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Approaching fluidic self-assembly of small silicon chips on laser structured thick film pads on LTCC
Keywords: self-assembly, laser structured, LTCC
LTCC is a common substrate material for sensor applications with a high grade of integration. Nevertheless, the potential of a silicon chip assembly offer new possibilities for an even higher integration of functionality and a higher grade of miniaturization. With advancing chip functionality also smaller chip sizes are possible. A Smaller chip size leads to more difficult assembly process. For the assembly of silicon chips with sizes smaller than 150 �m a surface tension directed fluidic self-assembly process on LTCC was developed at the Institute of Micro- and Nanotechnologies of the TU Ilmenau � IMN MacroNano�. First small screen printed silver palladium pads on DuPont 951 with dimensions of 100 �m and smaller were laser structured with a pulsed picosecond laser. This leads to a very precise pad geometry with a high reproducibility [1]. On top of the laser structured thick film pads a low melting solder alloy was placed by dip-coating. Chips with gold metallization on one side are suspended in a fluid. The fluid is heated to the melting point of the solder and the chips get agitated by means of rotation and vibration over prepared LTCC substrate. The chips get assembled by spontaneous contact between chip metallization and molten solder alloy drop. The driving force behind is the reduction of the surface free energy between molten alloy and metal contact pad, forming an intermetallic phase which cause mechanical as well electrical bind of the parts [2]. Patterned solder receptors provide necessary information to mount the chips on desired positions. The paper will present results of the geometrical measurements of the laser structured thick film pads as well as the results of the characterization of soldering and different steps of the surface tension directed fluidic self-assembly process.
Nam Gutzeit,
TU Ilmenau
Ilmenau, Thuringia

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