Screen E-Book (.PDF) - MacDermid Autotype

Let me give a specific example so youcan see the scale of the problem. Let’stry to screen print a flat-panel display usingstate-of-the-art plastic transistors andpolymer light emitting diodes (PLEDs).Let’s assume that the screen printing ofeach component is not a big problem initself. With modern stainless meshes, thelatest low-EOM, low-Rz stencils and withinks optimized to reduce “slump”, we canproduce high-quality fine-line work downbelow 50µm. I’m not claiming that any ofthis would be easy, but I just want to takethis part of the process for granted andconcentrate on the real problem of registration.To simplify even further, let’s just concentrateon two elements of the display andassume (wrongly!) that we can print atransistor in one pass and the PLED in thesecond pass. In other words we need toregister 1 million PLED printed dots on topof 1 million transistor dots.Assuming a display that’s 300x300mm with1000x1000 resolution, each pixel occupies300µm square. Let’s say that the PLEDelement must be 250µm square, leavinga 25µm border around each pixel. If ourtransistor dot is smaller, say 160µm squarethen in perfect registration we have a borderof 45µm around the transistor. To makesure that our PLED always fully coversthe transistor we have to make sure thatwe are accurate to 45µm over the whole300x300mm. The diagram illustrates theidea. The dots on the left are all perfectlyarranged with the nice 45µm border. Bythe time we reach the other end of the imagesome of the dots are just about OK, butone of them has gone over the 45µ limit.4 ways misregistration might move the central square39