Stencils chemical etching

In etching technology, where a surface resist stencil is produced from photoresist imaging, screen stencil, or maskant cutting, chemical attack can occur into the body of the substrate, and once a sidewall has been formed, the etchant can attack beneath the stencil to form what is known as undercut (U) where U = 0.5 (B-A) (see Fig. 2). Normally the etch factor (DAJ) is required to be as high as possible so that smaller holes can be etched into thicker materials. 

---