The camera assembly integrated into DEK systems is a compact assembly of optics, lighting and one or two CCIR camera’s depending upon the system type.


Camera Types
Three camera variants are available (depending upon machine configuration). The Gold camera has the largest field of view, whilst the Green camera has a smaller field of view it retains the fully programmable (via the machine product file) lighting system used by the Gold camera.

The Graphite camera is DEK’s entry-level system although it still retains the same field of view as the Green camera but has reduced software lighting control.


The DEK Gold camera system gives a field of view three times larger than that available with the Green camera system. This speeds up the inspection process by the reduction in the number of sites the system is required to visit to accomplish the inspection task.

Each DEK camera systems use special optical designs to maximise their capability. However all systems capture the board and stencil images simultaneously in order to minimise any relative movement between the two targets. All assemblies also benefit from Telecentric lens technology and custom LED lighting to permit reliable and accurate capture of images across a wide spectrum of materials and target finishes.


Lighting

Essential for any vision system is to have the highest quality images with which to process. Poor quality images may result in a degradation of image processing leading to less accurate alignment and if inspection is used, misleading results.

DEK's camera systems have been specifically designed to enable low quality boards to be aligned and inspected with equal accuracy. Very typically these lower quality boards will have uneven Hot Air Solder Levelled (HASL) pads and features. The uneven surface texture and irregularities of these features and pads can cause dead zones, i.e. areas where there is no light and hot spots of light caused by reflection of light from solder pads and wet solder paste.

Therefore for high accuracy and reliable image processing especially in applications with difficult pad finishes as described previously DEK has incorporated a flat lighting design within the camera assembly. This is achieved by utilizing two light sources:




Direct lighting - producing normal incidence and angles up to 25°

Indirect/Oblique lighting - producing angles from 25° - 50°



Direct Lighting

A bank of LED’s shining through a diffuser to produce a very uniform light source achieves direct lighting. In addition to this the light is passed through a cube beam splitter, which increases the illumination and the range of angles reaching the board.


Indirect / Oblique Lighting

Indirect / Oblique lighting is used in addition to direct lighting to create uniform illumination, eliminating hot spots of light.

An array of LED’s sited in a polished ring around the lens aperture produce a light source which is reflected and scattered by the polished surface and white paint of the assembly to the fine ground conical inner ring. This produces very uniform illumination, which is radiated in all directions providing a very balanced illumination of the board.









Fiducials

DEK’s range of automatic mass imaging products uses the vision system to capture and process alignment marks or fiducials. Fiducials are produced as part of the artwork of the board and stencil design and are therefore in the same comparative positions between the two images. When captured by the vision system the fiducials relative positions are analysed and this data is then used to accurately to align the stencil to each board before it is printed.

The vision system has a library of synthetic fiducials of the most commonly found shapes used today. In each individual instance of the fiducial the specific dimensions of the synthetic shape can be adjusted by the operator to match the fiducials on the board and stencil. The system requires a minimum of two fiducial locations to be programmed (board and stencil in each instance); three fiducial alignment is a further selectable option at product set-up time. After the vision system has been taught these fiducial parameters all the data is saved to the product file. The system is then able to search the field of view of the camera at run time to recognize any features that resemble fiducials.

After finding a shape it is assigned a score comparing its shape and size to the shape and size of the fiducial in the vision system library. This score is set between 1 and 999, the better the fit the higher the score.


Video Model

The video model is an alternative to using fiducials for stencil to board alignment. Video model uses the correlation between the image of an area of the stencil and the image of the same area of the board to align the two. This is useful if the board or stencil has no fiducials or the condition of the fiducials does not allow satisfactory recognition.