Self-Assembly and Self-Tiling: Integrating Active Dies Across Length Scales on Flexible Substrates

Abstract

Abstract-This paper reports on recent progress in the field of directed self-assembly, wherein discrete inorganic semiconductor device components are assembled on flexible substrates, and compares these results with prior work. The research aims to develop self-assembly-based chiplet assembly processes that can extend minimal die sizes and throughput beyond what is currently possible with robotic pick and place methods. This manuscript concentrates on self-assembly that is driven by the reduction of surface free energy between liquid solder-coated areas on a substrate and metal-coated contacts on semiconductor dies that act as binding sites. Scaling prior results to sub-100 micrometer-sized components has required a transition to a new self-assembly platform. Specifically, recent work has moved from a drum delivery concept to a new scheme that uses a stepwise reduction of interfacial free energy at a triple interface between oil, water, and a penetrating solder-patterned substrate to introduce components. Finally, this paper also discusses design rules to produce highly periodic "selftiled" domains on rigid, flexible, and curved substrates. We describe discrete, self-tiled, and microconcentrator-augmented solar cell modules as applications that are fault tolerant and reduce the amount of Si material used by up to a factor of 22 when compared to conventional cells.

Surface tension-driven self-alignment

“…20-60 mm-sized semiconductor components were assembled on a vertically pulled substrate at a silicon oil/water/substrate triple interface. 59,78 The surface chemical treatment of the components and the chosen immiscible fluid couple made the trapping of the chiplets at the interface energetically favourable. The authors reported the largest self-assembly throughput to date with 62 500 chips assembled in 45 s, equivalent to 1388 s À1 .…”

“…14d). The structure hosting the assembly system can be a bath, 28,29,137 a rotating drum, 78 or a reel-to-reel machine. 127 The benefit lies in the parallelism and precision of the process achieved without high-precision mechanism.…”

“…Mechanical trapping based on three-dimensional geometric features has been exploited to direct component assembly, program multistep assembly sequences and enforce unique component orientation. Examples include stochastic component feeding over a planar template for batch pre-alignment, 92 alignment wells and pedestals for univocal component assembly, 78 shape-specific recessed receptors for the simultaneous and non-interferring assembly of matching components 128,137 and three-dimensional shape-encoded sequential self-assembly. 138 Capillary self-alignment can correct the initial translational and rotational offsets of the feeding step relative to the final, correctly aligned position (see Section 2.2).…”

“…The earliest and simplest strategy consists in the use of an electrically conductive fluid material as the medium for the self-alignment. Dating back to the original IBM's C4 process, 14 molten solder driven self-alignment 111,112 has been object of intense research through the years and is still actively employed in advanced implementations of parallel roll-to-roll stochastic assembly of microcomponents 12,59,78,127 (see also Sections 3.1.1 and 6.2.1). In this version of capillary self-alignment, a solder material is coated on the metal-finished surface of the receptor or of its fractions where the interconnections need to be established.…”

Self-Assembly Kinetics of Microscale Components: A Parametric Evaluation

“…Many efforts have also succeeded at augmenting the strengths of microscale SA by adding more complex process capabilities. While this text offers a brief review on this topic, other reviews are useful for complementing the information given here (Cohn et al, 1998;R. Knuesel & Park, 2012;M Mastrangeli, Abbasi, et al, 2009 Besides showing a functional product, this work demonstrated the integration of components and substrates that come from incompatible fabrication processes (J.…”