Active Test Chips for in Situ Wire Bonding Process Characterisation

The real-time monitoring of an industrial ball bonding process is reported using a new type of test chips with custom-made integrated sensors (microsensors). These sensors were fabricated using a commercial double-metal CMOS process [1]. Two types of integrated monitors are reported, a temperature [2] and an ultrasound shear force sensor [3]. The temperature sensor uses the thermoelectric properties of the lower aluminium metallisation of the test chip. The sensor is integrated as a meander around a circular test pad, at an average distance of 102 μm from the pad centre. During bonding at a chip temperature of 106°C, the sensor first experiences a decrease in temperature of –3 K due to the cooling by the capillary. Subsequently, the temperature increases by 2.3 K due to the ultrasound dissipation. The ultrasound shear force sensor is based on the piezoresistive p+-diffusion and is integrated in a Wheatstone bridge configuration. The sensor design provides a high sensitivity to oscillating stresses while suppressing the bonding force and temperature signals. Based on evaluations of the fundamental and harmonic components of the microsensor signal, four consecutive phases were identified, and the first three were found to be necessary for successful ball bond formaACTIVE TEST CHIPS FOR IN SITU WIRE BONDING PROCESS CHARACTERISATION Michael Mayer, Juerg Schwizer*, Daniel Bolliger, Oliver Paul**, and Juergen Steinbichler ESEC, 6330-Cham, Switzerland *Physical Electronics Laboratory, ETH Hoenggerberg, 8093-Zurich, Switzerland **IMTEK–Materials, University of Freiburg, 79110-Freiburg, Germany