355 nm Nd : YAG laser ablation of polyimide and its thermal effect

Ablation results of polyimide (PI) by a single pulse of an acoustic-optical Q-switched Nd:YAG laser at 355 nm are reported for the first time and are compared with the results for RCCR (resin coated copper, trade mark of Alli ed Signal) and PI at other wavelengths. The difference of the ablation dept h of PI from that of RCCR is small for a same fluence ranging from 3 to 184 J cm(-2), especially the ablation depth of the two materials is nearly the same for a same fluence ranging from 5 to 100 J cm(-1), although the ablat ion threshold of the former is much lower than that of the latter, which ar e 0.1 and 0.7 J cm(-2), respectively. Comparing the ablation results of PI at 355 nm with those at shorter wavelengths, both the threshold and slope o f the ablation rate against the fluence are higher than those at shorter wa velengths. At the same time, melting is evident in the process. The tempera ture profile and temperature change with time caused by the laser at differ ent wavelengths and different pulse frequencies are calculated the calculat ed results being in agreement with the experimental studies reported by pre vious authors. It is shown that the advantage of the small thermal effect o ccurring in the acoustic-optical Q-switched laser ablation is offset signif icantly because of a small absorption coefficient for laser energy, althoug h the ablation rates can be increased at a relatively high power density. ( C) 2000 Elsevier Science S.A. All rights reserved.