The microelectronics industry is moving toward smaller feature sizes. The main driving forces are to improve performance and to lower cost. From the performance point of view the small distances between chips together with the short interconnection routes have of great importance in order to achieve faster operation. The application of polymeric materials for the insulating and protective layers of interconnect substrates is beneficial to the performance and to the cost of a circuit module as well. An advanced technology for the fabrication of very high density interconnects applies microvia flexible substrates. This technology has particular significance for the interposers of chip scale packages. Laser processing of polymeric materials applied for via generation, image transfer, contour cutting, etc. has proved to be an efficient tool for the fabrication of interconnect substrates. The paper describes some results of a research project that aims at the application of CO2 and frequency multiplied Nd:YAG lasers for drilling via holes into copper clad flexible laminates of polyimide, epoxy and polyester base materials. The effect of the application of an interfacing (adhesive) layer is also the topic of the investigations. The physics of processing using a wavelength range from the far infrared radiation of the CO2 laser till the UV wavelengths of frequency quadrupled Nd:YAG lasers are considered to be modeled, examined and evaluated.