Ultra-thin flexible interposer - a flexible hybrid integration approach to replace wire bonds

An innovative, advanced packaging concept for integrating thin dies is presented. The novel packaging technique is based on a flip chip approach where an anisotropic conductive adhesive was used to bond thin dies on a flexible, polymeric interposing substrate. After bonding of the chip, a flexible potting material was coated over the chip and the substrate to complete the housing of the package. The package thus realised was mechanically bendable and it had a thickness of ~140 µm. Since the package is free of any wire bonds, overall heights of less than 200 µm can be realized. The paper describes the process flow followed for preparing the flexible interposer demonstrator samples. Furthermore, assembly techniques for integrating the flexible interposers on a flexible wiring substrate are discussed. Besides, mechanical and environmental reliability tests were performed with the samples which revealed a good reliability of the samples.