| Cause |
Failure condition |
Countermeasure |
D
r
i
l
l
B
i
t
D
e
s
i
g
n |
Small chip pocket (flute volume) |
Chip clogging causes increased roughness. |
Enlarge chip pocket volume, change web thickness web taper, and
flute land ratio. |
| Short flute length and body length |
If swarf clogging occurring at the end of flute, it causes a
rough finish. |
Set suitable flute length for stack height. |
| Unsuitable drill bit geometries (helix angle) |
A drill bit with a low helix angle (30-36 degrees) does not evacuate
swarf smoothly, causing roughness |
Higher helix angle (40 - 45deg.) |
| Large margin length |
Increased area of contact between the drill bit surface and the
hole wall raises drilling temperature causing roughness. |
Smaller margin width. |
| Unsuitable tungsten carbide material |
Increased wearing blunts the drill's cutting edges, causing roughens |
Use wear-resistant WC material. |
M
a
n
u
f
a
c
t
u
r
e |
Excessive repointing amount |
Reduced flute volume causes swarf clogging and roughness of hole
wall |
Control amount removed of material at repoint (0.05-0.10mm).
Check overall length of repoint drill bit. |
D
r
i
l
l
i
n
g
C
o
n
d
i
t
i
o
n |
High chipload |
High chipload drilling increases the volume of chips, making
it hard to evacuate, causing a rough finish. It is also possible
that a damaged cutting edge can influence roughness of hole wall. |
Apply suitable chipload. (Please refer to drilling parameters.) |
| Low chipload |
Low chipload promotes wearing, and causes a rough finish. |
| Unsuitable pec drilling |
If the number of stepsand the amount of feed don't match the
PWB setup, it worsens swarf evacuation and causes a rough finish. |
Recalculate pec drilling step increments/parameters |
| 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. |
Apply suitable penetration depth. |
P
W
B
S
e
t
t
i
n
g |
Panel stack height to high |
Large volume of chips causes Swarf clogging |
Lower chipload. Decrease PWB stack height. |
| Hinge number and thickness of PWB copper layers |
Spiral Copper chip form blocks chip evacuation and high copper
content causes wearing. |
Lower chipload. Decrease PWB stack height. Use pec drilling and
double drilling. |
| Thick and few layers PWB (Example t1.6, D/S) |
Likely to have grubbed and rough finish. |
Lower chipload. Use a type which has enough chip pocket to promote
good roughness of hole wall |
| Hard cutting PWB material |
The increase of cutting resistance causes wear and worsens accuracy. |
Decrease PWB stack heights and reduce hit count to minimize drill
bit damage. |
| Unsuitable entry board |
Using aluminum entry board, fine roughness of hole wall can not
always be expected. The lubricant type offers better comparability
for fine hole wall condition |
Use high quality entry board like attached water soluble resin
type, multi-layer aluminum type, etc. |
| Unsuitable Stack preparation |
A gap between the entry board and PWB causes poor chip evacuation. |
Prepare stack with no gaps between entry board and PWB |
| PWB qualities |
Uneven resin and fibber intersections worsen roughness of hole
wall |
Check PWB quality. Example: Check
unevenness of PWB using an image processor/AOI machine for measuring
hole positioning accuracy.
---> An extreme striped pattern, etc. |
E
q
u
i
p
m
e
n
t |
Unsuitable Vacuum force |
Low vacuum force worsens chip evacuation, and causes rough hole
wall. |
Set suitable vacuum force. (Recommended value: 0.4dia. 100-150
hPa, 0.1dia. 70-140 hPa) Maintain dust catcher system of the drilling
machine. |
| Unsuitable force of pressure foot |
A wider inner bush cause poor chip evacuation and roughness of
hole wall. |
Using small inner diameter bush. Example: Change from 10mm to
3mm inner dia. |
