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|UV-Laser Drilled µ-Vias in Dielectric Layers on LTCC as Part of a Build-Up Technology for High Density Interconnections|
|Keywords: LTCC, Laser drilling, dielectric|
|The wiring density of LTCC circuits is limited by the printing resolution and the via diameters. Mechanical punching with an acceptable yield works with diameters of 100 µm and more, 50 to 75 µm vias are manufacturable in well equipped laboratories. Laser drilling in LTCC is also a well introduced technology, lasers with different wavelengths are used. The advantage of UV-lasers is the small possible spot size in the range of 10 to 20 µm. But the short wavelength of 355nm is also related to a small depth of focus, unfortunately. One way to increase the wiring density on LTCC substrates is the use of additional post processed thin dielectric layers combined with high-resolution structuring of the conductor artwork. For this technology via drilling by UV-lasers is a good solution. The small depth of focus is no longer a disadvantage in this case due to the small layer thickness. The paper describes investigations with different dielectric materials (25 µm to 65 µm thick) and different laser patterns and parameters with the aim to optimize the technological parameters for vias with diameters of 50 µm and below. The influence of parameters like laser power, Q-switch-frequency, cutting speed and focus setup on the shape of the vias is discussed. The influence of conductive patterns underneath the dielectric layers was also investigated. The via geometries strongly depend on the material properties and the process parameters during the build up of the dielectric layers -some options are shown.|
|Karl-Heinz Drüe, Dr.-Ing.
Technische Universität Ilmenau (Ilmenau University of Technology)
Ilmenau, Thüringen 98684,