Removable biasing board for automated testing of integrated circuits

A "personality" card (bias adapter board) is employed to program power supply connections in a DUT (Device Under Test) fixture in an automated test environment. The DUT fixture is designed to provide access to power supply voltages from the automated test equipment (ATE) and to selected (configurable) pins of the device under test. Specific connections are established between designated power supply pins of the DUT and the ATE via the bias adapter card, thereby eliminating the need for a separate, expensive DUT board for each different DUT.

TECHNICAL FIELD OF THE INVENTION 
The invention relates to automated testing of integrated circuits using 
Automated Test Equipment (ATE), and more particularly to test fixtures 
used in conjunction with such testing. 
BACKGROUND OF THE INVENTION 
Due to the high degree of complexity and high density of modern integrated 
circuitry, manufacturers of integrated circuits (ICs) typically use 
highly-sophisticated Automated Test Equipment (ATE) to test integrated 
circuits, to ensure that they perform as designed (e.g., to 
specification). Some high-volume integrated circuit users also utilize 
ATEs to verify the function of integrated circuits (usually on a sampled 
basis). Without using an ATE, or the like, it would be virtually 
impossible to achieve high confidence levels with respect to integrated 
circuit functionality and reliability. 
Automated test equipment (ATE) provides the ability to generate test signal 
sequences on a large number of pins of an integrated circuit device under 
test (DUT), in some cases simultaneously. Unlike ordinary digital 
equipment, however, ATE is capable of tightly controlling signal timing 
and voltage characteristics to within a small margin of error. Timing 
relationships between signals, rise times, fall times, etc., provided by 
the ATE are all well defined at the pins of the DUT. Additionally, the ATE 
is capable of making accurate measurements of voltage levels and timing of 
signals emanating from the DUT in response to the signal sequences (e.g., 
test vectors). These capabilities are provided at very high speed under 
the control of a pre-defined test program. Further, most automated test 
equipment include programmable voltage sources for applying to the DUT. 
These voltages are sometimes referred to as "bias" voltages or "bias" 
signals, and are generally used to supply power to the DUT via its power 
and ground pins. 
For analog integrated circuit functions, some automated test equipment 
includes high-speed waveform signal generators, the outputs of which can 
be applied to analog function pins of the DUT. Similarly, such analog 
capability usually includes some sort of high-speed voltage sampling 
capability. Sometimes, these analog capabilities are applied to digital 
functions as a part of a test in order to ensure compliance of a DUT with 
pre-specified signal threshold levels, hysteresis, etc. 
FIG. 1a is a block diagram of a typical automated tester (ATE) for 
integrated circuits. The ATE 100 comprises a test sequencer 130 which 
operates under the control of a stored test program 140 to control 
programmable pin drivers/monitors 110 and programmable power supplies 
(voltage sources) 120. The programmable power supplies 120 are controlled 
by the program 140 to generate suitable power supply voltages to be 
applied to a DUT 170. The specific power supply voltages are selected to 
suit specific test requirements. For example, it might be desirable to 
test a DUT 170, e.g., a CMOS (Complementary Metal Oxide Semiconductor) IC, 
at minimum, nominal, and maximum power supply voltages to ensure 
compliance of the DUT with specified performance parameters at those 
voltages. Accordingly, three sets of test signal sequences would be 
generated under control of the program 140, each sequence altering the 
power supply voltages to reflect minimum, nominal, or maximum rated power 
supply specifications for the DUT 170. The programmable pin 
drivers/monitors 110 would be controlled by the program 140 (via the test 
sequencer 130) to generate high-speed digital test signals (vectors) to be 
applied to the DUT 170 and to monitor and measure various parameters of 
specific signals generated by the DUT 170 in response to the test signals. 
(ATE pin drivers can usually also be set to a high-impedance state, 
essentially leaving the associated DUT pin "unconnected"). 
The output signals (and monitor inputs) of the programmable pin 
drivers/monitors 110 and the outputs of the programmable power supplies 
120 are provided to the DUT 170 via a DUT interface board 160 connected to 
a test interface connector 150 on the ATE 100. The signals and supply 
voltages are routed through the test interface connector 150 via contacts 
or connections on the DUT board 160 to pins of a DUT socket or connector 
165 mounted to the DUT board 160. The DUT 170 "plugs into" the test 
interface connector 165. (The term "plugs into" is used loosely here, 
since the DUT connector 165 is usually a specialized test connector, such 
as a "zero-insertion-force" connector, designed to minimize the mechanical 
stress placed upon the pins or contacts of the DUT 170). 
Referring to FIG. 1b, the DUT board 160, is essentially a test fixture 
designed to adapt the DUT 170 to the test interface connector 150 of the 
ATE 100. Typically, the DUT board 160 is a very thick, rigid printed 
circuit board with contact pads on a bottom side thereof (not shown) to 
make contact with spring-loaded contactors in the test interface connector 
150. Often, the DUT board is clamped to the test interface connector 150 
via a camlocking arrangement (not shown). Signal traces 162 (a 
representative few shown) on the top of the DUT board connect the contact 
pads (on the bottom of the DUT board) to the DUT connector 165. 
Although most modern integrated circuits are assembled into one of a 
relatively small number of different package types, there is little 
standardization of pinouts on these packages, particularly with respect to 
power supply connections. Most PLCC (plastic leaded chip carrier), PQFP 
(plastic quad flat pack), and PGA devices, particularly those with large 
numbers of "pins" (e.g., 100 or more), will have several "pins" dedicated 
to each of the power supply voltages. Unfortunately (e.g., for testing 
purposes), the selection of these power supply pins is usually different 
for different ICs, despite the use of identical package types. 
Consequently, it has been necessary to provide a different DUT board 
(e.g., 160) for each different IC. Each different DUT board will have 
power supply signals (bias signals) routed to different pins of the DUT 
connector, as required by the specific IC to be tested. 
There is considerably greater flexibility with respect to the programmable 
pin drivers/monitors (e.g., 120) since their operation is governed by a 
test program. A specified test signal sequence can be routed to any 
connected pin (other than the power supply pins, of course) simply by 
specifying the appropriate pin driver/monitor in the test program (e.g., 
140). 
DUT boards must generally be built to relatively tight mechanical 
tolerances and must use relatively expensive, high-quality materials to 
ensure good contact between the various connections, and to ensure long 
service life. As a result, a DUT board can sometimes cost as much as 
$4000.00. This is particularly troublesome to ASIC (Application Specific 
Integrated Circuit) vendors, for whom practically every customer has a 
different IC design. As a result, each IC for each customer must have a 
custom-built DUT board. These DUT boards add expense to the cost of 
developing the IC, represent a significant storage problem (these boards 
are relatively large, and must be kept on hand for subsequent production 
runs of the customers ICs) and can potentially delay delivery of initial 
quantities of ICs to the customer (due to the fabrication time required 
for the DUT board). 
Evidently, it would be highly advantageous to provide some means of 
eliminating or minimizing the delay, storage requirements, and expense 
associated with the design and fabrication of DUT boards. 
DISCLOSURE OF THE INVENTION 
It is therefore an object of the present invention to provide a technique 
for minimizing cost associated with the development of DUT boards for 
automated test equipment. 
It is a further object of the present invention to provide a technique for 
minimizing delay associated with the fabrication of DUT boards for 
automated test equipment. 
It is a further object of the present invention to provide a technique for 
accommodating a variety of DUTs with different power supply pin 
connections on a single DUT board. 
It is a further object of the present invention to provide a simple, 
inexpensive technique for reconfiguring DUT power supply connections on a 
DUT board. 
It is a further object of the present invention to reduce the amount of 
storage space required for ATE DUT boards when a large number of different 
ICs are to be accommodated. 
According to the invention, a DUT base board is designed to accept a DUT 
connector (socket), into which a DUT is installed for test. The DUT base 
board may installs into the ATE (via a test interface connection) in a 
conventional manner. The DUT base board routes power supply signals to 
specific locations on the DUT base board assembly whereby a separate bias 
adapter can gain access to the power supply signals. Further, means are 
provided for the separate bias adapter to gain electrical access to pins 
of the DUT connector. The bias adapter routes the power supply signals to 
specific pins of the DUT connector which are designated as power supply 
pins for a specific integrated circuit. 
According to an aspect of the invention, a different bias adapter card is 
employed for each different IC to be tested (DUT). 
In one embodiment of the invention, a receptacle is employed in which 
receptacle pins (elongated conductive pins which have a pin-receiving 
receptacle at one end) are installed. Pin portions of the s receptacle 
pins extend completely through the DUT base board. Both signals and power 
supply voltages are carried by the receptacle pins. The DUT connector 
(Socket) plugs into selected ones of the receptacle pins (those not 
connected to power supply voltages). The extension of the receptacle pins 
through the DUT base board provides the means by which the bias adapter 
gains access to the power supply voltages and pins of the DUT connector 
(socket). 
According to an aspect of the invention, the bias adapter is fitted with 
contactors to make contact with the power supply connected receptacle pins 
and with selected ones of the receptacle pins which connect to the DUT 
connector (socket). The selected ones of the DUT connector pins are those 
which are designated as power supply pins for a specific IC type. 
Electrical connections are established on the bias adapter between 
appropriate contactors to connect power supply voltage to appropriate pins 
of the DUT connector (socket). 
In one embodiment of the invention, a threaded nut is embedded into the 
receptacle and clearance holes for a screw are provided through the DUT 
base board and bias adapter. A screw is inserted through the clearance 
holes and into the threaded nut, and is tightened to clamp the bias 
adapter to the DUT base board and receptacle. 
According to another aspect of the invention, power supply decoupling 
capacitors can be employed on the bias adapter. 
The receptacles, being designed to accept a variety of connectors (sockets) 
which may accommodate a variety of IC package types. The specific power 
supply connections for each different IC (DUT) are determined via the 
installed bias adapter, which essentially "programs" the power supply 
connections for the DUT. In this manner, virtually any power supply pin 
configuration can be accommodated by employing a properly configured bias 
adapter board. It is only necessary to provide as many different DUT base 
boards (including assembled test receptacle) as are necessary to 
accommodate all of the different DUT connectors to be employed. Storage 
requirements are thus minimized by eliminating the need for storage of a 
much larger custom designed DUT board for every Ic type. 
Further, each IC need only have a custom bias adapter board. These boards, 
which are considerably smaller and simpler than the prior art DUT boards, 
require little storage space, are relatively inexpensive, and can be 
assembled from a relatively small number of common blank boards. The 
commonality between bias adapter boards is defined by the number of 
different receptacle pin patterns which must be accommodated. 
The bias board provides an easy, inexpensive method to provide power and 
ground connections to a device under test (DUT) using automatic test 
equipment. When personalizing, or "programming" a bias board, a customer 
specification is reviewed to determine where power supply connections are 
needed. The bias board is wired and decoupling caps are added for all 
power connections. Contactors, such as Augat HolTights (tm) are then 
installed at each biased pin. The bias board is then inserted and secured 
with a screw which threads on a nut embedded in the receptacle. By 
employing a relatively simple bias adapter scheme, potential delays are 
avoided in the initial production cycle, since no elaborate fabrication 
techniques are required to adapt an existing DUT fixture to a new IC. Only 
a new bias adapter card is require. 
Other objects, features and advantages of the invention will become 
apparent in light of the following description thereof.

DETAILED DESCRIPTION OF THE INVENTION 
FIGS. 1a and 1b illustrate an automated test environment for testing 
integrated circuit devices, and have been discussed hereinabove. 
Generally, it has heretofore been required to fabricate a unique base 
board for each different integrated circuit device undergoing test, 
notably with regard to the power supply connections to the device under 
test (DUT). 
FIG. 2a is a block diagram of an automated test system 200 embodying the 
principles of the present inventive technique. The automated test system 
200 employs an ATE tester 100 (see, e.g., FIG. 1a) having a test interface 
connector 150. A modified DUT base board 260 (comparable to interface 
board 160) and "bias adapter" board 262 (described in greater detail 
hereinbelow) are connected to the test interface connector. A test 
receptacle 265 is mounted to the modified DUT base board 260. The test 
receptacle 265 receives a DUT connector 266 and is connected thereto via, 
for example, by pin connections on the DUT connector 266 and socket-type 
connections on the test receptacle 265. One of ordinary skill in the art 
will immediately recognize that any suitable connection scheme can be 
employed. The DUT connector 266 receives a DUT 170. 
FIG. 2b is a more detailed block diagram of a portion of the automated test 
system 200 showing the path of signal connections between the various 
components of the inventive ATE test system (fixture). The test interface 
connector 150 provides a plurality of signals 220, which include driven 
test signals, monitored "signals, and power supply or "bias" signals to 
the DUT base board 260. The power supply signals are separately routed 
(via lines 230) on the DUT base board 260 to by a suitable connection 
scheme (one such scheme is described in greater detail hereinbelow) to the 
bias adapter board 262. The bias adapter board 262 configures the power 
supply connections to the test receptacle 266 by routing the power supply 
signals back to specific pins of the DUT connector 265 on the DUT board 
(via lines 230b). In this way, the DUT 170 receives power supply 
connections to the appropriate pins. Since pin drivers (see, e.g., 110, 
FIG. 1a and descriptions with respect thereto) can generally be set to a 
high-impedance state, the power supply connections 230b from the bias 
adapter board 262 to the DUT connector 266 (via the DUT base board 260) 
can usually be connected in parallel with a fixed signal connection from 
the ATE 100 to the same pin on the test receptacle 265. The test program 
(e.g., 140, FIG. 1a) simply sets the corresponding pin driver (e.g., 110 
FIG. 1a) to a high impedance, or undriven, state. 
FIG. 3a is a cross-sectional view of a DUT fixture assembly 300 comprising 
a DUT base board 310, a DUT test receptacle 360, a "bias" adapter board 
262, and a DUT connector 266. In this FIG., it can be seen how the 
aforementioned signal and power supply connections are made between the 
ATE (e.g., 100, FIG. 1) and the "DUT connector 66. The test receptacle 360 
is essentially a planar substrate (e.g., material such as, for example, 
non-conductive plastic fiberglass or the like) with a plurality of 
elongated "socket pins" 316 and 318 assembled to it. Each of the elongated 
pins 316 is disposed at a connection location on the base board. 
The socket pins 316 and 318 have a socket (pin-receiving) portion (at the 
top of the pin, as viewed in the figure) at one end thereof and an 
elongated pin portion (extending downwards, as viewed in the FIG.). The 
socket pins (316, 318) are assembled to the test receptacle 360 such that 
the socket portion is accessible from one side thereof (top, as viewed in 
the figure) while the pin portions extend from an opposite side thereof. 
The length of the extending pin portions of the socket pins 316 and 318 is 
such that they will extend completely through holes 314 in the DUT base 
board 310. Conductive signal traces 312 (one representative trace shown) 
on the DUT base board are used to establish connections between the ATE 
and the socket pins. For example, a spring pin 350 in a test interface 
connector (e.g., 150, FIG. 1a) of an ATE tester makes contact with a 
signal trace 312 on the DUT base board 310, preferably by means of a pad 
(i.e., an enlarged area of the trace 312). The signal trace traverses the 
surface of the DUT base board 310 to a hole 314 through which a socket pin 
316 extends. By any suitable means (e.g., a solder connection, press-fit 
connection, etc.) the socket pin connects electrically (and possible 
mechanically) to the signal trace 312. This causes the signal carried by 
the signal trace 312 to be accessible from below the DUT base board (via 
the pin portion of the socket pin 316) and above (via the socket portion 
of the socket pin 316). Pins 366 of the DUT connector 266 are plugged into 
the Socket portion of the socket pins 316 to complete connections between 
signals in the ATE test interface connector (via, e.g., spring contacts 
350) and the DUT connector 266. 
A number of socket pins 318 (one shown) are used to connect to the power 
supply signals generated by programmable voltage sources in the ATE in 
similar fashion (e.g., by spring contacts, signal traces on the DUT base 
board, etc.). In order to minimize illustrative clutter, this connection 
is not explicitly shown in the figure, but the connection technique is 
similar or identical to that described above for tester signals (see, 
e.g., spring contact 350). Unlike the socket pins 316, into which the DUT 
connector 266 plugs, the DUT connector 266 does not directly contact the 
power-supply carrying socket pins 318. (one of ordinary skill in the art 
will immediately recognize that the socket portion of these socket pins is 
not needed, and that a substitution can readily be made of simple pins for 
the socket pins 318. It is within the spirit and scope of the invention to 
do so.) 
The bias adapter board 262 has a plurality of holes 320 formed 
therethrough. The holes are positioned to align with the positions of the 
pin portions of the socket pins (316, 318) extending through the DUT base 
board 310. At the location of holes 320 corresponding to the locations of 
the power supply connected socket pins 318, contactors 322b are inserted 
into the holes 320. Similar contactors 322a are inserted into holes 320 
corresponding to the locations of socket pins 316 which connect to power 
supply pin positions in the DUT connector 266. Electrical connections 
(illustrated by a conductive trace 324 in the figure, but which may be 
soldered wire connections or any other suitable connection technique) 
connect the contactors 322a to the contactors 322b. At hole (320) 
locations where no contactor (322a or 322b) is installed, no electrical 
contact is made with the socket pins (316) at those locations. The 
contactors can be, for example, Augat HolTight (tm) connectors. One of 
ordinary skill in the art will understand that any suitable removable 
connection scheme may be employed herein. 
The test receptacle 360 has a threaded nut 332 embedded into the top (as 
viewed in the figure) surface thereof and a clearance hole 334c through 
which a screw 330 is inserted and screwed into the nut. The screw 330 also 
passes through holes 334b and 334c through the DUT base board 310 and bias 
adapter card 262, respectively. The head of the screw contacts the bottom 
(as viewed in the figure) surface of the bias adapter card 262. The screw 
is tightened to hold the bias adapter card 262 to the assembly of the test 
receptacle 360 and the DUT base board 310. 
Generally, according to the present invention, it is evident from the 
description contained hereinabove how a "standard" base board 310 can be 
customized for different power supply connections by use of individual 
bias boards 262. In this manner, the standard base board can be used and 
reused for a wide variety of DUTs, requiring only that new bias boards be 
fabricated for each pin configuration (new socket/DUT connector patterns) 
of a given DUT. Customized test receptacles 360 may be required for each 
DUT connector pattern. 
FIG. 3b is a top view of an embodiment of the bias adapter card (board) 
262, showing a pattern of holes 320 disposed so as to align with the 
positions of socket pins (e.g., 316, 318) extending from the test 
receptacle (e.g., 360) through the DUT base board 310. The clearance hole 
334a for the screw 330 is shown at the center of the bias adapter card 
262. As illustrated, the DUT connector 266 has an open center. In other 
words, the connector 266 has an array of pins (366), but no pins in a 
central area of the array. Accordingly, the design of the DUT arrangement 
300 takes advantage of this by positioning the power supply carrying 
socket pins (318) at the center of the test receptacle 360. Four socket 
pins (318) are employed for each of two supply voltages. (e.g., ground and 
Vd). Those of ordinary skill in the art will immediately recognize that 
this scheme can be extended to accommodate any number of supply voltages.) 
Contactors 322a are installed in holes 320 (a representative two shown) 
corresponding to the positions of socket pins (316) which connect to 
designated power supply pins in the DUT socket 266. Contactors 322b are 
installed to connect to power supply carrying socket pins 318. In this 
case, four contactors 322b are used for each of the two supply voltages 
(corresponding to the number of socket pins 318 employed for this 
purpose). Conductive metal rings 340a and 340b connect the contactors 322b 
which are connected to like supply voltages. In this case, the conductive 
metal rings are formed concentrically. (No specific pattern is required, 
but rings are convenient for distribution of power). Electrical 
connections 324 (in this case, wires) are used to connect the power supply 
voltages, (from the conductive metal rings) to the appropriate contactors 
322a. 
The specific power supply connections for each different IC (DUT) is 
determined by the configuration of the installed bias board (e.g., 262). 
The bias board 262 essentially "programs" the power supply connections for 
the test fixture 300, conveying the supply voltages from a first portion 
(e.g., 318) of the plurality of elongated pins to another portion (e.g., 
316) of the plurality of elongated pins. In this manner, virtually any 
power supply pin configuration can be accommodated by employing a properly 
configured bias adapter board. It is only necessary to provide as many 
different DUT base boards (including assembled test receptacle) as are 
necessary to accommodate all of the different DUT connectors to be 
employed. This number can be significantly fewer than the number of DUT 
connector types by virtue of the fact that more than one IC DUT can be 
accommodated by a single DUT base board. Storage requirements are thus 
minimized by eliminating the need for storing a custom designed DUT board 
for every IC type. 
Further, each IC need only have a custom bias adapter board. These boards, 
which are considerably smaller and simpler than the prior art DUT boards, 
require little storage space, are relatively inexpensive, and can be 
assembled from a relatively small number of common blank boards. The 
commonality between bias adapter boards is defined by the number of 
different test receptacle DUT connector pin patterns which must be 
accommodated. 
Those of ordinary skill in the art will immediately understand the 
desirability of providing decoupling capacitors (326) on each of the power 
supply pins. Such capacitors may readily be added to the bias board. It is 
within the spirit and scope of the present invention to do so. It will 
further be recognized by those of ordinary skill in the art that 
inexpensive, custom bias adapter cards (boards) can readily be designed 
wherein the connections between the power supply carrying receptacle pins 
and socket pins connected to power supply pins of the DUT are accomplished 
by conductive traces on the bias adapter board, especially where so-called 
"micro-strip" traces are employed. These traces can also be routed to 
conductive pads to which surface-mounted decoupling capacitors are 
assembled. 
The bias board provides an easy, inexpensive method to provide power and 
ground connections to a device under test (DUT) using automatic test 
equipment. For example, when personalizing, or "programming" a bias board, 
a customer specification would be reviewed to determine where power supply 
connections are needed. The bias board is wired and decoupling capacitors 
are added (as desired) for all power connections. HolTights are then 
installed at the location of each biased pin. The bias board is then 
mounted to the base board, by the fastening means (e.g., screw 330, nut 
332) described hereinabove, or the like. By employing a relatively simple 
bias adapter scheme, potential delays are avoided in the anode cycle, 
since no elaborate fabrication techniques initially are required to adapt 
an existing DUT fixture to a new IC. Only a new bias adapter card is 
required. 
Although the DUT fixture 300 is described above with respect to a specific 
mechanical configuration, one of ordinary skill in the art will 
immediately recognize that the technique is readily adaptable to a variety 
of different ATE test interface connection schemes. Further, the specific 
arrangement of test receptacle, DUT baseboard, and bias adapter card 
described herein is not intended to be restrictive. Any technique which 
uses a bias adapter to connect between power supply connections and DUT 
connector pins independent of the DUT base board may be employed, 
regardless of the specific pin/socket/contactor arrangement which is 
employed. It is within the spirit and scope of the present invention to do 
so. 
The above, and other objects, features, advantages and embodiments of the 
invention, including other (i. e., additional) embodiments of the 
techniques discussed above may become apparent to one having ordinary 
skill in the art to which this invention most nearly pertains, and such 
other and additional embodiments are deemed to be within the spirit and 
scope of the present invention.