I just was able to engrave a touch pad from ITO on PET.
I've used the following cutter I have and diamond engraving tips.
It was only able to engrave only with diamond tips.http://knkusa.com/product/knk-zing-air-2/
I've used 10 speed and 60 force initially, but probably I can go much lower.
Trace width initially was 0.5mm but I think I can finer as well..
The touchpad will be used with mpr121 capacitive sensor.