Optical Device Packaging Process
The packaging technologies of TOSA and ROSA mainly include TO-CAN coaxial packaging, butterfly packaging, COB (ChipOnBoard) packaging, and BOX packaging.
TOSA, ROSA and electrical chips are the three parts with the highest cost ratio among optical modules, accounting for 35%, 23% and 18% respectively. The technical barriers in TOSA and ROSA are mainly in two aspects: optical chip and packaging technology.
In general, ROSA is packaged with a splitter, a photodiode (replacement of light pressure into voltage) and a transimpedance amplifier (amplified voltage signal), and TOSA is packaged with a laser driver, laser and multiplexer.
The packaging technologies of TOSA and ROSA mainly include the following:
1) TO-CAN coaxial package;
2) Butterfly package;
3) COB (ChipOnBoard) package;
4) BOX packaging.
TO-CAN coaxial package: The shell is usually cylindrical, because of its small size, it is difficult to build in refrigeration, it is difficult to dissipate heat, and it is difficult to use for high power output at high current, so it is difficult to use for long-distance transmission. At present, the main application is also 2.5Gbit / s and 10Gbit / s short-distance transmission. But the cost is low and the process is simple.
Butterfly package: The shell is usually a rectangular parallelepiped, and the structure and implementation functions are usually more complicated. It can be equipped with a refrigerator, heat sink, ceramic base block, chip, thermistor, backlight monitoring, and can support the bonding wires of all the above components. The housing has a large area and good heat dissipation, and can be used for transmission at various speeds and long distances of 80km.
COB packaging means chip-on-board packaging, and the laser chip is adhered to the PCB substrate, which can achieve miniaturization, light weight, high reliability and low cost. The traditional single-channel 10Gb / s or 25Gb / s rate optical module uses SFP package to solder the electrical chip and TO packaged optical transceiver components to the PCB board to form the optical module. For a 100Gb / s optical module, when using a 25Gb / s chip, 4 sets of components are required. If SFP packaging is used, 4 times the space will be required. COB packaging can integrate the TIA / LA chip, laser array and receiver array in a small space to achieve miniaturization. The technical difficulty lies in the positioning accuracy of the optical chip patch (affecting the optical coupling effect) and the bonding quality (affecting the signal quality and bit error rate).
The BOX package is a butterfly package, used for multi-channel parallel package.
25G and below rate optical modules mostly use single-channel TO or butterfly packages, with standard process and automation equipment, and low technical barriers. However, for high-speed optical modules with a rate of 40G and above, limited by the rate of the laser (mostly 25G), it is mainly realized through multiple channels in parallel. For example, 40G is realized by 4 * 10G, and 100G is realized by 4 * 25G. The packaging of high-speed optical modules puts forward higher requirements for the heat dissipation problems of parallel optical design, high-rate electromagnetic interference, reduced size, and increased power consumption. With the increasing speed of optical modules, the baud rate of single channel has already faced a bottleneck. In the future, to 400G and 800G, parallel optical design will become more and more important.