A new process has been developed to remove the polymeric layer formed on a printed circuit board. A piece of polymeric film was removed from the polymeric layer with a single shot of infra-red (IR) laser irradiation of a wavelength which is transparent in the polymer. In order to apply this process to a laser drill, technical data were obtained about the dependencies of hole diameter on laser fluence, radiation field, and polymeric layer thickness. The mechanism of the process has been investigated.

The luminescent spectra measured during the IR laser irradiation significantly depend on the degree of fluence. When a single IR laser pulse was shot at a higher fluence of 8.6J/cm², several intense peaks were observed on the spectrum, but these peaks disappeared at a low laser fluence of 1.2J/cm². This suggests that the polymeric film was removed without decomposition into atomic species.　Therefore, this process differs considerably from ordinary ablation processes.

Based on these experimental data, this process is considered to remove the radiated polymer film without decomposing the polymer to the level of atom or molecule. This new process has the following potential advantages compared with the conventional laser ablation processes: (1) the piece of polymeric layer is removed completely by a single shot of IR laser pulse, and (2) the problems such as debris, delamination and smear which occur by CO2 or UV laser irradiation are avoided. These are the specific characteristics of this new process.