| Cause |
Failure condition |
Countermeasure |
D
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B
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Poor drill bit strength |
Accuracy becomes worse. |
To increase strength, change web thickness and web taper. Use
VT type drill bit for superior hole registration accuracy |
| Small chip pocket (Flute volume) |
Drill chip pocket is clogged with chip, Which worsens accuracy
. If chips go between the entry board and PWB, accuracy will worsen
notably. |
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 drill bit geometries (Point Angle and helix angle
etc.) |
Unsuitable drill bit geometries for the PWB application, drilling
conditions, and equipment condition worsen accuracy. |
Optimize drill bit geometries, (Select suitable geometries for
drilling condition) |
| Unsuitable tungsten carbide material |
Increased wearing blunts the drill's cutting edges, causing poor
accuracy |
Use wear-resistant WC material. |
M
a
n
u
f
a
c
t
u
r
e |
Unbalanced drill point geometries (Chisel point inconcentricity,
Rip height gap, Chipping, and one sided taper or flare, etc.) |
Hole position accuracy gets worse from the upper surface of a
PWB. |
Check drill point geometry. |
| Unsuitable repointing (See above) |
Hole position accuracy gets worse from the upper surface of a
PWB. |
Check drill point geometry. |
D
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g
C
o
n
d
i
t
i
o
n |
High chipload |
Accuracy is worsened by poor chip evacuation and damaged drill
bits etc. |
Apply suitable chipload. (Please refer to drilling parameters.) |
| Low chipload |
Promotes wearing, causing poor accuracy. |
| High spindle speed |
Tool load increases as cutting resistance increase, making accuracy
worse. |
Apply suitable spindle speed. (Please refer to drilling parameters.) |
| Low spindle speed |
Burned swarfl will stick to the drill point, and accuracy will
worsen. |
| Hit count to high |
Promotes wearing, causing poor accuracy. |
Apply suitable hit counts. |
| To many repoints |
It promotes diameter wear, and accuracy will worsen. |
Reconsider the number of repoints. |
P
W
B
S
e
t
t
i
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|
Panel stack height to high |
Drill deflection will increases in proportion to PWB Stacks,
making accuracy worse. |
Apply suitable PWB stack heights to achieve the quality target. |
| High number and thickness of PWB copper layers |
The increase of cutting resistance causes wear, and worsens accuracy. |
Decrease PWB stack heights and hit count to reduce drill bit
damage. Use double drilling method. |
| Hard cutting PWB material |
The increase of cutting resistance causes wear and chipping,
worsening accuracy. |
Decrease PWB stack heights and hit count to reduce drill bit
damage. |
| Unsuitable entry board |
Using low performance entry board on PWB's with high hole qualities
may not obtain the accuracy demanded. |
Use high quality entry board like attached water soluble resin
type, multi-layer aluminum type, etc. Control suitable thickness. |
| Scratching and dust on the front side of entry board |
Drill bit is deflected by the unevenness of the entry board,
worsening accuracy. |
Control the management and handling of entry board. Check the
bush for defects. |
| Unsuitable backup board |
Hard back up board causes wear, which worsens accuracy. |
Consider suitable hardness. |
| Unsuitable Stack preparation |
Loosely stacked entry board and PWB's (poor PWB stack preparation)
causes poor accuracy. |
Check stud pins and tapering of the PWB stacking to prevent the
entry board flapping and gaps in PWB stack. |
| Uneven and scratched surface on the PWB |
Drill bit was deflected by the unevenness and scratching on the
front side of entry board, worsening accuracy. |
Check PWB quality. |
| PWB qualities |
Uneven resin and fiber intersections worsen hole accuracy. |
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. |
Control spindle run out (maintenance
and repair). Recommended value <10 micron (<5 micron is better for <0.3mm
drill bits) |
| Drilling machine's condition |
A worn or un-smooth ball screw or linear bearing from constant
use worsens accuracy. |
Maintain the drilling machine, the checking machine precision,
and routine major services |
| Unsuitable Vacuum force |
A high vacuum force lifts the entry board allowing chips to go
in between the entry board and PWB, causing the drill not to center
properly. In the case of low vacuum, it worsens chip evacuation
and causes chip clogging. |
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 pressure foot force |
Low pressure foot force prevents proper clamping of the bush
to the entry board, causing chip clogging and poor accuracy. |
Set correct pressure foot force. (Recommend: About 100-150 N,
Suitable value is depends on application) |
| Unsuitable bush diameter |
A large diameter bush prevents good chip evacuation and worsens
accuracy. |
Using small inner diameter bush. Example: Change from 10mm to
3mm inner dia. |
| Uneven contact of bush with entry board |
Uneven bush contact, a damaged bush or poor surface condition
of the bush contact area causes poor accuracy. |
Check whether pressure foot is parallel with the machine table.
Check bush contact using PV-Checker. (Recommendation: Over 80%
surface touching bush) |
