Wearables require flexible hybrid electronics with die thinned to less than 30mum, and handling these ultrathin die is turning out to be a critical part of the manufacturing process.
Ultrathin die (<50 µm) have been in production for years in stacked 3D ICs. Building on this experience, NextFlex is developing new manufacturing processes that integrate ultrathin die onto flexible substrates.
Availability of ultrathin die for development and prototyping is currently a major hurdle to creating flexible hybrid electronics for the wearables market. Working with Disco, a dicing and thinning equipment supplier, NextFlex has produced stress-free ultrathin wafers and die with thicknesses as low as 10 µm. This capability will enable ultrathin die to be made available both to the institute’s member base and to the commercial market.
Once wafers are thinned and the die singulated onto tape, it is necessary to develop a process for removing the die from the tape and placing them on flexible substrates. The Datacon die bonder from assembly equipment supplier Besi helped remove ultrathin die from the tape and enabled a high-accuracy placement onto flexible substrates.
Process development at NextFlex is currently focused on the use of polyimide (PI) and PET (polyethylene terephthalate) substrates suitable for additive processing of conductors. Stretchable materials and materials compatible with thermoforming will be added to the process development in the future. The process flow for removing ultrathin die from tape and attachment to flexible PI and PET substrates has been established for 50 µm and 30 µm die, with 10 µm die process now in development.
Silicon die need to slim down to new levels to meet the requirements of flexible hybrid electronics. (Source: NextFlex)
Not only is the process of thinning and handling die challenging, but having access to chips on a wafer for wafer-level thinning has proven to be difficult as well. Few IC makers can offer wafers in small lots and, yet, it is essential to the development of flexible hybrid electronics.
A big part of NextFlex’s focus is on enabling devices or the Internet of Things. The IoT vision of putting sensors everywhere depends on flexible hybrid electronics and its use of ultrathin die.
--Wilfried Bair is a senior engineering manager responsible for device integration and system-level hardware projects at NextFlex.