Integrated circuit device test tool with double corner cavity

Abstract

The present disclosure provides an integrated circuit device testing tool with a dual angle cavity. A test probe assembly for testing a packaged integrated circuit (IC) device includes: a plurality of probes, a pad, and a PCB / interposer. The plurality of probes are configured to repeatedly maintain reliable electrical contact with a corresponding plurality of DUT contacts when under a compliant force, for example, reliable grounding. Reliability and / or grounding can be achieved by introducing a small angle difference between the hole axis of the upper block and the hole axis of the main block.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of and priority to pending U.S. Provisional Application No. 63 / 083,575 (Attorney Docket No. ES-2001-P), filed on September 25, 2020, which is hereby incorporated by reference in its entirety. Technical Field

[0003] The present invention relates to a system and method for a reliable test tool for packaged integrated circuit (IC) devices. In particular, an improved ground probe structure for an IC device test tool is provided. Background Art

[0004] Current test plug solutions for packaged IC devices suffer from deviations and inconsistencies in the ability to penetrate the contact points and, therefore, in electrical connectivity due to lifecycle wear and tear stresses. These unavoidable effects continue to result in invalid test failures, higher retest rates, longer test tool downtime, and result in higher IC device test costs. In particular, as operating frequencies in many consumer electronics increase significantly from one or two hundred megahertz to several gigahertz, various aspects of the test plug solution become more important. While most signal connections can tolerate degradation in the series resistance introduced by wear of the probe assembly, ground connections are much less tolerant of the introduction of series resistance because ground currents can cause crosstalk between signal connections and signal distortion.

[0005] In general, the cost of ownership (CoO) of existing IC device test tools is still high because their life cycle can usually reach 100,000-500,000 times in practice, depending on the IC device test environment, IC device connection layer quality, contamination and oxidation sensitivity, and other negative factors, such as economic pressure for lower cost IC devices.

[0006] The contact probes of the test tools used to test IC devices are usually made of conductive metals and metal alloys (such as BeCu, brass and steel alloys). Depending on the specific application, these contact probes can also be coated and / or plated with suitable conductive materials, such as gold, iridium, nickel, palladium and cobalt.

[0007] However, during repeated testing of IC devices, for example, after 100,000 test cycles, these contact probes of the test tool will continue to be affected by repeated connection and disconnection to and from the IC device under test. As a result, the contact probes often suffer from contact degradation due to peeling of the electroplated conductive layer, metal oxidation, adhesion of foreign matter, etc., resulting in a significant decrease in contact ability. Although signal connections can tolerate the introduction of resistance into the circuit when small currents are involved, high current areas (such as shared ground connections) present serious problems. To avoid ground loops (a technical term that describes the application of false signal voltages due to current flowing elsewhere in the device), it is important that unintentional resistance increases do not occur in the shared ground connection, as this will cause changes in the input signal.

[0008] In addition, after repeated continuous testing of the above IC devices, the penetration ability of the test tool contact probes is also affected by the substantial loss of inherent compliance force generated by the spring or elastic element housed by the corresponding contact probe body or post. The reduced contact pitch size of IC devices (e.g., from 1.27 mm to 0.2 mm or less) exacerbates this problem.

[0009] Therefore, it is clear that there is a pressing need to improve the reliability of ground contact probes of IC test tools after repeated testing. Such improved contact probes allow for reliable testing of ever-shrinking IC devices over a longer period of time without any unnecessary downtime of the IC test tool associated with failure or significant degradation of the contact probes. Summary of the invention

[0010] To achieve the above objectives and in accordance with the present invention, a system and method for reliable testing of packaged high-speed integrated circuit (IC) devices are provided.

[0011] In one embodiment, a test probe assembly is configured for testing packaged integrated circuit (IC) devices. The test probe assembly includes: a plurality of probes (probes), a termination pad interposer that allows the test probes or probes to be connected to one side of a test device, and a docking assembly that ensures repeatable alignment of the device under test. The plurality of probes are configured to repeatedly maintain reliable electrical contact with corresponding plurality of contacts on a device under test (DUT) when under a compliant force. The interposing pad provides mechanical and electrical coupling for the plurality of probes, and also provides termination points for routing from various test devices, each of which is used to send signals to and receive signals from the DUT.

[0012] In some embodiments, the test probe assembly includes an upper block for accommodating a plurality of probes, a main block, and a lower block. The main block includes a plurality of inclined main probe cavities oriented at a first acute angle to a vertical axis of the test probe assembly, and the upper block includes a plurality of inclined upper probe cavities oriented at a second acute angle to the vertical axis. The first acute angle and the second acute angle are offset relative to each other by a small incremental angle.

[0013] It should be noted that the various features of the present invention described above can be practiced individually or in combination. These and other features of the present invention will be described in detail below in the detailed description of the invention and in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly identify the present invention, some embodiments will be described by way of example with reference to the accompanying drawings, in which:

[0015] Figure 1A is a plan view showing a typical high-density test fixture, greatly enlarged for easier viewing;

[0016] Figure 1B Shows Figure 1B A representative view of a small portion of a typical test probe setup as seen in;

[0017] Figure 2A A schematic diagram of a simple circuit is shown to help understand grounding issues;

[0018] Figure 2B Shows Figure 2A Representative solutions to the problems described in;

[0019] Figure 3A An exemplary top view showing inadequate grounding at high frequencies is shown;

[0020] Figure 3B A cross-sectional diagram showing a proper grounding strategy at elevated frequencies;

[0021] Figure 4 shows a plan view of a single symmetrical depressible stylus assembly representative of the type used in making the test fixture;

[0022] Figure 5A shows a cross-sectional view of some of the components in the test system;

[0023] Figure 5B yes Figure 5A Detailed view of a portion of the diagram;

[0024] Figure 6 shows an improved performance layout of one embodiment of an exemplary test fixture according to the present invention; and

[0025] Figure 7 It is shown Figure 6 Graph illustrating the advantages of the illustrated embodiment. DETAILED DESCRIPTION

[0026] The present invention will now be described in detail with reference to several embodiments of the present invention shown in the accompanying drawings. In the following description, numerous specific details are set forth to provide a thorough understanding of embodiments of the present invention. However, it is apparent to those skilled in the art that some embodiments may be practiced without some or all of these specific details. In other examples, known processing steps and / or structures are not particularly described in detail to avoid unnecessarily obscuring the present invention. The features and advantages of the embodiments may be better understood with reference to the accompanying drawings and subsequent discussion.

[0027] The various aspects, features and advantages of the exemplary embodiments of the present invention will become better understood by the following description in conjunction with (one or more) drawings. It should be clear to those skilled in the art that the embodiments described in the present invention provided here are only illustrative and non-restrictive, and are presented only by way of example. Unless otherwise expressly stated, all features disclosed in this specification can be replaced by alternative features for the same or similar purpose. Therefore, many other embodiments of the modification of the present invention are expected to fall within the scope of the present invention and its equivalents defined herein. Therefore, the use of absolute and / or sequential terms, such as "will", "will not", "should", "should not", "must", "must not", "first", "initially", "next", "subsequently", "before", "after", "last" and "finally" does not mean to limit the scope of the present invention, because the embodiments disclosed here are merely exemplary.

[0028] The present invention relates to systems and methods for improved contact probes for reliable testing tools for packaged integrated circuit (IC) devices. Probes of the type described in this document typically allow a complex set of test equipment to be connected to an integrated circuit having a large number of connections, the test equipment often including a power supply, a signal source or generator, a data collection device, and an analysis device. The test equipment can be hardwired to any test probe assembly, but modern implementations of testers routinely terminate the equipment on a termination disk or board, an intermediate pad, which is then attached to an assembly containing the probe. In this way, one end of the probe that constitutes the probe assembly is coupled to the termination board so that the other end is ready to be connected to the device under test. An important aspect to keep in mind is that automated test equipment is intended to test a large number of devices, so repeated connections and disconnections are a fundamental design consideration.

[0029] Repeated connections and disconnections result in wear of the probe assembly in the probe station associated with the probe assembly, with the consequence of such wear resulting in changes in the quality of the connection to the DUT. Degradation is problematic because the resulting improper rejection of the component being tested can have serious cost implications, especially with modern high-density technology. The connection density is very significant, as we often find interconnect pitches ranging from about 0.020 inches or about 0.8 mm or less, down to 0.5 mm. The actual probe layout and distribution of this probe density is of course determined by the individual component parts to be tested. By constructing the termination board for the test equipment separately from the probe assembly containing the stylus, it becomes feasible to effectively replace the probe assembly, either when the probe begins to wear or according to an intended maintenance plan, thereby avoiding unplanned production losses in the test equipment; it is noted that the connection between the probe assembly and the intermediate pad will only change when a new probe assembly is placed to replace the old worn component. As described above, the purpose of the present invention is to provide a mechanism for improving the performance of an assembly including a stylus and its mounting fixture, as well as extending the performance of the probe itself.

[0030] To facilitate discussion, Figure 1A is a plan view of the layout of probes (probes) for testing an exemplary high-density component. It should be noted that the "site A" and "site B" marked on the left and right sides respectively accommodate probe (probe) arrangements according to various embodiments of the present invention, including reference standard probes and / or test probes. It is noted that in the simple description of a typical portion of this exemplary test fixture, the typical probe spacing in the fixture is generally between 0.5 and 0.8 mm.

[0031] Figure 1B is a plan view showing a small portion of an IC test fixture with high probe density. Here, the bulk or body 100 of the test fixture is typically made by machining a block of aluminum to align its upper and lower surfaces and punch holes that will allow for the insertion of connecting probes or probe heads. Although the same physical probe or probe assembly can be used in any hole location, in a given application, the functions can be divided into one of three types: power connections, such as voltage; ground connections; and signal input or output connections. Figure 1B As shown, the signal input 110 is shown next to an adjacent ground connection 120, and the power input 130 is also adjacent to the ground or return connection 120, and the signal output 140 of the DUT is also adjacent to the ground or return connection 120.

[0032] In simple systems, it is not uncommon to find only a single power connection and a single shared ground connection. However, in systems and circuits where the input circuits are very sensitive and the output circuits consume a lot of power, the interaction between them can be a very significant concern. This problem is often solved by ensuring that the input circuits are properly isolated from the output circuits. In fact, the difficulty can be so severe that manufacturers often publish guidelines to be followed through recommended printed wiring layouts to ensure proper operation. Two common concerns are shared current paths between high-current and low-current parts of the devices used, and high-speed transmission lines that must be properly designed and planned to minimize the effects of signal reflections. The same considerations for carefully selecting current paths also apply to devices where both analog and digital circuits are present. In this invention, we are specifically concerned with common-mode problems caused by insufficient grounding when planning current paths.

[0033] As a simple example, consider the two most familiar sources of feedback in the context of audio systems. The "howling noise" that is often perceived as a loud scream is often caused by the acoustic signal from the loudspeaker being picked up and then re-amplified by the microphone circuit. The acoustic properties of the auditorium and the frequency response of the amplification system will determine its nature. This can often be solved simply by reducing the gain of the amplifier or by hanging absorptive curtains in the auditorium to attenuate some of the acoustic reflections. However, a second common and annoying problem is residual hum in the system, which is caused by voltage changes detected by the microphone circuit not coming from the microphone but from the ground connection (where other currents than the microphone current are also drawn, i.e., a "ground loop"). In general, the wiring layout is often the culprit and must be changed to reduce or eliminate this "hum". A complementary effect of the ground loop is to distort the applied signal so that the output sounds rough or unpleasant.

[0034] Now, with the ground loop problem explained, let's turn to Figure 2A2 shows a circuit diagram of a simple audio amplifier. In this example, amplifier 200 is shown connected to its power supply 205 and to its ground return 240 via conductor 245; in a single-ended system, the ground return is often the connection point for the negative terminal of the power supply. The output drives a speaker 210, which is also connected to ground via conductor 245, and a microphone 220 is also connected between the input and ground via conductor 245. So the current flowing in conductor 245 includes amplifier current 253, which is drawn along with current 250 that can be drawn by the speaker circuit and current 255 produced by the microphone to operate the device. The voltage measured at point 247 is used for reference, the microphone input is different from the actual ground 240 because the resistance "R" of conductor 245 is not zero; this voltage is actually the applied microphone signal minus a voltage, which is the resistance of the conductor times the sum of the three currents 250, 253 and 255 flowing into it, which will be a varying voltage because the amplifier consumption changes over time due to the amplifier amplifying the audio signal. So the amplifier input voltage 235 will be different from the applied microphone voltage 230 .

[0035] Because the current drawn by the amplifier and the current drawn by the speaker vary depending on the signal produced by the microphone, and the microphone signal is changed by the changes produced at the current 247, the system will amplify the combination of these two signals. This means that the version of the signal delivered to the speaker will be a distorted version of the intended signal from the microphone. The fact that this occurs in the grounded portion of the system has led to the term "ground loop", although it may not be a loop in the strict sense. The important aspect is that the shared ground connection can cause significant noise or interference, which will change the system response. The solution to this problem is to ensure that the amplifier only senses the microphone signal, and not the combination of signals caused by the shared current path.

[0036] Figure 2B It is shown that the microphone ground return 243 for the amplifier is now separated from the power supply and speaker ground return 245. In this case, the reference for the microphone signal is at ground potential at 240 and is no longer dependent on the current flowing into 245. This illustrates the tendency to have ground connections in the test fixture be independent and not dependent on shared paths that could cause unwanted distortion in the signal path. Typically, these types of distortion in digital devices are often seen as timing jitter, where distortion of the applied signal pulses causes the DUT to malfunction because the signal level is not achieved within the necessary time specification.

[0037] Returning to the DUT being tested in a system where the signal levels are relatively high, such as a logic system where a logic zero (0) is approximately below the part’s supply voltage (V in the conventional style of a specification sheet). ccor V dd ), and logic one (1) is a voltage two-thirds higher than this supply voltage, the noise level is not usually very significant. However, in systems where the supply voltage is very low (in the vicinity of 1.1 to 1.8 volts, as an example) and the current may be sufficient to deregulate the voltage reference point at the connection probes in the test fixture, the resulting noise may introduce uncertainty in the logic levels presented to the part. This is similar to the "hum" problem in the audio amplifier system described above. Knowing that a common source of interference is improper system grounding, where current is allowed to flow along a path used as a reference connection for sensitive inputs, a careful solution is required. Another, although less common, concern is improper grounding of electrostatic shields (such as the braid of a shielded cable), which allows radiated noise from a nearby transmitter to appear on the input line and be rectified in some way to deregulate the reference voltage of the input amplifier stage.

[0038] In high frequency probe systems such as those found in modern high speed integrated circuits, simple solutions are generally less clear. Since the wavelengths of the test frequencies are very short, high quality grounding is essential to prevent interference due to the physical distance between current paths being a significant fraction of the wavelength of the applied signal. This requires ground connections that are close to the signal connections and not dependent on other nominal ground points in the test fixture; it is noted here that even though dc testing may show the various ground points to be at the same potential, this rarely holds true at the operating frequencies. In fact, at RF it is easy to provide a structure that appears to be an open circuit at the operating frequency, yet is at ground potential for the purposes of the supply current.

[0039] To minimize the noise generated by current flowing into the ground path or return of the device under test, it is important to ensure that the ground path is as short as possible because the distance between ground points can be a large fraction or even multiple of the wavelength at higher test frequencies as device technology continues to advance. An example of path length minimization is seen in most high-frequency printed circuit designs, where multiple vias (conductive plated holes that connect to a ground plane covering a large portion of one side of the circuit board) are located near the signal path conductors, thereby reducing the distance the ground current must travel.

[0040] consider Figure 3A, where the actual ground point is set to be a quarter wavelength from the intended ground. The emitter of transistor 305 is connected to DC ground 320 via a conductive element 310 that is a quarter wavelength long at a certain frequency. In this case, at that frequency, the transistor will not see ground but will be an open circuit, even though current from the actual ground can still reach the transistor to allow it to be biased to operate. A typical effect is that the circuit may exhibit a tendency to oscillate uncontrollably, but of course there are examples where this effect can be exploited, such as making the distance a half wavelength at a specific frequency so that an effective ground is only available at that specific frequency; this is one way in which a filter can be created. This type of problem, where the actual ground point is uncertain, is the main reason for using double-sided boards, where the connection layer is on one side of the board and the other side is almost entirely a conductive layer representing the actual signal ground. Depending on the actual circuit, the ground may only be continuous in certain areas of the board and components may be connected to the nominal ground side of the board; in complex arrangements, power and ground connections may be buried in a sandwich arrangement and component connections may only be accessible on either physical side of the board.

[0041] Now go to Figure 3B , showing Figure 3A A cross-sectional view of the diagram, in which Figure 3A In addition to the details of the substrate layer 340, a conductive layer 325 can be added below the substrate layer 340, providing the component 310, a conductive link 315 to connect to the ground layer 325, so that the ground at the connection point at one end of the component 310 looks more correct and is no longer replaced by a frequency-dependent component. The line at 322 represents the upper edge of the ground plate 320, at Figure 3A This understanding can now be used to formulate solutions to grounding problems that arise when developing test fixtures for critical applications such as testing of high-speed, low-voltage integrated circuits.

[0042] When a test fixture must pass high frequency signals to the device under test (DUT) alone, it is not uncommon for the test fixture to allow relatively simple ground connections using only a small number of probes. Because some test applications require signal and ground connectivity to the DUT to not only maintain signal fidelity but also provide isolation from other signals passing into and out of the DUT and maintain impedance matching to reduce signal distortion due to unexpected reflections of the signal, a high density of probes must be provided to make good grounding possible.

[0043] Figure 4A typical test probe comprising four components is shown. Two test probes 410a and 410b are disposed within a conductive shell 480, and a compression spring 420 is used to keep the probes apart. Since the probes are in repeated contact with the component being tested, they are made of wear-resistant materials and can be plated with suitable materials such as gold or palladium or similar materials to ensure good conductivity. Although the probes at both ends may be identical in some implementations, this is not always the case. These components are precision components that generally rely on conducting electricity through springs and along the outer shell 480. The wear surface can be treated to extend the life of these contact pins, but as will be explained, careful design of the test fixture can have a beneficial effect on this. In some applications, the outer surface of the shell 480 can be passivated so that the shell is electrically insulated from the block and several neighbors (as part of the assembly fixture) used to place the probes. If conductivity between the outer surface and the block is required, a corrosion-resistant material that does not require separate treatment can be selected.

[0044] Figure 5A A cross-sectional view of a portion of a typical test fixture is shown that maintains signal and return or ground connectivity all the way to the DUT itself, rather than simply terminating on the device side of the probe interface and trusting that the probe structure has minimal impact. It should be appreciated that, especially in systems where very small signals are considered, the series resistance presented by the probe can be a critical aspect of testing and must be maintained consistent and, ideally, minimized. Because the ground path is often a shared current path, the presence of significant series resistance means that a corresponding undesirable but significant voltage drop may occur. This inconsistency in resistance can lead to unpredictable or irreproducible test results, which in turn can mischaracterize critical components during test. Since some applications cannot be repaired after construction or assembly, accurately testing and characterizing the device is a key point in the manufacturing process to avoid waste.

[0045] By way of example, the signal is transmitted to the test fixture via an exemplary coaxial cable 520, which leads to pads 515 on a mating connection board (not shown) or substrate, which are printed or mounted on the connection board or substrate. This can be achieved using conventional printed circuit board technology, selecting substrate and pad materials to match the application. When the carrier or connection board is placed in contact with the test fixture assembly, the probes at 505 and 510 are usually pressed and maintained in contact with the pads by spring pressure, and cables carrying various test voltages and signals are terminated on the carrier or connection board so that they are applied to the DUT.

[0046] exist Figure 4An illustration of an individual probe assembly is shown for reference. The device under test 540 is located on the side of the fixture opposite the connection plate supporting the connection pads 515 so that the associated probes can contact the connection points 550 on the DUT, the connection point arrangement setting Figure 5A Layout of the stylus in the test fixture shown. In this portion of the illustration, the body 525 of the stylus assembly is primarily housed in the main locating block 535. The hole in the main locating block into which the probe assembly is inserted may be anodized, plated, or chemically treated to form a very durable insulating or connecting layer between the probe housing and the block.

[0047] In most cases, the main positioning block is essentially at power ground potential, which may also be the same as signal ground, but as frequency increases, the latter may not be correct, so measures must be taken to ensure the quality of the signal ground. In one implementation, the mounting block is maintained at an elevated potential relative to safety ground and is configured to couple it to the signal ground at the frequency of interest using a capacitive or resonant coupling structure. The gap distance between the probe housing and the block can be selected according to the design requirements. Since the anodized layer is only a few microns thick, it can form a low impedance path at the signal frequency, or there may be a considerable air gap, so that the probe housing forms the center conductor of the coaxial structure. The housing can be treated to form a good conductive path between the probe housing and the block.

[0048] pass Figure 5A In the example shown, the center probe 510 is the signal probe and the two probes 505 on either side are the ground connections of the DUT, which may be more inclined to rely entirely on the outer conductor of the coaxial feed line 520 than the signal ground. It is generally preferred if the fit of the pair of outer probes is tight (easy push fit), while the fit of the signal probe may be looser, depending on the design requirements of that section of the transmission line now involved. A tight fit can be achieved in more than one way. The upper retaining block 530 secures the housing of the contact pin assembly and cooperates with the matching lower retaining block 532, which will maintain good contact with the ground probe housing. The insulating washer 507 captures the signal probe at either end and ensures that it is insulated from the ground connection.

[0049] Figure 5B The grounding quality quickly becomes a concern, as repeated connections and disconnections cause the probe to wear as it moves in the fixture. As a result, the resistance of the grounding probe 505 becomes uncertain, generally increasing with wear. Figure 7This is shown in Figure 5. Similar effects on the signal connection probe 510 are generally less of a concern because it is often connected to a higher impedance point on the DUT and therefore has less impact. In one implementation, the operating specification requires that any ground connection must not exceed 100Ω, so the test fixture implementation requires steps to compensate for wear. The insulating washer 507 is easier to discern in this figure.

[0050] Figure 6 A cross-sectional view of an exemplary dual angle ("DA") test fixture 600 according to one embodiment of the present invention is shown when in a loaded operating position. Here, the termination board to which the signal and power lines are attached is a printed circuit board assembly 660, which is located at the lower part of the assembly. Not shown are the contact pads aligned to the contact probes 682 and their connection to the external test equipment that drives the device for testing. The lower block or retaining layer 650 can be any suitable material and is generally a composite material or plastic material that is drilled to receive the probe assembly when the probe assembly is placed into the main block 640 of the fixture. The upper block has at least one probe cavity with a hole axis 676 that is rotationally offset from the cross offset axis 678 by a certain angle. The effect of this is to make the outer housing of the probe assembly very tightly together after assembly. The offset angle is the difference between the longitudinal axis of the hole in the main block 640 and the longitudinal axis of the hole in the upper block 620, and the offset angle is approximately between 2° and 5°; for example, 2.9°.

[0051] Typically, the laminate layer 630 holding the upper retaining layer 620 is adhered to the main block and the probe assembly is simply pushed over. The laminate layer 630 may be perforated to create a hole before the probe assembly is inserted, or the laminate layer 630 may simply be pierced to simplify the probe insertion task. The DUT 610 is positioned so that it is aligned with the contact position of the fixture. As shown in FIG. Figure 4 The springs shown in FIG. 6A separate the two probes and preload them against the housing of the probe assembly, so in this unloaded state, there may be slight contact between the sides of the probes, but as the probes are loaded by positioning the test fixture against the termination plate 660, the lateral forces caused by the angled positioning of the probes cause movement toward and contact with the wall of the housing, establishing an initial contact area 689. Similarly, when the DUT 610 is pushed toward the opposing probe in the probe assembly, this actuation causes further displacement relative to the housing wall, creating additional contact area 686 and also providing inherent support for the top probe during actuation.

[0052] The resulting arrangement effectively eliminates any electrical effects of the springs within the probe assembly. In some embodiments, instead of offsetting the position between the upper block 620 and the main block 640, a selection Figure 6Angular offset as shown. This produces the same locking effect on the probe assembly and is easy to construct when tolerances are appropriate. It is worth noting that the probe assembly does not need to rely on the main block 640 for any electrical connection, and the receiving hole that accommodates the probe assembly is preferably passivated; this can be an anodizing process to obtain insulation, or if a soft conductive layer is preferred, it can be a chromic acid anodizing (alodining) process. The peripheral shell of the probe assembly can also be passivated, which may be helpful if high voltage is present.

[0053] Now turn to Figure 7 , extensive laboratory testing has been performed to verify Figure 6 The properties of the double-angle embodiment are described and its advantageous properties are recorded. Figure 1A A system was developed to test the grounding performance of implementations of the present invention using the test fixture shown in FIG. 1. The figure shows the effectiveness of grounding normalized to the best level achieved in either implementation. Thus, 100% performance is defined as that achieved by the dual angle setup of the probes in the test fixture (designated Site A). This DA probe setup uses Figure 7 678) and the hole in the upper block 620 (i.e., angle #2 676). Here, the angular change in the centerline of this implementation causes the probe to be mechanically constrained by the sides of the hole. The horizontal scale shows the number of connect-disconnect cycles applied to the test fixture, and it can be seen that at ten thousand cycles, the grounding performance has degraded by about 0.5%, but as the test continues, a slightly accelerated wear rate begins to occur.

[0054] Real world testing has shown that the acceptable limit for a specific set of tests on actual devices that triggered this critical need for special management of grounding performance is typically set at 70%. Below this, the false rejection rate is completely unacceptable. From a maintenance perspective, using a guard band indication set at 80% grounding performance to ensure accuracy of device testing, it is clear that the DA setting provides the certainty that the test is reliable. Actual verification results to the date of this submission show that performance is still acceptable after 300,000 cycles.

[0055] In contrast, the conventional fixture setup at site B, the reference setup, showed that not only was the grounding performance already at a surprisingly low level at the start of the test, nearly 6% worse than the DA setup, but that the performance degraded very quickly with use. After only 5,000 cycles, the conventional setup had already intruded into the protection space, which is usually used as an alarm for upcoming maintenance. At 10,000 cycles, performance degradation put the conventional setup on the cusp of failure, and it wasn’t long before the device was experiencing an unacceptable false rejection rate. At this point, the device manufacturer was faced with an unavoidable need for maintenance.

[0056] Repair disassembly of the test fixture removed from service, followed by a period of ultrasonic cleaning of the stripped base blocks and then reassembly, showed that some recovery of grounding performance did occur, but only to a level slightly above the guard band level, and this would probably only extend the life of the test fixture by less than an additional 10,000 cycles. The root cause is unclear, other than some contamination of the fixture, but this was greatly reduced using the DA setup and no mid-term repair treatment was required.

[0057] Although the present invention has been described in terms of several embodiments, there are variations, modifications, permutations, and alternative equivalents that fall within the scope of the present invention. For example, many modifications are possible, and the above-described features from various embodiments may be used alone or in combination. It is also contemplated that the novel features (one or more) of the above-described systems and methods may be used in non-grounded probe configurations. Although section headings are provided to help describe the present invention, these headings are illustrative only and are not intended to limit the scope of the present invention.

[0058] It should also be noted that there are many alternative ways to implement the methods and apparatus of the present invention. Therefore, it is intended that the appended claims be interpreted as including all such changes, modifications, permutations and alternative equivalents that fall within the true spirit and scope of the present invention.

Claims

1. A test probe assembly capable of being used to test a packaged integrated circuit (IC) device under test (DUT), the test probe assembly comprising: a main block having a plurality of angled main probe cavities oriented at a first acute angle to a vertical axis of the test probe assembly; an upper block having a plurality of inclined upper probe cavities oriented at a second acute angle to the vertical axis, and wherein the first acute angle and the second acute angle are offset relative to each other by a small incremental angle; a plurality of angled compressible probes configured to repeatedly maintain reliable electrical contact with a corresponding plurality of DUT contacts when under a compliant force, each of the probes having a probe barrel contained within a probe holding cavity of the probe and oppositely extending probe tips, the oppositely extending probe tips of each of the probes being capable of being depressed within the probe barrel; a lower block having a plurality of inclined cylindrical channels oriented at a third acute angle to the vertical axis; as well as The PCB has a corresponding plurality of pads, and the plurality of pads are configured to support the plurality of probes.

2. The test probe assembly of claim 1, wherein: As each of the probes is loaded by positioning the test probe assembly against a termination plate, lateral forces due to the angled positioning of each of the probes cause the probe barrel to move toward and establish initial contact with a lower region of the corresponding tilted main probe cavity, and wherein as each of the probes is further loaded by positioning the test probe assembly against the DUT toward an upper probe tip, the probe barrel further displaces toward and establishes additional contact with an upper region of the corresponding tilted main probe cavity.

3. The test probe assembly of claim 1, further comprising a laminate layer between the main block and the upper block.

4. The test probe assembly of claim 1, wherein: The plurality of compressible probes are spring probes.

5. The test probe assembly of claim 1, wherein: The plurality of compressible probes are ground probes.

6. The test probe assembly of claim 1, wherein: The small increment angle is between 2° and 5°.

7. The test probe assembly of claim 6, wherein: The small increment angle is 2.9°.

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