IWLPC (Wafer-Level Packaging) Conference Proceedings


ELECTRONICS ON DEFORMABLE ULTRA-THIN SUBSTRATES

Author: M. Bartek et al.
Company: Delft University of Technology
Date Published: 11/3/2005   Conference: IWLPC (Wafer-Level Packaging)


Abstract: In this paper, results of our work on mechanical reliability issues of ultra-thin (<1 µm) poly- and single crystalline silicon layers transferred onto a thin polyimide carrier (thickness ~8-9 µm) using substrate transfer technology for highly flexible RF-ID tags applications are presented. By embedding the ultra-thin silicon layers into a thin flexible polyimide substrate and patterning of silicon into square or hexagonal segmentations (segment side length of 150-2000 µm), increased mechanical flexibility and resistance against cracks could be reached. Generation of cracks within the silicon and dielectric layers is studied under controlled bending and tensile loads using bending and tensile tools, being specially designed for this purpose. Specimen observation was performed, using optical microscopy with possibility of digital recording and evaluation by pattern recognition software.

The results show that the cracks appear first in the dielectric layers in-between the silicon layer segments and only at higher loads propagate or are initiated within the silicon itself. The development of first cracks depends significantly on the silicon-layer segmentation dimensions. This affects both the crack density and the crack width. On optimized structures under the bending tests, no crack detection down to a bending radius of 1 mm was observed.

Key words: RF-ID tag, flexible substrate, substrate transfer technology, ultra-thin substrate.



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