One of the main obstacles to the continuation of scaling of modern electronic systems can be found in the minimal component size that can be assembled and electrically connected effectively. Current technology for chip-scale packaging and assembly relies on robotic pick-and-place. For example, a high-end assembly system is able to assemble about 8000 chips per hour with a placement accuracy of 30 micrometer considering a typical chip size of 1 mm. Microscopic chips and higher alignment accuracy decrease the throughput dramatically and can generally not be assembled effectively. Moreover, robotic pick-and-place faces challenges in cases where the substrates are not rigid and perfectly planar. However, the next generation of electronics is going to be mechanically flexible and in some cases stretchable. An alternative assembly process that enables assembly on any substrate (hard, soft, flexible, stretchable) and topology (curved, convex, concave, etc.) are in high demand.
Researchers have been constantly seeking an alternative to serial robotic pick-and-place on a single component basis, and several highly-parallel assembly techniques have been proposed. Two novel assembly options have emerged. Read more
The first option uses the concepts of parallel transfer to transfer chip and nanoscopic device segments from a donor wafer to a target substrate in large quantities.
Transfer processes are challenged when it comes to the redistribution of chips, assembly on curved topologies, alignment to soft or flexible substrates with non-uniformity in localized expansion coefficients. Furthermore, the assembly of large quantities of disparate parts from several donor wafers is more challenging.
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The second option is to utilize concepts of directed and engineered self-assembly. In contrast to parallel transfer, self-assembly is advantageous because it can distribute chips over larger areas. For example, a binned container full of semiconductor dies/chiplets of a certain type and quality can be redistributed and assembled at precise locations on a substrate at any desired pitch or functional density using methods of directed self-assembly.
Directed self-assembly is a fairly old technique. For example, the concept of surface tension has been used extensively before as a method for alignment or to fold structures out of plane.