A layout engineer drops the microvia from 0.15 mm to 0.10 mm to escape a 0.4 mm pitch BGA. The board still passes DRC, the stackup still builds, and the quote comes back 30–40% higher with a yield caveat.
The drill size is not a free parameter. At 0.1 mm the via moves into a different process window: different laser recipe, different capture pad, different fill, and a much smaller margin for registration error.
What changes at 0.1 mm
- Aspect ratio. A 0.1 mm via through a 0.1 mm dielectric is 1:1. Through 0.15 mm it is 1.5:1, which plates less uniformly at the bottom.
- Capture pad. The pad must shrink with the via, but registration tolerance does not. The annular ring becomes the limiting feature.
- Dielectric. The laser stops on the target pad; a thinner dielectric gives less margin for depth error.
- Fill. Smaller vias are harder to fill without voids, and via-in-pad requires a planar surface.
The cost stack
| Item | 0.15 mm | 0.10 mm | Why |
|---|---|---|---|
| Laser drilling | Standard | Slower, tighter recipe | More pulses, more inspection |
| Capture pad | Larger | Smaller, tighter | Registration limits |
| Via fill | Standard | Higher void risk | Smaller aperture |
| Plating | Standard | Bottom coverage risk | 1:1 aspect helps, chemistry limits |
| Yield | Baseline | Lower | Pad breakout, fill voids |
The price difference is rarely the drilling time alone. It is the yield and the inspection.
Where it fails
Pad breakout. Registration off by 25 µm on a 0.1 mm via with a 0.25 mm pad leaves a thin ring. The pad lifts in thermal cycling.
Bottom void. The laser stops on copper; if the surface is not clean, the bottom plates poorly and the via opens in reflow.
Fill voids. Via-in-pad with a 0.1 mm via traps air; the fill must be vacuum-assisted and inspected by cross-section.
Stacked microvias. Stacking 0.1 mm vias concentrates stress; two levels are common, three need a reliability review.
When 0.1 mm is necessary
- 0.4 mm pitch BGA with escape routing on two layers.
- Via-in-pad under a fine-pitch component where the pad cannot grow.
- A stackup where the dielectric is 0.1 mm and the aspect ratio must stay at 1:1.
When 0.15 mm is enough
- 0.5 mm pitch and above, if the escape routing fits.
- Non-functional vias used only for thermal or shielding.
- Designs where the capture pad can be 0.3 mm or larger.
The difference in routing density is often smaller than the difference in yield. Run the escape routing at 0.15 mm before accepting the 0.1 mm cost.
Three rules that save money
- Keep the capture pad at least 0.15 mm larger than the drill, even if it costs routing space.
- Do not stack more than two 0.1 mm microvias without a thermal cycling review.
- Ask for the fabricator's qualified drill-to-pad ratio before the layout is frozen; it is usually tighter than the sales deck.
If the design can escape at 0.15 mm, the 0.1 mm via buys density you may not need and yield you cannot recover.
Send your HDI stackup for a drill review, or read what blind and buried vias cost and review our HDI capability.
