Simpex's Micro Laser Ultrasonic Technology combines a pulse laser and a continuous wave laser detector forming a cause-and-effect sensing device.  Simply, the pulse laser sends a single pulse of controlled light energy to pulse the object of interest (i.e. a ball bond) causing a thermoelastic excitation response.  This excitation induces an ultrasonic propagation (surface and bulk waves) on and through its neighboring materials.  The continuous wave laser (detector) picks up the configuration and magnitude of the surface waves, which in turn, correlate to the bonding status of the joined materials (Picture 1).  

This technique can be described as the classical "pebble in the pond" scenario, whereby a pebble is dropped into the middle of the pond, which causes a "wake" or a series of waves on the surface of the water (Picture 2).  This "wake" propagates outwards from the center of the pond.  By observing and correlating the characteristics of the wake, one can determine the fluidity of the water in the pond, as well as the size, the height, and the velocity of the pebble.

Since our cause-and-effect device consists of well-controlled light beams, their footprints can be focused to accommodate the miniaturization trend of microcircuits.  Picture 3 shows the pulse (cause) and detect (effect) beams are about 0.0005 inch in diameter, while Picture 4 displays the power density control to accommodate varying test point sizes. 

Our Micro Laser Ultrasonic Technology is much improved from the traditional contact type methods.  The test points need not be contacted, nor would its shape be modified.  The excitation is much gentler than that required in a contact test.  Since light is being used as a carrier of information, the speed of testing is much faster (less than a millionth of a second) than any automated wire bonding machines, lending itself to automation and real-time process control.

Instead of current pulling and shearing, materials under test can be 'steered' to the laser beams using a high speed transport stage.  The bond integrity test, therefore, can be performed by a point and shoot scenario (Picture 5).  With embedded machine vision, high resolution sensors, and digital signal processing algorithms, this technology can be used to automatically search, target and test the bonding integrity with no operator intervention.  The operator is only required to load and unload the part under test.