Broadband impedance matching probe

Details Broadband impedance matching probe Broadband impedance matching probe

1997-05-30

2001-05-08

Ballato, Josie (Department: 2858)

Electricity: measuring and testing

Fault detecting in electric circuits and of electric components

Of individual circuit component or element

C324S761010

Reexamination Certificate

active

06229327

ABSTRACT:

FIELD OF THE INVENTION
This invention generally relates to a probe device for testing integrated circuits such as amplifiers, signal processors, mixers, filters, and analog to digital converters. The probe device may be employed for testing integrated circuits before separation from the semiconductor wafer, after separation, after the circuit has been placed into a package or after insertion into a circuit board. In general, the probe device is intended to transfer signals to and from a circuit during testing and to provide an impedance transformation to match the circuit impedance to that of the test instruments.
BACKGROUND OF THE INVENTION
Testing of integrated circuits (IC's), also called chips or dies, is an important part of the design and manufacture of the circuits. Initial testing is usually performed while the chips are still held together as parts of a semiconductor slice or wafer. Such testing requires a microprobe device that contacts the test pads on the chip and provides connections to the instruments employed for testing the circuits. Standard testing instruments for such circuits operate at a 50 ohm impedance level. Most integrated circuits operate at impedance levels that differ from 50 ohms. The impedance mismatch between the integrated circuit and the testing instruments makes accurate testing difficult and in some cases impossible. Fortunately methods for impedance matching are very well known in the electrical engineering art. There are reactive networks described for example on pages 206 to 215 of The Radio Engineer's Handbook by Terman, McGraw-Hill, 1943 (Reference 1). Another reference is Radio Engineering, third edition by Terman, McGraw-Hill, 1947 (Reference 2) where pages 100 to 104 describe the same reactive networks referred to above and pages 104 to 109 describe transmission line methods including tapered transmission lines, quarter wave matching sections and shorted stubs. A third reference is The ARRL Antenna Book, Published by The American Radio Relay League, Newington, Conn., 1994. The use of transformers to match impedances is also well known.
Another testing difficulty occurs when the chip to be tested has balanced input or output circuits. This presents a problem because the testing instruments are almost universally unbalanced with system ground on the external shield of 50 ohm coaxial cables and with the test signals on the center conductors. Fortunately circuits to convert from balanced to unbalanced modes (commonly referred to as Baluns) are also well known. See for example page 690 of the reference 2 above, and pages 26-9 to 26-13 of Ref. 3. Although application of the techniques of impedance matching are well known, particular structures for implementing those techniques in ways that are advantageous in the microprobing environment may not be obvious.
This specification describes an impedance matching probe employing a tapered transmission line that includes mechanically resilient contacting tips and structures to allow impedance matching over a broad frequency range and large impedance ratios.
OBJECTS OF THE INVENTION
This invention is directed toward probe apparatus for matching unequal impedances over a broad frequency range. A coaxial transmission line (cable) having a cylindrical center conductor separated from a surrounding outer conductor by an insulator has dimensions that provide an impedance to match a first impedance at a first end of the line and a different impedance to match a second impedance at a second end of the line. Mechanically resilient electrically conducting structures on the first end of the line are adapted to contact a device to be tested and a connector structure on the second end of the line is adapted to connect with test instruments. The insulator between the inner and outer conductors may be air, a solid dielectric, a dielectric foam, a dielectric powder or a more complicated dielectric structure.


REFERENCES:
patent: 1921117 (1933-08-01), Darbord
patent: 2438915 (1948-04-01), Hansen
patent: 3209287 (1965-09-01), Oxner et al.
patent: 5168538 (1992-12-01), Gillespie
patent: 5432450 (1995-07-01), Rubinson
patent: 5565788 (1996-10-01), Burr et al.
The Radio Engineer's Handbook by Terman McGraw-Hill, 1943 pp. 206 215 (Month Unavailable).
Radio Engineering (third edition) by Terman McGraw-Hill, 1947 pp. 100 to104 (Month Unavailable).
ARRL Antenna, published by the American Relay League Newington, CT, 1994 (Month Unavailable).

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