Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
1999-12-21
2002-07-30
Le, N. (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
Reexamination Certificate
active
06426637
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to spring contact probe needles for high frequency testing of integrated circuits and semiconductor wafers, and especially to providing accurate alignment and probe tip stability for spring probe needles, hereinafter referred to simply as probes, of the kind disclosed in FIGS. 2A-2G of commonly assigned patent “PROBE ASSEMBLY AND METHOD FOR SWITCHABLE MULTI-DUT TESTING OF INTEGRATED CIRCUIT WAFERS”, U.S. Pat. No. 5,923,178 issued Jul. 13, 1999 by Higgins et al., entirely incorporated herein by reference. This invention also relates to similar probe assemblies for providing high frequency test signal transmission between a printed circuit board of an integrated circuit “tester” or “test system” and a probe card. The invention also relates to probe assemblies for providing high frequency test signal transmission between a printed circuit board of a test system and bonding pads of a large number of die of an integrated circuit wafer being tested.
U.S. Pat. No. 5,521,518 (Higgins), U.S. Pat. No. 5,589,781 (Higgins et al.), U.S. Pat. No. 5,416,429 (McQuade et al.), U.S. Pat. No. 4,554,506 (Faure et al.), U.S. Pat. No. 4,843,315 (Bayer et al.), U.S. Pat. No. 5,534,784 (Lum et al.) and U.S. Pat. No. 4,636,722 (Ardezzone) are generally indicative of the state of the art. It is known that insulative aluminum oxide is usually present on aluminum bonding pads of integrated circuit wafers. It also is known that there may be hundreds of integrated circuit die on a single semiconductor wafer and that it is necessary to “probe test” each die or device under test (DUT) before the wafer is cut into individual integrated circuit die. The die testing often needs to be performed at high speed or high frequency, for example at a 100 MHz data rate, or even much higher.
The above references disclose various known techniques for supporting “probe cards” that support a plurality of probes, tips of which must provide reliable electrical contact (i.e., low probe contact resistance) with the bonding pads of the DUT during the testing. The shank of a probe is typically 5 to 10 mils in diameter. In a typical probe test system, a “test head” supports an “interface assembly”, that is supported between a “pin electronic board” of an integrated circuit test system and a “probe card” from which all of the probes required to probe test a particular semiconductor die extend. Typically, the wafer is supported on a “wafer chuck” of a “wafer probe machine” that automatically handles wafers. The chuck provides indexed translation in the x and y directions to bring the individual chip bonding pads into alignment with the probes supported by a probe card. The chuck ordinarily is moveable in the z (vertical) direction to press the chip bonding pads against the contact tips of the probe needles. After alignment of the probes with the corresponding bonding pads of the integrated circuit die, the wafer chuck and wafer thereon are raised approximately 3 mils so that the typically inclined probes “scrub” through brittle insulative aluminum oxide on the aluminum bonding pads of the wafer to allow good mechanical and electrical contact of the probe tip with the bonding pad metal and thereby ensure low probe contact resistance. It often would be desirable to perform the die testing at high frequencies, for example within a bandwidth of 2 to 6 Gigahertz or even much higher.
The C-shaped flex portions of the spring probes of the above referenced U.S. Pat. No. 5,923,178 have tips which extend beyond an insulative support. A problem of that structure is that the metal probe tips tend to be laterally skewed in various directions because of inaccuracies in the manufacturing process. This causes difficulty and inaccuracy in aligning the probe tips with the bonding pads of the integrated circuit under test. Another problem is that the probe tips have no lateral support in any direction, and therefore they tend to be somewhat unstable as they contact bonding pads as the wafer is raised so that its bonding pads are pressed against the spring probe tips.
Another problem with the structure of FIGS. 2A-2G of commonly assigned U.S. Pat. No. 5,923,178 is that the probe tips extend approximately 80-100 mils beyond the edge of the shank support structure and a ground plane associated with the shank support structure. This is a problem because although the portions of the probe needles supported on a thin insulator parallel to the ground plane act like a transmission line and provide very high bandwidth for test signals, the portions extending beyond the ground plane have appreciable inductance that significantly limits the bandwidth of probe test signals.
It would be beneficial to provide the numerous advantages of the “rocking tip” of the arcuate spring needles described in the above referenced commonly assigned U.S. Pat. No. 5,923,178 without the above mentioned disadvantages of probe tip misalignment, instability, and probe tip inductance.
There are applications other than wafer probing for probe assemblies with probes of the kind described above. One such application includes providing high speed electrical signal coupling to conductors of a printed circuit board or between conductors of different printed circuit boards, wherein the probes electrically contact corresponding conductors on the surface or surfaces of one or more printed circuit boards.
A problem of prior art interface assemblies coupling a pin electronics board of a typical integrated circuit test system to a printed circuit board portion of a probe card is the very large force, often many hundreds of pounds, required to compress the spring-loaded pins so that their opposite contact tips reliably contact conductors of the pin electronics board and corresponding conductors of the probe card. Another problem with such prior interface assembles is the relatively low density of test signal paths that can be provided therein. The number of test signal paths is limited by the large pitch, approximately 100 mils, of the probe conductors contacting the pin electronics board. This is in sharp contrast to the pitch of approximately 20 mils of contact pads on the printed circuit board portion of a typical probe card, and is even sharper contrast to the approximately 5 mil pitch for bonding pads of some integrated circuits. At the present state of the art of integrated circuit test systems, it is not practical to simultaneously produce the test signals needed to probe test more than approximately 64 chips of a semiconductor wafer, each chip having roughly 60 bonding pads. Nor is it practical at the present state of the art to provide enough electric circuitry on each pin electronics board driven by the integrated circuit test system to test more than four chips or “sites”.
It would be desirable to provide an improved probe interface assembly for use between a “pin electronics board” of a typical integrated circuit tester and a probe card. It also would be highly desirable to provide an improved assembly for conducting a much higher “density” of high frequency test signals, with bandwidth in excess of several gigahertz, directly between the pin electronics board of a typical integrated circuit tester and probe needles contacting the bonding pads of an integrated circuit wafer than has previously been achieved. It also would be highly desirable to provide simultaneous high speed, uniform impedance signal transmission directly between the pin electronics board of a typical integrated circuit tester and to bonding pads of a large number of die, e.g., 128 or more die, in an integrated circuit wafer being tested.
SUMMARY OF THE INVENTION
Accordingly, it an object of the invention to provide a probe card having a high density of flex probes and which avoids problems associated with uncontrolled impedance along the signal paths through the flex probes, and which also provides improved flex probe alignment and stability compared to the prior art.
It is another object of the invention to provide a high density of probe needles in an integrated circ
Back Gerald W.
Dang Son N.
Higgins H. Dan
Williams Scott R.
Cahill Sutton & Thomas P.L.C.
Cerprobe Corporation
Le N.
LeRoux Etienne P
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