Comparison of the metallization of chemically and laser-etched structures in BPDA-PDA polyimide

Polyimide is an insulating polymer that is used in multichip module applications as a dielectric material. For high density packaging, structures in polyimide have to be minimized to features of about 20 μm by 20 μm. The metallization of such vias has to be optimized for this purpose. The authors studied chemical and laser etching of vias and lines and compared the influence of the resulting features on the metallization. For the laser etching an excimer laser with a wavelength of 248 nm was used. The metallization was performed using a standard electroless copper bath. To start the metallization a layer of gold was employed. The authors could observe no visible damage to the PI layer even after 4 h in the electroless copper bath