June 2008

Etching Limits for Fine Lines and Spaces

In August 2006 a customer requested a test to etch 50ìm lines and spaces in 18ìm foil that had been panel plated to a total thickness of 30ìm. At that time, we were willing to guarantee etcher performance for 50ìm lines and spaces in 18ìm (1⁄2 oz.) foil, but not in 35ìm (1 oz.) foil. While we were able to etch 50ìm lines and spaces in 35ìm foil in our lab in the past, it was only by carefully optimizing the pre-etch process steps and paying strict attention to every detail in the cleaning, laminating, exposure, and developing steps that we were able to achieve any success at all on a standard 18” x 24” panel and even then, yields were not spectacular. Because the final etch results are so dependent on pre-process steps we have no control over, we have never offered an unconditional etcher performance guarantee for 50ìm lines and spaces for foil thicknesses greater than 18ìm. While all the tests were run with cupric chloride on copper foil, etching iron and steel with ferric chloride tends to follow the same trends. Therefore, we feel the results and conclusions reached from these tests will also be of interest to the chemical machiner, especially since they seem to confirm one of the old rules of thumb long used by chemical machiners.

Don Ball and Dr. Juming Wong, Chemcut Corporation