Thin Dice Research Articles

Scalable Batch Transfer of Individual Silicon Dice for Ultra-Flexible Polyimide-Based Bioelectronic Devices.

Demands on flexible neural interfaces in terms of functionality, spatial resolution and longevity have increased in the past years. These requirements can be met by sophisticated integrated circuits developed in CMOS (complementary metal oxide semiconductor) technology. Embedding such fabricated dice into flexible polymeric substrates greatly enhances the adaption to the mechanical environment in the body. With the process developed here, 100 % of individual dice (n = 34, 390 x 390 μm2) could be transferred simultaneously into polyimide (PI) substrates with simple and exact positioning (0.2° rotational and 5 μm translational error). Levelled layer build-up and standard microfabrication technologies could be used for CMOS-post-processing in order to manufacture metal interconnections between contact pads of 100 μm thin dice and PI insulation as selectively patterned device substrate. The process allows for individual positioning according to desired shape of the final chip-in-foil-system and for upscaling the number of dice to be transferred. Furthermore, final distribution and embedding of dice on the flexible substrate is independent from their distribution on the CMOS fabrication wafer the and does not require additional adhesion promoters. During fabrication the transfer method is insensitive to high temperatures (450 °C in this study) and hence enables a wide range of post-processes. Shear strength between dice and PI substrate was characterized by shear tests and results (58.1 ± 13.7 MPa) are in the range achieved with the adhesive benzocyclobutene (BCB).

Fabrication and Electrical Evaluation of Via Last Polymer Liner TSVs

Imec is developing two TSV flavors for Si thicknesses of 50 and 100 μm for various wafer level packaging (WLP) applications where thin dice are stacked and electrically connected to each other through post CMOS processed TSVs and microbumps. As a differentiator, these TSV technologies use spin-on dielectric polymers as the insulating liner. A three-mask process sequence is implemented for fabrication of both TSV types; however, the TSV shape, the process flow, and the Si thickness are different for each one of them. All processes employed in the fabrication of the TSVs are performed at low temperature (<200°C) for post CMOS compatibility. For both TSV types, electrically yielding TSV connected daisy chains are measured on the fabricated wafers and the reliability of the TSVs while undergoing thermal cycle tests is analyzed.

Printing technology for ubiquitous electronics

PurposeThe purpose of this paper is to analyze the economics of various printing processes proposed for small‐scale electronic products such as radio frequency identification tags, smart cards, and wireless sensors, and to present a new transfer printing method.Design/methodology/approachThe costs of several types of microstructuring techniques were calculated from commercial product data, along with a detailed spreadsheet simulation of inkjet printing for microelectronics. A new material for transfer printing was developed, along with suitable tooling for placing small and thin dice on flexible substrates.FindingsThe cost analysis of inkjet printing suggests that it may not be substantially less expensive than conventional silicon technology for this purpose, while achieving inferior performance. Offset printing is cheaper but further from practicality. The new transfer printing process successfully prints very small silicon dice at high speed, and appears to meet the market needs with respect to cost, product performance and flexibility in readily producing different designs.Research limitations/implicationsThe cost analysis depends on assumptions which are not all well known, and which change with time. The new method has not yet been run in a high‐volume production mode. Such experience will be necessary to fully confirm its value.Originality/valueThis analysis identifies cost factors which have not been generally appreciated in public discussions of printed electronics. The transfer printing process offers a unique way to make cost‐effective use of silicon integrated circuits which are much smaller than any that appear in products today, and may have ramifications beyond the original target of tags and sensors.