Test probe for a finger tester for testing printed circuit boards, finger tester for testing printed circuit boards, and method for testing printed circuit boards

Abstract

The invention relates to a test probe for a test finger for testing printed circuit boards. The test probe comprises a contact sleeve and a test needle, which has a contact tip at one end. Furthermore, the test probe comprises at least one sleeve spring arm for elastically holding and electrically connecting the contact sleeve. The test needle in the contact sleeve can be moved in the axial direction such that the contact sleeve can be brought into contact with a printed circuit board test point of the printed circuit board to be tested. The test probe comprises a needle spring arm which is electrically and mechanically fastened to a connection end of the test needle such that the needle spring arm prevents movement of the connection end of test needle out of the contact sleeve. Thus, the test needle forms an inner sensor and the contact sleeve forms an outer sensor for probing a printed circuit board test point.

Description

[0001] 19 / 11 / 2025

[0002] International patent application atg Luther & Maelzer GmbH

[0003] Test probe for a finger tester for testing printed circuit boards, finger tester for testing printed circuit boards and method for testing printed circuit boards

[0004] The invention relates to a test probe for a finger tester for testing printed circuit boards, a finger tester for testing printed circuit boards and a method for testing printed circuit boards.

[0005] Test devices for printed circuit boards (PCBs) can generally be divided into two groups: finger testers and parallel testers. Parallel testers are devices that use an adapter to simultaneously contact all or at least most of the contact points of a PCB under test. Finger testers are devices for testing unpopulated or populated PCBs, using two or more test fingers to sequentially scan the individual contact points.

[0006] When testing unpopulated printed circuit boards, significantly more PCB test points need to be contacted compared to testing with populated printed circuit boards (in-circuit testing). Therefore, the key criterion for the successful marketability of a finger tester for unpopulated printed circuit boards is the throughput of contacted PCB test points within a predetermined time.

[0007] The test fingers are typically attached to a carriage that can be moved along crossbeams, which in turn are guided and movable on guide rails. This allows the carriages to be positioned at any point within a generally rectangular test area. To contact a contact point on the circuit board under test, the carriage is vertically movable along the crossbeam, enabling the test finger to be placed onto the contact point of the circuit board from above or below.

[0008] A finger tester is described in EP 0468 153 A1, and a method for testing printed circuit boards using a finger tester is described in EP 0 853 242 A1. EP 0 990 912 A discloses a test probe for a finger tester in which a test needle is guided in such a way that it can be extended from the probe to contact a printed circuit board test point. When a printed circuit board test point is contacted, the test needle can deflect laterally, thereby limiting the mechanical stress on the test point. The test needle is driven by an electromagnetic actuator. Furthermore, test probes are known in which a spring-loaded test needle is used. With a perpendicular arrangement of the test needle with respect to...The disadvantage of the circuit board to be tested is that two closely adjacent circuit board test points cannot be contacted, because due to the size of the spring-loaded test needles, their test tips cannot be arranged arbitrarily close to each other.

[0009] To avoid this disadvantage, the probe is positioned at an angle to the circuit board under test in a suitable test fixture. This allows two probes with their probe tips to be placed very close together. However, this has the disadvantage that when the spring-loaded probes compress, the probe tip moves along the surface of the circuit board, which can cause a scratch on the board at high contact speeds. Furthermore, the angled probe position makes the point of contact with the circuit board less precise, as the probe tip moves parallel to the board's surface.

[0010] To avoid these problems, test probes have been developed that feature a relatively long, horizontally arranged spring arm with the test needle at its end. The advantage of this long spring arm is that even a small deflection generates a relatively large spring travel. This minimizes, but does not completely eliminate, movement parallel to the surface of the circuit board under test. However, even with such a probe, there is a risk of scratching the surface of the circuit board. Furthermore, the size of the spring arm makes the probe relatively heavy, which can damage the circuit board when the probe tip is struck at high speed. To reduce such damage, a light barrier is integrated into the spring arm to detect any deflection of the arm.When the spring arm deflects, the movement of the test probe is slowed down, so that further damage to the circuit board should be avoided as much as possible.

[0011] Due to the considerable size of the spring arm, it is very complex to shield it from electrical radiation, which is useful when measuring with high-frequency signals.

[0012] Another known test probe uses a rigid needle as its test point, which is attached to a holder by means of a parallel link. The parallel link consists of two plastic support arms, one end of which is attached to a holder, and the other end of which holds the rigid needle. This needle can be moved vertically upwards when the parallel link pivots. The end of the test needle, which carries the test tip, is angled relative to the rest of the needle, so that the test tip protrudes slightly from the probe. This allows two closely spaced circuit board test points to be contacted with two test probes. The support arms of the parallel link are designed to minimize movement parallel to the circuit board surface when the parallel link pivots.

[0013] A disadvantage of this test probe is that the cable used to supply the measurement signal, which is attached to the probe, generates a significant impulse due to its rigidity and mass when the probe quickly strikes a circuit board. This impulse can damage the circuit board under test. This is particularly true in an embodiment where two probes, each with a cable attached, are mounted on a parallel link to enable 4-wire measurement.

[0014] US Patent 5,804,982 discloses a test probe for testing the contact points of integrated circuits. This test probe has two elastic holding arms, one end of which is attached to a frame of a test fixture. The two holding arms are parallel to each other and have a non-magnetic body at their end furthest from the frame, positioned between the two endpoints of the holding arms. A test needle is located in the lower part of this body. Magnetic coils are provided between the holding arms, which interact with another magnet in such a way that they can exert a vertically downward force on the holding arms.

[0015] A contact point of an integrated circuit is contacted by means of this test probe by exciting the magnetic coils arranged in the test probe, so that the test needle is moved towards the contact point.

[0016] WO 96 / 24069 concerns a device for testing printed circuit boards (in-circuit testing). The test probe of this device has a pivotable test needle, which contacts the test points of the printed circuit board at one end and has a movement mechanism at the other end for pivoting the test needle.

[0017] US Patent 4,123,706 discloses a test probe with an upper and a lower elastic holding arm for a test needle. The two test arms consist of a strip of sheet metal that tapers towards the test needle when viewed from above. The holding arms are electrically conductive and electrically connected to the test needle, allowing measurement signals to be transmitted via the holding arms. This test probe is used for testing semiconductor circuits.

[0018] US Patent 3,648,169 discloses another probe for testing semiconductor circuits. This probe has a probe element designed as a thin plate. A rectangular opening is incorporated into this plate, defining two arms that are integral to the probe element. These arms allow the probe tip to deflect vertically, minimizing scratching of the surface of the object under test.

[0019] EP O 660387 A2 describes a probe for testing semiconductor components, which has a test needle held by means of elastic arms.

[0020] EP 0 460 911 A2 shows a test probe in which a probe tip arrangement is attached to a probe holder by means of two parallel spring arms that can be bent upwards and downwards.

[0021] EP 1 451 594 B1 discloses a test probe for a finger tester of unpopulated printed circuit boards with a shielding sleeve, a test needle and two holding arms.

[0022] From RF-Probes: Plug Connector, Miniature Switch and PCB Contacting, page 169ff, a probe with an inner conductor and an outer conductor is described. On page 173, coaxial test probes with an inner and outer conductor are disclosed, wherein the conductors are spring-loaded, with the spring element arranged inside the outer conductor.

[0023] The invention is based on the objective of creating a test probe for a finger tester for testing unpopulated printed circuit boards, wherein the test probe is suitable for contacting small contact points for multi-point measurements, even if the contact points are arranged adjacent to contours protruding on the printed circuit board.

[0024] Another task is to design the test probes in such a way that the circuit board to be tested can be contacted at high speed without causing any damage to the contact points of the circuit board.

[0025] Another task is to precisely measure the resistance of conductor tracks on unpopulated printed circuit boards. One or more of these tasks are solved by the subject matter of the independent claims. Advantageous further developments and preferred embodiments are the subject matter of the dependent claims.

[0026] One aspect of the invention relates to a test probe for a test finger for testing unpopulated printed circuit boards. The test probe comprises a contact sleeve and a test needle, which has a contact tip at one end. Furthermore, the test probe includes at least one sleeve spring arm, which is formed at one end at a base of the test probe and at the other end at the contact sleeve for elastically holding and electrically connecting the contact sleeve. The test needle in the contact sleeve is axially displaceable, so that the contact sleeve can be brought into contact with a test point of the printed circuit board under test. The test probe has a needle spring arm, which is electrically and mechanically attached to a connecting end of the test needle projecting from the contact sleeve and away from the contact tip, so that the needle spring arm counteracts movement of the test needle with the connecting end out of the contact sleeve.This allows the test probe to form an internal sensor and the contact sleeve an external sensor for scanning a circuit board test point.

[0027] In this test probe, the contact sleeve and the needle spring arm are designed to be movable relative to each other, and both elements are elastically actuated by their respective spring arms. This eliminates the need for a spring element within the contact sleeve to exert a spring force relative to the test needle. As a result, the contact sleeve and test needle unit can be designed to be very simple and thin.

[0028] In this description, the terms "lower" and "raise" are used as if the printed circuit board (PCB) is horizontal and the test probe is positioned above the PCB, so that "lower" refers to a direction from the test probe to the PCB and "raise" refers to a direction from the PCB to the test probe. However, the test setup can be configured with test probes on both sides of the PCB, in which case the corresponding directions are reversed. The test setups can also be configured with vertically oriented or inclined PCBs, in which case the corresponding directions to and from the PCB are always perpendicular to the surface.

[0029] The test probe can be mounted on a carriage via a holder, forming a test finger, also called a test finger. The test finger can be moved along crossbeams, which in turn can be guided and moved on guide rails. During the test procedure, when the test probe is lowered onto the test point of the circuit board under test, the contact tip of the test needle first makes contact with the test point. This pushes the needle spring arm upwards, moving the test needle within the contact sleeve.

[0030] Next, the contact sleeve lowers towards the circuit board and also makes contact with the circuit board test point. If further pressure is applied to the test probe and contact sleeve from above, the sleeve spring arm is also pushed upwards, thus establishing a secure contact with the circuit board test point.

[0031] Because the test probe has two sensors (inner sensor and outer sensor), a single test probe can contact a circuit board test point twice, enabling measurements that previously required two conventional test probes.

[0032] This allows more inaccessible printed circuit board test points to be reached with two sensors on the circuit board, e.g. in recesses of printed circuit boards.

[0033] This means the test probe can be used flexibly with different geometries and layouts, and makes it possible to test even complex circuits more efficiently than with two separate test probes.

[0034] Furthermore, the reliability of a dual sensor is higher than that of two separate sensors, since the number of moving parts that move the test probe is halved.

[0035] Another advantage is that the distance between the indoor and outdoor sensors always remains constant, whereas with two individual sensors it can vary slightly due to inaccuracies in the movement of the device or fluctuations in the sensors themselves. This allows for more accurate measurement results.

[0036] The elastic sleeve spring arm holds the contact sleeve securely yet flexibly. This distributes the pressure when the probe is placed on the circuit board, preventing pressure concentrations that could cause damage. As a result, the test probe can be placed on the circuit board under test at high speed without damaging it.

[0037] The elastic sleeve spring arm and the sliding mechanism of the test probe within the contact sleeve ensure precise contact with the circuit board. This enables accurate measurement of the resistance of bare circuit boards. The test probe features two sensors: an inner and an outer sensor. This allows even small, hard-to-reach contact points to be reliably scanned. In particular, for example, only half as many test probes are required for a four-point measurement compared to probes with only a single sensor. Since the test probes occupy a certain amount of space, a smaller area can be measured for the same measurement method compared to probes with only one sensor each. This makes small contact points reliably accessible for multi-point measurements. Furthermore, the inner and outer sensors are positioned very close to each other, allowing even the smallest circuit board test points to be reliably contacted with both sensors.

[0038] Alternatively, the two sensors can be used in parallel to capture the same signal, thus achieving increased measurement precision. This minimizes incorrect readings, e.g., due to suboptimal contacts.

[0039] A test probe can be used to perform various types of measurements. These include, among others, measuring contact resistance, in which the resistance between two points on the circuit board is checked to ensure that the connection is correct and that there are no high-resistance contacts.

[0040] A pair of sleeve spring arms may be provided, which are connected to the base and the contact sleeve in the manner of an elastic parallel link.

[0041] The pair of sleeve spring arms thus offers more stability and support for the test probe during operation than a single sleeve spring arm. This reduces fluctuations during measurement, resulting in increased stability of the measurement signal.

[0042] Furthermore, the load-bearing capacity is increased to support larger loads, e.g. from heavier sensors, with the same material consumption.

[0043] The needle spring arm can be attached to the sleeve spring arm or directly to the base at its end furthest from the test needle.

[0044] When the needle spring arm is connected to the sleeve spring arm, part of the test needle's movement is also transmitted by the sleeve spring arm. Since the sleeve spring arm is larger than the needle spring arm, this results in more stable control of the movement, and consequently, more stable movement of the test needle itself. The relative movement of the test needle to the contact sleeve is therefore smaller than when the needle spring arm is connected directly to the base. Again, this smaller relative movement can result in greater control.

[0045] If the needle spring arm is directly attached to the base, the range of motion is greater, resulting in greater flexibility.

[0046] Furthermore, the relative tilt of the test needle to the sleeve is smaller because the radius of the tilt has been increased.

[0047] Each sleeve spring arm can be triangular in plan view, with one corner of the triangle connected to the contact sleeve and the side of the triangle opposite this corner connected to the base.

[0048] This spatial design of the holding arms makes the test needles very stable and ensures they are held securely in the holder.

[0049] An electrical insulator can be arranged between the test needle and the contact sleeve.

[0050] This prevents a short circuit from occurring between the test needle and the contact sleeve inside the test probe. Such a short circuit would disrupt or even completely prevent measurements.

[0051] Such an insulator can also serve as a guide for the relative movement of the test needle to the contact sleeve, so that the radial distance between the test needle and the contact sleeve always remains the same.

[0052] The contact tip of the test needle can have one of the following shapes: conical cut, ball cut, shaft cut, cutting edge or triangular cut.

[0053] The choice of needle shape should be based on the specific test scenario, such as circuit board material, type of component being tested, and environmental conditions.

[0054] A conical tip ensures secure and precise contact with the printed circuit board surface while maintaining some flexibility in the probe's orientation. This is particularly useful when a small contact area and / or non-standard orientations are required.

[0055] A spherical polish creates a larger contact area, which reduces resistance and / or minimizes the risk of oxidation. Such profiles are particularly useful in high-frequency applications and digital measurements. They may also be advantageous in other situations where good thermal contact is required.

[0056] A shank grind does not produce sharp edge angles and can lead to better electrical contact, as the needle can penetrate the material more easily. However, this can also cause more wear than other shapes.

[0057] A cutting edge also has a sharp, elongated edge and can also establish precise contact, although abrasion and damage to the surface are possible here as well. This allows for very precise contact.

[0058] Triangular grinding can improve contact stability and simultaneously ensure good electrical contact. However, not every orientation of the test probe is equally effective. Certain angles may perform worse than others.

[0059] The contact edge of the contact sleeve, which allows the contact sleeve to be brought into contact with the printed circuit board test point, can have one of the following shapes: asymmetrical cutting edge, shed roof edge, conical edge, triangular edge, beveled edge, wing edge, trocar edge and square edge.

[0060] The asymmetrical cutting edge is characterized by the fact that the contact sleeve is predominantly ground with a cutting edge, resulting in a sharp cutting edge along a main surface. The tip of the sleeve is provided with a counter-grind. Here, the grinding plane of the main surface and the grinding plane of the counter-grind intersect in a horizontal line and form an angle. This line preferably runs tangentially to the inner surface of the sleeve (Fig. 2a). The line therefore does not pass through the center of the sleeve, which is why this grind is described as asymmetrical. With the counter-grind, wall thickness is reduced in the region of the sleeve tip, and a contact tip is offset by the wall thickness relative to a tip without a counter-grind, as can be seen in Fig. 2a. The contact tip is thus located in the region of the inner surface of the sleeve.The sloping roof grind is similar to the asymmetrical cutting grind, but the main surface of the grind is recessed a few micrometers upwards, and the ground surface ends at a boundary line tangential to the inner surface. This boundary line runs parallel to a boundary line of the opposing grind, which also runs tangentially to the inner surface. The two boundary lines are offset along the inner surface of the sleeve. This creates a grind whose cross-section corresponds to an inverted, offset sloping roof. A new grinding edge is formed between the main surface and the grinding plane of the opposing grind, pointing perpendicularly along the contact sleeve.

[0061] The previously mentioned conical shapes have the same advantages as the test probe.

[0062] An angled cut creates a single narrow contact surface on the contact sleeve, while a wing cut creates two opposing contact surfaces.

[0063] In trocar grinding, a single point is also created, but it is sharper than in an oblique grinding.

[0064] A square grind creates four edges and therefore four contact surfaces.

[0065] In principle, the same grinding patterns used for the contact tip can be used for this purpose, and vice versa. Other grinding patterns are also conceivable.

[0066] The contact tip and the contact edge can be arranged in such a way that their contact points have the smallest possible distance between them.

[0067] Such an arrangement will be called a Kelvin arrangement in the following.

[0068] Such an arrangement is used particularly for applications where measurements need to be carried out within recesses of printed circuit boards.

[0069] Furthermore, such an arrangement is very suitable for Kelvin or four-point measurements, since the distance between at least two test points is very small and therefore a precise measurement can be carried out.

[0070] The distance between the contact points of the test probe and the contact sleeve can be minimized by the grinding and alignment of these components. The test probe should be ground so that the contact point is located at the edge of the probe, for example, by means of a cutting edge.

[0071] The contact edge should be ground in such a way that the contact surface of the contact sleeve lies on the inner edge of the sleeve, e.g. by a conical grind.

[0072] The distance between the two contact surfaces between the contact tip and the contact edge is then only determined by the distance between the test needle and the contact sleeve and can be in the range of 30 pm depending on the embodiment.

[0073] Another aspect of the invention is a finger tester for testing unpopulated printed circuit boards with at least one and preferably two test probes, as previously described. The test probes are each arranged on a test finger, with the test needles being arranged at different angles to each other.

[0074] Finger testers are testing devices for testing unpopulated or populated printed circuit boards, which use two or more test fingers to sequentially scan the individual contact points.

[0075] Due to the alignment, the two test probes point towards each other and can be positioned / applied very close to each other on the circuit board surface, so that the at least four contact surfaces can be very close together.

[0076] This is particularly advantageous when four-point measurements need to be carried out in recesses of printed circuit boards.

[0077] Another aspect of the invention is a finger tester for testing unpopulated printed circuit boards (PCBs) with at least one, and preferably two, test probes as previously described, and with a receiving area for the PCBs to be tested. The test probes are each arranged on a test finger, with at least one probe being substantially perpendicular to the receiving area.

[0078] Such a vertical probe can be brought very close to the boundary wall of a cavity.

[0079] Another aspect of the invention is a method for testing unpopulated printed circuit boards with a finger tester, as previously described. The at least two contact tips and the at least two contact edges form four contact points for a four-point measurement. A current or voltage of the printed circuit board under test is measured between each pair of contact points. From the measured voltage and current, the resistance or conductivity of the printed circuit board or parts thereof can be determined.

[0080] Since the four contact points can be arranged very close together on the circuit board, the electrical conductivity of the circuit board can be determined within a very narrow area.

[0081] The invention is explained in more detail below by way of example, using the examples shown in the drawings.

[0082] The drawings show schematically:

[0083] Figure 1 shows a test probe according to the invention in perspective view,

[0084] Figure 2a shows a first grinding type of a test tip and a contact sleeve tip of a test probe in perspective view,

[0085] Figure 2b shows a second grinding type of a test tip and a contact sleeve tip of a test probe in perspective view.

[0086] Figure 3 shows a test probe tip and a contact sleeve tip of a test probe according to Fig. 2a over a printed circuit board to be tested in a perspective view.

[0087] Figure 4 shows a test tip and a contact sleeve tip of a test probe according to Fig. 2a over a circuit board to be tested in perspective view, Figure 5 shows a finger tester in perspective view.

[0088] A test probe 1 has a test needle 2, which in the present embodiment is formed from a needle 3 and a contact sleeve 4 surrounding the needle 3. The needle 3 has, for example, a diameter d of 0.3 to 0.5 mm (Fig. 1). It is made, for example, of steel or tungsten. The needle 3 is encased in an insulating layer, which is, for example, made of Teflon.

[0089] This sheathing with the electrically conductive layer forms a contact sleeve 4, which, like the test needle 2, can be lowered onto a circuit board to be tested in order to examine the circuit board to be tested via electrical signals that flow through the contact sleeve 4 and / or through the test needle 2.

[0090] The contact sleeve 4 comprises a large-walled tube 4a, which points away from the circuit board, and a smaller tube 4b with a thinner wall, which points towards the circuit board, such that the smaller tube 4b encloses the probe 3 adjacent to a probe tip 5 of the probe 3. The two tubes 4a and 4b are electrically and mechanically connected. The larger tube 4a provides high stability, while the smaller tube forms a small probe tip, thus enabling good spatial resolution. The contact sleeve 4 can be manufactured by inserting the smaller tube 4b a short distance into the larger tube 4a and soldering them together.

[0091] The needle 3 is displaceable along its longitudinal axis within the contact sleeve 4. The insulating layer also serves as a sliding layer, preventing radial movement that would cause the needle 3 to tilt relative to the contact sleeve 4.

[0092] The needle 3 protrudes at both ends from the contact sleeve 4, with the lower end of each end tapering to a point to form the test tip 5. The test tip 5 is the lowermost point of the needle 3, which can be placed on a conductor track to be tested.

[0093] At the upper end opposite the test tip 5, the test needle 2 or the contact sleeve 4 is connected via a sleeve cap 12 to two retaining arms 6, 7, which are referred to below as the upper retaining arms. In a top view, the upper retaining arms 6, 7 are arranged in a V-shape, with the apex of the “V” being formed by the sleeve cap 12.

[0094] Between the two retaining arms 6, 7 are arranged two connecting webs 11a, 11b, which give stability to the upper retaining arms.

[0095] A needle retaining arm 13 is integrally formed on the connecting piece 11b, which is located closer to the test needle 2. This needle retaining arm is connected to the upper end of the needle 3, which protrudes through a hole in the sleeve cover 12. The length of the needle retaining arm 13 is approximately one-third the length of one of the retaining arms 6, 7.

[0096] The needle holder arm 13 pushes the needle 3 upwards through the contact sleeve 4 upon contact with the surface of a circuit board under investigation, causing the needle 3 to move upwards through the sleeve cover 12.

[0097] Two further retaining arms 8, 9 are attached to the contact sleeve 4 a short distance downwards from the connection point between the upper retaining arms 6, 7 and the test probe 2. The retaining arms 8, 9 are hereinafter referred to as the lower retaining arms. The upper retaining arms and the lower retaining arms are separated from each other on the test probe 2 by a spacer tube 14, which surrounds the contact sleeve 4 and terminates at the sleeve cover 12.

[0098] The two pairs of retaining arms 6, 7 and 8, 9 are each made from a single sheet of metal. The two pairs of retaining arms 6, 7 and 8, 9 thus each form an isosceles triangle, with the test needle 2 located at the apex of the isosceles triangle.

[0099] The holding arms 6 to 9 are attached to a bracket 10 at their ends furthest from the test probe 2. The bracket 10 is an electrically insulating plastic part provided on its upper surface with a series of contact surfaces (not shown).

[0100] In the side view, the upper and lower retaining arms 6, 7 and 8, 9 together with the corresponding limiting edge of the holder 10 and the section of the test needle 2 arranged between the upper and lower retaining arms form a trapezoid.

[0101] Due to the inclination of the test probe relative to the vertical and the double linkage formed by the spring arms, when the test probe 1 is moved towards the circuit board and when the spring arms 6, 7, 8, 9 are deflected, the test tip moves along a straight line approximately parallel to the direction of movement and approximately perpendicular to the surface of the circuit board. This results in no or only a very small movement component parallel to the surface of the circuit board under test, thus ensuring that the test tip 5 does not scratch the surface of the circuit board. The test tip is therefore not moved, or only very slightly, when the test probe is placed on the test piece.

[0102] Below the holder 10 is a retaining plate 15, which extends towards the test needle 2 but does not touch the test needle 2 or the lower retaining arms, neither in the deflected nor the non-deflected state. Its shape is approximately modeled on the shape of the lower retaining arms, although the retaining plate 15 does not extend as far from the holder 10.

[0103] The needle 3 is electrically connected to the needle holding arm 13. The needle holding arm 13 is electrically connected to the upper holding arms 6, 7, which in turn are each electrically connected to the contact surfaces via conductor tracks.

[0104] The contact sleeve 4 is electrically connected to the lower retaining arms 8, 9, which in turn are each electrically connected via a conductor track to the contact surfaces (not shown). These contact surfaces are connected via further conductor tracks (not shown) to an electrical connector (not shown) formed on the holder 10.

[0105] The upper retaining arms 6, 7 and the needle retaining arm 13 are electrically insulated from the lower retaining arms 8, 9 by the sleeve cover 12 and the spacer tube 14.

[0106] The holder 10 is designed as a plug-in element that can be plugged into a test head of a finger tester.

[0107] In the present embodiment, the holder 10 has two insertion elements 18. In a top view, with the retaining arms 6, 7, 8, 9 projecting forward, the insertion elements 18 are arranged projecting laterally upwards onto the holder 10. The insertion elements 18 are contoured so that the holder 10 can be slid onto the probe head along the axis in which the retaining plate 15 runs and fixed with a through-hole 19 and a corresponding hole in the probe head using a through-hole pin. When the holder 10 is slid or inserted onto the probe head, the conductor tracks connected to the contact surfaces are electrically connected to corresponding conductor tracks of the probe head.

[0108] A light barrier element 16 is arranged on the side surface of the mounting plate 15, which is adjacent to the upper mounting arms. In side view, the light barrier element 16 is egg-shaped with a base and two legs. A light source is arranged on the inside of one of the two legs at its end, and a light sensor that receives the light signal is arranged on the other leg. The light source and the light sensor thus form a light measuring section. The light source and the light sensor have a certain longitudinal extent in the horizontal plane, which is, for example, 1 mm. A measuring flag 17, which is, for example, made of a thin metal sheet, is attached to the upper mounting arms on the connecting web 11a. This measuring flag points vertically downwards and is therefore parallel to the test probe 2. The lower edge of the measuring flag 17 is designed as a measuring edge and is arranged directly above the light measuring section.

[0109] When the contact sleeve 4 is placed on a circuit board to be tested, a force is applied to the contact sleeve 4, causing the retaining arms to pivot from their initial position into a deflected position. This directs the measuring flag 17 into the light measuring path. The angled measuring edge interrupts the light measuring path proportionally to the movement of the test probe relative to the holder 10, so that the signal measured by the light barrier is proportional to the movement of the test probe. The light barrier element 16 is connected to each of the contact surfaces via four conductor tracks, and these contact surfaces, like the other contact surfaces, are connected to the probe head via an electrical connector.

[0110] Preferably, the test tip 5 is ground with a cutting edge, such that the tip is arranged at a radial end of the needle 3.

[0111] The contact sleeve 4 has a contact sleeve tip 20 which is ground in an asymmetrical cutting edge, as described above (Fig. 2a).

[0112] The asymmetrical cutting edge is characterized by the fact that the contact sleeve is predominantly ground with a cutting edge, resulting in a sharp cutting edge along a main surface 20a. The tip of the sleeve has a counter-cut. Here, the cutting plane of the main surface 20a and the cutting plane 20b of the counter-cut intersect in a horizontal line 20c (perpendicular to the plane of the drawing in Fig. 2a) and enclose an angle 20d.

[0113] Alternatively, the contact sleeve tip can be ground as a sloping roof finish (Fig 2b).

[0114] The sloping roof grind is similar to the asymmetrical cutting grind; however, the main surface 20a, also referred to here as the grinding surface 20a, of the grind is recessed a few micrometers upwards, and the grinding surface 20a terminates at an upper boundary line 20e of the grinding surface 20a that runs tangentially to the inner surface and parallel to a boundary line 20f of the grinding surface 20b of the counter-grind that runs tangentially to the inner surface. The two boundary lines 20e and 20f are offset along the inner surface 21 of the sleeve 4. This results in a grind whose cross-section corresponds to an inverted, offset sloping roof. A new grinding edge 20g is created between the main surface 20a and the grinding plane 20b of the opposing grind, which points perpendicularly along the contact sleeve 4.

[0115] Several other combinations of the alternatives described here are also conceivable. However, the following discussion refers to the type of cut shown in Fig. 2a.

[0116] The contact sleeve 4 is ground radially outwards at the point closest to the probe tip 5, such that an inner surface 21 of the contact sleeve 4 forms the lowest point and thus the probe tip 20. The remaining side of the contact sleeve 4 is recessed. The distance between the probe tip 5 and the probe tip 20 is therefore determined solely by the distance between the probe tip 3 and the contact sleeve 4 and, in this embodiment, is d = 30 micrometers.

[0117] Thus, the test probe 1 with the test needle 2 can be brought particularly close to an edge 22, a recess of a circuit board to be tested, in order to measure a two-point measurement through the contact sleeve 4 and the needle 3.

[0118] The following describes an application of the test probe 2 with reference to Figure 3 for contacting printed circuit board test points in a recess, where identical elements as explained above are designated with the same reference numeral. The explanations given above apply to identical elements unless otherwise stated below. In this application, one or more printed circuit board test points 24a, which are arranged in a recess (cavity) of a printed circuit board 24 (Fig. 3), are to be checked or measured.

[0119] For this purpose, the test needles 2 of the test probes 1 are preferably oriented such that they are arranged on the test probes 1 of a test device 23 approximately perpendicular to the plane of the printed circuit board 24. This allows the test needles, with their test tip 5 and contact sleeve tip 20, to be positioned very close to a boundary wall 22 of the recess. This enables contact to be made with small printed circuit board test points 24a at the edge of a recess. The arrangement of the test needles 2 is called a cavity arrangement.

[0120] Furthermore, the test needles 2 of the test probes 1 are preferably designed such that the test tip 5 and the contact sleeve tip 20 of a test needle 2 are arranged eccentrically on it, and are positioned as close as possible to the boundary wall 22 of the recess during use. The test needles 2 can be arranged perpendicular to the plane of the circuit board 24 or at an angle to the plane of the circuit board 24.

[0121] For this purpose, it is advantageous that, in a test device 23 with two probes 1, each having a test needle 2, the test tips 5, which are eccentrically formed on the two test needles 2, and the contact sleeve tips 20 are spaced as far apart from each other as possible. In other words, this means that the test needles 2 are arranged on the test device such that they are mirror images of each other, such that the test tip 5 and the contact sleeve tip 20 are located on the outside with respect to the area between the two test needles 2.

[0122] The following section explains another application of the test needle 2 with reference to Figure 4, where identical elements as in the first two applications are designated with the same reference numeral. The explanations given above apply to identical elements unless otherwise stated below.

[0123] Here, two closely adjacent printed circuit board test points 24a are contacted. Each printed circuit board test point is connected to a conductor running between the two printed circuit board test points 24a using one of the test probes 2 for, e.g., a Kelvin measurement, also called a 4-wire measurement. The arrangement of the test probes 2 is called a Kelvin arrangement. The test probes 2 are arranged such that the eccentrically shaped test tips 5 and the contact sleeve tips 20 on the test probes are positioned as close to each other as possible. The test probes are positioned so that the test tip 5 and the contact sleeve tip 20 of the test probes point towards each other.

[0124] The test probes 2 can be positioned at an angle to a circuit board 24 being tested. In a side view, the test probes 2 form approximately an upward-facing V-shape, with the two probes 2 forming the respective sides of the "V". Since they contact two different circuit board test points 24a, they do not meet exactly but are slightly spaced apart. However, the two test probes 2 can be brought closer together by their mutually pointing tips 5, 20 than in the cavity application described above. In the cavity application, however, the test probes 2 can be brought closer to an edge 22.

[0125] An advantage of the test probe according to the invention, according to one of the embodiments described above, is that in the event of a collision of the test probes, which can occur in the case of faulty programming of the finger tester, the retaining arms act as predetermined breaking points, whereby only the relatively small module of the test probe 1 according to the invention is damaged on a test head, which can also be repaired by attaching a new test needle and new retaining arms.

[0126] Preferably, the test probe 1 according to the invention is moved by a linear motor.

[0127] The applications described above according to Figures 3 and 4 can be used in a test device 23, hereinafter referred to as a finger tester, for testing unpopulated printed circuit boards 24 (Fig. 5). The finger tester 23 has several probe heads 25, each of which is formed from a test probe 1 according to the invention and one of the linear motors described above.

[0128] The finger tester 23 has a section for receiving the printed circuit board 24 to be tested, which is held by means of retaining elements 26. At least one crossbeam 27 is arranged in the area above this receiving section, extending over this receiving section. Preferably, there are several crossbeams 27, which are either fixed or movable on the finger tester. If the crossbeams 27 are fixed on the finger tester, the probe heads can be moved along them. Each probe head has a carriage that can be moved along the respective crossbeam by a linear drive, and a swivel arm that is pivotably mounted at one end about the vertical. A test probe 1 is arranged at the other end of the swivel arm. The linear drive can be a linear motor or a conveyor belt 28.

[0129] In the applications shown in Figures 3 and 4, the retaining elements 26 are arranged in such a way that they do not cross each other.

[0130] Preferably two probe heads 25 are arranged on a traverse.

[0131] During operation, the test probes 1 with their test tips 5 are positioned over a circuit board test point 24a to be tested by moving them in the plane parallel to the circuit board 24. The contact tip is then lowered onto the circuit board test point 24a by means of a lifting device, which is, for example, a linear motor, until the test tip 5 makes contact with the circuit board test point. The electrical measurement then follows, after which the test probe is raised again and moved to the next circuit board test point.

[0132] The finger tester 23 shown in Fig. 5 has probes 25 on only one side of the circuit board 24 to be tested. Within the scope of the invention, it is of course possible to design the finger tester with probes, crossheads, etc. on both sides of the circuit board to be tested.

[0133] For the embodiments listed here, full reference is made to the European patents with publication numbers EP 1451594 B1 and EP 4348277 A1, unless the features are described differently above. This applies in particular to the description of the movement of the contact sleeve (referred to as a shield in EP 1451594 B1), the contacting of the contact surfaces, and the linear motor.

[0134] EP 1451594 B1 describes alternative embodiments regarding the shape of the holder 10 and how it can be attached to a test head of a finger tester. These embodiments can also be applied to the holder shown here.

[0135] 1 test probe 18 insertion element

[0136] 2 test needles 19 bore

[0137] 3 Needle 25 20 Contact sleeve tip

[0138] 4 Contact sleeve 20a Main surface

[0139] 4a larger tube 20b polished plane of the opposite

[0140] 4b small tube ten cut

[0141] 5 test probe 20c horizontal line

[0142] 6 Support arm 30 20d angle

[0143] 7 Support arm 20e upper boundary line

[0144] 8 Holding arm 20f lower boundary line

[0145] 9 Holding arm 20g sanding edge

[0146] 10 Bracket 21 Inner surface

[0147] 11 a Connecting bridge 35 22 edge

[0148] 11 b Connecting bridge 23 Test device

[0149] 12 sleeve covers, 24 circuit boards

[0150] 13 Needle holding arm 25 Probe

[0151] 14 Spacer tube 26 Holding element

[0152] 15 Mounting plate 40 27 Crossbeam

[0153] 16 light barrier elements 28 conveyor belts

[0154] 17 Measuring flag

Claims

International patent application atg Luther & Maelzer GmbH Claims 1. Test probe (1) for a finger tester for testing unpopulated printed circuit boards, comprising a contact sleeve (4) and a test needle (2) which has a contact tip at one end, at least one sleeve spring arm which is formed with one end at a base of the test probe (1) and the other end at the contact sleeve (4) for elastically holding and electrically connecting the contact sleeve (4), wherein the test needle (2) is axially displaceable in the contact sleeve (4) so ​​that the contact sleeve (4) can be brought into contact with a printed circuit board test point of the printed circuit board to be tested, a needle spring arm which is electrically and mechanically attached to a connecting end of the test needle (2) projecting from the contact sleeve (4) and away from the contact tip, so that the needle spring arm counteracts a movement of the test needle (2) with the connecting end out of the contact sleeve (4),so that the test probe (2) forms an internal sensor and the contact sleeve (4) an external sensor for scanning a printed circuit board test point.

2. Test probe (1) according to claim 1 , characterized in that a pair of sleeve spring arms are provided which are connected to the base and the contact sleeve (4) in the manner of an elastic parallel link.

3. Test probe (1) according to claim 1 or 2, characterized in that the needle spring arm is connected with its end furthest from the test needle (2) to the sleeve spring arm or directly to the base.

4. Test probe (1) according to one of claims 1 to 3, characterized in that each sleeve spring arm is triangular in plan view, wherein one corner of the triangle with the contact sleeve (4) and the side of the triangle opposite this corner is connected to the base.

5. Test probe (1 ) according to one of claims 1 to 4, characterized in that an electrical insulator is arranged between the test needle (1 ) and the contact sleeve (4).

6. Test probe (1) according to one of claims 1 to 5, characterized in that the contact tip of the test needle (2) has one of the following shapes: conical cut, spherical cut, shaft cut, cutting cut or triangular cut.

7. Test probe (1) according to one of claims 1 to 6, characterized in that a contact edge of the contact sleeve (4) with which the contact sleeve (4) can be brought into contact with the printed circuit board test point has one of the following shapes: Asymmetrical cutting edge, sloping roof edge, conical edge, triangular edge, oblique edge, wing edge, trocar edge, square edge.

8. Test probe (1) according to claim 7, characterized in that the contact tip and the contact edge are arranged to each other such that their contact points have the smallest possible distance.

9. Finger tester for testing unpopulated printed circuit boards, with at least two test probes (1 ) according to one of claims 1 to 9, each arranged on a test finger, wherein the test needles (2) are arranged at different angles to each other.

10. Finger tester for testing printed circuit boards, comprising at least two test probes (1 ) according to one of claims 1 to 9, each arranged on a test finger, and comprising a receiving area for the printed circuit boards to be tested, wherein at least one test needle (2) is substantially perpendicular to the receiving area.

11. Methods for testing unpopulated printed circuit boards, with a finger tester according to claim 9 or 10, wherein the at least two contact seats and the at least two contact edges form four contact points for a four-point measurement, such that a current or a voltage is measured between each pair of contact points along the circuit board to be tested in order to determine a resistance or a conductivity of the circuit board or parts of the circuit board from the measured voltage and the measured current.

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