BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the field of integrated circuit testing. More particularly, the present invention relates to the field of coupling integrated circuit devices to test equipment for device characterization.

2. State of the Art

Development of new integrated circuit devices includes performance characterization of the devices for design integration purposes and for the publication of data sheet specifications relating to the integrated circuit device. Conventionalcharacterization of an integrated circuit device has utilized a socket or other reusable coupling device for receiving the integrated circuit device-under-characterization. However, the utilization of a socket for characterization of an integratedcircuit device introduces significant mechanical coupling to the electrical contacts of the integrated circuit device-under-test. Such an introduction of an extensive mechanical interface further introduces significant electrical impedance contributionsto the characterization process that yet requires inherent characterization of the introduced socket components. Generally, viewing an integrated circuit device through a socket in and of itself requires significant characterization of the socket. Additionally, a reusable mechanical coupling device, such as a socket, introduces further characterization variations due to the non-repeatable coupling nature resulting in inconsistent socket contact pressure and alignment as well as integrated circuitdevice pin orientation variations.

With regard to former socket characterization approaches, the semiconductor testing discipline has yet to reach a consensus on a representative test methodology for characterization of a socket. For example, some socket characterizationmethodologies utilize a shorting plate for determining the characteristic impedance of the socket while other approaches advocate an open-circuit methodology wherein the socket pins are open-circuited and electrically driven with a variable signal whilesearching for a resonant frequency from which the impedance may be calculated. Therefore, the socket impedance calculation according to accepted methodologies for socket characterization is grossly approximate at best. Therefore, it would be desirableto characterize an integrated circuit device in an environment that minimizes the introduction of extraneous impedance-contributing structures as well as providing a consistent contact characterization environment for multiple pins of a multi-pinintegrated circuit device.

BRIEF SUMMARY OF THE INVENTION

An integrated circuit characterization printed circuit board is provided for improving the uniformity of impedance introduced by a test fixture across all of the contacts or pins of an integrated circuit device. In one embodiment of the presentinvention, a printed circuit board is provided for mechanically and electrically coupling between an integrated circuit device-under-characterization and the respective test equipment. The printed circuit board includes an array of substantially similartest contacts numbering greater than the pins of the integrated circuit device. The array of test contacts includes (i) an active portion configured for electrically coupling with the corresponding pins on the integrated circuit device and (ii) aninactive portion adjacent to the active portion and electrically coupled to a reference signal on the printed circuit board.

In another embodiment of the present invention, a method for manufacturing the printed circuit board is provided by forming the structures, including the substantially similar contact pins of both the active and inactive portions. Additionally,a method of characterizing an integrated circuit device is provided including forming the printed circuit board, coupling the integrated circuit device to the printed circuit board and subjecting the combined assembly to the test equipment signals.

In yet a further embodiment, a test system for characterizing an integrated circuit is provided by electrically coupling a printed circuit board that provides uniformity of impedance to all contact pins on an integrated circuit undergoingcharacterization. The printed circuit board is electrically coupled to test equipment for the performance of a characterization test of an integrated circuit device.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the drawings, which illustrate what is currently considered to be the best mode for carrying out the invention:

FIG. 1 illustrates interrelated capacitances of an array of contact pads on a printed circuit board;

FIGS. 2A and 2B illustrate arrays of contact pads, configured in accordance with embodiments of the present invention;

FIG. 3 is a cross-sectional diagram of a printed circuit board configured for testing an integrated circuit device, in accordance with an embodiment of the present invention;

FIGS. 4 and 4A are plan views of a device-side of a PCB configured for characterizing an integrated circuit device, in accordance with an embodiment of the present invention;

FIG. 5 is a detailed cross-sectional diagram of an alignment structure for improving repeatability of alignment of an integrated circuit device with a PCB during characterization of the device, in accordance with an embodiment of the presentinvention; and

FIG. 6 is a circuit diagram including an electrical circuit for reducing the inserted impedance between an integrated circuit device-under-characterization and associated test equipment, in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a method and circuit for more closely standardizing the electrical conditions presented to pins or contacts of an integrated circuit device that is undergoing a characterization process for determining theperformance and capabilities of the integrated circuit device. As mentioned, prior approaches utilized less-repeatable coupling mechanisms (e.g., sockets) for interfacing between an integrated circuit device-under-characterization and the associatedtest equipment. The various embodiments of the present invention facilitate a more uniform environment to minimize introduced extraneous impedance components associated with providing the interface between the integrated circuit device and the testequipment.

FIG. 1 illustrates an array of contact pads on a printed circuit board (PCB), and a portion of the contact pad capacitances of representative pads, resulting from the configuration of the array. An array of contact pads 2 is illustrated as asingle combined array; however, for purposes of illustration of the associated capacitances, two individual contact pads 4, 40 of the array of contact pads 2 are illustrated with two contact pad groupings, a first group surrounding contact pad 4 and asecond group surrounding contact pad 40. FIG. 1 illustrates each of the contact pads of the array of contact pads 2 as being "active" contact pads. As used herein, "active" contact pads means pads that couple or are for coupling with correspondingpins, leads or contacts (hereinafter "pins") of an integrated circuit device. Furthermore, as used herein, "inactive" contact pads means contact pads that are present as part of the array of contact pads, but are not arranged for placement or couplingto pins of the integrated circuit device. Furthermore, as used herein, the term "integrated circuit device" includes not only memory devices but also microprocessors, signal processors and other forms of integrated circuits.

In FIG. 1, a contact pad 4 is illustrated as being surrounded by other contact pads 6 20, which are also illustrated as being active contact pads for further coupling with pins of an integrated circuit device. It is appreciated by those ofordinary skill in the art that the coupling of a PCB to an integrated circuit device for the characterization process of, for example, the capacitance associated with contact pad 4 introduces additional capacitance as seen by contact pad 4. By way ofexample, FIG. 1 illustrates capacitances 22-36 resulting from the respective adjacent orientation of contact pads 6-20, which surround active contact pad 4. Those of ordinary skill in the art appreciate that the capacitance measured at contact pad 4prior to the coupling of the integrated circuit device therewith varies significantly from the resultant capacitance as seen at active contact pad 4 once the integrated circuit device has been coupled therewith.

Similarly, active contact pad 40 of FIG. 1 is partially surrounded by other active contact pads 42-50, which exhibit respective capacitances 52-60 as seen at active contact pad 40. As illustrated, however, the capacitances as observed at activecontact pad 4 and active contact pad 40 differs significantly. Therefore, characterization of any integrated circuit device coupled therewith results in an individualized characterization of the extraneous capacitances as observed at various activecontact pads, for example, active contact pads 4 and 40. Therefore, it would be desirable to define a structure and method capable of providing a more uniform interface between an integrated circuit device-under-characterization and the respective testequipment to provide improved uniformity across the active contact pads of the array of contact pads 2.

An embodiment of the present invention provides a more uniform introduced-impedance across each of the active pads in the array of active contact pads. This uniformity improves the ability to characterize the impedance introduced by the couplingmechanism (e.g., the PCB) between the integrated circuit device and the test equipment, thereby simplifying the removal of the PCB-introduced impedance when characterizing the performance of the integrated circuit device individually, such as, forexample, for reporting in integrated circuit device data sheets.

FIGS. 2A and 2B illustrate exemplary contact pad arrangements, in accordance with embodiments of the present invention. In FIG. 2A, an array of contact pads 62 includes a group of active contact pads 64 82 configured on a PCB for coupling withcorresponding pins of an integrated circuit device. For clarity, the corresponding capacitances associated with each of the active contact pads 64 82 are not illustrated; however, they are consistent with the capacitances illustrated in FIG. 1. Arrayof contact pads 62, in accordance with one embodiment of the present invention, further includes an arrangement of inactive contact pads 84 98, separated by a hypothetical boundary illustrated as dashed line 100. Inactive contact pads 84 98 create anelectrical extension of the array of active contact pads, for purposes of consistency in the characterization process, and are further fabricated using techniques and processes reusable and consistent with the formation of active contact pads 64 82.

FIG. 2B illustrates another exemplary arrangement of an array of contact pads, in accordance with another embodiment of the present invention. An array of contact pads 102 includes an arrangement of active contact pads 104 122 and inactivecontact pads 124 158 forming an extension of the arrangement of the active contact pads, illustrated as being separated by a hypothetical boundary illustrated as dashed line 160. In the present embodiment, the geometry of the contact pads is furtherextended to simulate a more consistent arrangement and present more consistent impedance characteristics to each of the active contact pads, thereby allowing a more consistent calculation of the impedance contributions of each active pad between theintegrated circuit device and the test equipment.

FIG. 3 illustrates a test system 161 including a printed circuit board (PCB) 162 for providing the coupling interface between an integrated circuit device 164 and a characterization test equipment 166. While various packaging embodiments for anintegrated circuit device are contemplated, for illustrative purposes the present illustration depicts the integrated circuit device as including a Ball Grid Array (BGA) contact pin interface and one or more integrated circuits. Integrated circuitdevice 164 includes a BGA of active contact pins 168 configured for making electrical connection to the integrated circuits (not shown) within integrated circuit device 164.

PCB 162 includes a top or first side 170 having a corresponding array of active contact pads 172 wherein the configuration and dimension of the array of active contact pads 172 include active contact pads 174-180. The location of each of activecontact pads 174-180 corresponds to and is configured to make contact with a corresponding active contact pin 168 of integrated circuit device 164. PCB 162 may be configured as a typical multilayer circuit board, the general configuration and materialsof which are known to those of ordinary skill in the art. PCB 162 further includes active test contacts 182-188 for coupling the active contact pins 168 with the corresponding probes or contacts of test equipment 166. Active test contacts 182-188include, in addition to active contact pads 174-180, active contact vias 190-196, which are further in electrical communication with active test pads 198-204. PCB 162 includes various dielectric layers 206 and interior conductive layers 208 and 210, anexample of which includes conductive layers for VDD, VDDQ, GND or other signals. The presently illustrated number of layers is exemplary and variations in layer quantity, structure and composition are also contemplated within the scope of the presentinvention.

PCB 162, in accordance with an embodiment of the present invention, further includes inactive test contacts 212 and 214 forming an array of inactive contact pads 216 configured and fabricated as an extension to the array of active contact pads172. Each of inactive test contacts 212 and 214 includes an inactive contact pad 218 and 220, respectively, and inactive contact vias 222 and 224 further coupled to inactive test pads 226 and 228. Inactive test contacts 212 and 214 are electricallycoupled to a reference potential through a reference potential conductor 230 internally or on one or both sides of PCB 162. By coupling inactive test contacts to a reference potential, the capacitance presented to an active test contact on the peripheryof integrated circuit device 164 more closely approximates the capacitance as seen at an interior active test contact 182 188 when the internal capacitances 232 are electrically coupled with the active test contacts 182 188 and the integrated circuitdevice 164 undergoes characterization.

In yet another embodiment of the present invention, a second level of inactive test pads 234 may further extend the electrical-consistency footprint of the array of active contact pads 172 to provide even more uniform impedance characteristics toactive contact pins 168 at the periphery of integrated circuit device 164.

FIG. 4 is a plan view of the top or first side 170 of a PCB 162, in accordance with an embodiment of the present invention. By way of example and not limitation, array of contact pads 236 is configured to receive a 90-pin BGA integrated circuitdevice for testing and characterization. Array of contact pads 236 is partitioned into a first group of active contact pads 238 and a second group of inactive contact pads 240. It should be noted that inactive contact pads 240 are coupled to referencepotential conductors 230, illustrated in FIG. 4A. In the present embodiment, array of contact pads 236, both inactive and active portions, include a reference potential grid 242, which is coupled to the individual pads of an array of inactive contactpads 240 by way of reference potential conductors 230.

FIG. 4 further illustrates another embodiment of the present invention wherein a test coupon 266 is configured with an active test contact pad 268 surrounded by a corresponding number of inactive test contact pads 270 coupled to a referencepotential by way of a reference potential conductor, one of which is illustrated as reference potential conductor 272. Test coupon 266 allows characterization of the intrinsic capacitance and inductance of the specific structure and layout of the arrayof conductive pads used for characterizing the integrated circuit.

FIG. 5 is a cross-sectional diagram of an alignment structure for improving the testability of integrated circuit devices, in accordance with an embodiment of the present invention. In the present embodiment, one contact, illustrated as a BGAcontact 244, exhibits an improved alignment with PCB 246 through the utilization of a solder mask 248 as applied to the top or first surface 250 of PCB 246. As shown, solder mask 248 substantially covers the first surface 250 of PCB 246 and includes viaopenings 252 to the active contact pad 254. In the present embodiment, solder mask 248 provides a steeper profile for facilitating an improved alignment of contact 244 onto active contact pad 254. By way of example and not limitation, solder mask 248may be a dry solder mask or of other form configured to provide an improved alignment of various integrated circuit devices by reducing coupling misalignment during the coupling of an integrated circuit device to a PCB.

FIG. 6 illustrates compensating componentry, which further standardizes impedance inserted between an integrated circuit device and a tester during characterization of an integrated circuit device. It is appreciated in the testing environmentthat once test signals reach a certain frequency, inductance within the PCB begins to contribute to the measured impedance between an integrated circuit device and test equipment. For illustrative purposes, FIG. 6 depicts a typical inverter input 256 ofan integrated circuit device. During testing of an integrated circuit device, an RE input signal may be applied by test equipment at inverter input 256 with the RF input signal passing through capacitor paths 258 and 260, resulting in a series-coupledimpedance of a capacitor and an inductor in each path, which causes an increased impedance. For impedance characterization purposes, it is desirable to clamp the impedance introduced by the PCB structure during high frequency testing. In yet anotherembodiment of the present invention, a series-configured resistor 262 and a capacitor 264 are coupled between the power signals and the ground signal to counteract the effects of the inductance of the PCB during high frequency testing of the integratedcircuit device.

While the invention may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. However, it should be understood that theinvention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope thereof as defined by the following appended claims.

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