Imaging inspection system measures microscopic bond connections

Sensors used in the automotive industry often fulfill high-risk safety functions, and as such, a missing or deficient bond wire within a sensor is unacceptable. Consequently, SMD Production-Technology and WENO were tasked by a leading provider of sensor technology with developing a testing system that can check every single bond wire on every sensor.

On the sensors, 30 µm aluminum wires are bonded/welded both to the chip and the gold pad, producing wires that measure approximately 10-15 µm in height and 35µm to 60µm in width. With this, the companies needed to develop an advanced imaging system that ensured precision below 100 µm, which had yet to be accomplished. As a result, the companies collaborated on the µ-Precision Inspection System, a testing facility that meets these technical challenges and demands.

Sensors are placed on a base board in a 10x8 matrix so that 80 sensors can be tested in a single test procedure. Individual sensors are loaded anywhere between 18 and 26 bond wires, depending on the design, that exhibit both bond positions “source” and “destination.” The system uses two monochrome Guppy F-146B cameras from Allied Vision Technologies (AVT). These models are small FireWire cameras for industrial inspection applications that are equipped with a 1.4MPixel Sony ICX267 CCD sensor which can deliver 17.7 fps at full resolution. Both cameras are equipped with telecentric measurement lenses, and with the aid of an LED light, the contrast between the bond/spot weld and the background is increased, according to the AVT case study.

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