Ultra-short pulse (USP) lasers are increasingly used in industrial manufacturing, and their main applications include glass processing, metal engraving, and medical device manufacturing. In the infrared (IR) wavelength range of ~1µm, short pulse widths enable high-quality processing with very low thermal effects compared to longer nanosecond and microsecond pulse widths, resulting in minimal melting and raw edges when machining metals and fewer chips and fractures when machining glass.
However, in many cases, shorter ultraviolet (UV) wavelengths offer additional benefits. Shorter wavelengths allow for smaller focused spots and longer processing depth. In addition, ultraviolet wavelengths can couple laser energy to a greater variety of materials than infrared wavelengths. One of the industries that combines many different materials is flexible printed circuit (FPC) manufacturing. FPC is already used in a variety of compact electronic devices such as smartphones, watches, and a growing number of "wearable" electronics. Materials are diverse, including copper, polymers, adhesives and even paper. Common processes include drilling and contour cutting.
For FPC, the polyimide protective film acts the same as the solder resistance film for FR4-based printed circuit board (PCB). Polyimides are typically 12 to 25µm thick, coated with pressure-sensitive adhesives, and bonded to paper-based materials. The key challenge was to ablate patterns at high speeds in polyimides while avoiding thermal effects such as adhesive melting and paper-based burning/charring. At present, the most advanced protective film drawing process is the combination of pulsed nanosecond ultraviolet laser and two-dimensional galvanometer to achieve high speed processing with very low thermal effect. However, in some applications, quality is critical, so the UV picosecond pulse width is more advantageous.
Compared to nanosecond UV lasers, picosecond UV lasers produce less debris, while being able to process at higher pulse frequencies (and thus at higher speeds) without causing unnecessary thermal effects in adhesives and paper bases. With shorter pulse widths and shorter wavelengths, laser processing tends to produce higher quality, as demonstrated by the various FPC processing results here. Uv picosecond lasers utilize shorter interaction times and shallower light penetration depths to achieve finer control of the ablation process and achieve finer machining accuracy while reducing thermal effects.