Embedding and assembly of ultrathin chips in multilayer flex boards

Purpose - The purpose of this paper is to present results from the EC funded project SHIFT (Smart High Integration Flex Technologies) on the embedding in and the assembly on flex substrates of ultrathin chips. Design/methodology/approach - Methods to embed chips in flex include flip-chip assembly and subsequent lamination, or the construction of a separate ultra-thin chip package (UTCP) using spin-on polyimides and thin-film metallisation technology. Thinning and separation of the chips is done using a dicing-by-thinning method. Findings - The feasibility of both chip embedding methods has been demonstrated, as well as that of the chip thinning method. Lamination of four layers of flex with ultrathin chips could be achieved without chip breakage. The UTCP technology results in a 60 mu m package where also the 20 mu m thick chip is bendable. Research limitations/implications - Further development work includes reliability testing, embedding of the UTCP in conventional flex, and construction of functional demonstrators using the developed technologies. Originality/value - Thinning down silicon chips to thicknesses of 25 mu m and lower is an innovative technology, as well as assembly and embedding of these chips in flexible substrates.