Chip Lid Molding ENGR Pre Lab

Micro-fabrication  How can we produce devices on a very small scale ?  e.g. Device dimensions 10 nm – 400 µm  Answer: Two ways  Top – Down conventional manufacturing approaches at a reduced scale, such as CNC milling and photolithography  Bottom – Up controlling molecular-level interactions to create substances with the required properties

Evolution of Top-Down Micro- fabrication  Originally developed by microelectronics silicon industry  Refined for nanoscale fabrication  Extended to polymer micro/nanofabrication  Polymers are flexible and bio-compatible

Photolithography  Photolithography is a common micro-fabrication technique used to transfer an image from a photomask to the surface of a substrate by using ultraviolet light.  The components needed for Photolithography are light source, photomask, lens and wafer.

LOC fabrication  For this LOC project chips will be produced in a three step process.  First, each team creates a CAD file of their LOC design.  Second, acrylic wafers are milled with a CNC machine from the CAD design.  Third, we will mold plain PDMS lids (no pattern) to enclose the channels and wells of the acrylic wafer.

Molding  LOC wells and channels will be sealed with a flexible lid.  In order to mold our LOC lids, we mix PDMS (silicone rubber) resin with its hardener(catalyst) in a disposable cup by stirring rigorously.  This mixing creates a lot of bubbles and we need to get rid of those bubbles since we do not want any optical defects in our molds.

Degassing Liquids  We get rid of these bubbles using vacuum  Lower pressure expands bubbles by increasing the volume of the gas  Lower pressure reduces the solubility of air in the liquid thus causing bubbles to surface.  Cycling vacuum and atmospheric pressure creates a driving force to remove bubbles from the liquid phase and have a defect free mold.

Learning Objectives of Lab  Expose students to a lab-on-a-chip fabrication technique utilizing polydimethylsiloxane (PDMS) to produce the lids for the acrylic chip bases.  Introduce student to the issues concerning material safety data sheets (MSDS) and safe or appropriate handling of materials based on the information provided in an MSDS.