US3691695A

US3691695A - Rapid acting abrasive trimmer for micro-electronic devices

Info

Publication number: US3691695A
Application number: US107975A
Authority: US
Inventors: Norman Green; William C Vergara
Original assignee: Individual
Current assignee: Individual
Priority date: 1971-01-20
Filing date: 1971-01-20
Publication date: 1972-09-19
Anticipated expiration: 1989-09-19

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.

Description

United States Patent Green et al.

[151 3,691,695 [451 Sept. 19,1972

1541 RAPID ACTING ABRASIVE TRIMMER FOR MICRO-ELECTRONIC DEVICES [72] Inventors: Norman Green, 119 Deep Dale Drive, Timonium, Md. 21093; William C. Vergara, 910 Dunellen Drive, Towson, Md. 21204 [22] Filed: Jan. 20, 1971 [21] Appl. No.: 107,975

[52] US. Cl. ..51/8, 51/165 R [51] Int. Cl. ..B24c 3/06, B24c 3/32 [58] Field of Search ..5l/8, l4, 15, 165 R [56] Reierences Cited UNITED STATES PATENTS 2,773,332 12/1956 Buchman et al ..5l/l5 2,884,746 5/1959 Rus et al. ..5l/l65 R X REF COMPARATOR MOTOR AND ABRASIVE CONTROL NOZZLE RETRACTOR Best et al. ..51/l4 Kulischenko ..5 l 8 Primary Examiner-Donald G. Kelly Attorney-William G. Christoforo [5 7] 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.

10 Claims, 4 Drawing Figures ABRASIVE SUPPLY I RAPID ACTING ABRASIVE TRIMMER FOR MICRO-ELECTRONIC DEVICES 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 heatup 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 Iongitudinal 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 overtrimming micro-electronic devices. I

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 l2 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 c. 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 so as to withdraw nozzle 200 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 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 attractablematerial. 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 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. I are seen in greater detail within the dashed boxes.

The comparator output signal, which is a negativegoing 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 63 to eliminate undesirable voltage spikes when transistor 64 subsequently becomes nonconductive.

The signal generated at collector electrode 63a is coupled through capacitor 66to 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.

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 wherebya relatively large current pulse 1s 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.

Claims

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.