possible reasons

way out

drilling
machine

exceeding RUNOUT

control RUNOUT within 15 μm

Discuss with
technicians

smeary collets

maintain collets regularly

uneven pressing tray or smeary tray

be sure pressing tray to keep more than 80 per cent total area and clean the trays regularly

smeary platform

clean platform

processing
parameters

immoderate processing parameters

proper chipload, rotate speed and feed speed.

too much reshaping times

reduce reshaping times

too much hits

reduce hits numbers

PCB physical
properties

hard working materials

reduce layer numbers and hits numbers

too much layers

reduce layer numbers

too much copper foil or too thick copper foil

reduce layers and hits numbers

unsuitable cover board or mat board

rectify thickness and hardness of cover board

uneven cover board or mat board

improve qualities of cover board and mat board

drills
design

low rigidity

use UCV type drills（UCV/STV）

Try different drill types and
check drills more carefully

unmatched shape with processing parameters

try different drills

drill
qualities

low quality tip

check tips more strictly