Researchers at IMEC (Interuniversity Microelectronics Consortium) and at Ghent University recently demonstrated results from a 3-D integration process using highly thinned ICs with flexible packaging, materials to create fully flexible circuit assemblies. Researchers thinned an IC die to a thickness of 25 microns. They then mounted the die in an ultrathin, flexible package, which they in turn embedded in a conventional flexible, two-layer PCB (printed-circuit board) using standard flexible-circuit equipment. Such assemblies could have a finished thickness of less than 60 microns.

The approach employs ultrathin interposers in the packaging process. The interposers make the packaged chip fully testable, solving the known-good-die problem, and increase the spacing of the pins on the package, eliminating the need for high-density traces on the flexible PCB.

In the demonstration, IMEC showed a flexible, wearable patient-monitoring board that can measure heart rate and muscle activity and transmit the data wirelessly to a monitoring station. The board includes a microcontroller with an ADC, a biopotential amplifier, and a radio transceiver.