"Printing" on the circuit board

　　movable type printing is one of the four great inventions in ancient my country. Bi Sheng of the Northern Song Dynasty took the lead in developing mud movable type. As the core of the modern electronics industry, printed circuit boards are also named after the word "printing". What is the connection between these ancient and modern inventions?

　　Bi Sheng thinks that the woodcut and stone printing at that time were very inconvenient, so he considered making molds for each character and printing movable type. Because mud type is as fragile as ceramics, this greatly limits its application and promotion. Then the Mongolian cavalry spread the four great inventions of China to Europe. Affected by this, a German Gutenberg in the 15th century invented type printing.

　　Soon, the Germans found themselves facing a problem, how to print pictures? Different from the Chinese's preference for wood and stone, the Germans chose copperplate. Engraving copper plates requires copper plate etching technology, which involves a series of fine chemical reactions. The first is the preparation of polymer photosensitive film. It has been found that the colloid prepared by mixing water-soluble polymer materials such as animal glue and resin with a dichromate solution has such properties that the exposed part is soluble in water, and the unexposed part is insoluble in water. This is because dichromic acid is a photosensitive material. After strong light is irradiated, the precipitation of hexavalent chromium ions will become trivalent chromium ions that are easily soluble in water. In this way, the chromate formed by the reaction with polymer materials Precipitate and dissolve in water after exposure. Then the photosensitive glue is coated on the copper plate under low light conditions, dried, and covered with a negative made of the original manuscript, and then exposed to the sun to expose the plate. In this way, the surface of the copper plate is covered with a protective layer designed according to the original manuscript. Finally, put the copper plate into the ferric chloride solution in the dark to soak and corrode. Using the principle of oxidation-reduction reaction between copper metal and ferric ion solution, the part of the copper plate without a protective layer after exposure is slowly "eaten" by the corrosion of the ferric chloride solution. After a day or two, the copper plate was taken out, washed and dried, and a printing master with fine strokes and concavities was obtained.

　　This kind of corrosion engraving technology is so successful, modern printed circuit board production also uses similar corrosion technology, that is, on the insulating substrate, coating metal coating, coating photosensitive material, printing according to the circuit diagram, corrosion, and then coating A protective film is applied, and finally holes are punched on the circuit board for soldering electronic components. The circuit board produced in this way has fine structure, high reliability, and is convenient for mass production. With the advancement of technology, now printed circuit boards can usually have an eight-layer structure and fully automatic punching and soldering. The holes between the layers of the multi-layer structure play the role of connecting electronic circuits, so extremely complex circuits can be realized on a small area of the board.

　　Because woodcut and stone printing were still popular in our country until the end of Qing Dynasty, although type printing and handwriting ink printing methods were introduced later, it soon jumped directly into the era of laser typesetting, so it did not accumulate enough copperplate printing experience. Copperplate printing is the forerunner of printed circuit board technology and even chip manufacturing technology. In the field of electronics industry, my country should work hard.

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