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

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 equipped with 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 that successively contacts the contact points of a printed circuit board (Leiterplatten) with one contact finger or test fingers. When testing unassembled PCBs, the wiring of the PCB under test is primarily tested for interruptions in the wiring and short circuits between the wiring. Measurements are generally performed as resistance and / or capacitance measurements. The basic design of such a finger tester can be found in US Pat. No. 5,623,499, which discloses a finger tester with several contact fingers mounted on slides that are rotatable around a vertical axis and adjustable in height, the slides of the individual contact fingers being slidably mounted on horizontal traverses. The traverses themselves can be moved horizontally, perpendicular to the longitudinal direction of each 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 high-speed vertical movement of the test head, allowing the test probes to quickly contact the contact points of the printed circuit board being tested.

[0006] Patent Document 4 discloses a traverse unit of a printed circuit board testing device, characterized in that it contains at least two mutually independent linear guides that each guide 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 that is not mounted on an air bearing, as it has a vertical guide rail with roller bearings.

[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 complex to manufacture and correspondingly more expensive. In 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 that carry 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 susceptible to damage. Therefore, the arms are easily damaged when replacing 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 contact points on the printed circuit board being tested. In principle, such parallel testers are much faster than finger testers, but require the manufacture of additional adapters for each type of PCB, which makes them very expensive.

[0010] The success of finger testers in the market is primarily determined by their test speed, which allows them to measure multiple contact points on the PCB being tested. Printed circuit boards typically have thousands of contact points. Because many printed circuit boards are manufactured only in small series or pre-production series required to ramp up mass production, it is often not profitable to manufacture adapters for parallel testers. However, these 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] German Patent Application Publication No. 102013102564 [Patent Document 5] International Publication No. 03 / 048787 Summary of the Invention [Problem to be solved by the invention]

[0012] The object of the present invention is to further develop finger testers in a way that, on the one hand, 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 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 so that the holding module can be moved vertically 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, and a rotating member of the pivoting device is disposed 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 configured as a direct drive 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 swivel device directly, without a gear unit. The rotating element surrounds the axle or shaft and therefore has a larger diameter than the axle or shaft. The rotating element represents the rotor of the motor on the one hand and is an integral part of the swivel device on the other hand. Furthermore, the relatively large diameter of the rotating element allows it to generate a high torque and, accordingly, allows for high acceleration during the rotational movement.

[0017] Preferably, the motor is a torque motor. Simply put, a torque motor can be considered 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 discovery.

[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 enable very fast vertical movement of the test head, thereby reducing movement time. However, the air bearings limit the moving mass of the test head supported by the air bearings, thereby limiting the use of test fingers with relatively short arm lengths of up to approximately 150 mm. Bearing arrangements using rolling bearings, such as ball bearings, cross roller bearings, or similar bearings, can also reliably transmit larger masses and torques, allowing for longer test finger arm lengths. A longer arm length offers several advantages. First, a longer arm length increases the movement speed of the test probe attached to the pivot arm at the same rotational speed. Second, a longer pivot arm allows for a larger test area. Applicant uses pivot arms only at angles ranging from 0° to a maximum of approximately 45°, where 0° means that the pivot arm is positioned parallel to the traverse on which the test probe slide is attached, and 45° means that the pivot arm is at a 45° angle relative to the traverse. This angle range allows for very fast movement of the test probe either away from or towards the traverse. As the angle increases, the speed of test probe movement decreases 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 includes steel shafts with a diameter of 8 mm and a distance of approximately 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 solid bodies. Due to the axial offset between the drive and the output, these shafts vibrate slightly when braking. 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 directly driven, the rotating member itself is not subject to torsion due to its size and rigidity, and is directly connected to the swivel device or forms an integral part of the swivel device, thereby avoiding the transmission of torque through a thin shaft. The axle or shaft only serves to support the swivel device and 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 conventional shafts. This is achieved by separating the bearings attached to the shaft or axle from the drive for the rotating member.

[0023] Preferably, the axle or shaft is formed so that the minimum outer diameter in the area where the bearing is arranged on the axle or shaft is at least 10 mm. The swivel device is supported on or by the axle. The axle or shaft may also have an outer 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 greater the torque generated by the rotating element / rotor.

[0025] When the test probe is set to pivot its probe tip into a 5-micron-wide target area, with a conventional 8-mm diameter shaft 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 25-micron target window, the vibrations require 5 ms to decay.

[0026] It shows that using a shaft or axis with an outer diameter of at least 15 mm and a test head design according to the present invention reduces the oscillation time to 7 ms for a 5 μm target window and to 1 ms for a 25 μm target window. With a shaft or axis 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 vibration of the shaft, but complex vibration behavior of the pivot arm and tilting vibration of the shaft or axis occur, and these vibrations become smaller the larger the diameter. Because the shaft or axis outer diameter is 55 mm, the high strength of the bearings means that the swing-out of the pivoting motion requires virtually no time.

[0027] Rather than being driven by a motor-driven shaft, the swivel is rotatably mounted on a fixed or non-rotating axle, or preferably, a shaft with a minimum outer diameter of 10 mm. Such an outer diameter requires correspondingly large and stable bearings. Furthermore, the torque motor engages the swivel directly, independent of the axle or shaft. Force is introduced into a rotating element whose diameter is larger than the diameter of the shaft or shaft. This avoids the offset between the drive and output along the axial direction of thin shafts, as is common in prior art swivels. In conventional swivels, the axial separation between the drive and output on thin shafts causes torsional vibrations in the shaft, which, as the inventors discovered, significantly delays transient vibrations at small contact points on the printed circuit board being tested.

[0028] In the applicant's finger tester, the PCB is positioned horizontally in the test area. Therefore, 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 positioned horizontally in the test device, but may be positioned, 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 that contacts the contact point on the printed circuit board being tested. The effective arm length is preferably at least 160 mm, particularly 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 alternatively the rotating member is supported on the shaft by 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 tilting moments that may be caused by an axial offset between the drive and the bearing are non-existent or very low. Furthermore, by arranging the motor, the rotating member and the bearings, especially the rolling bearings, substantially flush, it 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 bearing is 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 bearing 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 more rigid it is.

[0036] The pivot arm is preferably tubular and made of a fiber 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 which are preferably carbon fibres, and such a monolithic body has a high rigidity.

[0038] On the one hand, such a pivoting arm is relatively long and lightweight, and on the other hand, its high strength helps to prevent vibration of the test probe as it approaches the contact point on the printed circuit board being tested. This applies in particular to the monolithic tubular design of the pivoting arm made of fiber composite material. This pivoting 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 in the prior art, and the rolling bearings of the lifting device allow the use of long pivoting arms.

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

[0040] The pivot arm can be curved in side view so that the free end of the pivot arm is slightly offset from the end attached to the pivoting device. The pivot arm can thus be positioned so that the free end is slightly offset away from the slide. The pivot arm is thus slightly bent toward the test area where the specimen is placed for testing. This bending of the pivot arm increases the rigidity of the pivot arm and provides space for a camera to be placed on the pivoting arm. The camera may be attached to the pivoting device so that it can detect the test probe, particularly the contact tip of the test probe, to determine whether the test point on the printed circuit board being 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 several permanent magnets on its outer periphery that interact with the field coils of the motor's stator. Because the field coils are located on the stator, they do not need to transmit current to the rotor to drive the motor, which simplifies the design of the device.

[0043] The stator and rotor of the motor are preferably designed to extend around a complete circle. Because the motor itself rotates only within a ±45° range during use, the stator and / or rotor may be designed in the form of only a portion of a circle. However, when the stator and rotor extend around a complete circle, a much larger torque can be achieved with a compact motor design than when the stator or rotor extends only a portion 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 individual contact points on the circuit board being 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 able to move the slide.

[0046] Preferably, the lifting device is positioned 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 increases the moment of inertia of the test head somewhat, but has the effect of significantly extending 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 includes at least two traverses, each of which is arranged with 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, requiring the test head to be moved more frequently. Therefore, the travel time to move the probe from one test point on one 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, along with the test needle, to be moved from one test point to another at very high speed.

[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, thereby allowing a runner of the linear motor provided on the test head to 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 present invention, there is provided a method of testing printed circuit boards, particularly unassembled printed circuit boards, using a finger tester as described above, in which after pivoting of one of the pivoting arms, a time period of typically less than 5 ms is waited for the pivoting arm to oscillate before contacting the contact point to be tested. [Brief explanation 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. [Figure 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] 10 is a cross-sectional view of a test head according to a further embodiment. DETAILED DESCRIPTION OF THE INVENTION

[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 made of 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 protrusions 8 protruding from each end of the longitudinal member 7. The top plate 6 and the base plate 5 are aligned in plan view by vertical columns 9 that are positioned 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 member 7, and the test head 4 can slide on the guide rails with corresponding mating guide elements 18.

[0057] The test area 13 is formed in the center of the longitudinal member 7 and parallel to the longitudinal member 7, and can accommodate 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 will 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 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 surface 15, and the runner 17 is disposed perpendicular to the traverse side surface 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 side surface 16 of the test head, and a lifting device 20 is formed on the side surface 16 of the test head for vertically moving a holding module 21, and a pivoting arm 22 is attached to the holding module 21. 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 swivel device 19 is designed to rotate the unit including the lifting device 20 , the holding module 21 , the swivel arm 22 and the test probe 23 around a rotation axis 41 , which is perpendicular to the test area 13 .

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

[0063] Rotating member 28 includes permanent magnets 29 evenly spaced around its circumference and forms the rotor of motor 30. Motor 30 is designed as a torque motor. The stator of motor 30 is fixedly attached to base body 14 and surrounds rotating member 28. Stator 31 includes a plurality of electromagnetic coils (not shown) that are controlled to exert a torque on rotating member 28, which forms the rotor of 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 movable vertically relative to the lift rail body 34. The lift rail body 34 includes a stator 38 of a linear motor, and the retaining module 21 includes a corresponding runner 39 of the linear motor. The rolling bearings 37 are part of a cross roller guide arranged between the retaining module 21 and the lift rail body 34.

[0068] The holding module 21, together with the runner 39, forms a T-shaped body in plan view, and the runner 39 is disposed 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 includes 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. 5,649,499.

[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. The electrical lines for transmitting measurement signals may be routed through the hollow vertical shaft 26 within the hollow pivot 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 geometric 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 eliminates tilting moments, which would exist 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 the rolling bearing 37, allows the use of a large pivot arm 22, so that the test head 4 can scan a wide 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 than test heads with air bearings. The special design of the pivoting device allows for fast rotation of the pivoting device, requiring no or only slight vibration when the contact point is reached. Therefore, a high throughput can 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 designated by the same reference numerals and will not be described again. Unless otherwise specified below, 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 shaft 26, a rotating shaft 42 is provided that 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 to the base body 14 of the test head 4. The shaft 42 has a thin, disk-shaped wall that extends radially and crosses the bushing 43, and is connected to the rotating member 28. Thus, the rotating member 28 is rotatably mounted to the base body or slide 14 of the test head 4 via the shaft 42.

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

[0075] The use of two types of test heads 4 allows for fast pivoting without requiring long pivot times. In combination with the stone rack 2 that integrally contains the traverse 3, a finger tester is provided that can reliably and quickly contact printed circuit boards with minimal contact points. The weight of the rack 2 and its rigidity prevent vibrations or other uncontrolled movements due to movement of the test head 4 that 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 racks 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 member 29 Permanent Magnets 30 Torque motor 31 Stator 32 Swivel base body 33 Central Section 34 Lifting rail body 35. Indemnification Section 36 Optical Sensor 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 move vertically 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 axle (26), a rotating member (28) of the swivel device (19) is arranged coaxially with the shaft (42) or the axle (26) so as to surround the shaft (42) or the axle (26), and the rotating member (28) is attached to the axle (26) with at least one bearing (27) or attached to the slide (14) with at least one bearing (27) via the shaft (42); the motor (30) is configured as a direct drive, and the rotating member (28) forms a rotor of the motor (30); A test head (4) characterized by:

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

3. The axle (26) or the shaft (42) is formed so that the outer diameter is at least 10 mm in the area where the bearing (27) is arranged on the shaft (42) or the axle (26).

3. A test head (4) according to claim 1 or 2, characterized in that:

4. The rotating member is formed to have a maximum outer diameter of at least 50 mm.

3. A test head (4) according to claim 1 or 2, characterized in that:

5. The pivoting arm (22) is tubular and made of fiber composite material.

3. A test head (4) according to claim 1 or 2, characterized in that:

6. The pivoting arm (22) is tapered in the direction of the free end (40) and / or curved in side view so that the free end (40) of the pivoting arm (22) is slightly offset relative to the end (40) fixed to the pivoting device (19).

6. A test head (4) according to claim 5, characterized in that:

7. The motor (30) and the rotating member (28) are arranged in the same plane as at least one of the bearings (27).

3. 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.

3. A test head (4) according to claim 1 or 2, characterized in that:

9. The lifting device (20) is arranged offset from the vertical rotation axis of the swivel device, so that the cable serving to transmit the measurement signal is guided substantially along the vertical rotation axis (41) in the area between the holding module (21) and the slide (14).

3. 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 the stator of the motor (30).

3. 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.

3. A test head (4) according to claim 1 or 2, characterized in that:

12. The lifting device (20) is disposed on the swivel device (19) and includes a linear motor for moving the holding module (21).

3. 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.

3. 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 tip of the test probe (23).

3. A test head (4) according to claim 1 or 2, characterized in that:

15. A finger tester (1) for testing printed circuit boards, 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, comprising using a finger tester (1) according to claim 15, After the pivoting movement of one of the pivoting arms (22), the time required for each of the pivoting arms to pivot until it contacts a corresponding contact point on the printed circuit board to be tested is essentially less than 5 ms.

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