Ultra-thin-chip stack (UTCS) and ultra-thin-chip flex (UTCF)
For integration of small pitch dies into flexible and eventually stretchable platforms, we developed the UTCF technique. This is a process related to UTCS (see section 3D-WLP: ultra-thin-chip stacking (UTCS)) but with the end result being not a 3D-stack, but thinned dies embedded in a flexible foil interposer, see figure 1. A first demonstration was given of test dies embedded in a BCB/Cu stack, as shown in figure 2, RP167.
Figure 1: Thin dies embedded into dielectric and interconnected with metals can be released from their carrier wafer and form a UTCF `chip-in-foil'.
Figure 2: Demonstration of daisy chain test dies embedded in a UTCF `chip-in-foil'.