Percussion drilling of polyimide using VUV and UV solid state lasers

Abstract

Percussion drilling of blind holes and vias in Kapton ® film was investigated using Q-switched solid state lasers operating at UV (355nm) and VUV (266nm) wavelengths. Holes were analyzed using different methods such as scanning electron microscopy (SEM) and surface profilometry. Ablation rates for the two wavelengths are compared. No abrupt thresholds were found and there was no evidence of an incubation effect within the first few pulses. Introducing pauses during the drilling increased the number of shots required for perforation of the film. The effects of fluence on diameter, depth and taper of the holes are presented. Smaller and neater holes are achieved more accurately with a lower fluence. An observed skin effect brought about by long exposure to low fluence VUV laser light is also discussed.

Laser microvia formation in polyimide thin films for metallization applications

“…Research is mainly focused on 266 and 355 nm wavelengths with short pulse widths and high fluence Pervolaraki et al, 2004;Mullan et al, 2005). As with the top diameter, the bottom (i.e.…”

“…Since then, many research papers have been published on the interaction between laser energy and polymers, and the debate continues as to whether the interaction with a particular laser wavelength and specific pulse characteristic is photochemical, photo‐thermal, or a combination of both. Polyimide film is one of the most studied polymers used to characterize laser material interactions (Srinivasan, 1993; Pan et al , 2007; Luk'yanchuk et al , 1997; Yung et al , 2000, 2001; Ilie et al , 2005; Mullan et al , 2005, 2007; Himmelbauer et al , 1996; Küper et al , 1993; Metayer et al , 2001; Bäuerle et al , 1997; Shin et al , 2007; Gordon et al , 2007; Gu et al , 2002; Zweig and Deutsch, 1992; Urech et al , 2007; Li et al , 2007). In the electronics industry polyimide is used to insulate conducting layers for flexible printed circuit board (FPCB) because of its high electrical resistance.…”

“…Polyimide is also used for its good mechanical strength, high thermal properties, and resistance to abrasive chemicals. Most research papers have concentrated their research on the Dupont™ brand of polyimide films (Srinivasan, 1993; Luk'yanchuk et al , 1997; Ilie et al , 2005, 2007; Mullan et al , 2005, 2007; Himmelbauer et al , 1996; Küper et al , 1993; Metayer et al , 2001; Bäuerle et al , 1997; Pervolaraki et al , 2004; Li et al , 2004; Hauer et al , 2003; Shin et al , 2006). There are many suppliers of polyimide film within the FPCB industry, but there are no comparison studies indicating how the various properties of these films can be used for microvia drilling.…”

“…Excimer lasers' broad range of UV wavelengths, small features sizes, and variable pulse widths have made them useful research tools. Nd:YAG lasers at 355 nm are the second most used laser for polyimide processing (Yung et al , 2000; Ilie et al , 2005; Shin et al , 2007; Gordon et al , 2007; Li et al , 2004, 2007; Yung et al , 2001; Mullan et al , 2005); however most studies use either Coherent ® or Spectra Physics ® laser sources. These commercially available lasers use short pulse widths as stated from the manufacturer's data sheets: 12 ns at 50 kHz for the Spectra Physics™ HIPPO ® laser and 35 ns at 60 kHz for the Coherent™ AVIA 4500 ® .…”

“…Dimensions of microvias when laser percussion drilled has been researched extensively (Ilie et al , 2005, 2007; Mullan et al , 2005, 2007; Shin et al , 2007; Gu et al , 2002). Many research studies use excimer lasers as noted above, but most FPCB manufacturers use Nd:YAG lasers operating at 355 nm.…”