A novel laser micro-machining technique to produce high density micro-structures called Synchronized Image Scanning (SIS) was introduced a couple of years ago. Over this period of time, the technique was refined in a major effort to meet the needs of various industries.
There is an increasing demand for micro-structuring of large and super large area optical films, e.g. for Rear Projection TV, anti counterfeit packaging material and 3D displays. Especially in the display industry, where the screens are ever increasing in size, established micro-structuring methods like e-beam milling, diamond turning or the reflow technique struggle to keep up with the development.
This paper explains how it is possible to direct laser etch hundreds of millions of lenses into a 2 m x 1.5 m substrate. It looks at the advances made in SIS in recent years regarding seam reduction, overall accuracy and precision when structuring super large area optical films, and it presents the tools and subsystems needed to generate the features in those films. Furthermore, the potential of this exciting laser micro-machining technique for rapid prototyping for all sorts of optical and non-optical structures is mapped out.
A new laser mask projection technique, Synchronised Image Scanning (SIS), has been developed for the efficient fabrication of dense arrays of repeating microstructures on large area substrates. This paper details the technique and provides specific examples of the type of structures that can be produced. SIS is a laser micro-machining technique where the information for the ablation of a specific 3D feature is stored as a linear array on a chrome-on-quartz mask. The feature is then written by synchronised motion and laser firing, such that the firing frequency of the laser corresponds to the spatial pitch of the features. This requires highly accurate laser triggering with low-jitter signals, and accurate stages with high resolution encoders. An add-in for CAD software has been developed to generate the mask pattern efficiently and error-free, using the 3D designs. SIS allows for major improvements in the accuracy and speed with which 3D patterns can be created over large areas by laser ablation. Feature sizes down to a few microns can be produced with excellent surface quality. Large areas of microstructures have wide ranging applications in many areas. One example is the machining of large polymer master panels for electroforming to produce moulds for replication of display enhancement films.
A facility for rapid prototyping of MEMS devices is crucial for the development of novel miniaturized components in all sectors of high-tech industry, e.g. telecommunications, information technology, micro-optics and aerospace. To overcome the disadvantages of existing techniques in terms of cost and flexibility, a new approach has been taken to provide a tool for rapid prototyping and small-scale production: Complex CAD/CAM software has been developed that automatically generates the tool paths according to a CAD drawing of the MEMS device. As laser ablation is a much more complicated process than mechanical machining, for which such software has already been in use for many years, the generation of these tool paths relies not only on geometric considerations, but also on a sophisticated simulation module taking into account various material and laser parameters and micro-effects. The following laser machining options have been implemented: cutting, hole drilling, slot cutting, 2D area clearing, pocketing and 2½D surface machining. Once the tool paths are available, a post processor translates this information into CNC commands that control a scanner head. This scanner head then guides the beam of a UV solid-state laser to machine the desired structure by direct laser ablation.
Two new laser mask projection techniques Synchronized Image Scanning (SIS) and Bow Tie Scanning (BTS) have been developed for the efficient fabrication of dense arrays of repeating 3D microstructures on large area substrates. Details of these techniques are given and examples of key industrial applications are shown.
The use of ceramic cores of high dielectric constant is an essential part of a strategy to miniaturize GPS antennas for mobile telephones. The core reduces the guide wavelength of the conducting structures on the antenna, thereby creating a need for high-resolution imaging to maintain very accurate dimensions. It is for this principal reason that a novel laser imaging technology has been developed using a positive electrophoretic photoresist and UV excimer laser mask imaging to produce the conducting features on the surface of the antenna. Furthermore, a significant process challenge in producing this type of antenna concerns the reproducibility of the right-hand circular polarization performance and the bandwidth over which this can be achieved - which becomes progressively smaller as antenna size is reduce. It is therefore a vital requirement that the antennas have the point to be tuned by a laser trimming process at an automatic RF testing station. A galvanometer controlled Nd:YAG laser spot is used to trim the conductive pattern on the top of the antenna following an RF measurement to characterize the resonant frequencies of the four helical conductors. Results demonstrate the laser imaging and trimming techniques ensure a high-speed method of guaranteeing the antenna performance. The technique is appropriate for other antenna types such as GSM, Bluetooth and Wireless LAN.