PCB Drilling Parameters: The Setup Numbers That Matter

The one thing to get right

Parameters and material are two different levers. A backup board sets the best exit a stack can produce; the presser foot, the depth and the stack height decide whether the stack actually reaches it. If a defect survives a parameter fix, only then is the board the variable to change — one at a time.

Hit count is limited by wear, not by the parameter sheet: how many hits per tool the program gets depends on wear staying inside the qualified window, and this guide is where that window is set. Exceed it and the wear curve, not the schedule, decides when the tool stops.

The five numbers

Everything below is the same short list, written out with the reason for each figure.

Setting	Working value	What it controls
Presser-foot pressure	≈ 7.5 kg	Holds the stack flat and seals it for vacuum
Presser-foot height	≈ 0.80 mm above the board	Clearance without lifting the stack
Drill-into-backup depth	≈ 0.5 mm	Exit support without packing the flutes
Stack height	≈ 6 × diameter (2-sided); 2–3 × (multilayer)	Throughput against breakage risk
Panel bake	145 °C ± 5 × 4 h	Removes absorbed moisture
Bit life / regrind	3000–3500 holes (2-sided); 500 (high-density multilayer)	Hole quality against tool cost

Presser-foot pressure and height

The presser foot does two jobs at once: it holds the stack flat and it seals the stack so the vacuum can pull chips away. Set it to about 7.5 kg of pressure with roughly 0.80 mm of clearance above the board face.

Too little pressure and the stack lifts, the seal leaks and the vacuum stops clearing debris — the classic route to curled debris and hole blockage. Too much and the foot crushes the entry board against the copper, marking the top surface and disturbing the bit's first contact. The foot height matters for the same reason: enough clearance to avoid contact with the panel, not so much that the stack is unheld. These values are starting points — panel size, stack height and machine type all shift the right figure, so confirm on your own equipment.

Drill-into-backup depth

Set the drill to enter the backup board by about 0.5 mm. This is the setting that decides the exit side of the hole.

• Too shallow — the exit is unsupported as the bit breaks through, which is what produces exit burr and a ragged hole mouth on the bottom copper.
• Too deep — the cutting flutes enter the board, pack the debris into the flutes and into the hole, and block holes. It also wears the bit faster for no gain in hole quality.

0.5 mm is a working target, not a tolerance to be maximised. The exit side is also where the board grade shows its effect; see exit burr control for the board-side half of this decision.

Stack height by bit diameter

Stack height trades throughput against risk. Size it from the bit diameter rather than from a fixed count:

• Double-sided panels: about 6 × the drill diameter.
• Multilayer panels: about 2–3 × the drill diameter.

A taller stack drills more panels per stroke, but every extra panel adds deflection and heat at the bit tip, and small-diameter bits break first. If you are trading stack height against bit breakage, the entry and backup layers are the levers that buy back margin — a flatter, harder-fusing backup board tolerates a taller stack than a soft one.

Panel bake before drilling

Bake the panels at 145 °C ± 5 for 4 hours before drilling. This is not a cure step; it is moisture removal.

Laminate absorbs atmospheric moisture, and moisture that is still in the board flashes to steam at the hole wall as the bit cuts. That is a direct route to resin smear, nail head and blocked holes — and it is why a fabricator can fix a "board problem" by drying the panels rather than changing the consumable. Storage conditions matter for the same reason; the moisture control guide covers how the backup board itself should be stored and the humidity range it should be kept in.

Regrind interval and bit life

Set both a regrind interval and a hard replacement limit — a bit that is "still cutting" is not necessarily cutting to tolerance.

• Regrind: in multilayer work, regrind every 500 holes.
• Replacement limit: two to three regrinds, then replace.
• Expected life in our field records: 3000–3500 holes in double-sided work, about 500 in high-density multilayer work.
• Material effect: FR-5 reduces life by roughly 30 percent.

These are field-record ranges, not guarantees — hole size, laminate and stack height move them, and your own tool-life log is the only figure worth standardising. What the numbers are good for is setting the interval before the bit is worn enough to distort hole size; the symptom of an overrun bit is hole-size distortion, not a visible break. To turn the interval into a schedule, the drill resharpening calculator takes tool life in hits, the hits already run and the permitted number of regrinds, and returns the cycles left and the next resharpening point.

The order to set them in

Set the parameters in this order, and change one at a time:

1. Presser foot — pressure to ≈ 7.5 kg, height to ≈ 0.80 mm.
2. Drill depth — into the backup board ≈ 0.5 mm.
3. Stack height — 6 × diameter (double-sided) or 2–3 × (multilayer).
4. Bake — 145 °C ± 5 × 4 h before the run.
5. Bit life — regrind interval and replacement limit set before the run, not after a defect appears.
6. Verify — re-run and check the exit side, the hole wall and the hole position against the program.

If a defect survives all six being correct, the consumable is now the suspect — work through the defect check order and change one layer at a time.

Questions engineers ask