Vacuum-actuated test fixture for testing printed circuit boards

A test fixture for testing a circuit board, comprising a top plate defining a board-bearing surface for receiving the circuit board to be tested thereon. The test fixture comprises a lid having a lid frame defining a peripheral rim, and a lid diaphragm movably mounted to the frame opposite the peripheral rim; the lid diaphragm defines an inner surface to which is mounted a circuit board securing member. The lid is movable between a first position where the frame rim engages the top plate to define a test chamber about the board-bearing surface and between the top plate, the frame and the diaphragm, and a second position where the lid is moved away from the top plate to allow access to the test chamber. The lid diaphragm is movable relative to the frame at least when the lid is in the first position between a rest position where the securing member is moved away from the board-bearing surface and an operative position where the securing member is moved towards the board-bearing surface for engaging and securely holding the circuit board thereon. The test fixture further comprises a diaphragm biasing member continuously biasing the diaphragm towards the rest position, and an actuator, for selectively forcibly moving the diaphragm towards the operative position against the bias of the diaphragm biasing member. Moreover, the test fixture comprises at least one test probe projecting from either one of the lid and the top plate towards the board-bearing surface when the lid is in the first position and the diaphragm is in the operative position for allowing the at least one test probe to engage the circuit board. The test fixture also comprises a circuit interface for connecting the probes to a computer.

FIELD OF THE INVENTION

The present invention relates to testing devices, and more particularly to a vacuum-actuated test fixture for testing printed circuit boards.

BACKGROUND OF THE INVENTION

Vacuum actuated test fixtures have been found to be highly effective for testing many types of printed circuit boards. Some of the heretofore available test fixtures of this type generally comprise a probe plate having a plurality of spring-loaded electrical probes thereon, and a casing supported above the probe plate and spaced away therefrom by a peripheral resiliently deformable seal. The casing includes a perforated top plate, the undersurface of which rests against the resilient seal and onto which a circuit board can be mounted. The probes of the probe plate can pass through the perforations of the top plate. The casing also includes a lid pivotally mounted to the upper surface of the top plate, which can be pivoted away from the top plate into an open position, and towards the top plate into a closed position. The lid comprises a peripheral lid frame and a lid plate fixedly attached to the top peripheral edge portion of the lid frame. Moreover, the lid plate comprises a number of downwardly projecting abutment fingers registering above the circuit board when the lid is closed. A peripheral resiliently deformable sealing member is attached to and depends downwardly from the lower rim of the lid frame, and rests against the top plate when the lid is closed.

To test a circuit board using such a test fixture, a circuit board is mounted on the top plate, the lid is set in its closed position with the lid's resilient sealing member sealing the inner chamber within the lid, and a vacuum is created between the top plate and the probe plate, and between the top plate and the lid. It is to be noted that when the lid is closed, but before a vacuum is created between the top plate and the lid, a substantial gap, typically of a few centimetres, separates the lid frame's lower rim and the top plate's upper surface, with the resilient sealing member filling this gap.

The creation of a vacuum between the top plate and the probe plate, and between the top plate and the lid, causes the following displacements to occur concomitantly:the lid is drawn downwardly towards the top plate which movement is allowed by the sealing member resiliently yieldingly compressing to allow the lower rim of the lid frame to move towards the top plate's upper surface. As the lid is drawn towards the top plate, the abutment fingers projecting from the lid plate are moved downwardly in order to press the circuit board against the top plate, and thus secure the circuit board to the top plate; andthe top plate is drawn downwardly towards the probe plate in order for the probes mounted on the probe plate ands extending through the perforations made across the top plate to abut against the undersurface of the printed circuit board to electrically connect the probes with corresponding predetermined circuits of the circuit board. When the probes come in contact with the circuit board, the probes apply upward pressure on the circuit board but the circuit board remains still since it is held down by the abutment fingers.

As useful as these test devices may be, their usage involve important security hazards. Indeed, it happens that an operator inadvertently places his finger(s) in the gap between the lower rim of the lid flame and the top plate, and then activates the vacuum pump to create a vacuum between the lid and the top plate. As the vacuum pump is activated, the lid is thrust downwardly against and crush the operator's misplaced finger(s), which can cause severe injuries.

Also, the above-mentioned prior art test devices also have some inaccuracy issues. Indeed, when the test fixture is made and assembled, there are often small undesirable plays that appear when the lid is installed on the top plate of the test fixture. This is at least partly due to the fact that the lid is designed to be pivotally movable relative to the top plate to allow access to the inner test chamber where the circuit board to be tested is installed, and consequently a high degree of precision is more difficult to achieve during the fabrication and assembly thereof. These undesirable plays may result in the lid slightly moving laterally when a vacuum is created therein, which results in turn in some lid-carried probes not engaging their corresponding contacts on the circuit board, among other problems related to this inaccuracy of the lid position.

SUMMARY OF THE INVENTION

The present invention relates to a test fixture for testing circuit boards, comprising:a probe plate to which is mounted at least one test probe;a top plate supported spacedly from and registering with said probe plate, said top plate defining at least one probe perforation made transversely thereon and through which said test probe can extend, said top plate further defining a board-bearing surface for receiving a circuit board thereon;a lid having a lid frame defining a peripheral rim, said lid being movable between a first position where said lid frame peripheral rim sealingly engages said top plate about said board-bearing surface, and a second position where said lid is moved away from said top plate, said lid further comprising a lid diaphragm sealingly connected to said lid frame, said lid diaphragm being movable relative to said lid frame at least when said lid is in said first position between a rest position where said lid diaphragm is moved away from said top plate, and an operative position where said lid diaphragm is moved towards said top plate, said lid diaphragm defining an inner surface to which is mounted at least one circuit board securing member for engaging the circuit board when said lid is in said first position and said lid diaphragm is in said operative position;a biasing member biasing said lid diaphragm towards said rest position and capable of yielding to allow said lid diaphragm to move towards said operative position;a test chamber, enclosed by said top plate and said lid when said lid is in said first position;at least one vacuum port in fluid communication with said test chamber, for connection to a vacuum pump which can be activated to create a vacuum within said test chamber; anda circuit interface for connecting said probes to data processing means;
wherein when said lid is in said first position and a vacuum is created in said test chamber, said lid diaphragm is moved towards said operative position against the bias of said biasing member for moving said circuit board securing member towards the circuit board to releasably secure the latter to said board-bearing surface.

In one embodiment, said biasing member includes a resilient diaphragm sealing strip between said lid frame and said lid diaphragm, said resilient diaphragm seal also providing a sealed interconnection between said lid diaphragm and said lid frame.

In one embodiment, an auxiliary seal is provided on said lid frame to enhance the sealed interconnection between said lid diaphragm and said lid frame when said lid diaphragm is in said operative position.

In one embodiment, said test fixture further includes a resilient probe plate seal spacing said top plate and said probe plate wherein a subchamber is enclosed by said probe plate, said resilient probe plate seal and said top plate, said subchamber being in fluid communication with said test chamber through an air passageway, and wherein upon creation of a vacuum in said test chamber, a vacuum is also created in said subchamber which causes said resilient probe plate seal to yield to allow said top plate to be moved towards said probe plate, for allowing said test probe to extend across said top plate through said probe perforation and come in electrical contact with the circuit board mounted on said top plate.

In one embodiment, said top plate includes a circuit board mounting member defining said board-bearing surface, with said circuit board securing member including an elongated finger affixed to and projecting from said lid diaphragm undersurface and destined to press the circuit board against said circuit board mounting member when said lid diaphragm is in said operative position.

In one embodiment, said test fixture further comprises at least another test probe affixed to said lid diaphragm, wherein a reading tip of said another test probe is destined to be brought in electrical contact with the circuit board when said lid diaphragm is moved towards said operative position.

In one embodiment, said test fixture further includes at least one guiding member projecting from said top plate towards said lid, said guiding member being sealingly and slidably engageable in a guide hole made in said diaphragm when said lid is in said first position, the displacement of said diaphragm between said rest and operative positions being defined along an axis of displacement and being guided by the slidable engagement of said guiding member in said diaphragm guide hole, said diaphragm being loosely carried by said frame so as to be at least slightly movable transversely relative to said axis of displacement for providing a self-aligning capacity to said diaphragm.

The present invention also relates to a test fixture for testing circuit boards, comprising:a top plate, having at least one probe perforation made thereon for allowing at least one test probe to extend therethrough, said top plate comprising circuit board mounting means defining a movable board-bearing surface for receiving a circuit board thereon, said board-bearing surface destined to be movable relative to the at least one test probe;a lid having a lid frame defining a peripheral rim, said lid being movable between a first position where said lid frame peripheral rim sealingly engages said top plate, and a second position where said lid is moved away from said top plate, said lid further comprising a lid diaphragm connected to said lid frame and defining an inner surface to which is mounted circuit board securing means, said lid diaphragm being movable relative to said lid frame at least when said lid is in said first position between a rest position where said circuit board securing means is moved away from said board-bearing surface, and an operative position where said circuit board securing means is moved towards said board-bearing surface for engaging the circuit board;sealing means allowing a sealed interconnection between said lid diaphragm and said lid frame;diaphragm biasing means biasing said lid diaphragm towards said rest position and capable of yielding to allow said lid diaphragm to move towards said operative position;a test chamber, enclosed by said top plate and said lid when said lid is in said first position;at least one vacuum port in fluid communication with said test chamber, for connection to a vacuum pump which can be activated to create a vacuum within said test chamber; andcircuit interface means for connecting said probes to data processing means;
wherein when said lid is in said first position and a vacuum is created in said test chamber, said lid diaphragm is moved towards said operative position against the bias of said biasing means for moving said circuit board securing means towards the circuit board to secure the latter to said board-bearing surface.

In one embodiment, said test fixture further includes a probe plate, and a resilient seal spacing said top plate and said probe plate, wherein a subchamber is enclosed by said probe plate, said resilient seal and said top plate, said subchamber being in fluid communication with said test chamber through an air passageway, and wherein upon creation of a vacuum in said test chamber, a vacuum is also created in said subchamber which causes said resilient seal to yield to allow said top plate to be moved towards said probe plate, for allowing said board-bearing surface and the at least one test probe to be moved towards one another for allowing the at least one test probe to come in electrical contact with the circuit board mounted on said board-bearing surface.

In one embodiment, said circuit board mounting means comprises:a support plate defining said board-bearing surface, said support plate being mounted to said top plate spacedly and movably relative thereto, said support plate being movable relative to said top plate between a first position where said board-bearing surface of said circuit board mounting means is moved away from said top plate, and a second position where said board-bearing surface is moved towards said top plate for bringing the circuit board mounted thereon in electrical contact with the at least one test probe; andsupport plate biasing means continuously biasing said support plate towards said first position, whereby when said lid diaphragm is moved towards said operative position, said circuit board securing means is moved towards said board-bearing surface for moving said support plate towards said second position against the bias of said support plate biasing means.

In one embodiment, said diaphragm defines an axis of displacement when it moves between said rest and operative positions, said text fixture further comprising guide means for guiding said diaphragm along said axis of displacement, said diaphragm being loosely carried by said frame so as to be at least slightly movable transversely relative to said axis of displacement for providing a self-aligning capacity to said diaphragm through said guide means.

The present invention further relates to a lid for use with a circuit board test fixture of the type having a top plate for mounting a circuit board thereon, said lid comprising:a lid frame defining a peripheral rim for releasable engagement on the top plate:a lid diaphragm carried by said lid frame opposite said peripheral rim, said lid diaphragm being movable relative to said lid frame between a rest position where said lid diaphragm is moved away from said peripheral rim, and an operative position where said lid diaphragm is moved towards said peripheral rim, said lid diaphragm defining an inner surface carrying at least one circuit board securing member for engaging the circuit board when said peripheral rim engages the top plate and when said lid diaphragm is in said operative position;a biasing member biasing said lid diaphragm towards said rest position and capable of yielding to allow said lid diaphragm to move towards said operative position: andsealing means carried by either one of said frame, said lid diaphragm and both said lid frame and said lid diaphragm, for sealingly linking said lid frame to said lid diaphragm.

The present invention also relates to a test fixture for testing a circuit board, comprising:a top plate comprising a circuit board-mounting member defining a board-bearing surface for receiving the circuit board to be tested thereon;a lid comprising a lid frame defining a peripheral rim, said lid further comprising a lid diaphragm movably mounted to said frame opposite said peripheral rim, said lid diaphragm defining an inner surface to which is mounted a circuit board securing member, said lid being movable between a first position where said frame rim engages said top plate to define a test chamber about said board-bearing surface and between said top plate and said lid, and a second position where said lid is moved away from said top plate to allow access said board-bearing surface, said diaphragm being movable relative to said frame at least when said lid is in said first position between a rest position where said securing member is moved away from said board-bearing surface and an operative position where said securing member is moved towards said board-bearing surface for engaging and securely holding the circuit board thereon;a diaphragm biasing member continuously biasing said diaphragm towards said rest position;an actuator, for selectively forcibly moving said diaphragm towards said operative position against the bias of said diaphragm biasing member;at least one test probe projecting from either one of said lid diaphragm and said top plate towards said board-bearing surface when said lid is in said first position and said diaphragm is in said operative position for allowing said at least one test probe to engage the circuit board; and
a circuit interface, for connecting said at least one test probe to data processing means.

In one embodiment, said actuator comprises vacuum means in fluid communication with said test chamber for creating a vacuum within said test chamber, with said lid comprising a diaphragm seal sealingly linking said frame and said diaphragm and a frame seal sealingly linking said frame rim and said top plate when said lid is in said first position to seal said test chamber when said lid is in said first position.

In one embodiment, said test fixture further comprises:a probe plate supported spacedly from and registering with said top plate opposite said lid when said lid is in said first position and carrying at least one probe plate test probe, said top plate comprising at least one probe perforation made transversely thereon with each said at least one probe plate test probe extending through a corresponding said probe perforation towards said board-bearing surface, said top plate being movable relative to said probe plate between a rest position away from said probe plate and an operative position where said top plate is moved towards said probe plate for allowing said at least one probe plate test probe to engage the circuit board through said top plate;a probe plate seal sealingly linking said probe plate and said top plate and defining a subchamber between said probe plate and said top plate;a top plate biasing member continuously biasing said top plate towards said rest position; andadditional vacuum means for creating a vacuum in said subchamber;
wherein upon a vacuum being created in said test chamber and in said subchamber, there is a dual movement of said top plate towards said top plate operative position and of said diaphragm towards said diaphragm operative position for engaging each said test probe against the circuit board.

In one embodiment, the first-named said vacuum means and said additional vacuum means include a vacuum port connected to either one of said test chamber and subchamber for operative connection to a vacuum creating device, and an air passageway linking said test chamber and said subchamber.

In one embodiment, said diaphragm biasing member is less resistant than said top plate biasing member whereby said diaphragm will move from said diaphragm rest position towards said diaphragm operative position before said top plate biasing member moves from said top plate rest position towards said top plate operative position upon a vacuum being gradually and simultaneously created in said test chamber and said subchamber.

In one embodiment, said diaphragm seal and said diaphragm biasing member are a resiliently yieldingly deformable sealing strip linking said diaphragm to said frame.

In one embodiment, said diaphragm biasing member further includes at least one spring provided between said diaphragm and said frame and acting cooperatively with said resilient diaphragm sealing strip to bias said diaphragm towards said rest position.

In one embodiment, said probe plate seal and said top plate biasing member are a resiliently yieldingly deformable sealing strip linking said top plate to said probe plate.

In one embodiment, said lid further comprises an auxiliary sealing O-ring carried by either one of said frame and said diaphragm and sealingly linking said frame and said diaphragm when said diaphragm is in said operative position.

In one embodiment, said circuit board mounting member comprises:a support plate defining said board-bearing surface, said support plate being mounted to said top plate spacedly and movably relative thereto, said support plate being movable relative to said top plate between a first position where said board-bearing surface of said circuit board mounting member is moved away from said top plate, and a second position where said board-bearing surface is moved towards said top plate for bringing the circuit board mounted thereon in electrical contact with said at least one test probe; anda support plate biasing member biasing said support plate towards its first position, whereby when said diaphragm is moved towards said operative position, said circuit board securing member is moved towards said board-bearing surface for moving said support plate towards said second position against the bias of said support plate biasing member.

In one embodiment, said diaphragm defines an axis of displacement when it moves between said rest and operative positions, said text fixture further comprising a first guiding member on said top plate and a second guiding member on said diaphragm cooperating with said first guiding member to guide said diaphragm along said axis of displacement, said diaphragm being loosely carried by said frame so as to be at least slightly movable transversely relative to said axis of displacement for providing a self-aligning capacity to said diaphragm through the cooperating first and second guiding members.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIGS. 1–4show one embodiment of a vacuum-actuated test fixture10for testing printed circuit boards. Fixture10includes a probe plate12carrying a number of spring-loaded probes14of known construction, which, through the instrumentality of suitable circuit interface means such as suitable multi-pin plug101, are electrically connected to a suitable data processing means such as a computer100. Probes14extend through holes made in probe plate12and are affixed thereto, and the interconnection between probe plate12and probes14is made airtight by suitable sealing means. A vacuum port16is made in probe plate12, and a nozzle17is fitted in vacuum port16which is intended to be connected to a vacuum pump102. A peripheral resiliently deformable probe plate seal18, made from a cross-sectionally rectangular strip of silicon-based foam for example (FIGS. 3–4), runs continuously and is affixed to the upper surface of probe plate12, parallel to and slightly inwardly offset relative to the outer peripheral edge of probe plate12. A leg member24, having a shank portion24aat one end of which a knob24bis attached, is provided at each of the four corners of probe plate12. The shank portion24aof each leg member24extends transversely and slidably across probe plate12, at the vicinity of one of its four corners. The free end of the shank portions24aopposite knobs24bis destined to engage corresponding apertures in a casing of an underlying circuit board data acquisition device (not shown) of known construction, which will carry the data processing means100and the vacuum pump102.

A so-called top plate22is supported spacedly and movably above probe plate12. The undersurface of top plate22rests against probe plate seal18. Each corner of top plate22comprises a bore fixedly engaged by shank portion24aof leg members24underneath knob24b, probe plate12thus being slidably movable relative to top plate22. Probe plate seal18spaces top plate22from probe plate12, biases top plate22in a rest position away from probe plate12, but as shown inFIG. 7, can yield and compress to allow top plate22to move downwardly towards probe plate12in an operative position, as detailed hereinafter. Furthermore, top plate22defines a number of perforations23each registering with a corresponding probe14, and the reading tip14aof probes14partly extends through perforations23. At least one air passageway25is also made across top plate22, for purposes detailed hereinafter. Moreover, a circuit board mounting means or member is provided on the upper surface of top plate22, which includes positioning pins26and spacers28. On one hand, positioning pins26are intended to engage complementary holes H, H made in a printed circuit board C (FIG. 1), to position the latter on top plate22such that circuit board C is precisely installed according to a predetermined position relative to and above perforations23. On the other hand, spacers28are intended to support circuit board C slightly spaced above the upper surface of top plate22; the plane shared by the free upper ends of spacers28thus forms a board-bearing surface of top plate22. Of course, any other suitable circuit board mounting means could be envisioned to mount a circuit board on top plate22; for example, a rectangular depression could be made in the upper surface of top plate22, in which a circuit board to be tested could be snugly fitted.

Two elongated guide fingers30project upwardly and are affixed to the upper surface of top plate22. In an alternate embodiment, fingers30could be affixed to probe plate12and extend through apertures made in top plate22to project beyond top plate22.

Test fixture10further comprises a lid32pivotally attached to top plate22as described hereinafter. Lid32comprises a peripheral frame34defining a lower rim37and including side walls34a,34band front and rear walls34c,34drespectively, within which a rigid lid diaphragm36, in the form of a flat rigid wall, is movably mounted. Side walls34a,34bextend rearwardly beyond rear wall34d, and are pivotally attached at their rear end to stationary pivot members38,38affixed to the upper surface of top plate22, to allow lid32to be pivotable relative to top plate22between an open position (FIG. 1) where the lid22is pivoted away from top plate22, and a closed position where the lower rim37of lid frame34engages the upper surface of top plate22(FIGS. 2–7). Moreover, dampening hydraulic cylinders40,40are attached at one end to lid frame side walls34a,34brespectively, and at the other end to flanges42,42projecting upwardly from the upper surface of top plate22. Cylinders40,40are extracted when lid32is pivoted in its open position, and are retracted when lid32is pivoted in its closed position. Cylinders40,40will dampen the movement of lid32between its open and closed positions, and can allow lid32to remain in its open position until forced towards its closed position.

The cross-sectional shape of lid frame walls34a,34b,3c,34dis best shown inFIG. 4. Each lid frame wall, for example wall34d, comprises a relatively thicker base portion50, the flat top surface of which will be further referred to as seat52, and also comprises a relatively thin lip portion54upwardly projecting from seat52, adjacent the outer edge thereof, and integrally to base portion50.

A peripheral groove56is made lengthwisely along the undersurface of base portion50of all four lid frame walls34a,34b,34cand34d, and a continuous peripheral frame seal44is mounted coextensively therein. When lid32is closed, frame seal44, made of a silicon-based foam for example, makes the mutual engagement of lid lower rim37and the upper surface of top plate22airtight. It is to be noted that when lid32is closed, lower rim37of lid32is applied directly on the upper surface of top plate22, i.e. no gap, or a very small gap caused by the presence of frame seal44, separates lower rim37and top plate22. In any case, the interstice between lower rim37and top plate22is too narrow for an operator to slip his fingers therein when lid32is closed.

Two longitudinal grooves60,62are made lengthwisely along seat52of all four lid frame walls34a,34b.34cand34d. The upper end of groove60is bevelled and broadened at60a. Groove60provides accommodation for a continuous, cross-sectionally rectangular biasing diaphragm seal64, which extends upwardly beyond seat52. Diaphragm seal64runs continuously and coextensively along groove60of all four walls of lid frame34. Diaphragm seal64is made from a resilient material; in one embodiment, the material forming diaphragm seal64is also compressible, and can be a silicon-based foam for example. Groove62is smaller than groove60, and provides accommodation for an optional auxiliary seal in the form of a peripheral O-ring66running continuously and coextensively therein.

Lid32is also provided with a front handle46affixed to lid frame front wall34c. A stopper plate48is secured atop handle46and extends beyond lip portion54of front lid frame wall34c, such that it partly overhangs seat52. Lid32is also provided with rear L-shaped brackets68. Each bracket68integrally defines a vertical attachment portion68asecured to the outer surface of lid frame rear wall34d, and a horizontal stopper portion68bextending beyond lip portion54of rear lid frame wall34dand overhanging seat52of rear frame wall34d.

As mentioned hereinabove, a rigid lid diaphragm36, defining a peripheral edge portion36a, is movably mounted to lid frame34, within the boundaries of lip portions54of the four lid frame walls34a,34b,34c,34d. Lid diaphragm36can be made from a translucent and resistant material, such as rigid translucent plastic. Lid diaphragm36is mounted within the four lid frame walls34a,34b,34c,34dsuch that the undersurface of its peripheral edge portion36ais supported on the free upper end of diaphragm seal64. Resilient diaphragm seal64biases lid diaphragm36towards a rest position, away from seat52, where the upper face of lid diaphragm edge portion36aabuts against stopper plate48and stopper portions68b,68bof brackets68,68. Upon lid diaphragm36being forced downwardly, as described hereinafter, diaphragm seal64will resiliently yieldingly deform in a compressed state to allow lid diaphragm36to reach an operative position, where the undersurface of lid diaphragm edge portion36aabuts against peripheral seat52of the four walls of lid frame34.

Two seal-provided guide holes70are made transversely on lid diaphragm36, and are disposed thereon such that they are sealingly and slidably penetrated by guide fingers30to guide the movement of diaphragm36between its rest and operative positions.

Furthermore, three C-shaped, security ribs72,74,74are affixed to and upwardly project from the upper surface of lid diaphragm36, as best shown inFIGS. 2 and 5. Rib72is arranged on lid diaphragm36so that it surrounds the front stopper plate48, and ribs74,74are arranged such that they surround rear bracket stopper portions68b,68b. When lid diaphragm36is in its lowered operative position, a substantially wide gap69(FIGS. 6–7) separates the upper surface of lid diaphragm36from stopper portions68b,68band stopper plate48; ribs72,74,74are intended to fence off these gaps69to prevent someone, e.g. an operator of the test fixture10, to inadvertently place his fingers therein.

In the embodiment shown in the figures, a number of optional spring-loaded upper probes15defining a reading tip15aand connected to suitable data processing means100, extend across lid diaphragm36and are disposed thereon such that they overhang circuit board C when lid32is closed.

Furthermore, a number of circuit board securing members, in the form of abutment fingers76, downwardly project from and are affixed to the undersurface of lid diaphragm36, and are disposed to register above circuit board C when lid32is in its closed position. Fingers76are more particularly disposed to register, when lid32is closed, above regions of circuit C devoid of electrical components.

As best shown inFIG. 3, when lid32is closed, test fixture10defines a sealed inner chamber80, which in turn defines two chambers: a test chamber80a, enclosed by lid32and top plate22, and a subchamber80b, enclosed by probe plate12, probe plate seal18and top plate22. The two chambers80a,80bare in fluid communication with each other through probe apertures16(although the latter may optionally be sealed), and through air passageway25made in top plate22(although non-sealed probe apertures16may act as air passageways instead of passageway25). When lid32is closed, inner chamber80is sealed from the atmosphere.

To test a circuit board C using test fixture10, an operator has to pivot lid32away from top plate22in its open position (FIG. 1) to have access to test chamber80a. A printed circuit board C is then laid onto top plate, such that it rests on spacers28, and such that holes H, H of circuit board C engage positioning pins26to properly align circuit board C according to a precisely calculated predetermined position. Lid32is then pivoted back towards top plate22in its closed position, as shown inFIGS. 2–4, where frame seal44of lid frame34engages the upper surface of top plate22and where the free ends of guide fingers30slidably engage guide holes70in an airtight fashion. The vacuum pump102connected to vacuum nozzle17is then activated to create a vacuum within inner chamber80.

As vacuum pump102is activated, the pressure within inner chamber80drops, and a vacuum within inner chamber80is generated, and thus within both chambers80a,80b. As a vacuum within test chamber80ais generated, as shown inFIGS. 5–7, lid diaphragm36is biased downwardly towards its operative position and towards top plate32, and diaphragm seal64yields and deforms to allow lid diaphragm36to move towards its operative position, where its peripheral edge portion36arests on seat52. In the embodiment where diaphragm seal64is made from a compressible material, when diaphragm seal64yields, it also compresses to fit entirely within the peripheral groove60and to fill the broadened portion60aof groove60(FIGS. 6–7). As described above, to guide the motion of lid diaphragm36towards top plate22, guide holes70of lid diaphragm36slide along guide fingers30projecting from top plate22. When lid diaphragm36is moved in its operative position, infiltration of air from the atmosphere into test chamber80athrough the interface between lid diaphragm edge portion36and seat52is obviated by the combined sealing actions of both diaphragm seal64and the optional auxiliary O-ring66. Furthermore, when lid diaphragm36is moved towards top plate22, abutment fingers76apply a substantial downward force on the upper surface of circuit board C, thereby pressing the latter against spacers28and ensuring that holes H, H of circuit board C remain engaged on positioning pins26. Thus, when a vacuum is generated in test chamber80a, circuit board C becomes securely anchored to top plate22by the pressure applied by abutment fingers76. Also, the passage of lid diaphragm36from its rest position to its operative position brings the reading tip15aof optional upper probes15in electrical contact with registering predetermined corresponding electrical components present on the upper surface of circuit board C.

As the vacuum is concomitantly generated in chambers80a,80b, the downward vacuum-borne pressure that forces lid plate36downwardly will further be transferred through lid frame34onto top plate22, the latter thus being biased downwardly. Probe plate seal18yields and compresses, as shown inFIGS. 6–7, to allow top plate22to relatively move towards probe plate12to reach its operative position, such relative movement being accomplished by the slidable engagement of probe plate12along leg member24. As top plate22is drawn towards probe plate12, the board-bearing surface and thus the printed circuit board C are moved towards probes14fixed to probe plate12, and their reading tips14aeventually come in electrical contact with registering predetermined corresponding electronic components located underneath circuit board C. When probes14come in contact with these components, they apply significant vacuum-borne upward pressure on circuit board C which biases the latter away from top plate22, but circuit board C is nevertheless steadfastly held in place against the bias of probes14and prevented from disengaging the circuit board mounting means, i.e. positioning pins26and spacers28, since the circuit board C is secured to top plate22by abutment fingers76and by optional lid probes15.

In one embodiment, the relative resiliency of probe plate seal18and diaphragm seal64is calibrated to allow diaphragm seal64to collapse first under the vacuum being created in inner chamber80. That is to say that diaphragm seal64will offer less resistance than probe plate seal18will. Consequently, diaphragm36will move downwardly towards its operative position before top plate22moves towards its own operative position when a vacuum is created. This will result in abutment fingers76abutting against circuit board C to securely hold it in place before the probe plate probes14apply any upward pressure against circuit board C.

Once the necessary electric data has been acquired by probes14and15, and that this data has been analysed by the afferent data processing means100, as known in the art, the test procedure is completed. The vacuum pump can then be deactivated, which causes inner chamber80to re-pressurize. As chambers80a,80bare re-pressurized, the biasing effect of resilient probe plate seal18is no longer overwhelmed by the pressure differential between the atmosphere and test chamber80a. Accordingly, probe plate seal18springs back to its original configuration, top plate22is thus moved back to its rest position away from probe plate12, and probes14are disconnected from circuit board C. Similarly, when chambers80a,80bare re-pressurized, diaphragm seal64can spring back to its original configuration, and lid diaphragm36, along with probes15and abutment fingers76, is moved back to its rest position. Lid32can then be opened, the tested circuit board C dismounted from the top plate, and another circuit board can be mounted on top plate22in order to be tested using the above-described test sequence.

The purpose of creating a vacuum in circuit board test fixtures such as test fixture10of the present invention, is to ensure that a proper connection will be established between the probe plate probes14and circuit board C. Indeed, considering that a very important number of probes14may have to be connected to circuit board C simultaneously, for example as many as several thousands of probes, a very significant pressure needs to be applied by the probes on the circuit board to ensure a proper connection of all probes14. Use of a lid having an upper horizontal wall that is movable under the vacuum being created to apply a downward counter-pressure on the circuit board is thus highly desirable, to counteract the upward pressure of the probes. This will prevent the circuit board from being dislodged by the probes. The movable upper lid wall is also useful if lid probes15are also used, to properly connect the lid probes to the circuit board, although most circuit boards are tested with only probe plate probes14.

One important advantage of the test fixture10according to the present invention over the prior art resides in the position of the lid deformable seal64that allows the lid top wall, which is in the form of a lid diaphragm36in the present invention, to move downwardly to apply the counteracting pressure on circuit board C.

Indeed, in prior art devices, the lid deformable seal is provided underneath the lid frame peripheral rim. This prior art deformable lid seal position results in the entire lid collapsing towards the top plate when a vacuum is created, including the lid frame. When test fixtures are used by a technician who is required to test an important number of circuit boards per hour, careless handling of the test fixture will often occur, which sometimes leads to the technician closing the lid too rapidly without having time to remove his fingers from underneath the lid after having placed a circuit board in the test fixture. With prior art test fixtures, injury results from such a situation when a vacuum is created before the technician has time to remove his fingers from underneath the lid frame: if the technician's fingers only very slightly protrude under the lid frame without reaching under the deformable seal, then the deformable seal is not prevented from properly sealing off the test fixture inner test chamber, and the frame is allowed to collapse under the vacuum being created to crush the technician's finger tips. Also, even if the technician's fingers protrude underneath the deformable seal of the test fixture lid, then upon the lid being closed over the technician's fingers, the deformable seal will deform around the technician's fingers and the lid will be allowed to reach, its closed, operative position, with the deformable seal substantially completely sealing off the test chamber, except in the immediate vicinity of the technician's fingers where only very small openings will exist. However, these small openings are not sufficient to prevent a vacuum from being created inside the inner chamber with sufficient negative pressure to bias the lid towards its downward operative position. Consequently, the technician's fingers stuck underneath the lid will effectively be crushed and possibly entirely cut off by the downwardly biased lid frame.

With the test fixture of the present invention, however, the lid's deformable seal64that allows diaphragm36to move downwardly against circuit board C to counteract the upward pressure of probes14, is not positioned between the movable lid frame34and the top plate22. Indeed, only a small flame seal44is located between frame34and top plate22, with this small frame seal44having no significant deforming capacity, in that even when no vacuum is created within inner chamber80, it is impossible for a technician to fit his fingers between the lid frame34and the top plate22when lid32is closed. The deformable diaphragm seal64is instead positioned between the lid frame34and the movable diaphragm36, to allow diaphragm36to react under the effect of a vacuum inside inner chamber80. Consequently frame34is not movable in any significant manner under the effect of a vacuum in inner chamber80. This has the consequence of preventing a technician from placing his fingers between the lid frame34and the top plate22once the lid32is closed which could result in his finger tips being crushed, and it further and foremost has the advantage of preventing a vacuum from being created inside the inner chamber80if the technician closes lid32over his fingers: indeed, if the technician closes lid32while his fingers still protrude underneath the lid rim, then lid frame34will not reach its closed, operative position but will instead remain angularly opened over top plate22without engaging top plate22in the airtight relationship required for a vacuum to be created within inner chamber80. Consequently, even if the vacuum pump102is activated when the lid32is closed over the technician's fingers, ambient air will be allowed to flow inside the inner chamber80and no vacuum will be created therein, thus effectively preventing injury to the technician who got his fingers stuck under the lid frame34. Moreover, when the vacuum pump is deactivated and lid diaphragm36springs back to its rest position, an operator cannot get his fingers inadvertently crushed between lid diaphragm36and one of stopper plate48or stopper portions68b,68b, since this area is fenced off by security ribs72,74,74.

It is noted that diaphragm36(as seen particularly inFIGS. 4 and 7) is slightly smaller than the area circumscribed by frame wall lip portion54so as to be loosely carried by frame34. Thus, a small play exists between the outer peripheral edge of diaphragm36and the inner surface of frame wall lip portion54, to allow a slight movement capacity of diaphragm36between frame wall lip portion54. This slight movement capacity will allow diaphragm36to self-align when it engages guide fingers30with guide holes70so as to properly position the circuit board securing members76and the optional lid probes15above the circuit board C for their eventual engagement against circuit board C when diaphragm36moves towards its operative position. This self-aligning of diaphragm36will compensate undesirable fabrication and assembly errors that resulted in lid32not being properly positioned relative to top plate22, and further positional errors resulting from the pivotal movement capacity of lid32. This is also an important advantage over prior art devices. It is understood that alternate cooperating first and second guiding members provided respectively on the top plate and the diaphragm could be used for guiding the movement of the diaphragm towards the top plate, such as for example a guide pin integrally attached to the diaphragm and engaging guide holes provided on the top plate, or any other suitable guiding means.

Alternate embodiments to the present invention could be envisioned.FIGS. 8–10show examples of respective alternate embodiments to the present invention, where primed, double-primed, and triple-primed reference numbers refer to similar structures having the same non-primed reference numbers in the first embodiment shown inFIGS. 1–7.

FIG. 8shows a fixture10′, comprising probe plate12′ having a number of probes14′ thereon, and a top plate22′ supported above probe plate12′ and on which a lid32′ is pivotally mounted. When lid32′ is closed, test fixture10′ defines a sealed inner chamber80′. Lid32′ comprises a lid frame34′, to which the outer edge64a′ of a peripheral flexible resilient membrane64′ is attached. The resilient membrane64′, at its inner edge64b′, carries a rigid lid diaphragm36′ having abutment fingers76′ and optional upper probes15′ thereon. By generating a vacuum within inner chamber80′, top plate22′ is moved towards probe plate12′ so that probes14′ are brought in electrical contact with circuit board C′. Also, upon generation of this vacuum, membrane64′ is resiliently stretched in order for lid diaphragm36′ to move downwardly, for upper probes15′ to come in electrical contact with circuit board C′, and for abutment fingers76′ affixed on the undersurface of lid diaphragm36′ to be pressed on the top surface of circuit board C′. Membrane64′ has the purpose of continuously biasing lid diaphragm36′ upwardly towards its upper rest position, of resiliently yielding to allow movement of rigid lid diaphragm36′ relative to circuit board C′ between its rest and operative positions, and of allowing a sealed interconnection between lid frame34′ and lid diaphragm36′.

FIG. 9shows a fixture10″, comprising probe plate12″ having a number of probes14″ thereon, and a top plate22″ supported above probe plate12″ and on which a lid32″ is pivotally mounted. Lid32″ comprises a lid frame34″, movably carrying a rigid lid diaphragm36″, on the undersurface of which a number of abutment fingers76′, and spring-loaded biasing members63″ (e.g. springs), are affixed. A number of adjacent peripheral sealing members67″ ensure a sealed interconnection between lid frame34″ and lid diaphragm36″ at all positions of diaphragm36″. When lid32″ is closed, the free end of spring-loaded biasing member63″ abuts against top plate22″ to bias lid diaphragm36″ upwardly in a rest position. Also, when lid32″ is closed, fixture10″ defines a sealed inner chamber80″. By generating a vacuum within inner chamber80″, top plate22″ is moved towards probe plate12″ against the bias of biasing member63″ so that probes14″ are brought in electrical contact with circuit board C″. Upon generation of this vacuum, biasing members63″ yield in order for lid diaphragm36″ to move downwardly, for upper probes15″ to come in electrical contact with circuit board C″, and for abutment fingers76″ to be pressed on the top surface of circuit board C″.

FIG. 10shows a test fixture10′″, comprising a top plate22′″ having a number of probes14′″ fixedly extending therethrough, and having a circuit board mounting means or member. This circuit board mounting means comprises a number of guiding members71′″ affixed to and upwardly protruding from the upper surface of top plate22′″, and a support plate27′″ having through-holes slidably engaging guiding members71′″ so as to be slidably movable relative to top plate22′″. Biasing means in the form of springs69′″ are interposed between the upper surface of top plate22′″ and the undersurface of support plate27′″, and continuously bias support plate27′″ upwardly away from top plate22′″ in a first position. Moreover, support plate27′″ comprises positioning pins26′″, for positioning a circuit board C′″ on support plate27′″ such that circuit board C′″ is precisely installed according to a predetermined position relative to and above perforations29′″. Support plate27′″ also comprises spacers28′″ which are intended to support circuit board C′″ slightly spaced above the upper surface of support plate27′″; the plane shared by the free upper ends of spacers28′″ thus forms a board-bearing surface of support plate27′″, which is slidably movable relative to top plate22′″.

A lid32′″ is pivotally mounted to top plate22′″, and is movable between an open and a closed position (shown in the closed position inFIG. 10). Lid32′″ comprises a peripheral lid frame34′″ defining a peripheral seat52′″, lid frame34′″ movably carrying a rigid lid diaphragm36′″ on the undersurface of which a number of abutment fingers76′″ are affixed. A number of optional upper lid probes15′″ sealingly extend through lid diaphragm36′″. A resilient biasing diaphragm seal64′″ is attached to seat52′″ and biases lid diaphragm36′″ away from seat52′″ in a rest position.

When lid32′″ is closed, the lower peripheral rim of lid frame34′″ sealingly engages top plate22′″, and fixture10′″ defines a sealed inner chamber80′″. By generating a vacuum within inner chamber80′″, lid diaphragm36′″ is moved in an operative position towards seat52′″ against the bias of diaphragm seal64′″. As lid diaphragm36′″ is moved towards its operative position, upper probes15′″ are brought in electrical contact with corresponding electronic components on the upper surface of circuit board C′″. Also, abutment fingers76′″ are moved towards the circuit board C′″ to exert a downward pressure thereon in order to secure the latter to support plate27′″, and to push support plate27′″ downwardly in a second position towards top plate22′″ against the bias of springs69′″. As support plate27′″ is moved downwardly in its second position, the undersurface of circuit board C′″ is brought in electrical contact with the tip of probes14′″.

In yet another embodiment of the present invention (not shown), the test fixture comprises a board-bearing plate, and a movable lid having a lid frame and a lid diaphragm movably mounted to the lid frame and having upper probes sealingly extending therethrough. When the lid is closed, the peripheral rim of the lid frame directly engages the upper surface of a circuit board laid on a board-bearing surface of the board-bearing plate, to maintain the circuit board fixed about the board-bearing plate. Upon creation of a vacuum in the area enclosed by the circuit board, the lid frame and the diaphragm, the diaphragm moves towards the circuit board such that the upper probes are brought in electrical contact with the upper surface of the circuit board. In this embodiment, the only probes would thus be carried by the lid diaphragm.

In one embodiment, the probe plate and diaphragm seals18,64are combined with springs (not shown) provided respectively between the probe plate and the top plate, and between the lid diaphragm and the lid frame, to increase the biasing effect of the biasing members formed by the combination of seals18,64and the springs. The springs and seals18,64would thus act cooperatively to bias the top plate relative to the probe plate, and the diaphragm relative to the lid frame.

Other alternate embodiments to the present invention could be envisioned where, instead of a vacuum pump, an alternate actuator is provided on the test fixture to actuate the top plate towards and away from the probe plate, and/or the lid diaphragm between its rest and operative positions. For example, a mechanical arm, or selectively magnetizable electromagnets, could be installed on the test fixture to actuate the top plate relative to the probe plate, and the lid diaphragm relative to the lid frame. Any other suitable actuating means could of course be provided on the test fixture.

Certain modifications and improvements could occur to skilled artisans upon a reading of the foregoing description. It should be understood that all such modifications and improvements have not been included herein for the sake of conciseness and readability but are properly within the scope of the following claims.