Processes
Screen printing
Screen printing is a printmaking technique that creates a sharp-edged image using a stencil. Squeegees are generally used to physically deposit and distribute the a paste evenly across the stencil. By properly rolling the squeegee over the stencil, the printing paste passes through the stencil apertures and gets deposited on designated areas on the substrate. The stencil is then lifted, leaving behind the intended paste pattern.
Printing electronics by screen printing means to produce structures with a resolution less than 100 µm and a thickness of 10 – 150 µm in a reproduce able way. Critical parameters for high-quality paste printing include print speed, print pressure, separation speed/distance (or the speed/distance at which the substrate and the stencil are separated), and printer alignment.
The environment in which paste printing is done is also important. Defects such as bridging and poor wetting can be caused by dust particles or microscopic fibers in the air that end up on the substrate or stencil. Quick drying of the printing paste, on the other hand, can be caused by high ambient temperature or the presence of air draft that accelerates solvent evaporation. The viscosity of the paste will also be difficult to keep under control in an environment with fluctuating ambient temperature and humidity. Therefore climate controlled environment is necessary, although it has not be a clean room facility.
Laser engraving and – cutting
Plastic electronic uses a hybrid laser system consisting of a CO2- and a Nd:YAG-laser with an active working area of 730 x 436 mm and a working speed of 200 cm/sec.
Laser engraving is the practice of using lasers to engrave or mark an substrate. The technique does not involve tool bits which contact the engraving surface and wear out. This is considered an advantage over alternative engraving technologies where bit heads have to be replaced regularly.
The setup of the laser table involves the fixed laser emitting light parallel to one axis of the table aimed at a mirror mounted on the end of an adjustable rail. The beam reflects off the mirror angled at 45 degrees so that the laser travels a path exactly along the length of the rail. This beam is then reflected by another mirror mounted to a movable trolley which directs the beam perpendicular to the original axis.
Engraving follows the line and curve of the pattern to be engraved, much like a pen-based plotter draws by constructing line segments from a description of the outlines of a pattern (no expensive masks are needed). There are only a few steps from the graphical template towards the finished product and due to a special software it is even possible to economically manufacture single items.
It should be mentioned that the high power lasers have the capability of not only engraving, but cutting material and that the same basic techniques and considerations are used in fabrication of any cut shapes.
