a thermosensitive resist used in the manufacturing of printed circuit boards comprising a mixture of polyacrylic acid , a salt of a long chain fatty acid such as silver behenate , an infra - red absorber and modifiers such as additional polymers . in the unheated form the resist can be easily washed away with water - based mild solutions or pure water . when selectively heated by an ir laser a non - soluble , etch resistant composition is formed protecting the copper clad printed circuit board from the etchants used in the process .