The mechanical drilling of vias in multi-layer PCBs creates a residual resin that smears along the walls of the vias, 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 for today’s multi-layer board designs 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.
The figures below illustrate the effect of a plasma desmear process. As displaying in the photograph on the left the copper inner layers within the via are not completely exposed due to drill smear. The photograph on the right displays the exposed copper inner layers after the plasma desmear process.
The figures below illustrate the effect of a plasma etch back process. The figure on the left displays copper layers that are even with the epoxy. After the plasma process the epoxy is etch back exposing more copper for the plating process (middle picture). The picture on the right shows the three-point contact after the plating process. The etch back process improves the reliability of the printed circuit board.