Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
1999-07-30
2001-09-11
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
Reexamination Certificate
active
06288560
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 self-soldering probe assembly that attaches a set of probes to input/output pins of a flat pack IC package.
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 normal operating environment. For example when the circuit board is installed in a backplane next to another circuit board there can be very little clearance between the circuit boards for accommodating a probe. Thus it would be beneficial to provide a probe that can be firmly connected to an IC mounted on a circuit board, that would remain attached when the circuit board is thereafter installed in its normal 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 that can be easily gripped by a probe. However flat pack IC packages having pins that are soldered flush with the circuit board 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 flat pack IC packages employing 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 probe assembly for easily and firmly holding a set of probes onto pins of a flat pack or other type of integrated circuit package 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 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 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 an integrated circuit (IC) package having a body with a set of pins extending horizontally outward from the body and soldered to pads on the surface of a circuit board.
In accordance with one aspect of the invention, the probe assembly includes a base providing a set of solder-coated contacts arranged to contact a corresponding set of IC pins when the base is placed over the IC pins. The base also includes a heating element for temporarily delivering heat to the contacts. When the base is placed over the IC with the contacts in resting on the IC pins, the heat provided by heating element temporarily melts the solder coating on the contacts. Thereafter, when the heating element stops delivering heat to the contacts, the solder cools and solidifies to form a firm bond between the contacts and the IC pins. To subsequently remove the probe assembly from the IC, the heating element again temporarily delivers heat to the contacts, thereby melting the solder holding the contacts onto the pins so that the probe assembly can then be easily lifted off the IC pins.
In accordance with another aspect of the invention, the heating element suitably comprises material that generates the heat needed to melt the solder in response to a pulse of current. Thus the probe assembly can be removed from the IC after supplying a current pulse through the heating element. The heating element may alternatively conduct heat from an external heat source (such as for example a soldering iron) to the contacts.
In accordance with a further 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 placed over the IC package body to act as guides for positioning the contacts on the IC pins.
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.
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 thereafter easily removed, that low occupies little vertical space above the IC package, that presents a minimal load at the IC pins, 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 remaining portions of the specification in view of the accompanying drawing(s) wherein like reference characters refer to like elements.
REFERENCES:
patent: 4055800 (1977-10-01), Fisk et al.
patent: 4362991 (1982-12-01), Carbine
patent: 4561006 (1985-12-01), Currie
patent: 4767985 (1988-08-01), Shearer, Jr. et al.
patent: 6094059 (2000-07-01), Frankeny et al.
Bedell Daniel J.
Credence Systems Corporation
LeRoux E
Metjahic Safet
Smith-Hill and Bedell
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