Eric Beyne, imec

In the medical field, electronic devices will be instrumental to control the increasing cost of health care, and in the field of energy, one sees an urgent need for increasing power efficiency. Consequently, we expect a strong increase in the microelectronic content in many applications. .

Jan Vanfleteren, imec - UGent

Recently, industry has consolidated to adopting the 3D-stacked IC approach as the most performing and economically most viable 3D technology for mainstream consumer and high performance applications, In order to optimize performance and cost of such applications, imec worked on scaling TSV diameter and chip-to-chip interconnect pitch. For this we investigated novel techniques and materials enabling to electrically isolate scaled TSVs and to metalize them. In the field of microbump, we identified and resolved specific integration and reliability challenges that pertain to the extreme scaling of the micro bump pitch.

Imec also explored the scaling potential of alternative, direct metal chip-to-chip interconnections. We also evaluated extended device thinning and handling of ultra thin wafers and dies and we researched and proposed solutions for challenges related to the integration of an extreme thinning process onto microbumped device wafers. Also 3D-stack packaging is an integral part of the work performed by imec and its partners in order to enable scaled 3D-systems to become reality.

Another development that is being addressed at ESTC is the ultrathin chip package (UTCP). In this technology bare Si or III-V semiconductor chips are thinned down from their initial thickness of a few hundreds of microns to a thickness of 20 to 30µm. Subsequently they are embedded in polyimide sheets, produced from spin-on precursors. The resulting package is as thin as 60 to 100µm.

Today, most electronic appliances are rigid, or at most mechanically flexible. In the future, many electronic assemblies on rigid substrates will be replaced by mechanically flexible or even stretchable alternatives. This is a consequence of the ambient intelligence vision where the user carries along more and more electronic systems near the body, on or even inside the body.

These systems must be light weight, take the shape of the object in which they are integrated, and follow all complex movements of these objects, explaining the need for elasticity. Typical examples are implants, intelligent textile, portable electronic equipment (e.g. mobile phones), robotics, car electronics, ...

A number of flexible technologies is currently under investigation. For implantable devices, biocompatibility of the package is an important aspect, and for intelligent textile applications, washability of the circuits is also under investigation. A first option is based on components with standard rigid packages that are connected with elastic electrical interconnections.

Another option contains electrical interconnections of meander shaped metal tracks, which under deformation act as 2-dimensional springs. And finally, a technology with circuits embedded in an elastic material like PDMS (silicone) or poly-urethane (PU) is under development. Stretchability of up to 100% (1-time stretching) of these circuits has been demonstrated.

At ESTC, imec together with the university of Ghent, presented an ultra-thin, flexible chip with bendable and stretchable interconnects integrated into a package that adapts dynamically to curving and bending surfaces. A commercially available microcontroller was thinned down to 30µm, preserving the electrical performance and functionality. This die was then embedded in a slim polyimide package (40-50µm thick).

Next, this ultrathin chip was integrated with stretchable electrical wiring. These were realized by patterning polyimide-supported meandering horseshoe-shaped wires, a technology developed and optimized at the lab. Last, the package was embedded in an elastomeric substrate, e.g. polydimethylsiloxane (PDMS). In this substrate, the conductors behave as two dimensional springs, enabling greater flexibility while preserving conductivity.