Inspection reaches micrometre precision to test electronic connections

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Automation system providers, SMD Production-Technology (SMD-PT) and Weno, have developed an inspection system for testing electrical wiring in automotive sensors.

The µ-Precision inspection system is designed to check sensor wiring only a few micrometres thick, any defects in which would result in failure of the electrical component. The inspection system was developed specifically for a sensor manufacturer supplying the automotive industry.

The sensors have 30µm aluminium wires welded both to the chip as well as to a gold pad. After welding, the wire has only 10-15µm height, and the width, or deformation, comprises 35µm to 60µm, according to specification. As a rule, tolerance falls within ±2-4µm.

Eighty sensors can be inspected at one go, with each sensor containing between 18 and 26 bond wires. One camera is used to align the position of the sensors in the test chamber based on fiducial markings. Two further cameras capture parallel images from two different sensors in more than 2,000 test positions.

Due to the combination of an ingenious illumination concept and patented software, the companies claim that µ-Precision is the only known device that achieves such precision in a single conventional imaging system.

The cameras used are Guppy F-146B monochrome models from Allied Vision Technologies. The Guppy F-146 is a small FireWire camera for industrial inspection. Equipped with a 1.4 megapixel CCD sensor, it delivers 17.7fps at full resolution. Both inspection cameras are equipped with telecentric measurement lenses. LED illumination increases the contrast between the spot weld and the background.

The images are limited to an area of interest of 500 x 700 pixels providing a resolution of approximately 0.8µm per pixel. Each wire forms an arc between two connection points. On the back of this arc, a light reflection is generated which is recognised by software based on the Matrox Imaging Library.

Using this information, the wires are counted and tested for integrity. The shape and position of the reflection provide further information about the arc’s height. Finally, the software analyses the images of the bond spot welds and calculates their dimensions with the highest precision using their geometry. The gap between spot weld and tail is measured as well.

Jürgen Kemenas, SMD-PT owner and Weno marketing and sales manager, commented: ‘We had mastered the greatest technical challenges, namely measuring bond wire connections with our imaging system with precision never achieved before. But the problem was that this hadn’t happened fast enough.’

One measurement cycle lasted eight minutes, while the customer’s specification sheet projected a maximum of six minutes. ‘In our efforts to accelerate the processes, we turned to AVT Support. The solution came from them in the form of another SDK. AVT engineers recommended the brand-new Vimba driver and supported us in integrating it into our application,' said Kemenas.

Using the new driver, they achieved a cycle time under the six-minute mark and the customer’s requirements were met. Since then, the system has been successfully used for quality assurance of sensors for well-known German automobile manufacturers.

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