Lithography

Summary

Lithography is an ink-based printing process first used in Europe at the end of the eighteenth century. Unlike older forms of the printing press, in which individual pieces of raised type are pressed down onto sheets of paper, lithography uses a flat plate to transfer an image to a sheet of paper. Since the 1960s, most books, newspapers, and magazines have been printed using lithography, along with posters and packing materials. A specialized subfield of lithography known as photolithography is also used in the making of semiconductors for computers. Career opportunities in lithography are growing in specialized areas but overall are neither increasing nor decreasing because of the dominance of electronic publishing and marketing.

Definition and Basic Principles

Lithography is the process of making an image on a flat stone or metal plate and using ink to print the image onto another surface. Areas of the plate are etched or treated chemically to attract or repel ink. The ink is then transferred, directly or indirectly, to the surface where the final image appears.

Unlike letterpress printing (relief printing), in which raised letters or blocks of type are coated with ink and pressed against a surface such as paper, lithographic printing yields a result that is smooth to the touch. Lithography differs from photocopying in that plates must be created and ink applied before prints can be made. Photocopying uses a process known as xerography, in which a tube-shaped drum charged with light-sensitive material picks up an image directly from a source. Laser printing is another application of xerography and is not the same as lithography.

Photolithography is a process that imitates traditional lithography in several ways but is not identical. Its high level of precision—a photolithographic image can be accurate down to the level of a micrometer or smaller—is useful in applications such as manufacturing computer components.

Background and History

In 1798, lithography was invented by Alois Senefelder, a German playwright. Senefelder, who was looking for a way to publish his plays cheaply, discovered that printing plates could be made by writing on a flat stone block with a grease pencil and etching away the stone surface around the writing. Eventually, Senefelder developed a process by which ink adhered only to the parts of a flat surface that was not covered by grease. He later expanded the process to include multiple ink colors and predicted that lithography would one day be advanced enough to reproduce works of fine art.

German and French printers in the early 1800s made additional innovations. A patent was issued in 1837 to artist Godefroy Engelmann in France for a process he called chromolithography, in which colors were layered to create book illustrations. Interest in lithography and color printing also spread to North America, where printers in Boston invented new technologies that made the mass production of lithographic prints both high quality and economical. The process quickly spread from books to greeting cards, personal and business cards, posters, advertisements, and packaging labels. Lithography is still the leading process by which mass-produced material and packaging with print and graphics are printed.

How It Works

Lithography, in the context of printing, follows a different set of steps than photolithography as used to make microprocessors.

Offset Lithography. While there are many ways to print on paper or packaging using lithographic techniques, most items involve a process known as offset printing. The term “offset” refers to the fact that the printing plate does not touch the paper or item itself.

In offset lithography, a plate is first created with the image to be printed. The plate may be made of metal, paper, or a composite such as polyester or Mylar. Lithographic printing plates were flat at one time, but modern printing presses use plates shaped like cylinders, with the image on the outside. To transfer the image to the plate, the surface of the plate is roughened slightly and covered with a light-sensitive chemical emulsion. A sheet of photo film with a reverse, or negative, of the image is laid over the emulsion. When an ultraviolet light is shone on the negative, the light filters through the image only in the areas where the negative is translucent. The result is a positive image—essentially, a negative of the negative—left on the printing plate.

The plate is treated again with a series of chemicals that make the darker areas of the image more likely to pick up ink, which is oil-based. The lighter areas of the image are made to be hydrophilic or water-loving. Because oil and water do not mix, water blocks ink from being absorbed by these areas. A water-based mixture called fountain solution is applied to the surface of the plate and is picked up by the hydrophilic areas of the image. Rollers then coat the plate with ink, which adheres only to the hydrophobic (water-fearing) areas that will appear darker on the final image. Once the plate is inked, the press rolls it against a rubber-covered cylinder known as a blanket. The ink from the plate is transferred to the blanket in the form of a negative image. Excess water from the ink as well as fountain solution is removed in the process. The blanket is rolled against the sheet of paper or another item that will receive the final image. Finally, the paper carrying the newly inked image passes through an oven, followed by a set of water-chilled metal rollers, to set the image and prevent the ink from smudging.

Photolithography. Like lithography, the process of photolithography depends on the making of a plate coated with a light-sensitive substance. The plate is known as the substrate, while the light-sensitive chemical is known as the photoresist. Instead of a photo negative with the image to be printed, a photomask is used to shield the photoresist from light in some areas and expose it in others.

However, the similarities to traditional lithography end here. In photolithography, the substrate—rather than a sheet of paper or packaging material—is the final product. Once the image is transferred through the photo mask onto the photoresist, the substrate is treated with a series of chemicals that engrave the image into the surface. In lithographic printing, the image is never engraved directly onto the plate. Unlike printing plates and blankets, which are cylindrical, substrates are always flat. The result is a thin sheet of silicon, glass, quartz, or a composite etched precisely enough to be used as a microprocessing component.

The photolithography process used in manufacturing electronics may be divided into microlithography and nanolithography. The chief difference between the two fields is the scale of operation (microns and nanometers, respectively), though other details of each process vary as well.

Applications and Products

Lithography as a printing technology has developed in multiple, almost opposing, directions throughout its history. Because lithographic plates can be used to make large numbers of impressions, the development of lithography allowed for the printing of images and type on a commercially-viable mass scale, a major change from the letterpress and intaglio methods of printing that came earlier. Over time, lithography came to be associated with lower-cost editions of books and other printed matter intended to be short-lived, such as newspapers, magazines, and catalogs. Lithography has also evolved as a method of artistic printmaking that can produce works of great beauty and high value. On the photolithography side, the technology has kept pace with the needs of generations of electronic equipment.

Web-Fed Offset Printing. Large numbers of copies of a printed work—in the range of 50,000 copies and up—require printing processes that can run quickly and efficiently. Web-fed offset printing takes its name from how the paper is fed into the press. A web press uses a roll of paper, known as a web, which is printed and later cut into individual sheets. The largest web presses stand nearly three stories tall, print images on both sides of a sheet at once, and can print at a rate of 20,000 copies per hour. Major newspapers and magazines, as well as best-selling books with high print runs, are printed on web presses. One of the disadvantages of using a web press is that post-print options, such as folding and binding, are limited. Page sizes are highly standardized and cannot be changed easily to meet the needs of an individual print run. Image quality is also not as high as other types of lithographic presses.

Sheet-Fed Offset Printing. As its name suggests, sheet-fed offset printing uses a paper supply of individually cut sheets rather than a paper roll. Each press has a mechanism that feeds paper sheets into the machine, one at a time. This process is less efficient than web-fed printing and can lead to a higher rate of mechanical problems, such as damage to the rubber blanket when more than one sheet is fed into the press in error. However, sheet-fed printing allows for a greater degree of customization for each printing job. The size and type of the paper can be changed, as can the area of the page on which each image is to be printed. A paper of heavier, higher-quality grade may be used in a sheet-fed printer. A wider range of post-print options are also available. Sheet-fed print runs can be bound using a number of different methods, including lamination and glue. These features make it more suitable for products such as sales brochures, corporate annual reports, coffee-table books, and posters.

Lithography in Art. When it first appeared in the United States in the mid-1800s, lithography was associated with high-quality printing, particularly reproductions of works of art. The later introduction of technologies such as photogravure printing eventually made lithographic illustrations in mass-produced printed matter obsolete. At the same time, a number of artists on both sides of the Atlantic Ocean were making advances in lithographic printing as an art form. Henri de Toulouse-Lautrec depended on lithography to achieve the bold lines and fields of color in his iconic posters for the Moulin Rouge and other French cabarets in the late 1800s. Another surge of interest in lithography came in the 1920s with works from painters Wassily Kandinsky, Georges Braque, and Pablo Picasso. In some cases, such as Toulouse-Lautrec's posters, these works were originally commercial in nature and intended to be reproduced in large print runs.

Artists who experimented with lithography in the twentieth century were more likely to be drawn to the medium for its visual characteristics and possibilities for expression, not for its ability to generate copies. Paris was a major center of lithographic art until World War II, at which point many artists relocated to New York. A revival of the technique emerged in the 1950s with new prints from artists such as Sam Francis, Jasper Johns, and Robert Rauschenberg. In the twenty-first century, Kara Walker has contributed contemporary lithographic art that explores gender, race, and sexuality. Lithography is taught in many fine arts schools. Some artists prefer to work directly with the stone or metal printing plates, while others draw or paint images and rely on third parties to transfer the work from the page to the plate.

Semiconductor Manufacturing. Photolithography has been used to manufacture semiconductors and microprocessing components. When it was first developed, photolithography depended on the use of photomasks that came into direct contact with the photoresist. This contact often damaged the photomasks and made the manufacturing process costly. Next, a system was developed in which photomasks were suspended a few microns above the photoresist without touching it. This strategy reduced damage, but also lowered the precision with which a photomask could project an image. Since the 1970s, manufacturing plants have used a system known as projection printing, in which an image is reflected through an ultrahigh-precision lens onto a photoresist. This technology has allowed manufacturers to fit increasingly higher numbers of integrated circuits onto a single microchip. In 1965, Gordon E. Moore, a technology executive who would go on to co-found Intel, predicted that the number of transistors that could be placed on a microchip would double about every two years. The prediction has been so accurate that the principle is now known as Moore's law. In the early twenty-first century, however, the validity of Moore's law came to be debated. In 2019, American technology company Nvidia’s chief executive officer stated how increasing expenses and technical difficulty might lead to the failure of the law. On the other hand, 2021 statistics revealed that the law’s death by its strictest meaning was trivial. With the development of the integrated circuit, system on a chip, especially by American technology company Apple, and innovative artificial intelligence applications, there is always room for expanded capabilities.

Integrated circuits are produced using next-generation lithography. Moreover, various new technologies have been introduced; maskless lithography is available for low volume chip designing; nanoimprint lithography increases resolution and reduces cost; extreme ultraviolet lithography (EUVL) is promising in producing less than 10 nm logic devices; optical lithography uses photosensitive polymers and is used for high volume nanoelectronic manufacturing. Micro-electro-mechanical systems are also produced using these techniques.

Thus, lithography is extensively used in nearly all electronic devices throughout various industries, including mobile technology, computers, weather forecasting, global positioning systems, microfluidics, sensors, medical equipment, missile systems, and automotive technology.

Careers and Course Work

The coursework required for a career in lithography varies widely with the nature of the product and the stage in the printing process. Specialists may be known as lithographers and frequently overlap with photoengravers.

In traditional lithography, one major professional area is media printing. Books, magazines, and newspapers must be designed and laid out page by page before lithographic plates can be created. Many of the professionals who hold these jobs have earned bachelor's or master's degrees in academic areas such as art, graphic design, industrial and product design, and journalism. A background of this type could include coursework in typography, color theory, digital imaging, or consumer marketing. Students seeking opportunities in media design also pursue internships with publishers and other companies in their fields of interest.

The mechanical process of lithography has become highly automated. Fewer employees are needed in printing plants than before. Most lithographic press operators receive their training on the job and through apprenticeships. Formal education is offered through postsecondary programs at community colleges, vocational and technical schools, and some universities. Students take courses in mechanical engineering and in the maintenance and repair of heavy equipment. Additional coursework may include mathematics, chemistry, physics, and color theory.

Lithography as an artistic printing technique is taught in many college and university art departments. While it is considered too specialized by most institutions for a degree, artists may choose to use lithographic printing to create visual works on paper and other materials.

Photolithography is a highly specialized area of technological manufacturing. Its coursework and career track are notably different from those in traditional lithography. Professionals working in photolithography have undergraduate or graduate degrees in fields such as engineering, physics, mathematics, and chemistry. An extensive knowledge of microtechnology and the properties of light-sensitive materials is needed. Because most of the world's semiconductor manufacturing takes place outside North America, careers in photolithography can involve frequent travel to areas such as Asia. Some popular companies include Taiwan Semiconductor Manufacturing Company, Samsung Electronics, and Tower Semiconductor.

Social Context and Future Prospects

As a broad category, lithographic printing offers minimal job growth. Consumers are increasingly concerned about the environmental impact of paper use in catalogs and other sources of bulk mail. To respond to these concerns, many companies have reduced their use of paper-based marketing campaigns. This change has lowered the demand for commercial offset lithography along with the rest of the printing industry. A similar trend has affected the printing of checks and invoices, which electronic systems and online banking have mostly replaced.

The growth of electronic media, from the Internet to handheld e-book readers, has also lowered the need for lithography in the publishing industry. Newspapers are reducing the circulation and length of their paper editions and have shifted the bulk of their publishing efforts to websites and news feeds. While the demand for paper-based books is not likely to disappear entirely, sales of new books in electronic formats are growing more rapidly than their print counterparts. In the print segment, new technology is boosting the use of print-on-demand systems for books, which use digital printing techniques rather than lithography. Still, artists continued to rely on a hybrid of traditional and digital lithography in their works. They also experimented with laser-engraving techniques, as well as more environmentally friendly inks and plates.

The prospects for growth in photolithography are more optimistic. Photolithography continues to be one of the most effective and precise ways to make semiconductors. Companies like Intel continue to advance in photolithography, experimenting with nanoimprint and extreme ultraviolet lithography, which have the ability to produce even smaller chips. Until a new technology replaces it, the field is expected to keep growing with new demand for smaller, faster computers.

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