Photochemical etching is one of the most
widely used methods for manufacturing lead frames. A high unit-cost
process, It can be tooled with low costs and minimal time requirements.
Etched lead frames are manufactured in flat sheets, made of either
copper or Alloy 42, on which both sides are coated with photoresist
film. Next, surface cleaning is performed, followed by lamination. The
photoresist is then exposed to the required lead frame pattern by means of an ultraviolet source and a precision pattern glass/film. The areas to be retained as metal are coated with resists and etched parts are kept free of the resist in the finished pattern during development process. The final steps include running the
material through a series of nozzles spraying an etchant, after which the protective photoresist film is stripped from the finished lead frames. Next, the etched panels are singulated into strips. The cut strips are cleaned and plated, usually with silver at the inner leads to facilitate wire bonding. The plated strips are then taped with lead lock tape and downset before the final inspection