PHOTOABLATIVE BEHAVIOR OF POLYIMIDE IRRADIATED BY SEVERAL SHORT PULSE LASERS

Abstract

The photoablative behavior of polyimide irradiated by short pulse lasers whose wavelengths are 248nm, 266nm, 532nm, and 1064nm has been studied for drilling viaholes on the high density circuit boards. The etching mechanism is discussed by the calculations based on the solution of the one- dimentional heat equation. These calculations reveal that a low-damage hole is obtained by irradiation with the short pulse laser of nanoseconds and the dense temperature distribution to surface accompanied with a high absorption coefficient for short wavelength laser. It is derived that the temperature raised by a single irradiation with the threshold energy for ablation is approximately equal to the volatile temperature on each laser. Lt is roughly estimated that a low-damage hole is produced on polyimide, even if the repeated irradiation of 1000pps is given by 248nm or 266nm lasers.