Preferential Orientation of Silicon Blocks During Fluidic Self-Assembly of Microelectronics

Abstract

Fluidic Self-Assembly (FSA) is a newly developed, high productivity method to assemble millimeter and submillimeter size silicon electronic components (blocks) into circuit boards. Large numbers of thin, truncated pyramid shaped components are released in water and move gravitationally down inclined substrates to fall into indentations (receptors) of complementary shape. To increase the rate of receptor filling and improve the process efficiency, the probability of proper alignment between blocks and receptors must be maximized. The present paper reports an experimental study aimed at determining the preferential orientation of the blocks in a practical FSA process. Blocks ranging in size from 1050 to 3050 microns were tested for: (i) in-plane orientation angle during their motion, and (ii) right-side-up (RSU) versus up-side-down (USD) landing upon dispensing. Results indicate that blocks exhibit a high degree of in-plane angular self-orientation, which depends on the block aspect ratio. Spatial orientation of blocks at the release point is a decisive factor on their correct (RSU) landing on the substrate. Based on this observation, an original dispensing strategy was developed that increased the RSU fraction to values typically over 90%.