Selective one-step plasma patterning process for fluidic self-assembly of silicon chips

Applying a tetrafluoromethane (CF₄) low pressure plasma process to the surface of a polymeric foil with a structured thin film copper layer on top results in an opposed wettability behavior of metal areas and polymer areas. Difference in the local water contact angle between the hydrophobic polymer and the hydrophilic copper after a maskless CF₄ plasma treatment is 95deg-105deg. By storing the plasma treated foils under nitrogen their programmed wetting behavior can be preserved for at least ten day. The special wetting properties of surface energy patterned foils favor them as substrate materials in fluidic self assembly processes. Self alignment of small and thin silicon chips on copper bonding sites on polyimide foils was observed. Specific design patterns are proposed that enable both bonding of dies at dedicated target positions and electrical interconnects at front side or rear side of electronic components with two connection pads. Using a droplet of water as assembly medium and an anisotropic conductive adhesive (ACA) coating lead to successfully assembled test chips on patterned polyimide foils that were pre-treated in the selective one-step CF₄ plasma.