Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
2002-06-25
2004-08-31
Cuneo, Kamand (Department: 2829)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C324S758010
Reexamination Certificate
active
06784675
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains generally to testing of printed circuit assemblies, and more particularly to a low-cost wireless test fixture adapter for a printed circuit assembly tester.
BACKGROUND OF THE INVENTION
Printed circuit assemblies (PCA's) must be tested after manufacture. PCA testing may be categorized into bare-board testing and loaded-board testing. During bare-board testing, a bare printed circuit board without components and devices attached is tested to verify the continuity of the traces between pads and/or vias on the board. During loaded-board testing, a printed circuit board with some or all of the electrical components and devices attached is tested in order to verify that all required electrical connections have been properly completed. Loaded-board testing may also include integrated circuit (IC) testing, which is performed to verify that the loaded components perform within specification.
In previous years, PCA's were designed and manufactured so that their electrical contacts which were probed during test were arranged in a regularly spaced pattern. During testing, the PCA was placed directly atop a regularly spaced pattern of interface probes located in the tester. As PCA and component geometries shrunk, PCA contact pads could no longer be placed in a regularly spaced pattern and probed directly by interface probes. A bare-board fixture was developed which utilized long, leaning solid probes to provide electrical connections between small, closely spaced, randomly located targets on the PCB and regularly spaced interface probes located in the tester.
A bare-board tester probes testpads, vias, and plated through-holes on bare printed circuit boards only and tests for electrical connectivity and continuity between various test points in the circuits on the printed circuit boards before any components are mounted on the board. A typical bare-board tester contains test electronics with a large number of switches that connect test probes to corresponding test circuits in the electronic test analyzer.
Although each bare-board fixture builder uses unique components and manufacturing processes, most bare-board fixtures resemble that shown in FIG.
1
and include regularly spaced spring probes
114
on a testbed
112
of a tester and long, solid test probes
102
and
116
inserted through several layers of guide plates
100
drilled with small through-holes and held in a spaced-apart fashion with spacers
110
. The bed of standard spring probes
114
actuate the solid test probes
102
and
116
. The long, solid probes may be inserted into the guide plates vertically or at an angle in order to facilitate an easy transition between the fine-pitch, or very close, spacing of testpads
104
and
106
on the PCB side of the fixture and the larger-pitch spacing of the spring probes on the tester side of the fixture. One such bare-board fixture is disclosed in U.S. Pat. No. 5,493,230 titled “Retention of Test Probes in Translator Fixtures” to Swart et al., which is incorporated herein for all that it teaches.
Existing bare-board fixtures can consistently hit test targets equal to or greater than 20 mils in diameter with equal to or greater than 20-mil pitch (center-to-center spacing). Unfortunately, heretofore, it is not been possible to use bare-board fixtures directly on a loaded-board tester because there are many unique features which render bare-board test equipment directly incompatible with loaded-board test equipment.
Prior art bare-board fixtures are not designed to accommodate printed circuit boards (PCBs) which are populated with electronic components; only PCB features which are flush with respect to the PCB (pads, vias, and plated through holes) can be probed. Bare-board testers are used to determine the connectivity and continuity of test points and circuitry in a PCB. Unlike bare-board testers, loaded-board testers cannot tolerate higher electrical resistance between a target on a PCB and the tester electronics. Loaded-board fixtures must provide low-resistance connections and interfaces between targets, fixture components, and tester electronics. Unlike loaded-board testers, bare-board testers cannot determine whether a component or a group of components exists and functions properly.
The probe spacing of bare-board fixtures which are designed to fit on bare-board testers is not generally compatible with the interface probe spacing of loaded-board testers. Bare-board fixtures translate a target on the PCA under test to the nearest interface probe in the bare-board tester. However, loaded-board tester resources must be uniquely assigned and linked to specific targets and circuits. In loaded-board testing, the nearest interface probe may not be appropriate for a given target. Bare-board fixtures are not able to provide unique electrical routing to adjacent, nonadjacent, and remote tester resources, cannot reach remote resources, and cannot provide the complex, loaded-board resource routing patterns required by a loaded printed circuit board.
FIG. 2
illustrates a first and second embodiment of a prior art loaded-board, guided-probe test fixture. The test fixture of the first embodiment comprises two major assemblies. The first assembly
240
is a translator fixture comprising a series of vertically spaced-apart and parallel guide plates
216
, which are supported in parallel by solid posts
222
that hold the fixture together as a solid unit. The fixture also includes an array of leaning probes
226
extending through guide holes in the translator guide plates
216
. The leaning probes
226
are in alignment on a first side of the translator fixture
240
with test targets
220
of a loaded circuit board
218
. The leaning probes
226
are in alignment on a second side of the translator fixture
240
with spring probes
214
on a first side of a probe-mounting plate
224
. The long leaning probes
226
are used to facilitate an easy transition from the fine-pitch targets
220
on the device under test
218
and larger pitch targets (spring probes
214
) on the probe-mounting plate
224
.
Probe-mounting plates are well known in the art; one such plate being a probe-mounting plate made of glass-reinforced epoxy. Personality pins
228
are embedded on a second side of the probe-mounting plate
224
and the personality pins are electrically connected to the spring probes
214
by wires
230
. The wirewrap posts
232
of the personality pins
228
pass through holes in an alignment plate
234
to make contact with tester-to-fixture interface probes
200
which interface the fixture to the pins of the testhead (not shown). Tester-to-fixture interface probes
200
are in a predetermined fixed, regularly spaced pattern and are arranged to electrically contact the test pins of the testhead at one end. The alignment plate
234
aligns the wirewrap posts
232
of personality pins
228
to correspond to the predetermined location of the tester-to-fixture interface probes
200
. The second major assembly
242
of the first embodiment is the unit of the probe-mounting plate
224
containing spring probes
214
and personality pins
228
and the alignment plate
234
which aligns the wirewrap posts
232
of the personality pins
228
with the tester-to-fixture interface probes
200
.
Accurate alignment of the test fixture is essential for reliable operation. Alignment for the printed circuit board
218
to the translator fixture
240
is maintained by means of tooling pins (not shown), which is well known in the art of board test. Alignment between the translator fixture
240
and the probe-mounting plate
224
is maintained by means of alignment pins (not shown) or other known means. Alignment between the alignment plate
234
and the tester-to-fixture interface probes
200
is controlled through the mounting and locking hardware well known in the art of loaded-board test.
The method of operation of the test fixture is as follows. The translator assembly
240
is mounted on the probe-mounting plate/alignment plate assembly
242
. T
Agilent Technologie,s Inc.
Cuneo Kamand
Hollington Jermele
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