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.
Microvia Plating Throw Ratio
Distribution Metric
Electroplating bath performance metrics quantify fluid transport and metal deposition uniformity between board surface copper and blind via interiors. Achieving an optimum microvia plating throw ratio ensures that microvia bottoms receive sufficient copper thickness without causing excessive surface copper build-up. The metric compares copper thickness deposited at the microvia base against copper thickness deposited on the flat outer foil surface.
Boundaries of this metric apply specifically to electrolytic copper plating operations inside microvia cavities.
Electrolyte Agitation
Fluid dynamics inside blind holes restrict natural ion diffusion, requiring forced electrolyte movement to replenish copper ions near the hole bottom. Organic plating additives consisting of suppressors, accelerators and levelers alter deposition rates across varying electric field densities. Suppressors adsorb onto high-current-density surface regions to retard copper growth, while accelerators concentrate at the microvia floor to increase local deposition speed.
Pulse periodic reverse plating applies alternating cathodic and anodic current cycles to clear depleted solution from deep microvias. Inadequate fluid movement leads to copper starvation inside microvias, causing void formation and thin plating walls that fail under thermal stress.
Thickness Ratio
Plating throw values approaching one to one indicate equal copper deposition depth inside the via and on the outer surface. Microvia plating throw ratio values below zero point eight indicate poor bath distribution that increases board scrap risks.