In today’s Display Daily, I would like to focus on a new production technique for light management sheets for use in LED backlights. Such technology is important in efficiently creating uniform light over the LCD panels from a series of LED point light sources — no small feat. While the design of these light management structures is obviously important, so is their manufacture, as they must be produced in high volume at low cost.

Art Berman
Insight Media Consultant

The Fraunhofer-Institut für Produktionstechnologie (Aachen, Germany) or IPT says they have developed means to produce fiber optic sheets for light management of LED backlights that appears to have great commercial potential. But, instead of focusing on the design of this element, let’s talk about the manufacture of it using a newly developed and innovative machine to cover large sheets with the necessary microstructures.

The process starts by making a master. The master, actually a stamp, consists of a thin nickel sheet that is 2 by 2 millimeters. Using ultra precise accuracy and special diamond tools, the machine produces a periodic sequence of micron-sized structures to the surface of the nickel sheet.

In a procedure similar to the step-and-repeat process used in semiconductor photolithography, the stamp is then precisely indexed across the surface of a plastic sheet. As it moves across the sheet, the surface is embossed with microstructures. It takes a few days for the machine to process the entire surface of the sheet, which can be as large as 2 by 1 meters. Although this may seem like a long time, it is actually far shorter than the weeks or even months required by previous methods.

After the sheet has been prepared, several parameters must be tested to determine if the microstructured master have the desired characteristics. Christian Wenzel, a Senior Engineer at IPT, stated that the machine can accomplish this task as well. "When about 80 percent of the surface is completely structured, the machine tests the properties of the sheet. If these properties do not meet optical design requirements, then the machine can implement necessary corrections during the imprint process, while the component is still in the machine." Wenzel says this as an important feature and advantage of IPT’s approach.

Once the plastic surface has the desired light control capabilities, the sheet is immersed in a nickel bath and galvanized. The resulting plastic panel can now serve as the master for mass replication.

IPT claims that sheets produced in this manner are the largest of their kind ever made in Europe. With the new process and equipment, IPT claims they are capable of producing optical components for a wide variety of lighting systems (including general illumination) and that they can be produced cost effectively when in mass production.