| Cause |
Failure condition |
Countermeasure |
D
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B
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Poor drill bit strength |
Large deflection causes drill bit to break at the end of the
flute. |
To increase strength, change web thickness and web taper. Use
VT type drill bit for superior hole registration accuracy. |
| Small chip pocket (Flute volume) |
Increased twisted moment/load causes breakage with breakage point
n the middle of flute. |
Enlarge chip pocket volume, change web thickness web taper, and
flute land ratio. |
| Long flute length and body length |
When flute length and body length are unnecessarily long, the
hole registration accuracy worsens. |
Set suitable flute length and body length. |
| Unsuitable tungsten carbide material |
Low Transverse Rupture Strength (TRS) causes drill breakage more
easily through cutting resistance. |
Use wear-resistant WC material. |
M
a
n
u
f
a
c
t
u
r
e |
Unbalanced drill point geometries (Chisel point excentricity,
Rip height gap, Chipping, and one sided taper or flare, etc.) |
Hole registration accuracy worsens
with asymmetrical drill bits. (inconcentricity, chisel point,
Lip height gap, chipping) |
Check drill point geometry. |
| Excessive diameter wearing of repointed drill bits |
Outside taper form front taper shape. The cutting resistance
increases and it breakage occurs |
Remove large worn part of drill by improved repointing. |
D
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l
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g
C
o
n
d
i
t
i
o
n |
Low chipload |
Progressive wearing worsens hole registration accuracy, resulting
in breakage problems. |
Apply suitable chipload. (Please refer to drilling parameters.) |
| High chipload |
Hole registration accuracy worsens
by swarf clogging and chipped drill bit, causing breakage. Thrust
load is also increased. |
| High spindle speed |
The bit is broken by cutting load with increased cutting resistance
(moment load). |
Apply suitable spindle speed. (Please refer to drilling parameters.) |
| Low spindle speed |
Increased frictional heat causes breakage. |
| Material deposit at drill point (PWB's copper) |
The bit deflects at the upper surface of entry board causes breakage. |
Consider suitable drilling conditions. Using short chisel line
(small web thickness) drill bit. Use large chip pocket drill bit. |
| Unsuitable pec drilling |
The increment of steps doesn't match PWB stack height, which
causes swarf clogging and breakage. |
Recalculate pec drilling step increments/parameters |
| Penetrating to deep into the backup board |
Materials such as backup board generate large particles of swarf
which can adhere to the drill causing breakage |
Apply suitable penetration depth. |
P
W
B
S
e
t
t
i
n
g |
Panel stack height to high |
Hole registration accuracy worsens
through swarf clogging, causing bit breakage. Thrust load is
also increased. |
Apply suitable PWB stack heights to achieve the quality target. |
| High number and thickness of PWB copper layers |
The bit wears more quickly, generating increased cutting load
and breakage |
Decrease PWB stack heights and hit count to reduce drill bit
damage. Use double drilling method. |
| Hard cutting PWB material |
As a result of increased tool load, the bit is broken by wearing
and possible deflection |
Decrease PWB stack heights and hit count to reduce drill bit
damage. |
| Unsuitable entry board |
In a thicker PWB's, the bit is broken by cutting resistance. |
Consider suitable PWB thickness. |
| Scratching and dust on the front side of entry board |
Unevenness of entry board causing deflection and breakage. |
Control the management and handling of entry board. Check the
bush for defects |
| Unsuitable backup board |
Hard backup board generates wearing and increased cutting resistance,
causing breakage. |
Consider suitable hardness. |
| Unsuitable Stack preparation |
Poor stack preparation causes loose entry board to flap and the
PWB's have poor rigidity causing deflection and breakage |
Check stud pins and taping of the PWB stacking to prevent the
entry board flapping and gaps in PWB stack. |
| Uneven and scratched surface on the PWB |
Unevenness and scratches on the front side of the entry board,
can cause the drill to deflect and break. |
Check PWB quality. |
| PWB qualities |
Uneven resin and fiber intersections worsen hole registration
accuracy and causes breakage. |
Check PWB quality. Example: Check
unevenness of PWB using an image processor/AOI machine for measuring
hole registration accuracy.
---> An extreme striped pattern, etc. |
E
q
u
i
p
m
e
n
t |
TIR (Total Indicated Runout) |
Large dynamic deflection worsens accuracy, and causes breakage. |
Control spindle run out (maintenance
and repair). Recommended value <10 micron (<5 micron is better for <0.3mm
drill bits) |
| Poor drill chucking (Dust in spindle chuck, spindle chuck wearing,
scratching, marking for identification, etc.) |
Increased dynamic deflection by poor chucking causes breakage. |
Maintain collet chuck.. |
| Uneven contact of bush with entry board |
Uneven bush contact, a damaged bush or poor surface condition
of the bush contact area causes breakage. |
Check whether pressure foot is parallel with the machine table.
Check bush contact using PV-Checker. (Recommendation: Over 80%
surface touching bush) |
