EP2702558A1

EP2702558A1 - Method and device for inspecting printed circuit boards

Info

Publication number: EP2702558A1
Application number: EP12722678.5A
Authority: EP
Inventors: Roman Franz Wieser
Original assignee: WITRINS sro
Current assignee: WITRINS sro
Priority date: 2011-04-27
Filing date: 2012-04-24
Publication date: 2014-03-05
Also published as: DE102011018823A1; WO2012146370A1

Abstract

The invention relates to an inspection device (10) and an inspection method for a defect analysis of printed circuit boards (PCBs) (14), comprising a translucent/light-conducting substrate (12) and at least one, in particular a plurality of layers (16) stacked one top of another. The device comprises at least one optical detecting means (24), a defect detecting means (30), and a layer printing means (20). The optical detecting means (24) is configured to record a first and/or second optical image B1, B2 of the layer (12) prior to and/or after a printing of a layer (12) of the PCB (14) by the printing means (20), wherein the defect detecting means (30) is configured to determine a difference image ΔB from the two images B1, B2 so that the difference image substantially corresponds to the print image of the layer (12), and can be analyzed for print defects. By means of the inspection device, PCBs, which are in particular translucent and have multiple layers, can be optically analyzed for manufacturing defects during the printing process with great precision and high speed and at low cost.

Description

description

METHOD AND DEVICE FOR INSPECTION OF PRINTED

CIRCUITS

State of the art

The invention is based on an inspection printing device and an inspection method for error analysis of printed PCBs (Printed

Circuit board - printed circuit board), which e e a translucent and / or li chtleitendes substrate and at least one, in particular a plurality of layered layers has. The device comprises at least one optical detection device, an error detection device and a layer printing device.

Generic printing devices are known in the field of thin or thick-film technology, in which usually ceramic substrates which are transparent or light-emitting, are used as basis for a single- or multilayered PCB. As carrier material, for a LTCC printing technique (LTCC = Low Temperature Cofired Ceramics) or HTCC printing technology (HTCC = High Temperature Cofired Ceramics) in many cases keramic substrates, z. B. Alumina ceramic substrates or ceramic foils. Printed circuit traces are generally applied to the substrate by means of a screen printing process by means of a printing process, it being possible to apply a plurality of layer planes separately by insulating layers. It can be manufactured electrical resistances, which can be adjusted for example by a laser trimming. Even capacitors of small capacity can be produced printable. The thus printed substrates are fired (fired), wherein the printed paste mixtures for resistors, insulation or printed conductors are fused to resistant and reliably conductive layers. As a matter of course, a thick-film circuit can be equipped with active components, such as capacitors, ICs or inductors, which can be connected to the printed circuit traces by means of reflow soldering or bonding.

Unlike conventional SMD technology, such thick film circuit boards can withstand higher thermal loads, higher ambient temperatures, and other extreme environmental conditions, such as vacuum. They are usually used where high reliability is required and adverse environmental conditions are expected.

As part of an LTCC printing technique, multi-layer circuits based on a sintered ceramic carrier can be produced, whereby printed conductors, capacitors, resistors and coils can be produced by printing technology. The elements are applied by screen printing or photochemical processes. The green ceramic substrates may be individually patterned and then stacked and laminated, after which they are fired by means of a defined sintering profile having a peak temperature of about 800 ° C to 900 ° C. A ceramic composition is provided with plasticizers for lamination under temperature and pressure and solvent, the thickness of which may be four to twelve mils (milli-inches). For inner layers, tracks and vias silver, silver adium or gold pastes are used, which are directly on a ceramic substrate or. imprinted on a ceramic sheet, and can shrink in almost the same way as the ceramic layer, so that hardly form stress cracks under thermal loads .. The outer layers can be separately burned (post-fired) to ensure extreme accuracy of fit for automatic assembly. Through holes (vias) can be punched or attached with a laser. Subsequently, the vias can be filled with a conductive paste. After drying, the printed conductors can be printed and the individual layers are aligned and stacked in a mold so that a multilayered PCB can be produced. The individual ceramic films can be laminated under heat and pressure, wherein a separation is carried out within half a second for two hours at 300 ° C to 400 ° C in a convection oven, wherein 85% of the ceramic B parts are burned out. In contrast, HTCC PCBs are usually sintered at 1600 ° C to 1800 ° C, with tungsten or molybdenum having relatively poor electrical conductivity properties being commonly used as conductor materials. Galvanic nickel plating or gilding is necessary after sintering to obtain solderable or bondable layers.

Based on this state of the art, the problem arises, in particular with multilayer PCBs, of guaranteeing seamless error control of each individual PCB layer in subsequent printing steps. Each individual printing step and therefore each layer has manufacturing and raw material tolerances, which must be individually checked for a 1 00% production control and possibly logged. The layer layers have different reflection parameters than an optical inspection method. In the case of several layers printed on top of each other, it is only possible with great effort to determine the position and tolerance of each individual layer layer on the basis of a reflection-based optical inspection method. For this reason, the previously known optical inspection methods often generate a series of pseudo errors.

For this purpose, it is known to recognize extraneous pseudo errors in the context of a complex analysis by means of an image processing method. This makes the inspection process expensive and slow, so that, especially in the case of mass production, the throughput of manufacturable PCBs of sufficiently high quality is subject to narrow limits. Due to the varying and different optical material properties, inspection is used. Part of the test light is partially reflected and partially guided in the light-conducting or semi-transparent material or thrown back in the lower layers. Partially absorbed light generates "negative" shadow impressions, so that, for example, when a second layer is applied, shadowing is caused by the first layer, and this undesired shadowing can be eliminated by additional image-analyzing calculations and corrections, with additional process time; Since the paste printing process is a serial process, one layer at a time is usually printed, and due to quality requirements, a 100% inspection of the production is required, requiring a high error detection rate. The currently achievable structure resolutions, which are decisive for the detection of printing errors, are in the range of 10 μηι, whereby a resolution accuracy of 5 μηι should be achieved in the near future, but this means an increase in the error detection Complexity by a factor of four compared to the previously used error detection method, the detection effort and the analysis time increase very strong, and the required accuracy can hardly be achieved.

JP 100 65 345 A discloses a method for producing multilayered ceramic-based PCBs, in which each individual layer is subjected to an optical inspection method after production. Thereafter, the layers are aligned and laminated against each other. Thus, each individual layer is inspected prior to assembly and alignment of the PCB, but no further inspection is performed after lamination. Therefore, no inspection of the entire multilayer PCBs is carried out in each case after application and printing of a further layer layer, so that, for example, the mutual orientation of the individual layers can not be checked, and alignment errors can not be detected. Since the PCB layers are light transparent, So far, it has been difficult or even impossible to post-assemble the individual layers to form a bearable PCB due to the fact that they are projected. The method proposed in this document can not be provided seamlessly in the flow production of the printing of each layer, as is possible in the present invention.

Both US 2006/002510 A1 and US 2006/001853 A1 show both inspection devices for mounting and soldering components on a PCB, instead of producing a multilayer PCB. Differential images of the bare PCBS and of the solder-wetted PCBS and of the populated PCBs before and after soldering are recorded by X-ray irradiation. An inspection of individual layer layers in the production of an optically transparent multilayer PCB is not addressed. These references relate to manufacturing steps in the assembly of an already produced single-layer or multi-layer PCB, but not to a production of a semitransparent multi-layer PCB to Si.

Based on the above-mentioned prior art, it is an object of the invention to propose an inspection pressure device inspection device and an inspection method which enables improved detection of errors with a high detection speed, so that multilayered PCBs of improved quality can be provided at low cost. Such a device and method are proposed according to the teaching of the independent claims. Disclosure of the invention

To overcome the above-mentioned problems of the prior art, the invention proposes an inspection printing device which allows error analysis of printed PCBs comprising a light-transmitting / light-conducting substrate and at least one, in particular more, stacked layers. The device comprises at least one optical detection device, an error detection device and a layer printing device. The optical detection device is set up before and / or after printing a layer of the PCB by means of the printing device to detect a first and / or second optical image B1 or B2 after printing the layer, wherein the error detection device is set up, a differential image ΔΒ be determined from the two images B l, B2, so that the di fferenzbild ΔΒ essentially the print image of the layer corresponds, and can be analyzed for printing errors. Thus, an image acquisition system, ie an optical detection device, is proposed which prepares an optical image B1, B2 of the PCB before and / or after a paste application process by the printing device. The two images B 1, B 2 can be recorded before and after printing the layer, but it is also conceivable that one of the two images B 1, B 2 is pre-stored, for example, as a reference image or optimal image, and only the other image in each case taken up by the PCB being produced. Thus, it is not necessarily two images aufgenomm en, are, it can also be used on a reference image and thus only an image can be recorded. By an error detection device a difference image ΔΒ from the two images B l, B2 is determined so that optical S chattings of the previously applied layer can be excluded. Thus, the apparatus can provide a difference image representing only an image of the uppermost layer layer and which can be examined for printing errors. Due to the incremental determination of the difference image, influences of underlying layers or structuring properties of the light-transmitting / light-conducting substrate can be eliminated. The difference image results from an optical subtraction of an image before and after printing, so that, for example, the application of unwanted pressure particles or broken lines can be detected, so that a 100% inspection with high accuracy and egg nem high throughput achieved can be. Furthermore, through the optical inspection of the PCB in the application of a further layer at the same time the alignment of the layer to each other when analyzing only one of the two bi ler B and B2 and the difference image .DELTA.Β checked against each other and alignment errors of the layers are found. By analyzing the slide images, it is possible to continuously inspect the intermediate product of the PCB during production during repetitive manufacturing steps of layer application and layer printing on the PCB and to record the production quality. It is not individual layers, but the entire PCB during the layer application by means of an optical process in the flow production process inspected. According to an advantageous further development, a transport device can transport the PCB between the optical detection device and the printing device. The transport device can first transport the PCB to a first optical detection device, by means of which an inspection image B 1 can be recorded. Hi after the transport device can transport the PCB to the layer printing device, in which a paste printing takes place, and for example, an insulating layer is applied. Subsequently, the transport device can transport the PCB to a subsequent second detection device, which can create a second inspection image B2, so that the error detection device can create a differential image ΔΒ and evaluate it for errors. The transport device can be set up as a linear transport device, which can guide the PCB from a first printing station to a second printing station and optionally further printing stations. Alternatively, the transport device can be designed as a ring transport device which, after a first paste pressure, guides the PCB back to the input of the layer printing device, so that a second and possibly further layer printing can be carried out with the same printing device. In Fal le a ring conveyor can egg nzige optical

Detection device are sufficient to take a picture B l before and B2 after printing. According to a preferred embodiment, a first optical detection device for detecting the image B l before the printing device and a second optical detection device for detecting the image B2 after the printing device may be arranged, preferably identical pixel resolutions of the two detection devices for the detection of the images B l, B2 are available. A nearly identical structure of the two detection devices with the same Pi xelauflösung allows ei ne direct subtraction of the two images B l, B2, so that no graphical conversion steps of the two images are necessary, and the image processing can be performed easily and quickly. An upstream and downstream detection device can be advantageous, in particular in the case of a linear arrangement of the layer printing devices, since high flow rates and fast printing processes are made possible. The second, the printing device downstream detection device can simultaneously as a detection device for

Creation of an image B l for the subsequent layer printing di enen, so that between rule serially arranged one behind another layer printing devices in each case only be arranged an optical pressure detection device rauss. Thus, a high production speed of the PCBs can be achieved.

According to an advantageous further development, the optical detection device may include an image correction unit which has a spatial image offset of at least +/- one pixel in at least one extension of the image B 1 and / or B 2 mechanically and / or electronically and / or an image brightness and / or image contrast offset before at least +/- a resolution level to adapt the images B l and B2 to each other can make. S o, the two recorded images B l before and B2 may be geometrically offset after the printing of a layer, or from the image brightness or. be designed differently to the image contrast. To form the difference image, it is ideally necessary to have identical spatial and optical equality of the two original images B l, B2. This further development proposes a subsequent correction of the spatial image offset by at least one pixel, ie a smallest spatial resolution level and / or a Hel ligkeits- or contrast offset of at least one resolution level, the mostly digitally present images before. The correction can be made mechanically by changing the spatial position of the image capture device as well as electronically by spatial adjustment of the image detail and subsequent processing of image brightness and / or contrast. Thus, the quality and location of the images B 1 and B 2 are adjusted to each other to provide a difference image Δθ that can accurately provide an image of the last deposited layer. This increases the error detection accuracy and eliminates tolerances within the production line. Also, by repeatedly correcting the images B l and / or B2 and respectively generating a differential image, printing errors can be accurately recognized and artefacts removed.

According to an advantageous embodiment of the invention, the detection device may comprise a camera unit and a lighting unit, in particular a line camera unit and / or an LED lighting unit, preferably an LED strip lighting unit, wherein in particular a scanner-type detection of the images B1 and B2 can be carried out is. In principle, the detection device can only comprise a camera unit which can produce a two-dimensional image of the PCB. To create defined illumination values, a lighting unit can additionally be included, which can bring about a defined light brightness, contrasting and intensity distribution. The camera unit can deliver black and white, grayscale or especially colored images. Particularly advantageously, the detection device can be designed as a scanner-like line detection device which comprises a line scan camera unit and / or a lighting strip unit. In particular, an LED-based unit which can generate defined colors or a white light of defined brightness and spectral mixing can be used as lighting unit. To improve the quality of light can preceded by a collimation unit in order to create as similar collimated light as possible in order to reduce parallax errors. A lens unit and / or an apparatus may be connected in front of the camera unit in order to detect only one image detail or collimated light. The line scan camera can be an RGB CCD unit, in which individual brightness values can be recorded and recorded separately. By a scannerarti ges method beispielswei se with a continuous transport of the PCBs a high-resolution image can be detected. Thus, the throughput speed of the PCBs and the quality of the detected images are increased, so that the error detection can be improved.

According to a preferred embodiment, the detection device may be designed to detect a three-dimensional height profile of the PCB layer, and may preferably be embodied as a laser-based or white light-based 3D scanner device. This further development proposes instead of a two-dimensional color and / or grayscale image to detect a 3 D height profile, for example by laser scanning by determination of pulse transit time, phase difference or tri angulation. Alternatively, a chromati cal depth measurement by splitting from whitish in a rainbow spectrum with different angles of radiation through a prism are made in the different component heights throw back different chroma values of reflected light. By evaluating the ink color, the height can be closed and thus a three-dimensional profile can be generated. By comparing the profile heights, the application of the paste can be checked at the pressure points of the print and printing errors can be detected. In contrast to a conventional two-dimensional image recognition method, errors in the printing thickness, material deposition or the like can be recognized very simply and quickly by means of a 3D height profile, so that only a purely optical qualitative comparison but also a quantitative comparison of the material Ablation can be performed on the layer.

Thus, a three-dimensional error correction of the deposited layers can be provided. According to an advantageous further development of the device, the detection device or the error detection device may comprise a vectoring unit, so that the detected images B1 and / or B2 can be vectorized for the purpose of image comparison. By means of a vectorization unit, two- or even three-dimensional structures can be represented by vectors, ie line-like links of reference points. The storage volume of the captured images or the difference image can be highly compressed, and a simplified image can be stored, for example, for archiving and logging purposes. Vectorized image files can be compared very quickly and efficiently with high accuracy of error, so that the image comparison can be significantly simplified.

According to an advantageous further development of the invention, the error detection device may comprise a memory unit for storing at least one pattern difference image ΔΒ _Μ and / or a pattern image B1 _M so that a difference image ΔΒ can be determined from a captured image B2 and the pattern image B1 _M and with a pattern difference image ΔΒΜ is comparable. Thus, this development proposes that pre-stored pattern difference images or pattern images can be used, so that subsequent paste printing processes can be compared with previously expired paste printing processes and can be recorded as protocol fragments. Thus, a detection of a first image Bl can be dispensed with prior to printing of the layer, and instead a pattern image B1M can be used, so that not only relative printing errors of the print just made are detected, but absolute errors can be recognized in relation to a sample print template. On the other hand, the difference image .DELTA.Β can be compared with a pattern image .DELTA.ΒΜ, so that the appearance of the layer image can be compared with a pattern player image to quickly and easily find printing errors. Also, process fluctuations can be revealed or quality comparisons can be analyzed and compared over several process steps or series of PCB production runs. By attracting In the case of pattern images that correspond to an ideal print or a first printing process, absolute quality standards can be defined and monitored. Thus, an improvement in the error detection and the PCB quality can be achieved. In a secondary aspect, the invention proposes a method for error analysis of printed PCBs using an aforementioned device. The method according to the invention comprises the steps:

S l: optical detection of an image B l of the PCB before printing; S3: printing the substrate of the PCB;

S4: optical detection of an image B2 of the PCB after printing;

S6: determination of a differential image ΔΒ;

S7: analysis of the differential image ΔΒ for errors;

S9: removal of the PCB in case of fault detection; S 10: Repeat from step S 1 to S 9 for further layers to be wound up.

With the aid of the method according to the invention, by using one or two optical recognition devices, images can be recorded before or after the printing of a layer, from this a

Difference image are generated and this difference image for errors, for example by comparison with a pattern difference image, checked. If an error of the Di fferenzbilds recognized, the PCB can be retired or repaired the error. In the case of multi-layered circuit boards, the process can be carried out until all layers are printed, so that a 100% quality control of all layers can be carried out. According to an advantageous embodiment variant of the aforementioned method, by predetermining the difference image ΔΒ, a spatial image correction of at least +/- one pixel in at least one extension direction of the PCB can be effected mechanically and / or electronically, and an image brightness and / or an image contrast offset of at least + /. - A resolution level to adapt the images B l and B2 are made to each other. By taking a spatial or optical image correction, which can be carried out both mechanically and electronically subsequently, the recording quality of the two images B 1, B 2 can be adapted to each other, so that an optimal difference image ΔΒ can be generated, which is the structure of the last printed layers. This increases the identity of the layer imaging structure, so that improved error accuracy can be achieved by forming the difference image ΔΒ. The image capture device can be corrected mechanically in the x or y direction in order to achieve the same position of the images, and can for example be photoelectrically reworked in order to achieve the same image brightness or the same image contrast. An adaptation can also be subsequently achieved by electronic means, for example by means of suitable image processing methods.

According to an advantageous further development, the method can make at least two, in particular several image corrections, and difference images ΔΒ 1. N determine, where an error is reliably detected only if in each of the difference images ΔΒ _Ι . Ν a fault deviation is recognizable in the same places. Thus, it is conceivable, for example, to geometrically offset the two images B 1, B 2 with one or more pixels in the x or y direction and to change their brightness and / or contrast levels by 1 to 2 steps, and thus difference magnets Δ Β _Ι .,. Ν to be determined. If all of these difference images show deviations at almost identical points, it can be assumed that an error is actually present. For example, if there are only five or fewer deviations for four or six comparisons, it can thus be assumed that there is no error, but only an inaccuracy (artifact) of the difference image ΔΒ, so that it can be assumed with high certainty that the layer is error-free. Since image comparisons can be made very quickly, they are not time-critical and may, for example, also be performed during the printing process or asynchronously to the process time to ensure runtime control of the layer. Thus, a consistently high speed of PCB fabrication can be achieved.

According to a further advantageous Ausführungsbei game of the aforementioned method, an error in the difference image ΔΒ with structure size deviations of at least> 10 μηι, in particular> 5 μηι. be recognizable. Thus, the optical detection device as well as the error detection device can be configured such that error deviations of less than 10 μm, in particular at least 5 μm, can be detected, so that increased miniaturization of the PCBs can be checked for errors. Thus, the inspection method can also be used for future highly miniaturized PCBs, and meets the requirements for highly concentrated assemblies with the highest quality requirements.

In principle, the entire image B 1 can be used with respect to the image B 2 to form a Duralference image ΔΒ. According to an advantageous embodiment of the method, at least one, in particular a plurality, of characteristic subregions of the images B 1, B 2 can be compared for errors. Thus, subregions, in particular characteristic subareas, can be compared, so that it can be concluded on their agreement that the entire layer or relevant parts thereof can be error-free. This can achieve a significant reduction of the error control effort and thus an increase in the flow rate.

Finally, in a further advantageous embodiment, the image B 1 can be recorded as a pattern image B 1 _M from a storage unit and the image B 2 can be acquired from a detection device after the printing on the PCB Layers for generating a difference image ΔΒ are determined, wherein the difference image ΔΒ mi t comparison with a stored in the memory unit pattern difference image ΔΒ _Μ , and in case of deviation, an error can be detected. By using a pattern difference image B 1 M before printing, absolute as well as relative errors can be detected in the di ference image ΔΒ in order to be able to compare the PCB production with a sample image, so that process-related changes and systematic errors can be detected ,

Figurbesch friction Further advantages will become apparent from the following drawing description. In the drawings, embodiments of the invention are shown. The drawings, the description and the claims contain numerous features and combinations. The person skilled in the art will expediently also consider the feature e individually and combine it into a meaningful further combination.

They show by way of example:

1 shows a first exemplary embodiment of an inspection printing device according to the invention;

2 shows a further embodiment of an inventive

Inspection printing apparatus;

Fig. 3: a wei teres Ausführungsbei play a erfind ungsgemäßen

Inspection printing apparatus;

4 shows an embodiment of an error detection device according to egg nem Ausführungsbeispi el an inspection printing device.

5 shows a flowchart of an exemplary embodiment of a method according to the invention; Embodiments of the invention

In the fi gures same or gl oak-like components are numbered with the same reference numerals.

Fig. 1 shows a first embodiment 10 of an inspection printing device according to the invention. The inspection printing device 10 comprises an error detection device 30 and a first optical detection device 24a, which is arranged in front of a layer printing device 20, and a second optical detection device 24b, which is arranged after the layer printing device 20. A PCB 1 4 is transported by means of a linear transport device 34 from the first detection device 24a to the printing device 20 and further to the second detection device 24b. The two detection devices 24a, 24b are connected to the error detection device 30 by means of a communication link 32. The communication connection 32 can be wired or wirelessly implemented, and can transmit both the optical images B l, B2 and adjustment data, such as contrast, brightness or spatial offset information of the images. It can be unidirectional or bidirectional in order to be able to transmit control commands of the error detection device 30 to the detection device 24. The optical detection device 24 includes a

Lighting unit 28, the fen may be, for example, as LED Leuchtstrei FEN, and a Kam eraeinheit 26, which may be constructed, for example, as a CCD line scan camera to make a scanner-like detection of the surface of the PCB 14. By means of the transport device 34, which may be a conveyor belt, for example, initially a ceramic substrate 1 2, which is permeable to light and / or light, is guided through the first optical detection device 24a. Their surface is scanned. Subsequently, the substrate 1 2 is printed by means of the printing device and a printing stencil 1 8 with a paste in order to conduct conductive components such as the printed conductors and resistances, capacitances or inductances. Subsequently, an insulation can be switched are applied (not shown t), and it is made a detection of the surface structures by means of the downstream second detection means 24b. By comparing the two images B l, B2 within the error detection device 30, the structure of the 5 printed layer can be analyzed on the substrate 12 and errors are detected.

Fig. 2 shows another Ausführungsbei play an inspection printing device 1 0, which is constructed in series, and in the at least two printing devices 20a, 20b two successive layers on the PCB

1 0 14 apply. A linear transport device 34 initially transports a ceramic substrate 12 through a first optical detection device 24a, the structure of which is similar to that of the detection device shown in FIG. Subsequently, the first layer 1 2 is printed with a printing stencil 1 8a in a first printing device

15 20a. Subsequently, a scan of the first printed layer 12 takes place, wherein via communication connections 32a, 32b the two images B 1, B2 are transmitted to the error detection device 30. Subsequently, for example, an insulating layer 16 can be applied, and by means of a further detection device 24c, a further scan can be carried out. Alternatively, the scan of the second detection means 24b may serve as the output image for the subsequent printing by means of the printing means 20b. By the printing device 20b, a further layer 1 2 is printed on the PCB 14, so that by means of the printing stencil 1 8b an additional structure is impressed on the PCB. Subsequently, a scan is carried out with a downstream detection device 24d, after which again an insulation layer is applied and a further scan can be carried out as a starting layer for a further subsequent printing of a third layer 12 by means of the detection device 24e. In this exemplary embodiment 10, a scan is subsequently performed on the printing device 20 by means of an optical detection device 24, after which an insulation layer is applied and again a scan is carried out as the output image for the subsequent printing. Age- natively, between two adjacent printing devices 20 only a single scanning or detection device can be arranged, which can provide both the difference image B2 of the previous print and the difference image B l for the subsequent printing. By seriel le arrangement of the individual printing devices 20, a very high production speed of the multilayered PCBs can be achieved.

FIG. 3 shows a further exemplary embodiment of an inspection printing device 10 according to the invention. The printing device 20, the detection device 24 and the error detection device 30 are based on the embodiment shown in FIGS. 1 and 2. The annular transport device 34 is designed to guide the PCB 14 from the output of the printing device 20 back to the input of the printing device 20, so that the printing device 20 can be configured after a first printing operation of the first layer 1 2, more layers on the PCB. 1 4 with the same print templates 1 8. In the upper partial image, a ceramic substrate 1 2 is first scanned by means of the detection device 24 and transmitted to the error detection device 30. Thereafter, with the first printing stencil 1 8a within the printing device 20, the substrate 1 2 is printed with the first layer structure 12. Afterwards, an insulating layer 16 is applied through the insulating layer device 22 and the transport device 34 transports the PCB 14 with the first layer layer 12 back to the detection device 24, in which they are scanned, and as shown in the lower part of the image, medium s of the printing device 20 and a second printing stencil 1 8b with a second layer layer 12 is printed. Thereafter, in turn, the application of a further insulating layer 1 6, ei n scanning and a wi ederholter pressure of dri tten and other layer layers 1 2. Thus, this embodiment proposes that a single printing device 20 for printing two or more layers 1 2 of the PCB 14th is used, and for this purpose a single detection device 24 can each perform a scan before or after printing the PCBs. The error detection device 30 stores the individual recorded images B l, B2, etc. and calculates therefrom the respective difference images ΔΒ, from which printing errors can be analyzed.

FIG. 4 schematically shows an embodiment of an error detection device 30, as can be used in one of the exemplary embodiments shown in FIGS. 1 to 3. The error detection device 30 is connected to optical detection devices 24 by means of communication links 32 wirelessly or by wire. It comprises an error detection unit 42, which can generate a difference image ΔΒ by image comparison of the images B 1 and B 2, and which can check this difference f bi Β for deviations and errors. For this purpose, the error detection unit 42 is connected to a memory unit 38, by beispielswei se a pattern difference image ΔΒ _Μ and / or a pattern image B 1 M are stored for the inspection of a first, a second and further layers. Furthermore, the error detection unit 42 is connected to an image correction unit 36, which has both a spatial

Position correction and cropping selection of the image B l, B2 in the x and y direction as well as an adjustment of brightness and contrast of respec gene images can make as identical images B l, B2 to produce egg nes difference image ΔΒ ready to provide. Finally, the error detection unit 42 is connected to a vectoring unit 40, which can undertake a vectorization from a difference image ΔΒ or from one or both images B1, B2 so that the image data is present as pure vector data which can be easily stored and compared. With the aid of such an error detection device 30, a deviation of the last printed layer from the preceding layers of the PCB can be achieved efficiently and with high precision.

5, an embodiment of the erfindun gsgem ae method is shown in a flow chart. After the start of the printing process, before the first layer 1 4 is printed on, in step S 1, an optical detection of the PCB 1 2 is carried out by means of the optical detection device 24 in order to acquire a first image B 1. This image B l becomes the Error detection device 30 transmitted. In the error detection device 30, an adaptation of pixel coordinates, brightness or geometry offset or geometric equalization as well as contrast or further image parameters can be carried out in a step S2. Subsequently, the PCB layer 1 2 is transported by means of a transport device 34 to a layer printing device 20, and printed in step S3. After a further transport to the subsequent detection device 24, an optical detection of the PCB 14 takes place after the printing in order to take an image B2 in step S4. This image B2 is also transmitted to the error detection device 30 in order to adapt pixel coordinates, brightness, geometry distortion and contrast or further image parameters in step S 5. Subsequently, in step S 6, the determination of a Di fferenzbilds ΔΒ by subtracting the two fields, preferably using a previous vectorization of the images B l, B2, and this difference image ΔΒ is in step S7 against a vorgespeich profiled template

ΔΒ Μ or other error criteria tested whether an error can be detected in the current print. In step S8, it is determined whether repair errors have to be remedied or the PCB 14 has to be declared scrap such that further printing of the PCB 14 is not possible, or if the layer is error free, and if more layers 12 are to be printed (Step S9), a new insulating layer is applied to the PCB 14 in step S10, and the process is repeated until all the layers 12 of the PCB 14 are printed.

The method according to the invention makes it possible to examine each individual layer independently of any interfering influence of the optical structure of previously printed layers of the PCB.

Thus, the first detection means may provide an image B1 having the same resolution as the second downstream detection means detecting the image B2. The image coordinates of both detection devices can be corrected and determined. The error detection means may determine the printing position of the current layer 3

21 and make a comparison as to whether the positional layer layer has been printed to the previous layers. The difference image can be examined for printing errors, and in the case of a 3 D-S can also the material deposition and thus any resistance parameters or the like can be investigated. It can be determined whether printed material arranged in the wrong places or missing in some places printing material. As part of the image capture, a geometric and an optical correction of the individual images can be made.

In this case, at least one resolution level or one pixel can be varied in a geometric expansion direction as well as in brightness and contrast resolution, and thus a plurality of difference images are generated, wherein an error is only reliably detected if all the difference images contain errors at identical or spatial have adjacent bodies. Thus, for example, a geometrical correction in +/- one pixel direction in one or both geometrical directions and in +/- one or two brightness levels can be effected so that four or more difference images can be generated, so that only if all the difference images have similar errors indicate that there is actually an error. Pre-stored folders can also be used to create slides or to analyze the difference picture. Also, the pre-stored images may be vectorized to save storage space and computation time. The resulting data can be used to obtain statistics on production quality and production progress. As a result, production fluctuations can be detected and production scrap can be recognized early. By using 3 D profiles, the material usage can be monitored, for example to study the material thicknesses of the individual layer layers, and to be able to rely on electrical and mechanical properties of the layer. Advantageously, a line sensor with three color values, for example, an RGB sensor, can be used for 3-D profile recognition.

Claims

claims

1. Inspection printing apparatus (10) for defect analysis of printed PCBs (14), which has a light-transmitting / light-conducting substrate (12) and at least one, in particular a plurality, layered layers (16), comprising at least one optical detection device (24), an error detection device (30) and a layer printing device (20), characterized by

in that the optical detection device (24) is set up before and / or after printing a layer (12) of the PCB (14) by means of the printing device (20) a first and / or second optical image Bl before or after printing of the Layers (16) to be detected, wherein the error detection means (30) is adapted to determine a difference image ΔΒ from the two images Bl, B2, so that the difference image ΔΒ substantially corresponds to the printed image of the layer (16), and can be analyzed for printing errors ,

2. Apparatus according to claim 1,

characterized,

in that a transport device (34) can transport the PCB (14) between the optical detection device (24) and the printing device (20).

3. Device according to one of the preceding claims,

characterized,

in that a first optical detection device (24) for detecting the image B 1 in front of the printing device (20) and a second optical detection device (24) for capturing the image B2 is arranged downstream of the printing device (20), preferably identical pixel resolutions of the two detection devices (20). 24) for the detection of the images Bl, B2 are provided.

4. Device according to one of the preceding claims,

characterized,

in that at least one optical detection device (24) or the error detection device (30) comprises an image correction unit (36) which mechanically and / or electronically and / or spatially displaces at least +/- one pixel in at least one extension direction of the image Bl and / or B2 a Bildhelligkeits- and / or image contrast offset of at least +/- a resolution level for adapting the images B 1 and B2 to each other can make.

5. Device according to one of the preceding claims,

characterized,

in that the detection device (24) comprises a camera unit (26) and a lighting unit (28), in particular a line camera unit and / or an LED lighting unit, preferably an LED strip lighting unit, wherein in particular a scanner-like detection of the images B and B2 can be carried out ,

6. Device according to one of the preceding claims,

characterized,

the detection device (24) is designed to detect a three-dimensional height profile of the PCB layer (16) and is preferably designed as a laser-based or white-light-based 3D scanner device.

7. Device according to one of the preceding claims,

characterized,

in that the detection device (24) or the error detection device (30) has a

Vectorization unit (40), so that the captured images Bl andoder B2 are vectorizable for the purpose of image comparison.

8. Device according to one of the preceding claims,

characterized,

in that the error detection device (30) comprises a memory unit (38) for storing at least one pattern difference image ΔΒ _Μ and / or a pattern image B1 _M so that a difference image ΔΒ can be determined from a captured image B2 and the pattern image B1 _M and is comparable to a pattern difference image ΔΒΜ ,

A method of error analysis of printed circuit board (14) using a device (10) according to any one of the preceding claims comprising the steps of:

Sl: optical detection of an image Bl of the PCB (14) before printing;

S3: printing the substrate (12) of the PCB (14);

S4: optical detection of an image B2 of the PCB (14) after printing;

S6: determination of a differential image ΔΒ;

S7: Analysis of the differential image ΔΒ for errors;

S9: rejection of the PCB (14) in case of error detection;

Sl 0: repetition steps S 1 to S 9 for further layers to be applied (12).

10. The method according to claim 9,

characterized,

in that, prior to the determination of the differential image ΔΒ, a spatial image correction of at least +/- one pixel in at least one extension direction of the PCBs (14) is mechanically and / or electronically and an image brightness and / or image contrast offset of at least +/- one resolution step for adapting the images B1 (S2) and B2 (S5) to each other.

11. The method according to claim 10,

characterized,

that at least two, in particular a plurality, make image corrections and difference images ΔΒΙ. _, .Ν are determined, wherein an error is detected only if in each difference image ΔΒΙ., Ν Fehler an error deviation is recognizable.

12. The method according to claim 9 to 11,

characterized,

that an error in the difference image .DELTA.Β in structure size deviations of at least 10μηι, in particular> 5μτη, recognizable.

13. The method according to any one of claims 9 to 12,

characterized,

in that at least one, in particular a plurality, of characteristic subareas of the images B 1, B 2 are compared for errors.

14. The method according to any one of claims 9 to 13,

characterized,

that the image Bl as a pattern image BIM from a memory unit (38) and the image B2 from a detection device (24), detected after the printing of the PCB layer (16), are determined to form a differential image ΔΒ, wherein the difference image ΔΒ with a in the memory unit (38) stored pattern difference image ΔΒ compared and an error is detected in deviation.