GB2086670A

GB2086670A - Test fixture with translator

Info

Publication number: GB2086670A
Application number: GB8132722A
Authority: GB
Original assignee: Everett Charles Inc
Current assignee: Everett Charles Inc
Priority date: 1980-10-30
Filing date: 1981-10-30
Publication date: 1982-05-12
Also published as: JPS57101769A; GB2086670B; DE3142817A1; FR2493671A1

Abstract

A translator includes first and second guide plates (40, 42) rigidly connected together in substantially parallel and spaced apart relation, and an array of first and second apertures extends through the first and second guide plate respectively, each second aperture corresponding to and forming a pair with a first aperture and at least some being transversely offset therefrom. An electrical elongate contact (38) extends between each pair of guide apertures, each electrical contact being axially non-compressible, and has at least a portion between the guide plates which is transversely flexible to permit extension between the offset guide apertures, the ends (38a and 38b) being slidably mounted in the first and second guide apertures respectively. <IMAGE>

Description

SPECIFICATION Translator, test fixture with translator, and method for forming a translator Test fixtures are known for probing or making electrical test connections with test points on a generally planar unit under test. Typically, the unit under test may be a printed circuit board (PCB), a back plane panel board, or the like, and may be assembled with electrical components (a loaded board) or unassembled (bare board). Often, the test heads have an array of spring-loaded probes arranged in a grid-like array, the probes being located in accordance to a desired test pattern for the unit under test. Systems which may employ mechanical, pneumatic, or vacuum actuating means are utilized to draw the array of spring probes and the unit under test relatively closer together and into electrical contact.An analyzer electrically connected to the spring probes is used for analyzing the unit under test for determining data such as continuity or isolation between the various test points on the unit under test.

One type of prior art test head disclosed in U.S. application Serial No. 40,704, filed May 21 1979, assigned to the same assignee as the present application, is a vacuum-actuated test head having a programming plate. The vacuum-actuated test head has an easily changeable test pin programming plate for making an electrical contact with selected points on a planar unit, such as a PCB. A plurality of contact probes are mounted in a rigid base.

Each contact probe is a spring probe which has a first end that is spring-loaded and a second that is electrically coupled to a circuit analyzer. The programming plate has mounted therein a plurality of axially elongated rigid and straight test pins which are axially movable relative to the programming plate. The total number of test pins is less in number than the contact probes. Each rigid test pin has a first end capable of making electrical contact with a desired point on the unit under test, and a second end in alignment with a respective one of the springloaded ends of a contact probe. Plate alignment means are provided for aligning the programming plate over the base for aligning each rigid test pin with a respective contact probe. Unit alignment means are provided for aligning a unit under test over the test pins.A vacuum chamber is formed between the base and the programming plate so that upon forming a vacuum in the chamber, the programming plate is drawn relatively closer to the base.

A principal advantage of this device is that the same array of spring probes is used for each different test pattern by replacing the programming plate with another programming plate with a different array of test pins therein.

It will be evident that the test pins can only probe test points which are on centre with the axis of the spring probes.

Another prior art device is disclosed in Technical Bulletin TB7005-1 dated October 1976, by Dit-MCO International, and entitled "Formed Pin Transition Board". The Technical Bulletin proposes to add a T board to a basic fixture matrix, so as to transfer the position of spring-loaded contact probes from a .1-inch grid location to random off-grid locations. The basic T board structure includes a fixed grid of spring probes and a pair of spaced-apart and parallel guide plates. Rigid pins extend through apertures provided in the guide plates. One end of the rigid pin probes a unit under test, such as a PCB, and the other end of the rigid pin engages the ends of the spring-loaded contact probes. The pins are free to move in the apertures provided in the guide plates so that the spring-loaded probes resiliently urge the pins against the printed circuit board.The purpose of the T board is to probe off-grid points from the grid of springloaded contact probes. Consequently, some of the rigid pins are bent along the length therof.

Because the rigid pins are bent, assembly of the T board is very difficult. As just mentioned, the rigidity and bend characterizing the rigid pins gives rise to several problems during assembly of the T board. More specifically due to the bends, the rigid pins are not easily manoeurved through the apertures provided in the T board guide plates. Subsequent to insertion through a first guide plate, a rigid pin is manually guided for insertion through apertures in the second guide plate. The bend portion of the rigid pin interfaces with bends of the priorily-installed pins so that completion of the assembly of the T board is significantly hindered.

Other problems arising from the use of such rigid pins include substantial side loading or frictional forces arising from the contact of the rigid pins and the respective apertures in the T board.

Another prior art device, which may be used to probe off centre test points, is disclosed in Catalog No. 103 by the Pylon Co., entitled "Pogo Contacts". The catalog discloses a probe that is a long, slender, springloaded contact for use in probing applications where close centreline spacing is required. A fine tungsten wire probe contact is slidable inside a flexible guide tube. The tungsten wire and guide tube is coupled to a polycarbonate holder surrounding a gold-lined brass body.

The brass body is connectable to a circuit analyzer for analyzing circuits for which probe is used. The utility of the probe is limited by virtue of the polycarbonate holder and goldlined brass body in that they are substantially thicker (in the order of fifteen times) in diameter than the guide tube. Thus, due to the thickness of the polycarbonate holder, the array size for a large number of probes is relatively high and thus the number of points to be probed is severely limited.

It is an object of the present invention to obviate or mitigate the problems and difficulties of the prior art.

The present invention provides a translator for translating between arrays of non-aligned electrical probe points comprising: first and second guide plates rigidly connected together in substantially parallel and spaced apart relation; an array of first apertures extending through the first guide plate; an array of second apertures each corresponding to and forming a pair with a different first aperture and each extending through the second guide plate, at least some of the second apertures being transversely offset from the corresponding first apertures; and a plurality of electrical contacts elongated along an axis between first and second opposite ends, a different contact being for slidably mounting in and extending between each pair of guide apertures, each electrical contact being axially non-compressible between the opposite ends when a force is applied between the opposite ends and having at least a portion between the guide plates which is transversely flexible to permit extension between the offset guide apertures.

Preferably, each guide plate has a side that is facing in the opposite direction from the other guide plate to form oppositely facing sides. The opposite ends of the contacts are positionable so that each is exposed at a different one of the oppositely facing sides of the guide plates at the same time. Also preferably, the opposite exposed ends of the contacts are guided so that they move along a path substantially normal to the guide plates as the contacts slide in the corresponding apertures. Additionally it is preferred that the contacts are mounted in apertures and adapted such that both of the exposed ends are movable relative to the guide plates as the contact slides in the apertures, and both ends of the contacts move together in the same direction during sliding movement of the contact.

Each of the contacts, according to a preferred arrangement, comprises a laterally flexible wire extending at least from one of the exposed ends thereof to at least a position between the guide plates and adjacent to the guide plate which is adjacent the other exposed end.

Preferably, there is an end portion adjacent to one of the ends of each of the contacts which is located in one of the apertures in the second guide plate. The end portion of each contact has enlarged stops for engaging and forming retainers with the second guide plate to retain the end portion within the corresponding aperture in the second guide plate.

The stops are preferably spaced for allowing sliding movement of the end portion in the second guide plate by a predetermined amount.

It is also preferred that the end portion within the aperture comprise an enlarged and rigid end portion.

According to preferred arrangements, there is a sharp probe tip at the end of each contact which is adjacent the end portion, and the guide plates are formed of electrically nonconductive material. Additionally it is preferred that the apertures in a first one of the guide plates has a countersunk portion opening between the plates in a direction toward the second guide plate.

Preferably, the electrical contact comprises a wire having a diameter of about .015 inch.

The present invention also provides a test fixture for electrically probing an array of substantially planar test points, comprising: a plurality of resiliently biased electrical contacts located in an array, a biased contact corresponding to each test point to be probed; means for urging the biased contacts and a plurality of electrical test points relatively closer together; and a translator for mounting in the test fixture comprising: a plurality of transversely flexible translator contacts elongated along an axis between first and second opposite ends, each translator contact extending between a different one of the biased contacts and a corresponding test point, a pair of parallel guide plates having in each a guide aperture corresponding to and receiving each translator contact, one of said guide apertures in the guide plates for each translator contact being transversely offset from the other and adapted for simultaneously guiding the movement of opposite ends of the corresponding translator contact in directions normal to the guide plates with a first end in opposed relation to the corresponding biased contact and the second end in opposed relation to the corresponding test point, each translator contact when mounted in the corresponding guide aperture being substantially non-compressible along the axis thereof so that as the corresponding biased contact and test points are urged closer together, a force, due to the corresponding biased contact, is exerted therethrough to the corresponding test point.

The present invention additionally provides a method of forming a translator from a plurality of contacts and a pair of spaced apart and interconnected guide plates, the contacts being elongated along an axis between first and second ends and comprising a transversely flexible and substantially axially rigid portion between the ends, each guide plate having a plurality of apertures, each of said apertures in one guide plate having a corresponding non-aligned aperture in the other guide plate, comprising the steps of: feeding a first end of each of the contacts through a different aperture in a first of said guide plates; locating the first end of each of the contacts in the corresponding offset aperture in the second guide plate, causing the contact to bend in the flexible portion in a direction tranverse to the axis therof and at a position between the guide plates; and passing the first end of each of the flexible contacts into the corresponding aperture in the second guide plate, leaving each of the flexible contacts with opposite end portions supported and guided by corresponding apertures in each guide plate.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of the test fixture embodying the present invention showing a drawer 1 8 in the extended position for locating and mounting a printed circuit board 22 thereon; Figure 2 is a partial front elevation and cross-sectional view of the test fixture of Fig.

1 in the test condition; Figure 3 is an exploded view of the left portion of the test fixture as shown in Fig. 2 in the non-test condition; Figure 3A is an exploded cross-sectional view showing detents in a translator guide plate; Figure 4 is a perspective view of a translator guide plate into which the translator is inserted and removed for use in the test fixture of Fig. 2; Figure 5 is a perspective view of the translator for use in the test fixture of Fig. 2; Figure 6 is an enlarged cross-sectional view depicting an elongated electrical contact and a spring probe, shown in Fig. 3, having a probe tip in contact with a printed circuit board mounted on a platen adaptor in the test condition; Figure 7 is a cross-sectional view similar to Fig. 6 showing an elongated contact in the non-test condition;; Figure 8 is a partial cross-sectional view of the translator guide plates using reference letters to indicate various different dimensions; Figure 9 is a cross-sectional view of a portion of the translator guide plates similar to Fig. 8 illustrating partial insertion of an elongated electrical contact through corresponding apertures in the translator guide plates; and Figure 10 is a view similar to Fig. 9 with the elongated electrical contact fully positioned in the apertures of the translator guide plates.

Refer now to the embodiment of the invention depicted in Figs. 1 to 1 0.

Fig. 1 shows a test fixture 10 of a form adapted to incorporate the teachings of this invention. The test fixture 10 has a test head holder 1 2 and a test fixture base 14, the holder 1 2 being capable of tilting upwardly about pivot axis 1 3 located in the base 14. In a closed position, the test head holder 1 2 is fastened to the base 1 4 by means of bolts 1 5 located along the upper edge of the base side walls 17.

The test fixture has an extendable and retractable drawer 1 8 for holding a product, such as a printed circuit board (PCB) to be probed in the test fixture. The drawer 1 8 is extendable and retractable on conventional drawer rollers (not shown in Fig. 1) by means of handle 20. While the drawer 1 8 is in the extended position, as shown in Fig. 1, a PCB 22 to be probed may be located on the drawer 1 8 by means of registration of the PCB alignment bores 24 and drawer alignment pins 26. While the drawer 18 is in the closed position, a probing of the PCB may be performed.

Referring now to Fig. 2, there is shown a partial cut away front view of the test fixture 10 with the drawer 1 8 in the fully closed position and with the test head holder 1 2 shown in the closed position. To be explained below, locking knobs 1 6 are connected to pull-up screws 28 (see Fig. 2) for securing several elements (shown in Fig. 2) to the test head holder 1 2.

An essentially planar probe plate 36 extends laterally across the lower edge of test head holder 1 2 and is secured at its side edges 1 9 between the holder 1 2 and the upper edges of the base side walls 1 7 by means of bolts 1 5. The probe plate 36 spans the area defined by the lower edges of the holder 1 2 and is formed preferably of electrically non-conductive rigid material such as glass-epoxy. A plurality of spring probes 34 are rigidly mounted in the probe plate 36.

The spring probes 34 are conventional spring probes and are of the type generally known in the test head art. An example of such a spring probe is disclosed in U.S. Patent 4,050,762 assigned to the same assignee as the present invention, the subject of which is incorporated herein by reference.

One embodiment of the invention has ten thousand spring probes 34 spaced .1 inch apart on centre in a rectangular coordinate grid array as generally depicted schematically in Figs. 2, 3 and 5. Although Fig. 2 only depicts five spring probes 34, additional spring probes are indicated by a horizontal dash line between the illustrated spring probes. The remainder of the spring probes 34 will be understood to be present but not shown for simplicity.

Each spring probe 34 (see Figs. 2, 5 and 6) has a spring-loaded end 34a (Figs. 3, 6, 7) that is retractable against a bias in response to an inwardly directed or compressive force, and an electrical connection end 34b that may be connected to a conductor (not shown) which in turn forms part of a cable of conductors connected either directly or indirectly to an analyzer (not shown). The spring probe 34 is adapted for providing an electrical signal path between probe ends 34a and 34b. The spring probes 34 are monted in the probe plate 36 such that in the absence of the compressive forces, the spring probe ends 34a lie in a substantially common plane, the ends 34a being urged away from the probe plate 36.

Preferably, a force of about 4 oz is required to compress the spring-loaded end 34a of each spring probe.

Located immediately below and in registration with each of the spring probe ends 34a is a first end 38a of a corresponding elongated electrical contact 38 (see Figs. 1, 2 to 7). The contacts 38 are mounted in a translator 21 (see Figs. 2, 3 and 5). The translator 21 comprises a planar first guide plate 40 and a planar second guide plate 42 rigidly connected together in an assembly by means of peripherally located side walls 44 and 46 such that the first and second guide plates are substantially parallel to each other. The first and second guide plates may be bonded to the side walls by any of a number of conventional attachment techniques known in the attachment art. The first guide plate 40 has an array of apertures 48 (Figs. 3, 6, 7), one for each electrical contact 38, extending through the guide plate and arranged for registration with a corresponding spring probe end 34a.

The second guide plate 42 has an array of apertures 50 (Figs. 3, 6, 7) extending through the guide plate, and each of such apertures forms a pair with a corresponding aperture in the first guide plate 40. At least some of the apertures 50 in the second guide plate 42 are transversely offset a predetermined amount "f" (see Fig. 6) from a corresponding aperture 48 in the first guide plate 40.

A substantially flat spacer or protector plate 51 (Figs. 3, 4) is bonded to the upper surface of the first guide plate 40. The protector plate has an array of apertures 55, each aperture 55 being in axial registration with a different corresponding aperture 48 located in the first guide plate 40. The diameter of each of the circular apertures 55 is slightly larger than the diameter of the spring probe ends 34a. Preferably the protector plate 51 is formed of phenolic material having a thickness of about .1 inch. Preferably, the diameter of the apertures 55 are about .04 inch for accommodating the spring probe end 34a.

Each contact 38 is elongated along an axis and is slidably mounted in and extends between one of the pairs of guide plate apertures 48 and 50. Preferably, the apertures 48 and 50 are circular having axes at right angles to or orthogonal to the plane defined by the respective translator first and second guide plates 40 and 42. By virtue of the orthogonality of the aperture axes and the spacing between the guide plates, the side loading defined as the frictional forces between the electrical contact 38 and the apertures is minimized. Preferably, the friction loading between an electrical contact 38 and the apertures is less then about 1 oz. Each electrical contact 38 is axially non-compressible between opposite ends 38a and 38b thereof, when mounted in the guide plates and under load between the spring probes and the PCB under test.Each electrical contact 38 has a portion between the first and second guide plates 40 and 42 respectively, which is transversely flexible to the axis of such contacts for permitting a bend in the contact between the offset apertures. The non-compressible nature of the contacts along the axis thereof when mounted in the first and second guide plates permits an axial force to be applied and transmitted between contact ends 38a and 38b.

A preferred embodiment of the invention contemplates elongated contacts formed of wire, such as music wire having a diameter of about .015 inch, being capable of bending transversely. The wire diameter is selected in accordance with the aperture diameter, and the spacing between the guide plates 40 and 42 is selected such that the electrical contacts 38 are axially non-compressible and do not buckle when in the test condition.

At least one of the first and second guide plates 40 and 42 are formed preferably of an electrically insulating clear material such as a polycarbonate (Lexan (Registered Trade Mark)). As previously described, the apertures 48 in the first guide plate 40 are oriented so that they are in registration with a corresponding spring probe end 34a of a corresponding spring probe 34 located in the probe plate 36. The apertures 50 located in the second guide plate 42 are axially offset from the apertures 48 located in the first guide plate 40 such that a contact end 38b is in opposed relation to a corresponding test point on PCB 22.

The lower extremity of each aperture 48 has a countersunk portion 52 (Figs. 8-10) positioned between the guide plate and opening toward the second guide plate 42 for aiding in the insertion of the elongated electrical contact 38 into the aperture 48 during assembly of a translator. The contact end comprises an elongated and substantially rigid end portion 38b (Fig. 9) sliding in the corresponding aperture 50. The end portion 38b also comprises an enlarged tip 56 for contacting a selected point on the PCB board, and enlargements or extensions 49 that have a lateral span slightly larger than the diameter or periphery of the aperture 50.

In assembling the translator with the electrical contacts in place, the end 38a of the elongated electrical contact 38 is first inserted into the aperture 50. The contact 38 may be manually guided as it is inserted through the aperture 50 until it contacts the countersunk portion 52 of a corresponding upper aperture 48 as shown in Fig. 9. The countersunk portion 52 faces between the guide plates and forms a tapered portion or guide such that the end 38a of contacts 38 is guided into and subsequently through the aperture 48 as generally depicted in Figs. 9 and 1 0. Locating the end 38a in the aperture 48 causes the contact to bend transverse to the axis thereof between the first and second guide plates.

During insertion a force is applied to the end 38b such that the enlargements 49 deform the material around aperture 50 and pass therethrough, the resiliency of the material causing the aperture to return to its original size. The tip has an enlarged portion having a diameter slightly larger than the diameter of aperture 50. Thus, once the enlargements 49 pass through the aperture 50, stops are formed (by enlargement 49 and tip 56) on opposite sides of the second guide plate 42 so that a contact end 38b (and hence contact 38) is confined to movement within the aperture 50 by an amount defined by the difference between the thickness of the second guide plate 42 and the distance between the enlargements 49 and the tip 56.

Preferably, the thickness of the guide plate 42 is about .2 inch and the stroke, defined as the amount of allowable axial travel in the probe plate, is about .125 inch. Preferably, the overall length of the contact 38 between the end 38a and tip 56 is about 2 inches.

The diameter of the central portion of the contact 38 is about .018 inch, and the diameter of the contact end 38b is about .055 inch.

Preferably, the diameter of each aperture 50 is about .060 inch, and the diameter of the aperture 48 is about .021 inch. Fig. 8 identifies by means of alphabetic characters the foregoing dimensions, and such is summarized below in Table 1.

Table 1 e = 1.437 inches f = -.075 inch h = -.021 inch = -.187 inch j = -.187 inch g = -.060 inch In summary, each guide plate has a side that is facing in the opposite direction from the other guide plate to form oppositely facing sides. The opposite ends 38c and 56 of the contacts are positionable so that each is exposed at a different one of the oppositely facing sides at the same time.

Each aperture in each pair of apertures comprises a wall, as depicted at the end of the lead lines for the numerals 48 and 50 in Fig. 6. The wall is in engagement with the corresponding contact for guiding the adjacent and exposed end of the corresponding contact, as the contact slides in the apertures, along a path substantially normal to the guide plates.

Each of the contacts is mounted in the corresponding portion of aperture and is adapted such that both of the exposed ends thereof are movable relative to the guide plates and in the same direction during sliding movement of the contact. This then permits forces to be applied between the tip 56 and the spring biased probes 34a without obstruction by the guide plates 40 and 42.

Additionally the contact comprises a laterally flexible wire which extends from the exposed end 38cto at least a position between the guide plates and adjacent to the guide plate adjacent to the exposed end 56. This then facilitates easy insertion of the contact through the apertures 48 and 50.

With reference to Fig. 10 it will be seen that enlarged exposed end or tip 56 and the enlargement 49 form spaced stops for allowing sliding movement of the end portion 38b in the guide plate 42 by a predetermined amount. Also with reference to Figs. 2, 3, and 5 to 10, there is a substantially open space around and along substantially the entire length of the portion of each of the contacts between the two guide plates. This facilitates easy insertion of the contacts into the guide plates.

The translator 21 is detachably mounted in an essentially planar translator guide plate 54 shown removed from the rest of the test fixture in perspective view in Fig. 4.

The translator guide plate 54 is in contact and alignment with the lower surface of probe plate 36 (Fig. 3). To be explained below, the translator guide plate 54 is adapted to receive and align the replaceable translator 21. The translator guide plate 54 is rigidly held in place by means of pull-up screws that pass through enlarged bores 39 in probe plate 36 (Figs. 2 and 3). The pull-up screws engage mating screw threads 60 (Figs. 2, 3, 4) located in translator guide plate 54 which are in registration with the enlarged bores 39.

The translator guide plate 54 has alignment bushings 57 (see Fig. 3) that align with alignment pims 58 located in the probe plate 36. The translator guide plate 54 is maintained in alignment with the probe plate 36 by virtue of the engagement of alignment pins 58 with the alignment bushings 57.

The translator guide plate 54 is a flat essentially U-shaped plate having a central portion 62 and parallel arms 64 and 66 that extend from the central portion 62. Each of the arms 64 and 66 have facing recessed rectangular channels 68 and 70, respectively. Springloaded detents 72 located midway along the length of each channel 68 and 70 have spring-loaded pins 73 that extend into each of the channels.

The first guide plate 40 of the translator 21 (see Fig. 5) is adapted for insertion into the recessed channels 68 and 70. Detent pin receiving recesses 74 for engaging the springloaded pins 73 of detents 72 are located on the upper surface of guide plate 40 such that in the inserted condition, the spring-loaded pins 73 extending from detents 72 are seated in respective recesses 74 (see Fig. 3A). In the seated condition, the ends 38a of the elongated electrical contacts 38 are in registration with a corresponding spring probe end 34a.

As best seen at channel 68 in Fig. 3, the widths of the channels 68 and 70 are slightly larger than the thickness of the first guide plate 40 for allowing confined vertical movement of the translator guide plate 54.

With the test head roller 1 2 in a lowered position (as depicted in Figs. 3 and 5), the lower extremity of the probe ends 34a lies above the apertures 55 in the protector plate 51 so that the translator is manually removable from the translator guide plate 54 by applying sufficient force (albeit minimal) to overcome the retention force exerted by the detents 72 on the translator. Similarly, the translator 21 may be replaced within the translator guide plate by inserting the first guide plate 40 into the receiving recess channels 68 and 70 until the detent 72 engages the detent receiving recesses 74.

Referring to Figs. 2 and 3, the test fixture 10 is shown in a ready-for-test condition. In the ready-for-test condition, the PCB 22 has been located on the platen adaptor 80 with alignment pins 26 (Figs. 1 and 2) on the platen adaptor projecting through the alignment bores 24 in the PCB board.

Alignment pins 81 located on and projecting downward from the translator second guide plate 42 are now arranged so that they will engage respective alignment bushings 83 located in the platen adaptor 80. With alignment pins 81 and the alignment bushings 83 aligned, raising of platen adaptor 80 causes engagement of pins 81 and bushings 83. At this time, the tips 56 of the electrical contacts 38 are in registration with selected ones of the points on the PCB 22 to be probed.

The platen adaptor 80 is coupled to a base 82 by means of a plurality of spaced apart risers 84. The base 82 forms the bottom of the drawer 1 8. The risers 84 are of equal length and are secured between and to the platen adaptor 80 and the base 82. It is understood that the securing may be accomplished by any one of a number of conventional securing techniques. By virtue of the equal length of the risers, the platen adaptor 80 is maintained parallel to the base 82.

The drawer 1 8 is coupled to a rigid casting 90 by means of a conventional drawer roller assembly 92 (Figs. 2 and 3). The drawer roller assembly 92 provides for inward and outward movement of the drawer 1 8 for removal and replacement of a PCB board 22.

A stationary portion 93 of the roller assembly 92 is secured to the casting 90 by means of attachment screws 94. A non-stationary or extendable portion 95 of the drawer roller assembly 92 is coupled, by means of bolts 88, to the base 82.

Rollers are provided (not shown) between the stationary portion 93 and the extendable portion 95 of the drawer roller assembly 92 such that the drawer is outwardly extendable a sufficient distance to permit the removal and replacement of the PCB under test.

Immediately below and extending laterally across the base side walls 1 7 is a support brace 96. The brace 96 is secured to the side walls 1 7 by means of securement screws 98.

To be discussed in more detail, the brace 96 forms a rigid support for mounting an expandable air bladder that upon inflation causes the rigid casting 90 to be moved upwardly.

More specifically, air bladder 100 is mounted between receiving recesses 102 and 104 located in the rigid casting 90 and brace 96 respectively. The air bladder is inflated by means of a conventional controllable pressurized air supply system (not shown). A pair of return springs 106 spaced equally on opposite sides of the air bladder 100 interconnects the rigid casting 90 to the brace 96. Each return spring 106 comprises a coil spring 108 (partially shown in Fig. 2) having an end 109 seated in a downward opening circular recess 110 located in the brace 96. The other end 111 of the coil spring 108 bears against an enlarged washer 11 2 that is held at end 11 9 of a bolt 114 by means of locking nut 113.

The bolt 114 extends through the coil spring 108 and through an opening 11 5 that extends through the brace 96, the opening 11 5 being coaxial with circular recess 11 0.

An end 11 6 of the bolt 114 is threadably engaged with corresponding bolt receiving threads 11 7 located in the rigid casting 90, mounted to bolts 114 are upper stops 1 21 that limit the downward travel of rigid casting 90 by virtue of contact of the stops 1 21 with the upper surface 1 25 of the brace 96. Also mounted to bolts 11 4 are lower stops 1 23 that limit the upward travel of rigid casting 90 by virtue of contact of the stop 1 23 with the interior surface 1 27 of recess 11 0.

Locking nut 11 8 engages a threaded end 11 6 of the bolt 114 and provides for adjusting the spacing between the rigid casting 90 and the translator second guide plate 42, and therefore a PCB 22 when the test fixture 10 is in the test condition.

Alignment pins 1 20 are provided for guiding the movement of the rigid casting 90 vertically. The alignment pins 1 20 extend vertically upward from pin housing 1 22 that is secured to the brace 96 by means of securement bolts 1 24. The alignment pin 1 20 extends within alignment groove 1 26 located in the rigid casting 90. Preferably, the alignment pin 1 20 is cylindrical and the alignment groove 1 26 is cylindrical having a diameter marginally larger than the diameter of pin 1 20 to permit motion of the rigid casting 90 in a direction parallel to the axis of the alignment pin 1 20.

Referring again to Fig. 3, there is shown in partial cross section the test fixture 10 in the deactuated or non-test condition. In such condition, the air bladder 100 is relaxed or deactuated. Normally, return springs 106 operate in compression such that in the absence of actuation of the air bladder 100 the ends of the coil spring 108 move apart causing the end 11 9 of bolt 114 to move vertically downward. By virtue of the interconnection of bolt 114 with the coil spring 108 and the rigid casting 90, said casting is drawn downward to the lowered position depicted in Fig. 3 representing the non-test condition.

In the lowered position, the drawer 1 8 may be extended away from the test fixture 10 by means of handle 20. A PCB 22 may be placed on the platen adaptor 80 in alignment with alignment pins 26. The drawer 1 8 is returned to its retracted position depicted in Fig. 3, and the air bladder 100 may be inflated and thereby actuated. Responsive to such actuation, air bladder 100 expands such that the rigid casting 90 moves in an upward direction defined by the travel of alignment groove 1 26 along alignment pins 1 20. Proper alignment of the platen adaptor 80 with the translator guide plate 54 is provided by the engagement of the alignment pins 81 with alignment bushings 83.Engagement of the alignment pins 81 with the alignment bushings 83 provides for the registration of the tips 56 and ends 38b of contacts 38 with respective test points on the PCB. Detents 72 in turn guide the translator 21 vertically so that the ends 38a of electrical contacts 38 mounted in the translator first guide plate 40 engages a corresponding probe end 34a.

In the test condition, the spacing between the second translator guide plate 42 and the platen adaptor 80 is maintained by individual stops 1 28 that are bonded to the lower surface of guide plate 42 in registration with respective side walls 44 and 46. The stops 1 28 are sized so that in the actuated or test position (Fig. 2) the tip 56 contacts a respective test point on the PCB without bottoming out the enlarged tip 56 against the lower side of the second guide plate 42 (see Fig. 6). As a result, a force is transmitted from the PCB under test through the elongated electrical contacts 38 to the spring probes 34 creating thereby an electrical path between a selected test point on the PCB and a corresponding spring probe.As a result, the translator is capable of moving in an axial direction relative to the contacts, leaving the contacts 38 free to be forced against the PCB by the spring probe ends 34a. Preferably, a force of about 3 oz for the spring probe end 34a is desirable for achieving proper electrical contact between the end 34a and the point on the PCB to be probed.

By virtue of the spaced apart risers 84, the upward force transferred to the platen adaptor 80 from the air bladder 100 is equally distributed along the platen adaptor, thus preventing any warping or bending of the PCB as the board comes in contact with the tips 56.

In the test condition, the contact tips 56 contact respective test points on the PCB under test. Circuit data may be transmitted to a circuit analyzer coupled to the spring probes for processing.

Subsequent to a PCB test operation, the air supply to air bladder 100 is removed and by virtue of return springs 106, the platen adaptor 80 is returned to the lowered or non-test condition. While the test fixture is in the nontest condition, drawer 1 8 may be extended for exchanging a PCB.

Although an exemplary embodiment of the invention has been disclosed for purposes of illustration, it will be understood that various changes, modifications and substitutions may be incorporated into such embodiment without departing from the spirit of the invention as defined by the claims appearing hereinafter.

Claims

1. A translator for translating between arrays of non-aligned electrical probe points comprising: first and second guide plates rigidly connected together in substantially parallel and spaced apart relation; an array of first apertures extending through the first guide plate; an array of second apertures, each corresponding to and forming a pair with a different first aperture and each extending through the second guide plate, at least some of the second apertures being transversely offset from the corresponding first apertures; and a plurality of electrical contacts elongated along an axis between first and second opposite ends, a different contact being for slidably mounting in and extending between each pair of guide apertures, each electrical contact being axially non-compressible between the opposite ends when a force is applied between the opposite ends and having at least a portion between the guide plates which is transversely flexible to permit extension between the offset guide apertures.

2. A translator as claimed in claim 1, wherein each guide plate has a side that is facing in the opposite direction from the other guide plate to form oppositely facing sides, and wherein the opposite ends of the contacts are positionable so that each is exposed at a different one of the oppositely facing sides of the guide plates at the same time.

3. A translator as claimed in claim 2, wherein each aperture in each pair of apertures comprises a wall in engagement with the corresponding contact for guiding the adjacent and exposed end of the corresponding contact, as the contact slides in the pair of apertures, along a path substantially normal to the guide plates.

4. A translator as claimed in claim 2, wherein the opposite and exposed ends of the contacts are guided so that they move along a path substantially normal to the guide plates as the contacts slide in the corresponding apertures.

5. A translator as claimed in claim 2, wherein each of the contacts is mounted in apertures and is adapted such that both of the exposed ends thereof are movable relative to said guide plates as the contact slides in the apertures.

6. A translator as claimed in claim 5, wherein both of the exposed ends of each contact move together in the same direction during sliding movement of the contact.

7. A translator as claimed in claim 2, wherein each of the contacts comprises a laterally flexible wire extending at least from one of the exposed ends thereof to at least a position between the guide plates and adjacent to the guide plate which is adjacent the other exposed end.

8. A translator as claimed in claim 1, wherein there is an end portion adjacent to one of the ends of each of the contacts which is located in one of the apertures in the second guide plate, the end portion of each contact having enlarged stops for engaging and forming retainers with the second guide plate to retain the end portion within the corresponding aperture in the second guide plate.

9. A translator as claimed in claim 8, wherein the stops are spaced for allowing sliding movement of the end portion in the second guide plate by a predetermined amount.

10. A translatdr as claimed in claim 9, wherein the end portion of each contact comprises an enlarged and rigid end portion.

11. A translator as claimed in claim 10, comprising a sharp probe tip at the end of each contact which is adjacent the end portion.

1 2. A translator as claimed in any preceding claim, wherein the guide plates are formed of electrically non-conductive material.

1 3. A translator as claimed in claim 1, wherein the apertures in a first one of the guide plates have a countersunk portion opening between the plates in a direction toward the second guide plate.

14. A translator as claimed in claim 1, wherein the electrical contact comprises a wire having a diameter of about .015 inch.

1 5. A test fixture for electrically probing an array of substantially planar test points, comprising: a plurality of resiliently biased electrical contacts located in an array, a biased contact corresponding to each test point to be probed; means for urging the biased contacts and a plurality of electrical test points relatively closer together; and a translator for mounting in the test fixture comprising: a plurality of transversely flexible translator contacts elongated along an axis between first and second opposite ends, each translator contact extending between a different one of the biased contacts and a corresponding test point, a pair of parallel guide plates having in each a guide aperture corresponding to and receiving each translator contact, one of said guide apertures in the guide plates for each translator contact being transversely offset from the other and adapted for simultaneously guiding the movement of opposite ends of the corresponding translator contact in directions normal to the guide plates with a first end in opposed relation to the corresponding biased contact and the second end in opposed relation to the corresponding test point, each translator contact when mounted in the corresponding guide aperture being substantially non-compressible along the axis thereof so that as the corresponding biased contact and test points are urged closer together, a force, due to the corresponding biased contact, is exerted therethrough to the corresponding test point.

1 6. A test fixture as claimed in claim 15, comprising: means for mounting a member containing a circuit with test points for test; and means for drawing the biased contacts and mounting means relatively closer together, the biased contacts exerting a contact pressure through the corresponding translator contacts to the corresponding test points, each of said translator contacts being substantially noncompressible along the axis thereof to permit a force due to each resiliently biased contact to be applied through the corresponding translator contact to the corresponding test point.

1 7. A test fixture as claimed in claim 15, wherein the assembly includes translator mounting means adapted for receiving and allowing the same to be removably mounted and for aligning the translator such that in the aligned condition the first opposite end of each translator contact is in alignment with a corresponding one of the biased contacts.

1 8. A test fixture as claimed in claim 1 5, including means for aligning the translator in the assembly comprising first alignment means in the assembly and second alignment means in the translator cooperating with said first alignment means such that the translator is removable from the assembly and in an aligned condition the translator remains aligned and relatively stationary in a transverse direction with respect to the biased contacts.

1 9. A test fixture as claimed in claim 18, wherein the second alignment means comprises at least one elongated alignment pin and the first alignment means comprises at least one alignment bushing adapted for receiving the alignment pin.

20. A test fixture as claimed in claim 19, wherein the translator mounting means inculdes detent means and the translator includes cooperating detent receiving means for allowing the translator to be removably mounted in the translator mounting means.

21. A test fixture as claimed in claim 20, wherein the detent means comprises at least one spring-loaded pin and the detent receiving means includes a receiving bore.

22. A test fixture as claimed in claim 21, wherein the mounting means includes test unit alignment means comprising third alignment means located in the translator and fourth alignment means located in the mounting means cooperating with said third alignment means for aligning the mounting means with the translator and a unit aligner comprising at least one alignment pin mounted in the mounting means and extending from the mounting means for insertion into an alignment opening in such a unit under test for aligning the second end of a translator contact with a corresponding unit test point.

23. A test fixture as claimed in claim 15, wherein said first and second guide plates are formed of electrically insulating material.

24. A test fixture as claimed in claim 16, wherein the second end of each translator contact comprises a tip portion having enlarged first and second ends forming stops with the second guide plate to retain the tip portion therein.

25. A test fixture as claimed in claim 16, wherein each guide plate has a side that is facing away from the other guide plate to form oppositely facing sides, and wherein the opposite ends of the translator contacts are positionable so that one is exposed at a different one of the oppositely facing sides of the guide plates at the same time.

26. A test fixture as claimed in claim 25, wherein each of the translator contacts is mounted in apertures and is adapted such that both of the exposed ends therof are movable relative to said guide plates as the contact slides in the apertures.

27. A test fixture as claimed in claim 26, wherein both of the exposed ends of each translator contact move together in the same direction during sliding movement of the contact.

28. A test fixture as claimed in claim 15, wherein each of the translator contacts comprises a laterally flexible wire extending at least from one of the exposed ends thereof to at least a position between the guide plates and adjacent to the guide plate which is adjacent the other exposed end.

29. A test fixture as claimed in claim 1 5, wherein there is an end portion adjacent to one of the ends of each of the translator contacts which is located in one of the apertures in the second guide plate, the end portion of each translator contact having enlarged stops for engaging and forming retainers with the second guide plate to retain the end portion within the corresponding aperture in the second guide plate.

30. A test fixture as claimed in claim 29, wherein the stops are spaced for allowing sliding movement of the end portion in the second guide plate by a predetermined amount.

31. A test fixture as claimed in claim 30, wherein the end portion of each translator comprises an enlarged and rigid end portion.

32. A test fixture as claimed in claim 31, comprising a sharp probe tip at the end of each contact-which is adjacent the end portion.

33. A method of forming a translator from a plurality of contacts and a pair of spaced apart and interconnected guide plates, the contacts being elongated along an axis between first and second ends and comprising a transversely flexible and substantially axially rigid portion between the ends, each guide plate having a plurality of apertures, each of said apertures in one guide plate having a corresponding non-aligned aperture in the other guide plate, comprising the steps of: feeding a first end of each of the contacts through a different aperture in a first of said guide plates: locating the first end of each of the contacts in the corresponding offset aperture in the second guide plate, causing the contact to bend in the flexible portion in a direction transverse to the axis thereof and at a position between the guide plates; and passing the first end of each of the flexible contacts into the corresponding aperture in the second guide plate, leaving each of the flexible contacts with opposite end portions supported and guided by corresponding apertures in each guide plate.

34. A method as claimed in claim 33, wherein each of the transversely flexible contacts comprises a substantially rigid end portion adjacent the second end, the method including the step of inserting said substantially rigid end portion of each contact into the corresponding aperture in the second guide plate.

35. A method as claimed in claim 34, wherein the substantially rigid end portion of each is enlarged relative to an adjacent por tion of each contact and comprising the step of inserting the enlarged end portion of each contact into the corresponding aperture in the second guide plate for sliding movement therein.

36. A method as claimed in claim 35, wherein the enlarged end portion of each of the contacts comprises spaced apart further enlargements which extend beyond the periphery of the corresponding aperture in the second guide plate, the method comprising the step of forcing one of the further enlargements in the enlarged end portion of each contact through the corresponding aperture to thereby cause the further enlargements to provide a stop on opposite sides of the second guide plate for the axial movement of the contacts in either direction of movement.

37. The method as claimed in claim 33, wherein each of the apertures in the first guide plate comprises an enlarged tapered aperture portion positioned and facing between the guide plates, the method comprising the step of inserting the first end of the contacts into the aperture portion of the corresponding aperture using the aperture as a guide for further inserting the contacts into the corresponding aperture in the first guide plate.

38. A translator for translating between arrays of non-aligned electrical probe points substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

39. A test fixture for electrically probing an array of substantially planar test points substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

40. A method of forming a translator from a plurality of contacts and a pair of spaced apart and interconnected guide plates, substantially as hereinbefore described with reference to the accompanying drawings.