CO₂ Laser Drilling of Microvias Using Diffractive Optics Techniques: I — Mathematical Modeling

This paper is the first of three parts summarizing the research to use diffractive optics at the CO₂ laser wavelength to drill microvias in the 40–50 μm range for organic packaging applications. This first part mainly focuses on mathematical modeling of the drilling process, which is used to define the characteristics of the laser beam necessary to achieve the required geometry of the microvias. These laser characteristics and the properties of the incoming laser beam of the CO₂ laser system are then used to provide a deterministic approach for obtaining performance data for the diffractive optics design. The targeted optics are designed based on the modeling result and are then integrated into a prototype system to execute the drilling operation. The model is based on the conversion of optical energy into thermal energy due to laser-substrate interaction, propagation of thermal energy in the substrate, thermal as well as radiation damage threshold of the substrate and other important laser drilling parameters (e.g., fluence, temporal and spatial characteristics of the beam, residue at the via bottom).