Advances in Dry Film Resists
Since solvent dry film resist was first introduced in 1968, the
demands on dry films have been ever increasing. Initially the
demands were chemical, leading to the introduction of aqueous
and semi-aqueous films; this reduced the significant cost of
processing equipment (stainless steel to PVC) and of the
processing media. The requirements evolved to be more user
related e.g. better colour contrast resist to copper, colour change
after exposure. Later, improvements were made to the
processing characteristics e.g. photo-speed, developing speed,
to increase production throughout. Latitude in processing has
become the latest challenge; more latitude equating to better
yields and ultimately lower costs. It is this subject that is the main
concern of this paper.
Finally, a brief description is given of t""o innovative dry film
resists; one to allow the imaging of a PCB directly from a CAD
system - laser imaging, the other, a high definition dry film
where the polyester is removed prior to exposure.
R.C. Linsdell, Morton Thiokol, Ltd.