Patent Publication Number: US-6903562-B1

Title: Integrated micromachine relay for automated test equipment applications

Description:
The present application claims priority from and is a divisional application of U.S. patent application Ser. No. 09/859,842, filed May 16, 2001, now U.S. Pat. No. 6,700,396, which is owned by the same assignee as the present patent application. 

   FIELD OF THE INVENTION 
   The present invention relates to test equipment, and more specifically, to relays used in test equipment. 
   BACKGROUND 
   Electronic devices are often tested using automatic test equipment (ATE). Generally, the tester includes a computer system that coordinates and runs the tests, and a testing apparatus. The testing apparatus includes a test head, into which the device under test (DUT) is placed. 
   Contacts in the test head are used to couple the trace of the DUT to the control mechanisms. These contacts, generally spring pins, are designed to send through a high fidelity and high speed signal from the computer system. A control circuit and timing generation generally controls access. Pin electronics are electronic components that control the individual pins. The individual pins are controlled by relays, electromagnetic devices for remote and automatic control of the pins. The relays are actuated by variation in conditions of an electric circuit controlled by the pin electronics integrated circuits. Relays are mechanical devices that are large in size, especially with respect to the other components on the test head. Reducing the size of the relays may result in the need for more complex control circuits. However, the size of the components that may be placed on a test head is limited. 
   Alternatively, electronic switches may be used in place of the relays in order to control the pins. However, electronic switches either have low bandwidth or high resistance when they are on, or low breakdown voltage and when they are off. Transistors are disadvantageous, as they combination of through bandwidth, on resistance, and 
   SUMMARY AND OBJECTS OF THE INVENTION 
   It is an object of this invention to provide for automatic test equipment that utilizes a micromachine relay for controlling pins. 
   It is a further object of this invention to reduce the electric length from the device under test (DUT) to the pin electronics. 
   A pin controller is described. A pin controller comprises at least one spring pin designed to movably couple the pin controller to a device under test (DUT) to provide signals to the DUT. The pin controller further includes a micromachine relay coupled to the at least one spring pin to control the movement of the at least one spring pin and an integrated circuit for controlling the micromachine relay. 
   Other objects, features, and advantages of the present invention will be apparent from the accompanying drawings and from the detailed description that follows below. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which: 
       FIG. 1  illustrates an overview block diagram of one embodiment of a testing system in which the present invention may be implemented. 
       FIG. 2  illustrates a block diagram of one embodiment of a test head. 
       FIG. 3  illustrates a perspective view of one embodiment of a test head. 
       FIG. 4A  illustrates a one embodiment of a control card. 
       FIG. 4B  illustrates a one embodiment of a pin electronics portion of the control card. 
       FIG. 4C  illustrates one embodiment of a top view of the control card. 
       FIG. 5  illustrates one embodiment of the relationship between the elements of the control card 
       FIG. 6  illustrates a detailed diagram of one embodiment of a control card of the present invention. 
       FIG. 7  illustrates one embodiment of the switching setup of a micromachine relay of the present invention. 
       FIG. 8  illustrates another embodiment of the switching setup of a micromachine relay of the present invention. 
       FIG. 9A  illustrates one embodiment of one stage of a micromachine relay. 
       FIG. 9B  illustrates a circuit diagram of one embodiment of the micromachine relay. 
       FIG. 9C  illustrates a physical layout path of one embodiment of one stage of the micromachine relay. 
       FIG. 9D  illustrates a cross-section of the physical layout of FIG.  9 C. 
       FIG. 10A  illustrates one embodiment of a set of spring pins implemented as an elastomeric connection. 
       FIG. 10B  illustrates one embodiment of a spring pin implemented as a micromachined bump connector. 
       FIG. 10C  illustrates another embodiment of a spring pin implemented as a micromachined bump connector. 
       FIG. 10D  illustrates one embodiment of a spring pin implemented as a liquid-based system. 
   

   DETAILED DESCRIPTION 
   A method and apparatus for using a micromachine relay in an automated test system is described. Using a micromachine relay in automated testing equipment reduces an electrical length between the pin electronics and the device under test (DUT). The micromachine relay could further be integrated onto the pin electronics integrated circuit (IC). The features of this design include a shorter electrical length between the device under test (DUT) and the pin electronics, increased bandwidth, and higher pin count by reducing associated control sizing. 
   Using micromachined relays further provides a lower fabrication cost. Furthermore, the pin electronics device may be mounted directly below the spring pin ring, since the reduction in size provides additional space. The use of micromachine relays also permits use of the system for mixed signal testing. Furthermore, because the pin electronics are dose to the center, there is a shorter electrical length, leading to better signals. However, using the relay and the pin electronics in close proximity creates a need for integrated cooling. Therefore, for one embodiment, a cooling mechanism is integrated into the integrated circuit card, as will be described below. 
     FIG. 1  illustrates an overall block diagram of one embodiment of the testing device  110  in which the present invention may be included. The testing device  110  includes a computer system  120 . For one embodiment, the computer system  120  includes at least one central processing unit (CPU). For one embodiment, the computer system  120  may be a mainframe. The computer system  120  is coupled via transmission lines  125  to a test head  130 . The transmission lines  125 , for one embodiment, comprise a bus. The test head  130  is designed to test a device under test (DUT)  140  that is coupled to the test head  130  via connectors  135 . The connectors  135  may comprise a set of pins within the test head  130 . For one embodiment, the connection  135  may be spring pins, an elastomeric connection, a bump connector, or another type of connector. The micromachine relays, discussed in more detail below, are used to couple and decouple the DUT  140  from the test head  130 . For one embodiment, the connectors  135  may be rigid, and an electric coupling may be established. For another embodiment, the connectors  135  may be moveable, such as moveable springs or micromachine bump connectors. If the connections  135  are micromachine bump connectors, for one embodiment, electrostatic force may be used to move the bump, and thereby establish a connection between the DUT  140  and the test head  130 . For simplicity, for the remainder of this application the term “spring pin” will be used. However, it is to be understood that the term “spring pin” may refer to any connector  135  which is used to couple the DUT  140  to a test head  130 , including a spring pin, an elastomer, a bump connector, or another type of connection. 
   An integral cooling mechanism  180  may be coupled to test head  130 . For one embodiment, integral cooling mechanism  180  may use liquid or gas cooling, as will be described below. The integral cooling mechanism  180  permits the ca location of the control circuits and relays, without damaging either by inadequate cooling. 
   The testing device  110  may further include a network  160 , coupled to a secondary controller  150 . The secondary controller  150 , for one embodiment, controls the probe used to test the DUT  140  on the test head  130 . 
   For one embodiment, the testing device  110  is designed to test a variety of integrated circuits. These devices under test (DUTs)  140  are placed in the testing device  110  and probed. For one embodiment, the bus  125  between the test head  130  and the computer system  120  is flexible and permits movement of the test head  130 . 
     FIG. 2  is a block diagram of the circuitry included in the computer system  120  and test head  130 . The timing generator  210  generates clocking/timing signals for the pin electronics IC (PEIC)  220 . For one embodiment, the timing generator  210  is located in the computer system  120 . Alternatively, the timing generator  210  may be moved to the test head  130 , reducing signal delays. The PEIC  220  is located on the test head  130 . The PEIC  220  is coupled to the micromachine relay  230 , which is also located on the test head  130 . The micromachine relay  230  controls the spring pins  270 , located on the test head. The spring pins  270  interface with the device under test (DUT). 
   A controller  240  generates the signals used for testing the DUT. For one embodiment, the controller  240  is located on the computer system  120 . A logic circuit  250  receives the signals from the controller  240 . For one embodiment, the logic circuit  250  is located on the computer system  120 . For an alternative embodiment, the logic circuit  250  is located on the test head  130 . The logic circuit transmits some signals to a driver IC  260 . For one embodiment, the logic circuit  250  is a field programmable gate array (FPGA). 
   A driver circuit  260  is coupled to the micromachine relay  230 , and drives the micromachine relay  230 . 
   The circuitry may further include cooling mechanism  180 , to cool the test head. For one embodiment, the cooling mechanism is integral with the printed circuit board on which the PEIC  220  resides. For one embodiment, cooling mechanism is designed to receive and circulate a chilled substance that is used for cooling. The chilled substance may be a gas, such as R134, or a liquid, such as water. For one embodiment, the cooling mechanism  180  comprises cooling channels within the integrated circuit card. The cooling channels may be etched, drilled, cast, or micromachined, or created in some other way in the printed circuit board. 
     FIG. 3  illustrates one embodiment of the test head  130 . For one embodiment, the test head  130  has a circular body  310 . The test head  130  further includes a plurality of integrated circuit cards  320 . The integrated circuit cards  130  are placed in a radial manner within the test head  130 . The integrated circuit cards  310  are designed to control a plurality of pins  330  extending from each integrated circuit card  320 . The pins  330  are designed to mate with the top of the test head  130 , and thereby couple various signals to a device under test (DUT)  140 . For one embodiment, the body of the test head  310  includes a plurality of wedge shaped cut-outs  340  on the top of the body  310 . These wedge shaped cut-outs  340  are designed to receive a portion of the integrated circuit cards  320 . The integrated circuit cards  320  are designed such that the portion containing the pins fit within the wedge shaped cut-outs  340 . For anther embodiment, the top of the body  310  includes a plurality of holes  330  sized to fit the pins. The integrated circuit cards  320  are designed to have the pins  330  extend through the holes within the body  310 . Alternative test head configurations may be used. But in any case, the test head includes a plurality of pins, arranged to connect a large number of pins to a single device under test coupled to the test head using the pins. For one embodiment, the pin density may be increased when using micromachine relays without increasing the wedge area, since pins may be placed more closely together. 
     FIG. 4A  illustrates a layout of one embodiment of a circuit board. The plug-in board  410  is designed to be plugged into the test head  130 . For one embodiment, in multiple plug-in boards  410  of similar configuration are plugged into a test head. For one embodiment, sixty-four plug-in boards  410  are plugged into a single test head. The plug-in board  410  includes cooling channels  415 . Cooling channels  415  are designed to lead a cooling substance to pin electronics card  440 , coupled to the plug-in board  410 . For one embodiment, cooling channels  415  may further include stiffening material, to add rigidity to the plug-in board  410 . 
   Other circuitry  420  may also be coupled to the plug-in board  410 . Backplane connection  435  may couple plug-in board  410  to the back plane. The backplane (not shown) provides certain signals to the plug-in board  410 , such as a ground and/or power signal. Other bussed signals may also be provided through the backplane. 
   The pin electronics card  440  is coupled to plug-in board. For one embodiment, the pin electronics card  440  includes input-output (I/O) channels  430 . For one embodiment, the I/O connectors  430  are coupled to plug-in board  410  through elastomeric connections. The I/O connectors  430  lead signals from the plug-in board  410  to the circuitry on the pin electronics card  440  (not shown). The pin electronics card  440  includes the circuitry to control the connection to spring pins  445 . The spring pins  445  (not shown) are used to couple various signals to a device under test. 
   The cooling channels  415  are connected through the pin electronics card  440 , to provide a cooling mechanism for circuitry on the pin electronics card  440 . This is described in more detail below. 
     FIG. 4B  illustrates a layout of one embodiment of the pin electronics card  440 . The pin electronics card  440  includes I/O connectors  430 . For one embodiment, each of the long I/O connectors shown corresponds to 120 I/O connections, while the short connector corresponds to 50 I/O connections. Thus, for one embodiment, up to 365 signals may be coupled to pin electronics circuit  440 . Coolant hoses  460  lead coolant from the cooling channels  415  to the pin electronics card  440 . The pin electronics card  440  may further include digital to analog converters (DACs). The DACs convert signals received from the test head into signals to control the micromachine relays  460  The pin electronics card  440  may further include sample and hold (S&amp;H) circuits  470 . An S&amp;H circuit  470  provides a constant voltage output that provides an input to an A/D converter. 
   Pin electronics circuits (PEIC)  465  are for controlling the signals that the micromachine relays  460  couple to the pogo-pin connector  455 . For one embodiment, a single micromachine relay controls each spring pin. 
   The spring pin, for another embodiment, may be an elastomeric connector, or a bump connector. The micromachine relay  460  controls the electrical connection between the spring pin and the pin electronics. For another embodiment, the spring pins may be mobile, and may be physically moved by the relay  460 . 
   Thus, for example, a spring pin may have coupled to it, via PEIC  465  a signal A, and the micromachine relay  460 , controlled by DAC, may couple the spring pin to a device under test (DUT) and thus couple the signal A to the DUT. In this way, testing of various devices may be accomplished using a test head having plug-in boards  410 , including pin electronics cards  440 . 
     FIG. 4C  illustrates one embodiment of the circuit board  410  from above, as it is in a test head. A single circuit board  410  is shown in detail, while an adjacent circuit board  490  is shown, to illustrate the relationship between the two boards. 
   The circuit board  410  includes pin electronics card  420 . From above, the spring pin connector  455  can be seen as occupying a forward portion of the pin electronics card  420 , and the extreme forward portion of the circuit board  410 . For one embodiment, the spring pin connector  455  is positioned such that a DUT (not shown) would be located directly over the spring pin connector  455 , such that by activating a spring pin, a connection to the DUT is established. 
   The pin electronics card  420  further includes PEICs and micromachine relays  460 / 465 . These devices are coupled to the circuit board, as shown, and are located adjacent to as well as underneath the spring pin connector. As indicated, the forward portion of the pin electronics card  420  is the relay portion of the card, where the micromachine relays reside, while the rear portion of the pin electronics card  420  is the PEIC portion of the card, where the PEIC circuits reside. 
   Further,  FIG. 4C  shows one embodiment of cooling channels  480 . Cooling channels are within the circuit board  410 , and are designed to receive a cooling substance to provide cooling to the PEICs, DACs, micromachine relays, and other circuits on the card  420 . For one embodiment, the cooling channels use water. Alternatively, HCFC, R134, xenon or another gas may be used. For one embodiment, the substance in the cooling channels  480  is circulated. For one embodiment, the material and location of the cooling channels  480  may be chosen to dissipate sufficient heat to maintain a device under test at a standard operating temperature, and to maintain the PEICs, DACs, and micromachine relays within their operating parameters. The adjustment of such cooling mechanisms is known in the art. 
   For one embodiment, cooling channel  480  may be micromachined. That is, micromachine devices may be used to form channels for the cooling substance. For another embodiment, cooling channel  480  may be etched into circuit board  410 . Such methods of etching are known in the art. Alternatively, cooling channel  480  may be drilled into the board. For yet another embodiment, the circuit board  410  may be made including the cooling channels  480 . For another embodiment, a heat sink may be cast and coupled to the pin electronics card  420 , to cool the device. For one embodiment, such a heat sink may be located at the base of the circuit board  410 . For one embodiment, such a heat sink may be integral with the coupling mechanism that couples the circuit board  410  to the test head. 
   Cooling channels  480 , in any case, are integral with circuit board  410 , and provides cooling for at least the pin electronics card portion  420  of the circuit board  410 . For another embodiment, cooling channels  480  may extend through the entire circuit board  410 , and may be used to cool other circuits on circuit board  410 . 
     FIG. 5  illustrates a block diagram of a pin electronics card  320  of the present invention. The pin electronics card  320  or control card  320  is coupled to a spring pin ring  560 . The spring pin ring  560  includes a plurality of spring pins  570  movably connected into the spring pin ring  560 . The spring pin ring  560  is designed to keep the spring pins  570  in place while permitting motion. For one embodiment, each of the spring pins  570  is separately controlled. The spring pin ring  560  is wedge shaped for one embodiment. The wedge shaped spring pin ring  560  is designed to fit into the wedge shaped cut out  330  within the body of the test head  310 . 
   A micromachine relay matrix (MRM)  550  is coupled to the spring pins  570 . The micromachine relay switch matrix (MRM)  550  controls the connection of each of the spring pins  570 . The MRM  550  is coupled to a pin electronics integrated circuit (PEIC)  530 . The pin electronics integrated circuits (PEICs)  530  control the micromachine relay matrix  550 . The PEIC  530  is coupled to the micromachine relay matrix (MRM)  550  via an interface  540 . The PEIC  530  is designed to feed the control signals to the MRM  550 , in order to control the spring pins  570 . For one embodiment, the MRM  550  is implemented on the same substrate as the PEIC  530 , and the interface  540  comprises traces on a printed circuit board. For another embodiment, the MRM  550  and the PEIC  530  together form a hybrid device. 
   Timing generation and control circuits  510  are located at the bottom of the block diagram. For one embodiment, the timing generation and control circuits  510  are located within the computer system  120 . For another embodiment, the timing generation and control circuits  510  are included within the test head  130 . The timing generation and control circuits  510  generates testing and motion signals for the spring pins  570  and test head  130 . The timing generation and control circuits  510  are connected via interface cabling  520  to the pin electronics integrated circuits (PEIC)  530 . For one embodiment, the interface cabling  520  is a bus designed to reduce deterioration of the timing and control signals generated by the timing generation and control circuits  510 . For one embodiment, the length of the interface cabling  520  is kept to a minimum. By reducing the size of the relays by using micromachine relays, the timing generating and control circuits  510  may, for one embodiment, be placed on the test head, thereby reducing the length of interface cabling  520 . 
     FIG. 6  illustrates a detailed diagram of one embodiment of a control card  320  of the present invention.  FIGS. 6  includes a side view  610  of a control card  320 , as well as a front view  615 . A plurality of pins  620  are shown extending from the control card  320 . The structure supporting the pins  620  is the spring pin ring  625 . 
   The micromachine relays  630  are coupled to the pins  620 . The micromachine relays  630  control the motion of the pins  620  within the spring pin ring  625 . A plurality of integrated circuits  640  are further coupled to the card. The integrated circuits include the pin electronics IC, and other integrated circuits. 
   For one embodiment, a cooling manifold is coupled to the control card. The cooling manifold  660  is used to cool certain integrated circuits. For one embodiment, some of the pin electronics ICs are in contact with the cooling manifold. For an alternative embodiment, heat sinks are coupled to the integrated circuits, and the heat sinks are coupled to the cooling manifold  660 . For one embodiment, the cooling manifold  660  is a metal element having a path for a cooling fluid, such as water. In an alternative embodiment, other cooling mechanisms may be used. 
     FIG. 7  illustrates one embodiment of the switching setup of a micromachine relay of the present invention. The micromachine relay comprises a plurality of switches which switch in or out a plurality of signal sources. For one embodiment, the pin electronics IC  430  is coupled to the device under test (DUT)  140  via a first switch S 1   710 . When the first switch S 1   710  is closed, the PEIC  430  is coupled to the DUT  140 . A tin-ing calibration input (TCAL)  720  is coupled between the PEIC  430  and DUT  140  via second switch S 2   725 . Additionally, another plurality of signals  740 ,  750 , and  760  are coupled to between the PEIC  430  and DUT  140  via a third switch  730 . For one embodiment, these plurality of signals may include a measure of DC power (MEAS)  740 , an analog resource (APIN)  750 , and an auxiliary path (AUX)  760 . For one embodiment, the auxiliary path  760  comprise a high quality radio frequency grade path. The signals MEAS  740 , APIN  750 , and AUX  760  are coupled to the third switch S 3  via a fourth S 4   745 , fifth S 5   755 , and sixth S 6   765  pin respectively. 
     FIG. 8  illustrates an alternative embodiment of the switching setup of a micromachine relay of the present invention. The PEIC  440  is coupled to the DUT  140  via a first switch S 1   810 . A plurality of signals  840 , and  860  are coupled to between the PEIC  430  and DUT  130  via a third switch  830 . For one embodiment, these plurality of signals may include a measure of DC power (MEAS)  840  and an analog resource (APIN)  850 . 
     FIG. 9A  illustrates one embodiment of one stage of a micromachine relay. For one embodiment, eight identical stages comprise the micromachine chip. For one embodiment, the eight independent stages, include 20 relays. In the stage shown in  FIG. 9A , relays  1 - 5 , designated RLA 1  through RLA 5 , are shown as switches  940 . Relays actually control movement of the signal to a device under test, shown as DUT output  930 . The inputs to the stage shown include DCL input  910 , PPMU input  915 , TMU input  920 , and AUX input  925 . DCL input  910  is from the pin electronics hybrid (PEHB). PPMU input  915  is from a pin parametric measurement unit, which is used to make low speed analog measurements, and DC voltage/current measurements. TMU input  920  is a time measurement unit input, and used to measure time response. AUX input  925  is used to make auxiliary measurements. 
   One set of specifications, derived from an exemplary implementation of the above circuit provides the following exemplary specification numbers:
         Actuator voltage/current (contacts closed): +2.0 to +5.5 Volts, &lt;25 mA; or 50V at &lt;1 mA for electrostatic systems   Switching characteristics of open/close settling time: &lt;100 μs   MIFB: 4 δ       

   For one embodiment, the specification met after 100 million switch operations should be:
         Capacitance between open contacts: &lt;25 fF   Capacitance between contacts and actuator: &lt;50 fF   Crosstalk between stages: &lt;20 dB at 5 GHz   Crosstalk between DCL and AUX when relays are open: &lt;20 dB at 5 GHz       

   Note that these numbers are design targets and may be varied during implementation. Furthermore, using the above defined circuit, the following target relationship data was obtained:
         Setup: RLA 1  ON, RLA 2 , RLA 3 , RLA 4 , RLA 5  OFF (DC to 5 GHz)
           Nominal impedance: 50 ohms;   VSWR: 1.2:1 Insertion loss: &lt;0.1 dB   Voltage/current handling capability: &gt;+/=100 V, 100 mA Setup: RLA 4  and RLA 5  ON, RLA 1 , RLA 2 , RLA 3  OFF (DC to 1 GHz)   Normal impedance: 50 ohms;   VSWR: 1.2:1   Insertion loss: &lt;0.1 dB   Voltage/current handling capability: &gt;+1=100 V, 100 mA Setup: RLA 3  and RLA 5  (or RLA  2  and RLA  5 ) ON, RLA 1 , RLA 4  OFF (DC to  5  HG)   DC ON resistance: &lt;100 mΩ   Cold-switch handling capability: +1-100 V, 500 mA   
               

     FIG. 9B  illustrates a circuit diagram of one embodiment of the micromachine relay. The relays are illustrated as resistors, showing the effect of the relays on signals being passed to the DUT. 
     FIG. 9C  illustrates a physical layout path of one embodiment of one stage of the micromachine relay. The relays RLA 1  through RLA 5  are shown on a substrate, each having an input signal on a trace. The CRLA signal  955  is coupled to all of the RLAs. As  FIG. 9D  shows, relays  960  are placed on substrate  980 . Traces  970  couple the appropriate primary signal to each of the relays  960 . Ground  990  is further coupled to relay  960 .  FIGS. 9C and 9D  illustrate an exemplary circuit layout of a micromachine relay, as shown in FIG.  9 A. It is to be understood that alternative layouts may be used. 
   The micromachine relays illustrated as switches may be implemented in a variety of ways. For one embodiment, a cantilever arm is designed, and the motion of the cantilever arm is controlled by electromagnetic attraction/repulsion. For another embodiment, disk drive technology may be used to implement the micromachine relays, using rhodium contacts and ferrite electromagnets. For another embodiment, a relay may be implemented using micromachined parts. For another embodiment, an electrostatic relay may be used. Alternatively, other implementations of the micromachine relay may be used. 
     FIG. 10A  illustrates one embodiment of a set of spring pins implemented as an elastomeric connection. The pins  1010  are designed to be coupled to a device under test. Each pin  1010  has a counterpart  1015 , which is located beneath the pin  1010 , and coupled to the pin via elastomeric material  1020 . Elastomeric materials  1020  include a plurality of small conductive wires. For one embodiment, elastomeric material  1020  includes vertical connections only, coupling counterpart  1015  to pin  1010 , when the actuator  1025  compresses the elastomeric material  1020 . The actuator  1025  is controlled by the micromachine relays. 
     FIG. 10B  illustrates one embodiment of a spring pin implemented as a micromachined bump connector. The spring pin  1030  is moved by electrostatic force, to couple the conductive layer  1030  to the device under test. In this system, either the pin may be rigid, and a conductor may be coupled to the pin, or the pin may itself move, and be physically coupled to and decoupled from the device. The alternative embodiment of  FIG. 10C  shows the pin  1035  being rigid, while a flexible coupling mechanism  1045  moves up and down, to electrically couple the pin  1035  to the device under test. 
     FIG. 10D  illustrates one embodiment of a spring pin implemented as a liquid-based system. The pin  1050  is rigid, and has a counterpart  1055 . The area between the pin  1050  and its counterpart  1055  is bridged by a material  1060  which may be made to expand to cause an electrical connection. Thus, for example, a liquid may be used, which is expanded by micromachined relays, to establish a connection. Alternative materials may be used if they are responsive to a signal to expand and contract. 
   The implementations of spring pins for use with micromachine relays discussed  FIGS. 10A-D  are merely exemplary. It is to be understood that alternative methods of establishing an electrical connection between a device under test and a pin electronics circuit may be used. 
   The use of the micromachine relays results in many benefits, including a reduced electrical length, by permitting the mounting of the relays and the hybrid circuits close to the spring pins. Furthermore, the use of rmicromachine relays increases bandwidth by reducing capacitance, using short PCB traces and bales. Furthermore, the use of the micromachine relays increases pin count and decreases the space necessary for a pin electronics card. These advantages are the result of using the micromachine relays described above. 
   In the foregoing specification, the invention has been described with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense. The present invention should not be construed as limited by such embodiments and examples, but rather construed according to the following claims.