In printed circuit board (PCB) manufacturing, plasma technology can deliver higher uniformity and reproducibility than chemical or mechanical processes and help improve reliability. It is efficient, economical and environmentally benign. Plasma processing increases the surface energy of advanced materials, including fluoropolymer, providing excellent lamination and wettability for plating through-holes without the use of wet chemicals. It also allows metalization to the inner layers by removing resin smear created in the drilling process and removes carbon byproducts from blind vias.
Desmear & Etch Back - The mechanical drilling of vias in multi-layer PCBs creates a residual resin that smears along the via walls, impeding metalization of the electrical connections. After drilling, resin removal from inner layer posts is required to ensure reliable electrical contact. Traditional methods of etching and desmearing are often not effective due to the capillary effect present with wet chemicals, and the limitations related to the use of advanced board materials. In contrast, plasma effectively removes epoxies, polyimides, high Tg blends, mixed materials, and other resins in standard and high aspect ratio panels.
Non-Stick Surface Activation - The Nordson MARCH plasma process can modify fluoropolymer surfaces and desmear resins to prepare hole walls for electro-less copper or direct metalization. Surface activation for double-sided and multi-layer fluoropolymer through-hole boards is necessary to increase surface wettability.
Carbon Removal - Plasma treatment removes carbon from both conventional through-hole board vias and blind vias. Laser-formed vias often produce a carbon by-product that prohibits electro-less adhesion. Carbon that mixes with epoxy or polyimide resin and becomes trapped in the vias must be removed prior to metalization. Plasma cleaning removes the carbon from both conventional through-hole board vias and blind vias typically used on boards where component space is restricted.
Inner Layer Preparation - Plasma alters the topography and wettability of inner printed circuit board layers to promote adhesion. Cover-coated inner board layers that contain flex materials with unsupported polyimides have smooth surfaces that are difficult to laminate. Plasma alters the topography and wettability of the inner layers to promote adhesion by allowing thin layer processing through use of flex clips. Other chemical processes are not as effective: it is difficult to control the amount of material removed, and unsupported polyimides are inert to most chemicals.
Residue Removal (Descum) - Plasma treatment removes resist residue from PCB inner layers and panels without affecting the circuit pattern. It also removes residual solder mask bleed from lands for better bonding and solderability. Resist residue sometimes remains after developing fine pitch circuitry. If the residue is not removed prior to etch, the board can short circuit. Plasma effectively removes resist residue from inner layers and panels without affecting the circuit pattern. It also removes residual solder mask bleed from lands for better bonding and solderability.