Test head assembly

Details Test head assembly Test head assembly

1999-12-01

2003-01-14

Sherry, Michael (Department: 2829)

Electricity: measuring and testing

Fault detecting in electric circuits and of electric components

Of individual circuit component or element

C324S1540PB, C324S761010, C324S072500

Reexamination Certificate

active

06507203

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to test head assembly for a test system.
BACKGROUND OF THE INVENTION
Electronic devices, such as integrated circuits (ICs), are normally tested after production and before use. As an example of a test system generally applied for testing purposes, automatic test equipment (ATE) is designed to conduct analysis of functional or static parameters to evaluate the degree of performance degradation and may be designed to perform fault isolation of unit malfunctions. The decision making, control, or evaluative functions are normally conducted with minimum reliance on human intervention.
FIG. 1A
illustrates, in a generalized cross sectional view, a typical test system as known in the art, such as the Hewlett-Packard HP 83000 or HP 95000 series. For testing a device under test (DUT)
20
, the test system
10
comprises a tester
30
and a test head assembly
35
. The test head assembly
35
represents the mechanical and electrical interface between the DUT
20
and the tester
30
. The tester
30
generally comprises test electronic for generating test signals and evaluating signals received from the DUT
20
.
The test head assembly
35
comprises a test head
40
and at least one DUT board
60
. The DUT
20
might be fixed directly or via a socket
50
to the DUT board
60
, which, again, is normally mechanically fixed to the test head
40
by means of a fixture
70
.
The DUT board
60
represents the mechanical and electrical interface between the DUT
20
and the test head
40
. The DUT board
60
is also employed to adapt electrical contacts from the DUT
20
to electrical contacts at the test head
40
. In particular with respect to miniaturized ICs, the necessity of such an adaptation of the miniaturized contacts of the DUT
20
to larger contacts of the test head assembly
35
becomes readily apparent.
The fixture
70
is employed for mechanically holding and fixing the DUT
20
via the DUT board
60
to the test head
40
and to allow exchanging the DUT board
60
.
FIG. 1B
illustrates, in an explosive side view, a typical principle for fixing the DUT board
60
to the test head
40
, as employed e.g. in the Hewlett-Packard. HP 83000 or HP 95000 series. The DUT board
60
can be mechanically affixed to the test head
40
by means of a plurality of screws
80
, whereby a stiffener-
90
, as part of the fixture, can be arranged therebetween. When the DUT board
60
is mechanically affixed to the test head
40
, one or more contact areas
95
A,
95
B and
95
C of the test head
40
electrically couple to contact areas
100
A,
100
B and
100
C of the DUT board
60
.
The contact areas
95
A,
95
B and
95
C comprise a plurality of pins (not shown in detail), such as spring loaded pins, which will be forced/pushed against respective contact pads
110
(shown in
FIGS. 2
) of the.contact areas
100
A,
100
B and
100
C of the DUT board
60
for providing a good electrical contact. Since the DUT boards
60
are generally formed of flexible plastic material, the stiffener
90
is employed for avoiding bending of the DUT board
60
under the influence of the contact pressure.
While the DUT board
60
in
FIG. 1B
is affixed to the test head
40
by means of mechanical connecting means such as the screws
80
,
FIG. 1C
illustrates another principle wherein the DUT board
60
is affixed to the test head
40
by means of negative pressure means as employed e.g. in the Teradyne Integra series J750. The top part of
FIG. 1C
shows a cross sectional view, while the lower part depicts a worm eye's view from the direction of arrows A. Vacuum slots
120
in the test head
40
are arranged close to the contact areas
100
A and
100
B for-removing air. Rubber seal lips
130
A and
130
B are provided for establishing a negative pressure between the DUT board
60
and the test head
40
, thus attaching the DUT board
60
.
It is to be understood that, in general, for each different DUT
20
a specific and thus different DUT board
60
has to be provided for adapting the specific layout of contacts of the respective DUT
20
to the contact areas
95
provided from the test head
40
. Employing exchangeable DUT boards
60
renders the test system
10
capable for testing a plurality of different DUTs
20
. It is clear that different test algorithms may have to be provided by the tester
30
for any different DUT
20
.
FIGS. 2A
to
2
D show examples of DUT boards
60
as known in the art. The one or more DUTs
20
are generally located in the center of the respective DUT board
60
. It is clear that number of DUTs
20
on one respective DUT board
60
is limited by the sizes and/or pin counts (i.e. the number of pins or other individual electrical contacts) of the respective DUTs
20
, the pin count (channels) of the test head
40
, and the available area in the center of the DUT board
60
. Each DUT board
60
comprises one or more contact areas
100
comprising a plurality of individual contact pads
110
electrically coupled to the (one or more) DUT
20
, preferably via strip conductors of the DUT board
60
.
When the DUT board(s)
60
is/are fastened to the test head
40
, individual contact areas
95
of the test head
40
couple to the respective contact areas
100
for providing an electrical contact between the test head
40
and the DUT(s)
20
. Spring-loaded cable assemblies designed in accordance with the respective contact areas
100
couple thereto for establishing the electrical contact, between the respective DUT boards
60
and thee test head
40
.
Changing between different DUTs
20
, however, generally requires a change in the hardware, of the test head assembly
35
adapted to the specific arrangement of DUTs
20
and their respective contact areas
100
. In most cases, however, only the respective DUT boards
60
have to be exchanged.
FIGS. 2A and 2B
illustrate center arrangements of the DUT board
60
. The DUT board
60
in
FIG. 2A
comprises four contact areas
100
A,
100
B,
100
C and
100
D substantially arranged around the DUT
20
. An example of an embodiments according to
FIG. 2A
can be found e.g. in the Hewlett-Packard HP 83000 Series. In
FIG. 2B
, only one contact area
100
is provided which substantially encircles the DUT
20
. An embodiment according to
FIG. 2B
can be found e.g. in the Teradyne J971 or Schlumberger S9000 series. The center arrangements of
FIGS. 2A and 2B
are mainly used for optimizing timing delay requirements in that the contact area
100
is designed in a way that the individual contacts thereof are located as close as possible to the corresponding contacts of the DUT
20
.
FIG. 2C
shows a device-specific arrangement for a plurality of individual (i.e. physically separated) DUT boards
60
. Each DUT
20
is located in the center of a respective DUT board
60
, whereby only one DUT
20
is applied on each DUT board
60
. The contact area
100
of each DUT board
60
is device-specific and may substantially correspond to the centered arrangement according to
FIG. 2A
, An example of an embodiment according to
FIG. 2C
can be found in the Hewlett-Packard HP 95000 Series. The device-specific arrangement according to
FIG. 2C
in particular fits the requirements of short timedelay and multi-site testing.
FIG. 2D
shows a DUT board
60
designed for the specific requirements of the negative pressure attachment systems as depicted in FIG.
1
C. One or more DUTs
20
are arranged in a row between parallel contact areas
100
.
It has to be understood and it is expressly noted that the different attaching systems as depicted in
FIGS. 1C and 1D
require entirely different solutions for the design of the, DUT board
60
. Whereas the mechanical connecting system according to
FIG. 1B
allows to arrange a plurality of individual DUT boards
60
as shown in
FIG. 2C
, the negative pressure attachment system of
FIG. 1C
requires that all DUTs
20
have to be located on one single. DUT board
60
since the negative pressure applied through the vacuum slots
120
requires an uninterrupted space b

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