Laser Microvia Aspect Ratio Impact on Fabricator Yields
Microvia aspect ratios above 0.8:1 cause exponential fabricator yield loss by obstructing fluid exchange during plating and creating latent thermal stress fractures.
Flat Glass Prepreg Ablation
Dielectric Removal
Machining steps performed after drilling operations utilize high energy beams to remove dielectric material from specific fiberglass fabrics. Flat glass prepreg ablation involves the use of spread glass weaves that provide a more uniform surface for laser drilling than traditional twisted yarns. These materials reduce the variation in pulse energy needed to penetrate the substrate.
Energy Interaction
Laser pulses interact differently with the flat glass filaments compared to standard bundles. Because the glass is spread thin, the flat glass prepreg ablation process experiences less beam scattering and more consistent absorption. This consistency leads to cleaner via walls and more predictable hole diameters across the entire panel.
Material Removal
Consistency in the dielectric removal affects the subsequent plating of the microvia. Irregular glass protrusions occur if the laser energy is insufficient to vaporize the spread glass filaments at the same rate as the resin. Using flat glass prepreg ablation minimizes the risk of voids by creating a smoother transition between the hole wall and the target pad.
Engineers monitor the cross sections of the vias to confirm that the glass fibers do not obstruct the copper deposition. Successful material removal ensures a reliable electrical path through the stackup.