Liquid encapsulant and uniaxial calibration mechanical stress measurement with the ATC04 assembly test chip

A new assembly test chip, ATC04, designed to measure mechanical stresses at the die surface has been built and tested. This CMOS chip, 0.25 in. on a side, has an array of 25 piezoresistive stress sensing cells, four resistive heaters and two ring oscillators. The ATC04 chip facilitates making stress measurements with relatively simple test equipment and data analysis. The design, use, and accuracy of the chip are discussed and initial results presented from three types of stress measurement experiments: four-point bending calibration, single point bending of a substrate with an ATC04 attached by epoxy, and stress produced by a liquid epoxy encapsulant.<>