PROCEDURE AND DEVICE FOR EXAMINING PRINTED CIRCUIT BOARDS.

Description DE 40 14 149 AI the invention concerns a procedure and a device to opticacontroof conventionally equipped, mix-equipped and with only oberflaechenmon 5 animalable construction units mounted boards, whereby the lit inspection surface with one or more video cameras is taken up and the taken up video signafor evaluation to an image processing unit and for visuacheck to 10 a monitor is if necessary passed on with automatic assembly devices forms the examination on error free assembly of printed circuit boards regarding presence and placing the assigned construction units an important factor in the per 15 duktionsprozess. In this connection opticacontrowith video cameras and image analysis units offers favourable solution types, a frequently used method for optical examination with video cameras is the Differenzbildverfah 20 ren, that in the magazine "PKI technicareports", 1988, number 1, pages 101 and 102, is described. There with a video camera a correctly equipped printed circuit board is taken up. On the basis of this admission the video signaof the admission 25 of the printed circuit board which can be tested develops subtracted in this way in each case a difference picture, in which only the differences of the two pictures are to be seen. With this procedure incorrectly equipped printed circuit boards are recognized, in addition, differences, for example 30 by same construction units, which have only different colors, lead to the error display.

A further possibility on page is described the 102 of the magazine specified above, is edge detection. With this procedure the Bauteilkan 35 ten, D h. of heli coil/dark or dark/light transitions, for presence and correct situation examines this kind of printed circuit board control seizes however then only if the construction unit edge against the environment take off-better results become with a procedure receive, which evaluates the shade throw of construction units. In the simplest case one lights up the inspection surface from diagonally above with a source of light and takes up a picture, that in an image processing unit evaluated 45 will from the shade surfaces, which are compared with a reference, can one on the situation of the elements close. In the case of successive lighting from several, preferably from four directions, whereby with each lighting direction a picture with the video is taken up in such a way camera, the situation and size of the construction units existing on the printed circuit board can be determined. The comparison with reference values to a statement about correct and/or incorrect assembly, with increasing miniaturization of the building 55 leads also here divides becomes printed circuit board control with this procedure ever more inaccurately. Particularly in neighbourhood of larger construction units the smaller can be easily covered.

In addition with all well-known procedures so the evaluation becomes very difficult, because the situation of the construction units is measured in each case related to the testing facility and thus with an easy disalignment of the printed circuit board error in the evaluation, which can be examined, to arise to be able.

It is therefore task of the invention to indicate a procedure as that the evaluation with optical-electrical printed circuit board control with more security during simpler evaluation takes place this task is solved, as for examination on error free assembly of a printed circuit board the size of the brightly reflecting mating surfaces, which serve for the connection with the element and which are not covered by the construction unit, is evaluated it thus not the absolute absolute of the building hurry on the printed circuit board, but the relative situation of the construction units its mating surfaces the assembly with SMDS (Surface Mounted DEVICE) become first the construction units the mating surfaces glued on with this procedure remains free a part of the mating surfaces, while another part is covered. In the case of correct positioning of the construction units in each case a certain part of the mating surface covers the portion of the covered and/or the not-binding mating surface is present as reference value. This reference value can be won from the admission of an error free equipped printed circuit board or it can theoretically by the draft data for the printed circuit board be calculated.

For error free evaluation is shade-free lighting necessary, so that the not-binding mating surfaces, which reflect because of their silvery, smooth surface strongly, are covered not by shadowing. The lighting must be therefore planar and vague. The camera is arranged over the printed circuit board, so that the directly reflected light of the silvery mating surfaces can be taken up. The video signal belonging to the taken up picture is then supplied to an image processing unit for evaluation the evaluation effected via counting of the bright pixels, D h. pixels, the one certain brightness limit value overwriting, from which on the size of the mating surface for each mating surface belonging to a construction unit is a reference value is closed available, with that the value of the not-binding mating surface of a construction unit is compared at the reference value is smaller deviations from little per cent certified, whereby the size of the allowable variation depends it on the demanded assembly accuracy becomes thus a frontier and/or range of tolerance serves in an educated manner, that as reference that the not covered part of a mating surface is more largely than certified smaller or, becomes determined an assembly error erkanntIn one favourable arrangement of the invention also the shape of the not covered mating surface is consulted as analysis criterion, so that also the kind of the false positioning can be determined. Thus a "L"-form of the uncovered mating surface results on shift of a SMD in diagonal direction, while a turn of the construction unit results in "a V-type.

In the case of assembly with conventional construction units for example a unbestuecktes solder eyelet a circle results, for an equipped solder eyelet arises a "C"-form, there the construction unit a part of the soldering eye covered and as a result of vague reflection in the case of the picture recording appears dark for the examination of soldered SMDS in the main reflection directions of the soldered connections additional video cameras to this Relflexionsrichtungen adapted Zes-axis to the picture recording is also attached for. On the pictures, which produce these cameras, the unplumbed mating surfaces appear dark, if the reflection direction of the printed circuit board not with the Zes-axis of the video cameras Ubereinstim DE 40 14 149 AImen. The inclined surfaces of the soldered connections reflect against it under an angle to the printed circuit board, that with the oh directions of the cameras coincide with the cameras attached in these reflection directions the soldering surface are brightly taken up. Since the 5 construction units are usually perpendicular or horizontally arranged and on two pages soldering surfaces have, preferably four video cameras must be attached for this test.

In the following the invention becomes on the basis the Flg. 1 10 to 4 describes. Show: Fig. 1 schematic arrangement for the execution of the procedure, Flg. 2 positions of SMDS (Surface Mounted DEVICE), Flg. , Fig equips and unbestueckt 3 solder eyelets. 4 arrangement for the examination of soldered SMDS.

In Flg. 1 is on the printed circuit board 1 exemplarily a surface-mountable construction unit 2, that on the mating surfaces 3 and 3 sits over the printed circuit board is 20 a camera 4 attached, those with an image processing unit 8 according to Flg. 1 is connected and to be attached to the one monitor 7 can. The planar source of light 6 is appropriate behind a ground-glass plate 3 and sends its light by this ground-glass plate 5 25 on a halfpermeable mirror 9, which returns the planar and vague light on the printed circuit board 1 in this way the necessary shade-free lighting produced, whereby also a ring light, which is appropriate around the camera objective, is usable here of the silvery mating surfaces 3 and 3 a part by the SMD 2 covers the other one, visible part reflects the light of the lighting predominantly toward camera and thus by the video camera than bright surface taken up and if necessary on 35 for visual check indicated to the monitor 7. In addition will the picture taken up by the video camera to a picture signal processing unit given, in that the size and form of the visible mating surfaces (represented in the figure without shading) on the basis Refe 40 renzwerten is evaluated in the sequences à to 2d to become possible positions of SMDS regarding the mating surfaces represented sequence à points a construction unit 2 to target position. The parts of the mating surfaces 3 and 3 not covered by the construction unit have rectangular form and are equivalent large. In sequence 2b the construction unit 2 is shifted to the right, the surface of the not covered mating surfaces, taken up of the camera as bright surface, does not become larger. Also with the shifts in the sequences 2c and 2d, in in such a way those the construction unit 2 and/or rotated touched down is increased or becomes smaller at least with a mating surface 3 or 3 the visible part, D h, a false positioning is upward shifted is recognized if at least with one of the two on 55 conclusion surfaces of a SMDS the visible part become larger or reduced according to the same principle it can already with the unbestueckten printed circuit board is recognized whether parts of the mating surfaces are covered by a foreign body the evaluation effected via counting the M of bright pixels in the range of the construction unit, whereby reference values regarding position and size of the bright picture parts via evaluating an error free equipped or unbestueckten printed circuit board to be won or by the draft data for the printed circuit board be calculated. With 65 of more complex image processing the kind of the false positioning can be determined by additional evaluating of the form of the uncovered mating surfaces. So devoted to the right and/or on the left of shifted construction units, represented in sequence 2b, a "L"-form of the uncovered mating surfaces, rotated construction units, represented in sequence 2d, result in "a V-type. With upward and/or downward veschobenen construction units, represented in sequence, change aspect ratios of the visible rectangles of the mating surfaces 2c.

Flg. á an equipped shows and a unbestuecktes solder eyelet. In the case of the picture recording unbestueckte solder eyelet results 10 a bright circle, that in the case of equipped solder eyelet the 1t from the connecting piece 12 of a construction unit interrupted is the Anschlussst Uck 12 appears in accordance with sequence 3b darkly in the case of the picture recording, there the light in the case of the impact the connecting piece to all sides and only a small part toward the camera reflected we DIN Flg for. 4 is an arrangement represented with that the soldering surfaces by SMDS up-soldered on the mating surfaces to be examined can. The light breaks in essentially perpendicularly on the printed circuit board 1 from direction of the camera 4 and becomes from the soldered surfaces 20 and 20 toward the cameras 42 and/or. those reflects 43 with the camera 42 and/or with the pictures. 43 to be taken up, forms the soldering surfaces 20 to 20 bright strip, while they appear dark with admission with camera 4. On the other hand surfaces do not appear, those by bent soldering surfaces covered are bright with pictures of the camera 4 and with the cameras 42 and 43 take place darkly also here the evaluation with the help of the image processing unit by comparison with a reference or via visual check on the monitor or several monitors.

There construction units also opposite in Flg. 4 represented construction unit 2 around 90° around the axle camera construction unit turned its koennnen, must be attached also in these additional reflection directions two further cameras, in order to ensure a complete examination of the solder-flat.

In place of the four additional cameras additionally four flatful, arranged radiating sources of light can be laterally appropriate, so that the picture recording with only one camera is taken up effected whereby a picture with normal lighting from above and second with lighting with the additional sources of light. With the procedure according to invention and/or with the device according to invention both assembly control and soldered connection control can be accomplished. In addition not the procedure, but only the dissolution must be changed with progressive miniaturization of the construction units.