U.S. patent application number 11/506725 was filed with the patent office on 2006-12-14 for closed loop backdrilling system.
Invention is credited to Patrick P.P. Lebens, Joseph A.A.M. Tourne.
Application Number | 20060278429 11/506725 |
Document ID | / |
Family ID | 34375488 |
Filed Date | 2006-12-14 |
United States Patent
Application |
20060278429 |
Kind Code |
A1 |
Tourne; Joseph A.A.M. ; et
al. |
December 14, 2006 |
Closed loop backdrilling system
Abstract
A multilayer circuit board is provided with at least one signal
layer, at least one feedback layer, and at least one dielectric
layer positioned between the signal layer and the feedback layer.
The signal layer is connected to at least one plated hole. The
feedback layer has a contact pad, which is positioned adjacent to
the plated hole, but is electrically isolated from the plated hole.
The contact pad is connected to a measurement unit. The dielectric
layer is positioned between the signal layer and the contact pad of
the feedback layer. A portion of the plated hole forms a stub
portion, which extends a distance away from the signal layer and
typically extends a distance away from the contact pad of the
feedback layer. To remove the stub portion, a hole is bored or
routed into the multilayer circuit board until electrical feedback
is received by the measurement unit upon contact of a portion of
the boring device with the contact pad. Upon receipt of the
electrical feedback by the measurement unit, the boring device is
retracted from the hole, and the hole formed by the boring device
is filled with an epoxy, or other filler material.
Inventors: |
Tourne; Joseph A.A.M.;
(Helmond, NL) ; Lebens; Patrick P.P.; (Sittard,
NL) |
Correspondence
Address: |
DUNLAP, CODDING & ROGERS P.C.
PO BOX 16370
OKLAHOMA CITY
OK
73113
US
|
Family ID: |
34375488 |
Appl. No.: |
11/506725 |
Filed: |
August 18, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10944583 |
Sep 17, 2004 |
7096555 |
|
|
11506725 |
Aug 18, 2006 |
|
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60504399 |
Sep 19, 2003 |
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Current U.S.
Class: |
174/266 ;
29/852 |
Current CPC
Class: |
H05K 1/0268 20130101;
Y10T 29/49718 20150115; Y10T 29/49117 20150115; H05K 3/0047
20130101; H05K 2203/175 20130101; H05K 1/0237 20130101; Y10T 408/03
20150115; H05K 2203/0242 20130101; Y10T 29/49126 20150115; H05K
2201/09845 20130101; H05K 3/429 20130101; Y10T 408/173 20150115;
H05K 2203/0207 20130101; Y10T 408/175 20150115; Y10T 29/49726
20150115; Y10T 29/49165 20150115 |
Class at
Publication: |
174/266 ;
029/852 |
International
Class: |
H05K 1/11 20060101
H05K001/11 |
Claims
1. A workpiece having a stub portion removed from a plated hole
wherein the amount of the stub portion removed is determined from
electrical feedback received from within the workpiece, the
workpiece produced by a method comprising the steps of: providing
the workpiece with a feedback layer; boring a hole into the
workpiece with a boring device to remove at least a portion of a
plated hole until the boring device engages the feedback layer; and
receiving an electrical feedback signal from the boring device
indicating engagement with the feedback layer.
2. The workpiece of claim 1, wherein the step of boring is defined
further as the steps of moving the a cutting device of the boring
device into the plated hole to remove a portion of the plated hole,
stopping the movement of the cutting device and restarting the
movement of the cutting device into the plated hole to remove more
of the plated hole, and wherein the step of receiving feedback is
defined further as receiving feedback responsive to the cuffing
device engaging the feedback layer.
3. The workpiece of claim 1, wherein the feedback layer is a ground
layer.
4. The workpiece of claim 1, wherein the feedback layer is a power
layer.
5. The workpiece of claim 1, wherein the feedback layer is a signal
layer.
6. The workpiece of claim 1, wherein the feedback layer is a
separate network.
7. A multilayer circuit board, comprising: a signal layer; a
feedback layer having a contact pad; a dielectric layer positioned
between the signal layer and the feedback layer; and a plated hole
connected to the signal layer, and positioned adjacent to the
contact pad, the contact pad being electrically isolated from the
plated hole, a portion of the plated hole forming a stub portion,
which extends a distance away from the signal layer and extends a
distance away from the contact pad of the feedback layer.
8. The multilayer circuit board of claim 7, wherein the feedback
layer is a ground layer.
9. The multilayer circuit board of claim 7, wherein the feedback
layer is a power layer.
10. The multilayer circuit board of claim 7, wherein the feedback
layer is a power layer.
11. The multilayer circuit board of claim 7, wherein the feedback
layer is a separate network.
12. The multilayer circuit board of claim 7, further comprising a
second plated hole which is electrically connected to the contact
pad.
13. The multilayer circuit board of claim 7, wherein the contact
pad substantially surrounds the plated hole.
14. A method for backdrilling a stub portion of a plated hole in a
multilayer circuit board, comprising the steps of: moving a cutting
device in a direction toward the plated hole such that the cutting
device removes a portion of the plating adjacent the stub portion
and disconnects a feedback layer from the plated hole; and
determining whether the feedback layer is disconnected from the
plated hole.
15. The method of claim 14, further comprising the step of
retracting the cutting device away from the plated hole so that the
conductivity of the cutting device will not interfere with the
determination of whether the feedback layer is disconnected from
the plated hole.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of Ser. No.10/944,583,
filed on Sep. 17, 2004, which claims priority to the provisional
patent application identified by U.S. Ser. No. 60/504,399, filed on
Sep. 19, 2003, of which the entire content of which is hereby
expressly incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] Multilayer circuit boards and/or wiring boards are well
known in the art. The multilayer circuit boards are formed with a
number of signal layers (conductive layers) which are arranged in a
predetermined pattern. The signal layers are insulated from each
other by dielectric layers. Thus, the multilayer circuit board is
formed from interleaved (e.g., alternating) signal layers and
dielectric layers.
[0003] Plated holes or "vias" are formed through the multilayer
circuit board to connect one signal layer to another signal layer.
The plated holes typically extend from one main side of the
multilayer circuit board to an opposite side of the multilayer
circuit board. In some instances, the plated holes or vias include
a "stub portion" which extends away from the signal layer toward
one of the sides of the multilayer circuit board. In some
circumstances, it is desirable to remove the stub portion to
enhance the signal to noise ratio in electronic systems that
utilize high-speed signals. The smaller the stub portion the better
the signal quality.
[0004] In the past, the stub portion of the plated holes is removed
in a process referred to as "back drilling". In the back drilling
process, the stub portion of the plated hole is removed by drilling
the stub portion to a predetermined depth. However, in practice the
thicknesses of the various layers in the multilayer circuit boards
are not uniform, and the depths of the signal layers within the
multilayer circuit boards vary, which often changes the amount of
the stub portion which needs to be removed. Drilling too deeply
will disconnect the signal layer from the plated hole, or leave an
unreliable connection; not drilling deep enough decreases the
signal to noise ratio.
[0005] The invention discussed herein uses a technique which
overcomes the problems associated with the variance in thickness of
the layers in the multilayer circuit board.
SUMMARY OF THE INVENTION
[0006] In general, the present invention relates to a multilayer
circuit board, and a closed loop backdrilling system for
backdrilling the multilayer circuit board. The multilayer circuit
board is provided with at least one signal layer, at least one
feedback layer, and at least one dielectric layer positioned
between the signal layer and the feedback layer. The signal layer
is connected to at least one plated hole. The feedback layer has a
contact pad, which is positioned adjacent to the plated hole and is
connected to a signal/electrical source, but is electrically
isolated from the plated hole. The dielectric layer is positioned
between the signal layer and the contact pad of the feedback layer.
A portion of the plated hole forms a stub portion, which extends a
distance away from the signal layer and typically extends a
distance away from the contact pad of the feedback layer. The
feedback layer can be any layer within the multilayer circuit
board, such as a separate network layer as shown in FIG. 2, or a
ground layer, signal layer, or power layer.
[0007] To remove the stub portion, a hole is bored or routed into
the multilayer circuit board until electrical feedback is received
from the feedback layer of the multilayer circuit board when a
certain depth is reached. Typically, the electrical feedback is
received from the multilayer circuit board upon contact of a
portion of the boring device with the feedback layer. Upon receipt
of the electrical feedback from the multilayer circuit board, the
boring device is retracted from the hole, and the hole formed by
the boring device can then be filled with an epoxy, or other filler
material.
[0008] In one preferred embodiment, the feedback layer is only used
during the manufacturing process of the multilayer circuit board.
In other words, in this embodiment, once the manufacturing process
is complete, the feedback layer is not used to connect any
components or signal layers or for any other electrical type of
purpose.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0009] FIG. 1 is a diagrammatic view of a closed loop backdrilling
system constructed in accordance with the present invention.
[0010] FIG. 2 is a top plan view of one embodiment of a feedback
layer formed in a multilayer circuit board wherein the feedback
layer forms a separate network.
[0011] FIG. 3 is a cross-sectional view of a portion of a
multilayer circuit board constructed in accordance with the present
invention.
[0012] FIG. 4 is a top plan view of a contact pad of a feedback
layer constructed in accordance with the present invention.
[0013] FIG. 5 is a cross-sectional view of a portion of a
multilayer circuit board constructed in accordance with an
alternate embodiment of the present invention.
[0014] FIG. 6 is a cross-sectional view of the portion of the
multilayer circuit board constructed in accordance with an
alternate embodiment of the present invention.
[0015] FIG. 7 is a top plan view of an alternate embodiment of a
contact pad constructed in accordance with the present
invention.
[0016] FIG. 8 is a diagrammatic view of an alternate embodiment of
a closed loop backdrilling system constructed in accordance with
the present invention.
[0017] FIG. 9 is a diagrammatic view of yet another alternate
embodiment of a closed loop backdrilling system constructed in
accordance with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0018] Referring now to the drawings and in particular to FIG. 1,
shown therein and designated by a reference numeral 10 is a closed
loop backdrilling system constructed in accordance with the present
invention. The closed loop backdrilling system 10 is used for depth
drilling an already plated hole 12 formed in a workpiece 14 using
electrical feedback from the workpiece 14 when a certain or
predetermined depth is reached. The feedback during the drilling
process makes it possible to yield much higher accuracy independent
of the depth of a particular layer within the workpiece 14. In one
preferred embodiment, the workpiece 14 is a multilayer printed
circuit board 16. Although the workpiece 14 will be described
herein as the multilayer circuit board 16, it should be understood
that the workpiece 14 can be any apparatus, or device where it is
desirable to drill to a certain or predetermined depth within the
apparatus or device.
[0019] The multilayer circuit board 16 is provided with at least
one or more signal layer 20, at least one or more feedback layer
22, and at least one or more dielectric layer 24. The signal layer
20 is connected to the plated hole 12. The feedback layer 22 has a
contact pad 26 (see FIG. 4). The contact pad 26 is spaced a
distance away from the signal layer 20 and is electrically
insulated from the plated hole 12. The dielectric layer 24 is
positioned between the signal layer 20 and the contact pad 26 of
the feedback layer 22 so as to electrically isolate the contact pad
26 from the signal layer 20. As will be discussed in more detail
below, the contact pad 26 is contacted during the manufacturing
process of the multilayer circuit board 16 to provide electrical
feedback.
[0020] The multilayer circuit board 16 is also provided with an
entry material 28, and a second plated hole 30. The entry material
28 extends over a first surface 32 of the multilayer circuit board
16. Entry materials, such as the entry material 28 are well known
in the art. Thus, no further comments are deemed necessary
regarding the entry material 28 to teach one skilled in the art how
to make or use the present invention. The second plated hole 30 is
electrically connected to the contact pad 26 of the feedback layer
22.
[0021] The closed loop backdrilling system 10 is provided with a
boring device 40. The boring device 40 is provided with a spindle
unit 42 supporting a cutting device 44, and a servo control unit 46
for the Z-axis motor control. The boring device 40 can be a drill,
milling machine or router.
[0022] The closed loop backdrilling system 10 is also provided with
a measurement unit 48. The measurement unit 48 communicates with 1)
the spindle unit 42 and/or the cutting device 44 of the spindle
unit 42, and 2 ) the second plated hole 30 for determining the
contact or proximity between the cutting device 44 and the contact
pad 26 of the feedback layer 22.
[0023] In general, the measurement unit 48 senses a transition of a
physical property indicative of contact or close proximity between
the cutting device 44 and the contact pad 26. In one preferred
embodiment, the measurement unit 48 includes a capacitive sensor
due to the airbearing construction in the drill spindle for sensing
the capacitance between the cutting device 44 and the contact pad
26. In another preferred embodiment, the measurement unit 48 is a
resistance meter for measuring the resistance between the cutting
device 44 and the feedback layer 22. In this instance, the cuffing
device 44 is constructed of a conductive material, or is plated
with a conductive material. The cutting device 44 can be
constructed of a cutting type material, e.g., a ceramic material or
a metallic substance, such as steel.
[0024] When the cutting device 44 contacts the feedback layer 22,
the resistance rapidly reduces. A signal indicative of this rapid
transition is transmitted to the servo control unit 46 for
controlling the spindle unit 42. When the cutting device 44 reaches
the feedback layer 22, the spindle unit 42 retracts the cutting
device 44 from the plated hole, or a signal is sent to the servo
control unit 46 to cause the servo control unit 46 to measure
further depth drilling beyond the feedback layer 22. The servo
control unit 46 can be programmed to cause the cutting device 44 to
move in a substantially continuous manner during the backdrilling
operation. The servo control unit 46 can also be programmed for
other drilling operations, such as pulse drilling, e.g., move
in-stop, move in-stop, etc, or customizable drilling operations.
The advantage of pulse drilling is that it breaks the burr (e.g., a
thin ridge or area of roughness produced in cutting or shaping
metal) while drilling and enhances the backdrilled effect. Although
the present invention is described as using the servo control unit
46, it should be understood that the present invention can use
other types of controllers for controlling the movement of the
spindle unit 42.
[0025] As shown in FIG. 3, the cutting device 44 forms an enlarged
portion of the hole 12 having a backdrill diameter 50 during the
back drilling operation. The backdrill diameter 50 (or
cross-sectional area of the enlarged portion) is greater than a
first drill diameter 52 (or cross-sectional area of the plated hole
12) of the plated hole 12 to remove the plating from the stub
portion 18 of the plated hole 12. Thus, the cutting device 44
removes the plating of the plated hole 12 during the backdrilling
operation until the cutting device 44 is retracted. It should be
understood that the diameter of the cutting device 44 can be any
size capable of removing the plating of the plated hole 12. In one
preferred embodiment, the cutting device 44 has a diameter
approximately 0.35 mm greater than the diameter of the cutting
device used to form the first drill diameter 52 of the plated hole
12. Preferably the cutting device 44 forms a round hole. However,
it should also be understood that the cutting device 44 can be
translated or paired with another cutting device so as to form a
substantially square hole, elliptical hole or the like.
[0026] One preferred embodiment of the contact pad 26 is shown in
FIG. 4. The contact pad 26 can have the general form of a
"doughnut" forming a hole 60 therein. The contact pad 26 can also
be provided with other shapes so long as a portion of the contact
pad 26 is positioned adjacent to the plated hole 12 to be
backdrilled. For example, shown in FIG. 7 is an alternate
embodiment of a contact pad 26a formed as a portion of a ground
layer within the multilayer circuit board 16. The contact pad 26a
forms one or more hole 60a, i.e., a clearance hole or antipad, with
the plated hole 12 extending through the clearance the hole 60a.
The contact pads 26 and 26a are desirably constructed of an
electrically conductive material. The size of the holes 60 and 60a
can vary widely, but are preferably greater than the first diameter
52, yet less than the diameter 50 so that the contact pads 26 and
26a do not come into electrical contact with the plated hole 12. In
this regard, the contact pads 26 and 26a extend adjacent to the
plated hole 12, but do not contact the plated hole 12.
[0027] Although the contact pads 26 and 26a have been shown and
described with regard to FIGS. 4 and 7 as having a doughnut design
or rectangular design, it should be understood that the contact
pads 26 and 26a can have any geometric, nongeometric or
asymmetrical shape so long as the contact pads 26 and 26a are
electrically insulated from the plated hole 12 and capable of
contacting the cutting device 44 during the back drilling
operation.
[0028] As shown in FIG. 2, it should be understood that, in one
preferred embodiment, for every back drilling depth a pattern (on a
specific layer) is used which is electrically connected to the
second plated hole 30. The second plated hole may also be referred
to herein as a "common pad". The common pad 30 is electrically
connected to a plurality of contact pads 26 with each of the
contact pads 26 being provided adjacent to a signal layer 20 and a
plated hole 12. In other words, in a preferred embodiment the
feedback layer 22 forms a predetermined pattern having a plurality
(two or more) of contact pads 26 with each of the contact pads 26
being electrically connected to the common pad 30 via a pattern of
conductors 72. In one preferred embodiment, the feedback layer 22
is not contacted or connected to any of the signals or signal
layers in the printed circuit board 16. It should be understood
that the feedback layer 22 is not limited to being implemented as a
separate network as shown in FIG. 2. In this regard, the feedback
layer 22 can be formed by any conductive layer within the
multilayer printed circuit board 16 capable of providing an
electrical signal to the contact pads 26 or 26a, such as a signal
layer, a power layer or a ground plane layer.
[0029] The measurement unit 48 is electrically connected to the
common pad 30 for transmitting electrical feedback to the servo
control unit 46 when the cutting device 44 contacts any one of the
contact pads 26 or 26a.
[0030] Although the closed loop backdrilling system 10, and in
particular, the multilayer circuit board 16 has been described
herein as having only one feedback layer 22, it should be
understood that any number of feedback layers 22 can be used within
the multilayer circuit board 16. For example, the multilayer
circuit board 16 can include 2 or more feedback layers 22.
[0031] The spacing between the contact pads 26 or 26a and the
signal layer 20 can vary widely depending on the size and the shape
of the cutting device 44 used during the back drilling operation as
well as the amount of the stub portion 18 that is desired to be
removed. The spacing should be as closed to the signal layer 20 as
possible but far enough away so that the spindle unit 42 of the
boring device 40 can be stopped. For example, the spacing between
the contact pads 26 or 26a and the signal layer 20 has been found
to be suitable between about 0.004 inches and 0.001 inches.
[0032] To remove the stub portion 18, the measurement unit 48 is
connected to the feedback layer 22, such as by connecting the
measurement unit 48 to the common pad or second plated hole 30. The
spindle unit 42 is then actuated and the servo control unit 46
causes the spindle unit 42 to move the cutting device 44 toward and
into the multilayer circuit board 16. The cutting device 44 is
moved into the multilayer circuit board 16 until electrical
feedback is received from the feedback layer 22 indicating that a
certain depth has been reached. Depending upon the application of
the closed loop backdrilling system 10, the servo control unit 46
either 1) causes the spindle unit 42 to retract the cutting device
44, or 2) causes the spindle unit 42 to move the cutting device 44
a predetermined distance past the feedback layer 22 before the
spindle unit 42 retracts the cutting device 44.
[0033] The process set forth above can then be repeated for each
and every plated hole 12 to be backdrilled. The hole(s) formed by
the cutting device 44 is/are then filled with an epoxy, or other
filler material.
[0034] The closed loop back drilling system 10 can also be provided
with a reporting system 80 for permitting usage of the closed loop
back drilling system 10 to be monitored. The reporting system 80
receives input from a portion of the boring device 40, such as the
servo-control unit 46 or the measurement unit 48 to count the
number of backdrilled holes in real-time and then provides a report
or an invoice periodically (daily, monthly, quarterly, etc.)
showing the number of holes backdrilled on which a license fee is
due. The report or invoice can be transmitted electronically to a
user of the closed loop backdrilling system 10, or a designated
collection entity.
[0035] The making and using of multilayer circuit boards is well
known in the art. Thus, a description of the particular materials,
adhesives and other factors utilized in the making of multilayer
circuit boards has not been discussed in detail herein. However,
examples of the various constructions and fabrication methods for
attaching and forming each layer of a multilayer circuit board are
disclosed in U.S. Pat. No. 5,677,515, the contents of Column 1,
Line 8 through Line 55 , Column 2 , Line 32 through Column 3, Line
7 , and the drawings referenced therein are hereby incorporated
herein by reference.
[0036] Shown in FIGS. 5 and 6 is an alternate embodiment of a
multilayer circuit board 100 constructed in accordance with the
present invention. The multilayer circuit board 100 is constructed
similarly to the multilayer circuit board 16 described above,
except that the multilayer circuit board 100 is provided with a
plated hole 102 having a stepped configuration. As will be
discussed in more detail below, the stepped configuration of the
plated hole 102 permits denser connections than the straight-sided
plated hole 12.
[0037] The plated hole 102 is provided with a first portion 104 and
a second portion 106. The first portion 104 and the second portion
106 are separated by a lateral protrusion 108. The second portion
106 has a cross-sectional area less than the cross-sectional area
of the first portion 104.
[0038] The plated hole 102 can be formed in any suitable manner.
For example, the plated hole 102 can be formed in one drilling
operation with the use of a stepped drill bit and then subsequently
plated. Alternatively, the plated hole 102 can be formed in
multiple drilling operations with the use of two cutting devices or
drill bits having different diameters and then subsequently
plated.
[0039] The multilayer circuit board 100 includes one or more signal
layer 120, one or more feedback layer 122, and one or more
dielectric layer 124. The feedback layer 122 has a contact pad 126.
The dielectric layer 124 is positioned between the signal layer 120
and the feedback layer 122. The plated hole 102 is connected to the
signal layer 120, and positioned adjacent to the contact pad 126.
The contact pad 126 is electrically isolated from the plated hole
102 by the dielectric layer 124. In general, the second portion 106
of the plated hole 102 forms the stub portion, which extends a
distance away from the signal layer 120 and also extends a distance
away from the contact pad 126 of the feedback layer 122.
[0040] The plated hole 102 of the multilayer circuit board 100 is
then backdrilled to remove the stub portion in a similar manner as
described above, with the exception that the diameter of the
cutting device used in the backdrilling operation can be the same
as or even a smaller diameter than the diameter of the first
portion 104 of the plated hole 102. This permits a denser
population of holes because the diameter of the plated hole 102 is
not increased during the backdrilling operation.
[0041] The concept of embedding a contact pad within a multi-layer
circuit board can be used in accordance with the present invention
for at least two other purposes, i.e., depth routing and guide
routing.
[0042] Depth routing can be used to determine the final level of a
the boring device 40 penetration depth for clearing out areas on
the multi-layer circuit board to receive a component or a
connector. In this application, the cutting device 44 of the boring
device 40 is moved in the direction of the multilayer circuit board
until the tip of the cutting device 44 contacts the contact pad.
The penetration of the cutting device 44 is then stopped or moved a
predetermined distance further into the multilayer circuit board.
The cutting device 44 is then translated laterally (x and/or y
axis) a predetermined amount to clear out the area for the
component or the connector.
[0043] Guide routing can be used to guide the lateral translation
(x and/or y axis) of the boring device. That is, once the cutting
device 44 reaches the contact pad, the penetration level of the
cutting device 44 is stopped or moved a predetermined distance
further into the multilayer circuit board. The boring device 40
begins to move the multilayer circuit board or the cutting device
44 laterally and continues to move laterally while the cutting
device 44 is in contact with the contact pad. When the cutting
device 44 loses contact with the contact pad, the boring device 40
retracts or stops.
[0044] Shown in FIG. 8 is an alternate embodiment of a closed loop
backdrilling system constructed in accordance with the present
invention. The closed loop backdrilling system 200 is used for
depth drilling the already plated hole 12 formed in the workpiece
14 using electrical feedback from the workpiece 14 when a certain
or predetermined depth is reached. The feedback during the drilling
process makes it possible to yield much higher accuracy independent
of the depth of a particular layer within the workpiece 14. As
discussed above, in one preferred embodiment, the workpiece 14 is a
multilayer printed circuit board 16. Although the workpiece 14 will
be described herein as the multilayer circuit board 16, it should
be understood that the workpiece 14 can be any apparatus, or device
where it is desirable to drill to a certain or predetermined depth
within the apparatus or device.
[0045] The multilayer circuit board 16 is provided with at least
one or more signal layer 20, at least one or more feedback layer
22, and at least one or more dielectric layer 24. The signal layer
20 is connected to the plated hole 12. The feedback layer 22 has a
contact pad 202, which is similar in construction and function as
the contact pads 26 or 26a discussed above, except that the contact
pad 202 is connected to the plated hole 12 to permit electrical
communication therebetween. The dielectric layer 24 is positioned
between the signal layer 20 and the contact pad 202 of the feedback
layer 22 so as to electrically isolate the contact pad 202 from the
signal layer 20. As will be discussed in more detail below, the
contact pad 202 is contacted during the manufacturing process of
the multilayer circuit board 16 to break the electrical connection
between the plated hole 12 and the contact pad 202.
[0046] The closed loop backdrilling system 200 is provided with the
boring device 40. The boring device 40 is provided with the spindle
unit 42 supporting the cutting device 44, and the servo control
unit 46 for the Z-axis motor control.
[0047] The closed loop backdrilling system 200 is also provided
with a measurement unit 204. The measurement unit 204 communicates
with a) the plated hole 12 and b) the feedback layer 22 for
determining loss of electrical communication between the plated
hole 12 and the feedback layer 22. As shown in FIG. 8, the
measurement unit 204 is provided in circuit with a resistor R and a
power supply P. The measurement unit 204 can, for example, be an
ammeter for measuring either AC or DC electrical current.
[0048] In use, the spindle unit 42 of the boring device 40 is
operated to move the cutting device 44 a predetermined amount in a
direction toward or into the plated hole l2. The spindle unit 42 is
then operated to retract the cutting device 44 a predetermined
amount in a direction away from the plated hole 12 so that the
conductivity of the cuffing device 44 will not interfere with the
reading of the measurement unit 204. The servo control unit 46 then
monitors the measurement unit 204 to determine whether the feedback
layer 22 is still connected to the plated hole 12. If so, the
spindle unit 42 is then operated to move the cutting device 44 in
the direction toward the plated hole 12 to remove more of the stub
portion 18 of the plated hole 12. The spindle unit 42 is then
operated to retract the cutting device 44 away from the plated hole
12 and the servo control unit 46 again monitors the measurement
unit 204 to determine whether the feedback layer 22 is connected to
the plated hole 12. This process is repeated until the measurement
unit 204 determines that the plated hole 12 has been disconnected
from the feedback layer 22.
[0049] Shown inFIG. 9 is another alternate embodiment of a closed
loop backdrilling system constructed in accordance with the present
invention. The closed loop backdrilling system 300 is used for
depth drilling the already plated hole 12 formed in the workpiece
14 using electrical feedback from the workpiece 14 when a certain
or predetermined depth is reached. The feedback during the drilling
process makes it possible to yield much higher accuracy independent
of the depth of a particular layer within the workpiece 14. As
discussed above, in one preferred embodiment, the workpiece 14 is
the multilayer printed circuit board 16. Although the workpiece 14
will be described herein as the multilayer circuit board 16, it
should be understood that the workpiece 14 can be any apparatus, or
device where it is desirable to drill to a certain or predetermined
depth within the apparatus or device.
[0050] The multilayer circuit board 16 is provided with at least
one or more signal layer 20, and at least one or more dielectric
layer 24. The signal layer 20 is connected to the plated hole
12.
[0051] The closed loop backdrilling system 300 is provided with the
boring device 40. The boring device 40 is provided with the spindle
unit 42 supporting the cutting device 44, and the servo control
unit 46 for the Z-axis motor control.
[0052] The closed loop backdrilling system 300 is also provided
with a signal generator and measurement unit 304. The signal
generator and measurement unit 304 communicates with a) the plated
hole 12 and b) the signal layer 20 for providing a signal to the
plated hole 12 and then determining the reflection or interference
of the signal caused by the stub portion 18. The signal generator
and measurement unit 304 can determine any appropriate physical
property indicative of the existence or amount of the stub portion
18, such as the signal to noise ratio.
[0053] In use, the spindle unit 42 of the boring device 40 is
operated to move the cutting device 44 a predetermined amount in a
direction toward or into the plated hole 12. The spindle unit 42 is
then operated to retract the cutting device 44 a predetermined
amount away from the plated hole 12 so that the conductivity of the
cutting device 44 will not interfere with the reading of the signal
generator and measurement unit 304. The servo control unit 46 then
monitors the signal generator and measurement unit 304 to determine
the relatedness between the physical property being measured and a
predetermined amount. For example, when the signal to noise ratio
is being monitored, a determination can be made (either by the
servo control unit 42 or the signal generator and measurement unit
304) whether the signal to noise ratio is above a predetermined
amount indicative of removal of a sufficient amount of the stub
portion 18. If not, the spindle unit 42 is then operated to move
the cutting device 44 a predetermined amount in the direction
toward the plated hole 12 to remove more of the stub portion 18 of
the plated hole 12. The spindle unit 42 is then operated to retract
the cutting device 44 away from the plated hole 12 and the servo
control unit 46 again monitors the signal generator and measurement
unit 304 to determine whether enough of the stub portion 18 has
been removed. This process is repeated until the signals output by
the signal generator and measurement unit 304 indicate that a
sufficient amount of the stub portion 18 has been removed.
[0054] The closed backdrilling systems 200 and 300 can be operated
either manually or automatically. In other words, the measurements
made by the measurement unit 204 or the signal generator and
measurement unit 304 can be made manually by an individual, who is
also controlling the servo control unit 204. Alternatively, the
measurements made by the measurement unit 204 or the signal
generator and measurement unit 304 can be automated such that the
retractions and advancements of the spindle unit 42 are controlled
by a software program typically operating in or controlling the
servo control unit 46.
[0055] Changes may be made in the construction and the operation of
the various components, elements and assemblies described herein or
in the steps or the sequence of steps of the methods described
herein without departing from the spirit and scope of the invention
as defined in the following claims.
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