Microetching Fabrication

Microetchings are made up of a tremendous number of microscopic ridges engineered to reflect light in a specific way.  The shear number of ridges requires what is known as a parallel process.  This means that opposed to fabricating each ridge sequentially, they must be fabricated simultaneously.  The difference is similar to hand writing a letter vs printing a book using a printing press.  The printing press of the microfabrication world is a process called lithography.

Lithography comes in many different flavors but the most prevalent technique uses ultraviolet(UV) light to chemically alter a layer of material called photoresist.  Photoresist is similar to spaghetti on a molecular scale.  The molecules are long and can be tangled.  Much like how a bowl of spaghetti left on the kitchen counter for too long will become a solid mass, negative resists will be solidified by exposure to UV light, creating bonds between the different strands.  On the other hand, exposure to UV light can also break bonds and in positive resists UV light exposure will essentially cut the molecular chains into smaller pieces that are more easily disentangled.  The resist is then placed in a development solution which is formulated to separate the exposed from the unexposed resists.  In a positive resist the exposed regions will wash away.  In a negative resist, the unexposed regions will wash away.  Complex patterns can be created in the resist by shining the UV light through an object referred to as a mask which is designed to block the UV light in the desired way.  Much like how the typeset block on the printing press is reused thousands of times, the mask can be used repeatedly.

In general, the purpose of this is to selectively uncover the layer under the resist.  For instance, a Printed Circuit Board (PCB) begins its life as a copper clad fiberglass board.  The board is laminated in photoresist, exposed to UV light through a mask, and then developed.  The remaining photoresist will protect the surface of the copper so that when the board is placed into a copper acid etch the exposed copper will be dissolved away.  What remains will be copper traces that can electrically connect different microchips thousands of leads on microchips.

We make use of this mature technology, but alter it for our own ends, but push it well beyond its intended limits.  We laminate a negative resist onto a sheet of metal which serves merely as a substrate.  Our mask consists of a clear plastic sheet onto which our microscopic ridge pattern has been printed using a specialty printer capable of producing 5µm pixels.  This is similar to an overhead projector transparency.  We expose the resist through the mask using a DIY exposure unit we built capable of producing bright collimated UV light over a large area.  However, unlike traditional lithographic processes, we do not attempt to develop the resist all of the way to the substrate.  Rather, we use the developer to nick the surface to leave the ridge pattern we need for the microetching.  Getting the proper ridge shape to make the most of our light isn't easy and requires us to maintain precise control over many of the secondary variables that most people in traditional lithography can ignore.

The photoresist now has the desired topography, but photoresist isn't particularly pretty or reflective.  Greg then carefully gilds the microetching in gold leaf.  Gold leaf has a thickness on the order of 100's of nanometers and is very maluable.  It can be pressed into the topography, effectively coating the resist ina layer of gold that will not tarnish and stay very reflective for a long time.

From there, the microetching can be mounted and lit with engineered light sources that have been designed to function with the ridge pattern to produce the desired effect for the audience.