Plasma treated PCBs increases the surface energy of advanced materials, including fluoropolymer, providing excellent lamination, wettability and metalization through-holes without the use of wet chemicals.
Plasma desmear and etch-back by plasma is an established practice in the PCB industry. Drilling vias through multilayer PCB’s leaves residue, or smear, on the via walls. This smear must be removed before metallization (to establish electrical connectivity) can occur. Gas plasma readily cleans smear in through-vias by the activation of oxygen and fluorinated compounds such as CF4. The plasma released oxygen and fluorine radicals attacks the resinous smear by a chemical etch process. The result is clean vias completely free of smear. Competing technologies using wet chemical methods fall short when it comes to fine through-vias, Teflon® core material, or acrylic adhesives used on polyimide based interposers. For those applications, low pressure gas plasma has proven to be the superior cleaning method. PVA TePla’s unique electrode design also ensures excellent plasma treatment uniformity, not only across each board, but also from one board to another and from process to process.
Metallization of through-vias is often impeded by carbonaceous deposits formed during laser drilling. To remove these deposits from vias, the printed circuit boards are immersed into gas plasma. The chemically energetic plasma safely cleans the carbon from the vias, in preparation for the metallization process. The carbon is converted into volatile reaction products that are completely removed from the plasma chamber by the vacuum pump.
Teflon® ( Polytetrafluoroethylene ), with its very low dielectric constant, is an excellent material to ensure fast signal propagation and superb isolation properties. The defining properties of Teflon®, however, also mean that it is difficult to plate. Prior to electrolysis copper plating the Teflon® surface must first be plasma activated to increase its surface energy so that the copper will adhere. PVA TePla has developed a proprietary gas plasma recipe that provides excellent wettability of Teflon®, and with an activation lifetime much longer than standard plasma processes that use N2 and H2 reactant gases.
