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The packaging process of optical devices includes TO56, COB, etc. The process used by high-speed optical modules 100G40G is COB (chip onboard). First, the chip is mounted. The PCB board with SMT mounted is placed on the optical chip mounter, dipped in silver and then mounted. After the mounting, there is a visual inspection to observe whether the amount of silver paste overflows, etc., and then the electrical chip is mounted, and the same operation is performed.
Wire bonding, wire bonding is to bond gold wires between the Driver TIA and the LD PIN array and between the Driver TIA and the PCB. It is usually performed by a wire bonding machine. SMD and wire bonding are crucial. The wire bonding needs to meet the tensile test. The length of the wire bonding also has certain requirements. Too long or too short will affect the actual performance, such as sensitivity, emission eye diagram, and optical module failure analysis. There are factors such as wire breakage. In actual R&D testing, it is specifically included to extend the wire bonding for performance testing. Each optical chip has about three wires (anode cathode ground), plus the peripheral wire bonding of the electrical chip,
usually about 20-30 wires, which requires the accuracy of the wire bonding machine. After the wire bonding, it is still visually inspected.
Plasma cleaning, put it in a plasma cleaning machine for cleaning, usually to remove debris from the chip, etc.
Coupling, coupling is to fix the lens on the PCB board so that the light emitted vertically by the VCSEL can be reflected and emitted in parallel through the lens. The coupling step is crucial. A crooked lens or unreasonable UV glue coating will cause changes and differences in the emitted light power and sensitivity. Especially for optical chip arrays, the crooked lens will cause differences in the sensitivity of each channel, which is a headache. The light reflected by the lens passes through the MT-MT optical fiber interface and then connects to the structural parts and MPO optical fiber. Common ones are passive coupling and active coupling. Active coupling is to power on the PCB and determine the position of the lens according to the optical power emitted by each channel; passive coupling is determined according to the projection position.
100G SR440G SR4VCSEL coupling is to fix the lens with UV glue, while others such as 100G CWDM4 are coupled by laser welding. The automatic coupling machine automatically couples to the best position according to the optical power, and then fixes it with laser welding.
After a series of processes are completed, aging is performed, and then the finished product is ready for use after assembling the structural parts. However, the module firmware has not been upgraded at this time, and the information such as A0 A2 code writing temperature compensation of each chip register table has not been imported. After completing these operations, it can be tested.
The COB process of the optical module, the previously described process includes patch, wire bonding, coupling, aging, etc. Coupling is to transmit and receive coupling after COC patch and wire bonding and importing the corresponding firmware. Coupling usually includes active and passive. Passive is to fix the lens according to the position of the projection, and active is to couple according to the light power emitted after the PCBA is powered on.
The type of 100G SR440G SR4 laser is VCSEL, vertical cavity surface emission. After bonding the optoelectronic chip and the chip, the lens is attached to it. After powering on, the position of the three-dimensional coupling table, that is, the position of the lens, is adjusted according to the light power emitted. When the light power of each channel meets the requirements and is relatively stable, the lens is fixed with black glue. Generally, this is manual coupling. Manually adjusting the position of the lens is a test of operating skills. For example, if the channel optical power increases, the lens will be skewed.
100G CWDM440G PSM4 is a DFB (distributed feedback) laser that emits light horizontally. Therefore, the general process is not to stick the optical chip on the PCB, but only stick the electrical chip and PINARRAY on the PCB. The DFB array is also stuck on a base, and the base and PCB are connected and fixed with black glue UV glue, wired, and then the lower set of isolators are installed for TX coupling. For RX coupling, you can choose to connect an external light source on the manual coupling table for manual coupling.
Coupling laser welding is mainly emission coupling, welding the connection position of the lower set and the isolator, and welding the TX base and the lower set to fix it. It is automatic during coupling, and the maximum optical power is automatically selected to select the best isolator position.
Laser welding steps:
Fix the PCBA on the fixture of the instrument and power on, put the upper and lower sets on the external optical fiber, click to select the channel and execute, then automatically start 4D coupling, XYZ three dimensions plus up and down flip dimensions. After coupling and finding the position with the maximum optical power, perform penetrating laser welding and select the tangent position for welding. After welding, it will be coupled again in the plane, and then perform bottom welding. Note that if the gap between the lower sleeve and the base is too large so that the melting point range of the welding cannot be completely covered, the welding will fail. At this time, the lower sleeve needs to be moved down a little. If the welding is not firm after the bottom welding, or the welding point in a certain direction is not firm and skewed, it will cause the optical power to be small and unstable. At this time, repair welding is required. Repair welding is to manually turn the lower sleeve to observe the optical power. If the optical power is high in the direction of the rotation, repair welding is performed in the corresponding direction. Repair welding requires operation and rich practical experience.