Abstract:
An integrated circuit package test station supports an integrated circuit package under test in a vertical orientation thereby allowing simultaneous access to both sides of the package. Probe assemblies are utilized on both sides of the package to increase the accuracy, efficiency, and simplicity of performing electrical characterization of the IC package. The IC package holder as well as the probe assemblies are adjustably positioned to allow accurate and precise measurements of through-package electrical characteristics. To aid in positioning the test equipment, a dual-display image magnification system is used which provides images from both sides of the IC package simultaneously.

Description:
FIELD OF THE INVENTION 
     The present invention relates to integrated circuit (IC) package testing and more particularly, to testing the electrical characteristics of an IC package and its interconnect structures. 
     BACKGROUND OF THE INVENTION 
     Predicting the performance of high speed integrated circuits requires accurate measurements of the electrical characteristics of the package and the interconnect structures which interface both the integrated circuit with the package and the package with an external board. Typically, time domain reflectometry and network analysis measurements are performed to characterize the electrical performance of the package which can dominate the performance limits of high speed integrated circuits. 
     Electrical characteristics of packages, which are frequently the subject of measurement, include cross-coupling with neighboring lines, spectral dispersion, electrical resonances, and loss by radiation into the surrounding dielectric. 
     The measuring stations of the prior art are traditionally constructed to support a package under test in a horizontal position. This arrangement provides direct physical access to only a single side of the package. Simultaneous access to both sides of a package is unavailable in these test stations. Looping fixtures are often required to achieve through-package electrical characterization. Also, specially constructed mounting cards are sometimes used which not only hold a package but also attempt to provide all connections on the top of the card for easy physical access and probing. The use of looping fixtures and other package mounting cards introduce effects into the measurement data which are not due to the package or its interconnects. These effects must, themselves, be determined and either compensated for or modeled into the final analysis of the data. Regardless, of how they are handled, these effects degrade both the efficiency and accuracy of the resulting package electrical characterization. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the needs for a method and apparatus to measure the electrical characteristics of an integrated circuit package in an efficient, precise and accurate manner. 
     The integrated circuit package test station of the present invention supports an integrated circuit package under test in a vertical orientation thereby allowing simultaneous access to both sides of the package. Probe assemblies are utilized on both sides of the package to increase the efficiency and simplicity of performing electrical characterization of the integrated circuit package. The integrated circuit package support as well as the probe assemblies are adjustably positioned to allow accurate and precise measurements of through-package electrical characteristics. To aid in positioning the test equipment, a dual-display image magnification system is used in certain embodiments which provides images of both sides of the IC package simultaneously. 
     The needs are also met by embodiments of the present invention which provide an electrical characterization of an IC package based on measurements from a first probe assembly which electrically probes a first side of an IC package and a second probe assembly which electrically probes a second side of the IC package, and a vertical package holder which supports the IC package in a substantially vertical orientation to allow simultaneous access to the first and second sides of the IC package. 
     The needs are further met by embodiments of the present invention which probe an IC package by supporting the IC package vertically wherein a first and second side of the IC package is simultaneously accessible, probing the first side of the IC package, probing the second side of the IC package, and determining an electrical characterization of the IC package based on the probing of both sides. 
     The foregoing features, as well as other aspects and advantages, of the present invention, will become more apparent from the following detailed description, claims and drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates an IC device for which an embodiment of the present invention performs testing. 
     FIG. 2 illustrates an exemplary flip-chip die footprint. 
     FIG. 3 illustrates a high-performance electrical probe used in certain embodiments of the present invention. 
     FIG. 4 illustrates a test apparatus arrangement according to an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A typical IC device  100 , as depicted in FIG. 1, include s a plurality of pins  102 , or other connectors, for electrically coupling the device  100  to a circuit board. The device  100  also includes a package substrate  104 , die  106 , and solder bumps, pads or pins  108  for connecting signal pads (not shown) of the die  106  to traces (not shown) on the substrate  104  and ultimately to the pins  102 . A lid  110  seals and protects the die  106  and its connections  108  to the substrate  104 . The region between the lid  110  and the substrate  104  may be filled with a resin or similar material for its protective and thermal properties. 
     The IC device  100  depicted in FIG. 1 is particularly known as a flip-chip arrangement. This arrangement of interconnections is typically used far IC dies having too many signal, or I/O, pads to be arranged along the die edges. Instead, the I/O pads are arranged on the die in an array, as depicted in FIG. 2, and solder bumps are formed on the pads. The die is then inverted and positioned on a matching array on the package substrate (FIG. 1,  104 ) and the solder bumps are reflowed. 
     A more traditional IC package positions the die face up on the package substrate and uses bonding wires to connect I/O pads on the die to corresponding pads on the substrate. 
     The present invention contemplates flip-chip package arrangements as well as more traditional arrangements within its scope. In either type of arrangement, the package and the interconnects between the die and the package affect the ultimate performance of an IC device utilizing the package. Therefore, an electrical characterization of the package is desirable. Within a package, the pins or connections  102  are connected through to the opposite side of substrate  104  where they are available for connection to the die  106 . Like all transmission lines, these interconnections attenuate and distort the signals to and from the die  106 . The electrical characterization of a package includes determining the characteristics of the package&#39;s interconnections in order to evaluate how they will impact the performance of an IC device using that package. 
     The electrical characterization of an IC package encompasses a number of measurements. One representative method involves injecting a signal at an I/O pad on the package substrate (FIG. 1,  104 ) and measuring the signal reflection and transmission characteristics. This method allows impedance and reactance measurements of an interconnect to be performed at high frequencies as well as DC voltage levels. Other methods involve measuring the effect of the injected signals on nearby interconnects. These methods allow the cross-coupling between interconnects due to mutual impedance and capacitance to be measured. Either of these methods can be performed on multiple interconnects simultaneously or only on a single interconnect. 
     FIG. 3 depicts an exemplary probe  300  used to measure the electrical characteristics of an IC package. In one embodiment of the present invention, the probe  300  is a precision, controlled-impedance transmission line probe as is known in the art. At the end of the planar region  302  are multiple contacts  304  which communicate with selected pads and terminals of an IC package under test. The contacts  304  in this embodiment illustrate an exemplary arrangement of a signal contact between two grounds contacts. This arrangement allows the same probe, with minor positional adjustments, to be either a signal or ground connection. 
     Because of the typical scale of integrated circuit packages, micro-manipulators are employed to precisely position the probe  300  and its planar region  302  in relation to a package under test. Similarly, a package is sometimes socketed on a test card with contacts specifically shaped to match the shape of a probe&#39;s contact  304 . Both these aids for performing electrical characterization of IC packages are useful in particular embodiments of the present invention. 
     FIG. 4 depicts a test station  400  according to an embodiment of the present invention. A base  402  supports two vertical platens  410   a  and  410   b  which include adjusters for gross vertical positioning of two probe manipulators  412   a  and  412   b . A horizontal platen  408  is attached to a lead screw  406  and positioned under the control of a servo motor  404  and also can be adjusted vertically. A holder  416  for the IC package under test  418  is attached to the horizontal platen  408 . The holder  416  securely holds the IC package  418  in a substantially vertical position thereby permitting physical access to both sides of the package  418  simultaneously. In particular to this embodiment, access to both probes  414   a  and  414   b  is provided by the vertical orientation of the IC package  418 . 
     Operation and positioning of the probes  414   a  and  414   b  are accomplished by the respective probe manipulators  412   a  and  412   b . The manipulators  412   a  and  412   b  allow the probes  414   a  and  414   b  to contact the appropriate areas of the IC package  418  and perform and collect the various electrical characterization measurements discussed earlier. Probe manipulators  412   a  and  412   b  which allow manual probe positioning, fly-by-wire probe positioning, as well as automated positioning sequences to be performed, are all considered within the scope of the present invention. Because both sides of the package under test  418  are accessible, the probes  414   a  and  414   b  are able to be positioned more efficiently, precisely and accurately than in a test station where the package is horizontally arranged and only a single side of the package is accessible. Furthermore, through-package electrical characterization can be performed by probes  414   a  and  414   b  directly in contact with both sides of the IC package  418 , without the errors and other effects introduced by looping fixtures. 
     Certain embodiments of the present invention include two video cameras  420   a  and  420   b  and dual-displays  422   a  and  422   b . The cameras  420   a  and  420   b  include optical components to provide a magnified image of each side of the package  418  and the position of a corresponding probe  414   a  or  414   b  in relation thereto. These images of both sides are simultaneously displayed on the corresponding display  422   a  or  422   b  and further facilitate accurate and efficient positioning of the probe  414   a  or  414   b . Another embodiment uses optical magnifiers or microscopes  430   a  and  430   b  on each side of the IC package  418  to aid in positioning the probes  414   a  and  414   b.    
     By holding a package in a vertical orientation, both sides of the package are simultaneously accessible to electrical probe assemblies. This accessibility improves the ease, accuracy and efficiency of positioning the probes. Also, through-package electrical characterization of the package and its interconnects are possible without the introduction of the errors and difficulties which accompany looping fixtures. 
     Although the present invention has been described and illustrated in detail, it is understood that the same is by way of illustration and example only, and is not to be taken as a limitation, in scope or spirit, of the present invention which is limited only by the terms of the appended claims.