DE3212190A1 - Opto-electronic distinguishing of structures on surfaces - Google Patents

Abstract

The distinguishing of insulating and metallic regions, for example on printed-circuit boards, is essentially based on three-dimensional detection and interpretation of the scatter behaviour of the relevant surfaces by means of opto-electronic components. To this end, the surface to be tested is illuminated and the scattering characteristic of each illuminated point is detected simultaneously by a plurality of detectors, and the surface is classified by a comparison of the scattering intensity.

Description

Opto-electronic differentiation of structures on

Surfaces.

The invention relates to an opto-electronic method for contactless Differentiation of different structures on surfaces, especially on electrical ones Printed circuit boards.

The production of printed circuits is done by physical / chemical Processes. Local defects (track constrictions and -interruptions, etching residues, insufficient isolation gaps) occur that the Significantly endanger the function and subsequent reliability of the circuit boards.

If, in mass production, each individual product is carried out by a Examiner is viewed visually to determine whether there is any given predetermined Requirements are sufficient, then it depends on his attention whether there are also faulty ones Specimens hatch through this test.

It is therefore desirable to have such a visual inspection as possible to automate far. This is even more true for the growing number of products for which the visual inspection is practically impossible to carry out, z. B. because of small dimensions of the product or because of large quantities. To the Objectification and rationalization of these important and extensive test tasks is involved in automatic procedures through methods of image processing and pattern recognition worked. A prerequisite for this, however, is a clear distinction in the case of printed circuit boards between the insulation and conductor area. The latter in particular can extremely have different optical properties.

The invention is based on the object described above To create prerequisites for image processing and pattern recognition, which enable a clear distinction between insulation and conductor area. This object is achieved in that the surface to be tested is illuminated locally and the scattering characteristics of each illuminated point by detectors from different, symmetrical spatial directions is detected at the same time and by a comparison the direction-dependent scattering intensities the surfaces are classified.

The invention is essentially based on spatial detection and interpretation of the scattering behavior of surfaces by means of opto-electronic Components.

A comparison of the scattering intensities with one another allows a clear one Separation of z. B. metallic and insulating surfaces even if the metallic Surfaces have significantly different angular orientations (e.g. tinned Conductor tracks). In the area of isolation are namely those from different directions measured intensities almost the same and relatively low. In the field of metallization the intensities can vary considerably due to a narrow reflection lobe differ from each other. Only with flat metallic surfaces and more perpendicularly Lighting, the scattering intensities are roughly the same as one another. However, are it is considerably lower than the light reflected back in the direction of illumination.

After a T.lleiterbildung the invention, the surface to be tested illuminated by a light beam (e.g. laser scanner) and the detectors measure almost independent of the location of the light trail, the scattered Intensity. When using a laser, the focusing is unproblematic and the location coordinates are given via control signals from the laser scanner. The laser beam does not necessarily have to be strike perpendicularly, but should generally have an almost constant angle to the surface in order to have the same directional relationships regardless of the location of the surface to guarantee.

In the context of the invention, the surface can also be evenly illuminated will. The detectors, which have a spatial resolution, measure the intensity of the reflected light depending on the location. This achieves that instead of a complex laser inexpensive other light sources such. B. halogen lamps are used can be.

According to a further embodiment of the invention, the detectors upstream optical filters of certain wavelengths are preferred. Through this the contrast can be improved because the spectral absorption-emission properties (Fluowscence) of the surface can be included in the evaluation.

In the context of the invention it is also possible that only one detector the reflected light from the surface from several different spatial directions receives radiant sequentially controlled light sources and through sequential Comparison of the scatter intensities of the same location points classifies the surface. This method has the advantage that the effort for the highly sensitive detectors is significantly reduced.

According to a further development of the invention, the detector can have a spatial resolution and the light sources illuminate the object over its entire surface. The advantage of one Such a method is due to the fact that the adjustment effort is thereby significantly is reduced and no Laser scanner is required.

In the method according to the invention, the detector (e.g. television camera or diode line) can be arranged vertically above the surface.

According to a further embodiment of the invention, the modulation of the light through electrical control of the light sources, through mechanical interruption of the light beam or by electro-optical influencing of the light beam. The mechanical interruption of the light beams is carried out, for example, by a Chopper disc. The electrical control of the light sources is z. B. for light emitting diodes expedient.

A light source can also be used to implement the method according to the invention Find use whose beam sequentially for lighting from several spatial directions is switched with the help of mirrors. With such a procedure the Power consumption significantly reduced.

According to the invention, the surface has a special angle-dependent one Scatter characteristics and the arrangement of the detectors and the evaluation of the scatter intensities are adapted to it. This has the advantage that the process can be tailored to the specific Can optimize surface properties of the object.

The invention is explained with reference to the figures. They show: FIG. 1 in the left part the scattering behavior of an isolating area, as well as in the right part Part of the scattering behavior of a flat metallic surface, figure 2 shows the scattering behavior of an inclined metallic surface and FIG. 3 in the upper one Part of a metallic conductor track on a circuit board, in the middle part that of four detectors emitted intensity signals and in the lower part those from the signals obtained binary information.

The figures relate only to one exemplary embodiment for the Exposure of a surface with a perpendicular, focused beam of light. In the figures, a partial section of a circuit board 1 is shown on which In Figures 1 to 3, a metallic conductor 2 is arranged. From that direction 3 the lighting takes place.

With JO to J3 are several, scattered in different spatial directions, or reflected light intensities. The dashed envelope in the Figures are intended to describe an area spanned by the vectors JO to J will. The length of these vectors is proportional to the magnitude of the involved Directions scattered or reflected intensities.

Insulating materials used in circuit board technology (e.g.

Epoxy, ceramic) act as well-scattering surfaces.

Incident light is uniform over a wide range of rawwn angles scattered (left part of Figure 1). The scattering intensities in the case of an isolating Area then behave: J0 ss J1 J2 J3.

Metallic surfaces (e.g. tinned conductor tracks, conductor tracks with copper surfaces) generally reflect the incident light into one narrow solid angle range corresponding to the local left-hand orientation of the surface. The scatter intensities then behave in the situation according to the right one Partial image of FIG. 1 like: J1 # J2 # J3 # J0. At figure 2 lie following conditions before: J0 # J2 # J3 # J1.

For reliable differentiation between insulating and metallic areas the surface is now corresponding to the necessary spatial resolution with a point of light lit tz. B. with the help of a laser scanner) and the scattering characteristics (e.g. B. JOS J1 'J2, J3) this point is detected by detectors at the same time, which are in different Spatial directions are evenly distributed.

A comparison of the scattering intensities Ji 'J2, 3 with the intensity JO, allows a clear separation of metallic and insulating surfaces. In this case, according to FIGS. 1 to 3, JO is in the direction of illumination the decreasing intensity denotes. If the lighting is not perpendicular 3 (not shown here) is reflected from a flat metal surface Light intensity defined as J0.

When the metallic surfaces have significantly different WirAcel orientations have such. B. with tinned conductor tracks according to Figure 2, however possibly to meet the following additional condition: Since with sufficiently strong Surface inclination the received intensities can be so low that they are due to the unfavorable signal-to-noise ratio are indistinguishable from each other, a threshold value Js has to be defined for the intensity which is just below the value for the scatter on insulation surfaces, all intensity values fall below at the same time this threshold J5 is generally metallized.

In the middle part, FIG. 3 shows the profile of JO, J1, J2 and J- recorded across a tinned conductor track 2, the measurement from J1 to J3 being symmetrical takes place from three spatial directions below about 300 to the normal.

The scattering characteristic of J0 is with a continuous line, the scattering characteristic J1 dotted, the scattering characteristic J2 dashed and the scattering characteristic J3 is shown with small circles.

A possible logical link to the binarization is the formation of a ratio of intensities J1, J2, J3 to J0 z. B.

logical 0: if J1J2 J3 (isolation) ~ # ~ # ~ 1 and J0, J1, J3 # Js J0 J0 J0 logical 1: if J1 J2 J3 (metal) - or - or - # 1 or J0, J1, J2, J3 <JS JO JOJO 10 claims 5 figures

Claims (10)

Patent application. Opto-electronic process for contactless differentiation various structures on surfaces, especially on electrical circuit boards, d a d u r c h e k e n n n z e i c h n e t that the surface to be tested (1, 2) locally illuminated (3) and the scattering characteristics (Joa J1, J2, J3) each illuminated Place through detectors from different, symmetrical spatial directions at the same time is detected and by a comparison of the direction-dependent scatter intensities the surfaces are classified. 2. The method according to claim 1, o a d u r c h g e -k e n n z e i c h n e t that the surface to be inspected by a light beam (e.g. a laser scanner) is illuminated and that the detectors are almost independent of the location of the light point measure the scattered intensity. 3. The method of claim 1, d a d u r c h g e -k e n n z e i c h n e t that the surface is evenly illuminated and the detectors one Have spatial resolution and the intensity of the reflected light as a function measure from place. 4. The method according to claims 1 to 3, d a cl u r c h g e k e n It is not stated that certain optical filters connected upstream of the detectors are used Ground wavelengths preferred. 5. The method of claim 1, d a d u r c h g e -k e n n z e i c h n e t that a detector detects the reflected light from the surface from several sequentially controlled light sources radiating in different spatial directions receives and by sequential comparison of the scatter intensities of the same location points the surface classified. 6. The method according to claim 5, d a d u r c h g e -k e n n z e i c h n e t that the detector has a spatial resolution and the light sources the object illuminate the entire surface. 7. The method according to claim 5 and 6, d a d u r c h g e -k e n n z e i c h n e t that the detector (e.g. television camera or D.odenzeile) is vertical is arranged above the surface. 8. The method according to claim 5 to 7, d a d u r c h g e k e n n z e i c h n e t that the modulation of the light by electrical control of the light sources, by mechanical interruption of the light beams or by electro-optical influence the light rays takes place. 9. The method according to claim 5 to 7, d a d u r c n g e k e n n z e i c h n e t that a light source is used, the beam of which is switched sequentially is used to illuminate the object from different spatial directions. 10. The method according to claims 1 to 9, d a -d u r c h g e k e n n z e i c h n e t s that the surface has a special angle-dependent scattering characteristic possesses and that the arrangement of the detectors and the evaluation of the scattering intensityel1 is adapted to it.