Abstract:
A test fixture for electrically connecting a plurality of limited-access test targets on a loaded circuit board with a plurality of interface probes of a tester may comprise a plurality of elongate test probes, a universal interface plate (UIP), and a wireless interface printed circuit board (WIPCB). A first end of each elongate test probe is substantially aligned with a limited-access target on the loaded circuit board when the test fixture is positioned adjacent the loaded circuit board. Each of a plurality of double-headed spring probes mounted to the UIP has a first spring loaded head located at its first end and a second spring loaded head located at its second end. Each double-headed spring probe is generally axially aligned with an elongate test probe so that its first spring loaded head contacts a second end of the corresponding elongate test probe. Each of a plurality of contact pads on the first side of the WIPCB is substantially aligned with a double-headed spring probe so that each contact pad contacts the second spring loaded head of the corresponding double-headed spring probe. Each of a plurality of contact targets on the second side of the WIPCB is electrically connected to a contact pad on the first side of the WIPCB and contacts an interface probe of the tester when the test fixture is mounted on the tester.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a division of U.S. application Ser. No. 09/348,523, filed Jul. 7, 1999, now U.S. Pat. No. 6,225,817, which is a divisional of U.S. application Ser. No. 08/739,387, filed Oct. 29, 1996, now U.S. Pat. No. 5,945,836, both of which are incorporated herein by reference for all that they disclose. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to the field of test equipment for testing printed circuit boards, and more particularly to board test fixtures and other mechanical interfaces for electrically interconnecting electronic circuit cards having electronic components and the like to the interface probes of a loaded-board tester. 
     BACKGROUND OF THE INVENTION 
     Loaded-Board Test Fixtures 
     After printed circuit boards (PCB&#39;s) have been manufactured and loaded with components, and before they can be used or placed into assembled products, they should be tested to verify that all required electrical connections have been properly completed and that all necessary electrical components have been attached or mounted to the board in proper position and with proper orientation. Other reasons for testing printed circuit boards are to determine and verify whether the proper components have been used and whether they are of the proper value. It is also necessary to determine whether each component performs properly (i.e., in accordance with the specification). Some electrical components and electro-mechanical components also may require adjustment after installation. 
     Loaded-board testing has complex multiplexed tester resources and is capable of probing soldered leads, vias and testpads on loaded boards with topside and bottom side components. Loaded-board testing includes analog. and digital tests, such as tests for electrical connectivity, voltage, resistance, capacitance, inductance, circuit function, device function, polarity, vector testing, vectorless testing, and circuit functional testing. Loaded-board testing requires very low contact resistance between the test targets and the fixture components. 
     Advances in circuit board and electronic component packaging technology have escalated the probe spacing demands placed on loaded-board test equipment. Existing state-of-the-art technology requires loaded-board test equipment capable of accessing test targets which are spaced apart by 50 mils (center to center) or less, where test targets are physical features on a PCB or electronic component which may be probed during testing. One of the greatest challenges faced by loaded-board test equipment manufacturers now and in the future is a high false failure and test malfunction rate caused by physical and electrical contact problems. These problems are exacerbated by existing fixture limitations in probing accuracy, probing pitch (center to center spacing), and surface contamination. 
     As component and board geometries shrink and become denser, loaded-board testing becomes more difficult using standard fixtures. Existing shortwire, loaded-board fixtures can consistently hit test targets equal to or greater than 35 mils in diameter with equal to or greater than 75-mil pitch. Targets which are smaller or more closely spaced cannot be probed with consistency due to prohibitive component and system tolerance stack-ups. 
     A variety of test fixtures have heretofore been available for testing loaded boards on test equipment. A device under test (DUT) typically embodies a PCB loaded with electronic components and electronic hardware. FIG. 1 shows a conventional shortwire, loaded-board fixture, which consists of a DUT  108  with outer-layer artwork, a standard  106  or variable  118  tooling pin for alignment, a probe protection plate  104 , standard spring probes  120  whose tips  116  exactly correspond to test target locations  110  and  112 , spacers  114  to limit the deflection of the DUT under vacuum loading, a probe-mounting plate  102  in which the spring probes  120  are installed, personality pins  100  which are wired to the spring probes  120 , and an alignment plate  122  which aligns the wirewrap tails of the personality pins  100  into a regularly spaced pattern so that they can line up with interface probes  124  mounted in the tester (not shown) Note: a spring probe is a standard device, commonly used by the test community, which conducts electrical signals and contains a compression spring and plunger that move relative to the barrel and/or socket when actuated. A solid probe also conducts electrical signals but has no additional parts which move relative to each other during actuation. 
     During test, the DUT  108  is pulled down by vacuum or other known mechanical means to contact the tips  116  of the spring probes  120 . The sockets of the standard spring probes  120  are wired to personality pins  100 , and an alignment plate  122  funnels the long, flexible personality pin tips  126  into a regularly spaced pattern. The tips  126  of personality pins  100  contact the interface probes  124  located in the tester (not shown). Once electrical contact between the DUT  108  and the tester is established, in-circuit or functional testing may commence. Hewlett-Packard Company Application Note 340-1 titled “Reducing Fixture-Induced Test Failures,” (printed December 1990 and can be obtained from Hewlett-Packard Company in Palo Alto, Calif.), discloses shortwire fixturing and is incorporated herein for all that it teaches. U.S. Pat. No. 4,771,234 titled “Vacuum-Actuated Test Fixture” by Cook et al. discloses a longwire fixture and is incorporated herein for all that it teaches. 
     FIG. 2 shows one conventional fixture that attempts to address limited-access problems during testing. The term “limited-access” refers to something that cannot easily be reached, or accessed, due to physical restrictions or constraints. For example, a limited-access PCB may contain many targets that are too closely is spaced to accurately probe using existing fixture technology. The term “standard-access” refers to that which can be reached, or accessed, using existing fixture technology. The fixture of FIG. 2 consists of a DUT  206  with testpads  208  and  210 , a tooling pin  204 , a probe protection plate  202 , standard spring probes  214  and  216  installed in a probe-mounting plate  200 , and short probes  212  and  220  commonly referred to as “ULTRALIGN” probes (Ultralign is a registered trademark of TTI Testron, Inc.) installed directly in the probe protection plate  202 . Upon actuation, standard spring probes  216  and  214  located in the probe-mounting plate  200  push against the floating plungers of “ULTRALIGN” probes  212  and  220 . These short plungers are forced upward to contact test targets  208  and  210 , while the sockets  218  and  222  remain fixed within the probe protection plate  202 . An “ULTRALIGN” fixture may contain a mixture of spring probes for probing standard-access targets and “,ULTRALIGN” probes for probing limited-access targets. 
     Despite its potential benefits, the “ULTRALIGN” fixture can be expensive and does not probe targets with a pitch of less than 50 mils. An “ULTRALIGN” fixture only permits limited probe travel which may result in poor connectivity between the probes  212  and  220  and the test targets  208  and  210 . Also, these probes are costly and require expensive maintenance to replace worn or broken “ULTPALIGN” probes. An example of this type of fixture is disclosed in U.S. Pat. No. 5,510,772 entitled “Test Fixture for Printed Circuit Boards” to Seavey, which is incorporated herein for all that it teaches. 
     FIG. 3 shows a conventional guided-probe protection plate fixture. Guided-probe protection plates are used in standard loaded-board test fixtures to improve the pointing accuracy of spring probes. These plates contain cone-shaped through-holes which guide, or funnel, the tips of spring probes toward test targets. Such a fixture consists of a probe-mounting plate  300  with standard spring probes  312  and  314 , a guided-probe protection plate  302  with spacers  310  and cone-shaped holes  316  for guiding the spring probes to the test targets  306  and  308  on the DUT  304 . Additional manufacturing steps and increased fixture maintenance are required due to increased wear on the probes and the probe protection plate, and generally only narrow probe tip styles can be used. Although probing accuracy is slightly enhanced with this method, targets with center-to-center spacing of less than 75 mils cannot be probed reliably. 
     Bare-Board Test Fixtures 
     Bare-board testing 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 huge number of switches connecting test probes to corresponding test circuits in the electronic test analyzer. 
     While loaded-board testing can determine an electronic component&#39;s existence, proper orientation, or functionality, bare-board testing only checks for electrical continuity on PCB&#39;s without components. Bare-board testing does not require the very low contact resistance that loaded-board testing requires, nor does bare-board testing utilize sophisticated and complex multiplexed tester resources which must be assigned to specific targets and circuits on the device under test. 
     In previous years, PCB&#39;s were designed and manufactured so that their features resided in a regularly spaced pattern. During testing, the PCB was placed directly atop a regularly spaced pattern of interface probes located in the tester. As PCB and component geometries shrunk, PCB features 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. Circuit Check, Inc. (Maple Grove, Minn.), Everett Charles Technologies (Pomona, Calif.), and Mania Testerion, Inc. (Santa Ana, Calif.), among others, make bare-board test fixtures which are commonly used on bare-board testers today. 
     Although each bare-board fixture builder uses unique components and manufacturing processes, most bare-board fixtures resemble FIG.  4  and include regularly spaced spring probes  414  on a tester and long, solid test probes  402  and  416  inserted through several layers of guide plates  400  drilled with small through-holes and held in a spaced-apart fashion with spacers  410 . The bed of standard spring probes  414  actuate the solid test probes  402  and  416 . The long, solid probes  402  and  416  may be inserted into the guide plates  400  vertically or at an angle in order to facilitate an easy transition between the fine-pitch, or very close, spacing of testpads  404  and  406  on the PCB side of the fixture and the larger-pitch spacing of the spring probes  414  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, it is not 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. 
     Bare-board fixtures are not designed to accommodate 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 spacing of bare-board tester interface probes is approximately 0.050 inches by 0.050 inches or 0.100 inches by 0.100 inches, while the spacing of Hewlett-Packard&#39;s tester interface probes is approximately 0.150 inches by 0.350 inches. The probe spacing of bare-board fixtures which are designed to fit on bare-board testers is not compatible with the interface probe spacing of Hewlett-Packard&#39;s loaded-board tester. Bare-board fixtures translate a target on the PCB 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. 
     The term “no-clean” refers to the non-conductive solder flux residue which remains on printed circuit assemblies after components have been attached. Unless this contamination is removed, no-clean targets, or targets which are coated with this non-conductive surface residue, provide poor electrical contact and are difficult to test. Furthermore, industry trends, such as smaller component packaging and denser PCBs, are forcing electronics&#39; manufacturers to confront smaller center-to-center target spacing, and small-diameter targets. These challenges require an improved loaded-board test fixture that is capable of providing reliable, consistent in-circuit and circuit functional testing of printed circuit assemblies by probing the smaller, more closely spaced targets on today&#39;s no-clean, loaded printed circuit boards, while at the same time probing vias and testpads on loaded-boards with top and bottom-side components and testing for electrical connectivity, voltage, resistance, capacitance, inductance, circuit function, device function, polarity, vector testing, vectorless testing, and circuit functional testing. 
     Loaded-board equipment manufacturers and fixture builders have designed several accessories and products to improve the testability of small, fine-pitch targets, but no design has completely solved the physical and electrical contact problems, while remaining competitively priced and easy to build and maintain. There is a need for such an improved loaded-board, guided-probed test fixture that solves the physical and electrical problems related to limited-access testing, is competitively ipriced, accommodates the sophisticated resource assignments required by loaded-board testing, and is relatively easy and inexpensive to build and maintain. There is a further need for such an improved loaded-board, guided-probe test fixture that has improved probing accuracy, improved no-clean testability, and improved fine-pitch probing ability. 
     SUMMARY OF THE INVENTION 
     A test fixture for electrically connecting a plurality of limited-access test targets on a loaded circuit board with a plurality of interface probes of a tester may comprise a plurality of elongate test probes, a universal interface plate (UIP), and a wireless interface printed circuit board (WIPCB). A first end of each elongate test probe is substantially aligned with a limited-access target on the loaded circuit board when the test fixture is positioned adjacent the loaded circuit board. Each of a plurality of double-headed spring probes mounted to the UIP has a first spring loaded head located at its first end and a second spring loaded head located at its second end. Each double-headed spring probe is generally axially aligned with an elongate test probe so that its first spring loaded head contacts a second end of the corresponding elongate test probe. Each of a plurality of contact pads on the first side of the WIPCB is substantially aligned with a double-headed spring probe so that each contact pad contacts the second spring loaded head of the corresponding double-headed spring probe. Each of a plurality of contact targets on the second side of the WIPCB is electrically connected to a contact pad on the first side of the WIPCB and contacts an interface probe of the tester when the test fixture is mounted on the tester. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will be better understood by reading the following more particular description of the invention, presented in conjunction with the following drawings, wherein: 
     FIG. 1 shows a cut-away view of a conventional shortwire test fixture; 
     FIG. 2 shows a cut-away view of a conventional ultra-alignment test fixture; 
     FIG. 3 shows a cut-away view of a conventional guided-probe protection plate fixture; 
     FIG. 4 shows a cut-away view of a conventional bare-board translator test fixture; 
     FIG. 5 shows a cut-away view of first and second embodiments of a loaded-board, guided-probe test fixture according to the present invention; 
     FIG. 6 shows a cut-away view of a third embodiment of a loaded-board, guided-probe test fixture according to the present invention; 
     FIG. 7 shows a cut-away view of a fourth embodiment of a loaded-board, guided-probe test fixture with a wireless interface printed circuit board according to the present invention; and 
     FIG. 8 shows a cut-away view of fifth and sixth embodiments of a loaded-board, guided-probe test fixture with a universal interface plate according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the schematic block diagram of FIG. 5, a first and a second embodiment of a loaded-board, guided-probe test fixture of the present invention are shown. The test fixture of the first embodiment comprises two major assemblies. The first assembly  540  is a translator fixture comprising a series of vertically spaced-apart and parallel guide plates  516 , which are supported in parallel by solid posts  522  that hold the fixture together as a solid unit. The fixture also includes an array of leaning probes  526  extending through guide holes in the translator guide plates  516 . The leaning probes  526  are in alignment on a first side of the translator fixture  540  with test targets  520  of a loaded circuit board  518 . The leaning probes  526  are in alignment on a second side of the translator fixture  540  with spring probes  514  on a first side of a probe-mounting plate  524 . The long leaning probes  526  are used to facilitate an easy transition from the fine-pitch targets  520  on the device under test  518  and larger pitch targets (spring probes  514 ) on the probe-mounting plate  524 . 
     Probe-mounting plates are well known in the art; one such plate being a probe-mounting plate made of glass-reinforced epoxy. Personality pins  528  are embedded on a second side of the probe-mounting plate  524  and the personality pins  528  are electrically connected to the spring probes  514  by wires  530 . The wirewrap posts  532  of the personality pins  528  pass through holes in an alignment plate  534  to make contact with interface probes  500  to the tester (not shown). Interface probes  500  of the tester are in a predetermined fixed, regularly spaced pattern. The alignment plate  534  aligns the wirewrap posts  532  of personality pins  528  to correspond to the predetermined location of the interface probes  500 . The second major assembly  542  of the first embodiment is the unit of the probe-mounting plate  524  containing spring probes  514  and personality pins  528  and the alignment plate  534  which aligns the wirewrap posts  532  of the personality pins  528  with the interface probes  500 . 
     Accurate alignment of the test fixture is essential for reliable operation. Alignment for the printed circuit board  518  to the translator fixture  540  is maintained by means of tooling pins (not shown), which is well known in the art of board test. Alignment between the translator fixture  540  and the probe-mounting plate  524  is maintained by means of alignment pins (not shown) or other known means. Alignment between the alignment plate  534  and the interface probes  500  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  540  is mounted on the probe-mounting plate/alignment plate assembly  542 . The entire fixture, which includes the translator fixture  540  and the probe-mounting plate/alignment plate assembly  542  is then mounted on the regularly spaced interface probes  500  on the tester. Next the loaded printed circuit board  518  to be tested is placed on the translator fixture assembly  540  by means of tooling pins (not shown). The test targets  520  of the loaded-printed circuit board  518  are then brought into contact with the leaning probes  526  of the translator fixture assembly  540  by any of several known means, including vacuum, pneumatic or mechanical actuating means. As the printed circuit board  518  is drawn toward the tester (not shown), the leaning probes  526  are sandwiched between the test targets  520  of the printed circuit board  518  and the spring probes  514 , thus making a good, low-resistance contact between the tips of leaning probes  526  and test targets  520 . The spring force of the spring probes  514  helps the tips of leaning probes  526  make a good contact with the test sites  520 , even if there is flux residue left on the printed circuit board  518  due to current no-clean, loaded-board manufacturing processes. Once electrical contact between the DUT and the leaning probes  526  is established, in-circuit or functional testing may commence. 
     The test fixture of the second embodiment comprises two major assemblies. The first assembly  546  is a translator fixture comprising a series of vertically spaced-apart and parallel guide plates  516 , which are supported in parallel by solid posts  522  that hold the fixture together as a solid unit. The fixture  546  also includes an array of translator pins such as leaning probes  526  extending through guide holes in the translator plates  516 . The leaning probes  526  are in alignment on a first side of the translator fixture  546  with test targets  520  on printed circuit board  518 . The leaning probes  526  are in alignment on a second side of the translator fixture  546  with double-headed spring probes  508  on a first side of a probe-mounting plate  506 . 
     Double-headed spring probes  508  extend through a second side of the probe-mounting plate  506  and make electrical contact with contact pads  512  on a wireless interface printed circuit board (WIPCB)  502 . The contact pads  512  on the first side of the PCB  502  are electrically connected to contact targets  504  on a second side of the PCB  502 . Contact targets  504  on the second side of the wireless interface PCB  502  are patterned to correspond with interface probes  500  of the tester (not shown). Interface probes  500  of the tester are in a predetermined fixed, regularly spaced pattern. The wireless interface PCB  502  allows the double-sided spring probes  508  to correspond to predetermined locations of the interface probes  500  by means of copper traces from the contact pads  512  that correspond to the locations of the double-headed spring probes  508  to contact targets  504  that correspond to the locations of the interface probes  500  of the tester. The second major assembly  548  of the second embodiment is the unit of the probe-mounting plate  506  containing double-sided spring probes  508  and the wireless interface PCB  502  which aligns the double-sided spring probes  508  with the interface probes  500 . 
     Alignment for the printed circuit board  518  to the translator fixture  546  is maintained by means of tooling pins (not shown), which is well known in the art of board test. Alignment between the translator fixture  546  and the probe-mounting plate  506  is maintained by means of alignment pins (not shown) or other known means. Alignment between the probe-mounting plate  506  and the wireless interface PCB  502  is maintained by means or alignment pins (not shown) or by other known means. Alignment between the wireless, interface PCB  502  and the interface probes  500  is controlled through 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  546  is mounted on the probe-mounting plate/wireless interface PCB assembly  548 . The entire fixture, which includes the translator assembly  546  and the probe-mounting plate/wireless interface PCB assembly  548  is then mounted on the regularly spaced interface probes  500  on the tester. Next the loaded printed circuit board  518  to be tested is placed on the translator fixture assembly  546  by means of tooling pins (not shown). The test targets  520  of the loaded-printed circuit board  518  are then brought toward the tester by any of several known means, including vacuum, pneumatic or mechanical actuating means. As the printed circuit board  518  is drawn toward the tester, the leaning probes  526  are sandwiched between the test targets  520  of the printed circuit board  518  and the double-headed spring probes  508 , thus making a good, low-resistance contact between the tips of leaning probes  526  and test targets  520 . The spring force of the double-headed spring probes  508  helps the tips of leaning probes  526  make a good contact with the test sites  520 , even if there is flux residue left on the printed circuit board  518  due to current no-clean loaded-board manufacturing processes. 
     Referring to the schematic block diagram of FIG. 6, a third embodiment of a loaded-board, guided-probe test fixture of the present invention is shown. Most of the components and features of FIG. 6 are similar to the components and features of FIG. 5, are numbered with the same numbers as in FIG. 5, and will not be explained again. The major difference between the embodiments of FIG.  5  and the embodiments of FIG. 6 are the different types of test probes that are used as will be explained below. 
     The test fixture of the third embodiment comprises two major assemblies. The first assembly  640  is a translator fixture, similar to assembly  540  in FIG. 5, comprising a series of vertically spaced-apart and parallel guide plates  516 , which are supported in parallel by solid posts  522  that hold the fixture together as a solid unit. The fixture also includes an array of various long, leaning or vertical test probes extending through guide holes in the translator guide plates  516 . The test probes are in alignment on a first side of the translator fixture  640  with test targets  520  of loaded circuit board  518 . The test probes are in alignment on a second side of the translator fixture  640  with larger-pitch targets on a first side of a probe-mounting plate  524 . 
     Personality pins  528  are embedded on a second side of the probe-mounting plate  524  and personality pins  528  are electrically connected to the various test probes by wires  530 . The wirewrap posts  532  of the personality pins  528  pass through holes in an alignment plate  534  to make contact with interface probes  500  to the tester (not shown). Interface probes  500  of the tester are in a predetermined fixed, regularly spaced pattern. The alignment plate  534  aligns the wirewrap posts  532  of personality pins  528  to correspond to the predetermined location of the interface probes  500 . The second major assembly  642  of the third embodiment is the unit of the probe-mounting plate  524  containing the various test probes and personality pins  528  and the alignment plate  534  which aligns the wirewrap posts  532  of the personality pins  528  with the interface probes  500 . 
     Limited-access targets  520  are accessed by any of various types of long, leaning or vertical test probes  600 ,  604 ,  608 ,  612 ,  620 ,  622 ,  626 ,  650 ,  652 ,  656 ,  660 ,  664 , and  690  that extend through holes in the guide plates  516 . The long test probes  600 ,  604 ,  608 ,  612 ,  620 ,  622 ,  626 ,  650 ,  652 ,  656 ,  660 ,  664 , and  690  are used to facilitate an easy transition from the fine-pitch targets  520  on the device under test  518  and larger-pitch targets on the probe-mounting plate  524  that are used to electrically connect test probes  600 ,  604 ,  608 ,  612 ,  620 ,  622 ,  626 ,  650 ,  652 ,  656 ,  660 ,  664 , and  690  to personality pins  528  in the probe-mounting plate  524 . Probe-mounting plates are well known in the art; one such plate being a glass-reinforced epoxy probe-mounting plate. 
     Long-socket spring test probe  600  includes a plunger  602  extending from a very long socket/barrel that is installed in probe-mounting plate  524  vertically or at an angle and extending through holes in guide plates  516 . Press rings  676  may be located at the base of the socket installed in probe-mounting plate  524 . Press rings  676  help keep the socket of test probe  600  securely in probe-mounting plate  524 . The tip of plunger  602  corresponds to the location of a corresponding test target  520  in DUT  518 . The long socket of test probe  600  contains a spring force means to hold the tip of plunger  602  in compressive contact with a corresponding test target  520  of DUT  518  when DUT  518  is brought into compressive contact therewith. A wirewrap post  678  of test probe  600  extends through probe-mounting plate  524  from a first side facing translator fixture  640  to a second side facing alignment plate  534 . Wirewrap post  678  of test probe  600  is electrically connected to a corresponding personality pin  528  on the second side of probe-mounting plate  524  by means of wirewrap  530 . Also, the socket of test probe  600  can be installed at specific predetermined depths within the probe-mounting plate  524  in order to accommodate unique probe and target geometries and heights. 
     Short-socket spring test probe  604  includes a very long plunger extending from a short socket/barrel  606  installed vertically in probe-mounting plate  524 . The plunger may sit vertically or at an angle with respect to the socket  606 . The plunger of test probe  604  extends through holes in guide plates  516 . The tip of the plunger of test probe  604  corresponds to the location of a corresponding test target  520  on DUT  518 . Press rings  680  help keep the socket  606  securely mounted in probe-mounting plate  524 . A wirewrap post  682  of socket  606  extends through probe-mounting plate  524  from the first side to the second side. Wirewrap post  682  of test probe  604  is electrically connected to a corresponding personality pin  528  on the second side of probe-mounting plate  524  by means of wirewrap  530 . Socket  606  contains a spring force means to hold the tip of the plunger in compressive contact with a corresponding test target  520  when the DUT  518  is brought into engagement therewith. Also, the socket  606  of test probe  604  can be installed at specific predetermined depths within the probe-mounting plate  524  in order to accommodate unique probe and target geometries and heights. 
     Test probe  608  includes a solid plunger extending from within a self-actuating spring probe that includes socket/barrel  610  with a spring force means inside of it. Test probe  608  sits atop a corresponding personality peg  672  that is installed in probe-mounting plate  524 . The solid plunger extends through holes in guide plates  516 . The tip of the plunger corresponds to the location of a corresponding test target  520  on DUT  518 . Personality peg  672  extends through the probe-mounting plate  524  from the first side which faces the translator fixture  640  to a second side which faces alignment plate  534 . Personality peg  672  is electrically connected to personality pin  528  on the second side of the probe-mounting plate  524  by means of wirewrap  530 . 
     Test probe  612  includes a plunger  614  extending from a long socket having a flat, rounded or pointed end  684  that sits atop a corresponding shortwire personality peg  672 . The long socket extends through holes in guide plates  516 . The tip of plunger  614  corresponds to the location of a corresponding test target  520  on DUT  518 . The long socket includes a spring means that holds the tip of plunger  614  in compressive contact with the corresponding test target  520  when the DUT  518  is brought into contact therewith. Personality peg  672  extends through probe-mounting plate  524  from the first side to the second side. Personality peg  672  is electrically connected to personality pin  528  on the second side of probe-mounting plate  524  by means of wirewrap  530 . 
     Test probe  620  includes a long plunger extending through guide plates  516  from a first side of double-sided socket/barrel  616 . Test probe  620  also includes a short plunger  618  extending from a second side of double-headed socket  616  and sitting atop a corresponding shortwire personality peg  672 . Double-headed socket  616  includes a spring force means that holds the tip of the long plunger of test probe  620  in compressive contact with a corresponding test target  520  and the tip of short plunger  618  in compressive contact with personality peg  672  when the DUT  518  is brought into contact therewith. Personality peg  672  extends through probe-mounting plate  524  from the first side to the second side. Personality peg  672  is electrically connected to personality pin  528  on the second side of probe-mounting plate  524  by means of wirewrap  530 . 
     Test probe  622  includes a solid plunger extending from within a waffle-ended socket/barrel  624  which rests atop a personality post  674  installed in probe-mounting plate  524 . Waffle-ended socket  624  includes a spring force means for holding the tip of the plunger in compressive contact with a corresponding test target  520  when the DUT  518  is brought into contact therewith. Personality post  674  extends through the probe-mounting plate  524  from the first side which faces the translator fixture  640  to a second side which faces alignment plate  534 . Personality post  674  is electrically connected to its corresponding personality pin  528  on the second side of the probe-mounting plate  524  by means of wirewrap  530 . 
     Test probe  626  includes a solid probe resting atop and actuated by a spring probe  638  installed in probe-mounting plate  524 . Spring probe  638  contains a spring force means for holding the tip of the solid probe in compressive contact with a corresponding test target  520  when DUT  518  is brought into contact therewith. Spring probe  638  extends through the probe-mounting plate  524  from the first side which faces the translator fixture  640  to a second side which faces alignment plate  534 . Spring probe  638  is electrically connected to its corresponding personality pin  528  on the second side of the probe-mounting plate  524  by means of wirewrap  530 . Spring probe  638  may also include press rings as described above with respect to test probes  600  and  604 . 
     Test probe  650  includes a solid plunger with a built-in spring  636 . Test probe  650  is a single unit and lacks a housing or socket. Test probe  650  sits atop a corresponding shortwire personality peg  672  and extends through holes in guide plates  516 . A tip of test probe  650  is held in compressive contact with a corresponding test target  520  of DUT  518  by the spring force of spring  636  when the DUT  518  is brought into contact therewith. Personality peg  672  extends through probe-mounting plate  524  from the first side to the second side. Personality peg  672  is electrically connected to personality pin  528  on the second side of probe-mounting plate  524  by means of wirewrap  530 . 
     Test probe  652  includes a plunger  654  extending from a first side of a long, double-sided socket. Test probe  652  also includes a short plunger  686  extending from a second side of the double-sided socket and sitting atop a corresponding personality peg  672 . The double-sided socket includes a spring force means that compressively holds test probe  652  between test target  520  and personality peg  672  when DUT  518  is brought into compressive contact therewith. Personality peg  672  extends through probe-mounting plate  524  from the first side to the second side. Personality peg  672  is electrically connected to personality pin  528  on the second side of probe-mounting plate  524  by means of wirewrap  530 . 
     Test probe  656  includes a solid probe resting atop a spring probe  658  that rests atop a corresponding personality peg  672 . It should be noted that since neither the solid probe nor the spring probe  658  are installed in probe-mounting plate  524 , the solid probe must extend through at least two guide plates  516  and the spring probe  658  must extend through at least two guide plate  516  in order to effectively maintain the position of test probe  656 . The tip of the solid probe of test probe  656  is held in compressive contact with a corresponding test target  520  by the spring force of spring probe  658  when DUT  518  is brought into contact therewith. Personality peg  672  extends through probe-mounting plate  524  from the first side to the second side. Personality peg  672  is electrically connected to personality pin  528  on the second side of probe-mounting plate  524  by means of wirewrap  530 . 
     Test probe  660  includes a plunger  662  extending from a first side of a long socket. Test probe  660  also includes a wirewrap tail  688  extending from a second side of the socket and sitting atop a corresponding personality peg  672 . The socket includes a spring force means that compressively holds test probe  660  between test target  520  and contact personality peg  672  when DUT  518  is brought into compressive contact therewith. Personality peg  672  extends through probe-mounting plate  524  and is electrically connected to personality pin  528  by means of wirewrap  530 . 
     Test probe  664  comprises a flexible, solid probe that extends through holes in guide plates  516 . Test probe  664  has a first end that contacts a corresponding test target  520  on DUT  518  and a second end that contacts a corresponding personality peg  672  on probe-mounting plate  524 . The holes in guide plates  516  are located at predetermined locations such that when test probe  664  is in compressive contact with a corresponding test target  520  of DUT  518  and a corresponding personality peg  672  of probe-mounting plate  524 , test probe  664  will bend compressively, but maintain contact with its corresponding test target  520  and personality peg  672 . Personality peg  672  extends through probe-mounting plate  524  and is electrically connected to its corresponding personality pin  528  by means of wirewrap  530 . 
     Test probe  690  includes a long, solid probe having a tip at a first end that contacts a corresponding test target  520  on DUT  518  and a ball  692  at a second end that mates with a plunger  694  of spring probe  696  mounted in probe-mounting plate  524 . Spring probe  696  contains a spring force means to hold the tip of the long, solid probe in compressive contact with a corresponding test target  520  when the DUT  518  is brought into compressive contact therewith. Spring probe  696  extends through probe-mounting plate  524  and is electrically connected to its corresponding personality pin  528  by means of wirewrap  530 . 
     The test probes  600 ,  604 ,  608 ,  612 ,  620 ,  622 ,  626 ,  650 ,  652 ,  656 ,  660 ,  664 , and  690  are in alignment on the first side of the translator fixture  640  with test targets  520  of loaded-circuit board under test  518 . The test probes  600 ,  604 ,  608 ,  612 ,  620 ,  622 ,  626 ,  650 ,  652 ,  656 ,  660 ,  664 , and  690  are in alignment on the second side of the translator fixture  640  with larger-pitch targets. 
     Alignment of the DUT  518  to the translator fixture  640  is maintained by means of tooling pins (not shown), which is well known in the art of board test. Alignment between the translator fixture  640  and the probe-mounting plate  524  is maintained by means of alignment pins (not shown) or other known means. Alignment between the alignment plate  534  and the interface probes  500  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  640  is mounted on the probe-mounting plate/alignment plate assembly  642 . The entire fixture, which includes the translator fixture  640  and the probe-mounting plate/alignment plate assembly  642  is then mounted on the regularly spaced interface probes  500  on the tester. Next the loaded printed circuit board  518  to be tested is placed on the translator fixture  640  by means of tooling pins (not shown). The test targets  520  of the loaded-printed circuit board  518  are then brought into contact with the test probes  600 ,  604 ,  608 ,  612 ,  620 ,  622 ,  626 ,  650 ,  652 ,  656 ,  660 ,  664 , and  690  of the translator fixture  640  by any of several known means, including vacuum, pneumatic or mechanical actuating means. 
     As the printed circuit board  518  is drawn toward the tester (not shown), the test probes  600 ,  604 ,  608 ,  612 ,  620 ,  622 ,  626 ,  650 ,  652 ,  656 ,  660 ,  664 , and  690  are sandwiched between the test targets  520  of the DUT  518  and the larger-pitch targets on probe-mounting plate  524 , thus making a good, low-resistance contact between the tips of the test probes  600 ,  604 ,  608 ,  612 ,  620 ,  622 ,  626 ,  650 ,  652 ,  656 ,  660 ,  664 , and  690  and the limited-access test targets  520 . The wiping action of tips of leaning test probes  600 ,  604 ,  608 ,  612 ,  620 ,  622 ,  626 ,  650 ,  652 ,  656 ,  660 ,  664 , and  690  across the targets  520  and the spring force of the various test probes  600 ,  604 ,  608 ,  612 ,  620 ,  622 ,  626 ,  650 ,  652 ,  656 ,  660 ,  664 , and  690  helps the tips of test probes  600 ,  604 ,  608 ,  612 ,  620 ,  622 ,  626 ,  650 ,  652 ,  656 ,  660 ,  664 , and  690  make a good contact with the test targets  520 , even if there is flux residue left on the printed circuit board  518  due to current no-clean, loaded-board manufacturing processes. Once electrical contact between the DUT and the various corresponding test probes is established, in-circuit or functional testing may commence. 
     There are actually two anticipated methods to initiate full electrical contact between the test targets  520  and the interface probes  500  on the tester. One method involves placing the DUT  518  directly on the tips of the test probes and then pushing the DUT  518  and the guide plates  516  toward the probe-mounting plate/alignment plate assembly  642 , where the translator fixture unit  640  and the probe-mounting plate/alignment plate unit  642  of the test fixture are aligned with tooling pins, but can move in the vertical direction in relation to each other. The second method involves placing the DUT  518  directly on the tips of the test probes and then pushing the DUT  518  towards the entire fixture, where the translator portion  640  and the probe-mounting plate/alignment plate portion  642  are fixedly secured to one another by spacers (not shown). As the DUT  518  is brought into compressive contact with the test fixture, the spring force of the various test probes will maintain compressive contact between each of the test probes and its corresponding test target  520 , regardless of the varying height and geometries of the different test targets  520  of DUT  518 . 
     The proposed test fixture of the present invention can probe a mixture of standard-access and limited-access targets  520 . Long, leaning or vertical test probes  600 ,  604 ,  608 ,  612 ,  620 ,  622 ,  626 ,  650 ,  652 ,  656 ,  660 ,  664 , and  690 , guide plates  516  and limited probe tip travel improve the test fixture&#39;s ability to probe small, fine-pitch targets  520 . Personality pins  528  and alignment plate  534  provide complex tester resource allocation. 
     Referring to FIG. 7, the test fixture of the fourth embodiment comprises two major assemblies. The first assembly  746  is a translator fixture, similar to assembly  546  in FIG. 5, comprising a series of vertically spaced-apart and parallel guide plates  516 , which are supported in parallel by solid posts  522  that hold the fixture together as a solid unit. The fixture also includes an array of various long, leaning or vertical test probes extending through guide holes in the translator plates  516 . The test probes are in alignment on a first side of the translator fixture  746  with test targets  520  of loaded circuit board  518 . The test probes are in alignment on a second side of the translator fixture  746  with larger-pitch contact pads  512  on a first side of a wireless interface printed circuit board (WIPCB)  502 . 
     The contact pads  512  on wireless interface printed circuit board  502  are electrically connected to contact targets  504  on a second side of the WIPCB  502 . Contact targets  504  on the second side of WIPCB  502  are patterned to correspond with interface probes  500  of the tester (not shown). Interface probes  500  of the tester are in a predetermined fixed, regularly spaced pattern. The WIPCB  502  allows the various limited-access test probes to correspond to predetermined locations of the interface probes  500  by means of copper traces (not shown) from the contact pads  512  that correspond to the locations of the test probes to the contact targets  504  that correspond to the locations of the interface probes  500  of the tester. The second major assembly  748  of the fourth embodiment of the present invention is the wireless interface printed circuit board  502  which aligns the limited-access test probes with the interface probes  500 . 
     Limited-access targets  520  are accessed by any of various types of long, leaning or vertical test probes  708 ,  712 ,  720 ,  722 ,  750 ,  752 ,  756 ,  760 , and  764  that extend through holes in guide plates  516 . The test probes  708 ,  712 ,  720 ,  722 ,  750 ,  752 ,  756 ,  760 , and  764  are used to facilitate an easy transition from the fine-pitch targets  520  on the device under test  518  to the larger-pitch targets  512  on the WIPCB  502  that are electrically connected to contact pads  504  via copper traces (not shown). 
     Test probe  708  includes a solid plunger extending from within a self-actuating spring probe that includes socket  710  with a spring force means inside of it. Test probe  708  sits atop a corresponding contact pad  512  on WIPCB  502 . The tip of the solid plunger of test probe  708  is held in compressive contact with a corresponding test target  520  by the spring force means in socket  710  when DUT  518  is brought into compressive contact therewith. Contact pad  512  is electrically connected to contact target  504  on the second side of the WIPCB  502  by means of a copper trace (not shown). 
     Test probe  712  includes a plunger  714  extending from a long socket having a flat, rounded or pointed end  784  that sits atop a corresponding contact pad  512  on WIPCB  502 . The long socket extends through holes in guide plates  516 . A tip of plunger  714  corresponds to the location of a corresponding test target  520  on DUT  518 . The long socket includes a spring means that holds the tip of plunger  714  in compressive contact with the corresponding test target  520  when the DUT  518  is brought into compressive contact therewith. Contact pad  512  is electrically connected to contact target  504  on the second side of the WIPCB  502  by means of a copper trace (not shown). 
     Test probe  720  includes a long plunger extending through guide plates  516  from a first side of double-headed socket/barrel  716 . Test probe  720  also includes a short plunger  718  extending from a second side of double-headed socket  716  and sitting atop a corresponding contact pad  512  on WIPCB  502 . Double-headed socket  716  includes a spring force means that holds the tip of the long plunger of test probe  720  in compressive contact with a corresponding test target  520  and the tip of short plunger  718  in compressive contact with its corresponding contact pad  512  on WIPCB  502  when the DUT  518  is brought into compressive contact therewith. Contact pad  512  is electrically connected to contact target  504  on the second side of the WIPCB  502  by means of a copper trace (not shown). 
     Test probe  722  includes a solid plunger extending from within a waffle-ended socket/barrel  724  which rests atop a contact pad  512  on WIPCB  502 . Waffle-ended socket  724  includes a spring force means for holding the test probe  722  in compressive contact between its corresponding test target  520  and its corresponding contact pad  512  on the WIPCB  502  when the DUT  518  is brought into compressive contact therewith. Contact pad  512  is electrically connected to contact target  504  on the second side of the WIPCB  502  by means of a copper trace (not shown). 
     Test probe  750  includes a plunger with a built-in spring  736 . Test probe  750  is a single unit and lacks a housing or socket. Test probe  750  sits atop a corresponding contact pad  512  on WIPCB  502  and extends through holes in guide plates  516 . Test probe  750  is held in compressive contact between its corresponding test target  520  of DUT  518  and its corresponding contact pad  512  on WIPCB  502  by the spring force of spring  736  when the DUT  518  is brought into compressive contact therewith. Contact pad  512  is electrically connected to contact target  504  on the second side of the WIPCB  502  by means of a copper trace (not shown). 
     Test probe  752  includes a plunger  754  extending from a first side of a long, double-headed socket. Test probe  752  also includes a short plunger  786  extending from a second side of the double-headed socket and sitting atop a corresponding contact pad  512  on WIPCB  502 . The double-headed socket includes a spring force means that compressively holds test probe  752  between its corresponding test target  520  and its corresponding contact pad  512  on WIPCB  502  when DUT  518  is brought into compressive contact therewith. Contact pad  512  is electrically connected to contact target  504  on the second side of the WIPCB  502  by means of a copper trace (not shown). 
     Test probe  756  includes a solid probe resting atop a spring probe  758  that rests atop a corresponding contact pad  512  on WIPCB  502 . It should be noted that both the solid probe and the spring probe  758  must extend through at least two guide plates  516  in order to securely maintain the position of test probe  756 . The tip of the solid probe of test probe  756  is held in compressive contact with a corresponding test target  520  by the spring force of spring probe  758  when DUT  518  is brought into compressive contact therewith. Contact pad  512  is electrically connected to contact target  504  on the second side of WIPCB  502  by means of a copper trace (not shown). 
     Test probe  760  includes a plunger  762  extending from a first side of a long, socket. Test probe  760  also includes a wirewrap tail  788  extending from a second side of the socket and sitting atop a corresponding contact pad  512  on WIPCB  502 . The socket includes a spring force means that compressively holds test probe  760  between its corresponding test target  520  and its corresponding contact pad  512  on WIPCB  502  when DUT  518  is brought into compressive contact therewith. Contact pad  512  is electrically connected to contact target  504  on the second side of WIPCB  502  by means of a copper trace (not shown). 
     Test probe  764  comprises a flexible, solid probe that extends through holes in guide plates  516 . Test probe  764  has a first end that contacts its corresponding test target  520  on DUT  518  and a second end that contacts its corresponding contact pad  512  on WIPCB  502 . The holes in guide plates  516  are located at predetermined locations such that when test probe  764  is in compressive contact with its corresponding test target  520  of DUT  518  and its corresponding contact pad  512  on WIPCB  502 , test probe  764  will bend compressively, but maintain contact with its corresponding test target  520  and contact pad  512 . Contact pad  512  is electrically connected to contact target  504  on the second side of WIPCB  502  by means of a copper trace (not shown). 
     It should be noted that other types of test probes may be used in conjunction with the fourth embodiment of the present invention. The fourth embodiment basically pertaining to long, leaning or vertical self-actuating spring probes directed by guide plates  516  and making electrical contact with tester interface probes  500  by means of contact pads  512 , wire traces (not shown) and contact targets  504  of a wireless interface printed circuit board  502 . 
     Alignment for the printed circuit board  518  to the translator fixture  746  is maintained by means of tooling pins (not shown), which is well known in the art of board test. Alignment between the translator fixture  746  and the wireless interface PCB  502  is maintained by means of alignment pins (not shown) or by other known means. Alignment between the wireless interface PCB  502  and the interface probes  500  is controlled through mounting and locking hardware well known in the art of loaded-board testers. 
     The method of operation of the test fixture is as follows. The translator assembly  746  is mounted on the WIPCB assembly  748 . The entire fixture, which includes the translator assembly  746  and the WIPCB assembly  748  is then mounted on the regularly spaced interface probes  500  on the tester. Next the loaded printed circuit board  518  to be tested is placed on the translator assembly  746  by means of tooling pins (not shown). The test targets  520  of the loaded-printed circuit board  518  are then brought toward the tester by any of several known means, including vacuum, pneumatic or mechanical actuating means. As the printed circuit board  518  is drawn toward the tester, the test probes are sandwiched between the test targets  520  of the printed circuit board  518  and the contact pads  512  of the WIPCB  502 , thus making a good, low-resistance contact between the tips of the test probes and the test targets  520 . The wiping action of the tips of the various leaning test probes across test targets  520  and the spring force of the test probes helps the tips of the test probes make good contact with the test targets  520 , even if there is flux residue left on the printed circuit board  518  due to current no-clean loaded-board manufacturing processes. 
     Referring to the schematic block diagram of FIG. 8, a fifth and a sixth embodiment of a loaded-board, guided-probe test fixture of the present invention are shown. Most of the components and features of FIG. 8 are similar to the components and features of FIGS. 5,  6  and  7  above, are numbered with the same numbers, and will not be explained again. The major differences between the embodiments of FIG.  8  and FIGS. 5,  6  and  7  will be explained below. 
     The test fixture of the fifth embodiment comprises three major assemblies. The first major assembly  840  is a translator fixture comprising a series of vertically spaced-apart and parallel guide plates  516 , which are supported in parallel by solid posts  522  that hold the fixture together as a solid unit. The fixture also includes an array of leaning probes  526  extending through guide holes in the translator guide plates  516 . The leaning probes  526  are in alignment on a first side of the translator fixture  840  with test targets  520  of a loaded circuit board  518 . The leaning probes  526  are in alignment on a second side of the translator fixture  840  with double-headed spring probes  854  on a first side of a universal interface plate  852 . The long leaning probes  526  are used to facilitate an easy transition from the fine-pitch targets  520  on the device under test  518  and larger-pitch targets (double-headed spring probes  854 ) on the universal interface plate  852 , the second major assembly  850  of the fifth embodiment being the universal interface plate  852 . 
     Double-headed spring probes  854  extend through a second side of the universal interface plate  852  and make electrical contact with either personality posts  856  or personality pegs  858  mounted in probe-mounting plate  524 . Probe-mounting plates are well known in the art; one such plate being a probe-mounting plate made of glass-reinforced epoxy. Personality posts  856  and personality pegs  858  extend through to a second side of the probe-mounting plate  524 . 
     Personality pins  528  are embedded on the second side of the probe-mounting plate  524  and the personality pins  528  are electrically connected to at least one of the personality posts  856  or personality pegs  858  by short wires  530 . The wirewrap posts  532  of the personality pins  528  pass through holes in an alignment plate  534  to make contact with interface probes  500  of the tester (not shown). Interface probes  500  of the tester are in a predetermined fixed, regularly spaced pattern. The alignment plate  534  aligns the wirewrap posts  532  of personality pins  528  to correspond to the predetermined location of the interface probes  500 . The third major assembly  842  of the fifth embodiment is the unit of the probe-mounting plate  524  containing personality posts  856  and/or personality pegs  858  and personality pins  528  and the alignment plate  534  which aligns the wirewrap posts  532  of the personality pins  528  with the interface probes  500 . 
     Accurate alignment of the test fixture is essential for reliable operation. Alignment for the printed circuit board  518  to the translator fixture  840  is maintained by means of tooling pins (not shown), which is well known in the art of board test. Alignment between the translator fixture  840 , the universal interface plate  852 , and the probe-mounting plate/alignment plate assembly  842  is maintained by means of alignment pins (not shown) or other known means. Alignment between the alignment plate  534  and the interface probes  500  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  840  is mounted on the universal interface plate  852  which is mounted on the probe-mounting plate/alignment plate assembly  842 . The entire fixture, which includes the translator fixture  840 , the universal interface plate  852 , and the probe-mounting plate/alignment plate assembly  842 , is then mounted on the regularly spaced interface probes  500  on the tester. Next the loaded printed circuit board  518  to be tested is placed on the translator fixture  840  by means of tooling pins (not shown). The test targets  520  of the loaded-printed circuit board  518  are then brought into contact with the leaning probes  526  of the translator fixture  840  by any of several known means, including vacuum, pneumatic or mechanical actuating means. 
     As the printed circuit board  518  is drawn toward the tester (not shown), the leaning or vertical probes  526  are sandwiched between the test targets  520  of the printed circuit board  518  and the double-headed spring probes  854 , thus making a good, low-resistance contact between the tips of leaning probes  526  and test targets  520 . The wiping action of the tips of the leaning, solid probes  526  across the test targets  520  and the spring force of the spring probes  854  helps the tips of leaning probes  526  make a good contact with the test targets  520 , even if there is flux residue left on the printed circuit board  518  due to current no-clean, loaded-board manufacturing processes. Once electrical contact between the DUT and the leaning probes  526  is established, in-circuit or functional testing may commence. 
     The test fixture of the sixth embodiment comprises three major assemblies. The first assembly  840  is a translator fixture comprising a series of vertically spaced-apart and parallel guide plates  516 , which are supported in parallel by solid posts  522  that hold the fixture together as a solid unit. The translator fixture  840  also includes an array of translator pins such as leaning or vertical probes  526  extending through guide holes in the guide plates  516 . The leaning or vertical probes  526  are in alignment on a first side of the translator fixture  840  with test targets  520  on printed circuit board  518 . The leaning or vertical probes  526  are in alignment on a second side of the translator fixture  840  with double-headed spring probes  854  on a first side of a universal interface plate  852 . The second major assembly  850  of the sixth embodiment being the universal interface plate  852 . 
     Double-headed spring probes  854  extend through a second side of the universal interface plate  852  and make electrical contact with contact pads  512  on a wireless interface printed circuit board (WIPCB)  502 . The contact pads  512  on the first side of the PCB  502  are electrically connected to contact targets  504  on a second side of the PCB  502 . Contact targets  504  on the second side of the WIPCB  502  are patterned to correspond with interface probes  500  of the tester (not shown). Interface probes  500  of the tester are in a predetermined fixed, regularly spaced pattern. The wireless interface PCB  502  allows the double-headed spring probes  854  to correspond to the predetermined locations of the interface probes  500  by means of copper traces from the contact pads  512  that correspond to the locations of the double-headed spring probes  854  to contact targets  504  that correspond to the locations of the interface probes  500  of the tester. The third major assembly  848  of the sixth embodiment is the unit of the WIPCB  502  which aligns the double-headed spring probes  854  with the interface probes  500 . 
     Alignment for the printed circuit board  518  to the translator fixture  840  is maintained by means of tooling pins (not shown), which are well known in the art of board test. Alignment between the translator fixture  840  and the universal interface plate  852  is maintained by means of alignment pins (not shown) or other known means. Alignment between the universal interface plate  852  and the wireless interface PCB  502  is maintained by means or alignment pins (not shown) or by other known means. Alignment between the wireless interface PCB  502  and the interface probes  500  is controlled through 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  840  is mounted on the universal interface plate  850 /WIPCB assembly  848 . The entire fixture, which includes the translator assembly  840  and the universal interface plate  850 /WIPCB assembly  848 , is then mounted on the regularly spaced interface probes  500  on the tester. Next the loaded printed circuit board  518  to be tested is placed on the translator assembly  840  by means of tooling pins (not shown). The test targets  520  of the loaded-printed circuit board  518  are then brought toward the tester by any of several known means, including vacuum, pneumatic or mechanical actuating means. 
     As the printed circuit board  518  is drawn toward the tester, the leaning or vertical, solid probes  526  are sandwiched between the test targets  520  of the printed circuit board  518  and the double-headed spring probes  854 , thus making a good, low-resistance contact between the tips of leaning or vertical, solid probes  526  and test targets  520 . The wiping action of the leaning, solid probes  526  across the test targets  520  and the spring force of the double-headed spring probes  854  helps the tips of leaning probes  526  make a good contact with the test targets  520 , even if there is flux residue left on the printed circuit board  518  due to current no-clean loaded-board manufacturing processes. 
     The foregoing description of the present invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and other modifications and variations may be possible in light of the above teachings. For example, the translator fixture could be milled out to accommodate even more types of test probes, such as the larger capacitive and inductive type test probes. Also, two guided-probe test fixtures could be used in a clamshell type tester in order to test printed circuit boards that are populated with electronic components on both sides or have test targets on both sides. 
     Furthermore, self-actuating test probes may come in many configurations, so long as the probes provide an electrical path between test targets  520  on the printed circuit board  518  and targets below. 
     Still further, the guided-probe test fixture of the present invention could be used in conjunction with an automatic tester in order to test printed circuit boards that are populated with electronic components on both sides or have test targets on both sides. The embodiment was chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and various modifications as are suited to the particular use contemplated. It is intended that the appended claims be construed to include other alternative embodiments of the invention except insofar as limited by the prior art.