Determining Endpoint of Plasma Desmear
Original Publication Date: 1984-Aug-01
Included in the Prior Art Database: 2005-Feb-04
Plasma etching has replaced wet etching as a means of removing the residual smear remaining within the drill hole after multilayer printed circuit boards are drilled. Because the plasma will etch both the epoxy smear and the epoxy in the through hole, no endpoint can be found by monitoring the reaction products. Also, the input gases (CF4 and O2) themselves will produce COF2, CO, and CO2 which are etching products. The amounts of HF and H2O in the products are relatively small, which makes it even more difficult to monitor the reaction rate. The following method determines the correlated endpoint, which is an endpoint very near the true endpoint: - Mix either boron, phosphorus or an iodine element with the epoxy solution.