Test head for finger tester and method for testing printed circuit board

Abstract

The invention relates to a test head for a finger tester for testing printed circuit boards, a finger tester and a method for testing printed circuit boards, the test head comprising a slide which can be movably arranged on the traverse of the finger tester, a holding module for holding a pivot arm, the pivot arm being formed at a free end remote from the holding module and receiving a test probe, a lifting device comprising a vertical guide rail with rolling bearings, the lifting device being formed such that the holding module is vertically movable relative to the slide by means of the lifting device, and a swivel device for rotating the holding module and thus the pivot arm around a vertical axis of rotation, the swivel device comprising a motor for rotating the swivel device.

Description

[Technical field]

[0001] The present invention relates to a test head for a finger tester, to a finger tester comprising several such test heads, and to a method for testing printed circuit boards using such a finger tester. [Background technology]

[0002] A finger tester is a testing device in which the contact points of a printed circuit board (Leiterplatten) are successively brought into contact with one contact finger or test finger. When testing unassembled PCBs, the wiring of the PCB to be tested is mainly tested for interruptions in the wiring and short circuits between the wiring. Measurements are generally carried out as resistance and / or capacitance measurements. For the basic design of such a finger tester, reference can be made to US Pat. No. 5,399,433, which discloses a finger tester with several contact fingers, which are mounted on slides so as to be rotatable about a vertical axis and adjustable in height, the slides of the individual contact fingers being slidably mounted on a horizontal traverse. The traverse itself can be moved in a horizontal direction perpendicular to the longitudinal direction of the respective traverse.

[0003] Finger testers are also known in which several traverses are arranged in fixed positions.

[0004] Patent Document 2 describes a method for testing a printed circuit board using a finger tester.

[0005] Patent Document 3 describes a finger tester for testing unassembled printed circuit boards, which includes an air-bearing linear motor in the test head. Such an air-bearing linear motor enables very fast vertical movement of the test head, so that the test probes can be quickly brought into contact with the contact points of the printed circuit board being tested.

[0006] Patent Document 4 shows a traverse unit of a printed circuit board testing device, characterized in that it contains at least two mutually independent linear guides each of which guides at least one of the positioning units.

[0007] The applicant of the present patent application sells such finger testers under the product names A7 and A8, which include a test head which is provided with a vertical guide rail with roller bearings and is therefore not mounted on an air bearing.

[0008] The applicant also manufactures and sells finger testers under the product names S2 and S3, which have a linear motor with an air bearing in the test head for vertical movement. Test heads with air bearings are significantly faster than test heads without air bearings, but are also significantly more complicated to manufacture and correspondingly more expensive. In the case of test heads with air bearings, the parts supported by the air bearings are very light. These parts are in particular the arms of the contact fingers carrying the test probes. These arms are very delicate. As a result, they generate a very low moment of inertia. However, these arms have a limited length and are sensitive to damage. They are therefore easily damaged when replacing the test probes.

[0009] In addition to finger testers, parallel testers for testing printed circuit boards are also known, each of which has an adapter for simultaneously contacting all the contact points of the printed circuit board to be tested. Such parallel testers are, in principle, much faster than finger testers, but additional adapters must be manufactured for each type of PCB, which results in them being very expensive.

[0010] The success of finger testers on the market is mainly determined by the test speed, which allows the measurement of multiple contact points on the PCB being tested. Printed circuit boards typically have thousands of contact points. Since many printed circuit boards are manufactured only in small series or in pre-production series required to increase mass production, it is often not profitable to manufacture adapters for parallel testers. However, they are very complex to test due to their complexity and the large number of contact points. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] European Patent No. 0468153 [Patent Document 2] European Patent Application Publication No. 0853242 [Patent Document 3] European Patent No. 1542023 [Patent Document 4] DE 102013102564 A1 [Patent Document 5] WO 03 / 048787 Summary of the Invention [Problem to be solved by the invention]

[0012] It is an object of the present invention to further develop a finger tester in a way that, on the one hand, it is simple to design and can be manufactured at low cost, and, on the other hand, allows a high throughput of printed circuit boards to be tested. [Means for solving the problem]

[0013] According to a first aspect of the present invention there is provided a test head for a finger tester for testing printed circuit boards, the test head comprising: a slide that can be movably positioned on the traverse of the finger tester; a holding module for holding a pivoting arm, the pivoting arm being adapted to receive a test probe at an end remote from the holding module; a lifting device including a vertical guide rail with rolling bearings, the lifting device being designed such that the holding module is vertically movable relative to the slide; a swivel device for rotating the holding module and thus the swivel arm around a vertical axis of rotation, the swivel device including a motor for rotating the swivel device; Includes.

[0014] In the test head, the pivoting device includes a shaft or an axis, the rotating member of the pivoting device is arranged coaxially with the shaft or the axis so as to surround the shaft or the axis, and the rotating member is attached to the axis with at least one bearing or attached to the slide via the shaft with at least one bearing; The motor is formed as a direct motor, the rotating member forming the rotor of the motor.

[0015] The axle is fixed to the slide, i.e. does not rotate, but the shaft can rotate relative to the slide.

[0016] The motor is adapted to drive the slewing device directly, without a gear unit. The rotating member surrounds the axle or shaft and therefore has a larger diameter than the axle or shaft. The rotating member represents the rotor of the motor on the one hand and is an integral part of the slewing device on the other hand. Furthermore, due to the relatively large diameter of the rotating member, a high torque can be developed and accordingly a high acceleration is possible during the rotational movement.

[0017] Preferably, the motor is a torque motor. In simple terms, a torque motor can be considered as a large servo motor optimized for high torque. Torque motors are typically manufactured as brushless DC motors. However, switched reluctance motors may also be used as torque motors. Preferably, the torque motor is a high pole servo motor, for example having at least 20 poles.

[0018] The present invention is based on the following findings.

[0019] 1. When measuring multiple contact points on the PCB under test, most of the time is spent moving the test fingers from one contact point on the PCB to another contact point on the PCB, rather than performing individual measurements.

[0020] 2. As explained above, air-bearing linear guides allow very fast vertical movement of the test head, thus reducing the movement time, but the drawback is that the air bearings limit the moving mass of the test head supported by the air bearings, and therefore only test fingers with relatively short arm lengths of up to about 150 mm can be used. Bearing arrangements using rolling bearings such as ball bearings, cross roller bearings or similar bearings can also reliably transmit larger masses and torques, allowing longer arm lengths of the test fingers. A longer arm length has several advantages. First, a longer arm length allows a faster movement speed of the test probe attached to the pivot arm for the same rotation speed. Second, a longer pivot arm allows a larger test area. The applicant uses the pivot arm only in an angle range from 0° up to about 45°, where 0° means that the pivot arm is arranged parallel to the traverse on which the slide of the test probe is attached, and an angle of 45° means that the pivot arm makes an angle of 45° to the traverse. This range of angles allows for very fast movement of the test probe away from or towards the traverse. As the angle increases, the speed of movement of the test probe decreases in the direction perpendicular to the traverse. The longer the pivot arm, the wider the area that can be covered by the test head along the corresponding traverse.

[0021] 3. At the end of the pivoting movement, the pivoting arm vibrates slightly. The test fixture described at the beginning comprises steel shafts, which are 8 mm in diameter and have a distance of about 20 mm between the engagement point of the motor (corresponding to the drive) and the attachment point of the pivoting arm on the shaft (corresponding to the output). These shafts are constructed of solid bodies. These shafts vibrate somewhat when braking due to the axial offset between the drive and the output. The shafts therefore form a body that is subjected to torsional vibrations.

[0022] In the present invention, these torsional vibrations are substantially avoided, because a rotating member, which is significantly larger than the shaft, is driven directly, which is itself not subject to torsion due to its size and rigidity, and which is directly connected to the swivel device or forms an integral part of it, thus avoiding the transmission of torque through a thin shaft. The axle or shaft only serves to support the swivel device, but does not serve to transmit the driving force applied by the motor to the main parts of the swivel device to be rotated, in particular the lifting device and the swivel arm. This avoids the torsion of the conventional shaft. This is achieved by separating the bearings attached to the shaft or axle and the drive for the rotating member.

[0023] Preferably, the axle or shaft is formed such that in the area where the bearing is arranged on the axle, the minimum outside diameter is at least 10 mm. The swivel device is supported on or by the axle. The axle or shaft may also have an outside diameter in the area of ​​the bearing of at least 20 mm, in particular at least 25 mm or at least 30 mm, or even at least 35 mm. The larger the diameter of the shaft or axle, the more stable the bearing of the swivel device.

[0024] Preferably, the rotating element is designed to have a maximum outer diameter of at least 50 mm. The rotating element may have a maximum outer diameter of at least 60 mm, in particular at least 70 mm, preferably at least 80 mm. The larger the outer diameter of the rotating element / rotor, the higher the torque generated by the rotating element / rotor.

[0025] When a test probe is set to pivot its probe tip into a target area 5 μm wide, with a conventional shaft of 8 mm diameter, and a 20 mm distance between the drive and output at the shaft, the torsional vibrations cause a 40 ms delay before decaying. With a target window of 25 μm, the vibrations require 5 ms to decay.

[0026] It shows that using an axis or shaft with an outer diameter of at least 15 mm and a test head design according to the invention, the oscillation time is reduced to 7 ms for a 5 μm target window and to 1 ms for a 25 μm target window. With an axis or shaft outer diameter of 55 mm, the swing-out time is reduced to less than 0.5 ms for a 5 μm target window. During this transient oscillation, there is no torsional oscillation of the shaft, but complex oscillation behavior of the pivot arm and tilt oscillation of the shaft or axis occur, the larger these diameters are, the smaller these oscillations become. With an axis or shaft outer diameter of 55 mm, the high strength of the bearings means that the swing-out of the pivoting motion requires practically no time.

[0027] The swivel is not driven by a shaft driven by a motor, but is rotatably mounted on a fixed or non-rotating axle, or preferably on a shaft with a minimum outer diameter of 10 mm. Such an outer diameter requires correspondingly large and stable bearings. Also, the torque motor engages the swivel directly, without reference to the axle or shaft. The force is introduced into a rotating member whose diameter is larger than that of the shaft or axle. This avoids the offset of the drive and output along the axial direction of the thin shaft, as is common in the prior art. In the conventional swivel, the drive and output on the thin shaft are axially separated from each other, which causes torsional vibrations of the shaft and, as the inventors have found, significantly delays the transient vibrations at small contact points of the printed circuit board being tested.

[0028] In the applicant's finger tester, the PCB is placed horizontally in the test area. Thus, in this specification, "vertical" refers to a direction perpendicular to the surface of the PCB to be tested placed in the finger tester. In principle, the PCB to be tested may not be placed horizontally in the test device, but for example at an angle or vertically. In this case, the individual elements of the test fixture must be aligned accordingly.

[0029] The arm length of the pivoting arm is preferably at least 150 mm. The arm length is measured from the vertical axis of rotation to the free end of the pivoting arm to which the test probe is attached. The effective arm length is the arm length from the vertical axis of rotation to the tip of the test probe which contacts the contact point of the printed circuit board to be tested. The effective arm length is preferably at least 160 mm, in particular at least 170 mm or at least 180 mm.

[0030] The bearings are preferably at least angular contact ball bearings.

[0031] Preferably, the shaft is supported on a slide or the rotating member is supported on the shaft in a set of at least two angular contact ball bearings, which allows the rotating part to be positioned and held very accurately relative to the axis of rotation.

[0032] The angular contact bearing preferably includes ceramic balls.

[0033] Preferably, the motor and the rotating member are arranged substantially flush with at least one rolling bearing. This means that there is no or very low tilting moment that may be caused by an axial offset of the drive and the bearing. Also, the substantially flush arrangement of the motor, the rotating member and the bearings, especially the rolling bearings, is very space-saving and compact.

[0034] By substantially coplanar it is meant that there is a plane which extends through the area in which the rolling bearings are located and at the same time extends through the rotating member and the motor, whereby the motor is located coaxially in the same plane as the bearings so that operation of the motor applies no or a very low tilting moment to the rotating member or shaft.

[0035] If the swivel device has a shaft, the maximum length of the shaft is preferably 40 mm, in particular only 30 mm. The shorter the shaft, the higher the stiffness.

[0036] The pivot arm is preferably tubular and manufactured from a fibre composite material, which gives it high strength and low weight.

[0037] In particular, the pivot arm is made of a monolithic body, the fibres of the fibre composite material being preferably carbon fibres, and such a monolithic body has a high stiffness.

[0038] On the one hand, such a swivel arm is relatively long and light, and on the other hand, due to its high strength, it helps to prevent vibrations of the test probe as it approaches the contact points of the printed circuit board to be tested. This applies in particular to the monolithic tubular design of the swivel arm, which is manufactured from fiber composite material. This swivel arm is therefore very advantageous in combination with the above-described direct drive and the mounting of the lifting device with rolling bearings. The direct drive avoids the torsional vibrations of the drive shaft known from the prior art, and the rolling bearings of the lifting device allow the use of long swivel arms.

[0039] The pivot arm may be tapered towards its free end, which reduces the weight in the direction towards the free end of the pivot arm and keeps the moment of inertia of the pivot arm low, and the tapering also helps to increase the stiffness of the pivot arm.

[0040] The pivot arm can be curved in side view such that the free end of the pivot arm is slightly offset from the end attached to the pivot device. The pivot arm can thus be positioned such that the free end is offset slightly away from the slide. The pivot arm is thus slightly bent in the direction of the test area where the specimen is placed for testing. This bending of the pivot arm increases the rigidity of the pivot arm and creates space for placing a camera on the pivot arm, which may be attached to the pivot device so that the test probe, in particular the contact tip of the test probe, can be detected to determine whether the test point of the printed circuit board to be tested is properly contacted by the test probe.

[0041] Thus, the test head may be provided with a camera for monitoring the positioning of the probe tips of the test probes.

[0042] The rotating member or rotor may include a number of permanent magnets on its outer periphery that interact with the magnetic field coils of the motor's stator. Because the magnetic field coils are located on the stator, no current needs to be transferred to the rotor to drive the motor, simplifying the design of the device.

[0043] The stator and rotor of the motor are preferably designed to extend around a complete circle. Since the motor itself only rotates within a range of ±45° in use, the stator and / or rotor may be designed in the form of only a part of a circle. However, if the stator and rotor extend around a complete circle, a much larger torque can be achieved with a compact design of the motor than if the stator or rotor only extended around a part of a circle. This larger torque allows the pivoting device to pivot quickly. This is particularly advantageous when combined with a long pivoting arm, as it allows the test probe to move very quickly between the individual contact points of the circuit board to be tested.

[0044] The lifting device is preferably arranged on the swivel device and includes a linear motor for moving the holding module.

[0045] A runner of the linear motor is formed on the slide and is capable of moving the slide.

[0046] Preferably, the lifting device is arranged offset from the vertical axis of rotation of the swivel device, so that the cable essentially responsible for transmitting the measurement signals and used for motor control is routed approximately along the vertical axis of rotation in the area between the holding module and the slide, which has the effect of somewhat increasing the moment of inertia of the test head, but significantly increasing the service life of this cable, since in other designs of the test head the cable moves more when the swivel head rotates.

[0047] According to a further aspect of the present invention, there is provided a finger tester for testing printed circuit boards, in particular unassembled printed circuit boards, which finger tester comprises at least two traverses, on each of which is arranged at least one test head as described above.

[0048] When testing unassembled PCBs, the wiring is tested for breaks and shorts between adjacent PCBs. Compared to assembled PCBs, PCBs have many more test points to contact and the test head needs to be moved more frequently. Therefore, the travel time to move the probe from one test point on a PCB to another test point on the PCB being tested is much longer when testing unassembled PCBs than when testing assembled PCBs. The test head of this finger tester allows the test probe to be moved very quickly from one test point to another along with the test needle.

[0049] Preferably, each traverse is manufactured from a steinblock. The steinblock may include a groove in which a stator of a linear motor is placed, so that a runner of the linear motor provided on the test head can move relative to the stator. Furthermore, guide elements or guide rails may be provided on the steinblock, and the slide is guided along the traverse by the guide elements or guide rails. The steinblock is preferably a granite block.

[0050] According to another aspect of the invention, there is provided a method of testing a printed circuit board, in particular an unassembled printed circuit board, using a finger tester as described above, in which after a pivoting movement of one of the pivoting arms, a time typically of less than 5 ms is waited for the pivoting arm to oscillate before contacting the contact point to be tested. [Brief description of the drawings]

[0051] The invention will now be explained in more detail by way of example with reference to the drawings, in which:

[0052] [Figure 1] FIG. 1 is a perspective view of a finger tester with four traverses and eight test heads. [Diagram 2] FIG. 1 shows a side view of the granite rack of the finger tester without the test head. [Figure 3a] The test head is viewed from the test area towards the test head. [Figure 3b] FIG. 3b is a cross-sectional view of the test head of FIG. 3a. [Figure 3c] FIG. 3b is a perspective cross-sectional view of the test head of FIG. 3a. [Figure 4] FIG. 13 is a cross-sectional view of a test head according to a further embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0053] An embodiment of a finger tester 1 according to the invention comprises a rack 2 with a total of four traverses 3, on each of which two test heads 4 are movably arranged.

[0054] The rack 2 is manufactured from granite blocks and includes a base plate 5 that is double-T shaped in plan view and a top plate 6 that is double-T shaped in plan view. The base plate 5 and the top plate 6 each include a longitudinal member 7 with a protrusion 8 protruding on each side at the end of the longitudinal member 7. The top plate 6 and the base plate 5 are aligned in plan view by a vertical pillar 9 that is disposed between the respective protrusions 8.

[0055] Two longitudinally extending grooves 10 are formed in each of the opposing surfaces of the longitudinal member 7, each of the grooves forming one of the traverses 3. A stator 11 of a linear motor is disposed in each of the grooves 10 and extends over most of the length of the groove 10.

[0056] Guide rails 12 are arranged adjacent to the grooves 10 on opposing surfaces of the longitudinal members 7, on which the test head 4 can slide with corresponding mating guide elements 18.

[0057] A test area 13 is formed in the centre of the longitudinal member 7 and parallel thereto and is capable of accommodating a printed circuit board to be tested. In figures 2 and 3a the test area 13 is shown only diagrammatically by a plate arranged at the position where the printed circuit board to be tested is to be placed. The test area 13 includes corresponding holding elements for holding the printed circuit board, but the holding elements are omitted here to simplify the drawings.

[0058] Each test head 4 includes a base body 14 that is substantially plate-shaped in a plan view, and includes a traverse side 15 facing the traverse, and a test head side 16 facing the opposite side to the traverse.

[0059] A plate-shaped runner 17 of the linear motor is attached to the traverse side 15 and is disposed perpendicular to the traverse side 15. A guide element 18 that slides on the guide rail 12 is provided adjacent to the runner 17.

[0060] A pivoting device 19 is provided on the test head side 16, which is formed with a lifting device 20 capable of vertically moving a holding module 21, to which a pivoting arm 22 is attached. The pivoting arm is formed at a free end remote from the holding module 21 and receives a test probe 23. The test probe 23 includes a test needle 24 with a probe tip 25 for contacting a contact point on the printed circuit board to be tested.

[0061] The pivoting device 19 is designed to rotate the unit including the lifting device 20 , the holding module 21 , the pivoting arm 22 and the test probe 23 about a rotation axis 41 , which is perpendicular to the test area 13 .

[0062] The swivel device 19 comprises a vertical shaft 26 fixedly mounted on the base body 14. In the present embodiment, the vertical shaft 26 is formed of a tubular body. Two rolling bearings 27 are arranged on the outer circumference of the vertical shaft 26. The vertical shaft 26 has a large outer diameter, which in the present exemplary embodiment is 35 mm in the area where the bearings 27 abut against the shaft. The rolling bearings 27 are angular contact ball bearings that are pressed against each other and aligned in opposite directions. This allows a bearing arrangement with high tilt resistance to be achieved. A rotating member 28 is arranged on the outer circumference of the rolling bearings 27. The rotating member 28 is an approximately cylindrical, rotationally symmetric body that is rotatably mounted around the vertical shaft 26 by the rolling bearings 27.

[0063] The rotating member 28 includes permanent magnets 29 evenly spaced around its circumference and forms the rotor of a motor 30. The motor 30 is designed as a torque motor. A stator of the motor 30 is fixedly attached to the base body 14 and surrounds the rotating member 28. The stator 31 includes a number of electromagnetic coils (not shown) that are controlled to exert a torque on the rotating member 28, which forms the rotor of the motor 30.

[0064] In this embodiment, the motor 30 has 28 poles, i.e. a corresponding number of permanent magnets are disposed on the rotating member 28. Preferably, the motor includes at least 20 poles.

[0065] The swivel base body 32 is attached to the rotating member 28 and includes a central section 33, a lift rail body 34, and a compensation section 35 located directly opposite the lift rail body 34 in the central section 33. The compensation section 35 has the shape of a circular segment in a plan view and functions as a counterweight for the lift rail body 34. As a result, the center of gravity of the swivel device 19 is located near the rotation axis 41. A line scale is formed on the outer periphery of the compensation section 35, and the line scale is scanned by an optical sensor 36. This allows the rotational position of the swivel device 19 to be detected.

[0066] The lift rail body 34 includes a vertical guide rail.

[0067] The retaining module 21 is attached to the lift rail body 34 by means of rolling bearings 37, so that the retaining module 21 is designed to be vertically movable relative to the lift rail body 34. The lift rail body 34 contains a stator 38 of a linear motor, and the retaining module 21 contains a corresponding runner 39 of the linear motor. The rolling bearings 37 are part of a cross roller guide that is arranged between the retaining module 21 and the lift rail body 34.

[0068] The holding module 21 forms a T-shaped body in plan view together with the runner 39, which is located in a groove formed by the stator 38, so that an upward or downward force moment can be applied to the linear motor to move the holding module 21 vertically. As a result, the holding module 21 moves upward or downward together with the pivot arm 22.

[0069] The pivoting arm 22 is a one-piece monolithic body made of a fiber-reinforced composite material. In particular, the pivoting arm is made of a fiber composite material containing carbon fibers. The pivoting arm has a tubular shape with a substantially circular or elliptical cross section. The pivoting arm has one end attached to the holding module 21 and comprises a free end 40 remote from the holding module 21. A test probe 23 is arranged at the free end 40 of the pivoting arm 22. Such a test probe is known, for example, from US Pat. No. 5,399,363.

[0070] Electrical lines for controlling the motor or transmitting measurement signals from the test probe 23 to an evaluation device (not shown) are not shown in the drawings for ease of illustration. Electrical lines for transmitting measurement signals may be routed through the hollow vertical shaft 26 in the hollow pivoting arm. The lifting device 20 is slightly offset from a rotation axis 41 that passes through the center of the hollow vertical shaft 26. The hollow vertical shaft 26 represents the body, and the rotation axis 41 is a geometrical line. The shaft 26, the rolling bearing 27, the rotating member 28 and the stator 31 of the motor 30 are all arranged coaxially with respect to the rotation axis 41 and all lie in the same plane. This arrangement saves space and there is no tilting moment, which would be present if the drive were offset from the bearing 27 with respect to the rotation axis 41.

[0071] This special type of drive or bearing, in combination with the lifting device 20 mounted by rolling bearings 37, allows the use of a large swivel arm 22, so that the test head 4 can scan a large scanning range along the traverse and the test probe 23 can move very quickly away from or towards the traverse. The test head 4 has a much simpler and cheaper design compared to test heads with air bearings. The special design of the swivel allows a fast rotation of the swivel, which requires no or only little vibration when the contact point to be contacted is reached. A high throughput can therefore be achieved in a simpler way when testing a particular printed circuit board.

[0072] A second embodiment of the present invention will be described below (FIG. 4). The second exemplary embodiment essentially corresponds to the first exemplary embodiment, and the same parts are given the same reference numerals and will not be described again. Hereinafter, unless otherwise specified, the description of the first embodiment above also applies to this second embodiment.

[0073] The second embodiment differs from the first embodiment in that instead of the fixed vertical axis 26, a rotating shaft 42 is provided which is rotatably mounted in a bushing 43 by means of a rolling bearing 27. The bushing 43 coaxially surrounds the shaft 42 and the rolling bearing 27 and is fixedly mounted in the base body 14 of the test head 4. The shaft 42 has a thin disk-shaped wall extending radially and intersecting the bushing 43 and is connected to the rotating member 28. The rotating member 28 is thus rotatably mounted in the base body or slide 14 of the test head 4 via the shaft 42.

[0074] The shaft 42 can also be designed as a solid or hollow shaft. The outside diameter of the shaft 42 in the region where it rests against the inside of the rolling bearing 27 is again 35 mm.

[0075] The use of the two types of test heads 4 allows fast pivoting movements to be performed without the need for long pivot times. In combination with the stone rack 2 which integrally contains the traverses 3, a finger tester is provided which can reliably and quickly contact printed circuit boards with a minimum of contact points. The weight of the rack 2 and its rigidity prevent vibrations or other uncontrolled movements due to the movement of the test heads 4 which could impair the positioning accuracy of the test probes.

[0076] Preferably, each secondary test head is provided with a camera 44 (FIG. 1) for monitoring the position of the test needles 24 or probe tips 25 relative to corresponding contact points on the printed circuit board being tested. [Explanation of symbols]

[0077] 1 Finger Tester 2 Rack 3. Traverse 4 Test Head 5 Base plate 6 Top Plate 7 Longitudinal members 8 Protrusion 9 Pillars 10 grooves 11 Stator 12 Guide rail 13 Test Area 14 Base body 15 Traverse Side 16 Test head side 17 Runner 18 Guide Elements 19 Swivel 20 Lifting device 21 Retention Module 22 Swivel Arm 23 Test Probe 24 Test Needle 25 Probe tip 26 vertical axis 27 Rolling bearings 28 Rotating members 29 Permanent Magnets 30 Torque motor 31 Stator 32 Swivel base body 33 Central Section 34 Lifting rail body 35. Indemnification Section 36 Optical Sensors 37 Rolling bearings 38 Linear motor stator 39 Linear motor runner 40 free end 41 Rotation axis 42 Shaft 43 Bushing 44 Camera

Claims

1. A test head (4) for a finger tester (1) for testing printed circuit boards, comprising: a slide (14) that can be movably arranged on the traverse (3) of the finger tester; a holding module (21) for holding a pivoting arm (22), said pivoting arm (22) being adapted to receive a test probe (23) at a free end (40) remote from said holding module (21); - a lifting device (20) including a vertical guide rail (12) with rolling bearings (37), the lifting device (20) being adapted to allow the holding module (21) to be vertically movable relative to the slide; a swivel device (19) for rotating the holding module (21) and thus the swivel arm around a vertical axis of rotation (41), the swivel device (19) including a motor (30) for rotating the swivel device (19); In a test head (4) comprising the swivel device (19) includes a shaft (42) or an axis (26), a rotating member (28) of the swivel device (19) is arranged coaxially with the shaft (42) or the axis (26) so as to surround the shaft (42) or the axis (26), and the rotating member (28) is attached to the axis (26) with at least one bearing (27) or is attached to the slide (14) with at least one bearing (27) via the shaft (42); the motor (30) is configured as a direct drive, the rotating member (28) forming a rotor of the motor (30); A test head (4).

2. The length of the pivot arm is at least 150 mm 2. A test head (4) as claimed in claim 1, characterized in that

3. the axle (26) or the shaft (42) is formed such that the outside diameter is at least 10 mm in the area where the bearing (27) is located on the shaft (42) or the axle (26); A test head (4) according to claim 1 or 2, characterized in that

4. The rotating member is formed so as to have a maximum outer diameter of at least 50 mm. A test head (4) according to claim 1 or 2, characterized in that

5. The pivot arm (22) is tubular and made of fiber composite material. A test head (4) according to claim 1 or 2, characterized in that

6. The pivot arm (22) is tapered in the direction of the free end (40) and / or curved in side view such that the free end (40) of the pivot arm (22) is slightly offset relative to the end (40) fixed to the pivot device (19). A test head (4) according to claim 5, characterized in that

7. The motor (30) and the rotating member (28) are disposed in the same plane as at least one of the bearings (27). A test head (4) according to claim 1 or 2, characterized in that

8. The swivel device (19) includes a shaft (42) having a maximum length of 40 mm, in particular a maximum length of 30 mm. A test head (4) according to claim 1 or 2, characterized in that

9. The lifting device (20) is arranged offset from the vertical axis of rotation of the swivel device, so that the cable serving to transmit the measurement signal is guided approximately along the vertical axis of rotation (41) in the area between the holding module (21) and the slide (14). A test head (4) according to claim 1 or 2, characterized in that

10. The rotating member (28) includes a plurality of permanent magnets (29) on its outer periphery that interact with the magnetic field coils of a stator of the motor (30). A test head (4) according to claim 1 or 2, characterized in that

11. The motor (30) includes a stator and a rotor each extending around a complete circle. A test head (4) according to claim 1 or 2, characterized in that

12. The lifting device (20) is disposed on the rotating device (19) and includes a linear motor for moving the holding module (21). A test head (4) according to claim 1 or 2, characterized in that

13. The slide (14) includes a runner for a linear motor for moving the slide. A test head (4) according to claim 1 or 2, characterized in that

14. The test head (4) includes a camera (44) for detecting the test tips of the test probes (23). A test head (4) according to claim 1 or 2, characterized in that

15. A finger tester (1) for testing printed circuit boards, in particular unassembled printed circuit boards, comprising: A finger tester (1), comprising at least two traverses (3), on each of which at least one test head (4) according to claim 1 or 2 is movably arranged.

16. Each traverse (3) is formed of stone blocks.

16. The finger tester (1) according to claim 15, characterized in that

17. A method for testing printed circuit boards, in particular unassembled printed circuit boards, comprising the steps of: wherein after a pivoting motion of one of the pivot arms (22), the time for each of the pivot arms to wait for pivoting until it contacts a corresponding contact point of the printed circuit board to be tested is essentially less than 5 ms.

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