COB
Chip On Board (COB) is a relatively new type of packaging technology. It has many advantages when compared to the hermetically sealed co-axial TO can packaging of Free Space Optics (FSO). COB utilises high precision die and wire bonders to attach chips and subcomponents to a PCB electronically. Optical coupling, with input and output optical fibers, is then achieved with lens arrays and waveguide structures.
The entire process can be highly automated and, because of the precise positioning of chips on the two-dimensional PCB, the difficulty of optical alignment is significantly reduced compared to FSO packaging. This makes COB the preferred choice of packaging technology for high volume manufacturing of transceiver modules.