METHOD AND DEVICE FOR TESTING A WORKPIECE

Description

[0001] The invention relates to a method and a device for testing a workpiece, in particular a printed circuit board, according to the preamble of claim 1 and 4, respectively, as well as to a use of an intrinsically active polymer according to claim 9. State of the art

[0002] In many everyday situations, objects must be moved. Electronic testing devices are referred to below as an example only. However, the invention is not intended to be limited to these. The description is intended only as an example. Likewise, the present invention does not limit the scope to movements that occur in miniature areas. It is particularly well suited for this purpose.

[0003] Such testing devices are known and commercially available in a wide variety of forms and designs. The present invention relates to any testing device with which a workpiece is to be scanned by a plurality of test pins arranged in a specific relationship to one another, although this arrangement may need to be changed. In particular, but not exclusively, the present invention relates to testing devices for examining electronic circuit boards for defects and functionality before they are incorporated into electronic devices.

[0004] In such devices, contact pins or needles are pressed into predetermined locations (contact positions) on the circuit board and then subjected to test signals according to a predetermined control system by a test computer to determine the functionality of the populated circuit board. To establish proper electrical contact between the contact pins and contact points on a circuit board that covers a large number of contact positions, several thousand contact pins are often necessary or possible.

[0005] Such test devices are described, for example, in DE 11 2006 003 034 T5, DE 196 46 252 A1, or DE 44 16 151 B. However, all of these devices require that the circuit boards to be tested are precisely assigned to the test pins. Since a large number of such tests must be performed within a single time unit, considerable problems arise with the positioning of the circuit board in relation to the test pins.

[0006] A common problem with this type of testing equipment, especially for printed circuit boards, is that the workpiece to be tested is subsequently modified. This means that the test adapter with the test pins must also be subsequently redesigned, which takes a long time because, for example, the angle of attack and the relative arrangement of the test pins must be recalculated, and the corresponding holders, such as perforated plates, must also be redesigned.

[0007] For example, it is known from US Pat. No. 5,635,849 A that a test probe is moved by an actuator. This essentially comprises a coil that generates a magnetic field and causes the test probe to deflect.

[0008] US Pat. No. 7,091,730 B1 discloses a test pin equipped with two tips, one of which is positioned eccentrically to the first. When the test pin is rotated, this second tip rotates around the first tip.

[0009] From US 2002 / 0013667 A1 an electrical test device for a printed circuit board is known, wherein a plurality of test pins are provided which can be moved electromagnetically in all three directions.

[0010] In DE 195 03 329 A1, corresponding test needles are coupled with carriages that can pivot the needles in the X and Y directions.

[0011] WO 2012 075033 A2 discloses a structural arrangement comprising microactuators. These are embedded in a substrate, which may be a hydrogel polymer. This hydrogel polymer is designed to react to environmental influences. As a result of these environmental influences, the microactuators move from a first to a second position due to a change in the volume of the hydrogel polymer.

[0012] WO 2008 113372 A2 discloses a device with an actuator made of an electroactive polymer. The device comprises two parts that are separated from each other by the actuator. Task

[0013] The object of the present invention is to develop a method and a device of the aforementioned type that facilitate and, in particular, accelerate the process of changing the relative arrangement of the test pins. The object of the present invention is also to improve the movement of test pins, especially in the field of electronics but also in micromechanics. Solution to the task

[0014] The features of claims 1, 4 and 9 respectively lead to the solution of the problem.

[0015] Intrinsically active polymers are plastics that undergo defined changes in their material properties when exposed to specific physical (e.g., temperature, light of a specific wavelength, electric and magnetic fields) or chemical (substance concentrations, pH) environmental parameters. These include, in particular, phase-reversible polymers (e.g., stimulus-sensitive hydrogels, polymer brushes), phase-change polymers, conductive polymers, and bielectric elastomers. Other examples of intrinsically active polymers include shape-memory polymers, piezoelectric polymers, electrostrictive polymers, and ferroelectric polymers.

[0016] The present invention primarily utilizes electroactive or so-called stimuli-sensitive hydrogels. These materials are solid-state effect carriers with the largest volume change usable for actuators and are therefore extremely easy to miniaturize.

[0017] The temperature-sensitive poly-(N-isopropylacrylamide) (PNIPAAm) is used as the basis.

[0018] In a first step according to the present invention, the mechanical and actuator properties of the actuator material are tailored to specific drive tasks. The expected mechanical stresses will exceed the achievable properties of the homopolymer PNIPAAm. Therefore, the polymer is functionalized with special nanomaterials from the group of layered silicates, which leads to an improvement in the mechanical and actuator hydrogel properties by more than an order of magnitude. The parameters of the active polymer are optimized by varying the crosslinking conditions and specifically modifying the starting materials, the degree of crosslinking, and the porosity of the crosslinking points.

[0019] Furthermore, the controllability of the actuator materials was optimized. In their unmodified state, the hydrogel actuators can be switched from a fully swollen to a fully deflated state within their volume phase transition region by varying the actuator temperature by just 5 K. To achieve high-precision actuator control, it may be necessary to expand the volume phase transition range, for example, to 10 K. This can be achieved by copolymerizing the N-isopropylacrylamide or by varying the thermodynamic quality of the solvent.

[0020] Furthermore, the actuator material should be microstructureable. For this purpose, the invention uses radical photopolymerization, which not only synthesizes the hydrogel but also microstructures it to give it its shape.

[0021] Another aspect is the actuator material's ability to integrate into a higher-level system. This involves ensuring the necessary material compatibility and finding suitable adhesion promoter systems for covalent adhesion.

[0022] A device or positioning drive for carrying out the process is designed as a compact, fully integrated system and comprises the following components: (i) at least one actuator, (ii) actuator control electrodes, (iii) a locking mechanism, (iv) a drive housing including mechanical interfaces, (v) at least one interface to higher-level systems and (vi) a hardware- and software-based control of the positioning drive.

[0023] The primary goal of the present invention is to apply these polymers to a holder using a screen-printing process so that they can surround the corresponding test pins. When they are then confronted with or exposed to a corresponding physical or chemical environmental variable, they change their position in a defined manner, like a muscle, thereby moving the test pin.

[0024] Overall, the idea is, of course, to precisely monitor the changes in the test pins. This is done using appropriate cameras. Within the scope of the present invention, the main idea is for the test pin to pass directly through a camera lens, allowing the camera to precisely observe the test pin's movement. Character description

[0025] Further advantages, features and details of the invention will become apparent from the following description of preferred embodiments and from the drawing, which shows in Figure 1 a schematic side view of part of a device for testing a workpiece; Figures 2 - 5 schematic side views of further embodiments of devices for testing workpieces; Figure 6 a schematic side view of an arrangement for observing test pins; Figure 7 a schematic side view of another arrangement for monitoring the activity of test pins; Figure 8 a schematic side view of a further embodiment of a part of a device for testing a workpiece; Figure 9 a top view of a holder for test pins; Figures 10 and 11 a schematically illustrated top view and side view of a section of Figure 9with electroactive polymer activators; Figure 12 a perspective top view of a basic structure of a multi-axial positioning drive; Figure 13 a perspective side view of a contact needle head according to the invention; Figure 14 a perspective view of a contact needle head; Figure 15 a perspective view of a multi-axial positioning drive with contact needle.

[0026] According to Figure 1 A test pin 2 is located on a holder 1, whereby it can naturally be assumed that this holder 1 usually has a plurality of such test pins 2. This test pin 2 is intended to test a printed circuit board 3.

[0027] The test pin 2, with a shaft 4, penetrates the holder 1, which is designed as a perforated plate. This shaft 4 is arranged in a corresponding recess in the perforated plate 1, rotatable about an axis A. A test probe 5 is located eccentrically to this axis A, the position of which relative to the workpiece (circuit board 3) can be changed when the shaft 4 is rotated. Of course, it is also possible to design the recess in the perforated plate 1, through which the shaft 4 passes, accordingly, so that the position of the test probe 5 can also be changed. For example, the recess could be an elongated hole or the like.

[0028] To fix the test pin 2 relative to the perforated plate 1, a magnet 6 is provided on the shaft 4. In this case, the perforated plate 1 is preferably at least partially magnetic, so that an attractive force acts between the magnet 6 and the perforated plate 1, as indicated by the arrows.

[0029] The shaft 4 is rotated by a key (not shown in detail), which can be placed on an auxiliary square adjustment tool 7. If a different position of the test probe 5 relative to the circuit board 3 is desired, the key can be used to rotate the test pin 2 about its axis A and move the test probe 5 in a circular motion. At the same time, or in addition, it is also possible to move either the perforated plate 1 and / or the circuit board 3 two-dimensionally horizontally, so that any point on the circuit board 3 can be approached with the test probe 5. Such a movement mechanism for the circuit board 3 is shown, for example, in DE 10 2012 106 291.9.

[0030] In the device for testing a workpiece according to Figure 3The perforated plate 1 is additionally assigned a fixing plate 8, wherein a distance a between the perforated plate 1 and the fixing plate 8 is adjustable. This fixing plate 8 has, among other things, the task of fixing the individual test pins 2 relative to the perforated plate 1 after they have been adjusted, ie it essentially supports the magnet 6 so that the test pins 2 are not lifted from the perforated plate 1 when lowered onto the circuit board 3 and the position of the test pins 2 is not accidentally changed.

[0031] In the device for testing workpieces according to Figure 3 Instead of a perforated plate, a semi-magnetic plate is used as the holder 1.1. This means that the basic position of the test pins 2.1 in this case does not depend on the hole pattern of a perforated plate, but rather the test pin 2.1 can be moved freely along a bottom surface 9 of the holder 1.1.

[0032] Rotation of the test pin 2.1 about its axis A is effected by a drive magnet 10, which is assigned to the holder 1.1 beyond the test pin 2.1. This drive magnet 10 can be moved in any direction along the holder 1.1, but can also be rotated so that the magnet 6 follows it, thus allowing the test pin 2.1 to be aligned with a circuit board (not shown).

[0033] Above the drive magnet 10, a magnetically conductive fixing plate 8.1 is provided, with which the entire arrangement can be fixed.

[0034] The device for testing a workpiece according to Figure 4 differs from that according to Figure 3only by arranging an additional tool 11 with which another task can be performed. For example, this could be a spring-loaded hold-down device that presses against the workpiece or a camera that monitors the test probe 5.

[0035] In the device for testing a workpiece 3 according to Figure 5 The test pin 2.2 is located on a carriage 11, which can be moved in any desired manner. Reference is again made to DE 10 2012 106 291.9 for example only. The movement of the carriage 11 or the position of the test pin 2.2 relative to the circuit board 3 can be observed and monitored by a separate camera 12 and / or by a camera 13 assigned to the carriage 11.

[0036] In Figure 6 It is indicated that the activity of the test pin 2 is observed by two inclined cameras 12.1 and 12.2.

[0037] In Figure 7the test pin 2 or a test probe 5 passes directly through the lens 14 of a camera, so that this lens 14 is directly aligned with an impact point 15 of the test probe 5 on the circuit board 3.

[0038] An embodiment of the present invention is described in the Figures 8 to 13 This involves the possibility of moving a test pin 2 by means of electroactive polymers 16, which act as actuators for the test pin 2.

[0039] In the Figures 9 to 13 Another possibility for the movement of the test pins 2 is shown, which is achieved by so-called intrinsically active polymers. They move in a muscle-like manner. For the present inventive concept, electroactive polymers (EAP) are particularly preferred, since the polymer can be directly and specifically influenced by an electric field.

[0040] According to Figure 9A corresponding test pin 2 is guided in a perforated plate 1. On or above the perforated plate 1 are EAP actuators 16.1 and 16.2, which act on the test pin 2. This is schematically shown in the Figures 10 and 11 The corresponding EAP actuator surrounds the test pin 2, whereby the EAP actuator 16 itself is Figure 10 is exposed to an electric field from four sides. This causes, for example, Figure 11 that a central region of the EAP actuator bulges, thereby lifting the test pin 2. By applying the electric field magnitude to the EAP actuator, a rotation of the test pin 2 can also be caused.

[0041] In the Figures 12 and 13 It is shown how a corresponding test pin 2 is integrated into a housing 17, wherein the test pin 2 is surrounded by an EAP actuator 16 in the upper area or within the housing 17.

[0042] A plurality of test pins 2 protrude from the housing 17. These contact needles or test pins 2 are enclosed by a polymer reactor 16, which is embedded in the housing 17.

[0043] This hydrogel-based actuator is designed to freely position the contact needle in the xy plane with a positioning accuracy of approximately 25 µm, with maximum positioning ranges of + / - 500 µm from the normal position. This complex multi-axial positioning can be achieved using a flexible solid-state reactor, which, when appropriately controlled, deforms in an analog manner so that it can move to any point in the positioning plane via the contact needle. This requires finding a suitable structural design and dimensioning. The achievable positioning accuracy is also determined by the performance of the actuator control electrodes. The resistive control electrodes are segmented and control the temperature field, which can be electronically rotated through 360°.Key investigation criteria are the number of electrodes required to position the contact needles with sufficient accuracy, the required heating power, the course of the thermal field, the heat coupling, and the thermal management to stabilize the controlling temperature field.

[0044] The contact needle positioning drive is only responsible for the actual positioning process. Once the contact needle has reached its final position, a locking mechanism is activated, securing the needles in place.

[0045] During needle positioning, it is important to ensure that the head maintains a constant, defined temperature in the area of ​​the positioning drives to ensure the independence of the positioning processes from any fluctuations in the ambient temperature. Active temperature management can be achieved using Peltier elements or active water cooling, for example.

[0046] The drive housing not only provides mechanical protection for the positioning drive, but also carries its mechanical and electrical interfaces.

[0047] The head must also have adjustment options for optimal adjustment or pre-positioning. Ideally, global adjustment is feasible for the positioning drives; alternatively, concepts for individual adjustment are being investigated.

[0048] Force-locking principles seem particularly suitable for the locking mechanism. List of reference symbols

[0049] 1 bracket 34 67 2 Test pin 35 68 3 circuit board 36 69 4 shaft 37 70 5 test probe 38 71 6 magnet 39 72 7 Auxiliary square 40 73 8 Fixing plate 41 74 9 bottom 42 75 10 drive magnet 43 76 11 Sleds 44 77 12 camera 45 78 13 camera 46 79 14 lens 47 15 Point of impact 48 16 EAP actuator 49 17 Housing 50 18 PCB board 51 19 Tool 52 A axis 20 53 21 54 a Distance 22 55 23 56 24 57 25 58 26 59 27 60 28 61 29 62 30 63 31 64 32 65 33 66

Claims

1. Method for testing a workpiece (3), in particular a printed circuit board, by means of a testing pin (2) which passes through a holder (1) with a shaft (4) and which approaches a predetermined position on or in the workpiece (3), a position of the testing pin (2) being changed relative to the holder (1), characterized in that in that a change in the position of the testing pin (2) relative to the holder (1) is effected by an intrinsically active polymer which at least partially surrounds the shaft (4) of the testing pin (2), the intrinsically active polymers being applied to the holder (1) by screen printing.

2. Method according to claim 1, characterized in that the change in the position of the test pin (2) is observed.

3. Method according to claim 2, characterized in that the change in the position of the testing pin (2) is observed by guiding the testing pin (2) through the lens (14) of a camera.

4. Device for testing a workpiece (3), in particular a printed circuit board, by means of a testing pin (2) which passes through a holder (1) with a shaft (4) and which approaches a predetermined position on or in the workpiece (3), the position of the testing pin (2) being changed relative to the holder (1), characterized in that the testing pin (2) is assigned an intrinsically active polymer (16) which is designed to change the position of the testing pin (2) relative to the holder (1), and which at least partially surrounds the shaft (4) of the testing pin (2), the intrinsically active polymer (16) being applied to the holder (1) by screen printing.

5. Device according to claim 4, characterized in that the intrinsically active polymer (16) is an electroactive polymer.

6. Device according to claim 5, characterized in that the polymer is subjected to an electric field from four sides.

7. Device according to claim 4, characterized in that the polymer (16) is a stimuli-sensitive hydrogel.

8. Device according to claim 7, characterized in that the intrinsically active polymer (16) is a temperature-sensitive Poly(N-isopropylacrylamide) (PNIPAAm).

9. Use of an intrinsically active polymer (16) for moving testing pins (2) which pass through a holder (1) with a shaft (4) and serve to test workpieces (3), in particular printed circuit boards, the testing pins (2) travelling to a predetermined position on or in the workpiece (3), wherein the change in the position of each testing pin (2) relative to the holder (19) is effected by the intrinsically active polymer, wherein the intrinsically active polymer (16) at least partially surrounds the shaft (4) of the testing pin (2), wherein the intrinsically active polymer (16) is applied to the holder (1) by screen printing.