Hole diameter

Diameter

The hole diameter (final hole size) is always the final dimension of the finished hole, including all metallic layers.
The tool diameter (drill size) is the measure that has to be used to drill bigger to reach the final dimension of the hole diameter.
Drilling tools have an undersize of approx. 0.01 to 0.02 mm.

Drill size and final hole size

holesize

D

Drill size

holesize

H

Final hole size

The choice of drill size depends on:
- tolerance of the final hole size
- type of drilling (plated, non plated)
- type of soldering surface (electroless, HAL, ...)
- copper thickness in the sleeve (25 µm or more)
- annular ring tolerances
- board thickness
- aspect ratio

Final hole size / drill size

Type of drilling

Electroless surfaces

Hot air leveling or PbSn reflowed

Board thickness ≤ 3.5 mm

Board thickness > 3.5 mm

Component drill

+ 0.10 mm

+ 0.15 mm

+ 0.20 mm

Through via

+ 0.10 mm

+ 0.10 mm

+ 0.15 mm

Blind via (SBU)

-

-

-

Buried via

-

-

-

Microvia (laser drilled)

-

-

-

Blind via (depth controlled)

-

-

-

The table refers to standard copper layer thickness in the sleeve of 25 µm (+ 100%). If thicker copper layers are needed, the drill size must be accordingly bigger. For blind vias (depth controlled) and microvias, the aspect ratio is 1:1 at most.

Component drills

Component drills incorporate components. Therefore, the final hole size is usually given with a + tolerance. After determining the drill size according to the above table, pad diameter, remaining annular ring and apect ratio have to be checked.

Non plated drills

Non-plated-through component drills (non plated drills) are usually drilled 0.05 mm bigger than the hole diameter.

Through vias, blind vias, buried vias, microvias

These drillings are used for the electrical connection of two or more layers. Normally, these drillings do not require a + tolerance in the hole diaemeter.