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MAY 2020 I PCB007 MAGAZINE 81 • Activation of plastic powders • The final surface finish Plasma processes performed in the PCB industry include: • Desmear of drilled holes and laser-drilled holes, carbon removal • Surface activation of PTFE (surface and drilled holes, laser-drilled holes) • Surface cleaning before solder mask • Surface treatment of PCBs after thermal cure of solder mask (increasing surface tension, improving adhesion of legend ink, conformal coating, and other coatings) • Cleaning/activation of prepregs before bonding • Desmear of hole fill paste before plating • Cleaning of a gold surface before soldering or bonding • Cleaning of surface, deoxidation before soldering, fluxless soldering • Drilling and milling of polyimide, flexible circuits • Surface activation of PI for fully additive copper plating • Panel/layer descumming • The final surface finish of a PCB, copper preservation (Semblant) • Conformal coating In this article, I will concisely summarize all of these processes, identify where this step is located in the manufacturing chain of events, and outline the specific plasmas and meth - ods used in each step; some steps have more than one plasma option. Some processes were, or are still, patented. The feasibility must also be checked under the local conditions. Before using such a procedure, check to confirm that no patent is infringed. The list of applications is open; some of the applications are carried out very rarely, and there are always new applications. Desmear of Drilled Holes and Desmear of Laser-drilled Holes/Carbon Removal [3] The removal of resin smear from drilling (desmear) is a process step after drilling, but before copper plating required to ensure elec- trical contact. It is usually done with potassium permanganate in a warm, aqueous solution. Instead of permanganate, a plasma process can be used with similar results on copper ad- hesion. Plasma processing removes epoxies, polyimides, cyanate ester, and blends of differ- ent resins (bismaleimide triazine). The plasma process is generally carried out in three steps, although it is possible to perform the process in one step. This process is also suitable to remove car- bon, which is a byproduct left after laser drill- ing. After laser drilling, a mixture of differ- ent resins and carbon remains. The resin is destroyed by CF 4 and oxygen. The carbon is burned and removed by oxygen/argon. This process in three steps is as follows: 1. Oxygen until 80–100°C is reached on the board surface (oxygen and 10% inert gas, nitrogen/argon). 2. Mixture of CF 4 and oxygen with 10% inert gas (15 minutes). 3. Oxygen with 10% inert gas to burn the residues. This step removes any ash, carbon, and fluorine left from step one or two. Time is adjusted to meet desmear or etch-back requirements. When etch-back is required, glass fiber removal is done before plating. The inert gas is very important; it makes the chemical attack more uniform, and for an inert gas, nitrogen or argon can be used. Helium is fine too but is not usual in Europe. This process in one step is as follows: 1. Mixture of CF 4 and O 2 with 10% inert gas, nitrogen or argon (5–30 minutes, depending on the energy of the RF generator). Surface Activation of PTFE (Surface and Holes) [3–5] Although PTFE does not smear during drilling, it must be activated in the hole wall to increase the wettability, and plasma treatment is a very good method for surface activation of PTFE. The process is carried out in one step. If other materi - als besides PTFE are involved, then the process