Breakaway test probe actuator used in a probing apparatus

A probe positioning apparatus for use in a probe testing system is disclosed. The probe positioning apparatus includes a probe tip, a probe actuator connected to the probe tip, a probe plate coupled to the probe actuator and a magnetic probe plate clamp that magnetically couples the probe plate. The magnetic coupling forms a slip plane that provides collision compliance for the probe positioning apparatus. One embodiment of the magnetic probe clamp uses a set of shoulder screws to provide quick attachment and release of the probe plate from the probe clamp. A second embodiment uses a magnetic shunt to disable the magnetic connection of the clamp from the probe plate.

BACKGROUND OF THE INVENTION 
1. Technical Field 
The present invention relates generally to probing apparatus using test 
probes, and more specifically to a test probe assembly that is easily 
disconnectable from the probe apparatus. More specifically still, the 
present invention relates to a quick disconnect probe assembly that 
readily breaks away from the probing apparatus upon collision with any 
other element. 
2. Description of the Related Art 
Probing apparatus for testing electronic components such as, for example, 
semiconductor wafers or circuit boards, are well known in the art. The 
probing apparatus use probe tips for providing electrical connection with 
device under test (DUT). These probe tips are small and do not endure the 
rigors of testing well; therefore, the probe tips are replaced frequently. 
The probe tips are small and they are placed on probe actuators or probe 
assemblies located well inside the probing apparatus. Thus, it is 
desirable to remove the probe assemblies from the probing apparatus to 
change the probe tips. 
The probing apparatus usually has a coarse positioning system that moves 
with very high accelerations. If there is an error in the test file, a 
collision may occur that might damage either the components within the 
apparatus or the DUT. 
Additionally, some DUT's are very thin and very small in relation to the 
overall positioned workspace in the probing apparatus. Typically, they are 
in a pocket in a support cradle that needs a minimum thickness for 
sufficient stiffness. This requires the probes to be in the pocket during 
testing, which leads to the possibility for collisions with the product 
support cradle from the side and rear, as well as with the opposing probe 
assembly from the front. Traditionally, slide bearing packages for 
collision compliance require a stack XY arrangement to give a 360.degree. 
freedom of movement. This stacking makes the mechanism fairly tall. 
Trying to limit stack height is important in probe stacking design. First, 
the distance from the probe tip to the course positions and encoders 
impacts the accuracy of positioning the probe tip. Any aberration errors 
in the bearings and distortions in the structure due to settling 
vibrations are amplified by the distance from the encoder. The encoder 
head location is used to determine the probe tip location, thus, it is 
desirable to minimize the distance between the encoder head and the probe 
tip. Second, the taller the structure to which the probe tip is mounted, 
the more the probe assembly weighs and the less stiff it is. Moving of a 
large probe assembly mass should be minimized for coarse positioning 
performance to be optimal. Further, the structure to which the probe tip 
is mounted should be as stiff as possible so as not to vibrate 
significantly due to the acceleration experienced by the probe tip 
assembly during positioning. 
Accordingly, what is needed is a probe tip assembly that is readily 
removable from the probing apparatus. Further, what is needed is a readily 
removable probe tip assembly that has collision compliance thus preventing 
damage to the expensive components or DUT within the probing apparatus. 
Furthermore, the probe tip assembly must have a low profile so as not to 
extend the probe tip too far above the course positioned thus leading to a 
decrease in accuracy of the tip positioning. 
SUMMARY OF THE INVENTION 
It is therefore one object of the present invention to provide a probing 
apparatus using test probes. 
It is yet another object of the present invention to provide an easily 
disconnectable test probe assembly from the probe apparatus. 
It is still yet another object of the present invention to provide a quick 
disconnect probe assembly that readily breaks away from the probing 
apparatus upon collision with any other element. 
According to the present invention, a probe positioning apparatus for use 
in a probe testing system is disclosed. The probe positioning apparatus 
includes a probe tip, a probe actuator connected to the probe tip, a probe 
plate coupled to the probe actuator and a magnetic probe plate clamp that 
magnetically couples the probe plate. The magnetic coupling forms a slip 
plane that provides collision compliance for the probe positioning 
apparatus. One embodiment of the magnetic probe clamp uses a set of 
shoulder screws to provide quick attachment and release of the probe plate 
from the probe clamp. A second embodiment uses a magnetic shunt to disable 
the magnetic connection of the clamp from the probe plate. 
Further connected to the probe tip assembly is a sensor bracket, which 
includes an opto-electric sensor for sensing the location of the probe 
tip, and a collision sensor, such as an inductive proximity sensor, for 
detecting when the probe plate experiences a collision. 
The above as well as additional objects, features, and advantages of the 
present invention will become apparent in the following detailed written 
description.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
FIG. 1 is a perspective view of a test probing apparatus 10. Test probing 
apparatus 10 further includes a probe positioning assembly 12 and a probe 
positioning and testing control unit assembly comprising a personal 
computer 20, a data entry device, such as a keyboard 22, and a data output 
device, such as a video monitor 24. 
Probe positioning apparatus 12 further includes an X positioned assembly 
14, for positioning the probe along a first or X axis, a Y positioning 
assembly 16, for positioning the probe along a second or Y axis, and a 
probe assembly 18 for positioning the probe along a third or Z axis. The 
device to be tested, or device under test (DUT), is placed upon a 
positioning table 26 that slides substantially under the probe assembly 
for testing of the DUT. 
Personal computer 20 is programmed so as to position automatically the 
probe assembly 18 over the DUT for fast and efficient testing. The profile 
for each DUT is programmed into computer 20, which allows it to locate the 
probe assembly 18 precisely onto the DUT without the need for manual 
positioning of probe assembly 18. Alternatively, probe assembly 18 can be 
lowered and positioned on the DUT via manual manipulation entering 
information through keyboard 22 to computer 20 in response to information 
displayed on video display 24. 
Probe assembly 18 is more fully depicted in FIGS. 2 and 3. Probe assembly 
18 includes a probe positioning unit 50, which is mounted to a probe plate 
52. Probe plate 52 further connects to a collision bumper 54, which is 
made from a magnetizable material such as a ferrous metal or the like. 
Collision bumper 54 is further connected to a magnetic clamp 56, which 
securely mounts to X or Y positioning assemblies 14 or 16 in probing 
apparatus 10 of FIG. 1. Magnets 58 are used to clamp collision bumper 54 
with a sufficient enough force so that probe positioning assembly 50 is 
normally magnetically secured and can slip in the event of a collision 
with another structure within the probing apparatus 10. 
Probe positioning assembly 50 further includes a probe actuator 60 to which 
a probe tip 62 is mounted. Actuator 60 and probe tip 62 act in response to 
a sensor bracket 64, which include an opto-electric sensor for sensing the 
position of probe tip 62 over the DUT. Both actuator 60 and sensor bracket 
64 are electrically coupled to the computer in FIG. 1 via flexible cable 
66. A collision sensor 67 is located within clamp 56 so as to sense any 
collision experienced in the assembly. Collision sensor 67 is an inductive 
proximity sensor used to sense movement of collision bumper 54 with 
respect to clamp 56. 
A pair of shoulder screws 68 are used to provide a quick connect and 
release necessary to detach probe positioning assembly 50 from collision 
bumper 54. As the pair of shoulder screws are removed, they release probe 
plate 52 from collision bumper 54. A second set of shoulder screws 69 are 
used to provide alignment of collision bumper 54 with magnetic clamp along 
line 70 56. Also, as shoulder screws 69 are turned, collision bumper 54 is 
lifted or separated from magnetic clamp 56 sufficiently enough so as to 
weaken the magnetic field holding the assembly in place. Once collision 
bumper 54 is sufficiently away from magnetic clamp 56, the operator can 
manually remove the probe actuator with little effort. Shoulder screws 69 
may also be cone point set screws. An alternative assembly for clamping 
positioning device 50 to the probing assembly is depicted in FIGS. 4 and 
5. 
FIG. 4 depicts a top plan view of a probe clamp 72. FIG. 5 depicts a 
cut-away side view of clamp 72. Clamp 72 includes a mounting surface 74 
and a clamping actuator 76. Actuator 76 includes a clamping lever 78, 
which can be rotated 90.degree. to place a magnetic shunt 80 in such a 
position so as to lessen the magnetic force of the magnet along the 
magnetic orientation 82. 
When lever 78 is in the clamped position shown in FIG. 5, a magnetic flux 
path 84 extends into mounting surface 74, thus providing a magnetic force 
sufficient enough to mount and clamp the probe positioning assembly to the 
probe clamp 72. 
The magnetic flux is sufficient enough to hold the probe positioning 
assembly rigidly in place during normal operation. By rotating lever 78 
90.degree. the magnetic force is shunted through magnetic shunt 80 thus 
decreasing the magnetic force nearly to zero thereby allowing the probe 
positioning assembly to be readily removed from the probing apparatus. 
Probe clamp 72 may further comprise a retaining clip or pin or rod for 
preventing the probe assembly from falling upon the shunting of the 
magnetic flux. 
The use of the magnetic clamp with collision compliance eliminates the need 
for traditional slide bearing packages that increase the stack height of 
the probe positioning assembly. This provides a rigid, repeatable mounting 
assembly for the probe, with quick disconnect capability in a low profile 
package. 
While the invention has been particularly shown and described with 
reference to a preferred embodiment, it will be understood by those 
skilled in the art that various changes in form and detail may be made 
therein without departing from the spirit and scope of the invention.