Adeon Technologies

Desmear and Etch Back

Plasma Solution for Printed Circuit Board Manufacturing

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.

Teflon Activation

Plasma Solution for Printed Circuit Board Manufacturing

Surface activation for double-sided and multi-layer Teflon through-hole boards is necessary to increase surface wettability. Chemical processes do not have the flexibility to treat Teflon and other resins mixed in the same panel. However, a single plasma process can modify Teflon surfaces and desmear resins, effectively preparing hole walls for electro-less copper or direct metalization.

The figures below display an untreated Teflon panel on the left where a water droplet beads on the hydrophobic surface. The figure on the right shows the effect of plasma by improving the wettability of the Teflon surface.

Carbon Removal

Plasma Solution for Printed Circuit Board Manufacturing

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.

The figures below show a via with carbon residue on the capture pad and a clean pad after plasma treatment.

Inner Layer Preparation

Plasma Solution for Printed Circuit Board Manufacturing

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. 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 Solution for Printed Circuit Board Manufacturing

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.