Screen: from mesh filter to precision printing tool

Outside the factory, a screen is a flat panel that displays light and images: a television, a monitor, a smartphone. The word evolved from the original sense of a physical barrier, a woven or slatted partition that shields one space from another while allowing air and sight to pass through.

In industrial printing, screen refers to a different but related object. It is a mesh of fine wires or threads, typically made from polyester, nylon, or stainless steel, stretched taut across a rigid frame. The holes in the mesh are uniform and precisely sized. A photographic emulsion is applied to the screen and exposed to light through a photographic negative, hardening the emulsion in some areas and leaving others soluble. The soluble areas are then washed away, leaving open mesh where ink will pass through and blocked areas where it will not. This prepared screen is the stencil used in screen printing, also called silkscreen printing. Ink is forced through the open mesh onto the substrate, paper or fabric or circuit board, below.

The fineness of the mesh, measured in threads per inch, controls the resolution and detail of the print. A coarse screen deposits thicker ink and is used for bold, high-coverage work. A fine screen holds back ink, allowing finer detail and thinner layers. The screen mask, a related component in electronics manufacturing, is a screen used to apply solder paste or conductive adhesive to circuit boards with micrometer precision, ensuring that components land on their pads and nowhere else.

The word screen as a filtering barrier reaches back to the sense of a physical partition or sieve. In printing, the screen is literally a sieve, selecting which parts of the surface will receive ink. The mesh itself blocks and allows, just as the dictionary definition states. The divergence between the visual display meaning and the printing meaning occurred in the 20th century as electronic screens became common, but they both inherit the original sense of a permeable barrier: one filters light and electrons; the other filters ink.