| Cause |
Failure condition |
Countermeasure |
D
r
i
l
l
B
i
t
D
e
s
i
g
n |
ST Type |
Increased contact area with the hole wall expands
copper edges. |
UC type |
| Large margin width |
Increased area of contact between the drill bit
surface and hole wall raises drilling temperature. |
Setting correct margin length. |
M
a
n
u
f
a
c
t
u
r
e |
Repointed drill bit which has excessive diameter
wearing at the drill tip. |
Higher drilling temperature can cause the copper
layers to expand. |
Check wearing condition. Repointing must remove
correct amount to return full diameter. |
D
r
i
l
l
i
n
g
C
o
n
d
i
t
i
o
n |
Low chipload and hit count to high |
Higher drilling temperature can cause nail heading
of the copper inner layers. |
Higher chipload |
P
W
B
S
e
t
t
i
n
g |
Hinge number and thickness of PWB copper layers |
Increased cutting resistance raises the drilling
temperature, causing smear. |
Decrease PWB stack heights and hit count to reduce
drill bit damage. Use double drilling method. |
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) |
