Mechanical and electrical properties of ultra-thin chips and flexible electronics assemblies during bending

•A bending test for measuring bending properties of ultra-thin chips at high curvature was developed.•Bending radii of less than 0.5mm were measured.•20μm thick microcontrollers were successfully flip-chip bonded directly on flexible foils.•Influence of bending on microcontroller electronic properties was measured. Ultra-thin chips of less than 20μm become flexible, allowing integration of silicon IC technology with highly flexible electronics such as food packaging sensor systems or healthcare and sport monitoring tags as wearable patches or even directly in clothing textile. The ultra-thin chips in these products will be bent to a very high curvature, which puts a large strain on the chips during use. In this paper a modified four-point bending method is presented, which is capable of measuring chip stress at high curvatures. The strength of several types of ultra-thin chips is evaluated, including standalone ultra-thin test chips and back-thinned 20μm thick microcontrollers, as well as assemblies containing integrated ultra-thin microcontroller chips. The effect of chip thickness, bending direction and backside finish on strength and minimum bending radius is investigated using the modified four point bending method. The effect of bonding ultra-thin chips to flexible foils on the assembly strength and minimum bending radius is evaluated as well as the effect of bending on electrical properties of the bonded microcontroller dies.