| Electronic engineers use the terms screen printing, | | | | board. The mark must be permanent and inerasable |
| screen printing legend and silk screen to denote writing | | | | and will usually contain 1D or 2D machine readable |
| on a printed circuit board. Screen printing is far more | | | | codes along with alpha numeric characters. |
| convenient and versatile than other traditional printing | | | | Large scale manufacturers of PCB say 1,000,000 |
| methods. For one thing, the surface does not have to | | | | boards and more per year use screen printing with |
| be printed under pressure, unlike etching or lithography, | | | | thermally cured ink to print the legends that cover each |
| and it does not have to be planar. Screen printing inks | | | | side of the board. In this manner, digital printing can not |
| can be used to work on a variety of surfaces - such | | | | print the whole side of a board at a price that will be |
| as textiles, ceramics, metal, wood, paper, glass, and | | | | competitive with screen printing costs. Several other |
| plastic. As a result, screen printing is used in many | | | | options for individualizing are however available |
| different industries, from clothing to product labels to | | | | including Preprinted Label Application, Solvent Based |
| PCB printing. | | | | Continuous Ink Jet Digital Printing, Laser Ablated Ink |
| The screen printing technology is rather simple and | | | | Patches etc. |
| does not call for high skills. A screen is made out of a | | | | Preprinted Label Application: People who manufacture |
| piece of porous, finely woven fabric - originally made | | | | low volumes of PCBs start with labels printed on |
| of silk, but now they are made of polyester or nylon - | | | | office equipment and hand applied to each PCB either |
| stretched over a wooden or aluminum frame. Areas | | | | prior to or after assembly. But if the product volumes |
| of the screen are blocked off with a non permeable | | | | shoot up, the reliability and cost of hand applying labels |
| stencil which is a negative of the image to be printed. In | | | | becomes a problem. Automated systems that print |
| other words, the open spaces are where the ink will | | | | and apply labels are also available. The handicap is |
| appear. The screen is placed on top of a piece of dry | | | | these systems must place labels very accurately due |
| paper or fabric. Ink is placed on top of the screen, and | | | | to PCB space constraints. |
| a squeegee or rubber blade is used to push the ink | | | | Solvent Based Continuous Ink Jet Digital Printing: This |
| evenly into the screen openings and onto the | | | | technology has been adapted to mark on a variety of |
| substrate. The ink passes through the open spaces in | | | | industrial products including PCBs. With these systems |
| the screen onto the paper or fabric placed underneath | | | | a continuous stream of ink droplets is applied to the |
| and then the screen is taken away. The screen can | | | | desired location using electromagnetic fields. Although |
| be re-used after cleaning. | | | | solvent based inks produce permanent marks on |
| The electronics Printed Circuit Board industry is | | | | porous surfaces, it may not be permanent on |
| evolving at a fairly rapid pace as new cost-effective | | | | non-porous surfaces. |
| production technologies are become available. Direct | | | | Many industries are today using lasers to engrave |
| digital printing is usurping the traditional photolithography | | | | marks onto a variety of industrial parts. Lasers have |
| and screen printing processes that have ruled the PCB | | | | been used to engrave marks onto PC boards with |
| industry for the last two decades. Direct digital printing | | | | limited success due to the lack of contrast of the |
| is used to individualize PCBs just prior to their | | | | resulting mark. Some further experiments are taking |
| assembly. The obvious aim is to print a unique mark on | | | | place to overcome and one of them is to have the |
| each board that can be later used to identify the | | | | circuit boards printed with ink patches. |