Negative tone photoresists can be used as positive photoresists when standard Photoresists cannot handle severe processing conditions.
Negative tone photoresists are more difficult to remove and require the use of stronger Strippers/solvents.
Negative tone photoresists can be metalized for possible use as redistribution layers.
Metalization or etching
Additional pretreatment of the surface may be necessary and beneficial for some surfaces. This might include but not limited to a primer adhesion promoter solution, plasma etch, corona process, etc.
Lamination equipment/roll temperature should be higher than 45°C to ensure the substrate reaches 45°C. NCAC roll temperature is set to 120°C for lamination of dry film.
An exposure ladder in combination with a PEB ladder should be done and optimized based on the severity of the metallization or etch step that the dry film needs to survive. Exposure doses will affect the taper/undercut of the sidewall as well as the subsequent removal of the resist.
In the event that “scum” or residue is found, plasma etch or higher temperature bath may be necessary to remove/clean the substrate.