Technologists from Belgian research association IMEC and its associated laboratory at Ghent University have unveiled a 3D integration process enabling flexible electronic systems with a thickness of less than 60 micrometres. The ultra-thin chip package (UTCP) technology allows the integration of complete systems in a conventional low-cost flex substrate. IMEC claims this paves the way to low-cost, unobtrusive wearable electronics such as that required for health and comfort monitoring.
For integration, the chip is first thinned down to 25 microns and embedded in a flexible ultra-thin chip package. Next, the package is embedded in a standard double-layer flex printed circuit board (PCB) using standard flex PCB production techniques. After embedding, other components can be mounted above and below the embedded chip, leading to a high-density integration.
The integration process uses UTCP interposers that solve the so-called “Known Good Die” issue by enabling easy testing of the packaged thin dies before embedding. Expensive high-density flexible substrates can be avoided by the fan-out UTCP technology that relaxes the interconnection pitch from 100 micrometres or lower to 300 micrometers or more, compatible with standard flex substrates.
The organisation demonstrated the integration technology with a prototype flexible wireless monitor that measures the heart rate (electrocardiogram, or ECG) and muscle activity (electromyogram, or EMG). The system comprised an embedded ultra-thin chip for the microcontroller and analogue-to-digital converter, an ultra-low power biopotential amplifier chip and a radio transceiver. By thinning down the chips for UTCP embedding, they become mechanically flexible making the system unobtrusive and comfortable to wear.