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The advantages of line confocal sensors over traditional point-based solutions are examined. Contributed by LMI Technologies

Line Confocal Imaging (LCI) is a unique optical technology for metrology requiring resolutions down to 50 nm.

In the past, confocal technology was limited to single point or multipoint sensors based on a coaxial design. With LCI, a major breakthrough is achieved using a novel off-axis confocal design that offers a line scan capability with numerous benefits over the traditional coaxial approach.

 

What Makes 3D Line Confocal Sensors Unique

The key advantage of line confocal sensors is their ability to generate 3D topography (3D surface geometry), 3D tomography (multi-layer 3D geometry and 2D intensity), and 2D intensity data simultaneously over a 2k line scan at fast scan rates (eg: 3 kHz). 

Confocal scanning avoids unwanted reflections from shiny metal surfaces and the off-axis arrangement is what permits multi-layer (tomography) scanning.

In addition, confocal sensors are much easier to mount to acquire high quality scan data with angular performance of +/- 20 degrees on mirror like surfaces, and +/- 80 degrees on opaque, matte surfaces. 

Excellent angular performance makes line confocal sensors less sensitive to surface orientation when acquiring scan data, and line confocal scanning can handle just about any surface — from transparent, mirror-like to opaque and shiny. 

Before line confocal was possible, single or multiple point coaxial confocal systems were the standard but required long scanning acquisition to generate a profile or area and were limited to measuring the top surface only.


Application Examples

Curved Edge Display Inspection

Excellent Performance on Large Surface Angles

Line confocal sensors are used to scan, measure, and inspect the profile of curved screen glass used in cell phone and tablet designs at a surface angle of up to +/- 20 degrees making this sensor ideal for quality control of 2.5D and 3D display glass. Conventional vision solutions can only capture quality data on surface angles of +/- 7 degrees or less.

 

Multi-Layered Transparent Material Inspection

Line confocal sensors are ideal for transparent material inspection and quality control. One of the key applications in capturing the surface of mobile device displays and detecting layers inside and under the screen.

The combination of 3D tomography (multi-layer) and 2D intensity imaging is used to identify defects such as delamination, scratches, or dust on the surface or inside of laminated glass, mobile phone displays, or any other type of transparent multilayered material like sealed medical packages. 

And, contrary to other types of imaging systems, line confocal sensors detect not only the location of the defect, they also identify in which layer the defect exists. The sensor even measures the dimensions of the defect down to the sub-micron level.

 

Additional Advantages Of Using 3D Line Confocal Sensors

  • No additional filtering is required for analysis
  • Ability to scan and measure materials with any colour combination
  • Ability to measure all surface types including mirror-like, glossy, transparent, translucent, curved, convex, concave, soft, fragile, or porous
  • Metrology-grade resolution and accuracy are provided at high speed (up to 3 kHz at full measurement range)
  • Easy to mount and acquire clean scan data on any surface feature

 

Component And Assembly Inspection

3D image of printed patterns on transparent PET using a FocalSpec LCI1600 sensor.

Fast and accurate component and final assembly inspection can be achieved using 3D line confocal sensors for both inline and offline applications. Particularly when measuring complex materials and surfaces, line confocal sensors exceed standard inspection methods.

Engineers can use these sensors for measuring component dimensions, orientation, step height, gap and offset, material thickness, and surface properties such as roughness and flatness. Line confocal sensors can also be used to inspect soldering and gluing quality on small parts such as PCBs.

The quality of generated scan data from these sensors is equal to traditional microscopic data, however unlike with a microscope, a 3D line confocal sensor generates millions of data points simultaneously and can acquire the object in motion. This facilitates full inspection of electronic components and their assembly for inline production environments.

 

Printed, Hybrid, And Flexible Electronics Inspection

Line confocal sensors can be used at various stages of the printed electronics manufacturing process, starting with substrate material development and manufacturing, where surface roughness is a key measurement.

All substrate materials can be detected with line confocal sensors whether they are shiny, glossy or transparent (for example glass or PET foil). Furthermore, defects can be identified, such as delamination, scratches, or impurities in coating and transparent substrates.

Line confocal sensors provide quick and accurate 3D topography (surface) imaging whether it is for screen-printing, inkjet printing, or dispensing materials. They also provide step height and width measurement of printed structures.

In addition, cemented or glued components on transparent substrates are easily captured. Traditional 3D dimensional measurements can still be taken, however line confocal sensors also allow for the inspection of air gaps, bubbles, and other types of delamination on or through the transparent substrate.

 

Medical applications

3D line confocal sensors are able to scan the depth and shape of embossed and etched 3D features, parting line flash of molded parts, surface roughness and texture of extruded parts and web products, and burr height in precision-stamped and micro-machined medical parts.

One of the most common applications leveraging the large measurement range of tomographic line confocal imaging is the non-destructive inspection of completeness and integrity of heat seals in sterile medical packages.

Conclusion

3D line confocal sensors provide a highly specialised vision solution for the most challenging, complex measurement applications. Their ability to simultaneously generate 3D tomography, 3D topography, and 2D intensity data allows these sensors to perform high accuracy measurement tasks that conventional solutions can’t solve, such as scanning and quality inspection of curved, transparent, multi-layered, and highly reflective materials.

In addition, these sensors offer much faster scan rates than competing metrology-grade technologies, making them suitable for inline production environments.

 

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