There are a few reasons to use a wire wheel brush on your photoresist film.
The wire wheel brush is a secondary application tool that is recommended with Self-Stick photoresist and best used for detailed designs or negative artwork. The wire wheel brush perforates the thin membrane, releasing any trapped air between the substrate and photoresist mask. Trapped air between the substrate and mask can cause lift of the mask in the detailed area or negative image area.
General use directions: roll the wire wheel brush once or twice over the entire image area with gentle pressure.