U.S. patent application number 09/755950 was filed with the patent office on 2001-10-18 for abbe error correction system and method.
Invention is credited to Cutler, Donald R..
Application Number | 20010029674 09/755950 |
Document ID | / |
Family ID | 22642517 |
Filed Date | 2001-10-18 |
United States Patent
Application |
20010029674 |
Kind Code |
A1 |
Cutler, Donald R. |
October 18, 2001 |
Abbe error correction system and method
Abstract
The present invention preferably employs non-contact,
small-displacement, capacitive sensors to determine Abbe errors due
to the pitch, yaw, or roll of a near linear mechanical stage that
are not indicated by an on-axis position indicator, such as a
linear scale encoder or laser interferometer. The system is
calibrated against a precise reference standard so the corrections
depend only on sensing small changes in the sensor readings and not
on absolute accuracy of the sensor readings. Although the present
invention is preferred for use in split-axis positioning systems
with inertially separated stages, the invention can be employed in
typical split-axis or stacked stage systems to reduce their
manufacturing costs.
Inventors: |
Cutler, Donald R.;
(Portland, OR) |
Correspondence
Address: |
STOEL RIVES LLP
900 SW FIFTH AVENUE
SUITE 2600
PORTLAND
OR
97204
US
|
Family ID: |
22642517 |
Appl. No.: |
09/755950 |
Filed: |
January 5, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60175993 |
Jan 11, 2000 |
|
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Current U.S.
Class: |
33/1M ; 33/568;
33/573 |
Current CPC
Class: |
G03F 7/70725 20130101;
G03F 7/70716 20130101; B23K 26/043 20130101; B23K 26/04 20130101;
H05K 3/0008 20130101; G05B 19/404 20130101 |
Class at
Publication: |
33/1.00M ;
33/568; 33/573 |
International
Class: |
B23Q 016/00 |
Claims
1. A positioning system for positioning a tool relative to a target
location on a workpiece in response to a positioning command,
comprising: a slow positioner for effecting a large range of
relative movement between the tool and the workpiece, the slow
positioner including a translation stage capable of movement
generally along an axis; a fast positioner for effecting small
ranges of relative movement between the tool and the workpiece; a
positioning signal processor for deriving from the positioning
command slow and fast movement-controlling signals; a slow
positioner driver for controlling the large range of relative
movement of the translation stage in response to the slow
movement-controlling signal; a fast positioner driver for
controlling the small ranges of relative movement of the fast
positioner in response to the fast movement-controlling signal; a
pair of spaced-apart displacement sensors in communication with the
fast positioner driver and coupled to move with the translation
stage along the axis; and a reference surface positioned in
proximity to the translation stage and parallel to the axis, the
translation stage being capable of moving along the reference
surface and the displacement sensors being capable of acquiring
information concerning their relative distances from the reference
surface and conveying the information to the fast positioner driver
to correct for an Abbe error associated with off-axis or rotational
movement of the translation stage.
2. The positioning system of claim 1 in which the rotational
movement is yaw.
3. The positioning system of claim 1 in which: the translation
stage is a first translation stage that supports a workpiece; the
slow positioner further comprises a second translation stage
capable of moving along a second axis that is substantially
perpendicular to the first axis; and the fast positioner is mounted
on the second translation stage.
4. The positioning system of claim 3 in which first and second
translation stages carry respective mutually exclusive first and
second inertial masses.
5. The positioning system of claim 3 in which the fast positioner
is a first fast positioner, and in which the second translation
stage supports a second fast positioner.
6. The positioning system of claim 3 in which multiple workpieces
are mounted on the first translation stage.
7. The positioning system of claim 3 in which the second
translation stage comprises a second pair of spaced-apart
displacement sensors in communication with the fast positioner
driver and coupled to move with the second translation stage along
the second axis, and in which a second reference surface is
positioned in proximity to the second translation stage and
parallel to the second axis, the second translation stage being
capable of moving along the second reference surface and the second
displacement sensors being capable of acquiring second information
concerning their relative distances from the second reference
surface and conveying the second information to the fast positioner
driver to correct for a second Abbe error associated with second
off-axis or rotational movement of the second translation
stage.
8. The positioning system of claim 7 in which the second rotational
movement is pitch or yaw.
9. The positioning system of claim 7 in which the second
translation stage comprises a third pair of spaced-apart
displacement sensors in communication with the fast positioner
driver and coupled to move with the second translation stage along
the second axis, and in which a third reference surface is
positioned in proximity to the second translation stage, parallel
to the second axis, the second translation stage being capable of
moving along the third reference surface and the third displacement
sensors being capable of acquiring third information concerning
their relative distances from the third reference surface and
conveying the third information to the fast positioner driver to
correct for a third Abbe error associated with third off-axis or
rotational movement of the second translation stage.
10. The positioning system of claim 9 in which the third rotational
movement is pitch or yaw.
11. The positioning system of claim 9 in which the second
translation stage comprises a fourth displacement sensor in
communication with the fast positioner driver and coupled to move
with the second translation stage in a plane including the second
axis, and in which a fourth reference surface is positioned in
proximity to the second translation stage, parallel to the second
axis, and in a second plane generally including the second
reference surface, the second translation stage being capable of
moving along the fourth reference surface and the fourth
displacement sensor in cooperation with one of the second
displacement sensors being capable of acquiring fourth information
concerning their relative distances from the respective fourth and
second reference surfaces and conveying the fourth information to
the fast positioner driver to correct for a fourth Abbe error
associated with fourth off-axis or rotational movement of the
second translation stage.
12. The positioning system of claim 9 in which the fourth
rotational movement is roll.
13. The positioning system of claim 1 in which the displacement
sensors comprise capacitive sensors.
14. The positioning system of claim 1 in which the displacement
sensors are capable of discerning relative distances as small as 10
nm.
15. The positioning system of claim 1 in which the displacement
sensors are capable of measuring relative distances as large as 50
.mu.m.
16. The positioning system of claim 1 in which the tool is a laser
beam.
17. A positioning system for positioning a laser beam relative to a
target location on a workpiece in response to a positioning
command, comprising: a first positioner effecting a large range of
relative movement between the laser beam and the workpiece, the
first positioner including a first translation stage capable of
supporting the workpiece in plane and moving generally along a
first axis; a fixed optical head including a fixed optical path
directed at, and transverse to, the plane of the workpiece; a
second positioner effecting a large range of relative movement
between the laser beam and the workpiece, the second positioner
including a second translation stage capable of supporting the
fixed optical head and moving generally along a second axis that is
transverse to the first axis; a positioning signal processor
deriving from the positioning command movement-controlling signals;
first and second positioner drivers controlling the large range of
relative movement of the respective first and second translation
stages in response to the movement-controlling signals; a pair of
spaced-apart first displacement sensors in communication with the
positioner driver and coupled to move with the first translation
stage along the first axis; and a first reference surface
positioned in proximity to the first translation stage and parallel
to the first axis, the first translation stage being capable of
moving along the first reference surface and the first displacement
sensors being capable of acquiring information concerning their
relative distances from the first reference surface and conveying
the information to the positioner driver to correct for an Abbe
error associated with off-axis or rotational movement of the first
translation stage.
18. The positioning system of claim 17 in which the rotational
movement is yaw.
19. The positioning system of claim 17 in which: the translation
stage is a first translation stage that supports a workpiece; the
slow positioner further comprises a second translation stage
capable of moving along a second axis that is substantially
perpendicular to the first axis; and the fast positioner is mounted
on the second translation stage.
20. The positioning system of claim 19 in which first and second
translation stages carry respective mutually exclusive first and
second inertial masses.
21. The positioning system of claim 19 in which the fast positioner
is a first fast positioner, and in which the second translation
stage supports a second fast positioner.
22. The positioning system of claim 19 in which multiple workpieces
are mounted on the first translation stage.
23. The positioning system of claim 19 in which the second
translation stage comprises a second pair of spaced-apart
displacement sensors in communication with the fast positioner
driver and coupled to move with the second translation stage along
the second axis, and in which a second reference surface is
positioned in proximity to the second translation stage and
parallel to the second axis, the second translation stage being
capable of moving along the second reference surface and the second
displacement sensors being capable of acquiring second information
concerning their relative distances from the second reference
surface and conveying the second information to the fast positioner
driver to correct for a second Abbe error associated with second
off-axis or rotational movement of the second translation
stage.
24. The positioning system of claim 23 in which the second
rotational movement is pitch or yaw.
25. The positioning system of claim 23 in which the second
translation stage comprises a third pair of spaced-apart
displacement sensors coupled to move with the second translation
stage along the second axis and in communication with the fast
positioner driver, and in which a third reference surface is
positioned in proximity to the second translation stage, parallel
to the second axis, and transverse to the second reference surface,
the second translation stage being capable of moving along the
third reference surface and the third displacement sensors being
capable of acquiring third information concerning their relative
distances from the third reference surface and conveying the third
information to the fast positioner driver to correct for a third
Abbe error associated with third off-axis movement of the second
translation stage.
26. The positioning system of claim 25 in which the third
rotational movement is pitch or yaw.
27. The positioning system of claim 25 in which the second
translation stage comprises a fourth displacement sensor coupled to
move with the second translation stage in a plane including the
second axis and in communication with the fast positioner driver,
and in which a fourth reference surface is positioned in proximity
to the second translation stage, parallel to the second axis, and
in a second plane generally including the second reference surface,
the second translation stage being capable of moving along the
fourth reference surface and the fourth displacement sensor in
cooperation with one of the second displacement sensors being
capable of acquiring fourth information concerning their relative
distances from the respective fourth and second reference surfaces
and conveying the fourth information to the fast positioner driver
to correct for a fourth Abbe error associated with fourth off-axis
movement of the second translation stage.
28. The positioning system of claim 27 in which the fourth
rotational movement is roll.
29. The positioning system of claim 17 in which the displacement
sensors comprise capacitive sensors.
30. The positioning system of claim 17 in which the displacement
sensors discern relative distances as small as 10 nm.
31. The positioning system of claim 17 in which the displacement
sensors measure relative distances as large as 50 .mu.m.
32. A method for positioning laser output relative to a target
location on a workpiece, comprising: providing slow and fast
movement-controlling signals from a positioning signal processor;
controlling with a slow positioner driver a large range of relative
movement of a translation stage, generally along an axis and along
a reference surface positioned in proximity to the translation
stage and parallel to the axis, in response to the slow
movement-controlling signal; controlling with a fast positioner
driver a small range of relative movement of a fast positioner in
response to the fast movement-controlling signal; effecting the
large range of relative movement between the laser output and the
workpiece on the translation stage; acquiring, with a pair of
spaced-apart displacement sensors coupled to move with the
translation stage along the axis, information concerning their
relative distances from the reference surface; conveying the
information from the displacement sensors to the fast positioner
driver; effecting with a fast positioner the small range of
relative movement between the laser output and the workpiece
including a correction for an Abbe error associated with off-axis
or rotational movement of the translation stage; and generating
laser output to impinge the target location on the workpiece.
33. The method of claim 32 in which the rotational movement is
yaw.
34. The method of claim 32 in which: the translation stage is a
first translation stage that supports a workpiece; the slow
positioner further comprises a second translation stage capable of
moving along a second axis that is substantially perpendicular to
the first axis; and the fast positioner is mounted on the second
translation stage.
35. The method of claim 34 in which first and second translation
stages carry respective mutually exclusive first and second
inertial masses.
36. The method of claim 34 in which the fast positioner is a first
fast positioner, and in which the second translation stage supports
a second fast positioner.
37. The method of claim 34 in which multiple workpieces are mounted
on the first translation stage.
38. The method of claim 34 in which the second translation stage
comprises a second pair of spaced-apart displacement sensors in
communication with the fast positioner driver and coupled to move
with the second translation stage along the second axis, and in
which a second reference surface is positioned in proximity to the
second translation stage and parallel to the second axis, the
second translation stage being capable of moving along the second
reference surface and the second displacement sensors being capable
of acquiring second information concerning their relative distances
from the second reference surface and conveying the second
information to the fast positioner driver to correct for a second
Abbe error associated with second off-axis or rotational movement
of the second translation stage.
39. The method of claim 38 in which the second rotational movement
is pitch or yaw.
40. The method of claim 38 in which the second translation stage
comprises a third pair of spaced-apart displacement sensors in
communication with the fast positioner driver and coupled to move
with the second translation stage along the second axis, and in
which a third reference surface is positioned in proximity to the
second translation stage, parallel to the second axis, the second
translation stage being capable of moving along the third reference
surface and the third displacement sensors being capable of
acquiring third information concerning their relative distances
from the third reference surface and conveying the third
information to the fast positioner driver to correct for a third
Abbe error associated with third off-axis or rotational movement of
the second translation stage.
41. The method of claim 40 in which the third rotational movement
is pitch or yaw.
42. The method of claim 40 in which the second translation stage
comprises a fourth displacement sensor in communication with the
fast positioner driver and coupled to move with the second
translation stage in a plane including the second axis, and in
which a fourth reference surface is positioned in proximity to the
second translation stage, parallel to the second axis, and in a
second plane generally including the second reference surface, the
second translation stage being capable of moving along the fourth
reference surface and the fourth displacement sensor in cooperation
with one of the second displacement sensors being capable of
acquiring fourth information concerning their relative distances
from the respective fourth and second reference surfaces and
conveying the fourth information to the fast positioner driver to
correct for a fourth Abbe error associated with fourth off-axis or
rotational movement of the second translation stage.
43. The method of claim 40 in which the fourth rotational movement
is roll.
44. The method of claim 32 in which the displacement sensors
comprise capacitive sensors.
45. The method of claim 32 in which the displacement sensors are
capable of discerning relative distances as small as 10 nm.
46. The method of claim 32 in which the displacement sensors are
capable of measuring relative distances as large as 50 .mu.m.
Description
RELATED APPLICATION
[0001] This application derives priority from U.S. Provisional
Patent Application No. 60/175,993, filed Jan. 11, 2000.
TECHNICAL FIELD
[0002] This invention relates to systems or methods for positioning
one or multiple "tools," such as laser beams or other radiation
beams, relative to target locations on one or multiple workpieces
and, in particular, to a system that accurately compensates for
Abbe errors associated with the movement of one or more stages of
such a beam positioning system.
BACKGROUND OF THE INVENTION
[0003] A variety of technologies employ tools to micro-machine, or
deposit patterns or materials on target locations on a workpiece.
For example, a micro-dimensioned punch may be used to punch holes
in a thin metal plate; a laser may be used to precisely machine or
selectively erode metallic, crystalline, or amorphous specimens;
and ion beams may be used to selectively implant charged particles
into an integrated circuit. All of the above-mentioned processes
share a common requirement for accurately and rapidly positioning a
pertinent tool to target locations on the workpiece.
[0004] The following background is presented herein only by way of
example to laser beam positioning systems, but skilled persons will
appreciate that the description is applicable to tool positioning
systems in general. Conventional tool positioning systems, and
particularly beam-positioning systems, typically provide movement
within a three-dimensional coordinate system and can be
characterized in several ways.
[0005] Traditional positioning systems are characterized by X-Y
translation tables in which the workpiece is secured to an upper
stage that is supported by a lower stage. Such systems typically
move the workpiece relative to a fixed beam position and are
commonly referred to as stacked stage positioning systems because
the lower stage supports the inertial mass of the upper stage and
the workpiece. These positioning systems have relatively good
positioning accuracy because interferometers are typically used
along each axis to determine the absolute position of each
stage.
[0006] In U.S. Pat. No. 4,532,402 of Overbeck, a high-speed
short-movement positioner ("fast positioner"), such as a
galvanometer, is supported by the upper stage of an X-Y translation
table ("slow positioner") and the upper stage and the workpiece are
supported by the lower stage. The combined movement of the two
positioners entails first moving the slow positioner to a known
location near a target location on the workpiece, stopping the slow
positioner, moving the fast positioner to the exact target
location, stopping the fast positioner, causing the tool to operate
on the target location, and then repeating the process for the next
target location.
[0007] However, the combined system of Overbeck is also a stacked
stage positioning system and suffers from many of the same serious
drawbacks as the aforementioned fixed beam system. The starting,
stopping, and change of direction delays associated with the
inertial mass of the stages and fast positioner unduly increase the
time required for the tool to process the workpiece. Overbeck's
system also imposes a serious drawback upon a computer-based
machine tool control file or "database" that typically commands the
tool to move to a series of predetermined target locations across
the workpiece. The database positioning the tool across the
workpiece must be "panelized" into abutting segments that each fit
within the limited movement range of the fast positioner when the
size of large circuit patterns exceeds this movement range.
[0008] U.S. Pat. Nos. 5,751,585 and 5,847,960 of Cutler et al.
describe split-axis positioning systems, in which the upper stage
is not supported by, and moves independently from, the lower stage
and in which the workpiece is carried on one axis or stage while
the tool is carried on the other axis or stage. These positioning
systems have one or more upper stages, which each support a fast
positioner, and can process one or multiple workpieces
simultaneously at high throughput rates because the independently
supported stages each carry less inertial mass and can accelerate,
decelerate, or change direction more quickly than can those of a
stacked stage system. Thus, because the mass of one stage is not
carried on the other stage, the resonance frequencies for a given
load are increased. Furthermore, the slow and fast positioners are
adapted to move, without necessarily stopping, in response to a
stream of positioning command data while coordinating their
individually moving positions to produce temporarily stationary
tool positions over target locations defined by the database. These
split-axis, multirate positioning systems reduce the fast
positioner movement range limitations of prior systems while
providing significantly increased tool processing throughput and
can work from panelized or unpanelized databases.
[0009] Such split-axis positioning systems are becoming even more
advantageous as the overall size and weight of the workpieces
increase, utilizing longer and hence more massive stages. At the
same time, feature sizes are continuing to decrease, causing the
need for dimensional precision to increase, and split-axis systems
are more likely to exhibit rotational errors that introduce Abbe
errors, which are errors indicative of the physical separation
between the effective position of a stage and the indicated
position of the stage. Abbe errors are typically caused by
imperfections or thermal variations in the bearings upon which the
stages slide and/or alignment or acceleration imperfections of the
drive mechanisms that provide movement to the stages.
[0010] FIG. 1 shows three mutually perpendicular translational
motion axes, such as X axis 10, Y axis 12, and Z axis 14 that
define a three-dimensional coordinate system 16, and three mutually
perpendicular rotational motion axes (hereafter referred to as a
roll axis 18, a pitch axis 20, and a yaw axis 22). Skilled workers
typically refer to roll as an angular rotation about X-axis 10,
pitch as an angular rotation about Y-axis 12, and yaw as an angular
rotation about Z-axis 14.
[0011] Although laser interferometer systems can be used to
indicate and compensate for certain Abbe errors, such systems are
costly and heavy because they typically require reference mirrors
that are nearly as long as the combined stage length plus the
length of travel, e.g. as much as two times the travel distance.
Such mirrors are difficult, if not impossible, to procure for the
long travel dimensions of large stages, such as with a lengthwise
dimension of 76 to 92 cm (30-36 inches), needed to accommodate
larger workpieces. Furthermore, split-axis systems would require at
least two interferometers for each stage and/or a very complex
system of optics to rat -indicate angle and position, and the
additive weight of the interferometers would increase the inertial
load on the stages at the expense of frequency response time to
changes in momentum.
[0012] U.S. Pat. No. 5,699,621 of Trumper et al. discloses the use
of small range displacement transducers to indicate pitch, yaw, and
roll angle errors. Trumper et al. correct angular errors by
controlling the bearing gap with electromagnets that require the
use of a highly compliant magnetic or air bearing system. The
correction speed of the Trumper et al. system is limited to the
bandwidth of the linear stage system and therefore has similar mass
versus bandwidth limitations as stacked stage positioning
systems.
[0013] A less expensive and/or less massive and very accurate Abbe
error correction system or method is therefore desirable.
SUMMARY OF THE INVENTION
[0014] An object of the present invention is to provide a method or
apparatus that employs non-contact small displacement sensors, such
as capacitive sensors, to determine Abbe errors due to mechanical
stage pitch, yaw and roll that are not indicated by an on-axis
position indicator, such as a linear scale encoder or laser
interferometer, and a means to compensate for such Abbe errors.
[0015] Another object of the invention is to employ such sensors to
determine and correct Abbe errors due to linear bearing variability
or distortions associated with acceleration or temperature
gradients.
[0016] The present invention provides a cost effective means to
determine and compensate for linear stage positioning system Abbe
errors that are errors at the effective position of the system that
are not indicated by a position indicator such as a metal or glass
scale encoder or laser interferometer due to pitch, yaw, or roll of
the linear stage and the resulting physical distance between the
effective position and the indicated position of a stage. To
minimize cost, the system is calibrated against precision X and Y
position reference standards so the corrections depend only on
sensing small changes in the sensor readings and not on absolute
accuracy of the sensor readings. Although the present invention is
preferred for use in split-axis positioning systems, it can be
employed in stacked stage systems to reduce their manufacturing
costs. Although a linear scale encoder can be employed to indicate
the nominal on-axis stage position to reduce costs further, a laser
interferometer can be used when a greater level of accuracy and/or
resolution is desired.
[0017] Additional objects and advantages of this invention will be
apparent from the following detailed description of preferred
embodiments thereof which proceeds with reference to the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 shows six axes, including three mutually
perpendicular translational motion axes, X, Y, and Z, and three
mutually perpendicular rotational motion axes, roll, pitch, and
yaw.
[0019] FIGS. 2A and 2B provide a pictorial block diagram of a
multi-stage laser beam positioning system of this invention.
[0020] FIG. 3 is a fragmentary pictorial side view showing a prior
art galvanometer-driven mirror positioner of a type suitable for
use with this invention.
[0021] FIG. 4 is a plan view showing preferred positions of Y-stage
Abbe error sensors mounted on a Y-axis stage (workpiece stage)
relative to a reference surface.
[0022] FIG. 5 is an end view showing preferred positions of the
sensors mounted on the Y-axis stage of FIG. 4.
[0023] FIG. 6 is a side elevation view showing preferred positions
of X-stage Abbe error sensors mounted on an X-axis stage (tool
stage) relative to a reference surface.
[0024] FIG. 7 is an end view showing preferred positions of the
sensors mounted on the X-axis stage of FIG. 6.
[0025] FIG. 8 is a plan view showing preferred positions of the
sensors mounted on the X-axis stage of FIG. 6.
[0026] FIG. 9 is an oblique pictorial view showing a multi-head
laser machining system employing the present invention.
[0027] FIG. 10 is a simplified electrical block diagram of a
digital signal processing system including multiple fast stage
signal processors employed in the multi-head laser machining system
of FIG. 9.
[0028] FIG. 11 is a simplified electrical block diagram of one of
multiple fast stage signal processors employed in the digital
signal processing system of FIG. 10.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
[0029] FIGS. 2A and 2B (generically FIG. 2) show a multi-stage tool
positioner system 50 having positioning command execution
capabilities in accordance with this invention. Positioner system
50 is described herein only by way of example with reference to a
single-head, laser-based hole cutting system that employs a digital
signal processor ("DSP") 52 to control a fast galvanometer
positioner stage 54 (scanner or "fast stage 54"), a slow X-axis
translation stage 56 ("slow stage 56"), and a slow Y-axis
translation stage 58 ("slow stage 58") to direct a laser beam 60 to
target locations on a single workpiece 62, such as an etched
circuit board.
[0030] With reference to FIG. 1, in a preferred split-axis
embodiment, the X-axis translation stage 56 is supported by
bearings on rails 46 and generally moves along an X-Z plane, and
the Y-axis translation stage 58 is supported by bearings on rails
48 and generally moves along an X-Y plane. Skilled persons will
appreciate that both stages 56 and 58 could alternatively be
adapted to move in parallel planes and be inertially separated or
dependent. In a preferred embodiment, positioner system 50 employs
high stiffness re-circulating or cross-roller bearing systems to
support and direct the movement of stages 56 and 58.
[0031] A system control computer 63 processes a tool path database
stored in a database storage subsystem 64. The database contains
the desired processing parameters for cutting holes and/or profiles
with laser beam 60 in workpiece 62. The database is conventionally
compiled using a tool path generating program, such as I-DEAS
Generative Machining provided by Structural Dynamics Research
Corporation located in Milford, Ohio. System control computer 63
conveys parsed portions of the stored database to a laser
controller 68 and position control portions of the database as a
data stream to a delta process 70. Delta process 70 resolves the
data stream into x and y components for delta position ("dp"),
delta velocity ("dv"), and delta time ("dt") for each intended
change in the path of laser beam 60 across workpiece 62.
Consequently, each movement of laser beam 60 is defined in dp, dv,
and dt components that are further processed by a position profiler
72 into move profiles including acceleration and/or constant
velocity segment position signals.
[0032] Delta process 70 preferably generates the dp, dv, and dt
components in accordance with a preferred BASIC language signal
processing procedure described in U.S. Pat. Nos. 5,751,585 and
5,847,960 of Cutler et al., which are assigned to the assignee of
this application.
[0033] Referring again to FIG. 2, the dp, dv, and dt components
generated by delta process 70 are further processed by position
profiler 72 into the move profile positioning signals required to
move fast stage 54 and slow stages 56 and 58 as commanded by the
database. Ideally, positioner acceleration is proportional to
motive force, and motive force is proportional to electrical
current supplied to a positioner driver such as a linear or rotary
servo motor or a galvanometer coil. Therefore, the positioning
signal produced by position profiler 72 is a series of
"full-spectrum" half-sine profiled acceleration-inducing and
constant velocity-inducing positioning steps that cause system
movements. The full-spectrum bandwidth need only be about 250
Hertz, a bandwidth sufficient to drive a typical
galvanometer-driven mirror positioner at its maximum frequency.
[0034] Instantaneous values of the full-spectrum positioning signal
are generated by DSP 52 at a rate of about 10,000 points per second
by employing the dp, dv, and dt components generated by delta
process 70 as variables for a sine value generation program running
in DSP 52. Alternatively, the dp, dv, and dt components may be
employed to address and fetch associated sinusoidal waveform values
stored in a sine value lookup table that is incorporated within DSP
52.
[0035] The resulting full-spectrum positioning signal has
acceleration and position components that are received by a
profiling filter 78 having a constant signal propagation delay and
a delay element 79 that compensates in DSP 52 for the constant
signal propagation delay of profiling filter 78. For example, delay
element 79 delays the laser triggering pulses generated by position
profiler 72 to coincide with the delayed movements of fast stage 54
and slow stages 56 and 58. Profiling filter 78 and delay element 79
also cooperate, as described below, to move slow stages 56 and 58
smoothly over the average position profile while limiting their
acceleration to .+-.1 g and cooperate to limit fast stage 54
positioning movements to .+-.10 millimeters.
[0036] The position component is received by profiling filter 78 to
produce filtered position command data for driving slow stages 56
and 58. Profiling filter 78 is preferably a fourth-order low-pass
filter.
[0037] Because profiling filter 78 produces filtered position
command data having a constant time delay with respect to the
half-sine positioning signal position component, the constant time
delay is compensated for by delay element 79. Delay element 79 is
preferably implemented in DSP 52 as a programmed delay in conveying
the half-sine positioning signal acceleration and position
components from position profiler 72 to fast stage 54 signal
processing elements, the first of which are adders 80 and 82.
Thereby, half-sine positioning signals directed to fast stage 54
are time synchronized with the filtered position commands directed
to slow stages 56 and 58.
[0038] The acceleration component from position profiler 72 is also
filtered by profiling filter 78 to provide a filtered acceleration
command to adder 80 and a feed forward process 94. Adder 80
functions as a high-pass filter by subtracting the filtered
acceleration command from the acceleration component of the
full-spectrum positioning signal to form a galvo acceleration feed
forward signal, which is conveyed to a feed forward process 86.
Likewise, the filtered position command from profiling filter 78
and the delayed position component of the half-sine positioning
signal are conveyed respectively to adders 90 and 82 for processing
and distribution, respectively, to slow stages 56 and 58 and fast
stage 54. A galvo filter 97 and a servo filter 98 are conventional
loop compensation filters that function to keep fast stage 54 and
slow stages 56 and 58 stable.
[0039] Profiling filter 78 is implemented by cascading two or more
second-order filters having critical damping ratios. As the number
of cascaded filters increases beyond two, their cutoff frequencies
increase by about the square root of the number of filters (e.g.,
two filters have cutoffs that are 1.414 times the cutoff for a
single filter). Preferably two filters are cascaded to provide good
smoothing while keeping the overall filter implementation
simple.
[0040] For profiling filter 78, the preferred 38 radian per second
cutoff frequency (about 6 Hertz (Hz)) is a very low frequency
compared to the 10 kHz rate at which DSP 52 updates positioning
data for slow stages 56 and 58. If profiling filter 78 runs at the
10 kHz slow stage update frequency, the discrete filter
coefficients become sensitive to roundoff errors because the poles
of the discrete filter move close to the unit circle. Profiling
filter 78 also receives the acceleration command from position
profiler 72 and generates the filtered acceleration command that is
conveyed to servo feed forward process 94 and to adder 80.
[0041] The desired move profile commands are preferably calculated
at the 10 kHz updating rate, and the slow stage acceleration and
actual (not commanded) position is subtracted therefrom at adders
80 and 82 to produce, respectively, the fast stage acceleration and
position command signals.
[0042] The fast stage acceleration command signal is processed
through adder 80 and feed forward process 86, while the fast stage
position command signal is processed through adder 82 and galvo
filter 97. The processed fast stage signals are combined in an
adder 84 and conveyed to a galvanometer driver 88.
[0043] Likewise, the slow stage filtered acceleration command is
processed through a feed forward process 94, while the slow stage
filtered position command is processed through adder 90 and servo
filter 98. The processed slow stage signals are combined in an
adder 92 and conveyed to a linear servo motor driver 96.
[0044] Galvanometer driver 88 provides deflection control current
to a pair of mirror deflecting galvanometers in fast stage 54, and
servo motor driver 96 provides control current to linear servo
motors that control the positioning of slow stages 56 and 58.
[0045] FIG. 3 shows a prior art galvanometer-driven mirror
positioner 100 of a type suitable for use as fast stage 54.
Galvanometer driver 88 (FIG. 2) provides rotational control current
on conductors 102 to respective X-axis and Y-axis high-speed
response D.C. motors 104 and 106 that rotate shafts 107 in bearings
108 to selectively pivot a pair of mirrors 110 and 112 that deflect
laser beam 60 through an optional lens 114 to a predetermined
target location on workpiece 62.
[0046] Alternatively, a nonbearing motion positioner, such as a
piezoelectric element, a voice coil actuator, or other limited
angle high-speed positioner device could be used in place of
galvanometer-driven mirror positioner 100 in positioner system
50.
[0047] Likewise with reference to FIG. 2, alternative accurate
rotary or linear positioner mechanisms may be substituted for the
linear servo motors driving slow stages 56 and 58. However, in
positioner system 50, linear motors that preferentially respond to
the slow stage position command are preferred.
[0048] Two signals are combined with the slow and fast stage
position commands to reduce positional errors between the commanded
position and the actual position of laser beam 60 on workpiece 62.
The delayed fast stage position command at adder 82 and the
filtered slow stage position command at adder 90 represent the
ideal signal values required to cause proper positioning of stages
54, 56, and 58. However, practical factors such as gravity,
friction, mass, and inaccuracies in the full-spectrum positioning
signal generated by position profiler 72 are not contemplated in
the unmodified position commands.
[0049] The practical factors are accounted for by sensing the
actual positions of stages 54, 56, and 58 with position sensors 120
and 122 to provide predictive position feedback data to adders 82
and 90 in DSP 52. Note that adder 82 in the fast stage positioning
path receives position feedback data from both position sensors 120
and 122. Position sensors 120 and 122 may be well-known types
employing rotating capacitor plates, linear and rotary encoder
scales, or interferometer motion detectors together with
appropriate analog-to-digital and/or digital-to-analog conversion
techniques.
[0050] As laser beam 60 undergoes movement across workpiece 62, the
sensed beam position is continuously compared to the commanded beam
position, with the positional difference representing a degree to
which the practical factors have caused positioning errors. In
particular, sensed position data of fast stage 54 and slow stages
56 and 58 are generated by position sensors 120 and 122 and
subtracted from the commanded position at adder 82 to generate
positional difference data that are combined in adder 84 with
acceleration data from feed forward process 86. Likewise, sensed
position data of slow stages 56 and 58 are generated by position
sensor 122 and subtracted from the commanded position at adder 90
to generate positional difference data that are combined in adder
92 with acceleration data from feed forward process 94.
[0051] Coordinated positioning is particularly beneficial for
applications such as laser beam hole cutting that requires rapid
movement between target locations along a tool path combined with
pauses at each target location to fire the laser to cut a hole but,
of course, is not limited to that application. Other features and
preferred processing parameters of a conventional laser drilling
system are disclosed in U.S. Pat. No. 5,841,099 of Owen et al.
[0052] FIGS. 4 and 5 are respective plan and end views showing
preferred positions of Y-stage Abbe sensors 124 mounted on Y-axis
translation stage 58 relative to yaw reference surface 126 in
accordance with an aspect of this invention, and FIGS. 6-8 are
respective side elevation, end, and plan views showing preferred
positions of X-stage Abbe sensors 128, 130, 131, and 132 mounted on
X-axis translation stage 56 relative to yaw and roll reference
surfaces 134 and pitch reference surface 136 in accordance with an
aspect of this invention.
[0053] With reference to FIGS. 2B and 4-8, Abbe sensors 124, 128,
130, 131, and 132 are preferably non-contact, small and lightweight
displacement sensors. The most preferred sensors measure
capacitance as a function of distance from a given reference
surface. In a preferred embodiment, the Abbe sensors have a gap
range (distance between sensor and reference surface) of 50 .mu.m
plus or minus 25 .mu.m and a resolution of less than 50 nm and
preferably less than or equal to 10 nm. Skilled persons will
appreciated that numerous other ranges are possible including a
wider or narrower gap range and better resolution when the
technology becomes cost effective. Non contact sensors are
preferred because they eliminate wear that might lead to
inaccuracies. Preferred Abbe sensors include Model PX405H series
probes available from Lion Precision of St. Paul, Minn. Other
suitable capacitance probes or sensors are available from ADE
Technologies of Westwood, Mass and Micro-Epsilon of Ortenburg,
Germany.
[0054] Reference surfaces 126, 134, and 136 may be formed on
appropriate sides of bearing rails 46 and 48 as shown in FIG. 2B or
may be otherwise positioned near but separated from translations
stages 56 and 58 as shown in FIGS. 4-8. (In FIGS. 4-8, four Y-stage
bearings 138 and three X-stage bearings 140 are depicted instead of
rails 46 and 48). The reference surfaces are preferably the same
length as the base for the stages or at least as long as the
movement ranges along bearing rails 46 and 48. The reference
surfaces are preferably stable but do not need to be perfectly
straight because the sensors are calibrated against the entire
length of the surfaces so the corrections depend only on sensing
small changes in the sensor readings and not on absolute accuracy
of the sensor readings or stage positions.
[0055] Although stages 56 and 58 could be adapted to move in
parallel planes and be inertially separated or dependent, the
following description is, for convenience, presented herein only by
way of example to addressing X and Y axis position errors in
split-axis positioning system 70 where substantially flat (100 to
10,000 times larger in the X and Y dimensions than in Z dimension)
workpiece 62 is carried on Y stage 58 and the tool (laser 76) is
directed by X-stage 56.
[0056] With reference again to FIGS. 2A, 2B, 4 and 5, the nominal
on-axis position of Y stage 58 is indicated by sensor 122a, which
is preferably a glass or metal scale encoder or a laser
interferometer depending on desired positioning accuracy
specifications. In a split-axis configuration, Y-stage yaw
typically produces the most significant X and Y Abbe errors. The
yaw error is indicated by preferably a pair of Y-stage Abbe sensors
124a and 124b (generically sensors 124) that are preferably mounted
as far apart as possible along Y axis 12 and as near to the top of
the side of Y stage 58, or a chuck that it may support, as
practical. Reference surface 126 is preferably integrated into rail
46 or the base of the Y stage assembly in a manner that results in
as stable an indication of the stage yaw as possible as a function
of other effects including bearing repeatability, temperature, and
stage acceleration.
[0057] The capacitances indicating the X components of the distance
from the reference surface of the Abbe error detected by sensors
124 due to yaw are preferably converted by a Y-stage yaw probe
driver 145 into a DC voltage suitable for processing into Abbe
error correction signals. These signals may be directed to separate
X-Abbe and Y-Abbe error adders 142 and 144 before being routed to
adder 82 and incorporated into scanner position commands.
[0058] With reference again to FIGS. 2A, 2B, and 6-8, pitch, yaw,
and roll of X stage 56 can also cause significant X and Y position
errors. The preferred split-axis configuration, as shown in the
figures, has X stage 56 oriented on edge, such that the planes
defined by the stages 56 and 58 are transverse and such that stages
56 and 58 are inertially separated. In a most preferred embodiment,
X stage 56 is oriented vertically while Y stage 58 is oriented
horizontally. Thus, pitch, yaw, and roll in this context are
defined with respect to the actual plane of movement of X stage 56
and not with respect to a more typical horizontal orientation.
[0059] The nominal on-axis position of X stage 56 is indicated by
sensor 122b, which is preferably a glass or metal scale encoder or
a laser interferometer depending on desired positioning accuracy
specifications. The X-stage Abbe sensors 128, 130, 131, and 132 may
all be the same types as or different types from Y-stage sensors
124. Sensors 128a and 128b (generically sensors 128) are preferably
mounted as far apart as possible along X axis 10. Similarly,
sensors 130 and 131 are preferably mounted as far apart as possible
along X axis 10. Sensor 132 is preferably mounted to be planar with
and as far apart as possible along Z axis 14 from sensor 131.
[0060] Because X stage 56 is preferably kinematically mounted on
three bearings 140 as shown in FIGS. 6-8, changes in distance from
reference surfaces 134 and 136 detected by X-stage Abbe sensors
128, 130, 131, and 132 will result predominately in movement of a
plane associated with X stage 56 and not from distortion of X stage
56. X-stage Abbe sensors 130 and 131 detect distances from X-stage
yaw reference surface 134a and indicate changes in the yaw angle of
the plane of X stage 56. X-stage Abbe sensors 131 and 132 detect
distances from X-stage role reference surfaces 134a and 134b,
respectively, and indicate changes in the roll angle of the plane
of X-stage 56. X-stage Abbe sensors 128 detect distances from the
pitch reference surface 136 and indicate changes in the pitch angle
of X stage 56.
[0061] The capacitances indicating the X and Y components of the
distance from the reference surface 134a of the Abbe error detected
by sensors 130 and 131 due to yaw are preferably converted by an
X-stage yaw probe driver 146 into a DC voltage suitable for
processing into Abbe error correction signals. Similarly, the
capacitances indicating the X and Y components of the distances
from the reference surfaces 134a and 134b of the Abbe error
detected by sensors 131 and 132 due to roll are preferably
converted by an X-stage roll probe driver 147 into a DC voltage
suitable for processing into error correction signals. Similarly,
the capacitances indicating the X and Y components of the distances
from the reference surface 136 of the Abbe error detected by
sensors 128 due to pitch are preferably converted by an X-stage
pitch probe driver 148 into a DC voltage suitable for processing
into error correction signals. Skilled persons will note that
sensor 131 feeds both yaw probe driver 145 and roll probe driver
146. Suitable probe drivers are well known to skilled persons;
however, the Compact Probe Driver manufactured by Lion Precision is
preferred. These yaw, roll, and pitch Abbe error correction signals
may be directed to separate X-Abbe and Y-Abbe adders 142 and 144
before being routed to adder 82 and incorporated into scanner
position commands.
[0062] The X and Y position components that correspond to these
Abbe errors are calculated in real time as positioner system 50
moves and process workpiece 62 and are added to or superimposed on
the scanner position commands to compensate for the Abbe position
errors. These angular changes are combined with the geometry of the
optics (including location of the beam path (or beam paths)
relative to the stage and distance of the work from the stage) to
indicate associated changes (errors) in effective beam position on
the work. Fast response is achieved by adding the Abbe error
corrections to the scanner position at adder 82 because the
bandwidth of the fast stage 54 is significantly higher than the
bandwidth of the linear stages 56 and 58.
[0063] However, the Abbe error corrections resulting from the
system of sensors could be added to the linear stage position servo
loop directly at adder 90. This implementation would be appropriate
when fast stage 54 is replaced by a fixed beam positioner. A fixed
beam positioner would typically provide more precise beam
positioning than is provided by fast stage 54 and would be employed
in applications where greater accuracy might be desirable such as
in severing micron or submicron sized links. Skilled persons will
appreciate that X-axis stage 56 could be adapted so that fast stage
54 may be interchangeable with a fixed beam positioner, or that
X-axis stage 56 may support both fast stage 54 and a fixed beam
positioner simultaneously. In the latter case, Abbe error
corrections would be fed to adder 82 whenever fast stage 54 is
employed and fed to adder 90 whenever a fixed beam positioner is
employed.
[0064] FIG. 9 shows a multi-head positioner 150 embodiment of this
invention in which multiple workpieces 152A, 152B, 152C, . . . 152N
are simultaneously processed. (Hereafter multiple elements are
referred to collectively without the letter suffix, e.g.,
"workpieces 152"). Multi-head positioner 150 employs one each of
slow stages 56 and 58 configured such that workpieces 152 are
fixtured and carried on Y-axis slow stage 58 and multiple fast
stages 154A, 154B, 154C, . . . 154N are carried on X-axis slow
stage 56. Of course, the roles of slow stages 56 and 58 may be
reversed, or two or more fast stages 154 may be carried by one or
more X-axis slow stages 56 while Y-axis 58 carries a single
workpiece 62.
[0065] As the number of fast stages 154 carried on slow stage 56
increases, their accumulated mass becomes increasingly difficult to
accelerate. Therefore, the number N of fast stages 154 carried on
slow stage 56 is preferably limited to four, although N may vary
with positioner types and applications.
[0066] Each of workpieces 152 has associated with it one or more
processing tools, preferably a laser 156A, 156B, 156C, . . . 156N
that directs processing energy toward associated fast stages 154A,
154B, 154C, . . . 154N by way of associated mirrors 158A, 158B,
158C, . . . 158N. Fast stages 154 deflect the processing energy to
target locations in substantially square, such as 20 by 20
millimeter processing fields 162A, 162B, 162C, . . . 162N located
on associated workpieces 152.
[0067] Video cameras 160A, 160B, 160C, . . . 160N are positioned on
slow stage 56 for viewing associated processing fields 162, sensing
the alignments, offsets, rotations, and dimensional variations of
workpieces 152, and aiming and focusing lasers 156.
[0068] In the preferred embodiment, the same processing pattern is
duplicated on workpieces 152 by each of lasers 156 and fast stages
154. However, in some processing applications, processing pattern
variations may be required to match the pattern to variations among
workpiece geometries, scale factors, offsets, rotations,
distortions. Alternatively, it may be desirable to have one or more
lasers 156 simultaneously processing different, but preferably
nominally identical or repetitive (slave to a single Y stage),
patterns on the same workpiece 152. It may also be necessary to
correct for fast stage nonlinearities and mounting inconsistences
introduced by mounting position variations among workpieces 152
mounted on slow stage 58. Unlike prior multi-spindle drilling
machines, multi-head positioner 150 can compensate for the
above-described variations by employing programmable correction
factors, described with reference to FIGS. 10 and 11, when driving
each of fast stages 154. Similarly, the Abbe errors, indicating the
degree to which a commanded tool position does not match a sensed
target location, can be compensated for in a manner similar with
that described with respect to FIGS. 2A, 2B, and 4-8.
[0069] FIG. 10 shows how multi-rate positioner DSP 52 (FIG. 2) may
be adapted to coordinate the positioning of multiple fast stages
154 and slow stages 56 and 58, resulting in a multi-head DSP 170.
In like manner to DSP 52, multi-head DSP 170 receives from system
control computer 63 dp, dv, and dt components that are further
processed by position profiler 72 into half-sine profiled
positioning signals. DSP 170 also includes some of the same signal
processing elements as DSP 52, namely profiling filter 78, delay
element 79, feed forward process 94, servo driver 96, slow stage
56, and position sensor 122. Because FIG. 10 is simplified, only
X-axis slow stage 56 processing elements are shown. Skilled workers
will understand that corresponding Y-axis elements are implied.
[0070] Only a single system control computer 63 is required to
drive slow stages 56 and 58 and N fast stages 154. Multiple fast
stage signal processors 172A, 172B, 172C, . . . 172N each receive
fast stage correction data from system control computer 63. In this
way, fast stage position commands and current slow stage position
data are received by each of fast stage signal processors 172 such
that each of fast stages 154 is directed to a common set of target
locations that are further positionable by unique error correction
data. If only a single X-axis stage 56 is employed to carry
multiple fast stages 154 and a single Y-axis stage 58 is employed
to carry one or multiple workpieces 152, then the Abbe error
detection system shown and described in connection with FIGS. 2A,
2B, and 4-8 can be employed without modification, and the Abbe
error correction data 190 can be fed to adder 80 of FIG. 10 or fast
stage correction processor 180 of FIG. 11 as shown.
[0071] FIG. 11 shows a representative one of fast stage signal
processors 172 receiving fast and slow stage positioning data from
DSP 170 and correction data from system control computer 63. The
correction data include slow stage and workpiece related correction
data that are conveyed to a geometry correction processor 180 and
fast stage linearity and scale factor correction data that are
conveyed to a fast stage correction processor 182. Skilled persons
will appreciate that if fast stages 154 are mounted on separate
X-axis stages 56, which preferably have synchronized movement but
may be unsynchronized, then each such X-axis stage 56 may be
commanded by its own processor 170 or subprocessor. Furthermore,
each such stage 56 would preferably be equipped with its own
position sensor 122 and five X-stage Abbe sensors to compensate for
any Abbe errors associated with the individual stages.
[0072] The correction data may be equation- or lookup table-based.
However, correction data employed by geometry correction processor
180 and fast stage correction processor are preferably
equation-based along lines described in U.S. Pat. No. 4,941,082 of
Pailthorp et al. ("the '082 patent"), which is assigned to the
assignee of this application and is incorporated herein by
reference.
[0073] Fast stage linearity and scale factor errors are relatively
constant and depend mostly on the individual characteristics of
fast stages 154. Therefore, fast stage correction processor 182
requires relatively small and infrequent correction data changes.
Generating this correction data entails, for example, directing
each of fast stages 154 to at least 13 calibration points on an
associated calibration target as described in the '082 patent. A
reflected energy detector senses any differences between the
directed and actual target point locations and provides difference
data to system control computer 63 for processing. The resulting
correction data are conveyed to and stored in each fast stage
correction processor 182. Also, any differences between the
directed and actual target point locations sensed by associated
video cameras 160 are calibrated and compensated for. Slow stage
linearity and scale factor errors are also relatively constant and
do not, therefore, require frequent correction data changes.
[0074] On the other hand, workpiece-related errors are relatively
variable and depend mostly on workpiece placement, offset,
rotation, and dimensional variations among workpieces 152.
Therefore, geometry correction processor 180 requires relatively
large correction data changes every time workpieces 152 are
changed. Generating this correction data entails, for example,
directing slow stages 56 and 58 to at least two, and preferably
four, predetermined calibration targets on each associated
workpiece 152. Alternatively, in an embodiment where the vision
system is working through the fast positioner, both the slow stages
56 and 58 and fast stages 154 are directed toward the calibration
targets. These calibration targets may be, for example, corners,
tooling holes, or photoetch targets of an ECB. Each video camera
160 senses differences between the directed and actual calibration
target locations and provides difference data to system control
computer 63 for processing. The resulting correction data for each
workpiece 152 are conveyed to and stored in the associated geometry
correction processor 180.
[0075] For each fast stage signal processor 172, corrected
positioning data for the Y-axis are conveyed from correction
processors 180 and 182 to feed forward process 86, galvo driver 88,
and fast stage 154. Position feedback data are generated by
position sensor 120 (as in FIG. 2A) and combined for correction in
adders 184 and 84. Skilled workers will understand that the same
process applies to X-axis fast positioning.
[0076] In applying the correction data to fast stages 154, each
fast stage is preferably limited to an 18 by 18 millimeter
positioning range within its 20 by 20 millimeter maximum linear
positioning range. The remaining 2 millimeters of positioning range
is employed for applying the above-described corrections.
[0077] The foregoing describes signal processing for a single axis
of motion for each of the fast and slow positioner stages. Skilled
workers will readily understand how to replicate the signal
processing to coordinate the motion of both axes, both stages, and
single or multiple fast positioners.
EXAMPLE
[0078] A typical tool application employing positioner system 50
and including Abbe error correction is laser cutting of holes, such
as blind via holes, in multilayer ECBs or other workpieces 62.
Multilayer ECBs are typically manufactured by registering, stacking
together, laminating, and pressing multiple 0.05- to
0.08-millimeter thick circuit board layers. Each layer typically
contains a different interconnection pad and conductor pattern,
which after processing constitutes a complex electrical component
mounting and interconnection assembly. The component and conductor
density trend of ECBs is increasing together with that of
integrated circuits. Therefore, the positioning accuracy and
dimensional tolerances of holes in ECBs is increasing
proportionally.
[0079] Unfortunately, the pressing step causes expansion and
dimensional variations that lead to scale factor and orthogonality
variations among the ECBs. Moreover, when multiple ECBs (workpieces
152) are attached to slow stage 58, fixturing variations can cause
dimensional rotation and offset errors among the ECBs. Adding to
that, ECB thickness variations make it difficult to mechanically
drill holes having an accurately predetermined depth.
[0080] Positioner systems 50 or 150 solve the above-described
problems as follows. Two to four calibration targets can be etched
at predetermined locations, preferably one at each corner, on each
ECB. Video cameras 160 sense differences between the commanded and
actual calibration target locations and provide difference data to
system control computer 63 for processing. The resulting correction
data are conveyed to and stored in geometry correction processor
180.
[0081] Two calibration targets provide sufficient difference data
to system control computer 63 to correct for rotation and offset
variations among the ECBs. Three calibration targets provide
sufficient difference data to system control computer 63 to correct
for rotation, offset, scale factor, and orthogonality variations
among the ECBs. Adding a fourth calibration target further allows
for correction of trapezoidal distortion in each of the ECBs.
[0082] ECB thickness variations are readily accommodated by the
.+-.0.13-millimeter (.+-.0.005 inch) laser depth of field.
[0083] Processing blind via holes presents a difficult challenge
for any hole processing tool because of the tight depth, diameter,
and positioning tolerances involved. This is because blind via
holes are typically processed through a first conductor layer
(e.g., copper, aluminum, gold, nickel, silver, palladium, tin, and
lead), through one or more dielectric layers (e.g., polyimide, FR-4
resin, benzocyclobutene, bismaleimide triazine, cyanate ester-based
resin, ceramic), and up to, but not through a second conductor
layer. The resulting hole is plated with a conductive material to
electrically connect the first and second conductor layers. Blind
via processing windows are presented in detail U.S. Pat. No.
5,841,099 of Owen et al.
[0084] Referring again to FIG. 9, multi-head positioner 150 is
configured as an ECB blind via cutting apparatus in which N equals
an even number, such as 2, 4, or 6, but preferably 4. Lasers 156A
and 156C are UV lasers (wavelength is less than about 400
nanometers and preferably about 355 or 266 nm), and lasers 156B and
156N are IR lasers (wavelength is in a range from about 1,000
nanometers to about 10,000 nanometers, preferably about 9,000
nanometers). Because the UV and IR lasers have substantially
different wavelengths, mirrors 158 and optics for fast stages 154
are configured for compatibility with each associated laser's
wavelength.
[0085] UV lasers 156A and 156C are capable of cutting both the
first conductor layer and the dielectric layer in a suitable
manner. However, the laser power levels and pulse repetition rates
are carefully controlled to prevent unacceptable damage to the
second conductor layer. This results in a narrow "process window."
Therefore, UV lasers 156A and 156C are preferably employed to cut
through only the first conductor layer and a portion of the
dielectric layer, a process that has a wide process window. Once
the first conductor layer is removed by the UV lasers 156, IR
lasers 156B and 156N, which have a wide process window for cutting
through the remaining dielectric layer without cutting through or
damaging the second conductor layer, are employed to remove the
last portion of the dielectric layer. Thus, the ECB blind via
cutting apparatus employs UV lasers 156A and 156C to cut through
the first conductor layers of workpieces 152A and 152C and IR
lasers 156B and 156N to cut through the dielectric layers on
workpieces 152B and 152N.
[0086] The time required for UV lasers 156A and 156C to cut through
the conductor layers is typically longer than the time required by
IR lasers 152B and 152N to cut through the dielectric layer.
Therefore, the longer processing time dictates the processing
throughput. Because the target locations are substantially
identical for all tools on multi-tool positioner 150, the different
processing times are accounted for by providing appropriately
different laser power levels and pulse repetition rates for the UV
and IR lasers.
[0087] Some applications require cutting relatively large hole
diameters of about 200 micrometers or less. Because UV lasers 154A
and 154C have a beam diameter of only about 20 micrometers,
multi-tool positioner 150 must cause the UV beam to follow a spiral
or circular path to cut such holes in a conductor layer. Therefore,
cutting these relatively large holes takes a proportionally longer
time. However, IR lasers 154B and 154N have a beam diameter of
about 400 micrometers, which is about 20 times the UV laser beam
diameter. Therefore, when cutting these relatively large diameter
holes through the dielectric layers, at least some portion of the
IR laser beam will cover the entire hole while the UV beam follows
the spiral or circular path to cut a hole in a conductor layer.
Under these circumstances, the IR laser beams are on the target
locations for a relatively longer time and the different effective
processing times are again accounted for by providing appropriately
different laser power levels and pulse repetition rates for the UV
and IR lasers.
[0088] If suitable laser power is available, a single laser may be
shared among multiple workpieces by employing suitable power
splitting devices. It is also envisioned that switchable-wavelength
lasers may be employed in this invention.
[0089] This invention provides an improved combination of
positioning accuracy, positioning speed, minimized or eliminated
stopping time, nonpanelized tool path databases, and minimized fast
stage movement range that dramatically improves processing
throughput while reducing workpiece rejects caused by dimensional
and orientation variations.
[0090] Skilled workers will recognize that portions of this
invention may be implemented differently from the laser beam
micro-machining implementation described above. For example, a wide
variety of tools, in single or multi-headed configurations, may be
moved by the fast positioner stage, such as micro-dimensioned
drills, punches, lasers, laser beams, radiation beams, particle
beams, beam producing devices, microscopes, lenses, optical
instruments, and cameras. Also, many different positioning devices
may be employed in different combinations drawn from among
galvanometers, voice coils, piezoelectric transducers, stepper
motors, and lead screw positioners. The DSPs need not be completely
digital and may, for example, include any suitable combination of
analog and digital subcircuits. Of course, the positioning signal
profiles, spectral bandwidth and amplitudes, and filter
characteristics described herein may all be modified to suit the
requirements of other positioning applications.
[0091] It will be obvious to skilled workers that many other
changes may be made to the details of the above-described
embodiments of this invention without departing from the underlying
principles thereof. The scope of the present invention should,
therefore, be determined only by the following claims.
* * * * *