Stacking of ultra-thin film packages

This paper brings into light a new ultra-thin and highly flexible package with embedded active chips. In this technology, no supporting and permanent substrates were needed. Copper foil was used as temporal substrate, and it became the bottom circuit after patterning and etching processes. Ultra-thin chips with 20~25 mum thickness were assembled directly on the structured copper foils in a flip-chip fashion. The gap between chip and copper foil was only about 10 mum. Subsequently, the chips were embedded into flexible adhesive/polyimide polymer layers or alternatively in highly elastic polyurethane materials, with a copper foil always laminated on the top. The resultant ultra-thin film package (UTFP) has a thickness of 100 mum only. Each package sticking on a rod with 10 mm diameter could pass the electrical measuring. Stacking of three-layer chip embedded packages had also been realized and passed electrical measurements. The process details on each core technique will be disclosed, and some results will be presented in the paper.