integration and reliability of optoelectronic devices. COC technology is widely used in microwave RF, optoelectronics, and sensor fields and is an important packaging technology.

The reason why SOAs need a COC supply form is determined by the characteristics of optoelectronic semiconductors and the packaging process. Pure electronic semiconductors involve only the flow of electrons. A single diode or transistor can be made very small, and hundreds of millions can be fabricated on a single chip, as seen in common IC integrated circuits such as CPUs and memory. However, optoelectronic semiconductor chips are different; in addition to electrons, photons also move within them. To generate more photons, optoelectronic semiconductor diodes are often made larger. Furthermore, different functional optoelectronic chips are doped with different elements, resulting in significant differences in their internal structures. Thus, optoelectronic chips often appear as independent units. To connect the optical paths of active or passive optical devices with different characteristics, the chip needs to be raised to a certain height; this height is provided by the carrier in the COC (Chip-on-Chip). Therefore, the COC becomes one of the available forms of optoelectronic semiconductors such as SOA (Optically Oriented Aspects).