One-dimensional transient analysis of volumetric heating for laser drilling

• Published in: Journal of applied physics Vol. 99; no. 11; pp. 113530 - 113530-10
• Main Authors: Zhang, Chong, Salama, Islam A., Quick, Nathaniel R., Kar, Aravinda
• Format: Journal Article
• Language: English
• Published: United States American Institute of Physics 01.06.2006
• Subjects: ABSORPTION; CERAMICS; CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; DIELECTRIC MATERIALS; EVAPORATION; HEATING; LASER BEAM MACHINING; LASER DRILLING; LASER RADIATION; LASERS; METALS; METASTABLE STATES; ONE-DIMENSIONAL CALCULATIONS; POLYMERS; SUBSTRATES; TEMPERATURE DISTRIBUTION; THERMAL CONDUCTION; WAVELENGTHS
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.2204828

Generally laser energy is considered to interact only with the substrate surface, as in metals, where the laser beam does not propagate into the substrate beyond a very small absorption depth. There are, however, many instances, particularly for ceramics and polymers, where the laser beam can penetrate into the substrate to substantial depths depending on the laser wavelength and laser-material interaction characteristics. Specifically there are polymeric dielectrics used as multilayer electronic substrates in which a laser beam of wavelength 9.3 μ m can penetrate into the substrate. The laser energy interacts at the substrate surface as well as inside the substrate. This particular aspect of laser-material interactions is important in laser drilling of blind microvias in polymeric multilayer electronic substrates. A one-dimensional transient heat conduction model including vaporization parameters is constructed to analyze this behavior. The absorption coefficient of the dielectric is also considered in this model and the problem is solved analytically. The microvia drilling speed, temperature distribution in the dielectric, and the thickness of the residue along the microvia walls and at the bottom of the microvia are studied for different laser irradiation conditions. An overheated metastable state of material is found to exist inside the workpiece. The overheating parameters are calculated for various laser drilling parameters and are used to predict the onset of thermal damage and to minimize the residue.