| Cause |
Failure condition |
Countermeasure |
D
r
i
l
l
B
i
t
D
e
s
i
g
n |
Small chip
pocket (flute volume) |
Poor chip evacuation causes clogging. |
Enlarge chip pocket volume, change web thickness
web taper, and flute land ratio. |
| Short flute length |
Poor chip evacuation at near the end of flute
causes clogging. |
Apply suitable flute length for stack height. |
| Small helix angle |
Poor chip evacuation in flute causes clogging. |
Higher helix angle. |
D
r
i
l
l
i
n
g
C
o
n
d
i
t
i
o
n |
High chipload |
High Infeed rate does not allow the chip to evacuate
properly |
Lower chipload. |
| Penetrating to deep into the backup
board |
Materials such as Backing Board generate large
particles of swarf which can adhere to the drill causing Bird
Nesting. |
Set suitable penetration depth. |
| No dwell time between drilling strokes |
Bird Nesting occurs because the
drill has not completed the evacuation process |
Use dwell time. |
P
W
B
S
e
t
t
i
n
g
|
Hinge number and thickness of PWB
copper layers |
Spiral copper chips prevent good chip evacuation |
Higher chipload |
E
q
u
i
p
m
e
n
t |
Unsuitable bush diameter (entry board
lifts) |
The chip/swarf penetrates the gap between the
top board and the entry board |
Control spindle run out (maintenance
and repair). Recommended value <10 micron (<5 micron is better for <0.3mm
drill bits) |
| Unsuitable vacuum force |
Both a low vacuum force and an excessive vacuum
force worsens chip evacuation. |
Set suitable vacuum force. (Recommended value:
0.4dia. 100-150 hPa, 0.1dia. 70-140 hPa) Maintain dust catcher
system of the drilling machine. |
