DE102013216196A1 - Detecting the 3D structure of a deposited on a component carrier depot of solder paste - Google Patents

Abstract

Disclosed is an image processing system (100) and a method for detecting the three-dimensional structure of at least one depot (190) made of solder paste, which is applied to a component carrier (180). The image processing system (100) comprises (a) an illumination arrangement (105, 305) with (a1) a first light source (110, 210) for illuminating the depot (190) by means of a first illumination light (110a) which is under a first oblique direction (a2) a second light source (120, 220) for illuminating the depot (190) by means of a second illumination light (120a), which under a second oblique direction on the surface of the device carrier (180) and (a3) a third light source (130, 330) for illuminating the depot (190) by means of a third illumination light (130a) which falls on the surface of the device carrier (180) under a third oblique direction. The image processing system (100) further comprises (b) a camera (150, 350) arranged and arranged for optically detecting the depot (190) of solder paste, (c) a control unit (162) arranged to control the illumination arrangement (105, 305) and the camera (150, 350) such that from the camera (150, 350) sequentially (c1) a first image of the depot (190) in the first illumination light (110a), (c2) a second image of the depot (c1) 190) in the second illumination light (120a) and (c3) a third image of the depot (190) in the third illumination light (130a) is taken, and (d) an evaluation unit (164), which the camera (150, 350) connected downstream and which is arranged to calculate the three-dimensional structure of the depot (190) based on intensity values of individual pixels in the first image, in the second image, and in the third image.

Description

Technical area

The present invention relates generally to the technical field of electronics manufacturing. More particularly, the present invention relates to an image processing system and method for detecting the three-dimensional structure of at least one solder paste depot deposited on a device carrier.

Background of the invention

To increase or to ensure process reliability in the production of electronic assemblies, it is necessary to visually inspect the solder paste applied to a printed circuit board or generally to a component carrier. Solder paste is usually transferred onto a printed circuit board by means of a so-called screen printer using a solder paste printing method. In such a solder paste transfer, a negative stencil is typically placed over the printed circuit board to be printed. This negative template has recesses at all points where the circuit board is to be printed with solder paste. The solder paste is then spread out by means of a so-called doctor blade and thus printed on the circuit board through the recesses in the negative template.

In order to detect process defects typical of such a solder paste printing process such as unwanted offset of the negative stencil to the printed circuit board or clogging of individual recesses, the inspection of the solder deposits thus deposited typically involves the following tasks: (a) measuring the position of the solder deposits applied to the printed circuit board; (b) checking the area to which the solder paste has been applied; (c) checking the height of the solder paste from which together with the area the volume of applied solder paste can be determined; and / or (d) detecting solder bridges between different ones Pads (so-called pads) on the circuit board.

In order to carry out the inspection tasks described above with sufficient accuracy, it is necessary to measure the depots of solder paste three-dimensionally (3D). Purely two-dimensional (2D) camera images contain too many interfering structures for a robust measurement of the solder paste depots or do not allow to obtain information about the solder paste height.

The result of a 3D measurement of the solder paste deposits is a so-called height map, which represents a so-called z-height (height of a surface element above the top of the printed circuit board) as a function of the so-called xy-position (position of the relevant surface element on the printed circuit board). On the basis of such a height map, the above-listed inspection tasks or checks can then be carried out in an evaluation unit.

Such a height map is typically determined by projecting a patterned light having a given intensity pattern (e.g., a stripe or wave pattern) onto the circuit board by detecting the light reflections of that pattern from the circuit board with a camera. The projection takes place here from "oblique" angle, i. inclined to the object plane. As a result, depending on the height of the surface element of the solder paste deposit on which surface element a part of the pattern falls, its phase shifts (phase-measuring triangulation method) or a specific interference pattern is generated (moiré projection method). These effects can be measured by repeated projection of mutually shifted patterns by means of a suitable image analysis and converted into corresponding height information. However, since the projection always takes place at an angle, this leads to unwanted asymmetries in the image evaluation, which are compensated by the fact that several projectors are used from different directions. As a result, however, the 3D measurement becomes very complicated both with regard to the execution of the corresponding optical measurements and with regard to the computing power required by an evaluation unit.

The invention is based on the object of simplifying detection of the three-dimensional structure of at least one depot made of solder paste, which is applied to a component carrier.

Summary of the invention

This object is solved by the subject matters of the independent claims. Advantageous embodiments of the present invention are described in the dependent claims.

According to a first aspect of the invention, an image processing system for detecting the three-dimensional structure of at least one depot of solder paste which is applied to a component carrier is described. The described image processing system comprises (a) an illumination arrangement with (a1) a first light source for illuminating the depot by means of a first illumination light which falls on a surface of the component carrier under a first oblique direction (a2) of a second light source for illuminating the depot and (a3) a third light source for illuminating the depot by means of a third illumination light incident on the surface of the device carrier under a third oblique direction, (b) a second illumination light incident on the surface of the device carrier under a second oblique direction; Camera, arranged and arranged for optically detecting the depot of solder paste, (c) a control unit, configured to control the illumination arrangement and the camera such that from the camera sequentially (c1) a first image of the depot at the first illumination light, (c2) a second picture of Dep ots in the second illumination light and (c3) a third image of the depot in the third illumination light is taken, and (d) an evaluation unit, which is connected downstream of the camera and which is arranged, the three-dimensional structure of the at least one depot based on intensity values of individual Calculate pixels in the first image, in the second image, and in the third image.

The image processing system described is based on the knowledge that the three-dimensional structure of the solder paste depot can be detected by using a single camera which optically detects at least one area of the component carrier with the solder paste depot to be measured (here also referred to as solder paste depot for short), if at least three different images of the solder paste depot are taken at different lighting. It is not necessary to illuminate the three-dimensional structure of the solder paste depot by means of so-called structured illuminations, which are distorted in a change in the altitude on the three-dimensional object to be measured (here the solder paste depot). Rather, in the method of the invention, only ordinary, i. spatially unstructured lighting is required, which illuminate the solder paste depot to be measured under different oblique illumination directions.

Illustratively, the brightness of a surface element of the solder paste deposit in each different image depends on the inclination of the surface element relative to the incident light. The steeper the illumination light concerned strikes the inclined surface element of the solder paste deposit, the brighter the surface element appears in the corresponding image. It is assumed that the camera detects essentially only diffuse light scattering, which occur at the respective surface element. A surface element will appear brightest when the illuminating light of the relevant image strikes the surface element at least approximately perpendicularly. Since each surface element in the different images was thus illuminated with a different illuminating light, a combination of the brightness values of a surface element on its inclination and by combining the inclination values of all surface elements on the 3D structure of the entire solder paste depot can be concluded. With knowledge of all inclinations of the surface elements then the three-dimensional structure of the solder paste depot can be calculated. The three-dimensional structure of the solder paste depot can be represented in particular in the form of a so-called elevation map and further processed as part of an automatic process control.

In this document, the term "illuminating light incident on the surface of the device carrier under an oblique direction" may mean, in particular, that the optical axis of the illuminating light is inclined with respect to the object plane. The surface of the component carrier coincides with the object plane. An oblique direction thus defines (a) an inclination angle of the optical axis of the corresponding illuminating light with respect to the surface of the device carrier, and (b) an azimuth angle between the optical axis of the corresponding illuminating light and a certain reference axis within the plane of the surface of the device carrier.

The term "component carrier" can be understood in this document to mean any type of substrate capable of mounting, in particular a printed circuit board. A component carrier can be rigid or flexible. A component carrier may also have both rigid and flexible areas. be understood.

The term "solder paste depot" in this document means any amount of solder paste that has been transferred to a connection pad of the component carrier as part of a component carrier printing process. After an assembly of the component carrier with electronic components, in which the components typically adhere to the solder paste with their connection elements, For example, the solder paste can be melted in a so-called reflow oven, in which the entire component carrier is placed together with the electronic components placed thereon. After a subsequent solidification of the solder paste, the electronic components are then firmly fixed to the component carrier taking into account a suitable contacting.

The term "intensity values" may in particular be values of gray scale, e.g. between 0 and 255, with low values for a low light intensity of the relevant pixel in the captured image, and higher values for a higher light intensity of the relevant pixel in the captured image.

A light source usable for the described image processing system may be any type of light emitting element emitting the respective illumination light. The light-emitting surface is preferably as small as possible, so that the surface area from which the respective illumination light is emitted, is as small as possible and thus the computational effort remains manageable, which must be made by the evaluation unit for the calculation of the three-dimensional structure of at least one Lotpastendepots. When using point light sources, the computational effort is minimal. It should be noted, however, that in practice the required calculations are usually always simplified and assume a point source. However, if the light is actually emitted by a spatially extended light source and the light incident on the solder paste deposit therefore covers a certain angular range, then the used calculation model no longer completely corresponds to reality and inaccuracies / deviations in the calculated height map can occur

In this connection, it is pointed out that, for example, when accepting a somewhat increased amount of computation, the image processing system described in this document can be realized with a known, already existing illumination arrangement which has an object to be measured (for example, a mark to be measured of a component carrier to be populated in a placement machine). obliquely illuminated at different illumination angles medium flat light sources. In order to avoid a costly conversion of the lighting arrangement, in many applications, the increased computational complexity associated with planar light sources or the inaccuracies / deviations associated with a planar light source can be accepted. As a rule, the inaccuracies / deviations are more likely to be accepted. This applies in particular because investigations have shown that the method carried out with the image processing system described here leads to extremely stable and robust results even with spatially extended light sources.

According to an embodiment of the invention, a first optical axis of the first illumination light, a second optical axis of the second illumination light, and a third optical axis of the third illumination light have at least approximately the same inclination angle with respect to the surface of the device carrier and have reference to a reference axis within the first Surface of the component carrier each have a different azimuth angle.

To put it clearly, this means that the different illuminations illuminate the solder paste depot to be measured at the same inclination angle, but from different directions (with different azimuth angles).

According to a further embodiment of the invention, the same inclination angle is at least approximately 45 °. With such a lighting structure, in practice, a good compromise can be achieved between the accuracy of the calculated height values and the problems which arise from shadowing effects.

The use of a uniform inclination angle of 45 ° has the advantage that with the described image processing system, a particularly high accuracy and a particularly high reliability in the three-dimensional measurement of the solder paste depot can be achieved.

According to a further embodiment of the invention, the image processing system has a central optical axis which coincides with an optical axis of the camera and an optical axis of the illumination arrangement.

This means that a sensor chip of the camera, possibly taking into account a beam deflection, lies on the optical axis of the illumination arrangement.

In particular, the optical axis of the illumination arrangement can represent an axis of symmetry of the illumination arrangement around which the various light sources are arranged. The spatial center of the area on the component carrier within which the solder paste deposit or a plurality of solder paste depots is detected three-dimensionally preferably coincides with the optical axis of the illumination arrangement and thus also with the optical axis of the camera as well as with the central optical axis the entire image processing system together.

A collapse of the various optical axes, i. the optical axis of the camera and the optical axis of the illumination arrangement to the central optical axis of the entire image processing system has the advantage that the computational effort required in the evaluation unit to calculate the three-dimensional structure of the solder paste deposit and the plurality of solder paste depots are minimized can be tolerated without sacrificing the accuracy of the three-dimensional measurement of Lotpastendepots or the plurality of Lotpastendepots.

Preferably, the camera is located, which sequentially under different illuminations to be measured solder paste depot or to be measured Lotpastendepots optically, with respect to the surface of the device carrier above the solder paste deposit to be measured or above the measured Lotpastendepots. In terms of clarity, the camera looks vertically from above onto the area of the component carrier to be measured.

According to a further exemplary embodiment of the invention, the light sources are distributed at least approximately uniformly around the central optical axis of the image processing system. This has the advantage that the at least one solder paste depot, which is to be measured three-dimensionally, is uniformly illuminated by different directions (each with a different azimuth angle).

Specifically, the light sources may be distributed around the central optical axis of the image processing system such that a difference between the azimuth angles of the optical axes of two light sources adjacent to each other is at least approximately equal.

According to a further exemplary embodiment of the invention, the first light source, the second light source and / or the third light source are respectively realized by means of an optical output of an optical waveguide which is optically coupled on the input side to one or more primary light sources.

By means of the described optical waveguide, the illumination light emitted by the respective primary light source can be forwarded to the point from which the relevant area of the component carrier is illuminated. Thus, e.g. one, several or preferably all used primary light sources on a common printed circuit board and thus be arranged within a common plane. It is therefore advantageously not necessary to lay electrical lines, via which the light sources are operated, outside the common printed circuit board.

The optical waveguide can be a plastic component into which light is coupled at an optical input side and the respective illumination light is emitted from an optical output side.

According to a further exemplary embodiment of the invention, the first light source, the second light source and / or the third light source each have at least one light-emitting diode. This has the advantage that the lighting arrangement can be realized with durable, low power consuming and inexpensive optical components.

According to a further exemplary embodiment of the invention, the first illumination light, the second illumination light and the third illumination light have at least approximately the same optical spectral distribution. This has the advantage that the (diffuse) light scattering that occurs at each surface element of the solder paste deposit and that are detected by the camera are basically at least approximately the same for all illuminating light, so that their intensity depends only on the orientation or the inclination of the corresponding Surface pixels depends. A spectral dependence of the light scattering therefore need not be taken into account. This also contributes to the fact that the computational effort, which is necessary for calculating the three-dimensional structure of the at least one solder paste deposit, remains manageable.

The illumination spectrum which is at least approximately the same for all light sources is preferably a monochromatic spectrum, which is emitted in particular by a light-emitting diode, for example by a light-emitting diode emitting in the blue spectral range.

According to a further exemplary embodiment of the invention, the illumination arrangement furthermore has a fourth light source for illuminating the depot by means of a fourth illumination light which falls onto the surface of the component carrier at a fourth oblique angle. The control unit is further configured to control the illumination arrangement and the camera such that a fourth image of the depot is taken by the camera in the fourth illumination light. Moreover, the evaluation unit is further configured to further calculate the three-dimensional structure of the depot based on intensity values of individual pixels in the fourth image. This has the advantage that the detection of the three-dimensional structure of the solder paste depot can be carried out with a particularly high accuracy. In particular, with the aid of the redundant information resulting from the fourth lighting level, disturbances due to any directly reflecting reflections can be effectively suppressed.

It should be noted that the number of different images whose pixel intensity values are used for calculating the three-dimensional structure of the solder paste deposit is not limited. In general, the larger the number of different images used, the higher the accuracy of the three-dimensional texture measurement will be. However, the time required by the described method and, in particular, the computational effort required to calculate the three-dimensional structure of the solder paste deposit becomes higher as the number of images used increases.

It is further noted that the fourth light source may be formed in a similar manner as the first, the second and / or the third light source, as described above. This also applies to the angle of inclination, which includes a fourth optical axis of the fourth illumination light with the surface of the device carrier and for the arrangement of the fourth light source relative to the central optical axis.

According to a further aspect of the invention, a method is described for detecting the three-dimensional structure of at least one depot made of solder paste, which is applied to a component carrier. The method described comprises (a) illuminating the depot by means of a first illumination light which falls on a surface of the component carrier under a first oblique direction, (b) taking a first image of the depot by means of a camera in the first illumination light (c ) illuminating the depot by means of a second illuminating light incident on the surface of the component carrier under a second oblique direction, (d) taking a second depot image by means of the camera in the second illuminating light, (e) illuminating the depot by means of a third illumination light falling on the surface of the device carrier under a third oblique direction, (f) taking a third image of the depot by the camera in the third illumination light, and (g) calculating the three-dimensional structure of the at least one depot based on intensity values of individual pixels in de m first image, in the second image and in the third image.

The described method is also based on the knowledge that the three-dimensional structure of the at least one solder paste deposit can be calculated by a combined image evaluation of at least three different images of the at least one solder paste deposit taken by one and the same camera under different illumination conditions. In this case, based on the intensity values or based on the brightness of individual pixels in the different images, the inclinations of the corresponding surface elements are determined with respect to the respective illumination direction. With a knowledge of the inclinations of all surface elements can then be calculated by a suitable three-dimensional composition of all surface elements, the entire spatial structure of each Lotpastendepots.

According to a further aspect of the invention, a computer program for detecting the three-dimensional structure of at least one depot made of solder paste, which is applied to a component carrier, is described. The computer program, when executed by a processor, is configured to perform the method described above.

For the purposes of this document, the mention of such a computer program is synonymous with the notion of a program element, a computer program product and / or a computer-readable medium containing instructions for controlling a computer system, the operation of a system or a method suitably coordinated in order to achieve the effects associated with the method according to the invention.

The computer program may be implemented as a computer-readable instruction code in any suitable programming language such as JAVA, C ++, etc. The computer program can be stored on a computer-readable storage medium (CD-ROM, DVD, Blue-ray disk, removable drive, volatile or non-volatile memory, built-in memory / processor, etc.). The instruction code may program a computer or other programmable device, such as a slot controller, to perform the desired functions. Further, the computer program may be provided in a network, such as the Internet, from where it may be downloaded by a user as needed.

The invention can be implemented both by means of a computer program, i. software, as well as by means of one or more special electronic circuits, i. in hardware or in any hybrid form, i. using software components and hardware components.

It should be noted that embodiments of the invention have been described with reference to different subject matters. In particular, some embodiments of the invention are described with apparatus claims and other embodiments of the invention with method claims. However, it will be readily apparent to those skilled in the art upon reading this application that, unless explicitly stated otherwise, in addition to a combination of features belonging to a type of subject matter, any combination of features that may result in different types of features is also possible Subject matters belong.

Further advantages and features of the present invention will become apparent from the following exemplary description of presently preferred embodiments.

Short description of the drawing

1 shows in a schematic representation of the basic structure of an image processing system for detecting the three-dimensional structure of at least one depot of solder paste, which is applied to a component carrier.

2a to 2c illustrate the process of calculating a height map of a plurality of solder paste depots on the basis of an image analysis of three gray level images taken at different illuminations.

3 shows the structure of a so-called printed circuit board vision system for placement machines, which can be used without a modification of optical or mechanical components for performing the method described in this document for detecting the three-dimensional structure of at least one depot of solder paste.

4a and 4b show a section of a solder paste printed circuit board and calculated using the method described here height map.

Detailed description

It should be noted that features of different embodiments, which are the same or at least functionally identical to the corresponding features or components of the embodiment, are provided with a reference numeral, which is different from the reference character of the same or at least functionally identical features or Components only in the first digit differs. In order to avoid unnecessary repetitions, features or components already explained on the basis of a previously described embodiment will not be explained in detail later.

It should also be noted that the embodiments described below represent only a limited selection of possible embodiments of the invention. In particular, it is possible to suitably combine the features of individual embodiments with one another, so that a multiplicity of different embodiments are to be regarded as obviously disclosed to the person skilled in the art with the embodiment variants explicitly illustrated here.

1 shows a schematic representation of the basic structure of an image processing system 100 with which the three-dimensional structure of at least one depot 190 From solder paste can be detected, which Lotpastendepot 190 on a circuit board 180 has been applied. The image processing system 100 has a lighting arrangement 105 on, which in turn is a first light source 110 , a second light source 120 and a third light source 130 includes. The light sources 110 . 120 . 130 light the solder paste depot 190 from above at different oblique angles. The corresponding light beams of the respective illumination light or their optical axes are denoted by the reference numerals 110a . 120a respectively. 130a characterized.

The image processing system 100 also has a camera 150 on which above the solder paste deposit to be measured 190 on a central optical axis 102 is arranged. The central optical axis 102 coincides with the optical axis of the camera 150 , which thus perpendicular to the top of the circuit board 180 looks, and with the optical axis of the lighting arrangement 105 together.

In addition, the image processing system has 100 a data processing unit 160 on which a control unit 162 and an evaluation unit 164 includes. The control unit 162 is with the camera 150 and dashed lines shown connecting lines with the light sources 110 . 120 and 130 connected. The control unit 162 controls the camera 150 and the light sources 110 . 120 and 130 so that, sequentially, a first image of the solder paste deposit 190 at the first illumination light 110a , a second picture of the Lotpastendepot 190 in the second illumination light 120a and a third picture of the solder paste depot 190 at the third illumination light 130a is recorded. The evaluation unit 164 is set up, the three-dimensional structure of the solder paste depot 190 based on intensity values of individual pixels in the first image, in the second image, and in the third image.

According to the embodiment shown here have a first optical axis 110a of the first illumination light, a second optical axis 120a of the second illumination light and a third optical axis 130a of the third illumination light with respect to a surface normal of the printed circuit board 180 or with respect to the central optical axis 102 the same inclination angle α. With respect to a reference axis within the surface of the circuit board 180 have the optical axis 110a . 120a . 130a each a different azimuth angle, the light sources 110 . 120 . 130 evenly around the central optical axis 102 of the image processing system 100 are arranged distributed around.

Clearly disengaged with the image processing system 100 calculates a height map of the solder paste deposits to be measured by that of the printed circuit board 180 or from the relevant section of the circuit board 180 multiple camera images are recorded, each camera image is taken with a made of different directions lighting. For each pixel of the camera images are now dependent on the number of light sources used 110 . 120 . 130 several (here three) intensity or gray values available, one value per light source. From these intensity values, it is now possible to determine the inclination (in both the x and y directions) of that surface element of the solder paste deposit relative to the optical axis 102 the camera, which is shown in the respective pixel. From the two inclinations (in the x and in the y direction), you can calculate the elevation map you are looking for.

2a to 2c illustrate a three-step process of calculating a height map of a plurality of solder paste depots on the basis of an image analysis of three gray scale images recorded under different illuminations. It is therefore a stereo process, but the images are not recorded as in the "classic" stereo of different, positioned at different locations cameras. Rather, the images are taken by a single camera in different lighting.

In 2a It is shown how an intensity vector is determined for each pixel based on the respective intensity values in the (here three) images. The three pictures in 2a are shown diagonally one behind the other, each schematically show an intensity distribution, which results in one of the three lights. From these intensity vectors whose dimension is determined by the number (here three) of the different light sources, a tilt map is calculated, in which each surface element, which is determined by its xy position on the printed circuit board, has two inclinations, an inclination p (x, y) along the x-direction and an inclination q (x, y) along the y-direction. 2 B shows above a tilt map in which the slopes p (x, y) are plotted along the x direction. 2 B below shows a slope chart in which the slopes q (x, y) are plotted along the y direction. Also the two in 2 B Tilt maps shown are intensity distributions. The brightness of each pixel is a direct measure of the strength of the slopes p (x, y) and q (x, y), respectively.

The two tilt maps p (x, y) and q (x, y) can be calculated based on the following physical considerations: The light intensity I _C observed by the camera is given by the following equation: I _C = I ₀ · ρ · cos (σ)

In this case, I _{0 is} the illuminance of the light emitted by the relevant light source, ρ is the albedo (the retroreflectivity of the respective optically scattering surface element) and σ is the angle between the illumination direction s and the normal n of the considered surface element (cos (σ) = s · n ). The target for the calculation of the inclination maps is the vector n. In this case, ρ, I ₀ and n are first combined into a vector n 'and cos (σ) is written as the scalar product s · n. The result is the following equation:

In matrix notation, the above equation yields the following linear equation system:

The solution of this linear system of equations and a subsequent normalization yields, as described in the following equations, the desired inclination n for each surface element.

It should be noted that in the event that four different light sources are used, and thus a total of four intensity values are recorded for each pixel, it can be determined separately for each pixel in a preliminary step with which three values the system of equations is set up and solved.

Based on the two in 2 B shown tilt maps p (x, y) and q (x, y) is then determined in a third step, a height map, which in 2c is shown in perspective.

The height map may be calculated based on a knowledge of the slope maps p (x, y) and q (x, y) by taking into account that p (x, y) and q (x, y) are from the partial derivative the height Z (x, y) to x (dZ / dx) or the partial derivative of the height Z (x, y) to y (dZ / dy). From this consideration the following differential equation for the error function J for the height map Z (x, y) results: J [Z (x, y)] = ∫∫ (∂Z / ∂x - p) ² + (∂Z / ∂y - q) ² dxddy

The error functional J describes the deviations of the derivatives of the calculated height map Z (x, y) to the observed tilt maps p (x, y) and q (x, y).

A minimization of this error function J [Z (x, y)] on the basis of the method of least squares is equivalent to a solution of the so-called Poisson equation ∇ ² Z (x, y) = div (p, q). That's it searched Z (x, y) the argument of the error function J, which argument minimizes the error function. The Poisson equation can be solved numerically in a known way.

The method described in this document for detecting the three-dimensional structure of at least one solder paste depot can be realized using an already known vision system, which is used, for example, in SIPLACE ^™ assembly machines from ASM for measuring printed circuit board markings. Such a vision system 303 is in 3 shown in an exploded view. It may be used without a modification of optical or mechanical components for carrying out the method described in this document for detecting the three-dimensional structure of at least one depot of solder paste. It is only necessary to have an in 1 to use the illustrated control unit, which controls the various light sources and the camera in a suitable manner. Furthermore, an in 3 not shown, so that the three-dimensional structure of the solder paste depots can be calculated based on intensity values of individual pixels in the different recorded images.

How out 3 apparent, the vision system points 303 as chassis a mounting plate 304 on, on which a camera 350 with an object lens 352 is appropriate. On the mounting plate 304 is also a lighting arrangement 305 attached, which is a printed circuit board 308 having. On the printed circuit board 308 a plurality of light emitting diodes is mounted, which allow to illuminate an object to be detected at different angles and possibly also with different colored light. For the detection of the three-dimensional structure of solder paste depots described in this document, however, only a few of the light-emitting diodes are required. These required light-emitting diodes, which are referred to in this document as primary light sources are denoted by the reference numerals 312 . 322 and 342 Mistake.

According to the embodiment described here, a total of four different light sources 310 . 320 . 330 . 340 provided, each with an optical waveguide 314 . 324 . 334 and 344 are realized. The optical output of the respective optical waveguide 314 . 324 . 334 and 344 , which output is realized in each case by the inwardly directed curved surface, then the light emitting surface of the respective light source 310 . 320 . 330 . 340 One in the direction of the printed circuit board 308 directed optical input of the optical fibers 314 . 324 . 334 and 344 is with the respective primary light sources 312 . 322 , respectively. 342 and another in 3 not shown primary light source optically coupled. In the perspective view of 3 are the the optical fiber 334 associated primary light sources can not be detected.

According to the embodiment shown here emit the primary light sources 312 . 322 . 342 and the more in 3 not shown primary light source, each one an optical waveguide 314 . 324 . 334 . 344 or a lighting sector are assigned, blue light. Of course, other spectral colors are possible.

• (A) Positionieren eines Portalsystems mit dem Vision System 303 so, dass sich die Kamera 350 über dem auszuwertenden Bereich der Leiterplatte mit den Lotpastendepots befindet.
• (B) Sequentielles Aufnehmen von vier Bildern, wobei für jedes Bild ein anderer Beleuchtungssektor eingeschaltet wird.
• (C) Berechnen der Höhenkarte aus den Intensitätswerten von diesen vier Bildern.
• (D) Durchführen diverser Inspektionsaufgaben auf Basis dieser berechneten Höhenkarte.

For detecting the three-dimensional structure of at least one solder paste depot, the following measuring sequence can then be used:

• (A) Positioning a portal system with the vision system 303 so that the camera 350 located above the evaluated area of the circuit board with the Lotpastendepots.
• (B) Sequentially taking four pictures, turning on a different lighting sector for each picture.
• (C) Calculate the height map from the intensity values of these four images.
• (D) performing various inspection tasks based on this calculated altitude map.

The 4a shows a section of a solder paste printed circuit board. 4b shows the altitude map calculated using the method described here.

Another possible application of the image processing system described in this document is to perform 2D position measurements based on the height map, e.g. to better recognize position markers located on the PCB. For example, the appearance of a structure in the brightness image may be so disturbed that a robust position measurement in the brightness image is not possible, but in a height map calculated using the method described here, since the structure is e.g. significantly higher than their environment is.

The image processing system described in this document and the corresponding method for detecting the three-dimensional structure of solder paste depots have the following advantages, among others:
Low complexity: All you need is an industrial camera and suitable lighting. In comparison to known moiré methods, no projectors are required (there are typically 2 to 4 projectors for producing the pattern in use, with which the evaluation area is exposed). Thus, no adjustment between projectors and camera is required.

Low Development Effort: The development effort to implement a way to three-dimensionally capture solder paste deposits in a placement machine is also substantially less than for the development of a vision system based on the moiré method, since the image processing system described here is much simpler.

Cost: Since a standard camera can be used for the image processing system described here, the hardware cost is only a fraction of the estimated cost of a moiré projection image processing system.

Space requirements: A standard camera including lighting requires only a fraction of the installation space, which would require a vision system with additional projector (s). Thus, with the method described here, a solder paste inspection can be integrated into existing placement machines, without having to limit other functionalities. There is no need for a separate external inspection machine or separate portal system.

The use of the method described here is especially suitable for SIPLACE ^™ SMT placement machines because the existing hardware (printed circuit board camera) can also be used for this measurement task. Only the control of the different lighting or lighting sectors must be modified. Thus, the hardware development effort is very small and there is no additional space required. Thus, no separate portal system for the solder paste inspection must be used or "sacrificed".

The method described here can also be carried out in an advantageous manner in a so-called printed circuit board printer in which solder paste is transferred through a printing stencil to a printed circuit board in a known manner. It can therefore be checked immediately after the application of solder paste on a circuit board, whether the solder paste deposits produced in the printed circuit board printer on pads of the circuit board have a desired volume. If this is not the case, then the relevant printed circuit board can be discarded as scrap and, if necessary, the print parameters for the printed circuit board printer can be changed.

LIST OF REFERENCE NUMBERS

100

 Image processing system

102

 central optical axis / optical axis of the camera / optical axis of the illumination arrangement

105

 lighting arrangement

110

 first light source

110a

 first illumination light / first optical axis

120

 second light source

120a

 second illumination light / second optical axis

130

 third light source

130a

 third illumination light / third optical axis

150

 camera

160

 Data processing unit

162

 control unit

164

 evaluation

180

 Component carrier / circuit board

190

 solder paste

303

 Vision system

304

 mounting plate

305

 lighting arrangement

308

 printed circuit board

310

 first light source

312

 first light emitting diodes / primary light sources

314

 first optical fiber

320

 second light source

322

 second light emitting diodes / primary light sources

324

 second optical fiber

330

 third light source

334

 third optical fiber

340

 fourth light source

342

 fourth light-emitting diodes / primary light sources

344

 fourth optical fiber

350

 camera

352

 objective lens

Claims (11)

Image processing system for detecting the three-dimensional structure of at least one depot ( 190 ) made of solder paste, which on a component carrier ( 180 ), the image processing system ( 100 ) comprising a lighting arrangement ( 105 . 305 ) with - a first light source ( 110 . 310 ) to illuminate the depot ( 190 ) by means of a first illumination light ( 110a ), which under a first oblique direction on a surface of the component carrier ( 180 ), - a second light source ( 120 . 320 ) to illuminate the depot ( 190 ) by means of a second illumination light ( 120a ), which under a second oblique direction on the surface of the component carrier ( 180 ), and - a third light source ( 130 . 330 ) to illuminate the depot ( 190 ) by means of a third illumination light ( 130a ), which under a third oblique direction on the surface of the component carrier ( 180 ), a camera ( 150 . 350 ), and arranged for optically detecting the depot ( 190 ) made of solder paste, a control unit ( 162 ) arranged to control the lighting arrangement ( 105 . 305 ) and the camera ( 150 . 350 ) such that from the camera ( 150 . 350 ) sequential - a first picture of the depot ( 190 ) at the first illumination light ( 110a ), - a second picture of the depot ( 190 ) in the second illumination light ( 120a ) and - a third picture of the depot ( 190 ) at the third illumination light ( 130a ), and an evaluation unit ( 164 ) which of the camera ( 150 . 350 ) and which is set up, the three-dimensional structure of the at least one depot ( 190 ) based on intensity values of individual pixels in the first image, in the second image, and in the third image. An image processing system according to the preceding claim 1, wherein a first optical axis ( 110a ) of the first illumination light, a second optical axis ( 120a ) of the second illumination light and a third optical axis ( 130a ) of the third illumination light with respect to the surface of the device carrier ( 180 ) have at least approximately the same angle of inclination and with respect to a reference axis within the surface of the component carrier ( 180 ) each have a different azimuth angle.  An image processing system according to the preceding claim 2, wherein the same inclination angle is at least approximately 45 °. Image processing system according to one of the preceding claims 1 to 3, wherein the image processing system ( 100 ) a central optical axis ( 102 ), which with an optical axis of the camera ( 150 . 350 ) and an optical axis of the illumination arrangement ( 105 . 305 ) coincides. Image processing system according to the preceding claim 4, wherein the light sources ( 110 . 310 . 120 . 320 . 130 . 330 ) at least approximately uniformly about the central optical axis ( 102 ) of the image processing system ( 100 ) are distributed around. Image processing system according to one of the preceding claims 1 to 5, wherein the first light source ( 310 ), the second light source ( 320 ) and / or the third light source ( 330 ) each by means of an optical output of an optical waveguide ( 314 . 324 . 334 ) is realized, which input side with one or more primary light sources ( 312 . 322 ) is optically coupled. Image processing system according to one of the preceding claims 1 to 6, wherein the first light source ( 110 . 310 ), the second light source ( 120 . 320 ) and / or the third light source ( 130 . 330 ) each at least one light emitting diode ( 312 . 322 ) exhibit. Image processing system according to one of the preceding claims 1 to 7, wherein the first illumination light ( 110a ), the second illumination light ( 120a ) and the third illumination light ( 130a ) have at least approximately the same optical spectral distribution. Image processing system according to one of the preceding claims 1 to 8, wherein the illumination arrangement ( 305 ) - a fourth light source ( 340 ) to illuminate the depot ( 190 ) by means of a fourth illumination light, which at a fourth oblique angle to the surface of the component carrier ( 180 ), the control unit ( 162 ) is further arranged, the lighting arrangement ( 305 ) and the camera ( 350 ) in such a way that from the camera ( 350 ) - a fourth picture of the depot ( 190 ) is received at the fourth illumination light, and wherein the evaluation unit ( 164 ), the three-dimensional structure of the depot ( 190 ) further based on intensity values of individual pixels in the fourth image. Method for detecting the three-dimensional structure of at least one depot ( 190 ) made of solder paste, which on a component carrier ( 180 ), the method comprising illuminating the depot ( 190 ) by means of a first illumination light ( 110a ), which under a first oblique direction on a surface of the component carrier ( 180 ), taking a first image of the depot ( 190 ) by means of a camera ( 150 . 350 ) at the first illumination light ( 110a ), Lighting the depot ( 190 ) by means of a second illumination light ( 120a ), which under a second oblique direction on the surface of the component carrier ( 190 ), taking a second picture of the depot ( 190 ) by means of the camera ( 150 . 350 ) in the second illumination light ( 120a ), Lighting the depot ( 190 ) by means of a third illumination light ( 130a ), which under a third oblique direction on the surface of the component carrier ( 180 ), taking a third picture of the depot ( 190 ) by means of the camera ( 150 . 350 ) at the third illumination light ( 130a ), and calculating the three-dimensional structure of the at least one depot ( 190 ) based on intensity values of individual pixels in the first image, in the second image, and in the third image. Computer program for capturing the three-dimensional structure of at least one depot ( 190 ) made of solder paste, which on a component carrier ( 180 ), wherein the computer program, when executed by a processor, is adapted to perform the method of claim 10.

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