Clean Stripping of Dry Film Photoresists on Non-Copper Surfaces

Dry film photoresists have been used in photochemical machining since their advent for printed circuit boards in the 1960’s. Although the metallic surfaces in photochemical machining are typically not copper as in circuit boards, the issues of good dry film adhesion through development and etching, combined with clean stripping are nevertheless the same. Cosmetic considerations make thin resist residues or a colored stain of the metal surface particularly objectionable. The objective of this study was to compare the stripping characteristics of four different dry film resists with regard to residual color stains on a variety of metals typically used in chemical milling by testing common stripping chemistries and judging stain residues visually and by different spectroscopic techniques.