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High-Quality CO(2) Laser Machining of LTCC Structures for Thermal Management of a Group of Single-Emitter Laser Diodes
Keywords: LTCC, Thermal management, Laser diode
There has been much recent interest in the use of LTCC (low temperature co-fired ceramics) technology as a platform for optical integration of both active and passive components because of its electrical, thermal and mechanical characteristics. We have demonstrated recently the placement and alignment of passive components such as lenses and optical fibres. Coupling losses of less than 1 dB, for example, have been obtained between two fibres using V-grooves. Active components require methods for removing the heat generated without compromising the passive alignment of surrounding components. Our objective is to investigate direct in-board cooling of multi single-emitter laser chips on LTCC substrates using buried water channels to avoid the problems present in the traditional copper coolers such as blockage of the channels due to electrolytic corrosion and erosion. We present a thermal-management structure formed from “green” layers of LTCC which were machined with sub-millimetre-size features to form a three-dimensional structure by multilayer lamination. A custom CO2 laser system is used with a “cold” technique for continuous cutting, drilling and gray-scale machining with 5 µm resolution. In addition, to eliminate the possibility of collapsing of the internal structures in the LTCC substrates during lamination and firing we used nanocarbon sacrificial layers from Harmonics Inc. as filler for the internal structures. The nanocarbon structures were machined precisely, using the same laser technique, to fit the internal structures of each LTCC layer. The fit between the nanocarbon and the LTCC was better than 20 µm. To avoid the deformation of the structure, due to gas pressurization during the burn out process of the nanocarbon layers, a modified firing profile was used. The sacrificial layer was completely burned out before the final stage of LTCC sintering yielding a clean (carbon-free) void structure in the LTCC substrate.
Alberto Campos Zatarain, Postgraduate Research Student
Heriot-Watt University
Edinburgh, Scotland EH14 4AS,

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