Contact mechanism cleaning

One embodiment of the present invention includes a method for reactively cleaning a contact mechanism. The method includes measuring contact resistance (CRES) associated with a plurality of electrical contacts of the contact mechanism. The method also includes generating at least one statistic of the measured CRES associated with the plurality of electrical contacts of the contact mechanism, and comparing the at least one statistic of the CRES associated with the plurality of electrical contacts of the contact mechanism with at least one CRES threshold parameter associated with an unacceptable level of CRES. The method further includes cleaning the plurality of electrical contacts of the contact mechanism based on the comparison of the at least one statistic of the CRES and the at least one CRES threshold parameter.

TECHNICAL FIELD

This invention relates to electronic circuit testing, and more specifically to systems and methods for reactively cleaning a contact mechanism.

BACKGROUND

To maintain product quality, manufacturers of semiconductor devices perform tests on their products prior to shipment to consumers. During testing, one or more devices-under-test (DUTs) are stimulated by signals from automatic test equipment (ATE) which is configured to receive and analyze the responses from the DUTs. As an example, DUTs can include dies on a wafer or integrated circuit (IC) chips. The stimuli and responses between the ATE and the DUTs are passed through interface equipment, including a contact mechanism that makes electrical contact with contact surfaces of the DUTs. By analyzing the responses of the DUTs to the stimuli, the ATE can determine whether a given DUT is to be accepted or rejected.

For example, during probe testing of a wafer, the contact mechanism can include a probe card affixed to a prober, such that the prober maneuvers a wafer to bring the contact surfaces of dies into electrical contact with needles of the probe card. As another example, during testing at a final stage of production, the contact mechanism can be a load board containing IC receptacles with contact pins, such that a handler manipulates IC chips and plugs them into the IC receptacles. Thus, a given contact mechanism, such as a probe card or a load board, is used to make electrical connections with contact surfaces of the DUTs to deliver stimuli and receive responses, respectively, between the ATE and the DUTs for a determination of whether a given DUT is to be accepted or rejected.

Contact surfaces of dies or IC chips, as well as electrical contacts of the contact mechanism may be formed from metals that can oxidize (e.g., aluminum, tin, and/or copper). As a result, the action of making contact cuts and/or scrubs through a formed oxide layer may result in the flaking-off and/or accumulation of debris. Oxides, debris from repeated contact action, moisture from the humidity controlled test environment, and/or contaminates inherent to semiconductor processes can adhere to the contact surfaces of the contact mechanism, degrading connectivity performances. Therefore, stimuli and responses between the ATE and the DUTs can become distorted, thus introducing the possibility of false negative test results. Accordingly, a semiconductor manufacturer can lose money by scrapping devices that falsely fail tests through unreliable test data measurements.

Typically, a semiconductor device manufacturer can occasionally clean the electrical contacts of the contact mechanism to remove debris and/or restore conductivity. Automated periodic cleaning may be used to clean the electrical contacts of the contact mechanism, such that user specified parameters govern when and how cleaning is to be performed. Typically, these parameters are set so as to preserve reliable test results under worst-case scenarios. Therefore, after cleaning the contact mechanism, reliable testing of the DUTs may be assured. However, cleaning too often or too aggressively can result in excessive mechanical wear of the contact surfaces of the contact mechanism. Thus, the useful life of a contact mechanism can be shortened, resulting in a need for frequent replacement at elevated testing costs.

SUMMARY

One embodiment of the present invention includes a method for reactively cleaning a contact mechanism. The method comprises measuring contact resistance (CRES) associated with a plurality of electrical contacts of the contact mechanism. The method also comprises generating at least one statistic of the measured CRES associated with the plurality of electrical contacts of the contact mechanism, and comparing the at least one statistic of the CRES associated with the plurality of electrical contacts of the contact mechanism with at least one CRES threshold parameter associated with an unacceptable level of CRES. The method further comprises cleaning the plurality of electrical contacts of the contact mechanism based on the comparison of the at least one statistic of the CRES and the at least one CRES threshold parameter.

Another embodiment of the present invention includes a functional test system. The functional test system comprises a contact mechanism configured to deliver stimuli to and obtain responses from a plurality of devices-under-test (DUTs). The contact mechanism comprises a plurality of electrical contacts. The responses can be determinative of one of acceptance and failure for each of the plurality of DUTs. The functional test system also comprises a CRES tester configured to measure CRES associated with at least one of the plurality of electrical contacts of the contact mechanism and to generate a statistical data set based on the measured CRES and at least one of the plurality of DUTs. The functional test system also comprises a data analysis system configured to generate and/or apply at least one CRES threshold parameter for the contact mechanism. The at least one CRES threshold parameter can be determinative of when to clean the contact mechanism based on at least one CRES statistic in the statistical data set.

Another embodiment of the present invention includes a functional test system. The functional test system comprises means for providing stimuli to and obtaining responses from a plurality of DUTs. The responses can be determinative of one of acceptance and failure for each of the plurality of DUTs. The functional test system also comprises means for measuring CRES associated with the means for obtaining the responses. The functional test system also comprises means for generating a statistical data set based on the calculated CRES associated with the means for obtaining the responses. The functional test system further comprises means for cleaning the means for obtaining the responses based on the statistical data set and at least one CRES threshold parameter.

DETAILED DESCRIPTION

The present invention relates to electronic circuit testing, and more specifically to a reactively cleaning a contact mechanism. A contact mechanism delivers stimuli to at least one device-under-test (DUT), and transmits corresponding responses to the stimuli from the at least one DUT to automatic test equipment (ATE). The contact mechanism can be a probe card and/or an integrated circuit (IC) receptacle that includes a plurality of electrical contacts. The DUT can be any of a variety of semiconductor devices having at least one electrical contact, such as a semiconductor die on a wafer, a printed circuit board, and/or an IC chip. Contact resistance (CRES) can be measured for a plurality of electrical contacts of the contact mechanism. For example, the ATE can measure the CRES associated with at least one pin of an IC receptacle or probe needle on a probe card.

The CRES measurements can be saved in a memory, such that a statistical data set can be generated. The statistical data set can be generated by using one or more statistical functions, algorithms, and/or techniques. One or more filtering methods may also be optionally applied while generating the statistical data set. As an example, the statistical data set can be analyzed to implement reactive and/or adaptive cleaning of the contact mechanism. As an example, at least one CRES statistic can be computed and compared with a threshold to determine when to clean the electrical contacts of the contact mechanism. As another example, the electrical contacts of the contact mechanism can also be cleaned periodically, or based on repeated failures or percentages of failures of the DUTs. The at least one CRES statistic can thus be compared with a threshold to adjust the frequency and/or aggressiveness of cleaning of the electrical contacts of the contact mechanism.

FIG. 1illustrates a functional test system10in accordance with an aspect of the invention. The functional test system10includes ATE12that is configured to generate stimuli for and receive responses from a set of DUTs, demonstrated in the example ofFIG. 1as a DUT set14. The responses can be determinative of acceptance or failure of a given DUT of the DUT set14based on the stimuli provided to the DUT. To provide the stimuli to the DUT set14, the ATE12utilizes a contact mechanism16. For example, the ATE12and the contact mechanism16can be electrically coupled, such that the contact mechanism16can provide electrical connection between the ATE12and the DUT set14. Thus, the ATE12can generate the stimuli and apply it to a given DUT of the DUT set14via the contact mechanism16. In addition, the ATE12can receive the responses from the given DUT of the DUT set14via the contact mechanism16. The ATE12can analyze the responses to determine whether the given DUT of the DUT set14should be accepted or rejected.

In the example ofFIG. 1, the functional test system10includes a prober/handler18. The ATE12provides commands to the prober/handler18via a prober/handler controller20that instructs the prober/handler18to index between the DUTs in the DUT set14for testing. The ATE12can also provide commands to the prober/handler18via the prober/handler controller20of when and how to clean the contact mechanism16, as demonstrated in greater detail below. Stimuli from the ATE12and corresponding responses from the DUT set14are passed via the electrical connections provided by the contact mechanism16. As an example, the DUT set14can include an IC set22that includes a plurality of IC chips on a rack, such that the contact mechanism16is a load board with one or more IC receptacles. As such, for example, the ATE12can control a handler18to retrieve one or more IC chips from the rack and insert them into IC receptacles, upon which the ATE12can provide stimuli to and obtain responses from the inserted one or more IC chips in the DUT set14via the electrical connections of the contact mechanism16. As another example, the DUT set14can include a plurality of dies on a wafer24, such that the contact mechanism16is a probe card. As such, for example, the ATE12can control a prober18to position the dies such that their contact surfaces are in electrical contact with the pins of the probe card, upon which the ATE12can generate the stimuli and obtain the responses via the electrical connections of the contact mechanism16. Therefore, it is to be understood that the prober/handler18is intended to represent either a prober or a handler in the example ofFIG. 1, depending on the types of DUTs in the DUT set14.

Through the repetitive action of testing DUTs in the DUT set14, the electrical contacts of the contact mechanism16can be repeatedly and/or continuously exposed to contaminates. For example, the contaminates can stem from such sources as humidity, semiconductor process contaminates, and/or debris generated by the cutting and/or scrubbing action resulting from the contacting process itself. The repeated and/or continuous exposure can result in accumulation of the contaminates on the electrical contacts of the contact mechanism16. Through the repeated contact of the contact mechanism16with the DUTs in the DUT set14, aggravated by vibration and electrical current flow, CRES of the electrical contacts of the contact mechanism16increases as conductivity degrades. Increased amounts of CRES can result in distortion of the stimuli generated by the ATE12, improper responses to the stimuli by the DUTs in the DUT set14, and/or inaccurate measurements of the responses by the ATE12. To avoid or eliminate this degradation, the electrical contacts of the contact mechanism16can be cleaned.

The prober/handler controller20can be configured to clean the contact mechanism16via a contact cleaning mechanism26. For example, the ATE12can command a prober to move the contact cleaning mechanism26to the contact mechanism16, such that the contact cleaning mechanism26cleans one or more of the electrical contacts of the contact mechanism16. As another example, the ATE12can command a handler to mechanically move the contact cleaning mechanism26to the contact mechanism16(e.g., IC receptacle), such that the contact cleaning mechanism26cleans one or more of the electrical contacts of the contact mechanism16. In addition, the contact cleaning mechanism26can be invoked manually, such that the ATE12provides an indication to an operator of the functional test system10that a cleaning of the contact mechanism16is necessary. Thus, the operator can invoke a cleaning event of the contact mechanism16, or perform a manual cleaning of the contact mechanism16, in response to the indication.

The functional test system10includes a CRES tester28. The CRES tester28is configured to obtain CRES data associated with the electrical contacts of the contact mechanism16. As an example, the CRES tester28can provide commands to the ATE12to obtain CRES data for a given DUT of the DUT set14. For example, the ATE12can send specific CRES stimuli to a given DUT in the DUT set14and receive a response from the given DUT. From the stimuli and response data, CRES may be computed. The measurement of CRES can be at regular intervals, for example, based on the testing of DUTs, such as a measurement of CRES once for every one hundred DUTs in the DUT set14. As another example, the commands to the ATE to measure CRES can be at regular intervals based on elapsed time, such as a measurement of CRES once every hour. The commands to the ATE12to measure CRES can also be event driven, such that CRES can be measured for the contact mechanism16upon startup of the functional test system10, upon receiving a new DUT set14, and/or upon one or more of the DUTs in the DUT set14failing based on received responses to stimuli.

In addition to obtaining the CRES for one or more of the electrical contacts of the contact mechanism16, the CRES tester28can also include a CRES data storage30. The CRES data storage30can be a memory, or can be a software based file, such as a database or spreadsheet. The CRES data storage30can be implemented to generate one or more statistics associated with the CRES data for the one or more electrical contacts of the contact mechanism16. The one or more statistics of the CRES data for the electrical contacts of the contact mechanism16can be compiled as a statistical data set that can be based on CRES measurements across one or more of the DUTs in the DUT set14.

As an example, the statistical data set of the CRES data storage30can include an aggregate measurement of the CRES associated with the electrical contacts of the contact mechanism16. For example, the statistical data set can include a mean value of the CRES, such as a moving average of the CRES associated with at least one of the electrical contacts of the contact mechanism16for at least some of the DUTs of the DUT set14, and/or a moving average of the CRES for at least some of the electrical contacts of the contact mechanism16across at least one of the DUTs in the DUT set14. As another example, the statistical data set can include standard deviation values of the CRES data, such as a standard deviation value of the CRES data associated with at least one of the electrical contacts of the contact mechanism16for at least some of the DUTs of the DUT set14, and/or a standard deviation value of the CRES data for at least some of the electrical contacts of the contact mechanism16across at least one of the DUTs in the DUT set14. Furthermore, the statistical data set can also include computational composite usage, such as an upper percentile statistical value minus a mean or median value to normalize data within the statistical data set.

The functional test system10also includes a CRES data analyzer32. The CRES data analyzer32is configured to access the statistical data set for a determination of when to clean the electrical contacts of the contact mechanism16. The CRES data analyzer32can include at least one CRES threshold parameter34. As an example, the ATE12can be configured to reactively clean the contact mechanism16. Thus, the CRES threshold parameter34can be a CRES value that is undesirable for one or more of the electrical contacts of the contact mechanism16. As such, the CRES threshold parameter34can be a value that signals a need to clean one or more of the electrical contacts of the contact mechanism16upon the one or more of the electrical contacts of the contact mechanism16having exceeded the CRES threshold parameter34. As another example, the ATE12can be configured to adaptively clean the contact mechanism16. Thus, the CRES threshold parameter34can be analyzed to determine if an adjustment to the frequency and/or aggressiveness of cleaning of the contact mechanism16is needed. For example, based on the CRES threshold parameter34, the ATE12can determine that the contact mechanism16needs to be cleaned more often than a preset frequency of cleaning.

In the example of a reactive cleaning configuration, the CRES threshold parameter34can include at least one CRES threshold value that, upon the measured CRES of one of the electrical contacts of the contact mechanism16exceeding the at least one CRES threshold value, the CRES data analyzer32can command the prober/handler controller20to clean the contact mechanism16. As an example, the CRES data analyzer32can analyze the statistical data set in the CRES data storage30to determine ideal CRES threshold values for at least one of the electrical contacts of the contact mechanism16, such that the CRES threshold parameter34includes individually adjustable CRES threshold values for at least one of the electrical contacts of the contact mechanism16. As such, the CRES data analyzer32can command the prober/handler controller20to clean the electrical contacts of the contact mechanism16upon the measured CRES of one or more of the electrical contacts exceeding its respective CRES threshold value, or exceeding a CRES threshold parameter34that is an average CRES threshold value based on the individually adjustable CRES threshold values.

As yet another example, the CRES data analyzer32can prompt cleaning of the electrical contacts of the contact mechanism16upon the mean value of the measured CRES of the electrical contacts exceeding a given CRES threshold value in the CRES threshold parameter34. As such, the ATE12may continue to test DUTs of the DUT set14even when some of the electrical contacts of the contact mechanism16have CRES values that exceed their respective threshold values. In addition, the CRES data analyzer32can include standard deviation information from the statistical data set in evaluating mean value of the measured CRES for a determination of when to clean the contact mechanism16. Furthermore, as the CRES threshold parameter34is adjustable, and may not be representative of all undesirable CRES data scenarios, the contact mechanism16can be cleaned based on a consistent determination of failure of a subset of the DUT set14based on the test data. For example, upon five consecutive failures of DUTs in the DUT set14based on the obtained test data, the contact mechanism16can be cleaned. It is therefore to be understood that the CRES data analyzer32can be configured in any of a variety of ways to invoke a cleaning of the contact mechanism16based on the CRES threshold parameter34and the statistical data set of the CRES data stored in the CRES data storage30.

In the example of an adaptive cleaning configuration, the contact mechanism16can be cleaned at periodic intervals, such as based on testing a predetermined number of DUTs in the DUT set14, or such as based on a predetermined amount of time. The CRES threshold parameter34can include at least one CRES threshold value that can be consulted at the conclusion of the predetermined periodic interval. The CRES data analyzer32can adjust the frequency and/or aggressiveness of the cleaning of the contact mechanism16based on a comparison of the measured CRES and the at least one CRES threshold value. For example, if the measured CRES of one or more of the electrical contacts of the contact mechanism16exceeds the at least one CRES threshold value, the CRES data analyzer32can reduce the predetermined periodic interval, such that the contact mechanism16can be cleaned more often. As another example, if the measured CRES of one or more of the electrical contacts of the contact mechanism16exceeds the at least one CRES threshold value, the CRES data analyzer32can adjust cleaning parameters associated with the contact cleaning mechanism26, such that the contact mechanism16is cleaned more thoroughly (e.g., additional scrubbing per clean, more cleaning overtravel, etc.).

If the measured CRES of one or more of the electrical contacts of the contact mechanism16is less than the at least one CRES threshold value, the CRES data analyzer32can increase the predetermined periodic interval, such that the contact mechanism16can be cleaned less often. As another example, if the measured CRES of one or more of the electrical contacts of the contact mechanism16is less than the at least one CRES threshold value, the CRES data analyzer32can adjust cleaning parameters associated with the contact cleaning mechanism26, such that the contact mechanism16is cleaned less thoroughly. As such, the at least one CRES threshold value can be set such that the timing of the cleaning the contact mechanism16is optimized, such that the contact mechanism16cleaned at the appropriate frequency and/or aggressiveness, thus extending the operable life of the contact mechanism16.

As yet another example, the CRES threshold parameter34can include two or more CRES threshold values that represent a range of acceptable values of measured CRES values for a given periodic testing interval and/or cleaning configuration. Thus, the frequency and/or aggressiveness of cleaning of the contact mechanism16can be increased if the measured CRES values are above the range, and the frequency and/or aggressiveness of cleaning of the contact mechanism16can be decreased if the measured CRES values are below the range. In addition, the one or more CRES threshold values representative of an acceptable range of measured CRES values can be compared with a mean value of the measured CRES. The CRES data analyzer32can also include standard deviation information from the statistical data set in evaluating the mean value of the measured CRES for a determination of how to adjust the frequency and/or aggressiveness of cleaning the contact mechanism16. It is therefore to be understood that the CRES data analyzer32can be configured in any of a variety of ways for the adaptive cleaning of the contact mechanism16based on the CRES threshold parameter34and the statistical data set of the CRES data stored in the CRES data storage30.

It is to be understood that the functional test system10is not intended to be limited by the example ofFIG. 1. For example, the contact mechanism16is not limited to a specific type of probe card or IC receptacle, but may include any of a variety of contact mechanisms that use a probe needle, Pogo Pin®, fuzz button, cobra needle, membrane pin, and/or any other means of making electrical connection. In addition, the DUT set14can include printed circuit boards (PCBs), and is thus not limited to dies on a wafer or IC chips. One or more components of the functional test system10can be integrated together, and/or subcomponents (e.g., the CRES data storage30) can be separated from components in which they are included. In addition, the functional test system10is not limited to implementing one of reactive cleaning and adaptive cleaning of the contact mechanism16, but can instead implement all of or selected elements of both reactive and adaptive cleaning configurations. Therefore, any of a variety of modifications are possible in the example ofFIG. 1.

FIG. 2illustrates another example of a test system50in accordance with an aspect of the invention. The test system50includes a CRES tester52that is configured to measure CRES associated with one or more electrical contacts of a contact mechanism56. In the example ofFIG. 2, the DUT54is demonstrated as an IC chip having sixteen pins58. However, it is to be understood that the DUT54can be any of a variety of semiconductor devices, such as a die on a wafer. In addition, the DUT54is demonstrated as having sixteen pins58for the sake of simplicity, but that it is to be understood that the DUT54can be an IC having any shape, size, or number of pins. The DUT54can be one of several DUTs in the DUT set14in the example ofFIG. 1. As such, reference will be made to the example ofFIG. 1in the following discussion of the example ofFIG. 2. In addition, in the example ofFIG. 2, the CRES tester52is demonstrated as directly coupled to the contact mechanism56. However, it is to be understood that the CRES tester52could be coupled to the contact mechanism56via ATE, such as demonstrated in the example ofFIG. 1, and that the CRES tester52could be included in the ATE itself.

The contact mechanism56is demonstrated in the example ofFIG. 2as an IC receptacle with a plurality of pin sockets60, each of the pin sockets60corresponding to one of the pins58of the DUT54. The CRES tester52can be communicatively coupled to each of the pin sockets60of the contact mechanism56, such that the CRES tester52can generate test signals to be applied to one or more of the pin sockets60of the contact mechanism56. In the example ofFIG. 2, the CRES tester52is demonstrated as coupled to the contact mechanism56at two of the pin sockets60. However, it is to be understood that the CRES tester52could be coupled to one or more of the other sixteen pin sockets60to obtain the CRES data for the respective one or more of the pin sockets60. Specifically, the CRES tester52is coupled to the pin socket60coupled to a ground pin GND of the DUT54and to the pin socket60that is coupled to pin1of the DUT54. In the example ofFIG. 2, the test system50includes a resistor61having a resistance value of RCRES. The resistor61is representative of the CRES value (e.g., RCRES) of the pin socket60associated with pin1of the DUT54. It is to be understood that the CRES value of the pin socket60of the ground pin GND may be negligible, as the DUT54and the contact mechanism56may include several parallel ground connections. The DUT54includes an internal electro-static discharge (ESD) diode62interconnecting the ground pin GND and pin1of the DUT54, with an anode coupled to the ground pin GND and a cathode coupled to pin1. It is to be understood that, despite the example ofFIG. 2demonstrating the ESD diode62interconnecting pin GND and pin1, any of a variety of conductive, resistive, and/or other circuit structures that can be measured for a conductive, resistive, and/or impedance path can be implemented in the example ofFIG. 2, such that the path could include, for example, resistive, capacitive, and/or inductive components.

The CRES tester52includes a fixed signal generator64and a signal meter66. The fixed signal generator64can be configured to output one or more signals having fixed values for current or voltage. As such, the signal meter66can be configured to input a received signal and measure an amount of voltage or current, respectively. In the example ofFIG. 2, the fixed signal generator64is demonstrated as having a first current source63configured to provide a constant current I1and a second current source65configured to provide a constant current I2. The signal meter66is thus demonstrated in the example ofFIG. 2to measure a first voltage V1that is associated with the first constant current I1and a second voltage V2that is associated with the second constant current I2, as is explained in greater detail below. It is to be understood that the fixed signal generator64and the signal meter66could be oppositely configured as to that demonstrated in the example ofFIG. 2. For example, the fixed signal generator64could instead be configured to provide one or more separate fixed voltages, such that the signal meter is instead configured to measure one or more current flows based on the fixed voltages.

For the CRES tester52to determine a resistance value RCRESof the pin socket60associated with pin1of the DUT54, the fixed signal generator64applies the first constant current I1from the first current source63. The first constant current I1forces a current flow through the ESD diode62. In the example ofFIG. 2, the first constant current I1can be considered a negative current, as the first constant current I1flows to ground. As such, the first constant current I1applied to the conductive or resistive path through the ESD diode62causes a resulting voltage V1at pin1that is negative relative to ground. Therefore, current is pulled from ground, through the ground pin GND, through the ESD diode62, and through pin1. The signal meter66measures the value of the resulting voltage V1. It is to be understood that the value of the first constant current I1can be chosen to provide a value for the voltage V1that is sufficient to bias the ESD diode62adequately for operation in a substantially linear region, as opposed to a substantially unstable region at or near an activation voltage associated with the ESD diode62.

It is to be understood that the voltage/current response of the ESD diode62may not be perfectly linear. As such, upon the signal meter66measuring the first voltage V1, the fixed signal generator64may deactivate the first current source63and activate the second current source65to provide the second constant current I2, which could be different from the first constant current I1. Thus, a separate current is forced through the ESD diode62, and the signal meter66measures the second voltage V2at pin1of the contact mechanism56. It is to be understood that the activation of the first current source63and the second current source65may not be mutually exclusive, but that one of two constant currents can be provided to generate the first voltage V1by concurrently activating both the first current source63and the second current source65. As such, one of the first current source63and the second current source65can be deactivated or changed to provide the other of the two constant currents to generate the second voltage V2.

The CRES tester52also includes a CRES data calculator68. The CRES data calculator68can be configured to calculate the CRES value RCRESfor the socket pin60that is coupled to pin1of the DUT54. For example, as the values for the first constant current I1, the second constant current I2, the first measured voltage V1and the second measured voltage V2are known, the resistance RCREScan easily be calculated for the socket pin60coupled to pin1of the DUT54. As an example, the CRES data calculator can divide the difference of the first measured voltage V1and the second measured voltage V2by the difference of the first constant current I1and the second constant current I2to calculate RCRES. It is to be understood that such a calculation can include other resistance values, such as resistances associated with the ESD diode62, connecting electrical conductors, the CRES tester52, and the DUT54. However, these resistance values can be known values, and thus can be subtracted from a calculated resistance to determine the CRES value RCRES. In addition, because both the first measured voltage V1and the second measured voltage V2are voltages sufficient to bias the ESD diode62in a substantially linear region, the calculated value for RCREScan be a substantially linear approximation of the CRES value associated with the pin socket60coupled to pin1of the DUT54. It is to be understood that the CRES tester52can perform a similar operation for one or more additional pin sockets60of the contact mechanism56to obtain a separate CRES value RCRESfor each of the one or more additional pin sockets60.

The CRES tester52also includes a CRES data storage70. The CRES data storage70can be a memory, or can be a software based file, such as a database or spreadsheet. The CRES data storage70can be implemented to store the calculated CRES values RCRESfor each of the measured pin sockets60of the contact mechanism56. In addition, the CRES data storage70can be configured to generate one or more statistics associated with the calculated CRES values for the one or more pin sockets60of the contact mechanism56. The one or more statistics of the CRES data for the one or more pin sockets60of the contact mechanism56can be compiled as a statistical data set. As an example, the statistical data set of the CRES data stored in the CRES data storage70can include aggregate measurements of the CRES associated with the pin sockets60of the contact mechanism56. For example, the statistical data set can include a mean value of the CRES data, such as a moving average of the CRES associated with the one or more pin sockets60of the contact mechanism56for the DUT54, and/or a moving average of the CRES for each of the one or more pin sockets60of the contact mechanism56across a plurality of DUTs54.

In a reactive cleaning configuration, the CRES tester52, or a CRES data analyzer (not shown), such as the CRES data analyzer32in the example ofFIG. 1, can determine whether the calculated CRES value is acceptable to continue testing additional DUTs or whether one or more of the pin sockets60of the contact mechanism56needs to be cleaned. Such a determination can also be made based on a determination of a failure of the DUT54as determined by ATE (not shown), such as the ATE12in the example ofFIG. 1, such that the CRES value can be calculated upon a determination of failure. In an adaptive cleaning configuration, the CRES tester52or a CRES data analyzer can determine whether the calculated CRES value is within an acceptable range of one or more CRES threshold values for a given periodic testing interval for a set of the DUTs54and/or set of cleaning configuration parameters. Thus, the frequency and/or aggressiveness of cleaning can be increased or decreased based on the measured CRES values relative to the one or more CRES threshold values.

It is to be understood that the test system50is not limited to the example ofFIG. 2. For example, the fixed signal generator64is not limited to two current sources, but can include more or less current sources, or can incorporate one or more voltage sources, to provide fixed signals to measure CRES. In addition, voltage and/or current measurements are not limited to measurements made associated with an ESD diode, such as the ESD diode62. Furthermore, the DUT54is not limited to including a single ESD diode62, but can include any of a variety of combinations of ESD diodes and other ESD protection devices, such that other signal measurements can be made to obtain CRES for the pin sockets60of the contact mechanism56.

In view of the foregoing structural and functional features described above, certain methods will be better appreciated with reference toFIG. 3. It is to be understood and appreciated that the illustrated actions, in other embodiments, may occur in different orders and/or concurrently with other actions. Moreover, not all illustrated features may be required to implement a method. It is to be further understood that the following methodologies can be implemented in hardware (e.g., a computer or a computer network), software (e.g., as executable instructions running on one or more computer systems), or any combination of hardware and software.

FIG. 3illustrates an example of a method100for reactively cleaning a contact mechanism in accordance with an aspect of the invention. At102, tests are performed on a set of DUTs via ATE. The tests can include stimuli generated by the ATE and provided to the set of DUTs via a contact mechanism, such that the ATE can receive responses from the set of DUTs based on the stimuli via the contact mechanism. The responses can be determinative of one of acceptance and failure of the at least one DUT. At104, CRES data associated with a plurality of electrical contacts of the contact mechanism and/or the set of DUTs is accumulated. The measured CRES can be accumulated by the ATE or by a dedicated CRES tester. In addition, the accumulated CRES data can be measured and/or calculated at regular intervals, such as based on a number of tested DUTs or based on regular intervals of time. Alternatively or additionally, the measurement or calculation of CRES can also be event driven, such that CRES data can be determined for the contact mechanism upon a given DUT failing based on measured test data, or can be measured upon startup of the test system.

At106, a statistical data set is generated based on the accumulated CRES data. The statistical data set can be based on CRES that is measured over a plurality of DUTs. The statistical data set can include mean values of the CRES data, such as a moving average of the CRES data associated with at least a portion of the electrical contacts of the contact mechanism for at least some of the plurality of DUTs, and/or a moving average of the CRES data for at least one electrical contact of the contact mechanism across the plurality of DUTs. The statistical data set can also include standard deviation values of the CRES data, such as a standard deviation value of the CRES data associated with at least some of the electrical contacts of the contact mechanism for at least some of the plurality of DUTs, and/or a standard deviation value of the CRES data for at least one electrical contact of the contact mechanism across the plurality of DUTs. The statistical data set can be stored in a CRES data storage, which can be a memory device or a software file.

In the example ofFIG. 3, reference numbers108and110refer to a reactive cleaning configuration. At108, the statistical data set is analyzed to determine if at least one CRES statistic exceeds a respective CRES cleaning threshold parameter. The CRES threshold parameter can include at least one value, such that it can apply to one or more of the individual electrical contacts of the contact mechanism, or can be applied to the mean value of the CRES data of the electrical contacts. The CRES threshold parameter can also be a plurality of values, one corresponding to one or more of the electrical contacts of the contact mechanism, such that the CRES threshold parameter is individually adjustable for one or more of the electrical contacts of the contact mechanism. At110, the contact mechanism is cleaned upon the at least one statistic of the statistical data set exceeding the at least one CRES threshold parameter. For example, the at least one statistic could be an average value of the CRES data of at least some of the electrical contacts relative to a CRES threshold, or a threshold number of electrical contacts exceeding a CRES threshold that is an average of the individual CRES thresholds for at least some of the electrical contacts of the contact mechanism.

In the example ofFIG. 3, reference numbers112and114refer to an adaptive cleaning configuration. At112, the statistical data set is analyzed to determine if at least one CRES statistic is within a range of acceptable values. The range of acceptable values can be a range of acceptable measured CRES values for a given periodic testing interval and/or a cleaning configuration associated with aggressiveness of cleaning. The periodic testing interval can be a time interval between periodic cleaning of the contact mechanism or can be a number of DUTs that are tested between cleanings of the contact mechanism. The cleaning configuration associated with aggressiveness of cleaning can include parameters associated with the cleaning operation of the contact mechanism, such as a number of contacts of the contact mechanism with a cleaning surface, a length of contact of the contact mechanism along the cleaning surface, or duration of contact of the contact mechanism with the cleaning surface. At114, the cleaning frequency and/or aggressiveness of cleaning associated with the DUTs is adjusted based on the at least one CRES statistic. The cleaning frequency and/or aggressiveness can be increased based on the at least one CRES statistic being greater than the range of acceptable values, and the cleaning frequency and/or aggressiveness can be decreased based on the at least one CRES statistic being less than the range of acceptable values. It is to be understood that, in the example ofFIG. 3, the method is not limited to implementing just one of reactive cleaning and adaptive cleaning, but can instead implement all of or selected elements of both the reactive and the adaptive cleaning configurations

FIG. 4illustrates an example of a computer system150that can be employed to implement systems and methods described herein, such as based on computer executable instructions running on the computer system. The computer system150can be implemented on one or more general purpose networked computer systems, embedded computer systems, routers, switches, server devices, client devices, various intermediate devices/nodes and/or stand alone computer systems. Additionally, the computer system150can be implemented as part of a network analyzer or associated design tool running computer executable instructions to perform methods and functions, as described herein.

The computer system150includes a processor152and a system memory154. A system bus156couples various system components, including the system memory154to the processor152. Dual microprocessors and other multi-processor architectures can also be utilized as the processor152. The system bus156can be implemented as any of several types of bus structures, including a memory bus or memory controller, a peripheral bus, and a local bus using any of a variety of bus architectures. The system memory154includes read only memory (ROM)158and random access memory (RAM)160. A basic input/output system (BIOS)162can reside in the ROM158, generally containing the basic routines that help to transfer information between elements within the computer system150, such as a reset or power-up.

The computer system150can include a hard disk drive164, a magnetic disk drive166, e.g., to read from or write to a removable disk168, and an optical disk drive170, e.g., for reading a CD-ROM or DVD disk172or to read from or write to other optical media. The hard disk drive164, magnetic disk drive166, and optical disk drive170are connected to the system bus156by a hard disk drive interface174, a magnetic disk drive interface176, and an optical drive interface184, respectively. The drives and their associated computer-readable media provide nonvolatile storage of data, data structures, and computer-executable instructions for the computer system150. Although the description of computer-readable media above refers to a hard disk, a removable magnetic disk and a CD, other types of media which are readable by a computer, may also be used. For example, computer executable instructions for implementing systems and methods described herein may also be stored in magnetic cassettes, flash memory cards, digital video disks and the like. A number of program modules may also be stored in one or more of the drives as well as in the RAM160, including an operating system180, one or more application programs182, other program modules184, and program data186.

A user may enter commands and information into the computer system150through user input device140, such as a keyboard, a pointing device (e.g., a mouse). Other input devices may include a microphone, a joystick, a game pad, a scanner, a touch screen, or the like. These and other input devices are often connected to the processor152through a corresponding interface or bus142that is coupled to the system bus156. Such input devices can alternatively be connected to the system bus156by other interfaces, such as a parallel port, a serial port or a universal serial bus (USB). One or more out device(s)144, such as a visual display device or printer, can also be connected to the system bus156via an interface or adapter146.

The computer system150may operate in a networked environment using logical connections148to one or more remote computers150. The remote computer148may be a workstation, a computer system, a router, a peer device or other common network node, and typically includes many or all of the elements described relative to the computer system150. The logical connections148can include a local area network (LAN) and a wide area network (WAN).

When used in a LAN networking environment, the computer system150can be connected to a local network through a network interface152. When used in a WAN networking environment, the computer system150can include a modem (not shown), or can be connected to a communications server via a LAN. In a networked environment, application programs182and program data186depicted relative to the computer system150, or portions thereof, may be stored in memory154of the remote computer150.

By way of further example, the application programs182can include executable instructions programmed to measure and accumulate CRES data for one or more contact mechanisms associated with a test system, such as the functional test system10in the example ofFIG. 1and/or the test system50in the example ofFIG. 2. For instance, the application programs can include executable instructions that measure CRES by forcing a fixed signal and measuring a voltage potential or a current flow associated with an ESD diode of a given DUT. The instructions can access DUT responses and/or test data (e.g., stored in a drive or RAM160of the computer150or memory154of a remote computer) to determine when to measure CRES or when to clean the contact mechanism based on events and/or consecutive failures of DUTs based on obtained responses. The instructions can also calculate a statistical data set of CRES data obtained for the electrical contacts of the contact mechanism over a plurality of DUTs, such as described herein. The instructions can analyze the statistical data set and can determine one or more CRES threshold parameters with which one or more statistics associated with the statistical data set can be compared. Upon determining CRES data, CRES threshold parameters, and/or statistics in the statistical data set generated based on the CRES data, the application programs182can display them to the user via the output device144, and/or employ the data in different application programs, which may be running on the computer system150or the remote computer150. As an example, the instructions can then provide a signal to an automatic test system to clean the contact mechanism, or can provide an indication to an operator via the output device144to clean the contact mechanism. As another example, the instructions can adjust a frequency and/or aggressiveness of cleaning of the contact mechanism.