High density logic analyzer probing system

A high density logic analyzer probing system has a probe mounting fixture for accurately positioning mounting posts to a device under test (DUT). The mounting posts includes a recess in one side for receiving a spring wire clip that mounts through holes in the DUT. The housing includes protrusions that receive screws for securing the probe head to the mounting posts on the DUT. The screws have a first shoulder that engages the protrusions and a second shoulder that engages the mounting post. The probe head is positioned between the mounting posts and tightened to the DUT using the screws. The first shoulder applies downward pressure on the probe head and the second shoulder provides a positive stop to prevent over tightening of the probe head which can cause damage to probe contacts in the probe head.

BACKGROUND OF THE INVENTION

The present invention related generally to logic analyzer probes and more particularly to a high density logic analyzer probing system for mounting logic analyzer probes to a device under test.

Logic analyzer probes are used for acquiring multiple signals from probing points, circuit traces, processor buses and the like on a device under test (DUT). Probing points may take the form of square pin connectors mounted on the DUT that are connected to circuit elements or circuit traces. Various types of high, speed, controlled impedance connectors may also be mounted on the DUT for coupling multiple high speed signals to the logic analyzer. One such connector is called a MICTOR® connector, manufactured and sold by Tyco Electronics, Corp., Harrisburg, Pa. A MICTOR® connector has a plug and closely mating receptacle. The transmission lines in the plug and receptacle are contained in mating housings. The ends of the transmission lines extending from the bottom of the receptacle are bent at an angle to form contact pads for soldering to parallel rows of conductive pads on the surface of a circuit board DUT. The ends of the transmission lines at the other end of the receptacle form electrical contacts that mate with corresponding electrical contacts in the plug when the closely mating plug and receptacle are connected together. In most probing applications of microprocessor boards, multiple MICTOR receptacles are mounted on the circuit board. The mating MICTOR plugs are mounted on multi-channel logic analyzer probe heads. The transmission lines of the MICTOR plug are electrically coupled to center conductors of a multiple coaxial cable type ribbon cable. Electrical elements, such as resistors, may be inserted between the MICTOR plug and the coaxial cables to provide electrical isolation for the device under test. One drawback to the use of MICTOR connectors is the amount of space the connectors take up on the DUT.

To reduce the amount of space take up by MICTOR connector and other such connectors, connectorless logic analyzer probes were developed. The connectorless logic analyzer probe mounts directly to the electrical contacts pads on the DUT and does not require the use of MICTOR connectors. One such connectorless logic analyzer probe is the P6860 Logic Analyzer Probe, manufactured and sold by Tektronix, Inc, Beaverton Oreg. and described in U.S. Pat. No. 6,447,339. The P6860 probe has a non-conductive plastic-type housing in which are secured substrates having electrical contacts formed on the one of the substrate ends and exposed at one end of the housing. The electrical contacts are electrically coupled to passive and active circuitry on the substrates. A removable signal contact holder is mounted over the open end of the housing. The removable signal contact holder has parallel rows of elastomeric contacts that correspond to the electrical contacts on the ends of the substrates. The probe is positioned on the DUT with the elastomeric contacts engaging a corresponding pattern of electrical contact pads on the DUT. The housing has attachment screws mounted on the sides of the housing that engage a retention block. The retention block has a stiffener member enclosed in a housing having alignment flanges that extend though holes in the DUT adjacent to the electrical contact pads on the DUT. The retention block is positioned on the reverse side of the DUT under the electrical contacts. The retention block flanges engage features on the housing to align the elastomeric contacts of the probe with the electrical contact pads on the DUT. The screws are tightened into the retention block to secure the probe to the DUT. The P6860 is designed for electrical contact pad patterns on the DUT of 85 contacts per square inch.

Another type of connectorless logic analyzer probe are PCIExpress Bus probes, manufactured and sold by Tektronix, Inc. The PCIExpress Bus probes have machined mounting posts that are positioned adjacent to the parallel rows of electrical contact pads on the DUT. The mounting posts have a base with apertures formed therein that receive mounting pins. The mounting pins extend into holes formed in the DUT adjacent to the electrical contact pads. The mounting pins are soldered to the DUT to secure the mounting post to the DUT. The mounting posts have upwardly extending studs with threaded apertures formed therein. An interconnect strip is positioned between the mounting posts. The interconnect strip have electrical contacts, such as a cLGA c-clip, manufactured and sold by InterCon Systems, Inc., Harrisburg, Pa., that correspond to the pattern of electrical contact pads on the DUT. The PCIExpress Bus probes has an open housing structure with substrates mounted on either side of a central support member. The substrates have electrical contacts formed on the one of its end surfaces that are exposed at the bottom of the housing. Side members attached to the central support member secure the substrates in the housing. Each side member has a central bore that receives a screw for securing the housing to the mounting posts. The probe is positioned between the mounting posts with the electrical contacts on the substrates engaging corresponding electrical contacts in the interconnect strip. The housing screws are tightened to secure the probe to the DUT. The PCIExpress Bus probe is designed for electrical contact pad patterns on the DUT of130contacts per square inch.

A drawback to the above described connectorless probes is the possibility of over tightening the probe heads to the DUT. In the case of the P6860 Logic Analyzer Probe, over tightening can cause the fine wires in the elastomeric connectors to take a permanent set causing the intermittent connections between the substrate contacts and the contact pads on the DUT. Further, the substrates may be forced into the soft plastic of the removable signal contact holder which may cause damage to the substrates themselves. In the case of the PCIExpress Bus probes, over tightening can cause damage to the electrical contacts in the interconnect clip. Further, the interconnect strip is separate from the probe head and not retained in the probe head as is the case with the P6860 probe.

Another type of connectorless probe are the E5387A, E5390A and the E5394A soft touch probes manufactured and sold by Agilent Technologies Inc., Palo Alto, Calif. The soft touch probes have a plastic retention module having downwardly facing metallic studs that are mounted into holes formed adjacent to the parallel rows of electrical contact pads on the DUT. The metallic studs are soldered to the DUT to secure the retention module to the DUT with the retention modules extending completely around the periphery of the parallel rows of electrical contact pads. The soft touch probe head has a plastic housing in which are secured parallel substrates. One end of each substrate has micro spring-pin electrical contacts that mate with the parallel rows of the electrical contact pads on the DUT. The micro spring-pin electrical contacts are coupled to wires of electrical ribbon cables extending from the other end of the housing via passive circuit elements. Mounting screws extend down opposing sides of the housing and are screwed into threaded apertures in the retention module. The soft touch probes are designed for electrical contact pad patterns on the DUT of 128 contacts per square inch.

A drawback to the soft touch probes is the use of the retention module which surrounds the electrical contact pad pattern on the DUT. The retention module requires more board space than is required with the PCIExpress Bus probe and further requires greater separation between adjacent contact pad patterns. Additionally, the micro spring-pin electrical contacts are mounted to the substrates and require the probes to be sent to a service center for repair if a micro spring-pin contact is broken.

There is a continuing customer need to increase the higher density electrical contact patterns on DUTs. As the contact density increases per square inch there is a corresponding decrease in the separation between adjacent electrical contacts. This requires greater precision in placing the logic analyzer probes on the DUT. What is needed is a high density logic analyzer probing system that accurately positions a probe mounting fixture on a device under test for accurately positioning a high density logic analyzer probe to the device under test. The high density logic analyzer probing system should also provide a positive stop that prevents damage to electrical contacts on the high density logic analyzer probe. Further, the high density logic analyzer probing system should be adaptable for use with various thicknesses of circuit boards and allow for placing the high density logic analyzer probes opposite of each other on opposing sides of the circuit board.

SUMMARY OF THE INVENTION

Accordingly, the present invention is a high density logic analyzer probing system for a device under test having a removable probe mounting fixture, a probe mounting system and at least a first high density logic analyzer probe. The removable probe mounting fixture has a handle and a mounting post alignment portion that receives the probe mounting system. The probe mounting system has mounting posts with threaded apertures formed in the top surfaces and positioned adjacent to the ends of the mounting post alignment portions. An alignment stud is extends from the bottom surface of one of the mounting posts form that engages an alignment hole on the device under test. The mounting posts are held in place by downwardly extending studs in the handle portion engaging the threaded apertures in the mounting posts. The mounting post are secured to a device under test by mounting post securing members engaging the mounting posts. The mounting post securing members are preferably spring wire clips with each spring wire clip having a central portion and end portions. The central portion of each wire clip disposed in a recess formed in a side surface of each mounting, post with the end portions of each spring wire clip extending below the mounting posts. The end portions of the spring wire clips are positioned through and secured in mounting holes in the device under test. The removable probe mounting fixture is removed from the mounting posts allowing the mounting post to accept a probe head. The probe head has electrically conductive contacts disposed at one end of a housing engaging electrically conductive contacts on the device under test. The housing has laterally extending protrusions formed on the opposite end of the housing for receiving mounting screws. Each mounting screw has a shaft and a threaded portion at one end and a integrally form cap at the other end. The cap forms a first shoulder on the shaft and a boss disposed between the threaded portion and the cap has a second shoulder. The threaded portions of the screws engage the respective threaded apertures of the mounting posts with the first shoulder providing downward force on the probe against the device under test as the screws are tightened in the mounting posts. The second shoulder provides a positive stop for the probe head as the screws are tightened to prevent excess force between the probe head and the device under test.

The high density logic analyzer probing system of the present invention may also be configured to provide for “sandwich probing” where two probes are mounted on opposite sides of device under test and mated with parallel rows of electrically conductive contacts that are vertically aligned with each other on opposite sides of the device under test. In such a configuration, modified mounting posts are positioned on the opposing surface of the device under test with each modified mounting post having a threaded aperture formed in a top surface. A lateral slot is formed in a side surface of the modified mounting posts that intersects vertical slots formed in adjacent side surfaces. The lateral slot receives a spring wire clip retention member having end portions separated by a central portion. Each end portion has an aperture formed therein. The end portions of the spring wire clips from the mounting posts on the other surface of the device under test extend along the vertical slots in the modified mounting posts and through the apertures in the end portions of the spring wire clip retention members. The end portions of the spring wire clips are secured to the end portions of the spring wire clip retention members to secure the modifies mounting posts to the device under test.

The objects, advantages and novel features of the present invention are apparent from the following detailed description when read in conjunction with appended claims and attached drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring toFIG. 1, there is shown a probe mounting fixture10as part of the high density logic analyzer probing system12of the present invention. The probing system12includes the probe mounting fixture10, a probe mounting system14and at least a first high density logic analyzer probe16. The probe mounting fixture10has a carrier18on which are positioned two mounting posts20. The carrier18has a handle portion22disposed adjacent to a mounting post alignment portion24. The handle portion22has protrusions26that extend laterally on both sides past the mounting post alignment portion24. Each protrusion26has a downwardly extending stud28that is closely received in a threaded aperture30formed in the top of each mounting post20. The mounting post alignment portion24may be formed with one or more ribs or grooves32that mate with corresponding ribs or grooves34formed on one side of the mounting posts20for positioning a particular post on one side or the other of the mounting post alignment portion24. Preferably, one side of the mounting post alignment portion24has a single rib or groove and the other side has two ribs or grooves. The width of the mounting post alignment portion24is controlled to allow accurate alignment of the mounting posts20with a matching land pattern36on a device under test (DUT)38, such as a circuit board or the like. The posts20are formed of a substantially hard and durable material, preferably a metal such as aluminum. A downwardly extending stud37is formed on the bottom surface of one of the mounting posts20for alignment purposes. Each post20has a recess40formed in one side for accepting a spring wire clip42, preferably formed of beryllium-copper. A variety of spring wire clips42, differing in length, may be used with the mounting posts20for installation on circuit boards38having various thicknesses.

The probe mounting fixture10with the mounting posts20is installed on the DUT38as shown in FIG.2. The DUT38has a land pattern44that includes parallel rows of electrically conductive contacts46(seeFIG. 3) and the land pattern36for the mounting posts20. The electrical contact pad pattern on the DUT has a substantially higher pad density of217contacts per square inch. The mounting post land pattern36has four mounting holes48and one unplated keying hole50for properly orienting and accurately aligning of the mounting system14. The wire clip leads42pass through the mounting holes48while at the same time the stud37on the bottom of one of the mounting posts20passes into the keying hole50. The wire clip leads42are soldered down to the DUT38. The excess lengths of the wire clip leads42are preferably bent over so they are substantially parallel to the bottom surface of the DUT38to prevent the mounting posts20from pulling out of the mounting holes48due to solder creep from pressure exerted by the logic analyzer probe16secured to the mounting posts20. When forces are applied to the logic analyzer probe16, the load will be supported by the bent leads of the wire clips42against the DUT38rather than the solder. The carrier18is then removed as shown in FIG.3and the probe mounting system14consisting of the mounting posts20is ready for the logic analyzer probe16installation.

Referring toFIGS. 4 and 5, the logic analyzer probe16has a probe head60consists of at least one active multi-chip module (MCM)62, a shielded coaxial ribbon cable64electrically coupled to the MCM62, an interface clip66, two mounting screws68, and a housing70. In the preferred embodiment the probe head60has two MCM modules62and corresponding shielded coaxial ribbon cables64. Each MCM module62is formed with a circuit board72made from a material such as FR4, TEFLON @ or the like, having one serrated edge74with the protrusions76of the serrated edge74being plated. Each plated protrusion76is coupled to active circuitry77mounted on the one side of the circuit board72. The outputs of the active circuitry are coupled to respective coaxial cables of the coaxial ribbon cable64. The MCM modules62are formed with side notches79that receive mating protrusions81of the housing70. The interface clip66has a substantially rectangular base78with two parallel rows of apertures80aligned with the long side of the rectangular base78. Each aperture80receives an electrically conductive contact82, such as a cLGA® c-clip, manufactured and sold by InterCon Systems, Inc., Harrisburg, Pa. The electrically conductive contacts82provide a low capacitance electrical connection from the MCMs62to the electrically conductive contacts46of the land pattern44on the DUT38. Other types of low capacitance electrical contacts82, such as electrically conductive elastomer may be used. Each of the long sides of the interface clip66is formed with an undercut84that mates with corresponding ribs85formed in the housing70. The interface clip66has upward extending protrusions86that mate with corresponding notches88formed in the housing70. The interface clip66is replaceable in case the electrically conductive contacts82of the clip66are damaged. In the preferred embodiment, the mounting posts20and the screws68are color coded to provide a visual key to help the user orient the logic analyzer probe16correctly during installation. A physical key between the interface clip66and the mounting system posts20also aids this orientation. Another physical key between the interface clip66and the housing70assures proper orientation of the interface clip66.

The housing70has opposing laterally extending protrusions90at one end that receive the mounting screws68. Each mounting screw68has a shaft92with a threaded portion94at one end and an integrally formed knurled cap96at the other end. The knurled cap96forms a first shoulder98with the shaft. The top of the cap96may be provided with slot or formed depression for receiving a securing bit, such as a screwdriver bit or the like. Disposed between the cap end and the threaded end of the mounting screw is a boss100forming a second shoulder102with the shaft92. In the preferred embodiment, the screws68are made of stainless steel.

The housing70is preferably formed of two plastic injection molded case-halves104,106. One of the molded case halves104has a base108and extending sidewalls110on opposing sides of the base. The sidewalls110are notched to form the upwardly extending protrusions81that mate with the notches79formed in the MCM modules. One end of the case half104includes the laterally extending protrusions90that has a thickness matching the thickness of the sidewalls110. The laterally extending protrusions90in the case half104has a concave channel112formed parallel to the sidewalls110and perpendicular to the ends of the case half. The other end of the base includes the rib formed inner surface of the housing that mates with the one side of the undercut94in the interface clip66and the notches88that mate with the upwardly extending protrusions86on one side of the interface clip. The other case half106has a periphery114coextensive with the shape of the first case half104and is secured to the first case half to capture the MCM modules62within a cavity formed by the two case halves104,106. The screws68are captured within 112 the channels112the laterally extending protrusions90. The case halves104,106are secured together via any number of fastening means, such as screws, adhesives, such as epoxy or the like, sonic welding or the like. In the preferred embodiment, the case halves104,106are sonic welded. Alternately, each case half104,106may be formed with notched sidewalls110and laterally extending protrusions90with each protrusion having a concave channel112. The case halves104,106are mated together at the notched sidewalls110and the laterally extending protrusions90and secured together.

The MCM modules62are positioned together back-to-back with the active components77facing outward. The MCM modules62are positioned in the case half104with the sidewalls with the upwardly facing protrusions81of the sidewalls110mating with the side notches79in the MCM modules62. The coaxial ribbon cables64connected to the MCM modules62extend outward from the end of the case half104,106with the laterally extending protrusions90. The upper shaft portions92of the screws68between the cap96and the boss100are positioned in the concave channels112of the laterally extending protrusions90. The other case half106is positioned on the first case half104with the laterally extending protrusions90of the first case half104aligned with the laterally extending protrusions90of the other case half106and the sidewalls110of the first case half104aligned with the side periphery114of the second case half106. The case halves104,106are secured together forming the cavity in which the MCM modules62are secured with the serrated edge76of each MCM module62being exposed at the opposing open end116of the housing70from the end having the laterally extending protrusions90. The screws68are secured in the laterally extending protrusions90of the case halves104,106.

The interface clip66is positioned over the open end116of the housing70and secured in place by the undercut84in the interface clip66engaging the ribs85on the inner surface of the housing70as shown in FIG.6. The assembled probe head60is positioned over the land pattern44on the DUT38as shown in FIG.7. The color coded mounting posts20and screws68provide for accurate orientation of the probe head60to the DUT38. The probe head60is positioned between the two mounting posts20with the threaded portions94of the screws68engaging the threaded apertures30in the mounting posts20. As the screws68are tightened into the mounting posts20, the shoulder of the cap96engages the laterally extending protrusions90of the housing70and force the probing head60against the DUT38. Continued tightening of the screws68brings the shoulders102of the bosses100into contact with the mounting posts20which prevents further tightening of the screws68. The use of double shouldered screws68prevents the over tightening of the probe head60onto the DUT38which can damage the electrically conductive contacts82of the interface clip66.

The mounting posts20may be modified in the present invention to provide for “sandwich probing” where two probes60are mounted on opposite sides of a DUT circuit board38and mate with parallel rows of electrically conductive contacts46vertically aligned with each other on opposite sides of the DUT. Referring toFIG. 9, a modified mounting post200is shown that is mountable on the opposite side of the circuit board38below a set of mounting posts20previously secured to the other side of the circuit board38. The mounting post200is formed of a substantially hard and durable material, preferably a metal such as aluminum. The mounting post200has a lateral slot202extending part way into the mounting post at a position between the base204and top206of the mounting post200. The top206of the mounting post has a threaded aperture208for receiving the threaded screw ends94of the probe head mounting screws68. Vertical slots210are formed in the sidewalls212of the mounting post200that extend past the lateral slot202. A spring wire clip retention member214is disposed in the lateral slot202in the mounting post200and receives the ends of the spring wire clip42that secures the mounting post20on the opposite side of the circuit board38. The spring wire retention member214has an arcuate center section216integrally formed with substantially rectangular portions218on each end. Each rectangular section218has an aperture220formed therein for receiving the respective ends of the spring wire clip42. A portion of each aperture220of the spring wire retention member214extends into the vertical slots210on the opposing sides of the mounting post200.

The modified mounting posts200are positioned on the carrier18as previously describe and positioned on the opposite side of the circuit board38from the previously secured mounting posts20. The ends of the spring wire clip leads42are positioned along the vertical slots210in the mounting posts200and threaded through the apertures220in the spring wire clip retention members214that is positioned in the slots212in the modified mounting posts200. The mounting posts200are then seated against the surface of the circuit board38and the spring wire clip leads42are soldered to the spring wire retention members214. The carrier18is removed and the mounting posts200are in position to receive a probe head60. The use of the modified mounting posts200allows two probe heads60to occupy the same footprint area on opposite sides of the DUT circuit board38.