U.S. patent number 3,691,695 [Application Number 05/107,975] was granted by the patent office on 1972-09-19 for rapid acting abrasive trimmer for micro-electronic devices.
Invention is credited to Norman Green, William C. Vergara.
United States Patent |
3,691,695 |
Green , et al. |
September 19, 1972 |
RAPID ACTING ABRASIVE TRIMMER FOR MICRO-ELECTRONIC DEVICES
Abstract
An abrasive trimmer for micro-electronic devices includes a
nozzle for directing abrasive at a micro-electronic device to be
trimmed. The nozzle is pivot mounted and spring biased into a
first, normally operative position. A circuit which senses the
electrical characteristics of the micro-electronic device being
trimmed generates a signal when predetermined characteristics are
sensed. This signal activates a solenoid winding which pivots the
nozzle against its spring bias into a second retracted
position.
Inventors: |
Green; Norman (Timonium,
MD), Vergara; William C. (Towson, MD) |
Family
ID: |
22319518 |
Appl.
No.: |
05/107,975 |
Filed: |
January 20, 1971 |
Current U.S.
Class: |
451/2;
451/78 |
Current CPC
Class: |
B28D
5/00 (20130101); B24C 3/322 (20130101) |
Current International
Class: |
B24C
3/00 (20060101); B24C 3/32 (20060101); B28D
5/00 (20060101); B24c 003/06 (); B24c 003/32 () |
Field of
Search: |
;51/8,14,15,165R |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Kelly; Donald G.
Claims
The invention claimed is:
1. Means for trimming a micro-electronic device including
operational means for actually effecting the trimming of said
micro-electronic device comprising:
means for biasing said operational means and said device into
trimming cooperation,
means for moving said operational means with respect to said device
to thereby effect trimming of said device; and,
means for rapidly removing said operational means out of said
trimming cooperation with said device against said biasing
means.
2. Means for trimming as recited in claim 1 with means for sensing
at least one selected characteristic of said device which is
altered as said device is trimmed and generating a first signal
when said characteristic attains a predetermined value, said
removing means being responsive to said signal for removing said
operational means out of said trimming cooperation with said device
against said biasing means.
3. Means for trimming as recited in claim 1 wherein said removing
means comprises:
electrical means responsive to a first signal for retracting said
operational means out of said trimming cooperation against said
biasing means;
means for sensing at least a preselected characteristic of said
device which varies as said device is trimmed; and,
means for generating said first signal when said sensed
characteristic attains a predetermined value.
4. Means for trimming as recited in claim 3 wherein said electrical
means comprises:
a winding energized for retracting said operational means out of
said trimming cooperation;
an initially charged capacitor means; and,
means responsive to said first signal for discharging said
capacitor through said winding.
5. Means for trimming as recited in claim 4 wherein said winding,
said capacitor means and said discharging means comprise a resonant
path for current discharged from said capacitor means through said
winding.
6. Means for trimming as recited in claim 5 wherein said capacitor
means includes:
a high source impedance voltage source; and,
a capacitor connected across said voltage source.
7. Means for trimming as recited in claim 5 wherein said first
signal is relatively long with respect to the discharge time of
said capacitor whereby a relatively large current pulse is
delivered to said winding from said capacitor at the beginning of
said first signal and a smaller current is delivered to said
winding from said voltage source during the remainder of said first
signal.
8. Means for trimming a micro-electronic device in a work space
including first means for actually effecting the trimming of said
device and comprising:
means for moving said first means with respect to said device
within said work space whereby said device is trimmed; and,
means for retracting said first means from said work space without
regard to said moving means.
9. Means for trimming as recited in claim 8 wherein said first
means is a nozzle means for directing an abrasive stream at a
preselected portion of said micro-electronic device to thereby
effect removal of said preselected portion, said moving means
moving said nozzle means along a path on said device to thereby
effect removal of said path, said retracting means retracting said
nozzle along the path so removed.
10. Means for trimming as recited in claim 9 wherein said moving
means includes means for biasing said nozzle means into an
operative position and said retracting means includes means for
retracting said nozzle into an inoperative position.
Description
BACKGROUND OF THE INVENTION
This invention relates to abrasive trimmers for micro-electronic
devices and more particularly to means for rapidly retracting the
abrasive head when the micro-electronic device being trimmed
attains a predetermined characteristic.
Many micro-electronic devices require final adjustment of their
form during or after fabrication to bring them into a desired
tolerance range wherein they may be used for their intended
purpose. Presently, this adjustment is performed by sensing certain
characteristics of the device, such as the resistance of a
resistive element, and eroding selected portions of the element
until the sensed characteristic attains a redetermined value. A
thin, predetermined controlled airborne stream of abrasive material
selectively directed at the micro-electronic device through a
nozzle is advantageously employed to effect this erosion. The
heat-up of the device which might be expected from the eroding
process is controlled by the air stream. The abrasive material may
be easily removed from the field of work by simple vacuum
pumps.
The nozzle is directed at the device to be trimmed and motor driven
along a slide in the proper direction for proper trimming of the
device. At the same time, the electrical characteristics of the
device are sensed and compared against a desired characteristic.
When the sensed characteristic is equal to the desired
characteristic, the air stream and supply of abrasive material is
cut off and the motor driving the nozzle is quickly reversed to
withdraw the nozzle from the work area. This system has the
disadvantage that expensive motors and control units are required
and relatively large masses must be accelerated in reversing the
drive motor. Additionally, there is a short and unpredictable time
delay after the desired characteristics are reached to fully shut
off the air stream and abrasive supply, and another subsequent
uncontrolled time delay during which abrasive material and
compressed air remaining in the nozzle system are expelled. This
results in an over-shoot or over-trim of the micro-electronic
device. The severity of the over-trim is dependent upon the rate of
trimming, that is, upon the rate of nozzle travel. Generally, the
problem of over-trimming has necessitated much slower trimming of
micro-electronic devices by abrasive means than would theoretically
appear possible.
SUMMARY OF THE INVENTION
Accordingly, a new type of nozzle mounting and driving means has
been devised for use with abrasive trimmers. This new mounting
means is provided by pivoting the nozzle mounting, conveniently at
a longitudinal central point, and spring biasing the nozzle
mounting into a first and operative position wherein the nozzle can
be directed at the device to be trimmed in the work area. A
solenoid winding is provided to attract and pivot, when energized,
the nozzle mounting into a second and retracted position wherein
the nozzle is withdrawn out of the work area directly back along a
path in the work area already traversed by the nozzle. The device
being trimmed is sensed, and as common in this art, an electrical
circuit is provided to compare the sensed characteristic of the
device against a standard and to generate a signal for driving the
solenoid winding when the sensed characteristic equals the
standard.
It is an object of this invention to provide an abrasive trimmer
for micro-electronic devices.
It is a further object of this invention to provide an abrasive
trimmer for micro-electronic devices which may be rapidly withdrawn
from the work area upon completion of trimming.
Another object of this invention is to provide an abrasive trimmer
which will permit micro-electronic devices to be rapidly
trimmed.
A further object of this invention is to provide an abrasive
trimmer which alleviates the problems of over-trimming
micro-electronic devices.
One further object of this invention is to provide a novel nozzle
mounting means which can be used with present abrasive
trimmers.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of the invention.
FIG. 2 is a more detailed view of a nozzle mount of the
invention.
FIG. 3 is an electrical schematic of a circuit used to retract the
nozzle of FIG. 2.
FIG. 4 is a plot of a typical waveform of current supplied by the
circuit of FIG. 3 to the solenoid winding.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring first to FIG. 1 there is seen a stylized block diagram of
an abrasive trimmer including the nozzle control means of this
invention. A micro-electronic device 10, shown here in greatly
enlarged form for clarity, and deposited on a substrate 15 in a
conventional manner, includes conductive lands 10a and 10b. In this
embodiment the micro-electronic device is represented as a thin
film resistor. It should be clear at the completion of this
description that the invention might be used to trim any
micro-electronic device capable of being trimmed by abrasive
trimmers. A hollow cylindrical pipe 20 having a nozzle end 20a is
connected at its opposite end via flexible tubing 26 to a supply of
abrasive and compressed air 27 which also suitably includes
solenoid valves for controlling the supply of abrasive material and
compressed air. Pipe 20 is mounted at pivot point 22 and biased by
spring 24 into a first and operative position as shown. Pivot point
22, pipe 20 and spring 24 are mounted on support 30 which is motor
driven along a track represented by line 32. These tracks and motor
drivers are standard in the art and need not be described further.
A solenoid winding also mounted on support 30, when energized, will
attract pipe 20 towards itself about pivot point 22 and against the
bias provided by spring 24.
Conductive lands 10a and 10b of micro-electronic device 10 are
connected by electrical leads 12 and 13 to a comparator 40 which
also receives a reference signal from a source not shown.
During actual trimming of the micro-electronic device an airborne
stream of abrasive material is supplied from abrasive supply 27 via
flexible tubing 26 and pipe 20 to nozzle 20a from whence it is
directed against micro-electronic device 10. Support 30 is driven
towards the micro-electronic device so that the abrasive stream
erodes therein the path designated at 10c. Of course, during this
operation the characteristics of the micro-electronic device are
monitored by comparator 40. Upon these characteristics reaching a
desired value, comparator 40 generates a signal which is applied to
the motor and abrasive control circuit 42 and also to nozzle
retractor 44. The motor and abrasive control circuit generates a
signal to reverse the motor driving support 30 and also to
deenergize the solenoid valve of the abrasive supply 27.
Simultaneously, nozzle retractor 44 generates a signal to energize
solenoid winding 35 to thus attract and retract pipe 20 so as to
withdraw nozzle 20a from the work area. In this figure, comparator
40, motor and abrasive control 42, abrasive supply 27, and support
30 are found in the prior art abrasive trimmers. Pivot 22, spring
24, solenoid winding 35 and nozzle retractor 44 are elements added
in the practice of this invention.
Refer now to FIG. 2 wherein there is seen in greater detail the
nozzle mount. In this figure, it can be seen that support 30 has
mounted thereon pivot 22 about which pivots lever 50 having a
dependent arm 50a and an upstanding arm 50b. At least arm 50a is
suitably made of a magnetically attractable material. A block 51,
having a central bore, is rigidly attached to arm 50a. Pipe 20
extends through the aforementioned central bore and is tightly
grasped thereby to form an essentially integral piece with block
51. As previously described, pipe 20 is hollow and has a nozzle 20a
at one end and receives an airborne abrasive supply via flexible
tubing at the other end. A second block 54 having a central
threaded hole through which an adjustable stop 55 is threaded, is
mounted on support 30. Block 54 includes an upstanding tab 56 which
is connected via spring 24 to lever arm 50b. In this manner, lever
50 is spring biased into the position shown against the adjustable
stop 55. Solenoid winding 35 is also mounted on support 30 in
position to attract, when energized, dependent arm 50a. Electrical
leads 35a and 35b connect solenoid winding 35 to the nozzle
retractor 44 of FIG. 1. In FIG. 1 leads 35a and 35b are represented
by the single line between nozzle retractor 44 and solenoid winding
35.
Refer now to FIG. 3, wherein the comparator 40 of FIG. 1 is also
seen. As previously described, this comparator generates an output
when the characteristic of the micro-electronic device being
trimmed reaches a predetermined value. Additionally, in FIG. 3, the
motor and abrasive control circuit 42 and nozzle retractor circuit
44 of FIG. 1 are seen in greater detail within the dashed
boxes.
The comparator output signal, which is a negative-going signal, is
resistively coupled via resistor 60 to the base electrode of PNP
transistor 64, which has its emitter electrode grounded. The
collector electrode of this transistor is connected through a relay
winding 63 to a source of negative voltage (not shown) designated
as A-. The comparator output signal triggers transistor 64
conductive to thereby energize relay winding 63 and to generate an
output signal at collector electrode 63a. Relay winding 63 operates
through relay contacts (not shown) which reverse the motor driving
support 30 of FIG. 1 and to deenergize the control valves of
abrasive supply 27, also of FIG. 1, in the manner well known to
those skilled in the art. A diode 61 shunts relay winding 63 to
eliminate undesirable voltage spikes when transistor 64
subsequently becomes nonconductive.
The signal generated at collector electrode 63a is coupled through
capacitor 66 to trigger one-shot 67 to generate its characteristic
output pulse. This pulse is coupled through resistor 69 to the base
electrode of NPN transistor 71. The collector electrode of this
transistor is connected in common with the collector electrode of a
second NPN transistor 73. The emitter electrode of transistor 71 is
connected to the base electrode of transistor 73 and through
resistor 74 to ground. The emitter electrode of transistor 73 is
connected directly to ground. A capacitor 78 has one plate
connected to ground and a second plate connected through resistor
76 to a source of positive voltage (not shown) designated as A+.
Solenoid winding 35, seen here and also in FIG. 1, is connected
between the second plate of capacitor 78 and the common collector
electrodes of transistors 71 and 73.
During the quiescent time of the nozzle retractor circuit 44, that
is before comparator 40 senses that the micro-electronic device
being trimmed has attained its desired characteristic, one-shot 67
is quiescent so that transistors 71 and 73 are nonconductive, thus
maintaining solenoid winding 35 unenergized. During this time
capacitor 78 charges through resistor 76 to the A+ voltage level.
When the micro-electronic device being trimmed attains its desired
value one-shot 67 is triggered, as previously described, to
generate its output pulse, which is a positive-going pulse which
renders transistors 71 and 73 conductive. The collector of
transistor 73 thus goes to ground so that the voltage now stored
across capacitor 78 discharges through winding 35. The inductance
of the winding 35 is matched to the capacitance of capacitor 78 to
produce a resonant circuit for optimum transfer of energy from the
capacitor to the inductor. This results in an extremely rapid
discharge of capacitor 78 with a resultant extremely high current
pulse flowing in winding 35. This, of course, produces extremely
high magnetic fields generated by the winding which urge pipe 20 of
FIG. 2 rapidly out of its first and operative position into its
retracted position. Subsequent to the discharge of capacitor 78 and
during the remainder of the one-shot 67 output pulse the A+ voltage
source continues to supply current through resistor 76 to winding
35, albeit at a lower value. However, since the pipe has already
been attracted to the winding this lower value of current will
retain the pipe and nozzle in its retracted position. The diode 80
shunted across winding 35 is provided to suppress undesirable
voltage spikes.
Refer now to FIG. 4 wherein there is seen a time plot of the
current flow through winding 35. Initially, that is when
transistors 71 and 73 of FIG. 3 are nonconductive, there is no
current flow in winding 35. However, immediately upon transistors
71 and 73 becoming conductive due to the one-shot 67 output pulse
the aforementioned extremely high current pulse flows in winding 35
due to the discharge of capacitor 78 into a resonant circuit. After
the discharge of capacitor 78 the current drops to a lower value
sustained by the A+ voltage source. The reference letter A in this
figure represents the length of the one-shot 67 output pulse, at
the termination of which it is seen the current through winding 35
drops once again to zero. The time duration A is arbitrary and
easily set by the system designer by proper choice of the elements
of one-shot 67 and need simply be long enough to permit the
reversing motor to withdraw support 30 of FIG. 1 from the work
area. Since this time is relatively long, the reversing motor used
to drive support 30 need be much less complex than those reversing
motors used in prior art abrasive trimmers, or conversely, will
allow even higher trimming rates.
Although only one embodiment has been shown of the invention, it
should now be obvious to one skilled in the art that certain
alterations and modifications may be made to adapt the invention to
specific requirements. Accordingly, this invention should be
limited only by the true scope and spirit of the appended
claims.
* * * * *