Etchants may be classified as wet or dry. A good wet etch for uncured polyimide is a standard photoresist developer or ammonium hydroxide. A common dry etch is a CF4-Oxygen plasma. The result is a polyimide bar on the substrate. A thick x-ray sensitive photoresist is next applied.
Thicknesses can be from a few microns to several centimeters.
A low stress application method is critical to avoid pattern distortion. At Wisconsin a glue down method has been developed which minimizes this stress. Stress free x-ray sensitive materials are purchased and glued to the substrate. PMMA is commonly called plexiglas by Rohm and Hass or acrylic. An x-ray mask containing the definition of the final metal bars must then be aligned to the sacrificial bars already on the substrate.