Miniature probe positioning actuator

Disclosed is a Probe Positioning Actuator which is low in cost and mass, capable of high accelerations, relatively long stroke and compact packaging, as well as high in efficiency. The actuator assembly comprises a frame, and at least one pair of spaced apart, laterally extending, conductor carrying, flexible beams attached to the frame. A non-magnetic armature, substantially U-shaped in cross section, is attached adjacent or approximate the extended terminal ends of the beams, and a probe is attached to the base of the "U" of the armature for contacting selected points in the electrical circuit associated with the device being tested. The heart of the actuator includes a coil mounted on the upstanding legs of the U-shaped armature and arranged so that the axis of the coil is perpendicular to the base of the armature but substantially parallel to the probe tip. This arrangement places the `motor` portion of the actuator adjacent the probe and permits accurate and repeatable, fast control of not only probe tip position but probe tip movement. To complete the motor portion of the actuator, means, carried by the frame create a magnetic field across the coil, whereby upon energization of the coil, deflection of the armature (and thus the beams) occurs, effecting movement of the prob into contact with selected portions of the device being tested.

CROSS-REFERENCES TO RELATED APPLICATIONS 
This application is related to co-pending application Ser. No. 08,451,634, 
filed on May 26, 1995, (the same date as this application) and bearing the 
title Miniature Probe Positioning Actuator., our designation BC9-95-017. 
BACKGROUND OF THE INVENTION & STATE OF THE PRIOR ART 
1. Field of the Invention 
The present invention relates to actuators and more particularly relates to 
highly efficient miniature actuators for use with probes employed in 
conjunction with electrical circuit testing on miniature devices such as 
integrated circuit chips, wherein the probe must move in a predetermined, 
accurate and rapid fashion into engagement with the electrical circuit 
under accurate and rapid fashion into engagement with the electrical 
circuit under test. 
2. Description of Related Art 
New technology has increased the density of very large scale integration 
electronic circuits (VLSI) which requires a reliable probing machine to 
perform fast and accurate electrical testing. For example, a single 
substrate may contain as many as 150,000 test points, and the circuits 
formed between selected points may require probing for different 
electrical properties at different stages of the manufacturing process. 
One of the crucial components of the probing machine is the probe 
positioning actuator. The actuator moves the probe tip in a vertical 
direction (Z-Axis) in order to make contact with the test pads of the 
circuitry to perform the desired or selected test. As can be imagined from 
the forgoing, competitive probe positioning actuators should be reliable, 
have low or no maintenance and if required be easy to maintain, should 
preferably have low or no wear parts or parts that are subject to fatigue, 
and should have excellent repeatability of position and capable of moving 
at high speed without damage to the substrate (semi-conductor chip) under 
test. 
Machines for probing and testing electrical circuits in integrated circuit 
chips usually include a stationary base member and an X-Y table mounted 
thereon for movement relative to the base member. A fixture or jig is 
conventionally provided attached to the table, the fixture being employed 
to accurately hold, position and vertically elevate the chip into contact 
with one or more probes for chip monitoring and test. In this arrangement 
the probes are fixedly connected to the base member, or if monitoring 
(testing) of the chip is to occur on opposite sides thereof 
simultaneously, other jig and fixture means are provided for swinging the 
testing probes into position. Because of the mass of the fixture or jig, 
(as compared with the mass of the probes), chip movement into engagement 
with the probe(s) is slow. Moreover, with fixed probes, it is extremely 
difficult to adjust the probe tips to ensure approximate uniformity of 
pressure when the chip engages the probes. Various means have been 
provided in an attempt to ensure substantially uniform probing force. 
These include planarization of both the probe tips and/or the surface of 
the chip under test. 
Other ways, such as pre-loading the probe arms, ensuring a constant 
deflection distance of the probe arms etc. have been partially successful 
but have resulted in differences when the chip surface is uneven, or the 
probe tip subscribes an arc when the chip comes into contact with the 
probe or probes effecting scratching of the chip surface resulting in 
damage to the delicate electrical circuits therein. In other instances, 
uncontrolled or poorly controlled probe tip forces on the chip surface can 
result in damage to either or both of the chip surface and probe tip. 
Other methods of control of the probe arm is to provide an actuator for 
each of the probes and move the chip under test only in the X-Y plane. 
Some of the actuators employed include that shown in U.S. Pat. No. 
5,153,472. While this probe actuator overcomes the problems of non linear 
probe movement in the Z-axis, and meets the requirements of controllable 
probe force it suffers from two major defects: (1) the ball bearing 
structure is subject to wear and stress concentration, resulting in 
non-repetitive or repeatable accurate alignment of the probe tip over a 
period of time, and (2) the high mass of the tip armature structure makes 
probe tip control difficult unless probe movement is deliberately made 
slow so as to prevent inadvertent high impact loads on the chip. 
Other actuator designs have included air bearings for their movement. 
However, air bearings are not stable at high speeds because of turbulent 
flow. 
Other problems relating to electrical signal interference when measuring 
with the probe tip, using electrically powered actuators, are overcome as 
shown in U.S. Pat. No. 4,123,706 by the use of fluid actuation. However, 
it is believed that the twin beam actuator shown in the '706 patent has 
damping problems with fast probing contacts moving at high speeds. 
Moreover, despite the characterization of "no arc" movement of the probe, 
it is believed that the probe tip of the '706 patent has to move in some 
arc which creates some difficulty in initial positioning of the 
actuator/probe tip, especially when the chip surface is uneven, or the 
alignment of chip surface and probe tip is not perfect. Also, because the 
principal actuation is in one direction or uni-sided, probe bounce may 
occur at high testing speeds and force. 
SUMMARY OF THE INVENTION 
In view of the above, it is a principal object of the present invention to 
provide an improved, more efficient, actuator/probe assembly for testing 
electrical circuits and the like on devices such as semi-conductor chips. 
A further object of the present invention is to provide a low mass, high 
speed actuator for a probe which inherently is capable of substantially 
perpendicular movement of both the coil and the probe tip with respect to 
the chip surface to inhibit probe scrubbing of the delicate surface of the 
chip under test. 
Another object of the present invention is to provide a low mass, high 
speed actuator for semi-conductor chip testing in which there are 
relatively no wearing parts so that the life of the actuator in use is 
substantially indefinite under normal usage conditions. 
Yet another object of the present invention is to provide an actuator for a 
probe for semi-conductor chip testing in which the structure is such that 
power and signal leads may be carried in the same cabling incorporated 
into the beam structure. 
In the illustrated instance, the forgoing is accomplished by providing an 
actuator for accurately and selectively positioning a probe into 
electrical contact with an electrical circuit associated with a device and 
for testing the same. The actuator is adapted for receipt adjacent to an 
X-Y positioning apparatus. The actuator is located in a plane parallel to 
the plane of the device with the circuit being tested so that it is 
positioned in overlapping relation to the device being tested. The device 
in turn is held in a predetermined position on the X-Y positioning 
apparatus by any conventional means such as a jig or fixture. The actuator 
assembly comprises a frame, and at least one pair of spaced apart, 
laterally extending, conductor carrying, flexible, cantilevered beams 
attached at one end to the frame. A non-magnetic armature, substantially 
U-shaped in cross section, is attached adjacent or approximate the 
extended free terminal ends of the beams, and a probe is attached to the 
base of the "U" shape of the armature for contacting selected points in 
the electrical circuit associated with the device being tested. The heart 
of the actuator includes a coil arranged so that its axis is perpendicular 
to the base of the U-shaped armature and mounted on the upstanding legs 
thereof. This places the `motor` portion of the actuator adjacent the 
probe and as will be discussed hereinafter, permits accurate and 
repeatable, fast control of not only probe tip position but probe tip 
movement. To complete the motor portion of the actuator, means, carried by 
the frame create a magnetic field across at least part of the coil, 
whereby upon energization of the coil, deflection of the armature (and 
thus the beams) occurs, effecting movement of the probe into contact with 
selected portions of the electrical circuit associated with the device 
being tested. The magnetic field is created, in the present instance, by a 
pair of permanent magnets mounted on interior portions of a pair of 
U-shaped iron cores, the cores being adapted to embrace, but in spaced 
apart relation, opposite legs of the U-shaped armature upon which the coil 
is sound. In this manner, the magnets confront opposite sides of the coil. 
Because of the iron core, the efficiency of the system is enhanced. The 
price, however, as compared to the co-pending application identified 
above, is that the weight and size of the actuator is increased. 
The iron cores are in turn attached to the frame with their leg portions 
parallel to the axis of the coil and on opposite sides thereof, the 
magnets being magnetically oriented so that the sides thereof facing the 
coils are of the same polarity, while the spaced apart leg of each of the 
cores is of the opposite polarity, thereby creating, in conjunction with 
their associated iron core leg, the desired magnetic field across the 
coil. Moreover, with this structure, the electromagnetic force applied to 
both sides of the coil is substantially uniform or evenly distributed, 
increasing the efficiency of the actuator. 
Other features of the actuator include at least one of the flexible beams 
being composed of a flexible circuit material carrying at least some 
electrical conductors for at least one of the probe and coil. 
Another feature of the actuator of the present invention is the inclusion 
of sensor means associated with the probe for indicating at least probe 
deflection when the coils are energized. 
Other objects and a more complete understanding of the invention may be had 
by referring to the following description taken in conjunction with the 
accompanying drawings in which:

DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENT 
Turning now to the drawings and especially FIGS. 1 & 2 thereof, an actuator 
50, constructed in accordance with the present invention, is shown 
therein. 
From a system standpoint, and as shall be more fully explained hereinafter, 
as illustrated best in FIG. 5, the actuator 50 includes a probe 70, the 
tip 71 of which is adapted to engage circuits or pads therefor and the 
like on the surface 41 of a work piece, for example a device such as a 
semiconductor chip 40. The device or chip 40 is held, in a conventional 
manner, by a jig or fixture (not shown) onto an X-Y table 35. The actuator 
is also adapted for receipt onto a jig or fixture independently mounted 
but associated with the X-Y table 35 for precisely locating the actuator 
50 in a plane parallel to the plane of the device with the circuit being 
tested. In this manner, the probe tip of the actuator is positioned in 
superimposed, overlapping relation to the device 40 being tested. The 
motion of the actuator 50 to effect engagement of the tip 71 of the probe 
70 against the surface 41 of the device or chip 40 includes a computer 10, 
which receives a control card 12 for operation with the computer 10, and a 
probe position sensor 30. The system and its operation will be explained 
more fully hereinafter. Suffice at this point in the description to note 
that the actuator 50 serves to move the probe 70 in the direction of the 
arrow 72 into and out of engagement with the surface 41 of the device 40 
under test. It should also be noted that the probe and actuator are 
position independent. This means that the actuator 50 and thus the probe 
70 may be employed in the fashion illustrated in FIG. 5, i.e. above the 
device being tested, or positioned below the device being tested with the 
probe tip 71 projecting upwardly so as to contact the underside of the 
device being tested. The latter position is shown in FIG. 1. 
Turning now to FIG. 1, the actuator 50 includes a cover portion 51 which 
serves as a protection for the internal conductors and partially for the 
motor structure, hereinafter described. The cover portion 51 is connected 
to a light weight actuator support member 53 which serves, in the present 
instance, as a frame, a separator for parts of the actuator mechanism, and 
a cover therefor. It should be recognized that the frame 53 in conjunction 
with the cover 51 forms a cavity 54 for receipt of the probe motor and 
probing mechanism 55 of the actuator 50. The frame 53 includes a platform 
base 43 connected to an upstanding L-shaped angle 44, the upstanding leg 
portion 44a thereof serving to close the rear of the cavity 54, acting as 
a support for the cover 51, and as will appear hereinafter, cooperating in 
conjunction with post 45, and clamps 46, 47 to serve as attachments for 
flexible circuit beams 56 and 57. 
In accordance with one feature of the invention, the probe motor and 
probing mechanism 55 of the actuator 50 comprises at least a pair of 
spaced apart, laterally extending, resilient and flexible, cantilevered 
beams 56, 57, each of which, in the illustrated instance, are bifurcated 
to form beam legs 56a, 56b and 57a, 57b respectively. (See FIGS. 1 & 2). 
As shown best in FIG. 1, the extended free ends of the beams 56 and 57 are 
connected to (by bonding or the like) a U-shaped armature 58, composed 
preferably of a non-magnetic, light weight material such as Ultem.RTM. (a 
trademark of General Electric Corp.), a polyetherimide resin (1000 series 
resin). At the upper portion, or base 58a of the "U" of the armature 58 is 
connected the probe 70, which projects through an aperture 51a in the 
cover 51. The probe 70 includes a probe tip 71, adapted to engage selected 
circuits and the like on the surface 41 of a device such as the 
semiconductor chip 40 illustrated schematically in FIG. 5. 
The beams 56 and 57 are preferably formed of a polyimide and copper flex 
cable such as Kapton.RTM. (a Registered Trademark of E. I. DuPont Corp.) 
and sold by E. I. Dupont Corp. As shown best in FIG. 2, the beams 56 and 
57 include a plurality of conductors 56c and 57c respectively. The beams 
may terminate in any desired construction. For example, as shown in FIG. 
1, they may pass through the leg 44a of the angle 44 so that external 
connections may be made to power sources, and as will be more completely 
described with regard to FIGS. 5 & 6, connection to the control card 12 
associated with computer 10. As shown in FIG. 1, the beams 56 and 57 are 
bonded as at 59a and 59b to the armature 58. The heart of the actuator 
includes a coil 60 wound on the upstanding legs 58b and 58c of the 
U-shaped armature and arranged so that its axis is perpendicular to the 
base 58a of the armature. This places the `motor` portion of the actuator 
adjacent the probe 70 and as will be discussed hereinafter, permits 
accurate and repeatable, fast control of not only probe tip 71 position 
but probe tip movement. 
To complete the motor portion of the actuator, means, carried by the frame 
53 create a magnetic field across at least part of the coil 60, and for 
increased efficiency in the present instance across the whole peripheral 
extent of the Coil. In this manner, upon energization of the coil, 
deflection of the armature 58 (and thus the beams 56 and 57) occurs, 
effecting movement of the probe tip 71 into contact with selected portions 
of the electrical circuit associated with the device being tested. The 
magnetic field is created, in the present instance, by a pair of permanent 
magnets 63, 64 mounted on the interiors of leg portions 65a, 66a of a pair 
of U-shaped iron cores 65, 66 respectively. The cores 65, 66 have interior 
leg portions 65b, 66b respectively which are adapted to embrace in spaced 
apart relation, in conjunction with their exterior leg portions 65a, 66b, 
opposite legs 58b, 58c of the U-shaped armature 58 so that the magnets 63 
& 64 confront opposite sides of the coil 60. Because of the iron core and 
the fact that a predetermined portion of the coil 60 is always in the 
magnetic field, the efficiency of the system is enhanced. This is because 
with this structure, the electromagnetic force applied to both sides of 
the coil is substantially uniform or evenly distributed, increasing the 
efficiency of the actuator. The price, however, as compared to the 
co-pending application identified above, is that the weight and size of 
the actuator 50 is increased. 
As may be appreciated by one skilled in the art, the iron cores 65, 66 may 
be joined as at the legs 65b, 66b. Regardless of the structure, i.e. 
whether the cores are separate or connected, they should be attached to 
the frame 53 with their leg portions 65a, 65b, 66a, 66b substantially 
parallel to the axis of the coil and on opposite sides thereof, the 
magnets 63, 64 being magnetically oriented so that the sides thereof 
facing the coil 60 are of the same polarity, while the spaced apart legs 
of each of the cores 65, 66 is of the opposite polarity, thereby creating, 
in conjunction with their associated legs, the desired magnetic field 
across the coil 60. The coil 60 preferably has its' terminal leads, 60a, 
60b joined to current carrying conductors, 57c of beam 57. (FIG. 1) 
It will be recognized to one skilled in the art, it is preferred that the 
exact position of the probe tip 71, relative to the semi-conductor chip 
40, be known so that the correct amount of current can be supplied to the 
coil 60. To this end, a position sensing apparatus 24 may be attached to 
the base 43 of the frame 53 in such a manner to detect the armature 58 
position under varying current created deflection conditions and 
controlled in a manner by suitable feedback to permit raising or lowering, 
in response to armature position, the current applied to the coil 60. As 
shown schematically in FIGS. 3 & 4, the position sensing apparatus 24 
comprises a light source 25, such as an infra red emitting diode, which is 
located on one side of a flag or tell-tale 26 which in turn is attached to 
the armature 58 so that as the armature is elevated or depressed in 
response to the current applied to the coil 60, a greater or lesser amount 
of light will be detected from the light source 25 by the sensor 30. The 
amount of light sensed by the detector or sensor 30 may be varied by the 
flag or tell-tale 26 having a shaped opening therethrough, for example the 
opening 27 being in the shape of a triangle such as illustrated in FIG. 4, 
so that as the armature 58 descends less light will be detected by the 
sensor (in the illustrated instance a photo-diode sensor) 30, and when it 
ascends, more light will be detected. (The arrangement may also be the 
opposite, merely depending upon the way in which the user decides to set 
the sensor output, i.e. more light higher or diminished output). 
As shown best in FIGS. 1 & 2, the sensor 30 may be covered by a simple 
receptacle like cover 32 mounted on the base 43 of frame 53. As the flag 
26 is attached to the probe 70 (see FIG. 3) it is adapted to be raised and 
lowered as the armature 58 reciprocates in the direction of arrow 72 (FIG. 
5). Moreover, as best shown in FIGS. 3 & 6, the sensor 30 and light 25 may 
be carried by the receptacle/cover 32 and electrically connected, as shown 
schematically in FIG. 3 to a current carrying wire pair 23 and 34 and 
then, if desired, into conductors in one of the flexible beams 56, 57. The 
output of the sensor 30 may be applied through wire pair 34 to the 
flexible beam 57, and as shown schematically in FIG. 6, applied to a 
control card 12, carried by a computer 10, e.g. as through lead 16. The 
computer 10 is preferably of the type that can accommodate plug in boards 
or cards which include local or board carrying micro-processors. The IBM 
micro-channel architecture machines, sold under the trade name PS/2.RTM., 
are ideal for this kind of activity. The micro-channel architecture 
machines are capable of bus-mastering (wherein the micro-processor on the 
board communicates with the computer's CPU, controls its own local bus and 
function, and is capable of other interrelated as well as other 
independent actions). In this connection, the control card 12 preferably 
includes a position sensor card 15 and an actuator driver card 20, all 
under control of a local microprocessor 11. The micro-processor 11 may be 
any convenient one readily available on the open market, for example a 
Texas Instrument TMS320C30. The position sensor card 15 receives a sense 
signal from the sensor 30 (FIG. 6) over line 16, which, after suitable 
modification is in turn fed back to the micro-processor 11 by line 17 for 
processing (e.g. required sense, amplification, etc.), as will be 
explained hereinafter with respect to FIG. 6. Suffice at this juncture, 
that the processor 11 outputs a signal over line 18 to actuator driver 20 
which is applied through conductor 19 to the motor coil 60. The actuator 
driver 20 is in actuality a current amplifier of suitable output 
sufficient to effect the necessary current flow to move the armature 58 
and thus the probe 70 into proper position. 
The system may employ any of a number of standard control algorithms for 
the actuator motor control. Proportional Integral Derivative (PID) control 
algorithms are well known in the industry and may be employed for suitable 
feedback control. As shown in FIG. 6, the microprocessor 11 may contain 
the PID control algorithm. Examples of the PID algorithm are set forth in 
the book "Feedback Control System" by Charles L. Phillips and Royce D. 
Harbor, Prentice Hall, 1988, pages 239 et. seq. The computer 10 provides a 
suitable machine initialization signal over line 10a (FIGS. 5 & 6) and 
tells the microprocessor 11, inter alia, what measurements to perform, 
e.g. resistance, capacitance, where the pad on chip is located, and how 
much deflection is required of the armature 58 to effect probe 71 contact 
with the surface 41 of device or chip 40. The microprocessor 11, may, for 
example, put out a positive (+) signal over line 10a to a summing junction 
or amplifier 11a, associated with the microprocessor 11, to which the 
feedback signal from the sensor 30 and position sensor card 15 outputs a 
negative (- ) signal. This means that an error signal is applied to the 
microprocessor 11, which error signal is appropriately handled by the PID 
control algorithm contained in the microprocessor. 
Because the microprocessor 11 may operate substantially independently of 
the computer 10 CPU while operating in a dedicated mode, it is preferable 
that the instructions sent by the computer 10 relating to the probe 
measurements, settings, and the like be handled by the microprocessor 11. 
As illustrated, the computer provides this necessary initial information 
to the microprocessor 11 over line 10b while receiving any feedback data 
or information over line 10b. These signals, including measurements, to 
and from the probe 70, are carried by selected conductors 56c in the upper 
beam 56, through connecting wires 74 (FIG. 1) to the probe 70, and through 
wire pair 75 (FIG. 5) to and from the microprocessor 11. 
From the forgoing, it should be recognized that the structure provided by 
the probe actuation scheme of the present invention allows for small 
structures, which because of its' low mass, increased motor efficiency and 
the ability to place the structures in close situations, permits of faster 
acting and more reliable probing of devices under test. 
Although the invention has been described with a certain degree of 
particularity, it should be recognized that elements thereof may be 
altered by person(s) skilled in the art without departing from the spirit 
and scope of the invention as hereinafter set forth in the following 
claims.