Post-Etch Cleaning Process for Decals Prior to Immersion Gold Plating
Original Publication Date: 1988-May-01
Included in the Prior Art Database: 2005-Feb-15
The following describes a method of cleaning a circuitized polyimide film chip carrier (PFCC) prior to immersion gold plating pads of the circuitry on the PFCC. The PFCC typically contains surfaces having residual chromium, heavy oxide deposits (copper), and residual organic matter accumulated from previous processing steps. These deposits must be removed prior to gold plating. The described method cleans the PFCC without harming the circuitry. Successful immersion gold plating depends on the presence of a clean, oxide-free copper surface because the plating reaction is specifically limited to the replacement of copper atoms by gold. Cu0(s) + Au(CN)2- ------ Cu(CN)2- + Au0 (s) The PFCC is immersed in a dilute solution of thiourea (0.05 M) in 0.1 M aqueous sulfuric acid heated to 60oC.