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Reliable packaging of semiconductor devices into fibre coupled structures requires a technology of multiple disciplines such as thermo dynamics, engineering mechanics, material science, geometrical optics and electrical engineering. In addition, field-proven practical know-how plays a vital role in realizing such technology into successful packaging works.
Bonding is the essential initiative process to build up design layers of internal module structure. A delicate fluxless soldering makes good adhesiveness between components layers as well as good thermal conductivity. Precise control on temperature, choice of solder alloy and degree of structural stability are essential for reliable bonding. In order to maintain consistent soldering quality, precisely designed solder preform is used. Our bonding process follows MIL-STD and gets periodic die-shear test as part of quality indicator. Coset eliminated all Pb alloy solders in its entire production line since RoHS compliance.
Optical Alignment & Fixing
Optical alignment and fixing process is the key process to decide performance and reliability of the fibre coupled device. Specially designed automatic alignment system guides peak output power position with sub-micron accuracy. Amongst several optional methods to fix the aligned optical axis to its optimum position, laser welding by simultaneous Yag laser shots is the most field- proven secured solution.
Seam-sealing (seam-welding) is the last step of packaging assembly to ensure hermeticity. The hermetically sealed package guarantees reliable environment for the diode functioning for long field life. Post vacuum baked module is sealed in the sealing chamber with humidity controlled inlet atmosphere. Fine tuned electric rod sealing condition makes sure leakage-free modules to be operated in the field.
Screening & Measurement
The expectation of reliability on fibre coupled otpo-electric device is much higher than other industrial products. It is mandatory all devices assembled go through several screening tests. Coset is operating all the necessary equipment to carry out different screening tests in conditions specified in Telcordia and MIL-STD.

Measurement is the final step where they make complete characterization of packaged devices. Accurate test data for modules with different target specifications are generated on those well calibrated measurement equipment.

Clean -Room Operation
All the assembly processes are operating in the cleanroom environment. Coset operates class 10,000 cleanroom with appropriate control on temperature, humidity and particle counts. It is the ideal working environment for such sensitive semiconductor diodes packaged. Frequently, ESD (electrical static discharge) is the major cause of semiconductor diode failures. ESD control rule is being kept rigorously in the entire manufacturing station including screening and final measurement.
In-house Lensed fibre fabrication
Lensed fibre is the critical key component in direct coupling structure. Coset is able to provide flexible and agile responses to various design and production needs with its own lensed fibre fabrication facility in house. Optimized lens design for different characteristics of diodes provides fast design guidelines for final products.
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