U.S. patent application number 09/504542 was filed with the patent office on 2002-01-31 for microwave probe for surface mount and hybrid assemblies.
Invention is credited to Grebliunas, John R., Heal, Mark D..
Application Number | 20020011855 09/504542 |
Document ID | / |
Family ID | 24006717 |
Filed Date | 2002-01-31 |
United States Patent
Application |
20020011855 |
Kind Code |
A1 |
Heal, Mark D. ; et
al. |
January 31, 2002 |
Microwave probe for surface mount and hybrid assemblies
Abstract
A microwave probe for use with densely populated surface mount
and hybrid microwave circuit assemblies includes a housing, a RF
signal pin, and ground pins, wherein the pins extend outwardly from
the housing. The pins are preferably individually spring loaded
contacts, and are oriented on the housing relative to each other so
as to permit contact with a planar transmission line when the pins
are substantially perpendicular to the surface of the transmission
line or circuit board.
Inventors: |
Heal, Mark D.; (Redondo
Beach, CA) ; Grebliunas, John R.; (Manhattan Beach,
CA) |
Correspondence
Address: |
JOHN A. ARTZ,ESQ.
ARTZ & ARTZ
28333 TELEGRAPH ROAD
SOUTHFIELD
MI
48034
US
|
Family ID: |
24006717 |
Appl. No.: |
09/504542 |
Filed: |
February 15, 2000 |
Current U.S.
Class: |
324/755.02 |
Current CPC
Class: |
G01R 1/06772
20130101 |
Class at
Publication: |
324/754 |
International
Class: |
G01R 027/00; G01R
031/02 |
Claims
What is claimed is:
1. A microwave probe for making temporary connections to a planar
transmission line integrated onto a circuit board, said probe
comprising: a housing; a radio frequency signal pin having a first
end protruding outwardly from said housing; and at least one ground
pin having a first end protruding outwardly from said housing,
wherein said signal pin and said at least one ground pin are
affixed to said housing having an orientation relative to each
other to permit contact with the planar transmission line when said
signal pin and said at least one ground pin are substantially
perpendicular to the transmission line.
2. The probe of claim 1 wherein said signal pin and said at least
one ground pin are spring-loaded.
3. The probe of claim 1 further comprising a coaxial transmission
line formed from a dielectric sleeve encapsulating said RF signal
pin within said housing.
4. The probe of claim 3 further comprising a field connector
mounted to said housing and coupled to said coaxial transmission
line at an end opposite the first end of said RF signal pin.
5. The probe of claim 1 wherein said at least one ground pin is
attached to said housing at an end opposite the first end.
6. The probe of claim 1 wherein said at least one ground pin
comprises two separate ground pins.
7. The probe of claim 6 wherein the pin orientation permits contact
with a coplanar waveguide to microstrip transmission line
transition integrated onto the circuit board.
8. A method for testing a microwave circuit having at least a
plurality of surface mounted circuit components and a planar
transmission line integrated onto a circuit board, said method
comprising the steps of: connecting an output jack of a microwave
probe to a signal analyzer, said probe comprising a radio frequency
signal pin having a first end protruding outwardly from a probe
housing, and at least one ground pin also having a first end
protruding outwardly from the housing; and orienting the probe so
that the signal pin the at least one ground pin are substantially
perpendicular to the planar transmission line; and bringing the
signal pin and the at least one ground pin into contact with the
planar transmission line while the pins are still substantially
perpendicular to the planar transmission line.
9. The method of claim 8 wherein the signal pin and the at least
one ground pin are spring-loaded so as to be normally biased
outwardly from the probe housing, and said method further comprises
the step of exerting a force on the probe housing after the pins
come into contact with the planar transmission line so as to
compress the pins.
10. The method of claim 8 wherein the probe comprises two ground
pins, and the planar transmission line comprises a coplanar
waveguide to microstrip transmission line transition integrated
onto the circuit board, said method further comprising the step of
bringing the probe pins into contact with the transmission line
transition so that the signal pin makes a substantially
perpendicular contact with the microstrip transmission line while
each ground pin makes a substantially perpendicular contact with a
respective one of a pair of coplanar waveguide contacts.
11. A microwave probe for making temporary connections to a planar
transmission line integrated onto a circuit board, said probe
comprising: a housing formed from two mating half-shells fastened
together, said housing including an output jack mounted thereon; a
radio frequency signal pin having a first end protruding outwardly
from said housing and, said signal pin being connected to said
output jack; and at least one pin grounded to said housing, said at
least one ground pin having a first end protruding outwardly from
said housing, wherein said signal pin and said at least one ground
pin are positioned on said housing having an orientation relative
to each other to permit contact with the planar transmission line
when said signal pin and said at least one ground pin are
substantially perpendicular to the transmission line.
12. The probe of claim 11 wherein said signal pin and said at least
one ground pin are spring-loaded.
13. The probe of claim 11 further comprising a coaxial transmission
line formed from a dielectric sleeve encapsulating said RF signal
pin between the two half-shells of said housing.
14. The probe of claim 13 wherein said output jack comprises a
field connector mounted to said housing and coupled to said coaxial
transmission line at an end opposite the first end of said RF
signal pin.
15. The probe of claim 11 wherein said at least one ground pin is
attached to said housing at an end opposite the first end.
16. The probe of claim 11 wherein said at least one ground pin
comprises two separate ground pins.
17. The probe of claim 16 wherein the pin orientation permits
contact with a coplanar waveguide to microstrip transmission line
transition integrated onto the circuit board.
Description
TECHNICAL FIELD
[0001] The present invention relates to microwave probes suitable
for insertion and detection of microwave signals in high frequency
circuit assemblies, and more particularly to a microwave probe
which can be used with densely populated surface mount and hybrid
circuit assemblies.
BACKGROUND ART
[0002] Generally, most modern RF microwave circuits and assemblies
use planar transmission line structures such as a microstrip or a
coplanar waveguide to transmit high frequency signals from one
circuit or device to another. Various probe structures have been
developed which facilitate "on-wafer" testing and various forms of
rapid characterization of high frequency circuits, such as
Microwave Integrated Circuits (MIC) and Monolithic Microwave
Integrated Circuits (MMIC). One such probe is generally known as an
RF wafer probe, which operates as a miniature transmission line
structure to permit interfacing with a coaxial transmission line.
With such a probe, RF characterization is possible for MMIC
devices.
[0003] The problem with known wafer probes derives from the fact
that the probe design utilizes a planar, blade-like contact
element, which requires contact with the microwave circuit at a
very low angle relative to the circuit board. Pressure must then be
applied to the probe assembly to slightly deflect the probe contact
tip to make positive contact with the RF circuit being tested. Such
probes were specifically designed to test microwave devices at the
flat wafer level, such as the aforementioned MMIC devices. In other
words, there are virtually no structures protruding from the
surface of the water that the probes are required to clear when
brought into contact therewith.
[0004] However, many RF and microwave assemblies and units are
fabricated using either surface mount technologies, or hybrid
circuits formed from combinations of surface mount and integrated
circuits. These technologies allow the combination of several RF
circuits, such as amplifiers, mixers, oscillators, and filters, to
be integrated into a planar receiver or synthesizer circuit. The
circuits and components in such assemblies are typically located as
close as possible to decrease overall size, weight, and cost of the
circuit. Because of dense packaging of components on planar
circuits, use of conventional wafer probes is either prohibited or
restricted due to the requisite low contact angle In other words,
because of the low angle at which known wafer probes contact a
circuit board, there are many configurations of surface mount and
hybrid circuits where such a probe would not be able to contact the
circuit due to the positioning of some nearby component attached to
the planar circuit, or due to the type of package in which the
circuit has been placed.
[0005] In addition, known wafer probes also have very limited
ability to make simultaneous contact with surfaces of different
heights. More specifically, most common microwave applications call
for a coplanar or "ground-signal-ground" type probe, which is used
to contact a type of transmission line known as a coplanar
waveguide. As shown in FIG. 1, a coplanar waveguide 10 is formed
from a substrate 12 having a plurality of metal strips formed on
the surface thereof. A center strip 14 provides a signal line,
while side strips 16 and 18 are located on both sides of the center
strip and separated by uniform gaps. Metal strips 16 and 18 connect
to a ground potential of the RF system. Electromagnetic fields are
supported between the center conducting strip and the strips which
form the ground. Known coplanar waveguide wafer probes are limited
in their ability to bridge nonuniform trace heights between the
signal and ground strips.
DISCLOSURE OF THE INVENTION
[0006] Therefore it is an object of the present invention to
provide an improved microwave probe which can be used with surface
mount, and hybrid microwave circuit assemblies.
[0007] It is another object of the present invention to provide a
microwave probe which can be used with microwave circuit assemblies
having probe contact points of non-uniform surface height.
[0008] In accordance with these and other objects, a probe is
provided for making temporary connections to a planar transmission
line integrated onto a circuit board, wherein the probe includes a
probe housing, a signal pin having a first end extending outwardly
from the probe housing, and at least one ground pin also having a
first end extending outwardly from the probe housing. The signal
pin and the at least one ground pin are affixed to the probe
housing with an orientation relative to each other to perm it
contact with the planar transmission line when the signal pin and
the ground pin(s) are substantially perpendicular to the
transmission line.
[0009] In accordance with one aspect of the present invention, each
pin on the probe is individually spring-loaded to allow
simultaneous contact of the probe with a transmission line or
circuit board having a non-uniform surface height.
[0010] Thus, the probe of the present invention allows contact with
a wide variety of planar transmission line circuits so that the
probe pins are substantially perpendicular to the surface of the
circuits. As a result, minimal surface area clearance is required,
thereby permitting use of the probe in close proximity to any
nearby component, circuit, or circuit package. Therefore, the
present invention overcomes the difficulties of known wafer probes
and allows individual circuit functions to be characterized or
tested in situ on surface mount or hybrid circuit assemblies. This,
in turn, allows test access to surface mount and hybrid circuit
assemblies without concern of packaging density.
[0011] The above objects and other objects, features, and
advantages of the present invention are readily apparent from the
following detailed description of the best mode for carrying out
the invention when taken in connection with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 shows a perspective view of a circuit substrate
having a coplanar transmission line integrated thereon;
[0013] FIG. 2 shows a side view of a probe in accordance with the
present invention;
[0014] FIG. 3 shows a view of the probe of FIG. 2 take along line
3-3; and
[0015] FIG. 4 shows the probe in contact with a microwave circuit
board in accordance with the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0016] Referring to FIGS. 2 and 3, a microwave probe 100 in
accordance with the present invention includes a housing 102 formed
by mating together two half-shells 104 and 106. Half-shells 104 and
106 are held together upon assembly by a plurality of fasteners
108.
[0017] A set of contact pins extend outwardly from one end of
housing 102 so as to be able to be brought into contact with the
surface of a printed circuit board. More specifically, the set of
contact pins are arranged so that one pin will function as a radio
frequency (RF) signal pin, and at least one pin will function as a
ground pin for connecting to a ground potential on the circuit
board.
[0018] As shown in FIGS. 2 and 3, a preferred embodiment of the
present invention is particularly designed to be used with surface
mounted or hybrid circuit microwave assemblies having a coplanar
waveguide transmission line, like that shown in FIG. 1, integrated
thereon. Thus, a middle pin 110 functions as the RF signal pin, and
is formed from a conductor of a coaxial transmission line 112
extending through housing 102. A dielectric sleeve 114 forms an
insulator for the coaxial line and provides structural support for
affixing pin 110 to housing 102. While it is not to be construed as
limiting, dielectric sleeve 114 is formed from a material such as
Rexolite, and creates a 50 ohm characteristic impedance for the
coaxial transmission line. In further accordance with the preferred
embodiment of the present invention, the at least one ground pin is
implemented as a pair of ground pins 116 and 118 respectively
positioned on opposite sides of center pin 110, and are each
affixed to housing 102 such as by soldering.
[0019] In further accordance with the present invention, each pin
is formed from a spring-loaded contact having a stationary outer
casing 120 supported by housing 102 for ground pins 116 and 118,
and the dielectric sleeve 114 for signal pin 110. Inner portion 122
of each pin is slidably movable relative to outer casing 120, and
is normally biased outwardly away from housing 102 and outer
casings 120, as is well understood to one having ordinary skill in
the art. In the preferred embodiment, inner portion 122 is capable
of moving at least one tenth of an inch relative to outer casing
120.
[0020] In addition an SMA-type pin adapter 124 is soldered to the
end of signal pin 110 for mating with a field replaceable SMA
connector 126. SMA connector 126 facilitates easy connection of
probe 100 with suitable testing equipment.
[0021] FIG. 4 illustrates use of the preferred embodiment for
allowing temporary connection to be made with a conventional
coplanar waveguide to microstrip transmission line transition 200
integrally formed on a circuit board 202. Transition 200 is
typically formed from a pair of coplanar waveguide contacts 204 and
206, and a pair of microstrip transmission lines 208 and 210 spaced
by a gap 212, and arranged to extend between contacts 204 and 206.
Each coplanar waveguide contact is provided with a hole 214 to
facilitate connection to a ground potential on circuit board
202.
[0022] In operation, as seen in FIG. 4, pins 110, 116 and 118 of
probe 100 are brought into simultaneous contact with transition 200
while the pins are substantially perpendicular to circuit board
202. In order to ensure a quality contact has been made, downward
pressure is applied to compress the pins. RF signals are then
picked-up and passed through probe 100 to SMA connector 126 via
coaxial transmission line 112. Thus, since probe 100 is
substantially perpendicular to the transmission line and circuit
board, contact with the board can be made without disturbing or
contacting any surrounding circuit components.
[0023] As a result, the probe of the present invention is ideally
suited for use with densely populated surface mounted and hybrid
microwave circuits, which, in turn, allows a significant reduction
in time and expense for testing such circuits during manufacture.
More specifically, in the past, conventional testing of surface
mount and hybrid assemblies has required individual components
thereof to be tested prior to unit assembly. In accordance with
conventional methods, testing of these individual components was
accomplished either by placement in a special test fixture, or
testing at the wafer level. Then, after complete assembly, the
entire unit would be tested via RF connectors coupled to the unit
input(s) and/or output(s).
[0024] However, because the present invention allows testing of
individual circuit components and subassemblies after placement on
the circuit board, the need for individual component test fixtures
and the time associated with the use of such fixtures is
obviated.
[0025] In addition, the use of individual spring-loaded pins
further facilitates testing of surface mount circuits because the
ability of each pin to make simultaneous contact with surfaces of
different heights relative to the circuit board allows the present
invention to accommodate differences in trace heights. This feature
is particularly advantageous with surface-mounted circuits because
build-up of solder on circuit traces can cause several thousandths
of an inch difference in trace height.
[0026] While the best mode for carrying out the invention has been
described in detail, those familiar with the art to which this
invention relates will recognize various alternative designs and
embodiments for practicing the invention as defined by the
following claims.
* * * * *