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Though Microsoft's Kinect for the Xbox is the first consumer product which uses the fringe detection principle, it was and still is a method commonly used to measure and analyze 3D objects and surfaces. Typical applications include the classification of grinding tools, quality control for engine parts (automotive, aerospace, defense), planarity measurements,  reverse engineering, and - of course - solder paste inspection in the PCB manufacturing process.

Most solder defects on printed circuit boards are caused either by placement errors (wrong part or position) or by errors during the screen printing. For example, too much solder can lead to shorts, too little paste can result in open connections on SMT parts. Having an inspection step right after solder paste printing is a safe and cost-effective way to avoid solder defects, which could still easily be repaired by cleaning and re-printing.

How does Fringe Detection work?

The fringe detection method, or "3D Line scanner" as the industry typically calls it, projects light patterns on the object of interest (solder paste), one or more cameras record the reflections, and software creates a 3D model of the object. The third dimension (height information) is crucial for this application: an AOI system with a regular 2D camera could measure two dimensions (x and y) of the solder paste spot, but without the height (z), no volume calculation would be possible. With a 3D Line Scanner all three values are available and shape, volume, and dimensions can be measured.

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In a fully automated assembly line, speed and flexibility is everything, and just like with its AOI and AXI equipment, GOEPEL has designed a highly modular SPI system which is able to achieve an inspection speed of up to 90 sqcm/s.

GOEPEL has introduced "OptiCon SPI-Line 3D", an in-line 3D solder paste inspection system that enables precise three-dimensional solder paste measurement in terms of height, volume, offset, and smearing. The core element is a specifically developed 3D camera head, functionally based on the fringe projection principle and operating without moving parts.  Three system configurations are available, differing in their lateral resolutions of 10 μm, 15 μm, and 20 μm. In high-speed mode, the system achieves an inspection speed of up to 90 cm²/s with extraordinary precision.

Datasheet: 

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