Die Bonding: Laser Diodes and Optical Components
Posted by Rich Hueners on Thu, May 14, 2009 @ 05:42 PM
The packaging process for an optoelectronic device challenges efforts to reduce costs. Because the purpose of an optical component is to manipulate light, the design rules for the packaging of optoelectronics are significantly more complex than those found in the semiconductor industry. For semiconductors, advances in wafer processing technology have resulted in a packaging process that is automated and planar. However, for optical components, the front-end process is significant, and for photonic devices, the controlled assembly processes and critical assembly tolerances create a challenge during the package design.
An example of the importance of a recipe-driven process control during optoelectronic assembly is the attachment of a laser diode within a source or pump laser; the laser diode is a temperature-sensitive device that requires careful process control during assembly. The output of a laser diode depends on the drive current passing through it, as long as the bias voltage is above the band-gap energy. Also, operating temperature of the laser is a key factor in device reliability as threshold current tends to increase with temperature, increasing the amount of waste heat generated. Furthermore, laser lifetime decreases as temperature increases. Thus, due to the stringent device requirements, a recipe-driven process control is important in reducing cost.
Figure: Laser emission as a function of drive current
A frequently used recipe-driven process is a eutectic reflow process. During this process, laser diodes are attached via a low-ohmic, high-thermal conductivity metallization in a precisely controlled place. The reflow profile during an automated in-situ eutectic die attach process is engineered to provide consistent melting and a void-free attach interface. This results in consistent heat transfer from the laser diode and contributes significantly to temperature stabilization during laser operation.
Programmable pulse heating coupled with automated component attach provides the recipe-driven process control essential to producing high-yield, high-performance laser diode assemblies. During the in-situ reflow process, temperature slopes for heating and cooling, overshoot and dwell times are programmable to enable process optimization and repeatability. Tightly-coupled temperature control ensures profiles are tracked repeatably in production.
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