Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
1999-07-30
2001-02-20
Karlsen, Ernest (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C324S072500, C324S758010
Reexamination Certificate
active
06191595
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to integrated circuit (IC) probes and in particular to a probe that attaches to a flat pack IC package via a thermal-releasing adhesive and which includes a heating element for weakening a bond provided by the adhesive.
2. Description of Related Art
When testing a circuit implemented by integrated circuits (ICs) mounted on a circuit board, a technician can access a circuit node by manually holding a probe to a pin of an IC. However it is difficult for a technician to concurrently access more than one or two IC pins using this method. It is also often difficult to access pins of an IC mounted on a circuit board when the circuit board is in its operating environment. For example when the circuit board is installed in a backplane next to another circuit board there is very little clearance between the circuit boards for accommodating a probe. Thus it would be beneficial to provide a probe that can be firmly attached to an IC mounted on a circuit board, that would remain attached when the circuit board is thereafter installed in its operating environment, and which has a low profile so that it requires very little space above the IC.
Probes have been developed which clamp to IC pins. For example U.S. Pat. No. 4,767,985 issued Aug. 30, 1988 to Shearer, Jr. et al describes a probe that clamps to the corner pins of an IC package. Such a probe is suitable for packages having pins with portions that can be easily gripped by a probe. However flat pack IC packages have pins that are soldered flush with the circuit board and would be difficult for such a probe to firmly grip. Also the described probe assembly is relatively tall and would not be useful where space above the IC is limited.
U.S. Pat. No. 4,362,991 issued Dec. 7, 1982 to Carbine describes a probe assembly for circuit board mounted flat pack IC packages that employs an external frame to hold a probe onto flat pack pins by pressure. However the assembly is large and inconvenient to use insofar as the circuit board has to be mounted within the probe assembly rather than installed in its normal operating environment.
U.S. Pat. No. 4,055,800 issued Oct. 25, 1977 to Fisk et al. describes a probe that clamps to the body of an IC rather than to its pins. While this type of probe can grasp relatively thick integrated circuit packages, a flat pack package is typically so thin that it would be difficult for such a probe to firmly grip its body. Also since the probe is held to an IC package body only by lateral pressure, it can easily fall off. This probe assembly is also relatively tall and therefore not practical where space above the IC is limited.
What is needed is a means for easily and firmly holding a set of probes onto pins of a flat pack or other type of integrated circuit package when mounted on a circuit board and which has a relatively low profile so that it does not require substantial space above the circuit board.
It would also be desirable to provide a low-profile probe assembly that can access a large number of IC pins. However such a probe assembly would require a large number of conductors to convey signals between the probe assembly and external test equipment requiring access to the IC pins. It would therefore also be helpful if the probe assembly itself could carry out some of the functions of the external test equipment so as to reduce the number of connections between the probe assembly and the external test equipment.
It would be of further benefit for a probe assembly to provide a relatively short signal path between an IC pin and a high impedance buffer amplifier. Prior art probes typically include high-impedance buffer amplifiers in the signal path between an IC pin and test equipment accessing the pin in order to reduce the load the probe presents at the pin. However, since prior art probe assemblies provide a relatively long signal path between an IC pin and buffer amplifier, the capacitance and inductance of those signal paths act as a load on the IC pin. By providing a very short path between buffer amplifiers and the IC pins, an improved probe assembly would reduce the load on the IC pins.
SUMMARY OF THE INVENTION
A probe assembly in accordance with the invention provides signal paths between test equipment and pins of a flat pack or other integrated circuit (IC) package of the type having a body with a flat upper surface and a set of pins extending horizontally outward from the IC package body. In accordance with one aspect of the invention, the probe assembly includes a base and an adhesive for bonding the base to the IC package body when they are pressed together. When the base is bonded to the upper surface of the IC package body, a set of conductive probes (suitably spring pins) attached to the base contact the IC pins.
In accordance with another aspect of the invention, the probe assembly also includes a set of guide fingers formed of resilient insulating material extending downward from the base. The guide fingers fit between separate pairs of the IC pins when the base is bonded to the IC package body and act as guides for positioning the probe base on the IC as they are pressed together.
In accordance with a further aspect of the invention, the adhesive is a thermal-releasing adhesive which, when sufficiently cool, firmly bonds the base to the IC package body when the base is pressed onto the IC package body. The base includes a heating element for selectively supplying heat to the adhesive when the probe assembly is to be removed from the IC package. The heat weakens the adhesive bond between the probe base and the IC package body, thereby allowing the probe assembly to be easily lifted from the IC. The heating element suitably comprises material that generates substantial heat when conducting current. Thus the probe assembly can be removed from the IC by supplying a current pulse through the heating element. Alternatively the heating element comprises a heat conductor such as copper for conducting heat from an external heat source (such as for example a soldering iron) to the adhesive.
In accordance with another aspect of the invention, the probe assembly base includes a printed circuit board upon which are mounted high-impedance amplifiers for buffering signals passing between the IC pins and external test equipment accessing those pins. Since the signal paths between the pins and the buffer amplifiers are short, the probe assembly presents very little load on the IC pins. An intelligent interface circuit may also be installed on the printed circuit board for carrying out test activities on the IC and for reducing the number of connections needed between the probe assembly and the external test equipment.
Thus the probe assembly is easily and firmly bonded with the adhesive to an IC when the probe base is sufficiently cool simply by pressing the probe base onto the IC using the guide fingers as positioning guides. The probe assembly can thereafter be easily removed from the IC by applying heat to the adhesive via the heating element to weaken the bond. Since the probe assembly consists of only a few relatively thin layers of material, it has a relatively low profile, occupies relatively little space above a circuit board, and provides a very short signal path to the IC pins.
It is accordingly an object of the invention to provide a probe assembly that is easily and firmly attached to a flat pack or other type of integrated circuit package and easily removed, that occupies little vertical space above the IC package, that provides a short signal path to buffer amplifier, and that minimizes the number of signal paths needed between the probe assembly and external test equipment.
The concluding portion of this specification particularly points out and distinctly claims the subject matter of the present invention. However those skilled in the art will best understand both the organization and method of operation of the invention, together with further advantages and objects thereof, by reading the remaini
Malech Douglas R.
Wohlfarth Paul D.
Bedell Daniel J.
Credence Systems Corporation
Karlsen Ernest
Smith-Hill and Bedell
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