Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
2001-01-12
2003-05-27
Nguyen, Vinh P. (Department: 2829)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C324S754090
Reexamination Certificate
active
06570399
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
N/A
BACKGROUND OF THE INVENTION
The present invention relates to probes that are used in printed circuit board test fixtures and more particularly, to a socketless, leaktight replaceable probe for use in a test fixture.
It is known to provide testing fixtures for printed circuits boards (PCBs) and the like, for testing the integrity of the electrical connectivity of the circuit boards. A conventional embodiment of a testing apparatus is shown in
FIG. 1
, and includes a fixed, stationary substantially horizontal probe plate
10
and an overlying vertically spaced movable top plate
12
. Top plate
12
is linked to probe plate
10
by means of a peripheral elastomeric spacer
14
which allows top plate
12
to vertically move towards probe plate
10
upon a vacuum being created inside the sealed enclosure formed by probe plate
10
, spacer
14
, top plate
12
, and an overlying pressure plate (not shown) sealingly engaging the upper face of top plate
12
. The downward movement of top plate
12
is accomplished by elastomeric spacer
14
partly collapsing under the movable top plate
12
being sucked downwards by the vacuum.
Top plate
12
holds on its upper surface a printed circuit board
18
which is securely anchored thereto by the above-mentioned pressure plate upon the vacuum being created. Circuit board
18
is spaced from top plate
12
by means of rigid spacers
20
,
22
and is aligned, relative to probe plate
10
, by means of a number of alignment rods
16
which are fixedly attached to probe plate
10
and which upwardly extend through and loosely engage respective vertically registering channels
23
provided in top plate
12
to engage alignment holes provided in circuit board
18
.
A number of tapered channels
24
extend transversely through top plate
12
, with a test probe
26
being located under and vertically registering with each channel
24
. Each test probe
26
is fixedly attached to probe plate
10
in a manner described hereinafter, and vertically extends above and below probe plate
10
. Top plate channels
24
further vertically register with electrical contact points
28
to be tested on printed circuit board
18
upon engagement with the probe tip of the test probe
26
. Thus, upon top plate
12
moving downward, the probe tip of the test probe
26
abuts the selected contact point
28
to be tested on the printed circuit board
18
. Through the instrumentality of known software, electric current is transmitted sequentially through selected probes to test the integrity of the electrical connectivity of the printed circuit board
18
.
The probes
26
of known construction are removably inserted in a sleeve (socket)
30
fixedly anchored to the probe plate
10
. Sleeve
30
in turn is connected to a computer-controlled circuit which allows electrical current to be selectively transmitted therethrough. Probe
26
includes a tube in which a plunger is vertically movable under the bias of a spring, between a lower and an upper limit position. The plunger, the tube and the sleeve are all electrically connected to each other, for allowing the electric current to be transmitted to the printed circuit board. The movable plunger is continuously biased upwardly, and is downwardly forced against the bias of the spring when the printed circuit board downwardly moves against the upper tips of the probes when the vacuum is created inside the sealed enclosure. The purpose of providing a probe which is distinct from its holding sleeve is that the probe has a limited life span, and will thus have to be changed after a certain number of uses because of wear.
Three important problems exist with the above-described conventional circuit board testing apparatus:
a) The first problem is that the stationary sleeves holding the probes prevent the use of more sturdy probes for any given probe spacing. In fact, the contact points of the probes on the printed circuit boards are closely adjacent to one another, and thus the probes need to be positioned in a closely adjacent fashion. This is becoming more and more important as the miniaturization of the printed circuit boards evolves. Thus, if the contact points of the probes on a printed circuit board are very close to one another, probes of a smaller diameter need to be used to allow the probes to be positioned closer to each other. Since the sleeves carrying the probes have a larger diameter than the probes themselves, circuit board contact points which are closer to one another require sleeves of smaller diameter, and consequently probes of even smaller diameter. Probes having a very small diameter are less sturdy and more prone to accidental breakage.
b) The second problem is that the vertical alignment of the probe tips with their respective registering circuit board contact points is in practice not always achieved. Indeed, when inserting the probes inside their respective sleeves, a certain vertical angular offset may occur. The top plate channels are tapered to promote self-alignment of the probes therein; however, the probe tips may still be slightly misaligned when they protrude beyond their respective channels in the space between the top plate and the printed circuit board. The consequence of this misalignment is that the probe tips may be allowed to contact the printed circuit board in a slightly offset fashion relative to their intended respective contact points, which may result in electric current not being transmitted to the circuit board. Thus, the testing software could falsely indicate a connection error.
c) The third problem also relates to a possible misalignment between the probe tips and their corresponding intended circuit board contact points, due to the fact that the alignment rods, which are used to position the circuit board, are fixed to the probe plate. Indeed, it is possible that a misalignment of the top plate relative to the probe plate may result in the top plate through-channels being laterally offset relative to their corresponding underlying probes, since the circuit board position is determined by the alignment roads which are integrally attached to the probe plate, while the position of the through-channels depends on the position of the top plate. If the through-channels are laterally offset relative to their corresponding probes, then certain probes may be laterally deflected by the edges of their corresponding through-channels when the top plate is lowered, which may result in the tips of these deflected probes abutting against the circuit board aside from their intended position. Again, the testing software would then detect a connection error on the printed circuit board where there is none.
Reference is here also made to U.S. Pat. No. 4,885,533 assigned to the assignee of the present application which discloses a probe which, in use, is firmly engaged in an electrically conductive socket mounted tightly in a dielectric plate of a PCB testing fixture.
BRIEF SUMMARY OF THE INVENTION
In accordance with the present invention an improved probe and connector are disclosed that are adapted for use in a printed circuit board test fixture. The probe includes a conductive tubular housing or body and a conductive plunger that is contained and movable within the housing. The plunger includes a contact tip that extends out one end of the housing. The plunger and tip are urged to a normally outward position by a bias force created by a coil spring disposed within the housing. At the opposing end of the probe from the contact tip, the probe end defines a bore that is suitable sized to receive a cooperative pin located at one end of a connector.
The connector includes a tubular body that may be mounted in a through-hole within a fixture plate. The connector may be fixedly retained within the fixture plate via an annular barb or a plurality of annular beads located on the tubular body. In a preferred embodiment, the connector includes the connector pin at one end and a terminal of a desired configuration at the opposing end. The term
DeBlois Marco
Melancon Rene
Parker Matthew R.
Yeghiayan Arra D.
Nguyen Vinh P.
QA Technology Company, Inc.
Weingarten Schurgin, Gagnebin & Lebovici LLP
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